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Status Structure

Model 6485 Picoammeter Instruction Manual

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

.

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.

Queues

Model 6485 uses two queues which are first-in, first-out (FIFO) registers:

•

Output queue — Used to hold reading and response messages.

•

Error queue — Used to hold error and status messages.

Model 6485 status model (

) 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 addressing 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.

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Summary of Contents for 6485

Page 1: ...Model 6485Picoammeter Instruction Manual A G R E A T E R M E A S U R E O F C O N F I D E N C E ...

Page 2: ...ECIAL 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 Instruments Inc 28775 Auror...

Page 3: ...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 ...

Page 4: ...ld incorporate immediately into the manual Addenda are numbered sequentially When a new Revision is created allAddenda 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 history page Revision A Document number 6485 901 01 November 2001 All Keithley product names are trademarks or registere...

Page 5: ...an sient over voltages Installation Category II connections require protection for high transient over voltages often associated with localAC 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 ca...

Page 6: ... 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 ...

Page 7: ...ction Manual 1 5 Additional references 1 6 Features 1 6 Front and rear panel familiarization 1 6 Front panel summary 1 6 Rear panel summary 1 8 Analog output 1 10 Display 1 12 Status and error messages 1 12 Power up 1 12 Line power connection 1 12 Line frequency 1 13 Front panel procedure 1 13 SCPI programming line frequency 1 13 Power up sequence 1 14 Default settings 1 15 Front panel setup opera...

Page 8: ... 2 10 Guard plate 2 10 Connectors terminals and internal wiring 2 10 Handling and cleaning test fixtures 2 10 Input protection 2 11 Floating measurements 2 12 Zero check and zero correct 2 13 Zero check 2 13 Zero correct 2 14 SCPI programming zero check and zero correct 2 15 A SYSTem ZCORrect ACQuire 2 15 B SYSTem ZCORrect STATe b 2 16 Measurement considerations 2 16 3 Measurements Measurement ove...

Page 9: ...ter 4 8 Digital filter classifications 4 8 Digital filter types 4 8 Response time 4 10 Operation consideration 4 10 Digital filter control 4 11 SCPI programming filters 4 12 Programming example 4 12 5 Relative mX b m X b reciprocal and log Relative 5 2 Setting and controlling relative 5 2 REL key 5 2 Displaying or manually keying in REL 5 3 SCPI programming relative 5 4 Programming example relativ...

Page 10: ...ont panel 7 7 SCPI programming 7 9 Programming example 7 11 External triggering 7 11 Input trigger requirements 7 12 Output trigger specifications 7 12 External trigger example 7 13 8 Limit Tests Limit testing 8 2 Front panel operation 8 5 Limit test configuration 8 5 Limits configuration menu 8 5 Arm layer configuration menu 8 5 Perform limit tests 8 6 Step 1 Configure test system 8 6 Step 2 Conf...

Page 11: ...clear 9 8 GET group execute trigger 9 9 SPE SPD serial polling 9 9 Front panel GPIB operation 9 9 Error and status messages 9 9 GPIB status indicators 9 9 LOCAL key 9 10 Programming syntax 9 10 Command words 9 10 Query commands 9 12 Case sensitivity 9 12 Long form and short form versions 9 12 Short form rules 9 12 Program messages 9 13 Single command messages 9 13 Multiple command messages 9 14 Co...

Page 12: ...e register 10 8 Service request enable register 10 8 Serial polling and SRQ 10 9 SPE SPD serial polling 10 9 Status byte and service request commands 10 9 Programming example set MSS B6 when error occurs 10 10 Status register sets 10 10 Register bit descriptions 10 10 Standard event status 10 10 Operation event status 10 12 Measurement event status 10 13 Questionable event status 10 15 Condition r...

Page 13: ... calculation 15 5 Calibrator voltage calculations 15 5 Performing the verification test procedures 15 6 Test considerations 15 6 Restoring factory defaults 15 6 Offset voltage calibration 15 7 Current measurement accuracy 15 7 20mA 20mA range accuracy 15 7 2nA 2mA range accuracy 15 8 16 Calibration Introduction 16 2 Environmental conditions 16 2 Temperature and relative humidity 16 2 Warm up perio...

Page 14: ... 16 13 Displaying the calibration count 16 13 17 Routine Maintenance Introduction 17 2 Setting line voltage and replacing line fuse 17 2 Front panel tests 17 3 DISP test 17 4 KEY test 17 4 A Specifications B Status and Error Messages C General Measurement Considerations Measurement considerations C 2 Ground loops C 2 Triboelectric effects C 3 Piezoelectric and stored charge effects C 3 Electrochem...

Page 15: ...mands F 10 Common commands F 11 SCPI commands F 11 Command codes F 11 Typical command sequences F 12 IEEE command groups F 13 Interface function codes F 14 G IEEE 488 and SCPI Conformance Information Introduction G 2 GPIB 488 1 Protocol G 3 Selecting the 488 1 protocol G 4 Protocol differences G 4 Message exchange protocol MEP G 5 Using SCPI based programs G 5 NRFD hold off G 5 NDAC hold off G 6 T...

Page 16: ... transients are smaller I 14 Steps to minimize impact of range change transients I 15 Run test with a fixed range I 15 Down range by starting at highest current necessary I 15 Using protection circuitry I 16 Reduce up ranging transient I 16 Zero check on off response I 16 Applications I 18 Diode leakage current I 18 Capacitor leakage current I 19 Measuring high resistance with external bias source...

Page 17: ...k enabled 2 14 3 Measurements Figure 3 1 Connections for amps 3 4 4 Range Units Digits Rate and Filters Figure 4 1 Speed vs noise characteristics 4 5 Figure 4 2 Digital filter averaging and advanced classifications 4 9 Figure 4 3 Digital filter types moving and repeating 4 10 6 Buffer Figure 6 1 Buffer locations 6 3 7 Triggering Figure 7 1 Trigger model front panel operation 7 2 Figure 7 2 Trigger...

Page 18: ... 12 Figure 10 6 Measurement event status 10 14 Figure 10 7 Questionable event status 10 15 13 DISPlay FORMat and SYSTem Figure 13 1 ASCII data format 13 4 Figure 13 2 IEEE 754 single precision data format 32 data bits 13 5 Figure 13 3 Key press codes 13 10 15 Performance Verification Figure 15 1 Connections for 20µA to 20mA range verification 15 8 Figure 15 2 Connections for 2nA to 2µA range verif...

Page 19: ...Connecting the HI terminal picoammeter to high resistance I 10 Figure I 8 Proper connection I 11 Figure I 9 Improper connection I 12 Figure I 10 Range change voltage transients I 13 Figure I 11 Transient Voltage I 14 Figure I 12 Down range voltage transients I 15 Figure I 13 Zero check transient I 17 Figure I 14 Connections diode leakage current test I 18 Figure I 15 Connections capacitor leakage ...

Page 20: ......

Page 21: ... 3 1 SCPI commands amps function 3 5 4 Range Units Digits Rate and Filters Table 4 1 Measurement ranges 4 2 Table 4 2 SCPI commands digits 4 4 Table 4 3 Ranges and values 4 5 Table 4 4 SCPI commands rate 4 6 Table 4 5 SCPI commands filters 4 12 5 Relative mX b m X b reciprocal and log Table 5 1 Range symbols for rel values 5 3 Table 5 2 SCPI commands relative null 5 4 Table 5 3 SCPI commands mX b ...

Page 22: ... IEEE 488 2 common commands and queries 11 2 12 SCPI Signal Oriented Measurement Commands Table 12 1 Signal oriented measurement command summary 12 2 13 DISPlay FORMat and SYSTem Table 13 1 SCPI commands display 13 2 Table 13 2 SCPI commands data format 13 3 Table 13 3 SCPI commands system 13 8 14 SCPI Reference Tables Table 14 1 CALCulate command summary 14 2 Table 14 2 DISPlay command summary 14...

