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1. i 2 6 CONNECTION Sorea N O 2 6 Voltages greater than 220V nssssseseeeesseeesseresssesssssesssssssssss 2 6 Input voltage overload OVRVOLT message 2 9 Test TAI RARE ARR OI 2 9 Test fixture CHASSIS rali 2 10 Guardplate eran 2 10 Connectors terminals and internal wiring 2 10 Handling and cleaning test fixtures 2 10 Apu protec ON eren arl 2 11 Floating measurements 2 12 Zero checkand Zero Corret ip lai 2 13 LTO CNG Cher etc Siete ian 2 13 ZETO COME CE srl 2 14 SCPI programming zero check and zero correct 2 15 A SYSTem ZCORrect ACQuire tt 2 15 B SYSTem ZCORrect STATe lt b gt 2 16 Measurement Considerations 2 16 Measurements Measurement OVCLVICW acirecrsicccancrsss pnsiasdion areata lei 3 2 PROCS OUTO 3 2 Step 1 Enable zero check ia 3 3 Step 2 Perform zero correction 3 3 Step 3 Select a manual measurement range Or cnable a to Tante aria 3 3 Step 4 Connect the current to be measured to thie PICOAMMINCICN Lirica 3 3 Step 5 Disable zero check and take a reading fom the display innreise a 3 3 SCPI programimin Lire 3 5 A SENSe DATA itinerante 3 5 Programming example curr 3 5 Range Units Digits Rate and Filters R nge units and dios orena is E 4 2 RACE ne EE RA 4 2 INA AI AT ATA NS hres tad s
2. 10 7 SLANG ALC eyen Stan gelosi 10 11 Operation event status ii 10 12 Measurement event statiS 0 sleale lai 10 14 Questionable event Status 10 15 DISPlay FORMat and SYSTem ASCH dota formatasi 13 4 IEEE 754 single precision data format 32 data bits 13 5 Keypress CodeS ani a 13 10 Performance Verification Connections for 20UA to 20mA range verification 15 8 Connections for 2nA to 2UA range verification 15 10 Calibration Connections for 20UA to 20mA range calibration 16 9 Connections for 2nA to 2UA range calibration 16 11 Routine Maintenance Line fuse TO CATION grillaio 17 3 General Measurement Considerations Power line ground 1OOpS irta C 2 Eliminating ground loops C 3 D Figure D 1 Figure D 2 Figure D 3 Figure D 4 F Figure F 1 Figure F 2 G Figure G 1 Figure G 2 Figure I 1 Figure I 2 Figure I 3 Figure I 4 Figure I 5 Figure I 6 Figure I 7 Figure I 8 Figure I 9 Figure I 10 Figure I 11 Figure I 12 Figure I 13 Figure I 14 Figure I 15 Figure I 16 Figure I 17 Figure I 18 Figure I 19 Figure I 20 Figure I 21 Figure I 22 Figure I 23 Figure I 24 DDC Emulation Commands USOS WO oreraa a ea E D 10 UI Stas Wy OR icerir a a ites D 11 U2 Status WO oiaoi a E ESO D 12 SS BYC iofinat abilita D 14 IEEE 488 Bus Overview TEEE 488 bus configurati
3. 4 12 Range Units Digits Rate and Filters Model 6485 Picoammeter Instruction Manual SCPI programming filters Table 4 5 SCPI commands filters For median filter SENSe 1 SENSe Subsystem MEDian Median Filter RANK lt n gt Specify filter rank 1 to 5 STATe lt b gt Enable or disable median filter For digital filter SENSe 1 SENSe Subsystem AVERage Digital Filter TCONtrol lt name gt Select filter control MOVing or REPeat COUNt lt n gt Specify filter count 1 to 100 ADVanced Advanced filter NTOLerance lt n gt Specify noise tolerance in 0 to 105 STATe lt b gt Enable or disable advanced filter STATe lt b gt Enable or disable digital filter Programming example The following command sequence configures and enables both filters Median Filter MED RANK 5 Set rank to 5 MED ON Enable median filter Digital Filter AVER COUN 20 AVER TCON MOV Set filter count to 20 Select moving filter AVER ADV NTOL 30 Set noise tolerance to 30 AVER ADV ON Enable advanced filter AVER ON Enable digital filter 9 Relative mX b m X b reciprocal and log e Relative Explains how to null an offset or establish a baseline value Includes the SCPI commands for remote operation e mX b m X b reciprocal and Logarithmic Covers these three basic math operations and includes the SCPI commands for remote operation 5 2 Relative mX b m X b reciprocal an
4. NOTE Buffer operation is covered in Section 6 Figure l 14 Connections diode leakage current test Metal Shield Programmable V Source 6485 Picoammeter Equivalent Circuit Model 6485 Picoammeter Instruction Manual Applications Guide I 19 NOTE The details on page I 12 on range change transients may be particularly rele vant to this application Capacitor leakage current Figure I 15 shows how to measure the leakage current for a capacitor The magnitude of the leakage is dependent on the type of dielectric and the applied voltage A resistor and a diode are used to limit noise for the measurement For this test a fixed bias voltage is to be applied to the capacitor for a specified time to allow the capacitor to fully charge current decays exponentially with time The leakage current is then measured After the measurement the voltage source is set to output OV for a specified time to allow the capacitor to discharge Figure I 15 Connections capacitor leakage current test Metal Shield 6485 Picoammeter Equivalent Circuit Measuring high resistance with external bias source The 6485 Picoammeter can be used to make high resistance gt 1GQ measurements when used with an external voltage source High resistance measurement applications include insulation resistance testing and resistivity measurements of insulators To measure high resistance a constant voltage source is placed in series with
5. Under Test 6485 VW Picoammeter Adding a resistor and two diodes 1N3595 as shown in Figure 2 7 will provide consider able extra protection The resistor must be large enough to limit the current through the diodes to 20mA or less and be large enough to withstand the supply voltage The protec tion circuit should be enclosed in a light tight conductive shield 2 12 Measurement Concepts Model 6485 Picoammeter Instruction Manual Figure 2 7 Capacitor test circuit with protection Protection Circuit 5 Capacitor Under Test 6485 __V Picoammeter Floating measurements Figure 2 8 shows an example where Model 6485 floats WARNING Before attempting floating measurements make sure to have a thor ough understanding of any dangers involved Take adequate precau tions before connecting any instruments or power sources Also make sure to read and understand information contained in Connection fundamentals page 2 3 Death or injury due to electrical shock can result if adequate safety measures are not taken The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis voltage Exceeding 42V can create a shock hazard If it is possible for the DUT or external supply to present more than 42V to the input HI it is imperative that the connection between input LO and the external voltage source be sufficiently low impedance and
6. To return a fresh new reading you can send the INITiate command to trigger one or more readings before sending DATA Details on INITiate are provided in Section 7 While Model 6485 is busy performing measurements the DATA command will not return the reading string until the instrument finishes and goes into the idle state NOTE The format that the reading string is returned in is set by commands in Table 14 3 If there is no reading available when DATA is sent an error 230 will occur The READ command can be used to return fresh readings This command triggers and returns the readings See Section 13 for details Programming example The following command sequence will perform one zero corrected amps measurement Return 6485 to RST defaults Enable zero check Select the 2nA range RST SYST ZCH ON CURR RANG 2e 9 INIT Trigger reading to be used as zero correction correct value Perform zero correction Enable auto range Disable zero check Trigger and return one reading SYST ZCOR ON CURR RANG AUTO ON SYST ZCH OFF SYST ZCOR ACO Use last reading taken as zero READ 3 6 Measurements Model 6485 Picoammeter Instruction Manual 4 Range Units Digits Rate and Filters Range units and digits Provides details on measurement range reading units and display resolution selection Includes the SCPI commands for remote opera tion Rate Provides details on reading rate s
7. A The buffer size command In is not used by the Model 485 The buffer size com mand is similar to the SCPI TRACe POINts command see Section 6 for details B The moving filter cannot be selected from the DDC language C For Model 6485 the terminator commands Y to set the terminator are different from the Y commands used by the 485 Also note that the YY response to the UO command is different D For the Model 6485 the Buffer Full bit in the UI X status word does not get cleared until either the buffer is resized or buffer storage is reactivated Note that requesting a buffer reading does not clear the U1 Buffer Full bit E The U2 status command is not used by the Model 485 The response message indi cates the buffer size In and the actual number of readings stored in the buffer F Calibration must be already unlocked and enabled G See CALibration subsystem Model 6485 Picoammeter Instruction Manual DDC Emulation Commands D 9 H Although there is not a Busy event in the Model 6485 Status Model there is an Operation Complete event the compliment of Busy This example refers to the use of the Operation Complete SRQ rather than Busy I The DDC errors do not map one to one mapping with SCPI errors There are two SCPI errors that cover all of the 6485 Error Events EE This will be fairly equiv alent to using the M39 DDC command After getting an SRQ on an Error Event to clear the event read th
8. MMediate is implied optional and does not have to be used Thus the above command can be sent in one of two ways INTTiate or INITiate IMMediate Notice that the optional command is used without the brackets When using optional command words in your program do not include the brackets Model 6485 Picoammeter Instruction Manual Remote Operation 9 11 e Parameter types The following are some of the common parameter types lt b gt lt name gt lt NRf gt lt NDN gt lt n gt Boolean Used to enable or disable an instrument operation 0 or OFF disables the operation and 1 or ON enables the operation DISPlay ENABle ON Enable the display Name parameter Select a parameter name from a listed group lt name gt NEVer NEXT CALCulate FORMat MXB Select Mx B calculation Numeric representation format A number that can be expressed as an integer e g 8 a real number e g 23 6 or an exponent 2 3E6 TRACe POINts 20 Set buffer size to 20 Non decimal numeric A non decimal value that can be used to program status enable registers A unique header identifies the format B binary H hexadecimal and Q octal SRE B10001 Set bits BO and B4 of Service Request Enable Register Numeric value Can consist of an NRf number or one of the fol lowing name parameters DEFault MINimum or MAXimum When the DEFault parameter is used the instrument is pro grammed to the RST de
9. One shot on X 6 Continuous on External Trigger 7 One shot on External Trigger Also see Byte 5 in Status Byte Model 6485 Picoammeter Instruction Manual Figure D 2 U1 Status word STATUS DATA CONDITION FORMAT PREFIX DATA STORE 1 Full N Zero Correct 0 Off 1 On B Reading Mode 0 Picoammeter 1 BufferReading 2 Maximum Reading 3 Minimum Reading Q Data Store Rate 0 Conversion Rate 1 One reading per second 2 One reading per 10 seconds 3 One reading per 60 seconds 1 minute 4 One reading per 10 minutes 5 One reading per hour 6 Trigger Mode 7 Disabled J Digits returned 4 3 1 2 digits resolution 5 6 7 4 1 2 digits resolution 5 1 2 digits resolution 6 1 2 digits resolution P Digital Filter Off Off Repeat filter on where filter size n NR DDC Emulation Commands D 11 D 12 DDC Emulation Commands Model 6485 Picoammeter Instruction Manual Figure D 3 U2 Status word STATUS BUFFER SIZE AND READINGS STORED FORMAT TORERE Loo GE E PREFIX Buffer Size Set using I command Delimiter Reading Quantity Number of readings currently stored in buffer Status Byte Format The status byte contains information relating to data and error conditions within the instru ment When a particular bit is set certain conditions are present Table D 2 lists the mean ings of the various bits and Figure D 4 s
10. SCPI programming relative Table 5 2 SCPI commands relative ee ie CALCulate2 a ee to configure and control limit testing CALC2 FEED lt name gt Specify reading to Rel SENSe 1 or CALCulate 1 SENS NULL Configure and control Relative ACQuire Use input signal as Rel value OFFSet lt NRf gt Specify Rel value 9 999999e20 to 9 999999e20 0 0 STATe lt b gt Enable or disable Rel ZO Off DATA Return Rel ed readings triggered by INITiate LATest Return only the latest Rel ed reading INITiate Trigger one or more readings A FEED lt name gt Specify reading to Rel With SENSe 1 selected the Rel operation will be performed on the input signal With CALCulate 1 selected the Rel operation will be performed on the result of the mX b or m X b calculation B STATe lt b gt Toggle state of Rel This command toggles the state of Rel without acquiring new values This operation is dif ferent than the REL key from front panel which toggles the Rel state the front panel key acquires new values when pressed unless CONFIG is pressed first If a NULL value has not been acquired before enabling Rel 0 000000E 00 will be used C DATA and DATA LATest With Rel enabled these commands will return one or more Rel ed readings They will not trigger fresh new readings Use the INITiate command to trigger new readings see Section 7 for details on INITiate If the instrument is programmed to
11. Select autorange upper limit 0 021 to 0 021 amps Query upper limit for autorange Select autorange lower limit 0 021 to 0 021 amps Query lower limit for autorange Path to control the Digital Filter Select filter control MOVing or REPeat Query filter control Specify filter count 2 to 100 Query filter count Advanced filter Specify noise tolerance in 0 to 105 Query noise tolerance Enable or disable advanced filter Query state of advanced filter Enable or disable digital filter Query state of digital filter Path to control median filter Specify n for rank 1 to 5 rank 2n 1 Query rank Enable or disable median filter Query state of median filter Note RST default is ON and SYSTem PRESet default is OFF Table 14 5 STATus command summary Default Ref Command Description parameter Section SCPI STATus MEASurement EVENt Note 1 10 V Measurement event registers Read the event register Note 2 ENABle lt NDN gt or lt NRf gt Program the enable register Note 3 Model 6485 Picoammeter Instruction Manual Table 14 5 continued STATus command summary Command ENABle CONDition OPERation EVENt ENABle lt NDN gt or lt NRf gt ENABle CONDition QUEStionable EVENt ENABle lt NDN gt or lt NRf gt ENABle CONDition PRESet QUEue NEXT ENABle lt list gt ENABle DISable lt list gt DI
12. Set limit 9 99999e20 to 9 99999e20 Query upper limit Configure lower limit Set limit 9 99999e20 to 9 99999e20 Query lower limit Enable or disable limit 1 test Query state of limit 1 test Return result of limit 1 test 0 pass or 1 fail Limit 2 Testing Configure upper limit Set limit 9 99999e20 to 9 99999e20 Query upper limit Configure lower limit Set limit 9 99999e20 to 9 99999e20 Query lower limit Enable or disable limit 2 test Query state of limit 2 test Return result of limit 2 test 0 pass or 1 fail Configure and control Rel Use input signal as Rel value Specify Rel value 9 999999e20 to 9 999999e20 Query Rel value Enable or disable Rel Query state of Rel Return all CALC2 readings triggered by INITiate Return only the last latest reading 2 NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI NI 14 4 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual Table 14 1 continued CALCulate command summary Default Ref Command Description parameter Section SCPI CALCulate3 Path to configure and control CALC3 calculations on buffer data FORMat lt name gt Select buffer statistic MEAN SDEViation Maximum MINimum or PKPK FORMat Query selected statistic DATA Read the selected buffer statistic Table 14 2 DISPlay command summary Default Ref Command Description parameter Section SCPI
13. 13 DISPlay DIGits lt n gt Set display resolution 4 to 7 4 DIGits Query display resolution ENABle lt b gt Turn front panel display on or off Note 1 ENABle Query display state WINDow 1 Path to control user text messages TEXT Note 2 IDATA lt a gt Define ASCII message a up to 12 characters DATA Read text message STATEe lt b gt Enable or disable text message mode Note 3 STATe Query state of text message mode a Hass DL ass i A Notes RST and SYSTem PRESet have no effect on the display circuitry Pressing LOCAL or cycling power enables ON the display circuit RST and SYSTem PRESet have no effect on a user defined message Pressing LOCAL or cycling power cancels all user defined messages RST and SYSTem PRESet have no effect on the state of the message mode Pressing LOCAL or cycling power disables OFF the message mode N Oo Model 6485 Picoammeter Instruction Manual SCPI Reference Tables 14 5 Table 14 3 FORMat command summary Default Ref Command Description parameter Section SCPI 13 FORMat DATA lt type gt lt length gt Specify data format ASCii REAL 32 or SREal DATA Query data format ELEMents lt item list gt Specify data elements READing UNITS TIME and STATus ELEMents Query data format elements BORDer lt name gt Specify byte order NORMal or SWAPped see Note BORDer Query byte order SREGister l
14. CAL PROT SENS 0 CAL PROT SENS 2e 4 CAL PROT SENS 2e 4 SENS CURR RANG 2e 3 CAL PROT SENS 0 CAL PROT SENS 2e 3 CAL PROT SENS 2e 3 SENS CURR RANG 2e 2 CAL PROT SENS 0 CAL PROT SENS 2e 2 CAL PROT SENS 2e 2 Model 6485 Picoammeter Instruction Manual Full scale calibration values for 2nA to 2uA ranges should be calculated from calibrator voltages and standard resistance values See Section 16 Values for 20uA to 20mA ranges can be used as shown Applications Guide Measurement considerations Covers measurement considerations for low current measurements including Leakage currents and guarding Input bias current Voltage bur den Noise and source impedance Electrostatic interference and shielding and also Making connections Applications Covers applications to measure Diode leakage current Capacitor leak age current Measuring high resistance with external bias source Cable insulation resis tance Surface insulation resistance SIR Photodiode characterization prior to dicing Focused ion beam applications and Using switching systems to measure multiple current sources as shown in External triggering page 7 11 l 2 Applications Guide Model 6485 Picoammeter Instruction Manual Measurement considerations Some considerations for making accurate amps measurements are summarized as follows Additional measurement considerations are covered in Appendix C For comprehensive information o
15. DIGITS key 7 REL key 23 RATE key 8 ZCHK key 24 Cursor left arrow key 9 25 10 26 SAVE key 11 RANGE up arrow key 27 SETUP key 12 AUTO key 28 STORE key 29 RECALL key 30 LIMIT key 31 AZERO key 32 EXIT key This command is used to simulate front panel key presses For example send the follow ing command to simulate pressing the MEDN key SYSTem KEY 2 The key press codes are also shown in Table 13 3 13 10 DISPlay FORMat and SYSTem Model 6485 Picoammeter Instruction Manual The queue for the SYST KEY query command can only hold one key press When SYST KEY is sent and Model 6485 is addressed to talk the key press code number for the last SYST KEY command is sent to the computer The value is 1 if a SYST KEY command has not been sent since the last time the unit was placed in remote Figure 13 3 Key press codes 1 8 16 RANGE enn MENU 2 QUE 12 RANGE POWER UN E Galea ar Ol 26 19 26 21 30 23 32 15 14 SCPI Reference Tables Table 14 1 CALCulate command summary Table 14 2 DISPlay command summary Table 14 3 FORMat command summary Table 14 4 SENSe command summary Table 14 5 STATus command summary Table 14 6 SYSTem command summary Table 14 7 TRACe command summary Table 14 8 TRIGger command summary Calibration commands See Appendix H 1422 SCPI Reference Table
16. Display OK NOTE Display messages indicate which test or tests have failed but they do not indi cate which limit HI or LO has failed When using remote operation you can determine which limit failed by reading the measurement event register See Ref B for the FAIL commands in Table 8 2 Relative Rel mX b m X b and log can be used with limit testing The tests will be done on the result of the math operation not the input values These math operations are covered in Section 5 Model 6485 Picoammeter Instruction Manual Limit Tests 8 5 Application A typical application for a 2 stage limit test is to sort a batch of DUT according to tolerance For example you may want to sort diodes all having the same nominal value into three groups 1 5 and gt 5 The limits for limit 1 would be the 5 tolerances and the limits for limit 2 would be the 1 tolerances If a diode passes both tests it belongs in the 1 group If it passes limit 1 but fails limit 2 it belongs in the 5 group If it fails both tests it belongs in the gt 5 group Front panel operation Limit test configuration Most aspects of limit testing are configured from the limit configuration menu Once in a menu structure use the A and W keys to display menu items Use the cursor lt and and the A and W keys to key in values To change polarity of a value place the cursor on or and press either of the A or W range keys To change ra
17. E 2 900 readings second to IEEE 488 bus E 3 IEEE 488 Bus Overview LINGO GUC iON uranio F 2 BUS CESCHIPUOM ssi F 2 BUs GIES aula F 4 Digli F 5 Bus management lines F 5 Handshake ines arerin F 5 B s command seien a aaa ia TREN A F 6 UMEN Commmand yona e N E marae F 9 Universal multiline commands F 9 Addressed multiline commands F 10 Address commands erre F 10 WUnaddress comimands oiae e E E F 10 Common commands erre F 11 SCRI commands snai F 11 Command CODES atlanti F 11 Typical command sequences F 12 IEEE command groups F 13 Interlace TUNCIION codes ssaa F 14 IEEE 488 and SCPI Conformance Information TINCT OGUCTION torrione G 2 GPIB 488 1 Protocol asL lilla G 3 Selecting the 488 1 protocol G 4 Protocol diferente S cutrelatalaval G 4 Message exchange protocol MEP G 5 Using SCPI based programs G 5 INTRA OI dazione tocco o ie die G 5 NDAC ROIO sli G 6 Tesero Aa K gaea E G 7 Message available lilla G 7 General operation notes G 7 SRQ when buffer fills with 200 readings G 7 Remote Calibration INTOdUCHo n aa H 2 Calibration commands sicilia H 2 Remote Calibration overview c cecsccec
18. NPLCyceles lt n gt Specify integration rate 0 01 PLCs 6 0 60Hz to 6 0 60Hz or 5 0 SOHz 5 0 SOHz Model 6485 Picoammeter Instruction Manual Range Units Digits Rate and Filters 4 7 Filters Programming example rate The following command sets the integration rate for all measurement ranges to 2 PLC CURR NPLC 2 Set integration rate to 2 PLC Filtering stabilizes noisy measurements caused by noisy input signals The Model 6485 uses two types of filters median and digital The displayed stored or transmitted reading is simply the result of the filtering processes Note that both the median and digital filters can be in effect at the same time With both filters enabled the median filter operation is performed first After the median filter yields a reading it is sent to the stack of the digital filter Therefore a filtered reading will not be displayed until both filter operations are completed The settings for the filter are global The MEDN key is used to control the median filter The AVG key is used to control the digital filter press CONFIG and then the AVG key to configure When either the median or digital filter is enabled the FILT annunciator is on Median filter The median filter is used to determine the middle most reading from a group of readings that are arranged according to size For example assume the following readings 20mA ImA 3mA The readings are rearranged in an ascending order
19. OFF The default is OFF but NRFD hold off will still be enabled and will prevent an instrument from accepting further commands See Figure G 1 for the complete IEEE 488 handshake sequence Figure G 1 IEEE 488 handshake sequence DATA SOURCE DAV SOURCE VALID NRFD ALL ACCEPTED NDAC ACCEPTOR Model 6485 Picoammeter Instruction Manual IEEE 488 and SCPI Conformance Information G7 Trigger on talk Trigger on talk functionality has been added for the 488 1 protocol If a query has not been received by the instrument the 6485 will automatically assume a READ command has been sent when it is addressed to talk This technique increases GPIB speed by decreasing the transmission and parser times for the command Trigger on talk is extremely useful in the single shot reading mode RST default and is the main reason for a gt 2x speed improvement over the SCPI protocol The ARM SOUR BUS and ARM COUN INF commands are not supported by READ with the 488 1 protocol selected If you send one of these commands a DCL or IFC may be required to reset the GPIB Message available The MAV message available bit in the Serial Poll byte will be set when the query is fin ished being processed not when there is data available in the output buffer as with the SCPI protocol For the 488 1 protocol output data will not be formatted until the first request for data is received This delay may cause unexpected time outs when using SR
20. capable of carrying the short circuit current of the source in order that the LO not exceed 42V CAUTION Connecting COMMON or ANALOG OUT to earth while floating the input may damage the instrument The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the instrument Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 13 Figure 2 8 Floating measurements 6485 Picoammeter Zero check and zero correct Table 2 3 lists the display messages associated with zero check and zero correct The two character message is displayed along with the reading Table 2 3 Display messages for zero check and zero correct Message ZC On Off ZZ On On CZ Off On Zero check When zero check is enabled on the input amplifier is reconfigured to shunt the input sig nal to low as shown in Figure 2 9 From the front panel enable disable zero check by pressing the ZCHK key Refer to Table 2 4 for bus commands Leave zero check enabled when connecting or disconnecting input signals 2 14 Measurement Concepts Model 6485 Picoammeter Instruction Manual Figure 2 9 Equivalent input impedance with zero check enabled Ze 500Q 200nF 2 mA 20 mA 100pF DUO z 50kQ 2nF 20 WA 200 pA Input T i 5MQ 20pF 200 nA 2 uA 500MQ 5pF 2 nA 20 nA Zero correct Model 6485 has a zero correct feature to algebraically subtract the voltage offset term from the measurement to a
21. contact information safety symbols and terms inspection and available options and accessories Features Summarizes the features of Model 6485 Front and rear panel familiarization Summarizes the controls and connectors of the instrument as well as providing information on the front panel display Power up Covers line power connection line voltage setting fuse replacement power line frequency and the power up sequence Default settings Covers the five instrument setup configurations available to the user three user defined GPIB defaults or factory defaults SCPI programming Explains how SCPI commands are presented in this man ual 1 2 Getting Started Introduction Model 6485 Picoammeter Instruction Manual The Model 6485 is a high resolution bus programmable RS 232 and IEEE 488 picoam meter The Model 6485 has the following current measurement ranges 8 ranges from 20mA down to the 2nA range with the 2nA range having the lowest noise Overview of this manual This manual describes how to connect program and maintain the Model 6485 Picoamme ter The sections of the manual are organized as follows Section 1 Section 2 Section 3 Section 4 Section 5 Section 6 Section 7 Section 8 Section 9 Section 10 Section 11 Section 12 Section 13 Section 14 Section 15 Section 16 Section 17 Getting Started Measurement Concepts and Connections Measurements Range Units Dig
22. e If installing a test circuit that is on a PC board handle the board by the edges Do not touch any board traces or components Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 11 Cleaning tips e Use dry nitrogen gas to clean dust off connector and terminal insulators DUT and other test circuit components e If you have just built the test fixture remove any solder flux using methanol along with clean foam tipped swabs or a clean soft brush Clean the areas as explained in the next tip e To clean contaminated areas use methanol and clean foam tipped swabs After cleaning a large area you may want to flush the area with methanol Blow dry with dry nitrogen gas e After cleaning the test fixture and any other cleaned devices or test circuits should be allowed to dry in a 122 F 50 C low humidity environment for several hours Input protection Model 6485 incorporates protection circuitry against nominal overload conditions How ever a voltage higher than the maximum voltage value for the selected current range and the resultant current surge could damage the input circuitry NOTE Maximum peak voltage 220V Peak A typical test circuit to measure the leakage current of a capacitor is shown in Figure 2 6 When Switch S is closed an initial charging current will flow and the high voltage will be seen across the input of Model 6485 Figure 2 6 Capacitor test circuit without protection gt Capacitor
23. the current that flows will be 1 Ys VB _ SmV 1mV Rg 5kQ 0 8uA 4 Applications Guide Model 6485 Picoammeter Instruction Manual The ImV voltage burden caused a 20 current reduction Percent error in a measured reading Iy due to voltage burden can be calculated as follows 100 I error M V V The voltage burden of Model 6485 depends on the selected range see specifications Voltage burden may be reduced by performing the voltage offset correction procedure Voltage offset correction procedure NOTE To maintain specified operation any time there is a substantial change in the ambient temperature the voltage offset procedure should be performed and saved 1 Press the MENU key to display the following CAL VOFFSET 2 Press ENTER The instrument will prompt as follows INPUT CAP 3 Itis not necessary to disconnect signal cables from the 6485 but it is recommended that signal currents be reduced to zero if possible During the calibration the input impedance will be 3 5MQ therefore continued signal currents will present a corre sponding voltage to the DUT 4 Press ENTER to complete offset voltage calibration 5 Press EXIT to return to normal display NOTE Like the other calibration procedures this calibration is not permanently stored until CAL UNLOCK and CAL SAVE have been performed Saving the results of this calibration at a temperature other than that at which the Model 6485 will be used will
24. tubing entry points and connectors or connector pan els With this in mind the Model 6485 display may be turned off either through the front panel by pressing the DISP or over the bus by sending the DISP ENAB OFF command Electrostatic interference Electrostatic interference occurs when an electrically charged object is brought near an uncharged object thus inducing a charge on the previously uncharged object Usually effects of such electrostatic action are not noticeable because low impedance levels allow the induced charge to dissipate quickly However the high impedance levels of many mea surements do not allow these charges to decay rapidly and erroneous or unstable readings may result These erroneous or unstable readings may be caused in the following ways 1 DC electrostatic field can cause undetected errors or noise in the reading 2 AC electrostatic fields can cause errors by driving the input preamplifier into satu ration or through rectification that produces DC errors Model 6485 Picoammeter Instruction Manual General Measurement Considerations C 5 Electrostatic interference is first recognizable when hand or body movements near the experiment cause fluctuations in the reading Pick up from AC fields can also be detected by observing the picoammeter analog output on an oscilloscope Line frequency signals on the output are an indication that electrostatic interference is present Means of minimiz ing electrostatic int
25. where V is the sourced bias voltage I is the measured current Figure I 18 Connections cable insulation resistance test Metal Shield l HI Programmable Meassiied V Source Current V Ti 1 6485 Picoammeter Equivalent Circuit l 22 Applications Guide Model 6485 Picoammeter Instruction Manual Surface insulation resistance SIR Figure I 19 shows how to measure the insulation resistance between PC board traces Note that the drawing shows a Y test pattern for the measurement This is a typical test pattern for SIR tests A bias voltage typically 50V is applied to the test pattern for a specified time typically one second to polarize the test pattern The test voltage typically 100V is then applied and after a specified time typically one second Model 6485 measures the current Sur face insulation resistance can now be calculated as follows V SIR T where V is the sourced test voltage I is the measured current Figure I 19 Connections surface insulation resistance test Metal Shield PC Board Test Pattern Measured Current I Programmable V Source V g 6485 Picoammeter Equivalent Circuit Photodiode characterization prior to dicing The Model 6485 can be used as part of a cost effective semiconductor photodiode leakage test system This test characterizes the photo current under various illumination condi tions In addition to the Model 6
26. 0 Hx Hexadecimal format x 0 to FF Qx Octal format x 0 to 377 lt NRf gt Oto 255 Decimal format Read the service request enable register Note CLS and STATus PRESet have no effect on the service request enable register Programming example set MSS B6 when error occurs The first command of the following sequence enables EAV error available When an invalid command is sent line 4 bits B2 EAV and B6 MSS of the status byte register set to 1 The last command reads the status byte register using the binary format which directly indicates which bits are set The command to select format FORMat SREGister is documented in Table 10 2 To determine the exact nature of the error you will have to read the error queue see Queues page 10 18 CLS Clear Error Queue SRE 4 Enable EAV FORM SREG BIN Select binary format BadCommand Generate error STB Read Status Byte Register NOTE An example program to demonstrate serial polling Generating SRO on buffer full is provided in Appendix E Status register sets As shown in Figure 10 1 there are four status register sets in the status structure of Model 6485 standard event status operation event status measurement event status and ques tionable event status Register bit descriptions Standard event status The used bits of the standard event register Figure 10 4 are described as follows Model 6485 Picoammeter Instruction Ma
27. 0810nA 200 000nA 199 590 to 200 410nA 2 00000uA 1 99690 to 2 003 10uA l Nominal resistance values shown Use actual characterized value for calculations Calculate actual calibrator voltage as follows V IR where I is desired applied current and R is actual standard resistance value 15 10 Performance Verification Model 6485 Instruction Manual Figure 15 2 Connections for 2nA to 2uA range verification DC Voltage Calibrator BNC to dual Model 6485 Picoammeter Banana Plug n m Adapter zer prio CE IEEE 488 ITH FRONT PANEL MENU CA y OOOOOO O OOO O amen Connect 9 0 000 000 00000 i Cable ooo oooO oo hied 0 lo00 000 20 Shield to 000 OC OO o Output LO Low noise Coax Cable BNC to Triax Adapter on INPUT 10062 10Ga Note Connect Calibrator to Triax Cable OUppUT Supplied with Meo A SuSE 100MQ or 1GQ Resistor Model 5156 io ia Link Shield and Chassis Model 5156 Calibration Standard 16 Calibration Environmental conditions Summarizes temperature and relative humidity warm up period and line power requirements Calibration considerations Lists considerations to take into account when cali brating the unit Calibration cycle States how often the Model 6485 should be calibrated Recommended calibration equipment Lists all equipment necessary for cali bration and gives pertinent specifications Calibration er
28. 488 Bus Overview Model 6485 Picoammeter Instruction Manual Addressed multiline commands Addressed commands are multiline commands that must be preceded by the device listen address before that instrument will respond to the command in question Note that only the addressed device will respond to these commands Both the commands and the address preceding it are sent with ATN true SDC Selective Device Clear The SDC command performs essentially the same func tion as the DCL command except that only the addressed device responds Generally instruments return to their power up default conditions when responding to the SDC com mand GTL Go To Local The GTL command is used to remove instruments from the remote mode With some instruments GTL also unlocks front panel controls if they were previ ously locked out with the LLO command GET Group Execute Trigger The GET command is used to trigger devices to perform a specific action that depends on device configuration for example take a reading Although GET is an addressed command many devices respond to GET without address ing Address commands Addressed commands include two primary command groups and a secondary address group ATN is true when these commands are asserted The commands include LAG Listen Address Group These listen commands are derived from an instrument s primary address and are used to address devices to listen The actual command byte is o
29. 5156 Electrometer Calibration Stan dard to the Model 6485 INPUT jack as shown in Figure 16 2 Initially make con nections to the 1GQ resistance 2 Set the calibrator to output volts and make sure the calibrator output is turned on 3 Select the Model 6485 2nA range 4 Press MENU select CAL then press ENTER At the CAL RUN prompt press ENTER again The unit will prompt for the zero calibration point 2NA ZERO 5 Set the calibrator voltage to OV then press ENTER 6 The instrument will prompt for the positive full scale calibration point 2NA CAL 7 Press ENTER The instrument will prompt for the positive full scale calibration current 2 000000 NA 8 Set the calibrator voltage to 2 000000V Calculate the actual calibration current from the calibrator voltage and the actual standard resistor value I V R Adjust the Model 6485 display to agree with the calculated current then press ENTER 9 The Model 6485 will prompt for the negative full scale calibration point 2NA CAL 10 Press ENTER The instrument will prompt for the negative full scale current 2 000000 NA 16 10 Calibration Model 6485 Instruction Manual 11 Set the calibrator output voltage to 2 000000V then calculate the calibration cur rent from the calibrator voltage and standard resistor value I V R Adjust the Model 6485 display to agree with the calculated current then press ENTER to complete calibration of the present range 12 Press EXIT to
30. 6485 must be set to IEEE 488 1 operation from the front panel see page G 4 RST FORM ELEM READ FORM BORD SWAP FORM DATA SRE Return 6485 to RST defaults Return readings only Set for swapped byte order Return single precision floating point binary Set trigger delay to zero seconds Set trigger count to 8 TRIG DEL 0 TRIG COUNT 8 SENS CURR NPLC 01 Set integration rate to 01 PLC SENS CURR RANG 002 Use 2mA range SENS CURR RANG AUTO OFF Turn auto range off SYST ZCH OFF Turn zero check off SYST AZER STAT OFF Turn auto zero off DISP ENAB OFF Turn display off OPC Operation complete query synchro nize completion of commands read back result of opc for i 1 to 1000 talk the Model 6485 In 488 1 mode this will automatically do a READ see Trigger on talk page G 7 read back the binary data next i DISP ENAB ON Turn display back on E 4 Example Programs Model 6485 Picoammeter Instruction Manual F IEEE 488 Bus Overview Fa2 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual Introduction The IEEE 488 bus is a communication system between two or more electronic devices A device can be either an instrument or a computer When a computer is used on the bus it serves as a Supervisor of the communication exchange between all the devices and is known as the controller Supervision by the controller consists of determining which device will talk and which device will list
31. 6485 until the terminator has been sent usually Line Feed with EOI Otherwise a DCL or IFC must be sent to reset the input parser When receiving data all data up to and including the terminator LF with EOD must be accepted Otherwise a DCL or IFC must be sent to reset the output task Empty command strings terminator only should not be sent Using SCPI based programs In general an existing SCPI based program will run properly and faster in the 488 1 pro tocol as long as it meets the above guidelines and limitations NRFD hold off OPC OPC and WAI are still functional but are not needed for the 488 1 protocol When sending commands the GPIB is automatically held off when it detects a terminator The hold off is released when all the commands have finished executing or if there is some parser or command error An exception is an initiate command which releases the hold off immediately and does not wait for all of the readings to be acquired This imme diate release of bus hold off is done to support GET SDC IFC TRG RCL RST SYSTem PRESet and ABORt during data acquisition G 6 IEEE 488 and SCPI Conformance Information Model 6485 Picoammeter Instruction Manual NDAC hold off NDAC hold off is included with the GPIB 488 1 protocol mode to allow a single instru ment to hold off all others on the bus until it is finished executing a command The follow ing command controls NDAC hold off SYSTem MEP HOLDoff ON
32. ATN is true while the instrument is being addressed but it is set high while sending the common command string Table F 5 Typical addressed command sequence Databus Step Command ATN state ASCII a Set low Stays low Set high Stays high Stays high Stays high Assumes primary address 14 Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 13 IEEE command groups Command groups supported by the Model 6485 are listed in Table F 6 Common com mands and SCPI commands are not included in this list Table F 6 IEEE command groups HANDSHAKE COMMAND GROUP NDAC NOT DATA ACCEPTED NRFD NOT READY FOR DATA DAV DATA VALID UNIVERSAL COMMAND GROUP ATN ATTENTION DCL DEVICE CLEAR IFC INTERFACE CLEAR REN REMOTE ENABLE SPD SERIAL POLL DISABLE SPE SERIAL POLL ENABLE ADDRESS COMMAND GROUP LISTEN LAG LISTEN ADDRESS GROUP MLA MY LISTEN ADDRESS UNL UNLISTEN TAG TALK ADDRESS GROUP MTA MY TALK ADDRESS UNT UNTALK OTA OTHER TALK ADDRESS ADDRESSED COMMAND GROUP ACG ADDRESSED COMMAND GROUP GTL GO TO LOCAL SDC SELECTIVE DEVICE CLEAR STATUS COMMAND GROUP RQS REQUEST SERVICE SRQ SERIAL POLL REQUEST STB STATUS BYTE EOI END F 14 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual Interface function codes The interface function codes which are part of the IEEE 488 standards define an instru ment s ability to supp
33. B3 4 Reading 5 Ai Ai Ai A A Aa B B B4 B B3 1 Ay A Ay Ay A3 B B B4 B By Type repeating Ai A A A DI Ay Bi By By Bi By i 0 Noise level 1 of range Reading Reading 4 10 Range Units Digits Rate and Filters Figure 4 3 Digital filter types moving and repeating Conversion 10 9 Conversion 11 10 9 8 7 Conversion 1 Conversion 2 A Class Average Readings 10 Type Moving Conversion 10 Conversion 20 9 19 18 17 16 Reading 415 1 14 13 12 Conversion 11 Conversion 1 B Class Average Readings 10 Type Repeating Response time Model 6485 Picoammeter Instruction Manual Conversion Reading 11 Conversion Conversion Reading 3 Conversion The various filter parameters have the following effects on the time needed to display store or output a filtered reading e Filter classification The time to the first reading is the same for both classifica tions but thereafter the moving mode yields a faster reading than repeating mode Also advanced has a faster response to changes in the input signal than averaging e Number of reading conversions Speed and noise are tradeoffs e Noise window For the advanced filter a tradeoff of speed noise and response to input signal changes Operation consideration e The digital filter operation will reset start over whenever the zero check operation is performed or the range is chan
34. CALL send addr stat pres status3 CALL send addr cls status3 CALL send addr stat meas enab 512 status3 CALL send addr ese 0 status CALL send addr sre 1 status CALL send addr init status3 WAITSRO WHILE srq 0 WEND CALL spoll addr poll status3 CALL send addr cls status3 PRINT BUFFER FULL END Model 6485 Picoammeter Instruction Manual Clear PC output screen Set instrument address Restore rst defaults Send Device Clear 200 trigger count Set buffer size to 200 Enable buffer Reset measure enable bits Clear all event registers Enable buffer bit B9 Disable standard events Enable measurement events Start measurement store process Wait for GPIB SRQ line to go true Clear rqs mss bit in status bit register Clear all event registers Display buffer full message H Remote Calibration Calibration commands Summarizes those commands necessary to calibrate the Model 6485 by remote Remote calibration overview Gives an overview of the basic procedure for cal ibrating the Model 6485 via remote H 2 Remote Calibration Model 6485 Picoammeter Instruction Manual Introduction This appendix contains a summary of Model 6485 remote calibration commands and a basic remote calibration procedure See Section 16 for complete calibration informa tion Calibration commands Table H 1 summarizes Model 6485 remote calibration commands
35. F 2 JEEE 488 handshake sequence DATA SOURCE DAV SOURCE VALID ALL READY ACCEPTOR NRFD a ALL ACCEPTED NDAC ACCEPTOR Bus commands The instrument may be given a number of special bus commands through the IEEE 488 interface The following paragraphs briefly describe the purpose of the bus commands which are grouped into the following three categories 1 Uniline commands Sent by setting the associated bus lines true For example to assert REN Remote Enable the REN line would be set low true 2 Multiline commands General bus commands which are sent over the data lines with the ATN line true low 3 Common commands Commands that are common to all devices on the bus sent with ATN high false 4 SCPI commands Commands that are particular to each device on the bus sent with ATN false Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 7 These bus commands and their general purpose are summarized in Table F 1 Table F 1 JEEE 488 bus command summary Command type Uniline Multiline Universal Addressed Unaddressed Command REN Remote Enable EOI IFC Interface Clear ATN Attention SRQ LLO Local Lockout DCL Device Clear SPE Serial Enable SPD Serial Poll Disable SDC Selective Device Clear GTL Go To Local UNL Unlisten UNT Untalk State of ATN line Comments Set up devices for remote operation Marks end of transmis
36. Model 6485 Picoammeter Instruction Manual Triggering 7 9 SCPI programming Table 7 3 SCPI commands triggering ABORt Reset trigger system goes to idle state INITiate Initiate one trigger cycle FETCh Request latest reading READ Trigger and request a fresh reading ARM SEQuence 1 Arm Layer LAYer 1 SOURce lt name gt Select control source IMMediate TIMer BUS TLINk or MANual COUNt lt n gt Set measure count 1 to 2500 or INF infinite TMMer lt n gt Set timer interval 0 001 to 99999 999 sec TCONfigure DIRection lt name gt Enable SOURce or disable ACCeptor bypass ASYNchronous Configure input output triggers ILINe lt NRf gt Select input trigger line 1 2 3 4 5 or 6 OLINe lt NRf gt Select output trigger line 1 2 3 4 5 or 6 OUTPut lt name gt Output trigger TRIGger or not at all NONE TRIGger Trigger Layer CLEar Clear pending input trigger immediately SEQuence 1 Trigger path SOURce lt name gt Select control source IMMediate or TLINk COUNt lt n gt Set measure count 1 to 2500 or INF infinite DELay lt n gt Set trigger delay 0 to 999 9998 sec AUTO lt b gt Enable or disable auto delay TCONfigure DIRection lt name gt Enable SOURce or disable ACCeptor bypass ASYNchronous Configure input output triggers ILINe lt NRf gt Select input trigger line 1 2 3 4 5 or 6 OLINe lt NRf gt Select output trigger line 1 2
37. PROTected SAVE CALibration PROTected LOCK Status Bits OSO Set MO Clears SRQ Data Mask None X STATus MEASurement EVENt ENABle 0 SRE lt value gt value current SRE value amp 0x01 MI Reading Overflow BO STATus MEASurement EVENt ENABle 128 SRE lt value gt value current SRE value l 0x01 M2 Data Store Full B1 STATus MEASurement EVENt ENABle 512 NEW SRE lt value gt value current SRE value l 0x01 M3 Data Store Full or Reading Overflow B1 BO STATus MEASurement EVENt ENABle 640 NEW SRE lt value gt value current SRE value l 0x01 D 4 DDC Emulation Commands Table D 1 continued Device dependent command summary Mode SRQ cont Command M8 M9 M10 MII M16 M17 M18 M19 M24 Description Equivalent SCPI commands Reading Done STATus MEASurement EVENt ENABle 64 SRE lt value gt value current SRE value l 0x01 Reading Done or Reading Overflow STATus MEASurement EVENt ENABle 192 SRE lt value gt value current SRE value l 0x01 Reading Done or Data Store Full STATus MEASurement EVENt ENABle 576 SRE lt value gt value current SRE value l 0x01 Reading Done or Data Store Full or Reading Overflow STATus MEASurement EVENt ENABle 704 SRE lt value gt value current SRE value I 0x01 Busy ESE 1 SRE lt value gt value current SRE value 0x20 Busy or
38. Press MENU 2 Scroll to the LFREQ menu item using the A and W range keys The present setting is displayed 3 Press the range key The present setting is now highlighted 4 Use the A and W range keys to scroll to the desired menu item AUTOXX 50 or 60 5 Press ENTER NOTE In the setting of AUTOXX XX is the currently detected frequency SCPI programming line frequency Table 1 2 SCPI commands line frequency SYSTem SYSTem Subsystem LFRequency lt freq gt Set power line frequency in Hz to 50 or 60 AUTO lt b gt Turn automatic frequency detection ON or OFF AUTO Read the present automatic detected line frequency state 1 on 0 off LFRequency Read present line frequency setting 1 14 Getting Started Model 6485 Picoammeter Instruction Manual Power up sequence The following power up sequence occurs when the Model 6485 is turned on L NOTE NOTE The Model 6485 performs self tests on its EPROM and RAM with all digits and annunciators turned on If a failure is detected the instrument momentarily dis plays an error message and the ERR annunciator turns on Error messages are listed in Appendix B If a problem develops while the instrument is under warranty return it to Keithley Instruments Inc for repair If the instrument passes the self tests the firmware revision levels are displayed For example 6485 BOl After the firmware revision levels are displayed the detected l
