I. Photoelectric Effect Principle
Optoelectronic components are the most important part of photoelectric sensors, and their core working principle is the photoelectric effect of different types. According to wave-particle duality, light is composed of photons traveling at the speed of light. When an object is irradiated by light, the electrons inside it absorb the energy of the photons and change their state, thus changing their electrical properties. This phenomenon is called the photoelectric effect.
II. Classification of Photoelectric Sensors
Photoelectric sensors are classified into diffuse reflection type, reflector type, and through-beam type according to their detection method. Based on the corresponding detection method, photoelectric sensors with the following different structures are available:
1. Slot-type photoelectric sensor
A slotted photoelectric switch consists of a light emitter and a receiver mounted face-to-face on opposite sides of a slot. The emitter emits infrared or visible light, which the receiver can pick up when there is no obstruction. However, when an object passes through the slot, the light is blocked, triggering the photoelectric switch. It outputs a control signal to cut off or connect the load current, thus completing a control action. The detection distance of a slotted switch is typically only a few centimeters due to the limitations of its overall structure.
2. Through-beam photoelectric sensor
Separating the emitter and receiver increases the detection distance. A photoelectric switch consisting of one emitter and one receiver is called a through-beam photoelectric switch, or simply a through-beam photoelectric switch. Its detection distance can reach several meters or even tens of meters. In use, the emitter and receiver are installed on opposite sides of the path of the object being detected. When the object passes by and blocks the light path, the receiver activates and outputs a switch control signal.
3. Reflector type photoelectric switch
A photoelectric switch that integrates the emitter and receiver into a single device, with a reflector mounted in front of it, and utilizes the principle of reflection to achieve photoelectric control, is called a reflector-type (or mirror-type) photoelectric switch. Under normal circumstances, the light emitted by the emitter is reflected back by the reflector and received by the receiver; however, if the light path is blocked by an object being detected, and the receiver cannot receive light, the photoelectric switch activates, outputting a switch control signal.
4. Diffuse-reflective photoelectric switch
Its detection head also contains a light emitter and a light receiver, but there is no reflector in front. Under normal circumstances, the light emitted by the light emitter cannot be detected by the light receiver. When the object being detected passes by, it blocks the light and reflects part of the light back, and the light receiver receives the light signal and outputs a switching signal.
The basic characteristics of photoelectric sensors include the relationship curve between the output current and the voltage across the receiver, the relationship curve between the output current and the input current of the transmitter, the relationship curve between the output current and temperature, and the pulse response characteristic curve.
