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1. 1 2 2 1 7261A Front Panel Controls Connectors and Indicators 2 2 2 2 7261A Rear Panel Controls and Connectors 2 5 2 3 Overload Protection eqns ee ROC RO Da ER t Care ne erac 2 4 Autoranging MM L RPSL 2 10 2 5 ambit ptm noci d NE M 2 16 3 1 NM irc Gate THEE eee een mem mem tmm mme Ee 3 3 3 2 017 Output Versus Instrument Function 3 10 3 3 Function ROM s Outputs M H 0 3 12 3 4 Instrument Function Coding FTN RR ca c 3 13 3 5 Instrument Resolution Coding 3 14 3 6 Control Logic 048 Pin Description esee hmmm 3 15 1 4 1 Required Test Equipment Nae T i Ron CIT 4 1 4 2 Static Sensitive Devices paa arcc ccr 4 4 4 6 Display terieri e ereere 4 6 4 4 FREQ A Function Check High Frequencies 4 10 i 4 5 FREQ A Function Check Low Frequencies 4 10 4 6 RATIO Function Check oc cise ehm hnnc mmm nre 4 11 4 7 A Function Check PRPEER
2. CREME e ROS 35 22 4 11 Check ADU GEL 4 13 Marker Check Sonne aca qc A a ER 4 15 Marker Output Waveform 4 15 Location of Test Points and Adjustments bug 4 17 4 18 Time Base Adjustment Location RO 4 20 10 100 MHz Multiplier PCB Adjustment and Test Point Location 4 2 Current Tracing TIUS iA BES pis 4 26 7261A Universal Cou nter Timer 1 1 INTRODUCTION l 2 The John Fluke Model 7261A is a bench type portable Universal Timer Counter A self check mode of operation is provided to verify overall instrument performance The instrument can make four types of measurements l Frequency both standard and normalized a Standard frequency measurements can be made up to 125 MHz the optional Channel C allows measurements of higher frequencies b CPM frequency measurements are normalized into units of 100 Counts Per Minute of the frequency input on Channel A 2 Time measurements of both the period of an input frequency and the time interval between any two events with averaging functions for both to improve accuracy and resolution of the measurements Period averaging allows a maximum resolution of 0 psec
3. set the controls to the following position UUT DISPLAY FUNCTION RATIO E RESOLUTION 10 kHz Channels A amp B T 5 00000 10 00000 25 00000 30 00000 35 00000 40 00000 45 00000 50 00000 55 00000 60 00000 65 00000 70 00000 AC DC Channels A amp B DC 2 On the Rear Panel of the UUT set the INT EXT REFERENCE control to the EXT position 3 Connect the equipment in the configuration shown in Figure 4 4 4 Program the LF synthesizer for an output of 2 0 MHz at a level of 100 mV rms 4 41 Period A Function Check 4 42 Usethefollowing procedure to check the Period A function of the UUT 5 Program the HF synthesizer so that the UUT input is the frequencies listed in Table 4 6 at a level of 100 mV rms l On the Front Panel of the UUT set the Function control to the PER A position 6 Verify that the UUT display agrees within 1 count with the value listed in Table 4 6 for each frequency programmed into the HF synthesizer 2 On the Rear Panel of the UUT set the INT EXT REFERENCE switch to the EXT position 4 11 HQ __ 284 4 0 x 7261 3 Connect the equipment as shown if Figure 4 3 Part A 4 On the Front Panel of the UUT set the Resolution control to the positions listed in Table 4 7 5 For each position of the Resolution control Program the LF synthesizer for an output 1 L
4. 6 Verify that the waveform displayed on the oscilloscope is a 10 MHz square wave with the logic high greater than 5V 4 9 7261A 4 35 Frequency A Function Check 4 36 Use the following procedure to check the FREQ function of the instrument 4 10 1 the Front Panel of the set the controls to the following position ON STBY ON FUNCTION FREQ A RESOLUTION 10 kHz AC DC CHANNEL A AC SEP COM SEP ATTN CHANN X1 SLOPE CHANN A a 2 On the Rear Panel of the UUT set the REF switch to the EXT position 3 Connect the HF synthesizer to the Channel A input terminal via a 50M termination as shown in Figure 4 3 Part B 4 Program the HF synthesizer for the UUT inputs shown in Table 4 4 for each position of the ATTENUATION switch on the UUT 5 Verify that the UUT display agrees with the frequency programmed 1 count 6 OntheFront Panel ofthe UUT set the Channel A switch to 7 Repeat steps 3 and 4 8 Disconnect the HF synthesizer and connect the LF synthesizer as shown in Figure 4 3 Part A 9 On the Front Panel of the UUT set the Resolution control to the positions indicated in Table 4 5 For each setting of the Resolution control program the LF synthesizer for the indicated output frequency and level 10 Verify that the display is within 1 count of the frequency programmed in each step of Table 4 5 11 On the Front Panel of the UUT set the sw
5. 9 Move the DVM connection from to TP2 10 Verify that the DVM display is 12 0 6 11 4 Move the DVM connection from TP2 to 12 Verify that the DVM display is 12 0 6V 13 On the Front Panel of the UUT in the POWER section set th ON STBY switch to the ON position 14 Move the DVM connection from TP4 to TP3 15 Verify that the DVM display is 5 0 0 15 16 Select the ac coupled mode on the oscilloscope 4 61 4 62 17 Connect the oscilloscope prabe to TPI tes in turn TP2 TP3 and 4 18 Verify that at each test point the ripple vol is less than 50 mV p p 19 Set the Variac output to local line voltage phai 10 of local line voltage 20 Usethe DVM to verify that the voltage presemt at TP1 TP2 and TP4 is within the range listed in steps 8 10 12 and 15 21 Repeat steps 16 through 18 22 Set the Variac output to local line voltage minus 10 of local line voltage 23 Repeat step 20 24 Repeat steps 16 through 18 25 Ifthe instrument is to be operated with other line power voltages a Rear Panel of the set the AC POWER switch to the OFF position b Set the Variac to zero volts c Set 54 and 55 to the proper position for the line voltage desired d On the Rear Panel of the UUT set the AC POWER switch to the ON position e Set the Variac to the desired line voltage f Perform steps 16 through 18 g Repeat
6. 06 07 22 541 D3 D2 D3 DOESN T USE DECIMAL POINT HK D2 p3 102 05 104 Figure 2 12 Decimal Point Placement 7261A 2 89 There are three status annunciators The GATE annunciator provides an indication of counting ortiming in progress The OVFL annunciator will illuminate when the capacity of the internal 8 decade accumulator is exceeded The OVEN annunciator should be on whenever an oven oscillator Option 131 or 132 is installed the instrument is connected to line or battery power STBY or ON and the Rear Panel REF switch is in the INT position 2 90 Accuracy 2 9 Techniques are available for improving the accuracy of any measurement Even with the controls set for optimum performance three error factors may degrade accuracy These errors one count error trigger error and time base error relate to each function as defined in the following accuracy statement l FREQ A FREQ C 1 count time base error 2 CPM XI00A 1 count time base error 3 RATIO A B FREQBx TRIGGER ERROR B FREQAxN N 4 PER A 1 count clock trigger error time base error 3 PER AVG A 10 nS trigger error N imebase error N 6 TI A B 1 count clock trigger error time base error 7 TIA A B 10 nS trigger error E n im VN WES ON 2 12 2 92 Dealing with 1 Count Error 2 93 There are several methods available fo
7. 2 14 2 106 Frequency Measurements FREQ 2 14 2 108 Measurements CPM 2 14 2 110 Frequency Measurements FREQ 2 15 2 112 Ratio Measurements RATIO 2 15 2 114 Period Measurements PER A D OX RE Ree er 2 15 2 117 Period Averaging Measurements TIA 2 15 2 119 Time Interval Measurements 2 16 2 121 Time Interval Averaging Measurements TIA 2 16 2 123 Totalizing Measurements TOT A B 2 16 2 125 dece EE 2 16 REMOTE OPERATION E Ce eos deas Dese 2 17 3 THEDRY OPERATION mana 3 1 3 1 INTRODUCTION H 3 1 4 3 3 FUNCTIONAL DESCRIPTION 5 3 1 a 3 5 Basil Hioeb Diagram qu Aa GS oe REIR OE ERES RR roe nn 3 1 i continued on page ii 7261A TABLE OF CONTENTS continued SECTION TITLE 3 7 Frequency FREQ A Measurements 3 10 Counts Per Minute CPM X100A Measurements 3 13 Frequency C FREQ C Measurements 3 15 Ratio RATIO A B Measurements 3 17 Period PER A Measurements 3 20 Period Averaging PER AVG A Measurement 3 23 Time Interval T I A B Measurements 3 25 Time Interval
8. 4 13 Input line power voltage is selected by positioning the two switches in the right rear corner of the Main PCB Each switch S4 and S5 shows a position identifying red or white dot Line voltage settings identified by dot color are presented in Figure 4 2 Factory line voltage settings are identified on the instruments s rear panel one of four 4 white dots will be darkened to signify 100 120 220 or 240V selection 7261A Figure 4 2 Line Voltage Selection 4 14 Fuse Replacement WARNING BEFORE ATTEMPTING FUSE RE PLACEMENT REMOVE LINE POWER FROM THE INSTRUMENT 4 15 The 7261A line power fuse is accessible on the rear panel Fuse requirements are 3 8A MDL slo blo for line inputs of 100V or 120V and a 3 16A MDL slo blo for line inputs of 220V or 240V CAUTION For continued five protection alway replace F1 with a 250V fuse of same type and rating 4 3 7261A 4 16 Channel A and Channel B inputs are fuse protected for maximum inputs of 250 mA Replacement of either of these fuses necessitates removal of the Main PCB Assembly and the Front Panel PCB Assembly refer to Instrument Disassembly for removal instructions Each fuse is soldered to the Front Panel PCB Assembly immediately below the respective BNC input connector Replacement fuses should be ordered from John Fluke Mfg Co Inc 4 17 Cleaning 4 18 Clean the instrument periodically to remove dust grease and other contamination U
9. 4 16 4 63 Channel B Trigger Level Adjustment SRR RARE KEN 4 19 4 65 Time Base Adjustment M D Ae 4 19 4 67 Coarse Time Base Adjustment C 4 20 4 69 100 MHz Times Base Adjustment 4 21 4 71 TROUBLESHOGTING iii V ewe FUSES RE eR E a RIRs 4 22 4 72 GOES OLSA emus a x ee UR CR CEST AER AN 4 22 4 77 WSUS THEBES ace c CER Ree SITS 4 22 4 79 Fault Isolation Guide 4 23 4 85 R 4 26 5 LIST OF REPLACEABLE PARTS 5 1 TABLE OF CONTENTS Lent mmm menm 5 5 1 INIKODUGIPBUIN Ree 5 2 5 4 HOW TO OBTAIN PARTS EVA E RANSN A C 5 2 6 OPTION AND ACCESSORIES 6 1 TABLE OP CONTEWES xe imu c ary ACER 6 1 7 GENERAL INFORMATION er ae E al vsu CD 7 1 MANUAL CHANGE INFORMATION 1 8 SCHEMATIC DIAGRAMS 8 1 Rr munt mt mme mtr mmm mora 8 1 iv 7261A List of Tables TABLE TITLE PAGE 1 1 7261A Options and Accessories 1 2 1 2 7261A
10. FUNCTIONS POWER RECEPTACLE Polarized 3 prong connector for line power input F1 Main Power Fuse AC POWER Connects ON or disconnects OFF line power to the primary side of the Main Power Transformer MARKER OUT Marker pulse output during and TIA functions to assist in oper ator in setting the Trigger Levels 10 MHz REF IN BNC terminal allows connection of an external time base OUT BNC terminal that has 10 MHz time base signal used by the instrument DATA 1 0 Connector for DOU Option 521 REF Two position slide switch to select time base used by the instrument INT position selects installed time base EXT position selects external time base connected to the 10 MHz IN terminal NOTE If either oven time base option is installed in the instrument the EXT position of the REF switch removes oven power allowing the internal time base to cool MODE Two position slide switch determines triggering mode of the instrument CONT position selects continuous triggering TRIG position selects single triggering TRIGGER LEVEL Two position slide switch determines whether the trigger level voltage of CHA CHB Channel A or Channel B is connected to the Trigger Level Out terminal OUT BNC connector with the trigger level of the channel selected by the Trigger Level control 7261A 2 17 OPERATING NOTES 2 18 The following paragraphs describe various conditio
11. These digits present the measured value of the unknown input The value may range between 00000000 and 99999999 3 Atthe right end the display units annunciators For all instrument functions except CPMX100A RATIO A B and TOT A B the LED beside the appropriate unit of measurement will be illuminated Connectors and Indicators om O RESOLUTION CHANNEL A Table 2 1 7261A Front Panel Controls Connectors and Indicators cont 7261A FUNCTIONS A ten position slide switch that determines what measurement function the instrument will perform Changing the position of the Function Switch auto matically resets the instrument The basic instrument function for each pos ition of the Function Switch is FREQ A Measures the frequency of signals applied to Channel A Can measure signals from 0 125 MHz CPM X100A Measures the frequency of the signal applied to Channel A and automatically displays the value inCounts Per Minute times 100 Range is 0 125 MHz FREOC Measures the frequency of signals applied to the optional Channel C 72X XA 310 Option has a range of 50 512 MHz RATIO A B Measures the ratio of the frequency of the signal applied to Channel A to the frequency of the signal applied to Channel B Apply the signal with the higher frequency to Channel A Range of the channels Channel A 0 125 MHz Channel 5 H
12. Trigger Status Indicators Each time Channel A triggers the appropriate indicators blink At high frequencies the indicators will appear to be lit continuously The indicators work in conjunction with the Trigger Level Control 2 Trigger Level Control This control is a variable resistor with a switch in the extreme counterclockwise position The switch position is PRESET PRESET selects a trigger level of zero volts This is the most sensitive trigger level for ac coupled symmetrical inputs When the control is rotated out of the PRESET position it adjusts the triggering point of Channel A about zero volts in a range of 1 5V to 1 5V 7261A Table 2 1 7261A Front Panel Controls Connectors and Indicators cont 3 ATTEN is a three position slide switch used to reduce high amplitude input signals so that they fall within the dynamic range of the input amplifier The input signal is attenuated by the factor indicated above the switch positions 4 AC DC is a two position slide switch that selects the type of signal coupling used DC oupling is used to maintain a consistent trigger point on input signals down to a frequency of zero AC coupling is used when measuring signal with a large DC offset When AC coupling is selected the trigger point changes with both the input frequency and duty cycle 9 t is a two position slide switch that selects which slope positive or negative of the input signal Channel A will tr
13. time base error trigger errors Frequency Range 0 2 MHZ Sinewave Min Pulse 500 ns OHz 100 kHz 250 ns 100 kHz 2 MHz Display Hsec msec or sec with decimal point Table 1 1 72614 Options and Accessories Table 1 2 7261A Specifications FUNCTIONS 5 for definition of terms OPTION MODEL No DESCRIPTION ACCESSORIES C Size Single Unit Offset Rack Mount C Size Dual Rack Mount C Size Panel Mount Attenuator Low Pass Filter 2 Foot Ribbon Cable Assembly 5 Foot Ribbon Cable Assembly Period Average A Range 0 1 ps 999 999 99 us Resolution 0 1 ps 10 ns in decade steps Accuracy 10 ns ttime base errors Trigger error Frequency Range 0 2 MHz Sinewave Min Pulse 500ns OHz 10kHz 250ns 100kHz 2M Hz Display Hsec msec or sec with decimal point Time Interval Range 10 5 99 999 999 Sec Resolution ns 1 ms in decade steps Frequency Range OHz 5MHz Sinewave Accuracy tcount time base error Trigger errors Min Pulse 10 ns Display MSec msec or sec with decimal point Time Interval Average Range 0 1ns 999 999 99 Ls Resolution 10 ns 1 105 in decade steps Accuracy 10 ns 2 time base errors Trigger error VN VN Min Pulse 19 ns Dead Time 4 us see Footnote 4 Display MSEC msec with decimal point Frequency Range 0 5 MHz Degrade