Page 23: ...us byte and mask interpretation D 13 F IEEE 488 Bus Overview Table F 1 IEEE 488 bus command summary F 7 Table F 2 Command codes F 8 Table F 3 Hexadecimal and decimal command codes F 11 Table F 4 Typical bus sequence F 12 Table F 5 Typical addressed command sequence F 12 Table F 6 IEEE command groups F 13 Table F 7 Model 6485 interface function codes F 14 G IEEE 488 and SCPI Conformance Information...

Page 24: ......

Page 25: ...izes 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 thre...

Page 26: ...m X b Reciprocal and Log Section 6 Buffer Section 7 Triggering Section 8 Limit test Section 9 Remote Operation Section 10 Status Structure Section 11 Common Commands Section 12 SCPI Signal Oriented Measurement Commands Section 13 DISPlay FORMat and SYSTem Section 14 SCPI Reference Tables Section 15 Performance Verification Section 16 Calibration Section 17 Routine Maintenance Appendices to this ma...

Page 27: ... to the operating instructions located in the manual The 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 i...

Page 28: ... throughout this manual Accessories as ordered Certificate of calibration Model 6485 User Manual P N LCHR 950 01 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 includ...

Page 29: ...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 lm long Rack mount kits Model 4288 1 single fixed rack mount kit Mounts a single Model 6485 in a standard 19 inch rack Model 4288 2 side by side rack mount kit...

Page 30: ...and factory defaults can be saved 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 readi...

Page 31: ...erform and configure properties of the mX b math function M X B Use to perform and configure properties of the m X b math function LOG Use to convert output display to log10 on off REL Use to control and configure properties of the rel ative function ZCHK Use to perform a Zero Check function ZCOR Use to control Zero Correct function on off 3 Operation keys COMM Use to control and modify communicat...

Page 32: ...d move to next choice or back to measurement display 4 Range keys 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 AUTO Enables disables autorange 5 Display annunciators asterisk Readings being stored in buffer more Indicates additional selections are available ...

Page 33: ...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 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 120 FUSE LINE 630mA LINE ...

Page 34: ...e 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 Exampl...

Page 35: ... nominal value Fuse Test Lead Poly fuse Auto resetting 120 FUSE LINE 630mA LINE RATING 50 60Hz 30 VA T SB 100 VAC 120 VAC 315mAT SB 220 VAC 240 VAC INPUT CHANGE IEEE ADDRESS WITH FRONT PANEL MENU IEEE 488 CAT I TRIGGER LINK RS 232 MADE IN U S A 220V PK ANALOG OUT Model 6485 Rear Panel RL Input Resistance of measuring device Input from Prescaler COM S S 0 1Ω 1kΩ Measuring Device i e Chart recorder ...

Page 36: ...ssages 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...

Page 37: ...tory 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 Press MENU 2 Scroll to the LFREQ menu item using the and range keys The present settin...

Page 38: ... 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 5 If the FACTory setup ...

Page 39: ...d as the power on setup NOTE At the factory the factory default setup is saved into the USR0 USR1 and USR2 setups Front panel setup operation To save a user setup 1 Configure Model 6485 for the desired measurement application 2 Press SAVE to access the save setup menu 3 Use the or key to display the desired memory location 0 USR0 1 USR1 2 USR2 4 Press ENTER NOTE Saved setups should not be used in ...

Page 40: ...up 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 Setting Factory SYStem PRESet GPIB RST Trig Layer CONF TRIG TRIG Arm In Source Event TRIG IN IMM Arm Layer CONF ARM Arm In Source Event Arm Count Input Trigger Link Line Source Bypass Output Trigger Link Line Output Trigger IMM INF 1 NEVER 2 Off 1 Buff...

Page 41: ...0 0 0 X Range AUTO Rate NPLC Slow 6 0 60Hz or 5 0 50Hz Rel Rel Value VAL Off 0 0 RS 232 All Settings 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 IMM 1 0 1 NEVER 2 Units No effect Zero Check Enabled Zero Correct Disabled Table 1 3 continued Default settings Setting Factory ...

Page 42: ...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 follow...

Page 43: ...t 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 command 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 is sent to the ...

Page 44: ...1 20 Getting Started Model 6485 Picoammeter Instruction Manual ...

Page 45: ...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 ...

Page 46: ...orresponding 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 ...

Page 47: ...zero SYST AZER OFF Disable autozero SYST AZER Query autozero 1 on 0 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 ...

Page 48: ...e 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 will be at same voltages as applied to the BNC she...

Page 49: ...ctors on each end One Model 4801 is included standard with every order Model 4802 10 This 10 ft 3m 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 15m 50 ft of low noise coax cable 10 male BNC connectors 5 female BNC chassis mount connectors NOTE As a general rule always use the shortest pos...

Page 50: ...ors 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...

Page 51: ...ess 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 Lowest range to be used Rin 2nA or 20nA 11MΩ 200nA or 2µA 3 5MΩ 20µA or 200µA 50kΩ 2mA or 20mA 500Ω The series limiting resistor should have a minimum power rating of Ex...

Page 52: ...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 t...

Page 53: ... 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 valid on scale level Extended ope...

Page 54: ... 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...

Page 55: ...tection 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 ini...

Page 56: ...aximum 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 impedan...

Page 57: ...ro 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 Table 2 3 Display messages for zero check and zero correct Display Message Zero Check Ze...

Page 58: ...e 3 Press ZCOR to enable zero correct ZZ message displayed 4 Press ZCHK to disable zero check 5 Readings can now be taken from the display The CZ message indicates that the displayed reading is zero corrected 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 correcte...

Page 59: ...Enable zero check CURR RANG 2E 4 Set instrument to 200uA range INIT Trigger one reading SYST ZCOR ACQ 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 ...

Page 60: ...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 conduc...

Page 61: ...3 Measurements Measurement overview Summarizes the current measurement capabilities of Model 6485 and provides a basic procedure to measure amps SCPI programming Covers the basic SCPI commands ...

Page 62: ...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 p...

Page 63: ...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 surroun...

Page 64: ... 4801 4802 10 or 4803 Input Metal Safety Shield Metal Noise Shield 120 FUSE LINE 630mA LINE RATING 50 60Hz 30 VA T SB 100 VAC 120 VAC 315mAT SB 220 VAC 240 VAC INPUT CHANGE IEEE ADDRESS WITH FRONT PANEL MENU IEEE 488 CAT I TRIGGER LINK RS 232 MADE IN U S A 220V PK ANALOG OUT HI LO Safety Earth Ground ...

Page 65: ...ommands 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 RST Return 6485 to RST defaults SYST ZCH ON Enable zero check CURR RANG 2e ...

Page 66: ...3 6 Measurements Model 6485 Picoammeter Instruction Manual ...

Page 67: ...units and display resolution selection Includes the SCPI commands for remote opera tion Rate Provides details on reading rate selection 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 ...

Page 68: ...ure the applied signal Up ranging occurs at 105 of range while down ranging occurs at the range value For example if on the 20µA range the instrument will go up to the 200µA range when the input signal exceeds 21µA While on the 200µA range the instrument will go down to the 20µA range when the input level goes below 20µA The AUTO key toggles the instrument between manual ranging and autoranging Th...

Page 69: ... the desired range is flashing NOTE 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 20µA trying to set the upper limit to 2µA will result in the TOO SMALL error Units Readings can be displayed using engineering ENG units i e 1 236 mΑ or scientific SCI notation i e 1 236E 03Α Perform...

Page 70: ...0mA range DISP DIG 3 5 Set display resolution to 3 1 2 digits Table 4 2 SCPI commands digits Commands Description Default DDC CURRent RANGe UPPer n AUTO b ULIMit n LLIMit n For Digits DISPlay DIGits n Measure current Range selection Specify expected reading 0 021 to 0 021 A See Table 4 3 Enable or disable autorange Specify upper range limit for autorange 0 021 to 0 021 A Specify lower range limit ...

Page 71: ...d 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 100ms Figure 4 1 Speed vs noise characteristics Table 4 3 Ranges and values Range n value Display 5 digit resolution DDC 20mA...

Page 72: ...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 1 Press CONFIG LOCAL and then RATE to display the present PLC value 2 Use the and keys to adjust to th...

