A method of measuring and recording the frequency error of alternating-current power supplies

Abstract

After referring briefly to various methods of measuring frequency, the paper describes in detail an instrument designed to give a statistical record of the inaccuracy in the frequency of a.c. mains supply.Records have been made, in the Dollis Hill Research Laboratories of the G.P.O., of the mains-frequency error at various times during 1937–40, and statistical analysis of the results obtained in four test periods shows that the distribution follows very closely the normal-error law. The standard deviation of the corresponding normal-error curve has been calculated for each of the test periods.The purpose for which the recorder was designed was to test the practicability of using a.c. mains supply to drive synchronous motors on teleprinters and multi-frequency generators used in the Post Office telegraph service; the test results are discussed from this standpoint.The reading of the paper was followed by a demonstration by Mr. L. Essen of the principles of the quartz-crystal clock.