Photoelectric sensors

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Photoelectric sensors

Photoelectric sensors , also called optical sensors, detect objects through a light beam. They are sensors that use energy transmission to detect transparent and opaque objects. They are made of a light source emitter and its receiver. The photoelectric sensor reacts to a change in the intensity of the light beam reaching it. It can be visible as well as infrared or laser, so the term photocell is often used for them. When the optical sensor has a built-in VR sensitivity regulator this allows for excellent detection performance.

Photoelectric sensors are often classified as proximity sensors, due to the similarity of their functions, such as detection, determination of features and condition of objects. The principle of operation differs in that they use energy transmission, not detection of field changes. Some photoelectric sensors have a built-in timer feature that allows time delay , power off or one time delay.

Application of photoelectric sensors

Thanks to their properties, photoelectric sensors are used on automated technological lines and in packaging machines. Unlike proximity sensors, they have a much longer service life and can be used in places where it is not possible to use mechanical sensors.

The most common application is the detection of a foreign body in a certain area. The device then acts as a photo switch. We find photoelectric sensors in the engineering, automotive, pharmaceutical, food and many other industries. The use of photoelectric sensors allows for more precise work, e.g. accurate positioning in steel processing .

How do photoelectric sensors work?

The basic principle of a photoelectric sensor is to detect objects through a beam of light emitted by the transmitter, incident on the photosensitive element of the receiver. The sensor is connected with a light source (often integrated in one housing) which is a transmitter. When any object is in the optical path between the transmitter and the receiver, the light intensity changes.

Photoelectric sensors - types

Different types of sensors are available depending on the application. The most frequently used are:

  1. Reflective - the transmitter and receiver are built in a common housing, the beam of rays is sent by the emitter, when an object appears on the path of this beam, it will be reflected by it, then it returns to the detector.
  2. Photo translucent switches (light barrier) - the observed object interrupts the light beam and affects the receiver (regardless of the surface properties) causing a change in the output signal. Under unfavorable conditions (e.g. dust, oil, fog), such one-way barriers give the best detection results.
  3. Reflective - the transmitter and receiver are in one housing, the beam of rays is reflected from the reflector, which is placed at the end of the sensor's detection area. The object is detected when the beam does not reach the receiver. The assembly is more complicated than with the reflective sensor, but the advantage is the greater range of up to several meters.

Photoelectric sensors can be differentiated according to their operating logic: NO (Normally Open) or NC (Normally Close).

Criteria for selection of an optical sensor

The sensors are selected according to the working conditions and we follow:

  1. ambient temperature,
  2. mechanical resistance,
  3. purpose of the sensor,
  4. the required detection range,
  5. with the available supply voltage.

An important criterion is the type of object (or objects) to be detected. Some photoelectric sensors even react to transparent films. Others, in turn, require almost complete opacity of the object. You should choose a model with a sensitivity adjustment potentiometer. This will allow you to precisely set the sensor threshold.