System for testing wattmeters under nonsinusoidal conditions

Electrical and electronic power meters, due to nonlinear principles of operation, can exhibit, under nonsinusoidal conditions, errors that are not predictable from their frequency characteristic. A minicomputer-based calibration system to produce such test conditions is described. It relies on a two-phase digital arbitrary waveform generator as a waveform source and on a sampling rms/power meter as a monitoring instrument. At 120-V 5-A sinusoidal operation the “phantom” power can be reproduced with accuracy ±100 ppm at 50 or 60 Hz and ±200 ppm for frequencies up to 1 kHz.