Detailed explanation of the proximity switch (Proximity Switch) working principle - Database & Sql Blog Articles

1. Introduction to working principle:

The proximity switch, also known as the non-contact travel switch, is not only a stroke control and limit protection, but also a non-contact type detection device, which is used for detecting part size and speed measurement, and can also be used for frequency conversion counters and variable frequency pulse generation. Automatic connection of liquid level control and machining programs. Features include reliable operation, long life, low power consumption, high re-positioning accuracy, high operating frequency and adaptable to harsh working conditions.
1, performance characteristics Among the various types of switches, there is a component that is "perceived" to its object - displacement sensor. The sensitivity of the displacement sensor to the approaching object is achieved by controlling the on or off of the switch. This is the proximity switch.
When an object moves toward the proximity switch and approaches a certain distance, the displacement sensor will "perceive" and the switch will act. This distance is usually called the "detection distance". Different proximity switches detect different distances.
Sometimes the objects being inspected are moved to the proximity switches one by one at a certain time interval, and are separated one by one, so that they are continuously repeated. Different proximity switches have different responsiveness to the detected object. This response characteristic is called the "response frequency."
2, type Because the displacement sensor can be made according to different principles and different methods, and different displacement sensors have different "perception" methods for objects, so the common proximity switches are as follows:
a, eddy current proximity switch This type of switch is sometimes called an inductive proximity switch. It uses a conductive object to create an eddy current inside the object when it approaches the 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 the presence or absence of the conductive object moving closer, thereby controlling the on or off of the switch. The object that this proximity switch can detect must be an electrical conductor.
b. Capacitive proximity switches The measurement of such switches is usually one plate of the capacitor and the other plate is the outer casing of the switch. This housing is usually grounded or connected to the housing 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 is always changed, so that the capacitance changes, so that the state of the circuit connected to the measuring head also occurs. Change, thereby controlling the switch to be turned on or off. The object to be detected by the proximity switch is not limited to a conductor, a liquid or powder that can be insulated, or the like.
c. Hall proximity switch The Hall element is a magnetosensitive element. A switch made of a Hall element is called a 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 a magnetic object nearby, thereby controlling the on or off of the switch. The detection object of such a proximity switch must be a magnetic object.
3, the main use of proximity switches in aerospace, aviation, aerospace technology and industrial production have a wide range of applications. In daily life, such as automatic doors for hotels, restaurants, garages, automatic hot air blowers are used. In terms of security and theft, such as data files, accounting, finance, museums, treasury, etc., it is usually equipped with anti-theft devices composed of various proximity switches. In measurement techniques, such as length, position measurement; in control technology, such as displacement, velocity, acceleration measurement and control, also use a large number of proximity switches.
4. Selection Considerations In general industrial production sites, eddy current proximity switches and capacitive proximity switches are commonly used. Because these two proximity switches have lower environmental requirements. When the object to be measured is a conductive object or an object that can be fixed on a metal object, the eddy current proximity switch is generally used because of its high response frequency, good anti-interference performance, wide application range, and low price. If the object to be tested is non-metal (or metal), liquid level, powder height, plastic, tobacco, etc. A capacitive proximity switch should be used. This switch has a low response frequency but good stability. The environmental factors should be considered during installation. If the object is a magnetically permeable material or the magnetic steel is buried in the object to be measured in order to distinguish it from the object moving together, the Hall proximity switch should be used, which has the lowest price.
In the case of better environmental conditions and no dust pollution, photoelectric proximity switches can be used. When the photoelectric proximity switch is working, there is almost no shadow on the object to be measured. Therefore, it is widely used in tobacco machinery on demanding facsimile machines.
In anti-theft systems, automatic doors typically use pyroelectric proximity switches, ultrasonic proximity switches, and microwave proximity switches. Sometimes, in order to improve the reliability of recognition, the above several proximity switches are often used in combination.
Regardless of which proximity switch is selected, attention should be paid to the requirements of various indicators such as working voltage, load current, response frequency, and detection distance.

Because different materials have different media parameters, the sensor can detect substances of different materials according to different media parameters accepted. Such as metal materials, non-metal, water and so on.

two. Selection main parameter

\\1. First ask the customer the material to be tested, make the metal or non-metal, etc., to confirm the large series.
2. Product shell material: According to different application environments and metal shells, non-metal shells, etc.
3. The installation shape of the switch, generally for the cylindrical type, ask the thread size and size of the outer diameter, such as: M18 (representing M18X1), M12 (representing M12X1) and so on.
4. Proximity distance: the distance between the sensor and the detected object, 2mm, 10mm, 20mm, etc.
5. Control output form: generally open collector NPN or PNP output, which is mostly NPN.

three. Application

This switch can be used to detect the presence or absence of the product, the number of products, and the presence of the monitoring object.