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Fluke 8840A User's Manual

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2. 6 24 69 1202 Pin Diagi m sece px RI V Arie eee e 6 32 6 10 Waveforms for In Guard Troubleshooting 6 33 6 11 Waveforms for Display 1 ees 6 35 6 12 Typical Dynamic Control 5 RE RR eau ae aA 6 38 6 13 Typical Output Waveforms for Track Hold Circuit 103 6 40 6 14 Output of A D Amplifier 101 4444 6 41 6 15 Waveforms at 0101 24 and 0101 25 6 42 6 16 Typical Bus Data Line 6 43 6 17 Waveforms at TP102 for Several Inputs on 2V DV 6 43 6 18 Calculating the A D Reading From TP102 Waveform 6 44 6 19 Option 05 Service 6 45 6 20 Option 09 Service 4 4 2 6 47 6 21 Guard Crossing Test Waveforms 6 49 805 1 Installing Option 05 2 22 805 3 809 1 Installing Option 09
3. 6 10 6 12 Prompts When Calibrating Individual Ranges 6 11 6 13 Tolerance 6 ES 6 12 6 14 Commands Used During Remote P PEE 6 13 6 15 Error Numbers Which Are Displayed When Commands Are Not Valid 6 15 6 16 Overall State 6 26 6 17 Circuitry Tested by the Analog 6 28 6 29 di 6 36 6 20 Analog Control Devices 2 2 4 4 4 6 36 6 21 Analog Control Logic 2 2 2 22 2 2 2 6 37 6 22 DC Scaling and Track Hold Supply 6 38 6 23 Power Supply Voltages 6 44 6 24 Diagnostic Modes bd ending ors EO Er cw Eder san wed 6 45 6 25 Port 2 2 2 6 46 6 26 Isolating a Defective AC Stage 6 47 6 27 AC Signal 2 6 48 6 28 Truth Table for 0804 and 2
4. e 10j99uuo sng 40 pesind 887 333 AjeunoN 74 1 indjno 3131d4WOO Error 30 AC function Selected without True RMS AC Converter option RE MC ERR Figure 2 7 Typical Error Message 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 2 13 Diagnostic Self Tests The 8840A features diagnostic self tests which check both the digital and analog circuitry in the instrument The self tests consist of 21 analog tests followed by the in guard program memory calibration memory and display self tests To initiate the self tests press the SRO 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 cali bration memory and display self tests The 8840A 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
5. 3 3 3 3 Typical Command Sting ia toris eec 3 4 3 4 Commands Which Correspond to the Front eS 3 5 3 5 Device Dependent Command Set aet do 3 6 3 6 Output Data 3 8 3 7 Trigger Selection Logic 3 13 3 8 Interpretation of 3 6 39 Serial Poll Register ass OS 3 19 3 10 Example Program Taking 10 p 3 22 3 11 Program Taking Readings with Local Control etes 3 23 3 12 Example Program Using the Serial Poll 3 24 3 13 Example Program Record Errors During 3 25 3 14 Example Programs Using the IBM PC E 3 26 4 1 Circuit Loading Error ire etie E 42 4 2 Measuring Input Bias Current 43 4 3 2 Wire Ohms Measurement 4 4 4 4 4 Wire Ohms
6. 2 22 2 222 6 48 Sel lt lt 8 1 ONES ok 8 1 805 1 IEEE 488 Interface PCA 805 5 809 1 True RMS AC BCA on 809 3 List of Illustrations FIGURE TITLE PAGE ll DIMENSIONS lose e e xc baa ae 17 2 1 Line Voltage Selection Settings pP PTT 2 2 2 2 Adjusting the 2 2 2 3 Rack Mount ide awk e ruht 2 3 2 4 Installing the Single Rack Mount 2 3 eee 2 4 2 6 Rear Panel Features 2 6 2 7 Typical Message am etra du le itia 2 7 2 8 Overrange oie aes do els 2 9 2 9 Measuring Voltage and 2 11 2 10 Measuring ers use ety ree 3 1 488 Address Selection panna 3 2 3 2 Remote Operation Block
7. CHAANOO PL zz 22 1001 0 88 T1032 5925 DAYW3HTS ONS NOS 9 A esros 0 0 0585 9 382824200 N yu SWHO aL OL ANIA oo v 9 6059 Ol SWHO 2 aran o Swov2S ol OL MS OL BOWS SALN AWO GSIO cwvotd 9925 20 Swine oL egeotonar Carle ese er sate SEI EE Gzsn JON 1022 cont m wy o 469274 5588535 asvad ILWIS 1091 0888 9 6 WEN 5 6 zayn FL E Qu 1099 MHF 10980 4092 1006 ASY 8020 401 2120 1091 1094 017911010 261992 5025 50182 20782 BES 70142 Sora HOTO 250180 cor 5 E 1025 as c 2 gt 1020077 t 23 5028 3620 0253 5021 Te 592 T dit 3 702 E 1725 4128 EIN J 7022 EO n 052 Sunat Toun 1062 ot i CIH O x 01582 2
8. 3 12 3 32 Yn Suffix Commands 3 12 3 33 20 Self Test 3 14 3 34 3 14 3 35 Single Ttigger 3 14 2230 INPUT SYNTAX S cueste eere ERU DUNT C doen s 3 14 3 37 Definitions Sse SSS e A OS A SD E 3 14 3 38 Input Processing 4 HEE NEE 3 14 3 39 Syntax VEL qa eat le E 3 15 3 40 OUTPUT DATA er REA Sax i 3 17 3 41 Loading Output Data 3 17 3 42 Types of Output Data 3 7 3 43 Numeric Data and Error 3 17 3 44 MEASUREMENT et eden wae fal died bund vee 3 17 3 45 OVERRANGE INDICATION uu ue E 3 17 3 46 ERROR MESSAGES a an ab ewe a Ws 3 17 3 47 Stat s Dalasi eri E HRS 3 18 3 48 Output PHOUDI oe deed ene Epl Ad CRAT 3 18 3 49 SERVICE REQUESTS acesse 3 18 3 50 The Serial Poll aha ae 3 18 3 51 The Mask
9. ITEM MIELE NC 809 2 88404 Digital Multimeter Section 1 Introduction and Specifications 1 1 INTRODUCTION This manual provides complete operating instructions and service information for the 8840A If you want to get Started using your 8840A right away proceed to the operating instructions in Section 2 If you intend to use the 8840 with the IEEE 488 Interface Option 05 read Sections 2 and 3 1 2 THE 8840A DIGITAL MULTIMETER The Fluke 8840A Digital Multimeter is a high performance 5 1 2 digit instrument designed for general purpose bench or systems applications Features of the 8840A include Highly legible vacuum fluorescent display Intuitively easy front panel operation Basic dc accuracy of 0 00596 for 1 year 2 wire and 4 wire resistance measurement current measurement to 100 readings second Closed case calibration no internal adjustments Built in self tests 1 3 OPTIONS AND ACCESSORIES A number of options and accessories are available for the 8840A which can be easily installed at any time The options include IEEE 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 o o RMS AC Option 09 featuring
10. 2 gewys 033 093 R 5 29 2282 28 2385 88 5 Ry ee 0949 40945 E 1022 amp HI t 3 TO ha g 5 Ec LI 2 0250 2 0241 20 Sod 2025 2062 ZOEN 95 es 5 2095 454 m W3ONn 98020 801 2721 yann 2028 0281 Ajuo pesn 51 022 lt i 9092 oE 85 0 2050 TRO 0 90 2 Greg uae Ger 1091 00998 9 6 2 6 52 j 991 20984 g 55 38 5092 0 CT ROI 00940 Q io p t 3 onn GTZ 20 T TEI c 1050 _ 200 5 2094 1934 3356 5 5 301 9021 401 2220 60241 E 091 1099 d 603 aono A 0776110106 ISTI es uem ned 1060 Ba 029 2 EE FE dit 3 r2 OUO 2 5 2 ROM Acne 5 f 0 8 5 8 6069 9160 w 7
11. 3 6 3 13 G1 Get SRQ 3 6 3 14 G2 Get Calibration m 3 6 3 15 G3 Get User Defined 3 9 3 16 G4 Get Calibration 3 9 3 17 65 Get TAB Liab jn Geb 3 9 3 18 G6 Get YW 3 9 3 19 Statis Ca e idee ah 3 9 3 20 G8 Get Instrument Identification 3 9 3 21 Numeric Entry Sesso 3 10 3 22 Put e ae gr Teide lr hys 3 10 3 23 PO Put Instrument Configuration 3 10 3 24 P1 Pat SRO 3 10 3 25 P2 Put Calibration Value 3 10 3 26 Put User Defined Message 3 12 3 28 Sn Reading Rate Commands 3 12 3 29 Tn Trigger Mode lt 3 12 3 30 Wn Terminator 3 12 3 31 XO Clear Error Register
12. patada ens Y 22 28 Power Up 2 2 2 9 Front and Rear Panel 2 2 2 10 Display A 2 3 2 11 Error Messages 4 45 PES 2 3 2 12 Overrange jen dis e P aie SIR Ea nce 2 3 2 13 Diagnostic Self TestS 2 7 2 14 Ranging ez e e 2 7 2 15 25 me e i 27 2 16 MANUAL RANGE eor ad eee 2 7 2 17 Triggering e a a 2 7 2 18 CONTINUOUS TRIGGER MODE 2 7 2 19 EXTERNAL TRIGGER 2 7 2 20 Reading Rates and Noise 2 9 2 21 Automatic Settling Time 2 9 2 22 External Trigger Input Option 05 Only PUE Lek e d is 2 9 2 23 Sample Complete Output Option 05 Only 2 9 2 24 MAKING MEASUREMENTS ee LLL LLL MEER 2 9 2 25 Input Overload Protection Limits a000 ooo ouia deee 2 9 2
13. UU ed eiie 5 12 5 25 DISPLAY a SE ERE a 5 12 25 KEYBOARDLS ot 5 13 5 27 DIGITAL CONTROLLER be 5 13 Table of Contents SECTION TITLE PAGE 5 28 In Guard 5 13 5 29 Function and Range 1 5 15 5 30 A D Control and Computation 5 15 5 31 Calibration 5 15 5 32 Keyboard Display 5 15 5 33 Troubleshooting 5 15 5 34 Guard Crossing 5 15 5 35 GUARD CROSSING 2550500 5 15 5 36 POWER SUPPLY Grama dees teas 5 17 5 37 488 INTERFACE OPTION 05 5 18 5 38 Out Guard Microcomputer 5 18 5 39 Guard Crossing poc NEN 5 18 5 40 Bus Interface UE 5 18 5 41 Signal Conditioning OPE COENA uS 5 18
14. n n l n n n an mW aa WW oo o O O a n aca Maintenance Test PERFORMANCE TEST Notes 7 3 Instruction Manua Figure 7 1 8840A Digital Multimeter MP13 TP 8840A amp 1014 List of Replaceable Parts 7 MP7 88404 O9 E R OPTIONAL 8840A 1 4 INTERFACE OPTIONAL MP26 MP1 SEE H10 H27 MP2 DETAIL 1 SCALE 88404 2 014 Figure 7 1 8840A Digital Multimeter cont 7 5 8840 Instruction Manual A2 DISPLAY PCA a 88404 amp 8 of 4 TREE Figure 7 1 8840A Digital Multimeter cont List of Replaceable Parts 7 o ne 53 Bw o Xo H22 MP22 8840A amp 4 of 4 ORE Figure 7 1 8840A Digital Multimeter cont 77 8840 INSTRUCTION MANUAL AR701 C101 103 311 C104 105 205 C209 304 305 C404 604 606 C609 610 C202 203 617 C618 C204 602 608 C612 C210 C212 C301 306 C302 C303 C307 C308 C309 310 C312 C314 C402 C403 C601 C603 C605 607 C611 C701 CR101 102 201 CR202 306 307 CR309 311 313 CR103 104 613 105 106 203 CR206 301 302 CR401 404 615 CR701 CR303 CR304 305 CR308 310 CR402 403 CR405 CR601 606 608 CR61 1 CR607 612 CR614 CR616 CR617 H1 51 H12 H2 57 H3 H5 H6 J201 J202 J20
15. Periode sa r dU gota 5 13 5 12 Vacuum Fluorescent 2 2 2 2222222222 22 2211 5 13 5 13 Digital Controller Block Gah sn Sa 5 14 5 14 Read Write Timing Diagrams for Internal 5 16 5 15 Guard Crossing Circuit ob hee acs 5 17 5 16 IEEE 488 Interface Block 5 18 5 17 True RMS AC Option Block Diagram 5 19 5 18 True RMS 2 2 5 20 6 1 Connections for Kelvin Varley Voltage 6 3 6 2 First A D Calibration 6 7 6 3 Calibration Functions 1 2 2 24 4 25 6 8 6 4 Optimizing Use of the 5450 22 2 244 4 6 13 6 5 Example A D Calibration EROR aS 6 16 6 6 8840A 2 6 18 6 7 Front Panel Disassembly sa 6 23 6 8 Removing the Display Window
16. CCCCCC 5 pulses 5 1 khz lt lt lt 8279 35 9 car sense 2 1 khz A8 POO 1 khz Por 1 2 1 knz CC GG GC Ani 1 khz ohms CC CP04 1 khz fit 5 1 lt lt lt rom bank lt PO6 1 khz Notes on use 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 O is TTL low lt 8 5 is TTL high gt 2 4 P36 a dtrig 80 hz P31 int 80 hz pulse lt P27 relay lt 26 relay 5 P25 5 relay lt lt 5 P24 dc relay 5 lt P23 lt sense lt lt 0 or 5 P22 cs 5 P21 sense lt lt 0 or 5 lt P20 freq sense P33 key int 5 P34 DM 5 P17 07 1 khz P16 DAD6 1 khz P15 2 05 1 P14 1 khz P13 7 1 knz
17. GALPAT test is performed on the internal RAM of the In Guard If there are any errors ERROR 25 is displayed This test is performed only upon powerup TEST 26 Display RAM U212 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 two byte check sum is calculated over the entire 4 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 dis played TEST 28 External Program Memory U222 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 15 dis played 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
18. INDICATION suppressed for error messages ERROR MESSAGES 9 99999E 9 1 00 21 9 99999E 9 1 00 21 9 99999E 9 1 00 21 9 99999E 9 1 00 21 9 99999 9 1 00 21 9 99999 9 1 00 21 317 Remote Programming OUTPUT DATA Example Explanation 1 0071 21 CR LF 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 3 47 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 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 except G8 is always a four digit integer plus terminators The terminators LF Line Feed and CR Carriage Return each add an extra ch
19. agp 0 SUG 000 9060 2021 8 ser goes 1 WEZ 5 2 01880 PR d tan ef Wer 2 401 A 401 0220 zeen TOTA 0128 023 902 a Lll 1070 NETT voza CUM 2025 _ uu TOTO 3 7 8 199 50180 HETE X t 2 2 6 4109 SWUO 2 6 g 19949 1001 Koss CXF 244 14 ew HO pA 24 140 2 552 208 aa QNIWVIS 59 OL 02 Swng ONMWIS 20 OL 01 OL ONITWIS IG OL 998 tovo 2072 ozsonz 135 toe x 1997 _______ 70 1995 _______ OD AY roe Au _______ 2098 Sopa pou SOS xw NOs aad qasnwn 1350 9350 bt NSS MOOT NT wes Siva O3 303 si BOSAL NAHM LON swes6eig 5 1091 0688 vod 6 obi 5 1095 830Nn 301 10245 5028 b02 902 017
20. 10 with a maximum of 250V at 50 60 400 Hz AC voltage for the 5V supply is rectified by CR601 and CR602 and regulated by VR601 The 45V output supplies mostly logic circuits The ac input to the 5V supply is sensed by the In Guard R604 CR615 and U221 12 13 to measure the line frequency AC voltage for the 30V and 30V supplies is recti ied by bridge network CR603 CR604 CR605 and CR606 and regulated by VR602 and VR605 The 30V and 30V outputs supply front end buffer amp U306 In addition the 30V output supplies the ani of the vacuum fluores cent display Zener diode CR612 supplies 6 2V to the A D Converter clamps AC voltage for 15 and 15V supplies is rectified by bridge network CR608 CR609 CR610 and CR611 and regulated VR603 and VR604 The 15V and 15V supply analog circuitry throughout the 8840A Zener diodes CR613 and CR614 supply 7 5V and 8 2V to the A D Converter analog filter and DC Scaling circuit IEEE 488 INTERFACE 5 17 Theory of Operation POWER SUPPLY Secondary T601 14 15 16 supplies the vacuum fluorescent display filament with 4 5V ac The center tap is connected to the in guard 45 supply in order to correctly bias the display An isolated secondary supplies 16V ac to the power supply on the TEEE 488 Interface Zener diode CR615 and SCR Q601 comprise a protective crowbar circuit If the line voltage exceeds the nominal value by approximately 30 perc
21. 2 20 Reading Rates and Noise Rejection The RATE button allows you to optimize either measure ment speed or noise rejection The 8840A 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 measure ment 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 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 8840 senses the line power frequency and adjusts the analog to digital converter timing characteristics for opti mum normal mode noise rejection The resulting reading rates are shown in the specifications in Section 1 2 21 Automatic Settling Time Delay When the external trigger mode is selected the 8840A automatically inserts a delay after receiving a trigger sig nal but before starting the first input sample The delay is just lon
22. 3 33 20 Self Test Command The 20 command initiates the diagnostic self tests as does pressing the front panel SRO button 3 seconds The 8840A then runs through the tests in sequence For a description of the self tests see the Maintenance section If the 8840A detects an error an error message is loaded into the output buffer and displayed on the front panel After the last test the 8840A is reset to the power up configuration and it begins taking readings is an error to send the 8840A device dependent com mands during the self tests However the controller can still make the 8840A 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 Error messages are indicated by an exponent of 421 For more about error messages see paragraph 3 40 Since the 8840A is reset at the end of self tests the 20 command should be the last command in a given com mand string The 8840A will ignore any subsequent com mands 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 d
23. G4 Calibration Status G5 Get AB Status Input F R Autorange Offset On Off G6 Get YW Status Suffix Enabled Disabled Terminator Selection 67 Error Status G8 Instrument Identification Note G2 valid only in calibration mode PUT COMMANDS Put Instrument Configuration F R S and Put SRQ Mask Put Variable Calibration Value 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 Remote Programming DEVICE DEPENDENT COMMAND SET SRQ MASK VALUES 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 Available 32 for SRQ On Any Error Note Add SRQ mask values for combinations Example 33 for 5 overrange or any error SELF TEST COMMAND 20 Begin Self Tests CALIBRATION COMMANDS CO Store Present Input as Calibration Value C1 Begin A D Calibration C2 Begin HF AC Calibration C3 Enter Erase Mode CAUTION The command string CO erases the entire calibration memory complete calibration must then be performed Note CO through are valid only i calibration mode TERMINATORS CR Carriage Return LF Line Feed EO Or Identify GET Group Execute Trigger Execute Execute Execute Trigger and execute Note GET is an i
24. display readings goto in Figure 3 14 Programs Using the 3 35 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 8840A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840A 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 88404 using the 2 wire ohms function in autorange The range and function commands are programmed using the Put Instrument Configuration PO command Microsoft C Version 6 0 Link this program with appropriate mcib obj i 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 serial poll response byte float 5 char rd string 11 ss 11 main brdO ibfind GPIBO initialize interface board dmm ibfind 188404 initialize 88
25. simple and predictable command set Fast measurement throughput Full talk listen capability including talk only opera tion Full serial poll capability with bit maskable SRO Full remote locai capability including local lockout Section 3 Remote Programming EXTERNAL TRIGGER SAMPLE COMPLETE connectors Remote calibration Programmable trigger sources including two bus trig gers Informative output suffix suppressible Selectable output terminators The 8840A supports the following interface function sub sets SH1 AH1 T5 14 SR1 DT1 E1 PPO and 3 3 BUS SET UP PROCEDURE To set up the 8840A on the IEEE 488 bus proceed as follows 1 Turn the 8840A POWER switch OFF and set the 8840A IEEE 488 address using the rear panel IEEE 488 address switches shown in Figure 3 1 2 With the 88404 POWER switch OFF plug the IEEE 488 cable into the 8840A rear panel 488 connector 3 Switch on the 8840 Whenever 8840A in the local state the IEEE 488 address can 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 3 2 Each block represents a register buffer etc contained in the 88404 The status registers in the center column indicate the instrument s status includ ing its function range reading rat
26. the P2 command 8840A must be in the calibration is coming from the controller the value can be specified mode enabled by pressing the front panel CAL ENABLE using any valid format signed integer real number or real Switch Otherwise the P2 command will generate an error number with exponent For example if the Le message prompts for an input value of 100Q for the next calibration The variable input is a measurement value that is to be coe used as the calibration value for next calibration step be specified EEE A d Its format is the same as a measurement value But since it N9897E 2 of these strings result in th Remote Programming DEVICE DEPENDENT COMMAND SET value being used for the next calibration step For com plete information about remote calibration refer to the Maintenance section Numeric values exceeding full scale and negative values for ohms and AC generate error messages 3 26 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 8840 12 17 83 Loads the message FL 8840 12 17 83 into cali bration memory Loads the message HIMOM into calibration memory The remaining eleven characters are assumed to be blank P3HIMOM The P3 command stores a user defined message in the internal calibra
27. 3331 DUS Aq pejqeue snq 3331 941 e DUS eyes Burpee 101 5409105 sayel 1sej pue mojs sejoAo sepow 496611 pue 591660 1X3 19 ui Buipee mou sabbu Figure 2 5 Front Panel Features cont Operating Instructions OPERATING FEATURES uo 10 8 eased s jeued OUL NOILOVO se pasu UB ui 1 oued 1891 eui jo eu 33 40 090UU0D uonoejes 10 L 18701 190 VOY pue uesu Figure 2 6 Rear Panel Features m JOQUINN SWUO 10 aqui 3SN3S 07 pue HOIH ejqejoojes 1 1 9144 uonoejes 5 887 3931 AINO
28. 59736 170 IBINIT2 IBINIT1 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 BFIND IBSICIBLOCIBPPC IBBNA IBONLJBRSC IBSRE IBRSV IBPAD IBSAD BIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF 200 CALL IBINITZ IBGTS IBCAC IBWAIT IBPOKE IBWRT JBWRTAJBCMD IBCMDAJIBRD IBRDA IBST IBRPP IBRSP IBDIAG IBXTRC IBRDI JBWRTLIBRDIAJBWRTIABSTAS IBERR96 IBCNT96 210 REM 220 REM IBM BASICA on IBM PC PC XT or PC AT 230 REM 240 18840 Device name is 188404 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 WRT F1IROSOTOY1 290 CALL IBWRT DVM96 WRT Write functions instrument 300 FOR I 1 TO 10 3 26 310 RD SPACE 18 11 characters for the reading 5 for the 320 suffix and 2 for the terminators 330 CALL IBRD DVM RD Get data from 8840A 340 PRINT I LEFT RD 16 Print to display 350 NEXT I i 360 END IBM IBM PC PC XT and PC AT are registered trademarks of Internationa Business Machine Corporation National Instruments is registered trademark of National Instruments Corporation Figure 3 14 Example Programs Using the Remote Programmi EXAMPLE PROC ning 10 REM The following application program is written in BASICA for the IBM PC PC XT or 20 REM The National Instruments Model
29. 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 4 SPECIFICATIONS Specifications for the 8840 are given in Table 1 1 External dimensions are shown in Figure 1 1 1 1 Introduction and Specifications SPECIFICATIONS Table 1 1 Specifications DC VOLTAGE Input Characteristics RESOLUTION 5 DIGITS 4 DIGITS FULL SCALE 5 DIGITS INPUT RESISTANCE 199 999 mV 210 000 1 99999 210 000 19 9999 210 000 199 999 10 MQ 1000 00V 4 digits at the fastest reading rate 10 NORMAL S READING RATE of Reading Number of Counts _ RANGE 24 HOUR 23 1 90 DAY 2345 1 YEAR 2345 0 007 4 0 008 4 0 004 3 0 005 3 0 005 3 0 006 3 0 005 3 0 006 3 0 005 3 0 007 3 1 Relative to calibration standards Using Offset control 3 When in fast reading rate with internal trigger and transmitting data out of the IEEE 488 interface the 8840A display must be blanked command D1 to ensure stated accuracy When offset control is not used the number of counts 5 7 and 9 for 24 hour 90 day and 1 year respectivo MEDIUM AND FAST RATES
30. Microsoft QuickBasic V 4 5 on IBM PC PC XT or PC AT SINCLUDE qbib45 dcl bdname GPIBO CALL IBFIND bdname BD devname 18840A Device name is 18840 CALL IBFIND devname dvm Initialize the device CALL IBCLR dvm Clear the device WRT N3001PO Y1 CALL IBWRT dvm RDS 18 CALL IBRD dvm RD first reading lt VAL RD Board name is GPIBO Initialize the Interface Board Write functions to the instrument PRINT LEFT RD 16 S 2 WIRE LOWEST READING DO Execute the statements up to the loop statement until new low is found WRITS CALL IBWRT dvm 5 SPR96 0 DO UNTIL SPR96 AND amp H40 amp H40 CALL IBRSP dvm SPR Serial poll the device until data available Trigger the device LOOP 80 SPACE 18 CALL IBRD dvm RD next data 5 VAL RD LOOP WHILE s gt Throw away data if not lowest r s Update lowest reading GOTO label1 Print new low END Figure 3 14 Example Programs Using the IBM cont Remote Programmin EXAMPLE PROGRA 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 88404 DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840A assigned to t
31. P12 2 02 1 khz P11 1 1 khz P10 ADO2 1 khz Figure 6 9 U202 Pin Diagram 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 8840A and remove the short from TP205 6 42 In Guard Microcomputer While the 8840A is in the In Guard Troubleshooting Mode check the following in the order shown 6 32 1 2 3 Power supplies 5 dc at 0202 1 OV dc U202 11 uC clock output 8 MHz at U202 2 3 Trigger line U202 40 TP201 Square wave 5096 duty low OV high 3 8V nominal The period of the trigger signal should be 12 500 ms for 60 Hz line Interrupt A D U202 39 Normally low dura tion 48 us occurs approximately 5450 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 test patterns Waveforms A and B in Figure 6 10 1 kHz square wave on indicated pins 50 duty cycle low high 3 8V nominal The waveforms are interrupted every 1 5
32. 5 5 30 Note 2 5 30 Note 2 5 5 5 5 10 30 1 Difference between first reading and final value for an in range step change coincident with trigger 2 For slow reading rate 50 counts for medium rate 10 counts for fast rate Introduction and Specifications SPECIFICATIONS Table 1 1 Specifications cont 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 wid ie AUTOMATIC SETTLING TIME DELAY A D CONVERSION 2 SAMPLE COMPLETE 3 DATA 1 2215 Time from single trigger to start of A D conversion See Automatic Setting Time Delay on previous page If the delay is disabled by using the T4 command then the delay is 1 ms 150 When the 8840 is triggered with an 488 command GET 2 the automatic setting time delay begins after the trigger command has been processed and recognized A D conversion time is dependent on the reading and power line frequency A D CONVERSION TIME ms Sample Complete is a 2 5 us pulse which indicates that the analog input may be changed for the reading 4 When talking to a fast contro
33. Figure 4 9 Reduction of Zero input Error 4 10 5 1 INTRODUCTION This section presents an overall functional description of the 8840A followed by a detailed circuit description The descriptions are supported by simplified schematics in text and by the complete schematics in Section 10 5 2 OVERALL FUNCTIONAL DESCRIPTION A functional block diagram of the 8840A 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 Dig ital 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 con verted 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 circuit 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 filter ing for certain ranges and reading rates AC inputs
34. It is controlled by U901 as a memory mapped peripheral through an data bus Bus transceivers 0912 and 0913 buffer 0911 from IEEE 488 bus They provide the bus with the output drive capability and receiver impedance 5 41 Signal Conditioning The SAMPLE COMPLETE and EXT TRIG signals 7903 and J904 are conditioned by U909 Diodes CR903 CR904 CR905 and CR906 and resistors R917 and R918 provide protection from excessive voltages Jumpers E902 and E903 allow selection of the polarity of the EXT TRIG IEEE 488 TALKER LISTENER IC U911 AND BUS TRANS CEIVERS U912 AND U913 Theory of Operation IEEE 488 INTERFACE OPTION 05 m DC I 22 signal A polarity selection procedure is given in the Maintenance section The 8840A is configured in the factory so that it is triggered on the falling edge of the EXT TRIG signal 5 42 488 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 trans former T605 on the Main 0908 and associated circuitry resets the Out Guard at power up and follow ing 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
35. TR2 5 HE ds us E UTE 3204 OU3ZOinV dr ce 3HOLS H3ONIVW3H 94 a 7 18 2 6 2 foo lt gt CEST 2 3HO1S H3ONIVIW3H E pae ev NONE REDE ui eH X 5 ul x 5 5 ee 8 P bs lt 4148 T 81 T E 3HO1S H3GNIVWaH lt 1j i 4 gt qq n 2 I e 3uvdWoo 3 Bill fr gp Jo eme v I 3 4 v rU 9 e 7 o MM 2 8 6 o 8 3 MERCIER mS m celi M NS LR 2 3 2 2 52 4 wd 9 o E amp allo lt 3 4 1 lt c c ec 5 lt 2 3 60 Hz line frequency line TR has 12 5 ms period as shown above Figure 5 5 Timing Diagram for One A D Cycle Theory of Operation OHMS PROTECTION REF AMP SUPPLY 7V SENSE Figure 5 6 Precision Voltage Reference Large positive input voltages are blocked by CR402 Large negative input voltages are dropped equally across three high volt
36. calibration procedure but not in others The Get Input Prompt G2 command for instance is not valid when the 8840A is taking verification readings The Rate Sn com mands for instance are valid when the 8840A is taking verification readings but they are not valid at any other 6 14 characters and can be recalled with the 33 command Other commands that may be used during calibration are P1 Put SRQ mask the remaining Get commands and XO time during calibration Table 6 15 shows when com mands are invalid 6 24 TIMING CONSIDERATIONS The command can take up to 22 seconds If during this time the controller continues to send the 8840A more commands the commands may fill up the 8840A 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 deter mine this 1 Monitoring the 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 11 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 check of the status until the command is complete 2 Setting the SRQ mask to generate an SRQ Step Complete An SRQ is generated and the Cal Step Complete bit in the serial poll status response is set when a cal command
37. lt 1460 mA Measurement Tutorial AC VOLTAGE AND CURRENT MEASUREMENT Source voltage measured E Burden voltage measured Load source resistance Rv 8840A internal resistance Es Ep Displayed current 1460 mA Es 15 measured with 8840A in VDC function E 0 4V measured with 8840A as described below Error in percent 100 2 67 15V 0 4 0 4V 40 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 8840A allows you to measure burden voltage E gt directly Leaving the 2A and LO INPUT 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 Figure 4 5 Burden Voltage Error Calculation increase for more pointed waveforms as shown in Figure 4 7 The 8840A has full scale crest factor limit of 3 0 for the 20V and 700V 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 8840A measure the signal wit
38. medium rate add2 counts to number of counts In fast rate use 3 counts for the number of counts Operating Characteristics TEMPERATURE COEFFICIENT lt 0 0006 of Reading 0 3 Count per C from 0 to 18 28 to 50 MAXIMUM INPUT 1000V dc or peak ac on any range NOISE REJECTION Automatically optimized at power up for 50 60 or 400 Hz Analog amp Digital Digital None 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 rate Common Mode Rejection Ratio at 50 or 60 Hz 0 1 with 1 in series with either lead The CMRR 2140 dB atdc for all reading rates 4 20 volts or 2 times Full Scale whichever is greater not to exceed 1000V Introduction and Specifications SPECIFICATIONS Table 1 1 Specifications cont TRUE RMS AC VOLTAGE OPTION 09 input Characteristics 5 DIGITS 4 FULL SCALE 5 DIGITS INPUT IMPEDANCE 199 999 mV 1 1 99995V shunted 19 9999V by 199 999V 100 pF 700 00V 4 digits at the fastest reading rate Accuracy NORMAL S READING RATE of Reading Number of Counts For sinewave inputs 210 000 counts FREQUENCY Hz 1 Y
