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Fluke 8842a User's Manual

1. REDUCING THERMAL AC VOLTAGE AND CURRENT MEASUREMENT True RMS enne nnne Waveform Compartison ansa nennen nennen Crest EP AC Coupled AC Measurements eese Combined AC and DC Measuremetnts Bandwidth ee Zero Input VAC MAKING ACCURATE MEASUREMENTS ON THE 20 mV AND 200 RANGES 4 14 MAKING ACCURATE HIGH RESISTANCE MEASUREMENTS VIDE SCALING VDC Protect OD DC Analog o TRACK HOLD CIRCUL P eor ertet Track Configuration sese Settling Configuration inet nie enne ee Hold Configu ratiori a eter ree Pre Charge PRECISION VOLTAGE iii 8842A Instruction Manual 5 15 OHMS CURRENT SOURCE reete 5 16 OHMS 0 00 01 5 17 OHMS
2. O GOO AAAS OOO O OO0Qv n o OQ QO nOn OO OOQOOQ vun meo OOO O 4 on 16 21 wmf Next move to U305 5 and repeat The slow reading rate gives the following pattern at U305 5 111111 00000 111000 1111000 000 6 53 8842A Instruction Manual 6 54 6 61 6 62 If the instrument is not in the slow reading rate it gives the following pattern at U305 5 000000 00000 000000 0000000 000 Next move to U305 7 and repeat The pattern at U305 7 will be 000000 00000 000000 1111111 000 Evaluating Dynamic Signals The procedure for evaluating the dynamic signals is only slightly more involved For example consider U302 7 in Table 6 21 At the right end of that row the table says to sync on U302 3 The sync pulse is negative going Apply it to channel 1 of a dual trace scope syncing on the leading negative going edge Observe the target U302 7 on channel 2 of the scope While stepping through the 24 ranges observe the state of the target pin exactly when the sync pulse goes from low to high See Figure 6 12 This procedure works best in the fast reading rate since the repetition rate of the sync pulse on U302 3 is greater Using this procedure the following pattern should be seen 00000 11111 00
3. Diagnostic Self Tests ciiin aqapana Rangia a wasu MANUAL RANGE CONTINUOUS TRIGGER EXTERNAL TRIGGER Reading Rates and Noise RejJection Automatic Settling Time External Trigger Input Option 05 Only Sample Complete Output Option 05 Only MAKING Input Overload Protection Limits Measuring Voltage and Resistance sese Measuring Current Current Fuse nennen Offset Measurements ener dieere EXTERNAL CLEEANINOG 2 rrr tete t nee 2 1 8842A Instruction Manual 2 2 2 1 2 2 INTRODUCTION This section provides instructions for installing and operating the 8842A Refer to Section 4 for measurement considerations INSTALLATION Installing the Power Line Fuse WARNING FOR POWER LINE VOLTAGES OF 198V TO 250V THE POWER LINE FUSE MUST BE REPLACED WITH A 1 8A 250V SLO BLO
4. RANGE COMMANDS SELF TEST Sensed RO Autorange On COMMANDS by G5 R1 200 mV 2000 R2 2V 2kQ Z0 Begins Self Tests 20V 20 kQ FUNCTION COMMANDS R4 200V 200 200 mA Fi VDC R5 1000V 700V F2 VAC 2 MQ 2000 mA 2 Wire R6 20MQ DEVICE CLEAR 4 Wire R7 Autorange Off COMMANDS F5 mADC R8 20 mV 200 Reset 8842A to F6 mA power up state GTL Go To Local OFFSET COMMANDS BO Offset Off B1 Offset On f3 04 wmf Figure 3 4 Commands Which Correspond to the Front Panel 3 7 8842A Instruction Manual 3 8 FUNCTON COMMANDS F1 VDC Default F2 VAC F3 2 WIRE F4 4 WIRE kQ F5 MA DC F6 MA AC RANGE COMMANDS RO Autorange R2 2 2 R3 20V 20 kQ R5 1000V dc 700V ac 2 2000 mA R6 20 mQ R8 20mV 202 READING RATE COMMANDS S0 Slow Default 51 Medium 2 Fast TRIGGER MODE COMMANDS COMMAND TRIGGER REAR PANEL SETTLING MODE TRIGGER DELAY TO Default Internal Disabled External Enabled On T2 External Disabled On T3 External Enabled Off T4 External Disabled Off Note Delay is enabled by entering EX TRIG mode while in local OFFSET COMMANDS BO B1 DISPLAY COMMANDS DO Offset Off Default D1 Offset On SUFFIX COMMANDS YO Normal Display Default Y1 Blank Display TERMINATOR COMMANDS WO Enable CR LF EOI Default Enable CR LF Only W2 Enable CR Only W3
5. G4 Get Calibration 5 G5 Get IAB GO Get YW Status Re G7 Get Error G8 Get Instrument Identification N Numeric Entry Command a Put Commands IILI PO Put Instrument Configuration PL Put SRO Ma Sk etre re ree Pens P2 Put Calibration Put User Defined Messa e Rn Range Commands sess Sn Reading Rate Commands sese Tn Trigger Mode Commands Wn Terminator Clear Error Register Command Yn Suffix ZO Self Test Command eese Device Clear Command esses enne enne 3 1 8842A Instruction Manual 3 35 Single Trigger 3 36 L 3 37 Ibin TE 3 38 3 30 Syntax 065 3 40 OUTPUT DATA tet te tenen tene PNE nente Rene segete 3 41 Loading Output Data 3 42 Types of Ou
6. eene 3 30 Wn Terminator Commands ccccecsssceceessccecessseceeessseeeeesseeeenes 3 3 Clear Error Register Command 3 32 Yn Suffix 45 210 000000 000000000000 enne 3 33 ZO Self Test Command LLL u a ener 3 34 Device Clear 3 35 Single Trigger 3 36 INPUT SYNTAX 3 37 Me cag arte nc 3 38 Inp t 3 30 Syntax RULES 3 40 OUTPUT DATA 3 41 Loading Output 3 42 Types of Output Data nene enne 3 43 Numeric Data and Error Messages see 3 44 MEASUREMENT DATA 3 45 OVERRANGE 3 46 ERROR MESSAGES 3 47 Sams Puyu Pm 3 48 Output Em 3 49 SERVICE REQUESTS e e akasini Contents continued 3 50 3 51 3 52 3 53 3 54 3 55 3 56 3 57 3 58 3 59 3 60 The Serial Poll R gISfep aaa B SRO Mask vi INTERFACE MESSAGES
7. O O 00 0020 rn O O O O O O O O O m u o O lt lt O P w O O O O O O O O O O o O K O O gt w O O O O rn B e O onn O O OH gt O O O lt gt gt OF Z Z lt Oo 9 K O O OO o O O m m WK O O O O O O 18 K401 ohas 19 6408 20 U402a 1 20000 20 21 U402h 5 02 9 2k 2k 9 20k 200k 22 U403a 1 200 23 00024 7 Z0 frohas 24 U402c 7 200 2000k 25 U403b 5 20k ohas 26 U403c 7 Witches 27 04034 9 02k 2k42k O G or Qom O O O o bi O 0 Om O gt O O O o gt Om o oO Oe Oo o OH Oar O Om lt on o lt u lt Oe Oe o
8. eere nee AC CALIBRATION AT OTHER FREQUENCIES OPTIMIZING USE OF THE 5450 Remote Calibration TIMING 5 REMOTE BRASURE EXAMPLE CALIBRATION DISASSEMBLY Case Removal etin True RMS AC PCA Removal Option 09 Only IEEE 488 Interface PCA Removal Option 05 Only Removal 3 14e eerte tem Led Front Panel Disassembly eene REASSEMBLY PROCEDURE eere INTERNAL FUSE 6 1 8842A Instruction Manual 6 35 6 36 6 37 6 38 6 39 6 40 6 41 6 48 6 59 6 62 6 63 6 64 6 65 6 66 6 67 6 68 6 69 6 70 6 71 6 72 6 73 6 74 6 75 6 76 6 77 6 78 EXTERNAL TRIGGER POLARITY SELECTION Option 05 Only TROUBLESHOOTING Initial Troubleshooting Diagnostic Self Tests Self Test Descriptions Digital Controller Troubl IN GUARD MICROCOMPUTER SYSTEM DISPLAY SYSTEM ANALOG CONTROL SIGNALS eee DC Scaling Troubleshoo
9. JTOH1NOO HOLVIONONNY 2 20 21 3 S3NI13SN3S eL 418 SS3uQQV 93 8 NOILVYEITWO AYOWSW TVNU341X3 4300030 SININ S 38GQVv SNA 1VNH31NI 39V4H31NI 4 4 30V3H31NI 889 333 08 98 3331 SNISSOHO Quvno eozn on Quvn9o Ni ees 1021 S3NI1 TOHLNOOD AV 138 318vN3 cien OL J31H3ANOO 3ounos 4 SLINOYIO an 1 ONIIVOS lov NOI1dO 3nul f5 13 wmf Figure 5 13 Digital Controller Block Diagram 5 20 5 28 Theory of Operation DIGITAL CONTROLLER In Guard Microcomputer The In Guard Microcomputer uC is a single chip Z8 microcomputer containing 4K bytes of ROM 144 bytes of RAM a UART and four 8 bit I O ports It communicates with the rest of the instrument via the internal bus and dedicated I O lines The In Guard is reset when pin 6 is pulled low either by C204 at power up or by the watch dog timer in the custom A D U101 Pin 6 is tied to 5V through 100 resistor inside the uC All internal bus communication is memory mapped Each component that sends or receives data on the bus has a unique address or range of addresses The inter
10. Rack Mount Kits Installing the Single Rack Mount Front Panel Features reete Rear Panel Peatures Overrange Indication aaa Measuring Voltage and Resistance Measuring Cuttent u ua ane ep eap bea TEEE 488 Address Remote Operation Block Diagram ana Typical Command String Commands Which Correspond to the Front Panel Device Dependent Command Set sese Output Data Format Qua Ero eU Trigger Selection Logic Diagram eese rennen nennen Interpretation of Messages eee rennen nennen nennen Example Pr gram e Example Program Taking Readings with Local Control Example Program Using the Serial Poll 2222 121 Example Program Record Errors During Selftest Example Programs Using the IBM Circuit Loading Error
11. m or gt gt O O gt O O N w m Qrup Ow or OF oF OH ow w On Orm o Qo lt AC Option 28 K801x Vactlec 29 K802 Wact r4 r5 Iac 30 18049 14 VacA r3 rS aC 31 1804 84 Vac rl lac 32 804 94 1 1 33 08049 16 Vac r2 r40 16 16 1 wmf 6 38 6 5 gt SE 8 EI u D z Table 6 16 Overall State Table cont 8 a 3 S 3 45 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 3 2 1 front end 00000000 1111 00001 0 1 0 01 000 0 0 0 0 9 1 000000011 Udc r8 risr2 r3 ohas 1 K301 9304 3PFILT 4 310 6 U301a 1 PC GC 7 03016 5 TR1 GC 1 0000910000 U301c 7 HD1 Zuohms r8 2r4 9 U301d 9 HD1 4wuhms 10 U302a 1 GB TR1 0000000090000090900000000 000001000000 1 11 1 11 U302b 5 HD2 x1 0 1 001 01 0 00 0 0 0 0 0 0 00 09 Q 1 1 1 12 U302c 7 1 13 U302d 9 RDI Idc 14 U303a 1 TR2 15 U303b 5 TR2 J 00 00001 10 09090941 0 0
12. List of Replaceable Parts SERVICE CENTERS Table 7 2 A1 Main PCA cont Reference Description Fluke Stock Tot Qty Notes Designator No J203 J204 CABLE DISPLAY 684167 2 J602 HEADER 1 ROW 156CTR 6 PIN 380378 1 JPR001 JPR002 RES JUMPER 0 02 0 25W 682575 2 K301 RELAY ARMATURE 2 FORM C 5VDG 615575 1 K401 RELAY REED 1 FORM A 5V HIGH VOLTAGE 714352 1 MP2 INSUL PT TRANSISTOR MOUNT DAP TO 5 152207 1 MP29 MP50 HLDR FUSE 13 32 PWB MT 516880 2 MP30 SHIELD AID 728907 1 MP33 HEAT DIS VERT 1 18X1 00X0 50 T0 220 414128 1 MP35 HLDR PART FUSE BODY PWB MT 602763 1 MP201 PAD ADHESIVE 735365 1 Q101 Q309 Q318 TRANSISTOR SI NPN 60V 1W T0 92 698225 4 Q408 698225 Q102 Q319 TRANSISTOR SI PNP 40V 350MW T0 92 698233 2 Q301 TRANSISTOR SI N JFET TO 92 601333 17 Q302 Q303 Q304 601333 Q307 Q308 Q310 601333 Q311 Q312 Q313 601333 Q315 Q316 Q317 601333 Q401 Q405 407 601333 Q305 TRANSISTOR SI NPN 300V 1W T0 92 722934 1 Q306 Q402 404 TRANSISTOR SI PNP 350V 0 6W SEL TO 92 650846 4 Q314 TRANSISTOR SI N JFET DUAL SEL TO 71 461772 1 Q320 TRANSISTOR SI N MOS 350MW T0 92 783449 1 Q601 THYRISTOR SI SCR VBO 100V 0 8A 742643 1 R101 R602 R603 RES CF 1K 5 0 25W 343426 4 R605 343426 R102 R203 R204 RES CF 470 5 0 25W 343434 8 R103 R104 RES CF 27K 5 0 25W 441501 2 R105 RES MF 50K 0 1 0 125W 25PPM 340257 1 R106 RES CF 560 5 0 25W 385948 1 R201 R215 R217 RES CF 15K 5 0 25W 348854 7 R305 307 R604 348854 R202 R315 R327 RES CF 100 5 0
13. 1 khz Ag C CCCC POI 1 khzCCCCCQCA10 P02 C1 khz lt A116 C6 C CC Pog 1 khz 4W ohms CCCCCPO4 C1 khz CCC git O44 CK POS 1 khz C lt rom bank P06 4 khz GC P07 40 P36 a dtrig 80 nz 1 int lt lt lt 80 hz pulse P27 relay 444 C44 CQ P26 ac relay lt K K es P25 ohms relay lt 5 P24 relay CCS P23 sense lt 0 or 5 P22 rom 68 2 5 P21 f rsense CCCCGCO or 5 P20 lt freg sense 44 4404 3 int 5 P34 DM 5 17 1 khz 16 6 1 15 05 1 khz P14 1 P13 2AD3 2 4 khz P12 2 1 P11 AD1 gt 1 khz 10 0 1 khz Closest to the z8 is the z8 pin definition Next out is the normal use definition Next out is the signal that should be present during in guard troubleshooting mode 0 is TTL low lt 5 is TTL high gt 2 4v f6 09 wmf Figure 6 9 U202 Pin Diagram 6 46 6 43 Maintenance TROUBLESHOOTING Power supplies 5V dc at U202 1 OV dc U202 11 2 HC clock output 8 MHz at U202 2 3 Trigger line U202 40 TP201 Square wave 50 duty low OV high 3 8V nominal The period of the trigger signal should
14. AC M MEDIUM READING SENSE ra f 2 aw S TG ADI LSE EXACT REPLACEMENT ONLY FRONT REAR SwitcH SHOWN iN FRONT PoST ow 1830 32 3426 38 4244 42 48 S30 es lz7lzslaiiaslas RELAY SHOWN IN NoW ESECEGIZED oo xd N Positions LTD pups e 35 Spes perpe es 24 amp ot 14 10 18 to 272 24 TOP VIEW BOTTOM VIEW SIG TAL 8842A 1001 Sheet 1 19 01 2 wmf Figure 9 1 Main PCA DC Scaling and F R Switch cont Schematic Diagrams 9 R319 x T R702 C105 105 2702 2701 O C102 mos 106 7 4702 U220 TOP 5 27 0214 UNDER TP201 JPRL 0307 CR310 5 2 EOD qe 230 2302 R216 6 5 JOICITAL LO R604 7601 0330 0303 UZO3 UNDER 4212 70P U208 UNDER j 3046 1 2 1 CR amp 07 C604 CEOS 1 Jd 4 Ceo P993 VRE02 URGOL 88424 1601 f9 02_1 wmf Figure 9 2 Main PCA A D Converter 8842A Instruction Manual AIO BOOTSTRAP PRECISION VOLTAGE REFERENCE Cw ioz T P7o2 2 BSZ REF 1 2 4 1 aioz TEIS LOV ROE 72 5 2702 VERT 2 778K 1SY yz LESI 4 2
15. QJ zu 5 9 8 uses 199 12 M339 V 2 290 2 qoia 2905 1 1748 3 3K 5 2903 2 airs 1 CS R911 12290314 3 3K 3290314 3 3K gt 908 3 SK LM339 V TPS 6 905 2915 CS02 9054 470 91 R916 C903 1 478 1 4 1N4002R R917 SAMPLE COMP EXT TRIG 1803 196 CRS9O5 1N4448 R918 AAA Ru9 1 100 921 L ISPF F CRS10 1N4448 R943 68K LAST USED NOT USED CS28 5981 CRS10 906 913 2804 URSO01 R94 Y99091 RUSO1 2903 C904 CSO06 901 910 C912 C913 RS20 R937 C916 917 Rg39 R842 C924 CRS 7 802 1904 906 29607 TPS04 2901 2322 ALL REFERENCE DESIGNATIONS START AT 901 9 16 mD Oja in 2 9 2 m 2 7 A Mi a D g NOTES UNLESS OTHERWISE SPECIFIED 1 ALL RESISTANCES ARE IN OHMS J981 IEEE 488 2 ALL CAPACITANCES ARE IN MICROFARADS 8840A 1005 Figure 9 7 IEEE 488 Interface PCA cont 19 07 2 wmf Schematic Diagrams 9 CONVERTER 728899 REV COPYRIGHT 1990 759266 REV MADE IN USA C803 Sor 5 Ys I CR802 lt gt 1 crso1 P 3 U806 TP808 U804 TP809 1 0829 C827 FLUKE TP810 J GND e 9 C813 O e
16. 1 26 S IVNIWNH3L H31lH3ANOO 1 3SN3H3433H NOISIO3Hd 1S31 3 SNE IYNYJLNI 4 SWHO f5 01 wmf Figure 5 1 Overall Functional Block Diagram 5 5 8842A Instruction Manual 5 6 5 5 VDC Scaling Scaling is performed in the VDC function by two precision resistors networks Z301 and Z302 These components are configured by relay K301 switching transistor Q311 and quad analog switches U302A and U301B to provide the correct scaling for each range Voltage follower U306 provides high input impedance for the 20V dc range A simplified schematic and a switch state table for the VDC function are shown in Figure 5 2 TO TRACK HOLD ANALOG FILTER HIGH SENSE FOR mA DC SENSE PATH FOR VDC 200 mV RANGE NOTE TABLES SHOW CONFIGURATION DURING TRACK PERIOD OF TRACK HOLD CYCLE FILTER SWITCH Q304 IS ON SWITCH STATES FOR mA DC FOR THE S READING RATE IN VDC Q311 RANGE Q310 K301 U301B 9302 U302D 2000 mA 200 mA Switch closed or relay energized f5 02 wmf Figure 5 2 DC Scaling VDC and mA DC Theory of Operation DC SCALING In the 20 mV 200 mV and and 2V ranges the input voltage is applied directly to the T H Amplifier via Q310 Q311 and U301B In the 20 mV range the T H Amplifier has a gain of 100 in the 200 mV range the T H Amplifier has a gain of 10 in all other d
17. Maintenance INTERNAL CLEANING 6 78 Cleaning After Soldering CAUTION T M C Cleaner and similar products can can attack the nylon latches and other plastic pieces A FIRST HALF OF CIRCUIT B SECOND HALF OF CIRCUIT 9221 11 U90522 p 4v iu U221 10 U905 3 OV 0 16 us 16uS i 484S 112 us 144 5 0 2V 0 2V U908 7 908 e SEEN ON U204 11 SEEN ON IEEE 488 MAIN INTERFACE 02V PCA ende 7 02V PCA U204 9 NOTE THESE WAVEFORMS SEEN IN IN GUARD TROUBLESHOOTING MODE REPETITION RATE 500 ws INTERRUPTIONS EVERY 1 5 SEC f6 21 wmf Figure 6 21 Guard Crossing Test Waveforms If a PCA has been soldered it should first be cleaned with SPRAYON T M C Cleaner rosin flux remover or equivalent The PCA should then be cleaned with water as described above 6 71 8842A Instruction Manual 6 72 7 1 7 2 7 3 7 4 7 5 INTRODUCTION Chapter 7 List of Replaceable Parts Title HOW TO OBTAIN PARTS eene ener MANUAL STATUS INFORMATION NEWER 5 SERVICE CENTERS 7 1 8842A Instruction Manual 7 2 7 1 7 2 List of Replaceable Parts INTRODUCTION INTRODUCTION This section contains an illustrated list of replaceable parts for the 884
18. port bits programmed as outputs are driven to a constant logic 1 or 0 level as determined by switch A2 e Dynamic means the Out Guard uC I O port bits programmed as outputs are driven with a 610 Hz 50 duty cycle square wave All odd port bit numbers are 180 degrees out of phase with even port bit numbers e Read Write means that data is read from and written to the NEC7210 IEEE chip U901 when DS U901 8 is low R W U901 7 determines whether the data is being read from or written to the NEC7120 The address bits are always 3 0011 and the data bits are incremented each time 6 65 8842A Instruction Manual Table 6 25 I O Port Configurations CONFIGURATION CONFIGURATION PORT BIT Static Read Write PORT BIT Static Read Write Dynamic Dynamic 0 OUT Address P1 0 OUT Data PO 1 OUT Address P1 1 OUT Data PO 2 OUT Address P1 2 OUT Data PO 3 OUT Address P1 3 OUT Data PO 4 IN IN P1 4 OUT Data PO 5 IN IN P1 5 OUT Data PO 6 IN IN P1 6 OUT Data PO 7 IN IN P1 7 OUT Data P2 0 IN IN P3 0 IN IN P2 1 IN IN P3 1 IN IN P2 2 IN IN P3 2 IN IN P2 3 IN IN P3 3 IN IN P2 4 IN IN P3 4 IN IN P2 5 IN IN P3 5 IN IN P2 6 IN IN P3 6 Clock Clock P2 7 IN IN P3 7 serial Serial NOTES e Due to external hardware conflicts the following bits are NEVER driven by the Out Guard uC in ANY diagnostic mode 0 4 5 6 7 P2 all bits P3 1 2 3 4 3 6 is the 4 MHz clock for the NEC7210 IEEE chip 0901 e 3 7 is progr
19. seen enn 5 11 u ua na Det 5 12 Vacuum Fluorescent Display eese en ener 5 13 Digital Controller Block Diagram eene 5 14 Read Write Timing Diagrams for Internal Bus eere 9 19 Guard Crossimme e ege 5 16 488 Interface Block Diagram eene emen 5 17 True RMS AC Option Block Diagram eere 5 18 True RMS AC to DC Converter n nene 6 1 DC Calibration 6 2 First A D Calibration Prompt rennen 6 3 Calibration iet ete rettet ee LEHRER 6 4 Optimizing Use of the 5450 nennen 6 5 Example A D Calibration Program emen rennen 6 6 8842A Disassembly i Cer P ec E ee EE ren ele ier 6 7 Bront Panel Disassembly aet tie neret 6 8 Removing the Display 6 9 U202 Pim Diagram tette oret ee lise ge eese er 6 10 Waveforms for In Guard Troubleshooting Mode 6 11 Waveforms for Display Logic 6 12 Typical Dynamic Control Signals eee 6 13 Typical Output Waveforms for Track Hold Circuit TP103 6 14 Output of A D Amplifier TP101 esee 6 15 Waveforms at 0101 2
20. 6 16 STORING VARIABLE INPUTS As a convenience the VAR IN variable input feature lets you calibrate the 8842A using reference source values which differ from the values prompted by the 8842A For example you may want to calibrate the 200Q range using a reference resistor with a precisely known value of 99 8750 rather than 100Q as prompted This feature is not available during A D Calibration To use the variable input feature proceed as follows 1 When the 8842A prompts you for an input press the VAR IN button The blank digits will be replaced with zeroes You can then increment each digit of the display by pressing the range buttons The 20Q mV button toggles the displayed sign 2 Change the displayed prompt to correspond to the desired reference source by pressing the appropriate range buttons 3 Connect the desired reference source to the appropriate input terminals of the 8842A 4 Press the STORE button To meet the specifications over all ranges the reference source for the high prompts must be between half and full scale The high prompts are those prompts that are between 50 and 100 of full scale The reference source for the low prompts must be equal to or greater than the prompted value but not more than that value plus 4000 counts The low prompts are those prompts that are zero or 5 of full scale For special applications the 8842A can be calibrated at values outside the recommended range This can enhanc
21. DIP IN COMPENSTD 8 PIN DIP AMP PRECISION JFET INPUT CABLE ASSY FLAT 20 CONDUCT 4 5 RNET CERM SIP 8840 HI V DIVIDER 714816 714378 715292 715243 733089 697409 733386 697417 697458 743351 715235 714766 714774 697284 714840 715169 715300 714832 348177 203323 682898 682906 853668 714352 404590 873732 784819 844845 698233 707968 435065 340620 340240 441675 348920 706143 348938 830646 830646 394130 441709 441469 348847 348854 343459 168252 340075 658963 512889 707976 741900 473223 586735 472779 418780 808097 714014 704478 1 1 1 1 3 3 3 2 1 1 1 1 2 1 1 1 1 1 2 3 4 4 1 1 1 1 1 1 3 3 2 2 1 1 4 1 1 4 a Ny EN 1809 1 wmf Option 09 True RMS AC LIST OF REPLACEABLE PARTS 61 50841 89 r0931 ET pes as Be ASL n St lt 2280 4 3 90891 2 50 o toen AS 282 Md 45297 6284 c 24004 50891 22 6084 24848 S282 Eum IN SS 080 Eray 1080 gt G 2 149 9 V600 vXb88 189 40802 02802 S 182 ETE j UND r 3 018441 17 aan 4288 9289 089 YSN NI 0661 LHOIWAdOD 3U 996694 66882 33 193 8842 1609 f809 2 wmf True RMS AC PCA 2
22. 0040 00 5 18 22 ONS 5 19 4 Wire E 25 20 A D CONVERTER eR pag 5 21 Timing Data Control 5 22 Precision aaa a 5 23 AUD Amp litter iecit era n ae e nid 5 24 Bootstrap Supple actes renti eire tt etes HE 3 25 DISPLAY 9 al 320 KEYBOARD au masqa te ee aqhaqa PINTA 5 27 DIGITAL 5 28 In Guard Microcomputer 5 29 Function and Range 5 30 A D Control and Computation sese 5 31 Calibration 7 5 32 Keyboard Display Control eene 5 33 Troubleshooting Modes sese 5 34 Guard Crossing Communication eese 5 35 GUARD CROSSING aasawa nens 5 36 POWER SUPPLY eet tete epe HR 5 37 488 INTERFACE OPTION 5 5 38 Out Guard Microcomputer seen eren 5 39 Guard Crossi ore 5 40 Bus Interface ione ici retener Ere ether nt pin 5 41 Signal Conditioning
23. DC Voltage Test LE Low and Mid Frequency AC Voltage Test eee High Frequency AC Voltage Resistance DC Current Tests DE AC Current Test paz A D Calibration Steps A D Calibration Verification Test n au Offset and Gain Calibration Steps a High Frequency AC Calibration Steps eese Prompts When Calibrating Individual Ranges eee Commands Used During remote Overall State 883 1 lt 8842A Instruction Manual 6 27 AC Tracing cioe ates ate 6 28 Truth Table for 0804 and K2 7 1 8842A Digital 1 2 P Te A2 Display PA u tato 8 2 EE 805 1 Option 05 IEEE 488 Interface PCA 809 1 Option 09 True RMS AC PCA op EO List of Figures External Dimensions sioe eer Peri eet etie et eo Line Voltage Selection Adjusting the
24. Taiwan Schmidt Scientific Taiwan Ltd 6th Floor No 109 Tung Hsing Street Taipei Taiwan R O C TEL 886 2 767 8890 or 746 2720 FAX 886 2 767 8820 Thailand Measuretronix Ltd 2102 31 Ramkamhang Road Bangkok 10240 TEL 66 2 375 2733 or 2734 FAX 66 2 374 9965 Turkey Pestas Prof Elektr Sist Tic V Selcuklar Caddesi Meydan Apt No 49 Daire 23 Akatlar 80630 Istanbul TEL 90 212 282 7838 FAX 90 212 282 7839 U A E Haris Al Afaq Ltd P O Box 8141 Dubai TEL 971 4 283623 or 283624 FAX 971 4 281285 United Kingdom Fluke U K LTD CSS Colonial Way Watford Hertfordshire WD2 4TT TEL 44 823 240511 FAX 44 923 225067 Uruguay Coasin Instromontos S A Casilla de Correo 1400 Libertad 2529 Montevideo TEL 598 2 492 436 659 FAX 598 2 492 659 Venezuela Coasin C A Calle 9 Con Calle 4 Edif Edinurbi Piso 3 La Urbina Caracas 1070 A Venezuela TEL 58 2 241 6214 FAX 58 2 241 1939 Vietnam Schmidt Vietnam Co Ltd Schmidt Tower Hanoi Intemational Tech Ctr KMB Highway 32 Cau Giay Tu Liem Hanoi Vietnam TEL 84 4 346186 or 346187 FAX 84 4 346 188 West Indies Western Scientific Co Ltd Freeprot Mission Road Freeport Trinidad West Indies TEL 809 673 0038 FAX 809 673 0767 Yugoslavia Jugoelektro Beograd T amp M Customer Support Servicies Knez Mihailova 33 11070 Novi TEL 38 11 182470 FAX 38 11 638209 Zimbabwe Field Technical Sales
25. 3 8 Cn Calibration 3 9 Dn Display Commands eese 3 10 Fn Function 3 11 Get Commands E E 3 12 GO Get Instrument Configuration 3 13 GT Ger SRO Mask nn RR 3 14 G2 Get Calibration Prompt 3 15 G3 Get User Defined Message 3 16 G4 Get Calibration Status 3 17 GG Get TAB Status uuu 3 18 G6 Get YW Status esses seen ia 3 19 G7 Get Error Status i 3 20 G8 Get Instrument Identification 3 21 N Numeric Entry Command 3 22 ei tete 3 23 PO Put Instrument Configuration 3 24 Put SRQ Mask 3 25 P2 Put Calibration 3 26 Put User Defined Messa e 3 27 Rn Range Commands essent entente 3 28 Sn Reading Rate seen 3 29 Tn Trigger Mode Commands
26. 350 PRINT ERROR RIGHTS E 3 OCCURRED 360 WRTS GO CALL IBWRT DVM WRT 370 ST SPACE 6 380 CALL IBRD DVM ST 390 IF LEFT ST 4 gt 9000 THEN GOTO 300 400 WRT G7 CALL IBWRT DVM WRTS 410 SPACE 6 420 CALL IBRD DVM E 430 IF LEFT E 4 1000 THEN GOTO 450 440 PRINT ERROR RIGHT E 3 OCCURRED 450 PRINT 460 PRINT SELFTEST COMPLETE 470 END Device name is 18842A Initialize the DMM Clear device Wait 1 second before sending commands Start selftest Read error status Check for errors Clear error register Print analog error Get instrument configuration Check for selftest still active Read error status Check for errors Print digital error f3 14 03 wmf Figure 3 14 Example Programs Using the IBM PC cont Remote Programming EXAMPLE PROGRAMS The following application program is written in QBASIC for the IBM PC PC XT or PC AT The National Instruments Model GPIB PCIIA board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842A assigned to the GPIBO board This program selects VDC F1 Autorange RO Slow rate SO Continuous trigger TO and suffixes enabled Y1 The program takes 10 readings displays them on the screen and then stops Microsoft QuickBasic V 4 5 on IBM PC PC XT or PC AT
27. 45 Kelvin Road North P O Box Cy535 Causeway Harare Zimbabwe TEL 263 4 750381 or 750382 FAX 263 4 729970 Figure 7 4 Service Centers cont List of Replaceable Parts SERVICE CENTERS service 2 wmf 7 19 8842A Instruction Manual 7 20 INTRODUCTION t petita cec ACCESSORIES u ua Chapter 8 Options and Accessories Title Page Rack Mount Kits Y8834 Y8835 and Y8836 Shielded IEEE 488 Interface Cables Y8021 8022 and 8023 Replacement Test Leads 70 Deluxe Test Lead Kits 8130 Slim Flex Test Leads Y8140 essere Temperature Probes 80T 150U and 80TK RF Probes 85RF and 8 4400000 Current Shunt 80J 10 esses eene enne Current Probes Y8100 Y8101 801 400 and 801 600 High Voltage Probes 80K 6 and 80 40 8842A Instruction Manual 8 2 Options and Accessories 8 1 INTRODUCTION A number of options and accessories are available which can enhance the 8842A s capabilities and increase operator safety The accessories are summarized in Table 8 1 and described in the following paragraphs The options are summarized in Table 8 2 and described in the following subsections Table 8 1 Accessories INTRODUCTION MODEL Y80
28. Numeric values exceeding full scale and negative values for ohms and AC generate error messages P3 Put User Defined Message Format Explanation P3 lt value gt Where lt value gt is a string of up to 16 ASCII characters Example Explanation P3FL 8842 12 17 83 Loads the message FL 8842 12 17 83 into calibration memory P3HIMOM Loads the message HIMOM into calibration memory The remaining eleven characters are assumed to be blank The P3 command stores a user defined message in the internal calibration memory during remote calibration The message may be read with a subsequent G3 command The message may consist of up to 16 ASCII characters and typically represents the instrument s identification calibration date calibration facility etc If fewer than 16 characters are specified spaces are appended to fill the message to 16 characters Spaces and commas in the 16 character input string are suppressed Lower case letters are converted to upper case NOTE If fewer than 16 characters are specified the P3 command must not be followed by other commands in the same input command string Otherwise the subsequent commands will be misinterpreted as part of the 16 character string To accept the P3 command the 8842A must be in the calibration mode enabled by pressing the front panel CAL ENABLE switch Otherwise the P3 command will generate an error message Rn Range Commands The Range commands duplicate the fr
29. e TEST 28 External Program Memory 17222 A two byte check sum is calculated over the entire 4K External Program Memory and compared with the checksum bytes at the end of that memory A special add and shift algorithm minimizes the possibility of double errors cancelling If something is wrong with the External Program Memory ERROR 28 is displayed e TEST 29 Calibration Memory U220 Numerous single byte checksums are placed in the Calibration Memory one at the end of each group of calibration constants They are calculated in such a way that the single byte sum of all bytes in the Calibration Memory add to zero all carries discarded and the single byte sums of each group also add to zero A new checksum is calculated and written to Calibration Memory each time a full or partial calibration is performed If the Calibration Memory is not properly configured or not working correctly ERROR 29 is displayed The accuracy of the 8842A is suspect Digital Controller Troubleshooting The basic strategy in troubleshooting the Digital Controller circuit is to check first whether the In Guard Microcomputer uC system is functional starting with the In Guard uC itself 0202 Most of this circuitry is tested using the specially provided In Guard Troubleshooting Mode If the In Guard HC system proves to be functional then basic instrument control is assured and troubleshooting efforts can proceed in one of two directions If the display and ke
30. igure 809 F 809 7 8842A Instruction Manual 809 8 Chapter 9 Schematic Diagrams 9 1 8842A Instruction Manual 9 2 Schematic Diagrams 9 R323 R413 R414 R402 0310 0303 CR308 0367 0302 08310 WH 0313 M amam u 03 8701 z792 L E 7 9752 TP201 JPR1 3 gt ac 105 CR105 R106 U208 UNDER 9 0209 UNDER R201 R602 47 59 8 24 8601 a lt CR613 CR i c 3 30 CR607 212509 6505 1191 1 603 vR602 Ce06 U212 TOP D Ce02 1 U220 TOP U219 UNOER R216 te CREISC 201 0 Re0u 1601 8842 1601 f9 01_1 wmf Figure 9 1 Main PCA DC Scaling and F R Switch 8842A Instruction Manual TO 255 RV402 2 an OHMS TRACK R32 4 MF Io 9302 5 5 24V Alo eo T E Tw crs Y VOC rierzer3 s DIGITAL Brun K Bor gt POLE FILTER N Co 0202 19 e 1 DIGITAL gt ess 6 22 NOTES VOC T3475 counts rs tra C VOC rerci r2 vray 3 4 z Be ea E VOC o rs 2 Cums TI T 2473 RATE f FAST READING HBOS
31. 0 EN C820 C807 11 07 884XA 3009A CKT 2 REV 6 8816 C812 R823 R814 R819 aso Q803 C808 s C825 TP803 E Vourt a R836 TP806 C806 TP802 N 0803 55 c 1 0822 PM 19 4 t 3 20 2 rP804 935 1 TP805 15V C821 5V 88424 1609 19 08 1 wmf Figure 9 8 IEEE 488 Interface PCA Option 08 9 17 8842A Instruction Manual jase 244 s 1AC ce eos S sz aoe T Pe ees gt 5 2 24S lt ce 680 P DETAIL I ceo AC TZ T lt 2 7 I 2 gt 4 LF 356 1 Reo 59 7 VAG TI n gt 5532 4 99v gt axa Z8o tisy LOM sej 14 N OYE S ONLESS SPECIFIED Yi z LOWEST R835 CBId 2 ALL RESISTANCE VarorS oe ALL ROSiISTOSCS ARC Vaw 5 ALL CAPACITOR VALLES E gt 5895 RBIS RSIS SZ R824 8842A 1009 CURFEENT out 19 08 2 wmf Figure 9 8 IEEE 488 Interface PCA Option 08 cont 9 18
32. 2 8 Power Up Features When the 8842A is turned on all display segments light up for about 2 seconds while the instrument performs an internal self test of its digital circuitry The 8842A then assumes the following configuration e VDC function e Autorange starting in the 1000V range e Slow reading rate e Continuous internal trigger e OFFSET off e Local front panel control While all display segments are lit during the power up self test you can freeze the display by pressing the SRQ button All display segments will then remain lit until you press any button Front and Rear Panel Features Front panel features are explained in Figure 2 5 Rear panel features are explained in Figure 2 6 The alternate functions embossed below the front panel range buttons and the special feature buttons are enabled by the CAL ENABLE switch These functions are for use only when calibrating the instrument See the Maintenance section for further explanation CAUTION To avoid accidentally uncalibrating the 8842A do not press the CAL ENABLE switch unless calibrating the instrument Never cycle power on or off while the CAL ENABLE switch is on Operating Instructions OPERATING FEATURES Note that the VAC and mA AC functions are available only with the True RMS AC option If this option is absent pressing the VAC and mA AC function buttons causes the 8842A to briefly display an error message ERROR 30 FUNCTION BUTTONS DC
33. 24 26 28 REFERENC XU222 3 5 7 9 12 15 17 19 23 24 waverornma J L _ U2204 3 5 7 10 13 15 17 22 U219 2 3 6 7 12 13 16 17 U202 13 15 17 19 21 23 25 27 29 33 4 o SJ 2 dI XU222 4 6 8 10 11 13 16 18 21 25 WAVEFORM B U220 2 4 6 8 9 11 14 16 19 23 U219 4 5 8 9 14 15 18 19 WAVE Wnn 9202 4 16 HS bit Guard crossing out FORM C 500 ws rep rate per word 0101 7 U202 40 Ip r pj 80 Hz A D INT Ner fl m suoi U101 8 f6 10 wmf Figure 6 10 Waveforms for In Guard Troubleshooting Mode 6 44 External Program Memory XU222 Sync on U219 3 Verify that XU222 3 5 9 12 15 17 19 23 24 are the same as Waveform A see Figure 6 10 on U219 3 Verify that XU222 4 6 8 10 11 13 6 47 8842A Instruction Manual 6 48 6 45 6 46 6 47 6 48 16 18 21 25 are the same as Waveform B The waveforms should be interrupted every 1 5 sec for 0 2 sec due to interrupts from the watchdog timer Note XU222 pins refer to a 28 pin socket Calibration Memory U220 Sync on U219 3 Verify that U220 1 3 5 7 10 13 15 17 22 are the same as Waveform A U219 3 Verify that 7220 2 4 6 8 9 11 14 16 19 23 are the same as Waveform B The waveforms should be interrupted every 1 5 sec for 0 2 sec due to interrupts from the watchdog timer Relay
34. 6 2V 0 10000V 20 Hz 220 0 09780 VAC 0 10220 VAC 7 2 1 90000 20 2380 1 87620 VAC 1 92380 VAC 8 2V 10000V 45 Hz 135 0 09865 VAC 0 10135 VAC 9 2V 1 90000V 45 Hz 765 1 89235 VAC 1 90765 VAC 10 200 0 001000V 100 Hz 204 00 796 mVAC 190 252 mVAC 11 200 mV 0 190000V 20 kHz 252 189 748 mVAC 190 252 MvAC Quick Test points 6 7 8842A Instruction Manual STEP NUMBER 1 2 3 4 5 6 7 8 VOLTAGE 200 mV 0 010000V 200 mV 0 010000V 2V 0 10000V 20V 1 0000V 200V 10 000V 700V 100 00V 20V 19 0000V 200 mV 0 190000V Table 6 4 High Frequency AC Voltage Test RANGE INPUT FREQUENCY 50 kHz 100 kHz 100 kHz 100 kHz 100 kHz 100 kHz 100 kHz 100 kHz ERROR IN COUNTS 169 350 350 350 350 350 1250 1250 TEST LIMITS IN VOLTS 09 831 mVAC 188 750 mVAC MIN 09 650 mVAC 0 09650 VAC 0 9650 VAC 09 650 VAC 96 50 VAC 18 8750 VAC MAX 10 169 mVAC 10 350 mVAC 0 10350 VAC 1 0350 VAC 10 350 VAC 103 50 VAC 19 1250 VAC 191 250 mVAC Quick test points Resistance Test The following procedure may be used to verify the accuracy of the 2 wire and 4 wire ohms functions Ensure the 8842A is on and has warmed up for at least 1 hour 1 2 Connect the Resistance Calibrator to the 8842A for 4 wire ohms For each step in Table 6 5 select the indicated range set the Resistance Calibrator for the
35. 9 Hassan Mazher St P O Box 2009 St Heliopolis 11361 Cairo Egypt TEL 20 2 417 8296 FAX 20 2 417 8296 Fed Rep of Germany Fluke Deutschland Gmbh Customer Support Services Servicestutzpunkt VFNS Oskar Messter Strasse 18 85737 Ismaning Munich TEL 49 89 9961 1260 FAX 49 B9 9961 1270 Fluke Deutschland CSS Servicestutzpunkt VFNS Meiendorfer Strasse 205 22145 Hamburg TEL 49 40 679 6434 FAX 49 40 679 7653 Finland Fluke Finland Oy Sinikalliontie 3 P L 151 SF 02631 Espoo TEL 358 0 6152 5600 FAX 358 0 6152 5630 France Fluke France S A 37 Rue Voltaire BP 112 93700 Drancy Cedex TEL 33 1 4896 6300 FAX 33 1 4896 6330 Greece Philips S A Hellenique Fluke Sales amp Service Manager 15 25th March Street P O Box 3153 177 78 Tavros Athens TEL 30 1 489 4911 or 4262 FAX 30 1 481 8594 Hong Kong Schmidt amp Co Ltd 1st Floor 323 Jaffe Road Wanchai TEL B52 9223 5623 FAX 852 834 1848 Hungary MTA 52 KFT Srv Gen Mgr Etele Ut 59 61 P O Box 58 H 1502 Budapest TEL 361 186 9589 or 209 3444 FAX 361 161 1021 Figure 7 4 Service Centers Iceland Taeknival HF P O Box B294 Skeifunni 17 128 Reykjavik TEL 354 1 681665 FAX 354 1 680664 India Hinditron Services Inc 33 44A 8th Main Road Raj Mahal Vilas Extension Bangalore 560 080 TEL 91 80 334 8266 or 0068 FAX 91 33 247 6844 Hinditron Services Pvt Ltd Hinditron House 23 B Mahal Indus
36. Figure 2 1 Line Voltage S election Settings Operating Instructions INSTALLATION 2 5 Adjusting the Handle The handle provides two viewing angles for bench top use To adjust its position pull the ends out to a hard stop about 1 4 inch on each side and rotate it to one of the four stop positions shown in Figure 2 2 To remove the handle adjust it to the vertical stop position and pull the ends all the way out 2 6 Rack Mounting Kits You can mount the 88424 in a standard 19 inch rack panel using the accessory rack mounting kits shown in Figure 2 3 To install the Single Rack Mount Kit remove the handle and handle mounting plates and attach the rack ears with the screws provided Figure 2 4 The Dual Rack Mount Kit is installed similarly Both kits include mounting instructions The rear feet may be rotated 180 degrees to clear a narrow rack space PULL ENDS OUTWARD 1 Viewing position 2 Alternate viewing position TO ROTATE 4 Removal position to remove pull ends out 3 Carrying position 12 02 wmf Figure 2 2 Adjusting the Handle Single Rack Mount Kit Dual Rack Mount Kit Accessory Y8834 Accessory Y8835 Center Rack Mount Kit Accessory Y8836 also available 12 03 wmf Figure 2 3 Rack Mount Kits 8842A Instruction Manual 2 4 REMOVE ATTACH HANDLE RACK EARS MOUNTING PLATES 12 04 wmf Figure 2 4 Installing the Single Rack Mount Kit 2 7 OPERATING FEATURES
37. Get command gets the content of the primary status registers and copies it into the output buffer A NOTE ABOUT EXAMPLES In the examples in this manual device dependent commands are shown enclosed within quotation marks as they would be entered in Fluke BASIC For clarity the commands are also separated by spaces However the spaces are are not necessary and may be omitted Example Explanation F3 R1 51 T2 This example is equivalent to F3R1S1T2 or F3 R1 S1 T2 Using the Fluke 1722A Instrument Controller these commands might be written into a BASIC program as shown in Figure 3 3 Examples using other controllers are given at the end of this section Here is a typical command string as it might be sent from a Fluke 1722A Instrument Controller The string configures the 8842A and triggers a reading The PRINT command automatically sends terminators CR LF and or EOI to the 8842A at the end of the command string PRINT Q3 R1 51 488 bus address X mE ME Resets the 8842 to the power up configuration Selects the 2 WIRE kQ function Selects the 200 range Selects the medium reading rate Selects the external trigger mode Rear panel trigger disabled Triggers a reading f3 03 wmf Figure 3 3 Typical Command String Examples of 8842A output data show the terminators CR and LF The terminator EOI is not shown because it is a uniline message However the terminators CR LF
38. INCLUDE qbib45 dcl devname 8842A Device name is 18842A CALL IBFIND devname dvm Initialize the DMM CALL IBCLR dvm Clear device WRTS F1R0S0T0Y1 up command string CALL IBWRT dvm WRT Write functions to instrument FOR i 1 TO 10 RD SPACE 18 11 characters for the reading 5 for the suffix and 2 for terminators CALL IBRD dvm RD Get data PRINT i LEFTS RD 16 Print to display NEXT i END Microsoft is a registered trademark of Microsoft Corporation QuickBASIC is a trademark of Microsoft Corporation 13 14 04 wmf Figure 3 14 Example Programs Using the IBM PC cont 8 41 8842A Instruction Manual The following application program is written in QBASIC for the IBM PC PC XT or PC AT The National Instruments Model GPIB PCIIA board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842 assigned to the GPIBO board This program selects VDC F1 Autorange Slow rate 50 Continuous trigger TO and suffixes enabled Y1 All readings appear simultaneously on the instrument display and the PC screen with suffixes enabled for function readout Full local control is given to the 8842A Note the local control must be given to the board and not the device Press lt CTRL gt BREAK to terminate this program Microsoft QuickBasic V
39. INTRODUCTION The IEEE 488 Interface turns the 8842A into a fully programmable instrument for use with the IEEE Standard 488 1978 interface bus IEEE 488 bus With the IEEE 488 Interface the 8842A can become part of an automated instrumentation system The 8842A can be under complete interactive control from a remote bus controller or it can be set to the talk only mode connected to a data logger or printer and dedicated to a single task This manual assumes you know the basics of the IEEE 488 interface bus For an introduction to the bus request Fluke Application Bulletin AB 36 IEEE Standard 488 1978 Digital Interface for Programmable Instrumentation CAPABILITIES The IEEE 488 Interface provides remote control of all front panel controls except for the POWER CAL ENABLE and FRONT REAR switches Other features include e A simple and predictable command set e Fast measurement throughput e Fulltalk listen capability including talk only operation e Full serial poll capability with bit maskable SRQ e Full remote local capability including local lockout e EXTERNAL TRIGGER and SAMPLE COMPLETE connectors e Remote calibration e Programmable trigger sources including two bus triggers e Informative output suffix suppressible e Selectable output terminators The 8842A supports the following interface function subsets SH1 AH1 5 L4 SR1 RL1 DC1 DT1 El PPO and BUS SET UP PROCEDURE To set up the 8842A on
40. If one or more ranges are functional but cannot be calibrated at high frequencies then either the digitally controlled filter U801B R832 and C826 C829 is defective or a defective component elsewhere in the circuit has rendered the response out of calibration range The high frequency calibration is designed to cover the range of error expected due to op amp variations input dividers PCA tolerances shielding etc A sweep generator is useful in troubleshooting difficult frequency response problems The calibration control lines to U808 are set by software to store a high frequency correction factor for each range A state table cannot be given for these signals but common sense will indicate if they are reasonable For example if all lines are at logic 0 for all ranges something is probably wrong Suspect U803 U808 or digital hardware on the Main PCA If the control signals do indeed change with range U808 or some part of the digitally controlled filter U801B R832 and C826 C829 may be defective Even with the worst possible error in the high frequency calibration code the reading should be within 10 of the correct value at frequencies up to 100 kHz If the error is larger there are analog problems 6 69 8842A Instruction Manual 6 70 6 75 It is safe to force one control line at a time high 5V or low OV to test the individual switches 0808 The on resistance of switches U808 should be less than 5000
41. LEGI cO INPUT HOR 5 VERT W FRONT END CONTROL SIGNALS GENERATED BY CONVERTER P 4 5 Bas t 9 3 gt 1 OTHERWISE SPECIFICO Bol ALL RESISTANCE VALLES ARE in OMS TIMING DATA ALL RESISTORS ARE 5 SONTROU ALL CAPACITOR VALLES AGC IN MICRO FARADS 27 ARE COMPONENTS oF A REF AMP SET OC SCALING FROM O G TA wie Alo CONVERTER Im s Biv VERT 7v Ovv 5LOPE 8842 1001 Sheet 2 19 02 2 wmf Figure 9 2 Main PCA A D Converter cont 9 6 Schematic Diagrams 9 2 DL CR106 S C105 105 R105 06 RV402 MIC 4220 10 UNI E O 0307 U219 UNDF O 0302 P20 2304 mg _ R306 A318 Koa 8305 R216 CRe iSt JDIGITAL LO ReO T601 89601 0203 UNDER y242 TOR U208 UNDER 0403 0402 0317 5 LU al 5 2 860 8 CR615 2 08613 2 0 CREI2 405 0407 0318 usos RL 8605 040 CR60 04026 CREO CREIS R413 0303 1 0601 0608 R41 TROT J CR302 8842A 1601 f9 03_1 wmf Figure 9 3 Main PCA Ohms Current Source 9 7 8842A Instruction Manual 4 02 15V NOTES 2 491 WHEN SIGNAL IS TELE iS CL
42. Operating Instructions EXTERNAL CLEANING SENSE terminals for 4 wire resistance measurement only 2 09 wmf 12 10 wmf Figure 2 10 Measuring Current 2 30 EXTERNAL CLEANING WARNING TO AVOID ELECTRIC SHOCK OR INSTRUMENT DAMAGE NEVER GET WATER INSIDE THE CASE TO AVOID INSTRUMENT DAMAGE NEVER APPLY SOLVENTS TO THE INSTRUMENT Should the 8842A case require cleaning wipe the instrument with a cloth that is lightly dampened with water or a mild detergent solution 2 15 8842A Instruction Manual 3 34 Chapter 3 Remote Programming Title Page INTRODUCTION CAPABILITIES RR ER BUS SET UP PROCEDURE AN OVERVIEW OF REMOTE OPERATION 5 DEVICE DEPENDENT COMMAND SE L Bn Offset Cn Calibration Commands Dn Display Fn Function Commands Get Commands GO Get Instrument Configuration Get SRO G2 Get Calibration G3 Get User Defined
43. SINGLE wiecs NOT USED 2 lt 7 LSK gt gt sav 5 R208 5 LSK 7e ozo 3 w cRtOU zuo LSK SINGLE w cut T gt X Xo a gt SCAUNG e a sense 1 DISPLAYPY INTERFACE F R SWITH Power SUPPLY PETES To SOS SCALING at A B Mw Pay e amp 7 Cif xx 1 outs OC SCALING so8o00 pon KEYINT 4 OC SCAUNG d 3 4 Ur any pe gt 20 M CAL SENSE CAL ENABLE 01000900000 moe 901820 amp tNv Nb 0 s 4 gt ON FRONT ENO SCHEMATIC 8842A 1001 205 C207 e208 A 22 22 22 122 Sheet 4 D ON POWER SCHEMATIC Ozi 19 04 2 wmf Figure 9 4 Main PCA Digital cont 9 10 Schematic Diagrams 9 R308 2343 64 ar U220 TOP 04308 0219 UNDER yu CR31 R318 4202 T R217 0301 C211 0305 CEC Ejo R211 272192 Pat Or Nr Teo u ER DIGITAL LO reges e 2 Rs 7501 fa ape NS x lalo 5 M CL301 0310 0303 E w les N 295 lt 0315 DO 4 R306 0373 D 5 E CR
44. TRACK HOLD Track Configurati n u aaa Settling Hold Configuration eee eee Rede inerat tore d cina Pre Charge Configuration essent PRECISION VOLTAGE REFERENCE OHMS CURRENT SOURCE OHMS PROTECTION ern tro netter OHMS 2 Wire 4 A D CONVERTER uu yanasan Timing Data Control a Precision DAG epe ter AID Amplifier ee ert Bootstrap Supplies DISPLAY uu ties In Guard Microcomputer a Function and Range Control eene A D Control and Computation eese Calibration COrrecton tentant date Keyboard Display Control eene Troubleshooting Modes esee Guard Crossing Communication eese GUARD CROSSING tee tren 5 1 8842A Instruction Manual 5 36 5 37 5 38 5 39 5 40 5 41 5 42 5 43 5 44 5 45 5 46 5 47 POWER SUPPLY IEEE 488 INTERFACE OPTION 05 Out Guard Microcomputer Guard Crossing Bus Interface Cir
45. The Precision Voltage Reference provides precise reference voltages for the A D Converter and the Ohms Current Source 5 3 8842A Instruction Manual 5 4 5 3 5 4 DETAILED CIRCUIT DESCRIPTION The following paragraphs give a detailed circuit description of each of the functional blocks in Figure 5 1 For clarity measurement ranges are referred to as r1 12 13 etc where r1 is the lowest possible range r2 the next higher range and so on Pins are designated by the respective integrated circuit e g U101 7 for U101 pin 7 DC SCALING The DC Scaling circuit scales all in range dc inputs so that the output of the Track Hold T H amplifier U307 is within 2V In addition the DC Scaling circuit provides input protection and analog filtering Additional scaling is provided by the the T H Amplifier The following paragraphs describe the configuration of the DC Scaling circuit in the and mA DC functions and also describe the analog filter The ohms functions described under a later heading because the T H Amplifier provides additional input switching for these functions 5 DC SCALING Theory of Operation Sn8 887 3391 Quvno NI AW1dSI0 3NI1 H3MOdl NOILdO 3OVd3H31NI 88t 333l 55 quvno HATIOYLNOO A1ddN 3 3 NOlido ov l4 98525 sid 3081 Q1OH 49VHl 3oviqoA oq SNI1vO9S
46. and EOI are all selectable using the Write commands For reference the ASCII and IEEE Std 488 1978 bus codes are shown at the back of this section DEVICE DEPENDENT COMMAND SET Device dependent commands are the heart of 8842A remote control They tell the 8842A how and when to make measurements when to put data on the bus when to make service requests etc Commands which correspond directly to the front panel controls or display are shown in Figure 3 4 The complete set of device dependent commands is listed in Figure 3 5 The commands may be entered using either upper or lower case letters See Table 6 15 for conditions under which certain commands are not valid Remote Programming DEVICE DEPENDENT COMMAND SET TRIGGER COMMANDS Trigger Measurement GET Trigger and Execute TRIGGER MODE COMMANDS TO Continuous Trigger T1 T4 External Trigger DISPLAY COMMANDS DO Normal Display SUFFIX COMMANDS Blank Display YO Disable Suffix Y1 Enable Suffix 50 Slow 61 Medium S2 Fast ENE 88424 MULTIMETER INPUT SENSE h EXTRIG SMF OVER ERROR CAL AUTO OFFSET TEST rouge a Ec k 7007 CALIBRATION SEAL LO 2 INPUTS RATE ce FRONTE neant WIRE MAY 20 2000 20 DIGIT 3 DIGITS DIGITS
