A simple zero-power-factor reference standard with an uncertainty of 1 ppm

A zero-power-factor (PF) reference standard is described which is based on the use of thermal converters. The circuit is basically that of a thermal wattmeter, but involves reversing either the input voltage or current to establish phase quadrature. The standard is independent of amplitude fluctuations in both input variables, to a first order, and is largely immune to the effects of harmonics. The overall one-standard-deviation (1 σ) uncertainty in zero PF is estimated to be ∼ 1 ppm amd experimental data derived from intercomparisons with mutual inductors are presented to support this.