Measurement Accuracy and Resolution - with shorter measurement intervals
The following table shows changes to the short-term measurement accuracy and resolution with
various number of power line cycle (NPLC) measurement settings. Changes are due to the A-to-D
converter’s noise performance. The table’s baseline is 1 NPLC with no added noise. To determine the
measurement accuracy at shorter averaging intervals, simply calculate the percent of range to add,
then add it to the fixed accuracy value in the specification table.
For example, to determine the percent of range to add to the accuracy specification of the voltage
measurement of an N6950A when making measurements at 0.003 NPLC, simply multiply the full
voltage rating by the "% of range added to spec value" as follows: 9 V x 0.006% = 0.54 mV. Add this
number to the offset part of the measurement accuracy specification: 1.5 mV + 0.54 mV. The new
voltage measurement accuracy is 0.03% + 2.04 mV at 0.003 NPLC.
Voltage Measurement Current Measurement Low Current Measurement
NPLC
@60Hz
Number of
averaged points
% of range added
to spec.
Effective
Resolution
(in bits)
% of range added
to spec.
Effective
Resolution
(in bits)
% of range added to
spec.
Effective Resolution
(in bits)
1 3255 0 >20 0 >19 0 >16
0.6 1953 0.00001% 19.9 0.00026% 18.6 0.002% 15.6
0.1 325 0.00076% 17.0 0.0019% 15.7 0.015% 12.7
0.06 195 0.0011% 16.5 0.0027% 15.2 0.022% 12.2
0.031 100 0.0016% 15.9 0.0041% 14.6 0.033% 11.6
0.010 33 0.0031% 15.0 0.0078% 13.6 0.063% 10.6
0.006 20 0.0041% 14.6 0.010% 13.3 0.082% 10.3
0.003 10 0.006% 14.0 0.015% 12.7 0.120% 9.7
0.0003 1 0.02% 12.3 0.049% 11.0 0.390% 8.0
The measurement A-to-D converter has an 18-bit resolution. However, the combination of
measurement noise and data-point averaging can yield a different effective resolution as shown in the
table. With single point measurements without averaging, the noise in the measurement signal is
much larger than the A-to-D converter’s resolution, thereby limiting successive measurement
repeatability. Averaging more data points can increase the measurement precision beyond the A-to-D
converter’s native resolution. For example, the measurement repeatability of an N7950A’s high
current range with a 0.6 NPLC setting yields an effective resolution of 18.6 bits. Convert the bits to
current by applying the bits to the full current rating as follows: 100 A x 2
-18.6
= 252 µA. The
measurement resolution is 252 µA.
Keysight N6900/N7900 Series Operating and Service Guide 61
1 Quick Reference
To Next Page
Loading...
Need help?
General
