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Keithley Instruments, Inc.
28775 Aurora Road
Cleveland, Ohio 44139
1-888-KEITHLEY
www.keithley.com
Model 2600-STD-RES
1GΩ Resistor
Introduction
The Keithley Instruments Model 2600-STD-RES 1GΩ resistor is a precision guarded re sistance standard that
may be used as a high-resistance physical constant to calibrate low-current instruments. An accurate current
measurement may be made from the physical constants of resistance and voltage if the initial value of these
constants is accurately determined.
The Model 2600-STD-RES resistor is recommended for calibrating the lowest current ranges o f Keithley
Instruments Models 2635 and 2636. Similar current-sourcing and measuring instruments and other Series
2600 System SourceMeters
procedures. Table 1 shows the Model 2600-STD-RES specifications and Table 2 shows the contents of the
Model 2600-STD-RES resistance standard.
Table 1
Model 2600-STD-RES specifications
Specification Value
Max input voltage 200VDC peak
Voltage coefficient 0.2 PPM/V
Dimensions 20mm x 57mm x 114mm (0.8in x 2.25in x 4.5in)
Connectors Two 3-lug Triax
Weight 180g (6.3 oz)
Operating environment 23°C (73°F), 30%-60% RH
Nominal value of standard
Max deviation from nominal ±1%
Accuracy of characterization <100 PPM
Temperature coefficient <10 PPM / °C
1-year stability 150 PPM
Table 2
Model 2600-STD-RES shipment contents
Quantity Description
1
1 Triax to banana cable pair (part number 2600-STD-RES-070)
2 Triax to Triax cables (part number 7078-TRX-3)
2 Triax 3-slot cap (part number CAP-31)
1 Support bracket1
1 Captive panel screw1
1
Included for rack-mounting the Model 2600-STD-RES (optional).
®
can also be calibrated in part using the Model 2600-STD-RES and similar
1GΩ
Model 2600-STD-RES 1GΩ precision standard
PA-961 Rev. A / June 2008 1
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Model 2600-STD-RES 1GΩ Resistor
The Model 2600-STD-RES provides two resistor terminals plus a third that prevents stray signals from cau s ing
errors in the current flow through the resistor branch (see Figure 1). These stray signals may be leakage paths or
external electromagnetic or electrostatic fields that do not contribute a significant error at higher current
measurement values, but which can significantly affect low-level measurements (refer to the Low Level
Measurement Handbook available free of charge from the Keithley Instruments website at www.keithley.com).
Figure 1
Model 2600-STD-RES guard terminal configuration
LO
Guard
HI
1GW
General testing information
The Model 2600-STD-RES standard has three key specifications that are critical to minimizing the overall
resistance uncertainty:
1. Low temperature coefficient of resistance.
2. Long-term stability.
3. Low calibration uncertainty (when calibrated by Keithley Instruments).
In addition to resistor standard errors, the following measurement errors must be considered:
1. Voltage source uncertainty and noise.
2. Voltage measurement standard uncertainty and noise.
3. Current measurement noise of device being calibrated.
4. Settling time required for full accuracy measurement of a low-current source.
The following guidelines should be followed when conducting low-current measurements:
• Avoid temperature variations of standards and devices under test.
• Avoid vibrations, which may cause triboelectric effects.
• Average readings using a long analog-to-digital converter (A/D) aperture and an appropriate math filter
such as median filtering to decrease noise effects and allow settling.
• Be aware of errors due to noise that may not be removed by filtering.
• Consider all standard measurement uncertainties and instrument setup.
• Avoid excessive external electrical events and use guarded Triax cables. Noisy readings are typically
caused by a noisy source or improper use of the guard.
• Always verify a calibration of a low current with a final verification measurement step.
2 PA-961 Rev. A / June 2008
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Model 2600-STD-RES 1 GΩ Resistor
WARNING The maximum common-mode voltage (voltage between LO and chassis ground) is
250VDC. Exceeding this value may cause a break down in insulation, creating a shock
hazard. The Input/Output terminals of the SourceMeters® are rated for connection to
circuits rated Installation Category I only, with transients rated less than 1500V peak. Do
not connect the Series 2600 terminals to CAT II, CAT III, or CAT IV circuits. Connection of
the SourceMeter® terminals to circuits higher than CAT I can cause damage to the
equipment or expose the operator to hazardous voltage.
