This picture shows the basic structure of an electronic counter. The gate circuit is controlled by the shaping signal with B channel input frequency fB, that is, one pulse opens the gate circuit and the next pulse closes the gate circuit. The time interval (TB) between two pulses is the door opening time. The pulse group with the shaping frequency fA input from channel A passes through the door within the door opening time, so that the counter counts, and the count value n = fa TB.

By making some choices on channels A and B, the electronic counter can have the following three basic functions. ..

① frequency measurement: the measured signal is input from channel a, if TB is 1 sec, the reading n is frequency fA, and the unit is Hz. The time base circuit properly divides the standard frequency signal output by the crystal oscillator to form a gate time signal to determine the value of TB.

② Period or time interval measurement: the measured signal is input into the control gate circuit by channel B, and the input signal of channel A is the clock pulse signal provided by the time base circuit. The number counted by the counter is the opening time of the door, that is, the period or time interval of the measured signal.

(3) Cumulative counting: manually trigger the gate opening, and the counter accumulates A-channel signals.

On the basis of these functions, some auxiliary circuits or devices are added, and the counter can also complete the functions of multi-period average, time interval average, frequency ratio, frequency expansion and so on. The performance indicators of electronic counter mainly include: frequency, period, time interval measurement range, input characteristics (sensitivity, input impedance and waveform), precision, resolution and error (counting error, time base error and trigger error), etc.