Optical (photoelectric) sensors. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Sensors. Optical (photoelectric) sensors. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electrician's Handbook

There are analog and discrete optical sensors. At analog sensors the output signal changes proportionally to the ambient light. The main area of application is automated lighting control systems.

SENSORS discrete type change the output state to the opposite when the specified illumination value is reached.

Photoelectric sensors can be applied in almost all industries. Discrete action sensors are used as a kind of proximity switches for counting, detection, positioning and other tasks on any technological line.

The optical contactless sensor registers a change in the light flux in the controlled area, associated with a change in the position in space of any moving parts, mechanisms and machines, the absence or presence of objects. Due to the large sensing distances, optical proximity sensors have found wide application in industry and beyond.

An optical proximity sensor consists of two functional units: a receiver and an emitter. These nodes can be made both in the same housing and in different housings.

On object detection method photoelectric sensors are divided into four groups.

Group 1 - beam crossing. In this method, the transmitter and receiver are separated into different housings, which allows them to be installed opposite each other at a working distance. The principle of operation is based on the fact that the transmitter constantly sends a light beam, which is received by the receiver. If the light signal of the sensor stops due to obstruction by a third-party object, the receiver immediately reacts by changing the output state.

Group 2 - reflector reflection. In this method, the transmitter and receiver of the sensor are in the same housing. A reflector (reflector) is installed opposite the sensor. Reflector sensors are designed in such a way that, thanks to a polarizing filter, they perceive reflection only from the reflector. These are reflectors that work on the principle of double reflection. The choice of a suitable reflector is determined by the required distance and mounting possibilities. The light signal sent by the transmitter, reflected from the reflector, enters the sensor receiver. If the light signal stops, the receiver immediately responds by changing the state of the output.

Group 3 - reflection from the object. In this method, the transmitter and receiver of the sensor are in the same housing. During the working state of the sensor, all objects that fall into its working area become a kind of reflectors. As soon as the light beam, reflected from the object, hits the sensor receiver, it immediately reacts by changing the output state.

Group 4 - fixed object reflection. The principle of operation of the sensor is the same as in group 3, but more sensitive to deviations from the adjustment to the object. For example, it is possible to detect a swollen cork on a kefir bottle, incomplete filling of a vacuum package with products, etc.

By its purpose The photosensors are divided into two main groups:

general purpose sensors;
special sensors designed to solve a narrower range of tasks. For example, detection of a color mark on an object, detection of a contrasting border, the presence of a label on a transparent package.

The task of the sensor is to detect an object at a distance. This distance varies between 0,3 mm - 50 m, depending on the selected sensor type and detection method.

Author: Koryakin-Chernyak S.L.

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