39. self tests are performed or the 8840A may indicate that errors are present If the 8840A 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 dis played even when the input terminals are disconnected there may be a hardware problem in your 8840A In that event refer to the Maintenance section or contact your local Fluke representative 2 14 Ranging Measurement ranges can be selected using either autorange by pressing the AUTO button or manual range by pressing another range button The 8840A displays explicit units in every range so that the display may be read directly Operating instructions OPERATING EATURES 2 15 AUTORANGE In autorange the 8840A 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 annun ciators always indicate what range the instrument is in Pressing the AUTO button when the instrument is already in autorange toggles the 8840A from 10 manual range This causes the instrument to remain locked in the present range 2 16 MANUAL RANGE In manual range the 8840A remains fixed in the selected range until you select anot
40. the 8840A returns to one of the following states a After complete erasure Begins A D Calibration b After A D erasure Begins A D Calibration After Offset and Gain erasure Begins Offset and Gain Calibration for erased function d After High Frequency AC erasure Begins High Frequency AC Calibration 6 20 TOLERANCE CHECK The 8840A 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 8840A displays ERROR 41 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 6 21 AC CALIBRATION AT OTHER FREQUENCIES For special applications where the 8840A is to be used to measure ac voltages or currents exclusively at a single frequency or narrow range of frequencies accuracy may be enhanced at that frequency or range of frequencies by performing calibration according to the following proce dure Note that this may degrade the accuracy at frequen cies significantly removed from the frequency of optimization Table 6 13 Tolerance Limits CALIBRATION TOLERANCE 1 A D Calibration 244 counts from prompt 2 Offset and Gain Calibration VDC mA DC Ohms 488 counts from promp
41. 028 3 0 023 3 1 Within one hour of zero using offset control Relative to calibration standard Applies to 4 wire ohms only When in fast reading rate with internal trigger and transmitting data out of the IEEE 488 interface the 8840A _ display must be blanked command D1 to ensure stated accuracy 5 When offset control is not used the number of counts are 5 7 and 9 for 24 hour 90 day and 1 year respectively 0 043 4 0 044 4 Introduction and Specifications SPECIFICATIONS Table 1 1 Specifications cont Accuracy cont MEDIUM AND FAST READING RATES in medium rate add 2 counts to the number of counts for the 20001 tnrough 200 kQ ranges and 3 counts for the 2000 kQ and 20 MQ ranges in fast reading rate use3 counts for the number of counts for the 200Q range and 2 counts for ail other ranges Operating Characteristics TEMPERATURE COEFFICIENT Less than 0 1 x accuracy specification per C from 0 C to 18 0 and 28 C to 50 C MEASUREMENT CONFIGURATION 2 wire or 4 wire OPEN CIRCUIT VOLTAGE Less than 6 5V on the 2000 through 200 ranges Less than 13v the 2000 and 20 ranges INPUT PROTECTION READING RATES READING RATES WITH INTERNAL TRIGGER Sensed automatically at power up AUTOMATIC SETTLING TIME DELAY Time in milliseconds from single trigger to start of A D conversion E T off READING RATE OFCOUNTS FROM FINAL VALUE
42. 1000 0 1 1 3 1 1 0 1 1 1 1 1 1 6 301 1 PC GC 1110111111 1111111111111 1 1 1 000 0 0 0 0 0 0 00 0 0 0 1 1 1 1 0 0 0 0 0 1 0 0 0 0 0 0 08000100001 7 03018 5 TR1 GC 8 U301C 7 3872 10 U3020 1 GB TR1 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 14 1 9 96 06 0 0 9 0 1 0 06 0 11111111111 1 111111111 1 1 4 4 1 1 1 1 1 1 4 11 11 U3028 5 a r1 ohas r4 P 12 U302C 7 RDI QMCHIAC 13 03020 9 FDi IDC 15 5 TR2 09 0 1 0 0 0 0 0 0 1 06 0 1 0 0 0 00 0 1 1 4 0 1 1 1 4 4 1 0 3 1 1 0 1 1 1 1 1 16 U303C 7 HD2 x10 17 03030 9 2 1 Section 009 0 0 0 0 1 4 1 1 14 1 4 1 1 1 14 1 0 4 0 ohas 18 K401x 0090 090 1 9 0 090 0 1 1 1 1 1 0 4 1 11 4 1 09 0 0 0 1 1 1 141 1 0 0 0 0 1 0 1 1 4 1 4 9 0 90 0 0 1 41 1 1 0 1 1 1 1 4 1 21 04028 5 2k 2k 20k 200k ohas 0 9 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 0 0 9 0 1 1 1 1 1090 0 0 1 1 1 1 1 1 0 1 1 1 1 1 1 00 0 6 0 0 0 0 1 1 06 0 0 1 0 0 1 1 1 4 1 0 9 06 06 0 0 0 1 0 1 0 1 1 1 1 109 0 0 1 1 1 1 14 1 0 1 1 4 4 1 000 0 0 0 0 0 1 1 0 0 0 0 0 1 4 1 1 24 0402 7 200 2000 25 U4038 5 20k ohas 26 U403C 7 00000002000000290000020 1110000 0 0 0 0 6 0 0 1 0 1 1 4 1 1 1 1 3 1 1 1 14 1
43. 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 3 Select the SHORT from the 5450 and measure this value at the 5450A OUTPUT terminals using the UUT in 4 wire ohms If in remote take the average of four 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 meas ure this value as in step 3 5 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 2000 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 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 Maintenance CALIBRATION 8 Select the 1000 output from the 54504 and cali 13 Using the same configuration shown in Figure 6 4 brate the high point for the 2000 range entering the verify that the UUT measures the same value within value computed in step 5 as a variable inpu
44. 5 1 Using Offset Control 2 4 1 2 Digit Counts 3 Applies to 4 Wire Ohms Only 4 When in fast reading rate with internal trigger and transmitting data out of the IEEE 488 interface the 8840A display must be blanked command D1 to ensure stated accuracy 6 5 Maintenance PERFORMANCE TEST 5 Set the Current Source for zero mA and disconnect it from the 8840A 6 8 AC Current Test Option 09 Only The following procedure may be used to test the mA AC function 1 Ensure the 8840A is on and warmed up for at least 1 hour Select the mA AC function 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 8840A can be checked at 10 mA by using a Fluke 5200 set at 100V and connected to the 8840A 2A terminal through a 10 2W 196 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 shown for each reading rate 5 Set the AC Current Source to Standby and disconnect it from the 8840A 6 9 CALIBRATION CAUTION To avoid uncalibrating the 8840A never cycle power on or off while the CAL ENABLE switch is on NOTE If 0220 is replaced perform the Erase bration Memory procedure located later in this section before attempting calibration Failure do so may result in an ERROR 29 on the 8
45. 5 42 IEEE 488 Interface Power 5 19 5 43 TRUE RMS AC OPTION 09 5 19 544 VAC MEE 5 19 5 45 AC wile Weve RN 5 19 5 46 Frequency Response O EE e dedu 5 19 5 47 True RMS AC to DC 5 19 6 1 6 1 INTRODUCTION Sel eet tou tase 6 1 6 2 PERFORMANCE TEST 6 1 6 3 Diagnostic 6 1 6 4 DC Voltage 6 1 6 5 AC Voltage Test Option 09 6 3 6 6 Resistance Testes due 6 4 6 7 DC Current Test 6 5 6 8 AC Current Test Option 09 Only 6 6 6 9 CALIBRATION mr be ep 6 6 6 10 Basic Calibration 6 6 6 11 INITIAL PROCEDURE 6 7 6 12 AD CALIBRATION 6 7 6 13 OFFSET AND GAIN 6 7 6 14 HIGH FREQUENCY AC 6 9 6 15 Advanced Features and Spec
46. 6 18 Calculating the A D Reading From TP102 Waveform Table 6 23 Power Supply Voltages LIMITS in volts TEST POINT 15 75 31 55 14 25 28 45 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 prob lem make certain that nothing else was damaged by the overvoltage If a supply is too low there are number of possible causes First check the input to the affected regulator If it is not at least 1V above the maximum output given in Table 6 23 the cause may be a bad transformer winding check the resistance open or shorted rectifiers 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 6 44 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
47. 8 Be Wife ORNS e EAR e dex Ni 4 3 4 9 Applications of the Ohms Functions 4 3 4 10 TESTING DIODES date aud 4 4 4 11 TESTING ELECTROLYTIC CAPACITORS etre cats 4 4 4 12 A PRECISION CURRENT SOURCE E SE 4 5 4 13 DC CURRENT 4 6 4 14 REDUCING THERMAL 4 6 4 15 VOLTAGE AND CURRENT 4 6 4 16 True RMS Measurement 4 6 4 17 Waveform ri OE SE 4 6 4 18 Crest Factorii os Le de pci Hee M I 4 6 4 19 AC Coupled AC 4 7 4 20 Combined AC and DC 49 A 2155 Bandwidth Riss SEE E S449 4 22 Zero Input VAC 4 9 5 Theory of Operation iux rig apie 5 1 5 1 INTRODUCTION oes E 5 1 5 2 OVERALL FUNCTIONAL DESCRIPTION E erem Qs 5 1 5 3 DETAILED CIRCUIT 5 1 2594 DO
48. Calibration True RMS AC option only Normally it is recommended that the entire calibration procedure be performed However under some circum stances the earlier parts may be omitted For example if Table 6 6 DC Current Test STEP INPUT 0 mA EI 1000 mA dc 000 04 ETT 04 999 56 1000 44 DISPLAYED READING MEDIUM FAST 000 06 000 06 000 2 000 2 1000 46 999 4 1000 6 Table 6 7 AC Current Test STEP NUMBER n 6 6 INPUT 2000 mA 1900 00 mA 1 kHz 1890 40 1909 60 2000 mA 100 00 mA 1 kHz 97 60 102 40 TEST LIMITS 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 fol lowed 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 8840A 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 8840A automatically uses this input to calibrate the offset for all ranges While the 8840A is executing a calibration step it ignores all of the front panel buttons and delays execution of all remote commands 6 11 INITIAL PROCEDURE Always begin the calibration procedure as
49. Calibration procedure HF AC Selects the High Frequency AC Calibration procedure ERASE 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 1 seconds of pressing this button CAUTION If any part of calibration memory is erased ail or part of the calibration procedure must be performed RATE Changes the reading rate Valid only when the 8840A is taking verification readings gnored at other times VAR IN Allows the use of reference sources that differ from the prompted values After pressing VAR IN variable input the range buttons can be used to change the displayed prompt The variable input feature is not available during the A D Calibration procedure A ER Figure 6 3 Calibration Functions Table 6 8 A D Calibration Table 6 9 A D Calibration Test ALLOWABLE ERROR STEP DISPLAYED PROMPT 0 V DC short A OV short 2 counts B 03 V DC B 0 03V z2 counts C 1 01 V DC 0 03V 2 counts D 99 V DC D 0 660V 3 counts E 51 DC E 0 660V 3 counts F 51 V DC F 1 970V 4 counts G 26 V DC G 1 970 4 counts H 26 V DC 135 135 0725 L 0725 V DC 6 8 Maintenance CALIBRATION EINEN CERE EIL MG M D c CT R on RSEN each function To save time the 8840A uses each input for as many ranges as possible A function is cal
50. Charge Configuration The pre charge configuration Figure 5 4F occurs hold configuration in VDC ranges r1 12 and r4 and ohms ranges 11 12 13 and r4 U306 is connected buffer to charge stray capacitance at the non inverting input of the T H Amplifier The pre charge is not used any other ranges 5 14 PRECISION VOLTAGE REFERENCE The Precision Voltage Reference Figure 5 6 provides precise reference voltages of 7 00000 and 47 O The Theory of Operation PRECISION VOLTAGE REFERENCE Figure 5 3 Track Hold Amplifier reference element is a reference amplifier ref amp The nominal ref amp voltage is 6 5V Resistor R701 precision resistor network 2701 and tran sistor zener diode combination U701 are produced 25 matched set so that the output of U702A is precisely 7 00000V 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 Ref
51. D CONVERTER monitored to indicate when the DAC output is larger than the input voltage The conversion process is broken up into an autozero period followed by five measurement intervals A timing diagram is shown in Figure 5 5 Six bits of the final A D sample are obtained during each interval During the first 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 r jected 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 con nected 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 BINARY LADDER NETWORK R105 50K Figure 5 9 Analog to Digital Converter DAC AMPLIFIER 7V NOTE A D CONVERTER SHOWN DURI
52. 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 The custom A D IC U101 generates five 6 bit numbers after each trigger from the uC and then pulls INT low telling the that data is ready The 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 exter nally triggered reading in the slow reading rate would cause the uC to send 32 pulses TR at 80 Hz rate The 32 A D samples would be calibrated and averaged by Theory of Operation DIGITAL CONTROLLER the and sent for display With internal triggering the A D runs continuously at 80 samples per second with reading being sent to the display every 32 samples 5 31 Calibration Correction The calibration constants used by the In Guard uC in computing each reading are stored in the EEROM elec tronically erasable read only memory Calibration Memory U220 The front panel CAL ENABLE switch protects the EEROM from accidental writes 5 32 Keyboard Display Control Keyboard Display Controller 0212 communicates with the In Guard uC ove
53. DURING PREVIOUS COMPARE PERIOD Figure 5 10 First Remainder Store Period senses inactivity on line CS7 for longer than 1 5 seconds it resets the In Guard uC by pulling RES 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 TR1 and TR2 provide control signals for the Track Hold circuit 5 22 Precision DAC The Precision Digital to Analog Converter DAC is com posed of DAC Amplifier U102B and a binary ladder network which consists of resistors in Z101 and digitally controlled analog bit switches contained in U101 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 5 23 A D Amplifier The A D Amplifier is composed of a comparator amplifier 9103 two remainder storage capacitors C103 and C102 an autozero storage capacitor C101 and several digitally analog switches contained 17101 5 12 A D AMP x16 STORAGE C102 KOR The A D Amplifier has three modes of operation TEE 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 wher
54. Low 6 29 Maintenance TROUBLESHOOTING floor reading In this range the first and second stage buffers effectively divide any noise at the input termi nals by 100 This test should be fairly immune from noise because the input terminals are always open circuited except for capacitive feedthrough across K801 TEST 2 700 VAC Zero Configures the 8840A in the 700V ac range and measures the open circuit floor reading this range the open circuit reading is divided by 1000 Again K801 is opened to reduce sensitivity to external noise TEST 3 mA AC Zero Configures the 8840A exactly as in the mA AC function and takes a reading of the voltage across the 0 162 current shunt at the slow reading rate TEST 4 mA DC Zero Configures the 88404 in the mA DC function and the slow reading rate and measures the reading across the 0 1 2 current shunt This test should be fairly immune to outside noise because the total driving impedance is typically less than 1 The reading is not a perfect because of the offsets generated by charge injec tion of U302 and the T H Amplifier X10 configura tion TEST 5 200 VDC Zero Configures the 8840A 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 and filtered by the 3 pole analog filter Any non zero reading under quiet input conditions is due to
55. MOCO MOOS mo lt gt mm HHO MOCO O O MOOS mm O MOON O O e MOC ADO em MO 6 37 Maintenance TROUBLESHOOTING Using this procedure the following pattern should be seen 00000 11111 000000 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 0803 itself is functioning correctly 6 62 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 4 SYNC PULSE LOGIC 1 AT TARGET PIN AN LOGIC 0 1 TARGET PIN Lene om we 17 OBSERVE TARGET PIN AT THIS TIME 221 Figure 6 12 Typical Dynamic Control Signals U301 U302 and U303 These should show digital signals with high 2 3V and low s 0 5V In the 20V range any voltage applied to the HI INPUT terminal relative to Reference Low should be present at U306 3 If not trace the volt
56. OUTPUT 0 0 PRINTS D PRINTS DISP PE ABS R VCT 3 lt SW T 1E 5 1E 6 THEN PRINT _ 6 27 DISASSEMBLY PROCEDURE WARNING TO AVOID ELECTRIC SHOCK REMOVE THE POWER CORD AND TEST LEADS BEFORE DISASSEMBLING THE INSTRU MENT OPENING COVERS MAY EXPOSE LIVE PARTS CAUTION avoid contaminating the printed cir cuit 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 taminated procedure and then verifies the The program uses the Fluke 1722A Instrument 54404 Direct Voltage Calibrator The 88404 is at address 7 97 4 1 97 4 0 66 3 1 LOOP TO READ IN VERIFICATION VALUES INITIALIZE SYSTEM TO DO RIFICATION ONLY INSTRUCTION NOTE STOP PROGRAM UNTIL RETURN IS HIT NO OF PASSES PUT 88404 IN A D CAL CALIBRATION LOOP 8840A CAL PROMPTS CLEARS POSSIBLE ERROR MESSAGE IN BUFFER LABELS DISPLAY PASS STEP INPUT VALUE SET OUTPUT OF 54404 i TIME FOR 5440A STORE 0 TEST 88404 FOR CAL STEP COMPLETE VERIFICATION LOOP SET 5 4 4 3 LINES FORMATS DISPLAY 12 3 SPLAY PASS ELSE PRINT FAIL Figure 6 5 Example A D Calibration Program 6 16 The following paragraphs present a disassembly procedure for the 8840A The
57. Offset and Gain Calibration Buttons procedure for the corresponding function R1 through R6 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 CORRESPONDING COMMENTS COMMAND Tells the 8840A that the requested calibration input is valid This command causes the 8840A to take readings and compute and store calibration constants NOTE The CO and C3 commands can take up to 22 sec onds to execute You must determine when these commands are complete before sending more com mands See Timing Considerations in text Selects the A D Calibration procedure Maintenance CALIBRATION Table 6 14 Commands Used During Remote Calibration cont FRONT PANEL CORRESPONDING COMMAND COMMENTS FEATURE HF AC C2 ERASE Selects the High Frequency AC Calibration procedure 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 command causes the 8840A to return to its previous state There is no timeout as with the front panel ERASE button CAUTION The command string erases the entire calibration memory A complete calibration must then be performed 50 through S2 Changes the readi
58. R Option 05 6 44 6 69 SERVICE POSITION 6 44 6 70 DIAGNOSTIC PROGRAM 6 45 6 71 True RMS AC Troubleshooting Option 09 6 46 6 72 SERVICE POSITION cro tt 6 46 6 73 MAJOR PROBLEMS 95 Nae cl 6 46 6 74 MORE OBSCURE PROBLEMS dug eur CEN VS 6 48 6 75 Guard Crossing Troubleshooting dfe ue wats 6 48 6 76 INTERNAL CLEANING EE eee RAE TIR 6 48 6 77 Cleaning Printed Circuit 6 48 6 78 Cleaning After 1 649 List of Replaceable 02 2 2 2 24 4 14 54 7 1 1 1 INTRODUCTION ital eres es 7 2 7 2 HOW OBTAIN PART Si vain veins tia nun cl cotra 7 2 7 3 MANUAL STATUS 22 22 2 7 2 74 NEWER INSTRUMENTS 7 2 7 5 SERVICE CENTERS 55 e 7 2 Options and 0 2 24 444444 8 1 8 1 INTRODUCTIONS tesi Adv a 8 1 8
59. RANGE NOTE TABLES SHOW CONFIGURATION DURING TRACK PERIOD OF TRACK HOLD CYCLE FILTER SWITCH Q304 IS ON FOR THE S READING RATE IN VDC Figure 5 2 DC Scaling VDC and mA DC Theory of Operation DC SCALI 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 reduced input voltage is buffered 10306 and divided by 10 as in the 20V range 5 6 Protection Input protection for VDC function is provided by 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 CON PONENTS In all 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 99 10W resistor network 2304 in the 200 mV 2V and 20V ranges by 10 MQ Z302 to ground in the 200V and 1000V ranges Z304 provides current limiting in extreme overvoltage condi tions in the 200 mV 2V and 20V ranges The non inverting in
60. SCALING TS Ha NH UN M 5 1 5 5 VDC 5 1 5 6 5 7 mA DC Scaling ES eee 5 4 5 8 Analog File 5 4 SU CIRCUIT lt esci 5 4 5 10 Track Configuration 4 d PS E 5 4 5 11 ven ea 5 4 5 12 Hold Configuration 5 4 5 13 Pre Charge 5 4 5 14 PRECISION VOLTAGE REFERENCE 5 4 5 15 OHMS CURRENT 1 42 5 5 2 10 OHMS PROTECTION caesos c rete es kde ena dan 5 5 5 172 OHMS FUNCTIONS 5 8 5 18 29 a 5 8 5 19 4 Wire ONMS tne n Ce AN S 5 8 320 A D CONVERTER Sae INE Senec own s dias 5 9 5 21 Timing Data Control sisi ete So ics qt saut au eh 5 11 5 22 Precision DAC os le XY 5 12 5 23 AD wedi 5 12 5 24 Bootstrap
61. Specifications SP CIFICATIONS Table 14 Specifications cont In medium rate add 50 counts to number of counts In fast reading rate for sinewave inputs 221000 counts and frequencies 2100 Hz the accuracy is 0 4 of reading 30 counts MEDIUM AND FAST READING RATES NONSINUSOIDAL INPUTS For nonsinusoidal inputs 210 000 counts with frequency components lt 100 kHz add the following 96 of reading to the accuracy specifications FUNDAMENTAL 1 CREST FACTOR FREQUENCY 1 0 TO 1 5 1 5 TO 2 0 2 0 TO 3 0 45 Hz to 5 kHz 20 Hz to 45 Hz Operating Characteristics TEMPERATURE COEFFICIENT Less than 0 1 x accuracy specification per from 0 C to 18 and 28 to 50 MAXIMUM INPUT 2A dc or rms ac Protected with 2A 250V fuse accessible at front panel and internal 3A 600V fuse BURDEN VOLTAGE dc or rms ac typical at full scale RESISTANCE input Characteristics RESOLUTION 5 DIGITS 4 DIGITS CURRENT THROUGH UNKNOWN FULL SCALE 5 DIGITS 199 9990 1 99999 19 9999 199 999 1999 99 19 9999 4 digits at the fastest reading rate Accuracy 1 YEAR 2345 0 011 45 0 014 45 0 01 3 0 013 3 0 01 3 0 013 3 0 01 3 0 013 3 0 027 3 0
62. 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 respec tively for a specific input The A D Converter communicates with the In Guard uC 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 and drive one data line at a time through a 1 kQ 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 pV indicate a short The voltage drop is caused by excessive current flowing through the line When troubleshooting the A D Converter it may be desira ble to determine what the reading is at the A D Converter when the display is definitely incorrect A dig
63. These corres pond 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 8840 interprets messages Illegal commands e g F9 generate an error message but are otherwise ignored and do not affect the instrument s configuration Example F9 This would load the output buffer with an error message and select F1 established by the command 3 39 Syntax Rules Explanation _ Four syntax rules should be followed when constructing input command strings They are RULE 1 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 8840A will not respond to the second attempt to read the output buffer However if the 8840A is in TO no intervening command is necessary RULE 2 Use no more than one output command per input command string Because the 8840A 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 the last command can be read Example Explanation F1 F2 Improper construction The second trigger writes over the first To obtain two readings send two complete command strings sepa tated by terminators F2 R3
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65. a S Single Rack Mount Kit Accessory Y8834 Center Rack Mount Accessory 8836 also available Operating Instructions _ OPERATING FEATURES ooo DODOCDDO e Dual Rack Mount Kit Accessory Y8835 Figure 2 3 Rack Mount Kits REMOVE HANDLE MOUNTING Figure 2 4 Installing the Single Rack Mount Kit absent pressing the VAC and mA AC function buttons causes the 8840A to briefly display an error message ERROR 30 2 10 Display Features The 8840A features a vacuum fluorescent display with a numeric field and annunciators The annunciators are explained in Figure 2 5 2 11 Error Messages If the 8840A detects an operator error or internal failure it displays an error message for about 2 1 2 sec onds 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 ATTACH RACK EARS 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 If the FRONT REAR switch is set to the REAR ERROR 2 12 Overrange Indication An input is overrange if it exceeds the full scale of the selected range In most ranges the 8840A indicates an input is overrange by lighting the OV
66. 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 3 44 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 NOTE In the fast reading rate the least signifi cant digit is always zero and should be dis regarded when interpreting accuracy specifications 3 45 OVERRANGE INDICATION If a reading is overrange 2200 000 counts the measure ment data has the following format 9 99999 9 suffix lt terminators gt Overvoltage readings 1000V dc or 700V ac do not result in this display 3 46 ERROR MESSAGES If 88404 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 Table 3 2 Numeric Output Data Format R1 R2 R3 R4 R5 R6 VDC VAC 1 0 MEASUREMENT 2 4 WIRE mA DC mA
67. as shown in Figure 3 6 The message is stored in calibration memory during cali bration 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 FL8840A 12 17 83 CR LF Meaning Identifies instrument and gives cal date 01 25 84 CR LF Gives date The last eight characters are blank 3 16 G4 Get Calibration Status The G4 command is used when calibrating the 8840A 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 calibra tion mode is enabled The fourth digit indicates whether or not the calibration mode is enabl d and if so which part of the calibration procedure the 8840A is in Example output strings follow Meaning 1 Leading 1 0 Leading 0 0 Not in cal verification 0 mode disabled 1 Leading 1 0 Leading 0 0 Not in cal verification 1 Cal mode enabled A D cal selected 3 17 G5 Get IAB Status The G5 command loads the output buffer with the IAB stat
68. 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 pas sive components or the post filter 08098 and associated passive components is defective The dc voltage at U802 6 should be the same as that at TP803 for frequen cies above 500 Hz and should be equal to the rms value of the input signal 6 74 MORE OBSCURE PROBLEMS Slow settling time or excessive jitter for low frequency inputs is caused by rms converter loop errors The cause 6 47 Maintenance TROUBLESHOOTING Table 6 27 AC Signal Tracing INPUT VOLTAGE VOLTAGE AT 801 VOLTAGE AT 802 1 kHz 1 1 1 100 100 mV 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 If one or more ranges are functional but cannot be cali brated at high frequencies then either the digitally con trolled 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
69. by pulling the latches upward Figure 6 61 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 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 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 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 7B Remove the the display assembly Display PCA spacer matrix and keypad from the chassis as follows see Figure 6 7 a 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 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 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 Remove the display window from the front panel as follows a Slidethe window u
70. components for common waveforms compares read ings for true rms meters and average responding meters For example consider the first waveform a 1 41421V zero to peak sine wave Both the 8840A 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 but only the 88404 correctly measures the ponent 1 00000V The average responding meter meas 1 110V which amounts to an 11 error Since meters have been in use for so long you may have accumulated test or reference data based on them The conversion factors in Figure 4 6 Should help you convert between the two measurement methods 4 18 Crest Factor Crest factors are useful for expressing ability bf an instrument 10 measure 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 vol tages 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 EXAMPLE LO INPUT E ERROR IN mA Displayed current X E ERROR IN PERCENT X 100 5 EM Error in mA
71. function button begins the Offset and Gain Calibration procedure for that function 5 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 AC Calibration at Other Frequencies later in this section 6 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 Table 6 10 Offset and Gain Calibration DISPLAYED PROMPT 00 0 mV DC short 10 0 mV AC 190 0 mV DC 100 0 mv AC 1 900 V DC 1 000 V AC 19 00 V DC 10 00 V AC 190 0 V DC 1000 V DC 100 0 V AC 500 V AC Step G not applicable for these functions NOTE 2 WIRE ko 4 WIRE 0 00 9
72. is 3 The response to a Get Error Status G7 command With no errors present is 1000 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 char 512 read data buffer int interface board number int dmm device number char selftest active 1 selftest active flag char 4 error code buffer main brdO ibfind GPIBO initialize interface board dmm ibfind 18840A initialize 8840A ibclr dmm clear device ibwrt dmm Z0 2 start 8840A self test do while self test active ibwrt dmm G7 2 get error status ibrd dmm rd 16 strncpy errcode rd 4 if stremp errcode 1000 0 test for error ibwrt dmm X0 2 printf Error 905 occurred r n errcode ibwrt dmm G0 2 get instrument configuration f 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 strncpy errcode rd 4 if 1000 1 0 test for last digital error printf Error 96s occurred r n errcode printf r nSelftest complete r n Figure 3 14 Ex
73. 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 1 Maintenance CALIBRATION Table 6 15 Error Numbers Which Are Displayed When Commands Are Not Valid NORMAL SELF TEST MODE Bn CO C1 C2 C3 Although not usually necessary these methods can be used for other commands as well 6 25 REMOTE ERASURE 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 after will abort the erasure To facilitate remote calibration the CO com A D CAL CALIBRATION MODE HF AC VERIFICATION CAL MODE OFFSET amp GAIN CAL 60 52 52 51 60 54 51 60 51 60 51 60 mand does not timeout as does the front panel ERASE button The selective erasure that is 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 Tim ing Considerations above 6 1 Maintenance CALIBRATION NOTE When erasing calibration memory it is good practice to send the commands C3 and CO in the sa
74. 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 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 problem 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 syn chronized 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 Teading is noisy 6 68 IEEE 488 interface Troubleshooting Option 05 6 69 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 accordin
