1, frequency measurement principle of digital frequency meter: the standard pulse signal of the timely oscillator 1MHz is divided into 1Hz period 1s by the frequency divider and connected to the control terminal of the control gate, and the measured signal is amplified and shaped into a positive half-wave spike pulse signal, which is connected to the signal terminal of the controller; The first second signal triggers the control gate to open, the sharp pulse passes through the control gate, and the control gate closes after the second second signal arrives. The pulse counter records that the number of sharp pulses passing through the control gate during the two-second signal interval is equal to the frequency value of the measurement signal.

2. Principle of measuring period of digital frequency meter: When measuring low-frequency signals with the above method, there may be a big error, because the arrival time of the first second signal is random, and the counter may record one more or one less number from opening to closing; Therefore, in order to ensure the accuracy of low-frequency signal measurement, the periodic measurement method can be adopted: that is, the measured signal pulse is used to control the opening of the gate circuit, so that the standard time enters the counter through the control gate to count, so that the value of the counter is equal to several standard time pulses in a period of the measured voltage, which is equivalent to a period equal to several time units. This is why the frequency of low-frequency models should be determined by the measurement period.