Question

What is this device here and how is it used in a PLC? AO IR LED 7 Photo Diode 1 KO

Answer 1

This device is basically a photoelectric sensing device that contains a light-emitting-diode usually an infrared LED, and photodiode at the other end. The basic operation of this device is that when IR light falls on the photodiode, the output of the photodiode would change from 0 to 1 i.e. from low to high, and when the path of the light blocks, the output of the photodiode would change from 1 to 0.
In PLC automation, this device is used heavily because of the various modes of operations that are depicted below
1.   Reflectivity of this device
This device can act as a reflective device i.e. if needed; the object reflects the radiated light into the photodiode.
In PLC system, this kind of principle is used for monitoring the liquid level of a container.
2.   Beam principle
In this case, when the IR transmitter and the photodiode are placed side-by-side, the IR light directly falls on the photodiode. Based on this scheme, the system can able to detect the position of the IR transmitter.
In PLC system, the object which blocks the path of the IR light to fall into the photodiode can be easily detected by the photodiode. Mostly, in conveyor system, this principle has been utilized.