The photocoupler consists of two light-emitting diode tubes and a phototransistor.
Light-emitting diode: A variable electrical signal is applied to the input end of the photocoupler, and the light-emitting diode generates an optical signal having the same regularity as the input signal.
Photoelectric three-stage tube: Conducted under the illumination of the optical signal, the degree of conduction is related to the strength of the optical signal. In the linear working area of the optocoupler, the output signal is linear with the input signal.
Input interface circuit working process: When the switch is closed, the diode emits light, and then the transistor is turned on under the illumination of light, and the signal is input to the internal circuit. When the switch is turned off, the diode does not emit light and the transistor does not conduct. Input signals to internal circuits. That is, the external switching signal is converted into a digital signal acceptable to the PLC through the input interface circuit.