Photoelectric sensors are key components in various photoelectric detection systems that achieve photoelectric conversion. They are devices that convert optical signals (infrared, visible, and ultraviolet radiation) into electrical signals. It can be used to detect non electric quantities that directly cause changes in light intensity, such as light intensity, illuminance, radiation temperature measurement, gas composition analysis, etc; It can also be used to detect other non electric quantities that can be converted into changes in light quantity, such as part diameter, surface roughness, strain, displacement, vibration, velocity, acceleration, as well as recognition of object shape and working status.
A photoelectric sensor generally consists of three parts: transmitter, receiver, and detection circuit.
Principle of photoelectric sensor:
Optoelectronic components are important components of photoelectric sensors, and their core working principle is different types of photoelectric effects. According to wave particle duality, light is composed of photons that move at the speed of light. When an object is illuminated by light, its internal electrons absorb the energy of the photons and change their state, resulting in a change in its electrical properties. This phenomenon is called the photoelectric effect. Optoelectronic sensors typically include a light source, optical path, and optoelectronic components. Controlling photoelectric sensors by converting changes in light intensity into changes in electrical signals.
Classification of photoelectric sensors:
Optoelectronic components include photoresistors, photodiodes, phototransistors, light-emitting diodes, photomultiplier tubes, photovoltaic cells, optocoupler devices, etc. There are various optical measurement and control systems made based on the principle of the effect of light flux on photoelectric elements. According to the output properties of photoelectric elements, photoelectric sensors can be divided into two categories: analog photoelectric sensors and pulse photoelectric sensors; Analog photoelectric sensors can be divided into three categories based on the measured method: transmissive, diffuse reflective, and opaque.
Application principle of photoelectric sensors:
1. Application of photoelectric sensors in high-voltage and high current testing
In recent years, the use of optical devices for high-voltage and high current measurement has developed rapidly in the power system. Many new types of photoelectric sensor systems have been put into operation on site, bringing many convenient conditions for monitoring high-voltage and high current. OCT has fast response speed and high measurement accuracy. OCT differs from CT (traditional current transformer) in that the signal power is small. OCT products modulate the measured current from high potential to low potential using light, and their optical instrument only has power at the micro watt level, while the secondary coil of CT requires power at the watt level.
2. Application of photoelectric sensors in speed measurement systems
In today's rapidly developing field of mechanical automation, rotational speed is an important characteristic parameter in power mechanical performance testing, and its magnitude and variation are related to whether the mechanical operation is normal. Many characteristic parameters of power machinery are often determined by the speed, such as the output power of the motor, and the vibration, pipeline airflow pulsation, and wear status of various working parts of power machinery are also closely related to the speed. Timely monitoring of changes in rotational speed can promptly eliminate many faults during machine operation and avoid causing greater losses. The speed measurement methods are classified according to the installation method of the sensor, and are divided into two categories: contact and non-contact. Non contact speed measurement includes disc magnetic measurement, shaft magnetic measurement, blocking photoelectric measurement, and reflective photoelectric measurement. The widely used among them is the photoelectric speed measurement system.
3. Application of photoelectric sensors in relay protection
With the development of the power industry, the transmission capacity and voltage level of the power system continue to increase. Traditional transformers have many shortcomings in measuring and monitoring the power grid. At present, the comprehensive automation system of fiber optic substations composed of fiber optic transformers using photoelectric sensors and fiber optic communication networks has become one of the promising development directions of power automation technology. Power transformer is an important electrical measurement device in the power system and a key equipment for achieving power automation. The new active photoelectric sensor can overcome the shortcomings of traditional power transformers, such as large size, large mass, poor anti-interference, and small information transmission capacity, which make the safe operation and automation level of the power system unable to meet the requirements. At the same time, it can output digital signals and eliminate a large number of secondary cables, providing a solid foundation for the safe operation, cost saving, oil-free high-voltage equipment, and optimization of secondary equipment of the power system.
4. Application of photoelectric sensors in monitoring smoke turbidity
Preventing smoke and dust pollution is one of the important tasks of environmental protection. In order to eliminate industrial smoke and dust pollution, it is necessary to first know the amount of smoke and dust emissions. Therefore, it is necessary to monitor, automatically display, and alert for excessive smoke and dust sources. The turbidity of smoke and dust in the flue is detected by the magnitude of changes in the transmission of light in the flue. If the turbidity of the flue increases, the light emitted by the light source is absorbed and refracted by the smoke particles, and the light reaching the photodetector decreases. Therefore, the strength of the output signal of the photodetector can reflect the changes in the turbidity of the flue.
Application Case 1: Optoelectronic Position Offset Detection
The photoelectric position offset detector is mainly used for detecting strip type materials. This technology can be used to detect materials during specific processing, to check whether the position, size, and direction of the materials meet the standards; By detecting these aspects, specific signals of misalignment positions can be provided, which helps to control the circuit. This technology is usually used for testing printing, dyeing, film, and other aspects. The basic principle of the photoelectric strip deviation detector is shown in the following figure. When the light emitted from the light source passes through lens 1, the light will become a beam due to the principle of focusing, and then be directed towards lens 2 before converging onto the photoresistor. Before the parallel beam reaches lens 2, some of the light rays will be affected by the tested strip, resulting in a decrease in the light flux reaching the photoresistor.
Application Case 2: Optoelectronic Height Detection
Generally speaking, there are specific requirements for the filling height during the packaging process of items to ensure that the appearance of the items meets the specified standards. Products that do not meet the filling height will be prohibited from leaving the factory. The basic principle of the application of photoelectric detection technology in controlling the filling height of goods is shown in the following figure. If the filling height of the product exceeds the specified standard value, the photoelectric connector will have no electrical signal, and other institutions will be asked to handle the item.
Application Case 3: Optoelectronic Color Quality Detection
The basic principle of photoelectric color quality detection used in packaging materials is shown in the following figure. Assuming that the base color of the packaging items according to the specified standards is white, but due to reasons such as not meeting the quality standards, some products may exhibit yellowing. When conducting photoelectric color quality testing on the products, voltage differences may appear in the yellowing parts of the products; Connect the solenoid valve based on the difference in output voltage, and finally discharge the yellowed product through compressed air.
Application Case 4: Industrial Production Process Inspection
In addition to the practical applications of the above-mentioned photoelectric sensors, they can also be used for production statistics of products on the flowline, detecting whether the accessories are properly configured, and checking whether the quality of the accessories meets the specified standards. For example, they can specifically detect whether the bottle cap is tightly pressed, whether there is a missing label on the trademark (see Figure 4), and whether there is a material breakage in the feeding mechanism (see the figure below).
Summary: Sensor Technology - The Future Driver of Intelligent Manufacturing