75. 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 6 38 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 8840A 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 8840A skips tests 3 and 4 and if Option 09 is not installed the 8840 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 8840A are not performing properly Passing the tests gives approximately a 90 probability that all VDC ranges and range 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 Maintenance TROUBLESHOOTING the instrument can be calibrated in VAC mA DC mA AC 4 wire ohms or ranges 11 to r5 of 2 wire ohms NOTE If t
76. more than one instru ment on the bus is capable of sending service requests the controller learn which one made the request by taking a serial poll Each device including the 8840A responds 10 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 8840A 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 8840A Service requests may also be initiated using the front panel SRQ button if it has been enabled by the mask 3 50 The Serial Poll Register The serial poll register is a binary encoded register which contains eight bits as illustrated in Figure 3 9 The troller can read the 8840A serial poll register at any time by taking a serial poll Because serial poll register data i is loaded directly onto the bus instead of being loaded into the output buffer first reading the serial poll register leaves data in the output buffer intact The eight bits of the serial poll register are in Figure 3 9 Note that the SRQ mask uses bits 1 through 6 to set bit 7 the ROS bit When the ROS bit is set true the 88404 sets the 5 line true wh
77. operate without interruption Fluke authorized resellers shall extend this warranty on new and unused products to end user customers only but have no authority to extend a greater or different warranty on behalf of Fluke Warranty support is available if product is purchased through a Fluke authorized sales outlet or Buyer has paid the applicable international price Fluke reserves the right to invoice Buyer for importation costs of repair replacement parts when product purchased in one country is submitted for repair in another country Fluke s warranty obligation is limited at Fluke s option to refund of the purchase price free of charge repair or replacement of a defective product which is returned to a Fluke authorized service center within the warranty period To obtain warranty service contact your nearest Fluke authorized service center or send the product with a description of the difficulty postage and insurance prepaid FOB Destination to the nearest Fluke authorized service center Fluke assumes no risk for damage in transit Following warranty repair the product will be returned to Buyer transportation prepaid FOB Destination If Fluke determines that the failure was caused by misuse alteration accident or abnormal condition of operation or handling Fluke will provide an estimate of repair costs and obtain authorization before commencing the work Following repair the product will be returned to the Buyer transportation prepai
78. rate of change depends on how leaky the capacitor is With some electrolytic capacitors the reading will increase This usually indicates the capacitor is defective To test the capacitor s dielectric absorption briefly Short the capacitor s leads together and then the voltage across the capacitor If the dielectric is good i e has low Mon absorption the voltage across the capacitor will be nearly zero volts HI INPUT OHMS CURRENT SOURCE UNKNOWN LO INPUT 8840 UNKNOWN Figure 4 4 4 Wire Ohms Measurement b If the dielectric is poor i e has high dielectric absorption the voltage across the capacitor will be significantly above zero 4 12 A PRECISION CURRENT SOURCE The ohms current source the internal current source used in the ohms functions makes a useful troubleshooting tool in itself It has excellent linearity and temperature stability Its compliance voltage is typically 5V in the lower four ohms ranges and 12V in the upper two ohms ranges The inputs are protected against accidental applications of volt age 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 OHMS CURRENT SOURCE Measurement Tutorial RESISTANCE MEASUREMENT HI SENSE DC VOLTAGE SENSING CIRCUITRY LO SENSE LO INPUT ean Four places 4 wi
79. resistors 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 8840A case require cleaning wipe the instru ment with a cloth that is lightly dampened with water or a mild detergent solution Operating Instructions EXTERNAL CLEANING 2 12 NOTE This section contains programming instruc tions for use with the IEEE 488 Interface Op tion 05 For installation instructions refer to the Options and Accessories section 3 1 INTRODUCTION The IEEE 488 Interface turns the 8840A into a fully programmable instrument for use with the IEEE Standard 488 1978 interface bus IEEE 488 bus With the IEEE 488 Interface the 8840A can become part of an automated instrumentation system The 8840A 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 Instrumenta tion 3 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
80. t to R W Not Valid 12 3 TdDW DSW Write Data Valid to DS Write 1 Delay 1 2 3 TdDS DW DS 1 to Write Data Not Valid Delay 1 2 3 TdA DR Address Valid to Read Data Required Valid 1 2 3 4 TdAS DS AS t to DS 1 Delay 80 12 3 MM NOTES 1 Test Load 1 All timing references use 2 0 V for a logic 1 and 0 8 V for a logic O 2 Timing numbers given for minimum TpC All units in nanoseconds ns 3 Also see clock cycle time dependent characteristics table f Timings are preliminary and subject to change 4 When using extended memory timing add 2 TpC Zilog and 289 are trademarks of Zilog inc with whom John Fluke Mfg Co inc is not associated Reproduced by permission 1983 Zilog Inc This material shall not be reproduced without the written consent of Zilog Inc Theory of Operation GUARD CROSSING Table 5 1 Sample Rates and Reading Rates Samples Samples Samples Samples per Sec per Reading per Sec per Reading FREQUENCY The circuit in Figure 5 15 has two stable states corre sponding to output high 5V and output low OV 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
81. take readings until you select another calibration procedure or exit the calibration mode Specifically the 8840A 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 8840A is taking verification readings certain buttons are active or function differently Maintenance CALIBRATION aalala aaaea 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 calibrated 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 can use the RATE button to verify the calibration at other reading rates CAUTION is still possible to erase the calibra tion memory while the 8840A is taking verification readings 6 19 ERASING CALIBRATION MEMORY The 8840A allows you to erase some or all of the correc tion 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
82. that point 3 Turn on power in the circuit and read the display 4 Turn off power in the circuit and disconnect the 8840A 2 28 Current Fuse Protection The 2 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 8840A will respond as though the input were zero WARNING TO AVOID ELECTRIC SHOCK REMOVE THE TEST LEADS BEFORE REPLACING THE FRONT PANEL FUSE 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 holder out of the front panel The internal 3A fuse should be replaced only by qualified service personnel 2 29 Offset Measurements WARNING WHEN THE OFFSET FEATURE IS USE DISPLAYED READINGS ARE RELATIVE AND MAY NOT INDICATE THE PRESENCE OF DANGEROUS POTENTIALS AT THE CONNEC TORS 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 8840A 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 rep
83. the In Guard Troubleshooting Mode This mode is established by short ing 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 uC programs U202 38 as an input it is normally an output to preclude any possibil ity of damage due to the short CAUTION To avoid damaging the 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 second 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 uC pins that are normally only programmed as inputs are also programmed as inputs to prevent contentions between them and the outputs from other ICs which drive them Data coming into all uC inputs except pin 38 is ignored 6 31 Maintenance TROUBLESHOOTING Mhz xtai2 3333005202022 100 DD GU GG Cuart out lt lt P30 Duart in p37 8 hz pulses RESET
84. the SENSE LO terminal In ranges r5 and 6 the SENSE LO and INPUT LO terminals are both switched into the dc input path by 04030 U403C U403D TO OHMS PROTECTION 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 the 2000 range and less than 1000 in the 20 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 Amplifier connected as a comparator is 5 9 Theory of Operation AID CONVERTER SENSE PATH FOR _ 2 WIRE OHMS 2000 RANGE DURING TRACK PERIOD TO TRACK HO OHMS CURRENT SOURCE ANALOG FILTER K301 K401 SHOWN ENERGIZED 4 4 4 4 4 4 PRA HLA HL Switch closed or relay energized 2 Switch closed only 2 WIRE ohms NOTE gt 1 4 Switch closed only 4 WIRE ohms reading rale ranges Figure 5 8 Ohms Sealing A
85. the amplifi ers and the various levels in the bootstrap circuits can be easily measured with a voltmeter Oscillations at the out puts of the amplifiers and other abnormal signals can easily be identified with an oscilloscope 6 67 Power Supply Troubleshooting If the display does 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 3 Is the rear panel fuse blown 6 42 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 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 1090 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 is nothing 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 If either component is shorted or if there is a large amount of le
86. the instructions in Section 8 Slide the case and rear bezel onto the chassis Install the two rear panel mounting screws Install the case grounding screw in the bottom of the case WARNING TO AVOID ELECTRIC SHOCK ENSURE THAT THE GROUNDING SCREW 15 FIRMLY ATTACHED TO THE CASE BOTTOM INTERNAL FUSE REPLACEMENT CAUTION For fire protection use exact fuse replacements The 8840A 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 disassem bly instructions The fuse is held in fuse clips on the Main PCA Do not use makeshift fuses or short circuit the fuse holder e 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 The 8840A is designed to be easily maintained and repaired Both the analog and digital circuits have built in diagnostic self tests and troubleshooting modes to facili tate troubleshooting and repair The instrument s circuits allow troubleshooting and repair with basic electronic troubleshooting equipment such as a multimeter and oscil loscope The troubleshooting mode in the digital controller circuitry generates specia
87. 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 8840A 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 pro grammed as follows 100 PRINT 03 Ti 2 F4 200 INPUT 63 A Rule 4 If an input command string contains a trigger enter the commands in the following order Commands to configure the instrument if any b The trigger command Commands to re configure the instrument if any d Terminator s The principle behind this rule is that the 8840A executes all commands in the exact order they are received from left to right as written Example F3 F4 Explanation Improper construction F3 is effectively discarded 3 15 Remote Programming INPUT SYNTAX 3 16 DEVICE DEPENDENT MESSAGES Single character Commands 2 Two character Commands Bn Cn Dn Fn Gn Pn Rn Sn Wn Xn Yn Zn Numeric entry Characters 0123456789 Terminators INTERFACE MESSAGES Address Messages 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 5 lt gt cows HIJKLMOQUV These two commands are comp
88. 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 0808 or digital hardware on the Main PCA 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 calibra Table 6 28 Truth Table for U804 and K2 PIN OR DEVICE usoa 2000 mA 1 200 mV 2 20V 200V 700V NOTE For U804 iogic 0 switch on Logic 1 is gt 2 4V logic 0 is 0 8V tion 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 It is safe to force one control line at a time high 45V or low 0V to test the individual switches in U808 The on resistance of switches 0808 should be less than 5000 the off resistance should be greater than 10 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 10 find the suspected s
89. voltage build up which is potentially hazardous Use probes when measuring circuits exceeding 2 amps Maintenance Options and Accessories SECTION GUIDE Introduction and Specifications Operating Instructions Remote Programming Theory of Operation List of Replaceable Parts Schematic Diagrams Index Table of Contents SECTION TITLE PAGE 1 introduction and Specifications Mead 11 INTRODUCTION 55 6 et 1 1 12 THE 88404 DIGITAL 1 1 1 3 OPTIONS AND ACCESSORIES 1 1 1 4 SPECIFICATIONS Mu apa A ao e 14 2 Operating eee secu ener 2 1 2 1 21 2 21 INSTALLATION dk hres ues Geass 552275026 2 3 Installing the Power Line 2 2 4 Connecting to Line 2 1 2 5 Adjusting th 2 1 2 6 Rack Mounting Kits esce eere soir peace Der REX ISI 2 1 2 7 OPERATING FEATURES 225 etes
90. with water based commercial cleaning systems such as dishwashers 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 distilled water for the final rinse in geographic areas with exceptionally hard water During the final rinse Maintenance INTERNAL CLEANING mE eno ieu cea ue eir E d LLL Le Spray or run the water so that the surface is thoroughly MEME M C covered to remove all ionized material 3 Thoroughly dry all PCAs using one of the following AY methods U221 11 Preferably the should be dried in a low 4 temperature drying chamber or infrared drying U221 10 Tack with a temperature range of 49 C to 72 ov 120 F to 160 F 4 b If neither drying chamber drying rack is JH available dry at ambient room tem OV perature for at least two days satisfactory cleaning method consists of holding the PCAs under hot running water until they are clean Follow j this wash with a final rinse See consideration 2 above 0901 5 0 6 78 Cleaning After Soldering us CAUTION 112 us T M C Cleaner and similar products can can attack the nylon latches and other 0 2V plastic pieces U908 7 SEEN ON OV 1 488 a PCA has been soldered i
91. 0 00000 000000 000000 0 0 Next move to U305 7 and repeat The pattern at U305 7 will be 00000 00000 000000 111111 00 6 61 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 pin 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 cc E M a 2 reading rate logic 1 if not in fast reading rate i e if in slow or medium ow reading rate ic 1 1f in 61 ic 1 if in fast DEFINITIONS lo 109 mac e am am gt ac Pin Func Port tion ut Table 6 21 Analog Control Logic States A11 these Sm 525 58 522 OO O mmm DOORN Om Om 1 0 et ee oo wt Vet OO 4 Yet mmm OO OO0m OO mH mHMmMOO 4 R
92. 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 when the input sampling portion of the A D conver sion is completed The signal is useful for interfacing with other equipment when the 8840A 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 TO AVOID SHOCK HAZARD AND OR INSTRUMENT DAMAGE DO NOT APPLY INPUT POTENTIALS THAT EXCEED THE INPUT OVERLOAD LIMITS SHOWN IN TABLE 2 2 The 8840A 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 2 9 Operating Instructions MAKING MEASUREMENTS 2 26 Measuring Voltage and Resistance To measure voltage or resistance select the desired func tion 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 con nect the test leads as follows 1 Turn off power in the circuit to be measured see Figure 2 10 2 Break the circuit preferably on the ground side to minimize the common mode voltage and place the 8840A in series at
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94. 0V 1W TO 92 TRANSISTOR SI PNP 40V 350MW TO TRANSISTOR SI N JFET TO 92 TRANSISTOR SI N JFET TO 92 TRANSISTOR SI NPN 300V 1W TO 9 TRANSISTOR SI PNP 350V 0 6W SE TRANSISTOR SI N JFET DUAL SEL TO 71 THYRISTOR SI SCR VBO 100V 0 8A 5 1 5 0 25 RES CF 470 5 0 25W RES CF 27K 5 0 25W RES MF 50K 0 1 0 125W 25PPM RES CF 560 5 0 25W RES CF 15K 5 0 25W RES CF 100 5 0 25W RES CF 1 5K 5 0 25W RES CF 33K 5 0 25W RES CF 2 4K 5 0 25W RES CC 100K 5 2W RES MF 90 9K 1 0 125W 100PP RES CF 1 5M 5 0 25W RES CF 1M 5 0 25W RES MF 1K 1 0 5W FLMPRF FUS RES CF 5 6K 5 0 25W RES CC 22K 10 2W RES CF 620 5 0 25W W W RESISTOR RES MF 10K 0 1 0 125W 50PPM RES WW HERM 1 4W 54 6K 05 RES CF 4 3M 5 0 25W RES CF 10M 5 25W RES CF 910 5 0 25W RES MF 1K 1 100PPM FLMPRF FUSIBLE RES MF 4 99M 1 0 125W 100PPM RES MF 576K 1 0 125W 100PPM RES MF 100 1 0 125W 25PPM RES CF 560 5 0 25W VARISTOR 390V 10 1MA VARISTOR 430V 10 1 0MA SWITCH CONDUCTIVE ELASTOMERIC SWITCH PUSHBUTTON DPDT PUSH PUSH ty 714352 152207 534446 516880 728907 414128 602763 682906 682898 735365 698225 698233 601333 0 420 O88 wa pHa 601333 722934 650846 461772 742643 343426 343434 441501 340257 385948 348854 348771 343418 348888 441493 285056 2
95. 1 00001 1 0 000 40000 0000 07 00 9 0 0 1 1 1 1 1 000000 000000 0 000 00000 0600000 000000 1 111 1111 1 111111 111111 1 111 11111 111111 111111 1 000 00000 100000 100000 1 111 11 11 1 011111 011111 0 000 00000 111111 111111 0 010 11 11 1 111100 111100 1 000 00000 000011 000202 11 0 111 11111 111100 111100 i 000 00000 000001 00002901 0 1 111 11111 111110 111110 1 00000 000110 000110 0 1 4 1 11211 001000 001000 1 11 1 1111 1 111110 1 1 1 1 1 0 1 0 00000 110000 110000 0 11111 000000 000000 0 000 00201 1 909 000909900 0 111 00101 111111 111111 1 000 10000 000000 000000 0 000 10000 000000 1 01 19 0600000 000000 0 O O O gt and 1 stands for it being it the switch relay Otherwise it is closed when lac TS t m 000 9 FY m m Maintenance TROUBLESHOOTING Table 6 16 Overall State Table cont TEST NUMBER 1234 5 67 8 9 10 11 12 13 14 15 16 17 18 19 20 21 DC Scaling 000 0 0 0 0 1 1 1 14 1 1 1 0 0 0 0 0 0 009 00 0 0 0 0 0 0 0 0 00 0 0 1 1 1 0 0 1 0 0 0 0 1 1 1 1 1 0 0 UDC r1 72473 1 UDC s Cohgs s r1 r 24732 6304 3 1111111111111 1 1 1 4 1 1 000 0 10 0 0 0 1 1 1 1 1 0 1 14 1 14 1 1 4 6310 000 0
96. 10 1011 0110 1100 0110 1101 0110 1110 0110 1111 0111 0000 0111 0001 0111 0010 0111 0011 0111 0100 0111 0101 0111 0110 0111 0111 4 1 INTRODUCTION This section discusses considerations and techniques to help you use the 88404 effectively Among other things this section discusses sources of error which are an inher ent 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 confi dence This section also discusses the relative benefits of 2 wire and 4 wire ohms describes special considerations for mak ing 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 Circuit Loading Error Whenever a voltmeter is connected to a circuit the volt meter 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 resis tance of the circuit under test the source impedance is small compared to
97. 120 PRINT 130 PRINT MONITORING SELFTEST 140 INIT PORT 0 Initialize port 150 CLEAR DA IClear device 160 PRINT DA 20 IStart selftest 170 180 PRINT DA G7 INPUT DA 190 IF E 1000 THEN 220 200 PRINT DA 210 PRINT ERROR RIGHT E 3 OCCURRED Print analog errors 220 PRINT DA GO INPUT DA 515 230 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 fPrint last digital error 270 PRINT SELFTEST COMPLETE 280 END Figure 3 13 Example Program Record Errors During Selftest 3 25 Remote Programming EXAMPLE PROGRAMS 10 REM The liodie Program is written 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 8840A 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 18840A assigned to the GPIBO board 60REM 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
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99. 2 ACCESSORIES uel 8 1 8 3 Rack Mount Kits 78834 Y8835 and 8836 8 1 8 4 Shielded TEEE 488 Interface Cables Y8021 Y8022 and 8023 METRE NE 8 1 y Table of Contents SECTION TITLE PAGE 8 5 Replacement Test Leads 0 81 8 6 Deluxe Test Lead Kits 8134 8 amp 1 8 7 Slim Flex Test Leads 8140 8 1 8 8 Temperature Probes 80 1500 and 80 8 1 8 9 RF Probes 85 and 8 82 8 10 Current Shunt 807 10 82 8 11 Current Probes Y8100 8101 801 400 and 801 600 82 8 12 High Voltage Probes 80K 6 and 80K 40 9096 82 805 Option 05 IEEE 488 Interface 805 1 809 Option 09 True RMS 809 1 9 Schematic 9 1 TABLE TITLE PAGE 1 1 ro vu 1 2 2 1 Error Codes ie Sou S Nue 2 8 2 2 Input Overload Limits PEN Knut CE NE ORE 2 10 31 Status Dae oh Se dieu date ae aba e
100. 2064 2 T 2050 2080 024 t 2 5020 5 2 8 t091 095 e eot onwaar 361940 e 10 9 LOEN S rgo E gt SUES a we 2 rtu e ats 18 2 59080 gt oN S 082 dyeb 1066 z 508 EDMAN 6 2021 OO sos 1 G 01632 575 dur ETE w E Wer 2220 5 we Js 20nd E Torn 10283 29 Cx a Q T0282 23 8028 E0 o 20 1137 2154 otha d gt _ TOTO foe ee 02 3028 zon mE TOTS 438 2 028 9 5079 TOZ 8 soo 99 0780 2027 au q 8 p TOTA 2 2 091770788 suluo 2 6 401 T0282 2029 5024 902 ea d 1091 50984 07 911910 2 5194 up o b0 5 _ 20780 30739 EOTS 0153 Tote 1 30 in bten 8729 401 0220 TOTO SOIN 073 50185
101. 213 4 5 6 7 9 10 11 12 Reference U213 4 for STROBE ZERO Check for strobe decoder inputs 510 511 512 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 approxi mately 30V 6 53 4 to 7 Segment Decoder U216 Check that 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 U218 Check that U218 1 through U218 4 all look like the waveform DIGIT DATA High level is 3 8V to 43V 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 U203 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
102. 22 6 33 REASSEMBLY 6 22 6 34 INTERNAL FUSE REPLACEMENT 6 24 6 35 EXTERNAL TRIGGER POLARITY SELECTION Option 05 Only 6 25 Table of Contents SECTION TITLE 6 35 TRIGGER POLARITY SELECTION Option 05 6 25 6 36 TROUBLESHOOTING 255 VE TID cs E ELLO 6 25 6 37 Initial Troubleshooting Procedure 6 25 6 38 Duisnostc SELL Tests chs aca dis ae Ss e 6 29 6 39 E E p A ree 6 29 6 40 Digital Controller Troubleshooting 2 4 4 6 31 6 41 IN GUARD MICROCOMPUTER SYSTEM 6 31 6 42 In Guard 6 32 6 43 Address Latch 0219 6 33 6 44 External Program Memory 0222 iR ME Sd Wate Y 6 33 6 45 Calibration Memory 0220 6 33 6 46 Relay Buffer 0201 rn 6 33 6 47 3 8 Chip Select Decoder 208 leiden u 6 34 6 48 DISPLAY SYSTEM sena een 6 34 6 49 Display Control 0212 4 sd Seats wah tr
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104. 26 Measuring Voltage and 2 10 2 27 Measuring Sa a a 2 10 2 28 Current Fuse Protection E as Qi E 2 10 2 29 Offset Measurements ube 66 ba od Re sles days sie 2 10 2 30 EXTERNAL CLEANING bes Ves 2 11 5 Table of Contents TITLE PAGE 3 Remote Programming 03940 2 4 9 INTRODUCTION LAA 3 1 2 2 CAPABILITIES Neb Ei 3 1 3 3 BUS SET UP 3 1 3 4 OVERVIEW OF REMOTE OPERATION 3 1 3 5 NOTE ABOUT 65 3 2 3 6 DEVICE DEPENDENT COMMAND 6 3 2 3 7 Bn Offset 5 ieee 3 2 3 8 Cn Calibration 3 4 3 9 Dn Display 3 4 3 10 Fn Function 5 3 4 3 11 Get See Oba TOTO NOI PME 3 4 3 12 GO Get Instrument
105. 3 12 6 56 Hex Inverter U221 Check that U221 5 is the same as STROBE ZERO and that U221 6 is STROBE ZERO inverted Maintenance TROUBLESHOOTING Se lt XS MR RR RR AT WHICH WAVEFORM NAME WAVEFORM WAVEFORM APPEARS SLO U213 1 usto pep cq 0212 32 7 0 1 2 3 4 5 6 7 0 1 SL1 U213 2 pag gt 7 0 1 2 3 4 5 6 7 0 1 512 0213 3 0212 34 7 0 1 2 3 4 5 6 7 0 1 0213 4 2 YES 4095 us U215 8 7 0 1 2 3 4 5 6 7 0 1 0221 5 STROBE es 585 us 4095 us U215 7 U203 9 7 0 1 2 3 4 5 6 7 0 1 U213 6 DIGIT U216 4 DATA U U LJ 6 and U216 9 140 us low for inter digit blanking 450 us high for data on through U U217 1 through U217 7 uc RR Figure 6 11 Waveforms for Display Logic 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 5 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 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 pressed and held an inverted version of STROBE ZERO waveform is applied to 0212 38 If range but
106. 3 11 3 2 Numeric Output Data 3 17 3 3 Immediate Mode Commands for Various 3 21 3 4 Std 488 1978 3 38 41 Test i os care 4 4 5 1 Sample Rates and Reading 5 17 6 1 Recommended Test 6 2 62 Voltage aede ER E E 4 16 3 Low and Mid Frequency AC Voltage Test MEE 6 4 6 4 High Frequency AC Voltage 6 5 6 5 Resistance edese 65 6 6 DC Current es eade 6 6 Gey 6 6 6 8 A D Calibration Steps 6 8 6 9 A D Calibration Verification Test 6 8 6 10 Offset and Gain Calibration 6 9 6 11 High Frequency AC Calibration Steps
107. 3 204 J601 J602 JPR1 2 K301 Table 7 2 A1 Main PCA Description REF AMP SET CAP POLYPR 0 1UF 10 160V CAP CER 0 22UF 80 20 50V Z5U CAP CER 0 01 UF 80 20 50V Z5V CAP TA 1UF 20 35V CAP CER 1000PF 20 50V X7R CAP POLYPR 0 12UF 10 50V CAP POLYPR 0 22UF 10 160V CAP POLYPR 0 33UF 10 160V CAP POLYES 0 22UF 5 50V CAP POLYPR 4700PF 10 63V CAP POLYPR 0 47UF 10 160V CAP CER 120PF 5 50V COG CAP POLYES 0 001UF 10 50V CAP POLYPR 0 047UF 10 160V CAP CER 330PF 5 50V COG CAP POLYES 0 47UF 10 50V CAP AL 6800UF 20 16V CAP AL 330UF 50 20 100V CAP AL 470UF 20 50V SOLV PR CAP AL 100UF 50 20 50V CAP CER 270PF 5 50V COG ZENER UNCOMP 3 9V 10 20 0MA 0 4W ZENER UNCOMP 7 5V 5 20 0MA 0 4W DIODE SI 75V 150MA DO 35 ZENER UNCOMP 10 0V 5 12 5MA 0 4W ZENER UNCOMP 6 8V 5 20 0MA 0 4W ZENER UNCOMP 24 0V 5 5 2MA 0 4W DIODE SI 1KV 1A DO 41 ZENER UNCOMP 5 1V 5 20 0MA 0 4W DIODE SI 100V 1A DO 41 ZENER UNCOMP 6 2V 5 20 0MA 0 4W ZENER UNCOMP 8 2V 5 20 0MA 0 4W ZENER UNCOMP 56 0V 596 2 2MA 0 4W ZENER UNCOMP 8 2V 5 20 0MA 0 4W RIVET S TUB OVAL STL 118 156 SCREW PH P SEMS STL 4 40 250 RIVET S TUB OVAL AL 118 312 NUT BROACH STL 4 40 NUT HEX STL 4 40 SCREW PH P SEMS STL 6 32 250 HEADER 2 ROW 100CTR 20 PIN CABLE ASSY FLAT 10 CONDUCT 6 0 CABLE DISPLAY PWR PLUG PWB 6A 250V 3 WIRE HEADER 1 ROW 156CTR 6 PIN RES JUMPER 0 02 0 25W RELAY ARMATURE 2 FORM C 5VDC 684209 44
108. 4 1 1 4 1 0 9 1 0 0 0 09 0 1 90 0 0 0 0 0 0 VACCIAC 28 K801x 29 K802x CVAC 94475 IAC VACA r3tr5 gt lt 1 30 1 31 08048 32 0824 9 1 IDC 199 0 0 0 0 90 0 0 0 0 0 06 0 0 0 0 0 9 0 33 8040 16 2 4 6 27 Maintenance TROUBLESHOOTING M M Table 6 17 Tested by the Analog Self Tests CIRCUITRY TESTED DC K301 Q310 Q311 0304 0304 19 R315 U306 2301 2302 2304 Amplifier U301 U302 U303 2303 5 Protection U401 U404 U402 U403 2401 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 problems in the display keyboard system 6 28 TEST NUMBER 11 12 13 14 Finally as in most processor based systems there are communication links between the various parts of the system Specifically in the 8840A 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 EE DC CDL LL ALERT generate problems that
109. 40A ibcir dmm clear device ibwrt 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 label1 printf sS 2 wire LOWEST READING r n rd do ibwrt dmm 1 trigger the device ibrsp dmm spr serial poll the device Y sed 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 5 gt 7 throw away data if not lowest r s 1 11 print new low f 3 36 Figure 3 14 Example Programs Using the IBM cont Remote Programing EXAMPLE PROGRAMS The following application program is written in C for the IBM The National Instruments Model AT GPIB board provides the interface between the PC and the Fluke 88404 DMM program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840A assigned to the GPIBO board This program illustrates a method of recording any errors produced by the 8840A selftest function It should be noted that 1 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
110. 5 Calculator FUNCTION PERFORMED INITIALIZE Port CLEAR Instrument REMOTE Commands INIT PORT 0 cli 7 CLEAR 04 cir 704 REMOTE 4 rem 704 CLEAR 7 INIT CLEAR 704 PRINT g4 REMOTE 704 WBYTE 836 17 LOCAL Control LOCAL Q4 704 LOCAL 704 WBYTE 936 1 EXTERNAL TRIGGER TRIGGER Instrument GET Output Data PRINT Data to Screen CONFIGURE for VAC CONFIGURE for 200Vac TRIGGER Continuously SUFFIXES Enable GET Data amp Suffix PRINT Data amp Suffix PRINT Q4 T1 TRIG 04 INPUT 4 A PRINT A prt A PRINT 4 2 PRINT 4 R4 PRINT 4 TO PRINT 4 Y1 INPUT Q4 PRINT Notes wrt 704 T1 trg 704 red 704 A wrt 704 F2 wrt 704 R4 wrt 704 TO wrt 704 Y1 red 704 Note 1 prt ASA OUTPUT 704 T1 TRIGGER 704 ENTER 704 A Note 2 PRINT A Note 2 OUTPUT 704 F2 OUTPUT 704 R4 OUTPUT 704 TO OUTPUT 704 Y1 ENTER 704 A A Note 2 PRINT A A Note 2 PRINT 94 T1 PRINT 04 INPUT 4 PRINTA PRINT 4 2 PRINT 4 R4 PRINT Q4 TO PRINT 94 Y1 INPUT 4 A A PRINT 5 Before using A on the 9825 is necessary to enter dim AS 6 to allocate a String variable This statement allows six characters the HP9816 system variables cannot be created from the keyboard they must be created by running a program See error 910 for that system To get around this type in a very short program as follows SCRATC
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112. 6781 733386 697284 697417 697458 851738 446799 520346 747519 721662 446807 721142 720938 446773 697441 697409 478784 484436 747493 649731 658898 113316 256446 203323 246611 260695 267807 707075 159798 742874 325811 386771 187757 386771 103424 185918 245290 380196 110635 178533 706986 714022 684167 461806 380378 682575 Notes 1 4 14 615575 Maintenance Test PERFORMANCE TEST K401 MP2 MP3 51 MP29 50 MP35 MP60 MP69 MP201 Q101 309 408 Q102 Q301 304 307 Q308 311 313 Q315 401 405 Q407 Q302 303 310 Q312 316 Q305 0306 402 404 0314 0601 101 602 603 605 R102 203 204 103 104 105 R106 R201 215 217 R305 307 604 R202 315 R205 207 208 R210 412 R206 209 312 R313 408 R216 406 R301 R302 303 R304 R308 316 317 R309 R310 409 415 R314 R318 R319 R321 322 R401 R402 R403 R407 R410 R413 R414 R416 R601 RV301 401 404 RV601 1 S201 Table 7 2 A1 PCA cont Description RELAY REED 1 FORM A 5V HIGH VO INSUL PT TRANSISTOR MOUNT DAP TO 5 BRACKET CONNECTOR MTG HLDR FUSE 13 32 PWB MT SHIELD A D HEAT DIS VERT 1 18 1 00 50 TO HLDR PART FUSE BODY PWB MT FASTENER PLUNGER NYL 271 FASTENER GROMMET POLYCARB 271 PAD ADHESIVE TRANSISTOR SI NPN 6