Page 73: ...dian 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 1mA 3mA The readings are rearranged in an ascending order as follows 1mA 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 cal...

Page 74: ... 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 ...

Page 75: ... B3 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A2 A2 A2 A2 A2 A2 A2 A2 A2 A2 A3 A4 A4 A4 A4 A4 A4 A4 B4 B4 B4 B4 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A1 A6 A6 A6 A2 A3 A3 A3 A3 A3 B3 B3 B3 B3 B3 B3 A1 Reading 1 Conversion Class averaging Reading 5 Type moving Conversion Class advanced Reading 5 Type moving Noise level 1 of range Conversion Class averaging Reading 5 Type Repeating Convers...

Page 76: ...r of reading conversions Speed and noise are tradeoffs Noise window For the advanced filter a tradeoff of speed noise and response to input signal changes Operation consideration The digital filter operation will reset start over whenever the zero check operation is performed or the range is changed Conversion 10 9 8 7 6 5 4 3 2 1 Conversion Reading 10 Conversion 12 11 10 9 8 7 6 5 4 3 Conversion ...

Page 77: ...mmediately 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 Use the range keys or to display the desired filter count value at the RDGS prompt Press ENTER to set 4 Set filter type REPEAT or MOVING AV Use the range keys or to display the desired filter typ...

Page 78: ...R ADV ON Enable advanced filter AVER ON Enable digital filter Table 4 5 SCPI commands filters Commands Description Default For median filter SENSe 1 MEDian RANK n STATe b For digital filter SENSe 1 AVERage TCONtrol name COUNt n ADVanced NTOLerance n STATe b STATe b SENSe Subsystem Median Filter Specify filter rank 1 to 5 Enable or disable median filter SENSe Subsystem Digital Filter Select filter ...

Page 79: ...ative Explains how to null an offset or establish a baseline value Includes the SCPI commands for remote operation mX b m X b reciprocal and Logarithmic Covers these three basic math operations and includes the SCPI commands for remote operation ...

Page 80: ...esult 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 ...

Page 81: ...esent Rel value will be displayed 2 To change the Rel value use the and keys and change the value To change Rel polarity place the cursor on the polarity sign and press or To change the Rel range place the cursor on the range symbol at the end of the read ing and use the and keys Table 5 1 3 With the desired Rel value displayed press ENTER to enable Rel Table 5 1 Range symbols for rel values Symbo...

Page 82: ...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 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 ...

Page 83: ...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 also changes it for m X b Pressing the mX b key togg...

Page 84: ...guration 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 and range keys The character can be any letter in the alphabet A through Z 7 Press ENTER The MATH annunciator and the units designa...

Page 85: ...eadings However you can use the DATA LATest command to return the last CALC1 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 CALC1 reading Table 5 3 SCPI commands mX b m X b and log Commands Description Default Ref DDC CALCulate 1 FORMa...

Page 86: ...performs 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 ...

Page 87: ...6 Buffer Buffer operations Explains how to store and recall readings including buffer statistics SCPI programming Covers the SCPI commands used to control buffer opera tions ...

Page 88: ...ough a power cycle Measurement function changes are permissible during the storage process Note however that the statistics will be based on the readings of the different measurement functions Store 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 displ...

Page 89: ...NGE RANGE RDG NO 10 Reading Value Timestamp RDG NO 9 Reading Value Timestamp RDG NO 8 Reading Value Timestamp RDG NO 7 Reading Value Timestamp RDG NO 6 Reading Value Timestamp RDG NO 5 Reading Value Timestamp RDG NO 4 Reading Value Timestamp RDG NO 3 Reading Value Timestamp RDG NO 2 Reading Value Timestamp RDG NO 1 Reading Value Timestamp STD DEV Standard Deviation Value AVERAGE Average Value PK P...

Page 90: ...e time between the readings Buffer statistics MIN and MAX provides the minimum and maximum readings stored in the buffer It also indicates the buffer location of these readings The PK PK peak to peak value is the difference between the maximum and minimum readings stored in the buffer PK PK MAX MIN Average is the mean of the buffer readings Mean is calculated as follows Where Xi is a stored readin...

Page 91: ...4 floating point format for statistics calculations Table 6 1 SCPI commands buffer Commands Description Default Ref TRACe CLEar FREE POINts n ACTual FEED name CONTrol name TSTamp FORMat name DATA FORMat ELEMents list CALCulate3 FORMat name DATA TRACe Subsystem Clear readings from buffer Query bytes available and bytes in use Specify number of readings to store 1 to 2500 Returns number of readings ...

Page 92: ...mber of readings the asterisk annunciator turns off NEVer Disables the buffer D TRACe TSTamp FORMat name Name parameters ABSolute Each timestamp is referenced to the first reading stored in the buffer DELTa Timestamps provide the time between each buffer reading 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 fou...

Page 93: ...ct 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 C...

Page 94: ...EAD TIME Select reading and timestamp Store and Recall Readings TRIG COUN 20 Set trigger model to take to 20 readings TRAC POIN 20 Set buffer size to 20 TRAC FEED SENS Store raw input readings TRAC FEED CONT NEXT Start storing readings INIT Trigger readings setup to SRQ on buffer full see Figure G 2 for example TRAC DATA Request all stored readings Acquire Mean Statistic for Buffer Readings CALC3 ...

Page 95: ...nt Also explains how to configure the trigger model from the front panel SCPI programming Includes the commands used to configure the trigger model and the commands to control the measurement process External triggering Explains external triggering which allows Model 6485 to trigger other instruments and be triggered by other instruments ...

Page 96: ...el front panel operation Arm In Source Immediate GPIB Timer Manual TLink Arm Event Detector Trigger Event Detector Trigger Delay MEASURE Action No Yes Idle Another Arm Another Trigger Yes No Arm Layer Trigger Layer Trigger In Source INF 1 Yes Halt No Once Bypass Arm Event Detector Never Bypass Trigger Event Detector Once Never Output Trigger VMC On Off Trigger Count Output Trigger TL Done On Off A...

Page 97: ...r Trigger In Source 0 0 sec No See Note INITiate Yes SOURce ARM DIRection ACCeptor ARM SOURce IMMediate ARM SOURce BUS ARM SOURce TIMer ARM SOURce MANual ARM SOURce TLINk TRIGger DIRection SOURce ACCeptor TRIGger DELay n TRIGger OUTPut SENSe NONE TRIGger COUNt n ARM OUTPut TRIGger NONE ARM COUNt n TRIGger SOURce IMMediate TRIGger SOURce TLINk Note The following commands place the Model 6485 into i...

Page 98: ...e 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 INITiate READ MEASure While operating within the trigger model not in idle most commands will not be exe cuted until...

Page 99: ...to 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 Not...

Page 100: ...here 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 ...

Page 101: ...ee 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 and range k...

Page 102: ...ontrol source to TLINK Set TLINK value 1 6 Enable set to ONCE or disable set to NEVER ARM Path to ARM layer submenus ARM IN IMM TLINK TLINK EVENT MAN TIMER GPIB 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 ...

Page 103: ...LINk or MANual Set measure count 1 to 2500 or INF infinite Set timer interval 0 001 to 99999 999 sec Enable SOURce or disable ACCeptor bypass Configure input output triggers Select input trigger line 1 2 3 4 5 or 6 Select output trigger line 1 2 3 4 5 or 6 Output trigger TRIGger or not at all NONE Trigger Layer Clear pending input trigger immediately Trigger path Select control source IMMediate or...

Page 104: ...f idle and all readings that are taken are returned See Section 13 for details on READ C ARM SOURce name With the TIMer control source selected use the ARM TIMer command to set the timer interval D ARM DIRection name The source bypass can only be used if the TLINk control source is selected E ARM ILINe NRf and ARM OLINe NRf Input trigger and output trigger cannot share the same trigger link line D...

Page 105: ...External triggering 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 connecti...

Page 106: ...fications 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 Trig...

