A photoelectric sensor consists mainly of a transmitter that emits light and a receiver that receives it. When the emitted light is interrupted or reflected by the sensing object, it changes the amount of light reaching the receiver. The receiver detects this change and converts it to an electrical output. Photoelectric sensors detect objects, changes in surface conditions, and other items through a variety of optical properties. The light source for most photoelectric sensors is infrared or visible light. Photoelectric switch transmitters mostly use semiconductor light-emitting diodes (LEDs) driven by narrow pulse currents at medium frequencies (around 40 kHz) as the light source to emit modulated light pulses. Accordingly, the output signal of the receiving photosensitive element (phototransistor) is processed by a 40kHz frequency-selective AC amplifier and a special demodulation chip, which can effectively prevent interference from sunlight, and fluorescent lamps, and can reduce the power consumption of the transmitting LED. The photoelectric sensor includes the through beam photoelectric switch, retroreflective photoelectric sensor, diffuse reflective photoelectric switch, slot photoelectric switch, and optical fiber photoelectric switch.

(1) Diffuse reflection type photoelectric switch. It is a kind of sensor that combines transmitter and receiver in one. When a detected object passes by, the object reflects a sufficient amount of light emitted by the photoelectric switch transmitter to the receiver, so the photoelectric switch produces a switching signal. When the surface of the object to be detected is bright or its reflectivity is extremely high, the diffuse photoelectric switch is the preferred detection mode.

(2) retro-reflective photoelectric switch. It is also a set of emitter and receiver in one, and reflective mirror relative installation with the use. A photoelectric switch transmitter emitted light through the reflector reflected back to the receiver, when the object is detected and completely blocks the light, the photoelectric switch produces a detection switch signal. A reflector using a polarized triangular prism can transmit issued light into polarized light reflected back, the light receiver surface covered with a layer of polarized lens, can only accept the reflector reflected back polarized light.

(3) Through beam photoelectric switches. It contains the structure of mutual separation and an optical axis placed opposite the emitter and receiver, and the emitter light directly into the receiver, when the object is detected between the emitter and receiver and blocks the light, a photoelectric switch produces a switch signal. When the detection object is an opaque object, the pair of photoelectric switches are the most reliable detection device.

(4) Slot-type photoelectric switch. It usually uses the standard U-shaped structure, its emitter and receiver are located on both sides of the U-shaped slot, and form an optical axis. When the object is detected through the U-shaped slot and blocks the optical axis, the photoelectric switch produces a switch signal. Slot type photoelectric switch is more suitable for detecting the high-speed movement of objects, and it can distinguish between transparent and translucent objects, safe and reliable to use.

(5) Optical fiber-type photoelectric switch. It uses a plastic or glass optical fiber sensor to guide the light and can detect the object to be detected at a distance. Fiber optic photoelectric switch is also divided into the opposite type and diffuse reflection type.