A precision thermal wattmeter having a sampling control system and an analog feedback loop
Kunihiko Takahashi · IEEE Transactions on Instrumentation and Measurement · 1991
A precision thermal wattmeter having a sampling control system and an analog feedback loop is described. A pair of thermal converters is used as a sum and difference multiplier and as an AC/DC power comparator simultaneously. The large error caused by insufficient open-loop gain in the wattmeter is removed by the sampling control system. The wattmeter is designed for use at relatively low frequency. The maximum sensitivity is better than 1 p.p.m., and total accuracy is estimated at better than 20 p.p.m. >