Hazardous voltages may be present on the output and guard terminals. To prevent
electrical shock that could cause injury or death, NEVER make or break connections to
the Series 2600 while the unit is on. Power off the equipment from the front panel or
disconnect the main power cord from the rear of the Series 2600 before handling cables
connected to the outputs. Putting the equipment into standby mode does not guarantee
the outputs are not powered if a hardware or software fault occurs.
Accuracy characterization of source-measure unit (SMU) low
current ranges
The 100pA through 100nA current ranges require a guarded current measurement to prevent errors such as
leakage from external error sources. A suitably guarded, characterized 1GΩ resistance standard (such as the
Model 2600-STD-RES) and an accurate digital multimeter (DMM) such as the Keithley Model 2002 (or
equivalent) can accurately characterize the lower ranges. The steps involve forcing a characterized voltage
across the 1GΩ resistor and comparing source measure unit (SMU) measured results against the stand ard
resistance and derived current.
Performance verification general overview
Here is a summary of how low-current range performance is characterized. The specific steps for
characterization and calibration are found in the next section.
Step 1: Characterize appropriate ± voltage source value
±100.00mV 1.5A compliance 100pA range
±1.0000V 1.5A compliance 1nA range
±10.000V 1.5A compliance 10nA range
±100.00V 100mA compliance 100nA range
Step 2: Characterize desired SMU measure current ranges
a. Measure the source voltage using an accurate DMM.
b. Determine the Model 2635/2636’s actual zero current by disconnecting the ca bles to the DMM and
capping the Model 2635/2636 terminals so that no current can flow (this is the offset of the current
measurement).
c. Connect the Model 2600-STD-RES. The source voltage (from step a, above) should be nearly perfect
so that current = voltage/resistance. This provides information for the gain error (note that this value
may vary from what the instrument is actually reporting).
PA-961 Rev. A / June 2008 3
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Model 2600-STD-RES 1GΩ Resistor
d. Measure the current with the Model 2635/2636. Average the readings using a long A/D aperture and an
appropriate math filter (such as median filtering) to decrease noise effects and to allow settling. Refer
to the Series 2600 System SourceMeter
aperture.
®
Reference Manual for more information on setting the A/D
Step 3: Characterize desired SMU source current ranges
a. Source a full-scale current value and a value near zero into the Model 2600-STD-RES.
b. Using the previously-obtained measurement values, determine the SMU source deviation from actual
values measured on the SMU.
Model 2635/2636 SMU low-current performance testing
Set up the instrument as outlined in the performance verification section of the Series 2600 System
SourceMeter
verification limits, and test equipment.
NOTE The low-current range verification and calibration process should be performed using Keithley
®
Reference Manual. The manual describes proper warm-up period, environmental conditions,
Instruments factory scripts. See your instrument’s documentation for more information on
calibrating the instrument. Factory test scripts are available for download at www.keithley.com.
Instrument settings
DMM settings are instrument-specific. Models 2635 and 2636 have front-panel settings that may be more
efficiently set by using Instrument Command Library (ICL) commands. All calibration commands are ICL
only. Predefined test scripts should be downloaded or new scripts can be created using Keithley
Instruments Test Script Builder. Test scripts and Test Script Builder are available on the Keithley
Instruments website at www.keithley.com.
Be sure to take time to review the script and embedded script comments for additional details on the test
procedure before beginning verification and calibration.
Instrument setup
1. Connect the Model 2635/2636 to a host PC and open the Test Script Builder program (or equivalent
terminal emulator) on the host PC. If you are using Test Script Builder, you can connect the host PC
and the Model 2635/2636 using any of the following methods:
• GPIB
• Serial
• RS-232
4 PA-961 Rev. A / June 2008
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Model 2600-STD-RES 1 GΩ Resistor
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
2. Install the Model 2635/2636 safety interlock as outlined in the Series 2600 System SourceMeter®
Reference Manual. Failure to install the interlock can result in inaccurate test results or cause the test
sequence to abort.
