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Keithley Model 238 High-Current Source-Measure Unit

1. Display Circuitry Checks 9 SECTION 4 Principles of Operation Table 4 1 Volts Range Relays cineca das xa aka E aqu EE 4 8 SECTION 1 Performance Verification 1 1 INTRODUCTION The procedures outlined in this section may be used to verify that the instrument is operating within the limits stated in the specifications at the front of this manual Performance verification may be performed when the in strument is first received to ensure that no damage or misadjustment has occurred during shipment Verifica tion may also be performed whenever there is question of instrument accuracy or following calibration if desired NOTE If the instrument is still under warranty less than 1 year from the date of shipment and its performance falls outside the specified range contact your Keithley representative or the factory to determine the correct course of ac tion Before attempting any of the following procedures make sure you are familiar with the controls and operation of the Model 238 Refer to the Model 238 Operator s Manual for complete information WARNING The procedures in this section are for use only by qualified service personnel Do not perform these procedures unless qualified to do so Many of these steps in this section may expose you to potentially lethal volt ages that could result in personal injury or death if normal safet
2. Allowable Reading Calculations for Low Current Measure Verification luA to l0mA Low Current Measure Verification tol0mA Allowable Reading Calculations for Low Current Source Verification to l mA Low Current Source Verification to l mA SECTION 2 Calibration Table 2 1 Table 2 2 Table 2 3 Table 2 4 Required Test Specifications for Alternate Equipment Model 263 I Source Characterization Calibration Error Messages SECTION 3 Maintenance Table 3 1 Table 3 2 Table 3 3 Table 3 4 Table 3 5 Table 3 6 Table 3 7 Table 3 8 Table 3 9 Table 3 10 Line Fuse Selection J uy s E e Ed Fra Recommended Troubleshooting Equipment Power Supply Cheeks Analog Switching Current Ranging Analog Switching Current Ranging Analog Switching Feedback Analog Switching Sensing ee Analog Switching A D Multiplexing Digital Circuitry Checks
3. U7 Calibration Status Word SECTION 3 Maintenance Figure 3 1 Figure 3 2 Figure 3 3 Figure 3 4 Figure 3 5 Line Voltage Switch and Line Fuse Digital dau ERAS Se CONS Gees Board pads Analog Board Shields Removed Model 238 Exploded View SECTION 4 Principles of Operation Figure 4 1 Figure 4 2 Figure 4 3 Figure 4 4 Figure 4 5 Overall Block Diagram Simplified Schematic of V I Control and Readback Output Module Simplified Schematic Diagram V I Feedback Simplified Schematic Damping Relay Contact Bounce save cuca etek ant nies List of Tables SECTION 1 Performance Verification Table 1 1 Table 1 2 Table 1 3 Table 1 4 Table 1 5 Table 1 6 Table 1 7 Table 1 8 Table 1 9 Required Test Equipment Specifications for Alternate Equipment Model 263 I Source Characterization Voltage Source Verification Voltage Measure Verification
4. 9 Send the following command to source on the 15V range C10X From the display of the Model 193A record the volt age reading VMsR 20 21 23 24 25 26 27 28 29 30 31 32 Send the measured voltage reading Vasr over the bus with the C11 command as follows to calibrate offset for the 15V source and measurement range C11 VmsrX Send the following command to source 14V on the 15V range C12X From the display of the Model 193A record the volt age reading Vmsr Send the measured voltage reading over the bus with the C13 command as follows to calibrate gain for the 15V source and measurement range 13 Send the following command to source 0V on the 15V range C14X From the display of the Model 193A record the volt age reading Vwsg Send the measured voltage reading over the bus with the C15 command as follows to calibrate offset for the 15V source and measurement range C15 VmsrX Send the following command to source 14V on the 15V range C16X From the display of the Model 193A record the volt age reading VMsR Vmsr Send the measured voltage reading Vmsr over the bus with the C17 command as follows to calibrate gain for the 15V source and measurement range C17 VMSRX Send the following command to source 0V on the 110V range C18
5. WARNING Hazardous voltage may be present on terminals KeyCheck 1 OUTPUT 16 N1X Put 238 in operate 1 OUTPUT 16 COX Put 238 in cal mode Performing voltage calibration Press ESC to abort procedure and restart program 2 TO 25 Loop for all cal points 5 IF INS CHR 27 THEN PRINT 1 CLEAR GOTO SelCal 1 OUTPUT 16 C I X Send cal command to 238 Delay Wait for settling 1 ENTER 10 Get reading from 193A 2 Vmsr Input 193A reading 1 Increment C command value 1 OUTPUT 16 C I Vmsr X Send cal value to 238 Loop back for next cal point 1 OUTPUT 16 C59X t Exit calibration procedure 1 OUTPUT 16 NOX Put 238 in standby 1 OUTPUT 10 ZORSX Disable 193A zero mode 1000V range XO KAKA KKK KIRK KAR KO OO CO KOC KKK IK KKK OK KC KKK IKK ROKK OK c o X X X0 Xo oe AKK Xo X X XO X X KKK x INA 10MA CURRENT RANGE CALIBRATION ROUTINES KR KKK KKK KK KK KK RRR RII III IKI K K K K e k e KI OR II IK OK k ke K aK CalLow CLS PRINT PRINT PRINT PRINT GOSUB ln 1 Current Range Calibration Make sure 263 and 238 are properly connected See Service Manual for complete details KeyCheck PRINT 1 OUTPUT 08 F1ROW1X 263 amps auto range guard on INPUT 263 CHARACTERIZATION PARAMETERS CharCheck INPUT Enter 263 characterization parameters y n INS INS LEFTSCINS 1 IF INS OR INS n THEN GOTO NoCha
6. spe Looking for more information A Artisan Scientific Visit us on the web at http www artisan scientific com for more information QUALITY INSTRUMENTATION GUARANTEED Price Quotations Drivers Technical Specifications Manuals and Documentation Artisan Scientific is Your Source for Quality New and Certified Used Pre owned Equipment Tens of Thousands of In Stock Items Fast Shipping and Delivery Equipment Demos Hundreds of Manufacturers Supported Leasing Monthly Rentals Consignment Service Center Repairs InstraView Remote Inspection Experienced Engineers and Technicians on staff in our Remotely inspect equipment before purchasing with our State of the art Full Service In House Service Center Facility Innovative InstraView website at http www instraview com We buy used equipment We also offer credit for Buy Backs and Trade Ins Sell your excess underutilized and idle used equipment Contact one of our Customer Service Representatives todayl Talk to live person 888 88 SOURCE 888 887 6872 Contact us by email sales artisan scientific com Visit our website http www artisan scientific com Model 238 High Current Source Measure Unit Service Manual Contains Servicing Information KEITHLEY WARRANTY Keithley Instruments Inc warrants this product to be free from defects in material and workmanship for a period of year from date of shipment Keithley Instruments Inc war
7. Chassis connections must only be used as shield connections for measuring circuits NOT as safety earth ground connections If you are using a test fixture keep the lid closed while power is ap plied to the device under test Safe operation requires the use of a lid interlock Ifa screw is present connect it to safety earth ground using the wire recommended in the user documentation The symbol on an instrument indicates that the user should re fer to the operating instructions located in the manual The symbol an instrument shows that it can source or mea sure 1000 volts or more including the combined effect of normal and common mode voltages Use standard safety precautions to avoid personal contact with these voltages The WARNING heading in a manual explains dangers that might result in personal injury or death Always read the associated infor mation very carefully before performing the indicated procedure The CAUTION heading in a manual explains hazards that could damage the instrument Such damage may invalidate the warranty Instrumentation and accessories shall not be connected to humans Before performing any maintenance disconnect the line cord and all test cables To maintain protection from electric shock and fire replacement components in mains circuits including the power transformer test leads and input jacks must be purchased from Keithley Instru ments Standard fuses with applicab
8. Figure 1 4 Setup for Voltage Measure Ranges Verification 1 9 SECTION 1 Performance Verification 1 5 5 Remote Sense Verification 1 While in standby place the Model 238 in remote sense and set it to source 10V witha compliance limit of 10mA on the 10mA measurement range Place the Set up the equipment as shown in Figure 1 5 The 1kQ re Model 238 in standby sistor R 263 1k is installed in the Kelvin test socket Per 2 Set the Model 193A DMM to and select the 20V form the following steps to verify remote sense accuracy range WARNING When a Model 238 is programmed for re mote sensing hazardous voltage may be pre sent on the SENSE and OUTPUT terminals when the unit is in operate regardless of the programmed voltage or current To avoid a possible shock hazard always turn off all power before connecting or disconnecting cables to the Source Measure Unit or the as sociated test fixture Warning Connect 3094 COMPOMET TEST to Safety Earth Ground 8006 Test Fixture A Connections 238 OUTPUTHI 9 Source V SENSE 6 SENSE LO OUTPUT LO Q B Schematic Equivalent Setup for Remote Sense Verification 1 10 3 Temporarily disconnect the banana cable from VOLTS HI of the DMM at the rear panel of the test fixture BINDING POST 1 and connect it to VOLTS LO of the DMM This shorts the input of the Model 193A DMM On the Model 193A DMM enable zero to cancel any o
9. Model 263 Amps function 0 90000HA on 24A range Guard enabled and output in standby Model 193A Ohms function on the 200kQ range Zero the Model 193A as follows A Atthe SENSE 1 HI terminal of the test socket disconnect the jumper whose other end is con nected to BINDING POST 2 on the Signal Panel B Connect that jumper to the SENSE 2 LO termi nalofthe test socket This shorts the Ohms Sense input of the Model 193A at the test socket C On the Model 193A enable zero to cancel test lead resistance Source HI Source LO p SECTION 2 Calibration Banana Plug Cables 5 lt lt lt Male to 3 19 Female Triax Adapter Model 263 Source ioe Volts 193A DMM R and V Sense LO D Relocate the jumper back to the SENSE 1 termi nal of the test socket Make sure the connections at the Component Test Module are correct as shown in Figure 2 2 In the space provided below use a pencil to record the actual value of the 100kQ resistor from the dis play of the Model 193A kQ Set the Model 193A to the DCV function and the 200mV range and disable zero To cancel any offset zero the Model 193A by short ing its input VOLTS HI to LO and enabling zero 2 3 SECTION 2 Calibration 7 Remove the short from the input of the Model 193A and place the Model 263 in operate to source 0 900001 A to the 100kQ resistor 8 Inthespace below
10. 583 578 537 TABLE 4 MODEL 238 OUTPUT MODULE PARTS LIST CIRCUIT DESIG C10 12 C17 19 C20 C21 30 C22 23 C24 25 C26 28 C27 29 CR18 26 CR19 27 CR20 21 CR7 9 CR8 10 12 17 22 25 K1 P16 23 Q1 2 Q18 23 Q19 25 Q21 24 Q27 Q34 40 Q35 Q36 Q37 Q38 Q39 44 45 47 Q41 Q42 Q43 46 Q7 8 Q9 20 22 26 28 R1 2 818 19 R20 34 36 39 R21 23 28 37 38 47 50 55 60 63 65 R24 26 R25 27 R29 30 R31 32 R45 46 R48 51 R49 52 R53 54 R56 58 DESCRIPTION CAP 3300PF 5 500V DIPPED MICA CAP 01UF 10 1000V CERAMIC CAP 01UF 2026 50V CERAMIC CAP 1UF 20 50V CERAMIC CAP 1800PF 1 500V MICA CAP 3300PF 1026 100V CERMANIC CAP 2200PF 1 500V MICA CAP 6800PF 1 100V MICA DIODE SWITCHING IN4149 DO 35 DIODE 1N5404 DIODE SCHOTTKY IN5711 DIODE SILICON IN4148 DO 35 DIODE SILICON 1N4937 RELAY HIGH SENSITIVITY 18W K HOUSING CONNECTOR TRANS N CHAN MOSPOW FET 2N7000 TO 92 TRANS N CHANNEL FET IRF630 TRANS PNP POWER MJE350 TRANS NPN SILICON MJE340 TRANS PNP SILICON 2N3906 TO 92 TRANS P FIELD EFFECT MTP20P06 TRANS PNP POWER TRANS TIP106 TO 220 TRANS P CHANNEL DMOSFET VP0104N3 TO 92 TRANS PNP POWER TRANS MJE250 TO 220 TRANS NPN POWER TRANS TIP101 TO 220 TRANS NPN COMP SILICON AMP 2N5089 TRANS N CHANNEL DMOSFET VNO101NS TO 92 TRANS NPN POWER TRANS MJE240 TO 220 TRANS N FIELD 20 08 TRANS P CHANNEL 200V FET IRF9630 TRANS NPN SILICON 2N3904 0 92 RE
11. Fax 0183 630821 SWITZERLAND Keithley Instruments SA Kriesbachstrasse 4 8600 D bendorf 01 821 94 44 Fax 01 820 30 81 TAIWAN Keithley Instruments Taiwan Fl 85 Po Ai Street Hsinchu Taiwan R O C 886 3572 9077 Fax 886 3572 903 10 99 Model 238 High Current Source Measure Unit Service Manual 1990 Keithley Instruments Inc Test Instrument Group All rights reserved Cleveland Ohio U S A Third Printing May 2000 Document Number 238 902 01 Rev C Manual Print History The print history shown below lists the printing dates of all Revisions and Addenda created for this manual The Revision Level letter increases alphabetically as the manual undergoes subsequent updates Addenda which are released between Revisions contain important change information that the user should incorporate immediately into the manual Addenda are numbered sequentially When a new Revision is created all Addenda associated with the previous Revision of the manual are incorporated into the new Revision of the manual Each new Revision includes revised copy of this print history page Revision B Document Number 238 902 01 RN August 1992 Revision C Document Number 238 902 01 et May 2000 All Keithley product names are trademarks or registered trademarks of Keithley Instruments Inc Other brand and product names are trademarks or registered trademarks of their respective holders The following safety precautions should be obser
12. Ical J X END IF GOSUB Delay Settling time J J Increment array index PRINT 1 OUTPUT 08 00 Put 263 in standby NEXT I Loop back for next cal point INA LOMA SOURCE CALIBRATION PRINT 1 OUTPUT 08 F2R1X 263 200mV range PRINT 1 OUTPUT 08 0 263 OnV output PRINT 1 OUTPUT 08 01X Put 263 in operate GOSUB Delay PRINT 1 TIME OUT 240 Select 4 minute bus time out PRINT PRINT Performing lnA lOmA source calibration PRINT Please wait approximately 3 4 minutes for completion PRINT 1 OUTPUT 16 C58X Cal 238 1 10 source PRINT 1 OUTPUT 16 C59X Exit 238 cal mode PRINT 1 OUTPUT 16 NOX Put 238 in standby PRINT 1 OUTPUT 08 00X Put 263 in standby t PRINT 1 TIME OUT 30 Restore 30 sec bus time out RETURN KeyCheck Check keyboard input routine PRINT Press SPACE or ENTER key to continue ESC to end program PRINT Lpl INS INKEYS IF INS lt gt THEN GOTO Lpl Lp3 INS INKEYS IF INS THEN GOTO Lp3 IF INS CHR 27 THEN Check for ESC CLS OutMsg PRINT Program terminated PRINT 1 CLEAR Send DCL PRINT 1 ABORT Send PRINT 1 LOCAL Restore local operation CLOSE 1 CLOSE 2 END END IF IF INS lt gt CHR 32 AND INS lt gt CHRS 13 THEN BEEP GOTO RETURN t Delay Delay subroutine t TIMER Lp2 IF TIMER t lt Dly THEN GOTO Lp2 RETURN ErrCheck Error check su
13. cillator Y1 is an 8MHz canned crystal oscillator I O con troller peripherals include a 64K X 8 ROM U31 which contains the program memory a 32K X 8 static CMOS RAM 1 30 which is battery backed up via U29 and the battery BT1 Calibration constants are stored in non volatile memory U33 A versatile interface adapter U28 provides peripheral interface to the 6809 microprocessor It is primarily used to interface with the display and keyboard It is also used to interface TRIG GER OUT and TRIGGER IN as well as monitor the test SECTION 4 Principles of Operation fixture lid detect interface A 9914 IEEE 488 standard in terface U27 is combined with two transceivers U34 and U35 to provide the interface function All of these pe ripheral chips are interfaced to the 6809 via a program mable logic device U26 PAL 16L8 A NOR gate package U32 is used to provide protection for calibration constants stored in non volatile memory U33 during power up and power down A power up reset control circuit U36 guarantees a de layed reset after power up and a prompt reset on power down by sensing power supply threshold 4 4 2 Source Measure Controller The schematic diagram for the source measure control ler is provided on page 2 of drawing 238 106 This controller system also uses a 68B09 microprocessor U15 As with the I O controller see previous para graph it derives its 2MHz operating frequency from the
14. 1 0000 nA 100 fA 03 450 100fA 10 fA 03 100 10 000 1 03 2pA 100 fA 03 1pA 310000 nA 10 0 21 20 10pA 1 021 1 0000 100 pA 0 05 200 100 10 0 04 60 pA 410 000 pA 0 05 2 1nA 100pA 0 035 700 pA 100 00 4A 10nA 0 05 20nA 10nA 1nA 0 035 1 0000 100 nA 0 05 200nA 100nA 10 0 035 60nA 10 000mA 3 00594 24A 100nA 0 038 600 nA 100 00mA 10 01 204A 104A 1pA 01 10000 100 0 12 700 100hA 10 012 754300 pA 1Specifications apply for 5 digit resolution For 4 digit resolution all offset terms are 200ppm of range Offset specification applies for 23 C 1 C with suppression Temperature coefficient 50fA C COMPLIANCE Bipolar voltage limit set with single value Maximum 110V 15V on the 1A range Minimum 1 of selected current range Accuracy Step Size Same as voltage source NOISE p p of range 0 1 10Hz lt 3ppm lt 20ppm on 1nA 10nA and 1A ranges OVERSHOOT lt 0 01 typical 10mA step R 10kQ SETTLING TIME lt 500 to 0 01 10mA step 10kQ OUTPUT R C gt 10 Q paralleled by 20pF on 1nA range 488 BUS IMPLEMENTATION MULTILINE COMMANDS DCL LLO SDC GET GTL UNT UNL SPE SPD UNILINE COMMANDS IFC REN EOI SRQ ATN INTERFACE FUNCTIONS SH1 AH1 T6 TEO L4 LEO SR1 R
15. 1 5 8 100mA and 1A Measure Ranges Verification 1 5 9 100mA and 1A Source Ranges Verification SECTION 2 Calibration 2 1 INTRODUCTION yew E 2 2 RECOMMENDED CALIBRATION EQUIPMENT 2 3 ENVIRONMENTAL CONDITIONS 2 4 WARM UP PERIOD 2 aha x aae de 2 5 CALLOCK p cc 2 6 CALIBRATION PROCEDURES 2 6 1 Equipment Characterization 224 Sek e Ero 2 6 2 VoltageCalibrati n uiua ad rocca Sed acd 2 6 3 100mA and 1A Ranges 2 6 4 Low Current Ranges Calibration 1 10mA 24 CALIBRATION ERRORS 2 8 CALIBRATION PROGRAM SECTION 3 Maintenance 3 1 INTRODUCTION a m xx ER e wa ques eR a VOR E RUE 3 2 LINE FUSE REPLACEMENT 3 3 FAN FILTER 3 4 BATTERY REPLACEMENT 3 5 HANDLING AND CLEANING PRECAUTIONS 3 6 DISASSEMBL
16. 4 After displaying the U1 error status word send the U7 command and address the Model 238 to talk 5 Display the character string U7 Calibration Status Since calibration error messages are briefly displayed by Word on the computer CRT and refer to Figure 2 7 theModel238 they can be easily overlooked For this rea to determine which calibration step failed This son itis strongly recommended that calibration errors be status word also provides the status of the CAL detected and displayed by the calibration program The LOCK switch Table 2 4 Calibration Error Messages Message Explanation o O Tried to set the instrument to a state that is illegal while in the calibration mode Legal com mands include C calibration N operate standby O output sense and U status From the front panel only SERIE standby and output sense can be set All illegal commands and operations are ignored The Model 238 is in standby The calibration command sent over the bus will not be executed See Note Compliance has occurred during calibration Check test setup connections and instrument settings Common mode calibration error Output of Model 238 is not shorted or unit is defective The cal constant from the previous calibration will be used Invalid calibration value sent to the Model 238 This calibration step is ignored not at tempted Calibration constant from previous calibration will be used Measure offset calibration
17. 8MHz crystal Y1 The peripherals for this 6809 include 32K of ROM U17 32K of static RAM 013 and a versa tile interface adapter U14 which provides interface to the analog circuitry as well as a few other miscellaneous functions Devices U18 U19 and U58 are binary counters that form the core of a software watch dog timer This timer moni tors software execution of both CPUs via lines that are regularly toggled If any line fails to toggle within ap proximately 4msec the entire system will be reset As with the I O controller all the peripheral chips of the source measure controller are decoded and controlled by a programmable logic device U16 PAL 16L8 A D control as well as A D counts accumulation are per formed by the VIA U14 with a prescale counter U21 Inverters U23 provide a software selectable enable for the high voltage converter in the Model 237 only 4 4 3 Communications The schematic diagram for the communications circuitry is located on page 4 of drawing 238 106 Communications are provided by opto couplers that serve as an interface between the source measure con troller and the analog circuitry This particular circuit is fairly unique in that control signals are sent through two optos that are driven 1805 out of phase with one another to provide immunity from false glitching The outputs of the complimentary opto couplers are de coded by programmable logic device U1 PAL 20L10 From U1 th
18. INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS INC HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES SUCH EXCLUDED DAMAGES SHALL INCLUDE BUT ARE NOT LIM ITED TO COSTS OF REMOVAL AND INSTALLATION LOSSES SUSTAINED AS THE RESULT OF INJURY TO ANY PERSON OR DAMAGE TO PROPERTY KEITHLEY Keithley Instruments Inc 28775 Aurora Road Cleveland OH 44139 440 248 0400 Fax 440 248 6168 http www keithley com BELGIUM Keithley Instruments B V Bergensesteenweg 709 B 1600 Sint Pieters Leeuw 02 363 00 40 Fax 02 363 00 64 CHINA Keithley Instruments China Yuan Chen Xin Building Room 705 12 Yumin Road Dewai Madian Beijing 100029 8610 62022886 Fax 8610 62022892 FRANCE Keithley Instruments Sarl 60 3 all e des Garays 91122 Palaiseau C dex 01 64 53 20 20 Fax 01 60 11 77 26 GERMANY Keithley Instruments GmbH Landsberger Strasse 65 D 82110 Germering 089 84 93 07 40 Fax 089 84 93 07 34 GREAT BRITAIN Keithley Instruments Ltd The Minster 58 Portman Road Reading Berkshire RG30 1EA 0118 9 57 56 66 Fax 0118 9 59 64 69 INDIA Keithley Instruments GmbH Flat 2B WILOCRISSA 14 Rest House Crescent Bangalore 560 001 91 80 509 1320 21 Fax 91 80 509 1322 ITALY Keithley Instruments s r l Viale S Gimignano 38 20146 Milano 02 48 30 30 08 Fax 02 48 30 22 74 NETHERLANDS Keithley Instruments B V Postbus 559 4200 AN Gorinchem 0183 635333
19. The controlling function and the programmed polarity or will determine which clamp is on The following ex ample will explain how this occurs Example 1 This example is divided into two parts Part 1 will explain circuit operation with the instrument sourc ing a constant current Part 2 will explain what happens when the source goes into voltage compliance Part 1 Assume that the instrument is sourcing 5mA with a 27V compliance to a 4kQ load Under these condi tions the instrument is not in compliance 5bmA x 4kQ 20V Thus current is the controlling function The I DAC outputs 5V Thus negative voltage appears at the non inverting input of U13 and positive voltage appears at the non inverting input of U17 The V DAC outputs approximately 3V Positive voltage appears at the non inverting input of U15A and negative voltage appears at the non inverting input of U15B Since the instrument is programmed for a positive out put the 10V REF will apply a positive voltage to the common side of the clamps This positive voltage will re verse bias diodes CR11 and CR9B and prevent the CLAMP and V CLAMP from turning on With the front end of the bootstrap amplifier set up as de scribed 5V will be fed back via I FEEDBACK to U17 and U13 The non inverting input of U17 will go to OV 5V 5V 0V forward biasing CR10 As a result the I CLAMP turns on The voltage drop across the load is 20V 5m
20. must be replaced and fastened securely WARNING To ensure continued protection against safety hazards verify that power line ground green wire attached to AC power re ceptacle and fan ground are connected to the rear panel 3 7 SPECIAL HANDLING OF STATIC SENSITIVE DEVICES CMOS devices operate at very high impedance levels for low power consumption As a result any static that builds up on your person or clothing may be sufficient to destroy these devices if they are not handled properly Use the following precautions to avoid damaging them 1 ICs should be transported and handled only in con tainers specially designed to prevent static build up Typically these parts will be received in anti static containers of plastic or foam Keep these devices in their original containers until ready for installation 2 Remove the devices from their protective containers only at a properly grounded workstation Also ground yourself with a suitable wrist strap 3 Handle the devices only by the body do not touch the pins 4 Any printed circuit board into which the device is to be inserted must also be grounded to the bench or ta ble Use only anti static type solder sucker Use only grounded tip solder irons Once the device is installed in the pc board it is nor mally adequately protected and normal handling can resume Non 3 8 TROUBLESHOOTING The troubleshooting information contained in this sec tion is inte
21. 09 10 counts 4 1 2 digit 2pA range 1 6 66 counts Electrometer x A range 1 6 7 counts range 1 6 1 count range 0 25 5 counts 20 0 25 1 count 200nA range 0 25 1 count 2 range 0 15 4 counts 20HA range 0 15 1 count Keithley 8006 Test Fixture Keithley 236 ILC 3 Interlock Cable Fluke 343A DC Voltage Calibrator 10V 100V ranges 0 002 Valhalla 2500E Current Calibrator 100mA 1A ranges 0 025 Keithley R 249 100 100Q Resistor 0 1 20ppm C R 263 1k 1kQ Resistor 0 1 10ppm C R 263 100K 100kQ Resistor 0 1 10ppm 8C Keithley 7078 TRX 3 slot triax cable 3 required Keithley 6172 2 slot male to 3 lug female triax adapter 2 required Pomona Banana plug cable 6 required SECTION 1 Performance Verifi ication Table 1 2 Specifications for Alternate Equipment Instrument Type Required Specifications DMM Same as Keithley 193A see Table 1 1 Source DC Current 0 9nA 9nA 90nA Same as Keithley 263 see Table 1 1 0 9UA 180ppm 904A 170ppm 90mA 230ppm 0 9A 625ppm Measure DC Current 250ppm rdg 500nA 1 5 1 Equipment Characterization In order to verify the 14A 101A 1004A lmA and 10mA source and measure ranges of the Model 238 the 0 9 904A 0 9m and 9mA outputs of the Model 263 are characterized 1 Connect the Model 263 source Model 1934 DMM and
22. 2 of drawing number 238 126 Error Amplifier Main To Output Stage From Feedback Simplified Schematic of V I Control and Readback SECTION 4 Principles of Operation Programming current and voltage sets the output volt age of the two digital to analog DAC circuits Program ming current controls the output of the I DAC 023 and U22 and programming voltage controls the output of the V DAC U25 and U24 Programming current or volt age for zero output will result with a OV output from the respective DAC Programming for a full scale output will result with a 10V output from the respective DAC The output voltage from the I DAC is applied to current clamps through resistor networks Op amp U13 and di ode CR11 form the negative current clamp CLAMP Theoutput from theI DAC is inverted by the x1 amplifier U51B x0 1 for the 1A range The inverted output of U51B is again inverted by U51A Op amp U17 and diode CR10 form the positive current clamp I CLAMP The output from the V DAC is inverted by the x1 ampli fier U12 x0 1 for the 1 1V range and similarly applied to current clamps through resistor networks Op amp U15A and diode CR12 form the positive voltage clamp V CLAMD Theinverted output of U12 is again inverted by 019 Op amp U15B and diode CR9 form the negative voltage clamp V CLAMD During operation only one of the four precision clamps will be on at one time to control the error amplifier 014
23. DESIG C12 16 C124 C127 128 C129 C13 17 19 135 142 150 151 152 160 161 C130 140 141 148 149 C131 C132 C132 C133 C138 139 159 C143 144 C153 154 C157 C158 C170 175 177 214 216 223 C176 215 224 246 C18 C20 C21 C22 120 C23 024 121 C25 C26 122 123 C28 37 C39 C40 41 134 156 162 C43 C50 51 C54 76 98 101 102 115 155 C6 C8 C9 10 CR1 4 7 22 26 28 33 CR34 CR5 6 DESCRIPTION CAP 22PF 2 596 630V POLYPROPYLENE 150 1 500 CAP 68PF 2 5 630V POLYPROPYLENE CAP 1000PF 1096 1000V CERAMIC CAP 15PF 5926 100V CERAMIC CAP 1000PF 1 50V CERMANIC 47000 10 100 10 10 1000 10 10 1000 15 10 200 5 10 1000 CAP 10PF 5 100V CERMANIC CAP 15PF 5 100V CERAMIC CAP 680PF 10 1000V CERAMIC CAP 470PF 5 500V POLYSTYRENE CAP 1UF 20 50V CERAMIC CAP 1UF 20 50V CERAMIC CAP 39PF 2 50V CERMANIC CAP 1500PF 10 1000V CERMANIC CAP 270PF 2 5 630V POLYPROPYLENE CAP 560PF 2 5 630V POLYPROPYLENE CAP 100PF 2 5 630V POLYPROPYLENE CAP 220PF 2 5 630V POLYPROPYLENE CAP 8PF 2 5 630V POLYPROPYLENE CAP 33PF 2 595 630V POLYPROPYLENE CAP 01UF 1096 1000V CERAMIC CAP 3300PF 10 100V CERMANIC CAP 150PF 1 100V CERMANIC CAP 1UF 20 50V CERAMIC CAP 01UF 20 50V CERAMIC CAP 10UF 20 100 25V ALUM ELEC CAP 22PF 10 1000V C
24. KR KKK KR KR KKK KK KKK KKK KKK KKK AK PRINT 1 OUTPUT 16 M32 X 238 SRQ on error PRINT 1 OUTPUT 16 0 Zero bias output level for safety t PRINT 1 OUTPUT 16 00 Local sensing PRINT 1 OUTPUT 16 Enable EOI hold off terminator ox x X X X G Xx X X X Xx XXX X K CHECK CAL LOCK SWITCH STATUS KKK KKK KKK KKK KKK KK KKK KKK KKK PRINT 1 OUTPUT 16 07 Request calibration status word PRINT 1 ENTER 16 Address 238 to talk LINE INPUT 2 515 Input cal status word IF MIDS STS 7 1 i THEN Check cal lock switch status BEEP PRINT Model 238 Cal Lock switch is in locked position PRINT Calibration will be only temporary PRINT 1 GOSUB KeyCheck END IF ENABLE BUS SRQ ERROR TRAPPING K K K k e e e e e e k ie k a ke aK yie aie Ok oe t ON GOSUB ErrCheck Point to error routine PEN ON Enable error detection PRINT 1 ARM SRQ Enable SRQ 1 MAIN PROGRAM LOOP xxxXXXXXXXKXXKXXXXXXKXXKXXXXKXKXXXKXKXXXXXKX t ON cal GOSUB CalVolt CalLow IF cal 3 THEN GOSUB CalVolt GOSUB CalLow END IF PRINT BEEP PRINT 1 CLEAR Send DCL PRINT msg cal calibration procedure completed PRINT E error s detected during calibration PRINT IF 1 THEN PRINT NOTE Calibration is temporary PRINT INPUT Rerun calib
25. Model 8006 test fixture as shown in Figure 1 1 Install the 100kQ resistor in Table 1 1 in the AXIAL KELVIN CLIPS test socket of the test fixture 2 Configure the source and DMM as follows Model 263 Amps function 0 90000LA on 24A range GUARD enabled and output in standby Model 193A Ohms function on the 200kQ range 3 Zero the Model 193A as follows A Atthe SENSE 1 terminal of the test socket disconnect the jumper whose other end is con nected to BINDING POST 2 on the Signal Panel B Connect that jumper to the SENSE 2 LO termi nalofthe test socket This shorts the Ohms Sense input of the Model 193A at the test socket C On the Model 193A enable ZERO to cancel test lead resistance D Relocate the jumper back to the SENSE 1 termi nal of the test socket Make sure the connections at the Component Test Module are correct as shown in Figure 1 1 4 In the space provided below use a pencil to record the actual value of the 100kQ resistor from the dis play of the Model 193A 14 15 16 17 18 19 20 21 Set the Model 193A to the function and the 200mV range and disable zero To cancel any offset zero the Model 193A by short ing its input VOLTS HI to LO and enabling zero Remove the short from the input of the Model 193A and place the Model 263 in operate to source 0 90000L A to the 100kQ resistor Inthe space below use a pencil to recor
26. QUERY rt ee oe RR E Heads Ka E POWER SUPPLY i e y Y IER ERA UR OE ROSTER q uqu e E OR V eR List of Illustrations SECTION 1 Performance Verification Figure 1 1 Figure 1 2 Figure 1 3 Figure 1 4 Figure 1 5 Figure 1 6 Figure 1 7 Figure 1 8 Figure 1 9 Setup for Equipment Setup for Common Mode Verification Setup for Voltage Source Ranges Verification Setup for Voltage Measure Ranges Verification Setup for Remote Sense Verification ae Setup for Low Current Measure Ranges Verification InA to 10mA Setup for Low Current Source Ranges Verification InA to 10 Setup for 100mA and 1A Measure Ranges Verification Setup for 100mA and 1A Source Ranges Verification SECTION 2 Calibration Figure 2 1 Figure 2 2 Figure 2 3 Figure 2 4 Figure 2 5 Figure 2 6 Figure 2 7 Calibration Switch Cal Lock 2er RE RR RR RERO A A n Setup for Equipment Characterization Setup for Volts Calibration 9 d Setup for 100mA and 1A Ranges Calibration Current Ranges Calibration 1nA to 10mA 01 Error Status Word
27. R46 R47 48 116 118 120 122 136 176 195 R5 6 R50 52 53 66 71 105 108 R51 R55 82 R58 67 R7 R76 R77 R78 RES 13 82K 1 1 8W METAL FILM RES 2734K 196 1 8W METAL FILM RES 300K 1 1 8W METAL FILM RES 5 1K 596 1 2W COMPOSITION OR FILM RES 1 8M 5 1 4W COMPOSITION OR FILM RES 137K 1 1 8W METAL FILM RES 1M 0 1 1 4W METAL FILM RES 10K 1096 1 2W COMPOSITION RES 2K 596 1 4 COMPOSITION OR FILM RES 3 9K 526 1 4W COMPOSITION OR FILM RES 51K 5 1 4W COMPOSITION OR FILM RES 56 2K 1 1 8W METAL FILM RES 510 595 1 4W COMPOSITION OR FILM RES 250 196 1 10W WIRE WOUND RES 1M 5 1 4W COMPOSITION OR FILM RESISTOR RES 10M 596 1 AW COMPOSITION OR FILM RES 182K 1 1 8W METAL FILM RES 10K 10 1W COMPOSITION RES 13K 5 1 4W COMPOSITION OR FILM RES 560K 5 1 4W COMPOSITION OR FILM RES 100K 1 1 10W METAL FILM SELECTED RESISTOR SET RES 49 9 195 1 8W COMPOSITION OR RES 10 101K 195 75W WIREWOUND RES 100K 5 1 4W COMPOSITION OR FILM RES 998K 1 1 4W METAL FILM RES 9 88M 0 526 1 2W 1200V METAL OR FILM RES 5 6K 596 1 4W COMPOSITION OR FILM RES 1G 2 1 5W HY MEG RES 100M 1 1 5W HY MEG RES 10K 1 1 8W METAL FILM RES 90K 1 1 8W METAL FILM RES 10K 1 1 8W METAL FILM RES 15K 5 1 4W COMPOSITION OR FILM RES 10K 5 1 4W COMPOSITION OR FILM RES 1K 5 1 4W COMPOSITION OR FILM RES 20K 5 1 4W COMPOSITION OR FILM RES 243K 5 1 4W COMPOSITION OR RES 150 5 1 4W COMPOSITION OR FILM RES 1 1M 5 1 4W COMP
28. When the source is programmed for a negative output Q19 becomes forward biased resulting with a negative voltage present on the output Transistor Q21 is reverse biased isolating the output from the positive supply Bias for the two power transistors are provided by the 30VF supplies and two 15V zener diodes VR10 and VR9 This bias circuit is referenced to floating common in order to maintain the bases of the transistors at a volt age that is higher than the output so that they can be for ward biased Bias control is performed by the output of the error amplifier MAIN drive The polarity and mag nitude of MAIN determines which transistor is forward biased and the amount of bias current that in turn deter mines the magnitude of the output voltage For example as a positive MAIN becomes more positive more bias current is delivered to the base of Q21 resulting in a higher output voltage From Control o Figure 4 3 1A Current Range When the 1A range is selected relay K1 and switches O41 and Q36 are closed The drive for the 1A stage is provided by the 1nA 100mA stage For low output currents 0 to 20mA the InA 100mA stage is used As the current is in creased the transistors in the 1A output stage start to turn to provide output current up to 1A To obtain the full voltage swing on the output transistors Q43 and Q40 are driven by 6 44 zeners 1 and VR2 4 2 3 Feedback A simplified schematic diagram
29. ZERO TEST The instrument can be placed in the A D test mode This message indicates that the A D converter is which allows the A D multiplexer U1 to be stopped in locked in the zero phase any one of its A D phases This allows switching states to 5 The instrument can be placed in any of the other be checked and signal tracing to the A D input see A D A D phases A D REF A D VOLTS and A D Multiplexing in paragraph 3 8 5 AMPS with the use of the SELECT buttons 6 To exit from the A D test mode press ENTER 7 To return the instrument to the normal source 1 Tum off the Model 238 measure display state press MENU 2 While holding in the MENU button turn on the Note The A D test will remain on the MENU until Model 238 Continue to hold in the MENU button power is cycled until the MENU indicator turns on SECTION 3 Maintenance Table 3 3 Line voltage switch Line fuse Line Power 3 8 3 Power Supply Checks Table 3 3 shows the various checks that can be made to the power supplies of the Model 238 In addition to the normal voltage checks it is a good idea to check the vari ous supplies with an oscilloscope for signs of noise or os cillations 3 8 4 Analog Control Lines Control lines managed by the source measure control ler are used to drive the various relays switching FETs and analog switches associated with analog circuitry op eration That is an appropr
30. any offset zero the Model 193A by short ing its input VOLTS HI to LO and enabling zero Remove the short from the input of the Model 193A and set the Model 263 to source 9 0000mA on the 20mA range and enable operate Record the voltage measurement from the Model 193A and calculate the current 0 Vion Toma mA Rion Isma is the characterized current for the 20mA range of the Model 263 It is used to check the 10mA meas urement range of the Model 238 Using a pencil re cord the calculated value of Isma in Entry 5 of Table 1 3 Place the Model 263 in standby Table 1 3 Model 263 I Source Characterization Programmed my Tux Value 0 900001A 9 0000 90 000HA 0 90000mA 9 0000mA Characterized I Source Value I Source Value Limits 0 9UA 450 4 3nA 902A 45nA 0 9mA 430nA 9mA 5 4 characterized I source values should be within the listed limits These limits are based on 90 day specifications of the Models 263 and 193A A characterized value that does not fall within these limits indicates a calculation error or that the Model 263 and or Model 193A is out of specification Rear 9 7078 TRX Cable Warning Connect to Safety Earth Ground Signal Component Test Model 8006 Test Fixture A Connections OUTPUT Source Hi 263 Source COMMON Source I Source LO B Schematic Equivalent Figure 1 1 Setup for Eq
31. error Calibration is attempted using a value that is not within ac ceptable limits The transmitted value is ignored and a default cal constant value is used in stead Possible problems include incorrect cal constant value defective calibration equip ment or connections or defective Model 238 Measure gain calibration error Calibration is using a value that is not within ac ceptable limits The transmitted value is ignored and a default cal constant value is used in stead Possible problems include incorrect cal constant value defective calibration equip ment or connections or defective Model 238 IN STBY CAL COMPLI CAL MODE ERR CAL VALUE ERR CAL ADC ZERO CAL ADC GAIN CAL SRC ZERO Source offset calibration error Calibration is attempted using a value that is not within accept able limits The transmitted value is ignored and a default cal constant value is used instead Possible problems include incorrect cal constant value defective calibration equipment or connections or defective Model 238 Source gain calibration error Calibration is attempted using a value that is not within accept able limits The transmitted value is ignored and a default cal constant value is used instead Possible problems include incorrect cal constant value defective calibration equipment or connections or defective Model 238 Note During the
32. use a pencil to record the voltage drop across the resistor from the display of the Model 193A Vika mV 9 Calculate to 5 1 2 digits the current through the 100kQ resistor as follows Viooko looiA Iosua is the characterized current for the 24A range of the Model 263 It is used to calibrate the 14A range of the Model 238 Using a pencil record the calculated value of Ios in Entry 1 of Table 2 3 10 Place the Model 263 in standby 11 Set the Model 193A to the 2V range 12 Set the Model 263 to source 9 0000LA on the 201A range and enable operate 13 As performed in steps 8 and 9 measure the voltage across the 100kQ resistor and calculate the current Vioo Topa is the characterized current for the 20 range of the Model 263 It is used to calibrate the range of the Model 238 Using a pencil record the calcu lated value of in Entry 2 of Table 2 3 14 Place the Model 263 in standby 15 In the test fixture remove the 100kQ resistor and in stall the 1 resistor R 263 1k 16 On the Model 193A select the Ohms function 2kQ range and disable zero 17 Repeat step 3 to zero the Model 193A 18 Measure and record the value of the 1kQ resistor 19 Set the Model 193A to DCV and the 200mV range and disable zero 20 To cancel any offset zero the Model 193A by short ing its input VOLTS HI to LO and ena
33. 00mA 9 4uA 9 0000mA 9 44 calculated allowable readings should be within listed typical limits These limits are based on the 90 day specifications of the Model 263 and 193A A calculated allowable reading that does not fall within these limits indicates a calculation error or that the Model 263 and or Model 193A is out of specification 1 11 SECTION 1 Performance Verification 6172 2 Slot to 3 Lug Female Triax adapter 238 Measure 1 Figure 1 6 263 Source Source l Note 263 GUARD enabled Setup for Low Current Measure Ranges Verification 1 to 10 263 Range 7078 TRX Cable Table 1 7 Low Current Measure Verification 1nA to 10mA 263 Output Standby Standby Standby Standby Standby Standby Standby Standby 0 90000nA 0 90000nA 9 0000 9 0000 90 000nA 90 000nA 0 900004A 0 900004 A 49 00004A 9 00004 A 90 000u4 90 0004 A 0 90000mA 0 90000mA 9 0000 9 0000mA 238 Compliance Limit amp Measure Allowable Readings 18 C to 28 C 0 00010nA 00 0010nA 000 006nA 0 000064 A 00 0007u A 000 0064 0 00006mA 00 0006mA 0 89720nA 0 89720 8 9720 8 9720 89 805 89 805 0 00010nA 00 0010nA 000 006nA 0 000064 A 00 0007u A 000 006 A 0 00006mA 00 0006mA 0 90280nA 0 90280nA 9 0280nA 9 0280nA 90 195nA 90 195 238 set to sou
34. 1 range From the display of the Model 193A record the cur rent Lisa Lissa Calculate the actual current Losa using the follow ing calculation Losa 0 9 Lisaa Send the calculated reading Los4 over the bus with the C33 command as follows to calibrate gain for the 1A source and measure range C33 LosAX Send the following command over the bus to exit calibration Note Check that the CAL LOCK switch is in the de sired position in for permanent calibration or out for temporary calibration C59X If the switch is in the out position the message TEMPORARY CAL will be briefly displayed to in dicate that newly entered cal constants will be lost when the Model 238 is turned off Permanent cali bration can still be done by setting the calibration switch to the in position and sending COX and C59X over the bus in that order After sending the C59X command the Model 238 will go into standby SECTION 2 Calibration 2 6 4 4 Send the following command over the IEEE 488 bus to calibrate offset for the InA measurement range C42X Low Current Ranges Calibration 1 10 Connect the characterized Model 263 calibrator to the Note Calibration takes approximately 20 seconds to Model 238 as shown in Figure 2 5 The characterized I complete source values Ispa Isona losma and Isma of the Model 5 Place the Model 263 in operate to source 0 9nA to the 263
