Frequency compensated A-C ammeters and voltmeters

The increased use of a-c instruments over a frequency range of 25 to 3,000 cycles for aircraft and industrial applications has imposed new requirements on instrument design. It is recognized that the standard type of a-c ammeters and voltmeters normally calibrated for use at a given frequency are subject to errors in indication when used at other frequencies. This paper describes the manner in which one line of a-c ammeters and voltmeters can be compensated to have minimum errors resulting from changes in frequency over a range of 25 to 3,000 cycles. Errors found in the uncompensated and compensated types of instruments with changes in frequency are shown, and a practical means of determining the amount of compensation and its application to ammeters and voltmeters is presented.