39. Reading Overflow ESE 1 STATus MEASurement EVENt ENABle 128 SRE lt value gt value current SRE value l 0x2010x01 Busy or Data Store Full ESE 1 STATus MEASurement EVENt ENABle 512 SRE lt value gt value current SRE value 0x2010x01 Busy or Data Store Full or Reading Overflow ESE 1 STATus MEASurement EVENt ENABle 640 SRE lt value gt value current SRE value 0x2010x01 Busy or Reading Done ESE 1 STATus MEASurement EVENt ENABle 64 SRE lt value gt value current SRE value 0x2010x01 Model 6485 Picoammeter Instruction Manual Note Default B3 B3 BO B3 BI NEW B3 BI BO NEW B4 H B4 BO B4 B1 NEW H B4 BI BO NEW H B4 B3 Model 6485 Picoammeter Instruction Manual DDC Emulation Commands Table D 1 continued Device dependent command summary Description MOLE Command Equivalent SCPI commands SRQ M25 Busy Reading Done or Reading Overflow cont ESE 1 STATus MEASurement EVENt ENABle 192 SRE lt value gt value current SRE value l Ox20I0x01 M26 Busy or Reading Done or Data Store Full ESE 1 STATus MEASurement EVENt ENABle 576 SRE lt value gt value current SRE value 0x2010x01 M27 Busy or Reading Done or Data Store Full or Reading Overflow ESE 1 STATus MEASurement EVENt ENABle 704 SRE lt value gt value current SRE value 0x2010x01 M32 Clears
40. Results Provides limit test results Model 6485 Picoammeter Instruction Manual DISPlay FORMat and SYSTem 13 7 Bit 6 Bit 5 0 0 All limit tests passed 0 1 CALC2 LIMI test failed 1 0 CALC2 LIM2 test failed Bit 7 Overvoltage Set to 1 if measurement performed with an overvoltage condition on the input Bit 9 Zero Check Set to 1 when zero check is enabled Bit 10 Zero Correct Set to 1 when zero correct is enabled Example The ASCII data string contains all three data elements The status value of 138 has a binary equivalent of 01001010 which indicates that bits B1 B3 and B7 are set Therefore the reading is 1 04056uA with null REL and the AVG filter enabled The reading was taken 223 6299 seconds after the instrument was turned on C FORMat BORDer lt name gt Parameters NORMal Normal byte order for IEEE 754 binary format SWAPped Reverse byte order for IEEE 754 binary format For normal byte order the data format for each element is sent as follows Byte 1 Byte 2 Byte 3 Byte 4 For reverse byte order data is sent as follows Byte 4 Byte 3 Byte 2 Byte 1 The 0 header is not affected by this command The header is always sent at the begin ning of the data string for each measurement conversion The ASCII data format can only be sent in the normal byte order The SWAPped selection is ignored when the ASCII format is selected NOTE The SWAPped byte order must be used when transmitting bin
41. SOP TESNE Process riali 8 6 SCREDIOSTAMIAE ariani EN 8 7 Programming example ail E N 8 8 Remote Operation Selecting and configuring an interface 9 2 Inicrla cessa 9 2 BILIE RR EI 9 2 Interface selection and configuration procedures 9 3 Configuring the GPIB interface 9 3 RS AES rarer 9 3 GPIB operation and reference iidesacuitedekivnsdledsiescinassaceadveansensesaesss 9 4 GPEIB bus stanidards iene 9 4 GPIB BUS COMME COLOMS ies tocss4 Cuter a E a TE 9 4 Pinia AGO CSS ask is cat sialon ta sali 9 7 General IEEE 488 bus commands 9 7 Commands and associated statements 9 7 REN remote enable ceeccccceesseccceeeeeceeeeneees 9 7 TPC interlace Clear asa ea 9 8 LLO ocal IOCKOUL iiscdcisicsiaccacdwnstsnsicssboasssonesieaseetecteness 9 8 Cr Es CO TOTOCAN cise dosastausds vsnan asholdea iss oensiandGenatheatsunes 9 8 TICE GEVICE Cle Al acral ie veli ii ai 9 8 SDC selective device clear a 9 8 GET group execute trigger siii 9 9 SPE SPD seral pollino rta 9 9 Front panel GPIB operation 9 9 Error and status messages siii si 9 9 GPIB status indicators ssaa 9 9 LOCAL KEY lean ze 9 10 Programming Syntax sicario 9 10 Command Words illa aa 9 10 Query COMMANA S aeron e E NRE EES 9 12 Cistica 9 12 Long form and short fo
42. SOR RO RR RR II 6 2 Recall vioceenscacalenecrdoumeesssusaasiwsegtser iii 6 3 Puna Omes tamps eusen E T A 6 4 Buffer statis CS astri ionan a i e cena 6 4 SCRIEprostimnm ice abi 6 5 Prosrammin e example csssrsnrondi ionnan i E 6 8 Triggering WATS CR MOdelS rinite 7 2 lde and initiate rara 7 4 Trigger model operation iii 7 4 Event detectors and control sources 7 5 MISS delay siano 7 6 Measure ACOM analisi 7 6 Output CCS aier a lla 7 7 COUNTS onr TE N S 7 7 Trigger model configuration front panel 7 7 SCPE ProStar 9 ollare 7 9 Programming example 7 11 External tric Cerino sli illa 7 11 Input trigger requirements 7 12 Output trigger specifications 7 12 External trigger example cccccccceseeceeeeceeeeeeeeeeeeeeeees 7 13 Limit Tests Emtiesnieara ie 8 2 Front panel operation iciccis iti sicctstsctoseiesisbigtscts adaticei Malis Wiaieelieges 8 5 Limuitest conisuratoni leali 8 5 Limits configuration MENU i 8 5 Arm layer configuration MENU 8 5 Pertotm imiittests sn steal 8 6 Step 1 Configure test system 8 6 Step 2 Configure measurement 8 6 Step 3 Configure imit tests alici 8 6 Step 4 Start testing process 8 6 Step 5
43. SRQ Error Mask ESE 0 this disables all events in the Standard Event Register SRE lt value gt value current SRE value amp ESB M33 IDDCO M34 IDDC M35 IDDC or IDDCO M36 Not in Remote M37 Not in Remote or IDDCO M38 Not in Remote or IDDC M39 Not in Remote IDDC or IDDCO ESE 48 Enables the SCPI command and Execution error events in the standard Event Register SRE lt value gt value current SRE value l ESB This Enables an SRQ on vents enabled in the Standard Event Register Note Default B4 B3 BO H B4 B3 BI NEW H B4 B3 B1 BO NEW H None B5 BO I B5 BI I BS BI BO I B5 B2 I B5 B2 BO I B5 B2 Bl I BS B2 B1 BO I D 6 DDC Emulation Commands Model 6485 Picoammeter Instruction Manual Table D 1 continued Device dependent command summary Description faul Mace Command Equivalent SCPI commands SOL NO Zero Correct disabled NEW X 7 SYSTem ZCORrect STATe OFF ero C NI Zero Correct enabled NEW orrect SYSTem ZCORrect ACQuire SYSTem ZCORrect STATe ON PO Filter off os l i PI Filter off Filter i Pn Repeat Filter on where filter size n 2 to 100 B a Q0 Conversion rate QI One reading per second See Q2 One reading every 10 seconds TRACE Data Store Q3 One reading per minute ARM and Buffer Q4 One reading every 10 minutes TRIGger Q5 One reading per hour sub O OO SS Sy ics Q6 Trigger mode Q7 D
44. Select the GPIB interface from the COMM menu structure access by pressing the COMM key while in local After selecting the GPIB interface press the CONFIG key and then the COMM key to configure the GPIB address and language From this menu you can check or change the following settings e Primary address 0 30 e Language SCPI SCPI 1996 0 which includes 488 2 488 1 or DDC Press the A or W range keys to scroll through ADDress and LANGuage available To make changes to a setting press the b key Then use the A or W range keys and the lt and gt cursor keys to select and modify the value as desired Press ENTER to save the changes and stay in the menu pressing EXIT also saves the changes but leaves the menu RS 232 interface NOTE Only the SCPI language can be used with the RS 232 interface The instrument defaults to the SCPI language when the RS 232 interface is selected enabled Select the RS 232 interface from the COMM menu structure access by pressing the COMM key while in local After selecting the RS 232 interface press the CONFIG key and then the COMM key to configure the RS 232 interface and check or change the fol lowing settings e BAUD Baud rate 57 6K 38 4k 19 2k 9600 4800 2400 1200 600 or 300 e BITS Data bits 7 or 8 e PARITY Parity none odd or even e TX TERMINATOR Terminator CR LF CRLF or LFCR e FLOW Flow control none or Xon Xoff 9 4 Remote Operation Model 6485 Picoammeter Instructi
45. Signals 220V Peak DC to 60Hz sine wave WARNING Ifitis possible for the DUT or external supply to present more than 42V to the input HI it is imperative that the connection between input LO and the external voltage source be sufficiently low impedance and capable of carrying the short circuit current of the source in order that the LO not exceed 42V CAUTION Current limiting resistors are required for DUTs capable of forcing voltages 220V or greater Damage to the instrument may result if volt ages greater than 220V are forced on the Model 6485 Input HI Voltages greater than 220V Often when making resistance measurements it is necessary to use an external voltage source with voltages greater than the maximum tolerable input voltage of 220V In the event that the resistance to be measured becomes shorted or an incorrect value of resis tance is inserted in the test setup the voltage source can permanently damage the Model 6485 To prevent this damage the following steps should be taken as a protection precau tion An alternate protection method is described in Measuring high resistance with external bias source page I 19 for cases not requiring the maximum sensitivity of the 6485 Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 7 To prevent accidental damage a series resistor should be added to the test setup The min imum value of this series resistor depends on the lowest current range to be used in th
46. Test limit or Rel readings are stored in the buffer See Section 8 for information on limit tests C TRACe FEED CONTrol lt name gt Name parameters e NEXT Enables the buffer and turns on the asterisk annunciator After the buffer stores the specified number of readings the asterisk annunciator turns off e NEVer Disables the buffer D TRACe TSTamp FORMat lt name gt Name parameters e ABSolute Each timestamp is referenced to the first reading stored in the buffer e DELTa Timestamps provide the time between each buffer reading e The timestamp data element can be included with each buffer reading see Ref F E TRACe DATA 1 The response message will include one to four data elements for each stored read ing Use the FORMat ELEMents command see Ref F to specify the elements 2 Reading an empty buffer will result in the ERROR 230 display message 3 Buffer data can be sent in the binary format See Table 14 3 Table FORMat command summary on page 5 for details F FORMat ELEMents lt list gt List parameters e READing Includes the buffer reading in each data string e UNITs identifies amps or math units e TIME Includes the timestamp for each reading Timestamp can be in the abso lute or delta format see Ref D Model 6485 Picoammeter Instruction Manual Buffer 6 7 STATus Includes a status word for each reading It provides status information on inst
47. accuracy 1 Connect the voltage calibrator and Model 5156 Electrometer Calibration Standard to the Model 6485 INPUT jack as shown in Figure 15 2 Initially make connec tions to the 1GQ resistor in the calibration standard Set the Model 6485 to the 2nA range With zero check enabled zero correct the instrument then disable zero check Set the calibrator voltage to 0 0000V and make sure the output is turned on Enable the Model 6485 REL mode Leave REL enabled for the remainder of the test oa ae LI Model 6485 Instruction Manual Performance Verification 15 9 6 Verify current measurement accuracy for each of the currents listed in Table 15 3 For each test point Make connections to the indicated calibration standard resistor Select the correct Model 6485 measurement range Calculate the actual required calibrator voltage V IR where I is the desired applied current and R is the actual standard resistor value Set the calibrator to the calculated voltage Verify that the Model 6485 current reading is within the reading limits listed in the table 7 Repeat the procedure for negative source currents with the same magnitudes as those listed in Table 15 3 Table 15 3 Reading limits for 2nA to 2uA ranges Nominal Calibrator Voltage Calibration Nominal Model 6485 Current Standard Applied Actual Reading Limits Resistor Current Voltage 1 Year 18 C 28 C 2 00000nA 1 99160 to 2 00840nA 20 0000nA 19 9190 to 20
48. adversely affect measurement results Model 6485 Picoammeter Instruction Manual Applications Guide I 5 Figure l 2 Voltage burden considerations 6485 Picoammeter Programmable V Source Voltage Burden Noise and source impedance Noise can seriously affect sensitive current measurements The following paragraphs dis cuss how source resistance and input capacitance affect noise performance Source resistance The source resistance of the DUT will affect the noise performance of current measure ments As the source resistance is reduced the noise gain of the picoammeter will increase as we will now discuss Figure I 3 shows a simplified model of the feedback picoammeter Rs and C represent the source resistance and source capacitance Vs is the source voltage and Vyojse 18 the noise voltage Finally Rp and Cx are the feedback resistance and capacitance respectively The source noise gain of the circuit can be given by the following equation Output Vworse Input Vworse Rp Rg Note that as Rs decreases in value the output noise increases For example when R Rg the input noise is multiplied by a factor of two Since decreasing the source resistance can have a detrimental effect on noise performance there are usually minimum recommended source resistance values based on measurement range Table I 1 summarizes minimum recommended source resistance values for various measurement ranges Note that the re
49. also changes it for m X b Pressing the mX b key toggles the state of the mX b math calculation on or off When pressed the MATH annunciator will toggle in addition to the presently selected units des ignator default is an X indicating the state of the mX b math function note that the m X b calculation uses the same designator as selected for the mX b calculation Configuring and controlling mX b and m X b To configure and control either of these math calculations perform the following steps NOTE Enabling or disabling by pressing the mX b key disables Rel if Rel is enabled 1 Press CONFIG and then MX B or M X B to display the present scale factor M 1 0000000 4 factory default 5 6 Relative mX b m X b reciprocal and log Model 6485 Picoammeter Instruction Manual Key in a scale factor value The lt and gt keys control cursor position and the A and W range keys increment and decrement the digit value To change range place the cursor on the range symbol and use the A and Y keys With the cursor on the polar ity sign the A and W keys toggle polarity NOTE Range symbols are defined in Table 5 1 3 Press ENTER to enter the M value and display the offset B value B 00 000000 P factory default Key in the offset value Press ENTER to set the B value and display the one character UNITS designator UNITS X factory default NOTE The configuration for mX b calculations consists of a units desig
50. as the movement of the person operating the instrument or others in the immediate vicinity causes fluctuations on the picoammeter s display To perform a quick check for interference place a piece of charged plastic such as a comb near the circuit A large change in the meter reading indicates insufficient shielding AC fields can be equally troublesome These are caused most often by power lines and RF fields If the AC voltage at the input is large part of this signal is rectified producing an error in the DC signal being measured This can be checked by observing the analog out put of the picoammeter with an oscilloscope A clipped waveform indicates a need to improve electrostatic shielding l 8 Applications Guide Model 6485 Picoammeter Instruction Manual Figure I 4 shows an example of AC electrostatic coupling An electrostatic voltage source in the vicinity of a conductor such as a cable or trace on a PC board generates a current proportional to the rate of change of the voltage and of the coupling capacitance This cur rent can be calculated with the following equation dV a dC LaL Fi V di Figure 1 4 Electrostatic coupling i r gt Ground referenced t signal conductor C Coupling capacitance Electrostatic dV dC voltage source Pat oe For example two conductors each with Icm area and spaced lcm apart by air will have almost 0 1pF of capacitance With a voltage difference of 100V and a vibration causing a change
51. by INITiate Return last latest CALC2 reading Trigger Subystem Arm Layer Select control source IMMediate Initiate one trigger cycle A FEED lt name gt Name parameters CALCulatel Limit tests will be performed on the result of a math calculation mX b m x b or log SENSe Limit tests will be performed on the input signal Note however that Rel can be used on the result of a math calculation as well as the input signal Limit tests will be performed on the result of the Rel operation see CALCulate2 NULL Details on rela tive mX b m X b and log are provided in Section 5 8 8 Limit Tests Model 6485 Picoammeter Instruction Manual B FAIL In the event of a failure you can read the measurement event register to determine which limit upper or lower failed See Section 11 to program and read the measurement event register C DATA The INITiate command must be sent to perform the programmed number of measure ments If the instrument is programmed to perform a finite number of measurements the DATA command will return all the CALC2 readings after the last reading is taken The DATA LATest command will only return the last latest CALC2 reading If the instrument is programmed to perform an infinite number of measurements arm count or trigger count set to infinite you cannot use the DATA command to return CALC2 readings However you can use the DATA LATest command to return the last CALC2 re
52. calibration constants proceed to Locking out calibration 1 Press MENU select CAL then press ENTER to access the calibration menu 2 Use either RANGE key to display the following CAL SAVE 3 Press ENTER The unit will prompt for today s calibration date DATE 11 15 01 4 Use the arrow and RANGE keys to set the date then press ENTER The unit will then prompt for the calibration due date NDUE 11 15 02 5 Set the calibration due date as desired then press ENTER The unit will prompt you as follows SAVE CAL YES 6 With the YES prompt displayed press ENTER to save and lock out calibration The unit will display CAL SAVED NOTE Calibration will also be locked out once saved 16 12 Calibration Model 6485 Instruction Manual Locking out calibration Use the following procedure to lock out calibration without saving new calibration con stants L Press MENU select CAL then press ENTER Use the up RANGE key to display the following CAL LOCK Press ENTER The instrument will display the following message CAL LOCKED Calibration support Changing the calibration code Follow the steps below to change the calibration code L Press MENU select CAL then press ENTER The instrument will display the fol lowing CAL VOFFSET Use the up or down RANGE key to display the following CAL UNLOCK Press ENTER The instrument will prompt for the present calibration code CODE 000000 Enter the
53. characters that are enclosed in brackets are optional and need not be included in the program message Program messages A program message is made up of one or more command words sent by the computer to the instrument Each common command is simply a three letter acronym preceded by an asterisk The following SCPI commands from the STATus subsystem are used to help explain how command words are structured to formulate program messages Command structure STATus Path Root OPERation Path ENABle lt NRf gt Command and parameter ENABle Query command PRESet Command Single command messages The above command structure has three levels The first level is made up of the root com mand STATus and serves as a path The second level is made up of another path OPERation and a command PRESet The third path is made up of one command for the OPERation path The three commands in this structure can be executed by sending three separate program messages as follows Stat oper enab lt NRf gt Stat oper enab Stat pres In each of the above program messages the path pointer starts at the root command stat and moves down the command levels until the command is executed 9 14 Remote Operation Model 6485 Picoammeter Instruction Manual Multiple command messages You can send multiple command messages in the same program message as long as they are separated by semicolons The following is an example showing two
54. choose from one of the following rates 57 6k 38 4k 19 2k 9600 4800 2400 1200 600 or 300 Make sure that the programming terminal that you are connecting to Model 6485 can sup port the baud rate you selected Both Model 6485 and the other device must be configured for the same baud rate Data and stop bits The RS 232 can be set to transfer data using seven or eight data bits and one stop bit Parity Parity for the RS 232 interface can be set to none even or odd Terminator Model 6485 can be configured to terminate each program message that it transmits to the controller with any of the following combinations of lt CR gt and lt LF gt e LF line feed e CR carriage return e LFCR line feed carriage return e CRLF carriage return line feed Flow control signal handshaking Signal handshaking between the controller and the instrument allows the two devices to communicate to each other regarding being ready or not ready to receive data Model 6485 does not support hardware handshaking flow control Software flow control is in the form of X_ON and X_OFF characters and is enabled when XonXoFF is selected from the RS232 FLOW menu When the input queue of Model 6485 becomes more than 3 4 full the instrument issues an X_OFF command The control pro gram should respond to this and stop sending characters until Model 6485 issues the X_ON which it will do once its input buffer has dropped below half full Model 6485 rec ogni
55. connector for sending and receiving trigger pulses among connected instru ments Use a trigger link cable or adapter such as Models 8501 1 8501 2 8502 and 8503 1 10 Getting Started Model 6485 Picoammeter Instruction Manual 6 RS 232 Female DB 9 connector for RS 232 operation Use a straight through not null modem DB 9 shielded cable 7 IEEE 488 Connector for IEEE 488 GPIB operation Use a shielded cable such as Models 7007 1 and 7007 2 8 Power module Contains the AC line receptacle and power line fuse The instrument can be configured for line volt ages of 115V and 230VAC nominal at line frequencies of 50 or 60Hz automatically and over the bus Changing line voltages requires changing fuses Analog output The Model 6485 has an analog output on the rear panel The ANALOG OUT provides a scaled inverting 2V output A full scale reading corresponds to 2V output WARNING The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis voltage Exceeding 42V can create a shock hazard CAUTION The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the instrument Connecting COMMON or ANALOG OUT to earth while floating the input may damage the instrument Connections for using this output are shown in Figure 1 3 For a full scale input i e 2mA on the 2mA range the output will be 2V Examp
56. correct SYSTem SYSTem Subsystem ZCHeck Zero check STATe lt b gt Enable or disable zero check ZCORrect Zero correct STATe lt b gt Enable or disable zero correct ACQuire Acquire a new zero correct value INITiate Trigger a reading A SYSTem ZCORrect ACQuire The zero correct value can only be acquired while zero check is enabled and zero correct state is off The internal offset measured at that moment will become the correction value Zero correction can then be applied and zero check disabled This acquire method makes it convenient if you need to re zero the instrument often The following command sequence uses the acquire method to zero correct the 200UA range RST Set instrument to known default conditions in one shot trigger mode SYST ZCH ON Enable zero check CURR RANG 2E 4 Set instrument to 200UA range INIT Trigger one reading SYST ZCOR ACO Acquire zero correct value SYST ZCH OFF Disable zero check SYST ZCOR ON Perform zero correction The INITiate command in the above sequence is used to trigger a reading This reading is the offset that is acquired as the zero correct value See Section 7 for more information on INITiate NOTE Sending the ACQuire command while zero check is disabled will result in an error The command will not be executed 2 16 Measurement Concepts Model 6485 Picoammeter Instruction Manual B SYSTem ZCORrect STATe lt b gt This method to per
57. correct the Model 6485 then disable zero check Set the calibrator current to 0 0000uA and make sure the output is turned on Enable the Model 6485 REL mode Leave REL enabled for the remainder of the test a Se a 6 Verify current measurement accuracy for each of the currents listed in Table 15 2 For each test point e Select the correct Model 6485 measurement range e Set the calibrator current to the indicated value e Verify that the Model 6485 current reading is within the limits given in the table 7 Repeat the procedure for negative source currents with the same magnitudes as those listed in Table 15 2 15 8 Performance Verification Model 6485 Instruction Manual Table 15 2 Reading limits for 204A to 20mA ranges Model 6485 Calibrator Model 6485 Current Reading Limits Range Current 1 Year 18 C 28 C 20 0000uA 19 9790 to 20 0210uA 200 000uA 199 790 to 200 210uA 2 00000mA 1 99790 to 2 00210mA 20 0000m A 19 9790 to 20 0210mA Figure 15 1 Connections for 20uA to 20mA range verification Low noise Coax BNC Cable INAFANIM GINO INTERNAL OPERAT BY QUALIFIED PERSONNEL OI KEITHLEY USA ry L aa ANALos out amp owo INPUT input TRIGGER LINK RS 232 A une RATING f 220V PK A 50 60Hz 30VA 42V PK Fuse JUNE 630mAT Model 6485 Picoammeter DC Current Calibrator BNC to dual Banana Plug Adapter Connect Cable Shield to Output LO 2nA 2UuA range
58. corresponding enable bit is set as programmed by the user the output summary of the register will set to 1 which in turn sets the summary bit of the status byte register Queues Model 6485 uses an output queue and an error queue The response messages to query commands are placed in the output queue As various programming errors and status messages occur they are placed in the error queue When a queue contains data it sets the appropriate summary bit of the status byte register Model 6485 Picoammeter Instruction Manual Figure 10 1 6485 status mode structure Questionable Event Registers Condition Event Register Register Calibration Summary Cal al dll dl O al wl ni lo oD vajajo N 5 D D Command Warning Always Zero 15 S dda a lol lo wif a wf rm D di VI Event Enable Register il il deri wl nt l o ov Faja WI N D di VI CONDition EVENT ENABle lt NRf gt ENABle Output Queue Standard Event Registers Event Event Enable Register Register Operation Complete OPC OPC e ty Query Error rove leave Ls Device Specific Error DDE P DDE O Execution Error EXE el Command Error ME MEL User Request URQ URQ O 5 Power On POR HoN s e H e H m e h ELE E ae e hH BE pg gy BE ee ogg E Always Zero ENT FEA ESR ESE lt NRf gt ESE Measurement Event Registers Condition Event Event Enable Register Register Register Low
59. editing values Use to save present setup to a memory location Use to restore setup to either GPIB or factory defaults or to a user memory location Also use to modify properties of power on defaults to either GPIB or factory defaults or to a user memory location Use to start buffer and modify the number of readings to store Use to display stored readings including maximum minimum peak to peak aver age and standard deviation The and w range keys scroll through the buffer and the 4 or key toggles between reading number reading and timestamp Use to perform and create limit tests Use to control auto zero function on off Use to cancel selection and move back to measurement display Use to accept selection and move to next choice or back to measurement display Use to select the next higher measurement range Also use to modify the upper auto range limit Use to select the next lower measurement range Also use to modify the lower auto range limit Enables disables autorange 5 Display annunciators 6 asterisk gf more AUTO BUFFER ERR FAST FILT LSTN MATH MED REL REM SLOW SRQ STAT TALK TIMER TRIG Handle Readings being stored in buffer Indicates additional selections are available Autorange enabled Recalling readings stored in buffer Questionable reading or invalid cal step Fast 0 1 PLC reading rate selected MEDIAN and or AVERAGE filter enabled Instrument address
60. for details on buffer operation Model 6485 Picoammeter Instruction Manual Triggering 7 15 To start the test press STEP on the switching mainframe to take it out of idle and start the scan The switching mainframes output pulse triggers Model 6485 to take a reading and store it Model 6485 then sends an output trigger pulse to the switching mainframe to close the next channel This process continues until all 10 channels are scanned measured and stored Figure 7 9 Operation model for triggering example 70010r 7002 Press STEP to start scan 6485 Wait for Trigger Link Wait for Trigger Link Trigger BB Trigger l l l Scan Make Channel l l l Measurement Output Trigger Trigger Output Trigger W U Trigger Scanned 10 Channels 7 16 Triggering Model 6485 Picoammeter Instruction Manual Details of this testing process are explained in the following paragraphs and are referenced to the operation model shown in Figure 7 9 A B E and F Operation of Model 6485 starts at point A in the flowchart where it waits for an external trigger Pressing STEP takes Model 7001 2 out of idle and places operation at point B in the flowchart For the first pass through Model the scanner does not wait at point B Instead it closes the first channel point C After the relay settles Model 7001 2 outputs a trigger pulse Since the instrument is p
61. has a significant level often several volts of line frequency common mode voltage Figure l 7 Connecting the HI terminal picoammeter to high resistance Current Source 6485 Picoammeter Model 6485 Picoammeter Instruction Manual Applications Guide l 11 As shown in Figure I 8 this will cause a current 1 to flow through the low to ground capacitance of the picoammeter A Picoammeter HI is connected to the highest resis tance side of the circuit being measured the R side of this current source This circuit is connected properly so this current does not flow through the picoammeter and therefore does not cause any measurement errors Figure l 8 Proper connection Current Source 6485 Picoammeter However when the HI of the picoammeter is connected to the low impedance power sup ply this AC current 1 flows through the picoammeter A as illustrated in Figure I 9 This current may affect the measurement accuracy especially at low signal levels I 12 Applications Guide Model 6485 Picoammeter Instruction Manual Figure l 9 Improper connection Current Source LO Picoammeter HI Refer to Input cables connectors and adapters page 1 4 for details on appropriate types of cabling and connectors to use when making picoammeter measurements Typical range change transients During a range change a picoammeter cannot perfectly maintain its voltage burden speci fication When a range cha
62. of capacitance of 0 01pF second a 10 fluctuation a current of 1pA will be gen erated To reduce the effects of the fields a shield can be built to enclose the circuit being mea sured The easiest type of shield to make is a simple metal box or meshed screen that encloses the test circuit Shielded boxes are also available commercially Figure I 5 illustrates an example of shielding Made from a conductive material the shield is always connected to the low impedance input of the electrometer or picoammeter If cir cuit low is floating above ground observe special safety precautions to prevent anyone from touching the shield See Floating measurements page 2 12 Model 6485 Picoammeter Instruction Manual Applications Guide l 9 Figure l 5 Shielding a high impedance device Metal Shield 6485 Picoammeter The cabling in the circuit also requires shielding Capacitive coupling between an electro static noise source and the signal conductors or cables can be greatly reduced by surround ing those conductors with a grounded metal shield as shown in Figure I 6 With this shield in place the noise current generated by the electrostatic voltage source and the cou pling capacitance flows through the shield to ground rather that through the signal conduc tors Figure l 6 Electrostatic shielding Shield Ground referenced signal conductor Ground Noise Shield to cable current NO capacitance Source
63. or more non SCPI parameters are explained by notes Path to configure and control CALCI calculations 5 y Select math format MXB mX b or RECiprocal V m X b or LOG10 Query math format y Configure math calculations Set m for mX b and m X b calculation i 9 99999e20 to 9 99999e20 Query m factor Set b for mX b and m X b calculation i 9 99999e20 to 9 99999e20 Query b factor Specify units for mX b or m X b result 1 character A Z Q Y Query units Enable or disable CALCI calculation y Query state of CALCI calculation y Model 6485 Picoammeter Instruction Manual SCPI Reference Tables 14 3 Table 14 1 continued CALCulate command summary Default Ref Command Description parameter Section SCPI CALCulate 1 continued DATA LATest CALCulate2 FEED lt name gt FEED LIMit 1 UPPer DATA lt n gt DATA LOWer DATA lt n gt DATA STATe lt b gt STATe FAIL LIMit2 UPPer DATA lt n gt DATA LOWer DATA lt n gt DATA STATe lt b gt STATe FAIL NULL ACQuire OFFSet lt NRf gt OFFSet STATe lt b gt STATe DATA LATest Return all CALCI results triggered by INITiate Return last latest reading Path to configure and control limit testing CALC2 Select input path for limit testing CALCulate 1 or SENSe 1 Query input path for limit tests Limit 1 Testing Configure upper limit
64. post processed readings After sending this command and addressing Model 6485 to talk the readings are sent to the computer This command does not affect the instrument setup This command does not trigger a measurement The command simply requests the last group of readings Note that this command can repeatedly return the same readings Until there is a new reading s this command continues to return the old reading s If your application requires a fresh reading use the READ command This command is automatically asserted when the READ or MEASure command is sent C READ Trigger measurement s and request reading s This command is used to trigger and acquire readings The number of readings depends on how the trigger model is configured For example if configured for 20 measurements arm count 1 trigger count 20 20 sets of readings will be acquired When this command is sent the following commands execute in the order they are pre sented e INITiate e FEICN If the instrument is in the idle state INITiate takes the instrument out of idle to perform the programmed number measurements If the instrument is not in the idle state execution of this command will wait until it goes back into idle The FETCh command is executed to acquire the reading s The readings are sent to the computer when Model 6485 is addressed to talk NOTE If the instrument is programmed to perform an infinite number of measurements a
65. subsequent pass is satisfied by an input trigger The bypass resets when Model 6485 leaves the trigger layer 7 6 Triggering Model 6485 Picoammeter Instruction Manual Trigger delay A programmable delay is available after event detection It can be set manually 0 to 999 9998 seconds or an auto delay can be used With auto delay selected the Model 6485 automatically sets delay according to range The auto delay settings are listed in Table 7 1 Table 7 1 Auto delay settings Measure action The measure action block of the trigger model is where a measurement is performed However if the repeating filter is enabled see Figure 7 3 the instrument samples the specified number of reading conversions to yield single filtered reading Only one reading conversion is performed if the digital filter is disabled or after the specified number of reading conversions for a moving average filter is reached Figure 7 3 Measure action block of trigger model Measure Action o Filter Process spa CONV 9 CONV CONV Reading Conversion Model 6485 Picoammeter Instruction Manual Triggering 7 7 Output triggers Model 6485 can send out an output trigger via the rear panel TRIGGER LINK connector right after the measure action and or when operation leaves the trigger layer An output trigger can be used to trigger another instrument to perform an operation e g select the next output step for a source Counters Programmable c
66. that occur in multiple instrument test setups can create error signals that cause erratic or erroneous measurements The configuration shown in Figure C 1 intro duces errors in two ways Large ground currents flowing in one of the wires will encounter small resistances either in the wires or at the connecting points This small resistance results in voltage drops that can affect the measurement Even if the ground loop currents are small magnetic flux cutting across the large loops formed by the ground leads can induce sufficient voltages to disturb sensitive measurements Figure C 1 Power line ground loops Signal Leads Instrument 1 Instrument 2 Instrument 3 x Ground 4 Loop i Current Power Line Ground To prevent ground loops instruments should be connected to ground at only a single point as shown in Figure C 2 Note that only a single instrument is connected directly to power line ground Experimentation is the best way to determine an acceptable arrangement For this purpose measuring instruments should be placed on their lowest ranges The configu ration that results in the lowest noise signal is the one that should be used A convenient way to make this connection uses the ground link at the rear of the 6485 Model 6485 Picoammeter Instruction Manual General Measurement Considerations C23 Figure C 2 Fliminating ground loops Instrument 1 Instrument 2 Instrument 3 Power Line Ground Triboelectric
67. that the unit meets factory specifications To determine if calibration is required Follow calibration to make sure it was performed properly WARNING The information in this section is intended only for qualified service personnel Do not attempt these procedures unless you are qualified to do so Some of these procedures may expose you to hazardous voltages which could cause personal injury or death if contacted Use standard safety precautions when working with hazardous voltages NOTE If the instrument is still under warranty and its performance is outside specified limits contact your Keithley representative or the factory to determine the cor rect course of action Verification test requirements Be sure that you perform the verification tests Under the proper environmental conditions After the specified warm up period Using the correct line voltage Using the proper test equipment Using the specified test signals and reading limits Environmental conditions Conduct your performance verification procedures in a test environment with An ambient temperature of 65 to 82 F 18 to 28 C A relative humidity of less than 70 unless otherwise noted Model 6485 Instruction Manual Performance Verification 15 3 Warm up period Allow the Model 6485 to warm up for at least one hour before conducting the verification procedures If the instrument has been subjected to temperature extremes those outside the ra
68. the event and event enable registers and the error queue are listed in Table 10 1 In addition to these commands any enable register can be reset by sending the 0 parameter value with the individual command to program the register NOTE SYSTem PRESet and RST have no effect on status structure registers and queues Table 10 1 Common and SCPI commands reset registers and clear queues To reset registers CLS Reset all bits of the following event registers to 0 Standard event register Operation event register Measurement event register Questionable event register STATus STATus subsystem PRESet Reset all bits of the following enable registers to 0 Operation event enable register Measurement event enable register Questionable event enable register To clear error queue CLS Clear all messages from error queue STATus STATus subsystem QUEue Error queue CLEar Clear messages from error queue SYSTem SYSTem subsystem ERRor Error queue CLEar Clear messages from error queue Notes 1 The standard event enable register is not reset by STATus PRESet or CLS Send the 0 parameter value with ESE to reset all bits of that enable register to 0 see Status byte and service request SRQ page 10 7 2 STATus PRESet has no effect on the error queue 3 Use either of the two clear commands to clear the error queue Model 6485 Picoammeter Instruction Manual Status Structure 10 5 Programming and reading register
69. the input level goes below 2014 The AUTO key toggles the instrument between manual ranging and autoranging The AUTO annunciator turns on when autoranging is selected To disable autoranging press AUTO or the RANGE A or W key Pressing AUTO to disable autoranging leaves the instrument on the present range Every time an autorange occurs a search for every available range of the selected function is performed The time it takes to perform the search could slow down range change speed significantly Setting upper and or lower autorange limits can reduce search time NOTE Range limits and groups are not in effect for manual ranging Every range is accessible with manual range selection Model 6485 Picoammeter Instruction Manual Range Units Digits Rate and Filters 4 3 Autorange limits Search time for amps can be reduced by setting upper and or lower autorange limits For example if you know the maximum input will be around 1yA set the upper current range limit to 2uA This eliminates the 20uA 200UA 2mA and 20mA ranges from the search thereby increasing the range change speed Should the input exceed 2 1uA the OVR FLOW message will be displayed Perform the following steps to set upper and or lower autorange limits L Zi 3 4 NOTE Units Press CONFIG key CONFIGURE will be displayed Display the desired limit UPPER or LOWER a Press the RANGE A key to display the present UPPER range limit b Pre
70. the instrument exist only after it has been addressed to listen SR Service Request Function SR1 defines the ability of the instrument to request service from the controller Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 15 RL Remote Local Function RL1 defines the ability of the instrument to be placed in the remote or local modes TE Extended Talker Function The instrument does not have extended talker capa bilities TEO LE Extended Listener Function The instrument does not have extended listener capabilities LEO E Bus Driver Type The instrument has open collector bus drivers E1 F 16 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual G IEEE 488 and SCPI Conformance Information G 2 IEEE 488 and SCPI Conformance Information Model 6485 Picoammeter Instruction Manual Introduction The IEEE 488 2 standard requires specific information about how the Model 6485 imple ments the standard Paragraph 4 9 of the IEEE 488 2 standard Std 488 2 1987 lists the documentation requirements Table G 1 provides a summary of the requirements and pro vides the information or references the manual for that information Table G 2 lists the cou pled commands used by the Model 6485 The Model 6485 complies with SCPI version 1991 0 Table 14 1 through Table 14 8 list the SCPI confirmed commands and the non SCPI commands implemented by the Model 6485 Table G 1 JEEE 488 do
71. the unknown resistance breaks down and becomes shorted The diodes should be in a light tight enclosure to prevent light induced leakage A diagram of the overload protection circuit is shown in Figure I 17 Figure I 17 Overload Protection Circuit for 6485 Picoammeter R HI NZ To 6485 Input IN 3595 LO Model 6485 Picoammeter Instruction Manual Applications Guide l 21 In the case that the source is connected directly across the protection circuit make sure the series resistance R is chosen so the current through the diodes is limited to lt 100mA If the current through the unknown resistance must be measured with an accuracy greater than 10pA use the protective method outlined in Voltages greater than 220V page 2 6 Cable insulation resistance NOTE For this test Model 6485 uses the source voltage measure current method to determine resistance Once a current measurement is performed resistance can be calculated Figure I 18 shows how to measure the insulation resistance of a cable The resistance of the insulator between the shield and the inner conductor is being measured The cable sample should be kept as short as possible to minimize input capacitance to the picoam meter For this test a fixed bias voltage is applied across the insulator for a specified time to allow the charging effects of cable capacitance to stabilize The current is then measured Cable resistance R can then be calculated as follows R I
72. up period 2 2 Warranty information 1 3 ZCHK 1 7 ZCOR 1 7 Zero Check D 2 Zero check and zero correct 2 13 Zero Correct D 6 Specifications are subject to change without notice All Keithley trademarks and trade names are the property of Keithley Instruments Inc All other trademarks and trade names are the property of their respective companies KEITHLEY Keithley Instruments Inc Sales Offices BELGIUM CHINA FINLAND FRANCE GERMANY GREAT BRITAIN INDIA ITALY KOREA NETHERLANDS SWEDEN SWITZERLAND TAIWAN 28775 Aurora Road Cleveland Ohio 44139 440 248 0400 Fax 440 248 6168 1 888 KEITHLEY 534 8453 e www keithley com Bergensesteenweg 709 e B 1600 Sint Pieters Leeuw 02 363 00 40 e Fax 02 363 00 64 Yuan Chen Xin Building Room 705 12 Yumin Road Dewai Madian Beijing 100029 8610 6202 2886 Fax 8610 6202 2892 Tietajantie 2 02130 Espoo Finland Phone 358 9 25105114 Fax 358 9 2510 5100 3 all e des Garays 91127 Palaiseau C dex 01 64 53 20 20 e Fax 01 60 11 77 26 Landsberger Strasse 65 82110 Germering 089 84 93 07 40 e Fax 089 84 93 07 34 Unit 2 Commerce Park Brunel Road Theale Reading Berkshire RG7 4AB e 0118 929 7500 Fax 0118 929 7519 Flat 2B Willocrissa 14 Rest House Crescent Bangalore 560 001 91 80 509 1320 21 Fax 91 80 509 1322 Viale San Gimignano 38 20146 Milano 02 48 39 16 01 Fax 02 48 30 22 74 FL URI Building 2 14 Yangjae Do
73. will not increase significantly Down range voltage transients are smaller With the exception of the change from the 2mA range to the 200UA range the down range voltage transient is significantly smaller than the up range transients Figure I 12 shows the voltage presented at the input measured during a change from 20UA to 2uA with a 2uA input current The vast difference from the previous figures in voltage scale and time scale should be noted Note also that the current limiting resistor will be that of the 2UA range 100 times greater than upranging across the same boundary The voltage transient of the 2mA to 200uA change with a 200UA input signal is similar to the up range response with the exception that the current limiting R will be 100 times greater in the case of down ranging Model 6485 Picoammeter Instruction Manual Applications Guide I 15 Figure l 12 Down range voltage transients a ih SI gr E 100mV M 100us A Chl 108mV i 20 00 11 01 11 Steps to minimize impact of range change transients When changing between the following range pairs up or down no input transients occur 2nA and 20nA 200nA and 2uA 20uA and 200UA 2mA and 20mA This is not true when auto ranging upwards across these boundaries Run test with a fixed range If possible run the test within a fixed range Choose the higher range from any of the range pairs listed above Alternatively the autorange upper limit RANGe AUTO U
74. within the idle state of the instrument Nomenclature in Figure 7 1 relates to the various names used for configuration menu items while Figure 7 2 provides the SCPI commands to control operation Idle and initiate While in the idle state the instrument cannot perform measurements While in idle the reading remains frozen or dashes replace the reading 1 e A Once Model 6485 is taken out of idle operation proceeds through the trigger model Front panel operation As shown in Figure 7 1 Model 6485 immediately leaves the idle state when it is turned on Typically operation remains in the arm and trigger layers of the trigger model However Model 6485 can be put into the idle state at any time by press ing the HALT key To take the instrument out of idle press the TRIG key Other front panel keys can be pressed instead but they may change the setup Remote operation As shown in Figure 7 2 an initiate command is required to take the instrument out of idle The following commands perform an initiate operation e INITiate e READ e MEASure While operating within the trigger model not in idle most commands will not be exe cuted until the instrument completes all of its programmed operations and returns to the idle state The IFC SDC and DCL commands can be executed under any circumstance while operating within the trigger model They will abort any other command or query The following commands can be executed whi
75. 0 000 2E 8 or 0 00000002 00 0000 2E 9 or 0 000000002 0 00000 The RATE key selects the integration time of the A D converter This is the period of time the input signal is measured The integration time affects the amount of reading noise as well as the ultimate reading rate of the instrument The integration time is specified in parameters based on a number of power line cycles NPLC where 1 PLC for 60Hz is 16 67msec 1 60 and 1 PLC for 50Hz and 400Hz is 20msec 1 50 In general Model 6485 has a parabola like shape for its speed vs noise characteristics and is shown in Figure 4 1 Model 6485 is optimized for the 1 PLC to 10 PLC reading rate At these speeds lowest noise region in the graph Model 6485 will make corrections for its own internal drift and still be fast enough to settle a step response lt 100ms Figure 4 1 Speed vs noise characteristics Lowest Voltage noise Noise region 166 7us 16 67ms 166 67ms Integration Time 4 6 Range Units Digits Rate and Filters Model 6485 Picoammeter Instruction Manual The rate setting is global for all ranges Therefore it does not matter what range is pres ently selected when you set rate There are two ways to set rate You can select slow medium or fast by using the RATE key or you can set the number of power cycles from the NPLC menu that is accessed by pressing CONFIG LOCAL while in LOCAL and then RATE Rate Key The RATE key selections a
