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Abstract

A method for measuring a frequency f=.omega./2.pi. of a sinusoidal signal V(t)=Asin(.omega.t+.alpha.) with an essentially constant amplitude A. Measured values are registered in the form of the instantaneous level of the signal V(t), V(t-h) and V(t-2h)at three points of time separated by a predetermined measuring period h, which corresponds to a measurement frequency f.sub.s =1/h. Then the measured values are applied to a calculating device, which recursively estimates the quantity y(t) given by: y(t)=y(t-h)+.eta.e(t)s(V(t-h)), where ##EQU1## V(t-h) and .eta.s(V(t-h))V(t-h).gtoreq.0, the choice of .eta. and s(.) controlling the convergence speed of y(t).fwdarw.cos(.omega.h)and the noise sensitivity of the measurement system. Finally the frequency is calculated or looked up in a table based on the expression f(t)=(f.sub.s /2.pi.)arccos y(t).

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First Claim