35. 2 relay switch closed 5V relay switch open K1 K3 K4 K5 K6 and K15 OV relay switch open 5V relay switch closed K1 Output Module OV relay switch open 15V relay switch closed 3 Maintenance FET Switch Drive N channel FET OV switch closed on 15V switch open off P channel FET OV switch closed on 15V switch open off Analog Switch Drive U45 U48 U49 and U50 OV switch closed 5V switch open Other control lines that are not used to drive switching devices are described as follows COMPLIANCE Used for compliance detection When the Model 238 is in compliance this control line is at OV Otherwise 5V is on this line POLARITY Used to provide the appropriate 10V refer ence for the clamping circuits When the instrument is programmed for a positive output this control line is at nominally 10V When programmed for a negative output this line is at nominally 10 100mA RANGE BIAS Used to select the appropriate current limit to the output stage With the instrument on the 100mA range source or measure this control line is at 5V On the other current ranges this line is at OV 3 8 5 Analog Switching Tables 3 4 through 3 8 provide the switching states of most of the analog circuit switching devices for the vari ous operating conditions Current Ranging Table 3 4 lists the switches that are closed for each of the nine
36. 250V AC external switch selectable 90 110V and 180 220 version available 120V A max DIMENSIONS WEIGHT 89mm high x 435mm wide x 448mm deep 3 in x 171 in x 17 in Net weight 9kg 19 75 Ibs ACCESSORIES SUPPLIED Model 7078 TRX 10 Triax to Triax Cable 3m 10 ft 2 supplied Model 236 ILC 3 Interlock Cable ACCESSORIES AVAILABLE Model 8000 10 Equipment Rack for 3 SMUs 10 in Model 8000 14 Equipment Rack for 4 SMUs 14 in Table of Contents SECTION 1 Performance Verification 1 1 INTRODUCTION 5 4529 a qu or doe d 1 2 ENVIRONMENTAL CONDITIONS re 1 3 INITIAL CONDITIONS ges ERR Cad ERE 1 4 REQUIRED TEST EQUIPMENT 1 5 VERIFICATION PROCEDURES 1 5 1 Equipment Characterization 1 5 2 Common Mode Verification 8 5 1 5 3 Voltage Source Verification 1 5 4 Voltage Measure Verification 1 5 5 Remote Sense Verification AC Cae e ERR eee 1 5 6 Low Current InA to 10mA Measure Ranges Verification 1 5 7 Low Current InA to 10mA Source Ranges
37. 59 will be ignored unless the CO command is first sent over the bus 6172 2 Slot to 3 Lug Female Triax adapter 7078 TRX X enc aga Banana Plug Cable Ground Link Removed m 263 Source l Note 263 GUARD enabled Current Ranges Calibration 1nA to 10mA to complete Place the Model 263 in operate to source 90nA to the Model 238 238 Measure 1 2 11 SECTION 2 Calibration 14 15 16 17 18 19 20 23 24 25 26 27 28 Send the following command over the bus to cali brate gain for the 100nA measurement range C47 90E 9X Note Calibration takes approximately four seconds to complete Place the Model 263 in standby and set it to 0 9 Send the following command over the bus to cali brate offset for the 14A measurement range C48X Place the Model 263 in operate Send the value for Iosua from Table 2 3 over the bus with the C49 command as follows to calibrate gain for the 11A measurement range C49 ToouaX For example if 0 90036 send C49 0 90036E 6X Place the Model 263 in standby and set it to 94A Send the following command over the bus to cali brate offset for the 104A measurement range C50X Place the Model 263 in operate Send the value for from Table 2 3 over the bus with the C51 command as follows to calibrate gain for the measurement range 51 Place the Model 263 in
38. 7 and storage capacitors C52 C54 C56 and C57 combine with adjustable regulators VR5 and VR6 and resistors R6 R7 R8 and R9 to provide the 30V outputs The 5V analog supply brown secondaries consists of the bridge rectifier CR5 filter capacitor C7 regulator VR2 and output capacitors C93 and C15 This power supply provides 5V for analog functions The 150V supply yellow secondaries is provided for the bootstrap amplifier A bridge rectifier is configured from four diodes CR8 CR9 CR10 and CR11 These diodes rec tify and use capacitors C58 and C59 as storage elements A 15V analog supply is derived from a shunt regulator circuit consisting of resistors R73 and R74 and regulators VR7 and VR8 in parallel with capacitors C95 and C96 The 30 supply blue white brown and blue white sec ondaries is used to drive the 1A output stage Bridge rec tifier CR12 provides full wave rectification while R80 R90 C110 and C119 suppress diode spikes Triac Q7 zener diodes VR9 and VR10 and resistor R81 provide clamping circuit that guarantees that the F1 fuse will clear when the instrument is set for 115V operation while con nected to the 230V line Minimum load is guaranteed by resistors R94 and R95 Filtering is provided by capacitors C10 and C118 SECTION 5 Replaceable Parts 5 1 INTRODUCTION This section contains replacement parts information component location drawings and schematic diagrams for the Model 238 5 2 PAR
39. 8 FH 21 FH 25 CS 507 590 314 4 590 314 10 236 329A 590 314 3 CS 288 3 CH 16 19 Q2 Q4 Q5 Q6 Q7 H1 R15 17 50 80 87 90 91 16 23 R2 R20 22 71 81 R25 72 77 R3 4 10 11 28 83 86 89 R32 R33 R34 R35 75 76 R36 R37 R38 39 59 62 65 R41 R42 R43 R44 47 R45 48 R46 R49 52 R51 R53 R54 R55 R56 R57 R58 R6 8 R63 R64 R7 R9 R70 R73 74 R78 79 R82 R92 R93 R94 95 1 2 3 T1 CABLE ASSEMBLY TRANS N CHANNEL FET TN06L TRANS CHANNEL JFET PN5434 TO 92 TRANS N CHANNEL DUAL FET MP842 0 52 TRANS NPN SILICON 2N3904 0 92 TRANS N CHANNEL FET 2N4392 TO 92 TRANS TRIODE THYRISTOR MAC223 6 RES 430 5 1 4W COMPOSITION OR FILM RES 1K 5 1 4W COMPOSITION OR FILM RES NET 3 3K 5 1 25W RES 330 5926 1 4W COMPOSITION OR FILM RES 100 5 1 4W COMPOSITION OR FILM RES 3 3K 5 1 4W COMPOSITION OR FILM RES 470 5 1 4W COMPOSITION OR FILM RES 560K 5 1 4W COMPOSITION OR FILM RES 6 2K 5 1 4W COMPOSITION OR FILM RES 2K 5 1 4 COMPOSITION OR FILM RES 47K 596 1 4W COMPOSITION OR FILM RES 100 196 1 8W METAL FILM RES 4 87K 196 1 8W METAL FILM RES 10K 5 1 4W COMPOSITION OR FILM RES 142 2K 02 1 8W PRECISION THIN FILM RES 100K 5 1 4W COMPOSITION OR FILM POT 10K 10 5W NON WIREWOUND RES 200 5 1 4W COMPOSITION OR FILM RES 20K 1 1 8W METAL FILM RES 32 4K 1 1 8W METAL FILM RES 7 87K 1 1 8W METAL FILM RES 2 15K 1 1 8W METAL FILM RES 15 4K 1 1 8W METAL FILM R
40. 90mA Verify that the current reading 58 on the Model 238 is within the following limits Loss 89 9041 to 90 096m A 8 Place the Models 343A and 238 in standby 1 16 1 Verification Perform the following steps to verify the 1 measure ment range 1 While in standby set the Model 238 to source OV on the 1 5V source range and set compliance to 1A 2 Remove the short from the test fixture and place the Model 238 in operate 3 Verify that the current reading Las on the Model 238 is within the following limits Lss 300UA 4 Place the short in the test fixture and set the calibra tion source to output 900mA on the 1A range 5 Verify that the current reading on the Model 238 is within the following limits L s 898 62mA to 901 38mA Set the calibration source to output 900mA 7 Verify that the current reading 1 gt on the Model 238 is within the following limits Lis 898 62mA to 901 38mA 8 Place the Models 343A and 238 in standby o 1 5 9 100 and 1A Source Ranges Verification Theequipmentsetup for both 100mA and 1A source veri fication is shown in Figure 1 9 SECTION 1 Performance Verification Interlock Cable 236 11 3 Banana Plug 343A DC Calibrator Banana Plug Cables 3 Warning Connect 9 to Safety Earth cum Ground 8006 Test Fixture 7078 TRX Cable Connections 2500 E
41. A CONVERT AD7538KN 8 STAGE SHIFT STORE REGISTER 4094 IC QUAD 2 1 LINE DATA SELEC MULT 74HC158 IC QUAD LOW POWER JFET LF444 IC QUAD 2 INPUT POS 74 08 IC DUAL D TYPE FLIP FLOP 74HC74 IC DARLINGTON ARRAY 2003 IC 3 TO8 LINE DECODER DEMULTI 74HC138 18 OP AMP AD744 IC RETRIG MULTIVIB 74HC123 IC OCTAL BUFFER 74HC244N IC SPST CMOS ANALOG SWITCH DG271 IC 15V 1007 IC LOW PWR OPAMP AD648 IC CMOS SERIAL INPUT 12 BIT DAC MP7543 IC DUAL HIGH SPEED OP AMP LT1057ACN8 DIODE ZENER 15V 1N4744A TO 41 DIODE ZENER 6 4V IN4579 DO 7 DIODE ZENER 200V 1N5388A CASE 17 DIODE ZENER 4 3V 1N749A DO 7 DIODE ZENER 12V IN9638 DIODE ZENER 15V 1N718 DO 7 TE 111 320 219 572 207 672 601 251 587 329 465 337 206 16 431 586 492 469 508 422 719 419 590 04 75 02 73 02 74 02 63 02 54 02 18 TABLE 2 MODEL 238 DIGITAL PARTS LIST CIRCUIT DESIG AT1 3 7 8 AT5 AT6 BT1 C1 C10 118 C106 107 C108 109 C110 119 C116 C120 C121 146 C147 176 C15 17 24 33 94 C4 C52 54 C53 55 C56 57 C58 59 C63 C64 C67 C68 70 72 C7 C71 C73 89 93 95 97 CR1 CR12 CR13 16 19 20 23 26 CR2 3 6 7 CR27 CR4 5 CR8 11 F1 J10 J16 23 J18 J20 J22 J8 L1 DESCRIPTION IC DUAL HIGH CMR SPEED OPTO HCPL 2631 IC OPTPCOUPLER 2601 I
42. A x 4kQ 20V This voltage is scaled down to 2V and inverted This 2V is fed back via V FEEDBACK to U15A and U15B The non inverting input of U15B will go posi tive keeping CR12 reverse biased As a result the V CLAMP remains off Current from 10 REF will flow into the I CLAMP which is turned on remember the other clamps are off As a result the feedback configuration and the I DAC output will apply a voltage to the error amplifier U14 that will effect a constant 5mA output current Part 2 Assume the instrument is still programmed to source 5mA with a compliance of 27V However for onereason or another the load resistance changes to 6kQ This load change causes the source to go into compliance making voltage the controlling function With the 4kQ load the I CLAMP is on making current the controlling function as explained in the Part 1 When the load resistance is increased to 6kQ the voltage drop across the load would be 30V 5mA x 6kQ 30V However voltage is limited at 27V and the source goes into compliance In voltage compliance the 27V is scaled down to 3V and inverted This 3V is fed back via V FEEDBACK to U15A The non inverting input of U15A will go to OV 3V 0V forward biasing CR12 As a result the V CLAMP will turn on Current from 10V REF starts flowing into the V CLAMP With less current flowing into the 1 CLAMP the voltage at the input of U14 decreases causing the o
43. AM U12 may be defective IOU EEROM FAILED The E7ROM 033 in the I O controller has failed making the instrument non functional DPRAM LOCKUP The source measure controller cannot respond to the I O controller due to RAM 013 EPROM 017 or microprocessor 025 failure The instrument is non functional DPRAM LINK ERR Communications error in the DPRAM 012 between the I O controller and the source measure controller The unit is non functional 030 failure The unit 15 non functional 2 EPROM 031 failure The unit is non functional NOTE There are error messages associated with calibration and are covered in the calibration section of this manual Display Test 3 Use the rotary knob to display A D TEST Note that the A D converter is still running normally at When the display test is run all display segments and this time front panel lights are turned on for a few seconds Per 4 Press ENTER The following message will be briefly form the following steps to run the display test displayed ENTER TO EXIT 1 Enable MENU and use the rotary knob to display DISPLAY TEST This is an instructional message indicating that once 2 Press ENTER to run the test in the A D test mode pressing ENTER will exit the Note The memory test can also be performed by test mode allowing the A D converter to run nor sending J2X over the bus mally The following message will then be dis played A D Test Mode A D
44. C OPTOCOUPLER HCPL 2400 BATTERY LITHIUM BATTERY HOLDER CAP 33PF 1026 1000V CERAMIC CAP 10 000UF 20 35V ALUM ELEC CAP 1UF 2096 50V CERAMIC CAP 02 20 500V CERAMIC CAP 1UF 20 100V EPOXY CAP 710PF 2 50V CERAMIC CAP 01UF 20 50V CERAMIC CAP 01UF 20 50V CERAMIC CAP 1UF 20 50V CERAMIC CAP 10UF 20 100 25V ALUM ELEC CAP 10000UF 20 30 25V ALUM ELEC CAP 100UF 20 63V ALUM ELEC CAP 1000UF 10 100 35V ELECTROLYTIC CAP 100UF 10 100 35V ALUM ELEC CAP 560UF 20 200V ALUM ELEC CAP 0047UF 10 100V POLYPROPYLENE CAP 820PF 1026 1000V CERAMIC CAP 22PF 1026 1000V CERAMIC CAP 47PF 10926 1000V CERAMIC CAP 4700UF 20 100 16V ALUMINUM CAP 22PF 20 500V CERAMIC CAP 1UF 20 50V CERAMIC DIODE BRIDGE PE05 DIODE BRIDGE KBU4B CASE KBU DIODE SILICON IN4148 DO 35 DIODE SWITCHING IN4607 DO 35 DIODE SILICON SCHOTTKY SB120 DIODE BRIDGE VM18 DIODE SILICON IN4006 00 41 FUSE 1 25A 250V FUSE HOLDER FUSE CARRIER CONN RIGHT ANGLE 24PIN MODIFIED CONNECTOR MODIFIED CONNECTOR MODIFIED CONNECTOR MODIFIED CONNECTOR CONN MALE 3 PIN CHOKE 1 UH KEITHLEY PART NO IC 588 239 464 44 34 C 64 33P C 433 10000 C 237 1 C 22 02 C 416 1 C 348 710P C 365 01 C 365 01 C 365 1 C 314 10 C 342 10000 C 403 100 C 309 1000 C 295 100 C 355 560 C 306 0047 C 64 820P C 64 22P C 64 47P C 313 4700 C 22 22P C 237 1 RF 48 RF 64 RF 28 RF 41 1 RF 78 RF 52 RF 38 FU 2
45. CEDURES The following paragraphs contain the detailed proce dures for verifying the one year accuracy specifications of the Model 238 using the equipment listed in Table 1 1 NOTE The allowable reading limits in these proce dures only reflect the specifications of the Model 238 They do not include error contrib uted by test equipment SECTION 1 F Performance Verification These procedures are intended for use only by qualified terlock circuit must be connected to the personnel using accurate and reliable test equipment If Model 238 the instrument is out of specifications and not under war ranty refer to the calibration section of this manual Connect the test fixture screw to safety earth ground using 18 AWG wire minimum be fore use Turn off all power before connect ing or disconnecting wires or cables WARNING Also keep in mind that GUARD is always Lethal voltages up to 100V will be con enabled Thus a lethal voltage on OUTPUT nected to the Model 8006 test fixture To HI is also present on the two GUARD termi avoid a possible shock hazard the safety in nals of the Model 238 Table 1 1 Basis Test Keithley 5 1 2 digit Calibrator 2nA 20nA ranges 0 0625 10 counts Source 200nA range 0 035 10 counts Keithley 5 1 2 digit DMM 200mV 2V ranges 0 005 2 counts 20V 1000V ranges 0 007 1 count 2000 200 ranges 0 007 2 counts 200uA 2mA ranges 0
46. COE alibrator 343A Source 1 238 Measure 1 DC Calibrator OUTPUT HI Source OUTPUT LO Schematic Equivalent Figure 1 8 Setup for 100mA and 1A Measure Ranges Verification SECTION 1 Performance Verification Interlock Cable 236 ILC 3 Banana Plug Cables 6 Required SENSE OUTPUT 343A DC Calibrator D MEM 2500E Current Warning Connect OUT IN Calibrator to Safety Earth T a 18 Ground 193A DMM 8006 Test Fixture 7078 TRX Cable A Connections 193A DMM Measure 1 Amps HI LO 2500 E Current SOLENT 238 Source 1 343A DC Calibrator OUTPUT HI Source 6 OUTPUT LO B Schematic Equivalent Figure 1 9 Setup for 100 and Source Ranges Verification SECTION 1 Performance Verification 100mA Source Range Verification 9 Place the Model 238 and the calibration source in standby Perform the following steps to verify the 100mA source range 1A Source Range Verification 1 While in standby set the Model 238 to source 0mA Perform the following steps to verify the 1A source on the 100mA source range and set compliance to range 1 5V 2 Set the Model 193A to the 2001A range 3 Set the Model343A to OV and place the Model 2500E on the 100HA range 4 Place the Model 238 in operate and verify that the current measurement on the Model 193A lissa is within the following limits 204 5 Set the Mod
47. D SUPPORT PRINTED CIRCUIT BOARD CABLE ASSY 3 LUG TRIAX MODIFIED PRINTED CIRCUIT SUPPORT BOTTOM SHIELD CAP FILTER FAN CAP 100PF 10926 1000V CERAMIC SUPPORT PRINTED CIRCUIT BOARD TRIAX CONNECTOR CONNECTOR RIGHT ANGLE SMB TRIAX CONNECTOR CONNECTOR RIGHT ANGLE SMB DECORATIVE STRIP ASSEMBLY DECORATIVE STRIP ASSEMBLY CABLE ASS Y TRIAX RIGHT ANGLE SMB CONNECTOR 3 PIN MALE CABLE ASS Y TRIAX RIGHT ANGLE SMB BINDING POST BINDING POST METAL CONNECTOR BNC LINE FILTER HOUSING CONNECTOR CONNECTOR HOUSING FRONT FOOT ASSEMBLY TOP COVER BOTTOM COVER KEITHLEY PART NO 238 302 CO 7 228 317 4 228 317 5 228 317 6 228 317 7 FE 21 228 319 236 304 236 305 236 311 236 312 236 314 1 236 315 236 316 236 317 236 323 236 332 236 309 238 306 228 318 CA 63 10 228 314 2 ST 137 2 CAP 28 1 FL 9 FN 25 C 64 100P 228 318 CS 723 CS 759 CS 723 CS 759 193 322 193 323 CA 72 2 CS 659 CA 72 1 BP 11 0 BP 15 CS 249 LF 2 CS 287 5 CS 287 3 706 317 236 324 228 313 Service Form Model Serial Date Name and Telephone No Company List all control settings describe problem and check boxes that apply to problem J Intermittent J Analog output follows display Particular range or function bad specify IEEE failure Obvious problem on power up Batteries and fuses are OK Front panel operational All ranges or functions are bad C
48. ERAMIC CAP 150PF 10 1000V CERAMIC CAP 33PF 10 1000V CERAMIC DIODE IN3595 00 7 DIODE BRIDGE DF10M DIODE SILICON SCHOTTKY SB120 KEITHLEY PART NO C 405 22P 209 150 405 68 C 64 1000P C 372 15P C 347 1000P C 371 47000P C 64 10P C 64 10P C 406 15P C 64 5P C 372 10P C 372 15P C 64 680P C 138 470P 365 1 237 1 C 348 39P C 64 1500P 405 270 405 560 405 100 C 405 220P C 405 8P C 405 33P 64 01 C 430 3300P C 372 150P C 237 1 C 365 01 314 10 64 22 64 150 C 64 33P RF 43 RF 79 RF 78 CR9 16 19 20 E1 J11 13 J15 J19 J27 K1 8 K12 15 K2 4 16 20 9 10 11 P18 PS Q18 019 31 Q24 Q25 28 Q29 Q32 43 44 46 48 Q36 Q39 40 Q4 7 10 14 33 35 37 38 51 54 Q41 42 45 47 Q49 50 08 9 R101 R102 R103 106 109 R104 R107 R110 R115 R119 R12 124 125 126 137 190 R128 129 131 R13 29 74 75 153 155 188 189 R132 R134 135 R138 139 146 DIODE SILICON IN4148 DO 35 SURGE ARRESTOR FOR P18 ASSY GROMMET CONN SMB MALE P C MOUNT CONN MALE 15 PIN CONN DUAL 7 PIN BERG CONN MALE 2PIN RELAY SPST RELAY SPST RELAY REED HI VOLTAGE RELAY REED HI VOLTAGE RELAY SPST CONNECTOR HOUSING 10 PIN MOLEX CONNECTOR HOUSING TRANS N CHANNEL JFET SELECTED J210 TRANS NPN SILICON 2N3904 92 TRANS N CHANNEL JFET SELECTED J210 TRANS NPN COMP SILICON AMP 2N5089 TRANS PNP SILICON 2N3906 T
49. ES 10K 1 1 8W METAL FILM RES 7 78K 02 1 8W PRECISION THIN FILM RES 1M 5 1 4W COMPOSITION OR FILM RES 15K 596 1 4W COMPOSITION OR FILM RES 5 1K 5 1 4W COMPOSITION OR FILM RES 5 62K 1 1 8W METAL FILM RES 51 1K 1 1 8W METAL FILM RES 26 7K 1 1 8W METAL FILM RES 243 1 1 8W METAL FILM RES 996K 1 1 4W METAL FILM RES 15K 10 2W COMPOSITION RES 4 3K 5 1 4W COMPOSITION OR FILM RES NET 1K 2 1 70W RES 510 5 1 4W COMPOSITION OR FILM RES 270 5 1 4W COMPOSITION OR FILM RES 5 6K 5 1 4W COMPOSITION OR FILM SWITCH PUSHBUTTON 6 POLE SWITCH SLIDE DPDT SWITCH PUSHBUTTON 2 POLE TR 277B JAPAN TRANSFORMER ASSY 27 12 TG 216 TG 174 1 TG 175 TG 47 TG 128 1 TG 172 R 76 430 R 76 1K TF 140 R 76 330 76 100 6 3 3K 6 470 7 7 76 560K 76 6 2K 76 2K 76 47K 88 100 88 4 87K 76 10K 365 142 2K 76 100K P 97 10K 6 200 8 20K 8 32 4K 8 7 87K 8 2 15K 8 15 4K 8 10K 65 7 78K 6 1M 6 15K 6 5 1K 8 5 62K 8 51 1K 8 26 7K 8 243 64 996K 15K 76 4 3 180 3 76 510 R 76 270 R 76 5 6K R R R R R R R R R R R R R R 7 R 8 R 8 R 8 R 8 R 8 R 8 R 3 7 7 7 R 8 R 8 R 8 R 8 R 2 R 3 R 7 T R SW 466 SW 476 SW 469 TR 276 TP1 2 U1 U12 U13 30 U14 28 U15 25 U16 U17 U18 19 58 U21 40 46 U23 U26 U27 U29 U31 U32 47 U33 U34 U35 U36 U38 U39 U41 U42 44 U43 52 U45 048 049 55 050 U51 57 59 U54 U56 VR1 VR2 VR3 VR4 VR5 VR6 V
50. L1 PPO DC1 DT1 E1 All front panel functions and setups are available over the IEEE 488 bus in addition to Status Service Request Output Format EOI Trigger and Terminator IEEE 488 address is set from front panel menu EXECUTION SPEED MINIMUM SOURCE DELAY MEASURE CYCLE TIME 1msec RESPONSE TO IEEE 488 COMMAND as a source 25msec MEASUREMENT RATE 1msec per point into internal buffer CONTINUOUS MEASUREMENT SPEED source DC value over IEEE 488 bus 110 readings per second TRIGGER LATENCY TIME 2msec GENERAL LOAD CAPACITANCE Stable into 20 000pF typical REMOTE SENSE Corrects for up to 2V drop in each output lead Maxi mum 1kQ per sense lead for rated accuracy Residual output resistance as a voltage source is 0 52 GUARD Output Resistance lt 12 Maximum Output Current 2mA Open Circuit Offset Relative to Output HI 2mV max ISOLATION Output LO to chassis Typically gt 10 Q in parallel with 650 MAXIMUM MODE VOLTAGE 200V CONNECTORS Outputs 3 lug triax Trigger Input Output BNC Interlock 3 pin miniature DIN TEMPERATURE COEFFICIENT 0 18 C amp 28 509 0 1 x applicable accuracy specification C ENVIRONMENT Operating 0 50 C 70 relative humidity up to 35 C Linearly derate 3 RH C 35 50 C Storage 25 to 65 C WARM UP One hour to rated accuracy COOLING Internal fan forced air cooling POWER 105 125 or 210
51. LSI 86 51 65 582 238 800 407 462 466 682 51 49 541 238 801 IC 412 LSI 83 298 299 602 469 431 500 251 283 1 488 219 337 540 354 351 501 38 2 240 5 22 32469 2 32469 5 32469 6 308 309 02 75 07 72 2 25 4 CR 29 ORDER CURRENTLY INSTALLED FIRMWARE LEVEL FOR EXAMPLE IF THE FIRMWARE REVISION LEVEL IS A06 ORDER PART NUMBER 238 800 A06 AND 238 801 A06 TABLE 3 MODEL 238 DISPLAY BOARD PARTS LIST CIRCUIT DESIG 1 4 C5 CR1 10 DS1 9 DS10 28 P24 R1 23 25 27 29 31 33 34 R24 R26 R28 32 1 2 34 U1 U2 U3 U4 7 8 U5 6 9 10 DESCRIPTION CAP 01UF 20 50V CERAMIC CAP 10UF 20 100 25V ALUM ELEC DIODE SILICON IN4148 00 35 DIGITAL DISPLAY PILOT LIGHT RED LED LED MOUNTS CABLE ASSEMBLY 20 CONDUCTOR RES 82 5 1 4W COMPOSITION OR FILM RES 15 5 1 4 COMPOSITION OR FILM RES 15 5 1 4 COMPOSITION OR FILM RES 3 3K 5 1 4W COMPOSITION OR FILM DIGITAL CONTACTING ENCODER SWITCH MOMENTARY IC QUAD 2 INPUT NOR 74HC02 IC 12 STAGE BINARY COUNTER 74HC4040 1 OF 10 DECODER 74HC42 IC 8 CHANNEL SAT SINK DRIVER UDN 2596A 8 SERIAL INPUT UNC5895A KEITHLEY PART NO C 365 01 C 314 10 RF 28 DD 39 PL 71 MK 22 1 CA 27 9 R 76 82 R 76 15 R 76 15 R 76 3 3K SW 472 SW 435 IC 412 407
