NBS wideband sampling wattmeter

Abstract

A special feature of the sampling wattmeter is the use of programmable time delay circuits to compensate for differential time delays between the two input channels.Performance tests of the wattmeter show that it has a measurement uncertainty of less than ±0.1 percent of full-scale amplitude over the above described frequency range This technical note gives schematic diagrams of the circuits used in this wattmeter and describes their operation.The software is also described, and flow charts and selected program listings are provided for the programs written in Pascal. The results of calibration of the instrument over the past year are also presented.

Standards for waveform metrology based on digital techniques

“…This wattmeter uses asynchronous sampling of its input waveforms to realize a measurement uncertainty of less than ±0.1% of the full scale range for fundamental frequencies from 1 Hz to 10 kHz (and harmonics up to 100 kHz) [ 14 ]. A prototype instrument, constructed in the mid 1980s, is programmable from the front panel and has-the necessary hardware and software to optimize the sampling frequency and to make corrections for truncation errors [ 39 ]. In the early 1970s the feasibility was demonstrated for making precision ac power measurements (±0.02% accuracy up to 2 kHz) using a sampling technique, and computing the power with a suitable algorithm [ 40 ].…”

Accurate RF Voltage Measurements Using a Sampling Voltage Tracker

“…In practice, At will have a random error component (time jitter), fixed pattern errors correlated with the sampling index, and a scale error such that nAt # kT, where T is the sine wave period. First, consider the scale error, which causes so-called truncation errors [ 6 ] . The first term of (3) represents the true mean squared value of the sine wave (defined over an integral number of periods); therefore, the second term represents the error E , resulting from sampling a nonintegral number of periods.…”

“…Define as in [6], the truncation angle 6 to be the difference between the summation interval, given by n y , and the nearest integral number of cycles c of the sine wave, i.e., 6 27rc -ny. Then the truncation error relative to the true mean squared value can be represented as…”

NIST high-accuracy sampling wattmeter

“…Voltage-Input Module Features 5 [1,2]. This report also describes the changes made to the Wideband Sampling Wattmeter.…”

“…The power measurement technique used in the new instrument is basically the same as that used in the earlier wattmeter: dual-channel sampling using commercial track-and-hold (T/H), analog-to-digital (A/D) conversion, real-time multiplication, and microcomputer control. The reports on the earlier wattmeter [1,2] should be used to understand the operation of those portions of the new wattmeter that were not changed and are not described in this report.…”