Accuracy Calculations; Calculating Dc Characteristics Accuracy; Calculating Ac Characteristics Accuracy - Keithley 3700A Series Reference Manual

Section 8: Theory of operation

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:
For ≥1 PLC, accuracy =
As an example of how to calculate the actual reading limits, assume that you are measuring 5 V on
the 10 V range. You can compute the reading limit range from one-year DCV accuracy specifications
as follows:
Accuracy =
Thus, the actual reading range is 5 V ± 320 µV or from 4.99968 V to 5.00032 V. Thus, the actual
reading range is: 5 V ± 145 µV or from 4.999855 V to 5.000145 V.
For ≤1 PLC, accuracy =
For example, to calculate the accuracy of the above example at 0.006 PLC:
Accuracy =
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 reading + % of range)
As an example of how to calculate the actual reading limits, assume that you are measuring 120 V,
60 Hz on the 300 V range. You can compute the reading limit range from ACV one-year accuracy
specifications as follows:
Accuracy =
In this case, the actual reading range is: 120 V ± 0.162 V or from 119.838 V to 120.162 V.
AC current calculations are performed in exactly the same manner using the pertinent specifications,
ranges, and input signal values.
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Series 3700A System Switch/Multimeter Reference Manual
±(ppm of reading + ppm of range)
(ppm = parts per million and 10 ppm = 0.001%)
±(25 ppm of reading + 2 ppm of range)
±[(25 ppm × 5 V) + (2 ppm × 10 V)]
±(125 µV + 20 µV)
±145 µV
±(ppm of reading + ppm of range + rms noise addr)
± (( 25 ppm of reading) + (2 ppm of range ) + ( 2.5 x 7 ppm of range ))
= ± (( 25 ppm x 5 V ) + ( 2 ppm x 10 V ) + ( 2.5 x 7 ppm x 10 V ))
= ± ( 125 µV + 20 µV + 175 µV )
= ± 320 µV
±(0.06% of reading + 0.03% of range)
±[(0.0006 × 120 V) + (0.0003 × 300 V)]
±(0.072 V + 0.09 V)
±0.162 V
3700AS-901-01 Rev. D/June 2018