Keithley 2500, Service Manual

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A-4 Specifications Model 2500 User’s Manual
Accuracy calculations
The following information discusses how to calculate accuracy for both current measure-
ment and voltage bias functions.
Current measurement accuracy
Current measurement accuracy is calculated as follows:
Accuracy = ±(% of r offset)
As an example of how to calculate the actual reading limits, assume that you are measur-
ing 1mA on the 2mA range. You can compute the reading limit range from one-year mea-
surement specifications as follows:
Accuracy = ±(% of r offset)
= ±
[(0.1% ×
1mA) + 50nA]
= ±(1
µ
A + 50nA)
= ±1.05
µ
A
Thus, the actual reading range is 1mA ±1.05
µ
A or from 0.99895mA to 1.00105mA.
Voltage bias accuracy
Voltage bias accuracy is calculated similarly, except that voltage bias specifications are
used. As an example of how to calculate the actual source output limits, assume that you
are sourcing 5V on the 10V range. You can compute the output limits from voltage bias
one-year accuracy specifications as follows:
Accuracy = ±(0.05% of s 5mV offset)
= ±
[(0.05% × 5
V
) + 5
mV
)]
= ±(2.5mV + 5mV)
= ±7.5mV
In this case, the actual voltage output range is 5V ±7.5mV or from 4.9925V to 5.0075V.