47. the 8842A goes to a higher range when the input exceeds full scale 199999 counts and goes to a lower range when the input falls below 9 of full scale 18000 counts While the instrument changes range the numeric field on the display is blanked until a new reading is completed However the decimal point and units annunciators always indicate what range the instrument is in Pressing the AUTO button when the instrument is already in autorange toggles the 8842A from autorange to manual range This causes the instrument to remain locked in the present range The 88424 autoranges up to the highest ranges in all functions down to the 200 mV range in the VDC and VAC functions and down to the 200Q range in the ohms functions To select the 20 mV dc 20 or 200 mA dc range press the respective range button or send the respective range command if using the IEEE 488 option 2 16 2 17 2 18 2 19 2 20 Operating Instructions OPERATING FEATURES MANUAL RANGE In manual range the 8842A remains fixed in the selected range until you select another range or press AUTO If you select a range which is not valid for the present function or select a function which is not valid for the present range the 8842A selects the nearest valid range For example if the 8842A is in the VDC function and you press the 20 MQ button the 8842A selects the 1000V range The range buttons have no effect in the mA AC functions since all measuremen
48. 0100 1100 0100 1101 0100 1110 0100 1111 12 014 CR 13 015 50 14 016 017 NUL 0 000 00 64 100 40 0100 0000 MTA SOH 1 001 01 A 65 101 0100 0001 STX 2 002 02 B 66 102 42 0100 0010 ETX 003 03 103 0100 0011 4 004 04 D 0100 0100 5 005 05 E 0100 0101 6 006 0100 0110 7 007 0100 0111 8 010 2 H 0100 1000 9 on 2 0100 1001 10 02 J 0100 1010 013 K 0100 1011 L M N 0 0101 0000 020 TALK ADDRESSES DC1 17 021 11 81 121 51 0101 0001 DC2 18 022 12 82 122 52 0101 0010 023 0101 0011 0101 0100 0101 0101 0101 0110 0101 0111 024 21 025 15 026 UNIVERSAL COMMANDS Rp gt gt lt lt gt lt 0110 0000 M M 0110 0001 M 0110 0010 MLA 0110 0011 044 0010 0100 MLA 0110 0100 045 0010 0101 MLA 0110 0101 046 0010 0110 MLA 0110 0110 MLA loom ZSRElSSSSISVLSIBLBS M 0010 0111 0110 0111 050 0010 1000 MLA 104 150 68 0110 1000 051 0010 1001 MLA 105 151 69 0110 1001 052 0010 1010 106 152 0110 1010 053 0010 1011 107 153 6B 0110 1011 054 0010 1100 MLA 0110 1100 055 0010 1101 MLA m 109 155 6D 0110 1101 056 0010 1110 MLA n 110 156 5E 0110 1110 0010 1111 0 111
49. 1 Ensure the 8842A is on and warmed up for at least 1 hour 2 Select the VAC function and the slow S reading rate 3 Connect the AC Calibrator to provide a voltage input to the HI and LO INPUT terminals 4 Low and Mid Frequency Test For each step in Table 6 3 select the indicated range set the AC Calibrator for the specified input and verify that the displayed reading is within the limits shown for each reading rate NOTE This procedure tests the extremes of each range You may shorten the procedure by testing only the quick test points indicated in Table 6 3 with asterisks 5 High Frequency Test For each step in Table 6 4 select the indicated range set the AC Calibrator for the specified input and verify that the displayed reading is within the limits shown for each reading rate NOTE This procedure tests the extremes of each range You may shorten the procedure by testing only the quick test points indicated in Table 6 4 with asterisks 6 Set AC calibrator to standby and disconnect it from the 8842A Table 6 3 Low and Mid Frequency AC Voltage Test Step Range Input Error in Display Readings Number Counts Voltage Frequency Minimum Maximum 1 2V 0 01000V 200 Hz 181 0 00819 VAC 0 01181 VAC 2 2V 0 10000V 200 Hz 87 09913 VAC 10087 VAC 3 2V 0 30000V 200 Hz 101 0 29899 VAC 0 30101 VAC 4 2V 1 00000V 200 Hz 150 0 99850 VAC 1 00150 VAC 5 2V 1 90000V 200 Hz 213 1 89787 VAC 1 90213 VAC
50. 1000V CAP CER 56PF 2 50V COG CAP CER 33PF 2 50V COG CAP CER 6 8PF 0 25PF 50V COG CAP POLYES 1UF 10 50V CAP POLYES 0 47UF 10 50V CAP CER 0 22UF 80 20 50V Z5U 10 20 35 CAP CER 1000PF 20 50V X7R CAP CER 680PF 5 50V COG CAP CER 1 2PF 0 25PF 50V COK CAP TA 10UF 20 10V CAP TA 10UF 20 25V CAP CER 0 01UF 80 20 50V Z5V CAP CER 39PF 2 50V COG CAP CER 12PF 2 50V COG CAP CER 68PF 2 50V COG CAP CER 22PF 2 50V COG DIODE S BV 20V IO 50MA SELECT IR DIODE SI BV 75V O 150MA 500MW FASTENER GROMMET POLYCARB 271 FASTENER PLUNGER NYL 271 SCREW PH P THD CUT STL 4 14 500 RELAY REED 1 FORM A 5V HIGH VOLTAGE RELAY REED 1 FORM A 4 5VDC SHIELD BOTTOM SHIELD TOP SPACER SNAP 180 RND NYL 125 TRANSISTOR SI PNP 40V 0 35W TO 92 TRANS SI N JFET SEL TO 92 RES MF 10K 0 1 0 125W 25PPM RES MF 20K 0 1 0 125W 25PPM RES MF 5K 0 1 0 125W 25PPM RES CF 8 2K 5 0 25W RES CF 100K 5 0 25W RES MF 2 222K 0 1 125W 25PPM RES CF 150K 5 0 25W RES CF 0 50 5 0 25W RES CF 75K 5 0 25W RES CF 91K 5 0 25W RES CF 2K 5 0 25W RES CF 12K 5 0 25W RES CF 15K 5 0 25W RES MF 10K 0 1 0 125W 50PPM RES MF 4 99K 1 0 125W 100PPM RES CF 10 5 0 25W RES CF 100K 5 0 25W TERM FASTON TAB 110 SOLDER IC OP AMP DUAL LO NOISE 8 PIN IC BPLR TRUE RMS TO DC CONVERTER IC LSTTL OCTAL D F F EDG TRG IC CMOS QUAD BILATERAL SWITCH AMP JFET INPUT 8
51. 157 6F 0110 1111 0111 0000 0111 0001 0111 0010 0111 0011 0111 0100 0111 0101 01110110 0111 0111 0011 0000 0011 0001 0011 0010 0011 0011 0011 0100 0011 0101 0011 0110 0011 0111 LISTEN ADDRESSES SECONDARY ADDRESSES lt 3 49 8842A Instruction Manual NOTE For the examples using the Fluke 1720A or 1722A the 8842A is plugged into port 0 The port is initialized by the INIT statement which sends IFC interface clear 3 50 4 1 4 3 4 4 4 5 4 7 4 8 49 4 10 4 11 4 12 4 13 4 14 4 15 4 16 4 17 4 18 4 19 4 20 4 21 4 22 4 23 4 24 Chapter 4 Measurement Tutorial Title Page INTRODUCTION DC VOLTAGE MEASUREMENT eere Circuit Loading Error iuis aa Input Bias Current Error nemen RESISTANCE MEASUREMENT eene 2 Wire ERR ae pansa eene EES Correcting for Test Lead Resistance in 2 Wire Ohms 4 Wire Applications of the Ohms 4 TESTING DIODES eset er EI ERR TESTING ELECTROLYTIC CAPACITORS A PRECISION CURRENT SOURCE eee DC CURRENT MEASUREMENT eere ene REDUCING THERMAL VOLTAGES eee AC VOLTAGE AND CURRENT MEASUREM
52. 2A INPUT and INPUT LO Any terminal to earth MAXIMUM INPUT 1000 dc 2000mA 300V rms 300V rms 700V rms 1000V peak or 2 x 10 V Hz whichever is less 2000 mA rms 1000V dc or peak ac 2 26 Measuring Voltage and Resistance To measure voltage or resistance select the desired function and connect the test leads as shown in Figure 2 9 Resistance can be measured in either the 2 wire or 4 wire configuration 2 27 Measuring Current To measure current select the desired function and connect the test leads as follows 1 Turn off power in the circuit to be measured Figure 2 10 2 Break the circuit preferably on the ground side to minimize the common mode voltage and place the 88424 in series at that point Turn on power in the circuit and read the display 4 Turn off power in the circuit and disconnect the 8842A 2 28 Current Fuse Protection The 2A input terminal is protected from overloads by a 2A 250V fuse which is accessible from the front panel and by an internal 3A 600V fuse If either fuse blows the 8842A will respond as though the input were zero WARNING TO AVOID ELECTRIC SHOCK REMOVE THE TEST LEADS BEFOREREPLACING THE FRONT PANEL FUSE 8842A Instruction Manual 2 29 To replace the front panel fuse first remove the test leads Then press in the lip of the 2A input terminal slightly and rotate it 1 4 turn counterclockwise Spring tension will force the fuse and fuse
53. 5 4095 us U215 7 U203 9 STROBE ONE 4 U213 6 U215 6 TWO 4095 us U203 5 DIGIT U216 4 DATA LI U U U 1 LI LJ LI U U 6 and U216 9 140 us low for inter digit blanking 450 us high for data on through U U217 1 through U217 7 f6 11 wmf Figure 6 11 Waveforms for Display Logic 6 49 Display Control U212 Check for the 1 MHz clock from the A D IC at U212 3 NOTE The following waveforms are illustrated in Figure 6 11 6 50 8 Bit Digit Driver 0215 Check for strobe waveforms 0 7 on U215 8 1 Reference U215 8 for waveform STROBE ZERO U215 7 is STROBE ONE U215 6 is STROBE TWO etc High level is 3 8V to 4 3V and low is near OV 6 49 8842A Instruction Manual Check for the same waveforms at outputs U215 11 through U215 18 However the high level should be approximately 30V If these waveforms are OK then strobe decoder U213 and display control U212 are OK in this regard 6 51 3 8 Strobe Decoder 0213 Check for strobe waveforms 0 7 on U213 4 5 6 7 9 10 11 12 Reference U213 4 for STROBE ZERO Check for strobe decoder inputs SLO SL1 SL2 on U213 1 2 3 respectively 6 52 8 Bit Segment Driver U217 Check that U217 1 through U217 7 all look like the waveform DIGIT DATA High level is 3 8V to 4 3V Check that U217 12 through U217 18 all look like the waveform DIGIT DATA except high level is approximately 30V 6 53 4 to 7 Segment Decoder U216 Check tha
54. 5 42 TEEE 488 Interface Power Supply eese 5 43 TRUE RMS AC OPTION 09 5 44 WAC SCINS badd eats 5 45 MAAC 5 46 Frequency Response Trimming 5 47 True RMS AC to DC Conversion 2 6 Mai t enance u onn c oO du 6 1 INTRODUCTION ther Rete pere enne quand 6 2 PERFORMANCE TEST 6 3 Diagnostic Self Tests ee C ede Cd Eta 6 4 DC Voltage Testori ete tese 6 5 AC Voltage Test Option 09 6 6 Resistance 6 7 DC Current Test d dnb aaae 6 AC Current Test Option 09 6 9 CALIBRATION 6 10 Basic Calibration 2 444404040 6 11 INITIAL PROCBDURE ete terrere eter 6 12 A D CALIBRATION 22 040440 40000 0 0 6 13 OFFSET AND GAIN 6 14 HIGH FREQUENCY AC CALIBRATION 6 15 Advanced Features and Special Considerations 6 16 STORI
55. 66 67 32 66 67 4 100 1 60 Hz 80 32 80 4 100 1 400 2 76 19 32 76 19 4 100 1 5 31 The custom A D IC 0101 generates five 6 bit numbers after each trigger from the HC and then pulls INT low telling the that data is ready The uC reads the five 6 bit numbers over the bus CS7 pulses low five times for five read cycles and computes the value of the A D sample using calibration constants The uC averages the appropriate number of samples for one reading which is then sent to the keyboard display interface for display For example with a 60 Hz power line frequency an externally triggered reading in the slow reading rate would cause the uC to send 32 pulses on TR at an 80 Hz rate The 32 A D samples would be calibrated and averaged by the and sent for display With internal triggering the A D runs continuously at 80 samples per second with a reading being sent to the display every 32 samples Calibration Correction The calibration constants used by the In Guard uC in computing each reading are stored in the EEROM electronically erasable read only memory Calibration Memory U220 The front panel CAL ENABLE switch protects the EEROM from accidental writes 5 23 8842A Instruction Manual 5 24 5 32 Keyboard Display Control Keyboard Display Controller U212 communicates with the In Guard over the internal bus During a write cycle address line AO tells U212 whether to consid
56. Address ee tere bn ie kaqa Universal Commands Addressed Commands TALK ONLY MODE erre arbe dee rie REMOTE TIMING CONSIDERATIONS IMMEDIATE MODE COMMANDS EXAMPLE PROGRAMS Measurement Tutorial rites token enr exea Coker Ere Ea 4 1 4 2 4 3 4 4 4 5 4 6 4 7 4 4 9 4 10 4 11 4 12 4 13 4 14 4 15 4 16 4 17 4 18 4 19 4 20 4 21 4 22 4 23 4 24 INTRODUCTION ort riter nun q DC VOLTAGE Circuit Loading Error ee e Input Bias Current Error na 4 4 2 Wi re OBI Correcting for Test Lead Resistance in 2 Wire Ohms 4 Wire Om ee eerte ede et Applications of the Ohms Functions TESTING TESTING ELECTROLYTIC CAPACITORS A PRECISION CURRENT SOURCE eere
57. Buffer U201 At this point it is necessary to return the 8842A to the normal operating mode by turning the power switch off removing the short from TP205 U202 38 and installing the True RMS AC option if present so that U201 14 15 may be checked Power up the instrument Unlike the previous checks outputs are steady state and therefore do not require a sync signal Logic 1 is approximately 4 3V dc Check that U201 14 is high 4 3V for mA AC and all ranges of VAC and low for all other functions Check that U201 15 is high 4 3V for mA AC and 200V ac and 700V ac ranges and low for all other functions Check that U201 16 is high 4 3V for all 2 wire and 4 wire ohms ranges and low for all other functions Check that U201 17 is high 4 3V for the lowest three VDC ranges and all 2 wire and 4 wire ohms ranges and low for all other functions 3 to 8 Chip Select Decoder U208 Make the following checks in the normal operating mode using the fast reading rate and any function and range These sequences begin 5 5 ms after the A D trigger which is the falling edge at U202 40 Check U208 13 for 0 2 us pulses normally high groups of 1 pulse spacing 10 ms Check U208 12 for 0 2 us pulses normally high groups of 1 pulse spacing 10 ms 10 us after pin 13 Check U208 11 for 0 2 us pulses normally high groups of 1 pulse spacing 10 ms 46 us after pin 13 Check U208 15 for 0 2 us pulses normally high groups of
58. Bulgaria Ac Sophilco Cust Supp Serv P O Box 42 1309 Sofia Bulgaria TEL 359 2 200785 FAX 359 2 220910 C S F R Elso NA Berance 2 16200 Praque 6 TEL 42 2 316 4810 FAX 42 2 364986 Data Elektronik BRNO Jugoslavska 113 61300 TEL 42 5 57400 2 FAX 42 5 574002 Canada Fluke Electronics Canada Inc 400 Britannia Rd East Ut 1 Mississauga Ontario 142 1X9 TEL 905 890 7600 FAX 905 890 6866 Chile Intronica Instrumen Electronica 1 Guardia Vieja 181 Of 503 Casilla 16500 Santiago 9 TEL 56 2 232 6700 China Fluke S C Room 2111 Scite Tower Jianguomenwai Dajie Beijing 100004 PRC TEL 86 10 512 6351 6319 3437 FAX 86 10 512 3437 Colombia Sistemas E Instrument Ltda Calle 83 No 37 07 Po Box 29583 Santa Fe De Bogota TEL 57 1 287 5424 FAX 57 1 218 2660 Costa Rica Electronic Engineering S A Carretera de Circunvalacion Sabanilla Av Novena P O Box 4300 1000 San Jose TEL 506 253 3759 or 225 8793 FAX 506 225 1286 Croatia Kaltim Zagreb Fluke Sis amp Serv Draga 8 41425 Sveta Jana TEL 385 41 837115 FAX 385 41 837237 Denmark Fluke Danmark A S Cust Supp Ejby Industrivej 40 DK 2600 Glostrup TEL 45 43 44 1900 or 1935 FAX 45 43 43 9192 Ecuador Proteco Coasin Cia Ltda Av 12 de Octubre 2449 y Orellana P O Box 17 03 228 A Quito TEL 593 2 230283 or 520005 FAX 593 2 561980 Egypt EEMCO Electronic Equipment Mkting Co
59. FROM PRECISION VOLTAGE REFERENCE TO OHMS SWITCH STATE TABLE PROTECTION RANGE U4028 U402C U402D U403A 04038 U403C U4030 rout e oio 200 2000 2 20 kQ 200 2000 20 MO Switch closed f5 07 wmf Figure 5 7 Ohms Current Source 5 12 Theory of Operation OHMS PROTECTION The second stage U404 precision resistor network Z401 and analog switches U402 and U403 is a current amplifier whose gain is controlled by the In Guard uC The In Guard uC sets the output current for each range by controlling U402 and U403 See switch state table in Figure 5 7 5 16 OHMS PROTECTION The Ohms Protection circuit Q402 Q403 Q404 Q405 Q406 and Q407 clamps the open circuit voltage of the Ohms Current Source and provides protection for the Ohms Current Source The circuit protects the Ohms Current Source from up to 300V across the INPUT terminals The circuit also clamps voltage transients larger than 1560V with four MOVs RV401 RV402 RV403 and RV404 In addition a 1 2W fusible wire wound resistor R410 in series with the output current path fails open circuit under extreme overvoltage conditions Large positive input voltages are blocked by CR402 Large negative input voltages are dropped equally across three high voltage transistors Q402 Q403 and Q404 If 300V is present at the collector of Q404 the voltage drops equally across Z402 so that large negative voltages never r
60. FUSE FOR FIRE PROTECTION TO AVOID ELECTRIC SHOCK REMOVE THE POWER CORD BEFORE REPLACING THE EXTERNAL LINE FUSE The 8842A has a rear panel power line fuse in series with the power supply A 1 4A 250V slow blow fuse is installed in the factory for operation from 90V to 132V For operation with power line voltages of 198V to 250V the fuse must be replaced with a 1 8A 250V slo blow fuse To replace the power line fuse first remove the power cord Then turn the rear panel fuse cover 1 4 turn counterclockwise with a screwdriver For power line voltages of 198V to 250V use only a 1 4 x 1 1 4 6 3mm x 32mm fuse with at least a 100A breaking capacity Connecting to Line Power WARNING TO AVOID SHOCK HAZARD CONNECT THE INSTRUMENT POWER CORD TO A POWER RECEPTACLE WITH EARTH GROUND TO AVOID INSTRUMENT DAMAGE CHECK THAT THE REAR PANEL LINE VOLTAGE SELECTION SWITCHES ARE SET TO THE POWER LINE VOLTAGE IN OUR AREA The 8842A be configured to accept line power of 100 120 220 240V ac 10 250V maximum at 50 60 or 400 Hz The voltage must be selected by setting the rear panel LINE SET switches as shown in Figure 2 1 The 8842A automatically senses the power line frequency at power up so that no adjustment for frequency is necessary FOR THIS LINE USE THIS SWITCH FOR THIS LINE USE THIS SWITCH VOLTAGE SETTING VOLTAGE SETTING 90 to 109V LINE 198V to 229 LINE SET SET 109V to 132V 229V to 250V 12 01 wmf
61. GUARD CROSSING 728840 2 w5 HARNESS ANALOG FRONT 765297 1 W6 HARNESS ANALOG REAR 765305 1 W10 CABLE LINE VOLTAGE GROUND 873740 1 CABLE LINE VOLTAGE LINE 873745 1 W12 CABLE LINE VOLTAGE NEUTRAL 873752 1 XU101 XU102 SOCKETJC 40 PIN DUAL WIPE RET 756668 3 XU212 756668 XU220 SOCKET IC 24 PIN DUAL WIPE BEAM TYPE 756650 1 XU222 756353 1 201 CRYSTAL 8 0OMHZ QUARTZ HC 18U 707133 1 Z101 RNET MF HERM SIP 8842 A TO D CONV 755983 1 2301 2303 RNET MF HERM SIP 8842 LO V DIVIDER 755934 2 902 RNET MF HERM SIP 8842 HI V DIVIDER 756130 1 Z304 Z402 RNET CERM SIP 8840 HI V PROTECT 715789 2 Z401 RNET MF HERM SIP LO V 1 SOURCE 755884 1 702 RNET MF HERM SIP 8842 LO V DIVIDER 756080 1 1 FUSIBLE RESISTOR TO ENSURE SAFETY USE EXACT REPLACEMENT ONLY List of Replaceable Parts 7 SERVICE CENTERS 5301 F303 UIT 3 t x 2 Jmm C105 crios R106 c312 R303 cR30e J 0307 N RU4 04 Ys 08310 1304 2305 i Ww 0305 n os 0316 OC m 0319 8310 0303 R413 0303 R414 wags 1 pa 9 7201 USED ON 8840A AF ONLY 1101 1 201 JPR2 O 0203 UNDER 2 208 UNDER R216 CROIS C IOIGITAL LO 1601 D C604 05 VR603 VREO cece 5 8842 1601 17 03 wmf A1 Main
62. Get Error Status The G7 command copies the error status register into the output buffer in the format shown in Figure 3 6 The first two digits are always 1 and 0 The second two digits represent the appropriate error code if an error has occurred Error codes are listed in Table 2 1 Section 2 If an error has not occurred the second two digits are 00 An example output string follows Example Explanation 1071 CR LF 1 Leading 1 0 Leading 0 71 Syntax error in device dependent command string The G7 command gives the error status as it exists when the command is executed at its position in the input string The G7 command does not clear the error status register For more information about error messages see paragraph 3 40 3 20 3 21 Remote Programming DEVICE DEPENDENT COMMAND SET G8 Get Instrument Identification The G8 command copies the 8842A instrument identification into the output buffer in the format shown in Figure 3 6 The identification is represented by four comma separated fields that are interpreted in Table 3 1 The first field indicates the manufacturer the second indicates the instrument model number the third is always zero and the fourth indicates the version number of the IEEE 488 interface software Example Explanation FLUKE 8842A 0 V4 0 CR LF This instrument is a Fluke 8842A with IEEE 488 interface software version 4 0 N Numeric Entry Command Format Explanation 3 22 3 23
63. MHz the 85RF has a frequency range of 100 KHz to 500 MHz The probes are calibrated so that the dc output is equivalent to the rms value of a sine wave input over a range of 0 25V to 30V rms For best accuracy the probes should be used with DMMs having 10 MO input impedance This condition is satisfied by the 8842A in the 200V and 1000V ranges The probes can also be used with the 8842A in the 200 mV 2V and 20V ranges if a 10 MQ resistor is connected in parallel across the 8842A input terminals Options and Accessories ACCESSORIES 8 10 Current Shunt 80J 10 The 80J 10 current shunt extends ac or dc current measurement up to 10A continuous or to 20A for one minute without overheating 8 11 Current Probes Y8100 8101 801 400 and 801 600 The current probes extend the ac and dc current measurement range The Y8100 current probe uses the Hall effect to measure dc or ac current up to 200A in two ranges without electrical contact The Y8101 is a low cost compact current probe which uses a transformer to measure ac current from 2A to 150A The 801 600 uses a transformer to measure ac current from 1A to 600A and features a large jaw opening for industrial use The 8101 801 400 and 801 600 measure ac current only 8 12 High Voltage Probes 80K 6 and 80K 40 The high voltage probes extend the dc and ac voltage measurement range while minimizing shock hazard The 80K 6 has a range of 0 to 6000V dc or peak ac with frequency res
64. Measuring Input Bias Current Error seen Wire Ohms Measuremoetnt enne ene nsnsi Wire Ohms Measurement esee nennen Burden Voltage Error Calculation eese nennen Waveform Comparison enne rennen enne Typical Crest Factors for Various Waveforms a Combined AC and DC Measurement Reduction of Zero Input Error n enne Shielding for Low Voltage Measurements eese nenne Shielding for Low Resistance Measurements seen 8842A Instruction Manual 4 12 Leakage Resistance in High Resistance Measurement 5 1 Overall Functional Block Diagram seen 5 2 DC Scaling VDC and mA 9 3 Track Hold a u ee ere trit ern aasawa Qaqa aayqa 5 4 Track Hold Circuit Configurations eese ener 5 5 Timing Diagram for One A D 5 6 Precision Voltage Reference a eene 9 72 Ohms Current eee dete E 528 2 Ohms be toc d Pe eae nd 3 9 Analog to Digital Converter aeter tre e iR enti Php 5 10 First Remainder Store Period
65. N Table 7 1 8842A Digital Multimeter MANUFACTURERS DESCRIPTION PART NUMBER OR GENERIC TYPE REFERENCE DESIGNATOR MAIN PCA 759365 DISPLAY PCA 728873 FUSE 406 1 375 3A 600V FAST 475004 FUSE 25 1 0 2 250 FAST 376582 FUSE 25X1 25 0 25A 250V SLOW 166306 FILTER LINE 250VAC 3A IEC RECEPTACLE 721274 ZUB2203 00 SCREW PH P LOCK STL 6 32 250 152140 19042 SCREW TH P SS 4 40 187 721118 COMMERCIAL SCREW FIH P STL 8 32 500 721134 COMMERCIAL SCREW PH P THD FORM STL 4 20 500 721449 COMMERCIAL SCREW FHU P LOCK SS 6 32 250 320093 320093 SCREW FH P LOCK STL 8 32 375 114116 114116 SCREW PH P LOCK STL 4 40 312 152116 19023 SCREW PH P SEMS STL 4 40 375 281196 COMMERCIAL NUT EXT LOCK STL 6 32 3440D 152819 501 060800 00 SPACER 735407 COMMERCIAL SPACER 735415 COMMERCIAL SCREW FH P LOCK STL 6 32 750 114504 18248 SPACER RND NYL 166 250 772889 11558 EXT LOCK STL 4 40 195255 501 040800 00 CONN ACC MICRO RIBBON SCREW LOCK 854737 LT43026 SHIELD MAIN BOTTOM 728998 728998 CASE METAL 656399 656389 FRONT PANEL MODIFIED 759241 759241 PUSHROD POWER 656413 656413 PUSH ROD RAI 656488 656488 PUSH ROD CAL ENABLE SWITCH 684142 684142 MOUNTING PLATE HANDLE LEFT 729004 729004 MOUNTING PLATE HANDLE RIGHT 660472 660472 10 HANDLE PAINTED BLACK 810127 810127 11 BEZEL REAR 660480 660480 12 SPACER MATRIX 684126 684
66. On Mode Enabled gxTRIG SMF OVER ERROR CAL AUTO OFFSET TEST w lt w w mA Function Self Test REMOTE 1 1 1 mV DCAC N and units Enabled TALK LISTEN 6060608 IEEE 488 Interface m ais MkQ 4 WIRE J Annunciators Annunciators 12 05 2 wmf Figure 2 5 Front Panel Features cont 2 6 Operating Instructions OPERATING FEATURES SAMPLE COMPLETE output TTL level Normally high pulsed low when samples for i a reading are completed EX TRIG input 3 HIGH and LO SENSE d Terminals for 4 Wire alling edge triggere TALK ONLY and IEEE 488 Ohms Only internally selectable ADDRESS Selection Switches ad TTLLEVELS ADDRESS SHELL NOT GROUNDED 15V MAX 488 Interface Bus Connector EXT TRIG SAMPLE SH1 T5 L4 SR1 10V MAX COMPLETE DC1 DT1 PPO E1 JOHN FLUKE CO INC IEEE 05 g g 240V W 220V EVERETT WA MADE IN U S A AC 09 220v PATENTS 100V LINE FUSE CAUTION A v and LO INPUT Rear feet rotate Line Voltage Terminals for rack mounting Selection Switches Power Line Cord Connector Serial Number Power Line Fuse Available with IEEE 488 Interface only Otherwise the upper portion of the rear panel is covered with an insert as shown at right CAUTION The rear panel insert is attached from inside the case Refer to Sec
67. PCA Figure 7 2 7 13 8842A Instruction Manual REFERENCE DESIGNATOR DS 1 MP 4 7 XU 203 204 NOTES 7 14 Table 7 3 A2 Display PCA FLUKE DESCRIPTION STOCK NO DISPLAY VACUUM FLUORESCENT 680843 PAD ADHESIVE 735365 SOCKET IC 16 PIN 291534 Static sensitive part MFRS SPLY CODE 89536 21958 91506 MANUFACTURERS PART NUMBER OR GENERIC TYPE 680843 735365 216AG 39D Figure 7 3 A2 Display PCA List of Replaceable Parts SERVICE CENTERS 8840A 1602 17 03 wmf 7 15 8842A Instruction Manual 7 16 00779 AMP Inc Harrisburg PA 01121 Allen Bradley Co Milwaukee WI 01295 Texas Instruments Inc Semiconductor Group Dallas TX 04222 AVX Corp AVX Ceramics Div Myrtle Beach SC 04713 Motorola Inc Semiconductor Products Sector Phoenix AZ 05791 Lyn Tron Inc Burbank CA 06665 Analog Devices Formerly Precision Monolithics Santa Clara CA 07047 Ross Milton Co The Southampton PA 07263 Fairchild Semiconductor North American Sales Cupertino CA 09214 General Electric Co Semiconductor Products Dept Auburn NY 0B445 Electri Cord Mfg Inc Westfield PA 12014 Chicago Rivet amp Machine Co Naperville IL 13103 Thermalloy Co Inc Dallas TX 13764 Micro Plastics Flippin AR Supply Codes for Manufacturers 13919 Burr Brown Corp Tucson AZ 14329 Wells Electronics Inc South Bend IN 15636 Elec Trol Inc Sa
68. TdA AS Address Valid to AS Delay TdAS A AS to Address Float Delay TdAS DR AS to Read Data Required Valid TwAS AS Low Width 0 0 OUT Notes t 1 2 3 1 2 3 1 2 3 4 1 2 3 1 TwDSR DS Read Low Width TwDSW DS Write Low Width TdDSR DR DS to Read Data Required Valid ThDR DS Read Data to DS Hold Time 10 TdDS A DS to Address Active Delay 11 TdDS AS DS 1 to AS Delay 12 TdR W AS R W Valid to AS Delay 13 TdDS R W DS 1 to R W Not Valid 2 3 4 5 TdAz DS Address Float to DS 6 7 8 9 14 TdDW DSW Write Data Valid to DS Write 1 Delay 15 TdDS DW DS 1 to Write Data Not Valid Delay 16 TdA DR Address Valid to Read Data Required Valid 17 TdAS DS AS 1 to DS Delay NOTES 1 2 3 4 Timing numbers given are lor minimum 1 2 3 4 1 2 3 4 1 2 3 4 0 1 70 1 2 3 70 1 2 3 08 60 1 2 3 50 1 273 70 1 2 3 1 2 3 4 80 1 2 3 Test Load 5 All timing references use 2 0 V lor a logic 1 end 0 8 V for logic All units in nanoseconds ns Also see clock cycle time dependen characteristics table T Timings are preliminary and subrect to change When using extended memory timing add 2 TpC Zilog and 28 are trademarks of Zilog Inc with whom John Fluke Mfg Co Inc is not associated Reproduced by permission 91983 Zilog Inc This material shall not be reproduced without the written consent of Zilog Inc Figure 5 14
69. Wiring Table 6 19 indicates which waveforms in Figure 6 11 are seen on keyboard inputs to U212 when each front panel button is pressed and held For example if the SRQ button is Maintenance TROUBLESHOOTING pressed and held an inverted version of STROBE ZERO waveform is applied to U212 38 If range button 20 is pressed then inverted STROBE ONE is applied to U212 1 and so forth Note that these waveforms are very noisy with many spikes That is normal Compare these waveforms with normal STROBE ZERO at U215 8 6 59 ANALOG CONTROL SIGNALS Table 6 19 Keyboard Wiring SIGNAL NAME RLO RL1 RL2 RL3 RL4 RL5 RL6 Table 6 20 is useful for determining whether the correct digital signals are being applied PIN U212 38 U212 39 U212 1 U212 2 U212 5 U212 6 U212 7 BUTTONS THAT PRODUCE INVERTED STROBE ZERO SRQ LOCAL RATE OFFSET 20 0 TRIG EX TRIG BUTTONS THAT PRODUCE INVERTED STROBE ONE 20 200 2 20 200 2000 Not used BUTTONS THAT PRODUCE INVERTED STROBE TWO VDC VAC 2 WIRE 4 WIRE KQ mA DC mA AC AUTO to the analog control devices indicated Since most of these devices the quad analog switches in particular have no digital outputs it cannot be determined directly whether the correct pattern is being latched That determination must be made indirectly by analog means Nevertheless it is valuable to know whether the correct dig
70. and ohms ranges r1 r2 r3 and r4 U306 is connected as a buffer to charge stray capacitance at the non inverting input of the T H Amplifier The pre charge configuration is not used in any other ranges 5 14 PRECISION VOLTAGE REFERENCE The Precision Voltage Reference Figure 5 6 provides precise reference voltages of 7 00000 and 7 00000 The reference element is a reference amplifier ref amp The nominal ref amp voltage is 6 5V REF AMP SUPPLY Z702 15 7V SENSE REF 2701 AMP f5 06 wmf Figure 5 6 Precision Voltage Reference 8842A Instruction Manual Resistor R701 precision resistor network Z701 and transistor zener diode combination 0701 are produced as a matched set so that the output of U702A is precisely 7 00000 This output is remotely sensed at the pins of the custom A D IC U101 Diode CR701 prevents the output from going positive at power up U702B functions as an inverter to provide the 7 00000V output and to supply the reference amplifier The gain of U702B is set by the two 20 kQ resistors in the resistor network 2702 5 15 OHMS CURRENT SOURCE The Ohms Current Source Figure 5 7 provides a precise test current for the ohms functions The first stage U401 R401 and Q401 produces a precise reference current using precision resistor R401 and a 7 0000V reference voltage from the Precision Voltage Reference REFERENCE CURRENT R416 R401 1 M F lt O Z401 2401 2401 7V
71. case it is merely looking for data available The function of the program is to display on the screen the lowest resistance value measured on the input terminals of the 8842A using the 2 wire ohms function in autorange The range and function commands are programmed using the Put Instrument Configuration command Microsoft QuickBasic V 4 5 on IBM PC PC XT or PC AT SINCLUDE qbib45 dcl bdname GPIBO Board name is GPIBO CALL IBFIND bdname BD Initialize the Interface Board devname 18842A Device name is 18842 CALL IBFIND devname dvm Initialize the device CALL IBCLR dvm Clear the device WRTS N3001P0 Y1 2 CALL IBWRT dvm WRTS Write functions to the instrument RD 5 18 CALL IBRD dvm RD Get first reading r VAL RD PRINT LEFT RD 16 S 2 WIRE LOWEST READING DO Execute the statements up to the loop statement until new low is found WRT CALL IBWRT dvm WRT Trigger the device SPR 0 DO UNTIL SPR AND amp H40 amp H40 CALL IBRSP dvm SPR Serial poll the device until data available LOOP RD SPACE 18 CALL IBRD dvm RD Get next data s VAL RD LOOP WHILE s gt r Throw away data if not lowest r s Update lowest reading GOTO label1 Print new low END 13 14 06 wmf Figure 3 14 Example Programs Using the IBM PC cont 3 43 8842A Instruction Manual The following application program is written in QBASIC for th
72. considerations in addition to those discussed under dc voltage and current measurement These include the concepts of rms conversion crest factor bandwidth and zero input error True RMS Measurement The True RMS AC Option measures the true rms value of ac voltages and currents In physical terms the rms root mean square value of a waveform is the equivalent dc value that causes the same amount of heat to be dissipated in a resistor True rms measurement greatly simplifies the analysis of complex ac signals Since the rms value is the dc equivalent of the original waveform it provides a reliable basis for comparing dissimilar waveforms By contrast many meters in use today use average responding ac converters rather than true rms converters The scale factor in these meters is adjusted so that they display the rms value for harmonic free sinusoids However if a signal is not sinusoidal average responding meters do not display correct rms readings The 8842A actually derives the rms value using analog computation This means that the 8842A readings represent true rms values not only for harmonic free sinusoids but also for mixed frequencies modulated signals square waves sawtooths random noise rectangular pulses with 10 duty cycle etc Waveform Comparison Figure 4 6 illustrates the relationship between ac and dc components for common waveforms and compares readings for true rms meters and average responding meters For examp
73. function the 2 kQ range and the medium reading rate 2 Connect the test leads to the capacitor with the INPUT HI lead to the lead and the INPUT LO lead to the lead The 8842A attempts to charge it to the open circuit voltage of the 2 kQ range about 6 V 3 Disconnect the test lead To test for leakage select the VDC function and the 20V range leave the 8842A in the medium reading rate and measure the voltage that was stored on the capacitor during step 2 a If the capacitor is good the voltage across the capacitor will be about 6V and will be relatively stable b Ifthe capacitor is leaky the voltage across the capacitor will be much less than 6V and the voltage will be decreasing The rate of change depends on how leaky the capacitor 15 c With some electrolytic capacitors the reading will increase This usually indicates the capacitor is defective 5 To test the capacitor s dielectric absorption briefly short the capacitor s leads together and then measure the voltage across the capacitor a If the dielectric is good 1 has low dielectric absorption the voltage across the capacitor will be nearly zero volts b If the dielectric is poor i e has high dielectric absorption the voltage across the capacitor will be significantly above zero 4 7 8842A Instruction Manual 4 8 4 12 A PRECISION CURRENT SOURCE The ohms current source the internal current source used in the ohms fu
74. ignored and are not placed in the input buffer If the 8842A receives a group of terminators such as CR LF or CR LF EOD only a single terminator is loaded into the input buffer Numeric values used in PUT commands may be in NR1 NR2 or NR3 format as described in the IEEE 488 Codes and Formats Recommended Practice These correspond to the signed integer real number and real number with exponent formats described under the N command For reference Figure 3 8 shows how the 8842A interprets messages 3 21 Instruction Manual DEVICE DEPENDENT MESSAGES Single character Commands Bn Cn Dn Fn Gn Pn Rn Sn Wn Xn Yn Zn Numeric entry Characters NE 0123456789 Terminators CR LF GET EOI INTERFACE MESSAGES Address Messages MLA MTA UNL UNT Universal Commands ATN DCL IFC LLO REN SPD SPE Addressed Commands GET GTL SDC Ignored Characters comma Space All Other ASCII non printing characters except CR and LF ERROR PRODUCING CHARACTERS lt gt HIJKLMOQUV Each of these commands requires the single numeric digit n These characters are used for entering numbers Carriage Return Line Feed Group Execute Trigger End Or Idenity used as END DAB My Listen Address My Talk address Unlisten Untalk Attention Device Clear Interface Clear Local Lockout Remote Enable Serial Poll Disable Serial Poll Enable Group Execute Trigger Go to Local Selected Device C
75. mode disabled 1001 CRLF 1 Leading 1 0 Leading 0 0 Not in cal verification 1 Cal mode enabled A D cal selected 3 13 8842A Instruction Manual 3 17 3 18 3 19 G5 Get IAB Status The G5 command loads the output buffer with the IAB status in the format shown in Figure 3 6 As Table 3 1 explains the IAB status is a four character string which indicates the status of the FRONT REAR switch front or rear analog inputs selected the autorange feature autorange on or off and the OFFSET feature OFFSET on or off The first digit is always 1 An example output string follows Example Explanation 1011 CR LF 1 Leading 1 0 FRONT inputs 1 Autorange off 1 OFFSET feature on It is useful to know whether autorange is on or off because this information is not available from the GO command For example the GO command could indicate that the 8842A was in the 200 mV range but it would not indicate whether the 8842A was in autorange or manual range G6 Get YW Status The G6 command loads the output buffer with the YW status in the format shown in Figure 3 6 The YW status is a four character string which indicates which terminators are selected and whether the output suffix is enabled or disabled as shown in Table 3 1 The first two digits are always 1 and 0 An example output string follows Example Explanation 1015 1 Leading 1 0 Leading 0 1 Y1 enable output suffix 5 W5 enable LF only G7
76. numeric part directly into a numeric variable and the suffix into a string variable The leading comma of the suffix serves as a convenient delimiter For example a BASIC program statement might be INPUT 1 A B The suffix status can be read using the G6 command The 8842A defaults to YO on power up and any device clear command DCL or SDC unless in talk only mode 0 Self Test Command The ZO command initiates the diagnostic self tests as does pressing the front panel SRQ button for 3 seconds The 8842A then runs through the tests in sequence For a description of the self tests see the Maintenance section If the 8842A detects an error an error message is loaded into the output buffer and displayed on the front panel After the last test the 8842A is reset to the power up configuration and it begins taking readings It is an error to send the 8842A device dependent commands during the self tests However the controller can still make the 8842A a talker to read the output buffer during the test and thus record each error that occurs except that only the last of the digital self test errors can be read After the tests only the last error is stored in the output buffer if more than one error occurred 3 19 8842A Instruction Manual Error messages are indicated by an exponent of 21 For more about error messages see paragraph 3 40 Since the 8842 is reset at the end of the self tests the 70 command should be
77. of counts 8842A Instruction Manual Operating Characteristics TEMPERATURE COEFFICIENT lt 0 0006 of reading 0 3 Count per C from 0 C to 18 C and 28 C to 50 C MAXIMUM INPUT 1000V dc or peak ac on any range NOISE Automatically optimized at power up for 50 60 or 400 Hz RATE READINGS FILTER NMRR PEAK NM CMRR SECOND SIGNAL S5 2 5 Analog amp Digital gt 98 dB 20V or 2x FS4 5140 dB 6 20 Digital gt 45 dB 1x FS gt 100 dB F 100 None 1x FS gt 60 dB TRUE RMS AC VOLTAGE OPTION 8842A 09 Input Characteristics 4 20 volts or 2 times full scale whichever is greater not to exceed 1000V 5 Reading rate 1 3 rdg sec in the 20 mV 20 200 mA dc ranges 6 Reading rate 1 25 rdg sec in the 20 mV 20 200 mA dc ranges 1 Reading rate with internal trigger and 60 Hz power line frequency See reading rates for more detail 2 Normal Mode Rejection Ratio at 50 or 60 Hz 0 1 The NMRR for 400 Hz 0 1 is 85 dB in S rate and 35 dB in M rate 3 Common Mode Rejection Ratio at 50 or 60 Hz 0 135 with 1 in series with either lead The CMRR is gt 140 dB at dc for all reading rates RANGE 200 mV 2V 20V 200V 700V DIGITS FULL SCALE 5 2 RESOLUTION 5 DIGITS 4 DIGITS 199 999 mV 1yuV 10 1 99999V 10 uV 100 19 9999 100 1 mV 199 999V 1mV 10 mV 700 00V 10 mV 100 mV 4
78. of the dc front end via U302 pins 15 and 14 The Track Hold Amplifier is set up for unity gain on all ac ranges static awareness A Message From Fluke Corporation Some semiconductors and custom IC s can be damaged by electrostatic discharge during handling This notice explains how you can o minimize the chances of destroying such devices s pili yy 1 Knowing that there is a problem 2 Leaning the guidelines for handling them 3 Using the procedures packaging and bench techniques that are recommended The following practices should be followed to minimize damage to S S static sensitive devices LL 3 DISCHARGE PERSONAL STATIC BEFORE HANDLING DEVICES USE A HIGH RESIS 1 MINIMIZE HANDLING TANCE GROUNDING WRIST STRAP 2 KEEP PARTS IN ORIGINAL CONTAINERS UNTIL READY FOR USE 4 HANDLE S S DEVICES BY THE BODY 5 USE STATIC SHIELDING CONTAINERS FOR 8 WHEN REMOVING PLUG IN ASSEMBLIES HANDLING AND TRANSPORT HANDLE ONLY BY NON CONDUCTIVE EDGES AND NEVER TOUCH OPEN EDGE CONNECTOR EXCEPT AT STATIC FREE WORK STATION PLACING SHORTING STRIPS ON EDGE CONNECTOR HELPS PROTECT INSTALLED S S DEVICES 6 DO NOT SLIDE S S DEVICES OVER ANY SURFACE C 9 HANDLE S S DEVICES ONLY AT A STATIC FREE WORK STATION 10 ONLY ANTI STATIC TYPE SOLDER SUCKERS SHOULD BE USED 11 ONLY GROUNDED TIP SOLDERING IRONS SHOULD BE USED 7 AVOID PLASTIC VINYL AND STYROFOAM IN WORK AREA PORTIONS REPRIN
79. panel LOCAL button The result is that the local mode is not accessible by front panel control Serial Poll Disable A multiline message which removes the serial poll enable state Serial Poll Enable A multiline message which causes the serial poll data rather than output buffer data to be transferred on the bus once ATN becomes false 3 55 Addressed Commands Addressed commands are multiline messages which are accepted and interpreted by only those devices currently addressed to listen The 8842A responds to the following addressed commands GET GTL SDC Group Execute Trigger Not to be confused with the device dependent Get commands GET loads a trigger command into the input buffer and also terminates the string at that point Only a single character is loaded into the input buffer The trigger command is executed in its proper turn in the input string rather than immediately When executed GET initiates a measurement Go To Local Causes the 8842A to switch to local This command does not enter the input buffer If the display has been blanked with a D1 command issue a DO command before sending GTL Selected Device Clear Identical to the universal command DCL but is accepted and interpreted by current listeners only Therefore it clears the 8842A only if it is addressed to listen 3 56 TALK ONLY MODE The talk only mode lets you take advantage of the remote capability of the 8842A without having to u
80. problems in the display keyboard system Finally as in most processor based systems there are communication links between the various parts of the system Specifically in the 8842A there is a bus interface between analog and digital control circuits and a guard crossing interface between logic circuits which may be separated by large potentials Failures in these links can generate problems that may be difficult to locate and repair However such failures will in turn cause failures in some analog and or digital section Thus indirectly troubleshooting the affected section will lead to correction of problems in the internal bus or guard crossing circuit Diagnostic Self Tests To run the diagnostic self tests disconnect the test leads and press the SRQ button for 3 seconds If the test leads are left attached to the input terminals the 8842A may indicate errors are present most likely errors 5 7 8 9 and 10 Also if the FRONT REAR switch is in the REAR position the 8842A skips tests 3 and 4 and if Option 09 is not installed the 8842A skips tests 1 2 and 3 For all tests there is a 0 5 second delay period before any readings are taken The tests are all contingent on the A D Converter being properly calibrated but do not depend on the Offset and Gain Calibration constants Failing the tests indicates that key portions of the 8842A are not performing properly Passing the tests gives approximately a 90 probability that all VDC
81. specified nominal input When the input is OQ short press the OFFSET switch and verify that the OFFSET anunciator is illuminated NOTE A new OFFSET must be stored for each new range selected a 6 8 2 Select the 4 wire ohms function Test the 4 wire ohms function 1 Verify that the displayed reading is within the limits shown for each reading rate b Test the 2 wire ohms function Select the 2 wire ohms function The SENSE test leads need not 1 be disconnected Verify that the displayed reading is within the limits shown for each reading rate Step o O Q N NN O 14 2 4 V digit counts Range 200 200 2000 2000 2 kO 2 20 kQ 20 kQ 200 200 2000 2000 20 20 1 Using offset control 3 Applies to 4 wire ohms only Input Nominal 0Q short 100 00 short 1000 00 short 1kQ 0Q short 10 kQ 0Q short 100 kQ 0Q short 1 MQ 0Q short 10 MQ Error From Input in counts Slow Medium Fast 40 60 20 49 69 21 4 6 3 11 13 4 3 5 2 8 10 3 3 5 2 8 10 3 3 5 2 9 11 3 3 6 2 28 31 5 4 7 2 44 47 6 Maintenance PERFORMANCE TEST Table 6 5 Resistance Test 6 7 DC Current Test The following procedure may be used to test the mA DC function 1 2 3 4 Ensure the 8842 is on and has warmed up for at least
82. stat 9 while selftest still active WRT G7 CALL IBWRT dvm WRT RD SPACE 18 CALL IBRD dvm RD Get error status errcode LEFT RD 4 IF errcode lt gt 1000 THEN Check for errors PRINT Error RIGHTS errcode 3 occurred END IF PRINT PRINT Selftest Complete END 13 14 07 wmf Figure 3 14 Example Programs Using the IBM PC cont 3 44 Remote Programming EXAMPLE PROGRAMS The following application program is written in C for the IBM PC AT The National Instruments Model AT GPIB board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842 assigned to the GPIBO board This program selects VDC F1 Autorange RO Slow rate 50 Continuous trigger TO and suffixes enabled Y1 The program takes 10 readings displays them on the screen and then stops Microsoft C Version 6 0 on IBM PC AT Link this program with appropriate mcib obj include lt stdio h gt include decl h char rd 512 read data buffer int dmm device number int i main dmm ibfind I18842A device name 15 18842A ibclr dmm clear device ibwrt dmm F1ROSOTOY1 10 write functions to instrument for i 0 i lt 10 i ibrd dmm rd get data printf d s i rd print to display f3 14 08 wmf Figure 3 14 Exampl
83. supplying additional gain In subsequent figures the T H Amplifier is represented as a single op amp 5 8 f5 03 wmf Figure 5 3 Track Hold Amplifier The circuit operates by cycling between the track settling hold and precharge configurations shown in Figure 5 4 The In Guard uC selects a particular settling and hold configuration for each function and range and suppresses the precharge configuration for certain ranges This control is achieved by latching function and range information in U301 U302 and U303 Basic timing for the T H circuit is provided by the A D Converter over clock lines PC and TR2 See the timing diagram in Figure 5 5 top The T H cycle is initiated when the In Guard uC pulls line TR low Theory of Operation TRACK HOLD CIRCUIT TRACK CONFIGURATION SETTLING CONFIGURATIONS B GAIN OF 1 C GAIN OF 10 GAIN OF 100 HOLD CONFIGURATIONS D GAIN OF 1 F GAIN 100 PRECHARGE CONFIGURATION NOTE IN 4 WIRE OHMS 3 RANGES R1 THROUGH R4 AND R8 INPUT OF THE T H AMP IS SWITCHED AS SHOWN U301C 1 U301D R314 SETTING SENSE LO DEPENDS TERMINAL ON RANGE f5 04 wmf Figure 5 4 Track Hold Circuit Configurations 5 9 8842A Instruction Manual TRACK HOLD CONTROL SIGNALS 39HVHO 3tud 2018 7 1 3HO1S H3QNIVW3H 3HVdWOO 3HVdWOO 3HO1S H3QNIVW3H 3dVdNOO 3HO1S H3 NIVW3H 4 S4 A D CONTROL SIG
84. switch or relay sed iva is closed ehen the control voltage is low oU Otherwise it is closed when fast the control voltage is high 5V range Udc r3tr5 Cohes r5 r6 Vdc trBeritr24704 1 2 736 4 SPFILT s tUdc Cohes r1402 73 PB P 997 rev a gt NORMAL OPERATING MODE 2 Dheas 4 Wire Ohas KK DC Scaling 78 r1 r2 r3 r4 r5 Tl r2 r3rT4T5 8 2 5 K301 Udc rBsri r24T3 ohas 1 8303 4wohas 0 6304 FILT 6310 Zechas 1 uc 1 U301a 1 1 U301b 5 TR1 GC 1 U301c 7 01 78 477 1 U301d HDl 4wohas 9 10 U302a 1 GB TR1 9 9 9 1 1 9 1 9 or ow o om m gt OO 6 O 11 U302b 5 HD2 x1 12 U302c 7 RDi Vac lac 13 U3024 9 PD ldc 14 U303a 1 TR2 15 03030 5 TR2 16 U303c 7 HD2 x10 17 3034 9 HD2 x100 34 9317 a rBeri Ghas ra P Ohms Section O O O O gt u O Qmm O O O O My O O lt O W w o O O O wv O O O O o O O O o om O O O
85. terminal is switched out of the dc input path by U301C This has the effect of measuring the SENSE HI terminal with respect to the SENSE LO terminal In ranges r5 and r6 the SENSE LO and INPUT LO terminals are both switched into the dc input path by U301C and U301D during the hold period This has the effect of measuring the SENSE HI terminal with respect to INPUT LO terminal rather than SENSE LO Although the resistance of the INPUT LO lead is in series with the unknown resistance accuracy is not affected as long as the resistance of the lead is less than 100 in the 2000 kQ range and less than 100Q in the 20 MQ range 5 20 A D CONVERTER The Analog to Digital A D Converter Figure 5 9 uses Fluke s patented recirculating remainder technique An input voltage Vin is compared to the output of the precision Digital to Analog Converter DAC The output of the A D Amplifier connected as a comparator is monitored to indicate when the DAC output is larger than the input voltage 5 15 8842A Instruction Manual BINARY LADDER NETWORK DAC AMPLIFIER A D AMPLIFIER A 2101 15 238 2101 10 667 NOTE A D CONVERTER SHOWN DURING FIRST COMPARE PERIOD f5 09 wmf Figure 5 9 Analog to Digital Converter The conversion process is broken up into an autozero period followed by five measurement intervals timing diagram is shown in Figure 5 5 Six bits of the final A D sample are obtained during each interval During the f