113. 720A or 1722A instrument controller The function 4 ofthis program is to display on the controller screen the lowest resistance measured 5 across the input terminals of 8840A using the 2 wire ohms function in autorange 7 8 FLUKE BASIC 17204 1722A 9 100 INIT PORT 0 X CLEAR PORT 0 X WAIT 500 Clear port instrument delay 110 PRINT Q4 N3001PO Y1 Instrument functions and trigger 120 INPUT Q4 first reading 130 PRINT 2 wire Lowest Reading i 140 TRIG 94 160 B SPL 4 Get serial poll register 170 IF 0 THEN 160 Looking for data available 175 INPUT 4 R A Get next data 180 IF R gt A THEN 140 Throw away data if not lowest 185 Update lowest reading 190 130 new low 900 END Figure 3 12 Example Program Using the Serial Poil Register 1 Remote Programming EXAMPLE PROGRAMS 444 10 This program demonstrates a method of recording any errors produced by the 8840A 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 Theresponse to the Get Instrument Configuration GO command during selftest is 60 3 The response to Get Error Status G7 command with errors present is 1000 70 80 FLUKE BASIC 1720 1722 90 100 DA 4 IDevice address 4 110 TIMEOUT 10000 110 second timeout
114. 75 SCREW PH P LOCK SS 6 32 312 SCREW PH P SEMS STL 4 40 375 SPACER SPACER SCREW FH P LOCK STL 6 32 750 SHIELD MAIN BOTTOM BRACKET TRANSFORMER CASE METAL FRONT PANEL PUSHROD POWER PUSH ROD RAI PUSH ROD CAL ENABLE SWITCH MOUNTING PLATE HANDLE LEFT MED PEW MOUNTING PLATE HANDLE RIGHT MED PEW HANDLE PAINTED DARK UMBER BEZEL REAR SPACER MATRIX CASE FOOT BLACK CHASSIS ASSEMBLY TERMINAL BLOCK RAI SEAL CALIBRATION SUPPORT PWB LENS FRONT PANEL DECAL FRONT DECAL REAR INSERT REAR PANEL IEEE CABLE GUIDE DECAL CSA SPACER RND NYL 166 250 SHIELD SUPPORT HLDR PART FUSE CAP 1 4X1 1 4 FUSE HOLDER CAP ASSEMBLY NAMEPLATE SERIAL REAR PANEL LABEL CE MARK BLACK SWITCH CONDUCTIVE ELASTOMERIC LINE VOLTAGE SELECTION SWITCH INSTRUCTION MANUAL GETTING STARTED MANUAL QUICK REFERENCE GUIDE CORD LINE R A 5 15 3 18 TEST LEAD ASSY TL70A 728857 728873 475004 376582 166306 166488 682906 682898 152819 152140 721118 721134 721449 320093 114116 424713 281196 735407 735415 114504 728998 765263 656389 656397 656413 656488 684142 729004 660472 810127 660480 684126 824433 684134 656504 735274 683987 656405 685081 698431 684191 728956 525527 772889 735308 460238 516039 472795 600707 680769 735258 879304 879291 879296 707018 855820 Qty Coco c o con oc oc o 5 oL oL oL goo n
115. 8 200 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 Ampli fier 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 cir cuit 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 input divider has not discharged to zero volts due to the long time constant of the filter TEST 20 200 VDC 2 Filter Off TEST 21 200 VDC Filter Off 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 TEST 25 In Guard uC Internal RAM U202
116. 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 Ve RMS 4 21 Bandwidth Bandwidth defines the range of frequencies to which an instrument can respond accurately The accuracy of the 8840A is specified for sinusoidal waveforms up to 100 kHz or for nonsinusoidal waveforms with frequency com ponents 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 Tise times such as high frequency square waves or switch ing supply waveforms 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 limita tions if the input slew rate is slower than 1V us x full scale of range 4 22 Zero Input VAC Error If the 8840A input terminals are shorted while the VAC function is selected the 8840A 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 inhere
117. 840A front panel display The 8840A features closed case calibration using known reference sources The 8840A automatically prompts you for the required reference sources measures them calcu lates 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 8840A can be calibrated by an automated instrumentation system The 8840A 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 8840A should also be calibrated if it fails the performance test or has undergone repair To meet the specifications in Section 1 the 8840A 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 6 10 Basic Calibration Procedure The basic calibration procedure consists of the following four parts These parts must be performed in the order shown l Initial Procedure 2 A D Calibration 3 Offset and Gain Calibration for each function and range 4 High Frequency AC
118. ANDLE 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 gt 9 HANDLE S S DEVICES ONLY 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 REPRINTED WITH PERMISSION FROM TEKTRONIX INC AND GENERAL DYNAMICS POMONA DIV Dow Chemical 9 93 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 8840A The section includes a performance test a calibra tion 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 recom mended equipment is not available equipment that meets the indicated minimum specifications may be substituted 6 2 PERFORMANCE TEST This test compares the performance of the 8840A with the spec
119. BCLR DVM Clear device 270 FOR W 1 500 NEXT W Wait 1 second before sending commands 280 WRT N3001P0 Y1 290 CALL IBWRT DVM96 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 8840A 330 VAL RD 340 PRINT LEFT RD 16 S 2 WIRE LOWEST READING Display readings 350 WRT 7 360 CALL IBWRT DVM WRTS Trigger the 88404 370 CALL IBRSP DVM SPR 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 THEN 350 Throw away data if not lowest 430 5 Update lowest reading 440 GOTO 340 Print new low 450 END i Figure 3 14 Example Programs Using the IBM pc cont 327 Remote Programming EXAMPLE PROGRAMS 10 REM The following application program is written BASICA for the IBM PC 20 REM PC AT The National Instruments Model GPIB PCIIA board provides the interface 30 REM between the PC and the Fluke 88404 The program assumes that the configuration 40 REM program IBCONF has been run to initialize the iet board with the device 50 REM name 18840A assigned to the GPIBO board 60 REM 70 REM The first 6 lines of code are required
120. CAL VALUE CALIBRATION CALIBRATION G2 STATUS _ CALIBRATION Figure 3 2 Remote Operation Block Diagram SERIAL POLL REGISTER Remote Programming DEVICE DEPENDENT COMMAND SET Here is a typical command string as it might be sent from a Fluke 1722A Instrument Controller The string configures the 8840A and triggers a reading The PRINT command automatically sends terminators CR LF and or EOI to the 8840A at the end of the command string IEEE 488 bus address Resets the 8840A to the power up configuration Selects the 2 WIRE function Selects the 2000 range Selects the medium reading rate Selects the external trigger mode Rear panel trigger disabled Triggers a reading Figure 3 3 Typical Command String 3 8 Cn Calibration Commands CAUTION The command string C3 erases the entire calibration memory A com plete calibration must then be per formed The Calibration commands allow the 8840A to be cali brated under remote control Commands C1 and C2 duplicate the front panel calibration functions STORE A D and AC respectively For a complete description of remote calibration see the Maintenance section of this manual For the 8840A to accept these commands the 8840A must be in the calibration mode enabled by pressing the front panel CAL ENABLE switch Otherwise the commands generate an error message i 3 9 Dn Display C
121. EAR 23 5 C 20 45 90 DAY 2345 24 HOURS 23 1 C 1 2 100 1 2 100 1 2 100 45 100 0 3 100 0 35 100 0 4 100 100 20 0 07 100 0 14 100 0 16 100 20k 50k 0 15 120 0 19 150 0 21 200 100 0 4 300 0 5 300 0 5 400 For sinewave inputs 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 to 50 kHz and 500 counts for 50 kHz to 100 kHz Relative to calibration standards When in fast reading rate with internal trigger and transmitting data out of the IEEE 488 interface the 8840A display must be blanked command D1 to ensure stated accuracy MEDIUM AND FAST READING RATES In medium rate add 50 counts to number of counts In fast rate the specifications apply for sinewave inputs 21000 counts and 2100 Hz NONSINUSOIDAL INPUTS For nonsinusoidal inputs 210 000 counts with frequency components lt 100 kHz add the following 96 of reading to the accuracy specifications CREST FACTOR 1 0 TO 1 5 1 5 20 201030 03 MAXIMUM INPUT 700V rms 1000V or2x 10 Volts Hertz product whichever is less for any range FUNDAMENTAL FREQUENCY 45 Hz to 20 kHz 20 Hz to 45 Hz and 20 kHz to 50 kHz Operating Characteristics 1 3 Introduction and Specifications SPECIFICATIONS T
122. EFECTIVE STAGE 200 mV 2000 mA 08068 20V R804 R805 2V 200V U806A 200V 700V 2V 20V 200V Input Q806 K802 2801 Input 0806 K802 2801 The input voltage should appear unchanged at pin 2801 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 If the signal at the input to U801A pin 5 is incorect U804 may be defective or the switch codes may be wrong 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 prob lems 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 If the signal at TP802 is incorrect but U801 5 is OK the digitally controlled filter section U801A and 0808 is probably defective 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
123. ER annunciator and showing a 1 on the display See Figure 2 8 The sign the position of the decimal point and the other annuncia tors are not affected As safety feature the 88404 treats the 1000V dc and 700V ac ranges differently In these ranges the 8840A 23 __ _ 82 60 ONL HO 135440 Em 19661 snonunuo2 eyes MOIS e 1501 4 E Gee M SUIN YOUMS 0002 10 UW 2 0001 9002 10 005 1894 JO 1404 19449 SNOLLNG 5120408 5 HV3u LNOHJ S3univad 1VIO3dS esse 2 Be LAdNI Ve xe iNOILNYO epou FI GU sieuiuJo 1 pue yams 318YN3 ON S Ke ds Q 9JIM P sjeuruse p 3SN3S 1 HOIH Aueuno OW 2 weno SHON OV SWYO 9JIM v SHOA OQ 90 SNOLLX8 NOILONNS Operating instructions OPERATING FEATURES Figure 2 5 Front Panel Features 2 4 Operating Instructi OPERATING FEA
124. Explanation N value P2 Where value can be an integer real number or real number with nent as described under the com mand Example Explanation N1 P2 If the 8840A is 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 pene VAR IN button To Remote Programming DEVICE DEPENDENT COMMAND SET Table 3 1 Status Data 1 6 as in Function commands Fn 9 for Seif Test 1 6 Range commands 0 2 as Reading Rate commands Sn t 0 4 as in Trigger Mode commands Tn 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 available 32 for SRQ on any em r Note SRQ mask values may be added for combinations Example 33 for SRQ on or any error 0 Not in cal verification 1 Cal verification m 0 Not in calibration mode 1 A D calibration 2 Offset and gain calibration 4 HF calibration 0 FRONT inputs selected 1 REAR inputs selected az 0 Autorange 1 Autorange off Manual range b 0 OFFSET off 1 OFFSET on 0 output suffix disabled 1 output suffix enabled 0 7 as in Terminator commands Wn FLUKE mmmmm 0 Vn n mmmmm 8840A Vn n _ IEEE 488 Interface software version number
125. FLUKE For the benefit and convenience of its customers Fluke Corporation Fluke has reproduced this copy of a manual which is no longer in production This manual has not been edited or updated since the revision date shown on the lower left hand corner of the first page Fluke will not be liable for any claims losses or damages of any kind incurred by any user arising from use of this manual 8840A Digital Multimeter Instruction Manual PN 879304 December 1991 Rev 3 5 97 1991 1994 1997 Fluke Corporation rights reserved Printed in U S A Ail product names are trademarks of their respective companies LIMITED WARRANTY amp LIMITATION OF LIABILITY Each Fluke product is warranted to be free from defects in material and workmanship under normal use and service The warranty period is one year and begins on the date of shipment Parts product repairs and services are warranted for 90 days This warranty extends only to the original buyer or end user customer of a Fluke authorized reseller and does not apply to fuses disposable batteries or to any product which in Fluke s opinion has been misused altered neglected or damaged by accident or abnormal conditions of operation or handling Fluke warrants that software will operate substantially in accordance with its functional specifications for 90 days and that it has been properly recorded on non defective media Fluke does not warrant that software will be error free or
126. H 10A 0 20 5 30 Hit RUN key Hit EXEC key Hit ENTER key Hit ENTER key Hit ENTER 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 3 58 TIMING CONSIDERATIONS To help you take the best advantage of the speed of the 8840A 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 8840A 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 con trollers These are provided for the convenience of instru ment demonstrations set up and check out and for those with limited experience with IEEE 488 bus operations As a general note The entire 8840A 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 8840A command set without repeating the clearing commands 3 60 EXAMPLE PROGRAMS Several example programs for the 8840A using various controllers are presented in the remaining figures in this section In a
127. If the IEEE 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 sec tion 2 7 Operating instructions OPERATING FEATURES Table 2 1 Error Codes ANALOG SELF TEST ERRORS 200 Zero 700 2 mA Zero mA DC Zero 200 VDC Zero 1000 VDC Zero 1000 20 20 20 20 VDC 2000 2 2000 2009 Overrange 2 20 Overrange 200 Overrange 1000 X10 20 MQ 200 200 200 20 200 2 200 VDC Filter 200 2 Filter Off 200 Filter Off DIGITAL SELF TEST ERRORS In Guard uC Internal RAM Display RAM In Guard uC internal Program Memory External Program Memory Calibration Memory OPERATION ERRORS AC functions available only with True RMS AC option mA AC or mA DC function selected while REAR inputs selected OFFSET selected with reading unavailable or overrange MEANING Computed calibration constant out of nay Previous cal may be wrong or there may a hardware problem Calibration input out of acceptable r Check that input is correct Previous cal may be wrong or there may be a Calibration memory write error Probably a hardware problem Guard crossing erto
128. Measurement 4 5 4 5 Burden Voltage Error 4 7 4 6 Waveform Comparison Chart 48 4 7 Typical Crest Factors for Various 4 9 4 8 Combined and DC 4 9 4 9 Reduction of Zero Inp t e ud 4 10 5 1 Overall Functional Block 15 2 5 2 DC Scaling VDC and mA ne rare ipis 53 5 3 Track Hold ltd ra 5 5 5 4 Track Hold Circuit Configurations 5 6 5 5 Timing Diagram for One A D 5 7 5 6 Precision Voltage Reference 5 8 Eas a 5 9 5 8 Ohms e eee Elend Saa Re 310 List of Illustrations FIGURE TITLE PAGE 5 9 Analog to Digital 2 2 5 11 5 10 First Remainder Store 5 12 2315
129. ND 322 Figure 3 10 Example Program Taking 10 Readings Remote Programming EXAMPLE PROGRAMS This is a sample program which commands the 8840A 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 8840A that any range or function may be invoked easily The controller always echos the 8840A display while this program is running FLUKE BASIC 17204 17224 INIT PORT 0 Clear Port CLEAR PORT O IClear instrument to default functions WAIT 1000 Wait 1 second before sending commands PRINT 04 F1 RO SO TO Y1 IF1 VDC RO Autorange SO Slow rate Continuous trigger Y1 suffix 0 LOCAL 94 Give local control to instrument INPUT 4 A A Get reading and suffix 88404 X X 1 increment reading count PRINT Display reading and suffix GOTO 110 END Figure 3 11 Example Program Taking Readings with Local Control EXAMPLE PROGRAMS Remote Programming A 3 24 6 command string sets up the 88404 by using the Put Instrument Configuration command 1 The following program illustrates one possible use of the serial poll register this 2 caseit is merely looking for data available The instrument is addressed on port 0 3 device 4 under control of a Fluke 1
130. NEXT i END Microsoft is a registered trademark of Microsoft Corporation QuickBASIC is a trademark of Microsoft Corporation Figure 3 14 Example Programs Using the IBM PC cont Remote rammi MAE PROGRAMS 4 again 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 8840A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840 assigned to the GPIBO board This program selects VDC F1 Autorange RO Slow rate SO Continuous trigger TO and suffixes enabled Y1 readings appear simultaneously on the instrument display and the PC screen with suffixes enabled for function readout Full local control is given to the 8840A 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 4 5 on IBM PC PC XT or PC AT SINCLUDE qbib45 del GPIBO Board is GPIBO CALL IBFIND BDNAMES BD Initialize IEEE Interface Board devname 18840 Device is 18840 CALL IBFIND devname dvm nitialize the device CALL IBCLR dvm Clear the device WRTS FIROSOTOY1 F1 Volts DC RO Autorange 350 Slow reading rate TO Inte
131. NG FIRST COMPARE 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 over line INT The In Guard uC then pulls line CS7 low five times causing U101 to send the uC the five six bit nibbles one at a time over lines ADO ADS In Guard uC then weights each nibble 1 16 of the value of the previous number and calculates the input voltage hardware for the A D Converter has four sec tions Timing Data Control Precision DAC A D pli fier and bootstrap supplies 5 21 Timing Data Control The Timing Data Control circuit the digital po of U101 times and controls the A D Converter by manipulat ing the switches in the A D Amplifier and the bit switches in the Precision DAC An A D conversion cycle is trig gered by the falling edge of line TR from the In Guard Once triggered the A D Converter under control by 0101 generates the five 6 bit nibbles without further interaction with the In Guard uC Timing Data Control circuit also provides watch dog timer line RES which resets the In Guard uC in case normal program execution is interrupted If the timer A D AMPLIFIER 2101 15 238 2101 10 667 E POL 01028 2101 159 97 Theory of Operation A D CONVERTER BIT SWITCHES SET
132. NPUT Eu TEST LIMITS IN VOLTS LIMITS IN TEST LIMITS IN VOLTS 1 0 010000V 50 kHz 0 009831 0 010169 2 0 010000V 0 009650 0 010350 3 0 10000V 0 09650 0 10350 4 1 0000 0 9650 1 0350 10 000V 9 650 10 350 6 100 00 96 50 103 50 7 19 0000V 18 8750 19 1250 8 0 190000 0 188750 0 191250 Quick test points 2 Zero the test lead resistance by pressing the l Ensure the 8840A is on and has warmed up for at OFFSET switch while shorting the HI and least 1 hour LO INPUT test leads together 2 Select the mA DC function 3 Verify that the displayed reading is within the limits shown for each reading rate 3 Connect the Current Source to the 2A and LO INPUT terminals 6 7 DC Current Test 4 For each step in Table 6 6 set the Current Source for The following procedure may be used to test the mA DC the indicated input and verify that the displayed read function ing is within the limits shown for each reading rate Table 6 5 Resistance Test ERROR FROM INPUT NP STEP dd In Counts stow FAST 1 20003 OQ short 2 20009 1000 3 2 kQ OQ short 4 2 kQ 1 5 20 052 short 6 20 kQ 10 kQ 7 200 OQ short 8 200 kQ 100 9 2000 OQ short 10 2000 1 11 20 OQ short h 20 10
133. NVERTER TO FILTERS TRACK HOLD CIRCUIT Figure 5 17 True RMS AC Option Block Diagram Theory of Operation TRUE RMS AC OPTION 09 which feedback is used to perform an equivalent analog computation The filter averages the divider output signal This filter consists of U809A C813 R815 and the internal 25 kQ resistor and op amp between pins 8 and 9 of U802 The output is further filtered by three pole post filter com prised of U809B and associated resistors and capacitors This output is then switched into the Track Hold Amplifier of the dc front end via U302 pins 15 and 14 The Track Hold Amplifier is set up for unity gain on all ac Tanges FILTER Figure 5 18 True RMS AC to DC Converter 5 20 Fluke Corporation static awareness Some semiconductors and custom IC s can be damaged by electrostatic discharge during handling This notice explains how you can minimize the chances of destroying such devices by 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 97 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 H
134. O e 00 4 MO aA RO MAOO OO OO OOO OO Ommm OO Ommm SOOO COO O eo 4 4 aA NO nin ge 82 5 SN ee 4 NTMA no 3 3333 5893 552 gua nals must 519 the ative be checked sync by on going 9 at the state ulse of the tar 0 2 us p indicated and lookin U303 GAS 9 7 5 02 50 dc 1 605 804 in at e risin et h p edge of the sync pulse t Inc on 0407 3 O TQ QM On Om Oo Om Om On Ome Om Ot Om Ow Om Om Qe On Qv On OO Om Ow Om Ot once Om O O wm O OHO Om Ow Sunc on 0203 3 QOO O eq en OOOO MOM Quo O e OOOO O Qe m O 4 4 O O mm O Qo Canad O Maintenance TROUBLESHOOTING M All these DUTPUTS are static Uncalibrated configuration en 464 4 AO e v O MM 0 MM mH 0 e OQ mm mw MOCO e
135. Q on any error range 3 14 G2 Get Calibration Prompt The G2 command is used when calibrating the 8840A 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 sh in Figure 3 6 The suffix may be enabled with the Y1 com mand Example output strings follow Examples 1 00000 0 CR LF 190 000 3 CR LF 1 90000 0 VDC CR LF Meaning Calibration prompt Calibration prompt 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 40 The G2 command is valid only when the calibration mode is enabled by pressing the front panel CAL ENABLE switch If the 8840A is not in the calibration mode the G2 command generates an error message Remote Programming E DEVICE DEPENDENT COMMAND SET OUTPUT DATA TYPE FORMAT NUMERIC DATA n nnnnnEtnn suffix CR LfI EOI from trigger or G2 EXAMPLES 12 3456 6 Measured value 12 3456E 6 OHM Measured value 9 99999 9 Overrange gt 200 000 counts 9 99999 9 gt Overrange gt 200 000 counts 1 0032 21 INSTRUMENT nnnn CR LF EO CONFIGURATION DATA From 60 G4 G5 EXAMPLE G6 an
136. SO T3 Correct construction The string contains only one output com mand F2 R3 50 Correct construction It is permissi ble for a string not to contain output command 3 Read the output data generated by one input command string before sending the next input com mand 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 8840A 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 3 T1 2 200 PRINT 3 F4 300 INPUT 3 In this incorrect example the INPUT statement is located incorrectly 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 200 INPUT 3 300 PRINT 3 F4 In this example
137. 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 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 connec tor 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 6 73 MAJOR PROBLEMS The signal flow through the True RMS AC option is straightforward with no feedback paths between individ ual stages This simplifies troubleshooting and often makes it possible to isolate a single defective stage without removing the instrument cover Table 6 25 Port Configurations address address address address NOTES 6 46 Due to external hardware conflicts the following bits are NEVER driven by the Out Guard uC in ANY diagnostic mode P0 4 5 6 7 P2 all bits P3 1 2 3 4 P3 6 the 4 MHz clock the NEC7210 IEEE U901 P3 7 is programmed as the serial output and constantly transmits hex 55 every 820 us at 62 500 baud in all four diagnostic modes This causes the front panel error message Maintenance TROUBLESHOOTING Figure 6 20 Option 09 Service Position Test the mid frequency response of the VAC function around 1 kHz If an ac
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139. The response to a Get Error Status G7 command with no errors present is 1000 140 REM 150 CLEAR 59736 160 IBINIT1 59736 170 IBINIT2 IBINIT1 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 IBFIND IBTRG IBCLR IBPCT ABSIC IBLOC IBPPC IBBNA IBONL IBRSC IBSRE IBRSV IBPAD IBSAD IBIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF i 200 CALL IBINIT2 IBGTS IBCAC IBWAIT IBPOKE IBWRT IBRPP IBRSP IBDIAG IBXTRC IBRDI IBWRTI IBRDIA IB 210 REM 220 REM 230 REM 240 DEVNAME 188404 250 CALL IBFIND DEVNAME DVM 260 CALL IBCLR DVM 270 FOR W 1 TO 500 NEXT W 280 PRINT MONITORING SELFTEST 290 WRTS 20 CALL IBWRT DVM WRTS 300 WRT G7 CALL IBWRT DVM WRT 310 SPACES 6 320 CALL IBRD DVM E 330 IF LEFT E 4 1000 THEN GOTO 360 340 WRTS XO CALL IBWRT DVM WRTS 350 PRINT ERROR RIGHT E 3 OCCURRED 360 WRTS GO CALL IBWRT DVM WRTS 370 ST SPACES 6 380 CALL IBRD DVM ST 390 IF LEFT ST 4 gt 9000 THEN GOTO 300 400 WRITS G7 CALL IBWRT DVM WRTS 410 E SPACES 6 420 CALL IBRD 5 430 IF LEFT E 4 1000 THEN 450 440 PRINT ERROR RIGHTS ES 3 OCCURRED 450 PRINT 460 PRINT SELFTEST COMPLETE 470 END IBWRTA IBCMD IBCMDA IBRD IBRDA IBSTOP WRTIA IBSTA IBERR IBCNT IBM BASICA on IBM or PC AT Device name is 18840 Initialize the DMM Clear device Wait 1 second before sending co
140. VICE DEPENDENT COMMAND SET FUNCTION COMMANDS F1 VDC Default F2 VAC 2 WIRE 4 4 WIRE 5 mADC mA 5 Autorange On Default 200 mV 2000 2V 2 20 20 200 200 1000 700V 2 2000 mA Autorange READING RATE COMMANDS SO Slow Default S1 Medium S2 Fast TRIGGER MODE COMMANDS TRIGGER REAR PANEL SETTLING TRIGGER TO Default Internal T1 External T2 External T3 External T4 External Disabled Enabled Disabled Enabled Disabled Note Delay is enabled by entering EXTRIG mode while in local OFFSET COMMANDS BO Offset Off Default B1 Offset On DISPLAY COMMANDS DO Normal Display Default D1 Blank Display SUFFIX COMMANDS YO Disable Output Suffix Default if talker listener Y1 Enable Output Suffix Default in talk only mode 3 6 Figure 3 5 Device Dependent Command Set TERMINATOR COMMANDS WO CR LF Default Enable CR LF Only W2 Enable CR Only Enable CR Only W4 Enable LF Only W5 Enable LF Only W6 Enable Only W7 Disable All Output Terminators CLEAR COMMANDS Device Clear Resets 8840A to default conditions XO Clear Error Register SINGLE TRIGGER COMMAND Trigger Measurement GET COMMANDS GO Get Instrument Configuration F R S and T G1 Get SRQ Mask G2 Get Calibration Input Prompt 63 Get User Defined Message
141. Voltage Range 0 1000V dc Voltage Accuracy 20 20 ppm of range Kelvin Varley Voltage Divider Fluke 720A Ratio Range 0 1 0 Absolute Linearity 1 ppm of input at dial setting Resistance Accuracy 0 005 Accuracy 0 025 General purpose 60 MHz with 10 probe Philips 3055 or 3355 Digital Voltage Accuracy 0 0196 in V dc 1 0 for 1V in V ac 9 100 kHz Input impedance 10 MQ or greater in V dc 1 MQ or greater in parallel with 100 pF in V ac Fluke 8840A with Option 09 AC Calibrator Fiuke 5700A and Fluke 5725A Minimum Required Accuracy By Range 1 10 100 20 Hz 30 Hz 1 005 30 Hz 20 kHz 20 kHz 50 kHz 50 kHz 100 kHz 12 005 04 004 08 005 1 01 1 of setting 2 of setting 96 of range AC Current Source Frequency Range Fluke 5700A or Fluke 51008 Minimum Required Accuracy All Ranges 30 Hz 1 kHz 07 1 mA 1 kHz 5 kHz 0796 1 mA X frequency in kHz Shorting Bar Resistance 1 5 mQ Pomona MDP S 0 Construction Soldered not rivetted 6 Inch Jumper 2 204 6W S or equivalent Optional Test 9010A 9005A or Micro System Troubleshooter 9000A 8048 Interface Pod Equipment 6 2 Maintenance Test PERFORMANCE TEST ILLO ee Ensure the 8840A is on and has warmed up for at least l Ensure the 8840A is on and warmed up f
142. YIO AN3uurno 1541 5 SWHO Figure 5 1 Overall Functional Block Diagram 5 2 DC SCALING nents are configured by relay K301 switching transistor Q311 and quad analog switches U302A and U301B to provide the correct scaling for each range Voltage fol lower U306 provides high input impedance for the 20V dc range simplified schematic and a switch state table for the VDC function are shown in Figure 5 2 In the 200 mV and and 2V ranges the input voltage is applied directly to the T H Amplifier via Q310 Q311 and LO 2302 2A Cy SN 100K 5 K301 SHOWN ENERGIZED 1 SWITCH STATES FOR mA DC 200 mA c Switch closed or relay energized ee eee RANGE Q311 amp pes 11 t n U301B In the 200 mV range the T H Amplifier has a gain of 10 in all other dc voltage ranges the T H Ampli fier 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 boot strapped by Q305 and Q306 so that the output voltage of U306 determines the midpoint of its supply voltages The TO TRACK HOLD SENSE PATH FOR VDC 200 mV
143. a DO command before sending GTL SDC Selected Device Clear Identical t universal command DCL but is accepted and interpreted by current listeners only Therefore it clears the 8840A only if it is 10 listen 3 56 TALK ONLY MODE The talk only mode lets you take advantage of the remote capability of the 8840A without having to use an instru ment controller To put the 8840A in the talk only mode 1 Turn the 8840A POWER switch OFF 2 Set the rear panel TALK ONLY bit switch to 1 ax up position 3 Connect the 8840A 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 88404 POWER switch ON 6 Configure the 8840A with the front panel controls The 8840A 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 8840 the IFC command 3 57 CALIBRATION The 8840A can be calibrated over IEEE 488 bus using remote commands Refer to the Maintenance section for details Remote Programming TALK ONLY MODE M MM M M d Table 3 3 immediate Mode Commands for Various Controllers TEK BASIC on 4051 Graphics System FLUKE BASIC on 1720A or 1722A HP HPL 9825 Caiculator HP BASIC on 9816 and HP 8
144. able 1 1 Specifications cont TEMPERATURE COEFFICIENT of Reading Number of Counts per 0 C to 18 28 10 50 FREQUENCY HERTZ wem max ccm 210 000 counts 0 019 9 0 021 9 0 027 10 21 000 counts 0 019 12 0 021 15 0 027 21 COMMON MODE REJECTION gt 60 dB at 50 or 60 Hz with 1 in either lead CURRENT Input Characteristic FULL SCALE RESOLUTION 5 DIGITS 5 DIGITS 4 DIGITS digits at the fastest reading rate DC Current Accuracy NORMAL S READING RATE of Reading Number of Counts MEDIUM AND FAST READING RATES Jn medium reading rate add 2 counts to number of counts In fast reading rate use 2 counts for number of counts When in fast reading rate with internal trigger and transmitting data out of the IEEE 488 interface the 8840A display must be blanked command D1 ot ensure stated accuracy AC Current Accuracy Option 09 NORMAL S READING of Reading Number of Counts 1 Year 23 5 for sinewave inputs 210 000 counts FREQUENCY IN HERTZ 2 0 200 0 5 2007 0 4 200 Typically 20 kHz Add 100 counts for sinewave inputs between 1000 and 10 000 counts When in fast reading rate with internal trigger and transmitting data out of the IEEE 488 interface the 88404 display must be blanked command 01 ensure stated accuracy Introduction and
