Keithley 6487 Reference Manual

Model 6487 Reference Manual Performance Verification 15-5
Verification limits
The verification limits stated in this section have been calculated using only Model 6487
one-year accuracy specifications and they do not include test equipment uncertainty. If a
particular measurement falls outside the allowable range, recalculate new limits based on
both Model 6487 specifications and corresponding test equipment specifications.
Example reading limits calculation
As an example of how verification limits are calculated, assume you are testing the 20mA
range using a 20mA input value. Using the Model 6487 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 5156 Calibration
Standard resistor values.
Calibrator voltages required for verification currents are calculated as follows:
V = IR
Where: V = required calibrator voltage
I = verification current
R = actual standard resistor value
For example, assume you are testing the 20nA range using an actual 100.5MΩ standard
resistor value. The actual calibrator voltage is: 20nA × 100.5MΩ = 2.01V.

Keithley 6487 Specifications

General

Type	Picoammeter/Voltage Source
Current Measurement Range	20 fA to 20 mA
Interfaces	GPIB, RS-232
Voltage Burden	< 200 µV
Input Impedance	>10^14 Ω
Power	100 V / 120 V / 220 V / 240 V
Basic Current Measurement Accuracy	0.4%