76. 00 readings filter off capped input limited to 10 rdgs sec under this condition 3 Measured at analog output with resistive load gt 100kQ IEEE 488 BUS IMPLEMENTATION MULTILINE COMMANDS DCL LLO SDC GET GTL UNT UNL SPE SPD IMPLEMENTATION SCPI IEEE 488 2 SCPI 1996 0 DDC IEEE 488 1 UNILINE COMMANDS IFC REN EOI SRQ ATN INTERFACE FUNCTIONS SH1 AH1 T5 TEO L4 LEO SR1 RL1 PPO DCI DT1 C0 El PROGRAMMABLE PARAMETERS Range Zero Check Zero Correct EOI DDC mode only Trigger Terminator DDC mode only Calibration SCPI mode only Display Format SRQ REL Output Format V offset Cal ADDRESS MODES TALK ONLY and ADDRESSABLE LANGUAGE EMULATION Keithley Model 485 emulation via DDC mode RS 232 IMPLEMENTATION Supports SCPI 1996 0 Baud Rates 300 600 1200 2400 4800 9600 19 2k 38 4k 57 6k Protocols Xon Xoff 7 or 8 bit ASCII parity odd even none Connector DB 9 TXD RXD GND ANALOG RISE TIME 3 10 to 90 8 ms 8 ms 500 ps 500 us 500 ps 500 us 500 ps 500 us GENERAL INPUT CONNECTOR BNC on rear panel DISPLAY 12 character vacuum fluorescent RANGING Automatic or manual OVERRANGE INDICATION Display reads OVRFLOW CONVERSION TIME Selectable 0 01 PLC to 60 PLC 50PLC under 50Hz operation Adjustable from 200us to 1s READING RATE To internal buffer 1000 readings second To IEEE 488 bus 900 readings second 2 Notes 0 01 PLC digit
77. 006485 Use the up and down RANGE keys to select the letter or number and use the left and right arrow keys to choose the position Press ENTER to complete the process and the unit will display CAL UNLOCKED Followed by NEW CODE N With N displayed press ENTER Offset voltage calibration Before performing the remaining calibration steps perform input bias current and offset voltage calibration as outlined below 1 From the calibration menu use the up or down RANGE key to display the follow ing CAL VOFFSET 2 Press ENTER The instrument will prompt as follows INPUT CAP 3 Connect the BNC shielding cap to the rear panel INPUT jack 4 Press ENTER to complete offset voltage calibration 5 Press EXIT to return to normal display Current calibration 20UA 20mA range calibration Connect the BNC shielding cap to the Model 6485 rear panel INPUT jack Select the Model 6485 20UA range Press MENU select CAL then press ENTER At the CAL RUN prompt press ENTER The unit will prompt for the zero calibration point 20uA ZERO With the BNC shielding cap connected to the INPUT jack for a OWA input current press ENTER The unit will prompt for the positive full scale cal point 20uA CAL Connect the current calibrator to the Model 6485 INPUT jack as shown in Figure 16 1 Press ENTER The unit will prompt for the positive full scale current 20 00000 LA Set the calibrator current to 20 00000LA then adjust the di
78. 1 or 7002 switch system Figure 7 7 DUT test system Model 6485 Picoammeter 7158 Low Current Card 7 14 Triggering Model 6485 Picoammeter Instruction Manual The trigger link connections for this test system are shown in Figure 7 8 The trigger link of Model 6485 is connected to the trigger link IN or OUT of the switching mainframe Note that with the default trigger settings of the switching mainframe line 1 is an input and line 2 is an output Figure 7 8 Trigger link connections 7001 or 7002 Switch System Model 6485 Picoammeter KEITHLEY MADE IN USA CHANGE IEEE ADDRE ANALOG OUT FRANS MENO RS 232 INPUT Link Trigger Link Trigger Link Cable 8501 For this example Model 6485 and switching mainframe are configured as follows Model 6485 Switching Mainframe Factory Defaults Restored Factory Defaults Restored Trig In Event TLink Scan List 1 1 1 10 Trigger Input Line 2 Number of Scans 1 Trigger Output Line 1 Channel Spacing TrigLink Trigger Output Event ON Trigger Count 10 Trigger Delay Auto To store readings in Model 6485 buffer first set the number of points to store in the buffer 1 Press CONFIG and then STORE 2 Set the buffer size to 10 using the A and W range keys and the lt and cursor keys 3 Press ENTER 4 The next time STORE is pressed the asterisk annunciator turns on to indicate the buffer is enabled See Section 6
79. 16 8 2nA to 2UA range calibration summary ee eeeeeeeeeeeee 16 10 Routine Maintenance Line PUSS tano lea 17 2 Front panel tests alle elisa 17 3 Status and Error Messages Status and error messages iii B 2 DDC Emulation Commands Device dependent command summary 000 D 2 Status byte and mask interpretation D 13 IEEE 488 Bus Overview TEEE 488 bus command summary F 7 Command COGS blu niente eer t ones terete F 8 Hexadecimal and decimal command codes F 11 Typical BUS SEQUENCE alii lea F 12 Typical addressed command sequence F 12 IEEE Command StOUDS alal igl F 13 Model 6485 interface function codes F 14 IEEE 488 and SCPI Conformance Information IEEE 488 documentation requirements G 2 Coupled commands ps lalla birra G 3 Remote Calibration Calibration commands H 2 Calibration commands by range H 4 Applications Guide Minimum recommended source resistance values 1 6 Internal impedance for zero check transient I 17 Getting Started Introduction Description of the Model 6485 Picoammeter Overview of this manual Provides content of this manual General information Covers general information that includes warranty infor mation
80. 16 9 Entering calibration dates and saving calibration 16 11 Locking out calibration 16 12 Calibration Sup POL lt ira a 16 12 Changing the calibration code 16 12 Resetting the calibration code 16 12 Displaying calibration dates 16 13 Displaying the calibration count 16 13 Routine Maintenance roduc TOM rtl ironia siasi 17 2 Setting line voltage and replacing line fuse 17 2 Front Pale TESS seniii ini nanses aE r EEE 17 3 DISP TES Llano 17 4 FEY otraa laziale 17 4 Specifications Status and Error Messages General Measurement Considerations Measurement considerations 0 erre C 2 Ground JOODS aies E iors artes C 2 Irnboclecmic eects alal C 3 Piezoelectric and stored charge effects C 3 Electrochemical effects lt ciccscsscesutesesateasveneacestaiaveieeaseashadecees C 4 FO EY aa E C 4 bora iii C 4 El ctrostatic Mterference cui C 4 Magnetic Molds girato C 5 Electromagnetic Interference EMI C 5 DDC Emulation Commands DPC Ta OU as Ce iter ucc aor she iii rea D 2 Status Byte FormnaL sara ei D 12 Example Programs PROS TAMING CX AMI ICS 553 siano relati E 2 1000 readings second into internal buffer
81. 3 4 5 or 6 OUTPut lt name gt Output trigger after measurement SENSe or not at all NONE 7 10 Triggering Model 6485 Picoammeter Instruction Manual A ABORt If operation has been started by the INITiate command ABORt will cancel all operations and immediately return to the instrument to the idle state If operation has been started by READ or MEASure ABORt has no affect B INITiate 1 After sending this command to take the instrument out of idle the instrument will perform one or more measurements and then return to idle The FETCh command can then be used to read the last reading that was measured 2 If INITiate is sent while the instrument is operating within the trigger model it will not execute until the operation returns to the idle state 3 One alternative to using INITiate is to use the READ command When READ is sent the instrument is taken out of idle and all readings that are taken are returned See Section 13 for details on READ C ARM SOURce lt name gt With the TIMer control source selected use the ARM TIMer command to set the timer interval D ARM DlRection lt name gt The source bypass can only be used if the TLINk control source is selected E ARM ILINe lt NRf gt and ARM OLINe lt NRf gt Input trigger and output trigger cannot share the same trigger link line Defaults set line 1 as the input and line 2 as the output F TRIGger CLEar When this action command is sent any
82. 485 specialized equipment is required This equipment includes a calibrated optical source in addition to semiconductor equipment probe card or needle Model 6485 Picoammeter Instruction Manual Applications Guide l 23 mounts etc as well as a triggerable voltage source the Model 2400 is used in our exam ple Several Model 6485 s can be connected to probe pads to provide leakage current readings forced by the bias voltage source As an alternative one or more 6485s could be switched through a switching mainframe and matrix switch card arrangement to take cur rent measurements from multiple pads Measuring photo diode leakage can be described in two steps 1 V I sweep Imeas IN total darkness 2 Vbias Imeas 1n calibrated optical flux In the Ist step voltage sweeps and the resulting current leakage is measured Then a bias voltage is applied and resulting current leakage is measured while light is incrementally increased in calibrated steps The results produce a graph similar to Figure I 20 Figure l 20 General photo diode leakage General photo diode P I N Positive Intrinsic Negative diodes respond as shown in Figure I 21 l 24 Applications Guide Model 6485 Picoammeter Instruction Manual Figure l 21 PIN photo diode leakage P I N photo diode In total darkness Avalanche diodes respond as shown by the solid line in Figure 1 22 Notice the small irregularity of the curve while sweeping around 10 12V This irregul
83. 5 for the limit tests as explained in Limit test configuration page 8 5 Step 4 Start testing process To enable the limit tests press the LIMIT key the testing process will start when LIMIT is pressed Step 5 Stop testing process The testing process can be terminated at any time by again pressing the LIMIT key Model 6485 Picoammeter Instruction Manual Limit Tests 8 7 SCPI programming Table 8 2 SCPI commands limit tests Command CALCulate2 FEED lt name gt LIMit 1 UPPer DATA lt n gt LOWer DATA lt n gt STATEe lt b gt FAIL LIM1t2 UPPer DATA lt n gt LOWer DATA lt n gt STATe lt b gt FAIL NULL OFFSet lt NRf gt STATe lt b gt DATA LATest ARM SOURce lt name gt INITiate CALCulate2 Subsystem Select input path for limit testing CALCulate 1 or SENSe 1 Limit 1 Testing Configure upper limit Set limit 9 99999e20 to 9 99999e20 Configure lower limit Set limit 9 99999e20 to 9 99999e20 Enable or disable Limit 1 test Return result of Limit 1 test 0 pass or 1 fail Limit 2 Testing Configure upper limit Set limit 9 99999e20 to 9 99999e20 Configure lower limit Set limit 9 99999e20 to 9 99999e20 Enable or disable Limit 2 test Return result of Limit 2 test 0 pass or 1 fail B Configure and control Rel Section 5 Specify Rel value 9 999999e20 to 9 999999e20 Enable or disable Rel Return CALC2 reading s triggered
84. 80 509 1322 ITALY Viale San Gimignano 38 20146 Milano 02 48 39 16 01 Fax 02 48 30 22 74 KOREA FL URI Building 2 14 Yangjae Dong Seocho Gu Seoul 137 130 82 2 574 7778 Fax 82 2 574 7838 NETHERLANDS Postbus 559 e 4200 AN Gorinchem 0183 635333 e Fax 0183 630821 SWEDEN c o Regus Business Centre Frosundaviks All 15 4tr 169 70 Solna 08 509 04 679 e Fax 08 655 26 10 SWITZERLAND Kriesbachstrasse 4 8600 D bendorf 01 821 94 44 Fax 01 820 30 81 TAIWAN 1FL 85 Po Ai Street Hsinchu Taiwan R O C 886 3 572 9077 Fax 886 3 572 9031 Copyright 2001 Keithley Instruments Inc Printed in the U S A 11 01 Model 6485 Picoammeter Instruction Manual 2001 Keithley Instruments Inc All rights reserved Cleveland Ohio U S A First Printing November 2001 Document Number 6485 901 01 Rev A 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 sub sequent updates Addenda which are released between Revisions contain important change in formation 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 a revised copy of this print hi
85. 99e20 to 9 99999e20 MBFactor lt n gt Specify offset B for mX b and m X b 9 99999e20 to 9 99999e20 MUNits lt name gt Specify units for mX b or m x b result 1 character A Z Q Y STATe lt b gt Enable or disable the selected calculation DATA Returns all CALCI results triggered by the INITiate DATA LATest Returns only the latest CALCI reading A DATA and DATA LATest The INITiate command must be sent to trigger the measurements and calculations The number of calculations depend on how many measurements the instrument is programmed to perform If the instrument is programmed to perform a finite number of measurements the DATA command will return all the CALCI readings after the last reading is taken The DATA LATest command will only return the last latest CALCI reading If the instrument is programmed to perform an infinite number of measurements arm count or trigger count set to infinite you cannot use the DATA command to return CALCI readings However you can use the DATA LATest command to return the last CALCI reading after aborting the measurement process After sending the INITiate com mand to start the measurement process use the ABORt command to abort the measure ment process then use DATA LATest to return the last CALCI reading 5 8 Relative mX b m X b reciprocal and log Model 6485 Picoammeter Instruction Manual Programming example mX b This command sequence p
86. ENABle lt NRf gt Idle Arm Trig OPC Operation Event B15 B11 B10 B9 B7 B6 B5 B4 B1 BO Enable Register ENABle Decimal Weights Idle In Idle amp Logical AND Trig Waiting for trigger event OR Logical OR Arm Waiting for arm event Cal Calibrating Model 6485 Picoammeter Instruction Manual Status Structure 10 13 Measurement event status The used bits of the measurement event register Figure 10 6 are described as follows Bit B1 low limit 1 fail LL1F Set bit indicates that the low limit 1 test has failed Bit B2 high limit 1 fail HL1F Set bit indicates that the high limit 1 test has failed Bit B3 low limit 2 fail LL2F Set bit indicates that the low limit 2 test has failed Bit B4 high limit 2 fail HL2F Set bit indicates that the high limit 2 test has failed Bit BS limits pass LP Set bit indicates that all limit tests passed Bit B6 reading available RAV Set bit indicates that a reading was taken and processed Bit B7 reading overflow ROF Set bit indicates that the reading exceeds the selected measurement range of Model 6485 Bit B8 buffer available BAV Set bit indicates that there are at least two read ings in the buffer Bit B9 buffer full BFL Set bit indicates that the buffer is full Bit B10 input overvoltage IOV Set bit indicates there is an input over voltage con dition 10 14 Status Structure Mo
87. Format D 3 Data lines F 5 Data Store Buffer D 6 DC current calibrator 15 8 DCL device clear 9 8 DDC language 9 2 Default settings 1 15 detected line frequency 1 14 Digital Calibration D 8 filter 4 8 D 6 filter control 4 11 digital board revision levels 11 3 DIGITS 1 8 Digits 4 3 DISP 1 7 DISP test 17 4 Display 1 12 display board revision levels 11 3 DISPlay command summary 14 4 display on or off 13 2 DISPlay subsystem 13 2 DISPlay FORMat and SYSTem 13 1 Displaying Rel 5 3 Electrochemical effects C 4 Electromagnetic Interference EMI C 5 Electrometer Calibration 15 4 Electrostatic interference C 4 I 7 Enable registers 10 4 10 5 engineering 4 3 units 1 12 ENTER 1 8 Entering calibration dates 16 11 Environmental conditions 15 2 EOI and Bus Hold off D 3 Equipment 16 3 ERR 1 8 Error and status messages 9 9 B 2 queue 10 18 Errors 16 4 Event detectors 7 5 Event enable registers 10 17 Event registers 10 16 Example reading limits calculation 15 5 Execute D 8 EXIT 1 8 External trigger example 7 13 External triggering 7 11 FAST 1 8 Features 1 6 FILT 1 8 Filters 4 7 firmware revision level 1 14 11 3 Floating measurements 2 12 Flow control RS 232 signal handshaking 9 17 Focused ion beam applications I 25 Focused Ion Beam signal connections I 26 FORMat command summary 14 5 FORMat subsystem 13 3 Front and rear panel 1 6 Front panel 1 7 Front panel GPIB operation 9 9 Front panel tests 17 3 Fu
88. I Conformance Information Model 6485 Picoammeter Instruction Manual Selecting the 488 1 protocol Perform the following steps to select the 488 1 protocol NOTE The 6485 must be set up to be remotely controlled over the GPIB to select the 488 1 protocol SCPI language is the only language available over the RS 232 bus To setup to use GPIB from the local measurement mode Press the COMM button Using the A or W range keys select GPIB Press Enter to complete the change 1 Press CONFIG CONFIGURE will be displayed 2 Press COMM to access the communications menu If a BAUD 1s displayed flash ing the 6485 is configured to use the RS 232 bus See Note above and change to control over the GPIB 3 Scroll using A range key until LANG is displayed Press the b cursor key to place the cursor on the currently selected language either DDC SCPI or 488 1 will be flashing 5 Scroll using A range key until 488 1 is displayed To change back to 488 2 scroll to the SCPI menu item 6 Press ENTER to save the change When switching between the SCPI protocol DDC protocol and 488 1 protocol the instrument resets The GPIB protocol setting is saved in EEPROM and the unit will power up with that selected protocol The GPIB protocol cannot be changed over the bus However there is a query command to determine the presently selected protocol When the 488 1 protocol is selected the mes sage exchange protocol MEP disables Therefor
89. ITY OR FITNESS FOR A PARTICULAR USE THE REMEDIES PROVIDED 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 INSTRUMENTS AND SOFTWARE EVEN IF KEITHLEY INSTRUMENTS INC HAS BEEN ADVISED IN ADVANCE OF THE POSSIBILITY OF SUCH DAMAGES SUCH EXCLUDED DAM AGES SHALL INCLUDE BUT ARE NOT LIMITED 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 Ohio 44139 e 440 248 0400 e Fax 440 248 6168 1 888 KEITHLEY 534 8453 e www keithley com Sales Offices BELGIUM Bergensesteenweg 709 e B 1600 Sint Pieters Leeuw 02 363 00 40 Fax 02 363 00 64 CHINA Yuan Chen Xin Building Room 705 12 Yumin Road Dewai Madian Beijing 100029 e 8610 6202 2886 e Fax 8610 6202 2892 FINLAND Tietajantie 2 e 02130 Espoo Phone 09 54 75 08 10 Fax 09 25 10 51 00 FRANCE 3 all e des Garays 91127 Palaiseau C dex 01 64 53 20 20 Fax 01 60 11 77 26 GERMANY Landsberger Strasse 65 82110 Germering 089 84 93 07 40 Fax 089 84 93 07 34 GREAT BRITAIN Unit 2 Commerce Park Brunel Road Theale Berkshire RG7 4AB 0118 929 7500 Fax 0118 929 7519 INDIA Flat 2B Willocrissa 14 Rest House Crescent Bangalore 560 001 91 80 509 1320 21 Fax 91
90. KEITHLEY Model 6485 Picoammeter Instruction Manual A GR ENES MEASUR Bee ONFIDENCE 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 warrants 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 INCLUD ING ANY IMPLIED WARRANTY OF MERCHANTABIL
91. LIMit see Voltages greater than 220V page 2 6 or Autorange lim its page 4 3 can be set so that the internal limiting resistor Rp cannot be reduced to the lower values Choose the appropriate range to accommodate the maximum current expected during normal measurements Down range by starting at highest current necessary Make use of down ranging by starting at the highest current necessary and reducing down to zero the range change transients can be reduced significantly compared to up ranging transients I 16 Applications Guide Model 6485 Picoammeter Instruction Manual Using protection circuitry Using the protection circuitry described in Figure I 13 or on Voltages greater than 220V page 2 6 can greatly reduce currents and voltages presented to devices being tested as well as serving to protect the 6485 from any externally generated transients The method from Figure I 13 is preferred when measuring nonlinear devices such as transistors diodes or photodiodes as long as the accuracy required during normal measurements is not tighter than 10pA If using the scheme from Voltages greater than 220V page 2 6 size the external current limiting resistor such that the sum of the external resistor and the lowest Rx will limit a 10V transient to a current level acceptable to the DUT Reduce up ranging transient If the application requires that up ranging be used and when the transient through the internal limiting resistor R
92. Limit 1 Fail M a E High Limit 1 Fail HL1F HL1F Oo _ Low Limit 2 Fail LL2F O High Limit 2 Fail Ter tor OH nr Logical OR Di ci EE Limis Pas e t 1p oH e e Reading Available Ra a oa H Logical Reading Overflow O ROLO LRD OR Buffer Available Pn PER O pes wuer ae EE PET e Input Overvoltage lov pt Pr eit ee da meda E nem E Always Zero E CONDition EVENt ENABle lt NRf gt ENABle Status Structure L ogical OR Error Queue Service Status Request Byte Enable Register Register MSB MSB TRES y i H g MSB Measurement Summary Bit EAV Error Available QSB Questionable Summary Bit MAV Message Available ESB Event Summary Bit RQS MSS Request for Service Master Summary Staus OSB Operation Summary Bit Note RQS bit is in serial poll byte MSS bit is in STB response Operation Event Registers Condition Event Event Enable Register Register Register Caibratins 1 J AT HH T 3 RE E a E a O o nanne ES Trigger Layer Tig 1 Trig Trig a Arm Layer campa ar Logical Z ANI Hr H oe Le idle TE TT HoH mi nalema E viel T4 Ta O_ 14 re CONDition EVENt ENABle lt NRf gt ENABle 10 3 10 4 Status Structure Model 6485 Picoammeter Instruction Manual Clearing registers and queues When Model 6485 is turned on the bits of all registers in the status structure are clear reset to 0 and the two queues are empty Commands to reset
93. NC shielding cap Keithley CAP 18 BNC to double banana plug adapter Pomona 1269 l 90 day 23 5 C full range accuracy specifications shown Uncertainty for 204A output current does not meet the recommended four times better uncertainty specification 2 23 3 C accuracy of characterization Model 6485 Instruction Manual Performance Verification 15 5 Verification limits The verification limits stated in this section have been calculated using only Model 6485 one year accuracy specifications and they do not include test equipment uncertainty If a particular measurement falls outside the allowable range recalculate new limits based on both Model 6485 specifications and corresponding test equipment specifications Example reading limits calculation As an example of how verification limits are calculated assume you are testing the 20mA range using a 20mA input value Using the Model 6485 20mA range accuracy specifica tion of 0 1 of reading IUA the calculated reading limits are Reading limits 20mA 20mA x 0 1 1uA 20mA 0 02mA 0 001mA 20mA 0 021mA 19 979mA to 20 021mA Calibrator voltage calculations When verifying the 2nA 2uA current ranges you must calculate the actual calibrator volt ages from the desired current values and the characterized Model 5156 Calibration Stan dard resistor values Calibrator voltages required for verification currents are calculated as follows V IR Where V re
94. NRf gt Select input trigger line 1 2 3 4 5 or 6 1 ILINe Query input trigger line OLINe lt NRf gt Select output trigger line 1 2 3 4 5 or 6 ps OLINe Query output trigger line OUTPut lt name gt Output trigger TRIGger or not at all NONE NONE OUTPut Query output trigger status TRIGger Trigger layer y CLEar Clear pending input trigger immediately SEQuence 1 Trigger path SOURce lt name gt Select control source IMMediate or TLINk IMMediate y SOURce Query trigger control source V COUNt lt n gt Set measure count to 2500 or INF infinite 1 V COUNt Query measure count y DELay lt n gt Set trigger delay 0 to 999 9999 sec 0 0 y AUTO lt b gt Enable or disable auto delay OFF y AUTO Query state of auto delay V DELay Query delay value y TCONfigure y Model 6485 Picoammeter Instruction Manual SCPI Reference Tables 14 11 Table 14 8 continued TRIGger command summary Default Ref Command Description parameter Section SCPI DIRection lt name gt Enable SOURce or disable ACCeptor ACCeptor bypass DIRection Query trigger source bypass ASYNchronous Configure input output triggers ILINe lt NRf gt Select input trigger line 1 2 3 4 5 or 6 ILINe Query input trigger line OLINe lt NRf gt Select output trigger line 1 2 3 4 5 or 6 OLINe Query output trigger line OUTPut lt name gt Output trigger after measurement SENSe or not a
95. Operation complete command _ Set the operation complete bit in the standard B event register after all pending commands have been executed Operation complete query Places an ASCII 1 into the output queue when all pending selected device operations have been completed OPT Option query Returns model number of any installed options RCL lt NRf gt Recall command Returns Model 6485 to the user saved setup RST Reset command Returns Model 6485 to the RST default conditions SAV lt NRf gt Save command Saves the present setup as the user saved setup SRE lt NRf gt Service request enable command Programs the service request enable register Section 10 SRE Service request enable query Reads the service request enable register Section 10 STB Status byte query Reads the status byte register Section 10 TRG Trigger command Sends a bus trigger to Model 6485 TST Self test query Performs a checksum test on ROM and returns the result WAI Wait to continue command Wait until all previous commands are executed Model 6485 Picoammeter Instruction Manual Common Commands 11 3 A IDN identification query Reads identification code The identification code includes the manufacturer model number serial number and firm ware revision levels and is sent in the following format KEITHLEY INSTRUMENTS INC MODEL 6485 xxxxxxx yyyyy zzzzz w Where xxxxxxx is the serial number yyyyy zzzzz is the firmware revision levels of th
96. Program currently running Illegal program name Cannot create program Expression error Hardware missing Data corrupt or stale Out of memory Illegal parameter value Too much data Parameter data out of range Settings conflict Parameter error Arm deadlock Trigger deadlock Init ignored Arm ignored Trigger ignored Trigger error Settings lost due to rtl Invalid while in local Execution error Expression data not allowed Invalid expression Expression error Block data not allowed Invalid block data Block data error Model 6485 Picoammeter Instruction Manual Model 6485 Picoammeter Instruction Manual Status and Error Messages B 3 Table B 1 continued Status and error messages String data not allowed String too long Invalid string data String data error Character data not allowed Character data too long Invalid character data Character data error Numeric data not allowed Too many digits Exponent too large Invalid character in number Numeric data error Header suffix out of range Undefined header Program mnemonic too long Header separator error Command header error Missing parameter Parameter not allowed GET not allowed Data type error Invalid separator Syntax error Invalid character Command error No error Measurement events Low limit 1 failed High limit 1 failed Low limit 2 failed High limit 2 failed Active limit tests passed Reading available B 4 Status and Error Messages Mode
97. Q on MAV for queries that take a long time to execute General operation notes e The TALK LSTN and SRQ annunciators are not functional in the 488 1 protocol This speeds up data throughput greatly The REM annunciator still operates since it is critical to fundamental GPIB operation e If the unit is in REMote the GTL command may not put the 6485 into the local mode Only the front panel LOCAL key is guaranteed to operate if not in local lockout LLO GTL will still disable LLO e IEEE 488 bus commands and features GET IFC SDC DCL LLO Serial Poll and SRQ are still fully supported e Multiple TALKs on the same query are supported as in the SCPI protocol This fea ture is useful when reading back long ASCII strings SRQ when buffer fills with 200 readings The following QuickBasic program Figure G 2 will store 200 readings in the buffer When the buffer fills to the set amount 200 readings an SRQ will occur and a message will be displayed on the computer to indicate the event G 8 Figure G 2 Program example INLCUDE ieeeqb bi CLS CONST addr 14 IEEE 488 and SCPI Conformance Information Init GPIB CALL initialize 21 0 CALL transmit unt unl listen STRS addr sdc unl status CALL send addr rst status3 CALL send addr trac cle status Clear buffer CALL send addr trig coun 200 status CALL send addr trac poin 200 status3 CALL send addr trac feed cont next status
98. QSB Set summary bit indicates that an enabled questionable event has occurred Bit B4 message available MAV Set summary bit indicates that a response message is present in the output queue Bit B5 event summary bit ESB Set summary bit indicates that an enabled standard event has occurred Bit B6 request service RQS master summary status MSS Set bit indicates that an enabled summary bit of the status byte register is set e Bit B7 operation summary OSB Set summary bit indicates that an enabled oper ation event has occurred Depending on how it is used bit B6 of the status byte register is either the request for ser vice RQS bit or the master summary status MSS bit e When using the serial poll sequence of Model 6485 to obtain the status byte a k a serial poll byte B6 is the RQS bit See Serial polling and SRQ page 10 9 for details on using the serial poll sequence e When using the STB command Table 10 3 to read the status byte B6 is the MSS bit Service request enable register The generation of a service request is controlled by the service request enable register This register is programmed by you and is used to enable or disable the setting of bit B6 RQS MSS by the status summary message bits BO B2 B3 B4 B5 and B7 of the sta tus byte register As shown in Figure 10 3 the summary bits are logically ANDed amp with the corresponding enable bits of the service req
99. RO 1 8 Baseline Suppression Rel D 8 Basic connection scheme I 25 connections to DUT 2 6 Baud rate 9 17 Buffer 1 8 6 1 Size D 3 Bus description F 2 management lines F 5 Cables 1 4 CAL VOFFSET 15 7 CALCulate command summary 14 2 Calibration 16 1 16 3 16 4 16 5 16 6 Displaying count 16 13 Displaying dates 16 13 Resetting code 16 12 SCPI commands 16 2 Calibration commands H 2 Calibration considerations 16 3 Calibration cycle 16 3 Calibration errors 16 4 Calibration menu 16 5 Calibrator 16 4 Calibrator voltage calculations 15 5 CAP 18 1 5 Capacitor leakage current I 19 Carrying case 1 5 Case sensitivity 9 12 Changing the calibration code 16 12 cleaning test fixtures 2 10 tips 2 11 Clearing registers and queues 10 4 COMM 1 7 Command codes F 9 F 11 execution rules 9 15 path rules 19 4 words 9 10 COMMON 1 9 Common Commands 11 2 F 11 Condition registers 10 15 CONFIG LOCAL key 1 7 9 10 Connections 2 6 fundamentals 2 3 Connections for 20uA to 20mA range calibration 16 9 Connections for 20uA to 20mA range verification 15 8 Connections for 2nA to 2UuA range calibration 16 11 Connections for 2nA to 2UA range verification 15 10 Connectors 1 4 2 10 Contact information 1 3 control sources 7 5 Counters 7 7 coupling electrostatic I 7 I 8 CS 565 barrel adapter 1 5 Current calculations 16 6 Current calibration 16 7 Current measurement accuracy 15 7 currently detected frequency 1 13 Data and stop bits 9 17
100. SPD polling sequence D 12 Special keys and power switch 1 7 Speed vs noise characteristics 4 5 SRQ 1 8 D 3 G 7 Standard event status 10 10 STAT 1 8 statistics 6 4 Status and Error Messages B 1 Status byte and mask interpretation D 13 and service request SRQ 10 7 format D 12 Status byte format D 14 Status byte register 10 8 STATus command summary 14 6 Status register sets 10 10 Status Structure 10 1 Status Word D 8 STD DEV 6 4 STORE 1 8 Store 6 2 Store Calibration D 3 Support 16 12 SYSTem command summary 14 8 TALK 1 8 terminals 2 10 Terminator 9 17 D 8 Test fixture 2 9 Test limit display messages 8 3 tests front panel 17 3 TIMER 1 8 timestamps 6 4 TRACe command summary 14 9 Triboelectric effects C 3 TRIG 1 7 1 8 TRIGger command summary 10 10 Trigger delay 7 6 TRIGGER LINK 1 9 Trigger Mode D 7 Trigger model configuration 7 7 menu structure 7 7 Typical addressed command sequence F 12 Typical bus sequence F 12 Typical command sequences F 12 UO Status word D 10 U1 Status word D 11 U2 Status word D 12 Unaddress commands F 10 undetected errors I 7 Uniline commands F 9 Units 4 3 Universal multiline commands F 9 Unpacking and Inspection 1 3 user setup 1 15 Using common commands and SCPI commands in the same message 9 14 Verification limits 15 5 Verification test procedures 15 6 Verification test requirements 15 2 VOFFSET 16 5 Voltage burden I 3 voltage transients I 13 Warm
101. Sable CLEar Parameters lt NDN gt Bxx x Hx Qx lt NRf gt Oto 65535 lt list gt 100 200 224 Notes MN BW WN Description Read the enable register Read the condition register Operation event registers Read the event register Program the enable register Read the enable register Read the condition register Questionable event registers Read the event register Program the enable register Read the enable register Read the condition register Return status registers to default states Read error queue Read and clear oldest error status code and message Specify error and status messages for error queue Read the enabled messages Specify messages not to be placed in queue Read the disabled messages Clear messages from error queue Binary format each x 1 or 0 Hexadecimal format x 0 to FFFF Octal format x 0 to 177777 Decimal format SCPI Reference Tables Default Ref parameter Section Note 2 Note 3 Note 2 Note 3 Note 4 Note 5 Note 5 Example of a range and single entry 100 through 200 and 224 STATus PRESet are explained by the following notes Event registers Power up and CLS clears all bits STATus PRESet has no effect Enable registers Power up and STATus PRESet clears all bits CLS has no effect Error queue Power up and CLS empties the error queue STATus PRESet has no effect Error queue mess
102. T and press ENTER to access the test menu Scroll through the menu choices with the RANGE keys and press ENTER Table 17 2 Front panel tests Test display KEY Test front panel keys 17 4 Routine Maintenance Model 6485 Instruction Manual DISP test The display test allows you to verify that each segment and annunciator in the vacuum fluorescent display is working properly Perform the following steps to run the display test 1 KEY test Press MENU select TEST and press ENTER to access the self test options Use the up or down RANGE key to display TEST DISP Press ENTER to start the test There are four parts to the display test Each time ENTER is pressed the next part of the test sequence is selected The four parts of the test sequence are as follows e All annunciators are displayed e The segments of each digit are sequentially displayed e The 12 digits and annunciators are sequentially displayed e The annunciators located at either end of the display are sequentially dis played When finished abort the display test by pressing EXIT The instrument returns to normal operation The KEY test allows you to check the functionality of each front panel key Perform the following steps to run the KEY test 1 Press MENU select TEST and press ENTER to access the self test options Use the up or down RANGE key to display TEST KEY Press ENTER to start the test When a key is pressed the label name for tha
103. Table H 1 Calibration commands CALibration Calibration subsystem PROTected Commands protected by code password CODE lt code gt CODE LOCK LOCK SENSe lt NRf gt DATA SAVE DATE lt yyyy mm dd gt DATE NDUE lt yyyy mm dd gt NDUE COUNt UNPRotected VOFFset Eight character code password used to enable or unlock calibration Default KI006485 Calibration code query Lock out further calibration Return 1 if calibration is locked 0 otherwise Calibrate active current range Query measurement cal constants Save all calibration data to non volatile memory Year Month Day when cal was last performed Query last cal date Year Month Day when 6485 is due for re cal Query cal due date Returns how many times 6485 has been calibrated Commands not protected by code password Voltage offset correction Model 6485 Picoammeter Instruction Manual Remote Calibration H 3 Remote calibration overview The steps below outline the general procedure for calibrating the Model 6485 using remote commands Refer to Section 16 for details on calibration steps calibration points and test equipment connections 1 Sendthe following command to unlock calibration CAL PROT CODE KI006485 Note that the above command uses the factory default code 2 Perform voltage offset correction by sending the following command CAL UNPR VOFF Be sure a BNC shielding cap is connected to
104. The following applications require an external voltage source NOTE External triggering and delay are covered in Section 7 With the proper use of external triggering between Models 6485 and voltage source the tests can be automated All of the applications require a bias time or delay which can be provided by the delay feature of Model 6485 When Model 6485 is triggered a measure ment will not be performed until the delay period expires Diode leakage current Figure I 14 shows how to measure the leakage current for a diode By sourcing a positive voltage the leakage current through the diode will be measured Note that if you source a negative voltage you will forward bias the diode Resistor R is used to limit current in the event that the diode shorts out or it becomes forward biased Select a value of R that will limit current to 20mA or less A profile for leakage current can be developed by measuring current at various voltage levels For example program the voltage source to source from 1 to 10V in 1V steps With the proper use of external triggering the Model 6485 performs a current measurement on each voltage step To ensure that the voltage is settled before each current measurement you can program Model 6485 for a delay For example if you program Model 6485 for a one second delay each measurement will be performed after the voltage step is allowed to settle for one second The current measurements can be stored in the buffer
105. Timestamps Recall Perform the following steps to view stored readings and buffer statistics 1 Press RECALL The message RDG NO 1 is displayed Note that the arrow annun ciator lt gt also turns on to indicate that additional data is available for viewing 2 Use the RANGE keys A and Y and the cursor keys and to navigate through the reading numbers and buffer statistics reading values and timestamps shown in Figure 6 1 For information on how to set buffer timestamps see Buffer times tamps page 6 4 3 Press EXIT to return to the normal display 6 4 Buffer Model 6485 Picoammeter Instruction Manual Buffer timestamps Use the TSTAMP menu item to change the timestamp format To access the menu 1 Press MENU 2 Scroll to the TSTAMP menu item using RANGE keys A and V 3 Press ENTER 4 Using RANGE keys A and Y select desired setting Available options are ABS absolute or DELT delta 5 ABS each timestamp is referenced to the first reading stored in the buffer The first reading always has a timestamp of 0000000 0000 6 DELT each timestamp provides the time between the readings Buffer statistics e MIN and MAX provides the minimum and maximum readings stored in the buffer It also indicates the buffer location of these readings e The PK PK peak to peak value is the difference between the maximum and minimum readings stored in the buffer PK PK MAX MIN e Average is the mean of the buf
106. Triggering Model 6485 Picoammeter Instruction Manual Table 7 2 continued Trigger model menu structure DELAY Set Trigger delay MAN Specify trigger delay 0 999 9998sec AUTO Enable auto delay TRIG OUT Configure output triggers LINE Select the output trigger link line TLINK Set trigger link value 1 6 EVENTS Select VMC voltmeter complete output trigger VMC Enable disable VMC on or off TRIG IN Path to control source SOURCE Set the TRIG IN control source IMM Set control source to IMMediate TLINK Set control source to TLINK Set TLINK value 1 6 Enable set to ONCE or disable set to NEVER Path to ARM layer submenus Path to ARM IN control source Set control source to IMMediate Set control source to TLINK Set TLINK value 1 6 Enable set to ONCE or disable set to NEVER Set control source to MANual Set control source to TIMER Set timer from 0 001S to 27H 46M and 39 992S Set control source to GPIB GPIB ARM OUT Path to ARM OUT trigger LINE Set the output trigger link line TLINK Set trigger link value 1 6 EVENT Set Trigger Layer Done event T L DONE Enable disable Trigger Layer Done on off COUNT Set ARM measure count INF Specify an INFinite measure count FIN Specify a FINite measure count 1 2500 NOTE Input trigger and output triggers cannot share the same trigger link line Defaults set line I as the input and line 2 as the output
107. URce TLINk ARM SEQuence 1 SOURce COUNt 1 TRIGger SEQuence 1 COUNt INF INITiate IMMediate One shot triggered by External Trigger ARM SEQuence 1 SOURce TLINk ARM SEQuence 1 SOURce COUNt INF TRIGger SEQuence 1 COUNt 1 INITiate IMMediate DDC Emulation Commands D 7 Note Default NEW NEW SCPI not available gt lt Only in 488 1 mode SCPI Not Available SCPI Not Available NDS NEW NDS NEW D 8 DDC Emulation Commands Model 6485 Picoammeter Instruction Manual Table D 1 continued Device dependent command summary Description Moue Commeane Equivalent Son commands pole UO Return status word See Figure D 1 Each parameter must be queried individually For example Status SENSe 1 CURRent RANGe o wore Ul Send data conditions See Figure D 2 NEW Ea U2 Buffer size and readings stored See Figure D 3 D NEW e Digital V Calibration commands V n nnnnE nn not supported G a Calibration X Execute other device dependent commands SCPI not i Execute applicable SCPI commands execute as they are received Y ASCII Not Available CNDS YO LFCR line feed carriage return C NDS a Terminator Y1 i carriage return line feed C NDS Y2 LF line feed CNDS Y3 CR carriage return C NDS a Y4 None C NDS a Baseline ZO Suppression Rel disabled So Suppres AA NULL STATe OFF sioni ZI Suppression Rel enabled Rel CALCulate2 NULL ACQuire i CALCulate2 NULL STATe ON
108. Use the RANGE A or V keys to display the desired rank 1 to 5 4 Press ENTER to set To return to the previously set value press EXIT instead of ENTER Digital filter Digital filter classifications Model 6485 has two classifications of the digital filter averaging and advanced Both are a simple average of one to 100 reading conversions The difference between them is the user programmable noise window for the advanced filter The noise window which is expressed as a percentage of range 0 105 allows a faster response time to large signal step changes A reading conversion outside the plus or minus noise window fills the filter stack immediately If the noise does not exceed the selected percentage of range the reading is based on an average of reading conversions In this case the advanced filter works the same as the averaging filter If the noise does exceed the selected percentage the reading is a single reading conversion and new averaging starts from this point The two filter classes are compared in Figure 4 2 Digital filter types An additional filter parameter is type type is either moving or repeating Filter types are compared in Figure 4 3 Moving Filter Every time a reading conversion occurs the readings in the stack are averaged to yield a single filtered reading The stack type is first in first out After the stack fills the newest reading conversion replaces the oldest Note that the instrumen
109. a alla 6 3 Triggering Trigger model front panel operation 7 2 Trigger model remote operation 7 3 Measure action block of trigger model 7 6 Trigger link connection operation c ssssesesseeeeeeeeeseeeees 7 11 Trigger link input pulse specifications 7 12 Trigger link output pulse specifications 7 12 DUT teSSYSONE erso en ena cna sengasusagasnesauneeuseteaisact 7 13 TAg sor link CONNCCUHIONS oe a N 7 14 Operation model for triggering example 7 15 8 Figure 8 1 Figure 8 2 Figure 8 3 9 Figure 9 1 Figure 9 2 Figure 9 3 Figure 9 4 10 Figure 10 1 Figure 10 2 Figure 10 3 Figure 10 4 Figure 10 5 Figure 10 6 Figure 10 7 13 Figure 13 1 Figure 13 2 Figure 13 3 15 Figure 15 1 Figure 15 2 16 Figure 16 1 Figure 16 2 17 Figure 17 1 C Figure C 1 Figure C 2 Limit Tests ET S EEE A AAN AT A EE 8 2 Limnitiestserample iii 8 2 Operation model for limit test 8 4 Remote Operation IEEE 488 connectof iena 9 5 Miulti unit connections iti 9 5 TEEE 488 connector location 9 6 RS lt 232 interface COMNECIOM ooruri 9 18 Status Structure 6485 status mode structure i 10 3 LO bIESIALIS TESS lea ies aah dy 10 6 Status byte and service request
110. ading after aborting the measurement process After sending the INITiate com mand to start the measurement process use the ABORt command to abort the measure ment process then use DATA LATest to return the last CALC2 reading Sending DATA or DATA LATest without first sending INITiate will return old read ings or cause an error 220 if limit is not enabled or there are no readings available D ARM SOURce lt name gt Typical start of test options e IMMediate Test starts when LIMIT key is pressed Programming example The following command sequence will test DUT using the limit tests example shown in Figure 8 2 RST Restore RST defaults CALC2 LIM UPP 2e 3 CALC2 LIM LOW 2e 3 CALC2 LIM STAT ON CALC2 LIM2 UPP le 3 CALC2 LIM2 LOW le 3 CALC2 LIM2 STAT ON Set upper limit for Limit 1 2mA Set lower limit for Limit 1 2mA Enable Limit 1 test Set upper limit for Limit 2 1mA Set lower limit for Limit 2 1mA Enable Limit 2 test Connect DUT to input SYST ZCH OFF Disable Z Check INIT Perform tests on DUT one measure ment CALC2 LIM FAIL Return result of Limit 1 test CALC2 LIM2 FAIL Return result of Limit 2 test 9 Remote Operation e Selecting and configuring an interface Explains how to select and configure an interface GPIB or RS 232 e GPIB operation and reference Covers the following GPIB topics GPIB Bus Standards GPIB Bus Connections Primary Address S
111. ages Power up enables error messages and disables status messages CLS and STATus PRESet have no effect Commands in this subsystem are not affected by RST or SYSTem PRESet The effects of cycling power CLS and 14 7 SCPI Roia ra a ee ee ee ee 14 8 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual Table 14 6 SYSTem command summary see Section 13 for detailed information Default Ref Command Description parameter Section SCPI 13 SYSTem ZCHeck STATe lt b gt STATe ZCORrect STATe lt b gt STATe ACQuire PRESet LFRequency lt freq gt LFRequency AUTO SYSTem LFRequency AUTO continued STATe lt b gt STATe AZERO STATe lt b gt STATe TIME RESet POSetup lt name gt POSetup VERSion ERRor NEXT ALL COUNt CODE NEXT ALL Zero check Enable or disable zero check Query state of zero check Zero correct Enable or disable zero correct Query state of zero correct Acquire a new zero correct value Return to SYSTem PRESet defaults Select power line frequency 50 or 60 Hz Query frequency setting Path to control auto frequency Enable or disable auto frequency Query state of auto frequency Path to control autozero Enable or disable autozero Query state of autozero Timestamp Reset timestamp to 0 seconds Select power on setup RST PRESet or SAVx where x 0 2 Query power
112. al filters off front panel off auto zero off 2 Binary transfer mode IEEE 488 1 BUFFER Stores up to 2500 readings PROGRAMS Provide front panel access to IEEE address choice of engineering units or scien tific notation and digital calibration EMC Conforms with European Union Directive 89 336 EEC EN61326 1 SAFETY Conforms with European Union Directive 73 23 EEC EN61010 1 TRIGGER LINE Available see manual for usage DIGITAL FILTER Median and averaging selectable from 2 to 100 readings ENVIRONMENT Operating 0 50 C relative humidity 70 non condensing up to 35 C Above 35 C derate humidity by 3 for each C Storage 25 to 65 C WARM UP 1 hour to rated accuracy see manual for recommended procedure POWER 100 120V or 220 240V 50 60Hz 30VA PHYSICAL Case Dimensions 90mm high x 214mm wide x 369mm deep 3 in x 8 in x 14 e in Working Dimensions From front of case to rear including power cord and IEEE 488 connec tor 394mm 15 5 inches Net Weight lt 2 8 kg lt 6 1 lbs Shipping Weight lt 5 kg lt 11 lbs b Status and Error Messages B 2 Status and Error Messages Status and error messages Description Query deadlocked Query unterminated Query interrupted Input buffer overrun Framing error in program message Parity error in program message Communications error Queue overflow Self test failed Save recall memory lost Configuration memory lost Program syntax error
113. alent to LLO Note Clearing the error queue power up and CLS clears the error queue RST SYSTem PRESet and STATus PRESet have no effect on the error queue Model 6485 Picoammeter Instruction Manual DISPlay FORMat and SYSTem 13 9 A SYSTem PRESet Returns the instrument to states optimized for front panel operation SYSTem PRESet defaults are listed in the SCPI tables in Section 15 B SYSTem TIME RESet Resets the absolute timestamp to 0 seconds The timestamp also resets when power is cycled or after the instrument is on for 99 999 99 seconds The TRACe TSTamp FOR Mat command is used to select the absolute timestamp See Section 6 Buffer for details C SYSTem POSetup lt name gt Parameters RST Power up to RST defaults PRESet Power up to SYSTem PRESet defaults SAVx Power up to setup stored in memory x memory location 0 1 or 2 The RST and SYSTem DEFaults are listed in the SCPI tables in the Section 15 A setup is saved in memory using the SAV command See Section 12 Common Commands for details D SYSTem VERSion Read the version of the SCPI standard being used by Model 6485 Example response mes sage 1996 0 E SYSTem KEY lt NRf gt 13 RANGE down arrow key 14 ENTER key 15 Cursor right arrow key 16 ZCOR key Parameters 1 CONFIG LOCAL key 17 MENU key 2 MEDN key 18 COMM key 3 AVG key 19 DISP key 4 MX B key 20 TRIG key 5 M X B key 21 HALT key 6 LOG key 22
