Photoelectric Sensor Explained (with Practical Examples)

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⌚Timestamps:
00:00 - Intro
00:27 - Applications
01:08 - Working principle
01:22 - Types of photoelectric sensors
01:38 - 1) Through-beam
04:16 - 2) Retroreflective
05:36 - 3) Diffused

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In this video, we will be talking about the three main types of Photoelectric Sensors: Through-Beam, Retroreflective, and Diffused.

A Photoelectric Sensor is a device that uses light to detect the presence or absence of an object.

Photoelectric Sensors can be used in many different ways and industries. They can be used to detect objects or the orientation of an object on a production line, they can be used to count, and they can also be used to stop an automatic closing door.

Photoelectric Sensors are used in the automotive, food, transportation, and material handling industries to name a few.

They can be used to detect most materials like metal, plastic, and wood. They can even detect clear items like glass, plastic, and liquids depending on what type of sensor it is.

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.

1) Through-Beam sensors have the emitter and the receiver in their own separate component.

The emitter and receiver have to be pointed at each other and be aligned. When 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.

The sensor’s output is the signal from the sensor to the PLC. Depending on the sensor, the output can be a positive signal or a negative signal.

- 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.

Some Photoelectric Sensors have a light-on, dark-on mode selector switch. With this switch, you can change when the sensor’s output turns on and off.

- In light-on mode, the sensor’s output will be on when the light can reach the receiver, and off when the light is blocked and is not reaching the receiver.
- In the dark-on mode, the sensor’s output will be on when the light is being blocked and not reaching the receiver, and off when the light is reaching the receiver.

Through-Beam Photoelectric sensors have a longer detection range than Retroreflective and Diffused Photoelectric Sensors. This is because the light only has to travel in one direction to get from the emitter to the receiver.

Some disadvantages of using a Through-Beam sensor compared to using a Retroreflective or Diffused sensor are they cost a little more, require more room to mount correctly, and do not detect thin clear objects well.

2)Retroreflective Photoelectric Sensors have the emitter and receiver together in the same component. The sensor’s emitter needs to be pointed at a reflector and aligned, so the light travels from the sensor’s emitter to the reflector and then bounces back to the sensor’s receiver.

Some disadvantages of using a Retroreflective sensor are you have to install the sensor with a reflector, if the object is shiny, it might turn on the sensor’s output instead of the reflector.

3) Diffused Photoelectric Sensors have the emitter and receiver together in the same component.

For the Diffused sensor to work, the sensor’s emitter needs to be pointed at an object so the light travels from the sensor’s emitter to the object and then bounces back to the sensor’s receiver.

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If you would like more information on sinking, sourcing, PNP, and NPN check out this video: https://realpars.com/sinking-and-sourcing/

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