Basic introduction Chinese name: photoelectric switch mbth: photoelectric switch category: switch full name: photoelectric proximity switch brief introduction, characteristics, uses, working principle, model type, structural classification, detection method classification, precautions, brief introduction photoelectric switch is the abbreviation of photoelectric proximity switch, which uses the shielding or reflection of the detected object to connect the circuit through the synchronous loop, thus detecting the presence or absence of the object. Objects are not limited to metals, and all objects that can reflect light (or block light) can be detected. The photoelectric switch converts the input current into an optical signal on the transmitter and emits it, and then the receiver detects the target object according to the intensity of the received light. Photoelectric switch smoke alarm is a common type of security system, which is often used in industry to count the action times of manipulator. Characteristic photoelectric switch is a kind of sensor, which converts the light intensity change between transmitter and receiver into the current change to achieve the purpose of detection. Because the output loop and input loop of photoelectric switch are electrically isolated (that is, electrically insulated), it can be used in many occasions. A new generation of photoelectric switch devices manufactured by integrated circuit technology and SMT surface mounting technology have intelligent functions such as delay, broadening, external synchronization, anti-interference, high reliability, stable working area and self-diagnosis. This new photoelectric switch is an active photoelectric detection system electronic switch with pulse modulation. It uses cold light sources, such as infrared light, red light, green light and blue light. , can control the state and action of solid, liquid, transparent body, blackbody, software, smoke and other substances quickly and lossless. It has the advantages of small volume, multi-function, long service life, high precision, fast reverberation speed, long detection distance and strong resistance to light, electricity and magnetic interference. Photoelectric switch has been used in many fields, such as crop liquid level detection, liquid level control, product counting, width discrimination, speed detection, fixed-length shearing, hole identification, signal delay, automatic door induction, color code detection, punching machine and shearing machine, safety protection and so on. In addition, it can also be used as an anti-theft alarm in banks, warehouses, shops, offices and other necessary occasions by taking advantage of the concealment of infrared rays. The commonly used infrared photoelectric switch uses the reflection principle of the object to detect the existence of the object by sensing the intensity of the reflected light through the synchronous loop. The photoelectric sensor first sends out an infrared beam to reach or pass through the object or mirror to reflect the infrared beam, and the photoelectric sensor receives the reflected beam to judge the existence of the object according to the intensity of the beam. There are also many kinds of infrared photoelectric switches, generally speaking, there are mainly mirror reflection photoelectric switches, diffuse reflection photoelectric switches, slot photoelectric switches, anti-radiation photoelectric switches and optical fiber photoelectric switches. Includes automatic selection of photoelectric switch. Different photoelectric switches are used in different occasions, for example, optical fiber photoelectric switch is often used in electromagnetic vibration feeder, diffuse reflection photoelectric switch is often used in feeding packaging film in intermittent packaging machine, and slot photoelectric switch is often used in continuous high-speed packaging machine. Working principle The picture on the right shows the working principle of reflective photoelectric switch. The modulation pulse generated by the oscillation circuit in the figure passes through the reflection circuit, and then the interference is eliminated by digital integration photoelectric switch or RC integration, and finally the driver is triggered to output the photoelectric switch control signal with delay (or without delay). Using optical elements to change the light beam in the middle of the medium; Reflect an object with a light beam; So that the light beam can return immediately after a long distance. The photoelectric switch consists of a transmitter, a receiver and a detection circuit. The transmitter aims at the target to emit light beams, which generally come from light emitting diodes (LEDs) and laser diodes. Continuously emit light beams or change the pulse width. The radiation intensity of the pulse modulated beam is selected many times in transmission, and it will not be indirectly directed at the target. The receiver consists of one or more photodiodes. In front of the receiver, optical elements such as lens and aperture are installed. Behind it is a detection circuit, which can filter out effective signals and apply them. Optocoupler is an electrical-optical-electrical conversion device that transmits electrical signals through light. It consists of a light source