114. and contact with hazardous live circuits Maintenance personnel perform routine procedures on the product to keep it operating properly for example setting the line voltage or replacing consumable materials Maintenance procedures are described in the manual The procedures explicitly state if the operator may perform 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 service personnel may perform installation and service procedures Keithley products are designed for use with electrical signals that are rated Installation Category I and Installation Category II as described in the International Electrotechnical Commission IEC Standard IEC 60664 Most measurement control and data I O signals are Installation Category I and must not be directly connected to mains voltage or to voltage sources with high tran sient over voltages Installation Category II connections require protection for high transient over voltages often associated with local AC mains connections Assume all measurement control and data I O connections are for connection to Category I sourc es unless otherwise marked or described in the Manual 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 ANSI states th
115. and recalled See Front panel setup operation page 1 15 mX b m X b reciprocal for resistance calculations and log10 These calculations provide mathematical manipulation of readings Section 5 Relative Null offsets or establish baseline values Section 5 Buffer Store up to 2500 readings in the internal buffer Section 6 Limits Set up to two stages of high and low reading limits to test devices Section 8 Remote interface Model 6485 can be controlled using the IEEE 488 interface GPIB or the RS 232 interface Section 9 GPIB programming language When using the GPIB the instrument can be pro grammed using the SCPI or DDC programming language Section 9 Front and rear panel familiarization Front panel summary The front panel of Model 6485 is shown in Figure 1 1 Model 6485 Picoammeter Instruction Manual Getting Started 1 7 Figure 1 1 Front panel KEITHLEY 5 axe 1 COMM DISP TRIG HALT DIGITS RATE Ca j gt SAVE SETUP STORE RECALL LIMIT AZERO EXIT ENTER REM STEP SCAN CHI CH2 CH3 CH4 CH5 CH6 CH7 CH8 CH9 CH10 MATH ism Mie Nie Nie Nhe Nie Nie Nhe Nie ie gt ie e SE UM VG VG Wis Wie UG Wis Us Ws i NG WR AT TIMER HOLD TRIG FAST MED SLOW REL FILT AUTO ERR BUFFER STAT 6485 PICOAMMETER NOTE To modify a key s properties press the CONFIG LOCAL key see Special keys and power switch and then the key Not all keys have configurable pro
116. anual DISPlay subsystem The commands in this subsystem are used to control the display over the bus Table 13 1 SCPI commands display DISPlay DIGits lt n gt Set display resolution 4 to 7 Section 4 DIGits Query display resolution ENABle lt b gt Turn front panel display on or off see Note ENABle lt b gt Query front panel display status WINDow 1 Path to control user text messages TEXT see Note DATA lt a gt Define ASCII message a up to 12 characters DATA Query defined ASCII message STATe lt b gt Enable or disable text message mode STATe Query text message status Note RST and SYSTem PRESet have no effect on the display circuitry and user defined text messages A DISPlay ENABle lt b gt With front panel circuitry turned off the instrument operates at a higher speed While dis abled the display is frozen and all front panel controls except LOCAL are disabled Nor mal display operations can be resumed by using ENABIle to enable the display pressing the LOCAL key or cycling power B DISPlay TEXT DATA lt a gt Message Types String aa a or aa a Indefinite Block 0aa a Definite Block X Yaa a where Y number of characters in message up to 12 X number of digits that make up Y 1 or 2 The display message can be up to 12 characters ASCII long A space is counted as a character Excess message characters result in an error Note tha
117. are Teflon polyethylene and sapphire Avoid materi als such as phenolics and nylon Refer to Keithley s Low Level Handbook for additional information on choosing the best insulator Humidity may also degrade low current measurements The amount of water an insulator absorbs will vary depending upon the insulator It is best to choose an insulator on which water vapor does not readily form a continuous film Sometimes this is unavoidable if the material being measured absorbs water easily so it is best to make the measurements in an environmentally controlled room In some cases an insulator may have ionic contami nants and especially in high humidity a spurious current may be generated Another way to reduce leakage currents is to use guarding A guard is a conductor con nected to a low impedance point in the circuit that is nearly at the same potential as the high impedance lead being guarded Guarding can isolate the high impedance input lead of the picoammeter from leakage current due to voltage sources Guarding may also be necessary to prevent leakage current due to text fixturing Figure I 1 shows a high megohm resistor supported on two insulators mounted in a metal test fixture This circuit is guarded by connecting the LO of the picoammeter A to the metal case This will put the top of the right insulator at almost the same potential as the bottom The Model 6485 Picoammeter Instruction Manual Applications Guide l 3 voltage di
118. arity is made larger under additional applied light see dashed lines of Figure I 22 Figure l 22 Avalanche photo diode leakage Avalanche photo diode mm 0 10 50 100 Connections are made to the Model 6485 through the BNC input connector located on the rear panel Figure I 23 In order to properly sequence voltage and measurement of leak age current the instruments triggering needs to be linked Trigger link connection to the Model 2400 is made to the Model 6485 through the Trigger Link connector located on the rear panel Model 6485 Picoammeter Instruction Manual Applications Guide l 25 Figure l 23 Basic connection scheme Calibrated Light Source TN Photo Diode Pads Probe Needles Probe Needles Model 2400 Bias Voltage _ Model 6485 SE Trigger Link Cable NOTE The details on page I 12 concerning range change transients may be particu larly relevant to this application Focused ion beam applications Focused Ion Beam FIB systems have been developed to perform nanometer scale imag ing micro machining and mapping in the semiconductor industry Typical applications include mask repair circuit modification defect analysis and sample preparation of site specific locations on integrated circuits FIB systems use a finely focused ion beam for imaging or for site specific sputtering or milling The magnitude of the beam current determines what type of operation is per form
119. ary data to any IBM PC 13 8 DISPlay FORMat and SYSTem Model 6485 Picoammeter Instruction Manual SYSTem subsystem Table 13 3 SCPI commands system SYSTem ZCHeck lt b gt Enable or disable zero check Section 2 ZCORrect Zero correct Section 2 STATe lt b gt Enable or disable zero correct ACQuire Acquire a new zero correct value PRESet Return to SYSTem PRESet defaults A LFRequency lt freq gt Select power line frequency 50 or 60 Hz Section 1 AUTO lt b gt Turn automatic frequency ON or OFF AZERO Path to control autozero Section 2 STATe lt b gt Enable or disable autozero TIME Timestamp RESet Reset timestamp to 0 seconds POSetup lt name gt Select power on setup RST PRESet or SAVx where x 0 to 4 VERSion Query SCPI revision level ERRor Read messages in error queue see Note Section 10 NEXT Return and clear oldest error code and message ALL Return and clear all errors code and message COUNt Return the number of errors CODE Error code numbers only NEXT Return and clear oldest error code only ALL Return and clear all errors codes only CLEar Clear messages from error queue Section 10 KEY lt NRf gt Simulate key press see Figure 13 3 E RS 232 interface Section 9 LOCal Take Model 6485 out of remote RS 232 only Equivalent to GTL REMote Put Model 6485 in remote RS 232 only Equivalent to REN RWLock Enable local lockout RS 232 only Equiv
120. as an event to control operation Model 6485 reacts to this trigger if BUS is the programmed arm control source The control source is programmed from the TRIGger subsystem NOTE Details on triggering are covered in Section 7 Model 6485 Picoammeter Instruction Manual Common Commands 11 5 Programming example The following command sequence configures Model 6485 to be controlled by bus triggers The last line which sends a bus trigger triggers one mea surement Each subsequent bus trigger will also trigger a single measurement RST Restore RST defaults ARM SOUR BUS Select BUS control source ARM COUN INF Set arm layer count to infinite INIT Take 6485 out of idle TRG Trigger one measurement F TST self test query Run self test and read result Use this query command to perform a checksum test on ROM The command places the coded result 0 or 1 in the output queue When Model 6485 is addressed to talk the coded result is sent from the output queue to the computer A returned value of zero 0 indicates that the test passed and a value of one 1 indicates that the test failed G WAI wait to continue Wait until previous commands are completed Effectively the WAI command is a No Op no operation for Model 6485 and thus does not need to be used Two types of device commands exist e Sequential commands A command whose operations are allowed to finish before the next command is executed e Overlap
121. as follows ImA 3mA 20mA From the above readings it is apparent that 3mA is the median middle most reading The number of sample readings used for the median calculation is determined by the selected rank 1 to 5 as follows Sample readings 2x R 1 where R is the selected rank 1 to 5 For example a rank of 5 will use the last 11 readings to determine the median 2 x 5 1 11 Each new reading replaces the oldest reading and the median is then determined from the updated sample of readings Median filter operation The median filter operates as a moving type filter For exam ple if the median filter is configured to sample 11 readings Rank 5 the first filtered read ing will be calculated and displayed after 11 readings are acquired and placed in its filter stack Each subsequent reading will then be added to the stack oldest reading discarded and another median filter reading will be calculated and displayed The median filter oper ation will reset start over whenever the Zero Check operation is performed or the range is changed 4 8 Range Units Digits Rate and Filters Model 6485 Picoammeter Instruction Manual Median filter control The MEDN key 1s a toggle key it will either enable the median filter displays MEDIAN ON or disable the median filter displays MEDIAN OFF To configure the median filter 1 Press the CONFIG key 2 Press the MEDN key The present rank will be displayed flashing 3
122. at a shock hazard exists when voltage levels greater than 30V RMS 42 4V peak or 60VDC are present A good safety practice is to expect that hazardous voltage is present in any unknown circuit before measuring Operators of this product must be protected from electric shock at all times The responsible body must ensure that operators are prevented access and or insulated from every connection point In some cases connections must be exposed to potential human contact Product operators 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 Do not connect switching cards directly to unlimited power circuits They are intended to be used with impedance limited sourc es NEVER connect switching cards directly to AC mains When connecting sources to switching cards install protective de vices to limit fault current and voltage to the card Before operating an instrument make sure the line cord is connected to a properly grounded power receptacle Inspect the con necting cables test leads and jumpers for possible wear cracks or breaks before each use When installing equipment where access to the main power cord is restricted such as rack mounting a separate main input pow er disconnect device must be provided in close proximity to the equipment and within easy reach of the operator For maxi
123. ble registers to 0 CLS has no effect 10 18 Status Structure Model 6485 Picoammeter Instruction Manual Queues Programming example program and read registers This command sequence programs and reads the measurement registers Registers are read using the binary format which directly indicates which bits are set The command to select format FORMat SREGister is documented in Table 10 2 FORM SREG BIN Select binary format to read registers STAT MEAS ENAB 512 Enable BFL buffer full STAT MEAS COND Read Measurement Condition Register STAT MEAS Read Measurement Event Register Model 6485 uses two queues which are first in first out FIFO registers e Output queue Used to hold reading and response messages e Error queue Used to hold error and status messages Model 6485 status model Figure 10 1 shows how the two queues are structured with the other registers Output queue The output queue holds data that pertains to the normal operation of the instrument For example when a query command is sent the response message is placed in the output queue When data is placed in the output queue the message available MAV bit in the status byte register sets A data message is cleared from the output queue when it is read The output queue is considered cleared when it is empty An empty output queue clears the MAV bit in the status byte register A message is read from the output queue by address
124. btained by ORing the primary address with 20 TAG Talk Address Group The talk commands are derived from the primary address by ORing the address with 40 Talk commands are used to address devices to talk SCG Secondary Command Group Commands in this group provide additional addressing capabilities Many devices including the Model 6485 do not use these com mands Unaddress commands The two unaddress commands are used by the controller to remove any talkers or listeners from the bus ATN is true when these commands are asserted UNL Unlisten Listeners are placed in the listener idle state by the UNL command UNT Untalk Any previously commanded talkers will be placed in the talker idle state by the UNT command Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 11 Common commands Common commands are commands that are common to all devices on the bus These com mands are designated and defined by the IEEE 488 2 standard Generally these commands are sent as one or more ASCII characters that tell the device to perform a common operation such as reset The IEEE 488 bus treats these commands as data in that ATN is false when the commands are transmitted SCPI commands SCPI commands are commands that are particular to each device on the bus These com mands are designated by the instrument manufacturer and are based on the instrument model defined by the Standard Commands for Programmable I
125. bus status Each of these indicators is described below e REM This indicator shows when the instrument is in the remote state REM does not necessarily indicate the state of the REM line as the instrument must be addressed to listen with REM true before the REM indicator turns on When the instrument is in remote all front panel keys except for the LOCAL key are locked out When REM is turned off the instrument is in the local state and front panel operation is restored e TALK This indicator is on when the instrument is in the talker active state Place the unit in the talk state by addressing it to talk with the correct MTA My Talk Address command TALK is off when the unit is in the talker idle state Place the unit in the talker idle state by sending a UNT Untalk command addressing it to listen or sending the IFC Interface Clear command e LSTN This indicator is on when Model 6485 is in the listener active state which is activated by addressing the instrument to listen with the correct MLA My Listen Address command LSTN is off when the unit is in the listener idle state Place the unit in the listener idle state by sending UNL Unlisten addressing it to talk or sending the IFC Interface Clear command over the bus 9 10 Remote Operation Model 6485 Picoammeter Instruction Manual e SRQ You can program the instrument to generate a service request SRQ when one or more errors or conditions occur When this indi
126. c ommended source resistance varies by measurement range because the R value also depends on the measurement range 1 6 Applications Guide Model 6485 Picoammeter Instruction Manual Table l 1 Minimum recommended source resistance values Range Minimum Recommended Source Resistance 2nA 20nA 1 MQ to 1 GQ 200nA 2uA 10 kQ to 10 MQ 20uA 200UA 100Q to 100 kQ 2mA 20mA 10Q to 1kQ Figure l 3 Simplified model of a feedback picoammeter Current 6485 Source Picoammeter Source capacitance DUT source capacitance will also affect the noise performance of the Model 6485 picoam meter In general as source capacitance increases the noise also increases To see how changes in source capacitance can affect noise gain again refer to the simplified picoam meter model in Figure I 3 The elements of interest for this discussion are the source capacitance Cs and the feedback capacitance Cp Taking into account the capacitive reac tance of these two elements the previous noise gain formula must be modified as follows Output Vworse Input Vworse Zp Zg Model 6485 Picoammeter Instruction Manual Applications Guide l 7 Here Zp represents the feedback impedance made up of Cx and Rp while Zs is the source impedance formed by Rg and Cg Furthermore R Zp n ll 2rfRpCp 1 and R S Z JEC2TfRCs 1 Note that as Cs increases in value Zs decreases in value thereby increasing the noise gain Again at the poin
127. cator is on a service request has been generated This indicator stays on until the serial poll byte is read or all the conditions that caused SRQ have ceased to exist LOCAL key The LOCAL key cancels the remote state and restores local operation of the instrument Pressing the LOCAL key also turns off the REM indicator and returns the display to nor mal if a user defined message was displayed If the unit is in local not in remote the local key acts as a configure key see Front panel summary page 1 6 If the LLO Local Lockout command is in effect the LOCAL key is also inoperative Programming syntax The following paragraphs cover syntax for both common commands and SCPI commands For more information see the IEEE 488 2 and SCPI standards Command words Program messages are made up of one or more command words Commands and command parameters Common commands and SCPI commands may or may not use a parameter The following are some examples SAV lt NRf gt Parameter NRf required RST No parameter used DISPlay ENABle lt b gt Parameter lt b gt required SYSTem PRESet No parameter used Put at least one space between the command word and the parameter e Brackets Some command words are enclosed in brackets These brackets are used to denote an optional command word that does not need to be included in the program message For example INITiate IMMediate These brackets indicate that
128. cause dam age to the instrument possibly voiding the warranty 2 Before plugging in the power cord make sure that the front panel power switch is in the off O position 3 Connect the female end of the supplied power cord to the AC receptacle on the rear panel Connect the other end of the power cord to a grounded AC outlet Model 6485 Picoammeter Instruction Manual Getting Started 1 13 WARNING The power cord supplied with the Model 6485 contains a separate ground wire for use with grounded outlets When proper connections are made instrument chassis is connected to power line ground through the ground wire in the power cord Failure to use a grounded outlet may result in personal injury or death due to electric shock 4 Turn on the instrument by pressing the front panel power switch to the on I posi tion Line frequency The Model 6485 operates at line frequencies of 50 or 60Hz When auto detect is enabled factory default line frequencies are automatically sensed and set accordingly therefore there are no switches to set Use the S YSTem LFRequency command query to read the line frequency The factory default setting is auto detect enabled If the power line is noisy auto detect may not be able to lock in on a frequency If this occurs set the frequency manually This may be accomplished using the front panel see the following procedure or over the bus Refer to Table 1 2 for commands Front panel procedure 1
129. ceccececceccccccecccecescascecs H 3 Applications Guide Measurement Considerations scsi I 2 Leakage currents and guarding I 2 Hipu has Cunen sorridi I 3 NOM ACS DULG CM prudenti I 3 Voltage offset correction procedure 1 4 Noise and source impedance in I 5 OUNCE TESISLANCE onanan ne Eee E EE I 5 Soue CAPACI siria I 6 Electrostatic interference and shielding 7 Shielding vs Guarding er I 10 Makina COMMECHONS ssis arreen ee ERSAN I 10 Typical range change transients I 12 Up ranseinput response ditte I 13 Down range voltage transients are smaller I 14 Steps to minimize impact of range change transients I 15 Run test with a fixed range in I 15 Down range by starting at highest CUITENEMNECOSSAT ssi risa I 15 Using protection Circuitry ii I 16 Reduce up ranging transient i I 16 Zero check on off response siii I 16 ADDII ilaele I 18 IDIOdE TAKA CS CULT CIE ni sessed sucasseanibondet lie I 18 Capacitor leakage Current usarla I 19 Measuring high resistance with external bias source I 19 Cable insulation resistance cceeesssscestecccceeeeceeeeeeeeeees I 21 Surface insulation resistance SIR eeeecceeeceeeee 1 22 Photodiode characterization prior to dicing 22 F
130. commands in one program message Stat oper stat oper enab lt NRf gt When the above is sent the first command word is recognized as the root command stat When the next colon is detected the path pointer moves down to the next command level and executes the command When the path pointer sees the colon after the semicolon it resets back to the root level and starts over Commands that are on the same command level can be executed without having to retype the entire command path Example Stat oper enab lt NRf gt enab After the first command enab is executed the path pointer is at the third command level in the structure Since enab is also on the third level it can be entered without repeating the entire path name Notice that the leading colon for enab is not included in the pro gram message If a colon were included the path pointer would reset to the root level and expect a root command Since enab is not a root command an error would occur Command path rules e Each new program message must begin with the root command unless it is optional e g SENSe If the root is optional simply treat a command word on the next level as the root e The colon at the beginning of a program message is optional and need not be used Stat pres stat pres e When the path pointer detects a colon it moves down to the next command level An exception is when the path pointer detects a semicolon whic
131. commended in the user documentation The A symbol on an instrument indicates that the user should refer to the operating instructions located in the manual The ZN symbol on an instrument shows that it can source or measure 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 information 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 war ranty 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 Instruments Standard fuses with applicable national safety ap provals 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 selected parts should be purchased only through Keithley Instruments to maintain accuracy and functionality of the product If you are unsure about the appl
132. ctually reduce the voltage at the input terminals see the Volt age Offset Correction procedure in Section 16 Perform the following steps to algebra ically zero correct the measurement NOTE The ZCOR key toggles zero correct on and off If zero correct is enabled ZZ or CZ message displayed press ZCOR to disable it Enable zero check ZC message displayed Select the range that will be used for the measurement or select the lowest range Press ZCOR to enable zero correct ZZ message displayed Press ZCHK to disable zero check Readings can now be taken from the display The CZ message indicates that the displayed reading 1s zero corrected ee ee hee NOTES With regard to the zero correct feature Model 6485 will remain zero corrected even if it is upranged If downranged re zero the instrument Model 6485 does not have to be re zero corrected as long as the ambient tem perature remains stable Zero correction cancels the voltage offset term of the amplifier With both zero check and zero correct enabled the instrument may not display a perfectly zeroed reading If Model 6485 is operating at or near Tc zero correction will have very little effect Tear is the internal temperature of Model 6485 when it was last cali brated Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 15 SCPI programming zero check and zero correct Table 2 4 SCPI commands zero check and zero
133. cumentation requirements Requirements Description or reference IEEE 488 Interface Function Codes See Appendix F Behavior of 6485 when the address is set outside Cannot enter an invalid address the range 0 30 Behavior of 6485 when valid address is entered Address changes and bus resets Power On Setup Conditions Determine by SYSTem POSetup Section 14 Message Exchange Options Input buffer size 2048 bytes Queries that return more than one response None message unit Queries that generate a response when parsed All queries Common Commands and SCPI Queries that generate a response when read None Coupled commands See Table G 2 Functional elements required for SCPI commands Contained in SCPI command sub systems tables see Table 14 1 through Table 14 8 Buffer size limitations for block data Block display messages 12 char acters max Syntax restrictions See Programming Syntax in Section 10 Response syntax for every query command See Programming Syntax in Section 10 Device to device message transfer that does not None follow rules of the standard Block data response size See Display Subsystem in Section 14 Common Commands implemented by 6485 See Common Commands in Section 12 Calibration query information Section 14 Trigger macro for DDT Not applicable Model 6485 Picoammeter Instruction Manual IEEE 488 and SCPI Conformance Information G 3 Table G 1 continued JEEE 488 documentation requ
134. cur Status messages are not enabled and will not go into the queue As listed in Table 10 7 there are commands to enable and or disable messages For these commands the lt list gt parameter is used to specify which messages to enable or disable The messages are speci fied by their codes The following examples show various forms for using the lt list gt parameter lt list gt 110 Single message 110 222 Range of messages 110 through 222 110 222 220 Range entry and single entry separated by a comma When you enable messages messages not specified in the list are disabled When you dis able messages each listed message is removed from the enabled list To prevent all messages from entering the error queue send the enable command along with the null list parameter as follows STATus QUEue ENABle 10 20 Status Structure Model 6485 Picoammeter Instruction Manual Table 10 7 SCPI commands error queue STATus subsystem Read error queue Command STATus QUEue Note 1 NEXT ENABle lt list gt ENABle DISable lt list gt DISable CLEar SYSTem ERRor NEXT ALL COUNt CODE NEXT ALL CLEar Notes Read and clear oldest error status code and message Specify error and status messages for error queue Read the enabled messages Specify messages not to be placed in queue Read the disabled messages Clear messages from error queue Note 2 No
135. d 19 inch rack Model 4288 2 side by side rack mount kit Mounts two instruments Models 182 428 486 487 2000 2001 2002 2010 2400 2410 2420 2430 6430 6485 6517 A 7001 side by side in a standard 19 inch rack Model 4288 4 side by side rack mount kit Mounts Model 6485 and a 5 25 inch instrument Models 195A 196 220 224 230 263 595 614 617 705 740 775A 6512 side by side in a standard 19 inch rack Carrying case Model 1050 padded carrying case A carrying case for Model 6485 Includes handles and shoulder strap Instruction Manual If an additional Model 6485 manual is required order the manual package The Keithley part number for the Instruction manual is 6485 901 010 The manual package includes an instruction manual and any pertinent addenda 1 6 Getting Started Model 6485 Picoammeter Instruction Manual Additional references While reading this document you may find it helpful to consult the following documenta tion for reference Low Level Measurements handbook Keithley s guide for effective low current low voltage and high impedance measurements Features The Model 6485 is a high performance picoammeter capable of measuring current Section 2 contains details on its measurement capabilities Measurement overview page 4 2 Features of Model 6485 Picoammeter include Setup storage Five instrument setups three user GPIB defaults and factory defaults can be saved
136. d log Model 6485 Picoammeter Instruction Manual Relative Relative Rel nulls an offset or subtracts a baseline reading from present and future read ings When a Rel value is established subsequent readings will be the difference between the actual input and the Rel value Displayed Rel ed Reading Actual Input Rel Value A Rel value is the same for all measurement ranges For example a Rel value of 1E 6 is 1uA on the 2UA range It is also 1uA on the 20UA range and the 200UA range Note changing ranges does not disable Rel When a Rel value is larger than the selected range the display is formatted to accommo date the Rel ed reading However this does not increase the maximum allowable input for that range An over range input signal will still cause the display to overflow For example on the 20uA range Model 6485 still overflows for a 21UA input NOTE Rel can be used on the result of the mX b m X b or LOG calculations How ever Rel will disable whenever a math function is enabled or disabled Setting and controlling relative From the front panel there are two ways to set the Rel value You can use the input reading as the Rel value or you can manually key in the Rel value REL key When the REL key is used to enable Rel the present display reading is used as the Rel value Perform the following steps to set a Rel value 1 Display the reading you want as the Rel value This could be a zero offset reading that
137. d offset Uncertainty for 20uA output current does not meet the recommended four times better uncertainty specification 2 23 3 C accuracy of characterization Calibration errors The Model 6485 checks for errors after each calibration step minimizing the possibility that improper calibration may occur due to operator error If an error is detected during calibration the instrument will display an appropriate error message The unit will then prompt you to repeat the calibration step that caused the error Model 6485 Instruction Manual Calibration 16 5 Table 16 2 Test uncertainty ratios with recommended equipment Test uncertainty Range 5700 5156 ratio 7ppm 300ppm 7ppm 200ppm Sppm 200ppm 7ppm 200ppm 550ppm 100ppm SSppm SSppm Calibration menu You can access the calibration menu by pressing MENU selecting CAL and then press ing ENTER The various selections are summarized in Table 16 3 Use the up and down RANGE keys to scroll through these selections Table 16 3 Calibration menu VOFFSET Performs offset voltage calibration COUNT Displays calibration count RUN Calibrates present range DATES Displays calibration and due dates UNLOCK Unlocks calibration using code LOCK Locks cal exits to the main menu SAVE Saves calibration constants Press MENU select CAL then press ENTER to access Use up or down RANGE to scroll through selections 16 6 Calibration Model 6485 Instructio
138. del 6485 Picoammeter Instruction Manual Figure 10 6 Measurement event status CONDition 2 IOV BFL BAV ROF RAV LP HL2F LL2F HL1F LL1F Measurement B15 B11 B10 B9 B8 B7 Be B5 B4 B3 B2 B1 BO Condition Register EVENt IOV BFL BAV ROF RAV LP _ HL2F LL2F HL1F LL1F Measurement B15 Pi 1 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 BO Event Register m o PERDER a 0 i To MSB bit e TT pia La a 0 4 e l F r t l l ee ENABle lt NRf gt IOV BFL BAV ROF RAV LP HL2F LL2F HL1F LLIF Measurement Event ENABle B15 BI1 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 BO Enable Register Decimal 1024 512 256 128 64 32 16 8 4 2 Weights C R RAE rS ATRA AA T 2 BFL Buffer Full HL2F High Limit 2 Fail amp Logical AND BAV Buffer Available LL2F Low Limit 2 Fail OR Logical OR ROF Reading Overflow HL1F High Limit 1 Fail RAV Reading Available LL1F Low Limit 1 Fail LP Limits Pass IOV Input Overvoltage Model 6485 Picoammeter Instruction Manual Status Structure 10 15 Questionable event status The used bits of the questionable event register Figure 10 7 are described as follows Bit B7 calibration summary Cal Set bit indicates that an invalid calibration constant was detected during the power up sequence This error
139. dings into the buffer and then calculates the mean average on the buffer readings Select data elements RST FORM ELEM READ TIME Store and Recall Readings TRIG COUN 20 TRAC POIN 20 TRAC FEED SENS TRAC FEED CONT NEXT INIT TRAC DATA Acquire Mean Statistic for CALC3 FORM MEAN CALC3 DATA Return 6485 to RST defaults Select reading and timestamp Set trigger model to take to 20 readings Set buffer size to 20 Store raw input readings Start storing readings Trigger readings setup to SRO on buffer full see Figure G 2 for example Request all stored readings Buffer Readings Select mean statistic Request mean statistic Triggering e Trigger models Explains the various components of the trigger models which control the triggering operations of the instrument Also explains how to configure the trigger model from the front panel e SCPI programming Includes the commands used to configure the trigger model and the commands to control the measurement process e External triggering Explains external triggering which allows Model 6485 to trigger other instruments and be triggered by other instruments 7 2 Triggering Model 6485 Picoammeter Instruction Manual Trigger models The flowcharts in Figure 7 1 and Figure 7 2 summarize triggering for Model 6485 They are called trigger models because they are modeled after the SCPI commands to control triggering operation Figur
140. displayed autozero state will be updated when the instrument is placed back in local Programming example The following examples enables or disables the autozero feature SYST AZER ON Enable autozero SYST AZER OFF Disable autozero SYST AZER Query autozero l on O off Connection fundamentals The following provides important fundamental information on input connections to the Model 6485 Typical connection drawings are included with the various measurement pro cedures provided in subsequent sections of this manual Input connector The rear panel INPUT connector is a 2 lug female BNC connector Figure 2 1 Make connections using a male terminated BNC cable Low noise input cables page 2 5 2 4 Measurement Concepts Model 6485 Picoammeter Instruction Manual Figure 2 1 BNC Input connector Input Center Conductor ANALOG OUT Shield a INPUT LO or GND 220V PK Maximum input levels The maximum input levels to Model 6485 are summarized in Figure 2 2 WARNING The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis voltage Exceeding 42V can create a shock hazard CAUTION The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the instrument Connecting COMMON or ANALOG OUTPUT to earth while floating the input may damage the instrument NOTE Analog outputs wi
141. e Ground loops page C 2 Fundamental information on making connections to the picoammeter input is provided in Section 2 Step 5 Disable zero check and take a reading from the display If the readings are noisy you may want to use filtering to reduce noise Use filtering if the noise is caused by a noisy input signal Filtering is covered in Section 4 3 4 Measurements Model 6485 Picoammeter Instruction Manual Figure 3 1 Connections for amps 4801 4802 10 or 4803 Metal Noise HI Shield Metal Safety n m Shield Input Cd 220V Peak Safety Earth Ground MADE IN U S A IEEE 488 ANALOG OUT CHANGE IEEE ADDRESS WITH FRONT PANEL MENU ommo GR G TRIGGER LINK RS 232 INPUT LINE RATING 220V PK N 50 60Hz 30 VA FUSE LINE 630MAT 100 VAC SB 120 VAC 315mAT 220 VAC SB 240 VAC CTION AGAINST FIRE HAZARD REPLAC Model 6485 Picoammeter Instruction Manual Measurements 3 5 SCPI programming Table 3 1 SCPI commands amps function SENSe SENSe Subystem DATA Return latest raw reading A INITiate Trigger one or more readings A READ Trigger and return reading s A A SENSe DATA This command does not trigger a reading It simply returns the last raw reading string It will not return the result of any instrument calculation The reading reflects what is applied to the input
142. e if you use the following query to request the state of MEP you will know which protocol is enabled SYSTem MEPI STATe If a 1 is returned MEP is enabled and the SCPI protocol is selected A 0 indicates that MEP is disabled and the 488 1 protocol is enabled To summarize 1 SCPI protocol 0 488 1 protocol Protocol differences The following information covers the differences between the 488 1 protocol and the SCPI protocol Model 6485 Picoammeter Instruction Manual IEEE 488 and SCPI Conformance Information 5 Message exchange protocol MEP When the 488 1 protocol is selected the MEP is disabled to speed up GPIB operation The following guidelines limitations must be followed when using the 488 1 protocol If a query is sent it must be the only command on the line this limitation also means no multiple queries can be sent Otherwise full SCPI command syntax is still supported including long form and short form commands multiple com mands and MIN MAX DEF parameter definitions For example the following command strings are invalid CURR RANG 020 OPC CURR RANG READ READ READ The following strings are valid curr nplc 1 0 curr rang min CURR RANG MAX READ When a query is sent either the data must be read back or a Device Clear DCL or Interface Clear IFC must be performed to reset the query When sending a command or query do not attempt to read data from the
143. e measurement If it will not be necessary to use the lower measurement ranges a smaller series resistor can be used reducing the effect it will have on measurement accuracy The lowest necessary measurement range can be determined from the measurement range accuracy specs the applied voltage and largest resistance desired to measure If using auto range program the Model 6485 to not use its lowest ranges when autoranging To set the auto range lower limit from the front panel Press the CONFIG key Press the down range key W Use the A and W range keys to scroll through the available lower limit settings e Press ENTER to save the displayed value as the lower limit Press EXIT to return to the previous setting To set the auto range lower limit over the bus use CURRent RANGe AUTO LLIMit Section 4 Use the following formula to determine the minimum resistance for proper current limit ing resistors MinR oes 20y A Lowest range to be used Rin 2nA or 20nA 11MQ 200nA or 2UA 3 5MQ 20UA or 20001A S0kQ 2mA or 20mA 500Q The series limiting resistor should have a minimum power rating of MinPowerRating SourceVoltage R series Example If measuring 100GQ resistances using an external voltage source of 500V and thus a lowest necessary current range of 20nA the minimum series resistance that will prevent damage in the case of a shorted resistor would be minimum Ryerieg 500V 220V 220VX11 MQ 14MQ minim
144. e 7 1 Trigger model front panel operation Turn 6485 ON O Press HALT O Idle Arm Layer Immediate Arm y GPIB Never Arm Count Timer INF Manual Arm Event TLink Detector Output Trigger F gt On Off TL Done Trigger Layer Trigger Count 1 Immediate Trigger In Trigger Event TLINk Source Detector Output Trigger gt On Off VMC 0 0 sec Trigger Delay MEASURE Action Factory Default gt Output Trigger Model 6485 Picoammeter Instruction Manual Triggering 7 3 Figure 7 2 Trigger model remote operation See Note Idle Arm Layer SOURce No ction ARM SOURce IMMediate A ARM SOURce BUS ARM SOURce TIMer ACCeptor Another N ARM COUNt lt n gt ARM SOURce MANual 2 ARM SOURce TLINk Aano Detector ARM OUTPut gt TRIGger NONE Trigger Layer R TRIGger DR DIRection ACCeptor Trigger Event Detector angie TRIGger COUNt lt n gt Trigger 2 TRIGger SOURce IMMediate Trigger In TRIGger SOURce TLINk Source TRIGger DELay lt n gt Trigger Delay TRIGger OUTPut gt SENSe NONE TRIGger DELay AUTO lt b gt 0 0 sec MEASURE Action Note The following commands place the Model 6485 into idle ABORt RST SYSTem PRESet RCL lt NRf gt lt gt Output Trigger DCL and SDC 7 4 Triggering Model 6485 Picoammeter Instruction Manual The difference between front panel operation Figure 7 1 and remote operation Figure 7 2 is
145. e Standard Event Register ESR then talk the instrument There may also be an Error Available event set in the status byte serial poll NDS Not Directly Supported in Model 6485 NEW Commands added to 6485 that were not available in the 485 command set D 10 DDC Emulation Commands Model 6485 Picoammeter Instruction Manual Figure D 1 UO Status word STATUS WORD pel weet ee TERMINATOR CRLF LFCR PREFIX LF CR ZERO CHECK None 0 Off SRQ Error Mask 1 On 00 SRO Disabled 01 IDDCO LOG 02 IDDC 0 Off 03 IDCCO or IDCC 1 On 04 Not in Remote 05 Not in Remote or IDDCO 06 Not in Remote or IDDC R AN a On 07 Not in Remote IDDCO 1 2nA or IDDC 2 20nA SRQ Data Mask see Legend 3 200nA 00 SRQ Disabled 01 Reading Overflow 4 2uA 02 DSF 03 DSF or Overflow 5 20uA 08 Done 09 Done or Overflow 6 20004 10 DSF or Done 11 DSF or Done or Overflow 7 Imi 16 Busy 17 Busy or Overflow 8 20mA 18 DSF or Busy 19 DSF or Busy or Overflow 9 Auto Off 24 Busy or Done 25 Busy Done or Overflow 26 DSF or Busy or Done 27 DSF or Busy or Done or Overflow RELATIVE SRQ Data Mask Legend 0 Off Overflow Reading Overflow 1 On DSF Data Store Full Done Reading Done EOI TRIGGER Busy Busy Value Send EOI Bus hold off on X 0 Continuous on Talk 0 Yes Enable 1 One shot on Talk 1 No Enable 2 Continuous on Get 2 Yes Disable 3 One shot on Get 3 No Disable 4 Continuous on X 5
146. e UP Pero sicario 15 3 LNE POWICE anian nats ince wands apghousen aa 15 3 Recommended test equipment 15 3 Vennen immissione a a 15 5 Example reading limits calculation 15 5 Calibrator voltage calculations 15 5 Performing the verification test procedures 15 6 TESE CONSIGETAU ONS ante 15 6 Restoring factory defaults rici ta 15 6 Offset voltage calibration i 15 7 Current Measurement accuracy usi cita 15 7 20mA 20mA range accuracy i 15 7 2nA 2MA range ACCULACY iii 15 8 Calibration INHOABCHON cina 16 2 Environmental Conditions i 16 2 Temperature and relative humidity 16 2 Warm up penod i rile 16 2 LETS POW GSE assiale 16 2 Calibration considerations i 16 3 Calibrauon ey clear 16 3 Recommended calibration equipment e 16 3 CAalbfalioh Crt OFS ara 16 4 Calibration MENU ilaele 16 5 Aborting calibration essssessseeereeeesseeessseessssesssssssnssssssssssssss 16 6 AAEE T AE E S E E 16 6 17 D Calibration procedure jardin 16 6 Preparing for Calibration 16 6 Offset voltage calibration erinin 16 7 Current CA brolin arianna 16 7 20mA 20mA range calibration 16 7 2nA 2mMA range Calibration i
147. e digital board ROM and display board ROM Note that yyyyy also provides build date and time information w is the board revision level B OPC operation complete Sets OPC bit OPC operation complete query Places a 1 in output queue When OPC is sent the OPC bit in the standard event register will set after all pending command operations are complete When OPC is sent an ASCII 1 is placed in the output queue after all pending command operations are complete Typically either one of these commands 1s sent after the INITiate command The INITiate command is used to take the instrument out of idle in order to perform measurements While operating within the trigger model layers all sent commands except DCL SDC IFC SYSTem PRESet RST GET and ABORt will not execute After all programmed operations are completed the instrument returns to the idle state at which time all pending commands including OPC and or OPC are executed After the last pending command is executed the OPC bit and or an ASCII 1 is placed in the output queue Programming example The following command sequence will perform 10 measure ments After the measurements are completed in approximately 10 seconds an ASCII 1 will be placed in the output queue RST TRIG DEL 1 ARM COUN 10 INIT OPC Return 6485 to RST defaults idle Set trigger delay for 1 second Program for 5 measurements and stop Start measurements S
148. e following CAL VOFFSET Use either RANGE key to select CAL COUNT from the calibration menu then press ENTER The unit displays the calibration count for example COUNT 1 Press EXIT to return to normal display 16 14 Calibration Model 6485 Instruction Manual 17 Routine Maintenance e Setting line voltage and replacing line fuse Describes how to set the line volt age properly and replace the line fuse with the correct rating e Front panel tests Covers testing the front panel keys and the display 1722 Routine Maintenance Model 6485 Instruction Manual Introduction The information in this section deals with routine type maintenance that can be performed by the operator and includes procedures for setting the line voltage replacing the line fuse and running the front panel tests Setting line voltage and replacing line fuse WARNING Disconnect the line cord at the rear panel and remove all test cables connected to the instrument before replacing the line fuse The power line fuse is located in the power module next to the AC power receptacle Figure 17 1 If the line voltage must be changed or if the line fuse requires replacement perform the following steps 1 Place the tip of a flat blade screwdriver into the power module by the fuse holder assembly Figure 17 1 Gently push in and to the left Release pressure on the assembly and its internal spring will push it out of the power module 2 Remove the f
149. e state Detection for each subse quent pass is satisfied when the programmed timer interval elapses The timer resets to its initial state when the instrument goes back into idle Manual ARM SOURce MANual Event detection for the arm layer is satis fied by pressing the TRIG key Model 6485 must be in the local mode for it to respond to the TRIG key Press LOCAL or send LOCAL 14 over the bus to place Model 6485 in local TLink ARM SOURce TLINk Event detection for the arm layer is satisfied when an input trigger via the TRIGGER LINK connector is received by Model 6485 Note that if the source bypass is set to ONCE ARM DIRection SOURce operation will initially loop around the source detector after the instrument leaves the idle state Detection for each subsequent pass is satisfied by an input trigger The bypass resets when the instrument goes into idle Trigger In source The Trigger In control sources are explained as follow Immediate TRIGger SOURce IMMediate Event detection for the trigger layer is satisfied immediately allowing operation to continue to perform a measure ment TLink TRIGger SOURce TLINk Event detection for the trigger layer is satisfied when an input trigger via the TRIGGER LINK connector is received by Model 6485 Note that if the source bypass is set to ONCE TRIGger DIRection SOURce operation will loop around the source detector on the initial pass through the arm layer Detection for each
150. eadings stored in buffer POINts Query buffer size FEED lt name gt Select source of readings for buffer SENSe 1 CAL Culate 1 or CALCulate2 CONTrol lt name gt Select buffer control mode NEXT or NE Ver CONT rol Query buffer control mode FEED Query source of readings for buffer TSTamp Timestamp FORMat lt name gt Select timestamp format A BSolute or DEL ta FORMat Query timestamp format Note SYSTem PRESet and RST have no effect on the commands in this subsystem The listed defaults are power on defaults 14 10 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual Table 14 8 TRIGger command summary Default Ref Command Description parameter Section SCPI INITiate Path to initiate measurement cycle s IMMediate Initiate one trigger cycle ABORt Reset trigger system goes to idle state V ARM SEQuence 1 Path to configure arm layer y LAYer 1 SOURce lt name gt Select control source IMMediate TIMer BUS IMMediate y TLINk or MANual SOURce Query arm control source y COUNt lt n gt Set measure count 1 to 2500 or INF infinite 1 y COUNt Query measure count V TIMer lt n gt Set timer interval 0 001 to 99999 999 sec 0 100 y TIMer Query timer interval y TCONfigure y DIRection lt name gt Enable SOURce or disable ACCeptor ACCeptor y bypass DIRection Query arm source bypass y ASYNchronous Configure input output triggers ILINe lt
151. ect any additional connectors from other instruments as required for your application 4 Make sure that the other end of the cable is properly connected to the controller Most controllers are equipped with an IEEE 488 style connector but a few may require a different type of connecting cable See your controllers instruction man ual for information about properly connecting to the IEEE 488 bus NOTE You can only have 15 devices connected to an IEEE 488 bus including the con troller The maximum cable length is either 20 meters or two meters times the number of devices whichever is less Not observing these limits may cause erratic bus operation Model 6485 Picoammeter Instruction Manual Remote Operation 9 7 Primary address Model 6485 ships from the factory with a GPIB address of 14 When the instrument pow ers up it momentarily displays the primary address You can set the address to a value of 0 30 Do not assign the same address to another device or to a controller that is on the same GPIB bus Usually controller addresses are 0 or 21 but see the controllers instruction manual for details Make sure the address of the controller is the same as that specified in the control lers programming language To make sure the units interface is properly selected and con figured or to check or change the GPIB address refer to Selecting and configuring an interface page 9 2 General IEEE 488 bus commands Commands and associat
