A Wideband Sampling Wattmeter1

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 microprocessor control led 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. The wattmeter uses both a hardware multiplier-accumulator and a direct-memory-access unit to capture the data. Programmable time delay circuits are used to compensate for differential time delays between the input channels. Performance checks show that measurement uncertainties of less than ±0. 1 percent of full-scale range (FSR) are obtainable.