145. age 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 1V and then OV a short across the HI and LO INPUT terminals If and then OV appear at TP302 U306 is probably OK If not the problem is in 0306 or its bootstrap supplies TP301 and 303 To check the bootstrap supplies put the 8840A 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 zero is displayed for ranges 13 and 15 but not for r1 12 and 14 then the signal path including Q311 and U301B is suspect To check 0311 apply 1V dc input in the 2V range and check that the voltage at the drain and source of Q311 is 1V If not 0311 or its driver is bad If 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 7301 or U302D is probably bad 6 63 Track Hold Troubleshooting If a problem is suspected in the Track Hold T H circuit first check the power
146. age transistors O402 Q403 and Q404 If 300V is present at the collector of 0404 the voltage drops equally across 7402 so that large negative voltages never reach the current source The circuitry associated with Q408 R406 R407 R408 R409 0406 0408 and CR403 clamps the open circuit voltage of the Ohms Current Source below 46 5V in the lower four ranges and below 13V dc in the higher two ranges The in guard uC turns Q408 on or off depending on range the lower four ohms ranges 0408 is effectively shorting R409 R406 and R409 then form a voltage divider which clamps the output of the ohms current source below 46 5 the higher two ohms ranges O408 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 5 8 voltage drop across the resistor is measured sensed as in the VDC function 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 the scaled input voltage is sampled In the lower four ranges the full scale input voltage 4 p A D Converter is 2V However in the 2000 an MQ ranges the f
147. aid to the technician CAUTION Once the calibration memory is erased the 8840A must be recalibrated To erase all or part of the calibration memory proceed as follows l 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 8840A 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 Table 6 12 Prompts When Calibrating Individual Ranges PROCEDURE Offset and Gain Calibration Not applicable High Frequency AC Calibration NOTES LOW PROMPT Zero Zero 50 of full scale 5 of full scale No low prompt 1 Exception The 1000V dc range has a high prompt of 1000V dc 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 prompt of 200V ac HIGH PROMPT 95 of full scale 5096 of full scale 5096 of full scale 6 11 Maintenance CALIBRATION STORE the entire 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 func tion d HF AC Erases the High Frequency AC Calibra tion constants 3 After an erasure is finished a complete erasure takes about 3 seconds
148. akage around or through CR615 fuses will continue to blow If everything looks OK but the fuse keeps blowing troubleshooting may be performed by powering the instru ment through a variac applying only enough line voltage to find the problem without blowing the fuse NEVER USE A LARGER FUSE do so will only turn a smali problem into a big one 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 03V INPUT 1V DIV 1 ms DIV Eram Maintenance TROUBLESHOOTING VERT IV DIV HORIZ 2 ms DIV Bm 03V INPUT 1V DIV 1 mV DIV Figure 6 17 Waveforms at TP102 for Several inputs on 2V DV Range Maintenance TROUBLESHOOTING NIBBLE 1 1 4BIT 1 16 1 8 1 E 01 N1 2 1 0 1 4 0 1 16 6875 d 2 0 0 0 1 4 1 8 1 16 NIBBLE 3 1 16 1 2BIT 2BIT 1 4BIT V 8BIT jalol of 0 o o 0 0 0 0 0 0 4375 0 0 A D Reading 1st 3 Nibbles 6875 1 16 4375 1 16 0 0 660156 Figure
149. ample Programs Using the IBM cont 3 37 Remote Programming EXAMPLE PROGRAMS PE 54 2 gt gt B pt de 8 a 63 077 DECIMAL HEX 9 0010 1001 8 22 9 gt Table 3 4 ASCI IEEE Std 488 1978 Bus Codes BINARY ogv 7654 3210 MESSAGE TRUE ADDRESSED COMMANDS UNIVERSAL COMMANDS 0010 0100 0010 0101 0010 0110 0010 0111 0010 1010 0010 1011 0010 1100 0010 1101 0010 1110 0010 1111 0011 0000 0011 0001 0011 0010 0011 0011 0011 0100 0011 0101 1 0011 0110 0011 0111 6011 1000 0011 1001 0011 1010 0011 1011 0011 1100 0011 1101 0011 1110 0011 LISTEN ADDRESSES BINARY 7654 3210 100 40 0100 0000 101 41 0100 0001 102 42 01000010 103 43 104 44 105 45 106 46 107 47 0100 0011 0100 0100 0100 0101 0100 0110 0100 0111 0100 1000 0100 1001 0100 1010 0100 1011 70100 1100 0100 1101 0100 1110 0100 1111 Q101 0000 0101 0001 0101 0010 0101 0011 0101 0100 0101 0101 0101 0110 0101 0111 0101 1000 0101 1001 0101 1010 0101 1011 0101 1100 0101 1101 0101 1110 0101 1111 0110 0000 0110 0001 0110 0010 0110 0011 0110 0100 0110 0101 0110 0110 0110 0111 0110 1000 0110 1001 0110 1010 01
150. aracter when enabled The 8840A 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 8840A 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 88404 at the time the command is executed at its place in the input command string 3 48 Output Priority Since only one output string is allowed per input command string the 8840A 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 1 Status data from 00 G1 G3 G4 G5 G6 G7 68 2 Error messages error exists 3 Numeric data from G2 or a trigger 3 18 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 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
151. are scaled by the True RMS AC Option The Track Hold T H circuit samples the scaled dc age 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 8840A It reads the front panel keyboard configures the instrument for each function and range triggers A D Converter calculates the result of each A D conversion cycle averages A D samples controls the _ Section 5 Theory of Operation 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 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 The Precision Voltage Reference provides precise reference voltages for the A D Converter and the Ohms Current Source 5 3 DETAILED CIRCUIT DESCRIPTION The following paragraphs give a de
152. bee e s hain lin soe ele ES 3 19 3 52 INTERFACE MESSAGES por EP 3 19 3 53 Address 5 ne CAR MEN NEM 3 20 3 54 Universal Commands e us esa wand S e Edu 3 20 3 55 Addressed 5 3 20 962 Sr VeL uA deed 3 20 3 57 REMOTE CALIBRATION te sale as 3 20 Table of Contents SECTION TITLE 3 58 TIMING 8 2 3 21 3 59 IMMEDIATE MODE mE 3 21 3 60 EXAMPLE 6 3 21 4 Measurement Tutorial 4 1 4 1 7 INTRODUCTION cro dete ue V nee Lak ge toca Ce tei 4 1 4 2 DC VOLTAGE 8 4 1 4 3 Circuit Loading ligare 4 1 4 4 Input Bias Current Medeae uestis RR RU 4 1 4 5 RESISTANCE MEASUREMENT 4 2 4 6 PODES NEUEM tals eat radian dC DERE 4 2 4 7 Correcting for Test Lead Resistance in 2 Wire Ohms 4 2 4
153. ber is displayed for about 1 second The instru ment can be stopped in any of the test configurations by pressing the SRQ button while the test number is dis played Pressing any button continues the tests After the last analog test is performed all display seg ments 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 con trol If the 8840 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 all diagnostic self tests does not necessarily mean the 88404 is 100 functional The test for example cannot check the accuracy of the analog circuitry If one or more errors are displayed the 8840A probably requires service 6 4 DC Voltage Test The following procedure may be used to verify the accuracy of the VDC function 6 1 Maintenance PERFORMANCE TEST Tabie 6 1 Recommended Test Equipment rod MINIMUM SPECIFICATIONS RECOMMENDED MODEL DC Calibrator PREFERRED Fluke 5700A or Fluke 5440A Voltage Range 0 1000V dc Voltage Accuracy 10 ppm Absolute Linearity 1 0 ppm ALTERNATIVE Fluke 343A Must be used with Kelvin Varley Voltage Divider
154. 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 Read Write means that data is read from and written to the NEC7210 IEEE chip 0901 when DS 0901 8 is low R W 0901 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 45 Maintenance TROUBLESHOOTING o M 3 Short TP903 to TP905 Power up the 8840A The 8840A should display ERROR 50 To exit the troubleshooting mode open the jumper and cycle the POWER switch from off to on Once the diagnostic program is started rear panel IEEE 488 address switches A3 A2 and A1 can be used to select one of four diagnostic modes as shown in Table 6 24 In this table Configuration indicates which Out Guard I O port bits are programmed as outputs and driven with a signal as shown in Table 6 25 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 l Remove the case from the chassis using the Case Disassembly procedure provided earlier in this sec tion 2 Release the four nylon latches that hold the True RMS AC PCA in place by pulling the latches upward
155. board provides the interface 30 REM between the PC and the Fluke 8840A 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 18840A 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 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 8840A using the 2 wire ohms function in autorange The range and function 130 REM commands are programmed using the Put Instrument Configuration P0 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 IBWRTL IBRDIA IBWRTIA IBSTA IBERR IBCNT 210 220 230 REM 2 240 188404 Device name is 18840 250 CALL IBFIND DEVNAME DVM Initialize the DMM 260 CALL I
156. cal rear panel trigger enabled TRIGGER METHOD DESCRIPTION 1 Continuous Trigger 2 Command 3 GET Command controller 4 Front Panel Trigger 5 Rear Panel Trigger Figure 3 7 Trigger Selection Logic Diagram response to G2 or trigger commands The suffix includes 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 Single trigger initiated fromrear panel EXTTRIG input Disabled by TO T2 74 Continuous trigger generated 8840A in internal trigger mode TO Single trigger initiated by command from controller Single trigger initiated by GET command an interface message from Single trigger initiated by front panel TRIG button convert the numeric part into a numeric variable However it is much easier to read the 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 ime be INPUT 1 5 Remote Programming DEVICE DEPENDENT COMMAND SET The suffix status can be read using the G6 command The 8840A defaults to YO on power up and any device clear command DCL or SDC unless in talk only mode
157. cters 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 Trigger and or EOI When the 8840 receives an input terminator it previous commands the order in which they were received As input characters are processed and executed space is made available in the input buffer for new oa ters If the input buffer becomes full the 8840A 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 88404 are never lost due to Remote Programming INPUT SYNTAX 12 In some instances a terminator is automatically transmit ted at the end of the controller s output string For exam ple 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 explic itly The 8840A accepts alphabetic characters in either upper or lower case Spaces commas and control codes are ignored and are not placed in the input buffer If the 8840A receives a group of terminators such as CR LF or CR LF EOI only a single terminator is loaded into the input buffer Numeric values used in PUT commands may be in NR1 NR2 or format as described in the IEEE 488 Codes and Formats Recommended Practice
158. curate 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 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 Test points are labeled on both sides to facilitate such troubleshooting If no ranges work the signal should be traced from input 10 output At any point where the signal disappears the preceding stage should be searched 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 Table 6 26 Isolating a Defective AC Stage DEFECTIVE RANGES D
159. 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 The following paragraphs 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 5 44 VAC Scaling AC voltage inputs are directed from the HI INPUT termi nal 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 input voltage is thus applied to C801 which blocks dc inputs R804 R805 r3 r5 AC INPUT VOLTAGE 500 FOR r4 r5 CURRENT SENSE 0807 and resistor network 7801 provide selectable attenu ation and 1 MQ input impedance In the upper two ranges K802 is closed and Q806 is off providing a gain of 1 500 In the lower three ranges K802 is open and Q806 is on shorting Z801 4 to ground this configuration pro vides a gain of 1 5 CR801 and CR802 provide protection by clamping the inverting input of U807 to approximately 0 6V Q805 sh
160. d are ASCII control codes sent over 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 The terminator selection can be read using G6 com mand The 8840A defaults to WO on power up and any device clear command 3 31 Error Register Command The command clears the 8840A s error status register After an X0 command is executed a G7 command Get Error Status would return 1000 no errors Note that the error status register is also cleared when 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 3 32 Yn Suffix Commands The Suffix commands enable or disable a suffix which the 8840A can append to all numeric data the data in Remote Progr mming DEVICE DEPENDENT TRIGGER METHOD CONTINUOUS TRIGGER BUS TRIGGER or GET FRONT PANEL TRIGGER REAR PANEL e TRIGGER T1 T3 DEVICE CLEAR EX TRIG BUTTON DEVICE CLEAR TOGGLED BY EX TRIG BUTTON MEASUREMENT CIRCUITRY LOCAL With EXTRIG enabled Switches represent effect of indicated commands buttons and remote local status Instrument shown in power up state TO lo
161. d G7 1100 Default GO valu MASK DATA nn CR LF EO From G1 EXAMPLE 32 SRQ on any error idola USER DEFINED MESSAGE aaaaaaaaaaaaaaaa CR LF From G3 EXAMPLE 1 8840 01 25 84 If no messages have ever been stored string of 16 nulis Hex 00 will be returned INSTRUMENT FLUKE mmmmm 0 Vn CR LF FLUKE 8840A with IEEE 488 IDENTIFICATION interface software version From G8 EXAMPLE FLUKE 8840A 0 V4 O 4 Numeric data is always in volts amps ohms The terminators LF and are selected with the Terminator Commands Wn suffix defined below is enabled with the Y1 command and disabled with the YO command Default vo 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 Leading Comma Always present in suffix Most versions of BASIC expect multiple input values to be separated by commas i e input e 1 S to acquire the numeric portion and suffix string Figure 3 6 Output Data Format Remote Programming DEVICE DEPENDENT COMMAND SET 3 15 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
162. d and the Buyer will be billed for the repair and return transportation charges FOB Shipping Point THIS WARRANTY IS BUYER S SOLE AND EXCLUSIVE REMEDY AND IS IN LIEU OF ALL OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE FLUKE SHALL NOT BE LIABLE FOR ANY SPECIAL INDIRECT INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSSES INCLUDING LOSS OF DATA WHETHER ARISING FROM BREACH OF WARRANTY OR BASED ON CONTRACT TORT RELIANCE OR ANY OTHER THEORY gt Since some countries or states do not allow limitation of the term of an implied warranty or exclusion or limitation of incidental or consequential damages the limitations and exclusions of this warranty may not apply to every buyer If any provision of this Warranty is held invalid or unenforceable by a court of competent jurisdiction such holding will not affect the validity or enforceability of any other provision Fluke Corporation Fluke Europe B V P O Box 9090 P O Box 1186 Everett WA 5602 B D Eindhoven 98206 9090 The Netherlands 5 94 MULTIMETER SAFETY The Fluke 8840A Digital Multimeter 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 Use of this equipment in a manner not specified here in may
163. d apply an input of less than 42V to TP103 If the A D Converter is OK the 8840A will display the applied voltage with the opposite polarity For example if you apply 1 it should display 1V The readings may differ by a slight offset 6 64 Ohms Current Source Troubleshooting Malfunctions in the ohms functions can be caused 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 2 3V and low lt 0 5 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 collec tor of Q404 and ground Reference Low Selecting the VDC function opens K401 and configures the Ohms Current Source in the 20 range If the voltage across the 10 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 To test whether the Ohms Current Source is actually being sourced out the HI and LO OUTPUT terminals select the 20 range and the 2 wire ohms function connect 10 resistor across the HI and LO INPUT termina
164. display also indicates U to show that HF AC cal 15 selected 2 Inputs should be between 90 kHz and 100 kHz 100 kHz nominal is recommended To use the variable input feature proceed as follows 1 When the 8840A 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 200Q 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 appro priate input terminals of the 8840A 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 5090 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 590 of full scale For special applications the 8840A can be calibrated at values outside the recommended range This can enhance the performance at the calibration value However perfor mance at other values may be degraded 6 17 CALIBRATING INDIVIDUAL RANGES During Offset and Gain and High Frequency AC Calibra tion it is possible to calibrate indiv
165. e ew E x REC ERES 6 34 6 50 8 Bit Digit Driver m vex pied 6 34 6 51 3 0 8 Strobe Decoder 0213 6 34 6 52 8 Bit Segment Driver 0217 6 34 6 53 4 0 7 Segment Decoder 0216 2 4442 6 34 6 54 8 Bit Digit Driver 0218 s eios aoo tere e re 6 34 6 55 Hex Inverter 0203 seres ease ced 6 34 6 56 Hex Inverter U221 etes ed eines eror 6 34 6 57 Quad Gate U21D andre eret rid di 6 35 6 58 Keyboard WIDE 6 35 6 59 ANALOG CONTROL oT 635 6 60 Evaluating Static 12 4 6 6 6 61 Evaluating Dynamic 2 2 2 2 2 2 6 36 6 62 DC Scaling Troubleshooting E 6 63 Track Hold Troubleshooting MS HU EINE MIO CU ER 6338 6 64 Ohms Current Source 6 39 6 65 Precision Voltage Reference Troubleshooting 6 39 6 66 A D Converter Troubleshooting s 00 0 cecsccaccecsceseccceecessceeneecseecces 6 41 6 67 Power Supply Troubleshooting 642 6 68 IEEE 488 Interface Ec
166. e 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 on to the IEEE 488 bus 3 1 Remote Programmir AN OVERVIEW OF OPERATION A ADDRESS TALK 5 4 A2 1 ADDRESS ONLY ONLY 0 0 0 0 0 0 0 0 0 0 0 OOO A O O OO OO 00 Figure 3 1 IEEE 488 Address Selection Information is transferred between blocks by device dependent commands Each command is shown next to an arrowhead which indicates the resulting information trans fer For example Put command takes a number from the input buffer and stores it in the primary status registers Likewise Get command GO gets the content of pri mary status registers and copies it into the output buffer 3 5 A NOTE ABOUT EXAMPLES In the examples in this manual device dependent com mands are shown enclosed within quotation marks as they would be entered in Fluke BASIC For clarity the com mands are also separated by spaces However the spaces are are not necessary and may be omitted Example Explanation F3 R1 S1 T2 This example is equivalent to F3RISIT2 or F3 R1 S1 T2 Using the Fluke 1722A Instrument Controller these com mands might be written into a BASIC program a
167. e U103 amplifies and stores the differ ence 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 nee are shown in Figures 5 9 and 5 10 5 24 Bootstrap Supplies The bootstrap supplies are composed of U102A diot 0102 CR103 CR104 and associated components bootstrap supplies enhance the gain accuracy of 10103 During compare periods the bootstrap supplies limit the output of U103 to minimize the time it takes to recover from being driven to a supply rail Both functions are achieved by the supplies of 0103 851 52 5 25 DISPLAY The vacuum fluorescent display is similar to vacuum tube containing eight control grids and 69 phosphor coated plates which form the display segments and annun ciators See Figure 5 12 The filament voltage is 4 5V ac with a 45V dc bias Each plate is controlled by line of Operation DISPLAY PRECISION DAC AMPLIFIER a 7V 2101 OK 15 238 2101 10 667K C101 Figure 5 11 Autozero Period and a P line The G lines go to the control grids and the P board Each button contains a conductive pad that shorts lines go to the plates two cont cts when pressed The Digital Controller sequentially enables the G lines by applying 30V dc nominal When line is enabled O CONTROLLER electron
168. e 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 0301 0302 0303 Basic timing for the T H circuit is provided the A D Converter over clock lines PC HD1 TR1 and TR2 See the timing diagram in Figure 5 5 top The T H cycle is initiated when the In Guard pulls line TR low 5 10 Track Configuration In the track configuration Figure 5 4 the T H circuit functions as a non inverting buffer The voltage on C308 tracks the scaled dc input voltage 5 11 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 config uration 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 5 12 Hold Configuration The X1 hold configuration Figure 5 4D is used for all VDC ranges except 1 and for all ohms ranges except r The output of 0307 is the negative of the input voltage The X10 hold configuration Figure 5 4 is used for the mA DC function the 200 mV dc range and the 200 range and provides a gain of 10 5 13 Pre
169. e test probe tips and the circuit being tested is unpredictable and therefore cannot be reliably corrected with a fixed offset NOTE In the 2 MQ and 20 MQ ranges of 4 wire ohms the voltage across the unknown resis tance 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 109 in the 2 range and less than 100 the 20 range Four Wire ohms measurements are especially important when using long test leads In a typical automated test system for example the test leads could connected through four or five switching relays each with 2Q of sist Te Istance 4 9 Applications of the Ohms Functions The 8840A makes 4 wire ohms measurements as shown in Figure 4 4 The HI and LO INPUT leads apply a known internal current source 10 the unknown resistance just as PIS EEEE EN LETE qui NERO 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 4 3 Measurement Tutorial RESISTANCE MEASUREMENT OHMS CURRENT SOURCE _ VOLTAGE SENSE Figure 4 3 2 Wire Ohms Measurement Table 4 1 Ohms Test Current TEST CURRENT FULL SCALE VOLTAGE 4 10 TESTING DIODES 2 wire ohms function can also be used to test diodes 1 Select the 2 wire ohms function and the 2 range 2 Measure
170. ector Figure 805 2 Release IEEE 488 Interface PCA from the chassis by pulling the two plastic latches upward Figure 805 1H 3 Raise forward edge of 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 from the IEEE 488 Inter face PCA by releasing the connector latches push outward see Figure 805 1F and pulling the ribbon cable out from the connector Figure 805 1 6 31 Main PCA Removal 1 Disconnect the leads from the four front panel input i terminals and the four rear panel input terminals by unplugging them Refer to Figure 6 6C 2 Remove cable harness from two cable clamps on the side of the instrument chassis Figure 6 6D Lift the cable harness clear of the sidewall cable guide 10 11 12 PCA as follows Figure 6 60 Maintenance _ DISASSEMBLY PROCEDURE 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 Disregard this step if the IEEE 488 Interface was installed Disconnect the ribbon cable from the panel insert by pushing outward on the snap tab on either side of the ribbon cable connector Disconnect the two ribbon cables from the Display PCA by pul
171. emaining devices by A11 The addresses of the remaining devices are decoded from 8 10 by U208 which combines the address with the data strobe DS to provide chip select 50 CS2 CS3 54 or CS7 for each device The In Guard performs the following functions range and function control A D control and computation cali bration corrections keyboard display control serial com munication with the IEEE 488 Interface and diagnostic self testing and troubleshooting 5 29 Function and Range Control The In Guard uC configures the DC Scaling circuit the Track Hold circuit and the Ohms Current Source to pro vide the proper input switching scaling and filtering for each function range and reading rate 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 per form any level shifting needed to control their internal MOSFET switches Some of the switches require dynamic timing signals from the custom A D 0101 these signals are combined appropriately in the quad analog switches with the configuration codes 5 30 A D Control and Computation The In Guard uC initiates each A D sample by pulling line TR low When the is reset it senses the power line frequency on line FREQ REF uC then sets its internal timer so that the A
172. ement Tutorial RESISTANCE MEASUREMENT R SOURCE TO MEASURE INPUT BIAS CURRENT ERROR 1 Select the VDC function and the desired range 2 Eliminate any offset voltages by shorting the HI INPUT and LO INPUT terminals and then pressing OFFSET 3 Selectaresistor which matches the source impedance Rsource of the circuitto 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 The input bias current error may be calculated as a percentage as follows VOLTAGE MEASUREMENT 100 ERROR IN The input bias current itself May be calculated as follows V leas ERROR SOURCE Figure 4 2 Measuring Input Bias Current Error 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 negligi ble 3 With the test leads still touching press the OFFSET button The 8840A should read 00 4 8 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 between th
173. ent or more CR615 con ducts turning on Q601 shorting out the power transformer secondary and blowing the line fuse In normal operation these components have no effect 5 37 IEEE 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 5 38 Out Guard Microcomputer The Out Guard Microcomputer uC U901 communi cates with the IEEE 488 talker listerner IC U911 and the In Guard U202 The Out Guard uC is similar to the In Guard Z8 uC except that it contains 8K bytes of ROM and 236 butes of IN GUARD 4202 TRANSFORMER T601 POWER SUPPLY 0901 SAMPLE COMPLETE EXTERNAL TRIGGER SIGNAL CONDITIONING Figure 5 16 IEEE 488 Interface Block Diagram OUT GUARD RAM For further description of the Z8 refer t the heading In Guard Microcomputer above 5 39 Guard Crossing The guard crossing circuit permits serial asynchronous communication between U901 and U202 while isol ting 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 circuit is described an earlier heading 5 40 Bus interface Circuitry The IEEE 488 bus protocol is handled by the Poa IEEE 488 talker listener 0911
174. erence 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 In Guard uC sets the output current for each range by con trolling U402 and U403 See switch state table in Figure 5 7 5 16 5 Ohms Protection circuit 0402 0403 0404 0405 0406 and 0407 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 1560 with four 401 RV402 RV403 and 404 In addition a 1 2W fusible wire wound resistor R410 series with the output current path fails open circuit under extreme overvoltage conditions 5 5 Theory of Operation OHMS PROTECTION TRACK CONFIGURATION SETTLING CONFIGURATIONS A B GAIN OF 1 C OF 10 18 U303B HOLD CONFIGURATIONS D GAIN OF 1 E GAIN OF 10 NOTE IN 4 WIRE OHMS RANGES R1 THROUGH R4 INPUT OF THE T H IS SWITCHED AS SHOWN SENSE LO TERMINAL PRECHARGE CONFIGURATION F U303B L stray V SETTING 18K DEPENDS ON RANGE 2K U303B Figure 5 4 Track Hold Circuit Configurations
175. evice dependent message which resets the 8840A 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 1 Implements the default settings F1 50 TO DO BO YO WO 2 Clears the error status register equivalent 10 3 Zeros the SRQ mask prohibiting service requests equivalent 10 P1 Zeros the numeric entry register equivalent to Zeros the serial poll register Sets the SRQ line false gt The asterisk command is executed in its proper turn string just like any other command without affecting the contents of the input buffer All commands which precede the asterisk command are performed asterisk command is useful to ensure that the 8840A 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 are all considered to be device clear commands because the results are 50 8 14 buffer overflow similar however DCL and SDC are not identical to the asterisk command described here and SDC are discussed further in the paragraph on interface 3 35 2 Single Trigger Command The Single Trigger command 7 causes the 8840A to take a reading and
176. follows 1 Allow the 8840 to stabilize in an environment with ambient temperature of 18 to 28 relative humidity less than 75 2 Turn the 8840A on and allow it to warm up for at least 1 hour 3 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 annuncia tor lights up and the 88404 displays the first prompt for the A D Calibration procedure Figure 6 2 To exit the calibration mode press the CAL ENABLE switch again 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 The following functions are inappropriate during calibra tion and are therefore unavailable Offset Autoranging External Trigger Figure 6 2 First A D Calibration Prompt Maintenance CALIBRATION Front Panel Trigger Front panel SRQ Under local control 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 8840A automatically selects the A D calibration procedure when the CAL ENABLE switc