152. ection changes The ZCHK key toggles zero check on and off When on the ZC or ZZ message is displayed See Section 2 for details on zero check Step 2 Perform zero correction To achieve optimum accuracy for low current measurements it is recommended that you zero correct the picoammeter See Section 2 for details on zero correction Select the 2nA range which is the lowest range Press the ZCOR key until the ZZ message is displayed Step 3 Select a manual measurement range or enable auto range Use the RANGE A and W keys to select a manual measurement range or press AUTO to enable auto range With auto range enabled the instrument will automatically go to the most sensitive range to make the measurement See Section 4 for details on range Step 4 Connect the current to be measured to the picoammeter Basic connections for measurements are shown in Figure 3 1 WARNING A safety shield is advisable whenever floating measurements are being made see Floating measurements page 2 12 Connections for the safety shield are shown in Figure 3 1 The metal safety shield must completely surround the noise shield or floating test circuit and it must be connected to safety earth ground using 18 AWG or larger wire NOTE When not making floating measurements it is recommended that you ground measurement LO at only one place in the circuit such as with the ground link connection on the rear panel of the 6485 Se
153. ed NDAC 1s also controlled by the accepting device The state of NDAC tells the source whether or not the device has accepted the data byte The complete handshake sequence for one data byte is shown in Figure F 2 Once data is placed on the data lines the source checks to see that NRFD is high indicating that all active devices are ready At the same time NDAC should be low from the previous byte F 6 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual transfer If these conditions are not met the source must wait until NDAC and NRFD have the correct status If the source is a controller NRFD and NDAC must be stable for at least 100ns after ATN is set true Because of the possibility of a bus hang up many controllers have time out routines that display messages in case the transfer sequence stops for any reason Once all NDAC and NRFD are properly set the source sets DAV low indicating to accept ing devices that the byte on the data lines is now valid NRFD will then go low and NDAC will go high once all devices have accepted the data Each device will release NDAC at its own rate but NDAC will not be released to go high until all devices have accepted the data byte The previous sequence is used to transfer both data talk and listen addresses as well as multiline commands The state of the ATN line determines whether the data bus contains data addresses or commands as described in the following paragraphs Figure
154. ed A low beam current results in very little material being sputtered and is therefore ideal for imaging applications Utilization of high beam currents resulting in a great deal of material being removed by sputtering and is subsequently well suited for precision milling operations Therefore whether the application calls for imaging or a complete circuit modification monitoring and control of the beam current is critical to the success of the process The ion beam current cannot be measured directly but requires the use of an ion detector There are several detectors commonly used throughout the industry including Channeltron Daly Microchannel plate and the Faraday cup The Faraday cup can only be used in an analog mode and is therefore not as sensitive as newer current pulse devices I 26 Applications Guide Model 6485 Picoammeter Instruction Manual The function of the detector is to develop a secondary current proportional to the current of the primary ion beam without interfering with the primary beam The basic operation of most detectors is similar an ion from the primary beam strikes the detector and a sec ondary ion is generated isolated from the primary ion stream This current is then mea sured and used to control the intensity of the beam The secondary currents generated by the detectors are very low and require a high degree of accuracy and measurement repeatability Currents as low as 5 or 6pA are not uncom mon ther
155. ed statements General commands are those commands such as DCL that have the same general mean ing regardless of the instrument Table 9 1 lists the general bus commands Table 9 1 General bus commands Effect on Model 6485 Goes into remote when next addressed to listen Reset interface all devices go into talker and listener idle states LOCAL key locked out Cancel remote restore front panel operation for Model 6485 Returns all devices to known conditions Returns Model 6485 to known conditions Initiates a trigger Serial polls Model 6485 REN remote enable The remote enable command is sent to Model 6485 by the controller to set up the instru ment for remote operation Generally the instrument should be placed in the remote mode before you attempt to program it over the bus Simply setting REN true does not actually place the instrument in the remote state You must address the instrument to listen after setting REN true before it goes into remote Note that the instrument does not have to be in remote to be a talker 9 8 Remote Operation Model 6485 Picoammeter Instruction Manual Note that all front panel controls except for LOCAL and POWER are inoperative while the instrument is in remote You can restore normal front panel operation by pressing the LOCAL key IFC interface clear The IFC command is sent by the controller to place all instruments on the bus in the local talker listener idle states Mode
156. ed to listen over GPIB mX b m X b or log10 calculation enabled Medium 1 PLC reading rate selected Relative enabled for present measurement function Instrument in GPIB remote mode Slow reading rate selected 6 PLC for 60Hz or 5 PLC for 50Hz Service request over GPIB Displaying buffer statistics Instrument addressed to talk over GPIB bus Timer controlled triggering in use External triggering GPIB or trigger link selected Pull out and rotate to desired position Rear panel summary The rear panel of Model 6485 is shown in Figure 1 2 Model 6485 Picoammeter Instruction Manual Getting Started 1 9 Figure 1 2 Rear panel IEEE 488 CHANGE IEEE ADDRESS WITH FRONT PANEL MENU TRIGGER LINK LINE RATING A 50 60Hz 30 VA FUSE LINE 630mAT 100 VAC SB 120 VAC INPUT 220V PK 315mAT 220 VAC SB 240 VAC 1 INPUT This standard female BNC connector is used to connect the signal to be measured to the input of the Model 6485 Mates to a BNC cable 2 CHASSIS This screw terminal is used to connect COMMON to CHASSIS ground via the ground link connector 3 COMMON This standard banana connector can be used as input LO or as the common for the ANALOG OUT Also can be used as a ground link 4 ANALOG OUT This standard banana connector provides a scaled inverting output inverting 2V full scale on all ranges 5 TRIGGER LINK Eight pin micro DIN
157. eeeeseeeeeeeeeeees 1 6 Front panel summary 1 6 Rear pane SUMMA annaia r 1 8 ANIOS OULU aa E A 1 10 DISPLAY ests ascetics cents errs ees eens odes data eda 1 12 Status and error MESSAGES 1 12 POW CISD rec aaa a 1 12 Line POW EF CONNECHON tcscssztccecteseasass arrecati 1 12 ToC IVCQUENCY lele 1 13 Front panel procedure 1 13 SCPI programming line frequency 1 13 POWEFUPFSEAQUENGE nerd iiin nO area 1 14 Deranlt scimes iii 1 15 Front panel setup operation 1 15 LO SAVA USCE Se lalla 1 15 To Testore ANY Seerne 1 15 TO SClECE POW CEO setup Liar 1 15 Remote setup operation 1 16 Saving and restoring user setups 1 16 Restoring factory or GPIB default setups 1 16 Selecting power o setup 1 16 SCPI programme ico 1 18 Optional command words 1 19 Query commands seniii EE E 1 19 Measurement Concepts Measurement overview i 2 2 Performance considerations sernir 2 2 Warm up period srecen a E 2 2 AULOZEro salle 2 2 SCRL programmino sarei 2 3 SYSTem AZERO STATe lt b gt iii 2 3 Connection fundamentals 2 3 Input Connector siriana 2 3 Maximum input levels sulle 2 4 Low noise input Cables menssa denies 2 5 Basic connections to DUT
158. een sent This bit is cleared when the status byte is read IDDC An illegal command will set this bit For example S1 is illegal since no such let ter exists in the command set The IDDC bit will be cleared on a reading of the status byte Not in remote Model 6485 in local mode of operation NOTE Once the Model 6485 has generated an SRO its status byte must be read to clear the SRQ line Otherwise the instrument will continuously assert SRO The Model 6485 may be programmed to generate an SRQ for more than one condition simultaneously Table D 2 Status byte and mask interpretation Bit Bit 5 0 Data Conditions Bit 5 1 Error Conditions TESB Overfow mo Data Store Full IDDC 2 mA a Na e se se D 14 DDC Emulation Commands Model 6485 Picoammeter Instruction Manual Figure D 4 Status byte format Data Conditions B5 0 l Data Reading Reading Busy Done oe Overflow 0 Data 1 SRQ 1 Error Not IDDC IDDCO in Remote Error Conditions B5 E Example Programs F 2 Example Programs Programming examples Model 6485 Picoammeter Instruction Manual This section contains example programs pseudo code to achieve speed specifications for a specific example of a QuickBasic program using SRQ see Figure G 2 1000 readings second into internal buffer NOTE This program configures the Model 6485 to 0 01 PLC digital filters off front panel off auto zero off as well as takes and stores 2500
159. effects Triboelectric currents are generated by charges created between a conductor and an insula tor due to friction Here free electrons rub off the conductor and create a charge imbalance that causes the current flow For example bending a triaxial cable causes friction between the center conductor HI and its surrounding insulator resulting in triboelectric currents Triboelectric currents can be minimized as follows e Use low noise cables These cables are specially designed to minimize charge generation and use graphite to reduce friction The Keithley Model 4801 4803 cables are low noise e Use the shortest cables possible and secure them 1 e taping or tying to a non vibrating surface to keep them from moving Piezoelectric and stored charge effects Piezoelectric currents are generated when mechanical stress is applied to certain insulating materials 1 e crystalline In some plastics pockets of stored charge cause the material to behave in a similar manner When building test fixtures choose good insulating materials and make connecting struc tures as rigid as possible Make sure there are no mechanical stresses on the insulators C 4 General Measurement Considerations Model 6485 Picoammeter Instruction Manual Electrochemical effects Error currents also arise from electrochemical effects when ionic chemicals create weak batteries on a circuit board These batteries could generate a few nanoamps of current bet
160. efore the measurement device must be capable of achieving resolutions below IpA The Keithley Model 6485 Picoammeter is ideal for this application because it offers a wide selection of range settings spanning from 20mA to 2nA This will result in 5 1 2 digit resolution ranging from 100nA to 10fA Numerous ranges and fine measurement granularity will meet all current requirements for this application as well as provide addi tional sensitivity for future development needs Signal connections to the picoammeter are made using the BNC connector mounted on the rear panel If the source on the ions is biased off ground then the ion detector will most likely be at ground potential A simple coaxial vacuum feedthrough can be used to make the connection between the detector and the picoammeter See Figure I 24 Figure l 24 Focused lon Beam signal connections 6485 Picoammeter lon Detector Coaxial Vacuum Feedthrough Using switching systems to measure multiple current sources Refer to External trigger example page 7 13 Symbols asterisk 1 8 gf more 1 8 4 gt 4 and w 1 8 acquire method to zero correct 2 15 Additional references 1 6 Address commands F 10 Addressed multiline commands F 10 ANALOG OUTPUT 1 9 Applications Guide I 1 ARM layer 7 7 configuration menu 8 5 AUTO 1 8 Autoranging 4 2 limits 4 3 Autozero 2 2 Avalanche photo diode leakage I 24 AVG 1 7 avoiding measurement errors I 10 AZE
161. elative null 5 4 SCPI commands mX b m X b and log 5 7 Buffer SCPLCommands DUET waters eines Acie adi 6 5 Triggering Auto delay senos ie 7 6 TTIGCEL model ment SIUC HUTS scsi 7 7 SCPI commands triggering isr ananin E an 7 9 Limit Tests Test limit display messages 8 3 SCPI commands limit tests c ccccecsesceccesceecesceceess 8 7 9 Table 9 1 Table 9 3 Table 9 2 10 Table 10 1 Table 10 2 Table 10 3 Table 10 4 Table 10 5 Table 10 6 Table 10 7 11 Table 11 1 12 Table 12 1 13 Table 13 1 Table 13 2 Table 13 3 14 Table 14 1 Table 14 2 Table 14 4 Table 14 3 Table 14 5 Table 14 6 Table 14 7 Table 14 8 15 Table 15 1 Table 15 2 Table 15 3 Remote Operation General DUS COMMIANS 555 sade prato rialza 9 7 PC seral port pnonta sione 9 19 RS 232 connector PINOUT seecae eei EE ii 9 19 Status Structure Common and SCPI commands reset registers and clear Queues cs iosinte a ees 10 4 SCPI command data formats for TEANO statis TE CISLEDS ilari nica 10 7 Common commands status byte and service request enable registers sicario 10 10 Common and SCPI commands condition registers 10 16 Common and SCPI commands event registers 10 16 Common and SCPI commands event SMA LS register yee eor titolo i 10 17 SCPI commands error queue 10 20 C
162. election General Bus Commands Front Panel GPIB Operation Programming Syntax e RS 232 interface reference Provides basic reference information for the RS 232 interface and explains how to make connections to the computer 9 2 Remote Operation Model 6485 Picoammeter Instruction Manual Selecting and configuring an interface Interfaces Model 6485 supports two built in remote interfaces e GPIB interface e RS 232 interface You can use only one interface at a time At the factory the GPIB bus is selected You can select the interface only from the front panel The interface selection is stored in non vola tile memory it does not change when power has been off or after a remote interface reset GPIB interface The GPIB is the IEEE 488 interface Model 6485 must be assigned to a unique address At the factory the address is set to 14 but can be set to any value from 0 to 30 However the address must not conflict with the address assigned to other instru ments in the system You can use either the SCPI or DDC language to program the instru ment RS 232 interface When using the RS 232 interface you must set baud rate data bits parity terminator and flow control For the RS 232 interface you can only use the SCPI language to program the instrument Languages For the GPIB interface there are three programming languages to choose from e SCPI language 488 2 e DDC language e 488 1 language NOTE For the RS 232 int
163. election Includes the SCPI commands for remote operation Filters Explains how to configure and control the digital and median filters Includes the SCPI commands for remote operation 4 2 Range Units Digits Rate and Filters Model 6485 Picoammeter Instruction Manual Range units and digits Range The ranges for current measurements are listed in Table 4 1 Table 4 1 Measurement ranges nA uA mA 2nA 2uA 2mA 20nA 20uA 20mA 200nA 2001A The full scale readings for every measurement range are 5 over range For example on the 20uA range the maximum input current is 21uA Input values that exceed the maxi mum readings cause the overflow message OVRFLOW to be displayed Manual ranging To select a range press the RANGE A or W key The instrument changes one range per key press If the instrument displays the OVRFLOW message on a particular range select a higher range until an on range reading is displayed Use the lowest range possible with out causing an overflow to ensure best accuracy and resolution Autoranging When using autorange the instrument automatically goes to the most sensitive available range to measure the applied signal Up ranging occurs at 105 of range while down ranging occurs at the range value For example if on the 20U A range the instrument will go up to the 200UA range when the input signal exceeds 21uA While on the 200uA range the instrument will go down to the 20uA range when
164. en As a talker a device will output information and as a listener a device will receive information To simplify the task of keeping track of the devices a unique address number is assigned to each On the bus only one device can talk at a time and is addressed to talk by the controller The device that is talking is known as the active talker The devices that need to listen to the talker are addressed to listen by the controller Each listener is then referred to as an active listener Devices that do not need to listen are instructed to unlisten The reason for the unlisten instruction is to optimize the speed of bus information transfer since the task of listening takes up bus time Through the use of control lines a handshake sequence takes place in the transfer process of information from a talker to a listener This handshake sequence helps ensure the credi bility of the information transfer The basic handshake sequence between an active con troller talker and a listener is as follows 1 The listener indicates that it is ready to listen The talker places the byte of data on the bus and indicates that the data is available to the listener 3 The listener aware that the data is available accepts the data and then indicates that the data has been accepted 4 The talker aware that the data has been accepted stops sending data and indicates that data is not being sent 5 The listener aware that there is no data on the bus i
165. end OPC 11 4 Common Commands Model 6485 Picoammeter Instruction Manual C SAV lt NRf gt save Save present setup in memory RCL lt NRf gt recall Return to setup stored in memory Parameters 0 Memory location 0 1 Memory location 1 2 Memory location 2 Use the SAV command to save the present instrument setup configuration in memory for later recall Any control affected by RST can be saved by the SAV command The RCL command is used to restore the instrument to the saved setup configuration Three setup configurations can be saved and recalled Model 6485 ships from the factory with SYSTem PRESet defaults loaded into the avail able setup memory If a recall error occurs the setup memory defaults to the SYS Tem PRESet values Programming example SAV 2 Save present setup in memory location 2 RST Set 6485 to RST defaults RCL 2 Return recall 6485 to setup stored in memory location 2 D RST reset Return Model 6485 to RST defaults When the RST command is sent Model 6485 performs the following operations 1 Returns Model 6485 to the RST default conditions see Default column of SCPI tables 2 Cancels all pending commands 3 Cancels response to any previously received OPC and OPC commands E TRG trigger Send bus trigger to Model 6485 Use the TRG command to issue a GPIB trigger to Model 6485 It has the same effect as a group execute trigger GET Use the TRG command
166. ent da commands NOK BO Picoammeter Readings NDS X READ FETCh MEAS or NEW SENSe 1 DATA LATest Bl Buffer reading returns one at a time NDS Reading TRACe DATA returns entire buffer NEW Mode B2 Maximum reading from buffer NDS CALCulate3 FORMat MAXimum NEW CALCulate3 DATA B3 Minimum reading from buffer NDS CALCulate3 FORMat MINimum NEW CALCulate3 DATA CO Zero Check off X Zero Check SYSTem ZCHeck OFF wee Cl Zero Check on SYSTem ZCHeck ON a DO LOG off CALCulate 1 STATe OFF 7 Model 6485 Picoammeter Instruction Manual Table D 1 continued Device dependent command summary DDC Emulation Commands D 3 Mode Command l nee Note Default Equivalent SCPI commands GO Reading with prefix NDCA 1 23456E 02 SCPI not X Data Gl Reading without prefix 1 23456E 02 avail Format G2 Reading with prefix and buffer suffix Gf in B1 s NDCA 1 23456E 02 012 NEW i subsystem Buffer Size In Set buffer size where n 1 2500 A 100 da Jn Set number of digits of precision to return over the bus NEW 5 Digits co where n 4 7 allowed range KO Enable both EOI and bus hold off on X SCPI not X available KI Disable EOI enable bus hold off on X SCPI not EOI and E available US K2 Enable EOI disable bus hold off on X SCPI not Hold off NEW available K3 Disable both EOI and bus hold off on X SCPI not NEW available Sibi none LO store calibration command not supported F G Cibanon CALibration
167. erface only the SCPI language can be used to program the instrument When the RS 232 interface is selected it automatically defaults to SCPI SCPI language Standard Commands for Programmable Instrument SCPI is fully supported by the GPIB and RS 232 interfaces Always calibrate Model 6485 using the SCPI language DDC language Model 6485 implements most DDCs device dependent commands available in the Keithley Model 485 picoammeter The available commands are provided in Appendix D See the Model 485 instruction manual for details on operation 488 1 language See Appendix G for details Model 6485 Picoammeter Instruction Manual Remote Operation 9 3 Interface selection and configuration procedures NOTE The unit will reset if the language is changed SCPI 488 1 and DDC When you select enable the GPIB interface the RS 232 interface disables Conversely selecting enabling the RS 232 interface disables the GPIB interface Select the interface from the COMM menu structure access by pressing the COMM key while in local Use the A and W range keys to change the selected interface RS 232 or GPIB Press enter to save the change note that the instrument will exit the menu structure and perform the power on sequence when changing the interface NOTE When an interface is enabled on or disabled off the instrument will exit from the menu structure and perform the power on sequence Configuring the GPIB interface
168. erference include 1 Shielding Possibilities include a shielded room a shielded booth shielding the sensitive circuit and using shielded cable The shield should always be connected to a solid connector that is connected to signal low If circuit low is floated above ground observe safety precautions and avoid touching the shield Meshed screen or loosely braided cable could be inadequate for high impedances or in string fields Note however that shielding can increase capacitance in the measuring cir cuit possibly slowing down response time 2 Reduction of electrostatic fields Moving power lines or other sources away from the experiment reduces the amount of electrostatic interference seen in the mea surement Magnetic fields A magnetic field passing through a loop in a test circuit will generate a magnetic EMF voltage that is proportional to the strength of the field the loop area and the rate at which these factors are changing Magnetic fields can be minimized by following these guidelines e Locate the test circuit as far away as possible from such magnetic field sources as motors transformers and magnets e Avoid moving any part of the test circuit within the magnetic field e Minimize the loop area by keeping leads as short as possible and twisting them together Electromagnetic Interference EMI The electromagnetic interference characteristics of the Model 6485 comply with the elec tromagnetic compatibil
169. erforms a single mX b calculation and displays the result on the computer CRT RST Restores RST defaults CALC FORM MXB Selects mX b calculation CALC KMAT MMF 2 Sets scale factor M to 2 CALC KMAT MBF 0 5 Sets offset B to 0 5 CALC STAT ON Enables calculation INIT Perform one measurement and calculate mX b CALC DATA Request mX b result 6 Buffer e Buffer operations Explains how to store and recall readings including buffer Statistics e SCPI programming Covers the SCPI commands used to control buffer opera tions 6 2 Buffer Model 6485 Picoammeter Instruction Manual Buffer operations Store Model 6485 has a buffer to store from one to 2500 readings It also stores overflow read ings Each reading has a timestamp The timestamp for each reading is referenced to the time the measure store process is started In addition recalled data includes statistical information maximum minimum peak to peak average and standard deviation The buffer fills with the specified number of readings and stops Readings are placed in the buffer after any filters and or math operations have been performed Math operations include relative mX b m X b LOG or limits Buffered data is overwritten each time the storage operation is selected The data is vola tile it is not saved through a power cycle Measurement function changes are permissible during the storage process Note however that the sta
170. eter Instruction Manual Remote Operation 9 5 Figure 9 1 IEEE 488 connector To allow many parallel connections to one instrument stack the connector Two screws are located on each connector to ensure that connections remain secure Current standards call for metric threads which are identified with dark colored screws Earlier versions had dif ferent screws which were silver colored Do not use these types of connectors on Model 6485 because it is designed for metric threads Figure 9 2 shows a typical connecting scheme for a multiunit test system Figure 9 2 Multi unit connections Instrument Instrument Instrument 9 Y Controller Y To avoid possible mechanical damage stack no more than three connectors on any one unit 9 6 Remote Operation Model 6485 Picoammeter Instruction Manual NOTE To minimize interference caused by electromagnetic radiation use only shielded IEEE 488 cables Available shielded cables from Keithley are Models 7007 1 and 7007 2 To connect Model 6485 to the IEEE 488 bus follow these steps 1 Line up the cable connector with the connector located on the rear panel The con nector is designed so that it will fit only one way Figure 9 3 shows the location of the IEEE 488 connector Figure 9 3 IEEE 488 connector location KEITHLEY MADE IN U S A dci e coe S C a WITH FRONT PANEL MENU Jo a Tighten the screws securely making sure not to over tighten them 3 Conn
171. fault value When the MINimum parame ter is used the instrument is programmed to the lowest allowable value When the MAXimum parameter is used the instrument is programmed to the largest allowable value ARM TIMer 0 1 Sets timer to 100 msec ARM TIMer DEFault Sets timer to 0 1 sec ARM TIMer MINimum Sets timer to 1 msec ARM TIMer MA Ximum Sets timer to 999999 999 sec Angle brackets lt gt Used to denote a parameter type Do not include the brack ets in the program message DISPlay ENABle lt b gt The lt b gt indicates that a Boolean type parameter is required Thus to enable the display you must send the command with the ON or 1 parameter as follows DISPlay ENABle ON or 1 9 12 Remote Operation Model 6485 Picoammeter Instruction Manual Query commands The query command requests the presently programmed status It is identified by the ques tion mark at the end of the fundamental form of the command Most commands have a query form ARM TIMer Queries the timer interval Most commands that require a numeric parameter lt n gt can also use the DEFault MINi mum and MA Ximum parameters for the query form These query forms are used to deter mine the RST default value and the upper and lower limits for the fundamental command ARM TIMer DEFault Queries the RST default value ARM TIMer MINimum Queries the lowest allowable value ARM TIMer MAXimum Queries the largest allowable value Case sen
172. fer readings Mean is calculated as follows n x y n i 1 Where X is a stored reading n is the number of stored readings e The STD DEV value is the standard deviation of the buffered readings Standard deviation is calculated as follows Where X is a stored reading n is the number of stored readings Avg is the mean of the buffer readings Model 6485 Picoammeter Instruction Manual Buffer 6 5 NOTE If any readings stored in the buffer are the result of an overflow or overvoltage condition the buffer statistics calculation will not be performed Buffer recall via front panel operation will show a series of dashes in place of the requested buffer statistics value In remote operation the corresponding buffer statistics will be represented by the value 9 91e37 SCPI programming Commands associated with buffer operation are listed in Table 6 1 The TRACe com mands are used to store and recall readings in the buffer The FORMat ELEMents com mand is used to specify which data elements to include in the response message for TRACe DATA which is the command to read the buffer The CALCulate3 commands are used to obtain statistics from the buffer data NOTE The Model 6485 uses IEEE 754 floating point format for statistics calculations Table 6 1 SCPI commands buffer Commands Description Default Ref TRACe TRACe Subsystem CLEar FREE POINts lt n gt ACTual FEED lt name gt CONTrol
173. fference is equal to the voltage burden of the picoammeter Since the top and the bottom of the insulator are at nearly the same potential no significant current will flow through it and nearly all the current from the device under test will flow through the picoammeter as well Figure l 1 Guarding to reduce leakage currents Metal Test Fixture KO Insulators Programmable V Source 0485 Picoammeter Equivalent Circuit Input bias current An ideal picoammeter would read OA with an open input In practice however ammeters do have some current that flows when the input is open This current is known as the input bias offset current and may be large enough to corrupt low current measurements The input bias current for Model 6485 is included in the offset portion of the accuracy specifi cation Voltage burden The input resistance of the picoammeter causes a small voltage drop across the input ter minals This voltage is known as the voltage burden If the voltage burden is large in rela tion to the voltage of the measured circuit then significant measurement errors will occur Refer to Figure I 2 to see how voltage burden affects current measurements Assume Vg 1s SmV and Rg is 5kQ to configure a 1UA current source 5mV 5kQ 1uA An ideal picoammeter with zero voltage burden would allow 1uA to flow and measure it accurately In practice however every picoammeter has a voltage burden If the voltage burden Vp is ImV
174. form zero correction is consistent with the way it is performed from the front panel That is zero correction is performed while zero check is enabled The zero correct state can be turned on and off repeatedly without requiring If no ACQ has not been performed since the most recent reset zero is used for the ACQ value Measurement considerations There are a variety of factors to consider when making low level measurements These considerations are listed and summarized in Table 2 5 and are detailed in Section 3 and Section C For comprehensive information on all measurement considerations refer to the Low Level Measurements handbook which is available from Keithley Instruments Table 2 5 Summary of measurement considerations Considerations Description See Section 3 for details Input bias current Offset current of Model 6485 could affect low current measurements Voltage burden Offset voltage of Model 6485 could cause errors if it is high in relation to the voltage of the measured circuit Noise Noise generated by source resistance and source capacitance See Section C for details Ground loops Multiple ground points can create error signals Triboelectric effects Charge currents generated in a cable by friction between a conductor and the surrounding insulator i e bending a triax cable Piezoelectric and stored Currents generated by mechanical stress on certain insulating charge effects materials Electrochemical effects Cur
175. ged Model 6485 Picoammeter Instruction Manual Range Units Digits Rate and Filters 4 1 Digital filter control The AVG key is a toggle key it will either enable the digital filter displays AVERAGE ON or disable the digital filter displays AVERAGE OFF To configure the median filter NOTE For the following procedure use the and b keys and the RANGE A and W keys to set values The and b keys provide cursor control while the A and W keys increment and decrement the value To return to the previously set value and cancel configuration press EXIT instead of ENTER Values change immediately when the ENTER key is pressed 1 Press the CONFIG key 2 Press the AVG key The present number of reading conversions to average filter count will be displayed flashing 3 Set filter count 1 to 100 e Use the range keys A or W to display the desired filter count value at the RDGS prompt e Press ENTER to set 4 Set filter type REPEAT or MOVING AV e Use the range keys A or W to display the desired filter type at the TYPE prompt e Press ENTER to set 5 Enable or disable advanced filter YES or NO e Use the range keys A or W to display the desired state at the ADVANCED prompt e Press ENTER to set 6 If the advanced filter is enabled ADVANCED YES enter the noise tolerance level at the NTOL prompt 0 105 0000 e Use the range keys lt gt A and W to display the desired value e Press ENTER to set
176. h is used to separate commands within the program message e When the path pointer detects a colon that immediately follows a semicolon it resets to the root level e The path pointer can only move down It cannot be moved up a level Executing a com mand at a higher level requires that you start over at the root command Using common commands and SCPI commands in the same message Both common commands and SCPI commands can be used in the same message as long as they are separated by semicolons A common command can be executed at any com mand level and will not affect the path pointer Stat oper enab lt NRf gt ESE lt NRf gt Model 6485 Picoammeter Instruction Manual Remote Operation 9 15 Program Message Terminator PMT Each program message must be terminated with an LF line feed EOI end or identify or an LF EOI The bus will hang if your computer does not provide this termination The following example shows how a program message must be terminated trac poin 10 lt PMT gt Command execution rules e Commands execute in the order that they are presented in the program message e An invalid command generates an error and of course is not executed e Valid commands that precede an invalid command in a multiple command program message are executed e Valid commands that follow an invalid command in a multiple command program mes sage are ignored e For fastest command execution Do not use optio
177. he GPIB defaults The RST command is documented in Section 11 and SYSTem PRESet is covered in Section 12 Selecting power on setup The SYSTem POSetup command is used to select which setup to return to on power up The SYSTem POSetup command is documented in Section 12 Table 1 3 Default settings i Factory GPIB Trig Layer CONF TRIG x TRIG Arm In Source Event Arm Layer CONF ARM Arm In Source Event Arm Count Input Trigger Link Line Source Bypass Output Trigger Link Line Output Trigger Buffer STORE Disabled Count No effect Digital Filter AVG Off Count 10 Type Moving Advanced No disabled Noise Tolerance 0 0 Display Resolution DIGITS 542 digits Format byte order Swapped This factory SYStem PRESet and bus RST GPIB defaults are the same Bus settings that are different from factory reset are as shown Model 6485 Picoammeter Instruction Manual Table 1 3 continued Default settings Setting Getting Started Factory SYStem PRESet GPIB RST 1 17 GPIB Address Language No effect On at factory No effect 14 at factory No effect SCPI at factory Limit Tests Limit 1 and Limit 2 HI and LO Values Disabled 1 1 Median Filter Rank Off 1 MX B M Value B Value Units Log Disabled 1 0 0 0 OFF M X B reciprocal M Value B Value Units Disabled Range Rate NPLC 6 0 60Hz o
178. he information and the appropriate software can be used to direct the information to the desired location F 4 IEEE 488 Bus Overview Figure F 1 JEEE 488 bus configuration TO OTHER DEVICES DEVICE 1 ABLE TO TALK LISTEN AND ae COMPUTER DEVICE 2 ABLE TO TALK AND LISTEN 6485 DEVICE 3 ONLY ABLE TO LISTEN PRINTER DEVICE 4 ONLY ABLE TO TALK Model 6485 Picoammeter Instruction Manual DATA BUS DATA BYTE TRANSFER CONTROL GENERAL INTERFACE MANAGEMENT DIO 1 8 DATA 8 LINES Bus lines DAV NRED NDAC i HANDSHAKE IFC ATN SRQ mi REN EOI The signal lines on the EEE 488 bus are grouped into three different categories data lines management lines and handshake lines The data lines handle bus data and com mands while the management and handshake lines ensure that proper data transfer and operation takes place Each bus line is active low with approximately zero volts represent ing a logic 1 true The following paragraphs describe the operation of these lines Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 5 Data lines The IEEE 488 bus uses eight data lines that transfer data one byte at a time DIO1 Data Input Output through DIO8 Data Input Output are the eight data lines used to transmit both data and multiline commands and are bi directional The data lines operate with low true logic Bus management lines The five bus management lines help to ensure pro
179. he instrument for one shot measurements Each subsequent READ command will then trigger a single measurement and acquire the reading see READ for details If the instrument is in idle this command will execute immediately If the instrument is not in idle execution of the command will execute when the operation returns to the idle state When this command is executed Model 6485 will be configured as follows e The specified function is selected e All controls related to the selected function are defaulted to the RST values e The event control sources of the trigger model are set to immediate e The arm and trigger count values of the trigger model are set to one e The delay of the trigger model is set to zero e Model 6485 is placed in the idle state e All math calculations are disabled e Buffer operation is disabled A storage operation presently in process will be aborted e Autozero is enabled This command is automatically asserted when the MEASure command is sent Model 6485 Picoammeter Instruction Manual SCPI Signal Oriented Measurement Commands 12 3 Programming example The following command sequence selects and configures Model 6485 for one shot measurements Each subsequent READ triggers a single measurement and requests the reading CONF CURR Perform CONFigure operations READ Trigger measurement and request reading B FETCh Request latest reading This command requests the latest
180. he instrument has been exposed to extreme temperatures allow extra time for the internal temperature to stabilize Autozero To help maintain stability and accuracy over time and changes in temperature the Model 6485 periodically measures internal voltages corresponding to offsets zero and amplifier gains These measurements are used in the algorithm to calculate the reading of the input signal This process is known as autozeroing When autozero is disabled the offset and gain measurements are not performed This increases measurement speed up to 3 times However the zero and gain reference points can eventually drift resulting in inaccurate readings of the input signal It is recommended that autozero only be disabled for short periods of time To disable autozero from the front panel press the AZERO button This button toggles autozero on and off It can also be enabled by restoring factory or GPIB default conditions When autozero is enabled a colon will be displayed after the reading For example Autozero disabled 0 00258 nA Autozero enabled 0 00258 nA Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 3 SCPI programming Table 2 2 SCPI commands autozero SYSTem SYSTem Subsystem AZERO STATe lt b gt Enable or disable autozero ON SYSTem AZERo STATe lt b gt Sending this command over the bus does not update the display while in remote To verify the AZERo state send the query The
181. hould be sent before attempting to program instruments over the bus EOI End or Identify EOI is used to positively identify the last byte in a multi byte transfer sequence thus allowing data words of various lengths to be transmitted easily IFC Interface Clear IFC is used to clear the interface and return all devices to the talker and listener idle states ATN Attention The controller sends ATN while transmitting addresses or multiline commands SRQ Service Request SRQ is asserted by a device when it requires service from a controller Universal multiline commands Universal commands are those multiline commands that require no addressing All devices equipped to implement such commands will do so simultaneously when the commands are transmitted As with all multiline commands these commands are transmitted with ATN true LLO Local Lockout LLO is sent to the instrument to lock out the LOCAL key and all their front panel controls DCL Device Clear DCL is used to return instruments to some default state Instru ments usually return to their power up conditions SPE Serial Poll Enable SPE 1s the first step in the serial polling sequence which is used to determine which device has requested service SPD Serial Poll Disable SPD is used by the controller to remove all devices on the bus from the serial poll mode and is generally the last command in the serial polling sequence F 10 IEEE
182. hows the general format of the status byte which is obtained by using the SPE SPD polling sequence If the status byte is read when no SRQ was generated by the Model 6485 bit 6 is clear the current status of the instrument will be read For example if a reading was done bit 3 would be set When an SRQ is generated by the Model 6485 bit 6 of the status byte will be set If the SRQ was caused by an error condition bit 5 will also be set along with one of the error condition bits BO B1 or B2 Only the error that caused the initial SRQ will be defined by the status byte If the SRQ was caused by a data condition bit 5 will be clear and the appropriate data con dition bits BO BI B3 and B4 will be set If the reading overflow condition caused the SRQ then only the reading overflow bit will be set After an SRQ the status byte will remain unchanged until it is read Model 6485 Picoammeter Instruction Manual DDC Emulation Commands D 13 The various bits in the status byte are described below Reading Overflow Set when an overrange input is applied to the instrument Data Store Full Set when the number of readings stored is equal to the buffer size Reading Done Set when the instrument has completed the present conversion and is ready to take another reading Busy The instrument is still executing a prior command and is not yet ready to accept a new command IDDCO An illegal command option such as R8 has b
183. icability 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 accord ing to instructions If the board becomes contaminated and operation is affected the board should be returned to the factory for proper cleaning servicing 11 01 Table of Contents 1 Getting Started roduc HON sea ence sda ceeee ela us iaia 1 2 Overview of his MANU all scorrerie risa 1 2 Generalinformatoni dillo 1 3 Warranty information 1 3 Contact1inio mato asl 1 3 Safety symbols and terms sciita ariana 1 3 Unpacking and inspection 1 3 Inspection for damage ii 1 3 Handhne precion anasa a 1 4 PACKAPCACONICHE rear 1 4 G PUIONS ANd ACCESSOMES dii liliillaaii 1 4 Input cables connectors and adapters 1 4 GPIB and trigger link cables and adapters 1 5 Rack MOUDE K i nanose i 1 5 Connotea 1 5 Instruction Manual 1 5 Additonal TElel ENCES nale 1 6 PC APCS cascata atrata 1 6 Front and rear panel familiarization 0cseeeeee
184. id on scale level Extended opera tion near but under 60V will produce heat inside the instrument and may require time to cool before returning to accurate readings Test fixture Whenever possible use a shielded low leakage test fixture to make precision measure ments A general purpose test fixture is shown in Figure 2 5 This test fixture will accom modate a variety of connection requirements Figure 2 5 General purpose test fixture From External A Insulated Power Supply Terminal Post To 6485 Input Q Metal Chassis Metal Guard Plate Safety Earth Ground A Banana Jacks typical from external power supply Female BNC Input Connector Model 6485 2 10 Measurement Concepts Model 6485 Picoammeter Instruction Manual Test fixture chassis e The chassis of the test fixture should be metal so that it can function as a shield for the DUT or test circuit e The test box must have a lid that closes to prevent contact with live circuitry e The test fixture must have a screw terminal that is used exclusively for connection to safety earth ground WARNING _ To provide protection from shock hazards the test fixture chassis must be properly connected to safety earth ground A grounding wire 18 AWG or larger must be attached securely to the test fixture at a screw terminal designed for safety grounding The other end of the ground wire must be attached to a known safety earth ground Guard plate A metal guard p
185. including the controller Thus any number of talkers and listeners up to that limit may be present on the bus at one time Although sev eral devices may be commanded to listen simultaneously the bus can have only one active talker or communications would be scrambled A device is placed in the talk or listen state by sending an appropriate talk or listen com mand These talk and listen commands are derived from an instrument s primary address The primary address may have any value between 0 and 31 and is generally set by rear panel DIP switches or programmed in from the front panel of the instrument The actual listen address value sent out over the bus is obtained by ORing the primary address with 20 For example if the primary address is 14 the actual listen address is 34 34 14 20 In a similar manner the talk address is obtained by ORing the primary address with 40 With the present example the talk address derived from a primary address of 14 would be 54 54 14 40 The IEEE 488 standards also include another addressing mode called secondary address ing Secondary addresses lie in the range of 60 7F Note however that many devices including the Model 6485 do not use secondary addressing Once a device is addressed to talk or listen the appropriate bus transactions take place For example if the instrument is addressed to talk it places its data string on the bus one byte at a time The controller reads t
186. ine frequency is dis played For example FREQ 60Hz After the detected line frequency is displayed information on the selected remote interface is displayed a GPIB If the GPIB is the selected interface the instrument will display the selected language SCPI or DDC and primary address Examples SCPI ADDR 14 DDC ADDR 14 b RS 232 If RS 232 is the selected interface the instrument will display the baud rate setting For example RS 232 9600b If the FACTory setup is selected as the power on setup the unit is placed in the default reading mode after the communication information is displayed If a setup other than FACTory is selected the configured setup will be displayed For exam ple if the USRI setup User Setup 1 is selected USING USR1 To configure power on Set up Display PWR ON menu press CONFIG and then SETUP Use A or range keys to scroll through the menu items Press Enter to select or Exit to quit without changing power on setup If DDC language is selected user setups cannot be saved as power on setup Model 6485 Picoammeter Instruction Manual Getting Started 1 15 Default settings The Model 6485 can be restored to one of five setup configurations factory default FACT three user saved USRO USR1 and USR2 and bus default GPIB As shipped from the factory Model 6485 powers up to the factory default settings Factory default set tings provide a general purpose setup for front pane
187. ing Model 6485 to talk after the appropriate query is sent Error queue The error queue holds error and status messages When an error or status event occurs a message that defines the error status is placed in the error queue When a message is placed in the error queue the error available EAV bit in the status byte register is set An error status message is cleared from the error queue when it is read The error queue is considered cleared when it is empty An empty error queue clears the EAV bit in the status byte register Model 6485 Picoammeter Instruction Manual Status Structure 10 19 The error queue holds up to 10 error status messages The commands to read the error queue are listed in Table 10 7 When you read a single message in the error queue the oldest message is read and then removed from the queue If the queue becomes full the message 350 queue overflow will occupy the last memory location On power up the error queue is empty When empty the message 0 No Error is placed in the queue Messages in the error queue are preceded by a code number Negative numbers are used for SCPI defined messages and positive numbers are used for Keithley defined messages The messages are listed in Appendix B As shown in Table 10 7 there are com mands to read the entire message code and message or the code only On power up all error messages are enabled and will go into the error queue as they oc
188. ing precautions e Always grasp the 6485 by the covers e After removing the 6485 from its anti static bag inspect it for any obvious signs of physical damage Report any such damage to the shipping agent immediately e When the 6485 is not installed and connected keep the unit in its anti static bag and store it in the original packing carton Package content The following items are included with every Model 6485 order e Model 6485 Picoammeter with line cord e Low Noise Cable with Male BNC on both ends Model 4801 e Protective BNC Shield Cap CAP 18 e Banana lead to screw terminal adapter Model CA 186 1B Referred to as ground link throughout this manual e Accessories as ordered e Certificate of calibration e Model 6485 User Manual P N LCHR 950 01 e Manual Addenda pertains to any improvements or changes concerning the instru ment or manual Options and accessories Input cables connectors and adapters Model 4801 Input Cable This 4 ft 1 2m low noise coax cable is terminated with male BNC connectors on each end One Model 4801 is included with every order Model 4802 10 This 10 ft 3m low noise coax cable is terminated at one end with a male BNC connector the other end is unterminated Model 4803 Low Noise Cable Kit This cable kit includes 15m 50 ft of low noise coax cable 10male BNC connectors 5 female BNC chassis mount connectors Model 7078 TRX BNC adapter 3
