Keithley SourceMeter 2400, Service Manual, Page: 110 / 137

A-20
Accuracy calculations
The information below discusses how to calculate accuracy for both sense and source
functions.
Measure accuracy
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 measuring
10V on the 20V range. You can compute the reading limit range from one-year measure
voltage accuracy specifications as follows:
Accuracy = ±(% of r offset)
= ±[(0.015%
×
10V) + 1.5mV]
= ±(1.5mV + 1.5mV)
= ±3mV
Thus, the actual reading range is 10V± 3mV or from 9.997 to 10.003V.
DC current measurement calculations are performed in exactly the same manner using the
pertinent specifications, ranges, and input signal values.
Source accuracy
Source accuracy is calculated similarly, except source specifications are used. As an example
of how to calculate the actual source output limits, assume that you are sourcing 0.7mA on the
1mA source range. You can compute the reading limit range from source current one-year
accuracy specifications as follows:
Accuracy = ±(0.034% of 200nA offset)
= ±[(0.034%
×
0.7mA) + 200nA]
= ±(238nA + 200nA)
= ±438nA
In this case, the actual current output range is 0.7mA ±438nA or from 0.69956mA to
0.70044mA.