The working principle of the electronic counter:

The gate circuit is controlled by the shaped signal with frequency fB input from channel B, that is, the door is opened with one pulse and the door is closed with the subsequent pulse. The time interval (TB) between two pulses is the door opening time. The pulse group with a shaped frequency of fA input from channel A passes through the gate during the door opening time, causing the counter to count, and the counted number is N=fA·TB.

By making certain selections for the A and B channels, 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 second, the reading N is the frequency fA in Hertz. The standard frequency signal output by the crystal oscillator is appropriately divided by the time base circuit to form a gate time signal to determine the value of TB.

② Period or time interval measurement: The measured signal is input from the B channel to control the gate circuit, while the input signal of the A channel is the clock pulse signal provided by the time base circuit. The number counted by the counter is the gate opening time, which is the period or time interval of the signal being measured.

③ Cumulative counting: The gate is opened manually and the counter accumulates the A channel signal.

By adding some auxiliary circuits or devices on the basis of these functions, the counter can also complete functions such as multi-cycle averaging, time interval averaging, frequency ratio and frequency expansion. Electronic counter performance indicators mainly include: frequency, period, time interval measurement range, input characteristics (sensitivity, input impedance and waveform), accuracy, resolution and errors (counting error, time base error and trigger error), etc.