86. the HI INPUT terminal relative to Reference Low should be present at U306 3 If it isn t trace the voltage from the HI INPUT terminal to U306 3 to isolate the problem To check U306 select the VDC function and the 2V range Measure the voltage at TP302 while applying first 1 V and then OV a short across the HI and LO INPUT terminals If 1V and then OV appear at TP302 U306 is probably OK If not the problem is in U306 or its bootstrap supplies TP301 and TP303 To check the bootstrap supplies put the 8842A in the 20V range and measure the voltage at TP301 TP302 and TP303 TP301 should be 6 3V nominal above TP302 and TP303 should be 6 2V nominal below TP302 If the bootstrap supplies are operating correctly measure the voltage at U306 3 and U306 6 for input voltages of 20V and 20V if the voltage at U306 3 differs from U306 6 then U306 is bad To check the dc input path after U306 short the HI and LO INPUT terminals and read the display If zero is displayed for ranges r3 and r5 but not for r1 12 and r4 then the signal path including Q311 and U301B is suspect To check Q311 apply a 1V dc input in the 2V range and check that the voltage at the drain and source of Q311 is 1V If not Q311 or its driver is bad If 1 V appears at U301 16 but not at the display then U301 may be bad If zero is not displayed for r3 and r5 with the HI and LO INPUT terminals shorted then Z301 or U302D is probably bad 6 55 8842A In
87. the VAC function around 1 kHz If an accurate reading can be obtained on at least one range the rms converter U802 is working properly Test the high frequency response around 100 KHz If after calibration an accurate reading can be obtained on at least one range the digitally controlled filter U801 U808 R832 and C826 829 is OK If some ranges are good and others are bad the defective stage may be isolated using Table 6 26 If this table is used the bad ranges must correspond exactly to the ranges listed in the first column and all other ranges must be good Most ac troubleshooting can be performed with the shields removed To remove both shields unscrew the Phillips screw on the back of the True RMS AC PCA The only time it should be necessary to work on the PCA with the shields in place is when there is subtle high frequency gt 20 kHz or low level lt 10 mV error In that case the PCA should be left in its operating position and the test points probed from the foil side of the PCA Test points are labeled on both sides to facilitate such troubleshooting Table 6 26 Isolating a Defective AC Stage DEFECTIVE RANGES DEFECTIVE STAGE 200 mV 2000 mA 20V 700V 2V 200V 200V 700V 2V 20V 200V U806B U806A U806A Input Q806 K802 Z801 Input Q806 K802 2801 If no ranges work the signal should be traced from input to output At any point where the signal disappears the preceding stage should be searched
88. the last command can be read Example Explanation FI T3 F2 Improper construction The second trigger writes over the first To obtain two readings send two complete command strings separated by terminators F2 0 T3 Correct construction The string contains only one output command F2 R3 S0 Correct construction It is permissible for a string not to contain an output command RULE 3 Read the output data generated by one input command string before sending the next input command string Output data remains available in the output buffer until it is read or until the next input command string is received As soon as the controller finishes reading the output buffer or as soon as the 8842A receives a new input terminator the Data Available bit in the serial poll register is set false When this bit is false data can no longer be read from the output buffer Therefore an output string which is available must be read by the controller before rather than after the next input command string is sent Rule 3 is most evident in the external trigger mode and is best demonstrated by a programming example The following program is written first incorrectly and then correctly in Fluke BASIC using the 1722A Instrument Controller Incorrect example 100 PRINT 03 T1 200 PRINT 03 F4 300 INPUT 03 A 3 23 8842A Instruction Manual 3 24 In this incorrect example the INPUT statement is located incorrectly
89. to calibrate the offset for all ranges While the 8842A is executing a calibration step it ignores all of the front panel buttons and postpones execution of all remote commands INITIAL PROCEDURE Always begin the calibration procedure as follows 1 Allow the 88424 to stabilize in an environment with ambient temperature of 18 C to 28 C and relative humidity less than 75 2 Turn the 8842A on and allow it to warm up for at least 1 hour Enable the calibration mode by pressing the CAL ENABLE switch with a small screw driver or other suitable instrument The CAL ENABLE switch is located on the right side of the display and is normally covered by a calibration seal When the calibration mode is enabled the CAL annunciator lights up and the 8842A displays the first prompt for the A D Calibration procedure Figure 6 2 To exit the calibration mode press the CAL ENABLE switch again f6 02 wmf Figure 6 2 First A D Calibration Prompt In the calibration mode the front panel controls assume the functions described in Figure 6 3 Some of these functions are advanced features and are not required for the basic calibration procedure The display blanks briefly when a button is pressed 8842A Instruction Manual voc VAC kn kn mA AUTO Ces Erg 2 WIRE 4 WIRE STORE A D RATE ERASE Nimy DIGIT 1 DIGIT 2 DIGIT 3 DIGIT 4 5 OGIT 6 Function Each button selects the Offset and Gai
90. to start of A D conversion Autorange off FUNCTION VDC VAC MA DC MA AC Ohms RANGE 20 mV 200 mV 2V 1000V All 200 mA 2000 mA 2000 mA 200 2000 2 20 200 2000 20 m FROM VALUE 342 342 9 30 342 61 9 5 942 17 9 9 551 551 551 30 Note 2 342 342 9 9 342 17 9 5 551 551 551 30 Note 2 395 395 17 40 395 106 17 5 322 17 13 5 342 17 13 5 141 121 21 5 141 101 81 10 1020 964 723 10 1 Difference beiesi first reading and final for an in range step change coincident with trigger For slow reading rate 50 counts for medium rate 10 counts for fast rate 8842A Instruction Manual EXTERNAL TRIGGER TIMING CHARACTERISTICS The following diagram shows the nominal timing for the various processes which take place between an external trigger and data sent out on the IEEE 488 interface Delays will vary if a second trigger comes before the data handshake is complete REAR BNC TRIGGER AUTOMATIC SETTLING TIME DELAY A D CONVERSION ee OC emu SAMPLE COMPLETES 2 11 ms Css s s DATA HANDSHAKE 1 2ms 4 t1 1 wmf NOTES 1 Time for single trigger to start of A D conversion See Automatic Settling Time Delay on previous page If the delay is disabled by using the T3 or T4 command then the delay is 1 ms 150 us W
91. will only turn a small problem into a big one 8842A Instruction Manual 6 62 Tf 7 n M 03V INPUT 1V DIV 1 ms DIV 03V INPUT 1V DIV 1 mV DIV f16 17 wmf Figure 6 17 Waveforms at TP102 for Several Inputs on 2V DV Range Since power supply problems can produce symptoms in many different sections of the instrument the first step in troubleshooting any problem should usually be a quick check of the power supplies For each power supply TP801 TP806 check the level with a voltmeter and check for ripple with an ac coupled oscilloscope The dc voltages should be within the limits given in Table 6 23 If a supply is too high either its three terminal regulator has failed or a fault elsewhere in the instrument has shorted two supplies together After repairing such a problem make certain that nothing else was damaged by the overvoltage Maintenance TROUBLESHOOTING NIBBLE 1 NIBBLE 2 NIBBLE 3 Ie T 110 N1 2 1 0 1 4 0 1 16 0 0 0 1 4 1 8 1 16 N3 0 0 0 0 0 0 6875 4375 0 0 A D Reading 1st 3 Nibbles 6875 1 16 4375 1 16 0 0 660156 f6 18 wmf Figure 6 18 Calculating the A D Reading From TP102 Waveform Table 6 23 Power Supply Voltages TEST POINT LIMITS in volts MINIMUM MAXIMUM 5V 4 75 5 25 7 5V 7 00 7 87 15V 14 25 15 75 30V 28 45 31 55 8 2 8 61
92. 0 0 0 000 16 U303c 7 HD2 x10 0000000002 01 17 03034 9 HD2 x100 9317 1PFILT 0 O ohms section 10101 111111 1 1 11 00090001 18 KA014 1000010009000 1 l i 1 20 U402a 1 2000 20 21 U402b 5 02k 2k 2k 20k 200k oRims 22 U403a 1 20 1 00001 00 01 1 000 00 0 1 0009011 ms 24 U402c 7 200k 2000k 23 04029 9 ZOH oh 1012000000 000 1 900000001 25 U403b 5 20k ohns 09000 0 0000000910001 1 1 1 27 U403d 9 02k 2k 2k 26 U403c 7 tohn 000001 1 1 0000000000 ac board 9059090 09 20600900009 090 0909090 Vac lac 28 KB01 29 WKB02x 00 001 001 000 000 O 1 1 1 5 3 75 1 30 1804 1 90 0 0 0 0 0 0 90900 1 9 31 8041 8 32 0804 9 000909090 000900000000 000000000006 00901 1 1 19 33 U804d 15 Vac r2 r4 16 16 2 wmf 6 39 8842A Instruction Manual Table 6 17 Circuitry Tested by the Analog Self Tests CIRCUITRY TESTED TEST NUMBER 6 40 10 11 12 13 14 15 20 21 22 K301 5 0310 Q311 Q304 R319 U306 Z301 2302 2304 Amplifier U301 U302 U303 2303 Protection U401 U404 U402 U403 7401 0802
93. 0 kHz 05 20 05 005 14 01 1 of setting uV 2 of setting of range AC Current Source Fluke 5700A Frequency Range Minimum Required Accuracy All Ranges 30 Hz 1 kHz 07 1 mA 1kHz 5 kHz 07 1 mA X frequency in kHz Shorting Bar Resistance lt 1 5 mQ Pomona MDP S 0 Construction Soldered not rivetted 6 Inch Jumper 7 204 6W S equivalent Optional Test 9010A 9005A or Micro System Troubleshooter 9000A 8048 Interface Pod Equipment 6 2 PERFORMANCE TEST This test compares the performance of the 8842A with the specifications given in Section 1 The test is recommended as an acceptance test when the instrument is first received and as a verification test after performing the calibration procedure If the instrument does not meet the performance test calibration or repair is needed To ensure optimum performance the test must be performed at an ambient temperature of 18 C to 28 C with a relative humidity of less than 75 Also the 8842A should be allowed to warm up for one hour prior to beginning any test other than the self test 6 3 Diagnostic Self Tests The diagnostic self tests check the analog and digital circuitry in the 8842A There are 21 analog tests followed by in guard program memory calibration memory and display tests Out guard program memory is tested when self test is initiated by a remote command Microcomputer RAM tests are done only at powerup Each tes
94. 0000 000000 0 1 Note that the last eight rows in Table 6 21 are actually outputs of U803 Therefore observing those pins proves not only that the control signals are correct but also that U803 itself is functioning correctly DC Scaling Troubleshooting Whenever there is a failure in the DC Scaling circuit first check the power supply voltages for all active components Supply voltages and pin numbers are listed in Table 6 22 A test of the bootstrap supplies for U306 is described later under this heading After checking the power supplies use an oscilloscope to check the digital logic input pins of quad analog switches U301 U302 and U303 These should show digital signals with high gt 3V and low lt 0 5V gt SYNC PULSE lt gt lt LOGIC 1 AT TARGET PIN I I I LOGIC 0 AT TARGET PIN OBSERVE TARGET PIN AT THIS TIME f6 12 wmf Figure 6 12 Typical Dynamic Control Signals Maintenance TROUBLESHOOTING Table 6 22 DC Scaling and Track Hold Supply Voltages PIN OR DEVICE SUPPLY VOLTAGE PIN OR DEVICE SUPPLY VOLTAGE U301 6 5V U303 20 7 5V U301 10 0303 11 8 2V U301 20 7 5V U304 4 8 2V U301 11 5V U304 7 7 5V U302 6 5V U305 3 5V U302 10 0305 12 5 5V Nom U302 20 7 5V U307 4 15V U302 11 5V U307 7 15V U303 6 5V Q305 c 30V U303 10 Q306 c 30V With OV input In the 20V range any voltage applied to
95. 03 906 910 CR 908 909 903 904 P2 911 912 913 514 915 916 919 917 918 938 343 944 945 947 H H H J 9 M R R R R R R R TP 501 903 905 906 U 901 905 808 303 910 511 912 913 VR 301 SRR RR Option 05 IEEE 488 Interface LIST OF REPLACEABLE PARTS Table 805 1 Option 05A IEEE 488 Interface PCA DESCRIPTION 1UF 20 35V 0 010 80 20 50v 25 CER 430PF 5 S50V COG CAP AL 4700UF 30 10 16V SOLV PROOF CER 0 22UF 80 20 50 250 1000 20 50V X7R 470 20 10V CER 1SPF 20 50V COG ZENER UNCOMP 3 9V 120 20 0MA 0 4W DIODE SI BV 7 0V 10 150MA 500MW DIODE 51 100 1 0 RES JUMPER 0 02 0 25W NUT HEX STL 4 40 SCREW PH P SEMS STL 4 40 250 FASTENER GROMMET POLYCARB 271 FASTENER PLUNGER NYL 271 CONN MICRO RIBBON REC PWB RTANG 24 POS HEADER 2 ROW 100CTR 10 PIN CONN COAX PWB RT ANG HEAT DIS VERT 1 18X1 00X0 50 T0 220 RES CF 33X S U 25W RES CF 1 5K 5 0 25W RES CF 470 5 0 25W 5 100 5 0 25 RES 68K 5 0 25 RES CF 51K S5 0 25W RES CF 10K S 0 25W FILTER 12 7 SURGES SWITCH DIP SPST PIANO SEALED 8 POS TERM FASTON TAB 110 SOLDER CMOS 28 RK R 40A 9271 IC LSTTL HEX INVE
96. 0803 0804 0809 16 17 wmf Some failures will cause many self tests to fail If this occurs the fault is usually in the Track Hold circuit the A D Converter the Digital Controller circuit or the Power Supply Again measure all of the power supply levels according to the limits specified in Table 6 23 The next step is to isolate the problem to a specific section If the self tests display a large number of errors or if readings are noisy and or in error the problem is usually in the A D Converter or Track Hold circuit A large number of errors can also be caused by a problem in the Ohms Current Source To isolate the problem connect a jumper between TP103 and Reference Low TP306 or the L shaped shield around U202 The display should typically read less than approximately 35 counts i e 000 where XX is less than 35 on the 2V dc range If a good reading can be obtained less than approximately 35 counts the A D Converter and Precision Voltage Reference circuits are most likely good A more conclusive test can be made by connecting a low impedance dc source between Reference Low and TP103 with an output voltage between 2 0V and 2 0V The reading on the display will be of opposite polarity to the voltage applied to TP103 Disconnecting one end of R318 will usually make it possible to display readings within 0 1 to 0 5 of the actual input After it has been determined that the A D Converter or the Track Hold circuit is not fun
97. 0PF 5 50V COG 697441 1 C403 CAP POLYES 0 47UF 10 50V 697409 1 0601 CAP AL 6800UF 20 16V 478784 1 0603 CAP AL 330UF 50 20 100V 484436 1 C605 C607 CAP AL 470UF 20 50V SOLV PROOF 747493 2 0611 CAP AL 100UF 50 20 50V 649731 1 1 C701 CAP CER 270PF 5 50V COG 658898 1 CL301 I REG DIODE 0 43MA 2096 SEL TO 0226AC 707836 1 CR101 CR102 ZENER UNCOMP 3 9V 10 20 0MA 0 4W 113316 10 CR201 CR202 113316 CR306 CR307 113316 CR309 CR311 113316 313 113316 CR103 CR104 ZENER UNCOMP 7 5V 5 20 0MA 0 4W 256446 3 CR613 256446 CR105 CR106 DIODE SI BV 75V 10 150MA 500MW 203323 12 CR203 206 203323 CR301 CR302 203323 CR401 CR404 203323 CR615 CR701 203323 CR303 ZENER UNCOMP 10 0V 5 12 5MA 0 4W 246611 1 CR304 CR305 ZENER UNCOMP 6 8V 596 20 0MA 0 4W 260695 2 CR308 CR310 ZENER UNCOMP 24 0V 596 5 2MA 0 4W 267807 2 CR402 CR403 DIODE SI 1K PIV 1 0AMP 707075 2 CR405 ZENER UNCOMP 5 1V 5 20 0MA 0 159798 1 CR601 606 DIODE S1 100 PIV 1 AMP 742874 70 CR608 611 742874 CR607 CR612 ZENER UNCOMP 6 2V 596 20 0MA 0 4W 325811 2 CR614 ZENER UNCOMP 8 2V 596 20 0MA 0 4W 386771 1 CR616 ZENER UNCOMP 56 0V 596 2 2MA 0 4W 187757 1 CR617 ZENER UNCOMP 8 2V 596 20 0MA 0 4W 386771 1 H1 H51 RIVET S TUB OVAL STL 118 156 103424 2 H3 NUT BROACH STL 4 40 380196 1 H5 NUT HEX STL 4 40 110635 1 H6 SCREW PH P SEMS STL 6 32 250 178533 1 H12 SCREW PH P SEMS STL 4 40 250 185918 1 J201 HEADER 2 ROW 100CTR 20 PIN 706986 1 J202 CABLE ASSY FLAT 10 CONDUCT 6 0 714022 1
98. 1 hour Select the mA DC function Connect the Current Source to the 2A and LO INPUT terminals For each step in Table 6 6 set the Current Source for the indicated input and verify that the displayed reading is within the limits shown for each reading rate Set the Current Source for zero mA and disconnect it from the 8842A Table 6 6 DC Current Test STEP 200 mA 2000 mA 200 mA 2000 0 mA 100 mA 0 mA DISPLAYED READING 1000 mA SLOW MIN MAX 00 040 400 040 99 920 100 080 000 04 000 04 999 56 1000 44 00 060 00 060 00 20 00 20 MEDIUM FAST MIN MAX MIN MAX 99 900 100 100 99 76 100 24 000 06 000 06 000 2 000 2 999 54 1000 46 999 4 1000 6 6 9 8842A Instruction Manual 6 8 AC Current Test Option 09 Only The following procedure may be used to test the mA AC function 1 Ensure the 8842A is and warmed up for at least 1 hour 2 Select the mA AC function 3 Connect the AC Current Source to provide a current input to the 2A and LO INPUT terminals If an ac current source is not available the functionality of the 8842A can be checked at 10 mA by using a Fluke 5200A set at 100V and connected to the 8842A 2A terminal through a 10 kQ 2W 1 resistor 4 For each step in Table 6 7 set the AC Current Source for the indicated input and verify that the displayed reading is within the limits sho
99. 10 Greenhills Metro Manita 1502 TEL 63 2 700 621 FAX 63 2 721 0491 or 700 709 Poland Elec Instr Srv Philips Cons UL Malechowska 6 60 188 Poznan TEL 48 61 681998 FAX 48 61 682256 Portugal Fluke Iberica S L Sasles Y Services Dept Campo Grande 35 7b 1700 Lisboa TEL 351 1 795 1712 FAX 351 1 795 1713 Romania Ronex S R L Cust Supp Serv Str Transilvaniei Nr 24 70778 Bucharest TEL 40 1 614 3597 or 3598 FAX 40 1 659 4468 Russia Infomedia UL Petrovsko Razumovsky Proezd 29 103287 Moscow TEL 7 95 212 3833 FAX 7 95 212 3838 Saudi Arabia A Rajab amp Silsilah Co S amp S Dept P O Box 203 21411 Jeddah TEL 966 2 661 0006 FAX 966 2 661 0558 Singapore Fluke Singapore Pte Ltd Fluke ASEAN Regional Office 27 03 PSA Building 460 Alexandra Road Singapore 119963 TEL 65 276 5161 FAX 65 276 5929 South Africa Spescom Measure PTY Ltd Spescom Park Cm Alexandra Rd amp Second St Halfway House Midrand 1685 TEL 27 11 315 0757 FAX 27 11 805 1192 Spain Fluke Iberica S L Centro Empresarial Euronora c Ronda de Poniente 8 28760 Tres Cantos Madrid Spain TEL 34 1 804 2301 FAX 34 1 804 2496 Sweden Fluke Sverige AB CSS P O Box 61 S 164 94 Kista TEL 46 8 751 0235 or 0230 FAX 46 8 751 0480 Switzerland Fluke Switzerland AG CSS Rutistrasse 28 CH 8952 Schlieren Switzerland TEL 41 1 730 3310 or 730 3932 FAX 41 1 730 3932
100. 126 13 56 CASE FOOT BLACK 824433 824433 14 CHASSIS ASSEMBLY 684134 684134 15 TERMINAL BLOCK RAI 656504 656504 16 SEAL CALIBRATION 735274 735274 17 57 49 SUPPORT 683987 683987 18 LENS FRONT PANEL 759274 759274 19 DECAL FRONT 685081 685081 20 DECAL REAR 765487 765487 21 TNSERT REAR PANEL 684191 684191 22 CABLE GUIDE 728956 728956 23 DECAL CSA 525527 525527 26 50 52 SHTELD SUPPORT 735308 735308 27 HLDR PART FUSE CAP 1 4Xi 1 4 460239 031 1666 32 FUSE HOLDER CAP ASSEMBLY 516039 516039 57 NAMEPLATE SERIAL REAR PANEL 472795 472795 58 BRACKET TRANSFORMER 765263 765263 RIVET PUSH TH NYL 620 L 852173 852173 KEYPAD CONDUCTIVE ELASTCMERIC 745638 745638 LINE VOLTAGE SELECTION SWITCH 735258 735258 INSTRUCTION MANUAL 879309 879309 GETTING STARTED MANUAL 879291 879251 CORD LINE 5 15 IEC 3 18AWG SVT 707018 ECM 490 BLACK TEST LEAD ASSY TL70A 855820 855820 WIRE ASSY AC CONNECT 684316 684316 NOTES 4 Static sensitive part Typ o Oo Q Q P PNP 1 1 1 1 d 1 2 2 2 4 1 2 2 1 3 1 2 2 2 2 2 L T 1 i 1 1 1 1 2 d i i m BOB OB ON BOO B OPP S p on pn 8842A Instruction Manual 7 6 180 FOR SHIPPING 8 Figure 7 1 8842A Digital Multimeter 8842A T amp B 17 01 1 wmf List of Replaceable Parts SERVICE CENTERS UE RMS OPTIONAL EA424 O9 TRI F302 E MP32 55 INTERF
101. 13 group width 100 us group spacing 10 ms 230 after pin 13 Check U208 7 for 0 6 us pulses normally high groups of 5 group width 50 us group spacing 10 ms 380 us after pin 13 This concludes testing of the basic uC system If the keyboard or display is still suspect at this point proceed to Display System below Otherwise proceed to Analog Control Signals below DISPLAY SYSTEM The display keyboard system is operated by a complex LSI IC U212 Generally this IC is checked indirectly by observing behavior of the simpler logic devices which it drives If the keyboard is working at all the 8842A display should be frozen to make the following tests This places the 8842A in a special display test configuration If it is not Maintenance TROUBLESHOOTING possible to freeze the display it should still be possible to observe the waveforms at U215 U213 U221 and U211 as described in the following paragraphs To freeze the display turn off the instrument press the POWER switch and within 1 second press the SRQ button If all is well all display segments will light and remain lit Do not press any other buttons as that will release the display allowing the instrument to resume its normal power up sequence This state should remain in effect for all of the following tests PINS AT WHICH WAVEFORM NAME WAVEFORM WAVEFORM APPEARS U213 1 U212 32 U213 2 U212 33 U213 4 4095 us U215 8 3 U221 5 U213
102. 2 1 99999 20 19 9999 200 199 999 2000 1999 99 20 19 9999 0 1 MQ 1 mQ 1 1 10 1 10 100 mQ 1 100 mQ 1 100 uA 1 10 10 pA 10 1000 5 1000 1 0 5 uA 1 412 digits at the fastest reading rate 2 Four wire ohms only 8842A Instruction Manual 1 8 Accuracy NORMAL S READING of Reading Number of Counts RANGE 90 DAY 23 5 1 YEAR 23 5 2 YEARS 23 1 202 0 007 30 0 009 40 0 012 40 0 015 40 2000 0 0040 3 0 007 4 0 010 4 0 012 4 2 kQ 0 0025 2 0 005 3 0 008 3 0 010 3 20 kQ 0 0025 2 0 005 3 0 008 3 0 010 3 200 kQ 0 0025 2 0 006 3 0 010 3 0 012 3 2000 kQ 0 023 3 0 025 3 0 027 3 0 030 3 20 MQ 0 023 3 0 040 4 0 042 4 0 050 4 Boom Relative to calibration standards Applies to 4 wire ohms only MEDIUM AND FAST READING RATES Operating Characteristics TEMPERATURE COEFFICIENT MEASUREMENT CONFIGURATION OPEN CIRCUIT VOLTAGE INPUT PROTECTION 1 Within one hour of ohms zero using offset control When offset control is not used the number of counts are 50 70 90 and 90 for 24 hours 90 day 1 year and 2 year respectively 5 When offset control is not used the number of counts are 5 7 9 and 9 for 24 hours 90 day 1 year and 2 year respect
103. 200 ka 10 pA 2 0V 2000 5 uA 10 0V 20 MO 500 nA 10 0V 4 10 Measurement Tutorial RESISTANCE MEASUREMENT NOTE In the 2 MQ and 20 MQ ranges of 4 wire ohms the voltage across the unknown resistance is sensed between the HI SENSE and LO INPUT terminals Accuracy is not affected as long as the resistance of the LO INPUT lead is less than 10 0 the 2 MQ range and less than 1000 in the 20 MQ range Applications of the Ohms Functions The 2 wire and 4 wire ohms functions can be used for a variety of purposes in addition to measuring resistance as the following applications show TESTING DIODES The 2 wire ohms function can also be used to test diodes 1 Select the 2 wire ohms function and the 2 kQ range 2 Measure the resistance of the diode If the diode is good when forward biased it will measure about 0 6 to 0 7 for silicon 0 25 to 0 3 for germanium and when reverse biased it will cause the 8842A to indicate overrange The forward biased reading depends upon the range used The 2 kQ range is used because its 1 mA test current provides a typical operating point and its 2V full scale voltage is sufficient to turn on most diodes even two diodes in series TESTING ELECTROLYTIC CAPACITORS The 2 wire ohms function can also give a rough test of an electrolytic capacitor s leakage and dielectric absorption This test works well for capacitors 0 5 WF and larger 1 Select the 2 wire ohms
104. 204 0203 UNDER 212 206 UNDER 0208 is 9201 17 58 8 24 r 901 0213 223 L lt zr Se CR612 20 VRe0S CRED CR amp O2 CREQ3 CREOS och CR903 0403 0 02 S YY I E d ind NY ON 7402 5 lt 235 0312 0405 Quo 03 8 NM 0306 _R316 CR307 2301 R607 5 D RN C605 Ce02 n VR603 8842A 1601 19 05 1 wmf Figure 9 5 Main PCA Power Supply 9 11 8842A Instruction Manual 260a 220 240 DIGITAL 2 2 LINE FILTER DISPLAY w s 4 5 AA SLOW AT 190 120 voit yaa AT 24 8842A 1001 Sheet 5 19 05 2 wmf Figure 9 5 Main PCA Power Supply cont 9 12 Schematic Diagrams 9 8840A 1602 19 06 1 wmf Figure 9 6 Display PCA 9 13 8842A Instruction Manual TOMAIN PWS PAS Taw TO MAIN P w E gt POWER SUPPLY MAIN PWB ot Q N g B M le E 9 14 8842A 1002 Figure 9 6 Display PCA cont 19 06 2 wmf Schematic Diagrams 9 0905 910 0901 9 TP905 8840A 1605 19 07 1 wmf Figure 9 7 IEEE 488 Interface PCA 9 15 8842A Instruction Manual
105. 21 Y8022 Y8023 Y8834 Y8835 Y8836 TL70A Y8134 Y8140 80T 150U 80TK 85RF 83RF 80J 10 Y8100 Y8101 801 400 801 600 80K 6 80K 40 DESCRIPTION IEEE 488 Interface Cable 1m IEEE 488 Interface Cable 2m IEEE 488 Interface Cable 4m Single Rack Mount Kit Dual Rack Mount Kit Center Rack Mount Kit Replacement Test Leads Replacement Test Leads Slim Flex Test Leads Temperature Probe K Type Thermocouple Converter RF Probe 100 kHz to 500 MHz RF Probe 100 kHz to 100 MHz Current Shunt Current Probe 200A ac dc Current Probe 150A ac Current Probe 400A ac Current Probe 600A High Voltage Probe 6 000V High Voltage Probe 40 000V Table 8 2 Options NUMBER OPTION IEEE 488 Interface True RMS AC 8 3 8842A Instruction Manual 8 4 8 2 ACCESSORIES Accessories include a variety of rack mounting kits cables test leads and probes The accessories include installation and or operating instructions Rack Mount Kits Y8834 8835 and Y8836 The rack mount kits allow the 8842A to be mounted in standard 19 inch rack panels The Y8834 kit allows the 8842A to be mounted either on the left or the right The Y8835 kit allows two 8842As to be mounted side by side The Y8836 kit allows the 8842A to be mounted in the center of the rack Installation instructions are given in Section 2 and are also included with each kit Shielded 488 Interface Cables 8021 8022 and 8023 Shiel
106. 25W 348771 3 R205 R207 R208 RES CF 1 5K 5 0 25W 343418 5 R210 R412 343418 R206 R209 R312 RES CF 33K 5 0 25W 348888 5 R313 R408 348888 R216 R326 R406 RES CF 2 4K 5 0 25W 441493 3 R301 RES CC 100K 5 2W 285056 1 R302 R311 R324 RES MF 46 4K 1 0 125W 50PPM 715185 4 R325 715185 R303 RES MF 110K 1 0 125W 100PPM 234708 1 R304 FiES CF 1 5M 5 0 25W 349001 1 R308 R316 R317 RES CF 1M 5 0 25W 348987 4 R323 348987 R309 RES MF 1K 1 0 5W FLMPRF FUSIBLE 733915 1 1 R310 R409 R415 RES CF 5 6K 5 0 25W 442350 3 R314 RES CC 22K 10 2W 109975 1 R318 RES CF 620 5 0 25W 442319 1 R319 W W RESISTOR 731950 1 R321 R322 RES MF 10K 0 1 0 725W 50PPM 343459 2 R401 RES WW HERM 1 4W 54 6K 05 762120 1 R402 RES CF 4 3M 5 0 25W 543348 9 R403 RES CF 10M 5 25W 875257 1 R407 RES CF 910 5 0 25W 442335 1 R410 RES MF 1K 1 100PPM FLMPRF FUSIBLE 474080 1 1 8842A Instruction Manual Table 7 2 A1 Main PCA cont Reference Description Fluke Stock Tot Qty Notes Designator No R413 RES MF 4 99M 1 0 125W 100PPM 715060 1 R414 RES MF 576K 1 0 125W OOPPM 344291 1 R416 RES MF 100 1 0 125W 25PPM 460527 1 R601 RES CF 560 5 0 25W 385948 1 RV301 RV401 404 VARISTOR 390V 10 1MA 697383 5 RV601 VARISTOR 430V 10 1 0MA 519355 1 5201 SWITCH PUSHBUTTON DPDT PUSH PUSH 875703 1 5601 SWITCH PUSHBUTTON DPDT PUSH PUSH 453605 1 201 202 TRANSFORMER PULSE 660589 2 T601 TRANSFORME
107. 2A Parts are listed by assembly alphabetized by reference designator Each assembly is accompanied by an illustration showing the location of each part and its reference designator The parts lists give the following information e Reference designator e indication if the part is subject to damage by static discharge e Description e Fluke stock number e Manufacturers supply code code to name list at the end of this section e Manufacturers part number or generic type Total quantity e Any special notes i e factory selected part CAUTION A symbol indicates a device that may be damaged by static discharge HOW TO OBTAIN PARTS Electrical components may be ordered directly from the manufacturer by using the manufacturers part number or from the Fluke Corporation and its authorized representatives by using the part number under the heading FLUKE STOCK In the U S order directly from the Fluke Parts Dept by calling 1 800 526 4731 Parts price information is available from the Fluke Corporation or its representatives Prices are also available in a Fluke Replacement Parts Catalog which is available on request In the event that the part ordered has been replaced by a new or improved part the replacement will be accompanied by an explanatory note and installation instructions if necessary To ensure prompt delivery of the correct part include the following information when you place an order e Instrument mo
108. 3 2 Each block represents a register buffer etc contained in the 8842A The status registers in the center column indicate the instrument s status including its function range reading rate etc The input buffer receives data from the IEEE 488 bus The output buffer receives data from the blocks to its left and sends data to the IEEE 488 bus Remote Programming AN OVERVIEW OF REMOTE OPERATION 7 FUNCTION 22 INSTRUMENT CONFIGURATION READING RATE TRIGGER MODE EU AREIS F R S T B Y W X0 P3 Co Dn INPUT BUFFER FRONT REAR INPUTS AUTORANGE ON OFF IAB STATUS 4 N VALUE NUMERIC ENTRY REGISTER OFFSET ON OFF PO P1 P2 SUFFIX ENABLE DISABLE YW STATUS lt OUTPUT TERMINATORS G0 G7 DATA DISPLAY MEASUREMENT ON OFF MEASURE CIRCUITRY MENT DATA OUTPUT GET TO BUFFER ERROR MESSAGES IEEE 488 INTERFACE BUS 2 STATUS USER SERIAL MESSAGE POLL REGISTER SRQ MASK VARIABLE CAL VALUE CALIBRATION CALIBRATION STATUS PROMPT CALIBRATION FUNCTION f3 02 wmf Figure 3 2 Remote Operation Block Diagram 8842A Instruction Manual 3 6 Information is transferred between blocks by device dependent commands Each command is shown next to an arrowhead which indicates the resulting information transfer For example Put command takes a number from the input buffer and stores it in the primary status registers Likewise
109. 4 5 on IBM PC PC XT or PC AT INCLUDE qbib45 dcl GPIBO Board name is GPIBO CALL IBFIND BDNAMES BD Initialize IEEE Interface Board devname 18842A Device name is 18842A CALL IBFIND devname dvm Initialize the device CALL IBCLR dvm96 Clear the device WRT F1ROSOTOY1 1 Volts DC RO Autorange 50 Slow reading rate TO Internal Trigger Y1 Enable suffix CALL IBWRT dvm WRT Write functions to the instrument CALL IBLOC dvm Give local control to the instrument V 0 x 0 CALL IBSRE BD V De assert the remote enable REN signal so the 8842A stays in local when an IBRD call is made RD SPACE 18 711 characters for the reading 5 for the suffix and 2 for the terminators CALL IBRD dvm RD Get data x 1 Increment reading count PRINT x LEFT RD 16 Display reading GOTO again END 8 14 05 wmf Figure 3 14 Example Programs Using the IBM PC cont 3 42 Remote Programming EXAMPLE PROGRAMS The following application program is written in QBASIC for the IBM PC PC XT or PC AT The National Instruments Model GPIB PCIIA board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842A assigned to the GPIBO board This program illustrates one possible use of the serial poll register In this
110. 4 and U101 25 6 16 Typical Bus Data Line Waveform sees 6 17 Waveforms at TP102 for Several Inputs on 2V DV Range 6 18 Calculating the A D Reading From TP102 Waveform 6 19 Option 05 Service cette ERR hane 6 20 Option 09 Service 6 21 Guard Crossing Test Waveforms 7 1 8842 Digital Multimeter essent rennen enne nennen 7 27 Matt PCA 7232 A2 Display phen din thease anemia iue BE 7 4 SEVICE 754 Service Centers CONE wii ete 805 1 Installing Option 5 2 DEEE 805 2 TEEE 488 Interface aeee 809 1 Installing Option 09 25 809 2 True RMS PCA LLL 9 1 Main PCA DC Scaling and F R Switch 9 2 Main PCA A D Converter nenne 9 3 PCA Ohms Current Source 9 4 Main PCAs Digital e cte 9 5 Main PC
111. 42A Instruction Manual 3 26 3 45 3 46 3 47 3 48 In the fast F reading rate the least significant digit is always zero and should be disregarded when interpreting accuracy specifications OVERRANGE INDICATION If a reading is overrange 200 000 counts the measurement data has the following format 9 99999 9 suffix lt terminators gt Overvoltage readings gt 1000V dc or 700V ac do not result in this display ERROR MESSAGES If the 8842A detects an error it loads an error message into the output buffer in the following numeric format 1 00 21 lt terminators gt The digits xx represent a two digit error code Error codes are listed in Table 2 1 Section 2 The suffix is always suppressed for error messages Example Explanation 1 0071E 21 CRLF ERROR 71 Syntax error in device dependent command string As with local operation none of the errors are latching except for ERROR 31 If the mA DC or mA AC function is requested while the FRONT REAR switch is in the REAR position ERROR 31 will persist until the switch is set to FRONT or another function is selected To check for an error condition test whether the output buffer data is greater than or equal to 1E 21 or test the Any Error bit bit 6 in the serial poll register Status Data Status data is the output in response to GO G1 G3 G4 G5 G6 G7 and G8 commands The data is formatted as shown in Figure 3 2 and
112. 7 60 15V 15 75 14 25 30V 31 55 28 45 If a supply is too low there are a number of possible causes First check the input to the affected regulator If it is not at least above the maximum output given in Table 6 23 the cause may be a bad transformer winding check the resistance open or shorted rectifiers a shorted filter capacitor or a shorted regulator The latter two failures will usually blow the line fuse All regulators incorporate current limiting which allows them to shut down in the event of a load failure Therefore if the power supply output is too low the first step should be to determine if it is due to a high load caused by a failure elsewhere in the instrument Frequently the faulty component can be found by using a multimeter with at least 5 digits resolution to check the supply pins of all components powered from that supply Connect one lead of the voltmeter to the appropriate test point for the power supply under test and use the other lead to probe the loads Small voltage drops across the PCA traces can be detected in this way and the fault isolated If any component other than one of the regulators is too hot to touch there is something wrong with it or with something connected to it 6 63 8842A Instruction Manual 6 64 6 68 6 69 6 70 The True RMS AC PCA if installed uses 5V and 15V If there is a problem with one of those supplies first disconnect the True RMS AC PCA If the p
113. 7 in high 8 5 in wide 14 6 in deep WEIGHT Net 3 4 kg 7 5 Ib shipping 5 0 kg 11 Ib INCLUDED ses Line cord test leads Instruction Service Manual IEEE 488 Quick Reference Guide Option 05 only and instrument performance record IEEE 488 INTERFACE FUNTION Option allows complete control and data output capability and supports the following interface funtion subsets SH1 AH1 T5 L4 SR1 RL1 DC1 DT1 E1 PPO AND Co ELECTROMAGNETIC COMPATIBILITY Specifications apply when used in an environment with fields strengths lt 1 V m 0 8 V m for DC Current For fields strengths up to 3 V m multiply floor adder by 12 for VDC and Resistance and 200 for DC current VAC and AC Current have no adders up to 3 V m f1 01 wmf Figure 1 1 External Dimensions 2 10 2 28 2 30 Chapter 2 Operating Instructions Title Page INTRODUCTION INSTALLATION Installing the Power Line 48 Connecting to Line Power Adjusting the Handle u reete eene Rack Mounting OPERATING FEATURES Power Up Front and Rear Panel Features Display Error Messages Overrange Indication
114. 8 Truth Table for U804 and K2 RANGE PIN OR DEVICE U804 1 U804 8 U804 9 U804 16 K2 2000 mA 1 0 1 1 0 200 mV 1 0 0 1 0 2 1 1 1 0 0 20 0 1 1 1 0 200 1 1 1 0 1 700V 0 1 1 1 1 NOTE For U804 logic 0 switch on Logic 1 is gt 2 4V logic 0 is lt 0 8V 6 74 If the signal at TP802 is correct but the output signal TP803 is incorrect the rms converter is probably the source of the problem Problems with U802 generally show up as an identical number of counts displayed in all ranges or as an overrange in all ranges First isolate faults in the buffer amplifier U802A by ascertaining that the signal at U802 13 is the same as that at TP802 when each is observed with an ac coupled oscilloscope and that the dc offset at U802 13 is less than 4 mV It is possible that a component in the loop filter U809A and associated passive components or the post filter U809B and associated passive components is defective The dc voltage at U802 6 should be the same as that at TP803 for frequencies above 500 Hz and should be equal to the rms value of the input signal MORE OBSCURE PROBLEMS Slow settling time or excessive jitter for low frequency inputs is caused by rms converter loop errors The cause may be a fault in the rms converter or loop filter If the output voltage is stuck at the supply rails the cause is probably a fault in the rms converter A less common cause is op amp oscillation this can be checked with a scope at 802
115. 8 bus Uniline messages are sent over one of the individual interface management lines in the IEEE 488 bus All universal commands except DCL are processed immediately by the 8842A ahead of any device dependent commands Only DCL enters the 8842A input buffer The 88424 responds to the following universal messages ATN Attention A uniline message which causes the 8842A to interpret multiline messages as interface messages AD AC or UC When false multiline messages are interpreted as device dependent messages 3 29 8842A Instruction Manual 3 30 IFC DCL LLO SPD SPE Interface Clear A uniline message which clears only the interface not the 8842A by placing it in a known quiescent state Remote Enable A uniline message which when received with MLA switches the 8842A to remote When REN is set false the 8842A switches to local and removes local lockout Device Clear A multiline message which is loaded into the input buffer as a special device clear command DCL performs the same operation as the device dependent command except that it is read before any other characters that are already present in the input buffer and clears the entire input buffer Processing then continues normally The action of DCL is not immediate if the 8842A is taking a reading when DCL is received the DCL command is executed after the measurement is finished Local Lockout A multiline message which disables the front
116. 8842A is specified for sinusoidal waveforms up to 100 kHz or for nonsinusoidal waveforms with frequency components up to 100 kHz The small signal bandwidth the frequency at which the response is 3 dB down is typically around 300 kHz For signals with components greater than 100 KHz the measurement accuracy is reduced because of frequency bandwidth and slew rate limitations Because of this accuracy may be reduced when measuring signals with fast rise times such as high frequency square waves or switching supply waveforms As a rule of thumb an ac voltage input signal is within the bandwidth limitations if the rise time is longer than 2 us and within the slew rate limitations if the input slew rate is slower than 1V us x full scale of range Zero Input VAC Error If the 8842A input terminals are shorted while the VAC function is selected the 8842A displays a non zero reading typically less than 80 digits in the highest four ranges and less than 300 digits in the 200 mV range Such readings are due to random noise combined with the inherent nonlinear response of computing type rms converters to very small input signals 4 13 8842A Instruction Manual The zero input error is quickly reduced when the input is increased The rms converter error a dc error and the internally generated noise a random ac error are both uncorrelated with the input signal Therefore when a signal is applied the resulting reading is not the simple add
117. 8842A should be calibrated with equipment meeting the minimum specifications given in Table 6 1 The following paragraphs first present a basic calibration procedure This is followed by a description of advanced features and special considerations and by a description of remote calibration using the IEEE 488 Interface Maintenance CALIBRATION 6 10 Basic Calibration Procedure 6 11 The basic calibration procedure consists of the following four parts These parts must be performed in the order shown 1 Initial Procedure 2 A D Calibration 3 Offset and Gain Calibration for each function and range 4 High Frequency AC Calibration True RMS AC option only Normally it is recommended that the entire calibration procedure be performed However under some circumstances the earlier parts may be omitted For example if installing the True RMS AC option it may be necessary only to perform Offset and Gain Calibration for the ac functions followed by High Frequency AC Calibration But if the A D Calibration is performed it must be followed by a complete Offset and Gain Calibration for all functions and then by High Frequency AC Calibration Some of the calibration calculations are complex and take the 8842A some time to execute For example when you store the zero input during the Offset and Gain Calibration for the VDC function it takes around 22 seconds before the next prompt appears The 8842A automatically uses this input
118. A Power Supply 9 0 Display Contents continued 9 7 488 Interface PCA Option 05 9 15 9 8 RMS AC PCA Option 9 17 Xi 8842A Instruction Manual xii 1 1 1 1 eh Chapter 1 Introduction and Specifications Title Page 21 000 000000 trennen tertiae tsi THE 8842A DIGITAL OPTIONS AND ACCESSORIES eere SPECIFICATIONS 8842A Instruction Manual 1 1 INTRODUCTION This manual provides complete operating instructions and service information for the 8842A If you want to get started using your 8842A right away proceed to the operating instructions in Section 2 If you intend to use the 8842A with the IEEE 488 Interface Option 05 read Sections 2 and 3 This meter has been designed and tested according to IEC publication 348 Safety Requirements for Electronic Measuring Apparatus This manual contains information and warnings which must be followed to ensure safe operation and retain the meter in safe condition 1 2 THE 8842A DIGITAL MULTIMETER The Fluke 8842A Digital Multimeter is a high performance 5 1 2 digit instrument designed for general purpose bench or systems applications The 8842A is the top of the line DMM in the 8840A family Using propriet
119. A THEN 140 Throw away data if not lowest 185 A R Update lowest reading 190 GOTO 130 Print new low 900 END f3 12 wmf Figure 3 11 Example Program Using the Serial Poll Register 3 35 8842A Instruction Manual 10 This program demonstrates a method of recording any errors produced by the 8842A during self test 20 30 It should be noted that 40 1 If more than one digital test error occurs only the last one will be reported 50 2 The response to the Get Instrument Configuration GO command during selftest is 60 3 The response to a Get Error Status G7 command with no errors present is 1000 70 80 FLUKE BASIC on 1720A 1722A 90 100 DA 4 Device address 4 110 TIMEOUT 10000 110 second timeout 120 PRINT 130 PRINT MONITORING SELFTEST 140 INIT PORT 0 Initialize port 150 CLEAR DA Clear device 160 PRINT DA 20 Start selftest 170 180 PRINT DA G7 INPUT DA 190 IF E 1000 THEN 220 200 PRINT DA X0 210 PRINT ERROR RIGHT E 3 OCCURRED Print analog errors 220 PRINT DA GO N INPUT DA ST 230 IF ST gt 9000 GOTO 180 240 PRINT DA G7 INPUT DA E 250 IF E 1000 THEN 270 260 PRINT ERROR RIGHT E 3 OCCURRED Print last digital error 270 PRINT SELFTEST COMPLETE 280 END f3 13 wmf Figure 3 12 Example Program Record Errors During Selftest 3 36 Remote Programming EXAMPLE PROGRAMS 10 REM The follo
120. AC Calibration at Other Frequencies later in this section When all functions have been calibrated exit the calibration mode by pressing the CAL ENABLE switch and attach a calibration certification sticker over the CAL ENABLE switch If the True RMS AC option is installed instead proceed to the High Frequency AC Calibration procedure which follows 6 14 HIGH FREQUENCY AC CALIBRATION The High Frequency AC Calibration procedure calibrates the response of the VAC function from 20 kHz to 100 kHz If the True RMS AC option is not installed selecting this procedure results in an error message The reference sources used in this procedure should normally be between 90 kHz and 100 kHz 100 kHz nominal is recommended For special applications performance may be optimized at other frequencies See Optimizing AC Calibration at Other Frequencies later in this section To perform High Frequency AC Calibration proceed as follows 1 2 4 Ensure Offset and Gain Calibration has been completed for the VAC function Select the High Frequency AC Calibration procedure by pressing the HF AC button The 8842A will display the first prompt 100 mV AC The U in the display indicates the High Frequency AC Calibration procedure has been selected Each time the 8842A prompts you for a reference amplitude apply this amplitude to the HI and LO INPUT terminals and press the STORE button When STORE is pressed the numeric display field blanks wh
121. ACE OPTIONAL t ul er A1W10 rer A1W12 rer A1W11 8842A T amp B 17 01 2 wmf Figure 7 1 8842A Digital Multimeter cont 8842A Instruction Manual lt M a E 0 0 lt 7 8 Figure 7 1 8842A Digital Multimeter cont 8842A T amp B 17 01 3 wmf List of Replaceable Parts SERVICE CENTERS PRESS STUD 9 36 REF u ae Mal 29 xo PRESS NUT 4 40 Z PLC 8842A T amp B 17 01 4 wmf Figure 7 1 8842A Digital Multimeter cont 8842A Instruction Manual Table 7 2 A1 Main PCA Reference Description Fluke Stock Tot Qty Notes Designator No AR701 REF AMP SET 759290 1 101 103 6311 CAP POLYPR 0 1UF 10 160V 446781 4 104 105 205 CAP CER 0 22UF 80 20 50V Z5U 733386 15 209 C304 C305 733386 C315 0404 C604 733386 C606 C609 C610 733386 C202 C203 C617 CAP CER 0 01UF 80 20 50V Z5V 697284 4 C618 697284 C204 C602 C608 CAP TA 1UF 20 35V 697417 4 0612 697417 0210 CAP CER 1000PF 20 50V X7R 697458 1 C301 C302 CAP POLYPR 0 33UF 10 160V 520346 2 C303 CAP POLYES 0 33UF 10 50V 715284 1 C306 CAP POLYPR 0 22UF 10 160V 446799 7 C307 CAP POLYPR 4700PF 10 63V 721662 t C308 CAP POLYPR 0 47UF 10 160V 446807 1 C309 CAP CER 120PF 5 50V COG 721142 1 C310 CAP CER 120PF 5 50V COG 721142 i C312 CAP POLYES 0 001UF 10 50V 720938 1 C314 CAP POLYPR 0 047UF 10 160V 446773 1 0402 CAP CER 33
122. ART universal asynchronous receiver transmitter which it uses to communicate across the guard to the IEEE 488 Interface The transmission speed is 62 500 bits per second 5 35 GUARD CROSSING The Guard Crossing consists of two identical circuits each of which transmits data in one direction across the guard isolation between the Main Printed Circuit Assembly and the TEEE 488 Interface One circuit is shown in Figure 5 15 the other circuit works identically A portion of each circuit is contained in the IEEE 488 Interface MAIN PRINTED CIRCUIT ASSEMBLY 488 INTERFACE U221 2 R203 INPUT C203 R204 f5 15 wmf Figure 5 15 Guard Crossing Circuit Theory of Operation POWER SUPPLY The circuit in Figure 5 15 has two stable states corresponding to output high 5V and output low 0V If the output is high the voltage present at the non inverting input of op amp A is approximately 140 mV Since the inputs to op amps A and B are inverted their outputs are always in opposite states If the output of A is high the output of B is low forcing the inverting input of A and the non inverting input of B to ground hence reinforcing the existing state The situation is analogous if the output of A is low A positive going transition at the input causes a positive pulse at the non inverting input of A and a corresponding negative pulse at the inverting input of A If the output is high to start with with the non inverting
123. B eerte dete 2 16 MANUAL RANGE vicirin 2 17 2 18 CONTINUOUS TRIGGER 2 19 EXTERNAL TRIGGER 2 20 Reading Rates and Noise Rejection eese 2 2 Automatic Settling Time Delay eene 2 22 External Trigger Input Option 05 Only 2 23 Sample Complete Output Option 05 Only 2 24 MAKING 2 25 Input Overload Protection Limits eene 2 26 Measuring Voltage and Resistance eene 2 27 Measuring Current 8842A Instruction Manual 2 28 Current Fuse Protection 2 29 Offset Measurements 2 30 EXTERNAL CLEANING Remote 3 1 INTRODUCTION ia u 3 2 CAPABILITIES 3 3 BUS 5 2 200 202022 5000000000000000000000058 3 4 AN OVERVIEW OF REMOTE OPERATION 3 5 A NOTE ABOUT EXAMPLES 3 6 DEVICE DEPENDENT COMMAND SEL 3 7 Bn Offset
