Section 8: Theory of operation
Series 3700A System Switch/Multimeter Reference Manual
8-20
3700AS-901-01 Rev. D/June 2018
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 =
±(ppm of r ppm of range)
(ppm = parts per million and 10 ppm = 0.001%)
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 =
±(25 ppm of r 2 ppm of range)
±[(25 ppm × 5 V) + (2 ppm × 10 V)]
±(125 µV + 20 µV)
±145 µV
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 =
±(ppm of r ppm of range + rms noise addr)
For example, to calculate the accuracy of the above example at 0.006 PLC:
Accuracy =
± (( 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
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 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 =
±(0.06% of r 0.03% of range)
±[(0.0006 × 120 V) + (0.0003 × 300 V)]
±(0.072 V + 0.09 V)
±0.162 V
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.
