In this video, I 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.
For example, 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.
Depending on the type of sensor, the light can travel directly to the sensor’s receiver
or it can travel to a reflector
or the object and then back to the receiver.
I will go over this in more detail as I explain each sensor type.
First, I 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.
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.
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.
If you would like more information on sinking, sourcing, PNP, and NPN
check out our video titled “PLC Inputs Sinking & Sourcing”.
There is a link for this video in the description.
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,
they require more room to mount correctly,
and they do not detect thin clear objects well.
Through-Beam sensors cost more because they have two components
that require two cables and two mounts,
this is also why they take up more space.
They do not detect thin clear objects
because the light can travel straight through the object to the receiver.
Retroreflective Photoelectric Sensors
have the emitter and receiver together in the same component.
For the Retroreflective Sensor to work,
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.
The Retroreflective sensor output works the same as the Through-Beam sensor output.
The output is on if the light is not blocked
and the output is off if the light is blocked.
Retroreflective Sensors can also have a light-on, dark-on mode selector switch
to change when the sensor’s output turns on.
Retroreflective sensors have a shorter detection range
compared to Through-Beam sensors.
This is because the light has to travel to a reflector
and then back to the sensor instead of just traveling straight to the 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,
and the light beam is not as focused as a Through-Beam sensor’s light beam.
If the object is shiny,
you can try adjusting the angle of the sensor and reflector compared to the object.
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.
The Diffused sensor output works the same as the Through-Beam
and Retroreflective sensor outputs.
Diffused Sensors can also have a light-on, dark-on mode selector switch
to change when the sensor’s output turns on.
The main disadvantage of using a Diffused Sensor
is it has the shortest detection range of the three sensors.
Because depending on the object’s shape, size, and color
it might not reflect light very well back to the sensor’s receiver.
In review, by watching this video you have learned about the three basic types of Photoelectric Sensors
Through-Beam, Retroreflective, and Diffused.
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.
That should do it for this video.
Please let us know if you have any questions
about the three basic types of Photoelectric Sensors in the comments below.
Also, make sure to like this video if you found it helpful.
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Thanks for watching!
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