A retro-reflective sensor with polarized reflector is provided with a so called polarisation filter. This filter is making sure that light with a given wavelength is reflected and the rest of the wavelengths not. By using this attribute, only the light with the wavelength of the emitted light is reflected.
Photoelectric sensor working principle
The basic operation of a Photoelectric Sensor is, the sensor sends out a light beam from the part of the sensor called the emitter, and this light beam travels to the part of the sensor that collects the light called the receiver. Different types of these sensors handle the light beam in various ways. Regardless of the sensor type, it acts like a photoelectric switch sensor.
Types of photoelectric sensors
Through-beam photoelectric sensor
First, we will talk about the Through-Beam Photoelectric Sensor type. Through-Beam sensors have the emitter and the receiver in their own separate component.
For the Through-Beam sensor to work, the emitter and receiver have to be pointed at each other and be aligned.
When they are aligned and nothing is blocking the light, the output of the sensor will be on.
If you put something between the emitter and receiver to block the light, the output of the sensor will turn off.
Sensor output signal
The sensor’s output is the signal from the sensor to the PLC. Remember, it acts like a photoelectric switch sensor, completing a circuit when activated. Depending on the sensor, the output can be a positive signal or a negative signal.
The type of sensor output signal you will use depends on what type of PLC input card the sensor is connected to.
For example,
– If the sensor is PNP, meaning it has a positive output signal, the sensor’s output wire will have to be connected to a sinking input card.
– If the sensor is NPN the output signal is negative and the output wire will need to be connected to a sourcing input card.
Summary
In review, by reading this article you have learned about the three basic types of Photoelectric Sensors:
– Through-Beam,
– Retroreflective,
– Diffused.
You learned that all three sensors use light to detect objects and all three sensors have output signals that trigger a PLC input.
You also learned about the different sensing ranges and some of the disadvantages of each sensor.
Post time: Aug-12-2025