and a light receiver. The light source and the light receiver are assembled in the same closed housing and separated from each other by a transparent insulator. The pin of the light source is the input end and the pin of the light receiver is the output end. The common light source is light-emitting diode, and the light receiver is photodiode and phototransistor. There are many types of photoelectric couplers, including photodiode type, phototransistor type, photoresistor type, photo-controlled thyristor type, photoelectric Darlington type, integrated circuit type and so on. Working principle: An electrical signal is applied to the input end of the photoelectric coupler to make the light source emit light, and the intensity of the light depends on the excitation current. After this light irradiates the encapsulated photoreceptor, it generates photocurrent due to photoelectric effect, which is led out from the output end of the photoreceptor, thus realizing the conversion of electricity, light and electricity. After the modulation pulse generated by the oscillation circuit passes through the reflection circuit, the light pulse is emitted by the light emitting tube GL. When the measured object enters the action range of the optical receiver, the reflected light pulse enters the photosensitive diode DU. The photoelectric switch demodulates the optical pulse into an electric pulse signal in the receiving circuit, which is amplified by an amplifier, synchronized gating and shaping, and then eliminates the interference by digital integration or RC integration. Finally, the delay (or no delay) triggers the driver to output the photoelectric switch control signal. Generally, photoelectric switches have good return error characteristics, so even if the detected object shakes in a small range, it will not affect the output state of the driver, thus keeping it in a stable working area. At the same time, the self-diagnosis system can also display the light receiving state and stable working area, so as to monitor the working situation of photoelectric switch at any time. Model type structure classification photoelectric switches can be divided into three types according to structure: amplifier separation type, amplifier built-in type and power supply built-in type. The amplifier separation type is to separate the amplifier from the sensor, which is made of special integrated circuit and mixed installation process. Because the sensor has the characteristics of subminiature and diversity, the amplifier has more functions. Therefore, this model adopts terminal station connection mode and can be used for AC and DC power supply. It has the function of on-off delay, can set the switch between light and sound, can control six output States, and has two output modes: contact and level. The built-in amplifier integrates the amplifier with the sensor, is made of special integrated circuit and surface mount technology, and works with DC power supply. Its echo velocity (0. 1ms and 1ms) can detect narrow and high-speed moving objects. Changing the polarity of power supply can switch between bright and dark motion, and self-diagnosis and stable working area indicator light can be set. It has two output modes of voltage and current, which can prevent mutual interference and is very convenient for system installation. The built-in power supply is an integrated amplifier, sensor and power supply device, which is made by ASIC and surface mount technology. Generally, AC power supply is used, which is suitable for replacing contact travel switch in production site and can be directly used in high voltage control circuit. You can also set up a self-diagnosis stable working area indicator light, and the output is equipped with SSR solid-state relay or relay normally open and normally closed contacts, which can prevent mutual interference and can be closely installed in the system. According to the detection methods, the detection methods of counting photoelectric switch can be divided into diffuse type, counting type, specular reflection type, slot photoelectric switch and optical fiber photoelectric switch. Counter-type photoelectric switch is composed of transmitter and receiver, which are separated from each other in structure. When the light beam is interrupted, the switching signal will change. Typically, the photoelectric switches located on the same axis can be separated by up to 50 meters. Features: distinguish opaque reflective objects; The effective distance is large, because the light beam only passes through the induction distance once; It is not easy to be disturbed and can be used reliably and properly in the wild or dusty environment; Equipment consumption is high, so both units need to lay cables. Diffuse reflection type means that when the switch emits light beam, the target will diffuse reflection, and the transmitter and receiver form a single standard part. When enough combined light returns to the receiver, the state of the switch changes, and the typical operating distance is generally 3 meters. Features: the effective action distance is determined by the reflection ability of the target and the surface properties and color of the target; The assembly cost is low, and when the switch is composed of a single element, rough positioning can usually be realized; The background suppression function is used to adjust the measuring distance; Sensitive to the dust on the target, sensitive to the change of target reflection performance. Specular reflection consists of a transmitter and a receiver, which is a standard configuration. The light beam emitted by the transmitter is reflected on the opposite mirror, that is, it returns to the receiver. When the light beam is interrupted, the switching signal will change. The transit time of light is twice as long as the signal duration, and the effective action distance ranges from 0. 