3. Load the test script into the Model 2635/2636 as outlined in the Series 2600 System SourceMeter
Reference Manual. If you are not using Test Script Builder, refer to your terminal emulator’s
documentation for information on loading test scripts.
4. Set the verification DMM to volts range and for 10 power line cycles (PLC). Filter readings by setting
the DMM to a 10-reading moving average.
5. Using the Model 2600-STD-RES-070 cables, connect the Model 2635/2636 to the DMM as shown in
Figures 2a and 2b.
6. Set the DMM to display the maximum number of digits.
Figure 2a
2635 connections for voltage verification
Input HI
®
SENSE
Input LO
HI
Digital Multimeter
U
L
C
IEEE-488
LISTED
SourceMeter
4ZA4
DIGITAL I/O
US
MADE IN
U.S.A.
LAN
NO AUTO-MDIX
SENSE
LO LO HI
RS-232
A LO
TSP-Link
CHANNEL A
GUARD
!
LINE RATING
LINE FUSE
SLOWBLOW
100-240VAC
3.15A, 250V
50, 60Hz
240VA MAX.
R
Model 2635
channel A connections
PA-961 Rev. A / June 2008 5
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Model 2600-STD-RES 1GΩ Resistor
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNE
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNE
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYP
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYP
Figure 2b
2636 connections for voltage verification
Input HI
Digital Multimeter
GUARD
SENSE
CHANNEL B
HI
DIGITAL I/O
IEEE-488
SENSELOLOHI
MADE IN
NO AUTO-MDIX
SENSE
LO LO HI
U.S.A.
LAN
RS-232
A LO
TSP-Link
CHANNEL A
GUARD
!
LINE RATING
LINE FUSE
100-240VAC
SLOWBLOW
3.15A, 250V
50, 60Hz
240VA MAX.
R
SENSE
Input LO
HI
Model 2636
channel A connections
Low-current range test procedure
NOTE When using Keithley Instruments test scripts, the verification and calibration adjustment
procedures are both performed during this test. For performance verification only, perform the
tests but do not save the calibration information at the end of the procedure. This will preserve
the current calibration constants and show you the Model 2635/2636’s current calibration
settings.
1. Load the test script into the Model 2635/2636 using a host PC running Test Script Builder or a terminal
emulator program. Notes in the script programming indicate the program name and version.
2. After loading the test script into the Model 2635/2636, run the script using Test Script Builder or the
terminal emulator on the host PC by typing the name of the program followed by (). The Model
2635/2636 immediately initiates the calibration sequence.
NOTE After running the script from the host PC using Test Script Builder or a terminal emulator, the
rest of the calibration procedure will be performed using the front panel as described below.
3. Enter the resistor value using the navigation wheel and press the ENTER key. The resistor value is
indicated on the Model 2600-STD-RES calibration certificate (included).
4. Rotate the navigation wheel to select the channel being tested and press the ENTER key.
5. The front panel display prompts you to connect the test cables to the DMM:
Connect Triax to DMM
Connect the 2635/2636 to the DMM as shown in step 4 of Instrument Setup, above. Press any key to
continue.
6 PA-961 Rev. A / June 2008
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Model 2600-STD-RES 1 GΩ Resistor
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNEL ONLY.
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYPE AND RATING.
6. The front panel display will ask you if you want to calibrate and verify the 100 pA range:
Cal/ver 100pA Range?
Select yes and press the ENTER key to verify and calibrate the 100 pA range. Select no and press the
ENTER key to go to the next test range (1nA).
7. The Model 2635/2636 outputs a voltage to the DMM. Enter the positive voltage value read by the DMM
using the navigation wheel. Press the ENTER key after entering the value. Do the same for the
negative voltage value.
8. While the unit settles, the front panel display shows the following message:
Cal/Verify Continue
Unit settling please wait
This may take several moments. Do not touch any of the front panel controls during this period or the
test will be aborted.
