Because the displacement sensor can be made according to different principles and different methods, and the different sensors have different “perceived” methods for objects, so common proximity switches have the following types:
1. Eddy current proximity switch
This type of switch is sometimes called an inductive proximity switch. It is the use of conductive objects in the proximity of this can generate electromagnetic field proximity switches, so that the object generates eddy currents. This eddy current reacts to the proximity switch, causing the internal circuit parameters of the switch to change, thereby recognizing whether or not the conductive object is moving closer, thereby controlling the on and off of the switch. The object that this proximity switch can detect must be a conductor.
2、Capacitive proximity switch
The measurement of such a switch is usually one plate constituting a capacitor, and the other plate is the housing of the switch. This enclosure is usually grounded or connected to the enclosure of the device during the measurement process. When an object moves toward the proximity switch, whether it is a conductor or not, due to its proximity, the dielectric constant of the capacitor always changes, so that the capacitance changes, and the state of the circuit connected to the measuring head also occurs. Changes, which can control the switch on or off. The object to be detected by this proximity switch is not limited to a conductor, an insulating liquid, a powder, or the like.
3, Hall proximity switch
The Hall element is a magnetosensitive element. A switch made using a Hall element is called a Hall switch. When the magnetic object moves close to the Hall switch, the Hall element of the switch detection surface changes the internal circuit state of the switch due to the generation of the Hall effect, thereby recognizing the presence of a magnetic object nearby, thereby controlling the on and off of the switch. The proximity switch must be a magnetic object.
4, photoelectric proximity switch
Switch made of photoelectric effect is called photoelectric switch. The light emitting device and the optoelectronic device are mounted in the same test head in a certain direction. When there is a reflective surface (detected object) approaching, the optoelectronic device receives the reflected light and then outputs the signal, thereby “sensing” the approach of the object.
5, pyroelectric proximity switches
A switch made of a device that senses temperature changes is called a pyroelectric proximity switch. This kind of switch is to install the pyroelectric device on the detection surface of the switch. When there is an object that is close to the ambient temperature, the output of the pyroelectric device changes, and thus the proximity of the object can be detected.
6, other types of proximity switches
When the observer or system changes the distance of the wave source, 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 using the Doppler effect. When there is an object approaching, the Doppler frequency shift is generated by the reflected signal received by the proximity switch, so that the presence or absence of the object can be identified.