Page 107: ... 7 which uses a Model 6485 to measure 10 DUTs switched by a Model 7158 low current card in a Model 7001 or 7002 switch system Figure 7 7 DUT test system 120 FUSE LINE 630mA LINE RATING 50 60Hz 30 VA T SB 100 VAC 120 VAC 315mAT SB 220 VAC 240 VAC INPUT CHANGE IEEE ADDRESS WITH FRONT PANEL MENU IEEE 488 CAT I TRIGGER LINK RS 232 MADE IN U S A RANGE DEPENDENT ANALOG OUT DUT 2 DUT 1 DUT 10 7158 Low Cu...

Page 108: ... 10 using the and range keys and the 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 for details on buffer operation 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 Cha...

Page 109: ...s 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 Idle Bypass B Wait for Trigger Link Trigger Scan Channel C Output Trigger Trigger D No Scanned 10 Channels Yes 7001or 7002 Make Measurement Made 10 Measurements 6485 Press STEP to start scan A W...

Page 110: ... the first channel point C D After the relay settles Model 7001 2 outputs a trigger pulse Since the instrument is programmed to scan 10 channels operation loops back to point B where it waits for an input trigger E and F 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 ...

Page 111: ...imit 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 ...

Page 112: ... shows an example where the HI and LO limits for limit 1 are 2mA and the Hi and LO limits for limit 2 are 1mΑ A 0mA 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 LO LO Limit Limit HI HI Limit Limit Limit 1 Test Wide Pass Band Limit 2 Test Narrow Pass Band Fail Fail Fail Fa...

Page 113: ...asses 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...

Page 114: ...emote 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 Pass Start Measure DUT Yes Limit 1 Test No Display L1 Limit 2 Test Pas...

Page 115: ...value place the cursor on or and press either of the or range keys To change range for the value place the cur sor on the range symbol and scroll using the and range keys P pico N nano µ 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...

Page 116: ...del 6485 for the desired measurement as covered in the previous sections of this manual Step 3 Configure limit tests Configure Model 6485 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 terminate...

Page 117: ...ULL OFFSet NRf STATe b DATA LATest 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 Conf...

Page 118: ... 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 name Typical start of test option...

Page 119: ...peration and reference Covers the following GPIB topics GPIB Bus Standards GPIB Bus Connections Primary Address Selection General Bus Commands Front Panel GPIB Operation Programming Syntax RS 232 interface reference Provides basic reference information for the RS 232 interface and explains how to make connections to the computer ...

Page 120: ...C 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 SCPI language 488 2 DDC language 488 1 language NOTE For the RS 232 inter...

Page 121: ...NFIG key and then the COMM key to configure the GPIB address and language From this menu you can check or change the following settings Primary address 0 30 Language SCPI SCPI 1996 0 which includes 488 2 488 1 or DDC Press the or range keys to scroll through ADDress and LANGuage available To make changes to a setting press the key Then use the or range keys and the and cursor keys to select and mo...

Page 122: ... 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 IEEE 488 1 1987 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 instrume...

Page 123: ... 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 To avoid possible mechanical damage stack no more than three con...

Page 124: ...ng sure not to over tighten them 3 Connect 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 proper...

Page 125: ...ommands such as DCL that have the same general mean ing regardless of the instrument Table 9 1 lists the general bus commands 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 act...

Page 126: ...he 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...

Page 127: ...tions GPIB status indicators The REM remote TALK talk LSTN listen and SRQ service request annunciators show the GPIB bus status Each of these indicators is described below 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 t...

Page 128: ... 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 NRf Parameter NRf required RST No parameter used DISPlay ENABle b Parameter b r...

Page 129: ... hexadecimal and Q octal SRE B10001 Set bits B0 and B4 of Service Request Enable Register n 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 default value When the MINimum parame ter is used the instrument is programmed to the lowest allowable value When the MAX...

Page 130: ...owable value Case sensitivity 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 is in...

Page 131: ...ach 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 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 anothe...

Page 132: ...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 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 The colon at the beginning of a program ...

Page 133: ...ays use the short form versions of commands and parameters 4 Minimize the amount of white space in command strings 5 Keep numeric parameters simple i e 1 vs 1 000e 00 6 Use all upper case Response messages A response message is 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 mess...

Page 134: ...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 Ta...

Page 135: ...eed 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 th...

Page 136: ... 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 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 thr...

Page 137: ...inal ready 5 GND signal ground 6 DSR data set ready 7 RTS ready to send 8 CTS clear to send 9 No connections RTS and CTS are tied together DCD DTR and DSR are tied together Table 9 3 PC serial port pinout Signal DB 9 pin number DB 25 pin number DCD data carrier detect 1 8 RXD receive data 2 3 TXD transmit data 3 2 DTR data terminal ready 4 20 GND signal ground 5 7 DSR data set ready 6 6 RTS reques...

Page 138: ...9 20 Remote Operation Model 6485 Picoammeter Instruction Manual ...

Page 139: ...ucture 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 status and questionable event status Queues Provides de...

Page 140: ... 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 regist...

Page 141: ... 12 13 15 Event Register 8 9 8 11 12 13 15 Register Logical OR Always Zero Operation Complete Query Error Device Specific Error Execution Error Command Error User Request Power On OPC QYE DDE EXE CME URQ PON ESR ESE NRf ESE MSB MSB 12 13 12 13 Event Register 12 13 Register Logical OR Condition Register 1 1 Calibration Summary Warn 2 2 2 4 IOV Cal 1 Cal 1 Cal 1 11 11 11 Trigger Layer Command Warnin...

Page 142: ...ear error queue CLS STATus QUEue CLEar SYSTem ERRor CLEar Reset all bits of the following event registers to 0 Standard event register Operation event register Measurement event register Questionable event register STATus subsystem Reset all bits of the following enable registers to 0 Operation event enable register Measurement event enable register Questionable event enable register Clear all mes...

Page 143: ...here 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 N...

Page 144: ...01 bits B5 B2 and B0 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 o...

Page 145: ... data format for reading status registers name ASCii Decimal format HEXadecimal Hexadecimal format OCTal Octal format BINary Binary format ASCii Status Summary Messages 6 OSB B7 RQS B6 MSS ESB B5 MAV B4 QSB B3 EAV B2 B1 B0 OR SRE SRE Status Byte Register Service Request Enable Register OSB Operation Summary Bit MSS Master Summary Status RQS Request for Service ESB Event Summary Bit MAV Message Ava...

Page 146: ...tandard 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 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...

Page 147: ...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 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 th...

Page 148: ... NOTE An example program to demonstrate serial polling Generating SRQ 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 ...

Page 149: ... bit indicates that Model 6485 detected an error while trying to execute a command Bit B5 command error CME Set bit indicates that a command error has occurred Command errors include IEEE 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 PON B7 CME B5 EXE B4 DDE B3 QYE B2 B1 OR Standard Event Regist...

Page 150: ...at Model 6485 is calibrating Bit B5 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 Bit B10 idle state Idle Set bit indicates Model 6485 is in the idle state Figure 10 5 Operation event status OR...

Page 151: ...has failed Bit B4 high limit 2 fail HL2F Set bit indicates that the high limit 2 test has failed Bit B5 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 b...

Page 152: ...2 2 21 Decimal Weights RAV B6 B15 B11 EVENt 64 26 BFL B9 BAV B8 LL1F B1 ROF B7 LP B5 HL2F B4 LL2F B3 HL1F B2 Measurement Condition Register B0 RAV B6 B15 B11 CONDition BFL B9 BAV B8 LL1F B1 Measurement Event Register ROF B7 LP B5 HL2F B4 LL2F B3 HL1F B2 B0 RAV B6 B15 B11 BFL B9 BAV B8 LL1F B1 512 29 256 28 HL2F High Limit 2 Fail LL2F Low Limit 2 Fail HL1F High Limit 1 Fail LL1F Low Limit 1 Fail EN...

Page 153: ... 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 is 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 OR...

Page 154: ...rs are listed in Table 10 5 For details on reading registers see Reading registers page 10 6 Table 10 4 Common and SCPI commands condition registers Command Description STATus OPERation CONDition MEASurement CONDition QUEStionable CONDition STATus subsystem Read operation condition register Read measurement condition register Read questionable condition register Table 10 5 Common and SCPI commands...

