Magnetoresistance Multiplier for the Accurate Measurement of Power in the Audio Frequency Range

The application of a commercially available component (Misto-R multiplier by American Aerospace Conntrols Inc.) to accurate power measurement over the audio frequenncy range is investigated. It is shown that the errors inherent to the magnetoresistive component can be considerably reduced by appropriate electronic circuitry. Two circuits were constructed and tested: a dc circuit and an ac circuit. The accuracy of the dc multiplier is better than 0.05 percent of full scale. The accuracy of the ac multiplier at a power factor of 1.0 is better than 0.1 percent of full scale up to a frequency of 4000 Hz and approaches 0.5 percent at 10 kHz. Expressions for static and dynamic errors are given and it is shown that the static errors are small with respect to the dynamic errors. It is believed that further broadening of the frequency and power factor ranges for the specified accuracy of 0.1 percent can be achieved by modifying the structure of the bridge and adopting suitable circuitry.