Analogue measurement of frequency error - generates error signal by reaction on feeding square wave signal into resonant circuit at harmonic of required frequency

摘要

In the method for the analogue measurement of small frequency changes an AC signal is transformed to a square wave. This is used to excite an oscillatory circuit having a natural frequency close to an exact multiple of the required frequency of the input signal. A superimposed oscillation then arises having an amplitude directly proportional to the difference between the actual signal frequency and the natural frequency of the resonant circuit at a frequency close to a harmonic frequency of the resonant circuit. The difference frequency which is generated is separated from the square wave signal by differentiation and from the first half-wave (17a) of the oscillation (15, 16) a triangular pulse (18) is formed whose amplitude is measured and displayed to show the frequency difference between the signal frequency and the resonant frequency representing its required value.