Design Sign of Delta Sigma Wattmeter

Abstract

Instantaneous power in a load is measured by multiplying the voltage across it by the current flowing through it. The multiplication is achieved in a delta sigma wattmeter by using two samplers rather than a multiplier. Sampling and multiplication are closely related. For example, double side-band suppressed carrier modulation can be produced by either multiplying an analogue signal with a sinusoidal carrier, or by sampling the analogue signal with a binary pulse train and filtering these samples. Alternatively these samples can be produced without a sampler if a multiplier is used. This is achieved by multiplying pulse train, whose binary values are arranged to be zero or unity, with the analogue signal.
The delta-sigma wattmeter is given this name because the voltage developed across the load in which the power is to be measured is encoded by a delta sigma modulator, d.s.m into a binary waveform. The d.s.m. decoder is just a low-pass filter