Structural analysis photoelectric sensor usually consists of three parts, namely: transmitter, receiver and detection circuit. The transmitter is equipped with a calibration lens to focus the light on the receiver, and the receiver outputs a cable to connect the equipment to the vacuum tube amplifier. There is a small white incandescent lamp as a light source in the metal tube. These small and powerful incandescent light sensors are the embryonic form of photoelectric sensors. The receiver consists of photodiode, phototransistor and photocell. Photosensitive diode is the most common sensor now. The shape of the photodiode of the photoelectric sensor is the same as that of the general diode, except that there is a window embedded with glass on its shell to facilitate the light to enter. In order to increase the light receiving area, the area of the PN junction becomes larger. The photodiode works under reverse bias and is connected in series with the load resistor. When there is no light, like a general diode, the reverse current is very small, which is called the dark current of a photodiode. When there is light, carriers are excited, resulting in electron holes, which are called photoelectric carriers. In addition, there are emission plates and optical fibers in the structural elements of photoelectric sensors. Corner reflector is a kind of solid emitting device, which is composed of small triangular cone reflective material and can make the light beam return from the reflector accurately. It can change the emission angle with the optical axis in the range of 0 ~ 25, so that the light beam is almost emitted from an emission line and still returns from this reflection line after reflection.