Photoelectric sensor is a small electronic device, a variety of photoelectric detection system to realize the key components of photoelectric conversion. It is mainly the use of various properties of light, detecting the presence or absence of objects and changes in surface state and other sensors. Photoelectric sensor has non-contact, fast response, reliable performance and other characteristics, so in industrial automation devices and robots are widely used.
　　1. Principle of photoelectric effect
　　The photoelectric element is the most important part of the photoelectric sensor, its core working principle is different types of photoelectric effect. According to wave-particle duality, light is composed of photons moving at the speed of light, when the object is irradiated by light, its internal electrons absorb the energy of the photons to change the state of their own electrical properties will change, such a phenomenon is known as the photoelectric effect.
　　Second, the classification of photoelectric sensors
　　Photoelectric sensors according to the detection method is divided into diffuse reflection type, reflective plate type, the opposite type, according to the corresponding detection method has the following photoelectric sensors of different structures:
　　1, slot photoelectric sensor
　　A light emitter and a receiver mounted face-to-face on both sides of a slot is a slot photoelectric. The emitter can emit infrared light or visible light, in the absence of resistance to the light receiver can receive light. However, when the object to be detected from the slot through, the light is blocked, photoelectric switch will act. A switch control signal is output to cut off or turn on the load current, thus completing a control action. The detection distance of the slot switch is generally only a few centimeters because of the limitations of the overall structure.
　　2, the counter-reflective photoelectric sensor
　　If the light emitter and light receiver separated, it can make the detection distance increase. By a light emitter and a transceiver composed of photoelectric switch is known as the counter-reflective separated photoelectric switch, referred to as the counter-reflective photoelectric switch. Its detection distance can reach several meters or even tens of meters. The use of light emitters and light receivers were installed in the detection of objects through the path on both sides, the detection of objects through the blocking of the light path, light receivers on the action of the output of a switch control signal.
　　3.Reflector type photoelectric switch
　　The light emitter and receiver into the same device, installed in front of it a reflector, the use of the principle of reflection to complete the role of photoelectric control is called reflector reflective (or reflector reflective) photoelectric switch. Under normal circumstances, the light emitted by the luminous emitter is reflected by the reflector back to be received by the receiver; once the light path is blocked by the detection of the object, the receiver can not receive the light, the photoelectric switch on the action, the output of a switch control signal.
　　4, diffusion reflection photoelectric switch
　　Its detection head is also equipped with a light emitter and a transceiver, but there is no reflector in front. Under normal circumstances, the light emitted by the light receiver is not found. When the detecting object passes by blocking the light and partially reflecting the light back, the light receiver receives the light signal and outputs a switching signal.
　　The basic characteristics of the photoelectric sensor include the relationship curve between the output current and the voltage at the two ends of the receiver, the relationship curve between the output current and the input current of the emitter, the relationship curve between the output current and the temperature change, and the impulse response characteristic curve.