189. irements a Requirements Description or reference Macro information Not applicable Response to IDN identification See Common Commands in Section 12 Storage area for PUD and PUD Not applicable Resource description for RDT and RDT Not applicable Effects of RST RCL and SAV See Common Commands in Section 12 TST information See Common Commands in Section 12 Status register structure See Status Structure in Section 11 Sequential or overlapped commands All are sequential except INIT which is overlapped Operation complete messages OPC OPC and WAI see Common Commands in Section 12 Table G 2 Coupled commands Sending Changes CALC2 NULL ACQ CALC2 NULL OFFS lt n gt Acquired value TRAC POIN lt n gt TRAC FEED CONT lt name gt NEV TRAC CLE TRAC FEED CONT lt name gt TRAC CLE NEV GPIB 488 1 Protocol The Model 6485 supports two GPIB protocols SCPI 488 2 and 488 1 The 488 1 proto col is included to significantly increase speed over the GPIB When using the 488 1 protocol throughput is enhanced up to 10 times for data sent to the 6485 command messages and up to 20 times for data returned by the Picoammeter response messages The speed of readings sent over the GPIB 1s also increased NOTE With the 488 1 protocol selected you will still use SCPI commands to program the 6485 Operation differences between the two protocols are discussed in this appendix G 4 IEEE 488 and SCP
190. is terminated 0 1 1 0 lt RMT gt Message exchange protocol Two rules summarize the message exchange protocol Rule 1 Always tell Model 6485 what to send to the computer The following two steps must always be performed to send information from the instrument other computer 1 Send the appropriate query command s in a program message 2 Address Model 6485 to talk Rule 2 The complete response message must be received by the computer before another program message can be sent to Model 6485 RS 232 interface reference Sending and receiving data The RS 232 interface transfers data using seven or eight data bits and one stop bit Parity selections include none odd or even When using the RS 232 interface the unit will not respond to DDC or general GPIB com mands undefined header error see Table 9 1 See Table 13 3 for SCPI equivalents to selected general commands RS 232 settings The procedure to select and configure the RS 232 interface is provided in Selecting and configuring an interface page 9 2 Make sure the controller you connect to Model 6485 also uses these settings NOTE You can break data transmissions by sending a C or X character string to Model 6485 This clears any pending operation and discards any pending out put Model 6485 Picoammeter Instruction Manual Remote Operation 9 17 Baud rate The baud rate is the rate at which Model 6485 and the programming terminal communi cate You can
191. isabled RO Auto Range SENSe 1 CUR Rent DC RANGe UPPer AUTO ON RI 2nA SENSe 1 CUR Rent DC RANGe UPPer 2e 9 R2 20nA SENSe 1 CUR Rent DC RANGe UPPer 20e 9 R3 200nA SENSe 1 CUR Rent DC RANGe UPPer 200e 9 R4 2UA SENSe 1 CUR Rent DC RANGe UPPer 2e 6 R5 20UA SENSe 1 CUR Rent DC RANGe UPPer 20e 6 R6 200UA SENSe 1 CUR Rent DC RANGe UPPer 200e 6 Model 6485 Picoammeter Instruction Manual Table D 1 continued Device dependent command summary Mode Range cont Trigger Mode Command R7 R8 R9 TO TI T2 T3 T4 T5 T6 T7 Description Equivalent SCPI commands 2mA SENSe 1 CUR Rent DC RANGe UPPer 2e 3 20mA SENSe 1 CUR Rent DC RANGe UPPer 20e 3 Cancel Auto range SENSe 1 CUR Rent DC RANGe UPPer AUTO OFF Continuous triggered by talk One shot triggered by talk ARM SEQuence 1 COUNt 1 TRIGger SEQuence 1 COUNt 1 Continuous triggered by GET ARM SEQuence 1 SOURce BUS ARM SEQuence 1 COUNt 1 TRIGger SEQuence 1 COUNt INF INIT IMMediate One shot triggered by GET ARM SEQuence 1 SOURce BUS ARM SEQuence 1 COUNt INF TRIGger SEQuence 1 COUNt 1 INIT IMMediate Continuous triggered by X One shot triggered by X Continuous triggered by External Trigger ARM SEQuence 1 SO
192. isters STATus STATus subsystem OPERation CONDition Read operation condition register MEASurement CONDition Read measurement condition register QUEStionable CONDition Read questionable condition register Event registers As Figure 10 1 shows each status register set has an event register When an event occurs the appropriate event register bit sets to 1 The bit remains latched to 1 until the register is reset Reading an event register clears the bits of that register CLS resets all four event registers The commands to read the event registers are listed in Table 10 5 For details on reading registers see Reading registers page 10 6 Table 10 5 Common and SCPI commands event registers ESR Read standard event status register STATus STATus subsystem OPERation EVENt Read operation event register MEASurement EVENt Read measurement event register QUEStionable EVENt Read questionable event register Note Power up and CLS resets all bits of all event registers to 0 STATus PRESet has no effect Model 6485 Picoammeter Instruction Manual Status Structure 10 17 Event enable registers As Figure 10 1 shows each status register set has an enable register Each event register bit is logically ANDed amp to a corresponding enable bit of an enable register Therefore when an event bit is set and the corresponding enable bit is set as programmed by the user the output Summa
193. its Rate and Filters Relative mX b m X b Reciprocal and Log Buffer Triggering Limit test Remote Operation Status Structure Common Commands SCPI Signal Oriented Measurement Commands DISPlay FORMat and SYSTem SCPI Reference Tables Performance Verification Calibration Routine Maintenance Appendices to this manual contain specification and also provide additional information on specific topics The appendices are organized as follows Appendix A Specifications Appendix B Status and Error Messages Appendix C Measurement Considerations Appendix D DDC Emulation Commands Appendix E Example Programs Appendix F IEEE 488 Bus Overview Appendix G IEEE 488 and SCPI Conformance Information Appendix H Remote Calibration Appendix I Applications Guide Model 6485 Picoammeter Instruction Manual Getting Started 1 3 General information Warranty information Warranty information is located at the front of this manual Should your Model 6485 require warranty service contact the Keithley representative or authorized repair facility in your area for further information When returning the instrument for repair be sure to fill out and include the service form at the back of this manual to provide the repair facility with the necessary information Contact information Worldwide phone numbers are listed at the front of this manual If you have any questions please contact your local Keithley representative or cal
194. ity EMC requirements of the European Union as denoted by the CE mark However it is still possible for sensitive measurements to be affected by exter nal sources In these instances special precautions may be required in the measurement setup Sources of EMI include e Radio and TV broadcast transmitters e Communications transmitters including cellular phones and handheld radios e Devices incorporating microprocessors and high speed digital circuits e Impulse sources as in the case of arcing in high voltage environments C 6 General Measurement Considerations Model 6485 Picoammeter Instruction Manual The effect on instrument performance can be considerable if enough of the unwanted sig nal is present The effects of EMI can be seen as an unusually large offset or in the case of impulse sources erratic variations in the displayed reading The instrument and experiment should be kept as far away as possible from any EMI sources Additional shielding of the instrument experiment and test leads will often reduce EMI to an acceptable level In extreme cases a specially constructed screen room may be required to sufficiently attenuate the troublesome signal External filtering of the input signal path may be required In some cases a simple one pole filter may be sufficient In more difficult situations multiple notch or band stop fil ters tuned to the offending frequency range may be required Connecting multiple capac itors
195. l and Log 5 1 REM 1 8 Remote calibration H 1 Remote setup operation 1 16 REN remote enable 9 7 Response 9 15 Message Terminator RMT 9 16 time 4 10 restore setup 1 15 Routine maintenance 17 1 RS 232 1 10 connections 9 18 RS 232 interface 9 2 9 3 9 16 RS 232 settings 9 16 safety shield 3 3 Safety symbols and terms 1 3 SAVE 1 8 Saving calibration 16 11 scientific SCI 4 3 scientific notation 1 12 SCPI commands F 11 amps function 3 5 autozero 2 3 buffer 6 5 limit tests 8 7 reset registers and clear queues 10 4 system 13 8 triggering 7 9 SCPI language 9 2 SCPI programming filters 4 12 line frequency 1 13 mX b m X b and log 5 7 range and digits 4 4 rate 4 6 relative 5 4 zero check and zero correct 2 15 SCPI Reference Tables 14 1 SCPI Signal Oriented Measurement Commands 12 1 SDC selective device clear 9 8 SDEViation 6 7 select power on setup 1 15 Sending a response message 9 15 Sending and receiving data RS 232 9 16 SENSe command summary 14 5 serial number 1 18 11 3 Serial polling and SRQ 10 9 Serial Port See RS 232 Service request enable register 10 8 Setting and controlling relative 5 2 Setting line voltage and replacing line fuse 17 2 SETUP 1 8 shielding I 7 I 8 Shielding vs Guarding I 10 Short form rules 9 12 Single command messages 9 13 SLOW 1 8 Source capacitance I 6 source impedance I 5 Source resistance I 5 Source Resistance minimum recommended 1 6 SPE SPD serial polling 9 9 SPE
196. l 6485 Picoammeter Instruction Manual Table B 1 continued Status and error messages Reading overflow Buffer available Buffer full Input overvoltage Standard events Operation complete Operation events Device calibrating Device sweeping Waiting in trigger layer Waiting in arm layer Re entering the idle layer Questionable events Questionable calibration Command warning Calibration errors Date of calibration not set Next date of calibration not set Calibration data invalid Measurement offset data invalid Measurement gain data invalid Not permitted with cal locked Not permitted with cal un locked Voltage offset not converging Current offset not converging Lost data errors GPIB address lost Power on state lost DC calibration data lost Calibration dates lost GPIB communication language lost Communication errors Invalid system communication ASCII only with RS 232 Model 6485 Picoammeter Instruction Manual Status and Error Messages B 5 Table B 1 continued Status and error messages Additional more informative command execution errors Illegal with storage active Insufficient vector data Expression list full Undefined expression exists Expression not found Definition not allowed Expression cannot be deleted Not an operator or number Mismatched parentheses Not a number of data handle Mismatched brackets Too many parentheses Entire expression not parsed Unknown token Error parsi
197. l 6485 responds to the IFC command by canceling front panel TALK or LSTN lights if the instrument was previously placed in one of those states Note that this command does not affect the status of the instrument settings data and event registers are not changed To send the IFC command the controller must set the IFC line true for a minimum of 100us LLO local lockout Use the LLO command to prevent local operation of the instrument After the unit receives LLO all its front panel controls except the POWER are inoperative In this state pressing LOCAL will not restore control to the front panel The GTL command restores control to the front panel GTL go to local Use the GTL command to put a remote mode instrument into local mode The GTL com mand also restores front panel key operation DCL device clear Use the DCL command to clear the GPIB interface and return it to a known state Note that the DCL command is not an addressed command so all instruments equipped to implement DCL will do so simultaneously When Model 6485 receives a DCL command it clears the input buffer and output queue cancels deferred commands and clears any command that prevents the processing of any other device command A DCL does not affect instrument settings and stored data SDC selective device clear The SDC command is an addressed command that performs essentially the same function as the DCL command However since each device must be i
198. l one of our Application Engineers at 1 800 348 3735 U S and Canada only Safety symbols and terms The following symbols and terms may be found on the instrument or used in this manual The AN symbol on an instrument indicates that the user should refer to the operating instructions located in the manual The A symbol on the instrument shows that high voltage may be present on the termi nal s Use standard safety precautions to avoid personal contact with these voltages The WARNING heading used in this manual explains dangers that might result in per sonal injury or death Always read the associated information very carefully before per forming the indicated procedure The CAUTION heading used in this manual explains hazards that could damage the instrument Such damage may invalidate the warranty Unpacking and inspection Inspection for damage The Model 6485 was carefully inspected electrically and mechanically before shipment After unpacking all items from the shipping carton check for any obvious signs of physi cal damage that may have occurred during transit There may be a protective film over the display lens which can be removed Report any damage to the shipping agent immedi ately Save the original packing carton for possible future shipment Before removing the 6485 Picoammeter from the bag observe the precautions on handling discussed below 1 4 Getting Started Model 6485 Picoammeter Instruction Manual Handl
199. l operation while the bus default GPIB settings do the same for remote operation Factory and GPIB default settings are listed in Table 1 2 The instrument will power up to whichever default setup was saved as the power on setup NOTE Atthe factory the factory default setup is saved into the USRO USRI and USR2 setups Front panel setup operation To save a user setup Configure Model 6485 for the desired measurement application 2 Press SAVE to access the save setup menu 3 Use the Aor W key to display the desired memory location 0 USRO 1 USRI 2 USR2 4 Press ENTER NOTE Saved setups should not be used in DDC mode and will not be recalled upon power up in DDC mode To restore any setup 1 Press SETUP to display the restore menu 2 Use the A or key to display the desired setup FACT USRO USR1 USR2 or GPIB 3 Press ENTER To select power on setup 1 Press CONFIG and then SETUP to display the power on menu 2 Use the A or key to display the desired setup FACT USRO USR1 USR2 or GPIB 3 Press ENTER 1 16 Getting Started Model 6485 Picoammeter Instruction Manual Remote setup operation Saving and restoring user setups The SAV and RCL commands are used to save and recall user setups These commands are documented in Section 9 Restoring factory or GPIB default setups The SYSTem PRESet command returns Model 6485 to the factory defaults and the RST command returns it to t
200. late will provide guarding or noise shielding for the DUT or test circuit It will also serve as a mounting panel for DUT or test circuits The guard plate must be insu lated with appropriate spacing from the chassis of the test fixture commensurate with the external source used Connectors terminals and internal wiring Basic connector requirements include a female BNC connector and two banana jacks The banana jacks provide for connection to an external power supply The banana jacks must be insulated from the chassis of the test fixture DUT and test circuits are to be mounted on the guard plate using insulated terminals To minimize leakage select terminals that use virgin Teflon insulators Inside the test fixture use an insulated wire to connect the shell of the BNC connector to the guard plate the guard plate will serve as a noise shield Handling and cleaning test fixtures Dust body oil solder flux and other contaminants on connector and terminal insulators can significantly decrease the leakage resistance resulting in excessive leakage currents Contaminants on DUT and test circuit components can create a leakage path The leakage currents may be large enough to corrupt low level measurements Handling tips e Do not touch the bodies of DUT or test circuit components If you can not handle them by their leads use clean cotton gloves to install them in the test fixture e Do not touch any connector or terminal insulator
201. le analog outputs are listed in Table 1 1 The 2V analog output signal is not corrected during calibration Gain errors of up to 3 may appear at this output depending on range The output impedance is 1kQ To minimize the effects of loading the input impedance of the device connected to the ANALOG OUT should be as high as possible For example for a device that has an input impedance of 1OMQ the error due to loading will be approx imately 0 01 High capacitance connected to the analog output will increase the rise time Rel and the result of mX b m X b or LOG have no affect on the analog output The 2V analog output is scaled only to the actual input Model 6485 Picoammeter Instruction Manual Getting Started 1 11 Figure 1 3 Typical analog output connections Test Lead Measuring Device Model 6485 Rear Panel i e Chart recorder A Connections Input from 1kQ ge Output Prescaler Input Resistance of die measuring device Fuse Model 6485 Poly fuse Auto resetting B Equivalent Circuit Table 1 1 Example 2V analog output values Applied Analog output 10 5nA 1 05V 1 65mA 1 65V Output values are within 3 of nominal value 1 12 Getting Started Model 6485 Picoammeter Instruction Manual Display Readings can be displayed in engineering units or scientific notation see Units page 4 3 for details Annunciators indicate various states of operation See Fr
202. le operating within the trigger model except when a READ or MEASure is being processed e ABORt e SYSTem PRESet e TRG or GET e RST e RCL lt NRf gt NOTE For fastest response use SDC or DCL to return to idle see Section 10 for details on general bus commands Trigger model operation Once the instrument is taken out of idle operation proceeds through the trigger model to perform a measurement measure action Model 6485 Picoammeter Instruction Manual Triggering 7 5 NOTE The following discussion focuses on the front panel trigger model Figure 7 1 However equivalent SCPI commands are included where appropriate Event detectors and control sources A control source holds up operation until the programmed event occurs and is detected Note that there are two detector bypasses A bypass around a detector is only enabled if the appropriate TLink control source is selected See TLink control source Arm In and Trig ger In as follows for details Arm In source The Arm In control sources are explained as follows Immediate ARM SOURce IMMediate Event detection for the arm layer is satisfied immediately allowing operation to continue into the trigger layer GPIB ARM SOURce BUS Event detection for the arm layer is satisfied when a bus trigger GET or TRG is received by Model 6485 Timer ARM SOURce TIMer Event detection for the arm layer is immedi ately satisfied after the instrument leaves the idl
203. limits for limit 2 are 1mA A OmA reading passes both limit 1 and limit 2 tests A 1 5mA reading passes limit 1 but fails limit 2 A 2 5mA reading fails both limit 1 and limit 2 Figure 8 2 Limit tests example 2mA lt Fail LO Limit 2mA os Fail gt HI Limit Pass ImA LO Limit i Pass se Fail 1mA HI Limit Limit 1 Test Wide Pass Band Limit 2 Test Narrow Pass Band Model 6485 Picoammeter Instruction Manual Limit Tests 8 3 The 2 stage limit testing process is shown in Figure 8 3 If limit 1 fails the L1 message is displayed and the test is finished Limit 2 is not tested because the pass band relationship between the two stages implies that if limit 1 fails limit 2 must also fail If limit 1 passes the limit 2 test is performed If limit 2 fails the L2 message is displayed If both limit 1 and limit 2 pass the OK message is displayed The display messages for limit tests are summarized in Table 8 1 A test is only performed if it is enabled Therefore you can perform a single stage test or a 2 stage test In the flowchart Figure 8 3 operation simply proceeds through a disabled test Table 8 1 Test limit display messages Display Limit 1 Limit 2 Message Test Result Test Result Pass Pass Fail Not Performed Pass Fail 8 4 Limit Tests Model 6485 Picoammeter Instruction Manual Figure 8 3 Operation model for limit test Measure DUT
204. ll be at same voltages as applied to the BNC shell Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 5 Figure 2 2 Maximum input levels Input HI Max Continuous Input Signal Input LO O 42V Peak Chassis Ground a Maximum Continuous Input Signals 220V Peak DC to 60Hz sine wave Low noise input cables When making precision measurements you should always use low noise cables The fol lowing low noise cables are recommended for use with Model 6485 Model 4801 Input Cable This 4 ft 1 2m low noise triax cable is terminated with male BNC connectors on each end One Model 4801 is included standard with every order Model 4802 10 This 10 ft 8m low noise BNC cable is terminated at one end with a male BNC connector the other end is unterminated Model 4803 Low Noise Cable Kit This cable kit includes e 15m 50 ft of low noise coax cable e 10 male BNC connectors e 5 female BNC chassis mount connectors NOTE Asa general rule always use the shortest possible cable for measurements 2 6 Measurement Concepts Model 6485 Picoammeter Instruction Manual Basic connections to DUT Connections Basic connections are shown in Figure 2 3 the DUT is the current to be measured Circuit high is connected to the center conductor of the input connector and circuit low is con nected to the connector s shell Figure 2 3 Basic connections HI O pu INPUT Maximum Continuous Input
205. lt name gt TSTamp FORMat lt name gt DATA Clear readings from buffer Query bytes available and bytes in use Specify number of readings to store 1 to 2500 Returns number of readings actually stored in buffer Select source of readings SENSe 1 CALCulate 1 or CALCulate2 Select buffer control mode NEVer or NEXT Timestamp Select timestamp format ABSolute or DELTa Read all readings in buffer FORMat FORMat Subsystem Section 13 ELEMents lt list gt Specify data elements for TRACe DATA response F message READing UNITs TIME and STATus On RST or SYSTem PRESet resets to default values CALCulate3 CALCulate3 Subsystem FORMat lt name gt DATA Select buffer statistic MINimum MA Ximum MEAN SDEViation or PKPK Read the selected buffer statistic Note SYSTem PRESet and RST have no effect on TRACe commands The listed defaults are power on defaults 6 6 Buffer Model 6485 Picoammeter Instruction Manual A TRACe FREE Two values separated by commas are returned The first value indicates how many bytes of memory are available and the second value indicates how many bytes are reserved to store readings B TRACe FEED lt name gt Name parameters e SENSe Raw input readings are stored in the buffer e CALCulatel The results of the mX b m X b or log calculation are stored in the buffer See Section 5 for information on mX b m X b or log e CALCulate2
206. mand requests queries the pro grammed status of that command When a query command is sent and Model 6485 is addressed to talk the response message 1s sent to the computer 1 20 Getting Started Model 6485 Picoammeter Instruction Manual Measurement Concepts Measurement overview Explains the basic measurement capabilities of Model 6485 Performance considerations Covers a couple of considerations that affect overall performance warm up and autozero Connection fundamentals Covers fundamental information about connecting test circuits to the picoammeter Zero check and zero correct Provides operation information on these two important aspects of the basic measurement process Measurement considerations Summarizes the various factors that affect low level measurements 2 2 Measurement Concepts Model 6485 Picoammeter Instruction Manual Measurement overview The basic measurement capabilities of Model 6485 are summarized in Table 2 1 Accu racy for each measurement function and range is listed in specifications Appendix A Table 2 1 Basic measurement capabilities Reading Range Available Ranges 20fA to 2I1mA 2nA 20nA 200nA 2uA 20uA 200uA 2mA and 20mA Performance considerations Warm up period Model 6485 can be used within one minute after it is turned on However the instrument should be turned on and allowed to warm up for at least one hour before use to achieve rated accuracy If t
207. mat for reading status registers ASC Section 10 ASCu HEXadecimal OCTal or BINary Note RST default is NORMal SYSTem PRESet default is SWAPped 13 4 DISPlay FORMat and SYSTem Model 6485 Picoammeter Instruction Manual A FORMat DATA lt type gt lt length gt Parameters ASCii ASCII format REAL 32 Binary IEEE 754 single precision format SREal Binary IEEE 754 single precision format NOTE lt length gt is not used for the ASCii or SREal parameters It is optional for the REAL parameter If you do not use lt length gt with REAL lt length gt defaults to 32 single precision format The double precision format lt length gt 64 is not supported by Model 6485 The response to READ FETCh MEASure TRACe DATA CALC1 DATA or CALC2 DATA over the GPIB can be returned in either the ASCui or binary format All other queries are returned in ASCu regardless of the selected format Over the RS 232 interface only the ASCII format is allowed NOTE Regardless of which data format for output strings is selected the instrument will only respond to input commands using the ASCII format ASCII data format The ASCII data format is in a direct readable form for the operator Most BASIC lan guages easily convert ASCII mantissa and exponent to other formats However some speed is compromised to accommodate the conversion Figure 13 1 shows an example ASCII string that includes all the data elements See ELEMents fo
208. mum 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 ca bles or jumpers 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 Al ways 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 equipment may be impaired Do not exceed the maximum signal levels of the instruments and accessories as defined in the specifications and operating in formation 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 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 applied 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 re
209. n 9 19 Table 9 2 RS 232 connector pinout Pin number Description DCD data carrier detect TXD transmit data RXD receive data DTR data terminal ready GND signal ground DSR data set ready RTS ready to send CTS clear to send No connections RTS and CTS are tied together DCD DTR and DSR are tied together Table 9 3 PC serial port pinout DB 9 DB 25 Signal pin number pin number DCD data carrier detect RXD receive data TXD transmit data DTR data terminal ready ina GND signal ground DSR data set ready RTS request to send CTS clear to send RI ring indicator 2 3 4 5 6 7 8 9 Error messages See Appendix B for RS 232 error messages 9 20 Remote Operation Model 6485 Picoammeter Instruction Manual 10 Status Structure Overview Provides an operational overview of the status structure for Model 6485 Clearing registers and queues Covers the actions that clear reset registers and queues Programming and reading registers Explains how to program enable registers and read any register in the status structure Status byte and service request SRQ Explains how to program the status byte to generate service requests SRQs Shows how to use the serial poll sequence to detect SRQs Status register sets Provides bit identification and command information for the four status register sets standard event status operation event status measure ment event sta
210. n Manual Aborting calibration You can abort the calibration procedure at any time by pressing the EXIT key Current calculations When calibrating the 2nA 2uUA current ranges you must calculate the actual current val ues from the applied calibrator voltages and the characterized Model 5156 Calibration Standard resistor values Calibration currents are calculated as follows I V R Where I required calibration current V calibrator voltage R actual standard resistor value For example assume you are calibrating the 20nA range using a 2V calibrator voltage with an actual 100 5MQ standard resistor value The actual calibration current 1s 2V 100 5MQ 19 9005nA Calibration procedure The calibration procedure should be performed in the following order Preparing for calibration Offset voltage calibration Current calibration Entering calibration dates and saving calibration Locking out calibration Preparing for calibration 1 Turn on the Model 6485 and the calibrator and allow them to warm up for at least one hour before performing calibration Press MENU select CAL then press ENTER The instrument will display the fol lowing CAL VOFFSET Use the up or down RANGE key to display the following CAL UNLOCK Press ENTER The instrument will prompt for the calibration code CODE 000000 Model 6485 Instruction Manual Calibration 16 7 Enter the current calibration code on the display Factory default
211. n and calibration information TSTAMP Timestamp format can be ABSolute or DEL Ta Section 6 UNITS Readings can be displayed in ENGineering units or Section 6 SClentific notation TEST Run display or key tests Section 17 SNUM Displays the units serial number Section 11 LFREQ Line frequency can be manually set to 50 or 60 Hz or Line frequency AUTOmatically set The number after AUTO indicates page 1 13 present detected frequency value SCPI programming SCPI programming information is integrated with front panel operation throughout this manual SCPI commands are listed in tables and additional information that pertains exclusively to remote operation is provided after each table The SCPI tables may refer ence you to other sections of this manual NOTE Except for Section 14 most SCPI tables in this manual are abridged That is they do NOT include most optional command words and query commands Optional command words and query commands are summarized as follows Model 6485 Picoammeter Instruction Manual Getting Started 1 19 Optional command words In order to be in conformance with the IEEE 488 2 standard Model 6485 accepts optional command words Any command word that is enclosed in brackets is optional and does not have to be included in the program message Query commands Most command words have a query form A query command is identified by the question mark that follows the command word A query com
212. n precision measurements refer to the Low Level Measurements handbook which is available from Keithley Instruments It is critical that the picoammeter perform the measurement without interfering with the flow of current in the circuit possibly affecting operation or inducing additional errors Voltage burden is the terminal voltage of a picoammeter and ideally this voltage should be zero no resistive effect Some meters such as DMMs utilize a shunt resistor to measure the voltage drop across a known resistance and a typical burden of 200mV is not unusual The Keithley 6485 uses an alternative approach referred to as a feedback picoammeter where the voltage burden is simply the input voltage of an operational amplifier Further more since the input voltage of the operational amplifier is the output voltage divided by the gain typically 500 000 the voltage burden is in the microvolt range Leakage currents and guarding Leakage currents are generated by high resistance paths between the measurements circuit and nearby sources These currents can considerably degrade the accuracy of low current measurements Some ways to reduce leakage currents are to use good quality insulators reduce humidity and use guarding Guarding can also be used to reduce the effect of shunt capacitance in the measurement circuit One way to reduce leakage currents 1s to use good quality insulators when building the test circuit Some good quality insulators
213. n the header can be upper or lower case The lt NRf gt numeric representation for mat parameter type is used to send decimal values and does not use a header The follow ing examples show the proper parameter syntax for setting bits B5 B3 and B2 b101100 Binary format lt NDN gt parameter type h2C Hexadecimal format lt NDN gt parameter type q54 Octal format lt NDN gt parameter type 44 Decimal format lt NRf gt parameter type Valid characters for the non decimal parameter values are shown as follows lt NDN gt Format Valid Characters Binary 1 s and 0 s Hexadecimal 0 through 9 and A through F Octal 0 through 7 10 6 Status Structure Model 6485 Picoammeter Instruction Manual Figure 10 2 16 bit status register Bit Position B7 B6 B5 B4 B3 B2 B1 BO Binary Value 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Decimal Weights 128 64 32 16 8 4 2 1 2 2 2 2 2 2 2 2 A Bits 0 through 7 Bit Position B15 B14 B13 B12 B11 B10 B9 B8 Binary Value 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Decimal Weights 32768 16384 8192 4096 2048 1024 512 256 2 27 Vag 2 2 2 2 2 B Bits 8 through 15 Reading registers Any register in the status structure can be read by using the appropriate query com mand The following explains how to interpret the returned value response message The actual query commands a
214. nal command words 1 e SENSE 1 Do not use the colon at the beginning of a program message Always use the short form versions of commands and parameters Minimize the amount of white space in command strings Keep numeric parameters simple 1 e 1 vs 1 000e 00 Oy Et I a Use all upper case Response messages A response message 1s the message sent by the instrument to the computer in response to a query command program message Sending a response message After sending a query command the response message is placed in the output queue When Model 6485 is addressed to talk the response message is sent from the output queue to the computer Multiple response messages If you send more than one query command in the same program message see Multiple Command Messages the multiple response messages for all the queries is sent to the computer when Model 6485 is addressed to talk The responses are sent in the order that the query commands were sent and are separated by semicolons Items within the same query are separated by commas The following example shows the response message for a program message that contains four single item query commands 0 1 1 0 9 16 Remote Operation Model 6485 Picoammeter Instruction Manual Response Message Terminator RMT Each response is terminated with an LF line feed and EOI end or identify The follow ing example shows how a multiple response message
215. nator a value for M and a value for B This configuration is used for both the mX b and the m X b calculations Therefore changing either configuration of the mX b or the m X b calculation also changes the other calculation s configuration 6 To change the units designator default is X press the cursor key and use the A and W range keys The character can be any letter in the alphabet A through 2 7 Press ENTER The MATH annunciator and the units designator will turn on and the result of the calculation will be displayed Note that the calculation will be applied to all measurement functions Logarithmic This calculation converts input readings to logarithm base 10 values The calculation is performed as follows log oX i where X is the input reading y is the logarithmic result For example Assume that exactly 1mA is being measured by the Model 6485 log j91 000000mA 3 NOTE This calculation uses the absolute value of the normal input reading as the log of a negative number cannot be computed Model 6485 Picoammeter Instruction Manual Relative mX b m X b reciprocal and log 5 7 SCPI programming mX b m X b and log Table 5 3 SCPI commands mX b m X b and log CALCulate 1 CALCulatel Subsystem FORMat lt name gt Select calculation MXB RECiprocal or LOG10 D1 LOGI0 KMATh Path to configure mX b and m X b MMFactor lt n gt Specify scale factor M for mX b and m X b 9 999
216. nction keys 1 7 General IEEE 488 bus commands 9 7 General Measurement Considerations C 1 General photo diode leakage I 23 GET group execute trigger 9 9 GPIB Protocol selection G 4 trigger link cables and adapters 1 5 GPIB 488 1 Protocol G 3 GPIB and trigger link cables and adapters 1 5 GPIB interface 9 2 9 3 GPIB status indicators 9 9 Ground link 1 4 1 9 C 2 Ground loops C 2 GTL go to local 9 8 Guard plate 2 10 Guarding to reduce leakage currents I 3 HALT 1 8 Handle 1 8 Handling precautions 1 4 Handling tips 2 10 Handshake lines F 5 Humidity C 4 identification query 11 3 Idle and initiate 7 4 IEEE command groups F 13 IEEE 488 1 10 bus command summary F 7 bus configuration F 4 Bus Overview F 1 connector 9 5 documentation requirements G 2 SCPI Conformance Information G 1 IEEE 488 handshake sequence F 6 IEEE 488 2 common commands and queries 11 2 IFC interface clear 9 8 Input 1 9 cables connectors and adapters 1 4 connector 2 3 protection 2 11 trigger requirements 7 12 Input bias current I 3 Inspection for damage 1 3 Instruction Manual 1 5 Interface available 9 2 configuration 9 3 function codes F 14 selection 9 3 internal wiring 2 10 Keithley 237 BNC TRX 15 4 Keithley 4801 15 4 Keithley CAP 18 15 4 Keithley Model 5156 15 4 KEY test 17 4 Languages 9 2 Leakage currents and guarding I 2 Light C 4 LIMIT 1 8 Limit test configuration 8 5 Limit Tests 8 1 Limits configuration menu 8 5 Line freque
217. ncy 1 13 Line fuse location 17 3 Line fuse ratings 17 2 Line power connection 1 12 LLO local lockout 9 8 Locking out calibration 16 12 LOG 1 7 D 2 Logarithmic 5 6 Long form and short form versions 9 12 Low noise input cables 2 5 LSTN 1 8 M X B 1 7 Magnetic fields C 5 Making connections I 10 management lines bus F 5 Manual ranging 4 2 manually keying in REL 5 3 MATH 1 8 Maximum input levels 2 4 MEAN 6 7 Measure action 7 6 Measurement considerations 2 16 C 2 I 2 measurement errors avoiding I 10 Measurement event status 10 13 Measurement overview 2 2 Measurement ranges 4 2 Measuring High Resistance Using the 6485 I 20 Measuring high resistance with external bias source I 19 MED 1 8 Median filter 4 7 MEDN 1 7 MENU 1 7 Menu 1 18 16 5 Model 1050 padded carrying case 1 5 Model 4288 1 single fixed rack mount kit 1 5 Model 4288 2 side by side rack mount kit 1 5 Model 4288 4 side by side rack mount kit 1 5 Model 4801 1 4 Model 4802 10 1 4 Model 4803 1 4 Model 6485 interface function codes F 14 Model 7078 TRX BNC adapter 1 4 Model 8502 trigger link adapter 1 5 Model 8503 DIN to BNC trigger cable 1 5 Models 7007 1 and 7007 2 shielded GPIB cables 1 5 Models 8501 1 and 8501 2 trigger link cables 1 5 Multiple command messages 9 14 Multiple response messages 9 15 MX B 1 7 mX b m X b reciprocal and Logarithmic 5 5 Noise I 5 Noise and safety shields 2 8 Noise and source im
218. nd the external voltage source be sufficiently low impedance and capable of carrying the short circuit current of the source in order that the LO not exceed 42V CAUTION The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the instrument The maximum input voltage and current to Model 6485 is 220V peak and 21mA Exceeding either of these values may cause damage to the instrument that is not covered by the warranty To achieve optimum precision for low level current measurements input bias current and voltage burden can be minimized by performing the offset correction procedure Informa tion about these offsets are provided in Measurement considerations on page I 2 NOTE After overloading with high voltage it may take several minutes for the input current to drop to within specified limits Input current can be verified by plac ing the protection cap on the input BNC connector and then use the ground link to connect COMMON and CHASSIS ground With the instrument on the 2nA range and zero check disabled allow the reading to settle until the input bias current is within specifications The specifications for input bias current are included in the offset portion of the accuracy specification listed in Appendix A Model 6485 Picoammeter Instruction Manual Measurements 3 3 Perform the following steps to measure current Step 1 Enable zero check Zero check should always be enabled before making conn
219. ndicates that it is ready for the next byte of data Bus description The IEEE 488 bus which is also referred to as the GPIB General Purpose Interface Bus was designed as a parallel transfer medium to optimize data transfer without using an excessive number of bus lines In keeping with this goal the bus has only eight data lines that are used for both data and with most commands Five bus management lines and three handshake lines round out the complement of bus signal lines A typical setup for controlled operation is shown in Figure F 1 Generally a system will contain one controller and a number of other instruments to which the commands are given Device operation is categorized into three operators controller talker and listener The controller controls the instruments on the bus The talker sends data while a listener Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 3 receives data Depending on the type of instrument any particular device can be a talker only a listener only or both a talker and listener There are two categories of controllers system controller and basic controller Both are able to control other instruments but only the system controller has the absolute authority in the system In a system with more than one controller only one controller may be active at any given time Certain protocol is used to pass control from one controller to another The IEEE 488 bus is limited to 15 devices
220. ndividually addressed the SDC command provides a method to clear only selected instruments instead of clearing all instruments simultaneously as is the case with DCL Model 6485 Picoammeter Instruction Manual Remote Operation 9 9 GET group execute trigger GET is a GPIB trigger that is used as an event to control operation Model 6485 reacts to this trigger if it is the programmed control source The control source is programmed from the SCPI TRIGger subsystem SPE SPD serial polling Use the serial polling sequence to obtain Model 6485 serial poll byte The serial poll byte contains important information about internal functions Generally the serial polling sequence is used by the controller to determine which of several instruments has requested service with the SRQ line However the serial polling sequence may be performed at any time to obtain the status byte from Model 6485 Front panel GPIB operation The following paragraphs describe aspects of the front panel that are part of GPIB opera tion including messages status indicators and the LOCAL key Error and status messages See Appendix B for a list of error and status messages associated with IEEE 488 program ming The instrument can be programmed to generate an SRQ and command queries can be performed to check for specific error conditions GPIB status indicators The REM remote TALK talk LSTN listen and SRQ service request annunciators show the GPIB
221. ng Seocho Gu Seoul 137 130 82 2 574 7778 Fax 82 2 574 7838 Postbus 559 4200 AN Gorinchem 0183 635333 Fax 0183 630821 C O Regus Business Centre Frosundaviks All 15 4tr SE 169 70 Solna Sweden Phone 46 8 509 04 679 e Fax 46 8 655 26 10 Kriesbachstrasse 4 e 8600 D bendorf 01 821 94 44 e Fax 01 820 30 81 IFL 85 Po Ai Street Hsinchu Taiwan R O C 886 3 572 9077 Fax 886 3 572 9031 Copyright 2001 Keithley Instruments Inc Printed in the U S A 10 01
222. ng mantissa Error parsing exponent Error parsing value Invalid data handle index Invalid with INFinite ARM COUNT Invalid with INFinite TRIG COUNT Internal system error DDC Status Model Rdg overflow Rdg ready Buffer full IDDC error IDDCO error Trig overrun No remote Number error DDC ready DDC Mode IDDC Error DDC Mode IDDCO Error B 6 Status and Error Messages Model 6485 Picoammeter Instruction Manual Table B 1 continued Status and error messages Keithley 6485 Serial Poll Byte Events DDC Ready DDC Reading Done DDC Buffer Full DDC Reading overflow EE error event SE status event SYS system error event NOTE Errors and status messages with a positive number are instrument dependent Negative errors are reserved by SCPI NOTE SCPI confirmed messages are described in Volume 2 Command Reference of the Standard Commands for Programmable Instruments Refer to the SYSTem ERRor command General Measurement Considerations C 2 General Measurement Considerations Model 6485 Picoammeter Instruction Manual Measurement considerations The following measurement considerations apply to all precision measurements Table 2 5 lists all measurement considerations and indicates where to find detailed information on them For comprehensive information on all measurement considerations refer to the Low Level Measurements handbook which is available from Keithley Ground loops Ground loops
223. nge for the value place the cur sor on the range symbol and scroll using the A and W range keys P pico y nano u micro m milli x1 K kilo M mega G giga T tera A menu item or value is selected by pressing ENTER Limits configuration menu The configuration menu for limits is structured as follows Bullets denote the main items of the menu To access the menu press CONFIG and then LIMIT LIMIT 1 Configure limit 1 test 1 CONTROL Enable or disable limit 1 test 2 HILIM Set the HI limit 9 999999T to 9 999999T 3 LOLIM Set the LO limit 9 999999T to 9 999999T LIMIT 2 Configure limit 2 test 1 CONTROL Enable or disable limit 2 test 2 HILIM Set the HI limit 9 999999T to 9 999999T 3 LOLIM Set the LO limit 9 999999T to 9 999999T Arm layer configuration menu To access the menu press CONFIG and then TRIG Use the A and W range keys to scroll to the ARM menu e ARM IN Select the start of test option IMM Immediate Test starts when LIMIT key is pressed 8 6 Limit Tests Model 6485 Picoammeter Instruction Manual Perform limit tests Step 1 Configure test system As previously explained testing the system could be as simple as connecting a DUT to Model 6485 Step 2 Configure measurement Configure Model 6485 for the desired measurement as covered in the previous sections of this manual Step 3 Configure limit tests Configure Model 648
224. nge occurs the picoammeter will momentarily become a cur rent limited voltage source as shown in Figure I 10 Model 6485 Picoammeter Instruction Manual Applications Guide I 13 Figure I 10 Range change voltage transients 6485 Picoammeter LO Range being R 2mA 20MA 20uA 200A 200nA 2uA 2nA 20nA NOTE The current that can be inadvertently delivered to the DUT is limited by an internal resistance This internal resistance varies as the range is changed For example manually up ranging from 2uA to the 20LA range can never deliver more than 10V 50k6 200uA to the DUT This current will be further limited by any impedance of the DUT Up range input response Figure I 11 illustrates the type of transient voltage that can be expected when up ranging with a full scale input signal 200uA signal on 200UA range up range to 2mA range Both the magnitude and duration of this voltage are reduced for lower current ranges The current limit imposed by the R is also greatly reduced The polarity depends on the polar ity of the input current Figure I 11 was measured with a positive input current l 14 Applications Guide Model 6485 Picoammeter Instruction Manual Figure l 11 Transient Voltage u 50 00 13 25 45 When it is necessary to up range during auto ranging operation multiple ranges may be crossed to find the correct range The duration of the transient in Figure I 11 can be extended in this case but the magnitude
225. nges stated above allow additional time for the instrument s internal temperature to stabilize Typically allow one extra hour to stabilize a unit that is 18 F 10 C outside the specified temperature range Allow the test equipment to warm up for the minimum time specified by the manufacturer Line power The Model 6485 requires a line voltage of 100 120V or 220 240V at a line frequency of 50 to 60Hz Verification tests must be performed within this range Be sure the line voltage setting agrees with the expected line voltage Section 17 Recommended test equipment Table 15 1 summarizes recommended verification equipment You can use alternate equip ment but keep in mind that test equipment accuracy will add to the uncertainty of each measurement Generally the test equipment should have accuracy or uncertainty at least four times better than corresponding Model 6485 specifications Note however that the recommended calibrator listed in Table 15 1 does not meet this requirement for 20uA output 15 4 Performance Verification Model 6485 Instruction Manual Table 15 1 Recommended performance verification equipment Calibrator Fluke 5700A DC Voltage 2V 7ppm 20V Sppm 200V 7ppm DC Current 20uA 550ppm 200uA 100ppm 2mA 55ppm 20mA 55ppm Electrometer Calibration Keithley Model 5156 Nominal Resistance Standard 100MQ 200ppm 1GQ 300ppm Low noise coax cable Keithley 4801 BNC to triax adapter Keithley 237 BNC TRX B