14. 3 Use an oscilloscope probe X10 as the input cable when measuring high impedance circuits 4 Use a low pass filter attenuator The front panel FILTER control can be utilized to attenuate signals above 100 kHz Alternately the Fluke Model Y7201 Filter Attenuator attached to the front panel input connector can be used to suppress unwanted noise This accesssory is described in Section 6 of this manual 2 100 SUMMARY 2 101 Some of the errors that affect accuracy are inherent and cannot be much improved without substituting different components time base error Accuracy can be improved by using the proper techniques 2 13 i 1 7261A triggering error or by selecting the correct function PER A versus FREQ A The accuracy of the event timing functions can be improved by using the appropriate averaging function And sometimes the technique that decreases the effect of one error source increases the effect of another error source Noise and distortion on the input signal or signals also affect the accuracy of measurement The operator has to be aware of all facets of the error sources and exercise discretion in using the instrument to make precise measurements 2 102 OPERATING DIRECTIONS 2 103 Operation of the 7261A for each function 15 described in the following paragraphs Function capabilities as well as useful operating hints are also presented here 2 104 Initial Procedure 2 105 The followin
15. A 4 30 Use the following procedure to verify that Channel A meets the sensitivity specifications listed in Table 1 2 l Onthe Front Panel of the UUT set the controls to the following position FUNCTION FREQ A RESOLUTION 10 Hz SEP COM SEP AC DC Channel A DC 2 On the Rear Panel of the UUT set the REF switch to EXT 3 Connect the equipment in the configuration shown in Figure 4 3 Part A 4 Programthe LF synthesizer for an output of 10 kHz at a level of 100 mV rms 5 Verify the UUT display is 10 00 kHz 1 count 6 Reducethe programmed output level of the LF synthesizer until the error is greater than 1 count The programmed level should be less than 10 mV rms 7 the Front Panel of the UUT set the Channel A ATTEN control to the X10 position 8 Program the LF synthesizer for an output level 23 dB above the sensitivity level measured in step 6 above 9 Verify that the UUT display is 10 00 kHz 1 count 10 Program the LF synthesizer for an output level 17 dB above the sensitivity level measured in step 6 above 1 Verify that the UUT display is either all zeros or no longer 1 count 12 On the Front Panel of the UUT set the Channel A ATTEN control to the X100 position 7261A 13 Program the LF synthesizer for an output level 43 dB above the sensitivity level measured in step 6 above 14 Verify that the UUT display is 10 00 kHz 1 count 15 Program the LF synthesizer f
16. Average TIA A B Measurements 3 30 Totalize A Gated by B TOT AeB Measurement 3 32 Self Check CHK Measurement 3 34 CIRCUIT ANALYSIS 3 36 Power Supply 3 38 Time Base 3 40 Input Circuitry 3 43 Function Logic 3 46 Resolution Logic 3 51 Control Logic 3 56 Main Gate Clocking Logic 3 58 Main Gate Enable Logic 3 60 Count Circuits 3 63 Display 3 65 Time Interval Logic 3 68 Time Interval Average Logic 3 72 10 100 MHz Multiplier PCB 3 74 Reset Logic 3 76 Marker Output Circuit 3 78 Single Continuous Operation 3 80 Remote Operation MAINTENANCE 4 INTRODUCTION 4 4 SERVICE INFORMATION 4 7 GENERAL MAINTENANCE 4 8 Disassembly 4 10 Reassembly 4 12 Input Power 4 14 Fuse Replacement 4 17 Cleaning 4 19 4 2 SOLDER PRECAUTIONS 4 23 PERFORMANCE CHECKS 4 25 Initial Instrument Set up 4 27 Display Check 22 22 22 4 29 Sensitivity Check Channel A Sensitivity Check Channel B Time Base Check Frequency Function Check XI00A Function Check Ratio A B Function Check Period A Function Check Period Average A Function Check TI A B Function Check TIA A B Function Check Continuous Single Trigger Check External Reference Input Check Marker Check Filter Check ii Ji TABLE OF CONTENTS continued 1 SECTION TITLE PAGE 4 59 Power Supply Voltage Adjustments 4 16 4 61 Channel A Trigger Level Adjustment
17. JFD 258 tuning tool to adjust the time base adjustment so that the UUT displayed vlaue is within 9999 9449 to 0000 0551 Ideally the display will be all zeros indicating an exact alignment Figure 4 10 shows the location of the time base adjustment hole in the bottom case cover off the UUT TIME BASE ADJUSTMENT Figure 4 10 Time Base Adjustment Location NOTE The OVFL annunciator will illuminate every time the displayed value is 10000 0000 kHz or greater 4 20 11 Ifthe time base cannot be adjusted and is of the standard free air type remove the top case cover and look at the top of the time base pcb perform the Coarse Time Base Adjustment procedure presented next in this section 12 If the time base cannot be adjusted within specifications and is not ofthe Lype described in step 11 troubleshooting is indicated 4 67 Coarse Time Base Adjustment 4 68 Some of the standard free air time bases have a coarse adjustment located on top of the Time Base PCB If the time base cannot be adjusted within proper limits using the previous time base calibration procedure use the following procedure to coarse adjust the time base I Connect the UUT to line power through a Variac set to the local line voltage 2 Remove the top case cover refer to the instrument access procedure presented earlier in this section 3 Front Panel of the UUT set the controls to the following positions FU
18. and TRIGGER LEVEL controls Channel A to ensure proper triggering 4 Observe that the display counts up stops continues the count stops continues the count etc NOTE Should just a totalized count of Channel A input signal be desired set the Channel A switch to the position and adjust the Channel A TRIGGER LEVEL control until the trigger status indicator goes out 2 125 Self Check CHK 2 126 The self check function can be used to verify the digital operation of the 7261A Each setting of the RESOLUTION control will provide a predictable display of the 10 MHz reference frequency To self check the 7261A use the following procedure l Press the power switch to ON 2 Setthe FUNCTION control to CHK 3 Momentarily press the RESET control the display should read 88888888 while RESET is depressed 4 Set the RESOLUTION control to AUTO the display should read 10000 00 kHz 5 Verify correct display for each of the remaining six RESOLUTION settings as defined in Table 2 5 Table 2 5 CHK Function Display RESOLUTION SWITCH SETTING DISPLAY 0000 0000 kHz 10000 000 kHz 10000 00 kHz 10 0000 MHz 10 000 MHz 10 00 MHz 2 127 REMOTE OPERATION 2 128 The 7261A can both Talk and Listen to remote stations The remote station programming can duplicate the use of the FUNCTION RESOLUTION FILT slope and RESET Front Panel controls The 7261A will provide measured value
19. be operated with an input line voltage of 100 120 220 or 240V ac 41095 Line frequency may vary between 47 and 63 Hz Before connecting the power cord verify that line voltage switches located inside the instrument are properly set and that an appropriate line fuse is installed Refer to section 4 of this manual for proper verification procedures see Line Voltage Selection and Fuse Replacement 7261 Section 2 Operating Instructions 2 8 Instrument Case Mating 2 9 The 7261A is contained in a molded instrument case with non marring feet a tilt down bail and a latching arrangement This instrument may be stacked and latched together with other Fluke instruments employing this type of case 2 10 Use the following procedure when attaching these molded cases together l For the top instrument pull out latches found on either side refer to Figure 2 1 2 Nestle top and bottom instruments together 3 Push latches in to secure instruments together CAUTION Instrument stacks should be limited to a total height of three feet and a total weight of 40 pounds 7261 2 11 Tilt Down 2 12 When used as separate instrument the 7261A may be tilted up or down with the aid of the tilt bail When extended the bail may be locked in place by firmly pressing the legs into slots provided in the bottom panel When retracted the bail lies flush with the instrument s bottom panel and does not
20. limit instrument input circuit gain by factors of X1 X10 and X100 Large signals causing distortion or non linear operation can therefore be reduced to within the instrument s dynamic range This dynamic range or area between the hysteresis level and the overload point varies with frequency Increased attenuation may also be used to compensate for noise on the input signal use of ATTENUATION in this case can prevent the noise from crossing one or both of the hysteresis levels 2 10 2 77 SLOPE CONTROL 2 78 The slope control determines instrument triggering order the initial trigger may occur on a negative going signal position or on a positive going signal position 2 79 FILTER CONTROL 2 80 The position of the Filter IN OUT switch determines whether or not frequencies above 100 kHz removed from the input signal When the control is at the IN position the upper bandpass limit of the input amplifier on the Preamplifier is lowered from 125 MHz to 100 kHz If high frequency noise is a problem with a low frequency signal the 100 kHz low pass filter may be used to advantage 2 81 TRIGGER LEVEL CONTROL 2 82 Trigger level is selected by the Trigger Level Control The Trigger Level Control is continuously adjustable between 1 5V and 1 5V The trigger indicators provide the operator with a coarse indication of trigger setting The exact level of trigger setting can be measured from the Rear Panel Trigger L
21. of Contents SECTION TITLE PAGE 1 INTRODUCTION Eu ERAT deat 1 1 1 1 1 INTRODUCTION E 1 1 1 6 OPTIONS AND ACCESSORIES 1 1 1 8 a m mem 1 1 2 OPERATING INSTRUCTIONS 2 1 2 1 a bo Rees 2 1 2 3 SHIPPING INFORMATION 24 14 INSTALLATION e 7 1 2 6 input POW T EVA SORE ERA WON mee aS E 2 1 2 8 Instrument Case oueseseeseseswwseveceeececrevwie s vasa 2 1 2 11 pog n4 oM T 7 7 2 2 2 13 Kack installation 2 2 2 15 OPERATING FEATURES mnt 2 2 IL OPERATING NOTES SCORER BREESE ei gares 2 6 2 19 ALD Lane COHBSCHODE 3 3 WR VYW RE XWexriak 2 6 2 21 IBI sue SS 2 6 2 23 Tipi er ONO 2 6 2 66 Der a TRE 2 9 2 87 xesebeb VER EEA orc mam eem 2 11 2 90 ARIARI 2 12 2 92 Dealing With 27 CORE BITOF ke ea os rV ense 2 12 210 OPERATING DIRECTIONS enis cry 2 14 2 104 A E
22. or about the length of time it takes light to travel about one ten thousandth of an inch Time interval averaging allows a maximum resolution of about 31 psec or about the length of time it takes light to travel about 3 1 2 inches J Ratio measurements of one frequency to another 4 Totalized count measurements 7261A Section 1 Introduction amp Specifications 1 3 Both Channel A and B have an input impedance of 1 MQ Both channels have trigger level controls trigger status lights slope selectio n 3 position attenuator switches AC DC coupling select controls 100 kHz low pass filter select switches analog trigger level outputs and the capability of being electrically connected to gether A marker output is available when either the TI A B or the TIA A B function is selected The optional Channel C has an input impedance of 500 and is ac coupled This channel is used for f requency measurements only and has no Front Panel controls 1 4 Measured data is displayed via an 8 digit LED readout on the front panel This display has leading zero suppression and automatic decimal point positioning Annunciators are provided to indicate Gate Overflow Oven and display units All displayed information is also available in serial BCD format at a rear panel connector when the unit is equipped with an optional Data Output Unit DOU 1 5 Power requirements are 100V 120V 220V or240V at 47 63 Hz The 010 Battery Option al
23. period Averaging the same signal would be maximum at a display of 1000 0000 us the resolution has increased to ns with a sample of 100 periods RESOLUTION control 10 position Use the following procedure when making period measurements l Set the front panel controls as follows FUNCTION PER RESOLUTION as desired or AUTO SEP COM SEP 2 Connect the signal to be measured to the CHANNEL A input connector 3 Adjust the ATTEN and TRIGGER LEVEL controls to ensure proper triggering 2 15 sass EE Lam 7261A 2 119 Time Interval Measurements TI A B 2 120 The elapsed time between events common or separate to CHANNEL A and B can be accurately measured and displayed using the Time Interval function CHANNEL 4A is used to provide a start signal and CHANNEL B provides the stop signal Dead time is 4 us the counter will ignore time intervals occuring during the dead time Use the following procedure when making time interval measurements l Set front panel controls as follows FUNCTION TI RESOLUTION as desired or AUTO SEP COM SEP if the start and stop signals are from separate sources COM if the start and stop signals are from the same source 2 For separate input signals connect the start signal to CHANNEL A input connector and the stop signal to CHANNEL B For common inputs connect the signal to Channel A 3 Use the information presented earlier in this secti
24. reflected waves Maximum input is 5V rms The input circuit is fuse protected RESET The RESET control is a momentary contact pushbutton that provides the capability to manually reset the instrument When the RESET control is depressed the display will be all 85 With this character displayed each seg ment of every digit of the display may be checked Decimal point position will depend on the position of the Resolution Switch POWER Both of these controls are two position push push switches do not attempt to pull either switch to the out position The ON STB Y switch in the ON position connects the outputs of the power supplies to the instrument cir cuitry If the ON STBY switch is in the STBY position the outputs of the power supplies are not connected to the instrument circuitry If an oven time base option is installed the oven receives power when the ON STBY switch is in the STBY position and the Rear Panel REF switch is in the INT position The BAT LINE switch is bypassed on instruments that do not have the 010 Battery Option installed If the option is installed refer to the Operating Instructions for the 010 Option in Section 6 TI HOLDOFF This control is a potentiometer It provides continuously variable time delay before the STOP pulse can be generated in the TI A B and TIA A B functions FUNCTIONS 2 4 Figure 2 3 7261A Rear Panel Controls and Connectors Table 2 2 7261A Rear Panel Controls and Connectors