Page 155: ...e 0 parameter value with the appropriate enable command i e STATus OPERation ENABle 0 Table 10 6 Common and SCPI commands event enable registers Command Description ESE NDN or NRf ESE STATus OPERation ENABle NDN or NRf ENABle MEASurement ENABle NDN or NRf ENABle QUEStionable ENABle NDN or NRf ENABle Program standard event enable register see Parameters Read standard event enable register STATus su...

Page 156: ...ut 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 ...

Page 157: ...nds 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 occur 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 list parameter is used to specify which messages to enable or disable The messages...

Page 158: ...ages for error queue Read the enabled messages Specify messages not to be placed in queue Read the disabled messages Clear messages from error queue SYSTem subsystem Read error queue 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 ...

Page 159: ...11 CommonCommands ...

Page 160: ...n complete command Set the operation complete bit in the standard event register after all pending commands have been executed B OPC Operation complete query Places an ASCII 1 into the output queue when all pending selected device operations have been completed B OPT Option query Returns model number of any installed options RCL NRf Recall command Returns Model 6485 to the user saved setup C RST R...

Page 161: ...the output queue after all pending command operations are complete Typically either one of these commands is 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 operati...

Page 162: ...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 pe...

Page 163: ...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 Sequ...

Page 164: ...11 6 Common Commands Model 6485 Picoammeter Instruction Manual ...

Page 165: ...12 SCPISignalOriented MeasurementCommands ...

Page 166: ...hen the operation returns to the idle state When this command is executed Model 6485 will be configured as follows The specified function is selected All controls related to the selected function are defaulted to the RST values The event control sources of the trigger model are set to immediate The arm and trigger count values of the trigger model are set to one The delay of the trigger model is s...

Page 167: ...hen 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...

Page 168: ...er 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 CONFigure function 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...

Page 169: ...SPlay subsystem Covers the SCPI commands that are used to control the display FORMat subsystem Covers the SCPI commands to configure the format that readings are sent over the bus SYSTem subsystem Covers miscellaneous SCPI commands ...

Page 170: ... ASCII long A space is counted as a character Excess message characters result in an error Note that 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 Table 13 1 SCPI commands display Command Description ...

Page 171: ...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 Command Description Default Ref FORMat DATA type length Specify data format ASCii...

Page 172: ...ii 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 fo...

Page 173: ...er un talk Model 6485 until after the data is read input to the computer 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 prod...

Page 174: ...econds 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 ...

Page 175: ...ment was turned on C FORMat BORDer name 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 ...

Page 176: ... 0 seconds Select power on setup RST PRESet or SAVx where x 0 to 4 Query SCPI revision level Read messages in error queue Return and clear oldest error code and message Return and clear all errors code and message Return the number of errors Error code numbers only Return and clear oldest error code only Return and clear all errors codes only Clear messages from error queue Simulate key press see ...

Page 177: ...lts 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 NRf 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 H...

Page 178: ...er 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 RANGE AUTO CONFIG LOCAL MENU POWER RANGE EXIT ENTER HALT RATE DIGITS STORE RECALL MEDN AVG MX B M X B LOG REL ZCHK ZCOR COMM DISP TRIG LIMIT AZERO SAVE SETUP 1 2 3 4 5 6 7 8 16 11 12 13 23 32 15 14 31 24 26 19 ...

Page 179: ...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 ...

Page 180: ...mand subsystem SCPI A checkmark 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 or more non SCPI parameters are explained by notes Table 14 1 CALCulate command summary Command ...

Page 181: ...tate of limit 1 test FAIL Return result of limit 1 test 0 pass or 1 fail LIMit2 Limit 2 Testing UPPer Configure upper limit DATA n Set limit 9 99999e20 to 9 99999e20 1 0 DATA Query upper limit LOWer Configure lower limit DATA n Set limit 9 99999e20 to 9 99999e20 1 0 DATA Query lower limit STATe b Enable or disable limit 2 test OFF STATe Query state of limit 2 test FAIL Return result of limit 2 tes...

Page 182: ...ery display state WINDow 1 Path to control user text messages TEXT Note 2 DATA a Define ASCII message a up to 12 characters DATA Read text message STATe b Enable or disable text message mode Note 3 STATe Query state of text message mode Notes 1 RST and SYSTem PRESet have no effect on the display circuitry Pressing LOCAL or cycling power enables ON the display circuit 2 RST and SYSTem PRESet have n...

Page 183: ...r BINary ASC 13 SREGister Query format for reading event registers Note RST default is NORMal SYSTem PRESet default is SWAPped Table 14 4 SENSe command summary Command Description Default parameter Ref Section SCPI SENSe 1 FUNCtion name Select measure function name CURRent DC CURR DATA Path to return instrument readings 3 LATest Return the last instrument reading CURRent DC Path to configure amps ...

Page 184: ... to 105 0 NTOLerance Query noise tolerance STATe b Enable or disable advanced filter OFF STATe Query state of advanced filter STATe b Enable or disable digital filter OFF STATe Query state of digital filter MEDian Path to control median filter 4 RANK NRf Specify n for rank 1 to 5 rank 2n 1 1 RANK Query rank STATe b Enable or disable median filter OFF STATe Query state of median filter Table 14 5 S...

Page 185: ...Sable list Specify messages not to be placed in queue Note 5 DISable Read the disabled messages CLEar Clear messages from error queue Parameters NDN Bxx x Binary format each x 1 or 0 Hx Hexadecimal format x 0 to FFFF Qx Octal format x 0 to 177777 NRf 0 to 65535 Decimal format list 100 200 224 Example of a range and single entry 100 through 200 and 224 Notes 1 Commands in this subsystem are not aff...

Page 186: ...frequency setting AUTO Path to control auto frequency SYSTem LFRequency AUTO continued STATe b Enable or disable auto frequency ON STATe Query state of auto frequency AZERo Path to control autozero 2 STATe b Enable or disable autozero ON STATe Query state of autozero TIME Timestamp RESet Reset timestamp to 0 seconds POSetup name Select power on setup RST PRESet or SAVx where x 0 2 PRES POSetup Que...

Page 187: ...r DATA as root command see Note 6 DATA Read the contents of the buffer data store CLEar Clear readings from buffer FREE Query bytes available and bytes in use POINts n Specify size of buffer 1 to 2500 100 ACTual Query number of readings stored in buffer POINts Query buffer size FEED name Select source of readings for buffer SENSe 1 CALCulate 1 or CALCulate2 SENS1 CONTrol name Select buffer control...

Page 188: ...Rection name Enable SOURce or disable ACCeptor bypass ACCeptor DIRection Query arm source bypass ASYNchronous Configure input output triggers ILINe NRf Select input trigger line 1 2 3 4 5 or 6 1 ILINe Query input trigger line OLINe NRf Select output trigger line 1 2 3 4 5 or 6 2 OLINe Query output trigger line OUTPut name Output trigger TRIGger or not at all NONE NONE OUTPut Query output trigger s...

Page 189: ...put output triggers ILINe NRf Select input trigger line 1 2 3 4 5 or 6 1 ILINe Query input trigger line OLINe NRf Select output trigger line 1 2 3 4 5 or 6 2 OLINe Query output trigger line OUTPut name Output trigger after measurement SENSe or not at all NONE NONE OUTPut Query output trigger status Table 14 8 continued TRIGger command summary Command Description Default parameter Ref Section SCPI ...

Page 190: ...14 12 SCPI Reference Tables Model 6485 Picoammeter Instruction Manual ...

Page 191: ...ge calculations Details the method for calculating calibrator voltages when testing the 2nA to 2µA 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 measur...

Page 192: ... 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 tes...

Page 193: ...d 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...

Page 194: ...pm 20mA 55ppm Electrometer Calibration Standard Keithley Model 5156 Nominal Resistance 2 100MΩ 200ppm 1GΩ 300ppm Low noise coax cable BNC to triax adapter BNC shielding cap BNC to double banana plug adapter Keithley 4801 Keithley 237 BNC TRX Keithley CAP 18 Pomona 1269 1 90 day 23 5 C full range accuracy specifications shown Uncertainty for 20µA output current does not meet the recommended four ti...

