Design of a Microprocessor-Based Digital Wattmeter

A microprocessor-based implementation of the sampling wattmeter is described. The measurement process is in two parts. First, the microprocessor measures the voltage waveform period and computes the sampling interval and number of samples. The measurement of average power then takes place over an integer number of cycles. Digitized samples of the voltage and current waveforms are multiplied together and the products accumulated over the measurement period. The sum is divided by the number of samples, scaled, and read out as a 4-digit display of average power.