How to fix a photoelectric sensor that does not work (well)?

The photoelectric sensor does not turn on, does not switch or performs false detections. In this article the most common issues with these sensors and ways to solve them are consicely described. With the help of special accessories you can get the most out of your sensor and automation!

Frequently encountered issues and quick fixes

Photoelectric sensors have a wide range of functionalities and configurations. This can bring along some challenges that look like a sign of a malfunctioning sensor. In reality it can be a frequently encountered issue that can be quickly identified with an inspection and thus be fixed. 

Photoelectric sensor does not have a switching output

Check the connections – When the sensor does not provide an output signal , the culprit is often the connection. A simple solution is checking whether everything is connected properly. In the datasheets of the sensors, that can be found on our website in the downloads of every product, you can find the color coding of the wires in the connection. The datasheets contain diagrams that illustrate how every wire and pin is configured and thus which one can provide an output signal.

Photoelectric sensors do not cooperate

Check for a transmitter + receiver combination – When it comes to photoelectric thru-beam sensors , these are installed in couples - a transmitter and a receiver. A frequently encountered mistake is the use of two transmitters or two receivers that face each other. In such configurations it will be impossible for the sensors to perform a detection or provide an output signal at all. The fix is easy: make sure you have installed a transmitter and a receiver facing each other. 

Signal output is too soon or too late

Check the time delay setting – Not all photoelectric sensors have this functionality. You can check the datasheets to make sure whether this applies to your sensor. An example of a sensor with this functionality is the SPTF 3315 5 from Telco Sensors.

When the sensor is equipped with a so-called time delay, it is highly advised to check the potentiometer for the adjustment of this functionality. If it is set too high or too low it will not be able for the sensor to perform a detection or measurement at the desired moment because it will be too early or too late.

The photoelectric sensors does not detect the object

Choose a right spot size – Photoelectric sensors have a specification called spot size. For convenience, think of a round object as an example. Let's say this object has a diameter of Ø5 cm. If the spot size of the sensor is 10 cm, the object will fall within this. However, because the spot is larger than the diameter of the object, it is not detected because the spot of the sensor also covers the area outside of the objects diameter. It will be susceptible to any target within its spot size. So make sure you have a smaller spot size than the object you want to detect.

Provide a good background – Photoelectric sensors are optical sensors, so these work with light. Because of this, the sensors are highly dependent on the ability to receive an emitted light. With a bad reflection you will experience an unreliable detection, or none at all. Choosing a dark or light background is dependent on the object that has to be detected: provide a strong contrast between object and background! Is this not feasible for your application? Then it is possible that non-optical sensors, photoelectric sensors with a reflector or a thru-beam sensor the better options.

Check the gain settings – A select number of photoelectric sensors is equipped with one or two potentiometers. One of these potentiometers serves the configuration of the so-called gain of the sensor. When the gain is set too high or too low, the range will be so high or low that an object will not be detected (correctly).

Get the most out of your photoelectric sensor

The photoelectric sensor is a very capable sensor. However, even for a good sensor there are still ways to make it even better. To get the most out of your photoelectric sensors there are special accessories that can change a good application into an excellent application. 

Special connection cables

Is your sensor ready for a challenging application such as those with heavy chemicals? Then it might be interesting to have a look at whethet your cables are in good shape.

This is relevant for sensors with a fixed cable connection as well as those equipped with a connector. For sensors with a connector there are a number of interface cables made from strong(er) materials such as PUR (chemical resistant) and TPE (high temperatures and impact).

Optical limiters for more precision

More precision for your photoelectric sensor? When you need a smalle spot size than the given specifications it is possible to make use of an optical limiter. Most photoelectric sensors can be equipped with this accesory. The limiters make sure that the emitted light can be focused to a desired spot size and shape.

The different optical limiters are available in stainless steel or plastic, with or without glass window and a limiter in the shape of a line or dot. See the table below:

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