Limit switch and proximity switch

Limit switch: Limit switch, also known as travel switch, can be installed on relatively stationary objects (such as fixed frames, door frames, etc., referred to as still life) or moving objects (such as driving vehicles, doors, etc., referred to as animals). When an animal approaches a still life, the connecting rod of the switch drives the contact of the switch to cause the closed contact to break or the open contact to close. The action of the circuit and mechanism is controlled by the change of the open and closed state of the switch contact. Limit switches can also be divided into rotary limit switches and straight travel limit switches.

Proximity switch: Proximity switch is also called non-contact travel switch. In addition to completing travel control and limit protection, it is also a non-contact detection device. It is used to detect the size of parts and speed measurement, etc. It can also be used for frequency conversion counters, Frequency conversion pulse generator, liquid level control and automatic connection of processing programs, etc. Features include reliable work, long life, low power consumption, high repositioning accuracy, high operating frequency, and adaptability to harsh working environments.

1. Performance characteristics 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 objects to be inspected are moved 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".

2. Types Because displacement sensors can be made according to different principles and methods, and different displacement sensors have different "perception" methods for objects, the common proximity switches are as follows:

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.

Capacitive proximity switch:

The measurement of this kind of switch is usually made up 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 enclosure of the device during the measurement process. When an object moves to 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, so that the capacitance will change, and the state of the circuit connected to the measuring head will also change accordingly. Change, thus can control the switch on or off. The objects detected by this proximity switch are not limited to conductors, but liquids or powders that can be insulated.

Hall proximity switch:

Hall element is a kind of magnetic sensitive element. The switch made by the Hall element is called the Hall switch. When the magnetic object moves closer to the Hall switch, the Hall element on the detection surface of the switch changes the state of the internal circuit of the switch due to the Hall effect, thereby identifying the presence of magnetic objects nearby, and then controlling the on or off of the switch. The detection object of this proximity switch must be a magnetic object.

Photoelectric proximity switch: The switch made by photoelectric effect is called 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 photoelectric device will output the signal after receiving the reflected light, so that it can "perceive" an object approaching.