Page 195: ...A input value Using the Model 6485 20mA range accuracy specifica tion of 0 1 of reading 1µA the calculated reading limits are Reading limits 20mA 20mA 0 1 1µA 20mA 0 02mA 0 001mA 20mA 0 021mA 19 979mA to 20 021mA Calibrator voltage calculations When verifying the 2nA 2µA current ranges you must calculate the actual calibrator volt ages from the desired current values and the characterized Model 51...

Page 196: ...afe 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 Restorin...

Page 197: ...adings are within required limits 20µA 20mArange 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 2 Set the Model 6485 to the 20µA range using the up or down RANGE key 3 With zero check enabled zero correct the Model 6485 then disable zero check 4 Set the calibr...

Page 198: ...rned on 5 Enable the Model 6485 REL mode Leave REL enabled for the remainder of the test Table 15 2 Reading limits for 20µA to 20mA ranges Model 6485 Range Calibrator Current Model 6485 Current Reading Limits 1 Year 18 C 28 C 20µA 20 0000µA 19 9790 to 20 0210µA 200µA 200 000µA 199 790 to 200 210µA 2mA 2 00000mA 1 99790 to 2 00210mA 20mA 20 0000mA 19 9790 to 20 0210mA 120 FUSE LINE 630mA LINE RATIN...

Page 199: ...le 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 2µA ranges Model 6485 Range Nominal Calibrator Voltage Calibration Standard Resistor1 Nominal Applied Current Actual Voltage2 Model 6485 Current Reading Limits 1 Year 18 C 28 C 2nA 2V 1GΩ 2 00000nA ______V 1 99160 to 2 00840nA 20nA 2V 100MΩ 20 0000nA __...

Page 200: ... PK MADE IN U S A CHANGE IEEE ADDRESS WITH FRONT PANEL MENU IEEE 488 CAT TRIGGER LINK RS 232 ANALOG OUT BNC to Triax Adapter on INPUT Triax Cable Supplied with Model 5156 Connect Calibrator to 100MΩ or 1GΩ Resistor Link Shield and Chassis Model 6485 Picoammeter DC Voltage Calibrator BNC to dual Banana Plug Adapter 100GΩ 100MΩ 10GΩ 1GΩ 1nF 100nF OUTPUT Connect Cable Shield to Output LO Low noise Co...

Page 201: ... 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 2µA ranges Calibration procedure Provides step by step procedures for calibrating ...

Page 202: ...mperature of 22 to 24 C with relative humidity of less 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 stabi...

Page 203: ... 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 calib...

Page 204: ...n Manufacturer Model Specifications Calibrator Fluke 5700A DC Voltage 1 2V 7ppm 20V 5ppm 200V 7ppm DC Current 1 20µA 550ppm 200µA 100ppm 2mA 55ppm 20mA 55ppm Electrometer Calibration Standard Keithley Model 5156 Nominal Resistance 2 100MΩ 200ppm 1GΩ 300ppm Low noise coax cable BNC to triax adapter BNC shielding cap BNC to double banana plug adapter Keithley 4801 Keithley 237 BNC TRX Keithley CAP 1...

Page 205: ...inty ratio 2nA 7ppm 300ppm 13 0 20nA 7ppm 200ppm 19 3 200nA 5ppm 200ppm 9 8 2uA 7ppm 200ppm 7 2 20uA 550ppm 1 8 200uA 100ppm 10 0 2mA 55ppm 18 2 20ma 55ppm 18 2 Table 16 3 Calibration menu Menu Item Description 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...

Page 206: ...e using a 2V calibrator voltage with an actual 100 5MΩ standard resistor value The actual calibration current is 2V 100 5MΩ 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 ...

Page 207: ...P 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 20µA 20mArange calibration 1 Connect the BNC shielding cap to the Model 6485 rear panel INPUT jack 2 Select the Model 6485 20µA range 3 Press MENU select CAL then press ENTER At the CAL RUN prompt press ENTER The unit will ...

Page 208: ... ENTER to complete calibration of the present range 12 Press EXIT to return to normal display 13 Repeat steps 1 through 12 for the 200µA through 20mA ranges using Table 16 4 as a guide Table 16 4 20µA to 20mA range calibration summary Model 6485 Range Calibrator Currents 20µA 0µA 20 00000µA 20 00000µA 200µA 0µA 200 0000µA 200 0000µA 2mA 0mA 2 000000mA 2 000000mA 20mA 0mA 20 00000mA 20 00000mA Cali...

Page 209: ...ion 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 nega...

Page 210: ...ake connections to the correct standard resistor and set the cali brator voltages to the correct values Table 16 5 2nA to 2µA range calibration summary Model 6485 Range Calibrator Voltages Standard Resistors1 Calibration Currents2 2nA 0V 2 000000V 2 000000V 1GΩ 1GΩ 1GΩ 0nA 2nA 2nA 20nA 0V 2 000000V 2 000000V 100MΩ 100MΩ 100MΩ 0nA 20nA 20nA 200nA 0V 20 00000V 20 00000V 100MΩ 100MΩ 100MΩ 0nA 200nA 2...

Page 211: ...tion due date as desired then press ENTER The unit will prompt you as follows SAVE CAL YES 6 With theYES 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 120 FUSE LINE 630mA LINE RATING 50 60Hz 30 VA T SB 100 VAC 120 VAC 315mAT SB 220 VAC 240 VAC INPUT INPUT COM M ON 42V PK 220V PK MADE IN U S A CHANGE...

Page 212: ...trument will prompt for the present calibration code CODE 000000 4 Enter the 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 5 Select Y then press ENTER The unit w...

Page 213: ...libration date for example DATE 11 15 01 3 Press ENTER to view the calibration due date for example NDUE 11 15 02 4 Press EXIT to return to normal display Displaying the calibration count To display the calibration count at any time 1 From normal display press MENU select CAL then press ENTER The unit will display the following CAL VOFFSET 2 Use either RANGE key to select CAL COUNT from the calibr...

Page 214: ...16 14 Calibration Model 6485 Instruction Manual ...

Page 215: ...nance 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 Front panel tests Covers testing the front panel keys and the display ...

Page 216: ...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 fuse 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 req...

Page 217: ...l through the menu choices with the RANGE keys and press ENTER Table 17 2 Front panel tests Test Description DISP Test display KEY Test front panel keys 120 FUSE LINE 630mA LINE RATING 50 60Hz 30 VA MAX T SB 100 VAC 120 VAC 315mAT SB 220 VAC 240 VAC INPUT INPUT COM M ON 42V PK 220V PK MADE IN U S A CHANGE IEEE ADDRESS WITH FRONT PANEL MENU IEEE 488 CAT TRIGGER LINK RS 232 ANALOG OUT Fuse Spring Wi...

Page 218: ...played The 12 digits and annunciators are sequentially displayed The annunciators located at either end of the display are sequentially dis played 4 When finished abort the display test by pressing EXIT The instrument returns to normal operation KEY test 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 TE...

Page 219: ...A Specifications ...

Page 220: ...LINE COMMANDS IFC REN EOI SRQ ATN INTERFACE FUNCTIONS SH1 AH1 T5 TE0 L4 LE0 SR1 RL1 PP0 DC1 DT1 C0 E1 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 IMPLEMEN...

Page 221: ...B StatusandErrorMessages ...

Page 222: ...lf test failed Save recall memory lost Configuration memory lost Program syntax error 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 Trig...

Page 223: ...t 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 l...

Page 224: ... 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 los...

Page 225: ...number Mismatched parentheses Not a number of data handle Mismatched brackets Too many parentheses Entire expression not parsed Unknown token Error parsing 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...

Page 226: ...dent 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 962 963 965 966 Keithley 6485 Serial Poll Byte Events DDC Ready DDC Reading Done DDC Buffer Full DDC Reading overflow SE SE SE SE Table B 1 continued Status and error messages Number Description Ev...

Page 227: ...C GeneralMeasurement Considerations ...

