METHOD FOR MEASURING THE FREQUENCY OF A SINUSOIDAL SIGNAL

摘要

The present invention relates to a method for measuring a frequency f = φ/2π of a sinusoidal signal V(t) = Asin(φt + α with an essentially constant amplitude A. The method comprises registration of measured values in the form of the instantaneous leevel 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 fs = 1/h. Then the measured values are applied to a calculating device [2], which recursively estimates the quantity y(t) given by: y(t) = y(t-h) + θ e(t) s(V(t-h)), where e(t) = V(t) + V(t-2h)/2 - y(t-h)V(t-h) and θ s(V(t-h)) V(t-h) ≥ 0, the choice of θ and s(.) controlling the convergence speed of y(t) → cos(φh) 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) = (fs/2π arccos y(t).