124. COMPLETE signal is inactive When the 8842A is taking verification readings the SAMPLE COMPLETE signal acts the same as in normal operation Note that a command may be valid in some parts of the calibration procedure but not in others The Get Input Prompt G2 command for instance is not valid when the 8842A is taking verification readings The Rate Sn commands for instance are valid when the 8842A is taking verification readings but they are not valid at any other time during calibration Table 6 15 shows when commands are invalid 6 24 TIMING CONSIDERATIONS Table 6 15 Error Numbers Which Are Displayed When Commands Are Not Valid Maintenance CALIBRATION COMMAND NORMAL SELFTEST CALIBRATION MODE AIDCAL OFFSET amp HF AC CAL VERIFICAT GAIN CAL ION MODE Bn 60 52 52 52 52 CO 51 60 54 C1 51 60 C2 51 60 C3 51 60 Dn 60 52 52 52 52 Fn 60 G2 51 60 54 G3 60 a G6 N 60 52 52 52 52 P1 P2 51 60 56 54 51 60 RO 60 52 52 52 52 R1 6 60 52 52 52 52 R7 60 52 52 52 52 R8 60 52 52 Sn 60 52 52 52 60 52 52 52 52 Wn x Pf Yn 70 60 52 52 52 52 60 52 52 52 52 I e J 0 6 23 8842A Instruction Manual 6 24 6 25 6 26 The CO command can take up to 22 seconds If du
125. D GAIN CALIBRATION This procedure calibrates the instrument s offsets and gains by applying a high and low input for every range of each function To save time the 8842A uses each input for as many ranges as possible A function is calibrated by pressing the corresponding function button Once a function is selected the 8842A automatically steps through each range of that function prompting you for the necessary reference sources The prompts are shown in Table 6 10 The 8842A does not automatically select another function after one function has been completely calibrated therefore the functions may be calibrated in any order To perform Offset and Gain Calibration proceed as follows Table 6 10 Offset and Gain Calibration Steps STEP DISPLAYED PROMPT VDC VAC 2 WIRE kO mA DC mA AC 4 WIRE kO 00 0 mV DC short 10 0 mV AC 0 00Q short 00 0 mA DC open 100 mA AC 19 0 mV DC B 10 00 4 wire 100 mA DC 190 0 mV DG 100 0 mV AC 100 0Q 1000 mA DC 1000 0 mA AC 1 000 1 0004 19 00 V DC 10 00 V AC 10 00 kQ 190 0 V DC 100 0 VAC 100 0 kQ Steps D H not applicable for these 1000 vDC 500 1000 ka Step H not applicable for these 10 00 MQ functions Inputs should be at 1 kHz 10 Performance be enhanced for specific frequencies see text 1 Ensure the A D Calibration procedure has been completed 2 Select the desired f
126. DADDDD 6 10 6 11 6 12 Tolerance aina e ee 6 14 Error Numbers Which Are Displayed When Commands Are Not Valid 6 16 Circuitry Tested by the Analog Self Tests Self Test Voltages u uu tree cease Eee ede Keyboard WINE te tiat ede eir Analog Control Analog Control Logic 5 DC Scaling and Track Hold Supply Voltages eee Power Supply TUR e pa PE repe ed oro T ATE Port Configurations 2 2 Isolating a Defective AC Stage n anus List of Tables Error COdES uu Ga haya una maa oh sete iran Input Overload Lamitts end m PD ne dion deities Stat s E Numeric Output Data Serial ree ponas Immediate Mode Commands for Various Controllers Std 488 1978 Bus Codes eene Ohms Test C tr nt ciet Sample Rates and Reading 1 Recommended Test Equipment
127. DO VERIFICATION ONLY PRINT PUT 8842AIN CAL MODE THEN HIT RETUR INSTRUCTION NOTE INPUT 7 STOP PROGRAM UNTIL RETURN IS HIT FOR M 1 TO 2 LOOP FOR NO OF PASSES us IT LIBUS SOUT 0 0 SET 54404 OUTPUT TO 0 0 PUT 8842 IN A D CAL TO 11 STEP 1 CALIBRATION LOOP PRINT 1 G2 INPUT 1 C 8842 CAL PROMPTS IF C 1000 GOTO 180 CLEARS POSSIBLE ERROR MESSAGE IN BUFFER PRINT 55 STEP INPUT LABELS PRINT DISPLAY PASS STEP INPUT VALUE PRINT 7 SOUT C SET OF 5440A SETTLING TIME FOR 5440A STORE CAL 1 1 i c NEYT AND 8 lt gt 8 GOTO 260 TEST 8840A FOR CAL STEP COMPLETE NEXT PRINT VERIFICATION WAIT 3000 FOR T 0 TO 6 STEP 1 PRINTO 7 SOUT V T WAIT 7500 i SETTLING TIME FOR VERIFICATION LOOP SET 54404 OUTPUT TABUT 1 READING FROM 8842 R NUMS R St 4 tte THIS AND NEXT 3 LINES FoRMATS DISPLAY IF MID R 2 1 Q THEN R LEFT R 10 RIGHT R 3 IF LEFT R 1 THEN R RIGHT R 2 PRINT R PRINTS DISPLAY NEX V T W 1 1E 54 1E 6 THEN PRINT PASS ELSE PRINT FAIL XT END f6 05 wmf Figure 6 5 Example A D Calibration Program 6 27 DISASSEMBLY PROCEDURE WARNING TO AVOID ELECTRIC SHOCK REMOVE THE POWER CORD AND TEST LEADS BEFORE DISASSEMBLING THE INSTRUMENT OPENING COVERS MAY EXPOSE LIVE PARTS CAUTION To avoid contaminating the pri
128. ENT True RMS Measurement enne nennen Waveform Comparison eese nen rennen Crest 9 HD AC Coupled AC Measurements a Combined AC and DC Measurements Bandwidth m Zero Input VAC BrrOr iita MAKING ACCURATE MEASUREMENTS ON THE 20 mV AND 200 RANGES spices MAKING ACCURATE HIGH RESISTANCE MEASUREMENTS 4 15 4 1 8842A Instruction Manual 4 1 INTRODUCTION This section discusses considerations and techniques to help you use the 8842A effectively Among other things this section discusses sources of error which are an inherent part of the measurement process and which occur for all multimeters By understanding why and when these errors occur and by knowing how and when to correct for them you can make accurate measurements with confidence This section also discusses the relative benefits of 2 wire and 4 wire ohms describes special considerations for making ac measurements and presents some unusual applications for example using the test current in the 2 wire ohms function as a troubleshooting tool in itself 4 2 DC VOLTAGE MEASUREMENT When measuring dc voltages in high impedance circuits there are two possible sources of error to consider circuit loading and input bias current 4 3 Circui
129. ET G3 Get User Defined Message The G3 command loads the output buffer with the user defined message stored in calibration memory during the calibration procedure The message consists of 16 ASCII characters as shown in Figure 3 6 The message is stored in calibration memory during calibration using the P3 command If fewer than 16 characters have been stored the remaining characters returned are spaces If no message has ever been stored a string of 16 null characters hex 00 will be returned Some example output strings follow Example Explanation FL8842A 12 17 83 CR LF Identifies instrument and gives cal date 01 25 84 CR LF Gives cal date The last eight characters are blank G4 Get Calibration Status The G4 command is used when calibrating the 8842A under remote control The command loads the output buffer with the instrument s calibration status in the format shown in Figure 3 6 The status is represented by a four digit integer which is interpreted in Table 3 1 The first two digits are always 1 and 0 The third digit indicates whether or not the calibration verification mode is enabled This mode is enabled only when the calibration mode is enabled The fourth digit indicates whether or not the calibration mode is enabled and if so which part of the calibration procedure the 8842A is in Example output strings follow Example Explanation 1000 CR LF 1 Leading 1 0 Leading 0 0 Not in cal verification 0 Cal
130. Enable CR Only W4 Enable LF Only W5 Enable LF Only W7 Disable All Output Terminators CLEAR COMMANDS Device Clear Resets 8842 to default conditions 0 Clear Error Register SINGLE TRIGGER COMMAND Trigger Measurement GET COMMANDS G0 Get Instrument Configuration F R S and T G1 Get SRQ Mask G2 Get Calibration Input Prompt G3 Get User Defined Message G4 Get Calibration Status G5 Get IAB Status input F R Autorange On Off Offset On Off G6 Get YW Status Suffix Enabled Disabled Terminator Selection G7 Get Error Status G8 Get Instrument Identification Note G2 valid only in calibration mode PUT COMMANDS PO Put Instrument Configuration F R S and T 1 Put SRQ Mask P2 Put Variable Calibration Value P3 Put User Defined Message Note P2 and P3 valid only in calibration mode PUT COMMAND FORMAT N value PO N value P1 N value P2 P3 16 ASCII characters Figure 3 5 Device Dependent Command Set Remote Programming DEVICE DEPENDENT COMMAND SET Device dependent commands are device dependent messages For the 8842A to receive them they must be sent over the IEEE 488 bus when the 8842A is in remote and has been addressed as a listener The following paragraphs describe the device dependent commands in alphabetical order Special characters and are described last Bn Offset Commands The Offset commands duplicate the function of the front panel OFFSE
131. FLUKE 8842 Digital Multimeter Instruction Manual PN 879309 Date December 1991 Rev 3 7 96 1999 Fluke Corporation All rights reserved Printed in USA All product names are trademarks of their respective companies Chapter 1 Table of Contents Title Introduction and Specifications J Il INTRODUCTION fr etre rb tet ie e ett 1 2 THE 8842A DIGITAL 1 3 OPTIONS AND ACCESSORIES eere 14 SPECIFICATIONS eerie rr rr rint ern Operating Instructions U 2 1 INTRODUCTION eerte tereti tre erunt rara 2 2 INSTALLATION rire ri e HERO 2 3 Installing the Power Line Fuse eene 2 4 Connecting to Line sese 2 5 Adjusting the Handle rennen 2 6 Rack Mounting 5 terere d ca 2 7 OPERATING 8 0 2 8 Power Up FEeat res eerie 2 9 Front and Rear Panel Features esee 2 10 Display Features eiie rete Ree na 2 11 2 12 Overrange 2 13 Diagnostic Self Test 2 14 M E 2 15 AUTORANGL
132. FREQUENCY 1 0 TO 1 5 1 5 TO 2 0 2 0 TO 3 0 45 Hz to 20 kHz 20 Hz 0 05 0 15 0 3 20 Hz to 45 Hz and 20 0 2 0 7 1 5 kHz to 50 kHz 700V rms 1000V peak or 2 x 10 Volts Hertz product whichever is less for any range TEMPERATURE COEFFICIENT of reading Number of Counts per C to 18 C and 28 C to 50 C FOR INPUTS 210 000 counts 21 000 counts 20 20k 20k 50k 50k 100k 0 019 9 0 021 9 0 027 10 0 019 12 0 021 15 0 027 21 FREQUENCY IN HERTZ COMMON MODE REJECTION gt 60 dB at 50 or 60 Hz with 1 kQ in either lead 8842A Instruction Manual CURRENT Input Characteristics RANGE FULL SCALE 51 RESOLUTION DIGITS 5 DIGITS 4 DIGITS 200 mA 199 999 mA 1 10 pA 2000 mA 1999 99 mA 10 uA 100 pA 1 412 digits at the fastest reading rate 2 200mA range is available for dc current only DC Accuracy NORMAL S READING RATE of reading number of counts RANGE 1 YEAR 29156 2 YEARS 29150 200 mA 0 04 40 0 05 40 0 08 40 2000 mA lt 1 0 04 4 0 05 4 0 08 4 gt 1 0 1 4 0 1 4 0 15 4 MEDIUM AND FAST READING RATES In medium reading rate add 2 counts 20 counts on 200 mA range to number of counts In fast reading rate use 2 4 digit mode counts 20 counts on 200 mA range for number 1 6 of counts AC Accuracy Option 09 NORMAL S READING of Reading Number of Co
133. G102JS5 DSS71091D223512 22M 1 435802 5 62395 1 879270 SN 4LS368AN LM339N SN74LS14N SN74LS32N JUPD7210 C OR D SN75161BN SN75160BN MC78051T 2 641516 1 FOX HC 18RU 8 00 MDP14 01 332J Static sensitive part TOT QTY o HNUNNP EH Non NN b OF RW UN Peer PPP 805 7 8842A Instruction Manual Ls 8 b U908 O o 88404 1605 f805 2 wmf 488 Interface PCA 2 IEEE Figure 805 805 8 809 1 809 2 809 3 809 4 809 5 Chapter 809 Option 09 True RMS AC Title Page INTRODUCTION waqan sqa INSTALLATION OPERATING INSTRUCTIONS a nennen MAIN TENANCE LIST OF REPLACEABLE PARTS 809 1 8842A Instruction Manual 809 2 Option 09 True RMS AC INTRODUCTION 809 1 INTRODUCTION The True RMS AC option gives the 8842A the ability to make ac voltage and current measurements The ac functions are selected with the front panel VAC and mA AC buttons or by remote commands if the IEEE 488 Interface option is installed Specifications for Option 09 are shown in Section 1 Table 1 1 809 2 INSTALLATION The True RMS AC option is contained on a single easy to install printed circuited assembly PCA To install the option proceed as follows WARNING TO AVOID ELECTRIC SHOCK DISCONNEC
134. IV f6 16 wmf Figure 6 16 Typical Bus Data Line Waveform The waveform at the storage capacitors can often be used to locate leakage problems The leakage can be due to contamination on the Main PCA or to defective switches in U101 Figure 6 15 shows the waveforms across storage capacitors C102 and C103 U101 24 and U101 25 respectively for a specific input The A D Converter communicates with the In Guard HC via the internal bus which also goes to several other sections of the instrument What looks like a problem in the A D Converter may actually be caused by a problem in another section of the instrument which is loading down the bus data lines U101 1 2 3 38 39 40 A typical waveform at one of the data lines is shown in Figure 6 16 One of the data lines can be loaded down so that the In Guard uC fails to recognize data sent over that line If so the amplitude of the signal of the bad line would be less than 3V peak to peak One technique of finding an overloaded or shorted data line is to remove the In Guard uC and drive one data line at a time through a 1 resistor Measure the voltage drop across a length of the line Normally the voltage drop across the line is zero volts less than 5 uV Voltage drops larger than 5 uV indicate a short The voltage drop is caused by excessive current flowing through the line When troubleshooting the A D Converter it may be desirable to determine what the reading i
135. Malfunctions in the ohms functions can be caused by a fault in the Precision Voltage Reference Ohms Current Source or Ohms Protection Malfunctions can also be caused by a fault in the DC Scaling circuit which loads the Ohms Current Source First check the power supply levels see schematic Then check all digital logic input pins of the quad analog switches U402 and U403 These should show digital signals with high gt 3V and low lt 0 5V To determine whether the Ohms Current Source is being loaded down by the DC Scaling circuit select the VDC function and connect a 10 resistor between the collector of Q404 and ground Reference Low Selecting the VDC function opens K401 and configures the Ohms Current Source in the 20 kQ range If the voltage across the 10 kQ resistor is then the Ohms Current Source is working at least in the 20 range and the problem is probably due to a defect in the DC Scaling circuit Maintenance TROUBLESHOOTING EUN NN Em INPUT 1V 08 Eni VERT H3 sa 0 5V DIV L HHH HORIZ 225 IIN LTT TT ty tT RANGE E A D INPUT SAMPLING INPUT 1V VERT 0 5V DIV HORIZ 2 ms DIV RANGE 2 INPUT 0V VERT 5 mV DIV HORIZ 2 ms DIV RANGE a L 4 i 200 mV cerser vox inae or mu Ter PAR AHH 0 5V DIV LLL T ane v 4252 ima f 2 ms DIV C
136. N numeric entry Where numeric entry is one of the following signed integer signed real number without exponent signed real number gt E lt signed exponent Example Explanation N12001 Enters the five digit integer 12001 N 1 23E2 Enters 1 23 x 10 N 154 33E 1 Enters 1 5433 x 10 The N command enters numeric values for use with subsequent Put commands The interpretation of the numeric value depends on which Put command it is used with The E can be used within an N command for entering an exponent of 10 The N can be used without an E but an E requires a prior N The exponent can be any integer from 9 to 9 The mantissa may exceed 5 1 2 digits The 8842A accurately calculates the appropriate exponent and then disregards all but the first 5 1 2 digits of the mantissa However a syntax error will occur if the numeric entry overflows the input buffer Example Explanation N123456789 Enters 1 23456 x 10 Put Commands The Put commands through set up the 8842A s configuration and operating modes by entering putting information in the appropriate registers The put commands are described further in the following paragraphs Put Instrument Configuration Format Explanation N frst PO Where lt frst gt is a four digit integer interpreted as arguments for the F R S and T commands Example Explanation 3 15 8842A Instruction Manual 3 24 3 25 N3120 PO Identical
137. NALS 3HVdWOO NOT TO SCALE 9 o E 5 N a lt FIVE MEASUREMENT INTERVALS 2 HD2 TR2 3 For 60 Hz line frequency line TR has 12 5 ms period as shown above f5 05 wmf Figure 5 5 Timing Diagram for One A D Cycle Track Configuration 5 10 inverting the T H circuit functions as a non buffer The voltage on C308 tracks the scaled dc input voltage 4A In the track configuration Figure 5 5 10 5 11 5 12 5 13 Theory of Operation PRECISION VOLTAGE REFERENCE Settling Configuration The circuit assumes a settling configuration between the track and hold configurations The circuit assumes the configuration in Figure 5 4B for unity gain and the configuration in Figure 5 4C for gain of 10 During this time the DC Scaling circuit is still connected to the T H amp However changes in the input do not affect the value to be measured which is stored on C308 Hold Configuration The X1 hold configuration Figure 5 4D is used for all VDC ranges except rl and for all ohms ranges except rl The output of U307 is the negative of the input voltage The X10 hold configuration Figure 5 4E is used for the mA DC function the 200 mV dc range and the 2000 range and provides a gain of 10 Pre Charge Configuration The pre charge configuration Figure 5 4F occurs after the hold configuration in VDC ranges r1 r2 and r4
138. NG VARIABLE 5 6 17 CALIBRATING INDIVIDUAL RANGES 6 18 6 19 ERASING CALIBRATION Contents continued 6 20 TOLERANCE CHECK 6 21 AC CALIBRATION AT OTHER FREQUENCIES 6 22 OPTIMIZING USE OF THE 5450 6 23 Remote Calibration ws 6 24 TIMING 5 6 25 REMOTEERASURB nat 6 26 EXAMPLE CALIBRATION 6 27 DISASSEMBLY 6 28 6 20 True RMS AC PCA Removal Option 09 Only 6 30 TEEE 488 Interface PCA Removal Option 05 Only 6 31 Main PCA Removal 6 32 Front Panel Disassembly eese 6 33 REASSEMBLY PROCEDURE eerte 6 32 6 34 INTERNAL FUSE 6 35 EXTERNAL TRIGGER POLARITY SELECTION Option 05 Only 6 36 TROUBLESHOOTING trennen ens 6 37 I
139. Now Magnum Div of Cooper Industries Inc St Louis MO 71590 CRL Components Inc Formerly Mepco Centralab A North American Philips Co Fort Dodge 71707 Coto Corp Providence RI List of Replaceable Parts SERVICE CENTERS Supply Codes for Manufacturers cont T3734 Federal Screw Products Inc Chicago IL 74594 Component Resources Inc Div of EPI International Corp Beaverton OR 78189 Illinois Tool Works Inc Shakeproof Div Elgin IL 83014 Hartwell Corp Placentia CA 85480 W H Brady Co Corp Industrial Products Div Milwaukee WI 89536 Fluke Corporation Everett WA 91506 Augat Inc Attleboro Falls MA 91637 Dale Electronics Inc Columbus NE S3385 Sanken Denki Corp Tokoyo Japan supply 2 wmf Instruction Manual USA California FLW Fluke Calibration Center C o FLW Service Corporation 3505 Cadillac Ave Bldg E Costa Mesa CA 92626 TEL 714 751 7512 FAX 714 755 7332 Dallas Fluke Service Center 2104 Hutton Drive Suite 112 Carroliton TX 75006 TEL 214 406 1000 FAX 214 247 5642 Fluke Service Center 42711 Lawrence Place Fremont CA 94538 TEL 510 651 5112 FAX 510 651 4962 Illinois Fluke Service Center 1150 W Euclid Av nu Palatine IL 60067 TEL 708 705 0500 FAX 847 705 9989 New Jersey Fluke Service Center W 75 Century Rd Paramus N J 07652 0930 TEL 201 599 9500 599 0919 FAX 201 599 2093 Washing
140. OC 2088181 PAR pees RANGE 200 mV ALL WAVEFORMS FOR SLOW READING RATE f6 13 wmf Figure 6 13 Typical Output Waveforms for Track Hold Circuit TP103 To test whether the Ohms Current Source is actually being sourced out the HI and LO OUTPUT terminals select the 20 kO range and the 2 wire ohms function connect a 10 resistor across the HI and LO INPUT terminals and measure the voltage across this resistor with another voltmeter There should be a 1V drop across the resistor 6 57 8842A Instruction Manual 6 58 6 65 If the ohms functions do not work in any range check the supplies at 0401 15V 0404 30 5 0402 15 5V and OV 7403 15 5V and OV and check the 7V reference at R416 Also test the Ohms Protection circuitry as follows Select the 20 kQ range and 2 wire ohms function connect a 10 kQ resistor to the HI and LO INPUT terminals and bypass the protection circuitry by connecting the emitter of Q402 to the junction of R410 and R309 If a reading of 10 kQ is displayed the protection circuitry is defective To isolate the problem successively short each part of the protection circuitry that is in series with the Ohms Current Source until the display reads 10 If the ohms functions work in only certain ranges suspect resistor network 7401 or analog switches U402 or U403 To test the analog switches select a defective range and connect a short across the s
141. OSED OSE EXACT REPLACEMENT ONLY Rais 5 lt lt o PRECISION CUREFENT Soocce Peas eae Sane emaor eesos evo mvaoa ese jessa L Zoom ZOM ZKEZK4 ZOK TOOK gt LOOK ZOoox ZOM WARNING SEL 2 PL Qao Q40q TO DIGITAL 5 2 X 4o CEAAL 340907 IX SCALING 4 z399 FOSIS LE TS OIGITAL 2 zaoz 5 24 33K ZONA CHMS lt o caos amp 2K 42K Ie CD 290v OC SCALING x TFAG 8842A 1001 a VEC y ey iva 6 rra v4 Sheet 3 19 03 2 wmf Figure 9 3 Main PCA Ohms Current Source cont 9 8 Schematic Diagrams 9 08903 0903 1 02 wy 0405 0407 V 0406 0402 0317 0307 08308 0392 58310 s REF 9702 220 0219 UNDER 12201 JPR1 CRe15t 0403 UNDER U208 UNDER A pee 8 24 R601 CRei t EM CR613 cR VREOS CR amp 0 CRGO CR amp 3 CR eo COKIN C605 IL ne 8842A 1601 Figure 9 4 Main PCA Digital 19 04 1 wmf 9 9 8842A Instruction Manual GLVaZD CHEOSSIOG Tee 8 SINGLE v e 5
142. PUT LEADS BEFORE REMOVING THE INSTRUMENT CASE 1 Remove the grounding screw from the bottom of the case and remove the two rear panel mounting screws Figure 805 1A 2 Holding the front panel slide the case and rear bezel off of the chassis Figure 805 1B Note At this point the rear bezel is not secured to the case 805 3 8842A Instruction Manual 3 Disconnect the ribbon cable from the plastic rear panel insert by pulling the tabs on either side of the ribbon cable connector outward Pull the ribbon cable directly toward the front panel Figure 805 1C 4 Remove the rear panel insert by releasing the two snap tabs inside the instrument Figure 805 1D NOTE The connection on the rear panel insert is used for factory calibration only The connector is electrically isolated from all measuring circuitry 5 Connect the the ribbon cable from the PCA to the connector on the IEEE 488 Interface PCA Figure 805 1E Latch the ribbon cable in place as shown in Figure 805 1F Make sure the heads of the plastic latches are in the extended position With the component side down guide the BNC and IEEE 488 connectors located on the rear of the IEEE 488 Interface PCA into the rear panel and seat the IEEE 488 Interface PCA on the mounting supports on the chassis Figure 805 1G 9 Fasten the IEEE 488 Interface PCA to the chassis by pressing the two plastic latches into the mounting supports See Figure 805 1H 10 S
143. R POWER 803270 1 TP101 105 TP201 TERM FASTON TA8 110 SOLDER 512889 25 TP202 TP204 207 512889 TP301 304 TP401 512889 TP403 TP601 605 512889 607 609 512889 0102 0702 AMP DUAL LO OFFST VOLT LO DRIFT 685164 2 U103 AMP LO OFF VOLTAGE LO DRIFT 685156 1 U201 IC BIPLR BCHNL DRIVER 685412 1 0203 IC LSTTL HEX INVERTER 393058 1 U204 U305 IC COMPARATOR QUAD 14 DIP 387233 2 U208 IC LSTTL 3 8 LINE DCDR W ENABLE 407585 1 U211 IC LSTTL QUAD 2 INPUT OR GATE 393108 1 0213 IC LSTTL 8BIT ADDRSABLE LATCH W CLR 419242 1 U215 U217 U218 IC BIPLR 8CHNL FLOURSCNT DISPLY DRIVR 685537 3 0216 IC LSTTL BCD TO 7 SEGMENT DCDR DRVR 697730 1 U219 IC CMOS OCTL D F F W 3 STATE EDG TRG 585364 1 0221 IC LSTTL HEX INVERTER W SCHMT TRIG 483180 1 U301 303 U402 IC CMOS QAS PLASTIC HIGH B GRADE 700013 4 U304 IC OP AMP FET LO NOISE PRECISIION 8DIP 780759 1 0306 AMP SPECIAL LOW DRIFT TO 99 650713 1 U307 AMP JFET IN COMPENSTD 8 PIN DIP 418780 1 0401 AMP LO OFFSET VOLTAGE LO NOISE 605980 1 U403 IC CMOS QAS PLASTIC HIGH A GRADE 803478 1 U404 AMP GENERAL 8 PIN 478107 1 VR601 IC VOLT REG FIXED 5 VOLTS 1 5 AMPS 428847 1 VR602 IC VOLT REG FIXED 24 VOLTS 1 5 AMPS 604074 1 VR603 IC VOLT REG FIXED 15 VOLTS 1 5 AMPS 413187 1 VR604 IC VOLT REG FIXED 15 VOLTS 1 5 AMPS 413179 1 VR605 IC VOLT REG FIXED 24 VOLTS 1 5 AMPS 418251 1 W1 W8 WIRE ASSEMBLY GUARD CROSSING 684399 2 W2 W9 WIRE ASSY
144. R POWER TRANS SUPPLY CEIVERS U912 AND U913 SAMPLE COMPLETE SIGNAL EXTERNAL CONDITIONING TRIGGER f5 16 wmf Figure 5 16 IEEE 488 Interface Block Diagram 5 38 Out Guard Microcomputer The Out Guard Microcomputer uC U901 communicates with the IEEE 488 talker listener IC U911 and the In Guard wC U202 The Out Guard uC is similar to the In Guard Z8 uC except that is contains 8K bytes of ROM and 236 bytes of RAM For futher description of the Z8 uC refer to the heading In Guard Microcimputer above 5 39 Guard Crossing The guard crossing circuit permits serial asynchronous communication between U901 and U202 while isolating the two electrically One half of the guard crossing circuit is contained on the Main PCA the other half is on the IEEE 488 Interface PCA Operation of the guard crossing circuit is described in an earlier heading 5 40 Bus Interface Circuitry The IEEE 488 bus protocol is handled by the uPD7210 IEEE 488 talker listener IC U911 It is controlled by U901 as a memory mapped peripheral through an 8 bit data bus Bus transceivers U912 and U913 buffer U911 from the IEEE 488 bus They provide the bus with the required output drive capability and receiver impedance 5 26 5 41 5 42 Theory of Operation TRUE RMS AC OPTION 09 Signal Conditioning The SAMPLE COMPLETE and EXT TRIG signals J903 and J904 are conditioned by U909 Diodes CR903 CR904 CR905 and CR906 and resistors
145. R917 and R918 provide protection from excessive voltages Jumpers E902 and E903 allow selection of the polarity of the EXT TRIG signal A polarity selection procedure is given in the Maintenance section The 8842A is configured in the factory so that it is triggered on the falling edge of the EXT TRIG signal IEEE 488 Interface Power Supply The IEEE 488 Interface power supply circuit provides the IEEE 488 Interface PCA with 5V The circuit consists of rectifying diodes CR908 and CR909 filter capacitor C910 and voltage regulator VR901 Power comes from transformer T605 on the Main PCA U908 and associated circuitry resets the Out Guard uC at power up and following power line voltage dropouts 5 43 TRUE RMS AC OPTION 09 The True RMS AC circuit Figure 5 17 performs two primary functions First it scales ac input voltages and ac current sense voltages to a range of OV to 2V ac rms Second it converts the scaled ac voltages to an equivalent dc voltage which is then directed to the A D Converter via the Track Hold Amplifier The True RMS AC circuit is trimmed for flat high frequency response using a variable filter which is set by the High Frequency AC Calibration procedure R804 R805 VAC r3 r5 RMS FILTER CONVERTER AC NPU TRACK VOLTAGE FILTERS HOUD 5 44 CIRCUIT 500 FOR r4 r5 CURRENT SENSE f5 17 wmf Figure 5 17 True RMS AC Option Block Diagram The following parag
146. RTER W 3 STATE OUT IC COMPARATOR QUAD 14 PIN DIP IC LSTTL HEX INVERTER W SCHMT TRIG IC LSTTL QUAD 2 INPUT OR GATE IC NMOS GPIB TALKER LISTENER CNTKLR IC LSTTL OCTAL GPIB ACTV PULL UP XCVR IC LSTTL OCTAL GPIB XCVR W OPEN COL IC VOLT REG FIXED 5 VOLTS 1 5 AMPS 12 40 PIN DUAL WIPE RETENTION CRYSTAL E 00KHZ QUARTZ liC 18U RES CERM DiP 14 PIN 15 5 3 3 5 FLUKE STOCK NO 897417 697284 697284 732644 460261 733386 733386 697458 733246 697524 113316 203323 742874 697060 110635 185518 682898 682906 911508 697355 911487 414128 348888 343418 343434 348771 376652 376434 348839 807545 658567 512889 512889 279270 654442 387233 483180 393102 773143 585232 585224 428847 756658 707133 735402 MFRS SPLY CODE 56289 60705 04222 62643 04222 04222 56289 04222 81349 65940 65940 59124 COMMER COMMER 34848 83014 00779 28213 69536 13103 81349 81349 81549 81349 81349 81349 81349 51406 00779 00779 89536 01295 04713 01295 01295 33297 01255 01295 04713 00779 61429 91657 MANUFACTURERS PART NUMBER OR GENERIC TYPE 199D105X0035AG2 562CZ5USESOEE103M SR 95A431JAA KME16VN472K23X27LLV SRSOSE224ZAA SR595C102MAA 199D476x0010DG2 SRS95A150MAA 1N748 1N4448 1N4002A 2 25 CIAL CIAL HN4G 44 1 4 44 4 1 554925 2 3446 6322 911487 6030B TT RCR07G333JS 07615215 RCRO7G4710S RCRO G101JS RCR07G683JS RCR07GS13JS RCR07
147. Read Write Timing Diagrams for Internal Bus f5 14 wmf 5 29 5 30 Theory of Operation DIGITAL CONTROLLER Function and Range Control The In Guard HC configures the DC Scaling circuit the Track Hold circuit and the Ohms Current Source to provide the proper input switching scaling and filtering for each function range and reading rate It does this by controlling dedicated output lines which control relays and FET switches and by sending configuration codes out on the bus The quad analog switches U301 U302 U303 U402 and U403 latch the configuration codes and perform any level shifting needed to control their internal MOSFET switches Some of the switches require dynamic timing signals from the custom A D IC U101 these signals are combined appropriately in the quad analog switches with the configuration codes A D Control and Computation The In Guard uC initiates each A D sample by pulling line low When the uC is reset it senses the power line frequency on line FREQ REF The uC then sets its internal timer so that the A D sample rate is as shown in Table 5 1 The number of readings per second for the slow and medium rates are chosen to provide rejection of input signals that are at the line frequencies Table 5 1 Sample Rates and Reading Rates SLOW MEDIUM FAST POWER LINE Samples Samples Samples Samples Samples Samples FREQUENCY per Sec per per Sec per per Sec per Reading Reading Reading 50 Hz
148. S Write functions to instrument 300 FOR I 1 TO 10 310 RD SPACE 18 711 characters for the reading 5 for the 320 suffix and 2 for the terminators 330 CALL IBRD DVM RD Get data from 8842A 340 PRINT I LEFT RD 16 Print to display 350 NEXT I 360 END PC PC XT and PC AT are registered trademarks of Intemational Business Machine Corporation National Instruments is a registered trademark of National Instruments Corporation f3 14 01 wmf Figure 3 13 Example Programs Using the IBM PC 3 37 8842A Instruction Manual 10 REM The following application program is written in BASICA for the IBM PC PC XT or 20 REM PC AT The National Instruments Model GPIB PCIIA board provides the interface 30 REM between the PC and the Fluke 8842 DMM The program assumes that the configuration 40 REM program IBCONF has been run to initialize the interface board with the device 50 REM name 18842 assigned to the GPIBO board 60 REM 70 REM The first 6 lines of code are required to properly link the NI drivers to BASICA 80 REM 90 REM This program illustrates one possible use of the serial poll register In this 100 REM case it is merely looking for data available The function of the program is to 110 REM display on the screen the lowest resistance value measured on the input terminals 120 REM of the 8842A using the 2 wire ohms function in autorange The range and function 130 REM commands are programmed using the Pu
149. T 94 Y1 GET Data amp Suffix INPUT 94 Red 704 A A ENTER 704 A A Note INPUT 4 A A Note 1 2 PRINT Data amp Suffix PRINT A A Prt PRINT A A Note 2 PRINT A A Notes six characters Hit RUN Key This program creates the variables A and A so that they may be accessed in immediate mode and changed at will This program is not necessary for the HP 85 Calculator SCRATCH Hit EXEC key 10 0 Hit ENTER key 20 A Hit ENTER key 30 END Hit ENTER key 3 60 EXAMPLE PROGRAMS Several example programs for the 8842A using various controllers are presented in the remaining figures in this section In all of these examples the 8842A is set to IEEE 488 address 4 rear panel switch setting 000100 Of course any other address 00 to 30 could be substituted 1 Before using A on the 9825 is necessary to enter dimA 6 to allocate a string variable This statement allows 2 Inthe HP9816 system variables cannot be created from the keyboard they must be created by running program See error 910 for that system To get around this type in a very short program as follows In each of these examples the instrument is cleared prior to configuration set ups This ensures that the 8842A configuration has been completely defined To run these programs it is not necessary to type in all the comments which appear to the right of the exclamation mark
150. T THE POWER CORD AND TEST LEADS BEFORE REMOVING THE INSTRUMENT CASE 1 Remove the grounding screw from the bottom of the case and remove the two rear panel mounting screws Figure 809 1A 2 Holding the front panel slide the case and rear bezel off of the chassis Figure 809 1B At this point the rear bezel is not secured to the case 3 Holding the True RMS AC PCA slightly above the chassis component side down connect the the ribbon cable from the True RMS AC PCA to the Main PCA and latch it in place See Figure 809 1C and D 4 Connect the red lead from the True RMS AC to stud W301 on the Main PCA See Figure 809 1C The stud is located next to the forward end of the FRONT REAR switch 5 Make sure the heads of the four plastic latches are in the extended position Guide the PCA into the 4 circuit board supports 6 Fasten the True RMS AC PCA to the chassis by pressing the four nylon latches into the mounting supports on the chassis See Figure 809 1E 7 Reinstall the cover and rear bezel on the chassis and attach the two rear panel mounting screws 8 Attach the grounding screw to the bottom of the case WARNING TO AVOID ELECTRIC SHOCK ENSURE THE GROUNDING SCREW IS FIRMLY ATTACHED TO THE CASE BOTTOM 9 Calibrate the VAC voltage and mA AC functions according to the calibration instructions given in the Maintenance section 809 3 8842A Instruction Manual 809 3 OPERATING INSTRUCTIONS For operat
151. T button When the 8842A receives the B1 command the 8842A stores the present reading as an offset for the present function The 0 command cancels the offset As with front panel operation only one offset is allowed at a time The offset status not the offset value can be read using the G5 command The 8842A defaults to BO on both power up and on any device clear command DCL or SDC Cn Calibration Commands CAUTION The command string C3 CO erases the entire calibration memory A complete calibration must then be performed The Calibration commands allow the 88424 to be calibrated under remote control Commands CO C1 and C2 duplicate the front panel calibration functions STORE A D and HF AC respectively For a complete description of remote calibration see the Maintenance section of this manual For the 8842A to accept these commands the 8842A must be in the calibration mode enabled by pressing the front panel CAL ENABLE switch Otherwise the commands generate an error message Dn Display Commands The Display commands allow the user to blank the numeric field in the 8842A front panel display The DO command causes the display to operate normally and is the default on power up and upon any device clear command DCL or SDC The D1 command blanks the numeric field in the display The annunciators remain active and all of the annunciators still flash if the input exceeds 1000V dc or 700V ac in the respectiv
152. TAGES 8842 REVERSE THESE LEADS FOR NEGATIVE INPUT KELVIN VARLEY VOLTAGE VOLTAGE TO 8842A DIVIDER FLUKE 720A B CONNECTIONS FOR FLUKE 5440 OR EQUIVALENT DC CALIBRATOR 54408 OR EQUIV 8842 SHIELD INPUT SENSE NOTE KELVIN VARLEY VOLTAGE DIVIDER IS NOT REQUIRED FOR INPUT VOLTAGES ABOVE 2 0V DC f6 01 wmf Figure 6 1 DC Calibration Connections Table 6 2 DC Voltage Test Displayed Reading STEP RANGE INPUT SLOW MEDIUM FAST V dc MIN MAX MIN MAX MIN MAX 20 OV 0 0030 0 0030 0 0050 0 0050 0 030 0 030 short 200 OV 00 003 00 003 00 005 00 005 00 03 00 03 short 2 20V 2 counts 2 counts 4 counts 4 counts 3 counts 3 200V short counts 1000V D 20 mV 10mV 9 9963 10 0037 9 9943 10 0057 9 970 10 030 E 200 mV 100 mV 99 993 100 007 99 991 100 009 99 97 100 03 F 2 1V 99996 1 00004 99994 1 00006 9997 1 0003 G 20V 10V 9 9995 10 0005 9 9993 10 0007 9 997 10 003 H 200V 100V 499 995 100 005 499 993 100 007 499 97 100 03 4999 7 1000V 1000V 999 95 1000 05 999 93 1000 07 1000 3 1 Relative to high quality short stored using OFFSET feature 6 6 Maintenance PERFORMANCE TEST 6 5 AC Voltage Test Option 09 Only The following procedure may be used to verify the accuracy of the VAC function
153. TED WITH PERMISSION FROM TEKTRONIX INC AND GERNER DYNAMICS POMONA DIV Dow Chemical 6 1 6 3 6 4 6 5 6 7 6 8 6 9 6 10 6 11 6 12 6 13 6 14 6 15 6 16 6 17 6 18 6 19 6 20 6 21 6 22 6 23 6 24 6 25 6 26 6 27 6 28 6 29 6 30 6 31 6 32 6 33 6 34 Chapter 6 Maintenance Title Page INTRODUCTION PERFORMANCE Diagnostic beer detent DC Voltage Testers AC Voltage Test Option 09 Resistance T6st a east DC Current 2 decere AC Current Test Option 09 CALIBRATION Basic Calibration INITIAL PROCEDURE eere mec terrre A D CALIBRATION 222 OFFSET AND GAIN CALIBRATION HIGH FREQUENCY AC CALIBRATION Advanced Features and Special Considerations STORING CALIBRATING INDIVIDUAL RANGES ERASING CALIBRATION TOLERANCE CHECK
154. TIA IBSTA IBERR IBCNT 210 REM 220 REM IBM BASICA on IBM PC PC XT or PC AT 230 REM 240 DEVNAME 18842A Device name is 18842 250 CALL IBFIND DEVNAME DVM Initialize the DMM 260 CALL IBCLR DVM Clear device 270 FOR W 1 TO 500 NEXT W Wait 1 second before sending commands 280 WRT N3001PO Y1 290 CALL IBWRT DVM WRT Write functions to instrument 300 RD SPACES 18 11 characters for the reading 5 for the 310 suffix and 2 for the terminators 320 CALL IBRD DVM RD first reading from 8842A 330 R VAL RD 340 PRINT LEFT RD 16 S 2 WIRE LOWEST READING Display readings 350 WRT 360 CALL IBWRT DVM WRT Trigger the 8842A 370 CALL IBRSP DVM SPR Get serial poll byte 380 IF SPR AND amp H40 lt gt amp H40 THEN 370 Check for data available 390 RD SPACE 18 400 CALL IBRD DVM RD next data 410 S VAL RD 420 IF S gt R THEN 350 Throw away data if not lowest 430R S Update lowest reading 440 GOTO 340 Print new low 450 END f3 14 02 wmf Figure 3 14 Example Programs Using the IBM PC cont 3 39 8842A Instruction Manual 10 REM The following application program is written in BASICA for the IBM PC PC XT or 20 REM PC AT The National Instruments Model GPIB PCIIA board provides the interface 30 REM between the PC and the Fluke 8842A DMM The program assumes that the configuration 40 REM program has been run to init
155. Volts 4 Wire Ohms acl AC Volts DC Current CAL ENABLE switch HIGH and LO SENSE 2 Wire Ohms Current enables calibration Terminals for 4 Wire Ohms Only mode CAUTION See text Display Terminals M CALIBRATION SEAL 2A INPUT Terminal _ Ives JI Le J ze ed Ge SPECIAL STORE RATE _ U ee FRONT REAR switch selects RANGE BUTTON either front or rear inputs 20 mV or 20 or 1000V dc 700V ac Calibration Functions 200 mV or 2000 B 2 or 2000 mA embossed 2V or 2kO 20 MQ POWER switch turns 8842A or off Also initiates 20V or 20k Autorange On Off ip self test and resets instrument to VDC function Autorange Slow reading rate Continuous trigger OFFSET off Local front panel control Available with 8842A 09 True RMS AC only For a description of the autorange feature Gives error message if option not installed see paragraph 2 14 12 05 1 wmf Figure 2 5 Front Panel Features 2 5 8842A Instruction Manual TRIG triggers a new reading Enabled in ext
156. ally 12V The 20V dc range scales this voltage and presents the A D Converter with 1 15V or 115 000 counts This is a good test to ensure that the maximum open circuit voltage of the Ohms Current Source is less than 13V This test is susceptible to capacitance greater than 0 01 at the input terminals e TEST 9 20 VDC 2000 kQ Puts the DC Scaling circuit in the 20V dc range and the Ohms Current Source in the 2000 range The infinite input impedance of the 20V dc range causes the 2000 current source to be clamped at typically 11 5V The reading at the A D Converter should be 1 15V Again tests that the maximum open circuit voltage of the Ohms Current Source is less than 13V Capacitances greater than 0 1 uF at the input terminals can cause an error e TEST 10 2 VDC 2000 kQ Puts the DC Scaling circuit in the 2V dc range and the Ohms Current Source in the 2000 range except that its maximum open circuit voltage is limited to less than 6 5V in this configuration This test as well as tests 11 13 checks clamps Q312 and Q313 and the analog filter The reading at the A D Converter should be an overload Capacitances greater than 0 5 uF at the input terminals can cause an error TEST 11 2000 Overrange e TEST 12 2 Overrange TEST 13 20 Overrange e TEST 14 200 Overrange 6 43 8842A Instruction Manual 6 44 These tests put the 8842A in the respective range of the 2 wire ohms function They c
157. ammed as the serial output and constantly transmits hex 55 every 820 us at 62 000 baud in all four diagnostic modes This causes the front panel error message 6 71 True RMS AC Troubleshooting Option 09 6 72 SERVICE POSITION To provide easy access to the True RMS AC PCA and the Main PCA the True RMS AC PCA can be placed in the specially provided service position as follows 1 Remove the case from the chassis using the Case Disassembly procedure provided earlier in this section 2 Release the four nylon latches that hold the True RMS AC in place by pulling the latches upward See Figure 809 1E in Section 8 3 Disconnect the red ac input lead from both the True RMS AC PCA and the Main PCA 6 66 6 73 Maintenance TROUBLESHOOTING 4 Position the True RMS AC PCA vertically as shown in Figure 6 20 and latch it in place by pressing the bottom two nylon latches into the specially provided mounting supports on the chassis 5 Connect the Main PCA ac take off point stud connector W301 to the True RMS AC PCA input the stud connector labeled AC IN with a 6 inch jumper E Z Hook 204 6W S or equivalent MAJOR PROBLEMS The signal flow through the True RMS AC option is straightforward with no feedback paths between individual stages This simplifies troubleshooting and often makes it possible to isolate a single defective stage without removing the instrument cover Test the mid frequency response of
158. and 7 00000V 250 ppm Also check that the reference amplifier output voltage U702 1 is nominally 6 5V If the outputs are grossly out of tolerance e g stuck at 15V or 15V the most likely cause is a bad op amp U702 or open resistor network Z701 or Z702 If the outputs are slightly out of tolerance the most likely cause is a defective or out of tolerance resistor in Z701 or Z702 Because Z701 is precisely matched with U701 Z701 and U701 must be replaced as a matched set Shorts between lands or runs can also cause small errors 10 ppm to several hundred ppm Shorts between sense and output lands can cause small errors that are not related to resistor networks Load regulation problems can also be caused by shorts between sense and load lines In some rare cases the op amps U702A and U702B could be out of spec causing a small error The maximum input offset voltage of the op amps used in the circuit is 3 mV 6 66 Maintenance TROUBLESHOOTING A D Converter Troubleshooting If there is a failure of the A D Converter all power supply levels should be checked at the op amps U102 and U103 and the A D IC U101 The A D Converter has a total of seven supplies 15V 15V 5V 7 5V 8 2V 7 00000V and 7 00000V supplies should be within 5 of their nominal values except for the 7 00000V and 7 00000V reference supplies which should be within 1000 ppm and 250 ppm respectively The bootstrap supplies line
159. ar bezel onto the chassis 20 Install the two rear panel mounting screws 21 Install the case grounding screw in the bottom of the case 6 35 8842A Instruction Manual 6 36 WARNING TO AVOID ELECTRIC SHOCK ENSURE THAT THE GROUNDING SCREW IS FIRMLY ATTACHED TO THE CASE BOTTOM 6 34 INTERNAL FUSE REPLACEMENT CAUTION For fire protection use exact fuse replacements only The 8842A has an internal 600V slow blow fuse F301 in series with the 2A input terminal To replace this fuse remove the case according to the disassembly instructions The fuse is held in fuse clips on the Main PCA Do not use makeshift fuses or short circuit the fuse holder 6 35 EXTERNAL TRIGGER POLARITY SELECTION Option 05 Only The EXT TRIG input is factory configured with negative polarity trigger on falling edge This polarity is set by jumper E902 on the IEEE 488 Interface PCA To select positive polarity trigger on rising edge remove jumper E902 and add jumper E903 6 36 TROUBLESHOOTING 6 37 The 8842A is designed to be easily maintained and repaired Both the analog and digital circuits have built in diagnostic self tests and troubleshooting modes to facilitate troubleshooting and repair The instrument s circuits allow troubleshooting and repair with basic electronic troubleshooting equipment such as a multimeter and oscilloscope The troubleshooting mode in the digital controller circuitry generates special test signal
160. ard supports on the chassis Press the latch heads to lock the board in the chassis Refer to Figure 6 6L 4 Install one side of the Main Shield bow it to install the the other side and secure it to the Main PCA with the retaining screw 5 Place the transformer bracket back into position and fasten down with the two screws Replace the push rod for the POWER switch as follows a Insert the button end of the push rod into the rear of the front panel b While supporting the opposite side of the plunger with your finger snap the other end of the push rod onto the POWER switch plunger Refer to Figure 6 6 Set the chassis right side up Insert the FRONT REAR switch push rod through the front panel and snap it into place Reinstall the CAL ENABLE switch push rod by inserting the cylindrical end of the push rod into the rear of the front panel then snapping it onto the CAL ENABLE switch plunger 6 33 8842A Instruction Manual REAR PANEL 4 2 lt z a u DISPLAY PCA MOUNTING SCREW SPACER MATRIX KEYPAD DISPLAY PCA DISPLAY PCA REAR VIEW f6 07 wmf Figure 6 7 Front Panel Disassembly 6 34 Maintenance REASSEMBLY PROCEDURE FRONT PANEL au DISPLAY WINDOW f6 08 wmf Figure 6 8 Removing the Display Window CAUTION Make certain that the CAL ENABLE switch shaft is in the out disabled position after the CAL ENABLE push rod is installed If the 8842A is swi
161. are all considered to be device clear commands because the results are so similar however DCL and SDC are not identical to the asterisk command described here DCL and SDC are discussed further in the paragraph on interface messages 3 35 Single Trigger Command The Single Trigger command causes the 8842A to take a reading and place the result into the output buffer To accept this command the 8842A must be in external trigger mode selected by the T1 T2 T3 or T4 command The Single Trigger command is one of five ways to trigger a reading See Figure 3 7 Of these only the Single Trigger command and the Group Execute Trigger command GET are loaded into the input buffer 3 36 INPUT SYNTAX The following paragraphs describe how to construct groups of commands for the 8842A A few definitions are presented first followed by a description of how the 8842A processes input commands Guidelines are then summarized in four syntax rules 3 20 3 37 3 38 Remote Programming INPUT SYNTAX Definitions Output commands Commands which load data into the output buffer The output commands are the Get commands GO through G8 the Single Trigger Command the Continuous Trigger command TO and Group Execute Trigger GET not to be confused with the Get commands e Input terminator An ASCII control code sent by the controller which tells the 8842A to execute all device dependent commands since the previous te
162. ary thin film resistor networks a stable reference amplifier and stable active components the 8842A offers superior measurement performance and stability It also offers additional 20 mV 20 ohm and 200 mA dc ranges Features of the 8842A include e Highly legible vacuum fluorescent display e Intuitively easy front panel operation e Basic dc accuracy of 0 003 for 1 year e 2 wire and 4 wire resistance measurement DC current measurement e Up to 100 readings per second e Closed case calibration no internal adjustments e Built in self tests 1 3 OPTIONS AND ACCESSORIES A number of options and accessories are available for the 8842A which can be easily installed at any time The options include JEEE 488 Interface Option 05 featuring Full programmability Simple and predictable command set Fast measurement throughput External Trigger input connector Sample Complete output connector Automated calibration Low cost e True RMS AC Option 09 featuring AC voltage measurement AC current measurement Accessories include a variety of rack mounting kits probes test leads and cables Full information about options and accessories can be found in Section 8 1 2 1 4 SPECIFICATIONS Introduction and Specifications SPECIFICATIONS Specifications for the 8842A are given in Table 1 1 External dimensions are shown in Figure 1 1 Table 1 1 Specifications DC VOLTAGE Input Characteri