Page 228: ...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 To prevent ground loops instruments should be connected to ground at...

Page 229: ...se 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 Use the shortest cables possible and secure them i 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 cer...

Page 230: ... and cleaning test fixtures page 2 10 for cleaning tips Light 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 c...

Page 231: ...nt 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 Locate the test circuit as far away ...

Page 232: ...d 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 ma...

Page 233: ...D DDCEmulationCommands ...

Page 234: ...he 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 Table D 1 Device dependent command summary Mode Command Description Equivalent SCPI command...

Page 235: ... bus hold off on X NEW SCPI not available K3 Disable both EOI and bus hold off on X NEW SCPI not available Store Calibration none L0 store calibration command not supported CALibration PROTected SAVE CALibration PROTected LOCK F G SRQ Status Bits Set M0 Clears SRQ Data Mask STATus MEASurement EVENt ENABle 0 SRE value value current SRE value 0x01 None X M1 Reading Overflow STATus MEASurement EVENt ...

Page 236: ...ent SRE value 0x01 B3 B1 B0 NEW M16 Busy ESE 1 SRE value value current SRE value 0x20 B4 H M17 Busy or Reading Overflow ESE 1 STATus MEASurement EVENt ENABle 128 SRE value value current SRE value 0x20 0x01 B4 B0 H M18 Busy or Data Store Full ESE 1 STATus MEASurement EVENt ENABle 512 SRE value value current SRE value 0x20 0x01 B4 B1 NEW H M19 Busy or Data Store Full or Reading Overflow ESE 1 STATus...

Page 237: ...SRE value 0x20 0x01 B4 B3 B1 B0 NEW H M32 Clears SRQ Error Mask ESE 0 this disables all events in the Standard Event Register SRE value value current SRE value ESB None X M33 IDDCO B5 B0 I M34 IDDC B5 B1 I M35 IDDC or IDDCO B5 B1 B0 I M36 Not in Remote B5 B2 I M37 Not in Remote or IDDCO B5 B2 B0 I M38 Not in Remote or IDDC B5 B2 B1 I M39 Not in Remote IDDC or IDDCO ESE 48 Enables the SCPI command ...

Page 238: ... per second Q2 One reading every 10 seconds Q3 One reading per minute Q4 One reading every 10 minutes Q5 One reading per hour Q6 Trigger mode Q7 Disabled X Range R0 Auto SENSe 1 CUR Rent DC RANGe UPPer AUTO ON X R1 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 2µA SENSe 1 CUR Rent DC RANGe UPPer 2e 6 R5 20µ...

Page 239: ...RIGger SEQuence 1 COUNt INF INIT IMMediate T3 One shot triggered by GET ARM SEQuence 1 SOURce BUS ARM SEQuence 1 COUNt INF TRIGger SEQuence 1 COUNt 1 INIT IMMediate T4 Continuous triggered by X SCPI Not Available T5 One shot triggered by X SCPI Not Available T6 Continuous triggered by External Trigger ARM SEQuence 1 SOURce TLINk ARM SEQuence 1 SOURce COUNt 1 TRIGger SEQuence 1 COUNt INF INITiate I...

Page 240: ...the actual number of readings stored in the buffer F Calibration must be already unlocked and enabled G See CALibration subsystem Status Word U0 Return status word See Figure D 1 Each parameter must be queried individually For example SENSe 1 CURRent RANGe U1 Send data conditions See Figure D 2 NEW U2 Buffer size and readings stored See Figure D 3 D NEW Digital Calibration V Calibration commands V...

Page 241: ...s 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 the 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 Suppor...

Page 242: ...Not in Remote IDDCO or IDDC TRIGGER 0 Continuous on Talk 1 One shot on Talk 2 Continuous on Get 3 One shot on Get 4 Continuous on X 5 One shot on X 6 Continuous on External Trigger 7 One shot on External Trigger Also see Byte 5 in Status Byte 4 8 5 C D R Z K T M d M e Y STATUS WORD SRQ Data Mask see Legend 00 SRQ Disabled 01 Reading Overflow 02 DSF 03 DSF or Overflow 08 Done 09 Done or Overflow 10...

Page 243: ...ore 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 P Digital Filter 0 Off 1 Off 2 Repeat filter on where filter size n 4 8 5 M N B Q J P P P P STATUS DATA CONDITION FORMAT J Digits returned 4 3 1 2 digits resolution 5 4 1 2 digits resolution 6 5 1 2 digi...

Page 244: ...eading 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 B0 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 dat...

Page 245: ...ent 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 SRQ its status byte must be read to clear the SRQ line Otherwise the instrum...

Page 246: ...485 Picoammeter Instruction Manual Figure D 4 Status byte format MSB B7 B6 B5 B4 B3 B2 B1 B0 LSB 0 Data Busy Reading Done Data Store Full Reading Overflow Data Conditions B5 0 Error Conditions B5 1 Not in Remote IDDC IDDCO 1 Error 1 SRQ ...

Page 247: ...E ExamplePrograms ...

Page 248: ...t to 2500 SENS CURR RANG AUTO OFF Turn auto range off SENS CURR NPLC 01 Set integration rate to 01 PLC SENS CURR RANG 002 Use 2mA range SYST ZCH OFF Turn zero check off SYST AZER STAT OFF Turn auto zero off DISP ENAB OFF Turn display off CLS Clear status model TRAC POIN 2500 Set buffer size to 2500 TRAC CLE Clear buffer TRAC FEED CONT NEXT Set storage control to start on next reading STAT MEAS ENA...

Page 249: ...turn 6485 to RST defaults FORM ELEM READ Return readings only FORM BORD SWAP Set for swapped byte order FORM DATA SRE Return single precision floating point binary TRIG DEL 0 Set trigger delay to zero seconds TRIG COUNT 8 Set trigger count to 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 ...

Page 250: ...E 4 Example Programs Model 6485 Picoammeter Instruction Manual ...

Page 251: ...F IEEE 488BusOverview ...

Page 252: ...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 2 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 availab...

Page 253: ...om 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 actu...

Page 254: ...es 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 DEVICE 1 ABLE TO TALK LISTEN AND CONTROL COMPUTER DEVICE 2 ABLE TO TALK AND LISTEN 2182 DEVICE 3 ONLY ABLE TO LISTEN PRINTER DEVICE 4 ONLY ABLE TO TALK DAV NRFD NDAC IFC ATN SRQ REN EOI DA...

Page 255: ...nes 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 ...

Page 256: ...uence 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 F 2 IEEE 488 handshake sequence Bus commands The instrument may be given a number of special bus commands through the IEEE 488 interface The following paragraphs brie...

Page 257: ...ble SDC Selective Device Clear GTL Go To Local UNL Unlisten UNT Untalk X X X Low X Low Low Low Low Low Low Low Low High High Set up devices for remote operation Marks end of transmission 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 condit...

Page 258: ... ACK BEL BS HT LF VT FF CR SO SI GTL SDC PPC GET TCT DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC FS GS RS US LLO DCL PPU SPE SPD SP 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 0 1 2 3 4 5 6 7 8 9 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 UNL A B C D E F G H I J K L M N O 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 P Q R S T U V W X Y Z 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 UNT a b c d e f g h i j...

Page 259: ... 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 addressi...

Page 260: ...nfiguration 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 ...

Page 261: ...er and are based on the instrument model defined by the Standard Commands for Programmable Instruments 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 t...

Page 262: ...ive listeners are present Note that ATN is true for both the listen command and the SDC command byte itself Table F 5 gives a typical common command sequence In this instance ATN is true while the instrument is being addressed but it is set high while sending the common command string Table F 4 Typical bus sequence Step Command ATN state Data bus ASCII Hex Decimal 1 2 3 4 UNL LAG SDC Set low Stays...

Page 263: ...R 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 TALK 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...

Page 264: ...es 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 the instrument exist only after it has been addressed to listen SR Service Request Function SR1 defi...

Page 265: ...ity 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 TE0 LE Extended Listener Function The instrument does not have extended listener capabilities LE0 E Bus Driver Type The instrument has open collector bus drivers E1 ...