25. timing Pulse inputs with low duty cycles should not be ac coupled as the coupling capacitor will not charge high enough for proper triggering DC COUPLED _ 9 HYSTERESIS WINDOW AC COUPLED 2 46 INPUT IMPEDANCE 2 47 The input impedance defines the impedance seen by a signal source Input impedance of Channels A and B 1 shunted by 45 pF The optional Channel C input impedance 15 500 2 48 LINEAR OPERATING RANGE 2 49 The linear operating range refers to the excursions of the input signal that can reliably trigger the input amplifier without distortion The 7261A s linear range varies between the smallest signal level acceptable by the input amplifier minimum and the largest attenuated signal that will not be clamped by the amplifier s input circuits maximum The minimum is defined by the instrument s sensitivity specifications Operation within maximum levels may be ensured through proper use of the ATTENUATION controls 2 50 NOISE 2 51 Noise is defined as spurious signals riding on the input waveform Unlike distortion the waveform is not changed Noise of sufficient amplitude can however cause false triggering resulting in inaccurate measurements during event timing functions The 7261A input amplifiers signal conditioners exhibit very low noise The signal applied to these amplifiers may however be plagued with noise from the signal source the electrical environment or from improper
26. trigger MODE control positioned to CONT the instrument s internal logic will automatically cycle through repetitive measurement routines When placed in TRIG a measurement on Channel A can be initiated by using the Channel B signal as a trigger If the 7261A is in TRIG during remote control operations with the DATA I O Option 521 installed refer to Section 6 for special instructions TRIGGER POINT INPUT SIGNAL CHANNEL PRIC OUTPUT START CHANNEL B PRICOUTPUT T I HOLDOFF x STOP mancare O Figure 2 11 T I Holdoff 2 87 Display 2 88 7261A display presents an eight digit LED readout with leading zero suppression Measurement unit annunciators of MHz or kHz will be activated in FREQ A or CHK modes For PER A PER AVG A or TI A B annunciators for msec or sec will illuminate There will be no units annunciation in RATIO TOT A B CPM 100 modes Decimal point placement 15 determined by RESOLUTION and FUNCTION settings as defined by Figure 2 12 1515151516 _ RESOLUTIO d 10 10 10 10 10 10 FUNCTION 10ns 100ns tus 10us 100 5 1ms 10kHz 1 2 100 2 10Hz 1Hz 0 1Hz FREQA 02 03 02 04 4 CPMX100 A DOESN T USE DECIMAL POINT 02 04102 03 04 RATIOA B D1 D2 D3 04 D5 __ 02 03 D2 D3 05 06 04 05
27. 10 MHz 10 MHz Aging Rate constant temperature 3 X 10 mo 1 X 10 mo t3 X 10 day 1 X 1076 yr 5 X 10 mol Temperature Accuracy 0 40 C 2 X 106 1 X 107 t3 X 10 Line Voltage 10 change 2 1078 2 X 108 t4 X 10 Battery 2 X 1078 5 10 8 X 107 Warmup 10min 5 X 107 tb X107 20 min t3 x 108 t3 x 107 After 5 days continuous operation Accuracy with temperature specification includes errors cuased b calibration errors when calibrated per procedure in the instrument s Compared to frequency 24 hours after turn on I Battery Pack Option 010 Operating Time 2 0 hours typical continuous Decreases to 1 5 hours typical worst case with option Charge Time 16 hours at room temperature Battery Type Nicad F cells Charge Protection Thermistor actuated shut down of charging circuit if battery temperature exceeds 65 Discharge Protection Automatic low voltage shut down to prevent over discharge Printer Interface Option 521 Description Serial BCD output of all digits and annunciator Levels TTL 1 state low Table 1 2 Specifications cont OPTIONS y temperature variations during operation as well as ervice manual IEEE Interface Option 529 Description Option for interfacing 7261A to IEEE 488 via the Fluke 1120A IEEE Trans lator Provides full measurement output cap ability as well as remote selection of all functions an
28. 2 Use the following procedure to verify that Channel B meets the sensitivity specifications listed in Table 1 2 On the Front Panel ofthe UUT set the controls as follows FUNCTION RATIO A B 7261A l6 Program the LF synthesizer for an output level 37 dB above the sensitivity level measured in step 6 17 Verify that the UUT display is either all zeros or greater than 1 count 18 On the Front Panel of the UUT set the Channel B ATTEN control to the X1 position 19 Program the LF synthesizer for an output of 2 MHz at a level of 50 mV rms RESOLUTION 108 20 Verify that the UUT display is 50 1 count 2 Connect the equipment in the configuration 21 Program the LF synthesizer for an output of 2 shown in Figure 4 3 Part C MHz at a level of 10 mV rms 3 Adjust the RF attenuator and program the HF 22 Verify that the UUT display is 50 1 count synthesizer for an input tothe UUT of 100 MHzata level of 50 mV rms 4 33 Time Base Check 4 Program the LF synthesizer for an output of 4 34 Use the following procedure to check the accuracy 100 kHz at a level of 50 mV rms of the time base and the operation of the REF OUT circuitry 5 Verify that the UUT display is 1000 1 count 6 Reduce the LF synthesizer programmed level until the UUT display has slightly more than 1 count error 7 Verify that the LF synthesizer programmed level 1s less than 10 mV rms 8 Front Panel ofthe UUT set the Channe
29. 4 10 TIA A B Function Check 00044 1 msec 000445 msec 445 usec 4450 44505 445055 t2 ns Time Base 10 ns Trig Error i es 7261 4 49 Continuous Single Trigger Check 4 50 Use the following procedure to verify that the UUT performs properly when either continuous or single triggering is selected l Onthe Front Panel of the UUT set the controls to the following positions ON STBY ON FUNCTION FREQ A RESOLUTION 1 Hz CHANNEL TRIGGER LEVEL CHANNEL B Fully Clockwise CHANNEL A PRESET 2 Onthe Rear Panel of the UUT set the MODE switch to the TRIG position J Connect the LF synthesizer to the Channel A input on the Front Panel ofthe UUT with as shorta length of RG 58 as possible via a 500 termination 4 Program the LF synthesizer for an output of 10 MHz at 100 mV rms 5 On the Front Panel of the UUT press and release the RESET pushbutton 6 Verify that the display is 0 000 kHz 7 On the Front Panel of the UUT rotate the Channel B Trigger Level control fully counterclockwise 8 Verify that a The GATE annunciator flashes once b 10000 000 kHz is displayed 9 On the Rear Panel of the UUT set the CONT TRIG switch to the CONT position 10 Verify that a The GATE annunciator is flashing b 100000 000 kHz is displayed 4 51
30. 8 88 MHz is displayed If any segment of any digit is not functioning that digit will not be an 8 5 Release the RESET pushbutton 6 Verify that a 10 00 MHz is displayed b The GATE annunciator is flashing approximately five times per second 7 Onthe Front Panel of the UUT in the Channel A signal conditioner section and in the Channel B signal conditioner section a Set the AC DC switch to the AC position b Set the switch to the position 8 Using Table 4 3 as a guide set the Function to each of the positions indicated At each of the Function Control positions sequence the Resolution control to each of its settings Verify that for each setting ofthe Function and Resolution control that the digits decimal point positions and units annunciator all agree with the values given in Table 4 3 NOTE When performing this step the OVFL annunciator illuminates when the Function control is set to the CHK position and the Resolution control is set to the 1 Hz position 4 5 7261A 4 6 FUNCTION RATIO A B PER AVG A Table 4 3 Display Check RESOLUTION DIGIT SWITCH DISPLAY 10 kHz 1 kHz 100 kHz 10 Hz 1 Hz 1 Hz AUTO h 0 00 0 000 0 0000 0 00000 0 00000 000000 0000 00000 000000 0000000 00000 10 00 10 000 10 0000 10000 00 10000 000 0000 0000 10000 000 OVFL annunciator turns on after 10 sec gate time ANNUNCIATOR 4 29 Sensitivity Check Channel
31. Adjustment and Test Point Location 7261A 6 Adjust C19 on the 10 100 MHz PCB for DMM display of 6 3 0 3V 7 Alter the LF synthesizer output to 9 7 and 10 3 MHz 8 Verify that the DMM display goes to approximately 3V to 11V 9 Disconnect the DMM 10 Connect the oscilloscope through an X10 probe to U5 7 on the Main PCB 11 Verify that the signal on the oscilloscope display is approximately 600 mV p p on a dc offset of approximately 3 5V 12 On the Front Panel of the UUT set the FUNCTION and RESOLUTION controls to the positions shown in Table 4 11 13 Verify that the 100 MHz signal is either present or absent from the oscilloscope display as listed in the table for each combination of control setttings 14 Perform the Time Base Adjustment procedure TP2 REAR 4 21 7261A Table 4 11 100 MHz Time Base RESOLUTION CONTROL CONTROL PRESENT ABSENT 10 ns X PER A any but 10 ns PER AVG A TI A B TIA any 10 ns any but 10 ns any 4 71 TROUBLESHOOTING 4 72 Introduction 4 73 The material in the remainder of this section is presented as a troubleshooting aid for the technician If the instrument fails to perform as expected select the CHK function if the instrument display is incorrect the fault is in the instrument But if the display is correct the fault may not lie in the instrument Ask the follow
32. BASE ERROR 2 59 Time base error stems from crystal aging temperature variation and line voltage fluctuation The 7261A may be fitted with one of several available time base oscillators specifications for each are included in Section of this manual 2 60 TRIGGER ERROR 2 61 Input signal irregularities noise distortion etc may cause premature or delayed triggering at the input circuitry s hysteresis levels During event counting functions this error is significant only when extra pulses are generated by the input circuitry In event timing functions triggering error may be significant improper triggering translates into inaccurate counting of the internal oscillator frequency Figure 2 9 illustrates possible trigger errors IDEAL _ SIGNAL SCHMITT TRIGGER OUTPUT NOISE SPIKES SCHMITT TRIGGER OUTPUT EXTRA COUNT UNCERTAINTY IN CROSSING TIME Figure 2 9 Noise and Distortion Effects 2 62 TRIGGERING 2 63 Signal conditioning circuits ideally provide a pulse train output representative of the input signal These pulses should occur at the same frequency in Event Counting functions The pulses are the Start or Stop times in Event Timing functions and must have the same time relationship as the input signals Each pulse is triggered on and off at the specified upper and lower hysteresis levels for the instrumen
33. Best Way prepaid The instrument should be shipped in the original packing carton or if it is not available use any suitable container that is rigid and of adequate size If a substitute container is used the instrument should be wrapped in paper and surrounded with at least four inches of excelsior or similar shock absorbing material CLAIM FOR DAMAGE IN SHIPMENT TO ORIGINAL PURCHASER The instrument should be thoroughly inspected immediately upon original delivery to purchaser All material in the container should be checked against the enclosed packing list The manufacturer will not be responsible for shortages against the packing sheet unless notified immediately If the instrumentis damaged in any way a claim should be filed with the carrier immediately To obtain a quotation to repair shipment damage contact the nearest Fluke Technical Center Final claim and negotiations with the carrier must be completed by the customer The JOHN FLUKE MFG CO INC will be happy to answer all applications or use questions which will enhance your use of this instrument Please address your requests or correspondence to JOHN FLUKE MFG CO INC P O BOX 9090 EVERETT WASHINGTON 98206 ATTN Sales Dept For European Customers Fluke Holland B V P O Box 5053 5004 EB Tilburg The Netherlands For European customers Air Freight prepaid John Fluke Mfg Co Inc P O Box C9090 Everett Washington 98206 Rev 6 81 7261A Table
34. CP PX EP UE 4 12 4 8 PER AVG Function CHECK 4 12 4 9 Function Check 2 2225 4525566 4 13 4 10 TIIA Function Check 4 13 4 11 100 MHz Time 4 22 4 12 Instrument Logic Levels 4 22 4 13 Fank olihan Int rnretatl fi RR E 4 25 v vi FIGURE 1 1 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 2 10 2 11 2 12 2 13 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 3 10 3 11 3 12 3 13 3 14 4 1 4 2 4 3 4 5 4 6 4 7 4 8 4 9 4 10 4 11 4 12 7261 List of Illustrations TITLE PAGE Gad arare 1 6 Instrument Case Mating V RR Ko ots Oe 2 7261A Front Panel Controls Indicators and Connectors SOLE S mici 2 2 7261A Rear Panel Controls and CORRECTS 2 5 Event PURE 2 7 Time Interval Repetition Rate Versus Time Base oiii 2287 Hysteresis Window EORR A EAT SER o HET NN 2 7 Input COUPER eeuesaaezcae ERE wa SE 2 8 tl Count Error VOTRE AA FE vis Rich n acn
35. ES A NOTE This manual documents the Model 7261A and its assemblies at the revision levels shown in Appendix 7A If your instrument contains assemblies with different revision letters it will be necessary for you to either update backdate this manual Refer to the supplemental change errata sheet for newer assemblies or to the backdating sheet in Appendix 7A for older assemblies 7261A Universal Counter Timer Instruction Manual P N 487512 January 1979 Rev 1 9 80 Rev 2 2 81 1981 John Fluke Co Inc all rights reserved Litho in U S A WARRANTY Notwithstanding any provision of any agreement the following warranty is exclusive The JOHN FLUKE MFG CO INC warrants each instrument it manufactures to be free from defects in material and workmanship under normal use and service for the period of 1 year from date of purchase This warranty extends only to the original purchaser This warranty shall not apply to fuses disposable batteries rechargeable type batteries are warranted for 90 days or any product or parts which have been subject to misuse neglect accident or abnormal conditions of operations In the event of failure of a product covered by this warranty John Fluke Mfg Co Inc will repair and calibrate an instrument returned to an authorized Service Facility within 1 year of the original purchase provided the warrantor s examination discloses to its satisfaction that the pr
36. External Reference Input Check 4 52 Use the following procedure to check proper performance of the instrument with an external reference input used as time base 4 14 NOTE Both synthesizers used must be synchronous to a common reference 1 the Front Panel of the UUT set the to the following positions ON STBY ON FUNCTION FREQ A RESOLUTION 10 Hz AC DC Channels A amp B DC l Channels A amp B T 2 On the Rear Panel of the UUT set the INT EXT REFERENCE switch to the EXT position 3 Connect the LF synthesizer to the EXT REF terminal on the Rear Panel of the UUT via a 500 termination 4 Program the LF synthesizer for an output of 10 MHz at a level of 300 mV rms 5 Connect the HF synthesizer to the Channel A input terminal of the Front Panel of the UUT 6 Program the HF synthesizer for an input to the UUT of 100 MHz at a level of 100 mV rms 7 Verify that the display of the UUT is 100000 00 kHz 1 count 8 Increase the programmed frequency of the HF synthesizer by 100 Hz 9 Verify that the display of the UUT is 100000 10 kHz 1 count 10 Increase the programmed frequency ofthe synthesizer by 100 Hz ll Verify that the display of the UUT is 10000 20 kHz 1 count 4 53 Marker Check Use the following procedure to check the MARKER output l Onthe Front Panel ofthe UUT set the controls in the following positions ON STBY ON FUNCTION RATIO A B RESOL
