NBS (National Bureau of Standards) Wideband Sampling Wattmeter

摘要

The design and operation of a wideband sampling wattmeter capable of measuring distorted power signals with fundamental frequencies from 1 Hz to 10 kHz and harmonics up to 100 kHz is described. The microcomputer controlled wattmeter uses asynchronous sampling of the voltage and current signals. The errors associated with this type of operation are described, as are various methods of correcting some of these errors. A hardware multiplier-accumulator allows a large number of power signal samples to be integrated for each measurement. Sampling rates are variable up to a maximum of 300 kHz. A direct-memory-access unit is used to capture 4096 samples of both the voltage and current signals. These data are used to calculate the average and rms values of these signals. The 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.