177. g data out of the EEE 488 interface the 88404 display must be blanked command D1 to ensure stated accuracy 6 Set the AC calibrator to standby and disconnect it 3 For each step in Table 6 5 select the indicated range from the 8840A set the Resistance Calibrator for the specified nominal input and proceed as follows a the 4 wire ohms function 1 Select the 4 wire ohms function 2 Verify that the displayed reading is within 6 6 Resistance Test The following procedure may be used to verify the accuracy of the 2 wire and 4 wire ohms functions 1 Ensure the 8840A is on and has warmed up for at the limits shown for each reading rate least 1 hour b Test the 2 wire ohms function 2 Connect the Resistance Calibrator to the 8840A for 1 Select the 2 wire ohms function The 4 wire ohms SENSE test leads need not be disconnected Table 6 3 Low and Mid Frequency AC Voltage Test STEP NUMBER VOLTAGE FREQUENCY 2V 0 01000V 0 01201 2 0 10000V 0 09886 0 10114 2N 0 30000V 0 29858 0 30142 2V 1 00000V 0 99760 1 00240 2V 1 90000 1 89634 1 90366 2 0 10000V 0 09780 0 10220 2 1 90000V 1 87620 1 92380 2V 0 10000V 0 09865 0 10135 2V 1 90000V 1 89235 1 90765 0 001000V 0 000799 0 001201 0 190000 0 189634 0 190366 N Qo 6 7 8 9 h 4 Quick test points 6 4 Maintenance PERFORMANCE TEST Table 6 4 High Frequency AC Voltage Test STEP I
178. g 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 For resistance measurements the delay also allows for settling when the Step change is made from an open circuit to an in range value 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 IEEE 488 interface bus to accommodate special timing considerations 2 22 External Trigger Input Option 05 Only The rear panel EXT TRIG input is TTL level input which can be used to trigger measurements when the 8840A 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 con trolled by a normally open switch A measurement is triggered when the switch is closed For 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 polarity of the EXT TRIG input can reversed by changing internal jumpers Refer to the Maintenance sec tion for instructions 2 23 Sample Complete Output Option
179. g to the Case Disassembly procedure provided earlier in this section Maintenance TROUBLESHOOTING A C CM M Ren 2 Release the two nylon latches that hold the IEEE 488 CAUTION Interface PCA in place by pulling the latches upward 3 Position the IEEE 488 Interface PCA vertically as equipment the 8840A must be discon c ied and d in place be pressing nected from all other IEEE 488 interface two nylon latches into the mounting supports E Specially provided on the chassis while the diagnostic pro gram is running To avoid damage to the 8840A or other 6 70 DIAGNOSTIC PROGRAM To facilitate troubleshooting the IEEE 488 Interface pro 1 Ensure the 8840A POWER switch is OFF vides a diagnostic program which places the instrument in known configurations To initiate the diagnostic program 2 Disconnect all cables from the rear panel 488 proceed as follows connector HE Figure 6 19 Option 05 Service Position Table 6 24 Diagnostic Modes CONFIGURATION Static odd port bits 1 even port bits Static odd port bits 0 even port bits Dynamic Read Write a X means switch setting does not matter Static means the Out Guard port bits programmed as outputs are driven to a constant logic 1 level as defined by switch A2 Dynamic means the Out Guard port
180. gure 6 67 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 Tod from the switch shaft then pull the rear of the POWER switch push rod out through the bottom of the chassis NOS c Lift the push rod out and toward the rear panel and remove it 6 17 Maintenance DISASSEMBLY PROCEDURE viel gi MOUNTING SCREW q0F2 REAR PANEL GROUNDING SCREW REAR BEZEL CHASSIS Figure 6 6 8840A Disassembly Maintenance DISASSEMBLY PROCEDURE Figure 6 6 8840A Disassembly cont 6 19 Maintenance DISASSEMBLY PROCEDURE Figure 6 6 8840A Disassembly cont 6 20 Maintenance DISASSEMBLY PROCEDURE a Figure 6 6 8840A Disassembly cont 6 21 Maintenance DISASSEMBLY PROCEDURE 13 14 15 16 17 18 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 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 that hold the Main PCA to the chassis
181. h both the 8840A and an ac coupled oscilloscope If the rms reading on the 8840A 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 measurements for instance cannot be made with dc coup ling Remember however that when the 8840A measures signals with the ac functions the reading on the display 4 7 Measurement Tutorial AC VOLTAGE AND CURRENT MEASUREMENT 4 8 PEAK VOLTAGES METERED VOLTAGES AC COMPONENT ONLY DC AND TOTAL RMS TRUE RMS Vac dc DC COMPONENT ONLY RECTIFIED SINE FULL WAVE RECTIFIED SQUARE K YD D TRIANGLE SAWTOOTH PK PK PK 4 RMS CAL IS THE DISPLAYED VALUE FOR AVERAGE RESPONDING METERS THAT ARE CALIBRATED TO DISPLAY RMS FOR SINE WAVES Figure 4 3 Waveform Comparison Chart Measurement Tutorial AC VOLTAGE AND CURRENT MEASUREMENT does not include the dc component if one exists For example consider Figure 4 8 which shows a simple ac signal riding on a dc level The VAC function would measure the ac component only 4 20 Combined AC and DC Measurements 8840A can be used to evaluate the true rms value of waveforms such as the one shown in Figure 4
182. h is first pressed The procedure must be performed in its entirety and may not be per formed 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 8840A then displays the prompt for the first reference source zero volts 1 a short 2 Each time the 8840A 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 8840A performs the necessary calculations Do not change the reference source while the display is blank The 8840A then displays the next prompt For reference all prompts are shown in Table 6 8 NOTE The 8840A automatically checks that the refer ence input is near the value prompted and displays ERROR 41 if it exceeds a specific tolerance See Advanced Features and Special Considerations later in this section 3 After the last input is stored the 8840A begins taking readings in the 2V range of the VDC function The CAL annunciator remains on Verify the A D calibra tion using the test points in Table 6 9 If you wish to repeat the A D Calibration procedure press the A D button The A D Calibration procedure is iterative process Each pass through the procedure uses the c
183. han 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 per centage of error can be calculated and corrected for using the formulas in Figure 4 5 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 typi cally occur at binding posts and can be greater than 10 uV Thermal voltages can also cause problems in the low ohms 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 Use clean 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 Use caution when handling the circuit under test 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 When making p
184. haracters that are already present in the input buffer and clears the entire input buffer Pro cessing then continues normally The action of DCL is not immediate if the 8840A is taking a reading when DCL is received the DCL command is executed after the measurement is finished LLO Local Lockout A multiline message which disables the front panel LOCAL button The result is that the local mode is not accessible by front panel control SPD Serial Poll Disable A multiline message which removes the serial poll enable 145 5 Serial Poll Enable 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 8840A responds to the addressed commands GET Group Execute Trigger Not to be NUM 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 GTL Go To Local Causes the 8840A to switch to local This command does not enter the input buffer If the display has been blanked with a D1 command issue
185. he 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 l While the error code is being displayed press the 5 button This latches the 88404 into the particular test configuration 2 Referring to Table 6 18 check that the test point voltages are as shown using another DMM 6 39 Self Test Descriptions TEST 1 200 VAC Zero Configures the 8840A in the 200V ac range except that K801 is opened and measures the open circuit Table 6 18 Self Test Voltages TEST TEST NUMBER POINT lt 5 mV lt 5 mV dc lt 5 mV dc lt 5 mV dc lt 5 mV dc 50 mV dc typical 11 5V dc typical 11 5V dc typical 26 BON OMA OD 50 typical 49 typical 53 typical 59 dc typical lt 5 mV 59 mV dc typical lt 5 mV dc VOLTAGE T H output waveform for zero input Figure 6 14 4 5V dc with possibly 1V ac 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 4 5V dc with possibly 1V ac p p at 10 Hz 4 5V dc with possibly 1V ac p p at 10 Hz Note To measure these correctly each test must be Stopped using the SRQ button Also use TP306 or the L shaped rec A Shield around U202 as the Reference
186. he GPIBO board This program illustrates a method of recording any errors produced by the 8840A 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 60 command during selftest is 9xxx 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 BDNAMES Initialize the interface board devname 18840A Device name is 18840A CALL IBFIND devname dvm Initialize the device PRINT MONITORING SELFTEST WRT 70 CALL IBWRT dvm WRT Start selftest DO WRT G7 CALL IBWRT dvm WRT RD 18 CALL IBRD dvm RD error status errcode LEFTS RD 4 IF errcode lt gt 1000 THEN Check for errors WRTS Clear error register CALL IBWRT dvm WRT PRINT Error RIGHTS errcode 3 occurred END IF CALL IBWRT dvm 515 16 CALL IBRD dvm 51 Get instrument configuration Stat LEFT st 1 LOOP WHILE stat 9 Loop while selftest still active WRT G7 CALL IBWRT dvm96 WRT RD 18 CALL IBRD dvm96 RD Get error status errcode LEFTS RDS 4 IF errcode lt gt 1000 THEN Check for er
187. he 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 0402 16 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 6 65 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 approxi mately 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 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 9702 or open resistor network 2701 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 preci
188. her 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 8840A selects the nearest valid range For example if the 8840A is in the VDC function and you press the 20 MQ button the 8840A selects 1000V range The range buttons have no effect in the mA DC and mA AC functions since all measurements in these functions are made in the 2000 mA range 2 17 Triggering Triggering causes the 88404 to execute measurement cycle and display the result During each measurement Cycle the instrument samples the input a of ines and then averages 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 ator flashes so rapidly it appears to be almost constant How the 8840A is triggered depends on whether the continuous trigger mode or external trigger mode is selected Pressing the EX TRIG external trigger button toggles the 8840A between the two modes 2 18 CONTINUOUS TRIGGER MODE In the continuous trigger mode readings are triggered bya continuous internal trigger The rate of the trigger is set by the RATE button 2 19 EXTERNAL TRIGGER MODE In the external trigger mode readings are triggered by pressing the TRIG button
189. hich when applicable is included with the manual 7 5 SERVICE CENTERS To locate an authorized service center call Fluke using any of the phone numbers listed below or visit us on the World Wide Web www fluke com 1 800 443 5853 in U S A and Canada 31 40 267 8200 in Europe 1 425 356 5500 from other countries a NOTE This instrument may contain 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 TWO FUSIBLE RESISTORS PN 474080 AND 733915 TO ENSURE SAFETY USE EXACT REPLACEMENT ONLY MANUAL STATUS INFORMATION REF OR OPTION NO ASSEMBLY NAME Main PCA Display PCA IEEE 488 Interface PCA True RMS AC PCA FLUKE PART NO REVISION LEVEL 728857 728873 879267 728899 7 2 1 Table 7 1 8840A Digital Multimeter Description MAIN PCA DISPLAY PCA FUSE 406 1 375 3A 600V FAST FUSE 25X1 0 2A 250V FAST FUSE 25X1 25 0 25A 250V SLOW FUSE 25X1 25 0 125A 250V SLOW FASTENER PLUNGER NYL 271 FASTENER GROMMET POLYCARB 271 NUT EXT LOCK STL 6 32 SCREW PH P LOCK STL 6 32 250 SCREW TH P SS 4 40 187 SCREW FIH P LOCK STL 8 32 500 SCREW PH P THD FORM STL 4 20 500 SCREW FHU P LOCK SS 6 32 250 SCREW FH P LOCK STL 8 32 3
190. ial 6 10 6 16 STORING VARIABLE 5 6 10 6 17 CALIBRATING INDIVIDUAL 6 10 6 18 VERIFYING 6 11 6 19 ERASING CALIBRATION 6 11 6 20 TOLERANCE CHECK cure mecs rr sae noid na ema ler a 6 12 6 21 AC CALIBRATION AT OTHER 6 1 6 22 OPTIMIZING USE OF THE Mad se 6 1 6 23 Remote 6 13 6 24 TIMING CONSIDERATIONS 6 14 6 25 2 6 15 6 26 EXAMPLE CALIBRATION PROGRAM 6 16 6 27 DISASSEMBLY 6 16 6 28 Case Rem val eerte io e coa ax cave Mone ED Sud EAE 6 17 6 29 True RMS AC Removal Option 09 6 17 6 30 IEEE 488 Interface Removal Option 05 6 17 6 31 Main 6 17 6 32 Front Panel Disassembly 6
191. ibrated by pressing the corresponding function button Once a function is selected the 8840A automatically steps through each range of that function prompting you for the necessary reference sources The prompts are shown in Table 6 10 The 8840A 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 fol lows 1 Ensure the A D Calibration procedure has been com pleted 2 Select the desired function by pressing the corre sponding function button The 8840A will display the first prompt for that function 3 Each time the 8840A 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 8840A performs the necessary calculations Do not change the reference source while the display is blank The 8840A then displays the next prompt For reference all prompts are shown in Table 6 10 NOTE To use reference sources that differ from the prompted values see Storing Variable Inputs later in this section 4 After the last range is calibrated the 8840A 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
192. ich generates a service request A bit is considered true when it is set to 1 Bit 1 the lowest order bit is set true on overrange When overrange occurs the output buffer is loaded 9 99999E 9 and a suffix if enabled 2 is not used is always set to 0 Bit 3 is set true when the front panel SRQ button is pressed Bit 4 Cal Step Complete is set true when a command is completed in the calibration Bit 5 Data Available is set true every time the output buffer is loaded regardless of the kind of output data including error messages This bit is cleared set to 0 when any new bus input occurs when the output buffer is read or when external trigger occurs 6 Any Error is set true whenever an error condi tion occurs At the same time that bit 6 is set true the output buffer is loaded with an error message Remote Programming SERVICE REQUESTS IHE CI LINK IC E E UE interface messages described here originate at the con troller 3 53 Address Messages Address messages are used by the controller to communi cate 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 mes sages are processed immediately and are not placed in the input buffer The address messages are MLA My Listen Address Addresses device to listen MTA My Talk Add
193. idually 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 8840A then prompts for a low reference source for that range See Table 6 12 During High Frequency AC Calibration the 8840A 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 8840 will then begin taking readings in the selected range so that you may verify the calibration The CAL annunciator remains on 5 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 When you complete certain parts of the calibration proce dure the 8840 automatically begins taking readings so that you can verify the calibration is correct It is recom mended that you do so The CAL annunciator remains lit The 8840A continues to
194. iffer from the prompted values see Storing Variable Inputs later in this section 4 After the last range is calibrated the 8840A 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 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 The 8840A has several advanced calibration features which are not necessary for the basic calibration proce dure but which can make calibration easier The following paragraphs describe these features and also discuss special considerations for optimizing the performance of the 8840 in special situations 6 16 STORING VARIABLE INPUTS As a convenience the VAR IN variable input feature lets you calibrate the 8840A using reference source values which differ from the values prompted by the 8840A For example you may want to calibrate the 2000 range using a reference resistor with a precisely known value of 99 8750 rather than 1000 as prompted This feature is not available during A D Calibration 6 10 6 11 High Frequency AC Calibration DISPLAYED PROMPT 100 0 mV AC 1 000 V AC 10 00 V AC 100 0 V AC 200 0 V AC NOTES 1 The
195. ifications 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 perfor mance test calibration or repair is needed To ensure optimum performance the test must be per formed at an ambient temperature of 18 to 28 with a relative humidity of less than 75 Also the 8840A 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 8840A 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 Section 6 Maintenance NOTE The inputs must be left open circuited while the self tests are performed Otherwise the 8840A 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 8840A skips tests 3 and 4 Also if Option 09 is not installed the 8840A skips tests 1 2 and 3 To initiate the self tests press the SRQ button for 3 seconds The TEST annunciator will then light up and the 8840A will run through the analog tests in sequence Each test num
196. ifts logic levels to control 0806 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 0804 When 08068 15 not used its non inverting input is connected to the CURRENT SENSE line 5 45 mA AC Scaling The mA AC function uses the same current shunt and protection network which is used for dc 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 5 46 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 5 47 True RMS AC to DC Conversion U801B buffers the input to rms converter 0802 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 VARIABLE RMS FILTER CO
197. imensions 2 1 INTRODUCTION This section provides instructions for installing and ting the 8840 Refer to Section 4 for measurement considerations NOTE Do allow the meter io be used if it is damaged or its safety is impaired 2 2 INSTALLATION 2 3 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 FUSE FOR FIRE PRO TECTION TO AVOID ELECTRIC SHOCK REMOVE THE POWER CORD BEFORE REPLACING THE EXTERNAL LINE FUSE The 8840 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 blo fuse To replace the power line fuse first remove the power cord Then turn the rear panel fuse cover 1 4 turn counter clockwise 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 Section 2 Operating Instructions 2 4 Connecting to Line Power WARNING TO AVOID SHOCK HAZARD CONNECT THE INSTRUMENT POWER CORD TO 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 YOUR AREA The 8840A can be config
198. impair the protection provided by the equipment Some common international electrical symbols used in this manual are shown below OFF power DANGEROUS SWITCH POSITION VOLTAGE ON power mu SWITCH POSITION EARTH GROUND AC ALTERNATING SEE EXPLANATION CURRENT IN MANUAL SEE MANUAL FOR DI CURRENT FUSE REPLACEMENT INFORMATION EITHER DC OR AC Before using the meter read the following safety information carefully In this manual WARNING is reserved for conditions and actions that pose hazard s to the user CAUTION is reserved for conditions and actions that may damage your meter Avoid working alone Follow all safety procedures for equipment being tested Inspectthe test leads for damaged insulation or exposed metal Checktest lead continuity Damaged leads should be replaced Be sure the meter is in good operation condition Select the proper function for your measurement To avoid electrical shock use caution when working above 60V dc or 25V ad RMS Disconnect the live test lead before disconnection the common test lead Disconnect the power and discharge high voltage capacitors before testing in When making a current measurement turn the circuit power off before connecting the meter in the circuit Check meter fuses before measuring transformer secondary or motor winding current See Section 6 MAINTE An open fuse may allow high
199. ing Output Data The output buffer is loaded when the 8840A receives an output command or when an error occurs Output com mands are those device dependent commands which load the output buffer with data commands GO through G8 Single trigger command Group execute trigger Continuous Trigger TO Because the 8840A 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 8840A as a talker This is done by sending the interface message MTA My Talk Address 3 42 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 3 43 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 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
200. ital problem between the A D Converter and the In Guard uC can cause erroneous or noisy readings or offsets Similar prob VERT 2V DIV HORIZ 2 ms DIV 1 0V INPUT Figure 6 14 Output of A D Amplifier TP101 6 41 Maintenance TROUBLESHOOTING RAMP UP OR DOWN INDICATES LEAKAGE PROBLEM AT 101 24 VERT 2V DIV HORIZ 2 ms DIV 1 01V INPUT RAMP UP OR DOWN INDICATES LEAKAGE PROBLEM AT U101 25 Figure 6 15 Waveforms at U101 24 and U101 25 lems may be caused by a failure of the Calibration Mem ory 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 17 The A D reading can be calculated by know ing the weight of each bit and by weighting each nibble correctly The first nibble is weighted 1 the second 1 16 the third 1 162 the fourth 1 163 etc Figure 6 18 shows how to read the A D output for an input of 0 66 by interpreting the waveform at TP102 using the first three nibbles Troubleshooting the A D Converter for defective compo nents 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
201. ition to remove pull ends out Figure 2 2 Adjusting the Handle 2 7 OPERATING FEATURES 2 8 Power Up Features When the 8840A 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 8840A then assumes the following configuration e VDC function Autorange starting in the 1000V range Slow reading rate Continuous internal trigger OFFSET off Local front panel control While all display segments are lit during the power up self test you can freeze the display by pressing the SRO button display segments will then remain lit until you press any button 2 2 2 9 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 Tange 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 8840A do not press the CAL ENABLE switch unless calibrating the instru ment Never cycle power on or off while the CAL ENABLE switch is on that the and mA AC functions are available only with the True RMS AC option If this option is p 2 50000 7 a a
202. k ohas 26 7 20fhohas 27 4030 9 2k42k Option 28 KB01x 29 2 30 1 31 48 32 0804 9 33 U804D 16x IAC VACA P3475 1 IAC 1 100 VACA r24r4 6 26 gt O O O O o Table 6 16 Overall State Table The variables HD1 HD2 PC 1 the A D 0101 2 TR2 corresponding dynamic si ate on only shen when HD 0 stands for the switch or relay being open Closed a reference designator has afte is closed when the control voltage 15 low 01 the control voltage is high 5V QDC ritr24r4 1 2 3 4 NORMAL OPERATING MODE and TR2 are dynamic signals generated by These variables are true onl 815 are true For example the 501 is true when the hes in line 8 voc 2 Mire qire Ohas IDC Ti r2 r3 r4 T5 r1 r2 r3 5 Ti r2 r3 4 5 r Ti r2 r3 r4 5 15 100 00000 12 11 21 4 11111 1 0 00000 000000 1 8 84 4 4 9 5 6 5 00000 6 5 6 000 5 5 5 0 0 0 0 11 1 1111 1 111111 000000 1 010 00000 111100 111100 9 010 00000 111100 111100 0 010 00000 4 1 1 1 0 111100 0 111 11111 111111 000011 1 000 99000 900000 111111 9 101 00000 00001
203. l bus according to the read and write cycles shown in Figure 5 14 During either cycle the Figure 5 12 Vacuum Fluorescent Display address strobe AS changes from low to high when an 5 13 8 18 SS3HQQV 153401 8 2220 WvuSOud WO3S zizn OL 30V3U341NI AV ldSIQ U31H3ANOO Diagram QuVOBA3 54 13934 3390939 5 iN3uuno 39V43U31NI AVdSIQ 08VOSA33 QIOH MOVHL 5 Say 99 333 30VJU31NI 88 3331 3NYL ISE TOHINOO Av13H Figure 5 13 Digital Controller Block ion Theory of Operat DIGITAL CONTROLLER 5 14 address is valid and the data strobe DS changes from low to high when the data is valid The address strobe latches the address 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 r
204. l test signals to allow trouble Shooting 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 8840A very efficiently 6 37 Initial Troubleshooting Procedure WARNING TO AVOID INJURY OR EQUIPMENT DAMAGE USE EXACT REPLACEMENT PARTS FOR ALL PROTECTION COM PONENTS When a problem occurs in the 8840A 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 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 8840A may indicate errors are present The test numbers will appear consecutively ERROR will appear on the display if a test should fail The 8840 can be held in each of the test configurations by momentarily pressing the SRQ button Press any but ton to continue the tests With the description of the self tests given below it may be possible to isolate the failure For refe
205. leshooting mode is described in detail in the Maintenance section 5 34 Guard Crossing Communication The In Guard uC contains UART universal asynchro nous receiver transmitter which it uses to communicate across the guard to the IEEE 488 Interface The transmis sion speed is 62 500 bits per second 5 85 GUARD CROSSING 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 IEEE 488 Interface One circuit is shown in Figure 5 15 the other circuit works identically A portion of each circuit is contained in the 488 Interface 5 15 Theory of Operation GUARD CROSSING External or Memory Read and Write Timing No Symbol Parameter Notes t 1 5 Address Valid to AS 1 Delay 1 2 3 2 AS 1 to Address Float Delay 1 2 3 3 TdAS DR AS 1 to Read Data Required Valid 1 2 3 4 4 5 5 AS Low Width 1 2 3 TdAz DS Address Float to DS 1 1 6 TwDSR DS Read Low Width 1 2 3 4 7 TwDSW DS Write Low Width 1 2 3 4 8 TdDSR DR 051 to Read Data Required Valid 1 2 3 4 9 ThDR DS Read Data to DS 1 Hold Time 1 10 TdDS A DS 1 to Address Active Delay 1 2 3 1l TdDS AS DS t to AS 1 Delay i 1 2 3 12 TdR W AS R W Valid to AS 1 Delay 1 2 3 13 TdDS R W DS
206. lete in them selves except for string terminator Each of these commands requires the single numeric c digit n _ These characters are used for entering numbers Line Feed Group Execute Trigger End Or Identify 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 Enable Group Execute Trigger Go To Local Selected Device Clear These characters may be inserted anywhere in character string without affecting the string They carry no special meaning and are ignored by the 8840A They are not placed in the input buffer The error annunciator is displayed on the 8840A front panel when of these characters is encountered ERROR 71 Figure 3 8 interpretation of Messages Remote Programming INPUT SYNTAX Correct construction 8840A is con figured in F3 and the trigger is executed Then the 8840 is left in F4 3 40 OUTPUT DATA The following paragraphs describe the data that can be loaded into the 8840A 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 output data and their relative priority F3 F4 Note that the 8840A can also send data to the IEEE 488 bus from the serial poll register For a description of this data see paragraph 3 50 3 41 Load
207. ling the two plastic pull tabs directly outward from the Display PCA Remove the two mounting screws on either side of the fear panel power receptacle Disconnect green power supply ground lead the rear panel mounting stud The stud is located near the rear panel power receptacle See Figure 6 6F Remove the Line Voltage Selection Switch LINE a Remove the upper screw that holds the LINE SET to the upper rear panel standoff b Unplug the ribbon cable from the and lift the LINE SET Remove push for CAL ENABLE switch as follows Figure 6 6H a While supporting the white plunger of the CAL ENABLE switch with a finger pop the push rod off the switch plunger by pulling the push rod directly upward NN b Rotate the push rod 90 degrees toward the center of the instrument Pull the push rod toward the rear panel remove it Remove the FRONT REAR switch push rod as fol lows Figure 6 61 Insert a 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 i 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 chassis on its side Remove POWER switch push rod as follows Fi
208. ll of these examples the 8840A is set to IEEE 488 address 4 rear panel switch setting 000100 Of course any other address 00 to 30 could be substituted In each of these examples the instrument is cleared prior to configuration set ups This ensures that the 8840A 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 marks Also spaces are placed between commands for ease of reading they are not required For the examples using the Fluke 1720A or 17224 the 8840A is plugged into port 0 The port is initialized by the INIT statement which sends IFC interface clear 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 8840 is addressed on port device 4 under control of Fluke 17204 or 1722 Instrument Controller In the INPUT statement the controller assigns the first part of the 8840A output response the measurement value to R and assigns the second part the suffix to R FLUKE BASIC on 1720A 1722A INIT PORT 0 Port CLEAR PORT O Clear instr to default functions PRINT 4 1 RO SO TO Y1 Write functions to instrument FORI 1TO10 INPUT Q4 R Get data from 8840A PRINT LRjR IPrint to 17224 display NEXT I mo td E
209. ller GENERAL COMMON MODE VOLTAGE 1000V dc or peak ac or 700V rms ac from any input to earth TEMPERATURE RANGE 0 to 50 operating 40 to 70 storage HUMIDITY RANGE 80 RH from 0 to 35 C 7096 to 50 WARMUP TIME 1 hour to rated specifications 100 120 220 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 Meets requirements of MIL T 28800C for Type Class 3 Style E equipment ELECTROMAGNETIC COMPATIBILITY Specifications apply when used in an environment with field Strengths 1 V m For field strengths up to 3 V m multiply floor adder by 12 for VDC and Resistance and 100 for DC Current VAC and AC Current have adders up to 3 V m ANSI C39 5 and IEC 348 Class 8 9 cm x 21 6 cm x 37 1 cm 3 47 in x 8 5 in x 14 4 in introduction and Specifications SPECIFICATIONS Table 1 1 Specifications cont Net 3 4 kg 7 5 Ib shipping 5 0 11 Ib INCLUDED Line cord test leads Instruction Service Manual IEEE 488 Quick Reference Guide Option 05 only and instrument performance record IEEE 488 INTERFACE Option allows complete control and data output capability and supports the following interface function s bsets SH1 AH1 T5 L4 581 RL1 DC1 1 1 PPO and CO Figure 1 1 External D
