Photoelectric position sensors - principle of operation and application

Sensors—in automatic control systems—are sensitive elements or devices that perceive the value of the observed parameter of the object and give a signal to a device to compare this value with a given value, until a difference or discrepancy signal is generated, which, through other devices , affects the managed object.

The field of application of photoelectric position sensors covers a wide industrial spectrum. Sensors of this type help to solve problems related to the control of technological production processes, where it is necessary to detect, position or simply count certain objects.

Due to their versatility, photoelectric sensors are today the most widely used where industrial automation is required. They are distinguished by the ability to perform non-contact measurements and counting of objects and display the relevant information in the form of a digital signal that is easy to perceive and process. any modern controller.

Digital outputs usually contain PNP or NPN transistors or simply relays. Power supply is carried out with a constant (or mains) voltage of 10 volts within 240 volts.

Principle of beam interruption

Two cases, transmitter and receiver, make up one device. They are installed on opposite sides of the place where the object is expected to pass. The receiver is statically fixed to the emitter so that the unreflected beam from the emitter always hits the receiver detector.

The working range (the size of the fixed object) is practically unlimited, and the defined objects can be both transparent and opaque.

If the object is opaque, the beam simply overlaps and is blocked by the object. If the object is transparent, the beam is deflected or diffused so that the receiver does not see it until the object leaves the location of its detection. This guarantees high reliability and accuracy of the photoelectric sensor based on the principle of beam interruption. These sensors can operate at distances between the emitter and the receiver from a few centimeters to tens of meters.

The principle of reflection of the beam from the reflector

The sensor consists of two parts — an emitter and a reflector. The receiver and the transmitter are located in the same housing, which is fixed stationary on one side of the investigated place, and on the other side a reflector (reflector) is mounted. Different reflectors allow this type of sensor to be used at different distances, and the sensitivity of the receiver can sometimes be adjusted.

These sensors are also suitable for detecting glass and other highly reflective surfaces.As in the case of beam interruption sensors, reflector-based sensors allow you to measure the overall dimensions of objects or simply read them.

As the case here is one, the device generally requires less installation space, sometimes this is an important advantage, especially for automation systems that require compactness. These sensors can operate at body-to-reflector distances from a few centimeters to a few meters.

The principle of reflection of a ray from an object

The entire device is a single housing containing an emitter and a receiver capable of responding even to the stray beam reflected from an object. Models of sensors of this type are mostly cheap, take up the least space for installation and do not need a reflector.

It is enough to statically fix the sensor not far from the investigated area and adjust its sensitivity according to the type of surface of the detected object. Sensors of this type are suitable for working at short distances to objects to be examined, on the order of several tens of centimeters, for example, with products moving on a conveyor belt.