Keithley 2750, Service Manual

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A-2 Accuracy and Optimization Model 2750 Multimeter/Switch System Service Manual
Accuracy calculations
The information below 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 measur-
ing 5V on the 10V range. You can compute the reading limit range from one-year DCV
accuracy specifications as follows:
Accuracy = ±(30ppm of r 5ppm of range)
±[(30ppm

5V) + (5ppm

10V)]
±(150µV + 50

V)
±200µV
Thus, the actual reading range is: 5V± 200µV, or from 4.9998V to 5.0002V.
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 measur-
ing 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: 120V ±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.