163. ation CORRESPONDING COMMENTS COMMAND G2 Loads the calibration prompt into the output buffer Not valid Maintenance CALIBRATION Function Buttons F1 through 6 when the 8842A is taking verification readings In the calibration mode these select the Offset and Gain Calibration procedure for the corresponding funtion Range R1 through R6 and R8 In the calibration mode these select the Offset and Gain Calibration Procedure for the corresponding range in the presently selected function For entering variable inputs see VAR IN below STORE CO A D C1 Tells the 8842A that the requested calibration input is valid This command causes the 8842A to take readings and compute and store calibration constants NOTE The command can take up to 22 seconds to execute You must determine when this command is complete before sending more commands See Timing Considerations in text Selects the A D Calibration procedure HF AC C2 Selects the High Frequency AC Calibration procedure ERASE C3 After receiving this command the display shows the erase mode prompt cl The prompt is not loaded into the output buffer To complete the erasure you must then send Sending any other command after the C3 command causes the 8842A to return to its previous state There is no timeout as with the front panel ERASE button CAUTION The command string C3 CO erases the entire calibration memor
164. ay be enhanced at that frequency or range of frequencies by performing calibration according to the following procedure Note that this may degrade the accuracy at frequencies significantly removed from the frequency of optimization To optimize performance at a frequency less than 1 kHz perform the offset and gain calibration procedure above using the frequency at which measurements will be made rather than 1 kHz This technique may be used for both the VAC and mA AC functions At the calibration frequency the 8842A will yield accuracy closely approaching the specified mid band performance To optimize performance at a frequency greater than 1 kHz perform calibration as follows 1 Perform the Offset and Gain Calibration procedure using inputs at 1 kHz 2 Perform the High Frequency AC Calibration procedure using inputs at the desired frequency of optimization rather than at 100 kHz Skip step 5 in that procedure 3 Again perform the Offset and Gain Calibration procedure this time using inputs at the desired frequency of optimization rather than at 1 kHz OPTIMIZING USE OF THE 5450A If the Fluke 5450A Resistance Calibrator is used to calibrate the 2 wire ohms function the following procedure is recommended to optimize the calibration of the lowest two ranges The 5450A has a 25 mQ floor which would otherwise result in 25 digits of error in the 200Q range of the 8842A In this procedure the 8842A is referred to as the unit unde
165. be 12 500 ms for 60 Hz line 4 Interrupt from A D U202 39 Normally low duration 48 us occurs approximately 5450 us after falling edge of trigger signal on TP201 U202 40 Guard crossing test pattern U202 4 Waveform C see Figure 6 10 Interrupts from watchdog timer U202 6 Pulsed low for 0 2 sec every 1 5 sec exponential rise between pulses 7 Output test patterns see Waveforms and B in Figure 6 10 1 kHz square wave on indicated pins 50 duty cycle low OV high 3 8V nominal The waveforms are interrupted every 1 5 sec for 0 2 sec due to interrupts from the watchdog timer To observe these patterns remove U220 attach a logic clip to address latch U219 and sync on U219 3 for Reference Waveform A on channel 1 of a dual trace scope Compare channel 1 with waveforms at U202 10 14 16 18 20 22 24 26 28 These should all be the same as reference Waveform A including phase Then compare channel 1 with waveforms at 17202 13 15 17 19 21 23 25 27 29 33 These should be the same as Waveform B which is simply the opposite phase of Waveform A Adaress Latch U219 Verify that U219 2 6 7 12 13 16 17 are the same as Waveform A see Figure 6 10 on U219 3 Verify that U219 4 5 8 9 14 15 18 19 are the same as Waveform B The waveforms should be interrupted every 1 5 sec for 0 2 sec due to interrupts from the watchdog timer PINS AT WHICH WAVEFORM APPEARS nhu U202 10 14 16 18 20 22
166. bwrt dmm N3001POY1 10 write functions to instrument ibrd dmm rd 16 get data strncpy rd string rd 11 r atof rd string convert from string to floating point labell printf sS 2 wire LOWEST READING r n rd do ibwrt dmm 1 trigger the device do ibrsp dmm spr serial poll the device while spr amp 0x40 0x40 until data available ibrd dmm rd 16 get next data s atof rd convert to floating point printf r while s gt n throw away data if not lowest r s goto label1 print new low 13 14 10 wmf Figure 3 14 Example Programs Using the PC cont 3 47 8842A Instruction Manual The following application program is written in C for the IBM PC AT The National Instruments Model AT GPIB board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842A assigned to the GPIBO board This program illustrates a method of recording any errors produced by the 8842A selftest function It should be noted that 1 If more than one digital error occurs only the last one will be reported 2 The response to a Get Instrument Config G0 command during selftest is 9xxx 3 The response to a Get Error Status G7 command with no errors present is 1000 Microsoft C Version 6 0 on PC AT Link this program with appro
167. c voltage ranges the T H Amplifier has a gain of 1 In the 20V range the input voltage is buffered by unity gain amplifier U306 and divided by 10 by Z301 To allow U306 to handle 20V inputs its power supplies are bootstrapped by 0305 and Q306 so that the output voltage of U306 determines the midpoint of its supply voltages The positive supply is approximately 6 2V above the input and the negative supply is approximately 6 2V below In the 200V and 1000V ranges K301 is de energized and the input voltage is divided by 100 by Z302 In the 200V range the reduced input voltage is then applied directly to the T H Amplifier as in the 2V range In the 1000V range the reduced input voltage is buffered by U306 and divided by 10 as in the 20V range VDC Protection Input protection for the VDC function is provided by a 1K fusible resistor R309 four metal oxide varistors MOVs RV301 RV402 RV403 and RV404 and additional protection resistors and clamp circuits WARNING TO AVOID INJURY OR EQUIPMENT DAMAGE USE EXACT REPLACEMENT PARTS FOR ALL PROTECTION COMPONENTS In all dc voltage ranges voltage transients greater than 1560V are clamped by the MOVs Extreme overvoltage conditions cause R309 to fail open circuit R309 is followed either by a 99 10W resistor network Z304 in the 20 mV 200 mV 2V and 20V ranges or by 10 MQ Z302 to ground in the 200V and 1000V ranges Z304 provides current limiting in extreme overvoltag
168. c with possibly 1V ac p p at 10 Hz 4 5V dc with possibly 1V ac p p at 10 Hz 4 5V dc with possibly 1V ac p p at 10 Hz 50 mV dc typical 49 mV dc typical 53 mV dc typical 59 mV dc typical lt 5 mV dc 59 mV dc lt 5 mV dc Note To measure these correctly each test must be stopped using the SRQ button Also use TP306 or L shaped shield around U202 as Reference low e TEST 1 200 VAC Zero Configures the 8842A in the 200V ac range except that K801 is opened and measures the open circuit floor reading In this range the first and second stage buffers effectively divide any noise at the input terminals by 100 This test should be fairly immune from noise because the input terminals are always open circuited except for capacitive feedthrough across K801 e TEST 2 700 VAC Zero Configures the 8842A in the 700V ac range and measures the open circuit floor reading In this range the open circuit reading is divided by 1000 Again K801 is opened to reduce sensitivity to external noise e TEST 3 mA AC Zero Configures the 8842A exactly as in the mA AC function and takes a reading of the voltage across the 0 1Q current shunt at the slow reading rate e TEST 4 mA DC Zero Maintenance TROUBLESHOOTING Configures the 8842A in the mA DC function and the slow reading rate and measures the reading across the 0 1Q current shunt This test should be fairly immune to outside noise because the total driving impe
169. caling 5 14 Theory of Operation A D CONVERTER 5 19 The voltage sensed at the INPUT terminals is scaled as shown by the simplified switch table in Figure 5 8 Refer to the track period of the track hold cycle during which the scaled input voltage is sampled In the lower five ranges the full scale input voltage to the A D Converter is 2V However in the 2000 kQ and 20 MQ ranges the full scale input voltage to the A D Converter is 1 V the in guard uC completes the scaling by multiplying the A D result by 2 4 Wire Ohms In the 4 wire ohms function the Ohms Current Source is connected to the INPUT HI terminal by ohms relay K401 as in 2 wire ohms Figure 5 8 The Ohms Current Source applies a known current to the resistance under test through the INPUT HI and INPUT LO leads The resulting voltage drop across the resistor is measured by the SENSE HI and SENSE LO leads The voltage at the SENSE HI terminal is connected to the DC Scaling circuit by Q303 Figure 5 8 The voltage is then scaled exactly as in the 2 wire ohms function Refer to the track period in the switch table in Figure 5 8 Q310 is turned off to isolate the SENSE HI terminal from the INPUT HI terminal Additional input switching occurs during the hold period of the track hold cycle Refer to the hold period in the switch table in Figure 5 8 In ranges r1 through r4 and r8 the SENSE LO terminal is switched into the de input path by U301D and the INPUT LO
170. ciators The blanking also occurs in the continuous trigger mode but usually isn t noticed because new measurements are triggered automatically The TRIG button does not trigger readings in the continuous trigger mode However it does blank the last reading to acknowledge a button was pressed Reading Rates and Noise Rejection The RATE button allows you to optimize either measurement speed or noise rejection The 8842A uses both analog and digital filtering to allow measurements in the presence of unwanted environmental noise especially line related noise However since filtering introduces a delay in response to a change in the input signal there is an inherent trade off between noise rejection and measurement speed The instrument has three reading rates slow S and medium M with a 5 1 2 digit display and fast F with a 4 1 2 digit display To provide optimum combinations of measurement speed and noise rejection the RATE button allows control of both the internal trigger rate and the degree of filtering The same degree of filtering is used in both the continuous and external trigger modes In the 20 mV 20Q and 200 mA dc ranges use of slow S filter provides maximum noise rejection 8842A Instruction Manual 2 21 2 22 2 23 In the continuous trigger mode the actual number of readings displayed per second for each reading rate is determined by the line power frequency At power up the 8842A senses the line p
171. ctioning properly proceed to the corresponding heading for detailed troubleshooting instructions and guidelines 6 38 Maintenance TROUBLESHOOTING A failure in the instrument may cause the 8842A to display random patterns or nothing at all Usually analog circuit failures do not cause the display to go blank or display random patterns The best place to start troubleshooting a dead instrument or an instrument with a non functional display is to check the power supply with a voltmeter for proper levels and to use an oscilloscope to check the supplies for oscillations If all of the supplies are working correctly check the clock for the In Guard uC at U202 2 The signal should be an 8 MHz sine wave approximately 3 5V peak to peak Then check the 1 MHz output of the A D IC U101 at U212 3 not present check at the A D IC at U101 14 signal should be a 1 MHz square wave approximately 5V peak to peak The 8 MHz sine wave is generated by the clock circuit of the In Guard uC and the 1 MHz signal is the 8 MHz signal divided by a counter in the A D IC If the clock signals are correct proceed to the heading Digital Controller Troubleshooting below for detailed troubleshooting instructions If a problem occurs in the keyboard display area the instrument may appear to be totally inoperative even when the measurement circuitry is still functional The heading Digital Controller Troubleshooting provides detailed instructions on locating
172. cuitry Signal Conditioning TEEE 488 Interface Power Supply TRUE RMS AC OPTION 09 VAC Scaling ess MA AC Frequency Response Trimming True RMS AC to DC Conversion 5 1 5 2 Theory of Operation INTRODUCTION INTRODUCTION This section presents an overall functional description of the 8842A followed by a detailed circuit description The descriptions are supported by simplified schematics in text and by the complete schematics in Section 10 OVERALL FUNCTIONAL DESCRIPTION A functional block diagram of the 8842A is shown in Figure 5 1 The basic signal path flows from left to right across the center of the page The input is sensed at the input terminals scaled directed through the Track Hold circuit converted into digital representation by the Analog to Digital A D Converter processed by the Digital Controller and sent to the display The DC Scaling circuit which constitutes the front end of the instrument has two major functions First it senses the input and produces an equivalent dc voltage for all functions except VAC and mA AC AC inputs are converted to a dc voltage by the True RMS AC Option Resistances are sensed as a dc voltage using a known test current from the Ohms Current Source A dc current input is converted to a dc voltage by a precision current shunt Second the DC Scaling circui
173. d 80TK 8 9 RF Probes 85 83RF esses 8 10 Current Shunt 807 0 8 11 Current Probes Y8100 8101 801 400 and 801 600 8 12 High Voltage Probes 80K 6 and 80 40 Option 05 488 Interface J J 805 1 605 2 CAPABILITIES EAR EIS 805 3 EXTERNAL 805 4 INSTALLATION rider erre Pee pectore 805 5 PROGRAMMING 5 805 6 MAINTENANCE icii one e neiii 805 7 LIST OF Option 09 True RMS 809 1 INTRODUCTION l u Ere eee bed ee 809 2 INSTALLATION serrare rne en aeri eot ts 809 3 OPERATING 5 809 4 MAINTENANCE 809 5 LIST REPLACEABLE PARTS vi Table QN S C9 C2 NR L Q 1 1
174. dance is typically less than 1 kQ The reading is not a perfect zero because of the offsets generated by charge injection of U302 and the T H Amplifier X10 configuration e TEST 5 200 VDC Zero Configures the 8842A in the 200V dc range and slow reading rate Input noise is divided by 100 Assuming no input of any kind the T H Amplifier is essentially shorted to ground by 100 kQ and filtered by the 3 pole analog filter Any non zero reading under quiet input conditions is due to the offset of the T H Amplifier X1 configuration e TEST 6 1000 VDC Zero Configures the 8842A exactly as in the 1000V dc range and slow reading rate with input noise being divided by 1000 The reading is very close to zero because of the inherent 2 driving impedance to the T H Amplifier configuration e TEST 7 1000 VDC 20 MQ Couples the 1000V dc range and 20 MQ current source together The result is nominally 500 nA through the 10 MQ input divider Since the 1000V dc range senses this voltage at the divide by 1000 point of the scaling circuit the reading should be 5 mV or 500 counts at the A D Converter This test could indicate an error if input capacitance is greater than 1000 pF e TEST 8 20 VDC 20 MQ Puts the DC Scaling circuit into the 20V dc range and the Ohms Current Source into the 20 MQ range The infinite input impedance of the 20V dc range causes the 20 MQ current source to be clamped at its maximum open circuit voltage typic
175. ded IEEE 488 cables are available in three lengths see Table 8 1 The cables attach the 8842A to any other IEEE 488 device Each cable has double 24 pin connectors at both ends to allow stacking Metric threaded mounting screws are provided with each connector Replacement Test Leads TL70A The TL70A replacement test leads feature safety designed input connectors Deluxe Test Lead Kits Y8134 Each deluxe test lead kit includes two test tip probes two alligator clips two large spade lug tips and one spring loaded hook tip and probe Slim Flex Test Leads Y8140 The Y8140 has adjustable flexible and insulated leads and can fit into small places The sharp steel needle points will pierce varnish and thin insulation Temperature Probes 80T 150U and 80TK The 80T 150U is a universal temperature probe designed to provide virtually any DMM with temperature measurement capability The probe provides direct temperature conversion of 1 mV dc per degree A three position switch acts as a power switch and is used for selecting Celsius or Fahrenheit scaling for the output The 80TK thermocouple module converts the microvolt output from a K type thermocouple to a 1 mV per degree signal The on off switch allows selection of degrees or F output scaling RF Probes 85RF and 83RF The RF probes 85RF and 83RF use the DMM dc volts function to measure radio frequency RF ac signals The 83RF has a frequency range of 100 kHz to 100
176. del and serial number e Part number and revision level of the containing the part e Reference designator e Fluke stock number e Description as given under the DESCRIPTION heading e Quantity MANUAL STATUS INFORMATION The Manual Status Information table that precedes the parts list defines the assembly revision levels that are documented in the manual Revision levels are printed on the component side of each pca 7 3 8842A Instruction Manual 7 4 NEWER INSTRUMENTS Changes and improvements made to the instrument are identified by incrementing the revision letter marked on the affected pca These changes are documented on a supplemental change errata sheet which when applicable is included with the manual 7 5 SERVICE CENTERS A list of service centers is located at the end of this section NOTE This instrument may contain a Nickel Cadmium battery Do not mix with the solid waste stream Spent batteries should be disposed of by a qualified recycler or hazardous materials handler Contact your authorized Fluke service center for recycling information WARNING THIS INSTRUMENT CONTAINS A FUSIBLE RESISTOR PN 733915 TO ENSURE SAFETY USE EXACT REPLACEMENT ONLY 7 4 List of Replaceable Parts SERVICE CENTERS Manual Status Information REF OF OPTION NO ASSEMBLY FLUKE PART NO REVISION LEVEL Al Main PCA 759365 BE A2 Display PCA 728873 05 IEEE 488 Interface PCA 879267 D 09 True RMS AC PCA 759266
177. e for the 8842A circuit loading error is less than 0 01 as long as the source impedance is less than 1 MQ in the 20 mV 200 mV 2V and 20V ranges and less than 1 in the 200V and 1000V ranges The exceptionally high input impedance on the 20V dc range allows high accuracy readings in CMOS and high impedance analog circuitry NOTE Input protection circuitry can reduce the input impedance to as low as 100 kQ when the input is overrange This may also occur momentarily when the instrument autoranges to a higher range 4 4 Input Bias Current Error Input bias current error occurs because a voltmeter s input bias current always changes the voltage of the circuit under test However the error is significant only when measuring voltages in circuits with very high source impedance The error can be measured as shown in Figure 4 2 BIAS Rsource TO MEASURE INPUT BIAS CURRENT ERROR Select the VDC function and the desired range Eliminate any offset voltages by shorting the HI INPUT and LO INPUT terminals and then pressing OFFSET Select a resistor which matches the source impedance Rsounce of the circuit to be tested and connect it to the HI INPUT and LO INPUT terminals 4 Allow the circuit to settle 5 Record the displayed voltage This is the input bias current error Vernon The input bias current error may be calculated as a percentage as follows VeRROR 0 ERROR IN VOLTAGE MEASUREMENT 100 The inp
178. e IBM PC PC XT or PC AT The National Instruments Model GPIB PCIIA board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program has been run to initialize the interface board with the device name 18842A assigned to the GPIBO board This program illustrates a method of recording any errors produced by the 8842 selftest function It should be noted that 1 If more than one digital error occurs only the last one will be reported 2 The response to a Get Instrument Config GO command during selftest is 3 The response to a Get Error Status G7 command with no errors present is 1000 Microsoft QuickBasic V 4 5 on IBM PC PC XT or PC AT SINCLUDE qbib45 dcl BDNAMES GPIBO Board name is GPIBO CALL IBFIND BDNAME BD Initialize the interface board devname 18842A Device name is 18842 CALL IBFIND devname dvm Initialize the device PRINT MONITORING SELFTEST WRT ZO CALL IBWRT dvm WRTS Start selftest DO WRT G7 CALL IBWRT dvm WRT RD 18 CALL IBRD dvm RD Get error status errcode LEFT RD 4 IF errcode lt gt 1000 THEN Check for errors WRT Clear error register CALL IBWRT dvm WRT PRINT Error RIGHT errcode 3 occurred END IF CALL IBWRT dvm 0 st SPACE 16 CALL IBRD dvm st instrument configuration stat LEFT st 1 LOOP WHILE
179. e Programs Using the IBM PC cont 3 45 8842A Instruction Manual 3 46 The following application program is written in C for the IBM PC AT The National Instruments Model AT GPIB board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842A assigned to the GPIBO board This program selects VDC 1 Autorange RO Slow rate 50 Continuous trigger TO and suffixes enabled Y1 All readings appear simultaneously on the instrument display and the PC screen with suffixes enabled for function readout Full local control is given to the 8842 Note the local control must be given to the board and not the device Press CTRL C to terminate this program Microsoft C Version 6 0 on IBM PC AT Link this program with appropriate mcib obj include lt stdio h gt include decl h char rd 512 int brd0 int dmm int x main brdO ibfind GPIBO dmm ibfind l8842A ibelr dmm ibwrt dmm F 1ROSOTOY1 10 ibloc dmm ibsre brd0 0 x 0 in ibrd dmm rd x x 1 printf d 5 goto in read data buffer interface board number device number initialize board initialize device clear device write functions to instrument local the device de assert the remote enable REN signal so the 8842A sta
180. e conditions in the 20 mV 200 mV 2V and 20V ranges The non inverting input of U306 is clamped to 25V by Q307 and Q308 mA DC Scaling In the mA DC function the unknown current causes a voltage drop across current shunt R319 This voltage drop is then measured as in the VDC function The DC Scaling circuit is configured as shown by the simplified switch table in Figure 5 2 Analog Filter The three pole low pass analog filter U304 has a Bessel response with corner frequency at 7 Hz giving approximately 50 dB of rejection at 50 Hz The filter is used for the slow reading rate and is used in the VDC ranges and lowest three ohms ranges The filter is also used in the 20mV DC 20 and 200 mA DC ranges when in the medium reading rate The filter is switched into the input signal path by Q304 Figure 5 2 In some ranges and functions additional filtering is provided by Q317 and C314 5 7 8842A Instruction Manual 5 9 TRACK HOLD CIRCUIT The Track Hold T H circuit presents a stable voltage to the A D Converter during the input period of the A D conversion cycle The circuit also provides a gain of 100 in the 20 mV 20Q and 200 mA ranges and gain of 10 in the 200 mV 2000 and 2000 mA dc ranges The circuit consists of the T H Amplifier Figure 5 3 T H capacitor C308 quad analog switches U301 U302 and U303 and associated components As shown in Figure 5 3 the T H Amplifier functions as an op amp with Q314
181. e only While doing this observe the state of U305 11 As shown in Table 6 21 this 24 range sequence will produce the following pattern at U305 11 QS IV Ds cms 111010 00000 111100 1111100 000 Table 6 21 Analog Control Logic States IMM Ezan oooo an Taar xa n x nee oan aan eco ein gt Ween rate 9 Pack Bin No 3 rt s gt B o a je v i fo v gt mW t 42 o Q bal 1 1f in slow reading rate 1 if in fast readin DEFINITIONS Func ut Port tion cooo ooo aona 74 6 4 E m o Ono 6 no 5 3 5 7 8 POS FILT ing mals must the neg 811 these on sig be checked bu sync U301 pin3 Sunc on U302 pin3 1 Sync 1 0 1 0 BYTE H2 going 0 2 us pulse ative ted ica d and locking at the state of the tar in on J pin3 9 0 0 1 in at get p he he risin edge of t Sunc on 0402 sync pulse 5 pune on U403 pin3 Maintenance TROUBLESHOOTING 11 these OUTPUTS are static iguration Uncalibrated conf O000n4O04 OO00O0 nQo OD
182. e ranges The D1 command is used for best performance when high IEEE 488 Interface Data rates are required 3 9 8842A Instruction Manual 3 10 3 11 Fn Function Commands The function commands duplicate the front panel function buttons The 8842A defaults to on power up and on any device clear command DCL or SDC If FO is sent to the 8842A it is internally converted to F1 The function setting can be read using the GO command As with the front panel commands selecting F6 automatically selects the 2000 mA range R5 If the instrument is in range R8 commanding F5 automatically selects the 200 mA range R4 If the instrument is in R1 through R6 commanding F5 automatically selects the 2000 mA range R5 If the 8842A is in a resistance function F3 or F4 and in R6 selecting any other function automatically selects R5 If the 8842A is in range R8 and F2 or F3 is commanded range R1 is selected Example Explanation Selects 2 WIRE function it does not affect any other settings B6 Selects mA AC function and 2000 mA range Resets all other settings to default Get Commands The Get commands get information from the 8842A for the controller Each Get command loads the output buffer with an output string in the format shown in Figure 3 6 Status data the output from Get commands GO G1 G3 G4 G5 G6 G7 and G8 is interpreted as shown in Table 3 1 The Get commands should not be confused with
183. e the performance at the calibration value However performance at other values may be degraded Maintenance CALIBRATION 6 17 CALIBRATING INDIVIDUAL RANGES During Offset and Gain and High Frequency AC Calibration it is possible to calibrate individually selected ranges This feature does not apply to the mA DC and mA AC functions and is not permitted during A D Calibration To calibrate an individual range proceed as follows 1 Select the desired calibration procedure by pressing the appropriate function button or press the HF AC button if High Frequency AC Calibration is desired 2 Press the range button for the range to be calibrated The 8842A then prompts for a low reference source for that range See Table 6 12 During High Frequency AC Calibration the 8842A prompts only for a high reference source In this case proceed to step 4 3 Apply the requested reference source and press STORE The display will blank briefly and then prompt for a high reference source See Table 6 12 4 Apply the requested reference source and press STORE The display will blank briefly and the 8842A will then begin taking readings in the selected range so that you may verify the calibration The CAL annunciator remains on 5 To continue select another range You may restart any of the calibration procedures by pressing the appropriate function button the A D button or the HF AC button 6 18 VERIFYING CALIBRATION Table 6 12 Pr
184. each the current source The circuitry associated with Q408 R406 R407 R408 R409 Q406 Q408 and CR403 clamps the open circuit voltage of the Ohms Current Source below 6 5V in the lower four ranges and below 13V dc in the higher two ranges The in guard uC turns 0408 on or off depending on range In the lower four ohms ranges Q408 is on effectively shorting R409 R406 and R409 then form a voltage divider which clamps the output of the ohms current source below 6 5V In the higher two ohms ranges Q408 is off including R409 in the voltage divider and clamping the output below 13V 5 17 OHMS FUNCTIONS 5 18 2 Wire Ohms In the 2 wire ohms function the Ohms Current Source is connected to the INPUT HI terminal by ohms relay K401 Figure 5 8 The Ohms Current Source applies a known current to the resistance under test and the resulting voltage drop across the resistor is measured sensed as in the VDC function 5 13 8842A Instruction Manual SENSE PATH FOR 2 WIRE OHMS 2000 RANGE DURING TRACK PERIOD TO TRACK HOLD OHMS CURRENT SOURCE PERIOD RANGE K401 Q310 Q303 Q311 U301B U302A U301C 93010 NOTE Filter switch Q304 is for the S reading rate ranges r1 r2 and r8 2000 kQ 20 Switch closed or relay energized 2 Switch closed only in 2 WIRE ohms 4 Switch closed only in 4 WIRE ohms pee penes bar had bb P p p ha RA to N N NHN f5 08 wmf Figure 5 8 Ohms S
185. ecure the IEEE 488 connector to the rear panel with the two screws and washers supplied 11 Replace the cover and rear bezel on the chassis and attach the two ear panel mounting screws 12 Attach the grounding screw to the bottom of the case WARNING TO AVOID ELECTRIC SHOCK ENSURE THE GROUNDING SCREW IS FIRMLY ATTACHED TO THE CASE BOTTOM 805 5 PROGRAMMING INSTRUCTIONS Programming instructions are presented in Section 3 That section also explains how to set up the 8842A on the IEEE 488 bus 805 6 MAINTENANCE All service information regarding Option 05 is contained in Section 6 The theory of operation is contained in Section 5 805 7 LIST OF REPLACEABLE PAHTS A list of replaceable parts for the IEEE 488 Interface printed circuit assembly PCA is given in Table 805 1 Refer to Section 7 for ordering information Caution The symbol indicates a device that may be damaged by static discharge 805 4 Option 05 IEEE 488 Interface LIST OF REPLACEABLE PARTS REAR BEZEL CHASSIS RIBBON CABLE f805 1 1 wmf Figure 805 1 Installing Option 05 805 5 8842A Instruction Manual VR ANM 6 IEEE 488 INTERFACE PCA REPLACE GROUNDING SCREW WHEN REASSEMBLING z z a lt z f805 1 2 wmf Figure 805 1 Installing Option 05 cont 805 6 REFERENCE DESIGNATOR 901 902 903 907 908 909 910 911 918 920 923 925 928 914 915 921 922 CR 901 902 CR 9
186. ed without 09 True RMS AC option 12 07 wmf Figure 2 7 Typical Error Messages Operating Instructions OPERATING FEATURES Table 2 1 Error Codes ERROR MEANING ERROR CODE MEANING CODE ANALOG SELF TEST ERRORS OPERATION ERRORS 1 200 VAC Zero AC funtions availible only with 8842A 09 True RMS AC option 2 700 VAC Zero mA AC or mA DC funtion selected while REAR inputs selected 3 mA AC Zero OFFSET selected with reading unavailible for overrange 4 mA DC Zero 40 Computed calibration constant out of range Previous cal may be wrong or there may be a hardware problem 5 200 VDC Zero Calibration input out of acceptable range Check that input is correct Previous cal may be wrong or there may be a hardware problem 6 1000 VDC Zero Calibration memory write error Probably a hardware problem 7 1000 VDC Zero Guard crossing error detected by In Guard uc 8 20 VDC 20MQ 51 Calibration command not valid unless calibration mode is enabled 9 20VDC 2000 52 Command not valid at this time 10 2 VDC 2000 kQ 53 Invalid calibration value Put command Example Sending a negative value during ac calibration 11 2000 Overrange Command not valid in calibration verification 12 2 kQ Overrange Variable inputs not allowed during A D calibration Use prompted value Device dependent commands not valid during self tests 13 20 kQ Overrange 14 200 kQ Overra
187. een the 8842A and the signal source For voltage measurements in most system applications where common mode voltages are typically present connect the test lead shielding to the 8842A INPUT LO terminal as shown in Figure 4 10 This configuration minimizes the error caused by current that would flow in the leads due to common mode voltages between the measurement and stimulus points and instrument ground The 8842A s INPUT LO terminal is internally connected to the instrument s internal guard which provides a shield between the instrument s ground and its sensitive analog circuits The 8842A s analog circuits are isolated from its digital circuits by an electrostatically shielded transformer whose shield is also connected to the guard Measurement Tutorial MAKING ACCURATE HIGH RESISTANCE MEASUREMENTS VOLTAGE SOURCE SHIELD INPUT SENSE OUTPUT NOTE THE 8842A INPUT LO TERMINAL IS INTERNALLY CONNECTED THE INSTRUMENT S GUARD f4 10 wmf Figure 4 10 Shielding for Low Voltage Measurements For low level resistance measurements connect the test lead shielding as shown in Figure 4 11 Use the 4 wire ohms function to minimize the error caused by the resistance of the test leads 8842A INPUT SENSE HI SHIELD f4 11 wmf Figure 4 11 Shielding for Low Resistance Measurements Errors due to thermal voltages should also be considered when making low level voltage or resistance measurements Technique
188. er This means that an error message always overrides numeric data but status data is sent even in the presence of an error However the status data does not clear the error message the error message is sent the next time numeric data is requested 3 49 SERVICE REQUESTS 3 50 Service requests let bus instruments get the attention of the system controller The requests are sent over the SRQ line one of the IEEE 488 bus lines If more than one instrument on the bus is capable of sending service requests the controller can learn which one made the request by taking a serial poll Each device including the 8842A responds to the poll by sending the contents of its serial poll register The serial poll register indicates whether or not the device requested service and if so the reason for the request The 8842A may be programmed to make a service request on user specified conditions The conditions are specified by entering a value for the service request mask SRQ mask with the P1 command The SRQ mask works by monitoring the serial poll register which in turn monitors various conditions in the 8842A The Serial Poll Register The serial poll register is a binary encoded register which contains eight bits as illustrated in Figure 3 9 The controller can read the 8842A serial poll register at any time by taking a serial poll Because serial poll register data is loaded directly onto the bus instead of being loaded into the output buf
189. er data being sent by the HC as configuration commands or as display data Display data is stored in the Keyboard Display Controller which automatically scans the display The Keyboard Display Controller selects one of eight grids using decoder U213 and buffer U215 The numeric display data is decoded from BCD to 7 segment by decoder U216 and buffered by U217 Additional annunciator data is buffered by U218 The Keyboard Display Controller is reset by the HC whenever the HC is reset It receives a 1 MHz clock signal from the custom A D IC U101 which uses the 8 MHz crystal for its clock input The Keyboard Display Controller scans the keyboard sensing pressed buttons on lines RLO RL7 It sends an interrupt to the via line KEYINT whenever a front panel button is pressed The uC then reads the keycode from the Keyboard Display Controller The status of the FRONT REAR switch is sensed separately by line F R SENSE 5 83 Troubleshooting Modes In addition to running the diagnostic self tests the In Guard uC has a troubleshooting mode which aids in finding digital hardware problems After the uC is reset it senses the relay control lines U202 35 through U202 38 as inputs If line U202 38 TP205 is shorted to ground the uC goes into the troubleshooting mode 17201 provides internal pull up The troubleshooting mode is described in detail in the Maintenance section 5 34 Guard Crossing Communication The In Guard HC contains a U
190. ernal trigger mode TRIG AUTO FH orrser LocaL VAR IN HF AC 200 2000 20 POWER DIGIT 3 DIGIT 4 DIGIT 5 DIGIT 4 OFF u OFFSET stores the displayed reading as an offset which the 8842A subtracts from all subsequent readings in the function presently selected Readings in the other functions remain unaffected Pressing OFFSET again cancels the offset or stores a new offset if in a different function Reading Rate Slow Medium Overrange and Fast Blinks off when a reading is triggered External Trigger EXT TRIG toggles between internal and external trigger modes RATE cycles between slow medium and fast reading rates Automatically selects the optimum filter for each reading rate SRQ generates a service request over the IEEE 488 bus if enabled by the SRQ mask IEEE 488 Interface option only When pressed for 3 m gt initiates diagnostic self tests NOTE Leave inputs disconnected during self tests or the 8842A may indicate errors If the 8842A is in remote LOCAL returns it to local control If the 8842A is in local the LOCAL button causes the 8842A to display its bus address for two and one half seconds Ignored if the IEE 488 Interface is not installed Error Condition Calibration Mode Enabled Autorange On Offset
191. es not light up first check the following 1 Is the instrument plugged in to an energized outlet providing alternating current at a frequency of 47 Hz to 440 Hz and a voltage within 10 of that selected by the rear panel line voltage selection switches 2 Is the POWER switch ON pushed in Is the rear panel fuse blown CAUTION For fire protection use exact fuse replacement only If the rear panel fuse is blown replace it with a 250V fuse of the proper rating for the line voltage selected Use 1 4A slow blow for 100V and 120V power line voltage and 1 8A slow blow for 200V and 240V power line voltage If the fuse keeps blowing measure the resistances of the power transformer T601 windings They should be within 1046 of the values shown on the schematic If not the transformer is probably shorted Also inspect the area around the transformer POWER switch and power cord connector to make sure there isnt something shorting out the traces If the IEEE 488 Interface board is suspected of causing the problem it can easily be unplugged Check the crowbar circuit CR615 and Q601 and R605 If CR615 or Q601 is shorted or if there is a large amount of leakage or R605 is open fuses may continue to blow If everything looks OK but the fuse keeps blowing troubleshooting may be performed by powering the instrument through a variac applying only enough line voltage to find the problem without blowing the fuse NEVER USE A LARGER FUSE To do so
192. event damage by electrostatic discharge observe the precautions described on the Static Awareness sheet in front of this section If visual inspection of the instrument shows excessive dirt build up in the instrument clean the appropriate section using clean oil free low pressure air less than 20 psi If necessary remove the option PCAs first Cleaning Printed Circuit Assemblies If conditions warrant individual printed circuit assemblies PCAs can be cleaned with water based commercial cleaning systems such as dish washers If such systems are used observe the following precautions 1 Remove all shield covers applies to the True RMS AC PCA and socketed ICs 2 Use Reagent Grade 2 or better water de ionized or distilled water for the final rinse in geographic areas with exceptionally hard water During the final rinse spray or run the water so that the surface is thoroughly covered to remove all ionized material 3 Thoroughly dry all PCAs using one of the following methods a Preferably the PCA should be dried in a low temperature drying chamber or infrared drying rack with a temperature range of 49 C to 72 C 120 F to 160 F b Ifneither a drying chamber nor a drying rack is available air dry the PCA at ambient room temperature for at least two days A satisfactory cleaning method consists of holding the PCAs under hot running water until they are clean Follow this wash with a final rinse See consideration 2 above
193. fer first reading the serial poll register leaves data in the output buffer intact Service requests may also be initiated using the front panel SRQ button if it has been enabled by the SRQ mask The eight bits of the serial poll register are described in Figure 3 9 Note that the SRQ mask uses bits 1 through 6 to set bit 7 the RQS bit When the RQS bit is set true the 8842A sets the SRQ line true which generates a service request A bit is considered true when it is set to 1 3 27 8842A Instruction Manual 3 28 Figure 3 8 Serial Poll Register BIT 8 7 6 5 4 3 2 1 0 RQS ANY DATA CAL STEP FRONT 0 OVER ERROR AVAILIBLE COMPLETE PANEL SRQ RANGE DECIMAL 64 32 16 8 4 2 1 VALUE Bit Name Cleared 1 Overrange An overrange condition occurs Device command received or Bus or Rear Panel Trigger or Output buffer is read 2 Not used Never Always 3 Front panel SRQ Front panel SRQ button Device command received pressed 4 Cal Step Complete Completion of store command Device command received CO 5 Data Availible Output buffer loaded with any Device command received or data Readings Error Bus or Rear Panel Trigger or Messages Get Responses Output buffer is read 6 Any Error An error condition occurs At Device command received or the same time the output buffer Output buffer is read is loaded with an error message This sets bit 5 7 RQS Any SRQ mask enabled bit is All SRQ mask enabled bits are
194. ff 1 OFFSET on 0 output suffix disabled 1 output suffix enabled 0 7 asin Terminator commands Wn G7 10nn nn represents error code See Table 2 1 G8 FLUKE mmmmm 0 Vn n Mmmmm 8842A Vn n 488 Interface software version number The output data from some Get commands starts with a leading 1 or 10 This prevents the controller from suppressing leading zeroes and gives a uniform four character length to all instrument configuration data the data from Get commands GO G4 G5 G6 and G7 The Get commands are described further in the following paragraphs For more information about output data see paragraph 3 39 8842A Instruction Manual 3 12 3 13 3 14 GO Get Instrument Configuration The GO command copies the 8842A function range reading rate and trigger mode into the output buffer in the format shown in Figure 3 6 The four digits returned represent the arguments for the equivalent F R S and T commands as shown in Table 3 1 An example output string follows Example Explanation 3410 CR LF 3 F3 2 WIRE kQ function 4 R4 200 kQ range 1 1 Medium reading rate 0 TO Continuous trigger The second digit which can vary from 1 to 6 indicates what measurement range the 8842 is in regardless of whether the 8842A is in autorange or manual range The output string from a GO command is acceptable as an argument for command This allows you to con
195. figure the 8842A from the front panel and then record the configuration over the bus for future use with a PO command However 9mmm meaning self test can not be used with the PO command G1 Get SRQ Mask command copies the present SRQ mask into the output buffer in the format shown in Figure 3 6 The SRQ mask values are explained in Table 3 1 An example output string follows For more about the SRQ mask see paragraph 3 47 Example Explanation 33 CR LF Enable SRQ on any error or overrange G2 Get Calibration Prompt The G2 command is used when calibrating the 8842A under remote control The command loads the output buffer with a calibration prompt that represents the input expected at the analog inputs The calibration prompt is formatted as a signed decimal with exponent as shown in Figure 3 6 The suffix may be enabled with the Y1 command Example output strings follow Examples Explanation 1 00000E 0 CR LF Calibration prompt 190 000E 3 CR LF Calibration prompt 1 90000E 0 VDC CR LF Calibration prompt Suffix enabled If an error has occurred the G2 command loads the output buffer with an error message instead of the prompt See paragraph 3 39 The G2 command is valid only when the calibration mode is enabled by pressing the front panel CAL ENABLE switch If the 8842A is not in the calibration mode the G2 command generates an error message 3 15 3 16 Remote Programming DEVICE DEPENDENT COMMAND S
196. for reading the measurement data from line 100 The new input command string F4 disallows the reading of data from the output buffer Correct example 100 PRINT 03 T1 2 200 INPUT 3 A 300 PRINT 3 F4 In this example the reading taken at line 100 is read at line 200 Then the F4 command is sent Note that in the external trigger mode the reading from line 100 flashes on the 8842A display too briefly to see This is because the function change at line 300 blanks the display until the next trigger The previous example could also be correctly programmed as follows 100 PRINT 3 T1 200 INPUT 803 A e RULE 4 If an input command string contains a trigger enter the commands in the following order a Commands to configure the instrument if any b The trigger command c Commands to re configure the instrument if any Terminator s The principle behind this rule is that the 8842A executes all commands in the exact order they are received from left to right as written Example Explanation F4 Improper construction F3 is effectively discarded F4 Correct construction The 8842A is configured in F3 and the trigger is executed Then the 8842A is left in F4 3 40 OUTPUT DATA 3 41 The following paragraphs describe the data that can be loaded into the 8842A output buffer and sent to the IEEE 488 bus The paragraphs describe how and when data is loaded into the output buffer the types of
197. gt digits at the fastest reading rate INPUT IMPENDANCE 1 MQ Shunted By lt 100 pF 1 4 Introduction and Specifications MEDIUM AND FAST READING RATES NONSINUSOIDAL INPUTS SPECIFICATIONS Accuracy NORMAL 5 READING of Reading Number of Counts For sinewave inputs 210 000 counts FREQUENCY 24 HOURS 23 1 C 90 DAY 23 5 1 YEAR 29450 2 YEARS 5 C 20 45 1 2 100 1 2 100 1 2 100 1 2 100 45 200 0 3 100 0 35 100 0 4 100 0 5 100 200 20 200 mV range 0 06 100 0 08 100 0 10 100 0 20 100 2V 200V range 0 05 80 0 07 80 0 08 80 0 15 80 700V range 0 06 100 0 08 100 0 10 100 0 20 100 20k 50k 0 15 120 0 19 150 0 21 200 0 25 250 50k 100k 0 4 300 0 5 300 0 5 400 0 5 500 1 For sinewave inpuis between 1 000 and 10 000 counts add to number of counts 100 counts for frequencies 20 Hz to 20 kHz 200 counts for 20 kHz and 500 counts for 50 kHz to 100 kHz 2 Relative to calibration standards E In medium rate add 50 counts to number of counts In the fast rate the specifications apply for sinewave inputs 21000 4 digit mode counts and 100 Hz epu te dd For nonsinusoidal inputs 210 000 counts with frequency components 2100 kHz add the following 96 of reading to the accuracy specifications Operating Characteristics MAXIMUM INPUT FUNDAMENTAL CREST FACTOR
198. hat hold the Main PCA to the chassis by pulling the latches upward Figure 6 6L Lift the front end of the Main PCA upward about 3 inches Free the white lead from the 2A INPUT tower as follows Figure 6 6M a Guide the wire spring and fuse contact toward the front panel b Thread the spring and fuse contact through the hole in the front end of the tower Slide the Main PCA forwards until it is free of the chassis 6 31 8842A Instruction Manual 6 32 Front Panel Disassembly 1 Holding the chassis vertically with the front panel downward remove the mounting screws from the four corners of the Display PCA Figure 6 7A 2 Holding the chassis vertically now standing the instrument on the rear panel pull the front panel off the chassis and set it aside Figure 6 78 3 Remove the the display assembly Display PCA spacer matrix and keypad from the chassis as follows see Figure 6 7C Release the two plastic tabs on the front of the chassis b Let the bottom edge of the display assembly swing toward the rear of the instrument c Pull the Display PCA toward the bottom of the chassis 4 Separate the spacer matrix from the Display PCA by releasing the two pairs of plastic snap tabs on the back of the Display PCA Figure 6 7D 5 Remove the keypad from the spacer matrix CAUTION The vacuum fluorescent display should not be removed from the Display PCA these are supplied as one part 6 Remove the display
