Correction of frequency errors in wattmeters

Wattmeter readings taken at low power factors or at higher frequencies should be corrected for frequency errors to insure the accuracy of which the instrument is capable. In addition to the error caused by the voltage circuit self-reactance, there exists an error due to the mutual reactance between the two circuits of a wattmeter. A practical method of correcting wattmeter readings for this error is presented and its use demonstrated. Wattmeter readings which have been corrected for the mutual reactance error in this way may be corrected for the voltage circuit self-reactance error by using the customary tables or correction factors in the conventional manner. Curves are shown of the two frequency errors as functions of the frequency and the deflection for a typical commercial low power-factor wattmeter.