37. NCTION FREQ A RESOLUTION 1 Hz TRIGGER LEVEL A PRESET ATTEN CH XI AC DC CH A AC t CH A 4 On the Rear Panel of the UUT set the REF switch to the INT position 5 Usethe JFD 258 tuning tool to adjust the fine time base adjustment to mid range 6 Connect the LF synthesizer to the Channel A input terminal of the UUT via a 500 termination 7 Verify that the display is stable 8 Using the JFD 258 tuning tool adjust the Coarse top time base adjustment until the display is as close as possible to 10000 000 kHz 9 Connect the top case cover 10 Wait at least 1 2 hour 11 Perform the Time Base Adjustment procedure eK eS _ 4 69 100 MHz Time Base Adjustment 4 70 Use the following procedure for adjusting the 100 MHz time base on the 10 100 MHz Multipler PCB Figure 4 11 shows the location of the test points and adjustments The test points are labeled on the land pattern side of the pcb l On UUT set the controls to the following positions FUNCTION PER A RESOLUTION 0 ns SEP COM SEP TRIGGER LEVEL PRESET MODE CONT REF EXT 2 Remove the top case cover of the UUT J Connect LF synthesizer as shown in Figure 4 3 Part A 4 Programthe LF synthesizer for an output of 10 MHz at a level of 300 mV 5 Connect the DMM to on the 10 100 MHz PCB to common Figure 4 11 10 100 MHz Multiplier PCB
38. R ERROR 2 97 Improperly triggered hysteresis levels can cause error when using any function When using ratio or event timing functions trigger errors produce gate time errors resulting in inaccurate counts Proper use of ATTENUATION and FILTER controls along with other noise reduction techniques will help solve this problem In addition the following considerations should be kept in mind 1 Period measurements use Channel A for both START and STOP pulses triggering errors are from one channel only Trigger error will be caused by noise on the input signal The period averaging function will reduce the effect of the triggering error by a factor of 1 N 2 Time interval measurements use both Channel A and channel B for the START and STOP pulses the trigger error may arise from either or both channels The averaging function will reduce the effect of the triggering error by a factor of 3 In the ratio mode the counts of Channel B trigger error increase as the frequency of the Channel A input signal increases 4 A pulse input signal with faster rise times will exhibit less trigger error than a sine wave input 2 98 REDUCING ERRORS DUE TO NOISE ON THE INPUT SIGNAL 2 99 following techniques may also be used to ensure noise rejection 1 Use an oscilloscope to identify the presence of noise 2 Use the X10 ATTEN control to limit noise levels while maintaining sufficient signal levels for triggering
39. S 2 39 Time Interval Averaging is a statistical reduction of both the time base and trigger errors Like all true statistical functions Time Interval Averaging depends upon random sampling If the repetition rate of the time interval is synchronous with the clock used time interval averaging may not give the increase in accuracy and resolution expected In worst case situation of a synchronous repetition rate Time Interval Averaging will decrease accuracy and resolution The repetition rate is synchronous with the clock if the time interval always starts in the same place with respect to the clock As Figure 2 5 shows asynchronous repetition rates can start anywhere but synchronous repetition rates have a fixed relationship to clock The 190 Jittered Time Base Option can be used to ensure asynchronous operation This option introduces a phase noise jitter on the 100 MHz clock frequency to insure asynchronous measurements 2 40 GATE TIME 2 41 Gate time refers to the length of time during which a frequency is being counted for display The frequency counted may be derived from the input signal or from the instrument s internal time base With longer gate times more counts are accumulated and measurement resolution improves N ASYNCHRONOUS TIME INTERVAL START SE PULSES SYNGHRONOUS TiMEBAsEFREQUENCY Figure 2 5 Time Interval Repetition Rate v
40. UTION 100 SEP COM COM AC DC Channels A amp B DC 2 Connect the LF synthesizer and dual trace oscilloscope to the UUT as shown in Figure 4 6 3 Program the LF synthesizer for an output of kHz at a level of IV rms 4 On the Front Panel of the UUT set the controls to Channel 4 Channel B 5 Verify that the waveform displayed on the oscilloscope is about the same as the waveform shown in Figure 4 7 Part A 6 On the Front Panel of the UUT set the controls to Channel A Channel B 7 Verify that the waveform displayed on the oscilloscope is about the same as the waveform shown in Figure 4 7 Part B OSCILLOSCOPE DUAL MARKER OUTPUT LF SYNTHESIZER 7261A 4 55 Filter Check 4 56 Usethe following procedureto check the opeation of the 100 kHz low pass filter on Channel A and Channel B of the UUT l Setthe Front Panel of the UUT set the controls to the following position FUNCTION FREQ A RESOLUTION 1 kHz FILTER OUT ON STBY ON Channels A amp B T AC DC Channels A amp B DC 2 On the Rear Panel of the UUT set the REF switch to EXT J Connect the equipment as shown in Figure 4 4 Program the LF synthesizer connected to Channel A for an output of 1 0 MHz at a level of 10 mV 5 Verify on the UUT that 1 000 MHz is displayed 6 Front Panel of the UUT set the Channel A FILTER switch to the IN po
41. able 4 8 b The unit s annunciation agrees with the unit listed for that display reading in Table 4 8 Table 4 8 PER AVG A Function Check ERROR COUNTS RESOLUTION DISPLAY 10 00000 usec 0 0000000 10 000000 usec 10 00000 usec 10 0000 usec 0 010000 msec 0 01000 msec nnunciator is illumina OVFLa md 4 45 Function Check 4 46 Use the following procedure to check the Time Interval A to B function of the UUT l Onthe Front Panel ofthe UUT set the controls as follows FUNCTION TI A B SEP COM COM AC DC DC i CHANNEL A CHANNEL 2 On the Rear Panel of the UUT set the INT EXT REFERENCE switch to the EXT position 3 Connect the equipment in the configuration shown in Figure 4 3 Part A 4 On the Front Panel of the UUT set the Resolution control to each of the positions listed in Table 4 9 5 For each position of the Resolution control Program the LF synthesizer for an output 1 Level of 2V rms 2 Frequency indicated in Table 4 9 for that position of the Resolution control b Verify on the UUT that 1 The displayed value agrees within 1 count of the value listed under Display for the position of the Resolution control selected and the LF synthesizer frequency programmed 2 The unit s annunciator agrees with the units for that Display value 6 Onthe Front Panel ofthe UUT set the controls t
42. ads and through hole connections 5 For IC removal first cut all pins and gently remove the pins by heating the solder joint Always work in one direction around the IC to allow previous pins and pads to cool After the pins are removed use the vacuum desolderer to remove the solder Sometines a small filip of solder will remain in the center of the hole and will not melt because not enough heat is carried to it by the copper plating Resolder the hole allow to cool then desolder it Enough heat must be applied to melt the solder all the way through before suction is applied Table 4 2 Static Sensitive Devices ASSEMBLY Standard Instrument Main PCB Assembly Printer Interface PCB Assy 7031 4078B 14511 Custom MC 14503CP MC 14013CP MC 14011CP 4028AN b21 4 4 4 23 PERFORMANCE CHECKS 4 24 The Performance Checks are used to comparethe performance of the instrument with the Specifications given in Section 1 The Performance Checks are recommended for incoming inspection preventative maintenance evaluation after repair or as an aid in troubleshooting All of the Performance Checks other than the Time Base Check should be performed quarterly The Time Base Check should bee performed monthly if operation within the Section Specifications is desired Should the instrument fail any portion of the Performance Checks calibration and or repair is indicated Refer to Table 4 2 when specific
43. bleshooting by performing the Performance Checks indicated by the results of the procedure The UUT can pass all parts ofthe procedure and still have faults Should the UUT pass the procedure do the Performance Checks Use the following 4 23 P 77 a im e Sigs i 7 gt 7261A steps to perform the Improper Performance Proced ures Perform the Improper Operation Procedure as follows 4 24 l Set the instrument controls as follows RESOLUTION 1 kHz SEP COM SEP FILTER OUT CHANNEL A amp B TRIGGER LEVEL PRESET ATTEN XI AC DC DC REF INT 2 Connect the LF synthesizer to the Channel A input terminal of the UUT via a 500 termination 3 Program the LF synthesizer for an output of 1 MHz at a level of 100 mV rms 4 check the FREQ A function a Setthe FUNCTION control to the FREQ A position b Verify that the GATE annunciator is flashing and that the display is 1 000 MHz 5 To check the 100 function Set the FUNCTION control to the CPM X100A position b Verify that the GATE annunciator is flashing and that the display is 600000 6 To check the FREQ C function Refer to Section 6 7 To check the RATIO A B function a Set the FUNCTION control to the RATIO position b Set the SEP COM switch to the COM position C Ver
44. cedure to adjust the standard time base or any of the three optional time bases YES Proceed to step 6 NO Increase the programmed 1 Connect the instrument to line power througha level of the LF synthes Variac set to local line voltage zer until the GATE annunciator flashes and 2 Allow the instrument to warmup at least 5 the display is a stable minutes with the case covers on The longer the 1 000 1 Then proceed instrument has warmed up the better to step 6 3 On the Front Panel of the UUT set the controls 7 Adjust R47 the PRESET B adjustment on the to the following positions Main PCB until the Channel B and trigger indicators glow with equal intensity FUNCTION FREQ A RESOLUTION Hz 8 Reduce the programmed level until the display TRIGGER LEVEL CH A PRESET becomes unstable ATTEN CH A AC DC A DC 9 Repeat steps 5 and 6 i T 4 19 7261A 4 On the Rear Panel of the UUT set the REF switch to the INT position 5 Connect the LF synthesizer to the Channel A input terminal on the UUT via a 500 termination and as short a length of RG 58 as possible 6 Program the LF synthesizer for an output of 10 0 MHz at a level of 100 mV rms 7 Verify that the UUT dis play is stable and reads about 10000 000 kHz 8 On the Front Panel of the UUT set the RESOLUTION control to the Hz position 9 Verify that on the UUT display the OVFL annunciator illuminates 10 Usethe
45. cedure to adjust the Channel B Trigger Level a The and trigger indicators glow with equal intensity 1 Front Panel of the UUT set the controls b The GATE annunciator is flashing to the following positions The display is a stable 1 000 1 FUNCTION RATIO A B RESOLUTION 103 13 On the Front Panel of the UUT rotate the AC DC CH A amp B DC Channel B Trigger Level control maximum t CH A amp B clockwise SEP COM SEP l TRIGGER LEVEL PRESET 14 Verify that 2 a Onthe UUT the trigger indicator is on and 2 Onthe Rear Panel of the UUT set the controls the trigger indicator is off to the following position b The DVM display is gt 1 5 rms REF EXT TRIGGER LEVEL CH B 15 On the Front Panel of the UUT rotate the AC POWER ON Channel B Trigger Level control counterclockwise as far it will go without switching to the PRESET 3 Connect the equipment as shown in Figure position 4 9B 16 Verify that 4 Program the LF synthesizer for an output of Onthe the trigger indicator is on th MHz at a level of l0 mV rms a Onthe UUT the trigger indicator is on the the trigger indicator is off 5 Program the HF synthesizer for an output of b The DVM display is lt 1 5V rms 1 0 MHz at a level of approximately 300 mV rms 4 65 Time Base Adjustment 6 Onthe UUT isthe GATE annunciator flashing and display stable 1 000 1 4 66 Use the following pro
46. citors or resistors in short paths are often discolored or burnt Abusively high overloads may blow carbon composition resistors glass diodes ceramic capacitors thermistors etc into fragments These symptoms or anything that looks suspect should be carefully checked before proceeding with involved troubleshooting 4 79 Fault Isolation Guide 4 80 The Fault Isolation Guide is a simplified check of instrument performance It is intended to direct the troubleshooter to the defective circuit or circuits There are three basic cases of improper operation l Theinstrument will not turn on Usethe Power Up procedure 2 The instrument turns on but the problems seem to be spread thoughout the instrument or erratic This may be due to any of a number of power supply related problems Use the Power Up procedure 3 The instrument has a problem in one or more function or range Use the Improper Operation procedure 4 81 POWER UP PROCEDURE CAUTION Line power voltage is present from the power cord throughout the primary circuit or the main power transformer Do not contact this voltage 4 82 If the instrument cannot be turned on the problem may lie in several areas the line power used may not be present the AC POWER switch may be in the OFF position the main power fuse F1 may be blown or there may be a power supply problem Power supply problems can be caused both by faults inthe power supply circuitry and by shorts in the
47. d ranges IEEE Repertoire 5 1 L4 LEQ SR1 RL2 PPO DC1 DT1 Cg Time Base Phase Modulation Option 190 Description Option for insuring valid time interval averaging of clock synchronous signals by phase modulating internal time base 520 MHz Channel C Option 310 Description Provides a third input channel for measuring frequencies from 50 MHz to 520 MHz Sensitivity 10 mV rms Input Impedance 500 VSWR 2 5 1 Max Input Voltage rms fuse protected See Figure 1 1 for dimensions Display Cycle Rate Reset Self Check Time Base Output Storage Temperature Operating Temperature Power Marker Output Trigger Level Output Autoranging Overflow Indicator Oven Indicator Trigger Status Indicators Gate Light Cont Trig Mode Battery Line Switch EMI Weight Dimensions PROTECTION CLASS FOOTNOTES 7261A Table 1 2 Specifications cont GENERAL 8 digit LED with leading zero suppression decimal point and annunciators Fixed 250 ms between readings Reset button clears display lights all display segments and on release activates a new measurement Uses internal 10 MHz signal to check digital circuits Buffered TTL compatible 10 MHz signal derived from crystal time base VOUT gt 500 mV into 502 40 to 70 C 0 to 40 C 47 63 Hz 100V 120V 200V 220V 10 32 VA max TTL compatible output positive going edge indicates A chan nel tri