52. O 92 TRANS CURRENT REGULATOR CR430 TRANS CURRENT REGULATOR CR120 TRANS N CHANNEL FET 2N4392 TO 92 TRANS SELECTED N CHANNEL JFET 5434 TRANS NPN CATV SILICON MPSH17 TRANS N CHANNEL JFET 5432 TO 92 TRANS P CHANNEL JFET J270 TO 92 RES 12 4K 196 1 8W METAL FILM RES 820K 5 6 1 4W COMPOSITION OR FILM RES 180K 526 1 4W COMPOSITION OR FILM 5 91 595 1 4 COMPOSITION OR FILM RES 1 5M 5 1 4W COMPOSITION OR FILM RES 300K 525 1 4W COMPOSITION OR FILM RES 200K 5 1 4W COMPOSITION OR FILM RES 4 99K 126 1 8W METAL FILM RES 10G 2 1 5W HY MEG RES 2 4K 596 1 4W COMPOSITION OR FILM RES 75K 1 1 8W METAL FILM RES 100 1 1 8W METAL FILM RES 681 1 1 10W METAL FILM RES 732K 19 6 1 4W PRECISION THIN FILM RES 10K 1 1 10W METAL FILM RES 51K 576 1 4W COMPOSITION OR FILM RES 100K 1026 1 2W COMPOSITION RES 22K 1076 1 2W COMPOSITION RES 794 196 1 10W METAL FILM RF 28 SA 3 GR 6 CS 545 CS 612 15 CS 389 5 CS 288 2 RL 141 RL 117 RL 119 RL 129 RL 117 CS 287 10 CS 287 3 236 601 TG 47 TG 167 1 TG 62 TG 84 TG 219 TG 159 TG 128 1 TG 179 R 263 794 14 147 R15 R150 R152 154 R156 R16 18 R160 161 R163 R164 165 R166 R167 R169 R170 R175 R177 184 R199 201 R185 R191 R2 R20 22 R25 32 35 49 81 174 R26 192 194 R27 30 171 173 R28 R3 21 23 24 133 R31 100 114 127 159 168 196 198 R38 R39 R4 R40 R41 43 54 83 84 148 149 44 187 R45 56 57 72 73 79 80 186
53. OSITION OR FILM RES 51 5 1 4W COMPOSITION OR FILM RES 237 1 1 8W METAL FILM RES 4 5K 196 1 10W METAL FILM RES 7 39K 1 1 10W METAL FILM 377 13 82 R 377 27 4K R 377 300K R 76 5 1K R 76 1 8M R 88 137K R 374 1M R 1 10K R 76 2K R 76 3 9K R 76 51K R 88 56 2K R 76 510 R 385 10 92 R 76 10M R 88 182K R 2 10K R 76 13K R 76 560K R 263 100K 238 600 R 88 49 9 R 384 10 101K R 76 100K R 264 998K R 265 9 88M R 76 5 6K R 289 1G R 289 100M R 88 10K R 377 90K R 377 10K R 76 15K R 76 10K 48 157 85 151 86 87 89 193 R9 42 68 123 162 R92 94 R93 95 R96 R97 R98 TE2 3 6 8 10 12 14 16 19 22 29 TE20 21 U1 45 48 50 U10 31 52 U11 U18 U19 47 U2 3 U23 25 U26 28 29 35 41 43 53 030 032 033 034 037 U38 U4 8 13 14 17 U44 U46 U49 U5 7 21 22 24 U51 U6 U9 12 15 VR1 6 VR11 VR14 15 VR2 5 VR3 4 VR9 10 RES 49 9K 196 1 8W METAL FILM RES 19 6K 1 1 8W METAL FILM RES 100K 1 1 8W METAL FILM RES 11 1K 1 1 8W METAL FILM RES 1K 596 1 4W COMPOSITION OR FILM RES 2 2K 596 1 4WN COMPOSITION OR FILM RES 3 57K 596 1 AW COMPOSITION OR RES 1 24K 1 1 8W METAL FILM RES 82K 5 1 4W COMPOSITION OR FILM RES 18K 5 1 4W COMPOSITION OR FILM TERMINAL TEFLON TEFLON TERMINAL IC SPST CMOS ANALOG SWITCH DG211 IC QUAD COMPARATOR LM339 IC WIDEBAND CURRENT BUFFER LH4001 IC 22V OP AMP OP 07 IC 20V OP AMP LT1055CN8 128 542 IC 14 BIT CMOS D
54. PB1 pin 12 PB2 Rotary knob data 5V to OV Data input VIA when rotary knob turned U28 pin 19 Variable pulse train OV to 5V 2MHz TTL 5V 5 Data output to display U25 pins 34 and 35 Bus clock U25 pin 37 Reset line goes low momentarily on power up INT line U27 pin 9 5 signal pulsed 0 to 5V every Imsec U27 pin 19 5V Logic 1 RESET line U27 pin 18 2MHz squarewave Clock OV to 5V U27 pin 28 Goes true 40V when command is sent ATN line See Figure 3 7 for required conditions U27 pin 24 NDAC 25 NRFD 26 DAV and data lines Handshake sequence U14 pin 19 Variable pulse train S M controller VIA data to optos OV to 5V U14 pins 2 9 7 Data to VIA from A D Variable pulse train OV to 5V U15 pins 34 and 35 2MHz TTL Clock 015 pin 37 5 Reset line goes low momentarily Power 3 13 SECTION 3 Maintenance 3 14 P24 pin 15 and 16 05 U6 U9 U10 OUTI thru OUT8 U4 pins 4 7 14 17 U7 pins 4 7 14 17 U8 pins 4 and 5 P24 pin 10 P24 pin 9 P24 pin 8 P24 pin7 Table3 10 Display Circuitry Checks 5V 5 Variable pulses Variable pulses Depress any switch located in the first column of switch array on schematic 236 116 Depress any switch located in the second column De
55. R7 8 VRQ 10 Y1 Y2 CONN TEST POINT IC PAL 20L10 IC CMOS DUAL PORT RAM IDT7130 32 8 STATIC CMOS RAM D43256C 15L IC VERSATILE INTERFACE ADAPTER G65SC22 8 MICROPROCESSING UNIT MC68B09 10 INPUT AND OR INVERT ARRAY PAL16L8 EPROM PROGRAM 12 STAGE BINARY COUNTER 74HC4040 IC DUAL 4 BIT COUNTER 74HCT393 74 05 10 INPUT AND OR INVERT ARRAY PAL16L8 IC GPIB ADAPTER 9914A IC NONVOLATILE CONTROLLER DS1210 EPROM PROGRAM IC QUAD 2 INPUT 74 02 IC PROGRAMMABLE E2ROM 2816B IC OCTAL INTERFACE BUS 75160 IC OCTAL INTERFACE BUS TRANSCEIVER 75161 IC SUPPLY VOLTAGE SUPERVISOR TL7705AC IC OCTAL BUFFER 74HC244N IC 3 TO8 LINE DECODER DEMULTI 74HC138 IC DUAL 4 BIT DECADE COUNTER 74HC390 8 STAGE SHIFT STORE REGISTER 4094 IC TRIPLE 2 CH MULTI DEMUX 4053 IC 8 BIT IDENTITY COMP 74HC688 IC QUAD COMPARATOR LM339 IC DUAL D TYPE FLIP FLOP 74HC74 IC DUAL LOW NOISE OP AMP 5534 INVERTER 74HC04 IC QUAD 2 INPUT NAND 74HC00 IC DUAL LOW NOISE OP AMP NE5532 USE ON TR WIRING CABLE TIE IC 5V REGULATOR 20MA LM323 HEAT SINK RIVET 1 8 DIA X 3 16 LG 1 STAKING HS 25 RIVET 1 8 DIA X 3 16 LG 1 STAKING HS 25 RIVET 1 8 DIA X 3 16 LG 1 STAKING HS 25 IC VOLTAGE REGULATOR LM317MP IC VOLTAGE REGULATOR LM337MP DIODE ZENER 15V 1N4744A TO 41 DIODE ZENER 100V IN5378B OSCILLATOR 8MHZ CRYSTAL 7 68MHZ CS 553 IC 643 LSI 88 LSI 76
56. RECAUTIONS When troubleshooting or otherwise working inside the instrument care should be taken not to indiscriminately touch PC board traces and open wires to avoid contami nating them with body oils or other foreign matter Areas covered by a shield within the Model 238 have high im pedance devices or sensitive circuitry where contamina tion could cause degraded performance The same general precautions apply when replacing parts in these areas When unsoldering and soldering parts be careful not to spread the flux around the board to adjacent areas 1 Using a squeeze bottle carefully apply clean uncon taminated methanol to the area to be cleaned Use sufficient solution to thoroughly wet the circuit board 2 Using asmall clean brush wipe the area thoroughly until it is free of flux or contaminants In some cases it may be helpful to tilt the board at an angle and brush contaminants away from the affected area al lowing contaminated residue and methanol to run off the board SECTION 3 Maintenance IEEE Connector Switch Figure 3 2 Digital Board SECTION 3 Maintenance 3 Wash the area again with fresh clean methanol al lowing it to drain flushing contaminants off the board Once the area is thoroughly cleaned it should be dried with pressurized dry clean air or nitrogen Do not use compressed air from an ordinary air com pressor as oil particles in the air could contaminate the circ
57. S 158 1 1 8W METAL FILM RES 1 1M 5 1 4W COMPOSITION OR FILM RES 3 3M 5 1 4W COMPOSITION OR FILM RES 51 5 1 4W COMPOSITION OR FILM RES 26 1 1 1 8W METAL FILM RES 619 1 1 8W METAL FILM RES 27 4 1 1 8W METAL FILM RES 11 3K 1 1 8W METAL FILM RES 1M 5 1 4W COMPOSITION OR FILM RES 10K 5 1 4W COMPOSITION OR FILM RES 51 5 1W COMPOSITION OR FILM RES 2 2M 5 1 4W COMPOSITION OR FILM RES 1 8M 5 1 4W COMPOSITION OR FILM KEITHLEY PART NO C 236 3300P C 64 01 C 365 01 C 237 1 C 209 1800P C 430 3300P C 278 2200P C 248 6800P RF 60 RF 74 RF 69 RF 28 RF 71 RL 140 CS 287 4 TG 195 TG 214 TG 210 TG 209 TG 84 TG 229 TG 231 TG 193 TG 186 TG 230 TG 62 1 TG 192 TG 185 TG 228 TG 215 TG 47 57 59 R61 64 R62 66 R67 68 VR1 2 RES 100K 526 1 4W COMPOSITION OR FILM RES 1 5M 526 1 4W COMPOSITION OR FILM RES 680K 5 1 4W COMPOSITION OR FILM RES 470 5 1 4W COMPOSITION OR FILM TX 17x1 4x1 1 2 P15 CONNECTOR HOUSING DIODE ZENER 6 44V IN4577AGED DO 7 DZ 58 CS 638 15 TABLE 5 MODEL 238 MISCELLANEOUS PARTS LIST CIRCUIT DESIG J1 2 J25 26 J3 J4 J5 J6 7 49 20 22 DESCRIPTION OVERLAY FRONT PANEL LINE CORD PUSHBUTTON PUSHBUTTON PUSHBUTTON PUSHBUTTON REAR FOOT MOUNTING RAILS FRONT PANEL KNOB A D SHIELD OUTPUT SHROUD WINDOW RED BOTTOM SHIELD INNER SHIELD TOP SHIELD ANALOG BOARD BOTTOM SHIELD INSULATOR FILTER SHROUD REAR PANEL POWER SUPPLY SHIEL
58. Switching Feedback Analog Switches Source I Measure V Source V Measure I Table 3 7 Analog Switching Sensing Local Open Closed Closed Remote Closed Open Open Relay states with 238 in OPERATE In standby relays go to local sense states Output For safety there are two relays that are used to disconnect OUTPUT HI and SENSE HI from the rear panel output triax connectors When the instrument is off relays 1 and K2 are open When turned on these re lay switches remain open until the instrument is first placed in operate These two switches then remain closed while the instrument is powered on A D Multiplexing During normal operation the A D multiplexer U1 continuously applies a sequence of sig nals to the input of the A D converter These signals in clude Zero Reference and Measure I or V Only one sig nal is switched to the A D input at one time The switch ing speed and sequence varies according to how the in strument is programmed to operate In the A D test mode see paragraph 3 8 2 the A D con verter is locked up in the desired A D phase This allows multiplexer switch states to be checked and signal tracing to the A D input to be performed Table 3 8 identifies the switch that is closed during each A D phase The pin numbers of multiplexer U1 are used to identify each switch 3 12 Operate Open Open Open Open Closed Closed Closed Closed Standby Closed Closed C
59. TS LISTS Parts are listed alphanumerically in order of their circuit designations The first parts list contains information for the display board of the Model 238 The next parts list contains information for the digital board of the Model 238 The next parts list contains information for the ana log board of the Model 238 The next parts list contains in formation for the output module The last parts list con tains information on miscellaneous parts that do not per tain to any of the pc boards 5 3 ORDERING INFORMATION To place an order or to obtain information concerning re placement parts contact your Keithley representative or the factory See inside front cover for addresses When or dering include the following information Instrument Model Number Instrument Serial Number Parts Description Circuit Designation if applicable Keithley Part Number If an additional service manual is required order part number 238 902 00 The manual package will contain the service manual and any applicable addenda 5 4 FACTORY SERVICE If the instrument is to be returned to the factory for serv ice please complete the service form which follows this section and return it with the instrument 5 5 SCHEMATIC DIAGRAMS AND COMPONENT LOCATION DRAWINGS Schematic diagrams and component location drawings follow the appropriate replaceable parts list for that par ticular board TABLE 1 MODEL 238 ANALOG BOARD PARTS LIST CIRCUIT
60. X From the display of the Model 193A record the volt age reading Vasr Send the measured voltage reading over the bus with the C19 command as follows to calibrate offset for the 110V source and measurement range C19X VusaX 33 35 36 37 38 39 40 41 42 SECTION 2 Calibration Send the following command to source 100V on the 110V range C20X From the display of the Model 193A record the volt age reading Send the measured voltage reading over the bus with the C21 command as follows to calibrate gain for the 110V source and measurement range 21 Send the following command to source the 110V range C22X From the display of the Model 193A record the volt age reading Send the measured voltage reading over the bus with the C23 command as follows to calibrate offset for the 110V source and measurement range 23 Send following command to source 100V on the 110V range C24X From the display of the Model 193A record the volt age reading VMsR VMsR Send the measured voltage reading Vmsr over the bus with the C25 command as follows to calibrate gain for the 110V source and measurement range C25 VusgX Send the following command over the bus to exit calibration Note Check that the CAL LOCK switch is in the de s
61. Y INSTRUCTIONS 3 7 SPECIAL HANDLING OF STATIC SENSITIVE DEVICES 3 8 TROUBLESHOOTING aod a an eae Dag SA 3 8 1 Recommended Test Equipment 5 3 8 2 3 8 3 3 8 4 3 8 5 3 8 6 Diagnostics i629 a Ss 6 Re YA EXE EE Power Supply Checks 443 ss MUSE E RERO TORR Analog Control Lines nn weg o raus a mee ee dd a Analog Switching E Digital Display Checks SECTION 4 Principles of Operation 4 1 4 2 4 2 1 4 2 2 4 2 3 4 3 4 4 4 4 1 4 4 2 4 4 3 4 4 4 4 5 5 1 5 2 5 3 5 4 5 5 INTRODUCTION ad VPE Ow sd E e heres ANALOG CIRCUITRY RE EORR a a E V I Control and 4 Output Module 344040694 6a VN V L Feedback ew tear RR ERG RAE eid ee eee a A D CONVERTER KES DIGITAL CIRCUITRY 2545555 ede ts a Mew Oe eee ew I O Controller e Gd Ge ew eg d Rex Source Measure Controller Communications sose resse o RE eee RE Display S23 du oen eR EYE Rr E EN
62. a 3 wire power cord that contains a separate ground wire and is designed to be used with grounded outlets When proper connections are made instrument chassis is connected to power line ground Failure to use a grounded outlet may result in injury or death due to electric shock Table 2 1 Required Test Keithley Source Keithley 5 1 2 digit DMM Test Fixture 1009 Resistor 1kQ Resistor 100kQ Resistor Keithley Keithley Fluke Valhalla Current Calibrator 5 1 2 digit Calibrator DC Voltage Calibrator 2nA 20nA ranges 0 0625 10 counts 200nA range 0 035 10 counts 200mV 2V ranges 0 005 2 counts 20V 1000V ranges 0 007 1 count 2009 200 ranges 0 007 2 counts 2004A 2mA ranges 0 09 10 counts 0 1 20ppm C 0 1 10 0 1 10 10 100V ranges 0 002 100mA 1A ranges 0 025 2 1 SECTION 2 Calibration Table 2 2 Specifications for Alternate Equipment Instrument Type Required Specifications DMM Same as Keithley 193A see Table 1 1 0 9nA 9nA 90nA Same as Keithley 263 see Table 2 1 0 94A 180ppm 9HA 90HA 900 9M A 170ppm 90mA 230ppm 0 9mA 625ppm Source DC Current Turn on the Model 238 and allow it to warm up for at least one hour before performing the calibration procedures If the instrument has been subjected to extremes of tem perature or humidity allow at least one additional hour for th
63. amp Figure 4 5 Damping Relay Contact Bounce Op amp U3 isa unity gain amplifier that serves as a buffer between the output and I FEEDBACK I FEEDBACK is fed back to V I Control and Readback where it completes the feedback loop and is also routed to the A D converter for measurement On the 1A range the AMPB output is switched directly to U8 via U50 bypassing U3 Guard The x1 output of U3 is also routed to another x1 buffer amplifier U4 whose output is used as the driven guard for the instrument Buffer U4 isolates the driven guard from I FEEDBACK Volts Ranging and Sensing The voltage range resistors are part of a voltage divider network In general OUT 15 applied to the top of divider The output of the divider is then routed to a differential amplifier The other input to the differential amplifier is effectively OUT The output of the x1 differential output is then fed back to the V I Control and Readback circuitry Op amp U2 is configured as a unity gain amplifier that serves as a buffer between the output and volts ranging circuitry In local sense K15 closed open the output is accessed internally In remote sense K15 open K3 SECTION 4 Principles of Operation 100mA Range closed the output is accessed at the load The x1 output of U2 is applied to the negative input of the differen tial amplifier U7 The output of U2 is also applied to the top of the voltage divider for volts
64. anges with a 1009 resis tor whose voltage drop ramps ina linear fashion towards OV This slow rate of voltage change allows the system to adjust itself keeping the output voltage constant spike free The circuitry that accomplishes this consists of FETs QA and QB and the 15V to 0V ramps that control them The following sequence takes place when current meas urement range change occurs Relay closes 2 The appropriate ramp is activated RANGE 2 RAMP for polarity or RANGE 1 RAMP for polarity The ramp on the gate of the appropriate FET results Volts Ranging with a corresponding voltage ramp across the 1002 resistor 3 The other ramp is activated Turning on the second FET increases the current carrying capability of the circuit With both FETs fully on the current ranges are shunted by the 1000 resistor 4 The new range relay and or FET is activated Note If the 100mA range is the new range it is al ready selected The range change sequence stops at this point If a different range is selected continue on to the next steps Thetwo voltage ramps are disabled in reverse order Relay K8 opens completing the range change na When the 100mA source range is selected K8 closes and both ramps are activated to turn on both FETS As long as the 100mA range is selected is maintained at the gates of the FETs to keep them on Range 1 Ramp 15V to OV Ramp 15V to OV Ramp Range 2 R
65. assembly to the analog board C Grasp the heat sink and lift up the output board assembly a few inches Disconnect P15 from J15 which is located on the analog board directly un der the output board D Lift the output board out of the instrument case Remove the analog board see Figure 3 4 as follows A Remove the analog board shield It is secured to the analog board with four screws Remove the inner shield It is secured to the ana log board with three screws Disconnect P19 ribbon cable from digital board from J19 Disconnect P8 and P18 from J8 and J18 on the digital board Disconnect the connector for the OUTPUT LO banana jack from J27 F Disconnect the SMB triax connectors from J11 J12 and 13 mon gw Screws 4 places Grommet SECTION 3 Maintenance Shield Figure 3 3 Output Board G Place the instrument on its right side and from WARNING the case bottom remove the seven screws that To provide protection from possible electric secure the analog board to the mounting rails shock when re assembling make sure the H Place the instrument in the normal upright posi ground wires from the AC power outlet and tion and carefully manipulate the analog board cooling fan are connected to the rear panel assembly out of the instrument case I Remove the bottom shield of the analog board It is secured to the analog board by the five remain ing screws accessible from the component side of 7 Remove
66. bling zero 21 Remove the short from the input of the Model 193A and set the Model 263 to source 90 000uA on the 200hA range and enable operate 22 Record the voltage measurement from the Model 193A and calculate the current Via mV Vira 2 4 23 24 25 26 27 28 29 30 31 32 33 35 36 Isa is the characterized current for the 200A range of the Model 263 It is used to calibrate the 100 range of the Model 238 Using a pencil record the calculated value of in Entry 3 of Table 2 3 Place the Model 263 in standby Set the Model 193A to the 2V range Set the Model 263 to source 0 90000mA on the 2mA range and enable operate Record the voltage measurement from the Model 193A and calculate the current Vira mA is the characterized current for the 2mA range of the Model 263 It is used to calibrate the 1mA range of the Model 238 Using a pencil record the calculated value of in Entry 4 of Table 2 3 Place the Model 263 in standby In the test fixture remove the 1kQ resistor and install the 1000 resistor R 249 100 On the Model 193A select the Ohms function 2000 range and disable zero Repeat step 3 to zero the Model 193A Measure and record the value of the 1000 resistor Q Set the Model 193A to DCV and the 2V range and disable zero To cancel any offset zero the Model 193A by short
67. broutine IF IOCTLS 2 lt gt 0 THEN RETURN Driver ready for command PRINT 1 SPOLL Check for non SRQ interrupt INPUT 2 SB IF SB 0 THEN RETURN PRINT 1 SPOLL 16 INPUT 2 SB IF SB AND 32 lt gt O THEN Serial poll 238 Input serial poll byte Check for error gt 1 Increment error counter BEEP PRINT 1 OUTPUT 16 U1X Request error word PRINT 1 ENTER 16 2 Errs t Input error word PRINT GOSUB CalStep PRINT Model 238 GOSUB DispErr PRINT Error on calibration step ST PRINT See calibration error message list in Service Manual PRINT COSUB KeyCheck PRINT Continuing END IF RETURN DispErr Display error subroutine IF MIDS Errs 7 1 1 THEN PRINT Interlock Present IF MIDS Errs 14 1 1 THEN PRINT In Standby MIDS CErr 13 1 1 THEN PRINT In Calibration FOR L 1 TO 9 Check cal error messages IF L 20 1 1 THEN PRINT Err L NEXT L RETURN CalStep PRINT 1 OUTPUT 16 07X PRINT 1 ENTER 16 LINE INPUT 2 STS ST VAL MIDS STS 4 2 RETURN t Determine cal step for cal error Request cal status word Address 236 to talk Input cal status word Convert step to variable w a TypeCheck Make sure unit is a 238 PRINT 1 OUTPUT 16 U0X PRINT 1 ENTER 16 INPUT 2 STS IF LEFTS STS 3 lt gt 238 THEN BEEP PRINT Uni
68. current ranges This table ap plies to both source and measure current ranges Notice that on the 1nA range none of the current range relays are closed Volts Ranging Table 3 5 lists the switches that are closed for each of the available voltage ranges This table applies to both source and measure voltage ranges Table 3 4 Analog Switching Current Ranging Relays Range Closed Range Switches Closed Q6 Q9 Q33 Q37 Q38 Q51 Q54 U50A U50B 05 009 Q37 Q38 U45A Q10 Q11 U45A Q12 Q13 U45A Q4 Q14 U45A Q4 U45A Q4 U45A Q4 U45A Q4 U45A Q4 Output module Table 3 5 Analog Switching Current Ranging K4 K7 Q24 Q33 Q35 Q53 K4 K6 K7 Q24 Feedback As listed in Table 3 6 analog switches U48 and U49 are used for feedback switching Each of these two devices has four individual switches and are identi fied by their circuit schematic pin numbers The table lists the states of these switches for standby and operate con ditions while programmed to source current and voltage Sensing As listed in Table 3 7 three relays are used to select local or remote sensing Note that when the instru ment is programmed for remote sensing the relay switches will default to the local sensing states when placed in standby That is relay K3 will open and relays K15 and K5 will close whenever the instrument is placed in standby 3 11 SECTION 3 Maintenance Table 3 6 Analog
