Proximity switch is also called non-contact travel swit […]
Proximity switch is also called non-contact travel switch. In addition to complete travel control and limit protection, it is also a non-contact detection device, used to detect the size of parts and speed measurement, etc., and can also be used for variable frequency counters and variable frequency pulse generation The automatic connection of machine, liquid level control and processing program. Features include reliable work, long life, low power consumption, high repositioning accuracy, high operating frequency, and adaptability to harsh working environments.
Among all kinds of switches, there is a component that has the ability to "perceive" objects approaching it-displacement sensor. Use the sensitive characteristic of the displacement sensor to approach the object to achieve the purpose of controlling the switch on or off, this is the proximity switch.
When an object moves to the proximity switch and approaches a certain distance, the displacement sensor will "sense" and the switch will act. Usually this distance is called "detection distance". Different proximity switches have different detection distances.
Sometimes the detected objects move to the proximity switch one by one at a certain time interval, and then leave one by one. This is repeated continuously. Different proximity switches have different responsiveness to the detected object. This response characteristic is called "response frequency".
Because displacement sensors can be made according to different principles and different methods, and different displacement sensors have different "perception" methods for objects.
Common proximity switches are as follows:
1. Eddy current proximity switch
This kind of switch is sometimes called an inductive proximity switch. It uses a conductive object to generate an eddy current inside the object when it approaches the switch that can generate an electromagnetic field. This eddy current reacts to the proximity switch, causing the internal circuit parameters of the switch to change, thereby identifying whether there is a conductive object approaching, and then controlling the on or off of the switch. The object that this proximity switch can detect must be an electrical conductor.
2. Capacitive proximity switch
The measurement of this kind of switch usually constitutes one plate of the capacitor, and the other plate is the shell of the switch. This enclosure is usually grounded or connected to the enclosure of the device during the measurement. When an object moves to the proximity switch, regardless of whether it is a conductor or not, due to its proximity, the dielectric constant of the capacitor is always changed, so that the capacitance changes, and the state of the circuit connected to the measuring head also occurs. Change, which can control the switch on or off. The objects detected by this proximity switch are not limited to conductors, liquids or powders that can be insulated.
3. Hall proximity switch
The Hall element is a magnetic sensitive element. The switch made by Hall element is called Hall switch. When the magnetic object moves closer to the Hall switch, the Hall element on the switch detection surface changes the internal circuit state of the switch due to the Hall effect, thereby identifying the presence of magnetic objects nearby, and then controlling the switch on or off. The detection object of this proximity switch must be a magnetic object.
4. Photoelectric proximity switch
The switch made by photoelectric effect is called photoelectric switch. The light-emitting device and the photoelectric device are installed in the same detection head in a certain direction. When a reflective surface (object to be detected) approaches, the optoelectronic device outputs the signal after receiving the reflected light, so that it can "perceive" an object approaching.
5. Pyroelectric proximity switch
A switch made of components that can sense temperature changes is called a pyroelectric proximity switch. This kind of switch installs the pyroelectric device on the detection surface of the switch. When an object with a temperature different from the environment approaches, the output of the pyroelectric device changes, so that an object approach can be detected.
6. Other types of proximity switches
When the observer or the system changes the distance from 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. The Doppler effect can be used to make ultrasonic proximity switches, microwave proximity switches, etc. When an object approaches, the reflected signal received by the proximity switch will produce a Doppler frequency shift, which can identify whether an object approaches.