199. heck that each range of the Ohms Current Source has enough compliance voltage to overload the dc front end e TEST 15 1000 VDC X10 T H 20 MQ Puts the Ohms Current Source in the 500 nA range The resulting current through Z302 the 10 MQ input divider causes a nominal divider output voltage of 50 mV The T H Amplifier is in X10 thus the A D Converter sees 50 mV or 5000 counts This test can be susceptible to input capacitances above 1000 pF e TEST 16 200 VDC 200 kQ TEST 17 200 VDC 20 KQ TEST 18 200 VDC 2 KQ These three tests put the DC Scaling circuit in the 200V dc range and the Ohms Current Source in the respective current range The 10M ohm input divider Z302 senses the maximum open circuit voltage of each range of the current source and the T H Amplifier X1 presents the compliance voltage divided by 100 to the A D Converter Nominal readings should be 49 mV for Test 16 53 mV for Test 17 and 59 mV for Test 18 All three tests have a pass limit of 65 mV insuring that no more than 6 5 volts appears at the input terminals TEST 19 200 VDC Filter On Test 18 above ties the 1 mA range of the Ohms Current Source into the 200V dc range with the three pole analog filter on such that the A D reads 59 mV nominal Test 19 decouples the DC Scaling circuit from the Ohms Current Source the In Guard uC waits 28 ms and determines if the voltage at Z302 3 the divide by 100 point of the 10 MQ input divider has not d
200. hen the 8842 is triggered with an IEEE 488 command GET or the automatic settling time delay begins after the trigger command has been processed and recognized 2 A Dconversion time is dependent on the reading rate and power line frequency RATE A D CONVERSION TIME ms 50 Hz 60 Hz 400 Hz s 472 3800 395 3195 414 3300 M 52 960 45 795 47 840 F 7 7 7 In 20 mV DC 20Q and 200 mA DC ranges Sample complete is a 2 5 us pulse which indicates that the analog input may be changed for the next reading 4 When talking to a fast controller Introduction and Specifications SPECIFICATIONS GENERAL COMMON MODE VOLTAGE 1000V dc or peak ac or 700V rms ac from any input to earth TEMPREATURE 0 to 50 C operating 40 to 70 C storage HUMIDITY RANGE 80 RH from 0 to 35 C 70 to 50 C WARMUP TIME 1 hour to rated specifications POWER 35 uote nu pe 100 120 220 or 240V ac 10 250V ac maximum switch selectable at rear panel 50 60 or 400 Hz automatically sensed at power up 20 VA maximum VIBRATION eee etm ee Meets requirements of MIL T 28800C for Type Ill Class 3 Style E equipment ANSI C39 5 AND IEC 348 Class I SIZE Avenida sett i a ee hes 8 9 cm high 21 6 cm wide 37 1 cm deep 3 4
201. holder out of the front panel The internal 3A fuse should be replaced only by qualified service personnel Offset Measurements WARNING WHEN THE OFFSET FEATURE IS IN USE DISPLAYED READINGS ARE RELATIVE AND MAY NOT INDICATE THE PRESENCE OF DANGEROUS POTENTIALS AT THE INPUT CONNECTORS OR TEST LEADS USE CAUTION TO AVOID ELECTRIC SHOCK OR INSTRUMENT DAMAGE The OFFSET feature allows you to store a reading as a relative reference value When the OFFSET button is pressed the 8842A stores the present reading and displays subsequent measurements as the difference between the measured value and the stored reading The OFFSET annunciator is lit whenever an offset is in use The OFFSET feature may be used in all functions Since the display represents a numeric difference it always has a sign even in the resistance and ac functions The offset can be canceled by pressing the OFFSET button again in which case the OFFSET annunciator disappears from the display The offset can also be canceled by storing an offset in another function If a reading is overrange or unavailable when the OFFSET button is pressed the 8842A indicates ERROR 32 and does not store the offset If you change functions while an offset is stored the OFFSET annunciator disappears and the offset temporarily disappears However when you return to the original function the offset is restored and the OFFSET annunciator reappears unless a new offset was established in another f
202. ialize the interface board with the device 50 REM name 18842 assigned to GPIBO board 60 REM 70 REM The first 6 lines of code are required to properly link the NI drivers to BASICA 80 REM 90 REM This program illustrates a method of recording any errors produced by the 8842A 100 REM selftest function It should be noted that 110 REM 1 If more than one digital error occurs only the last one will be reported 120 REM 2 The response to a Get Instrument Config GO command during selftest is 130 REM 3 The response to a Get Error Status G7 command with no errors present is 1000 3 40 140 REM 150 CLEAR 59736 160 IBINIT1 59736 170 IBINIT2 IBINIT1 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 IBFIND IBTRG IBCLR IBPCT IBSIC IBLOC IBPPC IBBNA IBONL IBRSC IBSRE IBRSV IBPAD IBSAD IBIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF 200 CALL IBINIT2 BGTS IBCAC IBWAIT IBPOKE IBWRT IBWRTA IBCMD IBCMDA IBRD IBRDA IBSTOP IBRPP IBRSP IBDIAG IBXTRC IBRDI IBWRTI IBRDIA IBWRTIA IBSTA IBERR IBCNT 210 REM 220 REM IBM BASICA on IBM PC PC XT or PC AT 230 REM 240 DEVNAME 18842A 250 CALL IBFIND DEVNAME DVM 260 CALL IBCLR DVM 270 FOR W 1 TO 500 NEXT W 280 PRINT MONITORING SELFTEST 290 WRT 70 CALL IBWRT DVM WRTS 300 WRT G7 CALL IBWRT DVM WRTS 310 E SPACES 6 320 CALL IBRD DVM E 330 IF LEFT E 4 1000 THEN GOTO 360 340 WRT CALL IBWRT DVM WRT
203. ibrated correctly 2 If you just calibrated an individually selected range pressing another range button begins the Offset and Gain Calibration procedure for the new range 3 You use RATE button to verify the calibration at other reading rates CAUTION It is still possible to erase the calibration memory while the 8842 is taking verification readings ERASING CALIBRATION MEMORY The 8842A allows you to erase some or all of the correction constants stored in calibration memory U220 It is recommended that you erase the entire calibration memory before beginning calibration if the calibration memory is replaced or accidentally altered The capability of erasing particular parts of the memory is mainly intended as a troubleshooting aid to the technician CAUTION Once the calibration memory is erased the 8842A must be recalibrated To erase all or part of the calibration memory proceed as follows 1 Press the front panel ERASE button The display should show the erase prompt cl for clear If you do not press another button within 1 1 2 seconds the 8842A returns to its previous state 2 To complete an erasure press one of the following buttons within 1 1 2 seconds of pressing the ERASE button a STORE Erases the entire memory b A D Erases the A D Calibration constants c Any function button Erases the Offset and Gain Calibration constants for all ranges of that function d HF AC Era
204. igh point for the 2 range entering the value computed in step 6 as a variable input 10 Calibrate the remaining ranges steps D G of Table 6 10 using the 5450A outputs 11 Recalibrate the low point for each 2 wire ohms range using a shorting link Pomona MDP S 0 or equivalent across the UUT s HI and LO INPUT terminals 12 Exit the calibration mode by pressing the CAL ENABLE switch 13 Using the same configuration shown in Figure 6 4 verify that the UUT measures the same value within 1 digit in 2 wire ohms using the offset feature to correct for 5450A floor error as in 4 wire ohms If the readings differ by more than 1 digit reenable the calibration mode and repeat steps 2 through 8 NOTE Only 4 wire ohm calibration is allowed in the 20 2 range 14 Cover the CAL ENABLE switch with a calibration certification sticker O INPUT HI SENSE OUTPUT SENSE HI INPUT LO SENSE LO OUTPUT LO SENSE LO f6 04 wmf Figure 6 4 Optimizing Use of the 5450A 6 23 Remote Calibration If the IEEE 488 Interface is installed the 8842A can be calibrated under remote control Remote calibration is very similar to local front panel controlled calibration Table 6 14 shows the remote commands which correspond to the front panel features To facilitate remote calibration there are some differences from local calibration 6 20 FEATURE Display Table 6 14 Commands Used During remote Calibr
205. ile the 8842A performs the necessary calculations Do not change the reference source while the display is blank The 8842A then displays the next prompt For reference all prompts are shown in Table 6 11 NOTE To use reference amplitudes that differ from the prompted values see Storing Variable Inputs later in this section After the last range is calibrated the 8842A begins taking readings in the highest range so that you may verify its calibration To verify the calibration for the other ranges push the corresponding range button The CAL annunciator remains on 6 15 8842A Instruction Manual 5 The calibration procedure is now completed Exit the calibration mode by pressing the CAL ENABLE switch and attach a calibration certification sticker over the CAL ENABLE switch 6 15 Advanced Features and Special Considerations Table 6 11 High Frequency AC Calibration Steps STEP DISPLAYED PROMPT A 100 0 mV AC B 1 000 V AC C 10 00 V AC D 100 0 V AC E 200 0 V AG 1 The display also indicates U to show that HF AC cal is selected 2 Inputs should be between 90 kHz and 100 nominal is recommended The 8842A has several advanced calibration features which are not necessary for the basic calibration procedure but which can make calibration easier The following paragraphs describe these features and also discuss special considerations for optimizing the performance of the 8842A in special situations
206. ing calibration and are therefore unavailable e Offset Autoranging 9 External Trigger 9 Front Panel Trigger 9 Front panel SRQ Under local control e Diagnostic self tests 6 12 A D CALIBRATION The A D Calibration procedure calibrates the analog to digital converter for offset gain and linearity The 8842A automatically selects the A D calibration procedure when the CAL ENABLE switch is first pressed The procedure must be performed in its entirety and may not be performed in part If the A D calibration is discontinued prior to completion the last complete set of A D calibration constants will be retained unchanged To perform A D Calibration proceed as follows 1 Ensure the Initial Procedure has been completed The 8842A then displays the prompt for the first reference source zero volts i e a short 6 12 Maintenance CALIBRATION 2 Each time the 8842A prompts you for a reference source apply the requested source to the HI and LO INPUT terminals and press the STORE button When STORE is pressed the numeric display field blanks while the 8842A performs the necessary calculations Do not change the reference source while the display is blank The 8842A then displays the next prompt For reference all prompts are shown in Table 6 8 NOTE The 8842A automatically checks that the reference input is near the value prompted and displays ERROR 41 if it exceeds a specific tolerance See Advanced Features and Specia
207. ing instructions refer to Section 2 For ac measurement considerations refer to Section 4 809 4 MAINTENANCE All service information regarding Option 09 is contained in Section 6 The theory of operation is contained in Section 5 809 5 LIST OF REPLACEABLE PARTS A list of replaceable parts for the True RMS AC printed circuit assembly PCA is given in Table 809 1 Refer to Section 7 for ordering information CAUTION The symbol indicates a device that may be damaged by static discharge 809 4 Option 09 True RMS AC LIST OF REPLACEABLE PARTS GROUNDING SCREW REAR BEZEL REAR PANEL CHASSIS lt Q lt RED LEAD WARNING REPLACE GROUNDING SCREW WHEN REASSEMBLING 1809 1 wmf Figure 809 1 Installing Option 09 809 5 8842A Instruction Manual 809 6 Reference Designator C801 0802 0803 C804 C805 C806 C813 C807 C808 C820 C809 C810 C824 C811 C812 C814 C816 C819 C821 C822 C823 C825 C826 C827 0828 0829 CR801 CR802 CR803 805 H1 H4 6 H2 H7 9 H3 K801 K802 MP1 MP2 MP3 Q801 Q803 Q805 Q802 Q804 Q806 R804 R805 R806 R811 R807 R809 810 825 827 812 R813 R814 R823 R836 R837 816 819 R817 R822 R828 R829 R830 R831 R832 R833 R834 R835 TP801 811 U801 U806 U802 U803 U804 U808 U807 0809 0810 w3 7801 Table 809 1 Option 09 True RMS AC PCA Description CAP POLYES 0 068UF 10
208. input of raised 140 mV above its inverting input these pulses reinforce the existing state raising the non inverting input and lowering the inverting input If however the output is low to start with the positive pulse which is greater than 140 mV raises the non inverting input of A above its inverting input switching the output to the high state The situation is analogous for a negative going input transition 5 36 POWER SUPPLY The Power Supply provides the following in guard outputs 30V 15V 6 2V 7 5 5V 5 and 8 2V and 4 5V ac The Power Supply also provides 16V ac center tapped out guard output Input line voltage is directed to the primary transformer winding through fuse F601 the front panel POWER switch and the rear panel LINE SET switches Metal oxide varistor RV601 clamps line transients at about 390V The LINE SET switches configure the Power Supply to accept line power of 100 120 220 or 240V ac 10 with a maximum of 250V at 50 60 or 400 Hz AC voltage for the 5V supply is rectified by CR601 and CR602 and regulated by VR601 The 5V output supplies mostly logic circuits The ac input to the 5V supply is sensed by the In Guard uC via R604 CR615 and U221 12 13 to measure the line frequency AC voltage for the 30V and 30V supplies is rectified by bridge network CR603 CR604 CR605 and CR606 and regulated by VR602 and VR605 The 30V and 30V outputs supply front end buffer a
209. irst compare period shown in Figure 5 9 the A D Converter determines the value of the scaled input voltage Vin by comparing Vin to the output of the DAC Each of the DAC bit switches is tried in sequence and kept or rejected left closed or reopened depending on the output polarity of the A D Amplifier which is configured as a comparator This process produces a string of six bits which is stored in the Timing Data Control circuit the digital portion of U101 During the following remainder store period Figure 5 10 the difference between the Vin and the DAC output is multiplied by 16 by the A D Amplifier and stored on capacitor C102 During subsequent compare and remainder store periods the remainder voltage is connected to the input of U103 and is resolved to six bits the remainder voltage multiplied by 16 is stored alternately on capacitor C102 and C103 Each of the five compare periods thus produces a six bit nibble which is stored in the Timing Data Control circuit 5 21 5 22 Theory of Operation A D CONVERTER A D AMP x16 2101 2101 15 238 159 97 STORAGE C102 CAPACITOR BIT SWITCHES SET I DURING PREVIOUS COMPARE PERIOD f5 10 wmf Figure 5 10 First Remainder Store Period This five interval process thus generates five nibbles which are processed by the In Guard uC to produce one A D sample After the fifth nibble is generated U101 interrupts the In Guard uC over line INT The In Guard uC then p
210. is connected to the CURRENT SENSE line mA AC Scaling The mA AC function uses the same current shunt and protection network which is used for de current In the mA AC function Q802 switches the CURRENT SENSE line to the non inverting input of U806B which provides a gain of 10 Frequency Response Trimming The frequency response is trimmed by software calibration using a digitally controlled one pole low pass filter R832 and a combination of C826 C827 C828 and C829 The analog switches in U808 configure the four capacitors to select one of 16 possible RC constants The input of the digitally controlled filter is buffered by voltage follower U801A The individual gain stages are also provided with fixed frequency compensation True RMS AC to DC Conversion U801B buffers the input to rms converter U802 U802 computes the rms value of the scaled input voltage as shown in Figure 5 18 Rather than explicitly squaring and averaging the input U802 uses an implicit method in which feedback is used to perform an equivalent analog computation FILTER f5 18 wmf Figure 5 18 True RMS AC to DC Converter The filter averages the divider output signal This filter consists of U809A C813 R815 and the internal 25 resistor and op amp between pins 8 and 9 of U802 The output is further filtered by a three pole post filter comprised of U809B and associated resistors and capacitors This output is then switched into the Track Hold Amplifier
211. is interpreted in Table 3 1 Examples of status data can be found in the description of the Get commands The user defined message loaded by the G3 command consists of 16 characters plus terminators The SRQ mask loaded by the G1 command consists of two integers plus terminators All other status data is always a four digit integer plus terminators The terminators LF Line Feed and CR Carriage Return each add an extra character when enabled The 8842A begins some status data with a leading ASCII one 1 or a one and a zero 10 This prevents the controller from suppressing any leading zeros present in the 8842A s output string It also gives a uniform four character length to all instrument configuration data Status data from the Get commands reflects the status of the 8842A at the time the command is executed at its place in the input command string Output Priority Since only one output string is allowed per input command string the 8842A gives priority to some types of data over others An input command string may call for more than one output string For example an input string may contain a Get command but also cause an error message However the output buffer is loaded with only one output string That string is selected according to the following priority Remote Programming SERVICE REQUESTS 1 Status data from GO G1 G3 G4 G5 G6 G7 and G8 2 Error messages if an error exists 3 Numeric data from G2 or a trigg
212. ischarged to zero volts due to the long time constant of the filter TEST 20 200 VDC 2 Filter Off e TEST 21 200 VDC Filter Off e TEST 22 x100 T H The T H Amplifier is configured in x100 mode DC stimulus of 5 mV similar to test 15 is amplified to 500 mV which is applied to the A D converter This test can be susceptible to input capacitance above 1000 pF Test 20 ties the 1 mA range of the Ohms Current Source into the 200V dc range with the 3 pole analog filter off such that the A D Converter reads 59 mV nominal Test 21 then decouples the DC Scaling circuit from the ohms current source the In Guard uC waits 28 ms and determines if the voltage at Z302 3 is at zero volts e TEST 25 In Guard uC Internal RAM U202 A GALPAT test is performed on the internal RAM of the In Guard uC If there are any errors ERROR 25 is displayed This test is performed only upon powerup TEST 26 Display RAM 0212 A pattern is written to the Display RAM and read back for comparison If there are any differences ERROR 26 is displayed TEST 27 In Guard uC Program Memory U202 A two byte check sum is calculated over the entire 4K Internal Program Memory and compared with the checksum bytes at the end of that memory A special add and shift algorithm minimizes the possibility of double errors cancelling If something is wrong with the Internal Program Memory ERROR 27 is displayed 6 40 6 41 Maintenance TROUBLESHOOTING
213. ital signals are reaching those devices 8842A Instruction Manual 6 52 Table 6 20 Analog Control Devices DEVICE REF DES Relay Buffer U201 Quad Comparator U305 Quad Analog Switch U301 Quad Analog Switch U302 Quad Analog Switch U303 Quad Analog Switch U402 Quad Analog Switch U403 8 Bit Latch U803 Quad Analog Switch U804 Quad Analog Switch U808 Option 09 only 6 60 Correct operation of 8 bit latch U803 situated on the True RMS AC PCA Option 09 only can be determined directly since all of its inputs and outputs are available Again outputs of quad analog switches U804 and U808 are not available and must be determined by analog means Evaluating Static Signals Table 6 21 may be used to determine whether or not proper signals are reaching any particular analog control device It may also be used to quickly exercise all of the devices before beginning analog troubleshooting if it is still unclear as to which devices are suspect A number of the inputs to these devices are static which makes them particularly easy to check For example suppose quad comparator U305 appears not to be working Connect a scope to U305 11 and step the 8842A through all functions and ranges in the following sequence VDC 20 mV 200 mV 2V 20V 200V 1000V VAC 200 mV 2V 20V 200V 700V 2 WIRE kQ 200Q 2k 20k 200k 2M 20M 4 WIRE 200 2000 2k 20k 200k 2M 20M mA DC 200 mA 2000 mA mA AC one rang
214. ition of the signal and the zero input error but the square root of the sum of their squares This reduces the effect of the error as shown in the example in Figure 4 9 EXAMPLE Given a zero input reading of 300 counts 0 300 mV in the 200 mV range andan input signal of 10 mV the 8842A might read Al 10 0 300 100 0 090 10 004 mV The effect of the zero input error is reduced from 0 300 mV to 0 004 mV f4 09 wmf Figure 4 9 Reduction of Zero Input Error As long as the 8842A reading is 1 000 counts or more readings will still be within specified accuracy 4 23 MAKING ACCURATE MEASUREMENTS ON THE 20 mV AND 202 RANGES NOTE When making low level uV measurements after a large step signal has been applied to the inputs allow sufficient time for thermal emfs and other system related sources of error to settle before taking readings The 20 mV dc and 20Q ranges are the 8842A s most sensitive ranges For that reason they are also the most susceptible to error from electrical noise thermal voltages and for resistance measurements test lead resistance You can minimize these sources of error by using good measurement practices The most common source of error is electrical noise Typical sources of noise include electrostatic noise inductive pickup noise radio frequency noise power line noise and noise generated by ground loop currents Noise pickup can be minimized by properly shielding the test leads betw
215. ively In medium rate add 2 counts to the number of counts for the 200Q through 200 kQ ranges 3 counts for the 2000 and 20 MQ ranges and 20 counts for the 200 range In fast reading rate use 412 digit mode counts for the number of counts for the 2000 range 20 412 digit mode counts for the 20Q range and 2 412 digit mode counts for all other ranges Less than 0 1 x accuracy specification per C from 0 C to 18 C and 28 C to 50 C 2 wire or 4 wire in all ranges accept 20Q range Only 4 wire configuration is allowed in the 20Q range Less than 6 5V on the 20 through the 200 ranges Less than 13V on the 2000 kQ and 20 MQ ranges To 300V rms Introduction and Specifications SPECIFICATIONS Reading Rates READING RATES WITH INTERNAL TRIGGER readings per second RATE POWER LINE FREQUECNCY 50 Hz 60 Hz 400 Hz 2 08 26 2 5 91 2 38 30 M 16 7 1 04 20 1 25 19 0 1 19 100 100 2 In 20 mV 20 ohm and 200 mA DC ranges 1 Sensed automatically at power up AUTORANGING The 8842A autoranges up to the highest ranges in all funtions down to the 200 mV range in the VDC and VAC funtions and down to the 200 Q ranges in the ohms funtions To select the 20 mV dc 20Q or 200 mA dc range press the respective range button or send the respective range command if using the IEEE 488 option AUTOMATIC SETTLING TIME DELAY Time in milliseconds from single trigger
216. l TEL 82 2 552 8582 4 FAX 82 2 553 0388 Kuwait Yusuf A Alghanim amp Sons W L L P O Box 223 Safat Alghanim Industries Airport Road Shuwaikh 13003 Kuwait TEL 965 4842988 FAX 965 4847244 Malaysia CNN SDN BHD 17D 2nd Floor Lebuhraya Batu Lancang Taman Seri Damai 11600 Jelutong Penang TEL 60 4 657 9584 FAX 60 4 657 0835 Mexico Metro Y Calibraciones Ind S A Diagonal No 17 3 Piso Col De Valle C P 03100 Mexico D F TEL 52 5 682 8040 FAX 52 5 687 8695 Netherlands Fluke Nederland B V CSS Afdeling Service Science Park Einhoven 5108 5692 EC Son TEL 31 40 2678 FAX 31 40 2678 New Zealand Phillips Scientific amp Ind Pty L Private Bag 41904 St Lukes 2 Wagener Place Mt Albert Auckland 3 TEL 64 9 894 4160 FAX 64 9 849 7814 2 06 Nigerla Philips Projects Centre Resident Delegate PMB 80065 8 Kofo Abayomi Street Victoria Island Nigeria TEL 234 1 262 0632 FAX 234 1 262 0631 Norway Fluke Norway A S Cust Support Box 6054 Etterstad N 0601 Oslo TEL 47 22 653400 FAX 47 22 653407 Pakistan Philips Philips Elec Ind of Prof Sys Div islamic Cham of Commerce St 2 A Block 9 KDA Scheme 5 Clifton Karachi 75600 TEL 92 21 587 4641 or 4649 FAX 92 21 577 0348 Peru Impor amp Repres Electronicas S A JR Pumacahua 955 Lima 11 TEL 51 14 23 5099 FAX 51 14 31 0707 Philippines Spark Electronics Corp P O Box 6
217. l Considerations later in this section 3 After the last input is stored the 8842A begins taking readings in the 2V range of the VDC function The CAL annunciator remains on Verify the A D calibration using the test points in Table 6 9 If you wish to repeat the A D Calibration procedure press the A D button Table 6 8 A D Calibration Steps STEP DISPLAYED PROMPT A 0 V DC short 03 V DC 1 01 V DC 99 V DC 51 V DC 51V DC 26 V DC 26 V DC l 135 V DC 135 V DC 0725 V DC 0725 V DG T ox e Table 6 9 A D Calibration Verification Test STEP INPUT ALLOWABLE ERROR A OV short 2 counts B 0 03V 2 counts C 0 03V 0 660V 2 counts D 0 660V 3 counts E 0 660V 3 counts F 1 970V 4 counts G 1 970V 4 counts 6 13 8842A Instruction Manual 6 13 Tm ou gt The A D Calibration procedure is an iterative process Each pass through the procedure uses the constants stored previously and improves them Normally one pass is adequate However if the calibration memory has been erased or replaced or the A D Converter has undergone repair the A D Calibration procedure must be performed twice Because the A D Calibration procedure is iterative the instrument s performance can be slightly enhanced by going through the procedure more than twice However this is not necessary to meet the published specifications OFFSET AN
218. le consider the first waveform 1 41421 zero to peak sine wave Both the 8842A and rms calibrated average responding meters display the correct rms reading of 1 00000V the dc component equals 0 However consider the 2V peak to peak square wave Both types of meter correctly measure the dc component OV but only the 8842A correctly measures the ac component 1 00000V The average responding meter measures 1 110V which amounts to an 11 error Measurement Tutorial AC VOLTAGE AND CURRENT MEASUREMENT PEAK VOLTAGES METERED VOLTAGES AC COMPONENT ONLY AC COUPLED DC AND AC TOTAL RMS INPUT 0 COMPONENT TRUE RMS WAVEFORM 5 RMS CAL 8842 ONEN Vac dc 2 828 1 414 1 000 1 000 0 000 1 414 1414 0 421 0 435 0 900 2 000 2 000 0 764 0 771 0 636 2 000 1 000 1 110 1 000 Y 0 000 PK PK PK RECTIFIED SINE FULL WAVE i F RECTIFIED SINE HALF WAVE RECTIFIED SQUARE 1 414 1 414 0 785 0 707 0 707 NS M TRIANGLE 3 464 SAWTOOTH 1 732 0 960 5 1 000 0 000 RMS CAL IS THE DISPLAYED VALUE FOR AVERAGE RESPONDING METERS RECTANGULAR PULSE 2 000 S 222 ofl n 2D D xv 2 K VD D PK 0 THAT ARE CALIBRATED DISPLAY RMS FOR SINE WAVES f4 06 wmf Figure 4 6 Waveform Comparison Chart Since average responding meters have been in use for so long you may have acc
219. leads in place for current measurement select the VDC function Then connect a third lead to the HI INPUT terminal and with it measure voltage at the 2A terminal f4 05 wmf Figure 4 5 Burden Voltage Error Calculation 4 14 REDUCING THERMAL VOLTAGES When making very low level dc measurements thermal voltages can present an additional source of error Thermal voltages are the thermovoltaic potentials generated at the junction between dissimilar metals Thermal voltages typically occur at binding posts and can be greater than 10 uV Thermal voltages can also cause problems in the low dc and ohms ranges particularly in the 20 mV and 20 ranges Some low value resistors are constructed with dissimilar metals Just handling such resistors can cause thermal voltages large enough to introduce measurement errors The effect of thermal voltages can be reduced by using the following techniques 1 Use tight connections 2 Useclean connections especially free of grease and dirt 3 Use similar metals for connections wherever possible e g copper to copper gold to gold etc 4 9 8842A Instruction Manual 4 Use caution when handling the circuit under test 5 Wait for the circuit to reach thermal equilibrium Thermal voltages are generated only where there is a temperature gradient 4 15 AC VOLTAGE AND CURRENT MEASUREMENT 4 16 4 17 When making precise measurements of ac voltage and current there are several
220. lear These characters may be inserted anywhere in a character string without affecting the string Character string without affecting the string They carry no special meaning and are ignored by the 8842A They are not placed in the input buffer The error annunciator is displayed on the 8842A front panel when one of these characters is encountered ERROR 71 Figure 3 7 Interpretation of Messages 3 99 Remote Programming INPUT SYNTAX Illegal commands e g F9 generate an error message but are otherwise ignored and do not affect the instrument s configuration Example Explanation WESBOS This would load the output buffer with an error message and select F1 established by the command Syntax Rules Four syntax rules should be followed when constructing input command strings They are RULE I Read output data only once To prevent old previously read data from being read a second time by mistake the output buffer is always cleared after it has been read If the output buffer is read twice without an intervening output command the 8842A will not respond to the second attempt to read the output buffer However if the 8842A is in TO no intervening command is necessary RULE 2 Use no more than one output command per input command string Because the 8842A has only one output buffer it writes new data over old If an input command string contains more than one output command only the data from
221. ll diagnostic self tests does not necessarily mean the 8842A is 100 functional The test for example cannot check the accuracy of the analog circuitry If one or more errors are displayed the 8842A probably requires service DC Voltage Test The following procedure may be used to verify the accuracy of the VDC function 1 Ensure the 8842A is and has warmed up for at least 1 hour 2 Select the VDC function 3 Connect the DC Calibrator see Table 6 1 to provide a voltage input to the HI and LO INPUT terminals Connections for the Kelvin Varley Voltage Divider and the Fluke 5440A are shown in Figure 6 1 4 For each step in Table 6 2 select the indicated range set the DC Calibrator for the specified input and verify that the displayed reading is within the limits shown for each reading rate For step A connect a short across the HI and LO INPUT terminals and press OFFSET The measurement in step C should be relative to this offset 5 Set the DC Calibrator to input negative voltage and repeat steps C thrugh G of Table 6 2 6 With the unit in the 2V range check the A D linearity by setting the DC Calibrator for each step in Table 6 9 while verifying the display reading is within the limit shown Set the DC Calibrator for zero volts and disconnect if from the 8842A 6 5 8842A Instruction Manual A CONNECTIONS FOR KELVIN VARLEY VOLTAGE DIVIDER DC CALIBRATOR FLUKE 343A CONNECTIONS ARE SHOWN FOR POSITIVE INPUT VOL
222. mit the output of U103 to minimize the time it takes to recover from being driven to a supply rail Both functions are achieved by manipulating the supplies of U103 BS1 and BS2 5 25 DISPLAY The vacuum fluorescent display is similar to a vacuum tube containing eight control grids and 69 phosphor coated plates which form the display segments and annunciators See Figure 5 12 The filament voltage is 4 5V ac with a 5V dc bias Each plate is controlled by a G line and a P line The G lines go to the control grids and the P lines go to the plates Theory of Operation KEYBOARD f5 12 wmf Figure 5 12 Vacuum Fluorescent Display The Digital Controller sequentially enables the G lines by applying 30V dc nominal When a G line is enabled electrons flow from the filament to the enabled grid If a P line is enabled i e raised to a nominal 30V dc by the Digital Controller the electrons continue past the grid and strike the respective plate causing it to glow 5 26 KEYBOARD The keyboard consists of a silicone rubber switch matrix located over metalized epoxy contacts on the printed wire board Each button contains a conductive pad that shorts two contacts when pressed 5 27 DIGITAL CONTROLLER The Digital Controller Figure 5 13 consists of the In Guard uC U202 External Program Memory U222 Calibration Memory U220 Keyboard Display Interface and associated components 5 19 8842A Instruction Manual
223. mp 0306 In addition the 30V output supplies the anodes of the vacuum fluorescent display Zener diode CR612 supplies 6 2V to the A D Converter clamps AC voltage for the 15V and 15V supplies is rectified by bridge network CR608 CR609 CR610 and CR611 and regulated by VR603 and VR604 The 15V and 15V supply analog circuitry throughout the 8842A Zener diodes CR613 and CR614 supply 7 5V and 8 2V to the A D Converter analog filter and DC Scaling circuit Secondary T601 14 15 16 supplies the vacuum fluorescent display filament with 4 5 V ac The center tap is connected to the in guard 5V supply in order to correctly bias the display An isolated secondary supplies 16V ac to the power supply on the IEEE 488 Interface Zener diode CR615 and SCR Q601 comprise a protective crow bar circuit If the line voltage exceeds the nominal value by approximately 30 percent or more CR615 conducts turning on Q601 shorting out the power transformer secondary and blowing the line fuse In normal operation these components have no effect 5 25 8842A Instruction Manual 5 37 488 INTERFACE OPTION 05 The IEEE 488 Interface has five major parts as shown in the block diagram in Figure 5 16 All components are contained in a single printed circuit assembly PCA Reference designations are numbered in the 900 series IN GUARD uc GUARD 0202 ICROSSING IEEE 488 Ll TALKER LISTENER IC U911 OUT GUARD AND BUS TRANSFORME
224. multiple of 3 as in engineering notation The position of the decimal point matches the front panel display Numeric data is of constant length It is 11 characters plus terminators when the suffix is disabled and 16 characters plus terminators when the suffix is enabled The suffix is enabled by the Y1 command and consists of five ASCII characters as shown in Figure 3 6 The suffix is appended only to numeric data never to status data The terminators are determined by the Terminator commands The default is CR LF EOI There are three types of numeric data measurement data overrange indication and error messages MEASUREMENT DATA Measurement data has the numeric data format shown in Table 3 2 and is always in the units of volts amps or ohms Table 3 2 Numeric Output Data Format RANGE MEASUREMENT DATA OVERRANGE ERROR VDC VAC 2 4 WIRE MA DC mA AC R8 1 3 1 0 9 99999E 9 1 00xxE 21 R1 1xx xxxE 3 1 0 ES 9 99999E 9 1 00xxE 21 R2 1 0 1 3 B 9 99999E 9 1 00xxE 21 R3 1 0 1X XXXXE 3 9 99999E 9 1 00xxE 21 R4 1 0 1 3 1 3 9 99999 9 1 00xxE 21 R5 1 0 1 3 1 3 9 99999E 9 1 00xxE 21 R6 1x xxxxE 6 9 99999E 9 1 00xxE 21 VDC only 4 wire ohms mA DC only 88
225. n Calibration procedure for the respective function Buttons Range These buttons have two functions Normally pressing a range button selects the Offset and Gain Buttons Calibration procedure for that range in the presently selected function When using the variable input feature these buttons are used to increment the digits of the displayed prompt The range buttons are ignored during the A D Calibration procedure Tells the 8842A that the input it is requesting is now present at the input terminals Pressing the STORE button causes the 8842A to compute and store calibration constants Selects the A D Calibration procedure Selects the High Frequency AC Calibration procedure Used to erase calibration constants from calibration memory To complete an erasure of all or part of calibration memory you must press another button within 11 seconds of pressing this button CAUTION If any part of calibration memory is erased all or part of the calibration procedure must be performed Changes the reading rate Valid only when the 8842A is taking verification readings Ignored at other times Allows the use of reference sources that differ from the prompted values After pressing VAR IN variable inpatt the range buttons can be used to change the displayed prompt The variable input feature is not available during the A D Calibration procedure f6 03 wmf Figure 6 3 Calibration Functions The following functions are inappropriate dur
226. n Diego CA 17856 Siliconix Inc Santa Clara CA 18324 Signetics Corp Military Products Div Orem UT 21958 Hughes RS Co Inc Los Angeles CA 22670 GM Nameplate Inc Seattle WA 24347 Penn Engineering Co S El Monte CA 24355 Analog Devices Inc Norwood MA 26806 American Zettler Inc Aliso Viejo CA 27014 National Semiconductor Corp Santa Clara CA 28213 Minnesota Mining amp Mfg Co Consumer Specialties Div 3M Center Saint Paul MN 2M021 EFAB Mfg Inc Charlottesville VA 30146 Symbex Corp Painesville OH 30800 General Instrument Corp Capacitor Div Hicksvilie NY 31918 ITT Schadow Inc Eden Prairie MN 34649 Intel Corp Santa Clara CA 34848 Hartwell Special Products Placentia CA 37942 North American Capacitor Co Mallory Div Greencastle IN 51406 Murata Erie No America Inc Symrna GA 54583 TDK Electronics Corp Port Washington NY 55566 RAF Electronic Hardware Inc Seymour CT 56289 Sprague Electric Co Nashua NH 56708 Zilog Inc Campbell CA 59124 KOA Speer Electronics Inc Bradford PA 60395 Xicor Inc Milpitas CA 60705 Cera Mite Corp Grafton WI 61429 Fox Electronics Fort Myers FL 61935 Schurter Inc Petaluma CA 62643 United Cherni con Inc Rosemont IL supply_1 wmf 65940 Rohm Corp Irvine CA 68919 Inter Technical Group Inc The Wima Division Elmsford NY 71400 Bussman
227. n Figure 4 3 An internal current source the ohms current source passes a known test current Itest through the resistance being tested Runknown The 8842A measures the voltage drop across Runknown calculates Runknown using Ohm s law Runknown Vtest Itest and displays the result OHMS CURRENT SOURCE VOLTAGE SENSE R UNKNOWN f4 03 wmf Figure 4 3 Wire Ohms Measurement Measurement Tutorial RESISTANCE MEASUREMENT The test current and full scale voltage for each resistance range are shown in Table 4 1 Since the HI INPUT test lead is positive with respect to the LO INPUT lead these test leads are not interchangeable when a semiconductor device is being measured Correcting for Test Lead Resistance in 2 Wire Ohms In 2 wire ohms the resistance of the test leads can introduce error when measuring low resistances Typical test leads may add as much as 0 5Q to 2 wire ohms readings With the 8842A it is easy to correct for this error using the OFFSET button 1 Select the 2 wire ohms function 2 Touch the test leads together The 8842A should indicate the resistance of the test leads 3 With the test leads still touching press the OFFSET button The 8842A should read 0Q 4 Wire Ohms Four Wire ohms measurements provide the highest accuracy for low resistance measurements The 4 wire configuration automatically corrects for both test lead resistance and contact resistance Contact resistance the resistance be
228. n system The 8842A can be under complete interactive control from a remote bus controller or it can be set to the talk only mode connected to a data logger or printer and dedicated to a single task 805 2 CAPABILITIES The IEEE 488 Interface provides remote control of all front panel controls except for the POWER CAL ENABLE and FRONT REAR switches Other features include e A simple and predictable command set e Fast measurement throughput e Fulltalk listen capability including talk only operation e Full serial poll capability with bit maskable SRQ e Full remote local capability including local lockout e External Trigger and Sample Complete connectors e Remote calibration e Programmable trigger sources including two bus triggers e Informative output suffix suppressible e Selectable output terminators The 8842A supports the following interface function subsets SH1 AH1 5 L4 SR1 RL1 DC1 DT1 El PPO and 805 3 EXTERNAL CONTROLS When the IEEE 488 Interface is installed the rear panel contains EXT TRIG External Trigger and SAMPLE COMPLETE connectors These controls can be used even when the 8842A is disconnected from the IEEE 488 bus Refer to Section 2 for details 805 4 INSTALLATION The IEEE 488 Interface is contained a single easy to install printed circuit assembly PCA To install the option proceed as follows WARNING TO AVOID ELECTRIC SHOCK DISCONNECT THE POWER CORD AND ANY IN
229. nal bus consists of lines ADO AD7 and 8 11 Lines ADO AD7 are time multiplexed to carry both the least significant address byte and the data Lines A8 A11 carry the most significant bits of the address The HC writes to and reads from the internal bus according to the read and write cycles shown in Figure 5 14 During either cycle the address strobe AS changes from low to high when an address is valid and the data strobe DS changes from low to high when the data is valid The address strobe latches the address on ADO AD7 into U219 which then provides static address inputs for those devices that need it while data is on the bus The data memory line DM divides the address space between program memory U222 and data memory all other devices on the bus The data memory address space is further divided between the calibration memory U220 and the remaining devices by A11 The addresses of the remaining devices are decoded from A8 A10 by U208 which combines the address with the data strobe DS to provide a chip select CSO CS2 CS3 CS4 or CS7 for each device The In Guard uC performs the following functions range and function control A D control and computation calibration corrections keyboard display control serial communication with the IEEE 488 Interface and diagnostic self testing and troubleshooting 5 21 8842A Instruction Manual 5 22 External I O or Memory Read and Write Timing No Symbol Parameter
230. nctions makes a useful troubleshooting tool in itself It has excellent linearity and temperature stability Its compliance voltage is typically 5V in the lower five ohms ranges and 12V in the upper two ohms ranges The inputs are protected against accidental applications of voltage up to 300V rms To use the ohms current source connect the test leads to the HI and LO INPUTS and select either the 2 wire or 4 wire ohms function Press the range buttons to select any of the current levels shown in Table 4 1 The ohms current source can be used to troubleshoot circuits by injecting current into selected nodes forcing the circuits to be in a specific test state For example the ohms current source can be used to set or modify the bias of amplifier circuits The current level can be changed simply by changing range The ohms current source can also be used to test mA or HA panel meters The accuracy of the current source is more than enough to verify panel meters whose accuracy is typically 1 to 5 To test an analog panel meter simply connect the current source across the meter movement as though measuring its resistance A 1 mA meter should show full scale when the ohms function is set on the 2 kQ range The same technique also works with digital panel meters 4 13 DC CURRENT MEASUREMENT To get the best accuracy using the mA DC function it is important to understand the concept of burden voltage error When a meter is placed in serie
231. nded equipment is not available equipment that meets the indicated minimum specifications may be substituted INSTRUMENT TYPE DC Calibrator Table 6 1 Recommended Test Equipment MINIMUM SPECIFICATIONS RECOMMENDED MODEL PREFERRED Fluke 5700A or Fluke 5440A Voltage Range 0 1000V dc Voltage Accuracy 10 ppm Absolute Linearity 1 0 ppm Must be used with Kelvin Varley Voltage Divider Voltage Range 0 1000V dc Voltage Accuracy 20 ppm 20 ppm of range Kelvin Varley Voltage Divider Fluke 720A Ratio Range 0 1 0 Absolute Linearity 1 ppm of input at dial setting Resistor Calibrator DC Current Source ALTERNATIVE Fluke 720A Resistance Accuracy 0 0005 Fluke 5700A or Fluke 5450A ESI DB62 Accuracy 0 025 Fluke 5700A or Fluke 5100B Oscilloscope General porpose 60 MHz with 10 Philips PM3055 or PM3355 MQ probe Digital Multimeter Voltage Accuracy Fluke 8842A with AC Option 09 0 01 in V dc 1 0 for 1V in V ac 100 kHz Input Impedance 10 MQ or greater in V dc 1 or greater in parallel with 100 pF in V ac 6 3 8842A Instruction Manual AC Calibrator Fluke 5700A and Fluke 5725A Minimum Required Accuracy By Range Frequency Range 1 10 100 1 10 100V 1000V 20 Hz 30 Hz 4 005 005 12 005 30 Hz 20 kHz 02 10 0 2 4 002 04 004 20 kHz 50 kHz 05 20 05 005 08 005 50 kHz 10
232. nge 71 Syntax error in device dependent command string 15 1000 VDC X10 T H 20 MQ 72 Guard crossing error detected by out Guard uC 16 200 VDC 200 kQ 73 Guard crossing error detected at power on or CAL ENABLE switch on at power on 17 200 VDC 20 kQ 77 IEEE 488 Interface self test error DIGITAL SELF TEST ERRORS 25 In Guard uC Internal RAM 26 Display RAM 27 In Guard uC Internal Program Memory 28 External Program Memory 29 Calibration Memory See the Maintenance section for a detailed description of self tests 8842A Instruction Manual 2 12 2 13 2 14 2 15 Overrange Indication An input is overrange if it exceeds the full scale of the selected range In most ranges the 8842A indicates an input is overrange by lighting the OVER annunciator and showing a 1 on the display See Figure 2 8 The sign the position of the decimal point and the other annunciators are not affected As a Safety feature the 8842A treats the 1000V dc and 700V ac rangesdifferently In these ranges the 8842A indicates when the input exceeds the input overload limit of 1000V dc or 700V ac respectively by lighting the OVER annunciator and flashing the display Readings are still displayed Diagnostic Self Tests The 8842A features diagnostic self tests which check both the digital and analog circuitry in the instrument The self tests consist of 21 analog tests foll
233. nitial Troubleshooting Procedure a 6 38 Diagnostic Self Tests esre esee 6 39 Sel Pest DESCEPIpUOnS 6 40 Digital Controller Troubleshooting eene 6 41 IN GUARD MICROCOMPUTER SYSTEM 6 48 DISPLAY SYSTEM 6 59 ANALOG CONTROL 5 6 62 DC Scaling Troubleshooting seen 6 63 Track Hold Troubleshooting eee 6 64 Ohms Current Source Troubleshooting 6 65 Precision Voltage Reference Troubleshooting 6 66 A D Converter Troubleshooting eene 6 67 Power Supply Troubleshooting eene 6 68 488 Interface Troubleshooting Option 05 6 69 SERVICE POSIT ION uu a ap terere treten ties 6 70 6 71 True RMS AC Troubleshooting Option 09 6 72 SERVICE POSITION scitu 6 66 6 73 6 67 6 74 MORE 5 6 75 Guard C
234. nted circuit assemblies PCAs handle the PCAs by their edges Do not handle the areas of the PCAs that are not solder masked unless absolutely necessary These areas must be cleaned if contaminated The following paragraphs present a disassembly procedure for the 8842A The procedure should be performed in the order presented Remove the case first and then remove Option 09 the True RMS AC PCA Option 05 the IEEE 488 Interface PCA the Main PCA and the front panel For reference see the final assembly drawing in Section 7 6 25 8842A Instruction Manual 6 28 Case Removal 1 Remove the grounding screw from the bottom of the case Remove two rear bezel mounting screws See Figure 6 6A 2 While holding the front panel slide the case and rear bezel off the chassis See Figure 6 6B At this point the rear bezel is not secured to the case MOUNTING SCREW 1 OF 2 REAR PANEL GROUNDING SCREW REAR BEZEL CHASSIS 16 06 1 wmf Figure 6 6 8842A Disassembly 6 26 6 5 eo SE a Ly 2 e Figure 6 6 8842A Disassembly cont 6 27 8842A Instruction Manual 16 06 3 wmf Figure 6 6 8842A Disassembly cont 6 28 Maintenance DISASSEMBLY PROCEDURE 6 06_4 wmt Figure 6 6 8842A Disassembly cont 6 29 8842A Instruction Manual 6 30 6 29 6 30 6 31 True RMS AC PCA Removal Option 09 Only The True RMS AC PCA sh