210. ls and measure the voltage across this resistor with another volt meter There should be a 1V drop across the resistor If the ohms functions do not work in any range check the supplies at 0401 x15V 0404 30 and 5V U402 15V 45V and OV and U403 15 45V 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 cir cuitry 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 kQ If the ohms functions work in only certain ranges suspect resistor network Z401 or analog switches U402 or 0403 To test the analog switches select a defective Tange and connect a short across the switches 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 7401 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 t
211. ls 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 5 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 lines BS1 and BS2 should be 47V and 7V 1090 referenced to input of the A D amplifier U103 3 Troubleshooting the bootstrap supplies can often be made easier by putting the 8840A 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 8840A 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 trouble shooting tool is the A D output waveform at TP101 which can be checked with an oscilloscope The waveform Maintenance TROUBLESHOOTING should look like the one shown in Figure 6 14 when the input voltage 15 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
212. mands F R S and T The codes for these commands are li ted in Figure 3 5 numeric entry for PO must within 1000 and 6724 Each of the four digits must not exceed its maximum allowed value 6 7 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 pat is ignored Example 3112 0 Sets the 8840A to F3 51 and T2 3 24 P1 Put SRQ Mask Format Explanation N SRQ mask gt P1 Where SRQ mask is a integer from 00 to 63 The P1 command is used to program the 8840A 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 47 Numeric entries for P1 command must be between 0 and 63 inclusive or an will occur and the SRO mask will remain unchanged The entry may be expr as an integer real number or real number with exponent 5 described under the N command Any fractional 5 ignored Example NO 17E 2 P1 Explanation Sets SRQ mask to 17 Enables SRO on data available or overrange N1 PI Sets SRQ mask to 01 Ac is assumed SRQ over range 3 25 P2 Put Calibration Value Format
213. me 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 6 26 EXAMPLE CALIBRATION PROGRAM 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 54404 Direct Voltage Calibrator to perform and then verify the A D Calibration procedure In this program the 8840A is at bus address 1 and the 5440 is at bus address 7 This A D Calibration is correct Controller and the Fluke bus address 1 and the 54404 is at bus 2210 DIM 20 DIM E 0 0 2 0 03 2 0 03 2 0 66 6 STEP 17 READ INIT PORT REMOTE 1 0 6 6 0 0 0 D GOTO 290 PROVIDES MEANS 110 PRINT PUT 8840 IN CAL MODE INPUT Z FOR M 1 TO 2 PRINT 27 SOUT 0 0 OPER WAIT 1000 PRINT 81 FOR 0 TO 11 STEP 1 PRINT 1 G2 INPUT 1 IF gt 1000 GOTO 180 E STEP INPUT SOUT C LI t IF SPL 1Z AND 8 GOTO 26 NEXT NEXT PRINT VERIFICATION WAIT 3000 FOR TzO TO 6 STEP 1 PRINT e7 SQUT V T WAIT 7300 INPUT 1 R RS NUMS R Ss 44399 IF MID R 2 1 O THEN RS IF LEFT R 1 THEN R PRINT R END program performs the A D Calibration THEN HIT lt LOOP SET 54404
214. mmands Start selftest Read error status Check for errors Clear error register Print analog error instrument configuration Check for selftest still active Read error status Check for errors Print digital error Figure 3 14 Example Programs Using the IBM cont 3 29 Remote Programming EXAMPLE PROGRAMS Et The following application program is written in QBASIC for the PC or PC AT The National Instruments Model GPIB PCIIA board provides the interface between the PC and the Fluke 8840A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device 18840 assigned to the GPIBO board x This program selects VDC F1 Slow rate SO Continuous trigger TO and suffixes enabled Y1 The program takes 10 zendings displays them on the screen and then stops Microsoft QuickBasic V 4 5 SINCLUDE qbib45 dcl devname 18840A Device name is 18840A CALL IBFIND devname dvm Initialize the DMM CALL IBCLR dvm Clear device WRT F1ROSOTOY1 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 data PRINT i LEFT RD 16 Print to display
215. mmands 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 8840 defaults to 0 power up and any device clear command DCL or SDC The reading rate can be read using the GO command 3 29 Tn Trigger Mode Commands The Trigger Mode commands duplicate the front panel EX TRIG button In addition 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 t 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 4721 In the continuous trigger mode 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 The trigger mode can be read using the command The 8840 defaults to TO both power up and any device clear command DCL or SDC 3 30 Wn Terminator Commands The Terminator commands select what terminators the 8840 appends to every output string The available termi nators are Carriage Return CR Line Feed LF and End Or Identify EOI an
216. nalog 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 8840A through all functions and ranges in the following sequence 1 VDC 200 mV 2V 20V 200V 1000V VAC 200 mV 2V 20V 200V 700V 2 WIRE 2009 2k 20k 200k 2M 20M 2 3 4 4 WIRE 2000 2k 20k 200k 2M 20M 5 mA DC one range only 6 AC one range 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 11010 00000 111100 111100 0 0 Next move to U305 5 and repeat The slow reading rate gives the following pattern at U305 5 11111 00000 111000 111000 0 0 6 36 BUTTONS THAT PRODUCE INVERTED INVERTED STROBE ONE STROBE TWO 20092 mV VDC 2 VAC 20 2 WIRE kQ 200 4 WIRE 2000 mA DC 20M mA AC Not used Not used BUTTONS THAT PRODUCE Table 6 20 Analog Control Devices Relay Buffer Quad Comparator Quad Analog Switch Quad Analog Switch 0302 Quad Analog Switch U303 Quad Analog Switch U402 Quad Analog Switch 8 Bit Latch Quad Analog Switch Quad Analog Switch U808 Option 09 only If the instrument is not in the slow reading rate it gives the following pattern at U305 5 0000
217. ndirectly by observing behavior of the simpler logic devices which it drives If the keyboard is working at all the 8840 display should be frozen to make the following tests This places the 8840A in a special display test configuration If it is not 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 SRO but ton 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 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 Figure 6 11 6 34 6 50 8 Bit Digit Driver U215 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 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 0213 and display control U212 are in this regard 6 51 3 to 8 Strobe Decoder U213 Check for strobe waveforms 0 7 on U
218. ng rate while the 8840A is taking verification readings Causes an error at any other time during calibration N value P2 Enters lt vaiue gt as a variable input See Entering Variable Inputs in text Causes an error if sent during A D Calibration or when the 8840A is taking verification readings You can check the command was successful by checking the error status by sending the Get Calibration Input command 62 or by checking the Cal Step Complete bit in the serial poll register Puts the string into calibration memory The string may contain up to 16 NOTE Clear Error Register To facilitate remote calibration there are some differences from local calibration 1 In remote calibration you can store 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 4 rear panel SAMPLE COMPLETE signal acts slightly differently During calibration the SAMPLE COMPLETE signal is inactive When the 8840A is taking verification readings the SAMPLE COM PLETE signal acts the same as in normal operation Note that a command may be valid in some parts of the
219. nt nonlinear response of computing type rms con verters to very small input signals 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 addition 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 _ WAVEFORM CREST FACTOR SQUARE WAVE SCR OUTPUT OF 100 1096 WHITE NOISE MAMMA AC COUPLED PULSE TRAIN s SINE WAVE TRIANGLE SAWTOOTH MIXED FREQUENCIES 1 414 to 2 0 1 414 to 3 0 3 0 to 4 0 3 0 Figure 4 7 Typical Crest Factors for Various Wave forms AC COMPONENT DC COMPONENT OV RMS Total rms component dc component Figure 4 8 Combined AC and DC Measurement As long as the 8840A reading is 1 000 counts or more readings will still be within specified accuracy 4 9 Measurement Tutorial AC VOLTAGE AND CURRENT MEASUREMENT EXAMPLE Given a zero input reading of 300 counts 0 300 mVin the 200 mV range and an input signal of 10 mV the 8840A might read 102 0 3002 m 100 0 090 The effect of the zero input error is reduced 0 300 mV to 0 004 mV
220. nterface message Figure 3 5 Device Dependent Command Set cont The Get commands are described further in the following paragraphs For more information about output data see paragraph 3 40 3 12 GO Get instrument Configuration The 60 command copies the 88404 function range read ing 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 S and T commands as shown in Table 3 1 An example output string follows Example 3410 CR LF Meaning 3 F3 2 WIRE function 4 R4 200 kQ range 1 S1 Medium reading rate 0 TO Continuous trigger The second digit which can vary from 1 to 6 indicates what measurement range the 8840A is in regardless of whether the 8840A is in autorange or manual range The output string from a 60 command is acceptable as an argument for an N command This allows you to con figure the 8840A from the front panel and then record the configuration over the bus for future use with a PO com mand However 9mmm meaning self test can not be used with the PO command 3 13 G1 Get SRQ Mask The G1 command copies the present SRQ mask into the output buffer in the format shown in Figure 3 6 The 33 CR LF mask values are explained in Table 3 1 An example output string follows For more about SRQ mask see paragraph 3 51 Meaning Enable SR
221. o a 28 pin socket 6 45 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 U220 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 6 46 Relay Buffer U201 At this point it is necessary to return the 88404 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 PINS AT WHICH WAVEFORM APPEARS U202 10 14 16 18 20 22 24 26 28 XU222 3 5 7 9 12 15 17 19 23 24 U220 1 3 5 7 10 13 15 17 22 0219 2 3 6 7 12 13 16 17 9202 13 15 17 19 21 23 25 27 29 33 XU2224 6 8 10 11 13 16 18 21 25 WAVEFORM U220 2 4 6 8 9 11 14 16 19 23 U219 4 5 8 9 14 15 18 19 WAVE UU tii 202 4 16 per bit Guard crossing out FORM C 500 rep rate w
222. 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 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 2009 Overrange TEST 12 2 kQ Overrange TEST 13 20 Overrange TEST 14 200 kQ Overrange These tests put the 8840A in the respective range of the 2 wire ohms function They check that each range of the Ohms Current Source has enough compliance voltage to overload the front end TEST 15 1000 VDC X10 T H 20 MQ Puts the Ohms Current Source in the 500 nA range The resulting current through 2302 the 10 input divider causes a nominal divider output voltage of 50 mV The 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 TEST 16 200 VDC 200 kQ TEST 17 200 VDC 20 kQ TEST 1
223. ommands The Display commands allow the user to biank the numeric field in the 8840A front panel display The DO command causes the display to operate normally and is the default on power up and upon any device clear com mand 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 respective ranges The D1 command is used for best performance when high IEEE 488 Interface Data rates are required 3 4 3 10 Fn Function Commands The function commands duplicate the panel function buttons The 8840A defaults to F1 on power up and on any device clear command DCL or SDC If FO is sent to the 8840A it is internally converted to F1 The function setting can be read using the command As with the front panel commands selecting F5 or F6 automatically selects the 2000 mA range R5 Also if the instrument is in a resistance function F3 or F4 and in R6 selecting any other function automatically selects R5 Exampie Explanation Selects 2 WIRE function it does not affect any other settings Selects mA DC function and 2000 mA range Resets all other settings to default 3 11 Get Commands The Get commands get information from the 8840A for the controller Each Get command loads the output buffer with an output string in the format
224. on N12001 Enters the five digit integer 12001 N 1 23E2 Enters 123 x 102 N 154 33E 1 Enters 1 5433 x 10 The N command enters numeric values for use with subse quent 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 49 The mantissa may exceed 5 1 2 digits The 8840A 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 N123456789 _ Explanation Enters 1 23456 x 108 3 22 Put Commands The Put commands PO through P3 set up the 8840A s configuration and operating modes by entering putting information in the appropriate registers The put com mands are described further in the following paragraphs 3 23 PO Put instrument Configuration Format Explanation N lt frst gt P0 Where frst is a four digit integer interpreted as arguments for the F R S and T commands Example Explanation 3 10 N3120 Identical to F3 Ri S2 TO Selects 2 WIRE function 2005 range fast sample rate continuous trigger The PO command allows broadside loading of the Func tion Range Reading Rate and Trigger Mode com
225. onents 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 NO In the U S order directly from 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 Part number and revision level of containing the part Reference designator Fluke stock number e Description as given under the DESCRIPTION heading Quantity e Instrument Model Serial Number and Firmware Numbers 7 3 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 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 manual supplement w
226. onstants 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 6 13 OFFSET AND GAIN CALIBRATION This procedure calibrates the instrument s offsets and gains by applying a high and low input for every range of 6 7 Maintenance CALIBRATION sooroo 855 T m AUTO es ERASE DIGIT 1 2 DIGIT 3 DIGIT 4 5 DIGIT 4 Function Each button selects the Offset and Gain Calibration procedure for the respective function Buttons Range These buttons have two functions Normaily 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 STORE Tells the8840A that the input it is requesting is now present at the input terminals Pressing the STORE button causes the 8840A to compute and store calibration constants A D Selects the A D
227. or at least 1 1 hour hour 2 Select the VDC function 2 Select the VAC function and the slow S reading 3 Connect the DC Calibrator see Table 6 1 to provide pue a voltage input to the HI and LO INPUT terminals If 3 Connect the AC Calibrator to provide a voltage input using the Fluke 343A and the Kelvin Varley Voltage to the HI and LO INPUT terminals Divider instead of the Fluke 5440A connect the test leads as shown in Figure 6 1 4 Low and Mid Frequency Test For each step in Table 6 3 select the indicated range set the AC 4 For each step in Table 6 2 select the indicated range Calibrator for the specified input and verify that the set the DC Calibrator for the specified input and displayed reading is within the limits shown for each verify that the displayed reading is within the limits reading rate shown for each reading rate For step A connect a NOTE Short across the HI and LO INPUT terminals and press OFFSET The measurement in step C should be This procedure tests the extremes of each range relative to this offset You may shorten the procedure by testing only the 5 Set the DC Calibrator to input negative voltages and Reus Wir repeat steps C through of Table 6 2 5 Test f UTEE igh Frequency Test for each step in Table 6 4 6 With the unit is the 2V range check the A D linearity select ihe adie tod range set the AC Calibrator for by setting the DC Calibrator for each ste
228. or partial calibra Maintenance TROUBLESHOOTING ID I RE NER tion is performed If the Calibration Memory is not properly configured or not working correctly ERROR 29 is displayed The accuracy of the 8840A is suspect 6 40 Digital Controller Troubleshooting The basic strategy in troubleshooting the Digital Controller circuit is to check first whether the In Guard Microcom puter uC system is functional starting with the In Guard itself U202 Most of this circuitry is tested using the specially provided In Guard Troubleshooting Mode If the In Guard uC 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 keyboard 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 appro priate 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 6 41 IN GUARD MICROCOMPUTER SYSTEM This procedure is performed entirely in
229. or the 8840A to receive them they must be sent over the IEEE 488 bus when the 8840 is in remote and has been addressed as a listener The following paragraphs describe the device dependent commands in alphabetical order Special characters 2 are described last 3 7 Bn Offset Commands The Offset commands duplicate the function of the front panel OFFSET button When the 8840A receives the B1 command the 8840A stores the present reading as an offset for the present function The command cancels the offset As with front panel only one o 1 allowed at a time The offset status not the offset value can be read 5 the G5 command 8840 defaults to both power up and on any device clear command DCL or 500 _ Remote Programming DEVICE DEPENDENT COMMAND SET FUNCTION 1 R6 INSTRUMENT CONFIGURATION READING 5 TRIGGER Tr MODE F R S T B Y W eee X0 P3 Cn Da INPUT BUFFER G5 AUTORANGE R7 AB STATUS ON OFF OFFSET 1 2 o ENTRY i REGISTER SUFFIX Yn lt ENABLE DISABLE G6 YW STATUS Wn OUTPUT al TERMINATORS G0 G7 DATA Bul PLAY Da MEASUREMENT uos 3 MEASURE CIRCUITRY MENT DATA OUTPUT 2 BUFFER ERROR MESSAGES ERROR Eco MES NS USER P3 G3 MESSAGE SRO P1 G1 MASK VARIABLE P2
230. ord Figure 6 10 Waveforms for In Guard Troubleshooting Mode Maintenance TROUBLESHOOTING 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 6 47 3 to 8 Chip Select Decoder 0208 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 0202 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 13 group width 100 us group spacing 10 ms 230 us 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 system If the keyboard or display is still suspect at this point proceed to Display System below Otherwise proceed to Analog Control Signals below 6 48 DISPLAY SYSTEM The display keyboard system is operated by a complex LSI IC U212 Generally this IC is checked i
231. ould 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 If not present check at the A D IC at U101 14 The 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 Trouble shooting below for detailed troubleshooting instructions 6 25 Maintenance TROUBLESHOOTING DEFINITIONS Logical AND Logical OR Logical e g D Slow reading rate Medium reading rate Fast reading rate Range ri lovest Tange 3 5 5 6 i gt DC Scaling K301x 6323 8394 VOC r1 702473 chas lt lt 1 2 3 310 2 9311 1 PC GC 03018 5 TR1 GC U301 7 HD1 C oheS Cr 4T2 5039520 03010 9 HD1 4Wohas 10 U302A 1 GB TR1 11 U3028 5 a ri ohas r4 T 12 U302C 7 ADIACVAC IAC 13 03020 9 14 1 TR2 15 U3038 5 TR2 16 U303C 7 HD2 x10 17 03030 9 HD2 x1 bh Section 18 401 19 408 5 20 4 2 1 72k 2k 20 FIO 21 14928 5 2k 2k 20 200 ORaS 22 1 20 23 U402D 9 29 24 UAO2C 7 200k42000k 25 14038 5 20
232. p in Table 6 the specified input and verify that the displayed 9 while verifying the display reading is within the reading is within the limits shown for each reading limit shown Set the DC Calibrator for zero volts and disconnect if from the 8840A 6 5 AC Voltage Test Option 09 Only 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 The following procedure may be used to verify the accuracy of the VAC function DC CALIBRATOR FLUKE 343A REVERSE THESE LEADS FOR NEGATIVE INPUT VOLTAGE TO 8840A KELVIN VARLEY VOLTAGE DIVIDER FLUKE 720A CONNECTIONS ARE SHOWN FOR POSITIVE INPUT VOLTAGES TO 8840A NOTE THE KELVIN VARLEY VOLTAGE DIVIDER 15 NOT REQUIRED FOR INPUT VOLTAGES ABOVE 2 0V DC Figure 6 1 Connections for Kelvin Varley Voltage Divider 6 3 Maintenance PERFORMANCE TEST Table 6 2 DC Voltage Test DISPLAYED READING 400 005 3 counts 3 counts 5 5 5 counts 2 counts 99 989 100 011 99 987 100 013 3 100 03 99993 1 00007 99991 1 00009 1 0003 9 9992 1 00008 9 9990 10 0010 10 003 99 992 100 008 99 990 100 010 100 03 999 92 1000 08 999 90 1000 10 1000 3 5 1 Relative to high quality short stored using OFFSET feature 2 When in fast reading rate with intemal trigger and transmittin
233. place the result into the output buffer accept this command 8840A must external trigger mode selected by the T1 T2 T3 or T4 com mand The Single Trigger command is one of five ways to trigger a reading See Figure 3 7 Of these only the Single Trigger command 7 and th 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 8840A A few definitions are presented first followed by a description of how the 8840A processes input commands Guidelines are thea summarized in four syntax rules 3 37 Definitions Output commands Commands which load data into the output buffer The output commands are the Get commands GO through G8 the Single Trigger mand the Continuous Trigger command and Group Execute Trigger GET not to be with the Get commands Input terminator An ASCII control code sent by the controller which tells the 8840A to execute all device dependent commands since the previous terminator Terminators are CR Carriage Return LF Line Feed EO End Or Identify and GET Group pre cute Trigger Input command string One or more commands followed by a terminator 3 38 Input Processing When the 8840 receives commands the bus it stores them in a 31 character input buffer as a continuous string of chara
234. procedure should be performed in the order presented Remove the case first and then remove Option 09 True RMS AC PCA Option 05 IEEE 488 Interface PCA the Main PCA and the front panel For reference see the final assembly drawing in Section 7 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 6 29 True RMS AC PCA Removal Option 09 The True RMS AC PCA should be removed by reversing the last three steps in Figure 809 1 see Section 8 1 Release the True RMS AC from the chassis by pulling the four plastic latches upward Figure 809 1E 2 Raise True RMS AC PCA slightly and disconnect the red lead from the connector 1301 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 224 the True RMS AC out of the chassis 6 30 IEEE 488 Interface PCA Removal Option 05 Only The IEEE 488 Interface 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 conn
235. put of U306 is clamped to 25V by Q307 and Q308 5 7 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 5 8 Analog Filter The three pole low pass analog filter U304 has a Butter worth response with corner frequency at 7 Hz giving approximately 50 dB of rejection at 50 Hz The filter is used only for the slow reading rate and is used only in the VDC ranges and lowest three ohms ranges The filter is switched into the input signal path by 0304 Figure 5 2 In some ranges and functions additional filtering is vided by U302B and C314 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 5 4 oe ye ae conversion cycle The circuit also provides a gain of 10 in the 200 dc 2002 and 2000 mA dc ranges The T H 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 supplying additional gain In subsequent figures the T H Amplifier is represented as a single op amp The circuit operates by cycling between the track settling hold and precharg
236. pward away from the buttons about 1 32 inch Figure 6 8A 6 22 M M A 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 Turn the chassis upside down Install the Main PCA through the bottom of the chassis as follows 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 pan el 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 into position on the chassis and guide the six plastic latches into the circuit board supports on the chassis Pres
237. r detected by In Guard Calibration command not valid unless bration mode enabled Command not valid at this time invalid calibration value in Put command Example Sending a negative value during ac calibration Command not valid in calibration verification Variable inputs not allowed during A D cali bration Use prompted value Device depender commands not valid dur ing self tests Syntax error in device dependent command string Guard crossing error detected by Out Guard Guard crossing error detected power on or CAL ENABLE switch on at power IEEE 488 Interface self test error NOTE See the Maintenance section for detailed description of self tests Operating instructions OPERATING FEATURES OVER l OVER input 22V dc in 2V range E Figure 2 8 Overrange Indication 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 annunciators 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 continu ous trigger mode However it does blank the last reading to acknowledge a button was pressed
238. r the internal bus During a uC write cycle address line AO tells U212 whether to consider data being sent by the as configuration commands or as display data Display data is stored in the Keyboard Dis play Controller which automatically scans the display The Keyboard Display Controller selects one of dis grids using decoder U213 and buffer 0215 The numeric display data is decoded from BCD to 7 segment by decoder U216 and buffered by U217 Additional annunciator is buffered by U218 The Keyboard Display Controller is reset by the uC when ever the uC is reset It receives 1 MHz clock signal from the custom A D 0101 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 front panel button is pressed The 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 33 Troubleshooting Modes In addition to running the diagnostic self tests the In Guard 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 U 02 38 as inputs If line U202 38 205 is shorted to ground the uC goes into the troubleshooting mode U201 pro vides int rnal pull up The troub
239. rd provides the interface between the PC and the Fluke 8840A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840A assigned to the GPIBO board d This program selects VDC F1 Autorange RO Slow rate SO 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 88404 Note the local control must be given to the board and not the device Press lt CTRL gt 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 read data butfer int interface board number int dmm device number int x main brdO ibfind GPIBO initialize board dmm ibfind 18840A initialize device ibclr dmm clear device AES ibwrt dmm F1ROSOTOY1 10 write functions to instrument af ibloc dmm local the device ibsre brd0 0 de assert the remote enable REN signal so the 8840A stays in local when an ibrd call is made 0 in ibrd dmm rd get data X X41 increment reading count 7 printf d 5
240. re 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 uA panel meters The accuracy of the current source is more than enough to verify panel meters whose accuracy is typically 1 to 596 To test an analog panel meter simply connect the current source across the meter move 4 5 Measurement Tutorial RESISTANCE MEASUREMENT ment as though measuring its resistance A 1 mA meter should show full scale when the ohms function is set on the 2 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 series 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 8840A is typically less t
241. recise measurements of ac voltage and current there are several considerations in addition to 4 6 4 16 True RMS Measurement those discussed under dc voltage and current measurement These include the concepts of rms conversion crest pos bandwidth and zero input error 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 dissipated ina resistor True rms measurement greatly simplifies the analysis of complex 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 Howev if a signal is not sinusoidal average responding meters do not display correct rms readings The 8840 actually derives the rms value using analog computation This means that the 8840A readings repre sent 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 4 17 Waveform Comparison Figure 4 6 illustrates the relationship between ac ahd
242. rence the states of various switches and logic lines are shown in Table 6 16 for each function range and reading rate Maintenance EXTERNAL TRIGGER POLARITY SELECTION Option 05 Only 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 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 be
243. resents a numeric difference it always has a sign even in the resistance and ac functions The offset can be cancelled by pressing the OFFSET button again in which case the OFFSET annunciator disappears from the display The offset can also celled by storing an offset in another function If a reading is overrange or unavailable when the OFFSET button is pressed the 8840A indicates ERROR 32 and does not store the offset 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 annuncia tor reappears unless a new offset was another function Note that the input overload limits are not changed by the use of the offset feature However the display flashes if 8840A is in the 1000V dc or 700V ac ranges and the input exceeds 1000V dc or 700V ac respectively Table 2 2 input Overload Limits CONNECTORS VDC INPUT HI and LO mA DC 2 WIRE 4 WIRE kQ mA AC All Functions 2 10 2A INPUT and INPUT LO INPUT HI and LO SENSE and LO VAC INPUT HI and LO 2A INPUT and INPUT LO Any terminal to earth 1000 2000 300 ms 300 ms 700V rms 1000V peak or 2 x 107 V Hz whichever is less 2000 mA rms 1000V dc or peak ac Operating MAKING MEASUREMENTS SENSE terminals for 4 wire resis