69. d Ioma are obtained from Table 1 3 Allowable reading limits are to be transferred to Table 1 9 Typical Limits 0 6500nA 6 500 65 00 0 65004 A 6 5001A The calculated allowable readings should be within listed typical limits These limits are based on the 90 day specifications of the Model 263 and 193A A calculated allowable reading that does not fall within these limits indicates a calculation error or that the Model 263 and or Model 193A is out of specification 1 13 SECTION 1 T Performance Verification 1 9 Low Current Source Verification InA to 10mA Source Source 617 Allowable Ratings Range ange Value 18 C to 28 C Standby 0 4500 0 4500 Standby 2 000 2 000 Standby 20 00 20 00 Standby 200 200 0 Standby 2 000nA 2 000nA Standby 20 00nA 20 00nA Standby 200 0nA 200 0nA Standby 2 000HA 2 000 0 9nA 3 150pA 3 150 0 9nA 9nA 29 00 29 00 9nA 90nA 209 0 209 0 90nA 0 9UA 0 9UA 9HA 9uA 904 90HA 0 9mA 0 9mA 9mA 9mA 238 compliance limit set to 1 1V on the 1 1V measurement range Allowable readings for the 1A thru 10mA source ranges are calculated in Table 1 8 For the 1A thru 10mA ranges program the Model 238 to source the characterized I source values from Table 1 3 1 4 SECTION 1 Performance Verification I
70. d the voltage drop across the resistor from the display of the Model 193A mV Calculate to 5 1 2 digits the current through the 100kQ resistor as follows Toya pA is the characterized current for the 24A range of the Model 263 It is used to check the 1 measure ment range of the Model 238 Using a pencil record the calculated value of Ios in Entry 1 of Table 1 3 Place the Model 263 in standby Set the Model 193A to the 2V range Set the Model 263 to source 9 00004 on the 20HA range and enable operate As performed in steps 8 and 9 measure the voltage across the 100kQ resistor and calculate the current Vi00Kn bya Riooxo Ispa is the characterized current for the 201A range of the Model 263 It is used to check the 101A measure ment range of the Model 238 Using a pencil record the calculated value of Ispa in Entry 2 of Table 1 3 Place the Model 263 in standby In the test fixture remove the 100kQ resistor and in stall the 1kQ resistor R 263 1k On the Model 193A select the Ohms function 2kQ range and disable zero Repeat step 3 to zero the Model 193A Measure and record the value of the 1kQ resistor Rio kQ Set the Model 193A to and the 200mV range and disable zero To cancel any offset zero the Model 193A by short ing its input VOLTS HI to LO and enabling zero Remove t
71. d without error refer to the troubleshooting information in this manual If the problem persists call your Keithley representative or the factory for further information Calibration of the Model 238 is performed over the TEEE 488 bus This section contains the step by step cali bration procedures and a program written in Microsoft QuickBASIC that can be used Before attempting any of the following procedures make sure you are familiar with the controls and operation of the Model 238 Refer to the Model 238 Operator s Manual for complete information WARNING The procedures in this section are for use only be qualified service personnel Do not perform these procedures unless qualified to do so Many of the steps in this section may expose you to potentially lethal volt ages that could result in personal injury or death if normal safety precautions are not observed 2 2 RECOMMENDED CALIBRATION EQUIPMENT Table 2 1 lists recommended calibration equipment Note that the Models 263 and 193A must be within their 90 day specifications as listed in the table Alternate equipment may be used as long as their accuracy is at least as good as the specifications listed in Table 2 2 2 3 ENVIRONMENTAL CONDITIONS Calibration should be performed under laboratory con ditions having an ambient temperature of 23 C 1 C and a relative humidity of less than 70 2 4 WARM UP PERIOD WARNING The Source Measure Unit is equipped with
72. e allowable limits listed in the first entry of Table 1 5 On the Model 238 change the compliance limit to 15V on the 15V measurement range and verify that the voltage reading is within the limits in the table Using Table 1 5 as a guide repeat step 6 to measure on the 110V range Set the calibrator to output 1 on the 10V range and set the Model 238 for a compliance limit of 1 5V on the 1 5V measurement range Verify that the volt age reading on the Model 238 is within the allowable limits in the table Repeat step 8 using a calibrator output of 1V Using Table 1 5 as a guide measure calibrator out uts of 10V and 100V SECTION 1 Performance Verification Table 1 5 Voltage Measure Verification 238 Compliance Limit Allowable Reading 343A Range 343A Output amp Measuring Range 18 C to 28 C 0 00045 to 0 00045V 00 0013 to 00 0013V 000 010V to 000 010V 0 99927V to 1 00073V 0 99927 to 1 00073V 9 9962 to 10 0038V 9 9962V to 10 0038V 99 965V to 100 035V 99 965 to 100 035V 238 set to source OnA on InA source range Interlock Cable 236 ILC 3 238 ESD Cables 2 8006 TEST FIXTURE Warning Connect to Safety Earth Ground A WARHING 8006 Test Fixture DC Calibrator A Connections 343 OUTPUT HI OUTPUT 238 doveri OUTPUT LO Measure V B Schematic Equivalent
73. e following command over the bus to exit calibration Note Check that the CAL LOCK switch is in the de sired position in for permanent calibration or out for temporary calibration C59X If the switch is in the out position the message TEMPORARY CAL will be briefly displayed to in dicate that newly entered cal constants will be lost when the Model 238 is turned off Permanent cali bration can still be done by setting the calibration switch to the in position and sending COX and C59X over the bus in that order After sending the C59X command the Model 238 will go into standby Warning Connect to Safety Earth Ground 8006 Test Fixture A Connections 2500 E Current Calibrator Source 343A DC Calibrator Source B Schematic Equivalent Figure 2 4 Setup for 100mA and 1A Ranges Calibration Interlock Cable 236 ILC 3 Banana Plug Cables 6 Required Calibrator 2500E Current Calibrator Measure 1 Amps LO 238 Source OUTPUT HI 6 OUTPUT LO SECTION 2 Calibration SECTION 2 Calibration 1A Range Calibration Perform the following steps to calibrate the 1A source and measure range 11 12 Set the Model 193A to the 2mA DC range Place the Model 238 in operate The calibration mode cannot be entered with the Model 238 in standby Over the IEEE 488 bus send the following command to enter the calibration mode COX Note All oth
74. e internal temperature to stabilize Typically it takes one additional hour to stabilize a unit that is 10 C 18 F outside the specified temperature range 2 5 CAL LOCK A switch CAL LOCK accessible through the rear panel with a thin shaft screwdriver see Figure 2 1 is used to prevent inadvertent calibration of the Model 238 CAL LOCK is a two position in and out pushbutton switch With the CAL LOCK switch in the locked out position storage of calibration constants in nonvolatile memory cannot take place Temporary calibration values can be entered and used with CAL LOCK in the out position However when power is turned off the newly entered calibration constants will be lost Rear Panel LINE VOLTAGE LINE FUSE SELECTED SLOWBLOW LOCK Calibration Switch Calibration Switch Cal Lock Figure 2 1 When calibration is performed with CAL LOCK in the unlocked in position calibration constants will be stored in nonvolatile memory when the C59 command is sent over the bus 2 6 CALIBRATION PROCEDURES The step by step procedures for calibrating the Model 238 are provided here Calibration is divided into three separate procedures that are independent of one another That is any or all in any order of the three procedures can be performed The three procedures include voltage calibration paragraph 2 6 2 100mA and 1A calibration paragraph 2 6 3 and low current ranges calibration paragraph 2 6 4 Ca
75. e signals are sent to various places on the ana log board by decoder U39 which determines one of four clock paths as set by the bank select signals 0 and 1 which are also derived from U1 This circuit topology provides for a very reliable communications scheme such that the analog circuitry can never receive false data Opto couplers AT1 AT2 AT3 AT7 and AT8 are all in volved in the transmission of clock data strobe and the two bank select signals from the VIA of the source meas ure controller to the analog board Opto coupler AT5 re turns a CV CC constant voltage or constant current level signal to the source measure controller so that the pre sent state of the analog output can be determined The A D converter counts are returned to the microprocessor of the source measure controller by AT6 which is a high speed opto coupler 4 4 4 Display Circuitry The schematic diagram for the display circuit is provided on drawing 236 116 The display which is controlled by the I O controller is basically an 18 digit alpha numeric LED display It con sists of nine two digit display elements DS1 through DS9 Each of these display elements are multiplexed in a matrix fashion Each display digit has its common cath ode connected to sink drivers U4 U7 and U8 These sink drivers are switched on in a rotating fashion The display is divided into two banks of ten columns such that the 051 left digit and DS6 left digit are on simul taneous
76. el 238 to output 9011 and set the cali bration source to output 90mA on the 100mA range 6 Verify thatthe current measurement from the Model 193A is within the following limits Tiosa 0 1100mA 7 Set the Model 238 to output 90mA and set the cali bration source to output 90mA on the 100mA range 8 Verify that the current measurement from the Model 193A lissa is within the following limits Losa 0 1100 While in standby set the Model 238 to source on the 1A range and set compliance to 1 5V Whileinstandby set the Model 343A to 0V and place the Model 2500E on the ImA range Placethe Models 238 and 343A in operate and verify that the current reading on the Model 193A lissa is within the following limits Losa 700UA Set the Model 238 to output 0 900A and the calibra tion source to output 0 900 Verify that the current reading on the Model 193A hsa is within the following limits hsa 1 78mA Set the Model 238 to output 0 900A and the calibra tion source to output 0 900 Verify that the current reading on the Model 193A lissa is within the following limits Iia 1 78MA 1 19 SECTION 2 Calibration 2 1 INTRODUCTION Calibration should be performed every 12 months or if the performance verification procedure Section 1 shows that the Model 238 is out of specifications If any of the calibration steps cannot be performe
77. ent settling User Delay Additional delay for device under test or system capaci tance MEASURE Integration Time Fast 416 psec 4 digit resolution Medium 4 msec 5 digit resolution Line Cycle 16 67 msec 60 Hz 5 digit resolution 20 00 msec 50 Hz Elapsed Time Measures and stores time from sweep trigger to mea surement complete for each step of sweep RANGING Source Auto ranging through keypad entry fixed range selection using rotary dial and SELECT keys DC function Fully programmable in SWEEP function Measure Auto or fixed range Fixed range selection made by choice of COMPLIANCE value FILTER Takes n measurements calculates and outputs average n 2 4 8 16 or 32 selectable SUPPRESS Subtracts displayed measurement from subsequent readings MENU DC Measurement Delay Default Delay On Off Local Remote Sense 50 60Hz IEEE Address Self Tests DATA ENTRY Numeric keypad or detented rotary dial TRIGGER Input and Output Set for any phase of SOURCE DELA Y MEASURE sequence or trigger output at end of sweep Origin Internal External including front panel MANUAL TRIGGER button IEEE 488 bus TALK GET X MEMORY Stores one full sweep up to 1000 points of source delay and measure values elapsed times and sweep parameters Lithium battery backup INTERLOCK Use with test fixture or external switch Normally closed open puts instrument in standby Specifications subject to change wit
78. er calibration commands Cl through C59 will be ignored unless the CO command is first sent over the bus Send the following command to source OmA on the 1A range C26X Set the Model 343A to OV and place the Model 2500E on the 1004 range From the display of the Model 193A record the off set current Loa Send the current reading 1 04 over the bus with the C27 command as follows to calibrate offset for the 1A source and measure range C27 LoAX Send the following command to source 40 9A C28X Set the calibration source to 0 9A on the 1A range From the display of the Model 193A record the cur rent 19 Calculate the actual current Losa using the follow ing calculation Losa 0 9A Send the calculated current reading T osA over the bus with the C29 command as follows to calibrate gain for the 1A source and measure range C29 LosAX 2 10 13 14 15 16 17 18 19 20 21 Send the following command to source 0A on the 1A range C30X Set the Model 343A to OV and place the Model 2500E on the 100A range From the display of the Model 193A record the off set current Loa Loa Send the current reading IoA over the bus with the C31 command as follows to calibrate offset for the 1A source and measure range C31 LoAX Send the following command to source 0 9A C32X Set the calibration source to 0 9 on the
79. execution of a calibration step in which the Model 238 takes a measurement conversion it is possible the instrument can transi tion from OPERATE to STANDBY This can occur beacuse it was specifically programmed to do so or because the test fixture safety interlock was opened In this event the OPERATE and STANDBY transition is detected and the measurement conversion used to compute the calibration constant is ignored The front panel message IN STBY is displayed when this occurs CAL SRC GAIN 2 13 SECTION 2 Calibration Figure 2 6 Identifier ch Identifier ERSbbb bbb TERM Most Significant Bit Least Significant Bit pA 26 Bit ASCII String 0 No Error 1 Error Most Significant Bit Trigger Overrun IDDC IDDCO Interlock Present illegal Measure Range Illegal Source Range Invalid Sweep Mix Log Cannot Cross Zero Autoranging Source with Pulse Sweep In Calibration In Standby Unit is a 236 IOU DPRAM Failed IOU EEROM Failed IOU Cal Checksum Error DPRAM Lockup DPRAM Link Error Cal ADC Zero Error Cal Gain Error Cal SRC Zero Error Cal SRC Gain Error Cal Common Mode Error Cal Compliance Error Cal Value Error Cal Constants Error Least Significant Cal Invalid Error U1 Error Status Word CSPnn a b TERM EOl Figure 2 7 2 14 0 Unit is Uncalibrated 1 Unit is Calibrated 0 Cal Lock Switch is Unlocked 1 Cal Lock Switch
80. ffsets Re connect the banana cable to BINDING POST 1 of the test fixture Place the Model 238 in operate and verify that the reading on the DMM is within the following allow able limit 9 9940V to 10 0060V Place the Model 238 in standby and local sense interlock Cable 236 ILC 3 Banana Plug Cables 2 7078 TRX Cables 3 SECTION 1 Performance Verification 1 5 6 Low Current 1nA to 10mA Measure Ranges Verification Set up the equipment as shown in Figure 1 6 and perform the following steps to verify the lnA to 10mA measure ranges 1 Use Table 1 6 to calculate the allowable readings for the through 10mA ranges The values for Iosua Iosma and Isma were previously calculated and recorded in Table 1 3 After calculating these readings transfer them to Table 1 7 2 While in standby configure the Model 238 to meas ure current by setting it to source OV on the 1 5V source range 3 Whileinstandby set the Model 263 to the2nA range and enable guard 4 Setthe compliance limit of the Model 238 to 1nA on the lnA measurement range and enable operate 10 11 Verify that the current measurement on the Model 238 is within the allowable limits listed in the first en try of Table 1 7 On the Model 238 change the compliance limit to 10nA on the 10nA measurement range Verify that the reading on this measurement range is within the limits specified in the table Using Tab
81. gh the Model 238 will operate without a battery it will not retain any setup conditions or sweep data when turned off The instrument will power up to the factory default conditions The battery may be replaced with any 2450 lithium coin cell It can also be ordered from Keithley part number BA 44 Replacement of the lithium battery is normally a safe pro cedure as long as these safety precautions are followed WARNING The precautions below must be followed to avoid possible personal injury 1 Do not short the battery terminals together 2 Do not incinerate or otherwise expose to excessive heat gt 60 C 3 2 Keep lithium batteries away from all liquids Do not recharge lithium batteries Observe proper polarity when inserting battery into holder go Replace the battery as follows 1 Turn off the power disconnect the line cord and re move all test leads 2 After allowing at least three minutes for internal ca pacitors to discharge remove the top cover see paragraph 3 6 3 The battery is on the digital board see Figure 3 2 for location Pry the battery out of its holder using a non metallic tool WARNING Do not use a metal tool to pry out the battery as you could short the terminals 4 Install thenew battery taking care to observe proper polarity as stamped on the battery holder The plus terminal of the battery faces up 5 Reinstall the top cover 3 5 HANDLING AND CLEANING P
82. hat reading on the 193A DMM is within the allowable limits Repeat step 9 for a source value of 1V Using Table 1 4 as a guide check source values of x 10V and 100V Program the Model 238 to 0V and place it in standby Banana Plug Cables 2 193A DMM Measure V 1 7 SECTION 1 Performance Verification Table 1 4 Voltage Source Verification 238 238 Source Value Source Range 193A Range OV Current compliance is set to 10mA 1 5 4 Voltage Measure Verification Set up the equipment shown in Figure 1 4 and perform the following steps to verify voltage measurement WARNING The following procedure uses hazardous voltages 100V that could cause injury or death Exercise extreme caution when en countering these lethal voltage levels 1 While in standby configure the Model 238 to meas ure volts by setting it to source OnA on the InA cur rent source range 2 While in standby set the Model 343A calibrator to output OV on the 10V range 3 On the Model 238 set voltage compliance to 1 5V on Allowable Reading on Model 193A 18 C to 28 0 800mV to 0 800mV 2 700mYV to 2 700mV 24 000mV to 24 000mV 0 99887V to 1 00113V 0 99887V to 1 00113V 9 9940V to 10 0060V 9 9940V to 10 0060V 99 94 to 100 057 99 943V to 100 057V Place the calibrator and the Model 238 in operate Verify that the measured voltage reading on the Model 238 is within th
83. he short from the input of the Model 193A and set the Model 263 to source 90 000UA on the 200A range and enable operate SECTION 1 Performance Verification 22 23 25 26 1 4 Record the voltage measurement from the Model 193A and calculate the current Vira mV Vika logia Rika JeoA is the characterized current for the 200 range of the Model 263 It is used to check the 1001A meas urement range of the Model 238 Using a pencil re cord the calculated value of Isa in Entry 3 of Table 1 3 Place the Model 263 in standby Set the Model 193A to the 2V range Set the Model 263 to source 0 90000mA on the 2mA range and enable operate Record the voltage measurement from the Model 193A and calculate the current Vira Vion Iosma mA Rion IosmA is the characterized current for the 2mA range of the Model 263 It is used to check the 1mA meas urement range of the Model 238 Using a pencil re cord the calculated value of losma in Entry 4 of Table 1 3 27 28 29 30 31 32 33 35 36 Place the Model 263 in standby In the test fixture remove the 1kQ resistor and install the 1000 resistor R 249 100 On the Model 193A select the Ohms function 2000 range and disable zero Repeat step 3 to zero the Model 193A Measure and record the value of the 1009 resistor Q Set the Model 193A to DCV and the 2V range and disable zero To cancel
84. he voltage source WARNING The following procedure uses hazardous voltages 100V that could cause injury or death Exercise extreme caution when en countering these lethal voltage levels Set the Model 193A to measure DCV on the 200mV range While in standby set the Model 238 to source 0 on the 1 5V range and set compliance to 10mA Temporarily disconnect the banana cable from BINDING POST 2 at the rear panel of the test fixture and connect it to VOLTS LO of the Model 193A This will short the input of the Model 193A DMM 8006 COMPONET TEST FIXTURE Warning Connect to Safety Earth Ground 8006 Test Fixture A Connections OUTPUT HI 238 Source V oureurio B Schematic Equivalent Figure 1 3 Setup for Voltage Source Ranges Verification 10 11 SECTION 1 Performance Verification OntheModel 193A press ZERO to cancel any meas urement offsets Reconnect the banana cable to BINDING POST 2 of the test fixture Place the Model 238 in operate and verify that the reading on the DMM is within the limits shown in the first entry of Table 1 4 Use the filter if the read ing is noisy Press the SELECT 4 button to select the 15V range and verify that the DMM reading is within the allow able limits in Table 1 4 Using Table 1 4 as a guide repeat step 7 to check the output on the 110V range From the keypad program the Model 238 to source 1V on the 1 5V range and verify t