235. o default functions WAIT 1000 Wait 1 second before sending commands PRINT 4 F1 RO SO TO Y1 F1 VDC RO Autorange SO Slow rate ITO Continuous trigger Y1 Enable suffix 0 LOCAL 24 Give local control to instrument INPUT 4 A A Get reading and suffix from 8842A X X 1 Increment reading count PRINT Display reading and suffix GOTO 110 END f3 11 wmf Figure 3 10 Example Program Taking Readings with Local Control 3 34 Remote Programming EXAMPLE PROGRAMS 1 The following program illustrates one possible use of the serial poll register In this 2 case it is merely looking for data available The instrument is addressed on port 0 3 device 4 under control of a Fluke 1720A or 1722A instrument controller The function 4 of this program is to display on the controller screen the lowest resistance measured 5 across the input terminals of the 8842A using the 2 wire ohms function in autorange 6 command string sets up the 8842A by using the Put Instrument Configuration command 7 8 FLUKE BASIC on 1720A 1722A 9 100 INIT PORT 0 CLEAR PORT 0 WAIT 500 Clear port instrument delay 110 PRINT N3001P0 Y1 2 Instrument functions and trigger 120 INPUT 4 A A Get first reading 130 PRINT A AS S 2 wire Lowest Reading 140 TRIG 24 160 B SPL 4 Get serial poll register 170 IF B 0 THEN 160 Looking for data available 175 INPUT 4 R A Get next data 180 IF gt
236. ompts When Calibrating Individual Ranges PROCEDURE FUNCTION LOW PROMPT HIGH PROMPT Offset and Gain VDC Zero 95 of full scale Calibration kQ Zero 50 of full scale VAC 5 of full scale 50 of full scale High Frequency AC Not applicable No low prompt 50 of full scale Calibration 1 Exception The 1000V dc range has a high prompt of 1000V 2 Exception The 700V ac range has a low prompt of 100V ac and a high prompt of 500V ac 3 Exception The 700V ac range has a prompt of 200V ac When you complete certain parts of the calibration procedure the 8842A automatically begins taking readings so that you can verify the calibration 15 correct It is recommended that you do so The CAL annunciator remains lit The 8842A continues to take readings until you select another calibration procedure or exit the calibration mode Specifically the 8842A begins taking verification readings after 1 Completing A D Calibration 2 Completing Offset and Gain or High Frequency AC Calibration 3 Completing the calibration of an individually selected range While the 8842A is taking verification readings certain buttons are active or function differently 8842A Instruction Manual 6 19 6 20 1 If you just completed the Offset and Gain or High Frequency AC Calibration for an entire function not just one range the range buttons can be used to change ranges in order to verify all ranges were cal
237. ond and the A D trigger U202 40 is a square wave at its normal frequency of 80 Hz and DM and P23 stay high The data received at U202 5 is meaningless Adjacent port outputs display opposite phases of the 1 KHz square wave HC pins that are normally only programmed as inputs are also 6 45 8842A Instruction Manual programmed as inputs to prevent contentions between them and the outputs from other ICs which drive them Data coming into all inputs except pin 38 is ignored NOTE If the A D IC 0101 is working properly its watchdog timer briefly interrupts all of the In Guard Troubleshooting Mode signals every 1 5 sec for a period of about 0 2 sec The signals are then re established If this occurs the main counter 0101 and its watchdog timer are operating correctly See step 6 below When the test is complete turn off the 8842A and remove the short from TP205 6 42 In Guard Microcomputer While the 8842A is in the In Guard Troubleshooting Mode check the following in the order shown Notes on use 8 12 xta C4400 C0040 CC Cuart out lt lt P30 in gt P37 8 hz pulses RESET CS CCGGGGG GGG GG GGG COR AW GGG GC GOODS putses CC C AS 1 khz CCCCa279 rst C CCCCO P35 203303000 00992000 GND sense P32 1 khz ABC CK CK CC
238. ont panel range buttons For example RO selects autorange and R3 selects the 20V 20 kQ range The R7 command turns autorange off just as the AUTO button does when it is toggled Command R7 puts the 8842A into manual range selecting whatever range the instrument is in when the command is received The 88424 defaults to RO on power up and any device clear command DCL or SDC The range setting can be read using the GO command Sn Reading Rate Commands The Reading Rate commands duplicate the front panel RATE button Like the RATE button the reading rate command also selects the number of digits displayed and the filter setting Filter settings are shown in the specifications in Section 1 The 88424 defaults to SO on power up and any device clear command DCL or SDC The reading rate can be read using the GO command 8842A Instruction Manual 3 29 Trigger Mode Commands The Trigger Mode commands duplicate the front panel EX TRIG button In addition the commands can enable or disable the rear panel trigger and the automatic settling time delay Figure 3 7 illustrates how to select among the five types of triggers continuous trigger front panel trigger rear panel trigger and two bus triggers Note that the front panel TRIG button is enabled only while the instrument is under local control TRIGGER METHOD CONTINUOUS TRIGGER DEVICE CLEAR TOGGLED BY EX TRIG MEASUREMENT BUS TRIGGER BUTTON CIRCUITRY 2
239. or GET REMOTE LOCAL FRONT PANEL TRIGGER SETTLING DELAY With EXTRIG enabled REAR PANEL TRIGGER T3 DEVICE CLEAR EX TRIG BUTTON Switches represent effect of indicated commands buttons and remote local status e Instrument shown in power up state TO local rear panel trigger enabled TRIGGER METHOD DESCRIPTION 1 Continuous Trigger Continuous trigger generated by 8842A in internal trigger mode TO 2 Command Single trigger initiated by command from controller 3 GET Command Single trigger initiated by GET command an interface message from controller 4 Front Panel Trigger Single trigger initiated by front panel TRIG button 5 Rear Panel Trigger Single trigger initiated from rear panel EXTTRIG input Disabled by TO T2 4 f3 07 wmf Figure 3 6 Trigger Selection Logic Diagram In the continuous trigger mode TO triggers are initiated at the selected reading rate Each new reading is loaded into the output buffer as it becomes available unless the instrument is busy sending previous output data 3 18 3 90 3 31 3 32 3 33 Remote Programming DEVICE DEPENDENT COMMAND SET The trigger mode can be read using the GO command The 8842A defaults to TO on both power up and any device clear command DCL or SDC Wn Terminator Commands The Terminator commands select what terminators the 8842A appends to every output string The available terminators are Carriage Re
240. ould be removed by reversing the last three steps in Figure 809 1 see Section 8 1 Release the True RMS AC PCA from the chassis by pulling the four plastic latches upward Figure 809 1E 2 Raisethe True RMS AC PCA slightly and disconnect the red lead from the connector J301 located on the Main PCA Figure 809 1C 3 Disconnect the ribbon cable from the Main PCA by releasing the ribbon connector latches push outward see Figure 809 1D and pulling the ribbon cable directly outward from the connectors Figure 809 1C 4 Lift the True RMS AC PCA out of the chassis IEEE 488 Interface PCA Removal Option 05 Only The IEEE 488 Interface PCA should be removed by reversing the last four steps in Figure 805 1 see Section 8 1 Remove the two jack screws and washers from the rear panel IEEE 488 connector Figure 805 1H 2 Release the IEEE 488 Interface PCA from the chassis by pulling the two plastic latches upward Figure 805 1H 3 Raise the forward edge of the IEEE 488 Interface PCA slightly pull the PCA towards the front panel guiding the IEEE 488 jack and BNC connectors out of the rear panel and lift the PCA out of the chassis Figure 805 1G 4 Disconnect the ribbon cable from the IEEE 488 Interface PCA by releasing the connector latches push outward see Figure 805 1F and pulling the ribbon cable out from the connector Figure 805 1E Main PCA Removal 1 Disconnect the leads from the four front panel input te
241. output data and their relative priority Note that the 8842A can also send data to the IEEE 488 bus from the serial poll register For a description of this data see paragraph 3 47 Loading Output Data The output buffer is loaded when the 8842A receives an output command or when an error occurs Output commands are those device dependent commands which load the output buffer with data e Get commands GO through G8 e Single trigger command e Group execute trigger GET e Continuous Trigger T0 3 42 3 43 3 44 Remote Programming OUTPUT DATA Because the 8842A gives priority to input processing it completely processes all characters in the input buffer before it loads the output buffer When the output buffer is loaded the Data Available bit in the serial poll register is set true Data from the output buffer is not actually loaded onto the IEEE 488 bus until the controller addresses the 8842A as a talker This is done by sending the interface message My Talk Address Types of Output Data The types of data that can be loaded into the output buffer are shown in Figure 3 6 Each type has its own format Error messages which are loaded into the output buffer if an error occurs are formatted as numeric data Numeric Data and Error Messages Numeric data is loaded into the output buffer in response to the G2 command or an instrument trigger and has the format shown in Table 3 2 The exponent is always a
242. overrange Sets SRQ mask to 01 A leading zero is assumed Enables SRQ overrange P2 Put Calibration Value Format Explanation lt gt 2 Where lt value gt be an integer real number real number with exponent as described under the N command Example Explanation NI P2 If the 8842A is in VDC the next calibration input expected is 1 00000V dc The P2 command is used to enter variable input calibration values just like the front panel VAR IN button To accept the P2 command the 8842A must be in the calibration mode enabled by pressing the front panel CAL ENABLE switch Otherwise the P2 command will generate an error message The variable input is a measurement value that is to be used as the calibration value for the next calibration step Its format is the same as a measurement value But since it is coming from the controller the value can be specified using any valid format signed interger real number or real number with exponent For example if the 8842A prompts for an input value of 100Q for the next calibration step but the available source is 98 970 the variable input can be specified as N 9 897E 1 N0 9897E2 N9897E 2 3 26 3 27 3 28 Remote Programming DEVICE DEPENDENT COMMAND SET etc All of these strings result in the same value being used for the next calibration step For complete information about remote calibration refer to the Maintenance section
243. owed by the in guard program memory calibration memory and display self tests To initiate the self tests press the SRQ button for 3 seconds The instrument can be stopped in any of the test configurations by pressing the SRQ button while the test number is displayed Press any button to continue the tests During the test the TEST annunciator lights and the numeric field displays the number of each analog test as it is performed Then all display segments light up while the instrument performs the in guard program memory calibration memory and display self tests The 8842A then returns to the power up configuration The self tests are described in greater detail in the Maintenance section NOTE The inputs must be left disconnected while the self tests are performed or the 8842A may indicate that errors are present If the 8842A detects an error it displays an error message for about 2 1 2 seconds Error codes 01 through 29 correspond to the self tests If self test errors are displayed even when the input terminals are disconnected there may be a hardware problem in your 8842A In that event refer to the Maintenance section or contact your local Fluke representative Ranging Measurement ranges can be selected using either autorange by pressing the AUTO button or manual range by pressing another range button The 8842A displays explicit units in every range so that the display may be read directly AUTORANGE In autorange
244. ower frequency and adjusts the analog to digital converter timing characteristics for optimum normal mode noise rejection The resulting reading rates are shown in the specifications in Section 1 Automatic Settling Time Delay When the external trigger mode is selected the 8842A automatically inserts a delay after receiving a trigger signal but before starting the first input sample The delay is just long enough so that the reading will be correct within a specified number of counts of the final value even if the trigger signal occurs as the input makes a step change between zero and full scale 10 000 counts and full scale in the ac functions The length of the delay depends on the range function and reading rate as shown in the specifications in Section 1 The delay is enabled only in the external trigger mode It can be turned off with a remote command over the 488 interface bus to accommodate special timing considerations OVER NE OVER Input Z2V dc in 2V range 12 08 wmf Figure 2 8 Overrange Indication External Trigger Input Option 05 Only The rear panel EXT TRIG input is a TTL level input which can be used to trigger measurements when the 8842A is in the external trigger mode A measurement is triggered on the falling edge of the input Since the EXT TRIG input is pulled high internally it can also be controlled by a normally open switch A measurement is triggered when the switch is closed For
245. ponse to 1 kHz the 80K 40 has a range of 0 to 40 000V dc or peak ac with frequency response to 60 Hz As the probes use 1000 1 dividers the probes have a high input impedance and cause minimal circuit loading The probes are impedance matched for both ac and dc measurements A plastic body protects the operator from the voltage being measured For best accuracy the probes should be used with DMMs having 10 MQ input impedance This condition is satisfied by the 8842A in the 200V dc and 1000V dc ranges The probes can also be used with the 8842A in the 200 mV dc 2V dc and 20V dc ranges if a 10 MQ resistor is connected in parallel across the input terminals 8842A Instruction Manual 8 6 805 1 805 2 805 3 805 4 805 5 805 6 805 7 Chapter 805 Option 05 IEEE 488 Interface INTRODUCTION 2 edo dete CAPADBILILIBS nennen nenne INSTALLATION PROGRAMMING INSTRUCTIONS MAINTENANCE 9 eiecit itt petere e LIST REPLACEABLE 2 2 0 805 1 8842A Instruction Manual 805 2 Option 05 IEEE 488 Interface INTRODUCTION 805 1 INTRODUCTION The IEEE 488 Interface turns the 8842A into a fully programmable instrument for use with the IEEE Standard 488 1978 interface bus IEEE 488 bus With the IEEE 488 Interface the 8842A can become part of an automated instrumentatio
246. possible from the front panel is intended as a troubleshooting aid and is not available over the IEEE 488 Interface Note that the erase command can take up to 3 seconds to execute To prevent timeout problems with the controller you must determine when the command is completed before continuing Several methods are presented in Timing Considerations above NOTE When erasing calibration memory it is good practice to send the commands C3 and CO in the same command string Sending C3 by itself could lead to accidentally erasing calibration memory since the C3 command does not time out as does the ERASE button EXAMPLE CALIBRATION PROGRAM An example A D calibration program is shown in Figure 6 5 The program is written in Fluke BASIC for the Fluke 1722A Instrument Controller It uses the Fluke 5440A Direct Voltage Calibrator to perform and then verify the A D Calibration procedure In this program the 8842A is at bus address 1 and the 5440A is at bus address 7 Maintenance DISASSEMBLY PROCEDURE This program performs the A D Calibration procedure and then verifies the A D Calibration is correct The program uses the Fluke 1722A Instrument Controller and the Fluke 54404 Direct Voltage Calibrator 8842A is at bus address 1 and the 54404 is at bus address 7 2 0 03 2 0 66 3 0 66 3 1 97 4 1 97 4 t LOOP TO READ IN VERIFICATION VALUES NEXT A INIT PORT t INITIALIZE SYSTEM REMOTE 1 GOTO 290 PROVIDES MEANS TO
247. pressed or if the trigger results in an overrange reading The SRQ mask is set to 05 which is 000101 in binary At power up or on any device clear command the SRQ mask is set to 00 decimal This prevents service requests by holding the RQS bit false under all conditions For other examples of the SRQ mask see the description of the 1 command 3 52 INTERFACE MESSAGES 3 53 3 54 The interface messages understood by the 8842A can be separated into the three main classes described in the IEEE 488 Standard address messages AD universal commands UC and addressed commands AC AII interface messages described here originate at the controller Address Messages Address messages are used by the controller to communicate talk and listen control to other devices on the bus Address messages are sent over the eight data lines of the bus while the controller holds ATN true Address messages are processed immediately and are not placed in the input buffer The address messages are MLA My Listen Address Addresses a device to listen MTA My Talk Address Addresses a device to talk UNL Unlisten Addresses all listeners to unlisten UNT Untalk Addresses all talkers to untalk Universal Commands Universal commands are accepted and interpreted by all devices on the bus The commands are of two types multiline messages and uniline messages Multiline messages are sent over the eight parallel data lines in the IEEE 48
248. priate mcib obj include lt stdio h gt include decl h include lt string h gt char rd 512 read data buffer int interface board number int dmm device number char selftest active 1 selftest active flag char errcode 4 error code buffer 1 brdO ibfind GPIBO initialize interface board dmm ibfind 18842A initialize 8842A ibclr dmm clear device ibwrt dmm Z0 2 start 8842A self test do do while self test active ibwrt dmm G7 2 get error status ibrd dmm rd 16 strncpy errcode rd 4 if stremp errcode 1000 20 test for error ibwrt dmm X0 2 printf Error 96s occurred r n errcode ibwrt dmm G0 2 get instrument configuration ibrd dmm rd 16 strncpy selftest active rd 1 while stremp selftest_active 9 0 check for self test active ibwrt dmm G7 2 get error status ibrd dmm rd 16 stmepy errcode rd 4 if strcmp errcode 1000 20 test for last digital error printf Error s occurred Nn errcode printf r nSelftest complete r n f3 14 11 wmf Figure 3 14 Example Programs Using the IBM PC cont 3 48 Remote Programming EXAMPLE PROGRAMS Table 3 4 ASCII IEEE Std 488 1978 Bus Codes BINARY DEV 7654 3210 MESSAGE ATN TRUE DECIMAL OCTAL HEX MESSAGE ATN TRUE BINARY 7654 3210 0
249. r test UUT 1 Complete Offset and Gain Calibration for the UUT s 4 wire ohms function The UUT will then be taking verification readings 2 Connect the UUT to the 5450A as shown in Figure 6 4 Select the SHORT from the 5450A and measure this value at the 5450A OUTPUT terminals using the UUT in 4 wire ohms If in remote take the average of four 6 19 8842A Instruction Manual readings In remote calibration the averaged value can be stored in the controller Record the value 4 Select the 1000 output from the 5450A and measure this value as in step 3 Find and record the numerical difference between the values calculated in steps 3 and 4 This value will be used as the variable input for calibrating the 200Q range in 2 wire ohms 6 Repeat steps 4 and 5 using the 1 output from the 5450A find and record the numerical difference between this and the SHORT measured in step 3 This value will be used as the variable input for calibrating the 2 kQ range in 2 wire ohms 7 Press the UUT s 2 WIRE button This selects the Offset and Gain calibration procedure for the 2 wire ohms function and prompts for zero input Select the SHORT from the 5450A and calibrate all the zeros by pressing STORE 8 Select the 1000 output from the 5450A and calibrate the high point for the 2000 range entering the value computed in step 5 as a variable input 9 Select the 1 output from the 5450A and calibrate the h
250. ranges and range r6 of 2 wire ohms can be calibrated Passing the tests also gives a reasonable probability that it will give accurate measurements in VDC and range r6 of 2 wire ohms However passing the tests does not guarantee that the instrument can be calibrated in VAC mA DC mA AC 4 wire ohms or ranges r1 to r5 of 2 wire ohms NOTE If the A D Converter or Precision Voltage Reference is not working all analog tests would show an error If the A D Converter is not calibrated tests 7 15 19 could show an error If the analog self tests indicate an error it may be possible to isolate the problem as follows 1 While the error code is being displayed press the SRQ button This latches the 8842A into the particular test configuration 2 Referring to Table 6 18 check that the test point voltages are as shown using another DMM 6 41 8842A Instruction Manual 6 42 6 39 Self Test Descriptions Table 6 18 Self Test Voltages TEST NUMBER TEST POINT 1 TP803 2 TP803 3 TP803 4 TP103 5 TP302 6 TP302 7 TP302 8 TP302 9 TP302 10 TP302 11 TP302 12 TP302 13 TP302 14 TP302 15 22 TP302 16 TP302 17 TP302 18 TP302 19 TP302 20 TP302 21 TP302 VOLTAGE 5 mV dc 5 mV dc 5 mV dc T H output waveform for zero input Figure 6 14 5 mV dc 5 mV dc 50 mV dc typical 11 5V dc typical 11 5V dc typical 4 5V dc with possibly 1V ac p p at 10 Hz 4 5V dc with possibly 1V ac p p at 10 Hz 4 5V d
251. raphs describe how these functions are performed Components are laid out on a single printed circuit assembly PCA Component reference designators are numbered in the 800 series VAC Scaling AC voltage inputs are directed from the HI INPUT terminal to the True RMS AC PCA through protection resistor R309 on the Main PCA In this way voltage transients greater than 1560V are clamped by MOVs RV301 RV402 RV403 and RV404 as in the VDC function With the VAC function selected K801 is closed The input voltage is thus applied to C801 which blocks dc inputs U807 and resistor network Z801 provide selectable attenuation and 1 MQ input impedance In the upper two ranges K802 is closed and 0806 is off providing a gain of 1 500 In the lower three ranges K802 is open and 0806 is on shorting Z801 4 to ground this configuration provides a gain of 1 5 CR801 and CR802 provide protection by clamping the inverting input of U807 to approximately 0 6V Q805 shifts logic levels to control Q806 5 27 8842A Instruction Manual 5 28 5 45 5 46 5 47 U806A U806B and a voltage divider R804 and R805 provide gain which is selected for each range by the analog switches in U804 The configuration for each range is shown in Figure 5 17 In this figure the CMOS analog switches are represented by mechanical switches When U806A is not used its non inverting input is grounded by Q804 When U806B is not used its non inverting input
252. rily pressing the SRQ button Press any button to continue the tests With the description of the self tests given below it may be possible to isolate the failure For reference the states of various switches and logic lines are shown in Table 6 16 for each function range and reading rate If only one or a few failures appear in the self tests the problem is usually in the DC Scaling circuit By carefully analyzing which failure s occurred the fault can be located to within a few components Table 6 17 shows which components are exercised by each of the analog tests The heading DC Scaling Troubleshooting provides detailed instructions on locating and repairing DC Scaling circuit problems However before troubleshooting the DC Scaling circuit all of the power supply levels should be measured to verify they are within the limits specified in Table 6 23 under Power Supply Troubleshooting later in this section 6 37 8842A Instruction Manual Table 6 16 Overall State Table DEFINITIONS The variables HD1 HD2 PC TR1 1 TR2 are dynamic signals generated by the A D chip HD2 TR2 These variables are true only ehen the logical and corresponding dynamic signals are true For example the switches in line logical or 8 are on only when HD1 is true logical not asserted low signal A 0 stands For the switch or relay being open and 1 stands for it being slow reading rate closed If a reference designator has after it the
253. ring this time the controller continues to send the 8842A more commands the commands may fill up the 8842A s input buffer If this happens errors will probably occur You can avoid this problem by knowing when these commands are completed There are three ways to determine this 1 Monitoring the Cal Step Complete bit in the serial poll status register This status bit is set false every time the remote processor sends a command to the in guard processor It is then set true when the in guard processor completes the command and is ready to accept more So you can send a command and loop on a check of the status until the command is complete 2 Setting the SRQ mask to generate an SRQ on Cal Step Complete An SRQ is generated and the Cal Step Complete bit in the serial poll status response is set when a cal command is complete This approach depends on capabilities of the controller being used 3 Executing a delay in controller software after sending each command Not recommended Although not usually necessary these methods can be used for other commands as well REMOTE ERASURE The C3 command allows you to erase the entire calibration memory The erasure is executed by sending the string C3 CO equivalent to pressing ERASE and then STORE Any command other than CO after C3 will abort the erasure To facilitate remote calibration the CO command does not timeout as does the front panel ERASE button The selective erasure that is
254. rminals and the four rear panel input terminals by unplugging them Refer to Figure 6 6C 2 Remove the cable harness from the two cable clamps on the side of the instrument chassis Figure 6 6D Lift the cable harness clear of the sidewall cable guide 3 Remove the front panel fuse by pressing in the lip of the 2A input terminal slightly and rotating it 1 4 turn counterclockwise Figure 6 6E 4 Disregard this step if the IEEE 488 Interface was installed Disconnect the ribbon cable from the rear panel insert by pushing outward on the snap tab on either side of the ribbon cable connector 5 Disconnect the two ribbon cables from the Display PCA by pulling the two plastic pull tabs directly outward from the Display PCA Remove the two mounting screws on either side of the rear panel power receptacle Disconnect the green power supply ground lead from the rear panel mounting stud The stud is located near the rear panel power receptacle See Figure 6 6F 8 Remove the Line Voltage Selection Switch LINE SET PCA as follows Figure 6 6G a Remove the upper screw that holds the LINE SET PCA to the upper rear panel standoff 10 11 12 13 14 15 16 17 18 Maintenance DISASSEMBLY PROCEDURE b Unplug the ribbon cable from the Main PCA and lift out the LINE SET PCA Remove the push rod for the CAL ENABLE switch as follows Figure 6 6H a While supporting the white plunger of the CAL ENABLE switch wi
255. rminator Terminators are CR Carriage Return LF Line Feed EOI End Or Identify and GET Group Execute Trigger e Input command string One or more device dependent commands followed by a terminator Input Processing When the 8842A receives commands from the bus it stores them in a 31 character input buffer as a continuous string of characters Commands in the input buffer are not executed or checked for syntax until an input terminator is received or the input buffer becomes full The only valid input terminators are CR LF GET Group Execute Trigger and or EOI When the 8842A receives an input terminator it executes the previous commands in the order in which they were received As input characters are processed and executed space is made available in the input buffer for new characters If the input buffer becomes full the 8842A stops accepting characters from the bus until all complete command strings currently in the input buffer have been executed In this way characters sent to the 8842A are never lost due to buffer overflow In some instances a terminator is automatically transmitted at the end of the controller s output string For example in Fluke BASIC the PRINT statement always finishes with a CR LF pair If a controller does not have this feature the programmer must transmit a terminator explicitly The 8842A accepts alphabetic characters in either upper or lower case Spaces commas and control codes are
256. roblem goes away troubleshoot the True RMS AC PCA using the procedure given later in this section With most power supply problems the output voltage is too low or too high More subtle problems that may be encountered include high ripple or oscillation If more than 10 mV of line frequency ripple exists on one of the power supply outputs it is usually caused by the input being too low causing the regulator to drop out of regulation It is also possible but not likely that the regulator itself is defective High frequency oscillation frequently synchronized with the 1 Mhz or 8 Mhz clock is usually the result of a bad regulator or output bypass capacitor A fair amount of high frequency noise is generally present on all the supplies particularly 5V and should not cause any concern unless the instrument behaves erratically or the reading is noisy IEEE 488 Interface Troubleshooting Option 05 SERVICE POSITION To provide easy access to the IEEE 488 Interface PCA and the Main PCA the IEEE 488 Interface PCA can be placed in the specially provided service position as follows 1 Remove the case from the chassis according to the Case Disassembly procedure provided earlier in this section 2 Release the two nylon latches that hold the IEEE 488 Interface PCA in place by pulling the latches upward 3 Position the IEEE 488 Interface PCA vertically as shown in Figure 6 19 and latch it in place be pressing the two nylon latches into the moun
257. rossing Troubleshooting eere 6 76 INTERNAL 6 77 Cleaning Printed Circuit Assemblies 6 78 Cleaning After List of Replaceable Parts u Joly INTRODUCTION estes 7 2 HOW TO OBTAIN 5 7 3 MANUAL STATUS 7 4 NEWER 5 720 SERVICE CENTERS erret tenete cente Options and Accessories 1 1 INTRODUCTION erint oper eerte hee atuk 8 2 ACCESSORIES ecer De e E phe e tee 8 3 Rack Mount Kits Y8834 Y8835 and Y8836 8 4 Shielded IEEE 488 Interface Cables Y8021 Y8022 and Y8023 8842A Instruction Manual 805 809 8 5 Replacement Test Leads TL70A 8 6 Deluxe Test Lead Kits Y8134 8 7 Slim Flex Test Leads Y8140 8 8 Temperature Probes 80T 150U an
258. s Also spaces are placed between commands for ease of reading they are not required 3 32 Remote Programming EXAMPLE PROGRAMS This program selects VDC F1 Autorange RO Slow rate SO continuous trigger TO and suffixes enabled Y1 The program takes 10 readings and stops The 8842A is addressed on port 0 device 4 under control of a Fluke 1720A or 1722A Instrument Controller In the INPUT statement the controller assigns the first part of the 8842A output response the measurement value to R and assigns the second part the suffix to R FLUKE BASIC on 1720A 1722A INIT PORT 0 Clear Port CLEAR PORT O Clear instr to default functions PRINT 24 F1 RO SO TO Y1 functions to instrument FOR I 1 TO 10 INPUT 84 R R Get data from 8842A PRINT LR R Print to 1722A display NEXTI END f3 10 wmf Figure 3 9 Example Program 3 33 8842A Instruction Manual This is a sample program which commands the 88424 to the state of VDC autorange slow rate continuous trigger and suffixes enabled All readings appear simultaneously on the instrument display while being logged on the controller display with suffixes enabled for function readout Full local control is given to the 8842A so that any range or function may be invoked easily The controller always echos the 8842A display while this program is running FLUKE BASIC on 1720A 1722A INIT PORT 0 Clear Port CLEAR PORT 0 Clear instrument t
259. s to allow troubleshooting and repair without a special test signal generator or complex logic analyzer Using the information in this section a technician should be able to troubleshoot and repair the 8842A very efficiently There is also a troubleshooting package available which utilizes the Fluke 9010A System Troubleshooter The 8842A 9000 Troubleshooting Kit is described in detail in Section 8 Initial Troubleshooting Procedure WARNING TO AVOID INJURY OR EQUIPMENT DAMAGE USE EXACT REPLACEMENT PARTS FOR ALL PROTECTION COMPONENTS When a problem occurs in the 8842A first verify the problem is actually in the instrument If the problem occurs when the instrument is in a system check to see if the same problem exists when under local control Watch the display as the instrument is turned on to see if any of the digital self test error codes appear indicating a digital failure If the malfunction does not involve the True RMS AC or IEEE 488 options remove the option s from the instrument before proceeding Maintenance TROUBLESHOOTING If the display lights up perform the self test by pressing the SRQ button for 3 seconds Remember the input terminals must be disconnected from the test leads during the self tests Otherwise the 8842A may indicate errors are present The test numbers will appear consecutively ERROR will appear on the display if a test should fail The 8842A can be held in each of the test configurations by momenta
260. s BS1 and BS2 should be 7V and 7V 10 referenced to the input of the A D amplifier U103 3 Troubleshooting the bootstrap supplies can often be made easier by putting the 8842A in EX TRIG to stop the A D Converter and connecting the input of the A D Converter TP103 to INPUT LO Reference Low on the schematic The bootstrap supplies are then referenced to instrument common Reference Low NOTE For the following tests set the 8842A to the VDC function and the 2V range and trigger the oscilloscope from the falling edge of line not TR TP201 If all supplies are correct the next most useful troubleshooting tool is the A D output waveform at TP101 which can be checked with an oscilloscope The waveform should look like the one shown in Figure 6 14 when the input voltage is at 50 of the selected range Various portions of the waveform correspond to different parts of the A D cycle By examining the waveform problems in the A D Converter can be isolated down to one or two components VERT 2V DIV HORIZ 2 ms DIV 1 0V INPUT f6 14 wmf Figure 6 14 Output of A D Amplifier TP101 6 59 8842A Instruction Manual RAMP UP OR DOWN INDICATES RAMP UP OR DOWN INDICATES LEAKAGE PROBLEM AT U101 24 LEAKAGE PROBLEM AT U101 25 VERT 2V DIV HORIZ 2 ms DIV 1 01V INPUT f6 15 wmf Figure 6 15 Waveforms at U101 24 and U101 25 VERT IV DIV LIT I HORIZ 2 ms D
261. s at the A D Converter when the display is definitely incorrect A digital 6 60 6 67 Maintenance TROUBLESHOOTING problem between the A D Converter and the In Guard uC can cause erroneous or noisy readings or offsets Similar problems may be caused by a failure of the Calibration Memory U220 or by bad A D calibration constants To check for bad A D calibration constants clear the calibration memory Readings at the A D Converter can be determined by interpreting the waveform at the DAC output TP102 Waveforms at TP102 for several input levels are shown in Figure 6 18 The A D reading can be calculated by knowing the weight of each bit and by weighting each nibble correctly The first nibble is weighted 1 the second 1 16 the third 1 16 the fourth 1 16 etc Figure 6 18 shows how to read the A D output for an input of 0 66V by interpreting the waveform at TP102 using the first three nibbles Troubleshooting the A D Converter for defective components can be simplified by setting the circuit in a quiescent state This can be done by selecting EX TRIG which causes all A D activity to stop The A D Converter is then in the autozero configuration and the offset of the amplifiers and the various levels in the bootstrap circuits can be easily measured with a voltmeter Oscillations at the outputs of the amplifiers and other abnormal signals can easily be identified with an oscilloscope Power Supply Troubleshooting If the display do
262. s for reducing thermal voltages are presented earlier in this section 4 24 MAKING ACCURATE HIGH RESISTANCE MEASUREMENTS When high resistances are measured typically 1 or greater leakage resistance at the test circuit can provide enough shunt resistance to degrade the accuracy of the measurement see Figure 4 12 To minimize leakage resistance watch out for contamination high humidity poor quality interconnections and poor quality insulation of the stand offs on which test resistors are mounted High resistance measurements are also susceptible to error from electrical noise pickup For accurate measurements use short test leads and enclose the test leads and test circuit in a proper shield that is connected to the 8842A s INPUT LO terminal Pickup of slowly fluctuating noise can also be reduced by using the OFFSET feature as described in paragraph 4 7 8842A Instruction Manual 4 16 INPUT SENSE ui INSULATED TEST FIXTURE Ri LEAKAGE RESISTANCE 14 12 wmf Figure 4 12 Leakage Resistance in High Resistance Measurement Q L A wd Eo CA CA CA CA CA 5 19 5 33 5 35 Chapter 5 Theory of Operation VDG Scaling eee tete VDC Protection u recti eene mA DC Scalig Analog Filter
263. s with a circuit to measure current error can be caused by the small voltage drop across the meter in this case across the protective fuses and current shunt This voltage drop is called the burden voltage and it is highest for full scale measurements The full scale burden voltage for the 8842A is typically less than 1V The burden voltage can present a significant error if the current source being measured is unregulated i e not a true current source and if the resistance of the fuse and shunt is a significant part of the source resistance If burden voltage does present a significant error the percentage of error can be calculated and corrected for using the formulas in Figure 4 5 Measurement Tutorial REDUCING THERMAL VOLTAGES Es Source voltage measured Burden voltage measured Load source resistance Rb 8842A internal resistance ERROR IN mA Displayed current X Es Ee E ERROR IN PERCENT X 100 EXAMPLE Displayed current 1460 mA Es 15V measured with 8842A in VDC function E 0 4V measured with 8842A as described below 0 4V Error in percent X 100 2 67 0 4V Error in mA 1460 mA X E 40 15V 0 4V To get the correct current add the error in mA to the displayed current Correct current 1460 mA 40 mA 1500 mA NOTE MEASURING BURDEN VOLTAGE The 8842A allows you to measure burden voltage directly Leaving the 2A and LO INPUT
264. se an instrument controller To put the 8842A in the talk only mode 1 Turn the 8842A POWER switch OFF 2 Set the rear panel TALK ONLY bit switch to 1 the up position 3 Connect the 8842A via the IEEE 488 bus to your printer data logger or other device 4 Configure the other device as a listener only 5 Turn the 8842A POWER switch ON Remote Programming REMOTE CALIBRATION 6 Configure the 8842A with the front panel controls The 8842A reads the TALK ONLY bit switch on power up and when it receives the interface command IFC You can therefore set the TALK ONLY switch to 1 after power up as long as you then send the 8842A the IFC command 3 57 REMOTE CALIBRATION The 8842A can be calibrated over the IEEE 488 bus using remote commands Refer to the Maintenance section for details 3 58 TIMING CONSIDERATIONS To help you take the best advantage of the speed of the 8842A external trigger timing for the IEEE 488 Interface is described in the specifications in Section 1 3 59 IMMEDIATE MODE COMMANDS Many controllers have some amount of immediate mode capability That is commands may be given interactively to the 8842A via the run time system without the need for actually running a program The controller accepts and executes these commands one at a time Some commonly used commands are listed in Table 3 3 for several controllers These are provided for the convenience of instrument demonstrations set up and check o
265. ses the High Frequency AC Calibration constants 3 After an erasure is finished a complete erasure takes about 3 seconds the 8842A returns to one of the following states After complete erasure Begins A D Calibration b After A D erasure Begins A D Calibration c After Offset and Gain erasure Begins Offset and Gain Calibration for erased function d After High Frequency AC erasure Begins High Frequency AC Calibration TOLERANCE CHECK The 8842A automatically checks that the reference input is near the value prompted This minimizes common errors such as applying a reference source with the wrong sign If the reference input exceeds the tolerances shown in Table 6 13 the 8842A displays ERROR 41 Maintenance CALIBRATION If ERROR 41 occurs the most likely cause is that the reference input is incorrect e g has the wrong polarity If the input is in fact correct refer to the Troubleshooting heading in this section Table 6 13 Tolerance Limits CALIBRATION TOLERANCE A D Calibration 244 counts from prompt Offset and Gain Calibration VDC mA DC 488 counts from prompt Ohms 3002 counts from prompt VAC mA AC 3002 counts from prompt HF AC Calibration 9999 counts from prompt 6 21 6 22 AC CALIBRATION AT OTHER FREQUENCIES For special applications where the 8842A is to be used to measure ac voltages or currents exclusively at a single frequency or narrow range of frequencies accuracy m
266. set cleared 8 Not used Never Always For example the serial poll register reads 00010000 binary when data is available This value is read in binary by the controller which might numerically reformat the value to 16 decimal or 10 hexadecimal The serial poll register is cleared whenever the 8842A receives a new input command string 3 51 SRQ Mask The SRQ mask is a two digit integer that specifies which conditions will generate a service request The SRQ mask is entered using the P command and can be read with the G1 command The conditions corresponding to each SRQ mask value are listed under Gl in Table 3 1 Remote Programming INTERFACE MESSAGES The SRQ mask can enable any combination of serial poll register bits 1 through 6 Its six bit binary representation is ANDed bit for bit with serial poll register bits 1 through 6 whenever the output buffer is loaded If any mask enabled bit in the serial poll register comes true the RQS bit bit 7 is set true generating a service request Example Explanation N4 SRQ is generated if the front panel SRQ button is pressed The string sets the SRQ mask to 04 which is 000100 in binary This mask is ANDed with the lower six bits of the serial poll register The mask thus enables bit 3 the Front Panel SRQ bit The SRQ mask codes can be added to select combinations of conditions Example Explanation x N5 An SRQ is generated if the SRQ button is
267. special applications using the IEEE 488 Interface the automatic setting time delay can be disabled using remote commands See Section 3 Refer to Section 1 for timing details The polarity of the EXT TRIG input can be reversed by changing internal jumpers Refer to the Maintenance section for instructions Sample Complete Output Option 05 Only The SAMPLE COMPLETE output indicates when analog input sampling for a reading is completed The output is a TTL level signal which is pulsed low for approximately 2 5 us when the input sampling portion of the A D conversion is completed The signal is useful for interfacing with other equipment when the 8842A is used in external trigger mode in an instrumentation system For example the SAMPLE COMPLETE output could be used to advance a scanner to the next channel 2 24 MAKING MEASUREMENTS 2 25 Input Overload Protection Limits WARNING Operating Instructions MAKING MEASUREMENTS TO AVOID SHOCK HAZARD AND OR INSTRUMENT DAMAGE DO NOTAPPLY INPUT POTENTIALS THAT EXCEED THE INPUT OVERLOAD LIMITS SHOWN IN TABLE 2 2 The 8842A is protected against input overloads up to the limits shown in Table 2 2 Exceeding these limits may damage the instrument and or pose a shock hazard FUNTION VDC MA DC 2 WIRE 4 WIRE VAC MA AC All Funtions Table 2 2 Input Overload Limits CONNECTORS INPUT HI and LO 2A INPUTand INPUT LO INPUT HI and LO SENSE HI and LO INPUT HI and LO
268. stics FULL SCALE 5 2 RESOLUTION INPUT RANGE DIGITS 5 DIGITS DIGITS RESISTANCE 20 mV 19 9999 mV 0 1uV 1uV 210 000 MQ 200 mV 199 999 mV 1uV 10 uV 210 000 MO 2V 1 99999V 10 uV 100 uV 210 000 MQ 20V 19 9999V 100 uV 1 mV 210 000 MQ 200V 199 999V 1 mV 10 mV 10 MQ 1000V 1000 00V 10 mV 100 mV 10 MQ 4V5 digits at the fastest reading rate Accuracy NORMAL S READING RATE of Reading Number of Counts 2 YEAR 23 5 RANGE 24 HOUR 23 1 C 90 DAY 23 5 1 YEAR 23 5 20 0 0050 20 0 0070 30 0 0100 30 0 0120 40 200 0 0030 2 0 0045 3 0 0070 3 0 0100 4 2V 0 0015 2 0 0025 2 0 0030 2 0 0050 3 20V 0 0015 2 0 0030 2 0 0035 2 0 0060 3 200V 0 0015 2 0 0030 2 0 0035 2 0 0060 3 1000V 0 0020 2 0 0035 2 0 0045 2 0 0070 3 1 Relative to calibration standards year and 2 year respectively 2 Within one hour of dc zero using offset control 3 When offset control is not used the number of counts are 50 70 90 and 90 for 24 hours 90 day 1 4 When offset control is not used the number of counts are 5 7 9 for 24 hours 90 day 1 year and 2 year respectively MEDIUM AND FAST RATES In medium rate add 3 counts 20 counts on 20 mV Range to number of counts In fast rate use 2 4 digit mode counts 30 counts on 20 mV range for the number
269. struction Manual 6 56 6 63 6 64 Track Hold Troubleshooting If a problem is suspected in the Track Hold T H circuit first check the power supply voltages of all active components See Table 6 22 Next check the T H output waveform at TP103 with an oscilloscope Set the 8842A to the VDC function and 2V dc range apply 1 V dc across the HI and LO INPUT terminals and trigger the scope from the falling edge of line not TR TP201 The waveform should look like that in Figure 6 13 The circuit may be checked as follows 1 Short the HI and LO INPUT terminals and select the 2V dc range 2 Short U301 14 to ground Reference Low The 8842A should read within 10 counts of zero The actual value is not as important as its stability 3 Connect U307 6 to U303 18 and monitor the voltage at TP103 using another multimeter The 8842A should read about the same as the external multimeter but with opposite sign If the 8842A fails step 2 but not step 3 then U303 is bad If the 8842A fails both steps 2 and 3 then the fault is in the A D Converter or the T H Amplifier To tell which lift the end of R318 closest to the front panel connected to U307 6 and apply an input of less than 2V to TP103 If the A D Converter is OK the 8842A will display the applied voltage with the opposite polarity For example if you apply 1V it should display 1V The readings may differ by a slight offset Ohms Current Source Troubleshooting
270. t Instrument Configuration command 140 REM 150 CLEAR 59736 160 IBINIT1 59736 170 IBINIT2 IBINIT1 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 IBFIND IBTRG IBCLR IBPCT IBSIC IBLOC IBPPC IBBNA IBONL IBRSC IBSRE IBRSV IBPAD IBSAD IBIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF 200 CALL IBINIT2 IBGTS IBCAC IBWAIT IBPOKE IBWRT IBWRTA IBCMD IBCMDA IBRD IBRDA IBSTOP IBRPP IBRSP IBDIAG IBXTRC IBRDI IBWRTI IBRDIA IBWRTIA IBSTA IBERR IBCNT 210 REM 220 REM IBM BASICA on IBM PC PC XT or PC AT 230 REM 240 DEVNAME 18842A Device name is 18842 250 CALL IBFIND DEVNAME DVM Initialize the DMM 260 CALL IBCLR DVM Clear device 270 FOR W 1 TO 500 NEXT W Wait 1 second before sending commands 280 WRT N3001P0 Y1 2 290 CALL IBWRT DVM WRT Write functions to instrument 300 RD 18 711 characters for the reading 5 for the 310 suffix and 2 for the terminators 320 CALL IBRD DVM RD Get first reading from 8842A 330 R VAL RD 340 PRINT LEFT RD 16 S 2 WIRE LOWEST READING Display readings 350 WRT 360 CALL IBWRT DVM WRT Trigger the 8842A 370 CALL IBRSP DVM SPR Get serial poll byte 380 IF SPR AND amp H40 lt gt amp H40 THEN 370 Check for data available 390 RD SPACE 18 400 CALL IBRD DVM RD Get next data 410 S VAL RD 420 IF S gt R THEN 350 Throw away data if not lowest 430R S Update lowest reading 440 GOTO 340 Print ne