226. nk 3 Trigger Link 4 Trigger Link 5 Trigger Link 6 Ground Ground CON DW oO BPW N 7 12 Triggering Model 6485 Picoammeter Instruction Manual Input trigger requirements An input trigger is used to satisfy event detection for a trigger model layer that 1s using the TLINK control source The input requires a falling edge TTL compatible pulse with the specifications shown in Figure 7 5 Figure 7 5 Trigger link input pulse specifications Triggers on heading Edge TTL High 2V 5V TTL Low lt 0 8V 2 us Minimum Output trigger specifications Model 6485 can be programmed to output a trigger immediately after a measurement and or when operation leaves the trigger layer of the trigger model The output trigger provides a TTL compatible output pulse that can be used to trigger other instruments The specifi cations for this trigger pulse are shown in Figure 7 6 A trigger link line can source 1mA and sink up to 50mA Figure 7 6 Trigger link output pulse specifications Meter Complete TTL High 3 4V Typical TTL Low 0 25V Typical 5us Minimum Model 6485 Picoammeter Instruction Manual Triggering 7 13 External trigger example In a simple test system you may want to close a switching channel and measure the current from a DUT connected to that channel Such a test system is shown in Figure 7 7 which uses a Model 6485 to measure 10 DUTs switched by a Model 7158 low current card in a Model 700
227. nstruments SCPI Consor tium s SCPI standard Generally these commands are sent as one or more ASCII characters that tell the device to perform a particular operation such as setting a range or closing a relay The IEEE 488 bus treats these commands as data in that ATN is false when the commands are transmit ted Command codes Command codes for the various commands that use the data lines are summarized in Table F 2 Hexadecimal and the decimal values for the various commands are listed in Table F 3 Table F 3 Hexadecimal and decimal command codes Foi 2 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual Typical command sequences For the various multiline commands a specific bus sequence must take place to properly send the command In particular the correct listen address must be sent to the instrument before it will respond to addressed commands Table F 4 lists a typical bus sequence for sending the addressed multiline commands In this instance the SDC command is being sent to the instrument UNL is generally sent as part of the sequence to ensure that no other active listeners are present Note that ATN is true for both the listen command and the SDC command byte itself Table F 4 Typical bus sequence n N bus Step Command ATN state ASCII Decimal Set low i Stays low Stays low Returns high Assumes primary address 14 Table F 5 gives a typical common command sequence In this instance
228. ntegration rate does not change display resolution Also changing display resolution does not change the rate setting SCPI programming range and digits Table 4 2 SCPI commands digits CURRent Measure current RANGe Range selection UPPer lt n gt Specify expected reading 0 021 to 0 021 A RO Auto on See Table 4 3 Also see Table 4 3 AUTO lt b gt Enable or disable autorange ULIMit lt n gt Specify upper range limit for autorange 0 021 to 0 021 A LLIMit lt n gt Specify lower range limit for autorange 0 021 to 0 021 A For Digits DISPlay Subsystem DISPlay Set display resolution 4 to 7 where lt n gt of DIGits lt n gt 4 3 digit resolution 5 4 digit resolution 6 5 digit resolution 7 6 digit resolution Note Rational numbers can be used For example to set 5 resolution send a value of 4 5 the 6485 rounds it to 5 Programming example range and digits The following command sequence selects the 20mA range and sets display resolution to 3 RST Restore RST defaults CURR RANG 0 02 Set to 20mA range DISP DIG 3 5 Set display resolution to 3 1 2 digits Model 6485 Picoammeter Instruction Manual Range Units Digits Rate and Filters 4 5 Rate Table 4 3 Ranges and values Display 5 digit resolution lt n gt value 2E 2 or 0 02 00 0000 2E 3 or 0 002 0 00000 2E 4 or 0 0002 000 000 2E 5 or 0 00002 00 0000 2E 6 or 0 000002 0 00000 2E 7 or 0 0000002 00
229. nual Status Structure 10 11 Bit BO operation complete Set bit indicates that all pending selected device operations are completed and Model 6485 is ready to accept new commands This bit only sets in response to the OPC query command See Section 12 for details on OPC and OPC Bit B2 query error QYE Set bit indicates that you attempted to read data from an empty output queue Bit B3 device dependent error DDE Set bit indicates that an instrument operation did not execute properly due to some internal condition Bit B4 execution error EXE Set bit indicates that Model 6485 detected an error while trying to execute a command e Bit B5 command error CME Set bit indicates that a command error has occurred Command errors include JEEE 488 2 syntax error Model 6485 received a message that does not follow the defined syntax of the IEEE 488 2 standard Figure 10 4 Standard event status Standard Event Register To ESB bit of Status Byte Register ESE lt NRf gt PON URQ CME EXE DDE QYE OPC Standard Event ESE B15 B8 B7 B6 B5 B4 B3 B2 B1 BO Enable Register Decimal 128 64 32 16 8 4 1 Weights 27 26 25 24 23 22 2 PON Power On amp Logical AND URQ User Request OR Logical OR CME Command Error EXE Execution Error DDE Device Dependent Error QYE Query Error OPC Operation Com
230. o irinin E 4 2 AOAIE siii 4 2 Autoranee MINUS pusilla oliena 4 3 Uil 4 3 Dello 4 3 SCPI programming range and digits e 4 4 Programming example range and digits 4 4 hall E TT 4 5 SCPI programinme Trate nc tensacainsashs rudd oowsmontagummaton senses 4 6 Programming example rate 4 7 PUNT e E AE E O E PEE A A A EE T 4 7 Medianet 4 7 MediansiliciGONtrol ritiri 4 8 bebe 4 8 Digital filter Classifications i 4 8 Dietak Neriy pes soi EN 4 8 Response imme 4 10 Operation consideration eseeeeeeeeeseeessseessssessssssssss 4 10 Distal MMEE CONMOL casier piatt 4 11 SCPI programming filters 4 12 Programming example ui ieri 4 12 Relative mX b m X b reciprocal and log Rebreahicaae te eil 5 2 Setting and controlling relative i 5 2 RELKOV st 5 2 Displaying or manually keying in REL 5 3 SCPI programming relative i 5 4 Programming example relative 5 5 mX b m X b reciprocal and Logarithmic 5 5 MXA b aNd M A HD hail 5 5 Configuring and controlling mX b and m X b _ 5 5 Losan ari 5 6 SCPI programming mX b m X b and log 5 7 A DATA and DATA LATest ssiraaiarnai 5 7 Programming example MX 4D 5 8 Buffer UME COPE FIONS rulli iaia 6 2
231. ocused ion beam applications 1 25 Using switching systems to measure multiple current SOULCES arnorik I 26 1 Figure 1 1 Figure 1 2 Figure 1 3 2 Figure 2 1 Figure 2 2 Figure 2 3 Figure 2 4 Figure 2 5 Figure 2 6 Figure 2 7 Figure 2 8 Figure 2 9 3 Figure 3 1 4 Figure 4 1 Figure 4 2 Figure 4 3 6 Figure 6 1 7 Figure 7 1 Figure 7 2 Figure 7 3 Figure 7 4 Figure 7 5 Figure 7 6 Figure 7 7 Figure 7 8 Figure 7 9 List of Illustrations Getting Started EFroitPalic l scale 1 7 FR Cab Pale RR RR RO PA 1 9 Typical analog output connections 1 11 Measurement Concepts BNG Input Connector sassi 2 4 Maximum mput eyel ae 2 5 Basic conmnechons ssaa 2 6 Shielding for measurements unguarded 2 8 General purpose test HIX Ur silla 2 9 Capacitor test circuit without protection 2 11 Capacitor test circuit with protection 2 12 ElIOAtNS Measurement rurali 2 13 Equivalent input impedance with zero check enabled 2 14 Measurements Connections for AMPS i 3 4 Range Units Digits Rate and Filters Speed vs noise characteristics 4 5 Digital filter averaging and advanced classifications 4 9 Digital filter types moving and repeating 4 10 Buffer Buffer locatrons sliailali
232. of widely different values in parallel will maintain a low impedance across a wide frequency range Keep in mind however that such filtering may have detrimental effects such as increased response time on the measurement D DDC Emulation Commands D 2 DDC Emulation Commands Model 6485 Picoammeter Instruction Manual DDC language Table D 1 The Model 6485 can be configured to accept device dependent commands DDC of the Keithley Model 485 picoammeter The commands for controlling the Model 6485 with the DDC language are provided in Table D 1 For details on Model 485 operation refer to the appropriate instruction manual Since the architecture of the Model 6485 differs from that of the other picoammeters some commands are different and cannot be used Be sure to refer to the notes at the end of the table for information on command restrictions Commands marked NDS are not directly supported in the SPCI command set For convenience some new DDC commands have been added to the 485 command set to allow use of the expanded capabilities of the 6485 These commands are marked NEW CAUTION The DDC language is intended to be used only over the IEEE 488 bus Using front panel controls in conjunction with this language may cause erratic operation In this case results cannot be guaranteed Device dependent command summary D1 LOG on CALCulate 1 FORMat LOG10 CALCulate 1 STATe ON Description Made Comano Equival
233. olof o tL M 3 EZ M Z D ET Z Z ALI 139 Z Lli lo A TT A 9 4 ce 9 9 9 NAS JV 9 o lt Lk o n 9 LZ N G J LZ S S Ndd AYN 49dd NI G Llol lo 1 p 07 il v a 07 v t Da 790 50S 103 v olo l o s 9 6l S 9 61 50 X19 Ll tf o jo J q 81 y E g gl Td Td IA XS 7 o ltLt oy o b 6 LI y ZI L i on 1590 115 HOS lL o o o0O d 91 d 0 91 0 0 dS 310 INN 0 0 o 0 0 TMOoH S tT 4 9 az v z a 9 v 9 ads ve avi wr el we a z v z a v a o v oj lt uwnjog af al al fa sug L o g 2 i e 3 o 2 L 2 0 3 L 9 0 rq L L q D 0 ZD 0 ga L ID L 0 3 0 sq L L 8s 1 8 amp lt 2 8 lt o 8 lt o o 3 0 q x x x x x x X a X za Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview F 9 Uniline commands ATN IFC and REN are asserted only by the controller SRQ is asserted by an external device EOI may be asserted either by the controller or other devices depending on the direction of data transfer The following is a description of each command Each command is sent by setting the corresponding bus line true REN Remote Enable REN is sent to set up instruments on the bus for remote opera tion When REN is true devices will be removed from the local mode Depending on device configuration all front panel controls except the LOCAL button if the device is so equipped may be locked out when REN is true Generally REN s
234. ommon Commands IEEE 488 2 common commands and queries 11 2 SCPI Signal Oriented Measurement Commands Signal oriented measurement command summary 12 2 DISPlay FORMat and SYSTem SCPLcommands diS play alli ii 13 2 SCPI commands data format i 13 3 SCPrceommands Syste M suore ela 13 8 SCPI Reference Tables CALCulate command summary 14 2 DISPlay command summary a A 14 4 SENSe command SUMMALY ea ana 14 5 FORMat command summary 14 5 STATus command summary 14 6 SYSTem command SUMMALY i 14 8 TRACE command summary ica 14 9 TRIGger comimand summary sissi 14 10 Performance Verification Recommended performance verification equipment 15 4 Reading limits for 20uA to 20mA ranges 15 8 Reading limits for 2nA to 2UA ranges 15 9 16 Table 16 1 Table 16 3 Table 16 2 Table 16 4 Table 16 5 17 Table 17 1 Table 17 2 B Table B 1 D Table D 1 Table D 2 F Table F 1 Table F 2 Table F 3 Table F 4 Table F 5 Table F 6 Table F 7 G Table G 1 Table G 2 H Table H 1 Table H 2 Table I 1 Table I 2 Calibration Recommended calibration equipment 16 4 Calibration MICH sura 16 5 Test uncertainty ratios with recommended equipment 16 5 20UA to 20mA range calibration summary
235. on F 4 TEEE 488 handshake sequence F 6 IEEE 488 and SCPI Conformance Information IEEE 488 handshake sequence G 6 Program example aLaaa G 8 Applications Guide Guarding to reduce leakage currents ii I 3 Voltage burden considerations I 5 Simplified model of a feedback picoammeter I 6 Blectrostatic COuplimig allea I 8 Shielding a high impedance device 1 9 Blectrostaticshieldine secin srl I 9 Connecting the HI terminal picoammeter to Highresistante cion iaia I 10 PEODET COMNCC NOM saties aa ESS I 11 EMproper cornecuoni pila aaa I 12 Range change voltage transients i I 13 Transient Vollazo Lecca I 14 Down range voltage transients I 15 ZCIO ChECK TTANSIENt israel I 17 Connections diode leakage current test I 18 Connections capacitor leakage current test I 19 Measuring High Resistance Using the 6485 I 20 Overload Protection Circuit for 6485 Picoammeter I 20 Connections cable insulation resistance test I 21 Connections surface insulation resistance test 22 General photo diod leak as Gen ccctsictuinenssidteteeessniiarncnararssduess I 23 PIN photodiode leakage ict varare oi 24 Avalanche pho
236. on Manual NOTE See RS 232 interface reference page 9 16 for information on RS 232 settings and connections to the computer Press the A or W range keys to scroll through the available RS 232 settings To make changes to a setting press the b key Then use the A or W range keys to select and modify the value as desired Press ENTER to save the changes and move to the next menu item pressing EXIT also saves the changes but leaves the menu At the last menu item FLOW ENTER will save and exit the menu GPIB operation and reference GPIB bus standards The GPIB bus is the IEEE 488 instrumentation data bus with hardware and programming standards originally adopted by the IEEE Institute of Electrical and Electronic Engineers in 1975 Model 6485 conforms to these standards e IEEE 488 1 1987 e IEEE 488 2 1992 This standard defines a syntax for sending data to and from instruments how an instru ment interprets this data what registers should exist to record the state of the instrument and a group of common commands e SCPI 1996 0 Standard Commands for Programmable Instruments This standard defines a command language protocol It goes one step further than IEEE 488 2 1992 and defines a standard set of commands to control every programmable aspect of an instrument GPIB bus connections To connect Model 6485 to the GPIB bus use a cable equipped with standard IEEE 488 connectors as shown in Figure 9 1 Model 6485 Picoamm
237. on setup Query SCPI revision level Read error queue see Note Read and clear oldest error status code and message Read and clear all errors status code and message Read the number of messages in queue Code numbers only Read and clear oldest error status code only Read and clear all errors status codes only Model 6485 Picoammeter Instruction Manual SCPI Reference Tables 14 9 Table 14 6 continued SYSTem command summary see Section 13 for detailed information Default Ref Command Description parameter Section SCPI CLEar Clear messages from error queue KEY lt NRf gt Simulate key press see Figure 13 3 KEY Query the last pressed key RS 232 interface LOCal While in LLO removes the LLO and places the Model 6485 in local RS 232 only REMote Places the Model 6485 in remote if not in LLO RS 232 only RWLock Places the Model 6485 in local lockout RS 232 only Note Clearing the error queue Power up and CLS clears the error queue RST SYSTem PRESet and STATus PRESet have no effect on the error queue Table 14 7 TRACe command summary Default Ref Command Description parameter Section SCPI TRACEl DATA Use TRACe or DATA as root command see Note DATA Read the contents of the buffer data store CLEar Clear readings from buffer FREE Query bytes available and bytes in use POINts lt n gt Specify size of buffer 1 to 2500 ACTual Query number of r
238. ont panel sum mary page 1 6 for a complete listing of display annunciators The Display and Keys Test allows you to test display digit segments and annunciators and check the functionality of front panel keys These tests are accessed through the MENU To access these tests 1 While in reading mode press MENU If not in reading mode press EXIT first then press MENU 2 Scroll using range keys A or V to the TEST sub menu TEST will be flashing 3 Press ENTER or lt p gt to select TEST DISP will be flashing 4 Scroll using range keys A or W to desired test DISPlay or KEY Refer to Section 13 for additional details Status and error messages Status and error messages are displayed momentarily During operation and programming you will encounter a number of front panel messages Typical messages are either of status or error variety as listed in Appendix B Messages both status and error are held in queues For information on retrieving mes sages from queues see Section 10 Power up Line power connection Follow the procedure below to connect the Model 6485 to line power and turn on the instrument 1 Checktoseethatthe line voltage indicated in the window of the fuse holder assem bly Figure 1 2 is correct for the operating voltage in your area If not refer to the procedure in Section 17 for setting line voltage and fuse replacement CAUTION Operating the instrument on an incorrect line voltage may
239. ort various interface functions and should not be confused with pro gramming commands found elsewhere in this manual The interface function codes for the Model 6485 are listed in Table F 7 Table F 7 Model 6485 interface function codes Interface function Source Handshake capability Acceptor Handshake capability Talker basic talker talk only serial poll unaddressed to talk on LAG Listener basic listener unaddressed to listen on TAG Service Request capability Remote Local capability No Parallel Poll capability Device Clear capability Device Trigger capability No Controller capability Open collector bus drivers No Extended Talker capability No Extended Listener capability The codes define Model 6485 capabilities as follows SH Source Handshake Function SH1 defines the ability of the instrument to initiate the transfer of message data over the data bus AH Acceptor Handshake Function AHI defines the ability of the instrument to guarantee proper reception of message data transmitted over the data bus T Talker Function The ability of the instrument to send data over the bus to other devices is provided by the T function Instrument talker capabilities T5 exist only after the instrument has been addressed to talk L Listener Function The ability for the instrument to receive device dependent data over the bus from other devices is provided by the L function Listener capabilities L4 of
240. ounters are used to repeat operations within the trigger model layers For example if the trigger count is set for 10 operation will keep looping around in the trigger layer until 10 measurements are performed If the arm count is set to 2 operation will then loop back through the arm layer and go back into the trigger layer to perform 10 more measurements Trigger model configuration front panel NOTE See SCPI Programming Table 7 3 for the SCPI commands to configure the trigger model over the bus Press CONFIG and then TRIG to configure both the TRIG and ARM layers of the trigger model NOTE When done configuring the trigger level press ENTER to confirm value and then use the EXIT key to save changes and leave trigger model configuration Once in trigger model configuration mode use the A and W range keys to display either the TRIGGER layer or the ARM layer menus Press ENTER to select the desired menu Then use the A and W range keys to display menu items Use the cursor lt q and p gt and the A and W keys to key in values A menu item or value is selected by pressing ENTER Use the EXIT key to exit from the menu saving all changes made Table 7 2 Trigger model menu structure CONFIG Path to TRIG and ARM menus Access by pressing CONFIG and then TRIG TRIG Path to TRIG layer sub menus COUNT Set TRIG measure count INF Specify an INFinite measure count FIN Specify a FINite measure count 1 2500 7 8
241. p would damage the DUT the up ranging transient can be reduced greatly by reducing the input current to lt 10 of the present range before forcing the range change up manual or fixed ranging over the bus This can be true when run ning the first I V curve on devices whose characteristics are not yet known so that sweep ing from low current towards high current is the only way to avoid exceeding a maximum current through the device Zero check on off response Figure I 13 shows the transient that can be expected from input HI to LO during a change in the zero check mode with no input current The transition is similar for entering and leaving zero check For current ranges 2UA and below the magnitude of the response is not as large but similar in duration As with range change transients the zero check tran sient is presented through an internal impedance which will limit the resulting current through the DUT Table I 2 If there is an input current while in zero check the input voltage will depend on the current and the zero check input impedance for the specific range Model 6485 Picoammeter Instruction Manual Applications Guide l 17 Figure l 13 Zero check transient Run HA Trig m 30 00 09 57 33 Table l 2 Internal impedance for zero check transient Range Zcheck ATARSIN impedance 2mA 20mA 20UA 200UA 200nA 2UA 2nA 20nA I 18 Applications Guide Model 6485 Picoammeter Instruction Manual Applications
242. ped commands A command that allows the execution of subsequent com mands while device operations of the overlapped command are still in progress The WAI command is used to suspend the execution of subsequent commands until the device operations of all previous overlapped commands are finished The WAI command is not needed for sequential commands 11 6 Common Commands Model 6485 Picoammeter Instruction Manual 12 SCPI Signal Oriented Measurement Commands 12 2 SCPI Signal Oriented Measurement Commands Model 6485 Picoammeter Instruction Manual The signal oriented measurement commands are used to acquire readings You can use these high level instructions to control the measurement process These commands are summarized in Table 12 1 NOTE The readings acquired by these commands depend on which data elements are selected See Table 14 3 for details Table 12 1 Signal oriented measurement command summary Command Description CONFigure lt function gt Places Model 6485 in a one shot measurement mode lt function gt CURR DC CONFigure Queries the selected function Returns CURR FETCh Requests the latest reading s READ Performs an INITiate and a FETCh MEASure lt function gt Performs a CONFigure lt function gt and a READ A CONFigure lt function gt Configure Model 6485 for one shot measurements lt function gt CURRent DC Configure current This command configures t
243. pedance I 5 noisy readings I 7 NPLC Menu 4 6 Offset voltage calibration 15 7 operating at a higher speed 13 2 Operation consideration 4 10 event status 10 12 Operation keys 1 7 Optional command words 1 19 Options and accessories 1 4 Output queue 10 18 Output trigger specifications 7 12 Output triggers 7 7 Overview of this manual 1 2 Package content 1 4 Parity RS 232 9 17 peak to peak 6 7 Performance considerations 2 2 Performance verification 15 1 Phone number 1 3 Photodiode characterization prior to dicing I 22 Piezoelectric and stored charge effects C 3 PIN photo diode leakage I 24 PKPK 6 7 polling sequence D 12 Pomona 1269 15 4 POWER 1 7 Power module 1 10 Power up 1 12 Power up sequence 1 14 Primary address 9 7 Procedure 16 6 Program Message Terminator PMT 9 15 Program messages 9 13 Query commands 1 19 9 12 Questionable event status 10 15 Queues 10 18 Rack mount kits 1 5 Range D 6 and values 4 5 keys 1 8 symbols for rel values 5 3 Units Digits Rate and Filters 4 1 range change transients I 12 Rate 1 8 4 5 Key 4 6 Reading limits for 20uA to 20mA ranges 15 8 Reading limits for 2nA to 2uA ranges 15 9 Reading Mode D 2 Rear panel 1 9 Rear panel summary 1 8 RECALL 1 8 Recall 6 3 Recommended test equipment 15 3 Registers Bit descriptions 10 10 Condition 10 15 Enable 10 4 10 5 Event 10 16 Reading 10 6 reinstate the previous Rel 5 2 REL 1 7 1 8 5 2 Relative mX b m X b Reciproca
244. pending latched input triggers are cleared imme diately When the picoammeter is being latched by another instrument it may inadvert ently receive and latch input triggers that do not get executed These pending triggers could adversely affect subsequent operation When using external triggering it is recommended that TRIGger CLEar be sent after sending the ABORt commend and at the beginning of a program before sending a initiate command See INITiate command Model 6485 Picoammeter Instruction Manual Programming example Triggering 7 11 The following command sequence will trigger and return 10 readings RST ARM SOURce IMMediate ARM COUNt 1 TRIGger SOURce IMMediate TRIGger COUNt 10 READ External triggering Return 6485 to RST defaults Set arm control source Immediate Set arm count to l Set trigger control source Immediate Set trigger count to 10 Trigger and return 10 readings Input and output triggers are received and sent via the rear panel TRIGGER LINK connec tor The trigger link has six lines At the factory line 2 is selected for output triggers and line 1 is selected for input triggers These input output assignments can be changed as previously explained in this section The connector pinout is shown in Figure 7 4 Figure 7 4 Trigger link connection operation Rear Panel Pinout 8 7 6 DO QO Trigger Link Pin Number Description Trigger Link 1 Trigger Link 2 Trigger Li
245. per interface control and management These lines are used to send the uniline commands ATN Attention The ATN state determines how information on the data bus is to be interpreted IFC Interface Clear The IFC line controls clearing of instruments from the bus REN Remote Enable The REN line is used to place the instrument on the bus in the remote mode EOI End or Identify The EOI line is used to mark the end of a multi byte data transfer sequence SRQ Service Request The SRQ line is used by devices when they require service from the controller Handshake lines The bus handshake lines operate in an interlocked sequence This method ensures reliable data transmission regardless of the transfer rate Generally data transfer will occur at a rate determined by the slowest active device on the bus One of the three handshake lines is controlled by the source the talker sending informa tion while the remaining two lines are controlled by accepting devices the listener or lis teners receiving the information The three handshake lines are DAV DATA VALID The source controls the state of the DAV line to indicate to any listening devices whether or not data bus information is valid NRED Not Ready For Data The acceptor controls the state of NRED It is used to sig nal to the transmitting device to hold off the byte transfer sequence until the accepting device is ready NDAC Not Data Accept
246. perform a finite number of measurements the DATA command will return all the Rel ed readings after the last reading is taken The DATA LATest command will only return the last latest Rel ed reading Model 6485 Picoammeter Instruction Manual Relative mX b m X b reciprocal and log 5 5 If the instrument is programmed to perform an infinite number of measurements arm count or trigger count set to infinite you cannot use the DATA command to return Rel ed readings However you can use the DATA LATest command to return the last Rel ed reading after aborting the measurement process After sending the INITiate com mand to start the measurement process use the ABORt command to abort the measure ment process then use DATA LATest to return to the last Rel ed reading Programming example relative This program fragment establishes a 1uA baseline for measurements CALC2 NULL OFFS le 6 Set Rel value of 1A CALC2 NULL STAT ON Enable Rel CALC2 FEED SENS Rel input signal INIT Trigger reading s CALC2 DATA Request Rel ed reading mX b m X b reciprocal and Logarithmic mX b and m X b The following math operations manipulate normal display readings X mathematically according to the following calculations Y mX b Y m X b where X is the normal display reading m and b are user entered constants for scale factor and offset Y is the displayed result NOTE Changing the m or b for mX b
247. perties 1 Special keys and power switch CONFIG LOCAL MENU POWER When in Local operation use to configure properties of the next button pressed When in Remote operation REM annunciator lit cancels GPIB remote mode Provides access to menu Power switch In position turns 6485 on I out position turns it off O 2 Function keys MEDN AVG MX B M X B LOG REL ZCHK ZCOR Use to control and modify properties of the median filter Use to control and modify properties of the digital filter Use to perform and configure properties of the mX b math function Use to perform and configure properties of the m X b math function Use to convert output display to log10 on off Use to control and configure properties of the rel ative function Use to perform a Zero Check function Use to control Zero Correct function on off 3 Operation keys COMM DISP TRIG Use to control and modify communication properties GPIB or RS 232 Use to turn display on off Trigger measurement s Takes 6485 out of idle state Use also to configure trigger properties 1 8 Getting Started 4 Range keys HALT DIGITS RATE 4 and gt SAVE SETUP STORE RECALL LIMIT AZERO EXIT ENTER hi AUTO Model 6485 Picoammeter Instruction Manual Stops measurement process Puts 6485 in idle state Use to set display resolution Use to select measurement rate Use to control cursor position for making selections or
248. plete 10 12 Status Structure Model 6485 Picoammeter Instruction Manual Semantic error Model 6485 received a command that was misspelled or received an optional IEEE 488 2 command that is not implemented The instrument received a Group Execute Trigger GET inside a program message Bit B6 user request URQ Set bit indicates that the LOCAL key on Model 6485 front panel was pressed Bit B7 power ON PON Set bit indicates that Model 6485 has been turned off and turned back on since the last time this register has been read Operation event status The used bits of the operation event register Figure 10 5 are described as follows Bit BO calibrating Set bit indicates that Model 6485 is calibrating Bit BS waiting for trigger event Trig Set bit indicates that Model 6485 is in the trigger layer waiting for a TLINK trigger event to occur Bit B6 waiting for arm event Arm Set bit indicates that Model 6485 is in the arm layer waiting for an arm event to occur e Bit B10 idle state Idle Set bit indicates Model 6485 is in the idle state Figure 10 5 Operation event status Idle Arm Trig Cal B15 B11 B10 B9 B7 B6 B5 B4 B1 BO Idle Arm Trig Cal B15 B11 B10 B9 B7 B6 B5 B4 B1 BO Operation Condition CONDition Regiser Operation Event EVENt Regiser To OPC bit of Status Byte Register
249. poll The serial poll automatically resets RQS of the status byte register This allows subsequent serial polls to monitor bit B6 for an SRQ occurrence generated by other event types After a serial poll the same event can cause another SRQ even if the event register that caused the first SRQ has not been cleared The serial poll does not clear MSS The MSS bit stays set until all status byte summary bits are reset SPE SPD serial polling The SPE SPD general bus command is used to serial poll Model 6485 Serial polling obtains the serial poll byte status byte Typically serial polling is used by the controller to determine which of several instruments has requested service with the SRQ line Status byte and service request commands The commands to program and read the status byte register and service request enable reg ister are listed in Table 10 3 For details on programming and reading registers see Pro gramming enable registers page 10 5 and Reading registers page 10 6 To reset the bits of the service request enable register to 0 use 0 as the parameter value for the SRE command i e SRE 0 10 10 Status Structure Model 6485 Picoammeter Instruction Manual Table 10 3 Common commands status byte and service request enable registers STB Read status byte register SRE lt NDN gt or lt NRf gt Program the service request enable register Note lt NDN gt Bxx x Binary format each x 1 or
250. present calibration code on the display Factory default 006485 Use the up and down RANGE keys to select the letter or number and use the left and right arrow keys to choose the position Press ENTER to complete the process and the unit will display CAL ENABLED Followed by NEW CODE Y N Select Y then press ENTER The unit will prompt for the new code CODE 000000 Enter the new code then press ENTER Using the LOCK selection in the calibration menu lock out calibration after changing the code Resetting the calibration code If you forget the calibration code you can unlock calibration by shorting together the CAL pads which are located on the display circuit board inside the unit Doing so will also reset the code to the factory default 006485 Model 6485 Instruction Manual Calibration 16 13 Displaying calibration dates To display calibration dates at any time 1 From normal display press MENU select CAL then press ENTER The unit will display the following CAL VOFFSET Use either RANGE key to select CAL DATES then press ENTER The Model 6485 will display the last calibration date for example DATE 11 15 01 Press ENTER to view the calibration due date for example NDUE 11 15 02 Press EXIT to return to normal display Displaying the calibration count To display the calibration count at any time L From normal display press MENU select CAL then press ENTER The unit will display th
251. puter Also to avoid erratic operation the readings of the data string and terminator should be acquired in one piece The header 0 can be read separately before the rest of the string The number of bytes to be transferred can be calculated as follows Bytes 2 Rdgs x 4 1 where 2 is the number of bytes for the header 0 Rdgs is the product of the number of selected data elements arm count and trigger count 4 is the number of bytes for each reading 1 is the byte for the terminator For example assume the instrument is configured to perform 10 measurements and send them to the computer using the binary format 2 10x4 1 43 Bytes 13 6 DISPlay FORMat and SYSTem Model 6485 Picoammeter Instruction Manual B FORMat ELEMents lt item list gt Parameters READing Current reading UNITs Units always Amps TIME Timestamp STATus Status information The specified elements are included in the data string in response to FETCh READ MEASure and TRACe DATA Note that each element in the item list must be sepa rated by a comma i e send ELEMents READing UNITs TIME STATus to include all elements in the data string The elements for the ASCii format are shown in Figure 16 1 An overflow or overvoltage reading is returned as 9 9E37 When a specified data element has invalid data associated with it NAN Not A Number will be the response NAN is returned as 9 91E37 Units Units refe
252. quired calibrator voltage I verification current R actual standard resistor value For example assume you are testing the 20nA range using an actual 100 5MQ standard resistor value The actual calibrator voltage is 20nA x 100 5MQ 2 01V 15 6 Performance Verification Model 6485 Instruction Manual Performing the verification test procedures Test considerations When performing the verification procedures e Be sure to restore Model 6485 factory front panel defaults and perform voltage offset calibration as outlined below e Make sure that the test equipment is properly warmed up and properly connected to the Model 6485 INPUT jack e Be sure the test equipment is set up for the proper function and range e Allow the input signal to settle before making a measurement e Do not connect test equipment to the Model 6485 through a scanner multiplexer or other switching equipment WARNING The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis voltage Exceeding 42V can create a shock hazard The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the instrument CAUTION Maximum continuous input voltage is 220V DC Exceeding this value may cause instrument damage Restoring factory defaults Before performing the verification procedure restore the instrument to its factory front panel defaul
253. r 5 0 50Hz Rel Rel Value VAL RS 232 All Settings Off 0 0 No effect Off at factory No effect Trigger Layer CONF TRIG Trig In Source Event Trigger Count Trigger Delay Input Trigger Link Line Source Bypass Output Trigger Link Line Units Paa P oo Zero ze Enabled Zero Correct Disabled This factory SYStem PRESet and bus RST GPIB defaults are the same Bus settings that are different from factory reset are as shown 1 18 Getting Started Model 6485 Picoammeter Instruction Manual Menu Many aspects of operation are configured through the menus summarized in Table 1 4 Refer to the Section listed in the table in depth information To access the menu press the MENU key Use the A and W range keys to scroll through the menu items and the and cursor keys to change options Press ENTER to save any changes made and leave the menu Press EXIT to leave the menu without saving changes NOTE The MENU key is used to access the menu structure However if in remote for IEEE 488 bus operation REM annunciator is lit pressing the menu key has no effect Press the LOCAL key to place the unit in local operation then press the MENU key to access the menu items Table 1 4 MENU structure Menu item Description Reference Provides path to the following calibration submenu items Section 15 VOFFSET COUNT RUN DATES UNLOCK LOCK and Section 16 SAVE See reference section for verificatio
254. r information on the data elements Figure 13 1 also shows the byte order of the data string Data elements not specified by the ELEMents command are simply not included in the string Figure 13 1 ASCII data format 1 040564E 06A 2 236299E 02 1 380000E 02 Reading Units Timestamp Status Model 6485 Picoammeter Instruction Manual DISPlay FORMat and SYSTem 13 5 IEEE 754 single precision format REAL 32 or SREal will select the binary IEEE 754 single precision data format Figure 13 1 shows the normal byte order format for each data element For example if all three data elements are selected the data string for each reading conversion is made up of three 4 byte data blocks Note that the data string for each reading conversion is preceded by a 2 byte header that is the binary equivalent of an ASCII sign and 0 Figure 16 2 does not show the byte for the terminator that is attached to the end of each data string Note that the byte order of the data string can be sent in reverse order Figure 13 2 IEEE 754 single precision data format 32 data bits Header s sign bit 0 positive 1 negative e exponent bits 8 f fraction bits 23 Normal byte order shown For swapped byte order bytes sent in reverse order Header Byte 4 Byte 3 Byte 2 Byte 1 The header and terminator are sent only once for each READ During binary transfers never un talk Model 6485 until after the data is read input to the com
255. re covered later in this section Table 10 3 through Table 10 6 The response message will be a value that indicates which bits in the register are set That value if not already binary will have to be converted to its binary equivalent For exam ple for a binary value of 100101 bits B5 B2 and BO are set The returned value can be in the binary decimal hexadecimal or octal format The FOR Mat SREGister command is used to select the data format for the returned value Table 10 2 For non decimal formats one of the following headers will accompany the returned value to indicate which format is selected B Header for binary values H Header for hexadecimal values Q Header for octal values Model 6485 Picoammeter Instruction Manual Status Structure 10 7 Table 10 2 SCPI command data formats for reading status registers FORMat FORMat subsystem SREGister lt name gt Select data format for reading status registers ASCII lt name gt ASCii Decimal format HEXadecimal Hexadecimal format OCTal Octal format BINary Binary format Status byte and service request SRQ Service request is controlled by two 8 bit registers the status byte register and the service request enable register Figure 10 3 shows the structure of these registers Figure 10 3 Status byte and service request Status Summary Messages 6 Service RQS Request STB OSB B6 ESB MAV QSB EAV MSB Status Byte Canio Se
256. re explained as follows SLOW Selects the slowest preset integration time 6 PLC for 60Hz or 5 PLC for 50Hz The SLOW rate provides better noise performance at the expense of speed MED Selects the medium integration time 1 PLC Select the MED rate when a compromise between noise performance and speed is acceptable FAST Selects the fastest preset integration time 0 1 PLC Select the FAST rate if speed is of primary importance at the expense of increased reading noise To change the rate setting press and release the RATE key until the desired rate annunci ator SLOW MED or FAST is displayed NPLC Menu From this menu you can set rate by setting the PLC value Perform the following steps to set NPLC L 2 NOTE Press CONFIG LOCAL and then RATE to display the present PLC value Use the lt gt A and W keys to adjust to the desired PLC value Valid values are 60Hz operation 0 01 to 60 50Hz operation 0 01 to 50 Press ENTER The SLOW MED or FAST annunciator will only turn on if the set PLC value corresponds exactly to the slow 5 or 6 PLC for the respective frequency of 50 or 60Hz medium 1 PLC or fast 0 1 PLC integration rate For example with the integration rate set to 2 PLC none of the rate annunciators will turn on SCPI programming rate Table 4 4 contains the path and the command to set rate Table 4 4 SCPI commands rate SENSe SENSe Subsystem CURRent
257. readings RST TRIG TRIG CURR RANG AUTO OFF CURR NPLC 01 SENS SENS SENS SYST SYST DISP CLS TRAC TRAC STAT SRE OPC DEL 0 COUNT 2500 CURR RANG 002 ZCH OFF AZER STAT OFF ENAB OFF POIN 2500 CLE TRAC FEED CONT NEXT MEAS ENAB 512 1 read back result of opc INIT DISP TRAC ENAB ON DATA read back result Return 6485 to RST defaults Set trigger delay to zero seconds Set trigger count to 2500 Turn auto range off Set integration rate to 01 PLC Use 2mA range Turn zero check off Turn auto zero off Turn display off Clear status model Set buffer size to 2500 Clear buffer Set storage control to start on next reading Enable buffer full measurement event Enable SRO on buffer full measurement event operation complete query synchronize completion of commands start taking and storing readings wait for GPIB SRQ line to go true turn display back on Request data from buffer Model 6485 Picoammeter Instruction Manual Example Programs E 3 900 readings second to IEEE 488 bus This program uses multiple reading queries to get high speed measurements over the bus in real time To improve continuity of readings reduce the trigger count To improve throughput increase the trigger count NOTE This program configures the Model 6485 to 0 01 PLC digital filters off front panel off auto zero off binary transfer and IEEE 488 1 language Model
258. rence the returned readings units of measure This will always be in amps with the current reading in scientific notation Timestamp Timestamp references the returned data string to a point in time The timestamp operates as a timer that starts at zero seconds when the instrument is turned on or when the timestamp is reset SYSTem TIME RESet After 99 999 99 seconds the timer resets to zero and starts over For buffer readings timestamp can be referenced to the first reading stored in the buffer absolute format which is timestamped at 0 seconds or to the time between each stored reading delta format The TRACe TSTamp FORMat command is used to select the timestamp format Status The status word provides information about Model 6485 operation The 16 bit status word is sent in decimal form The decimal value has to be converted to the binary equivalent to determine the state of each bit in the word For example if the returned status value is 9 the binary equivalent is 00000001001 Bits 0 and 3 are set The bits are explained as follows Bit 0 OFLO Set to 1 if measurement performed while in over range overflowed reading Bit 1 Filter Set to 1 when measurement performed with the averaging filter enabled Bit 2 Math Set to 1 when measurement performed with CALCI enabled Bit 3 Null Set to 1 if null for CALC2 is enabled Bit 4 Limits Set to 1 if a limit test CALC is enabled Bits 5 and 6 Limit
259. rents generated by the formation of chemical batteries on a circuit board caused by ionic contamination Humidity Reduces insulation resistance on PC boards and test connection insulators Light Light sensitive components must be tested in a light free environment Electrostatic interference Charge induced by bringing a charged object near your test circuit Magnetic fields The presence of magnetic fields can generate EMF voltage Electromagnetic interference EMI from external sources 1 e radio and TV transmitters can EMI affect sensitive measurements 3 Measurements e Measurement overview Summarizes the current measurement capabilities of Model 6485 and provides a basic procedure to measure amps e SCPI programming Covers the basic SCPI commands 353 Measurements Model 6485 Picoammeter Instruction Manual Measurement overview Measurements Model 6485 can make amps measurements from 20fA to 21mA using 8 measurement ranges 2nA 20nA 200nA 2uA 20uA 200UA 2mA and 20mA NOTE Accuracy specifications are provided in Appendix A Procedure WARNING The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis voltage Exceeding 42V can create a shock hazard If it is possible for the DUT or external supply to present more than 42V to the input HI it is imperative that the connection between input LO a
260. return to normal display 13 Repeat steps 3 through 12 for the 20nA through 2UA ranges using Table 16 5 as a guide Be sure to make connections to the correct standard resistor and set the cali brator voltages to the correct values Table 16 5 2nA to 2uA range calibration summary Model 6485 Range Calibrator Voltages Standard Resistors Calibration Currents 2nA OV 1GQ OnA 2 000000V 1GQ 2nA 2 000000V 1GQ 2nA 20nA OV OnA 2 000000V 20nA 2 000000V 20nA n 200nA OV OnA 20 00000V 200nA 20 00000V 200nA 24A OV 200 0000V 200 0000V Nominal resistance values 2 Nominal currents Calculate actual currents from calibrator voltage and actual standard resistor value I V R Calibrate zero positive full scale and negative full scale for each range Model 6485 Instruction Manual Calibration 16 11 Figure 16 2 Connections for 2nA to 2uA range calibration DC Voltage Calibrator BNC to dual Model 6485 Picoammeter Banana Plug E Adapter su T ai el 00000000000 Connect la 000 000 00000 Cable O00 000 00 i 0 oo0oo0o 000 00 O Output LO Low noise BNC to Triax Coax Cable Adapter on INPUT Tia Cable p r mo gua Note Connect Calibrator to Supplied with ne O es 100MQ or 1GQ Resistor Model 5156 WO Orie Link Shield and Chassis Model 5156 Calibration Standard Entering calibration dates and saving calibration NOTE For temporary calibration without saving new
261. rial Poll B7 MSS B5 B4 B3 B2 B1 BO Register F P E cL_ PL cre 2 o TT 2 SRE OSB ESB MAV QSB EAV MSB Service Request SRE B7 B6 B5 B4 B3 B2 B1 BO Enable Register Decimal Weights OSB Operation Summary Bit amp Logical AND MSS Master Summary Status OR Logical OR RQS Request for Service ESB Event Summary Bit MAV Message Available QSB Questionable Summary Bit EAV Error Available MSB Measurement Summary Bit 10 8 Status Structure Model 6485 Picoammeter Instruction Manual Status byte register The summary messages from the status registers and queues are used to set or clear the appropriate bits BO B2 B3 B4 B5 and B7 of the status byte register These summary bits do not latch and their states O or 1 are solely dependent on the summary messages 0 or 1 For example if the standard event register is read its register will clear As a result its summary message will reset to 0 which in turn will reset the ESB bit in the sta tus byte register The bits of the status byte register are described as follows Bit BO measurement status MSB Set summary bit indicates that an enabled measurement event has occurred e Bit B1 Not used e Bit B2 error available EAV Set summary bit indicates that an error or status message is present in the error queue e Bit B3 questionable summary bit
262. rm count or trigger count Set to infinite you cannot use the READ command to trigger and acquire readings Use INITiate to start trigger the measurement process send ABORt to abort the measurement process and then use SENSe DATA LATest to return the last latest reading 12 4 SCPI Signal Oriented Measurement Commands Model 6485 Picoammeter Instruction Manual D MEASurel lt function gt Configure and perform one shot measurement lt function gt CURRent DC Measure current This command combines all of the other signal oriented measurement commands to per form a one shot measurement and acquire the reading When this command is sent the following commands execute in the order that they are presented e CONFigure lt function gt e READ When CONFigure is executed the instrument goes into a one shot measurement mode See CONFigure for details When READ is executed its operations will then be performed In general an INITiate is executed to perform the measurement and a FETCh is executed to acquire the reading See READ for details 13 DISPlay FORMat and SYSTem e DISPlay subsystem Covers the SCPI commands that are used to control the display e FORMat subsystem Covers the SCPI commands to configure the format that readings are sent over the bus e SYSTem subsystem Covers miscellaneous SCPI commands 13 2 DISPlay FORMat and SYSTem Model 6485 Picoammeter Instruction M
263. rm versions 9 12 SHON LOM TUNES sabot 9 12 Prostam messan eS criptati alari rate 9 13 Single command messages 9 13 Multiple command messages i 9 14 Command path TUES sima 9 14 Using common commands and SCPI commands in the same message 9 14 Program Message Terminator PMT 9 15 Command execution rules 9 15 Response mMessate iii ria 9 15 Sending a response message 9 15 Multiple response messages 9 15 Response Message Terminator RMT 9 16 Message exchange protocol 9 16 RS 232 interface reference c cscesccscessceccsscsccssceccsscecsescs 9 16 Sending and receiving data eseese 9 16 RS 2232 SCUIIOS sro 9 16 Baad AUS sanre 9 17 Data and stop DIIS iii las 9 17 Pica 9 17 NCTM AVON sirena 9 17 Flow control signal handshaking 9 17 RS 232 CONNECUOMS ieena i E 9 18 Error Messa CS rada aida 9 19 10 Status Structure VCE VIEW seta nie 10 2 Clearing registers and queues ccicceccceveicnadidacdecutcoessseeat vssnssesesress 10 4 Programming and reading registers 10 5 Programming enable registers 10 5 Reddimatesisici isla 10 6 Sta
