Proximity switches - types

Proximity switch - Type 1. Eddy current proximity switch. This type of switch is sometimes also called inductive proximity switch. It uses a conductive object to generate eddy currents inside the object when it approaches the proximity switch that generates an electromagnetic field. This eddy current reacts to the proximity switch, causing the internal circuit parameters of the switch to change, thereby identifying whether a conductive object is approaching, and then controlling the on or off of the switch. The objects that this proximity switch can detect must be electrical conductors. 2. Capacitive proximity switch The measurement of this switch usually consists of one plate of the capacitor, and the other plate is the shell of the switch. This enclosure is usually grounded or connected to the equipment chassis during measurements. When an object moves toward the proximity switch, no matter whether it is a conductor or not, due to its proximity, the dielectric constant of the capacitor will always change, thus causing the capacitance to change, and the state of the circuit connected to the measuring head will also change. changes, thereby controlling the switch on or off. The objects detected by this proximity switch are not limited to conductors, but can insulate liquids or powders, etc. 3. Hall proximity switch Hall element is a magnetic sensitive element. A switch made of Hall elements is called a Hall switch. When a magnetic object moves close to the Hall switch, the Hall element on the detection surface of the switch changes the internal circuit state of the switch due to the Hall effect, thereby identifying the presence of magnetic objects nearby and controlling the on or off of the switch. The detection object of this proximity switch must be a magnetic object. 4. Photoelectric proximity switch The switch made by using the photoelectric effect is called a photoelectric switch. The light-emitting device and the optoelectronic device are installed in the same detection head in a certain direction. When a reflective surface (object to be detected) approaches, the optoelectronic device receives the reflected light and outputs a signal, so that it can "perceive" that an object is approaching. 5. Pyroelectric proximity switch A switch made of a component that can sense temperature changes is called a pyroelectric proximity switch. This type of switch installs a pyroelectric device on the detection surface of the switch. When an object with a different temperature from the ambient temperature approaches, the output of the pyroelectric device changes, thus detecting the approach of an object. 6. Other types of proximity switches When the distance of the observer or system to the wave source changes, the frequency of the approaching wave will shift. This phenomenon is called the Doppler effect. Sonar and radar are made using the principle of this effect. Ultrasonic proximity switches, microwave proximity switches, etc. can be made by using the Doppler effect. When an object moves closer, the reflected signal received by the proximity switch will produce a Doppler frequency shift, thereby identifying whether an object is approaching.