48. data strobes decimal point 7261A GATE OVFL and Unit s Annunciators and command functions The 7261A must be interfaced through the JF 1120A The PCB installed in the 7261 Ais the 72X X A 521 Option which is part of the total interface 72X X A 529 Option Detailed operation is described under these options in Section 6 2 17 2 18 7261A Section 4 Maintenance WARNING THESE SERVICING INSTRUCTIONS ARE FOR USE BY QUALIFIED PERSONNEL ONLY TO AVOID ELECTRIC SHOCK DO NOT PERFORM ANY SERVICING OTHER THAN THAT CONTAINED IN THE OPERATING INSTRUCTIONS UNLESS YOU ARE QUALIFIED TO DO SO 4 1 INTRODUCTION Universal Counter Timer Test equipment recommended for performance tests calibration and troubleshooting is 4 2 This section of the manual provides information listed in Table 4 1 If the recommended equipment is not concerning warranty general maintenance performance available equipment with equivalent specifications may tests calibration and troubleshooting for the 7261A be used Table 4 1 Required Test Equipment Oscilloscope Dual trace DC 200 MHz wide band Tektronix 475 125 MHz at a level of 1V rms Time Base 1 X 10 per day Up to 10 MHz at a level of 1V rms Time base 1 X 10 per day Impedance match the UUT High Frequency John Fluke 6160B with 02 Option Signal Generator Low Frequency Signal Generator 2 500 Termination 3 BNC Tee Digital Multimeter J
49. e E 2 8 Noise and Distortion Effects TEE SEE AES e ema tc e 2 9 Trigger Level Control Since cal woe TID 2 11 Pd ROGI ae CILE EE A 2 11 Decimal Point Placement on RE UR RUE C PES eio uii Accuracy and Resolution Versus soo 05 RTL 2 13 7261A Functional Block DART pe RUN RR 3 2 Frequency Measurement NUR VU TO E ae 3 5 Counts Per Minute Measurements E DPI ir 3 5 Ratio Measurements etitm ra e RATE OEC EEA RE 3 6 enneren dee 3 7 Interval 3 8 Time Interval Average Measurements VT ARM 3 9 Totalized A Gated by B Measurements MA A Ae 3 10 self Check Function KK RN COR IRI ae cece TEN 3 10 Input Circuit EL rn ORS AUR uim ecce creer ARATE cR EISE SU BE Main Gate Enable Logic 3 18 Counter Latches and Multiplexer CALAN 2419 Time Interval Average Control 3 20 Disassembly Screw Access T Se VEU a S ala 4 2 Line Voltage Selection VR ncmo Roc Ceca 4 3 FREQ A Check om rmm OP EO LEER ARI STERNE RUE 4 8
50. en placed in AUTO the 7261A will automatically step through a predetermined series of resolution settings The settings available for each function are defined in Table 2 4 When autoranging the instrument seeks the greatest resolution possible without overflow for the function selected and the signal being measured As an example with FREQ selected the 7261A will step through the first four resolutions to maximize its display capacity when measuring a frequency of 1 2 MHz the reading will be 1200 000 kHz If a 1200 Hz is measured maximum resolution allowable will again be found at the last step but the reading will be 1 200 kHz NOTE During autoranging in the PER A mode the GATE LED may flash more than once for each display update 7261 RATIO A B PER AVG A Table 2 4 Autoranging Autoranging not used in TOT A B or CPM X100A 2 73 SEPARATE COMMON CONTROL 2 74 The SEP COM control is used to select the input to the Channel B amplifier In SEP the Channel B input connector is tied to the Channel B amplifier In the COM position the Channel A input connector is tied to both the Channel A and B Amplifiers the Channel A ATTEN and AC DC controls now influence the signal to both amplifiers All other Channel B controls affect Channel B signals as usual NOTE In COM the Channel B input is not connected 2 75 ATTENUATION CONTROLS 2 76 The ATTEN controlisa three position switch that can
51. ersus Time Base 2 42 HYSTERESIS 2 43 Ininstruments such as the 7261A proper counting and timing requires a pulsed output from the input circuitry To form this pulse each input waveform regardless of its shape triggers the input circuitry on or off at predetermined triggering or hysteresis levels An input waveform must pass through both of these hysteresis levels for the input circuitry to generate a pulse The voltage difference between the two levels is termed the hysteresis window the minimum signal that can trigger both levels therefore defines the instrument s sensitivity Generation of the hysteresis window is illustrated in Figure 2 6 HYSTERESIS WINDOW HYSTERESIS LEVEL TRIGGER OUTPUT Figure 2 6 Hysteresis Window 2 44 INPUT COUPLING 2 45 Either ac or dc coupling may be used to transfer the input signal to the input conditioning circuitry If the input signal is riding on a dc level it may not lie within the range of the hysteresis window The instrument cannot measure the signal The top waveform in Figure 2 7 shows such a dc coupled waveform The lower waveform shows the same waveform ac coupled With ac coupling the signal can be measured AC coupling causes no problems for repetitive signals of a fixed frequency but the trigger 2 7 7261A point will shift with a change in frequency or duty cycle This is not important in event counting but is very important to event
52. evel Out Terminal The PRESET position of the control selects the zero volts position The position of the switch determines whether the instrument is set up to trigger on the positive or the negative slope of the waveform Figure 2 10 shows the effects of this control Use of both the Trigger level and slope controls will be discussed later in this section under Triggering RANGE OF TRIGGER LEVEL ADJUSTMENT 150mV OV 150mV 150mV OV 150mV POSITIVE SLOPE TRIGGING Figure 2 10 Trigger Level Control 2 83 TI HOLDOFF 2 84 The TI Holdoff control provides a continuously adjustable time delay in generating the STOP pulse The time delay begins from the START pulse This allows the operator to accurately measure the time interval of some extremely noisy signals Figure 2 11 shows the waveform of a signal generated by relay contact closure The noise from contact bounce is so great that without TI Holdoff the STOP signal would occur almost immediately after the START pulse The time interval measurement would be grossly inaccurate But the TI Holdoff signal prevents the output of the Channel B signal conditioner from generating the STOP pulse After the end of th TI Holdoff period the next pulse out of the Channel B signal conditioner will generate the STOP pulse The time interval of the signal has been accurately measured 2 85 MODE CONTROL 2 86 The rear panel
53. evel of 100 mV rms 2 Frequency indicated in Table 4 7 b Verify on the UUT that 1 The display agrees with the appropriate Display value listed in Table 4 7 the appropriate error listed in the table 2 The unit s annunciator agrees with the units following the display value Table 4 7 PER A Function Check LF FREQUENCY RESOLUTION PROGRAMMED SWITCH COUNTS 2 MHz 10 nsec 0 50 usec t1 100 kHz 10 nsec 10 00 psec 10 kHz 100 nsec 0 1000 psec t3 1 kHz 1 usec 1 000 msec T3 100 Hz 10 psec 10 00 msec 3 10 Hz 100 usec 0 1000 sec 3 1 msec 1 000 sec t3 1 Hz 4 43 PER AVG A Function Check 4 44 Use the following procedure to check the Period Averaging function of the UUT 1 On the Front Panel of the UUT set the Function control to the PER AVG A position 2 On the Rear Panel of the UUT set the INT EXT REFERENCE control to the EXT position J Connect the equipment in the configuration shown in Figure 4 3 Part A 4 On the Front Panel of the UUT set the Resolution control to the positions listed in Table 4 8 4 12 5 Program the LF synthesizer for an output frequency of 100 kHz at a level of 100 mV rms 6 On the Front Panel of the UUT set the Resolution control to the positions listed in Table 4 8 7T Verify on the UUT that for each position of the Resolution switch a The display agrees with the value listed in T
54. g procedural checks should be performed prior to using any of the function operating directions 1 Check that the instrument has been connected to appropriate line power 2 Ensure that the rear panel EXT INT select switch is set to INT 3 Press power to ON 4 Ensure adequate time for instrument warmup especially if an optional oven time base is installed typically 10 minutes 2 106 Frequency Measurements FREQ A 2 107 Frequencies on Channel from 0 125 MHz can be counted and directly displayed using this function The gate times available range from 0 1 ms through 10s in six decade steps selectable with the RESOLUTION control respective markings of the 10 KHz through 0 1 Hz Input amplitudes should not exceed 250V rms from 45 Hz to 50 kHz lowering to 5V rms at MHz and above Use the following procedure when making frequency measurements 1 Set front panel controls as follows FUNCTION FREQ A RESOLUTION as required or AUTO ATTENUATION X100 TRIGGER LEVEL PRESET SEP COM SEP FILTER Out 2 Connect the signal to be measured to the CHANNEL A input connector 3 Adjust the ATTEN and TRIGGER LEVEL controls for a stable display 4 Set the RESOLUTION control to obtain desired resolution of the displayed frequency The OVFL annunciator will light if the display s capacity is exceeded NOTE When dealing with low frequencies period measurements yield greater accuracy 2 108 Counts
55. gger negative going edge indicates B channel trigger 30 ns delay typical from time signal triggers input amplifier to the time marker changes level at rear panel 1 5V level Indicates DC trigger level set on either Channel A or Channel switch selectable Automatically selects range that optimizes both resolution and measurement time 2096 ranging hysteresis is provided to eliminate unnecessary ranging on signals near range edge LED is illuminated to indicate loss of most significant digit information LED is illuminated whenever power is being applied to internal oven oscillator Two per channel Provide relative indication of whether the input signal is triggering input amplifier and where on the signal the trigger occurs LED is illuminated whenever counter is making a measurement Switch activates external trigger mode for initiating a measurement Switch provides for manual selection of line power or optional battery power Internal metal RFI shield tested and passed MIL STD 461 notice 3 contact factory for test data 3 1 kg 6 Ibs 14 oz Standard type PTI case see figure 1 1 CLASS 1 As defined in IEC 348 N 10910 105 in decade steps set by resolution switch Indicates the number of periods averaged in Period Average mode the number of cycles of B averaged in Ration mode and the number of intervals averaged in Time Interval Average mode 2 Time base error is the sum of all errors specified in
56. han the instrument time base oscillator 10 MHz b PER A provides the best measurement accuracy if the input signal is lower in frequency than the instrument time base oscillator 5 When using these guidelines the operator mos exercise discretion In a high noise environment where a great deal of non harmonic distortios might be expected gate time errors due toi triggering may be significant FREQ might be te better choice regardless of the input Signa frequency ACCURACY AND RESOLUTION X CLOCK Y FREQUENCY Clock Frequency used for PER A and TIA B Function RESOLUTION SWITCH SETTING CLOCK FREQUENCY 1 kHz 10 kHz 100 kHz 1 MHz 10 MHz 100 MHz Figure 2 13 Accuracy and Resolution versus Frequency 2 94 DEALING WITH TIME BASE ERROR 2 95 Some of the effects of crystal related time base errors can be reduced If the temperature of the instrument environment is maintained at a constant value temperature error is minimized If tight control of the instrument environment fails to produce the accuracy desired the time base crystal related error can be reduced through recalibration or by substituting a time base with smaller errors This time base may either be one of the optional internal time bases described in Section 6 or external 10 MHz reference connected to the instrument via the rear panel 7261 2 96 DEALING WITH TRIGGE
57. ify that the GATE annunciator is flashing and that the display is 1 0 d Set the SEP COM switch to the SEP position 8 To check the PER A function Setthe FUNCTION control to the PER A position b Verify that the GATE annunciator is flashing and that the display is 0 0010 msec C Setthe RESOLUTION control to the 10 ns position d Verify that the GATE annunciator is flashing and that the display is 1 00 usec RO check 9 To check the PER AVG A function a Set the FUNCTION switch to the PER AVG A position b Verify that the GATE annunciator is flashing and the display is 0 00100 msec 10 check the TI function a Set SEP COM switch to COM and the FUNCTION control to the TI A B position b Set the Channel control to the position Verify that the GATE annunciator is flashing and that the display is 0 50 psec d Setthe RESOLUTION control to the 100 ns position Verify that the GATE annunciator is flashing and that the display is 0 0005 msec ll To check the TIA A B function Setthe FUNCTION control to the TIA A B position b Verify that the GATE annunciator is flashing and that the display is 0 000500 msec 12 To check the TOT A B function a Set the SEP COM switch to the SEP position b Rotate the Channel B TRIGGER LEVEL control maximum counterclock wise Set the FUNCTION control to the TOT A B position d Press and release the RESET button on
58. igger on 6 BNC connector used to apply input signal to Channel A Impedance at this terminal is 1 far connecting directly across an input signal with minimum input waveform distortion Important for all time measurement functions i e period time interval time interval averaging etc The amplitude of signals applied to this input should not be below 10 mV rms or above the levels shown in Table 2 3 The input circuit is fuse protected CHANNEL B This outlined position of the front panel contains the controls indicators and connector for Channel B inputs Item locations and functions correspond directly with those of Channel SEP COM A two position slide switch that determines whether the inputs of Channel A and Channel B are tied together COM or separate SEP For most types of measurements this switch will be in the SEP position but the COM position is useful for measurements made on a single signal from a single input cable Such as rise time and fall time FILTER OUT IN A two position slide switch that effectively places a 100 kHz low pass filter in series with the input signals on Channels A and B the IN position or allows the input signals to pass with no filtering the OUT position CHC BNC connector for the optional Channel C Only the frequency of Channel C inputs may be measured The range of the 310 Option is 50 512 MHz The input impedance is 500 to provide proper impedance matching for 500 cables to minimize