9. Once settling is complete, the front panel display will prompt you to connect the Model 2600-STD-RES
using the Model 7078-TRX-3 cables as shown in Figures 3a and 3b:
Connect R Standard
After the Model 2600-STD-RES is connected, press any key to continue.
Figure 3a
2635 connection to Model 2600-STD-RES
IN/OUT
HIGH
Model 2600-STD-RES
SENSE
1GW standard
CHANNEL A
SENSE
HI
GUARD
!
LINE RATING
LINE FUSE
100-240VAC
SLOWBLOW
50, 60Hz
3.15A, 250V
240VA MAX.
R
MADE IN
U.S.A.
IEEE-488
U
L
C
LISTED
SourceMeter
4ZA4
DIGITAL I/O
SENSE
US
LAN
NO AUTO-MDIX
A LO
LO LO HI
RS-232
TSP-Link
Model 2635
channel A connections
PA-961 Rev. A / June 2008 7
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Model 2600-STD-RES 1GΩ Resistor
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNE
WARNING:
NO INTERNAL OPERATOR SERVICABLE PARTS,SERVICE BY QUALIFIED PERSONNE
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYP
CAUTION:
FOR CONTINUED PROTECTION AGAINST FIRE HAZARD,REPLACE FUSE WITH SAME TYP
Figure 3b
2636 connection to Model 2600-STD-RES
IN/OUT
HIGH
Model 2600-STD-RES
SENSE
1GW standard
CHANNEL A
SENSE
HI
GUARD
!
LINE RATING
LINE FUSE
SLOWBLOW
100-240VAC
3.15A, 250V
50, 60Hz
240VA MAX.
R
SENSE
HI
GUARD
CHANNEL B
DIGITAL I/O
IEEE-488
SENSELOLOHI
MADE IN
U.S.A.
NO AUTO-MDIX
SENSE
LO LO HI
RS-232
LAN
A LO
TSP-Link
Model 2636
channel A connections
10. Once the Model 2600-STD-RES is connected, the Model 2635/2636 calibrates itself. The front panel
display shows the following message:
Cal/Verify Continue
Unit settling please wait
This may take several minutes. Do not touch any of the front panel controls during this period or the
test will be aborted.
11. Once the Model 2635/2636 has completed the calibration for that range, the resulting SMU
measurements for that range are displayed on the host PC by Test Script Builder or the terminal
emulator. Record these readings and compare them to the specifications for each range found in Table
3. Note that the information in Table 3 is based on 90% of full-scale values (see the Series 2600
System SourceMeter® Reference Manual for more information).
NOTE After listing the SMU measurements in step 11, the front panel display of the Model 2635/2636
may continue to display the following message for several more minutes. This is normal.
Cal/Verify Continue
Unit settling please wait
8 PA-961 Rev. A / June 2008
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Model 2600-STD-RES 1 GΩ Resistor
Table 3
Model 2635/2636 current measurement accuracy limits
Source and
measure range
100pA 90.000pA 89.7850 to 90.2150pA
1nA 0.90000nA 0.89841 to 0.90159nA
10nA 9.0000nA 8.9835 to 9.0165nA
100nA 90.0000nA 89.9060 to 90.0940nA
1
Measure range coupled to source range when simultaneously sourcing and
measuring current.
2
As measured by precision digital multimeter. Use closest possible value, and
modify reading limits accordingly if necessary.
Source current
1
12. After completing the calibration of each range, the front panel display asks if you wish to calibrate the
next range. Repeat steps 2 through 10 for all ranges.
13. When the calibration for all selected channels is complete, the front panel display asks if you wish to
save calibration changes. Select yes or no by turning the navigation wheel, then press the ENTER
key.
Current reading limits
2
(1 year 18°C – 28°C)
NOTE Selecting no will not save the correction factors. All calibration adjustments will be lost at the
next system boot.
14. If you selected yes when prompted to save calibration changes, follow the front panel display prompts
to enter the current calibration date and the next calibration date using the navigation wheel and the
ENTER key.
15. Press the EXIT key to exit calibration mode after the front panel display shows the following message:
Cal complete!
16. Once calibration is complete, run the procedure a second time to verify proper calibration results.
PA-961 Rev. A / June 2008 9
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