244. ress Addresses a device to talk UNL Unlisten Addresses all listeners to unlisten e Untalk Addresses all talkers to untalk 3 54 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 mes sages are sent over the eight parallel data lines in the IEEE 488 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 8840A ahead of any device dependent commands Only DCL enters the 8840A input buffer The 8840 responds to the following universal messages ATN Attention uniline message which causes the 8840A to interpret multiline messages as interface messages AD AC or UC When false multiline messages are interpreted as device dependent messages IFC Interface Clear A uniline message which clears only the interface not the 8840A by placing it in a known quiescent state REN Remote Enable A uniline message which when received with MLA switches the 8840A to remote When REN is set false the 8840A Switches to local and removes local lockout DCL Device Clear A multiline message which is loaded into the input buffer as special device clear command DCL performs the same operation as the device dependent com mand except that it is read before other c
245. rnal 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 V De assert the remote enable REN signal so the 8840A stays in local when an IBRD call made RD 18 711 characters for the reading 5 for the suffix and 2 for the terminators CALL IBRD dvm RD data x96 x 1 Increment reading count PRINT x LEFT RD 16 Display reading GOTO again END Figure 3 14 Example Programs Using the IBM cont WT 3 31 Remote Programming EXAMPLE PROGRAMS 3 32 label1 The following application program is written QBASIC for the PC or PC AT The National Instruments Model GPIB PCIIA board provides the interface between the PC and the Fluke 8840A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840A 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 isto _ display on the screen the lowest resistance value measured on the input terminals of the 8840A using the 2 wire ohms function in autorange The range and function commands are programmed using the Put Instrument Configuration PO command
246. rors PRINT Error RIGHT errcode 3 occurred END IF PRINT PRINT Selftest Complete END Figure 3 14 Example Programs Using the PC cont 3 33 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 8840A DMM The program assumes that the configuration program IBCONF has been run to initialize the interface board with the device name 18840 assigned to the GPIBO board This program selects VDC F1 Autorange RO Slow rate 50 Continuous trigger and suffixes enabled Y1 The program takes 10 readings displays them on the screen and then stops Microsoft C Version 6 0 on PC AT Link this program with appropriate mcib obj include lt stdio h gt include decl h 512 int dmm int i main dmm ibfind 18840A ibcir dmm ibwrt dmm F1ROSOTOY1 10 for i 0 i lt 10 i ibrd dmm rd printf d s i rd Figure 3 14 Example Programs Using the IBM PC cont read data buffer device number device name is 18840A clear device write functions to instrument get data print to display Remote Programming EXAMPLE PROGRAMS The following application program is written in C for the IBM PC AT The National Instruments Model AT GPIB boa
247. s flow from the filament to enabled grid If a P Digital Controller Figure 5 13 consists of In line is enabled i e raised to a nominal 30V dc by the Guard 0202 External Program Memory 0222 Digital Controller the electrons continue past the grid and Calibration Memory U220 Keyboard Display Interface strike the respective plate causing it to glow and associated components 5 26 5 28 In Guard Microcomputer The keyboard consists of a silicone rubber switch matrix 8 The In Guard Microcomputer uC is a single chip 28 located etalized epoxy contact th d OES microcomputer containing 4K bytes of ROM 144 bytes of RAM 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 uC 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 IC U101 Pin 6 is tied to 5V through 100 resistor inside the uC 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 internal bus consists of lines ADO AD7 and A8 A11 Lines AID0 AD7 are time multiplexed to both the least significant address byte and the data Lines A8 A11 carry the most significant bits of the address The writes to and reads from the interna
248. s shown in Figure 3 3 Examples using other controllers are given at the end of this section Examples of 8840A output data show the terminators CR and LF The terminator EOI is not shown because it is a uniline message However the terminators LF 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 3 2 ADDRESS TT 29 5 4 2 1 O CO OO TALK ONLY ADDRESS 5 4 2 1 ONLY ui ake od che a 0 1 0 1 1 0 1 1 0 allowed X X X setting does not matter 4 4 3 6 DEVICE DEPENDENT COMMAND SET Device dependent commands are heart of 88404 remote control They tell the 8840A how and when to make measurements when 10 put data on the bus when to make service requests etc Commands which cor is directly to the front panel controls or display are shi Figure 3 4 The complete set of device dependent com mands 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 m not valid Device dependent commands are device dependent mes sages F
249. s the latch heads to lock the board in the chassis Refer to Figure 6 6L 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 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 6J Maintenance REASSEMBLY PROCEDURE zj 2 lt lt ui FRONT PANEL DISPLAY PCA MOUNTING SCREW 1 OF 4 SPACER MATRIX DISPLAY PCA DISPLAY PCA REAR VIEW Figure 6 7 Front Panel Disassembly 6 23 Maintenance REASSEMBLY PROCEDURE 10 11 12 FRONT PANEL DISPLAY WINDOW Figure 6 8 Removing the Display Window 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 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 8840A is s
250. sec for 0 2 sec due to interrupts from the watchdog timer To Observe these patterns remove 0220 attach 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 U202 13 15 17 19 21 23 25 27 These should be the same as Waveform B which is simply the opposite phase of Waveform A 6 43 Address 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 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 0219 3 Verify that XU222 4 6 8 10 11 1 KHz REFERENCE WAVEFORM er cec 101 7 40 80Hz U101 7 U202 80 Hz A D INT sete U101 8 ___ Maintenance TROUBLESHOOTING M M 13 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 t
251. sely 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 6 39 Maintenance TROUBLESHOOTING x INPUT ier 0 5V DIV T Hu o onm Er 4 2V A D INPUT SAMPLING INPUT 1V m 0 5V DIV HORIZ 2 ms DIV RANGE 2V INPUT OV VERT 5 mV DIV HORIZ di CIEL 1 200 mv OFFSET VOLTAGE OF 0314 TIR 100 VERT 0 5V DIV EIS f E dd ms GENE UR d 9 200 ALL WAVEFORMS FOR SLOW READING RATE M M 6 40 Figure 6 13 Typical Output Waveforms for Track Hold Circuit TP103 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 0702 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 A D Converter Troubleshooting If there is a failure of the A D Converter all power supply leve
252. short 00 0 mA DC open 100 mA AC 100 0 1000 mA DC 1000 0 mA AC 1 000 10 00 100 0 1000 10 00 MQ Steps C G not applicable for these functions 1 Inputs should be at 1 kHz 10 Performance may be enhanced for specific frequencies see text 6 9 Maintenance CALIBRATION The reference sources used in this procedure should nor mally be between 90 kHz and 100 kHz 100 kHz nomi nal 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 Ensure Offset and Gain Calibration has been com pleted for the VAC function 2 Select the High Frequency AC Calibration procedure by pressing the AC button The 8840A will dis play the first prompt 100 mV AC The U in the display indicates the High Frequency AC Calibration procedure has been selected 3 Each time the 8840A prompts you 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 while the 8840A performs the necessary calculations Do not change the reference source while the display is blank The 88404 then displays the next prompt For reference all prompts are shown in Table 6 11 NOTE To use reference amplitudes that d
253. shown in Figure 3 6 Status data the output from Get commands GO Gi G3 G4 G5 G6 G7 and G8 is interpreted as shown in Table 3 1 The Get commands should not be confused with the interface message GET Group Execute Trigger The output data from some Get commands starts with a leading 1 or 10 This prevents the controller from sup pressing leading zeroes and gives a uniform four character length to all instrument configuration data the from Get commands G0 G4 G5 G6 and G7 fee Remote Programming DEVICE DEPENDENT COMMAND TRIGGER MODE COMMANDS TO Continuous Trigger T1 T4 External Trigger DISPLAY COMMANDS TRIGGER COMMANDS DO Normal Display Trigger Measurement 01 Blank Display GET Trigger and Execute READING RATE COMMANDS SUFFIX COMMANDS 80 Slow YO Disable Suffix 51 Medium Yi Enable Suffix S2 Fast Sensed by G5 RANGE COMMANDS SELF TEST RO Autorange On 1 200 2000 20 Begins R2 20 2 Self Tests FUNCTION COMMANDS R3 20V 20kQ F1 VDC 4 2004 200 GTL Go Local F2 5 1000 700 2WIRE 2 2000 DEVICE CLEAR COMMAND F4 4WIREkQ R6 20 Reset 88404 to power up state F5 mADC R7 Autorange Off F6 OFFSET COMMANDS BO Offset Off B1 Offset On Figure 3 4 Commands Which Correspond to the Front Panel Remote Programming DE
254. supply voltages of all active compo nents See Table 6 22 Table 6 22 DC Scaling and Track Hold Supply Voltages PIN OR SUPPLY DEVICE VOLTAGE U301 6 0301 10 OV U301 20 7 5V U301 11 5V U302 6 5V U302 10 OV U302 20 7 5V U302 11 5V U303 6 5V U303 10 OV With OV input 6 38 PIN OR DEVICE 0303 20 0303 11 0304 4 U304 7 9305 3 0305 12 9307 4 U307 7 Q305 c Q306 c SUPPLY VOLTAGE 7 5V Maintenance TROUBLESHOOTING aaa aaae Next check the T H output waveform at TP103 with an oscilloscope Set the 8840A to the VDC function and 2V dc range apply 1V dc across the 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 8840A 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 8840A should read about the same as the external multimeter but with opposite sign If the 8840A fails step 2 but not step 3 then U303 is bad If the 88404 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 an
255. sure the voltage of the under tes lead is positive with respect to the LO INPUT lead 1 Note that this procedure does not correct for circuit load test leads ate not interchangeable when a semiconductor _ ing error Also note that if input bias current error is not device is being measured corrected for it may be added to the circuit loading error 4 7 Correcting for Test Lead Resistance in 4 5 RESISTANCE MEASUREMENT 2 Wire Ohms The 8840A allows you to measure resistance in both In 2 wire ohms the resistance of the test leads can 2 wire and 4 wire configurations Each has its benefits introduce error when measuring low resistances Typical 4 6 2 Wire Ohms test leads may add as much as 0 50 to 2 wire ohms readings Two Wire ohms measurements are simple tc set up and yield good results for most measurement conditions Mea With the 8840A it is easy to correct for this error using surements are made as shown iri Figure 4 3 An internal the OFFSET button current source the ohms current source passes a known test current through the resistance being tested 1 Runknown The 8840A measures the voltage drop across Runknown calculates Runknown using Ohm s law 2 Touch the test leads together The 8840A should Runknown Vtest itest and displays the result indicate the resistance of the test leads Select the 2 wire ohms function 2 2 Measur
256. t 3002 counts from prompt 3002 counts from prompt VAC mA AC 3 HF AC Calibration 9999 counts from prompt 6 12 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 8840A 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 proce dure using inputs at the desired frequency of optimiza tion rather than at 100 kHz Skip step 5 in that procedure 3 Again perform the Offset and Gain Calibration proce dure this time using inputs at the desired frequency of optimization rather than at 1 kHz 6 22 OPTIMIZING USE OF THE 5450A If the Fluke 5450A Resistance Calibrator is used to cali brate 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 8840 In this procedure the 8840A is referred to as the unit under test UUT 1 Complete Offset and Gain Calibration for the UUT s
257. t 1 digit in 2 wire ohms using the offset feature to correct for 5450 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 14 Cover the CAL ENABLE switch with a calibration certification sticker 9 Select the 1 output from the 5450A and brate the high point for the 2 kQ 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 623 Remote Calibration using a shorting link Pomona MDP S 0 or equiva If the IEEE 488 Interface is installed the 8840A can be lent across the UUT s HI and LO INPUT terminals calibrated under remote control Remote calibration is very similar to local front panel controlled calibration Table 12 Exit the calibration mode by pressing the CAL 6 14 shows the remote commands which correspond to the ENABLE switch front panel features 0 0 O INPUT HI SENSE HI OUTPUT HI SENSE HI INPUT LO SENSE LO OUTPUT LO SENSE LO O Figure 6 4 Optimizing Use of the 5450A Table 6 14 Commands Used During Remote Calibration FRONT PANEL FEATURE Display G2 Loads the calibration prompt into the output buffer Not valid when the 8840A is taking verification readings Function F1 through F6 in the calibration mode these select the
258. t should first be cleaned with T SPRAYON Cleaner rosin flux remover or 0908 5 hy equivalent The PCA should then be cleaned with water as described above THESE WAVEFORMS SEEN IN IN GUARD TROUBLESHOOTING MODE REPETITION RATE lt 500 us INTERRUPTIONS EVERY 1 5 SEC REI Figure 6 21 Guard Crossing Test Waveforms c Trademark of E E DuPont De Nemours amp Co 6 49 Maintenance INTERNAL CLEANING 6 50 Section 7 List of Replaceable Parts TABLE OF CONTENTS ASSEMBLY NAME DRAWING TABLE FIGURE NO NO PAGE NO PAGE Digital Multimeter Assembly 8840A T amp B 7 1 7 3 7 1 7 4 1 8840 7601 7 2 7 8 7 2 7 11 A2 Display 8840A 7602 7 3 7 12 7 3 7 12 7 1 8840 INSTRUCTION MANUAL 7 1 INTRODUCTION This section contains an illustrated list of replaceable parts for the 8840A 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 Reference designator indication if the part is subject to damage by static discharge Description Fluke stock number Total quantity special notes 1 factory selected part CAUTION A symbol indicates a device that may be damaged by static discharge 7 2 HOW TO OBTAIN PARTS Electrical comp
259. tage 6 75 Guard Crossing Troubleshooting To troubleshoot the Guard Crossing circuit place the 8840A 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 Figure 6 22 To troubleshoot the other half of the circuit run the diagnostic program as described under IEEE 488 Interface Troubleshooting earlier in this section The program causes the IEEE 488 Interface PCA to send the same test pattern to the In Guard uC You should be able to observe the waveforms shown in Figure 6 21 at the corresponding points in this half of the circuit 6 76 INTERNAL CLEANING 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 prevent damage by electrostatic dis charge 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 6 77 Cleaning Printed Circuit Assemblies If conditions warrant individual printed circuit assemblies PCAs can be cleaned
260. tailed circuit descrip tion 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 12 tlie next higher range and so on Pins are designated by the respec tive integrated circuit e g U101 7 for U101 pin 7 5 4 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 DCV and mA DC functions and also describe the analog filter The ohms functions are described under a later heading because the T H Amplifier provides additional input switching for these functions 5 5 VDC Scaling Scaling is performed in the VDC function by two preci sion resistors networks 2301 and Z302 These compo 5 1 Theory of Operation DC SCALING H3MOdl NOILdO 887 33 Y 88 3331 Quvno 1no pene u3TIOHLNOO U31H3JANOO WLIDIG 5 39V11OA Q31Vv9S 5 ov __9 gt LIND
261. tance measurement only o TiS LI LI Lf LI AWIRE Figure 2 9 Measuring Voltage and Resistance 50000 oc Figure 2 10 Measuring Current While an offset is enabled the 8840A indicates an over range condition if either of the following conditions occur The input signal is overrange 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 8840A selects the appro priate for the input signal regardless of any stored offset If for example 10V offset is stored and a 1 input is applied the 8840A will autorange to the 2V e and display an overrange condition since it cannot di lay 9V on the 2V range Manual range control could be used to lock the 8840A 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 devi ations and matching
262. te 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 _ Meaning 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 G8 Get Instrument Identification The G8 command copies the 8840A instrument identifica tion 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 indi cates the instrument model number the third is always 9 Remote Programming DEVICE DEPENDENT COMMAND SET zero and the fourth indicates the version number of the IEEE 488 interface software Example Explanation FLUKE 8840A 0 V4 0 This instrument is Fluke LF 8840 with IEEE 488 inter face software version 4 0 3 21 N Numeric Entry Command Explanation Where numeric entry is one of the following Format N numeric entry signed integer signed real number without exponent signed real number gt E lt signed exponent Example Explanati
263. the input impedance of the meter As the source impedance approaches the input impedance of the voltmeter the error can be considerable The percent age of error can be calculated using the formula in Figure 4 1 The input impedance of the 8840A is 10 MQ in the 200V and 1000V ranges and is greater than 10 000 the 200 mV 2V and 20V ranges Therefore for the 88404 circuit loading error is less than 0 01 as long as the source impedance is less than 1 in the 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 Section 4 Measurement Tutorial NOTE Input protection circuitry can reduce the inpu impedance to as low as 100 when the 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 rer 4 2 With the 88404 it is easy to correct for this error using the OFFSET button Select the VDC function and the desired range 2 Connect the 8840A INPUT terminals to a resistor which matches the so
264. 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 input of A 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 out puts 30 x15V 6 2V 7 5V 5V 5V and 8 2V dc MAIN PRINTED CIRCUIT ASSEMBLY 0221 202 203 Figure 5 15 Guard Crossing Circuit Samples per sec 4 and 4 5V ac The Power Supply also provides 16V 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 Sup ply to accept line power 100 120 220 or 240V ac
265. the offset of the T H Amplifier X1 configuration TEST 6 1000 VDC Zero Configures the 8840A 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 TH Amplifier X1 configuration TEST 7 1000 VDC 20 Couples the 1000V dc range and 20 MQ current source together The result is nominally 500 nA through the 10 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 TEST 8 20 VDC 20 Puts the DC Scaling circuit into the 20V dc range and the Ohms Current Source into the 20 range The infinite input impedance of the 20V dc range causes the 20 MQ current source to be clamped at its maxi mum open circuit voltage typically 12V The 20V dc range scales this voltage and presents the A D Con 6 30 verter 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 uF at the input terminals TEST 9 20 VDC 2000 Puts the DC Scaling circuit in the 20V dc range and the Ohms Current Source in the 2000 range The infinite input impedance
266. 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 8840A 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 series 4 11 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 uF and larger 4 4 1 Select the 2 wire ohms function the 2 range and the medium reading rate Connect the test leads to the capacitor with the INPUT HI lead to the lead and the INPUT LO lead to lead 88404 will try to charge it to the open circuit voltage of the 2 kQ range about Ed Disconnect the test lead To test for leakage select the VDC function and the 20V range leave the 8840A 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 the capacitor is leaky the voltage across the capacitor will be much less than 6V and the voltage will be decreasing The
267. tion 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 8840A must be in the calibration mode enabled by pressing the front panel CAL ENABLE switch Otherwise the P3 command will gener ate an error message 3 27 Rn Range Commands The Range commands duplicate the front panel range buttons For example RO selects autorange and R4 selects the 200V 200 kQ range The R7 command turns autorange off just as the AUTO button does when it is toggled Command R7 puts the 8840A into manual range selecting whatever range the instrument is in when the command is received The 8840A defaults to RO on power up and any device clear command DCL or SDC The range setting can be read using the GO command 3 12 3 28 Sn Reading Rate Commands The Reading Rate co
268. to instrument 330 CALL IBLOC DVM Give local control to instrument 340 V96 0 X 0 350 CALL IBSRE BD V Deassert the remote enable REN 360 so the 8840A stays in local when a call 370 to IBRD is made 380 RD SPACES 18 11 characters for the reading 5 for the 390 suffix and 2 for the terminators 400 CALL IBRD DVM96 RD Get data from 8840A 410 X96 1 420 PRINT X96 LEFT RD 16 Display readings 430 GOTO 380 440 END 3 28 Figure 3 14 Example Programs Using the IBM cont i Remote Programming EXAMPLE PROGRAMS 10 The following application program is written in BASICA for the PC PC XT or 20 REM The National Instruments Model GPIB PCIIA board provides the interface 30 REM between the PC and the Fluke 8840A 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 18840A 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 a method of recording any errors produced by the 8840A 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
269. to properly link the NI drivers to BASICA 80 REM 90 REM This program selects VDC F1 Autorange R0 Slow rate SO Continuous trigger TO 100 REM and suffixes enabled Y1 All readings appear simultaneously on the instrument 110 REM display and the PC screen with suffixes enabled for function readout Full local 120 REM control is given to the 8840A Note the local control must be given to the board 130 REM and not the device Press lt CTRL gt BREAK to terminate this program 140 REM 150 CLEAR 59736 160 IBINIT1 59736 170 IBINIT2 IBINIT1 4 3 180 BLOAD bib m IBINIT1 190 CALL IBINIT1 IBFIND IBTRG IBCLR IBPCT IBSICJBLOC IBPPC IBBNA IBONL IBRSC IBSRE IBRSV IBPAD IBSAD IBIST IBDMA IBEOS IBTMO IBEOT IBRDF IBWRTF 200 CALL IBINIT2 IBGTS IBCACJIBWAIT IBPOKE IBWRT IBWRTA IBCMD IBCMDA IBRD IBRDA IBST IBRPP IBRSP IBDIAG IBXTRC IBRDLIBWRTI JBRDIAJBWRTIAJBSTA96 IBERR96 IBCNT96 210 220 BASICA PC XT 230 240 BDNAME GPIBO Board name is GPIBO 250 CALL IBFIND BDNAMES BD96 Initialize the interface board 260 DEVNAME 18840A Device name is 18840 270 CALL IBFIND DEVNAME DVM Initialize the DMM 280 CALL IBCLR DVM Clear device 290 FOR W 1 TO 500 NEXT W Wait 1 second before sending commands 300 WRITS FIROSOTOY1 F1 VDC RO autorange SO slow rate 310 continuous trig Yl enable suffix 320 CALL IBWRT 15 Write functions
270. ton 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 20 is useful for determining whether the correct digital signals are being applied 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 digital signals are reaching those devices Correct operation of 8 bit latch 0803 situated on the True RMS AC PCA Option 09 only can be determined 6 35 Maintenance TROUBLESHOOTING MMM M Table 6 19 Keyboard Wiring BUTTONS THAT PRODUCE INVERTED STROBE ZERO SIGNAL NAME U212 38 U212 39 U212 1 U212 2 U212 5 U212 6 U212 7 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 6 60 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 a
271. tween TP103 and Reference Low TP306 or the L shaped shield around U202 The display should typi cally read less than approximately 35 counts i e 000XX where XX is less than 35 on the 2 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 conclu sive 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 0 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 functioning properly proceed to the corresponding heading for detailed troubleshooting instructions and guidelines A failure in the instrument may cause the 8840A 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 trouble shooting 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 sh
272. ull scale input voltage to the A D Con verter is 1V the in guard uC completes the soling by multiplying A D result 2 5 19 4 Wire Ohms In 4 wire ohms function the Ohms Current Sour e is connected 10 INPUT HI terminal by ohms relay K401 as in 2 wire ohms Figure 5 8 The Ohms Current 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 the SENSE HI terminal is connected to the DC Scaling circuit by Q303 Figure 5 8 The 15 then scaled exactly as 2 wire ohms function Refer to the track period i in the switch table in Figure 5 8 Q310 Theory of eration OHMS FUNCTIONS REFERENCE CURRENT R416 R401 100 54 6K 7V FROM PRECISION VOLTAGE REFERENCE SWITCH STATE TABLE mman Switch closed Figure 5 7 Ohms Current Source is turned off to isolate the SENSE HI terminal from the INPUT 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 the SENSE LO terminal is switched into the dc input path by U301D and the INPUT LO terminal is switched out of the dc input path by U301C This has the effect of measuring the SENSE HI terminal with respect to
273. urce impedance of the 10 be tested 3 Allow the displayed reading to settle 4 Press the OFFSET button 5 6 Remove the resistor Proceed with the desired measurement Example Measure a 1 5V source with 1 source impede correcting for input bias current 1 Connect a 1 resistor between the 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 Measurement Tutorial DC VOLTAGE MEASUREMENT 100x Rs CIRCUIT LOADING ERROR IN Rs FR Ri where Rs Source impedance Ri 8840A input impedance _ Ri gt 10 000 MQ 200 2 and 20V ranges Ri 10 in 200V and 1000V ranges EXAMPLE When measuring the voltage across the 10 leg of a90 over 10 voltage divider the circuit loading error is less than 0 196 in the upper ranges and less than 0 000196 in the lower ranges i VOLTAGE Rs 90 x 10 90 10 E Error in the 200V and 1000 ranges 100 x 10 0 09 9 ines lt lt 0 Error in the 200 mV 2V and 20V ranges 100 x 10 000 0 00009 Figure 4 1 Circuit Loading Error Calculation 5 Remove the 1 resistor The test current and full scale voltage for each resistance 6 i range are shown in Table 4 1 Since the HI INPUT test Mea
274. ured to accept line power of 100 120 220 or 240V 1096 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 8840A automatically senses the power line frequency at power up so that no adjustment for frequency is 5 Sary 2 5 Adjusting the Handle The handle provides two viewing angles for bench top use To adjust its position pull the ends to 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 8840A 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 mount ing instructions The rear feet may be rotated 180 degrees to clear a narrow rack space 2 1 Operating Instructions OPERATING FEATURES FOR THIS LINE USE THIS SWITCH VOLTAGE SETTING 90V to 109V 109V to 132V PULL ENDS OUTWARD TO ROTATE 3 Carrying position FOR THIS LINE USE THIS SWITCH VOLTAGE SETTING 198V to 229V LINE SET 229V to 250V LINE SET 1 Viewing position 4 Removal pos
275. us 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 au torange on or off and the OFFSET feature OFFSET on or off The first digit is always 1 An example output string follows Example 1000 CR LF 1001 CR LF Example 1011 CR LF Meaning 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 8840A was in the 200 mV range but it would not indicate whether the 8840A was in autorange or manual range 3 18 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 Meaning 1015 LF CR 1 Leading 1 0 Leading 0 1 1 enable output suffix 5 WS enable LF only 3 19 G7 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 appropria
276. witched on with the CAL ENABLE switch in the enabled position the 8840A may require recalibration 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 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 Attach the two mounting screws on either side of the rear panel power receptacle 6 24 13 14 15 16 17 18 19 20 21 6 34 Connect the two ribbon cables to the Display to the connectors Push the cables straight in to avoid damage Reinstall the harness in the sidewall cable guide and secure the harness to the chassis with the cable clamps Connect the leads to the four front panel input termi nals according to the color codes marked on the rear side of the Display PCA Connect the leads to the four rear panel input termi nals following the color codes as shown in Figure 6 6B Option 05 only Install the IEEE 488 Interface PCA according to the instructions in Section 8 Option 09 only Install the True RMS AC PCA according to

Fluke 8840A User's Manual

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