59. ing questions l Are the instrument controls set to the proper position 2 Are the controls of associated equipment set to the proper positions 3 Are the connections between the instrument and associated equipment correct 4 Are the interconnecting cables in working order 5 Is the associated equipment functioning properly 6 Is the instrument designed to do what is being attempted If the answers to these questions are all yes then the fault is probably in the instrument 4 74 The ease with which a technician isolates a fault in any instrument depends primarily upon just how well that technician knows the instrument Sections 2 and 3 of this manual should be read and thoroughly understood before attempting to troubleshoot As an aid to the troubleshooter three additional subsections follow Visual Inspection Fault Isolation Guide and Troubleshooting Techniques The Visual Inspection should be performed first The F ault Isolation Guide is a brief check of all instrument functions The procedure 4 22 should enable the technician to isolate the fault to a circuit or circuits Once a Suspect circuit js identified the Troubleshooting Techniques provide the technician with suggestions for troubleshooting IC technology circuits 4 75 When working with the instrument either to troubleshoot or to make repairs observe the warning given at the beginning of this section dealing with handling tehcniques and pre
60. instrument loading the power supply down Points to consider when attempting to isolate power problems are listed below If the UUT will operate but the symptoms are erratic or widespread seemingly disassociated then go directly to item number 6 1 Insure that line power is present at the receptacle being used 2 Insure that the Rear Panel AC POWER switch is in the ON position 3 Check Fl the main power fuse 4 Make continuity measurements between chassis common and the three pins of the power receptacle The ground pin to common should be zero volts The other two pins to common should be infinity 5 Make the continuity measurement between the two non ground pins of the Rear Panel power receptacle The AC POWER switch should be in the ON position There should be some slight resistance because the measurement is taken through the primary windings of the main power transformer 7261A 6 Measure the power supply voltages at 2 TP3 and TP4 with the Front Panel POWER ON STBY switch in both positions Use El for the common reference when making these measurements If all voltages are within the limits listed in the Power Supply Voltage Adjustment procedure proceed to item 7 If one or more voltage is incorrect when the POWER ON STBY switch is in the STBY position the problem is in the power supply proceed to item 6 Part A If one or more voltages is are incorrect only when the POWER ON STBY switch is in
61. interfere with case mating This bail will normally be mounted toward the front of the instrument s bottom panel To remove the bail compress either of its legs toward the center of the case and pull out Installation may then be made in identical mounts at the rear of the bottom panel 2 13 Rack Installation 2 14 The 72614 may be installed standard 19 inch equipment rack or a DIN panel mount Mounting kits foe these accessories are described in Section 6 of _ manual A list of all available accessories and Options presented in Section 2 15 OPERATING FEATURES 2 16 The location of front panel controls indicators and connectors is shown in Figure 2 2 Referenced number these items briefly described in Table 2 1 Rear panel controls and connectors are covered similar fashion in Figure 2 3 and Table 2 2 It is suggested that the operator become acquainted with this information before operating the instrument Figure 2 2 7261A Front Panel Controls Connectors and Indicators REF Display Table 2 1 7261A Front Panel Controls The display has three sections 7 At the left end the instrument status annunciators GATE Indicates that the instrument is sampling the input signal OVFL Indicates that the capacity of the display has been exceeded OVEN If one of the oven time base options is installed indicates that the oven is receiving power 2 In the center the eight LED digits
62. itch in the position 12 Repeat steps 8 and 9 Table 4 4 FREQ A Function Check High Frequencies HF SYNTHESIZER PROGRAMMED VALUES LEVEL rms Table 4 5 FREQ A Function Check Low Frequencies LF SYNTHESIZER PROGRAMMED FREQUENCY FREQUENCY LEVEL rms a RESOLUTION CONTROL 4 37 X100A Function Check 4 38 Use the following procedure to check the CPM X1004A function of the instrument l Onthe Front Panel ofthe UUT set the controls to the following position FUNCTION 100 RESOLUTION 0 1 Hz FILTER IN ON STBY ON 2 Connect the LF synthesizer to the Channel A input of the UUT via a 500 termination 3 Program the LF synthesizer for an output of 5 kHz at a level of 100 mV rms 7261A 4 Verify on the UUT that a 3000 is displayed RF VOLTMETER b Decimal point is blank No units annunciator is illuminated 3 On the Front Panel of the UUT sequence Resolution control to all of its positions 6 Verify on the UUT that a The display remains unchanged b No decimal point is illuminated c Nounits annunciator is illuminated LF SYNTHESIZER 4 39 Ratio A B Function Check mV rms 4 40 Use the following procedure to check the Ratio function of the UUT Figure 4 4 Ratio A B Check Table 4 6 RATIO A B Function Check HF SYNTHESIZER PROGRAMMED FREQUENCY MHz 1 On the Front Panel of the
63. l B ATTEN control to the X10 position 9 Program the LF synthesizer for an output level 23 dB above the sensitivity level measured in step 6 10 Verify that the UUT display is 1000 1 count 11 Program the LF synthesizer for an output level 17 dB above the sensitivity level measured in step 6 12 Verify that the display is either all zeros or greater than 1 count error 13 On the Front Panel of the UUT set the Channel B ATTEN control to the X100 position 14 Program the LF synthesizer for an output level 43 dB above the sensitivity level measured in step 6 15 Verify that the UUT display is 1000 1 count l On the UUT set the Front Panel controls as follows FUNCTION FREQ A RESOLUTION l Hz ON STBY ON 2 Connect the LF synthesizer to the Channel A input terminal of the UUT via a 500 termination and the shortest length of RG 58 possible J Program the LF synthesizer for an output of 5 MHz at a level of 1V OPEN 4 Verify on the UUT that the display reading is 5 MHz maximum allowable count error of 28 Hz The maximum allowable count error can be computed for any input signal by multiplying the frequency of the input signal by the total time base accuracy 56 X107 and then adding the 1 count to the product 3 Connect the oscilloscope to the REF OUT terminal on the UUT through as short a length of RG 58 as possible The oscilloscope end of the test cable must have a 500 termination
64. led This option is discussed in detail in Section 6 Assuming the option is installed l Setthe Front Panel controls as follows FUNCTION RESOLUTION FREQ C as required 2 Connect the signal to be measured to the Channel C input connector 3 Set the RESOLUTION control to obtain maximum resolution of the displayed frequency The OVFL annunciator will illuminate if the display capacity is exceeded 2 112 Ratio Measurement RATIO A B 2 113 The ratio function can be used to measure the numeric ratio of two input signals The input on CHANNEL A is divided by that on CHANNEL B The result is displayed without measurement unit annunciation The RESOLUTION control influences the display resolution in the normal manner Use the following procedure when making ratio measurements 1 Set front panel controls as follows FUNCTION RATIO A B RESOLUTION set to optimize displayed resolution SEP COM SEP FILTER Out both channels 2 Connect the higher of the two frequencies to CHANNEL A input connector 3 Connect the lower of the two frequencies to CHANNEL B input connector 5 Hz through 2 MHz 4 Adjust the ATTEN and TRIGGER LEVEL controls on both channels for proper triggering GATE LED flashing Gating is derived from the CHANNEL B signal when in the Ratio function generally the greater the level of the signal on CHANNEL B the greater the accuracy of the Ratio measurement will be NOTE It may be
65. lows operation of the instrument away from ac power sources 1 6 OPTIONS AND ACCESSORIES 1 7 The options and accessories available for use with the 7261A are described in Section 6 Table 1 1 lists these optiohs and accessories 1 8 SPECIFICATIONS 1 9 Table 1 2 lists the specifications of the 7261A 1 1 7261A OPTION E IP MODEL NO DESCRIPTION OPTIONS 7261A 190 Jittered Time Base 72XXA 010 Battery 72XXA 112 2 ppm Time Base 72XXA 131 72XXA 132 72XXA 310 72XXA 521 72XXA 529 Low Power Oven Time Base Superior Low Power Oven Time Base 520 MHz Direct Data Output Unit IEEE Interface Option See Footnote Frequency A Range 0 125 MHz Resolution 1 Hz 10 kHz in decade steps Accuracy 1 count ttime base errors Display kHz or MHz with decimal point CPM X100A Range 0 125 MHz Resolution 100 CPM fixed Accuracy 1 count ttime base errors Display no decimal point or annunciators Frequency C Option 310 Range 50 520 MHz Resolution 1 Hz 10 kHz in decade steps Accuracy 1 count base errors Display kHz or MHz with decimal point Ratio A B Range A 0 125 MHz B 0 2 MHz Resolution Freq B Freq Freq Freq X Trig Error B Freq A N Display decimal Point without annunciator Period A Range 10 ns 99 999 999 sec Resolution TO ns 1 ms in decade steps Accuracy 4 count
66. mple the FREQ A function can be used to measure the precision frequency output of a signal synthesizer and the CPM function can be used to determine the rotational speed of a conveyor belt spindle 2 35 When using any function that counts events the instrument must trigger once and only once for each event Use of the front panel controls must be directed toward this end Noise must be filtered or attenuated to prevent false triggering and the input signal must be kept within the dynamic range of the instrument 2 36 EVENT TIMING 2 37 During event timing functions an internal oscillator frequency is counted for a period determined by the input signal In the 7261A two types of event timing measurements can be made period and time interval Period measurement PER A or PER AVG A determines the period or inverse of frequency of a repetitive signal The instrument measures period by counting an internal oscillator s frequency for single PER A or multiple PER AVG A cycles of the input Time interval measurements TI A B can be made to determine the period of time between any two events repetitive or not Average time interval measurements TIA A B can be made on signals with repetitive time intervals For either type of event timing separate start and stop signals must be generated from the input refer to Figure 2 4 Figs 2 4 Event Timing 2 38 SYNCHRONOUS VERSUS ASYNCHRON OUS TIME INTERVAL REPETITION RATE
67. nal of the shorted gate 4 89 HEAT AND COLD 4 90 fast and effective method of locating the faulty area in the instrument is by alternately heating and cooling areas in the instrument with a heat gun and freon spray This check can be used on large areas or even individual components IC s can open or short internally and this method of troubleshooting can be especially effective 4 26 4 91 LOGIC CLIP 4 92 Logic clips such as the John Fluke lestclip 200 provide the troubleshooter with visual indication of the logic levels in the instrument as the instrument operates This test device is easier to use it clips onto the IC than such test equipment as an oscilloscope and allows all inputs and outputs to be observed simultaneously 4 93 TEMPERATURE 4 94 Shorted components overheat Temperature can be measured with the Fluke 801 150 and any of its associated DMMs CURRENT TRACER Figure 4 12 Current Tracing
68. necessary to check each signal separately in FREQ A or PER A to verify correct levels 7261 5 Set the RESOLUTION control to obtain maximum resolution of the ratio measurement 2 114 Period Measurements PER A 2 115 This function can be used to measure the period of an input signal with frequencies from 5 Hz through 2 MHz 2 116 The period function provides a great improvement in both accuracy and resolution of measurements made on low frequency signals To make period measurements the instrument measures the time interval between two consecutive cycles of a repetitive signal Channel A is used to generate start and stop pulses The RESOLUTION control is used to specify the value of the least significant digit 10 0 ns 1 0 ms Use the following procedure when making period measurements 1 Set the front panel controls as follows FUNCTION PER A RESOLUTION as required or AUTO SEP COM SEP 2 Connect the signal to be measured to the CHANNEL A input connector 3 Adjust the ATTEN and TRIGGER LEVEL controls Channel A until a stable display 15 seen 2 117 Period Averaging Measurements PER AVG A 2 118 Multiple periods of frequencies between 5 Hz and MHz may be averaged to obtain greater resolution and accuracy than with Period measurements For example with a Period measurement of a 1 kHz signal the display would read 1000 00 the maximum resolution of the Least Significant Digit is 10 ns In
69. ns and information which should be considered before operating the Model 7261A Counter Timer 2 19 Line Connection 2 20 The input power cord is a three pin polarized connector which permits connection to any of the power voltages described in INPUT POWER Ensure that the ground pin is connected to a high quality earth ground 2 21 Maximum Inputs WARNING ALL BNC CONNECTOR SHELLS ON THE 7261A ARE TIED DIRECTLY TO EARTH GROUND THROUGH THE POWER PLUG DO NOT CONNECT THE ACTIVE LEAD OF THE INPUT SIGNALS TO THE SHELL IRREPARABLE DAMAGE TO THE INSTRU MENT OR THE SIGNAL SOURCE MAY RESULT 2 22 Table 2 3 defines the maximum allowable signal level input for each input terminal Channels and B are fuse protected 250 mA Refer to Section 4 of this manual for fuse replacement instructions Table 2 3 Overload Protection INPUT TERMINAL Channel A Channel B MAXIMUM INPUT 100V rms from 0 to 45 Hz 250V rms from 45 Hz to 50 KHz then the maximum decreases linearly to 5V rms at 1 MHz and remains at 5V rms above 1 MHz 2 23 Counter Timer Terminology 2 24 The following definitions are useful in understanding how and when to use the 7261A s controls 2 25 ATTENUATION 2 26 Attenuation is used to limit the input signal within the input amplifier s dynamic range On the 7261A attenuation control is provided to limit the input amplifiers gain The ATTEN control allows selection fact
70. o the following positions RESOLUTION 10 HOLDOFF Maximum counter clock wise but not in OFF position 7 Program the LF synthesizer for an output of 2 MHz at a level of 2V rms 8 Verify that the display is not greater than 0 01 Y Y msec Y don t care 9 On the Front Panel of the UUT rotate the TI Holdoff control maximum clockwise 10 Verify on the UUT that the display reading is not less than 20 Y YYY msec Y don t care Table 4 9 TI A B Function Check LF SYNTHESIZER RESOLUTION e CONTROL koe cdi 10 nsec 5 00 usec 100 nsec 0500 msec 1 usec 0 500 msec 10 usec 5 00 msec 100 usec 0500 sec AUTO 0500 msec 4 47 TIA A B Function Check Use the following procedure to check the Time interval A to B averaging function of the UUT 1 On the Front Panel of the set the controls to the following positions 7261A FUNCTION TIA A B SEP COM SEP AC DC AC CHANNEL A CHANNEL B 2 On the Rear Panel of the UUT set the INT EXT REFERENCE switch to the EXT position 3 Connect the equipment in the configuration shown in Figure 4 5 4 Program the LF synthesizer for an output frequency at 1 12345 MHz at a level of 2V rms 5 On the Front Panel of the UUT set the Resolution control to the positions indicated in Table 4 10 6 Verify that the UUT display agrees with Table 4 10 3 WAY SPLITTER LE Figure 4 5 TIA A B Check Table
