In all types of switches, there is a displacement sensor that has a "perceptual" ability to approach its object. Using the displacement sensor to the sensitive property of the close to the object to control the switch pass or break, this is the proximity switch.
When an object moves toward the proximity switch and is close to a certain distance, the displacement sensor is "perceived" and the switch moves. This distance is usually called "checkout distance". Different proximity switches have different checkout distances.
Sometimes detected objects are at a certain time interval, one after another to move to the proximity switch, another one to leave, so repeat. The different proximity switches have different response ability to the detection object. This response feature is called the response frequency.
Because the displacement sensor can be made according to different principles and different methods, and different displacement sensors on the object's "perceptual" method is different, so the common proximity switches are as follows:
1, vortex-type proximity switch
This switch is sometimes called an inductive proximity switch. It is the use of conductive objects near this can produce electromagnetic field close to the switch, the inside of the object generated eddy current. The eddy current reacts to the proximity switch, which changes the internal circuit parameters of the switch, thereby recognizing that there is no conductive object moving close to the control of the switch's pass or break. The object that the proximity switch can detect must be a conductive body.
2. Capacitive Proximity switch
The measurement of this switch is usually a plate that forms the capacitor and the other plate is the shell of the switch. This enclosure is usually grounded or connected to the chassis of the device during measurement. When an object moves toward the proximity switch, whether or not it is a conductor, due to its proximity, the capacitor will always change the dielectric constant, so that the electrical capacity changes, so that and the measurement of the head connected to the circuit state also changes, which can be controlled switch to connect or disconnect. This proximity switch detects objects that are not limited to conductors, can be insulated from liquids or powdered objects, etc.
3, Hall proximity switch
The hall element is a magnetic sensitive element. A switch made from hall elements is called the hall switch. When the magnetic object is moved near the hall switch, the hall element on the switch detection surface changes the internal circuit state of the switch because of the Hall effect, thus identifying the presence of a magnetic object nearby, thereby controlling the pass or break of the switch. This proximity switch must be detected by a magnetic object.
4. Photoelectric Proximity switch
The switch made of photoelectric effect is called photoelectric switch. The light-emitting device and the photoelectric device are mounted in the same inspection head in a certain direction. When there is a reflective surface (detected object) Close, the photoelectric device receives the reflected light in the signal output, thus can "perceive" the object approach.
5, pyroelectric type proximity switch
A switch called a pyroelectric proximity switch is made with a component that can perceive temperature changes. The switch is to install the pyroelectric parts on the test surface of the switch, when the object with different ambient temperature is approaching, the output of the pyroelectric device will change, thus can detect the object approaching.
6, other type of proximity switch
When the distance between the observer or the system changes to the sources, the frequency of the approaching waves is shifted, a phenomenon called the Doppler effect. Sonar and radar are made using the principle of this effect. The ultrasonic proximity switch and microwave Proximity switch can be made by using Doppler effect. When an object moves near, the reflected signal received by the proximity switch produces a Doppler shift, which can be used to identify the object approaching.