1 m to 20 m. Features: distinguishing opaque objects; With the help of the mirror assembly, a high effective distance range is formed; It is not easy to be disturbed and can be used reliably and properly in the wild or dusty environment. The slot photoelectric switch is usually a standard U-shaped structure, and its transmitter and receiver are located on both sides of the U-shaped slot and form the optical axis. When the detected object passes through the U-shaped groove and blocks the optical axis, the photoelectric switch generates the detected switch signal. The slot photoelectric switch is safe and reliable, and is suitable for detecting high-speed changes and distinguishing transparent and translucent objects. Optical fiber photoelectric switch uses plastic or glass optical fiber sensor to guide light and realize the detection that the detected object is not in the near area. Generally, optical fiber sensors are divided into two types: retroreflection type and diffuse reflection type. Precautions The photoelectric switch can be used in various applications. In addition, when using photoelectric switch, we should also pay attention to environmental conditions, so that photoelectric switch can work normally and reliably. Strong light source: when the ambient illumination is high, the photoelectric switch can generally work stably. However, direct pointing of the optical axis of the sensor to strong light sources, such as sunlight and incandescent lamps, should be avoided. When the angle between the optical axis of the sensor (light receiver) and the strong light source cannot be changed, a light shielding plate or a long light shielding tube can be installed around the sensor. Mutual interference: MGK series new photoelectric switches usually have the function of automatically preventing mutual interference, so there is no need to worry about mutual interference. However, when several groups of opposed HGK series infrared photoelectric switches are installed side by side, adjacent groups and mutual interference should be prevented. The most effective way to prevent this kind of interference is that the projector and receiver cross, and when there are more than two groups, the distance between the groups is also widened. Models with different frequencies can also be used. An effective way to prevent the mutual interference of HGK series reflective photoelectric switches is to open the interval. Moreover, the farther the detection distance is, the larger the interval should be, and the specific interval should be determined according to the debugging situation. Of course, models with different operating frequencies can also be used. Mirror angle: when the measured object is shiny or meets a smooth metal surface, the reflectivity is generally high, similar to a mirror. At this time, the projector and the detected object should be installed at an included angle of10 ~ 20, so that its optical axis is not perpendicular to the detected object to prevent misoperation. Background: When using reflective diffusion projectors and receivers, sometimes the photoelectric switch may be unstable because the detected object is close to the background, and the photoelectric switch or the background is smooth and other objects with high reflectivity. So you can use a projector and receiver with limited distance instead, or you can remove the background by staying away from it, moving it, painting it dark black, or trying to make it rough and gloomy. Self-diagnosis: In the process of installation or use, due to the influence of the table or background and the vibration during use, there are sometimes problems such as slight deviation of the optical axis, lens pollution, dust accumulation, external noise, and environmental temperature out of range. These problems may make the photoelectric switch deviate from the stable working area. At this time, the self-diagnosis function of photoelectric switch can be used to make it send out a notice through a stable green indicator light to remind users to adjust in time. Table Influence: When the projector and receiver are installed near the table, some light beams reflected by the table may irradiate the receiver, resulting in unstable work. To this end, the receiver and projector can be separated from the table by a certain distance, and a shading plate can be added. It is forbidden to use chemicals such as thinner to avoid damaging the plastic mirror. The wiring of high-voltage lines, power lines and photoelectric sensors should not be placed in the same conduit or trough, otherwise the photoelectric switch will be misoperated or damaged (sometimes) due to induction, so the wiring should be separated in principle.