Electronic wattmeters are devices used in direct, small power measurement applications. They can also be used for power measurements at frequencies beyond the range of electrodynamometer-type instruments.
A modern digital electronic wattmeter/energy meter works by sampling the voltage and current thousands of times a second. The average of the instantaneous voltage multiplied by the current is the true power. The true power divided by the apparent volt-amperes (VA) is known as the power factor. A complex computer circuit uses the sampled values to calculate RMS voltage, RMS current, VA, power (watts), power factor, and kilowatt-hours. The simple models display that information on LCD. More sophisticated models retain the information over an extended period of time, and can transmit it to remote field equipment or a central location. Wattmeters have come a long way from the old school analog meters found in ham radio rigs of yesteryear.
