Measurement Accuracy and Resolution - with shorter measurement intervalsThe following table shows changes to the short-term measurement accuracy and resolution withvarious number of power line cycle (NPLC) measurement settings. Changes are due to the A-to-Dconverter’s noise performance. The table’s baseline is 1 NPLC with no added noise. To determine themeasurement 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 voltagemeasurement of an N6950A when making measurements at 0.003 NPLC, simply multiply the fullvoltage rating by the "% of range added to spec value" as follows: 9 V x 0.006% = 0.54 mV. Add thisnumber to the offset part of the measurement accuracy specification: 1.5 mV + 0.54 mV. The newvoltage measurement accuracy is 0.03% + 2.04 mV at 0.003 NPLC.Voltage Measurement Current Measurement Low Current MeasurementNPLC@60HzNumber ofaveraged points% of range addedto spec.EffectiveResolution(in bits)% of range addedto spec.EffectiveResolution(in bits)% of range added tospec.Effective Resolution(in bits)1 3255 0 >20 0 >19 0 >160.6 1953 0.00001% 19.9 0.00026% 18.6 0.002% 15.60.1 325 0.00076% 17.0 0.0019% 15.7 0.015% 12.70.06 195 0.0011% 16.5 0.0027% 15.2 0.022% 12.20.031 100 0.0016% 15.9 0.0041% 14.6 0.033% 11.60.010 33 0.0031% 15.0 0.0078% 13.6 0.063% 10.60.006 20 0.0041% 14.6 0.010% 13.3 0.082% 10.30.003 10 0.006% 14.0 0.015% 12.7 0.120% 9.70.0003 1 0.02% 12.3 0.049% 11.0 0.390% 8.0The measurement A-to-D converter has an 18-bit resolution. However, the combination ofmeasurement noise and data-point averaging can yield a different effective resolution as shown in thetable. With single point measurements without averaging, the noise in the measurement signal ismuch larger than the A-to-D converter’s resolution, thereby limiting successive measurementrepeatability. Averaging more data points can increase the measurement precision beyond the A-to-Dconverter’s native resolution. For example, the measurement repeatability of an N7950A’s highcurrent range with a 0.6 NPLC setting yields an effective resolution of 18.6 bits. Convert the bits tocurrent by applying the bits to the full current rating as follows: 100 A x 2-18.6 = 252 μA. Themeasurement resolution is 252 μA.Keysight N6900/N7900 Series Operating and Service Guide 611 Quick Reference
