| 摘要 |
A method for measuring a frequency f=omega/2pi of a sinusoidal signal V(t)=Asin(omegat+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 fs=1/h. Then the measured values are applied to a calculating device, which recursively estimates the quantity y(t) given by:whereV(t-h) and etas(V(t-h))V(t-h)>=0, the choice of eta and s(.) controlling the convergence speed of y(t)->cos(omegah)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/2pi)arccos y(t).
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