71. oduct was defective The warrantor may at its option replace the product in lieu of repair With regard to any instrument returned within 1 year of the original purchase said repairs or replacement will be made without charge If the failure has been caused by misuse neglect accident or abnormal conditions of operations repairs will be billed at a nominal cost In such case an estimate will be submitted before work is started if requested THE FOREGOING WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO ANY IMPLIED WARRANTY OF MERCHANTABILITY FITNESS OR ADEQUACY FOR ANY PARTICULAR PURPOSE OR USE JOHN FLUKE MFG CO INC SHALL NOT BE LIABLE FOR ANY SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES WHETHER IN CONTRACT TORT OR OTHERWISE If any failure occurs the following steps should be taken 1 Notify the JOHN FLUKE MFG CO INC or nearest Service facility giving full details of the difficulty and include the model number type number and serial number On receipt of this information service data or shipping instructions will be forwarded to you 2 On receipt of the shipping instructions forward the instrument transportation prepaid Repairs will be made at the Service Facility and the instrument returned transportation prepaid SHIPPING TO MANUFACTURER FOR REPAIR OR ADJUSTMENT All shipments of JOHN FLUKE MFG CO INC instruments should be mad via United Parcel Service or
72. ohn Fluke 6011A GR874 AC volts up to 250V ac DC volts to 1V 0 01V rms Resistance 0 to infinity John Fluke 8012A Boonton 92 BD Boonton 91 8B Tektronix P6054A Variac RF Voltmeter 10 mV rms to 5V rms 500 Adapter Oscilloscope Probe Variable AC Power supply Frequency and Time Standard RF Attenuator Impedance match UUT to RF Voltmeter X10 DC to 125 MHz Variable Voltage from 0 250V ac Aging rate of 5 X 107 day or less HP5061A HP255D HP11667A 0 120 dB in 10 dB steps 5052 3 way splitter 7261A 4 3 Insome parts of the text of this section referring to the Model 7261A by instrument number by names such as instrument may lead to confusion Therefore the instrument may sometimes be referred to as the UUT Unit Under Test 4 4 SERVICE INFORMATION 4 5 The instrument is warranted for a period of year upon delivery to the original purchaser The WARRANTY is located on the back of the title pags of this manual 4 6 Factory authorized calibration and service for each Fluke product is available at various worldwide locations A complete list of these service centers is included in Section 7 of this manual If requested an estimate will be provided to the customer before any work is begun on instruments that are beyond the warranty period 4 7 GENERAL MAINTENANCE NOTE To avoid contaminating the pcb
73. om its Front Panel Connector until free With a gentle rocking motion now lift the assembly out of its Main PCB connector Avoid bending individual connector pins on the Signal Conditioners NOTE The Signal Conditioners must not be interchanged Each assembly is component matched to a hysteresis resistor on the Main PCB 6 To remove the Front Panel Assembly A2 from the Main PCB Assembly first pull off the following switch buttons in the panel s lower left corner a STBY green b BAT LINE white c RESET blue 7 Gently pry the Front Panel Assembly away from its 40 pin connector left and guide pin right Avoid bending individual connector pins on the Main PCB 8 Refer to Section 6 of this manual when removing any optional assemblies 4 10 Reassembly 4 11 For reassembly the disassembly procedures can generally be followed in reverse Keep the following considerations in mind 1 When reinstalling the Signal Conditioners or the Front Panel Assembly care should be taken not to bend the connector pins 2 When reconnecting the top and bottom case halves ensure that the Front and Rear Panels fit into their appropriate grooves in the case top half Slide the top half into place uniformly Firmly squeeze top and bottom together at front and rear and reinstall the six securing screws NOTE Proper RFI shielding depends on top and bottom case halves being securely mated 4 12 Input Power
74. on to ensure proper triggering 2 121 Time Interval Averaging Measurements TIA A B 2 122 Multiple time intervals can be averaged to obtain greater resolution and accuracy than with Time Interval measurements Use the following procedure when making Time Interval Averaging measurements 1 Set the Front Panel controls as follows FUNCTION A B ATTENUATION 100 TRIGGER LEVEL PRESET 2 Set all other instrument controls as necessary for the application at hand 3 For input from separate sources connect the start signal to Channel A input terminal and set the SEP COM switch to the SEP position For inputs from a single source connect the signals to the Channel A input terminal and set the SEP COM switch to the COM position 4 Adjust the instrument controls as described in the Operating Notes earlier in this section to insure stable display triggering at the proper points 2 123 Totalizing Measurements TOT 2 124 In the totalize mode the 7261A can be used to continuously count and display the number of events occurring on Channel during each event on Channel B Only a reset will reinitialize the count Use the following procedure for totalize measurements 2 16 Overflow annunciator should be illuminated l Set front panel controls as follows FUNCTION TOT A RESOLUTION not used SEP COM SEP 2 Connect signal to betotalized to CHANNEL A input connector 34 Adjust the ATTEN
75. or an output level 37 dB above the sensitivity level measured in step 6 above 16 Verify that the UUT display is either all zeros or no longer 1 count 17 On the Front Panel of the UUT set the Resolution control to the 1 Hz position 18 Connect the equipment in the configuration shown in Figure 4 3 Part B 19 Adjust the RF attenuator and program the HF synthesizer for an input to the UUT of 50 MHz at a level of 100 mV 20 Verify that the UUT display is 500000 000 kHz 1 count 21 Reduce the level input to the UUT until display is no longer 1 count 22 Verify that the voltmeter reading is less than 10 23 On the Front Panel of the UUT set the Resolution control to the 10 Hz position 24 Adjust the RF attenuator and program the HF synthesizer for an inputto the UUT of 125 MHz at a level of 100 mV 25 Verify that the UUT display is 125000 00 kHz 1 count base error 26 Reduce the level of the UUT input until the error is greater than 1 count 27 Verify that the voltmeter reading is less than 35 mV 7261A LF SYNTHESIZER REF QUT 300 mV rms RF VOLTMETER RF ATTENUATOR 91 8B SYNTHESIZER REF OUT LF SYNTHESIZER REF REF IN OUT 5 MHz RF ATTENUATOR RF VOLTMETER HF SYNTHESIZER CH A UUT 5012 TERM LF CHB SYNTHESIZER Figure 4 3 Check 4 31 Sensitivity Check Channel B 4 3
76. ors X1 X10 and X100 2 6 Channel 2 27 CYCLE RATE 2 28 This term refers to the minimum time necessary for the instrument to process and display a measurement It does not include the actual measurement time In the 7261A each cycle time is 250 ms 2 29 DISTORTION 2 30 Distortion refers to an unwanted change in the input waveform It may occur at equally spaced harmonic or random non harmonic intervals 2 31 DUTY CYCLE 2 32 Duty cycle specifies the ratio of signal on time to off time The greater the percentage of off time the lower the duty cycle Measure low duty cycle signals with dc coupling selected AC DC switch in the DC position 2 33 EVENT COUNTING 2 34 The accumulation of a number of events over a period of time is termed event counting Several 7261A functions perform this operation The FREQ A mode counts events for a specific length of time to determine the Channel A input frequency In the CPM mode the Channel A input frequency is counted in the same manner then a conversion factor is used to normalize the frequency counts per second into counts per minute In TOT A B mode a continuously updated count of events on Channel A gated by events on Channel is displayed Finally in RATIO A B mode the 7261A will count events on Channel A during a gate time determined by the signal on Channel The instrument can measure events generated by a wide variety of sources For exa
77. p 6 12 On the Front Panel of the UUT rotate the NO Increase the level pro Channel A Trigger Level control maximum gramed into the LF clockwise synthesizer until the UUT display is a stable 1 00 MHz Then continue to 13 Verify that tep 6 Sem a The trigger indicator is on and the trigger 6 Adjust R49 the PRESET A adjustment onthe indicator is off Main PCB until the Channel A and trigger z indicators glow with equal intensity b The DVM display is lt 1 5V 7 Reduce the programmed level until the display 14 On the Front Panel of the UUT rotate the becomes unstable Channel A Trigger Level control counterclock wise as far as it will go without switching into the 8 Repeat steps 5 and 6 PRESET position HF SYNTHESIZER LF SYNTHESIZER REF OUT REF OUT REF IN LF SYTHESIZER REF OUT 10 MHz 300 MV rms 10 MHz 300 MV rms Figure 4 9 Trigger Level Adjustment 4 18 7261 15 Verify that 10 Repeat steps 7 and 8 until maximum sensitivity or a programmed level of 8 mV rms is a The trigger indicator is on and the trigger reached Maximum sensitivity must be less than 10 indicator is off mV rms b The DVM display 15 gt 1 5V rms 11 On the Front Panel of the UUT set the switch to the position 4 63 Channel B Trigger Level Adjustment 12 Verify that on the 4 64 Usethe following pro
78. per Minute Measurements X100A 2 109 The 7261A can be used as a tachometer to read out revolutions per minute The input to Channel A in this function must be from a 100 pulse per revolution transducer For transducers having other pulse per revolution rates the 7261 readout can be converted to RPM with the formula Correct RPM 100 Displayed RPM Where the number of pulses per minute of the transducer When the CPM X100A function is selected gate time is set to 0 65 the RESOLUTION control is disabled and the display will not indicate a decimal point or units annunciator Use the following procedure when making counts per minute measurements l Set front panel controls to FUNCTION 100 SEP SEP Out 2 Connect the transducer output to the CHANNEL A input terminal 3 Adjust the ATTEN and TRIGGER LEVEL controls to ensure proper triggering NOTE The output voltage from magnetic transducers will vary with speed of revolution The ATTEN and TRIGGER LEVEL control settings may in such cases need to be changed Alternately a photo electric transducer will provide an output level not dependent on frequency 2 110 Frequency Measurements FREQ C 2 111 Frequency measurements can be made above the range of FREQ measurements using this optional function Direct frequency measurements can be made in the range 50 520 MHz with the 310 Option instal
79. r reducing the effect of one count error The following considerations may be useful l By selecting a longer gate time the percentage error caused by the 1 count gate uncertainty is decreased 2 Theaccuracy of functions affected by 1 count A depends upon the frequency of the input signal As frequency increases accuracy increases As frequency decreases accuracy decreases The sloped line 1 count A in Figure 2 13 illustrates this concept With a higher frequency input more counts will be made per gate time and 1 count error will become less significant The percentage error is thereby reduced 3 The accuracy of functions affected by the 1 count clock depends upon the frequency of the clock used Since the clocks are all based on the precision time base accuracy is a constant for each clock and is completely independent of the frequency of the input signal The straight line 1 count clock that intersects the count A line at clock frequency in Figure 2 13 illustrates this function Any noise or distortion on the input signal will degrade the accuracy level 4 FREQ A and PER A functions can be used selectively to maximize accuracy of frequency measurements over the range of Channel A The relationship between the two measurement functions is shown in Figure 2 13 The following can be drawn by this function comparison a FREQ A provides the best measurement accuracy if the input signal is higher in frequency t
80. s to 4 ns when operating on batteries Totalize A B Range A 0 125 MHz 0 2MHz Count Capacity 0 99999999 Display no decimal point or annunciator Time Interval Holdoff Range 20 Msec 20 msec continuously adjustable Channel A amp B Range 0 125 MHz DC coupled 5 Hz 125 MHz coupled Sensitivity 10 mV rms 0 50 MHz 15 mV rms 50 100 MHz Table 1 2 Specifications cont SIGNAL INPUTS 7261A Channel C Range 50 MHz 520 MHz Option 310 Sensitivity 10 mV rms Impedance 500 2 5 1 VSWR Max Input Voltage 5V rms fused 35 mV rms 100 125 MHz Min Pulse 10 ns and 50 mV peak Linear Operating Range 2 5 to 2 5V Trigger Level Range 1 5V to 1 5V Input Impedance 1 shunted by 55 pf nominal Coupling AC or DC switchable Attenuator X1 X10 X100 Slope or switchable Channel Input separate or common A switchable Filter 3 dB point 100 kHz low pass nominal External Time Base Input Frequency 10 MHz AC coupled Sensitivity 300 mV rms Impedance 1 shunted by 30 pF norminal Max Input Voltage 3V rms Maximum Input Voltage 250V rms 250V rms 100V rms 5V rms 50kHz 1MHz 125 MHz 45 Hz TIME BASES Standard Frequency 10 MHz Aging Rate 5 X 1077 mon Temperature Stability 5 X 10 5 0 40 C Line Voltage 10 1 X107 Battery 1 X 1077 e 112 131 132 10 MHz
81. s with oil from the fingers handle the pcbs by their edges or wear gloves If a pcb does become contaminated refer to the cleaning procedure 4 8 Disassembly 4 9 To disassemble the instrument use the following procedure l Press the power switch STBY and remove the line power cord 2 On the case bottom remove the six securing screws Two of these screws will be found in the middle of the case under the latches To access either middle screw as shown in Figure 4 1 alternately push the two latching rails away from the triangular stop Pull the latch out far eno ugh to reveal the screws 3 The top half of the case may now be separated from the bottom NOTE Do not hold the case bottom while lifting off the case top Damage to the Main PCB could otherwise result 4 2 Figure 4 1 Disassembly Screw Access Alternating between front and back panels pry the case top free of the rest of the instrument In the front press down on the BNC input connectors while gently pulling up on the case top lip In the rear press down on the External Reference BNC connector while pulling up on the top case lip NOTE For most test and calibration procedures stop at this step 4 Remove the single screw at the middle of the Main PCB and separate the case bottom 5 Remove the Signal Conditioner Assemblies A3 and A4 from connectors on the Main PCB and the Front Panel PCB Pry either assembly gently away fr