85. hecked all cables Display or output check one Drifts 2 Unable to zero C Unstable Will not read applied input 1 Overload J Calibration only Certificate of calibration required LY Data required attach any additional sheets as necessary Show a block diagram of your measurement system including all instruments connected whether power is turned on or not Also describe signal source Where is the measurement being performed factory controlled laboratory out of doors etc What power line voltage is used Ambient temperature F Relative humidity Other Any additional information If special modifications have been made by the user please describe Be sure to include your name and phone number on this service form spe Looking for more information A Artisan Scientific Visit us on the web at http www artisan scientific com for more information QUALITY INSTRUMENTATION GUARANTEED Price Quotations Drivers Technical Specifications Manuals and Documentation Artisan Scientific is Your Source for Quality New and Certified Used Pre owned Equipment Tens of Thousands of In Stock Items Fast Shipping and Delivery Equipment Demos Hundreds of Manufacturers Supported Leasing Monthly Rentals Consignment Service Center Repairs InstraView Remote Inspection Experienced Engineers and Technicians on staff in our Remotely inspect equipment bef
86. hout notice VOLTAGE SOURCE V MEASURE V RANGE ACCURACY ACCURACY STEP 1 Year RESOLUTION 1 Year Value SIZE 18 28 4 Digit 5 Digit 18 28 C 1 5000 100 uV 0 033 800KV 100 10 pV 0 028 450 10 5 x 600 Vy 10 71 x 600 VP 15 000 1mV 0 033 2 7 mV 1mV 100 pV 0 025 1 3mvV 110 00 10mV 0 033 24mV 10 0 025 10 I Output current Js Full scale on selected current range Specifications apply for 5 digit resolution For 4 digit resolution add 100ppm of range Assumes remote sense for I gt 1001 2 the 1A range use I T x 250 COMPLIANCE Bipolar current limit set with single value Maximum 100mA on the 110V range Minimum 1 of selected voltage range Accuracy Step Size Same as current source NOISE p p typical Range 0 1 10Hz 110 lt 3ppm of range 15 lt 3ppm of range 15V lt 10ppm of range WIDEBAND NOISE 0 1 to 20 2 8mV typical OVERSHOOT lt 0 01 110V step 10mA range SETTLING TIME lt 500 to 0 01 110V step 10mA range NMRR gt 60dB at 50 or 60Hz LINE CYCLE integration time selected CMRR 120dB at DC 50 or 60Hz LINE CYCLE integration time selected INPUT IMPEDANCE as a voltmeter gt 10 Q paralleled by 20pF CURRENT SOURCEI MEASUREI RANGE ACCURACY ACCURACY STEP 1 Year RESOLUTION 1 Year Value SIZE 18 28 4 Digit 5 Digit 18 28
87. iate voltage level present on a control line will cause the respective switch to close or open These control lines located on schematic 238 126 page 1 drive relay coils gates of switching FETs and inputs of analog switches The following summarizes the nominal voltage levels that should be present on the control lines to drive these switching devices 3 10 power on 5V Digital supply 5V 0 25 Reference to digital common 15 Analog supplies 15V 1V Reference to floating common 15V 1V 30 Analog supplies 30V 2V Reference to floating common 30V 2V 5V Analog supply 5V 0 25 Reference to floating common 150V Floating supply 150V 20V Reference to output common 150 20V 15V Floating supply 15V 1V Reference to output common 15V 1V 24V Floating supply 30V 6V Reference to output common 30V 6V Power Supply Checks Stp Ttem Component Required Condition Set to 115V or 230V as required Line voltage selection Check for continuity Plugged into live receptacle Remove fuse to check NOTE To check voltage levels on control lines refer ence the measurement to floating common CAUTION On the Model 238 remove the ground link from output common when using chassis grounded equipment to make measure ments referenced to floating ground Other wise erroneous measurements or possible instrument damage may result Relay Drive K8 K9 K10 K11 and K1
88. ide panel board This shield assembly is secured to the Note To reinstall align the strip in the re board by four screws cessed part of the side panel and press the 8 Remove the display board as follows strip at the locations of the fasteners A Atthe front panel pull off the rotary knob E Remove the four screws that secure the front B Remove each of the four decorative strips from panel assembly to the side panels and disengage the side panels as follows the front panel assembly from the chassis a From inside the case place a thin blade F Loosen the four Allen set screws securing the screwdriver into one of the holes where the bezel assemblies to the front panel Remove the decorative strip is secured bezel assemblies from the front panel C Carefully push outwards until the strip dis G Lift the display board away from front panel engages from one of the fasteners Output board located here J13 Output LO 412 J11 Output HI Sense HI Figure 3 4 Analog Board Shields Removed 3 6 Figure 3 5 Model 238 Exploded View Decorative Strip 4 af 8 8 ez Mounting Rail 3 Bezel Assembly 2 SECTION 3 Maintenance SECIION 3 Maintenance 9 Theinstrument can re assembled by reversing the above procedure Make sure that all parts are prop erly seated and secured and that all connections are properly made To ensure proper operation shields
89. ing its input VOLTS HI to LO and enabling zero Remove the short from the input of the Model 193A and set the Model 263 to source 9 0000mA on the 20mA range and enable operate Record the voltage measurement from the Model 193A and calculate the current Vicon Q Vioon Toma mA Ima is the characterized current for the 20mA range of the Model 263 It is used to calibrate the 10mA range of the Model 238 Using a pencil record the calculated value of Joma in Entry 5 of Table 2 3 Place the Model 263 in standby NOTE To store calibration constants in nonvolatile memory place the CAL LOCK switch to the unlocked in position see paragraph 2 5 With the switch in the locked out position calibration will be temporary That is the new calibration constants will be lost when the in strument is turned off SECTION 2 Calibration Table 2 3 Model 263 I Source Characterization I Source Value Limits 0 9 450pA Characterized I Source Value Ie Source 0 9000 9 000hA 4 3nA 90 000nA 90 45 0 9000mA 0 9mA 430nA 9 000mA 9mA 5 4HA The characterized I source values should be within the listed limits These limits are based on 90 day specifications of the Models 263 and 193A A characterized value that does not fall within these limits indicates a calculation error or that the Model 263 and or Model 193A is out of specification 2 6 2 With the
90. ired position in for permanent calibration or out for temporary calibration C59X If the switch is in the out position the message TEMPORARY will be briefly displayed to in dicate that newly entered cal constants will be lost when the Model 238 is turned off Permanent cali bration can still be done by setting the calibration switch to the in position and sending and C59X over the bus in that order After sending the C59X command the Model 238 will go into standby SECTION 2 Calibration 2 6 3 100mA and 1A Ranges Calibration To calibrate the 100mA and 1A ranges connect the circuit shown in Figure 2 4 100mA Range Calibration Perform the following steps to calibrate the 100mA source and measure range 10 11 2 8 Set the Model 193A to the 200 DC range Place the Model 238 in operate The calibration mode cannot be entered with the Model 238 in standby Over the IEEE 488 bus send the following command to enter the calibration mode COX Note All other calibration commands C1 through C59 will be ignored unless the CO command is first sent over the bus Send the following command to source 0mA on the 100mA range C34X Set the Model 343A to output and place the Model 2500E on the 100 range From the display of the Model 193A record the off set current Loma Loma Send the current reading Loma over the bus with the C35 co
91. is Locked Present Cal Constants Will Not be Saved Calibration Step in Progress U7 Calibration Status Word 2 8 CALIBRATION PROGRAM The following program can be used to calibrate the Model 238 Configure the recommended equipment and software per manufacturers instructions and type in the program NOTE The program does not calibrate the 1 range since the equipment used to calibrate that range is not programmable and thus cannot be controlled over the IEEE 488 bus Rev 10 11 90 tX OXOX X KKK KKK KKK KKK KKK KKK KKK KR OK OK OC KARA KK KAKA AKER KKK AK KAKA KKK KKK oe c Gk KKK KKK KK AK KK tx Model 238 Calibration Program x NOTE Program calibrates voltage and lnA lOmA current ranges only x Equipment Required Model 193A DMM Model 263 Calibrator 193A address 10 238 address 16 263 address 8 Computer IBM PC AT or compatible tx IEEE 488 interface card IOtech or National PC II or IIA Operating system PC DOS or MS DOS version 3 0 or later Programming language Microsoft QuickBASIC version 4 0 or later x x x IEEE 488 bus driver IOtech Driver488 version 2 3 or later occ e eoo XX X CLs OPTION BASE 1 DIM char 5 char 5 1 8 msg 3 Dimension arrays DIM Errs 9 FOR I 1 TO 5 READ 1 NEXT I Read prompt strings FOR I 1 TO 8 READ Ica
92. istors R63 and R64 The input current is applied to the gate of O4 via FET switch Q2 converting the bipolar 10V input to a unipolar current Operational amplifier U50 and Q4 form an integrator with capacitor C63 This integrator ramps in a positive direction since the current is negatively offset until it reaches a threshold or until a timebase interval occurs and switches on a balance current This continues for a length of time that is determined by the value in reg ister U44 which is programmed by the source measure controller Device U45 is an 8 bit magnitude comparator which con tinuously compares the set value to the count value in counter 046 When these two numbers match the output on pin 19 of U45 stops the A D converter thus signaling the end of the charge balance phase After determining that the charge balance has stopped by monitoring counts or timing out the software sets the final slope balance line high This clears U46 making it ready for a new charge balance phase and starts the final slope phase of the A D converter The final slope phase essentially removes all charge re maining on the integrator by ramping the output of U50 to OV Counts are accumulated during the final slope and used for calculation of the effective input signal The A D converter is run through a number of phases that 4 8 are used to null any error signals present in the A D or analog front end The time base for the A D converter is p
93. l I NEXT I 1 Read cal currents FOR I 1 TO 3 READ msg I NEXT I Read procedure messages FOR I 1 TO 9 READ NEXT I Read error messages Diy 3 Measurement delay seconds t XX X o XX o Xo o o o X x INITIALIZE IEEE 488 INTERFACE XO KKK KKK RK X X X X X X X xXx OPEN ADEVAIEEEOUT FOR OUTPUT AS 1 OPEN DEV IEEEIN FOR INPUT AS 2 Start IOCTL 1 BREAK Reset interface PRINT 1 RESET Warm start interface Open IEEE 488 output path PRINT 1 REMOTE Assert remote enable t Open IEEE 488 input path PRINT 1 CLEAR Send device clear PRINT 1 TIME OUT 30 30 second bus time out PRINT Z1 LOL Enable Local Lockout CLS Clear screen LOCATE 12 23 PRINT Model 238 Calibration Program LOCATE 21 12 PRINT NOTE This program does NOT calibrate 100mA and 1A ranges LOCATE 22 12 PRINT Refer to Service Manual for complete information LOCATE 14 10 GOSUB KeyCheck Check for operator signal xxx x xXx KK RK KK KKK SELECT FUNCTION S TO CALIBRATE SelCal CLS GOSUB TypeCheck E 0 C120 t Clear error counter PRINT Select function to calibrate PRINT FOR I 1 TO 3 Loop for all 3 selections PRINT Us I te msg CID calibration NEXT I PRINT InCal INPUT Select calibration function 1 3 cal IF cal lt 1 OR cal gt 3 THEN BEEP GOTO InCal PRINT t 3 X KKK KK IKK KK K KR KKK X X X INITIALIZE 238
94. le 1 7 check the rest of the Model 238 cur rent ranges with the output of the Model 263 in standby Set the Model 263 to output 0 90000nA on the 2nA range and set the Model 238 compliance limit to 1nA on the InA measurement range Verify that the reading is within the limits specified in the table On the Model 263 change the output to negative po larity and verify that the reading is within the limits specified in the table Using Table 1 7 as a guide check the 10nA through 10mA measurement ranges of the Model 238 Place the Model 263 in standby Table 1 6 Allowable Reading Calculations for Low Current Measure Verification 10 to 10mA 238 Allowable Reading Measure Typical Range Reading Calculations Upper Limit Limits HosyA 0 0004 60pA losua 0 0004 Iosua 60pA 0 00035 Isua 700pA Ispa 0 00035 Isua 700pA Isoua 0 00035 Isya 6nA 0 00035 6nA 0 00035 Iooma 60nA Tooma 0 00035 Iosna 60nA I ma 0 00038 Ima 600nA I ma 0 00038 Isma 600nA 1 losua Iopa Isona Iosma and Ia are obtained from Table 1 3 Allowable reading limits are to be transferred to Table 1 7 0 90000 870 0 90000HA 870 49 00001A 8nA 9 0000 8nA 90 0004 83nA 90 0001LA 83nA 0 90000mA 8001 0 90000mA 800nA 9 00
95. le national safety approvals may be used if the rating and type are the same Other components that are not safety related may be purchased from other suppliers as long as they are equivalent to the original component Note that se lected parts should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product If you are unsure about the applicability of a replacement component call a Keithley Instruments office for information To clean an instrument use a damp cloth or mild water based cleaner Clean the exterior of the instrument only Do not apply cleaner directly to the instrument or allow liquids to enter or spill on the instrument Products that consist of a circuit board with no case or chassis e g data acquisition board for installation into a computer should never require cleaning if handled according to in structions If the board becomes contaminated and operation is af fected the board should be returned to the factory for proper cleaning servicing Rev 10 99 Model 238 Source Measure Unit Specifications SOURCE MEASURE UNIT Sources voltage while measuring current or sources current while measuring voltage FUNCTION Can be used as DC source or meter sweep source or full source measure unit SOURCE DELAY MEASURE CYCLE Source Source Delay Measure Cycle Default Measure Delay Delay Integration Time Default Delay Fixed delay for instrum
96. libration is performed using the C command over the IEEE 488 bus Details concerning the use of the C command and other commands are contained in Section 3 of the Model 238 Operator s Manual WARNING Lethal voltage up to 100V will be connected to the Model 8006 test fixture To avoid pos sible shock hazard the safety interlock cir cuit must be connected to the Model 238 Connect the test fixture screw to safety earth ground us ing 18 AWG wire minimum before use Turn off all power before connecting or disconnecting wires or ca bles Also keep in mind that GUARD is always enabled Thus alethal voltage on OUTPUT Hl is also present on the two GUARD terminals of the Model 238 2 6 1 Equipment Characterization In order to calibrate the In A 10HA 100 1mA and 10mA source and measure ranges of the Model 238 the 94A 904A 0 9m and 9mA outputs of the Model 263 are characterized 1 Connect the Model 263 source Model 193A DMM and Model 8006 test fixture as shown in Figure 2 2 Install the 100kQ resistor in Table 2 1 in the AXIAL KELVIN CLIPS test socket of the test fixture Eg pP 19 Pa manva Rear Panel e 7078 TRX Cable Warning Connect to Safety Earth Ground Signal Model 8006 Test Fixture A Connections OUTPUT e 263 Source Source 1 B Schematic Equivalent Figure 2 2 Setup for Equipment Characterization 2 Configure the source and DMM as follows 3
97. located at the rear of the instrument Re move those two screws C Slide the bottom cover towards the rear until it completely separates from the chassis CAUTION When reinstalling the bottom cover use the proper screws to install the four feet Screws that are too long will cause damage to the in ternal circuit boards The front feet are se cured by 6 32x5 8 screws the rear feet are secured by 6 32x1 2 screws If leaving the feet off in order to install the instrument in a rack do not use the original screws to secure the bottom cover Instead use the four short screws 6 32 1 4 sup plied with the rack mount kit 3 If the cooling fan needs to be removed proceed as follows Otherwise proceed to step 4 A Disconnect P22 fan from 22 on the digital board see Figure 3 2 B Disconnect the ground wire from the rear panel C Remove the four fasteners that secure the fan to the rear panel D Pull the fan out of the instrument case Removetheoutput board see Figure 3 3 as follows Note The output board is mounted on the analog board adjacent to the rear panel WARNING To avoid burns from excessive heat make sure that the heat sink on the output board is cool enough to handle If the heat sink is hot wait until it is cool before attempting to re move the output board A Disconnect P16 from 16 on the digital board see Figure 3 2 B Remove the four screws that secure the output board
98. losed Closed Open Open Operate Closed Closed Closed Closed Open Open Table 3 8 Analog Switching A D Multiplexing U1 Switch Closed pins Reference V Measure I Measure Zero 3 8 6 Digital and Display Checks The digital and display circuitry can be checked out by using the troubleshooting data found in Table 3 9 and 3 10 Note The firmware that controls the Model 238 is con tained in two EPROMs U17 and U31 If itis necessary to replace one or both of the EPROMs make sure that both EPROMs installed in the instrument have the same firm ware revision level After installing new firmware per form factory initialization to write firmware changes to the E2ROM Factory initialization is performed by ena bling MENU displaying FACTORY INIT with the rotary knob and then pressing ENTER CAUTION The EPROMs are static sensitive devices that are susceptible to damage by routine han dling Be sure to handle the devices as ex plained in paragraph 3 7 SECTION 3 Maintenance Table 3 9 Digital Circuitry Checks U12 U13 U17 U30 U31 and U33 Pass RAM EPROM DPRAM Display will lock if failure occurs and tests on power up TTL level pulse every 1msec 028 pin 18 I O controller VIA display clock U28 pin 6 PA4 pin 7 5 pin 8 PA6 pin 9 PA7 Data input to VIA when button presse Switch data 5 or 0V U28 pin 11
99. ly as can be evidence by the common connec tions of the inputs of U4 pin 3 and U7 pin 8 This allows the display to be refreshed faster thus eliminating flicker associated with line frequency beating with lighting and such The front panel indicator LEDs DS10 through 0529 are driven in a similar manner by sink drivers of 08 The anodes of the two separate banks of display ele ments are driven by source drivers U5 and U6 leftbank and U9 and U10 right bank These are serial input par 4 9 SECTION 4 Principles of Operation allel output combination shift register drivers They in terface directly to the 1 controller VIA clock data inter face A strobe is provided by software to load the outputs of the drivers with data The displays are indexed at a 100 2 1ms rate Circuit components U1 and U2 provide a timer function that allow the selection of either a bright or dim digit and is used for flashing cursor digits A counter U2 times out after 256usec and bit 16 of the two serial bank source drivers is fed back into U1 pin 12 and U1 pin 6 Depend ing on the states of these bits the LEDs will be on for the entire 1msec duration or 1 4 256jisec duration The col umn drivers are selected by a one of ten decoder U3 which is directly driven from the VIA of the I O control ler These columns as they are selected also select col umns in the front panel key switch matrix through di odes through CR 10 The colum
100. mmand as follows to calibrate offset for the 100mA range C35 LonAX Send the following command to source 90mA C36X Set the calibration source to output 90mA on the 100mA range and from the display of the Model 193A record the current reading Losa Calculate the actual current It90mA using the fol lowing calculation Loma 90mA mA Send the calculated current reading TeomA over the bus with the C37 command as follows to calibrate 12 13 14 15 16 17 18 19 20 21 gain for the 100mA source and measurement range C37 LomaX Send the following command to source on the 100mA range C38X Set the Model 343A to OV and place the Model 2500E on the 100A range From the display of the Model 193A record the off set current Loma Toma Send the current reading LomA over the bus with the C39 command as follows to calibrate gain for the 100mA source and measurement range C39 TomaX Send the following command to source 90mA C40X Set the calibration source to 90mA on the 100mA range From the display of the Model 193A record the cur rent reading L 34 Lissa Calculate the actual current using the following cal culation Tooma 90mA 1934 mA Send the calculated current reading Loma over the bus with the C41 command as follows to calibrate gain for the 100mA source and measure range C41 Lsoma X Send th