264. rogrammed to scan 10 channels operation loops back to point B where it waits for an input trigger With Model 6485 at point A the output trigger pulse from Model 7001 2 triggers a measurement of DUT 1 point E After the measurement is complete Model 6485 outputs a trigger pulse and then loops back to point A where it waits for another input trigger The trigger applied to Model 7001 2 from Model 6485 closes the next channel in the scan which then triggers Model 6485 to measure that DUT This process continues until all 10 channels are scanned and measured O Limit Tests Limit testing Explains the basic Limit 1 and Limit 2 testing operations Front panel operation Explains how to configure and run tests from the front panel SCPI programming Covers the SCPI commands for remote operation 8 2 Limit Tests Limit testing Model 6485 Picoammeter Instruction Manual As shown in Figure 8 1 there are two limit tests that can be performed on a DUT Limit 1 is used as the wide pass band and Limit 2 is used as the narrow pass band It is up to the user to specify limits that conform to this pass band relationship Figure 8 1 Limit tests LO HI lt Fail Pass Fail gt Limit Limit LO HI lt Fail Pass Fail gt Limit Limit Limit 1 Test Wide Pass Band Limit 2 Test Narrow Pass Band Figure 8 2 shows an example where the HI and LO limits for limit 1 are 2mA and the Hi and LO
265. rors Discusses error messages that might occur during calibra tion Calibration menu Discusses error messages that might occur during calibra tion Aborting calibration Describes how to halt the calibration procedure at any time Current calculations Details how to calculate currents from calibrator voltages and standard resistor values when calibrating the 2nA to 2uA ranges Calibration procedure Provides step by step procedures for calibrating all cur rent ranges The 2nA to 2uA and 20UA to 20mA ranges require separate proce dures because of the different calibration equipment involved Calibration support Describes how to change the calibration code reset the calibration code and view calibration dates and count 16 2 Calibration Model 6485 Instruction Manual Introduction Use the procedures in this section to calibrate the Model 6485 from the front panel See Appendix H for information on remote calibration These procedures require accurate test equipment to source precise DC voltages currents and resistances WARNING The information in this section is intended only for qualified service personnel Do not attempt these procedures unless you are qualified to do so Some of these procedures may expose you to hazardous voltages Environmental conditions Temperature and relative humidity Conduct the calibration procedures at an ambient temperature of 22 to 24 C with relative humidity of less
266. rument operation See Table 14 3 At least one data element must be in the list Listed elements must be separated by a comma i e FORMat ELEMents READing TIME Elements not listed will not accompany the response message for TRACe DATA Data in the response mes sage will be in order of the listed data elements set by this command G CALCulate3 FORMat lt name gt This command selects the statistic to be returned by CALCulate3 DATA see Ref H Name parameters MINimum Select the lowest reading stored in the buffer MAXimum Select the largest reading stored in the buffer MEAN Select the mean average statistic for the readings stored in the buffer SDEViation Select the standard deviation statistic for the readings stored in the buffer PKPK Select the peak to peak statistic for readings stored in the buffer Peak to Peak is calculated as follows PKPK MAXimum MINimum H CALCulate3 DATA 1 If the number of data points in the buffer is one or none CALCulate3 DATA will result in an error 230 If there is a lot of data in the buffer some statistic operations may take too long and cause a bus time out error To avoid this send calc3 data and then wait for the MAV message available bit in the Status Byte Register to set before addressing the Model 6485 talk Section 11 6 8 Buffer Programming example Model 6485 Picoammeter Instruction Manual The following program fragment stores 20 rea
267. ry of the register will set to 1 which in turn sets the summary bit of the status byte register The commands to program and read the event enable registers are listed in Table 10 6 For details on programming and reading registers see Programming enable registers page 10 5 and Reading registers page 10 6 NOTE The bits of any enable register can be reset to 0 by sending the 0 parameter value with the appropriate enable command i e STATus OPERation ENABle 0 Table 10 6 Common and SCPI commands event enable registers ESE lt NDN gt or lt NRf gt Program standard event enable register see Parameters ESE Read standard event enable register STATus STATus subsystem OPERation Operation event enable register ENABle lt NDN gt or lt NRf gt Program enable register see Parameters ENABle Read enable register MEASurement Measurement event enable register ENABle lt NDN gt or lt NRf gt Program enable register see Parameters ENABle Read enable register QUEStionable Questionable event enable register ENABle lt NDN gt or lt NRf gt Program enable register see Parameters ENABle Read measurement event enable register Parameters lt NDN gt Bxx x Binary format each x 1 or 0 Hx Hexadecimal format x 0 to FFFF Qx Octal format x 0 to 177777 0 to 65535 Decimal format Note Power up and STATus PRESet resets all bits of all ena
268. s Programming enable registers The only registers that can be programmed by the user are the enable registers All other registers in the status structure are read only registers The following explains how to ascertain the parameter values for the various commands used to program enable registers The actual commands are covered later in this section Table 10 3 and Table 10 6 A command to program an event enable register is sent with a parameter value that deter mines the desired state 0 or 1 of each bit in the appropriate register An enable register can be programmed using any of the following data formats for the parameter value binary decimal hexadecimal or octal The bit positions of the register Figure 10 1 indicate the binary parameter value For example if you wish to sets bits B4 B3 and B1 the binary value would be 11010 where B4 1 B3 1 B1 1 and all other bits are 0 When you use one of the other formats con vert the binary number to its decimal hexadecimal or octal equivalent Binary 11010 Decimal 26 Hexadecimal 1A Octal 32 Note that Figure 10 2 includes the decimal weight for each register bit To set bits B4 B3 and B1 the decimal parameter value would be the sum of the decimal weights for those bits 16 8 2 26 The lt NDN gt non decimal numeric parameter type is used to send non decimal values These values require a header B H or Q to identify the data format being sent The letter i
269. s Model 6485 Picoammeter Instruction Manual General notes Table 14 1 CALCulate command summary Default Ref Command Description parameter Section SCPI CALCulate 1 FORMat lt name gt FORMat KMATh MMFactor lt NRf gt MMFactor MBFactor lt NRf gt MBFactor MUNIts lt name gt MUNIts STATEe lt b gt STATe Brackets are used to denote optional character sets These optional characters do not have to be included in the program message Do not use brackets in the program message Angle brackets lt gt are used to indicate parameter type Do not use angle brackets in the program message The Boolean parameter lt b gt is used to enable or disable an instrument operation 1 or ON enables the operation and 0 or OFF disables the operation Upper case characters indicated the short form version for each command word Default parameter Listed parameters are both the RST and SYSTem PRESet defaults unless noted otherwise Parameter notes are located at the end of each table Ref Refers you to the section Sec that provides operation information for that command or command subsystem SCPI A checkmark V indicates that the command and its parameters are SCPI con firmed An unmarked command indicates that it is a SCPI command but does not con form to the SCPI standard set of commands It is not a recognized command by the SCPI consortium SCPI confirmed commands that use one
270. sion Clears interface Defines data bus contents Controlled by external device Locks out local operation Returns device to default conditions Enables serial polling Disables serial polling Returns unit to default conditions Returns device to local Removes all listeners from the bus Removes any talkers from the bus Programs IEEE 488 2 compatible instruments for common operations Programs SCPI compatible instru ments for particular operations Model 6485 Picoammeter Instruction Manual IEEE 488 Bus Overview Command codes F 8 Table F 2 area uUog X 8010 4d LOIG G 9 0N 96919 jepow Aq pajuawajdu JOU JONLNOD IAVL LOL pue AUNDIANODNN 110d TATIVYVd Add AINDIHNOI 110d 1ITIVAVA Ddd DAS 99d dNOND dNOYND GNVWWOD GNVWWOD AYVONODIS AUVWI dd EcR t amp l lt lt JF lt lt x lt eoc c lt elorl e N iN qQ OYL 9V1 DDN DIV dNOND dNOYND dNOND dNOND ssaudav ss3JAAY GNVWWOD GUNVWWWOD IVE NILSIT IVSYSAINN CISSINAOV ee E 130 O INN co GI o INN GI sn IS GI L t L L u o rl N oE lt rl Su OS VI o Lt kLk lt kL w 67 l W 67 EL n SD XD l L O L 27 Zl 7 27 gt cl S4 44 Zl Jof ti J LZ LL gt ZZ LL ISI LA LL 1 Lt ok L Z 97 Z OL 97 OL e ANS 4 OL o Lt oj ktL A GZ A 6 G7 6 6 GdS WI LOL 1H 6 L o Oo L x y vz X 8 H vz 8 g JdS NWO 19D sg g
271. sitivity Common commands and SCPI commands are not case sensitive You can use upper or lower case and any case combination Examples RST rst DATA data SYSTem PRESet system preset Long form and short form versions A SCPI command word can be sent in its long form or short form version The command tables in this manual use the long form version However the short form version 1s indi cated by upper case characters SYSTem PRESet long form SYST PRES short form SYSTem PRES long form and short form combination Note that each command word must be in either long form or short form For example SYSTe PRESe is illegal and will generate an error The command will not be executed Short form rules Use the following rules to determine the short form version of any SCPI command e If the length of the command word is four letters or less no short form version exists auto auto Model 6485 Picoammeter Instruction Manual Remote Operation 9 13 These rules apply to command words that exceed four letters e If the fourth letter of the command word is a vowel delete it and all letters after it immediate imm e If the fourth letter of the command word is a consonant retain it but drop all the letters after it format form e Ifthe command contains a question mark or a non optional number included in the command word you must include it in the short form version delay del e Command words or
272. slot male triax to female BNC Model 8607 Banana cable set 1m CA 186 1B Banana lead to screw terminal adapter one model CA 186 1B is included with every order Model 6485 Picoammeter Instruction Manual Getting Started 1 5 CAP 18 Protective shield cap for BNC connectors one model CAP 18 is included with every order CS 565 barrel adapter This is a barrel adapter that allows you to connect two BNC cables together Both ends of the adapter are terminated with 2 lug female BNC connec tors GPIB and trigger link cables and adapters Models 7007 1 and 7007 2 shielded GPIB cables Connect Model 6485 to the GPIB bus using shielded cables and connectors to reduce electromagnetic interference EMI Model 7007 1 is Im long Model 7007 2 is 2m long Models 8501 1 and 8501 2 trigger link cables Connect Model 6485 to other instru ments with Trigger Link connectors e g Model 7001 Switch System Model 8501 1 is Im long Model 8501 2 is 2m long Model 8502 trigger link adapter Lets you connect any of the six trigger link lines of Model 6485 to instruments that use the standard BNC trigger connectors Model 8503 DIN to BNC trigger cable Lets you connect trigger link lines one Volt meter Complete and two External Trigger of Model 6485 to instruments that use BNC trigger connectors Model 8503 is Im long Rack mount kits Model 4288 1 single fixed rack mount kit Mounts a single Model 6485 in a standar
273. splay to agree with the calibrator current 16 8 Calibration 9 Press ENTER The unit will prompt for the negative full scale calibration point 204A CAL 10 Press ENTER The Model 6485 will prompt for the negative full scale calibration current 20 00000 uA 11 Set the calibrator output to 20 00000uA then adjust the display to agree with the calibrator value Press ENTER to complete calibration of the present range 12 Press EXIT to return to normal display 13 Repeat steps 1 through 12 for the 200UA through 20mA ranges using Table 16 4 as a guide Table 16 4 20uA to 20mA range calibration summary Model 6485 Range Calibrator Currents 20UA OUA 20 00000uA 20 00000uA 200u A OUA 200 0000u0A 200 0000UA 2mA OmA 2 000000mA 2 000000mA 20mA OmA 20 00000mA 20 00000mA Calibrate zero positive full scale and negative full scale for each range BNC shielding cap used for zero calibration point for all ranges See procedure Model 6485 Instruction Manual Model 6485 Instruction Manual Calibration 16 9 Figure 16 1 Connections for 20uA to 20mA range calibration Low noise Coax BNC Cable 00000000000 ooo DDD OO ooo 000 000 00 000 000 00 O ogo 0 oO Model 6485 Picoammeter DC Current Calibrator BNC to dual Banana Plug Adapter Connect Cable Shield to Output LO 2nA 2uA range calibration 1 Connect the voltage calibrator and the Model
274. ss the RANGE Y key to display the present LOWER range limit Scroll through the available range limits using the A and W range keys Press ENTER when the desired range is flashing If you attempt to select an incompatible range limit it will be ignored and TOO LARGE or TOO SMALL will be displayed briefly For example if the lower range limit is 20uA trying to set the upper limit to 2uA will result in the TOO SMALL error Readings can be displayed using engineering ENG units i e 1 236 mA or scientific SCI notation 1 e 1 236E 03A Perform the following steps to change the units setting I 2 NOTE Digits Press MENU key Scroll down to the UNITS item using the A or W range keys UNITS will be flash ing Press ENTER to select setting ENG or SCI will be flashing Use the A or W key to display the desired units setting Press ENTER 1 The units setting can only be changed from the front panel no remote operation 2 Scientific notation provides more resolution on small values than engineering units The DIGITS key sets display resolution for Model 6485 Display resolution can be set from 3 to 6 digits This single global setting affects display resolution for all measure ment ranges 4 4 Range Units Digits Rate and Filters Model 6485 Picoammeter Instruction Manual To set display resolution press and release the DIGITS key until the desired number of digits is displayed NOTE Changing the i
275. story page Revision A Document number 6485 901 01 November 2001 All Keithley product names are trademarks or registered trademarks of Keithley Instruments Inc Other brand names are trademarks or registered trademarks of their respective holders KG Safety Precautions The following safety precautions should be observed before using this product and any associated instrumentation Although some instruments and accessories would normally be used with non hazardous voltages there are situations where hazardous conditions may be present This product is intended for use by qualified personnel who recognize shock hazards and are familiar with the safety precautions required to avoid possible injury Read and follow all installation operation and maintenance information carefully before us ing the product Refer to the manual for complete product specifications If the product is used in a manner not specified the protection provided by the product may be impaired 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 equip ment is operated within its specifications and operating limits and for ensuring 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 instrument They must be protected from electric shock
276. strument Figure 2 4 Shielding for measurements unguarded Metal Noise Metal Noise Shield Shield HI HI Metal Safety er Shield INPUT INPUT Jj T Safety 220V Peak 220V Peak cui Ground A Noise Shield B Safety Shield Model 6485 Picoammeter Instruction Manual Measurement Concepts 2 9 Input voltage overload OVRVOLT message During normal operation there should not be a significant voltage between the input HI and LO terminals of the Model 6485 However occasionally as in the case of a DUT fail ure a customer voltage source can become shorted directly to the Model 6485 Under that condition protection circuits within the 6485 will limit the current flow for higher current ranges 20uA to 20mA Additionally when operating on the 2mA and 20mA ranges or when the 6485 auto ranges up to these ranges as a response to the applied voltage if the input voltage exceeds 60V the Model 6485 will change from a current limit to a IMQ 3MQ input impedance to prevent excess power dissipation The OVRVOLT message will be displayed to indicate the change in the protection circuit The same information is avail able with remote operation see Measurement event status page 10 13 To return the instrument to normal operation the over voltage condition must be removed Once the input voltage is reduced to under 60V the protection circuit will return to its cur rent limit operation until the current is reduced to a val
277. t all NONE OUTPut Query output trigger status 14 12 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual 15 Performance Verification Verification test requirements Summarizes environmental conditions warm up period and line power requirements Recommended test equipment Lists all equipment necessary for verification and gives pertinent specifications Verification limits Describes how reading limits are calculated and gives an example Calibrator voltage calculations Details the method for calculating calibrator voltages when testing the 2nA to 2UA ranges Performing the verification test procedures Summarizes test considerations and describes how to restore factory defaults Offset voltage calibration Lists steps necessary to null voltage offset before performing verification Current measurement accuracy Lists detailed steps for verifying measure ment accuracy of all current ranges The 2nA to 2UA and 20UA to 20mA ranges are covered separately because of the different test equipment required 1522 Performance Verification Model 6485 Instruction Manual Introduction Use the procedures in this section to verify that Model 6485 accuracy is within the limits stated in the instrument s one year accuracy specifications You can perform these verifica tion procedures When you first receive the instrument to make sure that it was not damaged during shipment To verify
278. t does not wait for the stack to fill before releasing readings Repeating Filter Takes a selected number of reading conversions averages them and yields a reading It then flushes its stack and starts over Model 6485 Picoammeter Instruction Manual Range Units Digits Rate and Filters 4 9 Figure 4 2 Digital filter averaging and advanced Classifications Current IENA B Window ZE Violation 1 of range A Integrated Time Conversion Class averaging A A gt A3 A4 As Ag Bj B B3 B4 Bs Ay Ay A2 3 4 As As B By B3 B4 Reading 5 A Ay Ay Ay A3 Aq Aq As B4 By B3 1 1 1 1 2 A3 A3 A4 As B By Type moving Ay Ay Ay 1 1 A2 A2 A3 Aq As B Reading Reading Reading Reading Reading Reading Reading Reading Reading Reading Reading 1 2 3 4 5 6 7 8 9 10 11 Conversion Class advanced Ay Ay A3 Ay As Ag B B By B B A A A A Ay As B Bj B B3 B Reading 5 Ai Ai Ai A A Aa B B B 2 B Ay Ay Ay Ai A2 A3 B B B B By Type moving Ay Ai Ai Ai Ai A2 Bj B4 B B Bi i 0 Noise level 1 of range Reading Reading Reading Reading Reading Reading Reading Reading Reading Reading Reading l 1 2 3 4 5 6 7 8 9 10 11 Conversion Class averaging Ay A A A As Ag B4 B B B B Reading Ay Ay Ay A A3 A4 A4 As B4 By B3 Ay 1 Ay Ay Ay A3 A3 Aq As B4 By Type Repeating Ay Ai A A Ai Ay Az Ag Aa As B1 Reading Reading l 1 2 Conversion Class advanced A Ay A A As Ag B B B By Bs 1 1 2 3 Ay As B B By
279. t for the string type the message must be enclosed by single or double quotes An indefinite block message must be the only command in the program message or the last command in the program message If you include a command after an indefinite block Model 6485 Picoammeter Instruction Manual DISPlay FORMat and SYSTem 13 3 message on the same line it will be treated as part of the message and is displayed instead of executed C DISPlay TEXT STATe lt b gt When the text message mode is enabled a defined message is displayed When disabled the message is removed from the display GPIB operation A user defined message remains displayed only as long as the instru ment is in remote Taking the instrument out of remote by pressing LOCAL or sending the GTL go to local command or cycling power cancels the message and disables the text message mode RS 232 operation A user defined message can be cancelled by sending SYS Tem LOCal pressing LOCAL or cycling power FORMat subsystem The commands in this subsystem are used to select the format for transferring data over the bus Table 13 2 SCPI commands data format FORMat DATA lt type gt lt length gt Specify data format ASCii REAL 32 or SREal ASCII ELEMents lt item list gt Specify data elements READing UNITS All 4 TIME and STATus BORDer lt name gt Specify byte order NORMal or SWAPped see Note SREGister lt name gt Select data for
280. t key is displayed to indicate that it is functioning properly When the key is released the message NO KEY PRESS is displayed Pressing EXIT tests the EXIT key However the second consecutive press of EXIT aborts the test and returns the instrument to normal operation A Specifications A 2 Specifications Model 6485 Picoammeter Instruction Manual 6485 Picoammeter Specifications 5 DIGIT ACCURACY 1YR DEFAULT RDG OFFSET TYPICAL RANGE RESOLUTION 18 28 C 0 70 RH RMS NOISE 2 2 nA 10 fA 0 4 400 fA 20 fA 20 nA 100 fA 0 4 1pA 100 fA 200 nA l pA 0 2 10pA l pA A UA 10 pA 0 15 100 pA 10 pA 20 pA 100 pA 0 1 InA 100 pA 200 pA l nA 0 1 10nA l nA 2 mA 10 nA 0 1 100 nA 10 nA 20 mA 100 nA 0 1 IlpA 100 nA TEMPERATURE COEFFICIENT 0 18 C amp 28 50 C For each C add 0 1 rdg offset to accuracy spec INPUT VOLTAGE BURDEN lt 200uV on all ranges except lt l1mV on 20mA range MAXIMUM INPUT CAPACITANCE Stable to 10nF on all nA ranges and 2pA range luF on 20pA and 200pA ranges and on mA ranges MAXIMUM CONTINUOUS INPUT VOLTAGE 220VDC NMRRI 50 or 60Hz 60dB MAXIMUM COMMON MODE VOLTAGE 42V ISOLATION Meter COMMON to chassis Typically gt 50010 0 in parallel with lt lnE ANALOG OUTPUT Scaled voltage output inverting 2V full scale on all ranges 3 2mV 1kQ impedance 1 At 1 PLC limited to 60 rdgs sec under this condition 2 At 6 PLC 1 standard deviation 1
281. t name gt Select data format for reading status registers ASCu HEXadecimal OCTal or BINary SREGister Query format for reading event registers NI NI Note RST default is NORMal SYSTem PRESet default is SWAPped Table 14 4 SENSe command summary SENSe 1 FUNCtion lt name gt Select measure function lt name gt CURRent DC DATA Path to return instrument readings LATest Return the last instrument reading CURRent DC Path to configure amps function NPLCycles lt NRf gt Set integration rate in line cycles PLC 6 60Hz 0 01 to 6 0 60 Hz or 5 0 SOHz 5 50Hz NPLCycles Query NPLC RANGe Configure measurement range UPPer lt NRf gt Select range 0 021 to 0 021 amps 2 1e 4 UPPer Query range value AUTO lt b gt Enable or disable autorange see Note Note RST default is ON and SYSTem PRESet default is OFF 14 6 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual Table 14 4 continued SENSe command summary Default Ref Command Description parameter Section SCPI AUTO ULIMit lt NRf gt ULIMit LLIMit lt NRf gt LLIMit AVERage TCONtrol lt name gt TCONtrol COUNt lt n gt COUNt ADVanced NTOLerance lt n gt NTOLerance STATe lt b gt STATe STATe lt b gt STATe MEDian RANK lt NRf gt RANK STATe lt b gt STATe Query state of autorange
282. t where Zs Zp the input noise is amplified by a factor of two The maximum value of source capacitance Cs for the lower ranges of the Model 6485 picoammeter is 10 000pF You can however usually measure at higher source capacitance values by inserting a resistor in series with the picoammeter input but remember that any series resistance will increase the voltage burden by I Rsgpizs For example the range of resistance listed in Table I 1 will result in voltage burden values in range of 2mV to 2V A useful alternative to a series resistor 1s a series diode or two diodes in parallel back to back The diodes can be small signal types and should be in a light tight enclo sure Electrostatic interference and shielding Electrostatic interference is probably the most common source of error when making low current measurements Electrostatic coupling or interference occurs when an electrically charged object is brought near an uncharged object At low impedance levels the effect of the interference are not noticeable because the charge dissipates rapidly However high resistance materials do not allow the charge to decay quickly which may result in unstable measurements The erroneous readings may be due to either DC or AC electrostatic fields so electrostatic shielding will help minimize the effects of these fields DC fields can produce noisy readings or undetected errors These fields can be detected when movement near an experiment such
283. te 2 SYSTem subsystem Read error queue Note 1 Read and clear oldest error status code and message Read and clear all errors status code and message Read the number of messages in queue Code numbers only Read and clear oldest error status code only Read and clear all errors status codes only Clear messages from error queue 1 Power up and CLS empties the error queue STATus PRESet has no effect 2 Power up enables error messages and disables status messages CLS and STATus PRESet have no effect Programming example read error queue The following command reads the error queue STAT QUE Read Error Queue 11 Common Commands 22 Common Commands Model 6485 Picoammeter Instruction Manual Common Commands Common commands summarized in Table 11 1 are device commands that are common to all devices on the bus These commands are designated and defined by the IEEE 488 2 standard Table 11 1 JEEE 488 2 common commands and queries CLS Clear status Clears all event registers and error queue Section 10 ESE lt NRf gt Event enable command Program the standard event enable register Section 10 ESE Event enable query Read the standard event enable register Section 10 ESR Event status register query Read the standard event enable register and clear Section 10 it IDN Identification query Returns the manufacturer model number serial A number and firmware revision levels of the unit OPC
284. than 70 unless otherwise noted Warm up period Allow the Model 6485 to warm up for at least one hour before performing calibration If the instrument has been subjected to temperature extremes those outside the ranges stated above allow additional time for the instrument s internal temperature to stabilize Typically allow one extra hour to stabilize a unit that is 10 C outside the specified temper ature range Allow the test equipment to warm up for the minimum time specified by the manufacturer Line power The Model 6485 requires a line voltage of 100 120V or 220 240V at a line frequency of 50 to 60Hz The instrument must be calibrated while operating from a line voltage within this range Be sure the line voltage setting agrees with the expected line voltage Section 17 Model 6485 Instruction Manual Calibration 16 3 Calibration considerations When performing the calibration procedures e Make sure that the test equipment is properly warmed up and connected to the Model 6485 INPUT jack e Always allow the source signal to settle before calibrating each point e Do not connect test equipment to the Model 6485 through a scanner or other switching equipment e Ifan error occurs during calibration the Model 6485 will generate an appropriate error message WARNING The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis
285. the INPUT jack before sending the above command 3 Send the appropriate command to select the range to be calibrated For example the following command selects the 20mA range SENS ICURR RANG 2e 2 4 Make appropriate connections then send the commands for each calibration point for the selected function and range For example send the following commands for the 20mA range CAL PROT SENS 0 CAL PROT SENS 2e 2 CAL PROT SENS 2e 2 NOTE Be sure the appropriate calibration signal is applied to the INPUT jack before sending the command for each calibration point See Section 16 for details 5 Repeat steps 3 and 4 for each range Table H 2 6 After all ranges are calibrated send the commands to program the calibration dates for example CAL PROT DATE 2001 12 15 CAL PROTINDUE 2002 12 15 7 Finally send the following commands to save calibration constants and then lock out calibration CAL PROT SAVE CAL PROT LOCK H 4 Remote Calibration Table H 2 Calibration commands by range SENS CURR RANG 2e 9 CAL PROT SENS 0 CAL PROT SENS 2e 9 CAL PROT SENS 2e 9 SENS CURR RANG 2e 8 CAL PROT SENS 0 CAL PROT SENS 2e 8 CAL PROT SENS 2e 8 SENS CURR RANG 2e 7 CAL PROT SENS 0 CAL PROT SENS 2e 7 CAL PROT SENS 2e 7 SENS CURR RANG 2e 6 CAL PROT SENS 0 CAL PROT SENS 2e 6 CAL PROT SENS 2e 6 SENS CURR RANG 2e 5 CAL PROT SENS 0 CAL PROT SENS 2e 5 CAL PROT SENS 2e 5 SENS CURR RANG 2e 4
286. the unknown resistance and the picoammeter Since the voltage drop across the picoammeter is negligi ble essentially all the voltage appears across the unknown resistance The resulting cur rent is measured by the picoammeter The resistance is then calculated using Ohm s Law V R I where V is the sourced test voltage I is the measured current I 20 Applications Guide Model 6485 Picoammeter Instruction Manual The basic configuration for measuring high resistance using the 6485 Picoammeter is shown in Figure I 16 The HI terminal of the 6485 is connected to one end of the unknown resistance R and the HI of the voltage source to the other end of the resistance The LO terminal of the 6485 is connected to the LO terminal of the voltage source Both LO termi nals are also connected to earth ground This should be done via the ground link on the rear of the 6485 Figure I 16 Measuring High Resistance Using the 6485 Metal Shield Programmable Measured 6485 V Source ni Current Picoammeter V 3 Equivalent Circuit To prevent generated current due to electrostatic interference place the unknown resis tance in a shielded test fixture The metal shield is connected to the LO terminal of the 6485 If the voltage source is greater than 220V a current limiting resistor in series with the 6485 HI terminal as well as protection diodes IN 3595 across the meter input should be used to prevent damage to the 6485 in the event
287. tistics will be based on the readings of the different measurement functions Perform the following steps to store readings 1 Set up the instrument for the desired configuration 2 Press CONFIG CONFIGURE will be displayed 3 Press STORE The present buffer size in readings is displayed 4 Use the cursor keys and gt and the RANGE keys A and to set the number of readings to store 1 to 2500 5 Press ENTER to save the buffer size Press the STORE key If in the immediate trigger mode the storage process will start immediately If in the external input trigger mode each input trigger or press of TRIG key will store a reading See Section 7 for information on triggering NOTE The asterisk annunciator turns on to indicate that the data storage operation is enabled It will turn off when the storage process is finished buffer full Model 6485 Picoammeter Instruction Manual Buffer 6 3 Figure 6 1 Buffer locations KEITHLEY KEITHLEY KEITHLEY 6485 PICOAMMETER 6485 PICOAMMETER 6485 PICOAMMETER 10 Reading Value Timestamp 9 Reading Value Timestamp 8 Reading Value Timestamp 7 Reading Value Timestamp 6 Reading Value Timestamp 5 Reading Value Timestamp 4 Reading Value Timestamp 3 Reading Value Timestamp 2 Reading Value Timestamp 1 Reading Value Timestamp Standard Deviation Value Average Value Peak to Peak Value Minimum Value Timestamp Maximum Value Timestamp Buffer Statistics Buffer
288. to diode leakage ii 24 Basic connection Scheme susesi anan ees 25 Focused Ion Beam signal CONNECTIONS I 26 List of Tables 1 Table 1 1 Table 1 2 Table 1 3 Table 1 4 2 Table 2 1 Table 2 2 Table 2 3 Table 2 4 Table 2 5 3 Table 3 1 4 Table 4 1 Table 4 2 Table 4 3 Table 4 4 Table 4 5 5 Table 5 1 Table 5 2 Table 5 3 6 Table 6 1 7 Table 7 1 Table 7 2 Table 7 3 8 Table 8 1 Table 8 2 Getting Started Example 2V analog output values 1 11 SCPI commands line frequency 1 13 DPetanlt setia Ssa a E 1 16 MENUSIICOIO sleale 1 18 Measurement Concepts Basic measurement Capabilities 2 2 SCPI commands autozero iii 2 3 Display messages for zero check and zero correct 2 13 SCPI commands zero check and zero correct 2 15 Summary of measurement considerations 2 16 Measurements SCPI commands amps function 3 5 Range Units Digits Rate and Filters IMIG ASUTEINENU TANCES alii nio ilari 4 2 SERI commands did1ts arailal ia la 4 4 Ranges ANd values prora 4 5 SCPLcommands fate unable 4 6 SCPLcommands Meis sleale 4 12 Relative mX b m X b reciprocal and log Range symbols for rel values 5 3 SCPI commands r
289. to shield capacitance Electrostatic voltage source To summarize error currents due to electrostatic coupling can be minimized by following these guidelines I 10 Applications Guide Model 6485 Picoammeter Instruction Manual e Keep all charged objects including people and conductors away from sensitive areas of the test circuit e Avoid movement and vibration near the test area e When measuring currents lt InA shield the device under test by surrounding it with a metal enclosure and connect the enclosure electrically to the test circuit common terminal Shielding vs Guarding Shielding usually implies the use of a metallic enclosure to prevent electrostatic interfer ence from affecting a high impedance circuit Guarding implies the use of an added low impedance conductor maintained at the same potential as the high impedance circuit which will intercept any interfering voltage or current A guard does not necessarily pro vide shielding Leakage currents and guarding page I 2 Making connections To avoid measurement errors it is critical to make proper connections from the picoam meter to the device under test To make a proper connection always connect the high resistance terminal of the meter to the highest resistance point of the circuit under test Figure I 7 shows a picoammeter connected to a current source that consists of a voltage source in series with a resistor An AC powered voltage source usually
290. ts as follows 1 Press SETUP The instrument will display the following prompt RESTORE FACT 2 Using either RANGE key select FACT then restore the factory default conditions by pressing ENTER NOTE You can use either RANGE key to select among FACT GPIB and USRO to USR2 setups Be sure you use FACT defaults for the verification procedure Model 6485 Instruction Manual Performance Verification 15 7 Offset voltage calibration Before performing the performance verification procedure perform offset voltage calibra tion as outlined below 1 Press the MENU key select CAL then press ENTER 2 The unit will display the following CAL VOFFSET 3 Press ENTER The instrument will prompt as follows INPUT CAP 4 Connect the BNC shielding cap to the INPUT jack 5 Press ENTER to complete offset voltage calibration 6 Press EXIT to return to normal display Current measurement accuracy Follow the steps below to verify that Model 6485 current measurement accuracy is within specified limits The test involves applying accurate DC currents and then verifying that the Model 6485 current readings are within required limits 20uA 20mA range accuracy 1 Connect the current calibrator to the Model 6485 INPUT jack as shown in Figure 15 1 Use the appropriate low noise coaxial cable and BNC to dual banana plug adapter where shown Set the Model 6485 to the 20UA range using the up or down RANGE key With zero check enabled zero
291. tus and questionable event status Queues Provides details and command information on the output queue and error queue 10 2 Status Structure Model 6485 Picoammeter Instruction Manual Overview Model 6485 provides a series of status registers and queues allowing the operator to mon itor and manipulate the various instrument events The status structure is shown in Figure 10 1 The heart of the status structure is the status byte register This register can be read by the users test program to determine if a service request SRQ has occurred and what event caused it Status byte and SRQ The status byte register receives the summary bits of four status register sets and two queues The register sets and queues monitor the various instrument events When an enabled event occurs it sets a summary bit in the status byte register When a summary bit of the status byte is set and its corresponding enable bit is set as pro grammed by the user the RQS MSS bit will set to indicate that an SRQ has occurred Status register sets A typical status register set is made up of a condition register an event register and an event enable register A condition register is a read only register that constantly updates to reflect the present operating conditions of the instrument When an event occurs the appropriate event register bit sets to 1 The bit remains latched to 1 until the register is reset When an event register bit is set and its
292. tus byte and service request SRQ iiii 10 7 SaS DYE FESISIOE ssaa 10 8 Service request enable register sil tide weciesiewhl node eds 10 8 Seal Polling and SRO 10 9 SPE SPD Serial polling ici 10 9 Status byte and service request commands 10 9 Programming example set MSS B6 When error OCCUIS sideris E 10 10 Stats TECIStEr SEIS aen a EE ote 10 10 Reister DIC AESCHPHONS cio 10 10 Standard Vent SlAtUS cricca 10 10 Operation vert Stalls ilaria 10 12 Measurement event Status i 10 13 Questionable event status 10 15 CONCITION TeCISTELS razor 10 15 PVCU CISICTS ela agi 10 16 Event enable registers ccccccccecccccccccnsccesseesseeenes 10 17 Programming example program and PCAC RCOIS CES ile ato 10 18 OQ US Shi as ac nae ante se Marler es ae ee ha ate raed 10 18 OUUTE drugie S 10 18 Pirrofguelef Lilli 10 18 Programming example read error queue 10 20 11 Common Commands Common Commands sso nei lidia apicali 11 2 12 13 14 15 16 SCPI Signal Oriented Measurement Commands DISPlay FORMat and SYSTem DISPlay Subsy Stem nr 13 2 BOR Mat SubS yster a iar Saieaates 13 3 SYS Tera SuDSy SlCM iatale 13 8 SCPI Reference Tables General noleSar ioni tas 14 2 Performance Verification hWodicionlsait 15 2 Verification test requirements ci tile a 15 2 Environmental conditions rakaa 15 2 Wat
293. uest enable register When a set 1 sum mary bit is ANDed with an enabled 1 bit of the enable register the logic 1 output is applied to the input of the OR gate and therefore sets the MSS RQS bit in the status byte register Model 6485 Picoammeter Instruction Manual Status Structure 10 9 The individual bits of the service request enable register can be set or cleared by using the SRE common command To read the service request enable register use the SRE query command The service request enable register clears when power is cycled or a parameter value of 0 is sent with the SRE command i e SRE 0 The commands to pro gram and read the SRQ enable register are listed in Table 10 6 Serial polling and SRQ Any enabled event summary bit that goes from 0 to 1 will set bit B6 and generate an SRQ service request In your test program you can periodically read the status byte to check if an SRQ has occurred and what caused it If an SRQ occurs the program can for exam ple branch to an appropriate subroutine that will service the request Typically SRQs are managed by the serial poll sequence of Model 6485 If an SRQ does not occur bit B6 RQS of the status byte register will remain cleared and the program will simply proceed normally after the serial poll is performed If an SRQ does occur bit B6 of the status byte register will set and the program can branch to a service subroutine when the SRQ is detected by the serial
294. um power rating 500V 14MQ 18mW NOTE The 14MQ in series will increase the measured resistance to 100 014GQ The 6485 can be programmed to calculate the resistance and subtract the series resistance Using the M X B function in the example above one would set M to 500 B to 14e6 and the units character to omega For more details on the M X B function see Section 5 2 8 Measurement Concepts Model 6485 Picoammeter Instruction Manual Noise and safety shields Figure 2 4 shows typical measurement shielding A noise shield is used to prevent unwanted signals from being induced on the picoammeter input Amps measurements below 1uA may benefit from effective shielding Typically the noise shield is connected to picoammeter input LO Additionally Figure 2 4 shows LO con nected to earth ground via the ground link WARNING The maximum safe voltage between picoammeter LO and chassis ground common mode voltage is 42V The Model 6485 does not inter nally limit the LO to chassis voltage Exceeding 42V can create a shock hazard If it is possible for the DUT or external supply to present more than 42V to the input HI it is imperative that the connection between input LO and the external voltage source be sufficiently low impedance and capable of carrying the short circuit current of the source in order that the LO not exceed 42V CAUTION The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the in
295. use and replace it with the type listed in Table 17 1 CAUTION For continued protection against fire or instrument damage replace the fuse only with the type and rating listed If the instrument repeat edly blows fuses it will require servicing 3 If configuring the instrument for a different line voltage remove the line voltage selector from the assembly and rotate it to the proper position When the selector is installed into the fuse holder assembly the correct line voltage appears inverted in the window 4 Install the fuse holder assembly into the power module by pushing it in until it locks in place Table 17 1 Line fuse ratings Line Voltage Keithley Part No 100 120V 0 63A 250V 5 x 20mm FU 106 630 slow blow 220 240V 0 315A 250V 5 x 20mm FU 106 315 slow blow Model 6485 Instruction Manual Routine Maintenance Figure 17 1 Line fuse location Model 6485 Picoammeter WARININ Gino INTERNAL OPERATOR SEFIVICABLE PARTS SERVICE 5Y QUALIFIED PERSONNEL ONLY ome KEITHLEY MADE IN U S A n ec ANALOG OUT vini FRONT PANEL MENU TRIGGER LINK RS 232 LINE RATING _ A 50 60Hz 30 VA MAX 42V PK Fuse HE 630mAT 100 VAC SB 120 VAC 815mAT 220 VAC SB 240 VAC Di CAUTION F0R CONTINUED PROTECTION AGAINST FIRE HAZARD REPLAC Fuse Holder Assembly Front panel tests The front panel tests are summarized in Table 17 2 To run a test simply press the MENU key select TES
296. voltage Exceeding 42V can create a shock hazard The LO to chassis breakdown voltage is 500V Exceeding this voltage may cause damage to the instrument CAUTION Maximum continuous input voltage is 220V DC Exceeding this value may cause instrument damage Calibration cycle Perform verification at least once a year to ensure the unit meets or exceeds its specifica tions Calibrate if necessary Recommended calibration equipment Table 16 1 lists the recommended equipment for the calibration procedures You can use alternate equipment but keep in mind that test equipment uncertainty will affect calibra tion accuracy Calibration equipment should have accuracy specifications at least four times better than corresponding Model 6485 specifications Note however that the rec ommended calibrator listed in Table 16 1 does not meet this requirement for 20UA output 16 4 Calibration Model 6485 Instruction Manual Table 16 1 Recommended calibration equipment Calibrator Fluke 5700A DC Voltage 2V 7ppm 20V Sppm 200V 7ppm DC Current 20uA 550ppm 200uA 100ppm 2mA 55ppm 20mA 55ppm Electrometer Calibration Keithley Model 5156 Nominal Resistance Standard 100MQ 200ppm 1GQ 300ppm Low noise coax cable Keithley 4801 BNC to triax adapter Keithley 237 BNC TRX BNC shielding cap Keithley CAP 18 BNC to double banana plug adapter Pomona 1269 l 90 day 23 5 C full range accuracy specifications shown Includes ppm of range an
297. ween conductors Ionic contamination may be the result of body oils salts or solder flux The problem is further enhanced by high humidity moisture that decreases insula tion resistance When building test fixtures select insulators that resist water absorption and use the fix ture in a moderate humidity environment Also be sure that all insulators are kept clean and free of contamination See Handling and cleaning test fixtures page 2 10 for clean ing tips Humidity Light Excess humidity can reduce insulation resistance on PC boards and in test connection insulators Reduction in insulation resistance can of course seriously affect high imped ance measurements Also humidity moisture can combine with contaminants to produce offset currents caused by electrochemical effects see Electrochemical effects page C 4 To minimize the effects of moisture keep humidity to a minimum ideally lt 50 and keep components and connectors in the test system clean See Handling and cleaning test fixtures page 2 10 for cleaning tips Some components such as semiconductor junctions and MOS capacitors on semiconduc tor wafers are excellent light detectors Consequently these components must be tested in a light free environment While many test fixtures provide adequate light protection oth ers may allow sufficient light penetration to affect the test results Areas to check for light leaks include doors and door hinges
298. will clear after successful calibration of Model 6485 e Bit B14 command warning Warn Set bit indicates that a signal oriented measure ment command parameter has been ignored Figure 10 7 Questionable event status Warn Cal B15 B14 B13 B8 B7 B6 BO Warn Cal B15 B14 B13 B8 B7 B6 BO Questionable CONDition Condition Register Questionable EVENt Event Register To QSB bit of Status Byte Register Questionable Event ENABle lt NRf gt Enable Register ENABle Warn Cal B15 B14 B13 B8 B7 B6 BO Decimal 16384 128 a Weights 214 27 Warn Command Warning amp Logical AND Cal Calibration Summary OR Logical OR Condition registers As Figure 10 1 shows each status register set except the standard event register set has a condition register A condition register is a real time read only register that constantly updates to reflect the present operating conditions of the instrument For example while Model 6485 1s in the idle state bit B10 Idle of the operation condition register will be set When the instrument is taken out of idle bit B10 clears 10 16 Status Structure Model 6485 Picoammeter Instruction Manual The commands to read the condition registers are listed in Table 10 4 For details on read ing registers see Reading registers page 10 6 Table 10 4 Common and SCPI commands condition reg
299. you want to null out or it could be an applied level that you want to use as a baseline 2 Press REL The REL annunciator turns on and subsequent readings will be the dif ference between the actual input and the Rel value 3 To disable REL press the REL key a second time or select a different measurement function The REL annunciator turns off NOTE When Rel is disabled the Rel value is remembered To reinstate the previous Rel value press CONFIG then press REL and finally press ENTER If the REL is disabled and then REL is pressed again it will determine and set a new null value Model 6485 Picoammeter Instruction Manual Relative mX b m X b reciprocal and log 5 3 Displaying or manually keying in REL Pressing CONFIG and then REL displays the present Rel value This displayed Rel value can be enabled pressing ENTER or a different Rel value can be entered and enabled 1 Press CONFIG and then REL The present Rel value will be displayed 2 To change the Rel value use the lt gt A and W keys and change the value To change Rel polarity place the cursor on the polarity sign and press A or W To change the Rel range place the cursor on the range symbol at the end of the read ing and use the A and W keys Table 5 1 3 With the desired Rel value displayed press ENTER to enable Rel Table 5 1 Range symbols for rel values 5 4 Relative mX b m X b reciprocal and log Model 6485 Picoammeter Instruction Manual
300. zes X_ON and X_OFF sent from the controller An X_OFF will cause Model 6485 to stop outputting characters until it sees an X_ON Incoming commands are processed after the lt CR gt character is received from the controller If NONE is the selected flow control then there will be no signal handshaking between the controller and Model 6485 Data will be lost if transmitted before the receiving device is ready 9 18 Remote Operation Model 6485 Picoammeter Instruction Manual RS 232 connections The RS 232 serial port can be connected to the serial port of a controller 1 e personal computer using a straight through RS 232 cable terminated with DB 9 connectors Do not use a null modem cable The serial port uses the transmit TXD receive RXD and signal ground GND lines of the RS 232 standard It does not use the hardware handshak ing lines CTS and RTS Figure 9 4 shows the rear panel connector for the RS 232 inter face and Table 9 2 shows the pinout for the connector Figure 9 4 RS 232 interface connector 96 7 6 RS232 Rear Panel Connector If your computer uses a DB 25 connector for the RS 232 interface you will need a cable or adapter with a DB 25 connector on one end and a DB 9 connector on the other wired straight through not null modem Table 9 3 provides pinout identification for the 9 pin DB 9 or 25 pin DB 25 serial port connector on the computer PC Model 6485 Picoammeter Instruction Manual Remote Operatio

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