82. se the following procedure CAUTION Do not use aromatic hydrocarbons or chlorinated solvents for cleaning They will react with plastic materials used in manufacture of the instrument Clean the front panel and case with soft cloth dampened with a mild solution of detergent and water 2 Clean the surface of the PCB using clean dry air at low pressure lt 20 psi If grease is encountered spray with Freon T F Degreaser or anhydrous alcohol and remove grime with clean dry air at low pressure 4 19 STATIC SENSITIVE DEVICES 4 20 CMOS and PMOS devices may be destroyed by electrostatic discharge resulting from improper handling Table 4 2 lists the static sensitive devices contained in the 7261A When working around or handling these devices use the procedures outlined on the yellow Static Awareness sheet located in this manual 4 21 SOLDERING PRECAUTIONS 4 22 The Main and Front Panel PCBs are multilayer boards Irreparable damage may be caused by careless removal or resoldering components The following board repair procedures are recommended by the John Fluke Mfg Inc I Restrict soldering iron tip temperatures to 7007 2 Use a heat regulated soldering iron 3 Use the compressed air driven vacuum type of desoldering tool 4 Do not reheat the same pin or pad until it has been allowed to cool Excessive heat build up can cause board warpage and separation of inner layers as well as loss of p
83. signal transfer to the 7261A 2 52 1 COUNT ERROR 2 53 The one count ambiguity inherent in any gate and counter type of frequency meter results from an out of phase relationship between the input signal and the internal oscillator signal The effect is demonstrated in 2 8 Figure 2 8 During a one second gate time the top 9 5 Hz signal accumulates a count of ten during the same gate time the phase shifted bottom signal accumulates only nine counts The ambiguity amounts to one displayed count FREO A as check input to 9 5 Hz signal Main Gate phase Main Gate Enable Signal 580 FREQAAs input to Main Gate Out of phase i 9 5 Hz SIGNAL Figure 2 8 1 Count Error 2 54 RESOLUTION 2 55 This term defines the value of the smallest displayed unit in a measurement In the 7261A this unit the least significant digit or LSD is defined by each combined setting of the FUNCTION and RESOLUTION controls 2 56 SENSITIVITY 2 57 Sensitivity defines the smallest signal amplitude capable of triggering the instrument This specification corresponds to an rms value of the peak to peak difference between hysteresis levels the hysteresis window Note that the waveform must pass both hysteresis levels before a count is generated from the input circuitry false triggering from noise or distortion on the input signal is thereby minimized 2 58 TIME
84. sition 7 Verify on the UUT that 0 000 MHz is displayed 4 57 CALIBRATION ADJUSTMENTS 4 58 These procedures should be performed whenever the instrument has been repaired or fails to pass the Performance Checks Figure 4 7 Marker Output Waveform 4 15 7261A 4 59 Power Supply Voltage Adjustments 4 60 Use the following procedure to adjust the power supply voltages in the UUT Figure 4 8 shows the location of test point and adjustments 4 16 1 Remove the top instrument case cover Use the disassembly procedure presented earlier in this section 2 Connect the instrument to line power througha Variac set to zero volts 3 Front Panel of the UUT inthe POWER section set the ON STBY switch to the STBY position 4 On the Rear Panel of the UUT set the AC POWER switch to the ON position 5 Usingthe line voltage selection guide presented earlier in this section set 54 and 55 to the proper position to select local line voltage If the instrument is to be used for areas with more than one line voltage set S4 and S5 for the line voltage used most This voltage will be considered local line voltage for the remainder of this procedure 6 Setthe Variac for an output voltage of 120V ac 7 Connect the DVM to the UUT to 1 to or any other common point See Figure 4 8 for aid in locating test points or adjustments 8 Adjust fora DVM display of 5 00 0 05V
85. sub steps a through f for each line voltage that the instrument will be powered on Channel A Trigger Level Adjustment Use the following procedure to adjust the Channel A Trigger Level 1 On the Front panel of the set the controls to the following position FUNCTION FREQ A RESOLUTION 10 kHz ATTEN CH A XI AC DC CH A DC CH A TRIGGER LEVEL CH A PRESET SEP COM SEP sjueunsn py pue 5 158 jo uone2o g p 4 C50 R47 PRESET B TP3 5V R49 PRESET A 000005 SET pa 0 oo ooo oo000000000000 R4 4 TP1 TP2 1921 5V ADJUST 1 2V 5V 12V 7261A 2 Onthe Rear Panel of the UUT set the controls 9 Repeatsteps 7 and 8 until maximum sensitivity to the following positions or a programmed level of 8 mV rms is reached maximum sensitivity must be less than 10 mV rms REF EXT TRIGGER LEVEL CH A AC POWER ON 10 On the Front Panel of the UUT set the Channel A t switch to the position 3 Connect the equipment as shown in Figure 4 9 A 1 Verify that on the UUT 4 Program the LF synthesizer for an output of a The and trigger indicators glow with MHz at a level of 10 mV rms i equal intensity 5 Is the UUT display stable 1 00 MHz b The display is a stable 1 00 MHz YES Go to ste
86. t 7261A 2 64 TRIGGER LEVEL 2 65 The voltage level nominally halfway between upper and lower hysteresis levels is termed the trigger level On the 7261A the ATTEN control reduces the input signal within the dynamic range or the input amplifier Then the TRIGGER LEVEL and slope controls select the trigger level Trigger Level for Channels and B are available as analog voltages on a rear panel terminal 2 66 Controls 2 67 FUNCTION CONTROL 2 68 The FUNCTION slide switch determines the type of measurement that the instrument will make Each change of the switch position generates an internal reset OPERATING DIRECTIONS provide descriptions operating limits and specific procedures for each function 2 69 RESOLUTION CONTROL 2 70 The front panel RESOLUTION control selects autoranging or one of six manual ranges Each of these settings is defined by three function related scales The scale used with FREQ A PER A PER AVG A RATIO A B CHK or TI A B is discussed with the appropriate OPERATING DIRECTIONS in this section 2 71 The RESOLUTION control will have no effect in two functions For totalizing measurements TOT A B resolution is set at the least significant integer On the counts per minute mode CPM 100 resolution is determined by dividing the number of counts per revolution by the number of minutes If a 100 count per revolution input is used resolution will translate directly to one RPM 2 72 Wh
87. test equipment is called for Use the RF voltmeter to set up the programmed level of the HF synthesizer 4 25 Initial Instrument Setup 4 26 Unless otherwise specified it will be understood that the following controls will be in the indicated position before beginning any Performance Check Onthe Rear Panel of the UUT set the controls to the following position ON OFF ON INT EXT INT CONT TRIG CONT Line cord connected to line power 2 Onthe Front Panel of the UUT set the controls to the following position ON STBY ON BAT LINE LINE TI HOLDOFF OFF RESOLUTION AUTO 5 SEP FILTER IN OUT OUT TRIGGER LEVEL A amp B PRESET ATTN A amp B XI AC DC A amp B AC A amp B 4 27 Display Check 4 28 Use the following procedure to check the function of all segments of the eight display digits decimal point postioning all annunciators except OVEN and the RESET control 1 On the Front Panel of the UUT a Set the ON STBY switch to the ON position 7261A b Inthe Channel B signal conditioner section 1 Set the Trigger Level control maximum clockwise position 2 Set the control to the position c Set the RESOLUTION control to the 10 kHz position d Set the FUNCTION control to the CHK position 2 Verify that a 10 00 MHz is displayed b GATE annunciator is flashing approximate ly five times per second 3 Depress and hold the RESET pushbutton 4 Verify that 88888
88. the Front Panel of the UUT Verify that all zeros is displayed f Rotate the Channel B TRIGGER LEVEL control maximum clockwise 8 Verify that a count begins to accumulate in the display and the GATE annunicator is lit 7261A Table 4 13 Fault Isolation Guide Interpretation 0 PER A R TROUBLESHOOT CIRCUITRY BELOW co 100 MHz Mult 10 F 100 MHz control Control Logi Ircultry TIA Ci ey try ircu sm Control C 4 U2 048 1 6 of correct val 15 Time Base U26 4 25 7261A 4 85 Troubleshooting Techniques 4 86 There are several techniques that can be used to isolate a fault in the instrument The techniques are discussed below by type 4 87 CURRENT TRACING 4 88 Current Tracer probes such as the HP 547A are usually the best way to locate shorts in the instrument If the short is so bad that the power supply is loaded down the Performance Checks or Fault Isolation Guide may not provide any help in isolating the faulty circuit Starting at the output of the loaded power supply logically move the Current Tracer through the instrument until the short is found Sometimes the short is minor and is located between two or more logic gates as shown in Figure 4 12 The Current Tracer will glow brightest at the termi
89. the ON position the fault does not lie in the power supply proceed to item 6 Part B a Problems in the power supply can be tracked down using conventional methods but remember that 1 The 5V supply tracks the 5V supply so if the 5 supply has a problem it will affect both power suppplies 2 The 5V supply tracks the 12V supply so if the 12V supply has a problem it will affect the 12V 5V and 5V supplies 3 The 12V supply after the rectifier is independent of the other supplies Problem in all four power supplies indicates that the fault lies in the primary circuit transformer or CRI b Shorts that load down a particular power supply can best be isolated by disconnecting the pcbs that plug into the Main PCB one at a time Remember to turn the instrument off before disconnecting or connecting cables plugs or pcbs If the short cannot be located by unplugging pcbs use the current probe tracing procedure described in Troubleshooting Techniques Start at the output of the power supply that is loaded down This is the logical point and also gives the approximate amount of current drawn by the short 4 83 IMPROPER OPERATION PROCEDURE 4 84 The Improper Operation Procedure is a simple dynamic test of the instrument The procedure provides a speedy overall view that is interpreted by Table 4 13 to guide the technician to the most likely circuits Additional information can be gained to aid trou
90. the time base section for the particular time base 3 Trigger error is the measurement error caused by noise on the input signal tiggering the input ampli fier too early or too late If is calculated as follows Trigger Error 2X peak noise voltage us signal slew rate at trig point Vj us 4 The counter will ignore time intervals occuring during the dead time 2 1 INTRODUCTION 2 2 Installation and operation of the 7261A Universal Counter Timer are explained in this section Read this information before attempting to operate the unit Should any difficulties arise contact your nearest Fluke sales Representative listed in Section 7 or the John Fluke Mfg Co Inc P O Box 43210 Mountlake Terrace WA 98043 Telephone 206 774 221 1 2 3 SHIPPING INFORMATION 2 4 The 7261A is packaged and shipped in a foam packed container An Instruction Manual and any accessories ordered will be included with the instrument Upon receipt of the instrument make a thorough inspection for proper contents and possible shipping damage Special instructions for inspection and claims are included with the shipping container If reshipment is necessary use the original container If the original container is not available a new container can be obtained from the John Fluke Mfg Co Inc Please reference the instrument model number when requesting a new shipping container 2 5 INSTALLATION 2 6 Input Power 2 7 The 7261A can
91. venting static discharge damage In addition care should be taken when soldering as hidden damage to the instrument can be caused as well as obvious damage 4 76 The instrument uses three basic types of logic ECL TTL and CMOS The circuits handling the high frequency signals employ Emitter Coupled Logic ECL because of its faster switching capability Positive ECL is used to reduce interfacing problems On the schematics in Section 8 ECL logic terms are usually identified by a prime symbol immediately following the term Circuitry using CMOS IC s work at CMOS logic levels The remainder of the instrument employs Transistor Transistor Logic TTL Table 4 12 lists the high and low logic levels for each of the three types of logic used in the instrument Table 4 12 Instrument Logic Levels LOGIC 22 5V gt 4 1V gt 3 5V gt 70 of supply 4 77 Visual Inspection 4 78 Visual inspection can sometimes quickly locate instrument faults saving the technician the time usually consumed in extensive troubleshooting Use the Disassembly procedure presented earlier in this section to remove the top case cover Carefully inspect the instrument inside and out Check for loose or broken wires and component leads improperly seated plug in assemblies physically damaged component discoloration due to arcing etc Shorted IC s usually have a small bubble or discoloration at the center of the package Shorted capa
92. z 2 MHz PERA Measures the period of signals from 0 2 MHz applied to Channel A PER AVG A Measures the period of a predetermined number of cycles of the signal applied to Channel A and displays the average value of these periods The range in frequency of the signal is 0 2 MHz TI A B Measures the interval in time between the arrival of a signal applied to Channel A and the arrival of a signal applied to Channel B Dead time time between one STOP pulse and the next START pulse must be greater than 200 ns TIA A B Measures a predetermined number of Time Intervals as defined above and displays the average value of these periods Minimum dead time is 200 ns TOT A B Counts the total number of events occuring on Channel A that are gated by events occuring on Channel B CHK This is an internal self test of the instrument It provides a confid ence check of all but the input circuits and time base The fre quency displayed should be 10 MHz A seven position slide switch that determines the resolution range of the display Generally the further right the Resolution Switch position the longer the instru ment s Gate Time Changing the position of the Resolution Switch automatically resets the instrument Except for the AUTO position the position of the Resol ution Switch determines the position of the decimal point in the display for all instrument functions except CPM X100A resolution permanently set at 100 Counts Per Minute 1

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