Page 266: ...F 16 IEEE 488 Bus Overview Model 6485 Picoammeter Instruction Manual ...

Page 267: ...G IEEE 488andSCPI ConformanceInformation ...

Page 268: ...of 6485 when valid address is entered Power On Setup Conditions Message Exchange Options Input buffer size Queries that return more than one response message unit Queries that generate a response when parsed Queries that generate a response when read Coupled commands Functional elements required for SCPI commands Buffer size limitations for block data Syntax restrictions Response syntax for every ...

Page 269: ...ssed in this appendix 15 16 17 18 19 20 21 22 23 Macro information Response to IDN identification Storage area for PUD and PUD Resource description for RDT and RDT Effects of RST RCL and SAV TST information Status register structure Sequential or overlapped commands Operation complete messages Not applicable See Common Commands in Section 12 Not applicable Not applicable See Common Commands in Sec...

Page 270: ...ed language either DDC SCPI or 488 1 will be flashing 5 Scroll using 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 protoc...

Page 271: ...not attempt to read data from the 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 EOI 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 ...

Page 272: ...he bus until it is finished executing a command The follow ing command controls NDAC hold off SYSTem MEP HOLDoff ON 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 DAV SOURCE SOURCE VALID ALL READY ACCEPTOR NRFD NDAC A...

Page 273: ... 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 SRQ on MAV for queries that take a long time to execute General operation notes The TALK LSTN and SRQ annunciators are not functional in the 488 1 protocol This speeds up data throughput greatly The REM annunciator still opera...

Page 274: ...c poin 200 status Set buffer size to 200 CALL send addr trac feed cont next status Enable buffer CALL send addr stat pres status Reset measure enable bits CALL send addr cls status Clear all event registers CALL send addr stat meas enab 512 status Enable buffer bit B9 CALL send addr ese 0 status Disable standard events CALL send addr sre 1 status Enable measurement events CALL send addr init statu...

Page 275: ...bration 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 ...

Page 276: ...assword CODE code Eight character code password used to enable or unlock calibration Default KI006485 CODE Calibration code query LOCK Lock out further calibration LOCK Return 1 if calibration is locked 0 otherwise SENSe NRf Calibrate active current range DATA Query measurement cal constants SAVE Save all calibration data to non volatile memory DATE yyyy mm dd Year Month Day when cal was last perf...

Page 277: ...mmand to select the range to be calibrated For example the following command selects the 20mA range SENS CURR 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...

Page 278: ...ANG 2e 6 CAL PROT SENS 0 CAL PROT SENS 2e 6 CAL PROT SENS 2e 6 20µA SENS CURR RANG 2e 5 CAL PROT SENS 0 CAL PROT SENS 2e 5 CAL PROT SENS 2e 5 200µA SENS CURR RANG 2e 4 CAL PROT SENS 0 CAL PROT SENS 2e 4 CAL PROT SENS 2e 4 2mA SENS CURR RANG 2e 3 CAL PROT SENS 0 CAL PROT SENS 2e 3 CAL PROT SENS 2e 3 20mA SENS CURR RANG 2e 2 CAL PROT SENS 0 CAL PROT SENS 2e 2 CAL PROT SENS 2e 2 Full scale calibratio...

Page 279: ...rence 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 sho...

Page 280: ...uality 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 is to use good quality insulators when building the test circuit Some good quality insulators are Teflon polyethylene and sapphire Avoid materi als such as phenolics and nylon Refer to Keithley s Low Level Handbook for ...

Page 281: ... 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 vol...

Page 282: ...ENU key to display the following CAL VOFFSET 2 Press ENTER The instrument will prompt as follows INPUT CAP 3 It is 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 5MΩ therefore continued signal currents will present a corre sponding voltage to the DUT 4 Press ENTER...

Page 283: ...source voltage and VNOISE is the noise voltage Finally RF and CF are the feedback resistance and capacitance respectively The source noise gain of the circuit can be given by the following equation Note that as RS decreases in value the output noise increases For example when RF RS the input noise is multiplied by a factor of two Since decreasing the source resistance can have a detrimental effect...

Page 284: ...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 CF Taking into account the capacitive reac tance of these two elements the previous noise gain formula must be modified as follows Table I 1 Minimum recommended source resistance values Range Minimum Recommended Source Resistance 2nA 20nA 1 MΩ t...

Page 285: ...atic 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 electrost...

Page 286: ... change 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...

Page 287: ... 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 I 6 Electrostatic shielding To summarize error currents due to electrostatic coupling can be minimized by following these guidelines A 6485 Picoammeter Metal Shield R V HI LO HI LO...

Page 288: ...t 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 termina...

Page 289: ...e 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 I 8 Proper connection However when the HI of the picoammeter is connected to the low impedance power sup ply this AC current i flows through the picoammeter A as illustrated in Figure I 9 This current may affect the measurement...

Page 290: ...nd 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 change occurs the picoammeter will momentarily become a cur rent limited voltage source as shown in Figure I 10 Current Source 6485 Picoammeter i HI LO R A Current Source 6485 Picoammeter i HI LO R A ...

Page 291: ...imited 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 200µA signal on 200µA 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 RF is also greatly reduced The polarity depends on ...

Page 292: ...ange 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 20µA to 2µA with a 2µA 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 2µA range 100 times greater t...

Page 293: ...xed range Choose the higher range from any of the range pairs listed above Alternatively the autorange upper limit RANGe AUTO ULIMit see Voltages greater than 220V page 2 6 or Autorange lim its page 4 3 can be set so that the internal limiting resistor RF cannot be reduced to the lower values Choose the appropriate range to accommodate the maximum current expected during normal measurements Down r...

Page 294: ...ternal limiting resistor RF would damage the DUT the up ranging transient can be reduced greatly by reducing the input current to 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 ...

Page 295: ... Instruction Manual Applications Guide I 17 Figure I 13 Zero check transient Table I 2 Internal impedance for zero check transient Range Zcheck Transient impedance 2mA 20mA 500Ω 20µA 200µA 50kΩ 200nA 2µA 3 5MΩ 2nA 20nA 11MΩ ...

Page 296: ...he 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 ...

Page 297: ...specified time to allow the capacitor to discharge Figure I 15 Connections capacitor leakage current test Measuring high resistance with external bias source The 6485 Picoammeter can be used to make high resistance 1GΩ measurements when used with an external voltage source High resistance measurement applications include insulation resistance testing and resistivity measurements of insulators To m...

Page 298: ...nt 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 the unknown resistan...

Page 299: ...med 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 ...

Page 300: ...res the current Sur face insulation resistance can now be calculated as follows where V is the sourced test voltage I is the measured current Figure I 19 Connections surface insulation resistance test 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...

Page 301: ...angement to take cur rent measurements from multiple pads Measuring photo diode leakage can be described in two steps 1 Vsweep Imeas in total darkness 2 Vbias Imeas in calibrated optical flux In the 1st 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...

Page 302: ...light see dashed lines of Figure I 22 Figure I 22 Avalanche photo diode leakage 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 Lin...

Page 303: ...d 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 b...

Page 304: ...thley 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 connecti...

Page 305: ...6 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 COM...

Page 306: ...nt 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 F 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 com...

Page 307: ... 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 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 ...

Page 308: ...14 Primary address 9 7 Procedure 16 6 Program Message Terminator PMT 9 15 Program messages 9 13 Q Query commands 1 19 9 12 Questionable event status 10 15 Queues 10 18 R 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 20µA to 20mA ranges 15 8 Reading limits for 2n...

Page 309: ...orm 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 I 6 SPE SPD serial polling 9 9 SPE 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...

Page 310: ...and Inspection 1 3 user setup 1 15 Using common commands and SCPI commands in the same message 9 14 V 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 W Warm up period 2 2 Warranty information 1 3 Z ZCHK 1 7 ZCOR 1 7 Zero Check D 2 Zero check and zero correct 2 13 Zero Correct D 6 ...

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Page 312: ...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 Reading 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 80 509 1322 ITALY Viale San Gimignano 38 20146 Milano 02 48 39 16 01 Fax 02 48 30 22 74 ...

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