271. t Loading Error Whenever a voltmeter is connected to a circuit the voltmeter s internal resistance changes the voltage of the circuit under test The resulting error is called circuit loading error The error is negligible as long as the resistance of the circuit under test the source impedance is small compared to the input impedance of the meter As the source impedance approaches the input impedance of the voltmeter the error can be considerable The percentage of error can be calculated using the formula in Figure 4 1 CIRCUIT LOADING ERROR IN 100 x Rs Ri where Rs Source impedance Ri 8842A input impedance Ri gt 10 000 MQ in 200 mV 2V and 20V ranges Ri 10 in 200V and 1000V ranges EXAMPLE When measuring the voltage across the 10 leg of a90 over 10 kQ voltage divider the circuit loading error is less than 0 1 in the upper ranges and less than 0 0001 in the lower ranges SOURCE VOLTAGE Rs 90 x 10 _ 90 KN 10 9 9 Error in the 200V and 1000V ranges 100 x kn 10MQ 0 09 9 h V V 1 0 9 rror in the 200 mV 2V and 20V ranges 00 x 10 000 MG 0 00009 f4 01 wmf Figure 4 1 Circuit Loading Error Calculation 4 2 Measurement Tutorial DC VOLTAGE MEASUREMENT The input impedance of the 8842A is 10 MQ in the 200V and 1000V dc ranges and is greater than 10 000 MQ in the 20 mV 200 mV 2V and 20V ranges Therefor
272. t U216 1 2 7 are low and U216 4 6 and U216 9 through U216 15 look like the DIGIT DATA waveform 6 54 8 Bit Digit Driver 0218 Check that U218 1 through U218 4 all look like the waveform DIGIT DATA High level is 3 8V to 4 3V Check that U218 15 through U218 18 all look like the waveform DIGIT DATA except that the high level should be approximately 30V 6 55 Hex Inverter 0203 At this point the display should be unfrozen by pressing any button The instrument should then complete the power up self test and begin normal operation Then do the following 1 Check that U203 9 is the same as STROBE ONE and that U203 10 is STROBE ONE inverted 2 Check that U203 5 is the same as STROBE TWO and that U203 6 is STROBE TWO inverted 3 Check that U203 11 shows positive pulses 50 us to 300 us while repeatedly pushing front panel buttons in normal mode and that U203 10 shows the inverse 4 Check that the waveform seen at U208 15 is the same at U203 13 4 and inverted at U203 3 12 6 50 6 56 Hex Inverter 0221 Check that U221 5 is the same as STROBE ZERO and that U221 6 is STROBE ZERO inverted 6 57 Quad OR Gate U211 Check U211 6 for 0 2 us pulses normally high in two groups of 3 and 15 group widths 50 and 100 us group spacing 10 ms in fast reading rate Check U211 8 for 0 4 us pulses normally high groups of hundreds group widths 3 5 4 ms group spacing about 8 ms variable 6 58 Keyboard
273. t is described in detail under the heading Troubleshooting All five digital tests are performed at powerup NOTE The inputs must be left open circuited while the self tests are performed Otherwise the 8842 may indicate errors are present Errors may also be caused by inductive or capacitive pick up from long test leads If the FRONT REAR switch is in the REAR position the 8842A skips tests 3 and 4 Also if Option 09 is not installed the 8842A skips tests 1 2 and 3 6 4 Maintenance PERFORMANCE TEST To initiate the self tests press the SRQ button for 3 seconds The TEST annunciator will then light up and the 8842A will run through the analog tests in sequence Each test number is displayed for about 1 second The instrument can be stopped in any of the test configurations by pressing the SRQ button while the test number is displayed Pressing any button continues the tests After the last analog test is performed all display segments light up while the instrument performs the in guard program memory calibration memory and display tests The instrument then assumes the power up configuration VDC autorange slow reading rate offset off local control If the 8842A detects an error during one of the tests it displays the ERROR annunciator and the test number for about 2 1 2 seconds and then proceeds to the next test The test number thus becomes an error code Error codes are listed in Table 2 1 Section 2 Passing a
274. t scales the equivalent dc voltages for in range inputs to within the input range of the A D Converter 2V In addition the DC Scaling circuit provides input protection and provides analog filtering for certain ranges and reading rates AC inputs are scaled by the True RMS AC Option The Track Hold T H circuit samples the scaled dc voltage and presents the A D Converter with a voltage that is constant for the input portion of each A D conversion cycle The T H circuit also provides additional scaling for certain ranges The Digital Controller controls the operation of virtually every part of the 8842A It reads the front panel keyboard configures the instrument for each function and range triggers the A D Converter calculates the result of each A D conversion cycle averages A D samples controls the display and communicates with the IEEE 488 Interface Option via the Guard Crossing circuit The heart of the Digital Controller is the In Guard Microcomputer uC The Guard Crossing circuit permits serial asynchronous communication between the Digital Controller and the IEEE 488 Interface Option while isolating the two circuits electrically Whereas the in guard power supply floats with the voltage at the INPUT LO terminal the IEEE 488 Interface Option operates with reference to earth ground The guard is the isolation between the in guard and out guard circuits The Power Supply provides supply voltages to all parts of the instrument
275. tched on with the CAL ENABLE switch in the enabled position the 8842A may require recalibration 10 Position the slot in the lower edge of the Line Voltage Selection Switch PCA in the slot on the lower rear panel standoff Secure the top of the Line Voltage Selection Switch PCA to the upper standoff using the single mounting screw and plug the ribbon cable into the Main PCA 11 Connect the power supply ground lead to the rear panel mounting stud The stud is located near the rear panel power receptacle as shown in Figure 6 6F WARNING TO AVOID ELECTRIC SHOCK ENSURE THAT THE POWER SUPPLY GROUND LEAD IS FIRMLY ATTACHED TO THE REAR PANEL MOUNTING STUD 12 Attach the two mounting screws on either side of the rear panel power receptacle 13 Connect the two ribbon cables to the Display PCA to the connectors Push the cables straight in to avoid damage 14 Reinstall the harness in the sidewall cable guide and secure the harness to the chassis with the cable clamps 15 Connect the leads to the four front panel input terminals according to the color codes marked on the rear side of the Display PCA 16 Connect the leads to the four rear panel input terminals following the color codes as shown in Figure 6 6B 17 Option 05 only Install the IEEE 488 Interface PCA according to the instructions in Section 8 18 Option 09 only Install the True RMS AC PCA according to the instructions in Section 8 19 Slide the case and re
276. th a finger pop the push rod off the switch plunger by pulling the push rod directly upward b Rotate the push rod 90 degrees toward the center of the instrument c Pull the push rod toward the rear panel and remove it Remove the FRONT REAR switch push rod as follows Figure 6 61 a Insert blade type screw driver in the slot visible on the top of the FRONT REAR switch push rod at the junction of the push rod and the switch b Twist the screwdriver slightly to release the push rod from the switch shaft then pull the FRONT REAR switch push rod out through the front panel Place the chassis on its side Remove the POWER switch push rod as follows Figure 6 6J a Insert blade type screwdriver in the slot visible on the top of the POWER switch push rod at the junction of the push rod and the switch b Twist the screwdriver slightly to release the push rod from the switch shaft then pull the rear of the POWER switch push rod out through the bottom of the chassis c Lift the push rod out and toward the rear panel and remove it Remove the two screws fastened to the transformer bracket then remove the bracket Remove the Main Shield as follows Figure 6 6K a Remove the screw that fastens the Main Shield to the Main PCA b Grasp the Main Shield supports on one side of the instrument and pull the supports toward the center of the chassis bowing the Main Shield Remove the main shield Release the six plastic latches t
277. th the 8842A and an ac coupled oscilloscope If the rms reading the 8842A is 1 3 or more of the waveform s zero to peak voltage the crest factor is 3 0 or less 4 19 AC Coupled AC Measurements Input signals are ac coupled in the ac functions One of the advantages of ac coupling is that ac measurements can be made on power supply outputs phone lines etc Ripple 4 20 4 21 4 22 Measurement Tutorial AC VOLTAGE AND CURRENT MEASUREMENT measurements for instance cannot be made with dc coupling Remember however that when the 8842A measures signals with the ac functions the reading on the display does not include the dc component if one exists For example consider Figure 4 8 which shows a simple ac signal riding on a de level The VAC function would measure the ac component only AC COMPONENT DC COMPONENT RMS Total rms Component dc component f4 08 wmf Figure 4 8 Combined AC and DC Measurement Combined AC and DC Measurements The 88424 can be used to evaluate the true rms value of waveforms such as the one shown in Figure 4 8 which includes both ac and dc components First measure the rms value of the ac component using the VAC function Next measure the dc component using the VDC function Finally calculate the total rms value as follows V nus AJ Vpc P Bandwidth Bandwidth defines the range of frequencies to which an instrument can respond accurately The accuracy of the
278. the interface message GET Group Execute Trigger SUFFIX FORMAT Function Indicator gt Reading is overrange gt 200 000 counts lt space gt Reading is not overrange but can be over voltage gt 1000 Vdc or 700 Vac Leading Comma Always present in suffix Most versions of BASIC expect multiple input values to be separated by commas e g input I S to acquire the numeric portion and suffix string f3 06 wmf Figure 3 6 Output Data Format COMMAND GO Frist F t 6asinFunioncommands Fn OUTPUT STRING Frst Remote Programming DEVICE DEPENDENT COMMAND SET Table 3 1 Status Data MEANING 1 Funtion commands Fn 9 for Self Test r 1 6 and 8 in Range commands Rn s 0 2 as in Reading Rate commands Sn t 0 4 as in Trigger Mode commands Tn G1 nn 00 for SRQ disabled default 01 for SRQ on overrange 04 for SRQ on front panel SRQ 08 for SRQ on cal step complete 16 for SRQ on data availible 32 for SRQ on any error Note SRQ mask values may be added for combinations Example 33 for SRQ on overrange or any error G3 G4 G5 G6 aaaaaaaaaaaaaaaa 10yw 16 user defined ASCII characters 0 Not in cal verification 1 Cal verification 0 Not in calibration mode 1 A D calibration 2 Offset and gain calibration 4 HF AC calibration 0 FRONT inputs selected 1 REAR inputs selected OAutorange on 1 Autorange off manual range 0 OFFSET o
279. the off resistance should be greater than 10 MQ Forcing the control lines high or low should cause the reading to change when the voltages in Table 6 27 are applied to the input terminals at 100 KHz If only certain ranges cannot be calibrated refer to Table 6 26 to find the suspected stage Guard Crossing Troubleshooting To troubleshoot the Guard Crossing circuit place the 8842A in the In Guard Troubleshooting Mode as described under Digital Controller Troubleshooting earlier in this section This causes the In Guard uC to send a test pattern to the IEEE 488 Interface PCA via one half of the Guard Crossing circuit You should be able to observe the waveforms shown in the left half of Figure 6 21 To troubleshoot the second half of the Guard Crossing circuit leave the 8842A in the In Guard Troubleshooting Mode This causes the IEEE 488 Interface PCA to send a test pattern to the In Guard HC You should be able to observe the waveforms shown in the right half of Figure 6 21 The IEEE 488 Interface PCA sends the test pattern in response to the test pattern sent by the In Guard uC therefore the first half of the Guard Crossing Circuit which was tested in the previous paragraph must be working properly before the second half can be tested 6 76 INTERNAL CLEANING 6 77 CAUTION Failures due to electrostatic discharge can be caused by improper handling of the PCAs and by the use of a vacuum cleaner with static inducing brushes To pr
280. the IEEE 488 bus proceed as follows 1 Turn the 8842A POWER switch OFF and set the 8842A IEEE 488 address using the rear panel IEEE 488 address switches shown in Figure 3 1 2 With the 8842A POWER switch OFF plug the IEEE 488 cable into the 8842A rear panel IEEE 488 connector 3 Switch on the 8842A 3 3 8842A Instruction Manual ADDRESS lt DD 5 1 TALK ONLY A 5 4 2 1 5 4 2 1 5 4 2 1 D A DIA D A D L DIL D L R K R K R K E E E s s N s s N s L s N L L Y Y Y 00 0 0 0 0 0 11 0 0 1 0 1 1 22 0 1 0 1 1 O 01 0 0 0 0 0 1 12 0 1 1 0 0 23 0 1 0 15 1 1 02 0 0 0 0 1 0 13 0 1 1 0 1 24 0 1 1 0 0 03 0 0 04 705 14 0 0 1 1 1 25 0 1 1 0 1 04 0 0 0 1 0 0 15 0 1 1 1 1 26 0 1 1 0 1 05 0 0 0 1 0 1 16 0 1 0 0 0 0 27 0 1 1 0 1 1 06 0 0 1 1 17 1 0 0 0 1 28 0 1 1 1 0 O 07 0 0 d d 18 1 0 0 1 0 29 0 1 1 1 0 1 08 0 0 1 0 0 0 19 0 1 0 0 1 1 30 0 1 1 1 1 09 0 0 1 0 1 20 1 0 1 0 0 81 Not allowed 10 0 0 1 0 1 21 0 1 0 1 1 TALK 1 X X X X X ONLY setting does not matter f3 01 wmf Figure 3 1 IEEE 488 Address Selection Whenever the 8842A is in the local state the IEEE 488 address be displayed on the front panel by pressing the LOCAL button 3 4 AN OVERVIEW OF REMOTE OPERATION An overview of remote operation is presented in the block diagram in Figure
281. the last command in a given command string The 8842A will ignore any subsequent commands in the same command string When the self tests are complete and no errors have occurred the serial poll register will have bit 5 Data Available true and bit 6 Any Error false See paragraph 3 50 for more about the serial poll register 3 34 Device Clear Command The asterisk command is a device dependent message which resets the 8842A to the power up default settings and clears all registers and buffers except for the input buffer The remote local status remains unchanged The asterisk command performs the following Implements the default settings 1 RO SO TO DO BO YO WO Clears the error status register equivalent to Zeros the SRQ mask prohibiting service requests equivalent to NO P1 Zeros the numeric entry register equivalent to NO Zeros the serial poll register Sets the SRQ line false The asterisk command is executed in its proper turn in a string just like any other command without affecting the contents of the input buffer All commands which precede the asterisk command are performed The asterisk command is useful to ensure that the 8842A is initialized to the same state each time a program is run By contrast the similar interface messages DCL Device Clear and SDC Selected Device Clear cause the entire input buffer to be cleared immediately DCL SDC and the asterisk command
282. thoroughly To trace the signal lock the instrument into one range 200 mV is usually a good choice and apply the appropriate voltage shown in Table 6 27 to the HI and LO INPUT terminals The input voltage should appear unchanged at pin Z801 1 and should appear at TP801 and TP802 as shown in Table 6 27 If no ranges work it is likely that the rest of the scaling circuitry U806B is functional 8842A Instruction Manual f6 20 wmf Figure 6 20 Option 09 Service Position If the signal at the input to U801A pin 5 is incorrect U804 may be defective or the switch codes may be wrong If the latter problem is suspected refer to Table 6 28 and test the control lines to U804 U804 1 8 9 16 If a logic error is found it may be due to excessive loading or a faulty data latch U803 or other cabling or main board digital problems High frequency oscillation problems are usually caused by switches being on when they should be off resulting in positive feedback loops being closed around portions of the scaling circuitry Table 6 27 AC Signal Tracing RANGE INPUT VOLTAGE 1 VOLTAGE AT TP801 VOLTAGE AT TP802 kHz 200 mV 100 mV 20 mV 1V 2 1V 200 mV 1V 20V 10V 2 1V 200V 10V 20 mV 100 mV 700V 100V 200 mV 100 mV If the signal at TP802 is incorrect but U801 5 is OK the digitally controlled filter section U801A and U808 is probably defective Maintenance TROUBLESHOOTING Table 6 2
283. ting eese Track Hold Troubleshooting eere Ohms Current Source Troubleshooting Precision Voltage Reference Troubleshooting A D Converter Troubleshooting eee Power Supply Troubleshooting een 488 Interface Troubleshooting Option 05 SERVICE POSITION DIAGNOSTIC PROG True RMS AC Troubleshooting Option 09 SERVICE POSITION MAJOR PROBLEMS MORE 5 Guard Crossing Troubleshooting 2 INTERNAL CLEANING Cleaning Printed Circuit Cleaning After Soldering esDOOLlnp RAM Maintenance INTRODUCTION WARNING THESE SERVICE INSTRUCTIONS ARE FOR USE BY QUALIFIED PERSONNEL ONLY TO AVOID ELECTRIC SHOCK DO NOT PERFORM ANY PROCEDURES IN THIS SECTION UNLESS YOU ARE QUALIFIED TO DO SO 6 1 INTRODUCTION This section presents maintenance information for the 8842A The section includes a performance test a calibration procedure troubleshooting information and other general service information Test equipment recommended for the performance test and calibration procedure is listed in Table 6 1 If the recomme
284. ting supports specially provided on the chassis DIAGNOSTIC PROGRAM To facilitate troubleshooting the IEEE 488 Interface provides a diagnostic program which places the instrument in known configurations To initiate the diagnostic program proceed as follows CAUTION To avoid damage to the 8842A or other equipment the 8842A must be disconnected from all other IEEE 488 Interface instruments while the diagnostic program is running Ensure the 8842A POWER switch is OFF Disconnect all cables from the rear panel 488 connector Short TP903 to TP905 Power up the 8842A The 8842A should display ERROR 50 To exit the troubleshooting mode open the jumper and cycle the POWER switch from off to on eee Once the diagnostic program is started rear panel IEEE 488 address switches 2 and 1 can be used to select one of four diagnostic modes as shown in Table 6 24 In this table Configuration indicates which Out Guard uC I O port bits are programmed as outputs and driven with a signal as shown in Table 6 25 Maintenance TROUBLESHOOTING f6 19 wmf Figure 6 19 Option 05 Service Position Table 6 24 Diagnostic Modes SWITCHES A3 A2 A1 CONFIGURATION 1 0 1 Static odd port bits 1 even port bits 0 1 1 1 Static odd port bits even port bits 1 1 X 0 Dynamic 0 X x Read Write NOTES e means switch setting does not matter Static means the Out Guard uC
285. tion 8 for instructions on removing it Rear Panel Insert SENSE Q 4 WIRE JOHN FLUKE CO INC 05 Wu 2407 EVERETT WA MADE IN U S A L AC 09 BE 220v 120V ents PENDING LINE FUS WARNING CAUTION 20v GROUNDING CONDUCTOR FOR FIRE PREVENTION IN POWER CORD MUST BE REPLACE ONLY WITH CONNECTED TO ENSURE 1 4 SLOW FUSE 100 120v PROTECTION FROM 1 8 A SLOW FUSE 220 240V ELECTRICAL SHOCK 20VA 50 60 400 Hz REMOVE GROUNDING SCREW BEFORE REMOVING COVER 2 06 wmf Figure 2 6 Rear Panel Features 2 7 8842A Instruction Manual 2 8 2 10 2 11 Display Features The 8842A features a vacuum fluorescent display with a numeric field and annunciators The annunciators are explained in Figure 2 5 Error Messages If the 8842A detects an operator error or an internal failure it displays an error message for about 2 1 2 seconds and then resumes normal operation During this time the front panel buttons are ignored The error message consists of the ERROR annunciator and a two digit error code See Figure 2 7 Error codes are explained in Table 2 1 If the FRONT REAR switch is set to the REAR position while the mA DC or mA AC function is selected ERROR 31 is displayed In this case the error message is displayed until you return the switch to the FRONT position or select another function Error 30 AC function select
286. to F3 R1 S2 TO Selects 2 WIRE kQ function 200Q range fast sample rate continuous trigger The PO command allows broadside loading of the Function Range Reading Rate and Trigger Mode commands F R S and T The codes for these commands are listed in Figure 3 5 A numeric entry for PO must be within 1000 and 6824 Each of the four digits must not exceed its maximum allowed value 6 8 2 and 4 respectively or an error message will occur and the instrument configuration will remain unchanged The entry may be expressed as an integer real number or real number with exponent as described under the N command Any fractional part is ignored Example Explanation N3112 PO Sets the 8842A to F3 R1 S1 and T2 P1 Put SRQ Mask Format Explanation N SRQ mask gt P1 Where lt SRQ mask gt is a two digit integer from 00 to 63 The P1 command is used to program the 8842A to make service requests on user specified conditions The two digit code for the SRQ mask is interpreted in Table 3 1 under the G1 command For more about the SRQ mask see paragraph 3 51 Numeric entries for the command must be between and 63 inclusive or an error will occur and the SRQ mask will remain unchanged The entry may be expressed as an integer real number or real number with exponent as described under the N command Any fractional part is ignored Example Explanation NO 17E 2 P1 Sets SRQ mask to 17 Enables SRQ on data available or
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288. tput 3 43 Numeric Data and Error Messages sese 3 44 3 45 OVERRANGE 3 46 ERROR MESSAGES 3 47 NICUI EBERT 3 48 Output Priority SCR 3 49 SERVICE REQUESTS 5 tete t 3 50 The Serial Poll Register 3 51 SRO Mask 3 52 INTERFACE 55 6 3 53 Address Messages eee seti 3 54 Universal Commands aaa 3 55 Addressed Commands eese 3 56 TALK ONLY 3 57 3 58 TIMING 5 3 59 IMMEDIATE MODE COMMANDS 3 60 5 3 1 Remote Programming INTRODUCTION NOTE This section contains programming instructions for use with the IEEE 488 Interface Option 05 For installation instructions refer to the Options and Accessories section
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290. ts in these functions are made in the 2000 mA range Triggering Triggering causes the 8842A to execute a measurement cycle and display the result During each measurement cycle the instrument samples the input a number of times and then averages the samples to compute a reading The number of samples averaged for each reading depends upon the reading rate Each time a reading is triggered the rate annunciator S M or F blinks off In the fast reading rate the F annunciator flashes so rapidly it appears to be almost constant How the 8842 is triggered depends on whether the continuous trigger mode or external trigger mode is selected Pressing the EX TRIG external trigger button toggles the 8842A between the two modes CONTINUOUS TRIGGER MODE In the continuous trigger mode readings are triggered by a continuous internal trigger The rate of the trigger is set by the RATE button EXTERNAL TRIGGER MODE In the external trigger mode readings are triggered by pressing the TRIG button If the 488 Interface option is installed readings can also be triggered by remote commands or by using the rear panel external trigger EXT TRIG connector See the Options and Accessories section In the external trigger mode pressing any front panel button blanks the numeric field on the display until a new measurement is triggered This ensures that all readings correspond to the instrument configuration indicated by the display annun
291. turn CR Line Feed LF and End Or Identify EOI CR and LF are ASCII control codes sent over the data lines just like output data EOI is a uniline message which is sent simultaneously with the last character in the output string Normally each output string is terminated with CR followed by LF and EOI The terminator selection can be read using the G6 command The 8842A defaults to WO on power up and any device clear command Clear Error Register Command The command clears the 8842A s error status register After an XO command is executed a G7 command Get Error Status would return 1000 no errors Note that the error status register is also cleared when any device clear command DCL or SDC is executed However is useful for clearing the error status register without forcing a complete instrument clear as do the device clear commands Yn Suffix Commands The Suffix commands enable or disable a suffix which the 8842A can append to all numeric data the data in response to G2 or trigger commands The suffix includes a comma an overrange indicator gt and a function indicator VDC VAC OHM IDC or IAC The suffix is illustrated in Figure 3 6 An example of suffixed data is given in paragraph 3 43 To read suffixed data with a controller using BASIC one can read the whole line into a string variable and then convert the numeric part into a numeric variable However it is much easier to read the
292. tween the test probe tips and the circuit being tested is unpredictable and therefore cannot be reliably corrected with a fixed offset Four Wire ohms measurements are especially important when using long test leads In a typical automated test system for example the test leads could be connected through four or five switching relays each with 2Q of resistance NOTE Instability of the test lead s resistance can cause significant error on low ohms ranges particularly on the 20 2 and 200Q ranges Therefore only 4 wire ohms measurement is permitted in the 200 range The 8842A makes 4 wire ohms measurements as shown in Figure 4 4 The HI and LO INPUT leads apply a known internal current source to the unknown resistance just as in 2 wire ohms See Table 4 1 However the voltage drop across the unknown resistance is measured with the SENSE leads rather than the INPUT leads Since the current flow in the SENSE leads is negligible the error caused by the voltage drop across the leads is also negligible 4 5 8842A Instruction Manual OHMS CURRENT SOURCE HI INPUT Q TEST R UNKNOWN O LO INPUT HI SENSE DC VOLTAGE SENSING CIRCUITRY LO SENSE OHMS CURRENT SOURCE LO INPUT R Four places R UNKNOWN 14 04 wmf Figure 4 4 Wire Ohms Measurement Table 4 1 Ohms Test Current RANGE TEST CURRENT FULL SCALE VOLTAGE 20 1 0 02V 2002 1 0 2V 2 ko 1 2 0V 20 ka 100 HA 2 0V
293. ulls line CS7 low five times causing U101 to send the uC the five six bit nibbles one at a time over lines ADO ADS The In Guard then weights each nibble 1 16 of the value of the previous number and calculates the input voltage The hardware for the A D Converter has four major sections Timing Data Control Precision DAC A D Amplifier and bootstrap supplies Timing Data Control The Timing Data Control circuit the digital portion of U101 times and controls the A D Converter by manipulating the switches in the A D Amplifier and the bit switches in the Precision DAC An A D conversion cycle is triggered by the falling edge of line TR from the In Guard uC Once triggered the A D Converter under control by U101 generates the five 6 bit nibbles without further interaction with the In Guard uC The Timing Data Control circuit also provides a watch dog timer line RES not which resets the In Guard HC in case normal program execution is interrupted If the timer senses inactivity on line CS7 for longer than 1 5 seconds it resets the In Guard uC by pulling RES not low The Timing Data Control circuit is supplied with a fixed rate 8 MHz clock and provides a 1 MHz output clock for the Keyboard Display Interface U212 In addition four output lines PC HD1 not TR1 and TR2 provide control signals for the Track Hold circuit Precision DAC The Precision Digital to Analog Converter DAC is composed of DAC Amplifier U102B and a binar
294. umulated test or reference data based on them The conversion factors in Figure 4 6 should help you convert between the two measurement methods 8842A Instruction Manual 4 18 Crest Factor Crest factors are useful for expressing the ability of an instrument to measure a variety of waveforms accurately The crest factor of a waveform is the ratio of its peak voltage to its rms voltage For waveforms where the positive and negative half cycles have different peak voltages the more extreme peak is used in computing the crest factor Crest factors start at 1 0 for square waves for which the peak voltage equals the rms voltage and increase for more pointed waveforms as shown in Figure 4 7 WAVEFORM CREST FACTOR SQUARE WAVE SINE WAVE TRIANGLE SAWTOOTH MIXED FREQUENCIES 1 414 to 2 0 SCR OUTPUT OF 100 10 1 414 to 3 0 WHITE NOISE 3 0 to 4 0 AC COUPLED PULSE TRAIN 3 0 14 07 Figure 4 7 Typical Crest Factors for Various Waveforms The 88424 has a full scale crest factor limit of 3 0 for the 20V and 700 ranges and 6 0 for the other ranges For full scale input signals with a crest factor above these limits dynamic range limitations can begin to cause large errors However as Figure 4 7 shows signals with a crest factor above 3 0 are unusual If you don t know the crest factor of a particular waveform but wish to know if it falls within the crest factor limit of the 8842A measure the signal with bo
295. unction Note that the input overload limits are not changed by the use of the offset feature However the display flashes if the 8842A is in the 1000V dc or 700V ac ranges and the input exceeds 1000V dc or 700V ac respectively While an offset is enabled the 8842A indicates an overrange condition if either of the following conditions occur e The input signal is overrange e The calculated reading is overrange For example suppose the instrument is in the 20V range of the VDC function and you store an offset of 15V The maximum positive voltage reading that can be displayed without overranging is 4 9999V which is actually a 19 9999V input signal The maximum negative voltage reading that can be displayed without overranging is 19 9999V which is actually a 4 9999V input signal You can measure a greater range of voltages by selecting a higher range When in autorange the 8842A selects the range appropriate for the input signal regardless of any stored offset If for example a 10V offset is stored and a 1 V input is applied the 8842A will autorange to the 2V range and display an overrange condition since it cannot display 9V on the 2V range Manual range control could be used to lock the 8842A into the 20V range in this case Applications of the offset feature include correcting for test lead resistance in 2 wire resistance measurements nulling offset currents or voltages measuring voltage deviations and matching resistors
296. unction by pressing the corresponding function button The 8842A will display the first prompt for that function 3 Each time the 8842A prompts you for a reference source apply this source to the appropriate terminals and press the STORE button When STORE is pressed the numeric display field blanks while the 8842A performs the necessary calculations Do not change the reference source while the display is blank The 8842A then displays the next prompt For reference all prompts are shown in Table 6 10 4 6 Maintenance CALIBRATION NOTE To use reference sources that differ from the prompted values see Storing Variable Inputs later in this section After the last range is calibrated the 8842A begins taking readings in the highest range so that you may verify its calibration The CAL annunciator remains on To verify the calibration for the other ranges press the corresponding range button Pressing a function button begins the Offset and Gain Calibration procedure for that function Repeat steps 2 3 and 4 for the remaining functions Note that both 2 wire and 4 wire ohms functions must be calibrated The VAC and mA AC functions require calibration only if the True RMS AC option is installed NOTE True RMS AC option only The VAC and mA AC functions should normally be calibrated using reference sources at 1 kHz 10 For special applications performance may be optimized at other frequencies See Optimizing
297. unts 23 5 C for sinewave inputs 210 000 counts FREQUENCY IN HERTZ Typically 20 kHz frequencies 20 Hz to 5 kHz typically 20 KHz 20 45 45 100 100 5K ONE YEAR 2 0 200 0 5 200 0 4 200 TWO YEAR 3 0 300 0 7 300 0 6 300 1 For sinewave inputs between 1 000 and 10 000 counts add to number of counts 100 counts for Introduction and Specifications SPECIFICATIONS MEDIUM AND FAST READING RATES NONSINUSOIDAL INPUTS In medium rate add 50 counts to number of counts In fast reading rate for sinewave inputs 21000 4 digit mode counts and frequencies gt 100 Hz the accuracy is 0 4 of reading 30 4 digit mode counts For nonsinusoidal inputs gt 10 000 counts with frequency components lt 100 kHz add the following of reading to the accuracy specifications Operating Characteristics TEMPERATURE COEFFICIENT MAXIMUM INPUT FUNDAMENTAL CREST FACTOR FREQUENCY 1 0 TO 1 5 1 5 TO 2 0 2 0 TO 3 0 45 HZ to 5 kHz 0 05 0 15 0 3 20 Hz to 45 Hz 0 2 0 7 1 5 Less than 0 1 x accuracy specification per C to 18 C and 2 8 C to 50 C 2A dc or rms ac Protected with 2A 250V fuse accessible at front panel and interval 3 600V fuse BURDEN VOLTAGE RESISTANCE 1 Input Characteristics RANGE FULL SCALE 5 DIGITS V dc or rms ac typical at full scale 5 DIGITS RESOLUTION CURRENT 4 DIGITS THROUGH UNKNOWN 200 19 999 200 199 9990
298. ut and for those with limited experience with IEEE 488 bus operations As a general note The entire 8842A command set should work well provided the port clear and device clear commands are given first You should then be able to send any other commands in the 8842A command set without repeating the clearing commands 3 31 8842A Instruction Manual Table 3 3 Immediate Mode Commands for Various Controllers FLUKE BASIC on FUNTION HP HPL on HP BASIC on TEK BASIC on PERFORMED 1720A or 1722A HP9825 HP9816 PC and HP 4051 Graphics Calculator 85 Calculator System INITIALIZE Port INIT PORT 0 cli 7 CLEAR 7 INIT CLEAR Instrument CLEAR 4 cir 704 CLEAR 704 PRINT 4 REMOTE Commands REMOTE 4 rem 704 REMOTE 704 WBYTE 36 17 LOCAL Control LOCAL 4 Icl 704 LOCAL 704 WBYTE 936 1 EXTERNAL TRIGGER PRINT 4 1 wrt 704 1 OUTPUT 704 T1 PRINT 94 T1 TRIGGER Instrument TRIG 4 trg 704 TRIGGER 704 PRINT 4 GET Output Data INPUT 4 A red 704 ENTER 704 A Note 2 INPUT 4 A PRINT Data to Screen PRINT A prt A PRINT A Note 2 PRINT A CONFIGURE for VAC PRINT Q4 F2 wrt 704 F2 OUTPUT 704 F2 PRINT 4 2 CONFIGURE for PRINT 4 4 wrt 704 R4 OUTPUT 704 R4 PRINT Q4 R4 200Vac TRIGGER Continuously PRINT 4 TO wrt 704 TO OUTPUT 704 TO PRINT Q4 TO SUFFIXES Enable PRINT 94 Y1 wrt 704 Y1 OUTPUT 704 Y1 PRIN
299. ut bias current itself las be calculated as follows Vernon leas SOURCE f4 02 wmf Figure 4 2 Measuring Input Bias Current Error With the 88424 it is easy to correct for this error using the OFFSET button 1 Select the VDC function and the desired range 2 Connect the 8842A INPUT terminals to a resistor which matches the source impedance of the circuit to be tested 4 3 8842A Instruction Manual 4 5 4 4 3 Allow the displayed reading to settle 4 Press the OFFSET button 5 Remove the resistor 6 Proceed with the desired measurement Example Measure a 1 5V source with 1 M source impedance correcting for input bias current Connect a 1 MQ resistor between the INPUT HI and INPUT LO terminals Select the VDC function and the 2V range Allow the display to settle Press OFFSET This zeroes the input bias current error Duta es ES Remove the 1 MQ resistor 6 Measure the voltage of the circuit under test Note that this procedure does not correct for circuit loading error Also note that if input bias current error is not corrected for it may be added to the circuit loading error RESISTANCE MEASUREMENT The 8842A allows you to measure resistance in both 2 wire and 4 wire configurations Each has its benefits 2 Wire Ohms Two Wire ohms measurements are simple to set up and yield good results for most measurement conditions Measurements are made as shown i
300. w low 450 END f3 14 01 wmf Figure 3 14 Example Programs Using the IBM PC cont 3 38 Remote Programming EXAMPLE PROGRAMS 10 REM The following application program is written in BASICA for the IBM PC PC XT or 20 REM PC AT The National Instruments Model GPIB PCIIA board provides the interface 30 REM between the PC and the Fluke 8842A DMM The program assumes that the configuration 40 REM program IBCONF has been run to initialize the interface board with the device 50 REM name 18842 assigned to the GPIBO board 60 REM 70 REM The first 6 lines of code are required to properly link the NI drivers to BASICA 80 REM 90 REM This program illustrates one possible use of the serial poll register In this 100 REM case it is merely looking for data available The function of the program is to 110 REM display on the screen the lowest resistance value measured on the input terminals 120 REM of the 8842A using the 2 wire ohms function in autorange The range and function 130 REM commands are programmed using the Put Instrument Configuration PO command 140 REM 150 CLEAR 59736 160 IBINIT1 59736 170 IBINIT2 IBINIT1 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 IBFIND IBTRG IBCLR IBPCT IBSIC IBLOC IBPPC IBBNAJBONL IBRSC IBSRE IBRSV IBPAD IBSAD IBIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF 200 CALL IBINIT2 BGTS IBCAC IBWAIT IBPOKE IBWRT IBWRTA BCMD IBCMDA IBRD IBRDA IBSTOP IBRPP IBRSP IBDIAG IBXTRC IBRDI IBWRTI IBRDIA IBWR
301. window from the front panel as follows a Slide the window upward away from the buttons about 1 32 inch Figure 6 8A b Push the window directly outward from the front panel Figure 6 8B 6 33 REASSEMBLY PROCEDURE To reassemble the instrument proceed as follows 1 Assemble the front panel assembly by reversing the front panel disassembly procedure Figure 6 7 It is easiest to lay the keypad on the Display PCA before installing the spacer matrix on the Display PCA CAUTION The four Display PCA mounting screws are self tapping To avoid damaging the threads ensure the screws are threaded properly before tightening Do not overtighten them 2 Turn the chassis upside down 3 Install the PCA through the bottom of the chassis as follows 6 32 Maintenance REASSEMBLY PROCEDURE NOTE When installing the Main PCA guide the rear ribbon cable around the shield connected to the rear panel so that the cable is next to the side of the chassis Make certain that the cable is not pinched between the shield and the Main PCA a Slide the Main PCA toward the rear panel and position the power connector and fuse to fit through their respective openings in the rear panel b Reinstall the white lead in the 2A INPUT tower and reinstall the 2A fuse in the front panel c Make sure the six plastic latch heads are extended Lower the Main PCA into position on the chassis and guide the six plastic latches into the circuit bo
302. wing application program is written in BASICA for the IBM PC PC XT or 20 REM PC AT The National Instruments Model GPIB PCIIA board provides the interface 30 REM between the PC and the Fluke 8842A DMM The program assumes that the configuration 40 REM program has been run to initialize the interface board with the device 50 REM name 18842A assigned the GPIBO board 60 REM 70 REM The first 6 lines of code are required to properly link the NI drivers to BASICA 80 REM 90 REM 100 REM This program selects VDC F1 Autorange RO Slow rate SO Continuous trigger TO 110 REM and suffixes enabled Y1 The program takes 10 readings displays them on the screen 120 REM and then stops 130 REM 140 REM 150 CLEAR 59736 160 IBINIT1 59736 170 IBINIT2 IBINIT1 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 IBFIND IBTRG IBCLR IBPCT IBSIC IBLOC IBPPC IBBNA BONL IBRSC IBSRE IBRSV IBPAD IBSAD IBIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF 200 CALL IBINIT2 IBGTS IBCAC IBWAIT IBPOKE IBWRT IBWRTA IBCMD IBCMDA IBRD IBRDA IBSTOP IBRPP IBRSP IBDIAG IBXTRC IBRDI IBWRTLIBRDIA IBWRTIA IBSTA IBERR IBCNT 210 REM 220 REM IBM BASICA on IBM PC PC XT or PC AT 230 REM 240 18842 Device name is 18842A 250 CALL IBFIND DEVNAME DVM Initialize the DMM 260 CALL IBCLR DVM Clear the device 270 FOR W 1 TO 500 NEXT W Wait 1 second before sending command 280 WRTS F1ROSOTOY1 290 CALL IBWRT DVM WRT
303. witches that are supposed to be closed in that range If the Ohms Current Source then works one of the analog switches is probably bad If the range still doesn t work then Z401 is probably bad To test the first stage of the Ohms Current Source short U402 19 to Reference Low through a 2 kQ resistor and check that the voltage across R401 is 7 0V nominal and that the voltage at U401 6 is 4V nominal If the voltages are correct the first stage of the Ohms Current Source U401 and Q401 is working If not suspect U401 or Q401 Under no circumstances should U401 6 ever be positive If the first stage of the Ohms Current Source is working test the second stage as follows 1 Select the 20 kQ range and apply a 10 kQ input 2 Check that the voltage between TP403 and U402 16 is 5V 3 Measure the voltage at U404 6 with respect to ground If the voltage at U404 6 is negative U404 is bad Under no condition should U404 6 ever be negative Precision Voltage Reference Troubleshooting If there is a failure of the Precision Voltage Reference check the power supply levels at U702 U702 requires two supplies 15V and 15V which must be within approximately 5 of their nominal value Using an oscilloscope check that the power supplies and op amp outputs U702 1 and U702 7 are free from ripple and oscillations If the supplies are correct check the output voltage levels at TP701 and TP702 The voltages should be 7 00000V 1000 ppm
304. wn for each reading rate 5 Set the AC Current Source to Standby and disconnect it from the 8842 Table 6 7 AC Current Test STEP RANGE INPUT TEST LIMITS NUMBER CURRENT FREQUENCY MINIMUM MAXIMUM 1 2000 mA 1900 00 mA 1 kHz 1890 40 1909 60 2 2000 mA 100 00 mA 1 kHz 97 60 102 40 6 9 CALIBRATION CAUTION To avoid uncalibrating the 8842A never cycle power on or off while the CAL ENABLE switch is on NOTE If U220 is replaced perform the Erase Cal Memory procedure located later in this section before attempting calibration Failure to do so may result in an ERROR 29 on the 8842A front panel display The 8842A features closed case calibration using known reference sources The 8842A automatically prompts you for the required reference sources measures them calculates correction factors and stores the correction factors in the nonvolatile calibration memory Closed case calibration has many advantages There are no parts to disassemble no mechanical adjustments to make and if the IEEE 488 Interface is installed the 8842A can be calibrated by an automated instrumentation system The 8842A should normally be calibrated on a regular cycle typically every 90 days or 1 year The frequency of the calibration cycle depends on the accuracy specification you wish to maintain The 8842A should also be calibrated if it fails the performance test or has undergone repair To meet the specifications in Section 1 the
305. y A complete calibration must then be performed RATE SO through S2 Changes the reading rate while the 8842A is taking verification readings Causes an error at any other time during calibration VAR IN N lt value gt P2 Enters lt value gt as a variable input See Entering Variable Inputs in text Causes an error if sent during A D Calibration or when the 8842A is taking verification readings You can check that the command was successful by checking the error status or by sending the Get Calibration Input command G2 P3 lt string gt Puts the lt string gt into calibration memory The string must contain up to 16 ASCII characters and be recalled with the G3 command commands and XO clear Error Register NOTE Other commands that may be used during calibration are P1 Put SRQ mask the remaining Get 6 21 8842A Instruction Manual 6 22 1 In remote calibration you can store a 16 character message in the calibration memory which can be read by the system controller Possible uses include storing the calibration date instrument ID etc 2 Although some buttons are ignored in local calibration e g the AUTO button the corresponding remote commands e g RO load the output buffer with an error message 3 The calibration memory is erased differently This is explained later The rear panel SAMPLE COMPLETE signal acts slightly differently During calibration the SAMPLE
306. y ladder network which consists of resistors in Z101 and digitally controlled analog bit switches contained in U101 8842A Instruction Manual 5 23 5 24 The bit switches determine the output voltage of U102B by controlling the binary ladder network The gain of U102B is set by the ratio of a precision feedback resistor Z101 7 8 and the equivalent output resistance of the ladder network A D Amplifier The A D Amplifier is composed of a comparator amplifier U103 two remainder storage capacitors C103 and C102 an autozero storage capacitor C101 and several digitally controlled analog switches contained 0101 The A D Amplifier has three modes of operation autozero mode where any offsets in the A D input are stored on C101 so as to be cancelled later compare mode where the A D input is compared to the DAC output and remainder store mode where U103 amplifies and stores the difference between the A D input and the DAC output on one of the two remainder storage capacitors C102 or C103 The autozero mode is shown in Figure 5 11 The other modes are shown in Figures 5 9 and 5 10 PRECISION DAC A D AMPLIFIER Z101 15 238K Z101 40 667K C101 f5 11 wmf Figure 5 11 Autozero Period Bootstrap Supplies The bootstrap supplies are composed of U102A Q101 Q102 CR103 CR104 and associated components The bootstrap supplies enhance the gain accuracy of U103 During compare periods the bootstrap supplies li
307. yboard appear to be malfunctioning then they should be checked next See Display System below If the display and keyboard are functioning correctly you can omit Display System troubleshooting and proceed to verify that signals are arriving correctly at the inputs of the analog control devices See Analog Control Signals below If these are also correct the digital controller is functioning correctly and you can proceed to the appropriate analog troubleshooting procedure NOTE For the convenience of the following tests Options 05 and 09 should be removed if present They should only be removed in the power off condition IN GUARD MICROCOMPUTER SYSTEM This procedure is performed entirely in the In Guard Troubleshooting Mode This mode is established by shorting TP205 U202 38 to Reference Low TP306 or the L shaped shield around U202 prior to turning on the instrument Refer to Figure 6 9 To maintain this mode the short must remain in effect after the instrument is turned on When this is done the programs U202 38 as an input it is normally an output to preclude any possibility of damage due to the short CAUTION To avoid damaging the uC the short must be initiated before the instrument is turned on not after The In Guard Troubleshooting Mode also programs all the normal port outputs to display a 1 kHz square wave except that the IEEE 488 output U202 4 sends the word 55 repeatedly at a rate of 2 000 words sec
308. ys in local when an ibrd call is made get data increment reading count display readings 8 14 09 wmf Figure 3 14 Example Programs Using the IBM PC cont Remote Programming EXAMPLE PROGRAMS The following application program is written in C for the IBM PC AT The National Instruments Model AT GPIB board provides the interface between the PC and the Fluke 8842A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18842A assigned to the GPIBO board This program illustrates one possible use of the serial poll register In this case it is merely looking for data available The function of the program is to display on the screen the lowest resistance value measured on the input terminals of the 8842A using the 2 wire ohms function in autorange The range and function commands are programmed using the Put Instrument Configuration 0 command Microsoft C Version 6 0 on IBM PC AT Link this program with appropriate mcib obj include lt stdio h gt include decl h include lt string h gt include lt math h gt char 512 read data buffer int brdO interface board number int dmm device number char spr serial poll response byte float r s char rd string 11 ss 11 main brdO ibfind GPIBO initialize interface board dmm ibfind 18842A initialize 8842A ibclr dmm clear device i

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