Keithley 2010, Service Manual, Page: 105 / 134

Specifications A-5
Accuracy calculations
The following information discusses how to calculate accuracy for both DC and AC
characteristics.
Calculating DC characteristics accuracy
DC characteristics accuracy is calculated as follows:
Accuracy = ±(ppm of r ppm of range)
(ppm = parts per million, and 10ppm = 0.001%)
As an example of how to calculate the actual reading limits, assume that you are measuring
5V on the 10V range. You can compute the reading limit range from one-year DCV accuracy
specifications as follows:
Accuracy = ±(24ppm of r 4ppm of range)
±[(24ppm
×
5V) + (4ppm
×
10V)]
±(120µV + 40µV)
±160µV
Thus, the actual reading range is 5V± 160µV or from 4.99984V to 5.00016V
DC current and resistance calculations are performed in exactly the same manner using the
pertinent specifications, ranges, and input signal values.
Calculating AC characteristics accuracy
AC characteristics accuracy is calculated similarly, except that AC specifications are given as
follows:
Accuracy = ±(% of r % of range)
As an example of how to calculate the actual reading limits, assume that you are measuring
120V, 60Hz on the 750V range. You can compute the reading limit range from ACV one-year
accuracy specifications as follows:
Accuracy = ±(0.06% of r 0.03% of range)
±[(0.0006
×
120V) + (0.0003
×
750V)]
±(0.072V + 0.225V)
±0.297V
In this case, the actual reading range is 20V± 0.297V or from 119.703V to 120.297V
AC current calculations are performed in exactly the same manner using the pertinent
specifications, ranges, and input signal values.