1. Definition of photoelectric switch:
Photoelectric switch (photoelectric sensor) is the abbreviation of photoelectric proximity switch. It uses the obstruction or reflection of the light beam by the detected object to turn on the circuit through the synchronous circuit, thereby detecting the presence or absence of the object. The photoelectric switch converts the input current into light signal and emits it on the emitter, and the receiver detects the presence or absence of the target object based on the intensity or absence of the received light.
2. Classification and working principles of photoelectric switches:
According to the detection method, it can be divided into diffuse-reflective type, through-beam type, mirror-reflective type, slot type photoelectric switch, and fiber optic photoelectric switch.
1. Through-beam type: It consists of an emitter and a receiver, which are structurally separated from each other. A switch signal change will occur when the light beam is interrupted.
Figure 2.1 Working principle diagram of through-beam type2. Diffuse-reflective type: A sensor that integrates the emitter and receiver. When a detected object passes by, it reflects a sufficient amount of light emitted by the photoelectric switch emitter to the receiver, thus generating a switch signal. The detection distance is generally 3 meters.
Figure 2.2 Working principle diagram of diffuse-reflective type3. Mirror-reflective type: It is a standard configuration composed of an emitter and a receiver. The light beam emitted from the emitter is reflected by the opposite mirror and returned to the receiver. A switch signal change will occur when the light beam is interrupted. The passage time of light is twice the signal duration, and the effective operating distance is from 0.1 meter to 20 meters.
Figure 2.3 Working principle diagram of mirror-reflective type4. Slot-type photoelectric switch: It is usually a standard U-shaped structure, with the emitter and receiver located on both sides of the U-shaped slot, forming an optical axis. When the detected object passes through the U-shaped slot and blocks the optical axis, the photoelectric switch generates a detected switch signal. Slot-type photoelectric switches are relatively safe and reliable, suitable for detecting high-speed changes and distinguishing transparent and translucent objects.
Figure 2.4 Working principle diagram of slot-type photoelectric switch5. Fiber optic photoelectric switch: It uses plastic or glass fiber optic sensors to guide light to achieve detection of objects not in the vicinity. Usually, fiber optic sensors are divided into through-beam type and diffuse-reflective type.
Figure 2.5 Working principle diagram of fiber optic photoelectric switch2. Fiber optic photoelectric switch: It uses plastic or glass fiber optic sensors to guide light to achieve detection of objects not in the vicinity. Usually, fiber optic sensors are divided into through-beam type and diffuse-reflective type.
3. Characteristics of photoelectric switches
1. Long detection distance: Compared with inductive proximity switches, it can obtain a long detection distance. For example, the through-beam type switch can detect distances of tens of meters.
2. Wide range of detection objects: Because it is based on the reflection and light transmission of the detected object, it can detect almost all objects such as metal, glass, rubber, wood, liquid, gas, etc.
3. Fast response speed: The detected medium itself is high-speed, and a very high detection speed can be obtained.
4. High resolution: Because light propagates in a straight line and has a short wavelength, it has high resolution and is suitable for detecting small objects and high-precision positions.
5. Unaffected by magnetic fields and vibrations: The detection switches are generally installed in places with strong magnetic fields and vibrations. Essentially, photoelectric switches are rarely affected by them, so they can operate reliably.
6. Long service life: Because it is non-contact detection and uses light-emitting diodes as the light source, and the control output adopts a non-contact method, it has a long service life.
However, photoelectric switches also have the following disadvantages:
1. The lens is prone to pollution by dust and oil. Once the lens is dirty, not only the light beam is scattered, but also a part of the light is blocked. Therefore, in harsh environments, practical protection measures must be taken.
2. The intensity of ambient light affects the switch. For ordinary lighting, the photoelectric switch is almost unaffected, but if the background light is too strong, exceeding tens of thousands of lux, it will cause the switch to malfunction.
3. The cost is higher than other detection switches.