101. n am plifier The four signals 10V reference V Measure I Measure and floating common are multiplexed U1 and routed to the A D converter via buffer U21 4 2 2 Output Module Theoutput stage of the bootstrap amplifier basically con sists of a class AB circuit whose bias is controlled by the output of the error amplifier The simplified schematic diagram of the output module is shown in Figure 4 3 The detailed schematic of the output stage is found on drawings 238 166 and 238 126 page 2 4 4 Low Current Ranges Atthe heart of the output stage are power transistors Q21 and Q19 The collector of Q21 is effectively connected to the 150V 120mA power supply while the collector of 019 is effectively connected to the 150 120m A power supply When programmed for a zero output both Q21 and Q19 are zero biased off The 150V supplies are dropped across the high impedance of these two transistors As a result zero voltage is present at the output floating com mon to output common When the source is pro grammed for a positive output Q21 becomes forward bi ased on The voltage drop across Q21 becomes less than 150V As a result the voltage present at the output is the difference between the supply voltage 150V and the voltage drop across Q21 For a positive output Q19 is re verse biased off keeping the negative supply isolated from the output Circuitry for a negative output functions in a similar manner
102. n driven low and the four lines fed back to the VIA of the I O controller iden tify which key is pressed 4 5 POWER SUPPLY The schematic diagram for the power supply is located on page 4 of drawing 236 106 The power supply consists of an off line transformer T1 which has selectable 115 230V operation It is essentially two 115 volts primaries either in series or parallel In par allel with one of the primary windings is the cooling fan allowing it to always operate on 115V The line select switch S2 allows user selectable line voltages Switch S1 is the main power switch F1 is the system fuse and J2 isa rear panel mounted line filter connector The secondary of the transformer provides all of the power supply volt ages The digital power supply gray transformer secondaries on schematic is capable of delivering 5V at 1 2A to 4 10 power all digital and front panel circuit components Full wave rectification is provided by the bridge rectifier CR1 Capacitors C106 and C107 provide spike suppression while C4 provides filtering Voltage regulation is pro vided by 1 with capacitor C24 on its output for stabil ity The 15V and 30V analog supplies are derived from the or ange colored secondaries The 15V power supply consists of a bridge rectifier CR4 filter capacitors C53 and C55 15V regulators VR3 and and stability capacitors C91 and C92 A voltage doubler circuit consisting of diodes CR2 CR3 CR6 and CR
103. nded for use by qualified personnel having a basic understanding of analog and digital circuitry The individual should also be experienced at using typical test equipment as well as ordinary troubleshooting pro cedures The information presented here has been writ ten to assist in isolating a defective circuit or circuit sec tion Isolation of a specific component is left to the techni cian Note that schematic diagrams and component loca tion drawings which are an essential aid to troubleshoot ing are included in Section 5 3 8 3 8 1 Recommended Test Equipment Success in troubleshooting complex equipment like the Model238 depends not only on the skill of the technician but relies on the use of accurate reliable test equipment Table3 2 lists the equipment recommended for troubleshooting the Model 238 Other equipment such as logic analyzers and capacitance checkers could also be helpful Table 3 2 Recommended Troubleshooting Equipment Five function DMM with Power supply and DC 0 1 basic DCV accuracy voltage checks analog 10M input impedance signal tracing continuity logic levels Dual trace triggered sweep oscilloscope DC to 50MHz Digital and analog waveform checks Digital frequency counter Checking clock frequencies 3 8 2 Diagnostics The Model 238 has some internal diagnostic capabilities to aid in troubleshooting Power up and MEMORY TEST On power up or when
104. necting sources to switching cards install protective devices to lim it fault current and voltage to the card Before operating an instrument make sure the line cord is connect ed to a properly grounded power receptacle Inspect the connecting cables test leads and jumpers for possible wear cracks or breaks before each use For maximum safety do not touch the product test cables or any other instruments while power is applied to the circuit under test ALWAYS remove power from the entire test system and discharge any capacitors before connecting or disconnecting cables or jump ers installing or removing switching cards or making internal changes such as installing or removing jumpers Do not touch any object that could provide a current path to the common side of the circuit under test or power line earth ground Always make measurements with dry hands while standing on a dry insulated surface capable of withstanding the voltage being measured The instrument and accessories must be used in accordance with its specifications and operating instructions or the safety of the equip ment may be impaired Do not exceed the maximum signal levels of the instruments and ac cessories as defined in the specifications and operating informa tion and as shown on the instrument or test fixture panels or switching card When fuses are used in a product replace with same type and rating for continued protection against fire hazard
105. nterlock Cable 236 ILC 3 Banana Plug 7078 TRX Cablas 2 Cables 3 6172 Adapter 0 OUTPUT MPONET Ca Warning Connect M to Safety Earth 9 9 ro Ground TID V rct 263 Source ux 8006 Test Fixture INPUT P op 617 Electrometer 8172 apter A Connections Note 617 GUARD dualled 238 OUTPUT 263 Source l output LO Source Source 1 617 Electrometer Measure B Schematic Equivalent Figure 1 7 Setup for Low Current Source Ranges Verification 1nA to 10mA SECTION 1 Performance Verification 1 5 8 100 and 1A Measure Ranges Verification Set up the equipment as shown in Figure 1 8 A copper short is installed in the test socket 100mA Measure Range Verification Perform the following steps to verify the 100mA meas urement range 1 While in standby set the Model 238 to source OV on the 1 5V source range and set compliance to 100mA 2 Remove the short from the test fixture and place the Model 238 in standby 3 Verify that the current reading on the Model 238 is within the following limits Ls 4 Place the short in the test fixture socket and set the calibration source to output 90mA 5 Verify that the current reading on the Model 238 is within the following limits LD3s 89 904mA to 90 096mA Set the calibration source to output
106. of the V I feedback cir cuitry is shown in Figure 4 4 The detailed schematic of this circuitry is provided by page 3 of drawing 238 126 Output Module Simplified Schematic Diagram SECTION 4 Principles of Operation 0 10 Sense K iAmpB Resistor Amps Ranging Current range selection is accom plished by activating the appropriate range FET and or relay The nominal range resistances relays and FETs for each of the nine current ranges are shown in the illustra tion Figure 4 4 The FET labeled QAB for the 100mA range is actually a composite P and N channel FET A more detailed look at the 100mA range is shown in Figure 4 5 In reality QA is comprised of P channel FETs Q8 and Q9 and is comprised of N channel FETs Q6 Q7 Q37 and Q38 Without special circuitry current measurement range changes may cause voltage spikes to occur at the output Voltage spikes are caused by contact bounce of the se lected range relay These spikes occur too fast for the bootstrap amplifier to react to the change in feedback voltage As a result the system cannot adjust itself ac cordingly to maintain a steady voltage output 4 5 SECTION 4 Principles of Operation Amps Ranging 10GQ 1 100 Output Stage Output Stage 1 B Feedback V Feedback igure 4 4 Feedback Simplified Schematic The Model 238 resolves this problem by using circuitry that in effect shunts the current r
107. onnel may perform installation and service procedures Exercise extreme caution when a shock hazard is present Lethal voltage may be present on cable connector jacks or test fixtures The American National Standards Institute ANST states that a shock hazard exists when voltage levels greater than 30V RMS 42 4V peak or 60VDC are present good safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring Safety Precautions Users of this product must be protected from electric shock at all times The responsible body must ensure that users are prevented access and or insulated from every connection point some cases connections must be exposed to potential human contact Product users in these circumstances must be trained to protect themselves from the risk of electric shock If the circuit is capable of operating at or above 1000 volts no conductive part of the circuit may be exposed As described in the International Electrotechnical Commission IEC Standard IEC 664 digital multimeter measuring circuits e g Keithley Models 175A 199 2000 2001 2002 and 2010 are Installation Category II All other instruments signal terminals are Installation Category I and must not be connected to mains Do not connect switching cards directly to unlimited power circuits They are intended to be used with impedance limited sources NEVER connect switching cards directly to AC mains When con
108. orary calibration Send the following command over the bus to exit calibration and store the cal constants C59X If the switch is in the out position the message TEMPORARY CAL will be briefly displayed to in dicate that newly entered cal constants will be lost when the Model 238 is turned off Permanent cali bration can still be done by setting the calibration switch to the in position and sending COX and C59X over the bus in that order After sending the C59X command the Model 238 will go into standby Place the 263 into standby SECTION 2 Calibration 2 7 CALIBRATION ERRORS following steps provide the general procedure required to detect calibration errors over the IEEE 488 bus Calibration errors and subsequent error messages that could occur during calibration are explained in Table 2 4 1 Program the Model 238 to generate an SRQ on an er It is important to realize that if any of these errors except ror by sending the M32 command over the bus IN CAL occur calibration is compromised Even though 2 When an SRQ occurs error send the U1 command some errors will cause default cal constants to be used and then address the Model 238 to talk they do not guarantee specified accuracy When a cali 3 Display the character string U1 Error Status Word bration error occurs find and fix the problem and repeat from the Model 238 on the computer CRT and refer calibration to Figure 2 6 to determine the error type
109. ore purchasing with our State of the art Full Service In House Service Center Facility Innovative InstraView website at http www instraview com We buy used equipment We also offer credit for Buy Backs and Trade Ins Sell your excess underutilized and idle used equipment Contact one of our Customer Service Representatives todayl Talk to live person 888 88 SOURCE 888 887 6872 Contact us by email sales artisan scientific com Visit our website http www artisan scientific com
110. play of the Model 193A record the volt 4 Over the IEEE 488 bus send the following command age reading to enter the calibration mode COX 11 Note All other calibration commands C1 through Send the measured voltage reading over the bus with the C5 command as follows to calibrate C59 will be ignored unless the CO command is first sent over the bus gain for the 1 5V source and measurement range C5 VmsrX 2 Calibration Interlock Cable 236 ILC 3 Warning Connect to Safety Earth Ground Figure 2 3 12 13 14 15 2 6 8006 Test Fixture A Connections OUTPUT HI 238 Source V output Lo B Schematic Equivalent Setup for Volts Calibration Send the following command to source on the 1 5V range C6X From the display of the Model 193A record the volt age reading VMsR Send the measured voltage reading Vwsg over the bus with the C7 command as follows to calibrate off set for the 1 5V source and measurement range 7 Send the following command to source 1V on the 1 5 range C8X 16 17 18 19 Model 238 Banana Plug Cables 3 Measure V From the display of the Model 193A record the volt age reading VMsR Send the measured voltage reading over the bus with the C9 command as follows to calibrate gain for the 1 5V source and measurement range
111. press any switch located in the third column Depress any switch located in the fourth column 5V supply Segment drivers Digit drivers Pulse present when button pressed Pulse present when button pressed Pulse present when button pressed Pulse present when button pressed SECTION 4 Principles of Operation 4 1 INTRODUCTION A simplified block diagram of the Model 238 is shown in Figure 4 1 The instrument may be divided into two sec tions analog and digital circuitry The analog and digital sections are electrically isolated from each other by the This section contains a general functional description of use of opto isolators for control and communications the Model 238 Detailed schematics and component loca Separate power supplies for the analog and digital sec tion drawings are located at the end of this manual tions ensure proper isolation Feedback Digital Source Measure RAM IEEE 488 y o TRIG IN Interface Controller TRIG OUT Front Panel Figure 4 1 Overall Block Diagram SECTION 4 Principles of Operation 42 ANALOG CIRCUITRY The heart of the source is an error amplifier that along with its complex scheme of feedback elements is config ured as a bootstrap amplifier Input stimulus for the am plifier is provided by two user programmed digital to analog converters DACs The controlling function cur rent or voltage and selected polarity of the source turns on one of four preci
112. r IF INS lt gt y AND INS lt gt Y THEN GOTO CharCheck PRINT InChar PRINT Enter the following 263 characterization parameters PRINT See Service Manual for 263 characterization procedure PRINT FOR I 1 TO 5 Loop for all parameters PRINT Enter parameter for 263 char I Prompt for parameter INPUT char I t Input parameter NEXT I t Loop back for next parameter NoChar FOR 1 1 TO 5 IF char I 0 THEN BEEP PRINT Improper characterization parameters are presently entered GOTO InChar END IF NEXT I PRINT GOSUB KeyCheck PRINT Performing 1 10mA current measurement calibration procedure PRINT Press ESC to abort procedure and restart program PRINT 1 OUTPUT 16 N1X Put 238 in operate PRINT 1 OUTPUT 16 COX Put 238 in cal mode Jel t Initialize array index counters FOR I 42 TO 57 Loop for ali cal points INS INKEYS IF INS CHR 27 THEN PRINT 1 CLEAR GOTO SelCal PRINT 1 OUTPUT 08 V Ical J X Program 263 current value GOSUB Delay Allow settling time PRINT 1 OUTPUT 16 C I X t Send cal offset command GOSUB Delay Settling time 1 Increment C command value PRINT 1 OUTPUT 08 01X Put 263 in operate GOSUB Delay Settling time IF I gt 47 THEN Use characterized values for gt 100nA PRINT 1 OUTPUT 16 C I char K X K K 1 Increment array counter ELSE PRINT OUTPUT 16 C I
113. r nal cleanliness and proper ventilation 3 1 SECTION 3 Maintenance Perform the following steps to remove and clean the fan filter element 1 Turn off the Model 238 The fan must be off in order to prevent dirt and dust from being ingested into the instrument case while removing the filter element 2 Position the instrument such that you are facing the rear panel The cooling fan is internally mounted to the right hand end of the rear panel The filter as sembly is mounted to the rear panel in front of the fan intake vents 3 Remove the two screws that secure the vented shroud of the filter assembly to the rear panel The filter assembly will swing away from the rear panel allowing the filter element to be removed 4 Toclean the filter element blow out the dust and dirt with pressurized air or nitrogen 5 Reinstall the filter assembly onto the rear panel The two hinges of the filter assembly shroud fit into the rear panel vents Make sure the filter element covers all the rear panel intake vents 3 4 BATTERY REPLACEMENT When line power to the Model 238 is turned off the lith ium battery on the digital board provides backup power to the memory in which user programmed setup condi tions and sweep data are stored The battery has enough capacity to maintain data for one year of continuous power off or two years if the Model 238 is on for 12 hours every day The battery by itself has a shelf life of eight years Althou
114. ranging The bottom of the voltage di vider network is connected to output common OUT via op amp U47 which is configured as a x1 buffer In lo cal sense K5 closed OUT is accessed internally In re mote sense K5 open OUT is accessed at the load Volts range relay K6 determines the resistance of the bot tom leg of the voltage divider Table 4 1 identifies the re lays for each voltage range The output of the voltage di vider is routed to the input of the differential amplifier U7 via op amp U5 which serves as a x1 buffer Op amp U7 is configured as a x1 differential amplifier The output voltage VOUT of this amplifier will be the algebraic difference of its two inputs Ei E VOUT V FEEDBACK is routed back as a bootstrap am plifier feedback loop and also to the A D multiplexer for measurement SECTION 4 Principles of Operation Table 4 1 Volts Range Relays Relays Energized 238 Range 1 5V 15 110V None 4 3 A D CONVERTER The Source Measure Unit uses a constant frequency vari able pulse width analog to digital converter The sche matic diagram for the A D converter is located on page 3 of drawing 238 106 Reading conversions start with a charge balance phase and end with a single slope phase thus producing two sets of counts from U47 back to the pre scale counter U21 and VIA of the source measure controller The A D input is applied to current offset res
115. rants the following items for 90 days from the date of shipment probes cables rechargeable batteries diskettes and documentation During the warranty period we will at our option either repair or replace any product that proves to be defective To exercise this warranty write or call your local Keithley representative or contact Keithley headquarters in Cleveland Ohio You will be given prompt assistance and return instructions Send the product transportation prepaid to the indicated service facility Repairs will be made and the product returned transportation prepaid Repaired or replaced products are warranted for the balance of the original warranty period or at least 90 days LIMITATION OF WARRANTY This warranty does not apply to defects resulting from product modification without Keithley s express written consent or misuse of any product or part This warranty also does not apply to fuses software non rechargeable batteries damage from battery leakage or problems arising from normal wear or failure to follow instructions THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES EXPRESSED OR IMPLIED INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE THE REMEDIES PRO VIDED HEREIN ARE BUYER S SOLE AND EXCLUSIVE REMEDIES NEITHER KEITHLEY INSTRUMENTS INC NOR ANY OF ITS EMPLOYEES SHALL BE LIABLE FOR ANY DIRECT INDIRECT SPECIAL INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OF ITS
116. ration program y n INS INS LEFTSCINS 1 IF INS y OR INS Y THEN GOTO PRINT 1 LOCAL t Restore local operation CLOSE 1 CLOSE 2 Close I O files END End of program TKK KK KKK KK KKK KIRK KK KKK RK KK KKK KKK KK RIK KK KKK KKK RK KR AK KKK KKK KKK ARK KKK KARA tx VOLTAGE FONCTION CALIBRATION ROUTINES YXXXXXXKXXXXKXXKXXKXXXXXXKXXXXXXXXKXXXKXXXKXXXXXXKXXXKXXKXKXXKXXKXKXXXXXKXKXKXXXKXKXXKXXKXKXKXKXXKXXKXKAKXKXXKDXXKXKXA CalVol CLS PRINT PRINT PRINT PRINT GOSUB PRINT PRINT PRINT PRINT PRINT PRINT PRINT PRINT BEEP PRINT PRINT PRINT PRINT PRINT BEEP PRINT PRINT 60808 PRINT PRINT PRINT PRINT FOR I INS PRINT GOSUB PRINT INPUT I PRINT NEXT 1 PRINT PRINT PRINT RETURN t t t Voltage Calibration Procedure See Service Manual for details on test connections Short 238 output and 193A input KeyCheck 1 OUTPUT 10 FOROS3G1X 193A DOV 6 1 2 digits auto range 1 OUTPUT 16 N1X Put 238 in operate 1 OUTPUT 16 COX Put 238 in cal mode Performing common mode adjustment Please wait approximately 30 seconds for completion 1 OUTPUT 16 C1X Calibrate 238 common mode 1 OUTPUT 10 Z1X Zero 193A 1 OUTPUT 16 C59X t Remove 238 from cal mode 1 OUTPUT 16 NOX t Put 238 in standby Remove short from 238 output and 193A input Make sure 238 output is properly connected to 193A input
117. rce OV the 1 5V source range Allowable readings for the 15A through 10mA ranges are calculated in Table 1 6 SECTION 1 Performance Verification 1 5 7 Low Current 1nA to 10 Source Ranges Verification Set up the equipment as shown in Figure 1 7 and perform the following steps to verify the lnA to 10mA source ranges Use Table 1 8 to calculate the allowable readings for the 1mA through 10mA ranges The values for Tosa Igoa and Isma were previously calculated and recorded in Table 1 3 After calculating the al lowable readings transfer them to Table 1 9 While in standby configure the Model 238 to source OnA on the lnA source range with a compliance limit of 1 5V on the 1 5V measurement range While in standby configure the Model 263 to source OnA on the 2nA range With Zero Check enabled zero correct the Model 617 on the 2pA range On the Model 617 disable Zero Check and place the Model 238 in operate Verify that the reading on the Model 617 is within the limits specified in the first entry of Table 1 9 Set the Model 617 to the 20pA range and set the Model 238 to source OnA on the 10nA range Verify that the reading on the Model 617 is within the limits specified in the second entry of Table 1 9 10 11 12 13 14 15 16 Using Table 1 9 as a guide set the Model 238 to source zero on the 100nA through 10mA ranges and check that the subsequent readings are within
