Tektronix 2600-STD-RES User manual

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

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

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