118. rovided by an os cillator that consists of inverter U57 and crystal Y2 The 7 68MHz time base which is a multiple of 60Hz is di vided by counters U41 and U40 to provide system timing functions for charge balance control The 7 68MHz is fed directly to NOR gate U47 where it is gated on and off by the rest of the A D function The A D power supply ref erence voltages 10V and 5V are derived from opera tional amplifier U56 and associated circuitry These are reference voltages used in generating currents and thresholds for the A D converter 4 4 DIGITAL CIRCUITRY The schematic diagrams for the digital circuitry are lo cated in last section of this manual drawing number 238 106 The Source Measure Unit is controlled by two 6809 8 bit 2MHz N MOS microprocessors These two microproces sors coordinate all instrument functions These include running the display and keyboard servicing the IEEE 488 interface and control of all analog functions 441 Controller The schematic diagram for theI O controller is provided on page 1 of drawing 238 106 The I O controller controls the display and front panel controls the IEEE 488 interface test fixture lid closure detection and TRIGGER IN and TRIGGER OUT It also maintains calibration constants and contains the major portion of the operating system for the instrument At the heart of the I O controller system is 8 bit 68809 microprocessor running at 2MHz The system master os
119. short still installed send the following com mand over the bus to perform common mode cali bration CIX Note Common mode calibration takes approxi mately 30 seconds to complete 6 Removetheshort Jumper A and send the following command to source 40V on the 1 5V range Voltage Calibration 5 For voltage calibration connect the Model 193A DMM to the Model 238 via the Model 8006 test fixture as shown in Figure 2 3 Jumper A is initially installed to short the out put of the Model 238 and the input of the Model 193A WARNING The following procedure uses hazardous C2X voltages 100V that could cause injury or 7 From the display of the Model 193A record the volt death Exercise extreme caution when en age reading countering these lethal voltage levels Make sure to connect the Model 8006 interlock cir cuit to the Model 238 8 Send the measured voltage reading over the bus with the C3 command as follows to calibrate off set for the 1 5V source and measurement range C3 VMsRX For example if the reading on the Model 193A is 0 00036V send C3 00036X or C3 36E 5X over the Perform the following steps to calibrate the voltage source and measure ranges bus k e odel 193A DMM to DC volts and 9 Send the following command to source 1 4V on the 2 With the short Jumper A installed zero the Model 15V range 193A by enabling zero C4X y eus ie E Mene 2 1 bes ey o 10 From the dis
120. sion clamps allowing an input signal to be applied to the error amplifier The output voltage from the DAC and the feedback configuration applies a voltage to the input of the error amplifier that will effect a constant level of current or voltage at the output Measurement is accomplished by routing properly con ditioned feedback levels for voltage and current through a multiplexer to the analog to digital A D converter Before proceeding to the details of circuit operation it may be helpful to clarify what is meant by controlling Feedback Switching A D Mux input Control Figure 4 2 4 2 function If the instrument is programmed to source a specific current and it does indeed source that current then it is considered to be current controlled That is cur rent is the controlling function If for some reason the in strument goes into compliance the programmed current will not be sourced Instead the instrument sources a constant voltage compliance voltage Thus voltage be comes the controlling function Conversely when pro grammed to source voltage voltage is the controlling function unless the instrument goes into current compli ance In compliance current becomes the controlling function 4 2 1 Control and Readback A simplified schematic diagram of the V I control and V I readback circuitry is shown in Figure 4 2 The de tailed schematic showing all circuit components is lo cated on page
121. standby and set it to 901A Send the following command over the bus to cali brate offset for the 1001A measurement range C52X Place the Model 263 in operate Send the value for ona from Table 2 3 over the bus with the C53 command as follows to calibrate gain for the 1004A measurement range C53 log AX Place the Model 263 in standby and set it to 0 9mA Send the following command over the bus to cali brate offset for the lmA measurement range 2 12 29 30 _31 32 35 the Model 263 in operate 37 38 39 C54X Place the Model 263 in operate Send the value for Iosma from Table 2 3 over the bus with the C55 command as follows to calibrate gain of the ImA measurement range C55 losmAX Place the Model 263 in standby and set it to 9mA Send the following command over the bus to cali brate offset for the 10mA measurement range C56X Place the Model 263 in operate Send the value for Isma from Table 2 3 over the bus with the C57 command as follows to calibrate gain for the 10mA measurement range C57 IsmaX Place the Model 263 in standby and set it to OmV Send the following command over the bus to cali brate the 1nA through 10mA source ranges C58X Note Calibration of the low current source ranges takes approximately four minutes to complete Note Check that the CAL LOCK switch is in the de sired position in for permanent calibration or out for temp
122. steps LINE FUSE SLOW BLOW LINE VOLTAGE SELECTED Figure 3 1 Line Voltage Switch and Line Fuse WARNING Make sure the Source Measure Unit is dis connected from the power line and other equipment before replacing the fuse 1 With the power off place the end of a flat blade screwdriver into the slot in the rear panel LINE FUSE holder Push in gently and rotate the fuse carrier one quarter turn counterclockwise Release pressure on the holder and its internal spring will push the fuse and carrier out of the holder 2 Remove the fuse and replace it with the type recom mended in Table 3 1 Table 3 1 Line Fuse Selection Line Keithley Voltage Fuse Type Part Number 195 250V 0 625A 250V 3AG Slo Blo FU 27 1 25A 250V 3AG Slo Blo CAUTION Do not use fuse with a higher current rating than specified or instrament damage may occur If the instrument repeatedly blows fuses locate and correct the cause of the trouble before replacing the fuse See para graph 3 8 for troubleshooting information 3 Install the new fuse and the fuse carrier into the holder by reversing the above procedure 3 3 FAN FILTER CLEANING The Model 238 has an internal cooling fan to vent heat out of the instrument case The fan has a filter to keep dirt and dust from entering the instrument case Contamination on boards could result in degraded performance The fan filter must be cleaned periodically to maintain inte
123. t is not a Model 238 GOTO OutMsg END IF RETURN t Characterization prompt strings DATA 2uA range approx 0 9uA DATA 20uA range approx 9uA DATA 200uA range approx 90uA DATA 2 range approx 0 9mA DATA 20mA range approx 9mA Current calibration data DATA 0 9 9 9 9 90 9 0 9 6 9 6 90 6 0 9 2 9 2 Procedure message data strings DATA Voltage DATA 1 to 10mA current ranges DATA Voltage and 1 to lOmA current ranges Error message strings DATA Cal ADC Zero Cal ADC Gain Cal SRC Zero Cal SRC Gain DATA Cal Common Mode Cal Compliance Cal Value DATA Cal Constants Cal Invalid SECTION 3 Maintenance 3 1 INTRODUCTION This section contains information necessary to maintain and troubleshoot the Model 238 WARNING Other than line fuse replacement and fan fil ter cleaning the procedures included in this section are for use only by qualified service personnel Do not perform these procedures unless qualified to do so Troubleshooting steps may expose you to potentially lethal voltages that could result in injury or death if normal safety precautions are not ob served 3 2 LINE FUSE REPLACEMENT A rear panel fuse located adjacent to the line voltage switch see Figure 3 1 protects the power line input of the Source Measure Unit If the fuse needs to be replaced line voltage switch setting changed or suspected blown fuse perform the following
124. that are used to calibrate the 1pA through 10mA Model 238 ranges were determined in the equipment characteriza 6 Send the following command over the bus to cali tion procedure paragraph 2 6 1 and recorded in Table brate gain for the measurement range 2 3 C43 0 9E 9X Note Calibration takes approximately 20 seconds to Sie S calibratethelnA through UTP Model263 in standby and set it to 9nA 8 Send the following command over the bus to cali brate offset for the 10nA measurement range C44X NOTE If controlling the Model 263 from the front Note takes approximately 10 seconds to anel always select the lowest possible cur complete range O the bus AUTO sane can be 9 Place the Model 263 in operate to source 9nA to the used Model 238 10 Send the following command over the bus to cali brate gain for the 10nA measurement range 1 In standby set the Model 263 to 0 9nA and enable Guard Note Calibration takes approximately 10 seconds to 2 Place the Model 238 in Operate The calibration complete mode cannot be entered with the Model 238 in 11 Place the Model 263 in standby and set it to 90nA standby 12 Send the following command over the bus to cali 3 Over the IEEE 488 bus send the following command brate offset of the 100nA measurement range to enter the calibration mode C46X COX Note Calibration takes approximately four seconds igure 2 5 Note All other calibration commands C1 through C
125. the listed limits Place the Model 617 in zero check and select the 20pA range Place the Model 238 in standby and program it source 0 9nA on the lnA source range While still in standby set the Model 263 to source 0 9nA on the 2nA range Place both the Models 238 and 263 in operate and disable Zero Check on the Model 617 Verify that the reading on the Model 617 is within the limits speci fied in the table Place the Model 617 in zero check and the Models 263 and 238 in standby On both the Models 263 and 238 reverse the polarity of the sources That is set the Model 238 to 0 9nA and the Model 263 0 9nA Place the Models 238 and 263 in operate and disable zero check on the Model 617 Verify that the reading on the Model 617 is still within the limits specified in the table Using Table 1 9 as a guide repeat the basic proce dure in steps 8 through 14 to check the 10nA through 10mA source ranges Note that for the 14A through 10mA ranges the source values for the Model 238 are taken from Table 1 3 Place the Model 617 in zero check and the Models 263 and 238 in standby Table 1 8 Allowable Reading Calculations for Low Current Source Verification InA to 10mA Allowable Reading Upper Limit Reading Calculations 0 0005 Tosa 200pA 0 00050 Isua 2 00nA 0 00050 Isoa 20 00nA 0 00050 Iosma 200 0nA 0 0005 Isma 2 00 Ioapa Iona Isoa Iosma an
126. the Memory Testis run the Model 238 performs a series of tests on its memory elements Ifa failure occurs one or more front panel messages are dis played Perform the following steps to perform the Memory Test 1 Enable MENU and use the rotary knob to display MEMORY TEST 2 Press ENTER If the test passes the display will blank for a couple of seconds and display the next menu item Otherwise a failure will cause one or more front panel messages to be displayed Note The Memory Test can also be run by sending J1X over the bus The front panel messages associated with memory ele ment failures are explained as follows SECTION 3 Maintenance Explanation CAL INVALID ERR On power up this message will indicate that one or more calibration errors exist The Model 238 needs to be re calibrated CAL CONSTANTS ERR One or more calibration constants are not within allowable limits Default cal constants will be used Try re calibrating the Model 238 Repeated failures may indicate defective 033 IOU CAL CHECKSUM Checksum test of calibration constants failed Try re calibrating instrument Repeated failures may indicate a defective U33 UNCALIBRATED There are no calibration constants stored in memory E7ROM 033 may be defective Note that the Source Measure light blinks IOU DPRAM FAILED The dual port RAM for the I O controller has failed making the instrument non func tional The DPR
127. the digital board see Figure 3 2 as follows the board A Disconnect the display board ribbon cable from 6 Remove the rear panel assembly as follows J24 A Disconnect P20 AC line filter and P22 fan B Place the instrument on its left side From the from J20 and 22 on the digital board bottom of the instrument case notice that there B At the back of the instrument remove the two are eight screws seven slotted and one Phillips nuts that secure the IEEE 488 interface connector securing the digital board to the three mounting to the rear panel rails The Phillips head screw installs into a kep C Remove the four screws that attach the rear nut on the other side of the board Remove this panel to the side panels of the instrument Two of screw first and make sure not to lose the kep nut these screws also secure the fan filter assembly to Remove the other seven screws that secure the the rear panel digital board to the mounting rails Be sure not to D To provide clearance pull the rear panel out let the digital board fall when the last screw is re ward a little and then disconnect P21 Trigger moved and Interlock from J21 on the digital board D Place the instrument in the normal upright posi E Separate the rear panel from the instrument case tion and remove the digital board from the case 3 5 3 Maintenance E Remove the top and bottom shield for the digital D Pull the strip away from the s
128. uipment Characterization SECTION 1 Performance Verification Banana Plug Cables 5 6172 2 Slot Male to 3 lug Female Triax Adapter rm Jo Ground Link Instailed Model 263 Source Volts o 8 Sense LO nm 193A DMM Measure and V 1 5 SECTION 1 se Performance Verification 1 5 2 Mode Verification 2 Place the Model 238 in OPERATE and using a pen cil record the voltage measurement in the space pro vided below Setupthe equipment as shownin Figure 1 2 and perform the following steps for common mode verification 8 step 3 From the keypad change the source value to 1 0000 and record that measurement 4 Subtract the two voltage measurements from each other Verify that the absolute value of the result is 1 20mV Vaya V a 1 20mV 1 Whileinstandby program the Model 238 as follows TIME at LINECYCLE PERIOD source at 1 000044 and compliance at 1V on the 1 5V range Interlock Cable 236 ILC 3 e Banana Plug Cable 8 7078 TRX Cable 8006 COMPONET TEST FIXTURE Warning Connect to Safety Earth Ground 8006 Test Fixture A Connections OUTPUT 238 Shorted Output OUTPUT LO Source Measure V B Schematic Equivalent Figure 1 2 Setup for Common Mode Verification 1 6 1 5 3 Voltage Source Verification Set up the equipment as shown in Figure 1 3 and perform the following steps to verify t
129. uit board After cleaning or parts replacement check to see that any components connected to the Teflon insula tors are not physically touching the board or adja cent parts 3 6 DISASSEMBLY INSTRUCTIONS If it is necessary to troubleshoot the instrument or to re place a component use the following disassembly proce dure Disassembly should be done in the order that it is presented since many steps depend on a previously per formed procedure 1 2 3 4 Connector designations on the illustrations use either a P or J prefix A P indicates that the connector is a plug type while J in dicates that it is a receptacle For example P10 is a plug connector that mates to receptacle J10 WARNING Disconnect the line cord and any test leads from the instrument and wait at least three minutes to allow high voltage capacitors to discharge before beginning disassembly Remove the top cover as follows A The top cover is secured to the chassis by six screws Four are located at the top of the instru ment and two are located at the rear Remove those six screws B Slide the top cover towards the rear of the instru ment until it separates completely from the chas sis Remove the bottom cover as follows A If installed remove the four plastic feet located on the bottom cover Each foot is secured with a single screw B The bottom cover is secured to the chassis by two screws
130. ut put current of the source to decrease The resultant feed back voltage to U17 will cause its 4 input to increase 4 3 4 Principles of Operation above OV causing CR10 to become reversed biased As a result the I CLAMP will turn off With the CLAMP on the instrument is voltage con trolled The output from the V DAC and the feedback configuration will apply a voltage to the error amplifier 014 that will effect a constant output voltage of 27V Bootstrap amplifier gain is controlled at the output of the error amplifier U14 by the FET switch Q24 and relay K4 On the 110V and 1100V ranges the switches are open and x110 gain is provided On the lower voltage ranges the switches are closed providing x11 gain Device U11isax1 buffer between the V I control circuit and the output module Measurement is accomplished by routing properly con ditioned voltage feedback levels I FEEDBACK and V FEEDBACK through a multiplexer to the analog to digital A D converter Op amp U9A is configured as a non inverting amplifier for I FEEDBACK On the 1A range the FET switch Q53 is closed providing x10 gain On the other current ranges the FET switch is open con figuring U9A as a unity gain amplifier Op amp U9B is configured as a non inverting amplifier for V FEED BACK On the 1 5V range the FET switch Q33 is closed providing x10 gain On the higher voltage ranges the FET switch is open configuring U9B as a unity gai
131. ved before using this product and any associated instrumentation Although some in struments and accessories would normally be used with non haz ardous voltages there are situations where hazardous conditions may be present This product is intended for use by qualified personnel who recog nize shock hazards and are familiar with the safety precautions re quired to avoid possible injury Read the operating information carefully before using the product The types of product users are Responsible body is the individual or group responsible for the use and maintenance of equipment for ensuring that the equipment is operated within its specifications and operating limits and for en suring that operators are adequately trained Operators use the product for its intended function They must be trained in electrical safety procedures and proper use of the instru ment They must be protected from electric shock and contact with hazardous live circuits Maintenance personnel perform routine procedures on the product to keep it operating for example setting the line voltage or replac ing consumable materials Maintenance procedures are described in the manual The procedures explicitly state if the operator may per form them Otherwise they should be performed only by service personnel Service personnel are trained to work on live circuits and perform safe installations and repairs of products Only properly trained ser vice pers
132. y precautions are not observed 1 2 ENVIRONMENTAL CONDITIONS All measurements should be made at 18 28 65 82 F and at less than 70 humidity INITIAL CONDITIONS WARNING The Source Measure Unit is equipped witha 3 wire power cord that contains a separate ground wire and is designed to be used with grounded outlets When proper connections are made instrument chassis is connected to power line ground Failure to use a grounded outlet may result in injury or death due to electric shock 1 3 The Model 238 must be turned on and allowed to warm up for at least one hour before beginning the verification procedures If the instrument has been subject to ex tremes of temperature outside the range specified in paragraph 1 2 additional time should be allowed for in ternal temperatures to reach normal operating tempera ture Typically it takes one additional hour to stabilize a unit that is 10 C 18 F outside the specified temperature range 1 4 REQUIRED TEST EQUIPMENT Table 1 1 lists all the test equipment required for verifica tion The procedures for performance verification are based on using this exact equipment Alternate equipment may be used as long as the substi tute equipment has specifications at least as good as those listed in Table 1 2 Note that equipment characteri zation paragraph 1 5 1 is not required if using equip ment that meets the specifications in Table 1 2 1 5 VERIFICATION PRO

Keithley Model 238 High-Current Source-Measure Unit

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