Proximity switch principle and selection

- Oct 12, 2019-

Proximity switch function

The proximity switch, also known as the proximity sensor, is a position switch that can be operated without moving the moving parts. When the moving object approaches the switch to a certain position, the switch sends a signal to a non-contact non-contact position switch that automatically controls the stroke control and counting. It consists of an inductive head, a high frequency oscillator, an amplifier and a housing. The proximity switch physical map and graphic text symbols are as follows:



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Proximity switch text symbol (SQ)


Proximity switch principle and wiring diagram

Capacitor / Inductance / Hall proximity switch works


1. Working principle of inductive proximity switch


The inductive proximity switch belongs to a position sensor with a switching output. It consists of an LC high-frequency oscillator and an amplification processing circuit. When a metal object approaches the oscillation induction head capable of generating an electromagnetic field, an eddy current is generated inside the object. This eddy current reacts to the proximity switch, causing the proximity switch to oscillate and the internal circuit parameters are changed, thereby identifying the presence or absence of a metal object, thereby controlling the on or off of the switch. The object that this proximity switch can detect must be a metal object. The workflow block diagram and wiring diagram are as follows:


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2, capacitive proximity switch working principle


Capacitive proximity switches also belong to a position sensor with a switching output. The measuring head is usually one plate of the capacitor, and the other plate is the object itself. When the object moves toward the proximity switch, the object and the proximity The dielectric constant of the switch changes so that the state of the circuit connected to the measuring head also changes, thereby controlling the switching on and off of the switch. The detection object of the proximity switch is not limited to a metal conductor, and may be an insulating liquid or a powder object. When detecting an object with a low dielectric constant ε, the multi-turn potentiometer can be adjusted clockwise (located at the rear of the switch) To increase the sensitivity of the sensor, the general adjustment potentiometer makes the capacitive proximity switch operate at the position of 0.7-0.8Sn. The workflow block diagram and wiring diagram are as follows:

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3, Hall-type proximity switch working principle


When a current-carrying metal or semiconductor wafer is placed vertically in a magnetic field, a potential difference is generated at both ends of the sheet. This phenomenon is called a Hall effect. The potential difference between the two ends is called the Hall potential U.


Its expression is U=K·I·B/d where K is the Hall coefficient, I is the current passing through the sheet, B is the magnetic induction of the applied magnetic field (Lorrentz), and d is the thickness of the sheet. It can be seen that the sensitivity of the Hall effect is proportional to the magnetic induction of the applied magnetic field. The Hall switch sold by our company belongs to this kind of active magnetoelectric conversion device. It is based on the Hall effect principle and is fabricated by integrated packaging and assembly process. It can easily convert the magnetic input signal into actual. The electrical signal in the application has the requirements of practical operation and reliability in industrial applications.


The input of the Hall switch is characterized by the magnetic induction B. When the B value reaches a certain level (such as B1), the trigger inside the Hall switch is turned over, and the output level state of the Hall switch is also reversed. The output terminal generally uses a transistor output, and the proximity switch is similar to NPN, PNP, normally open, normally closed, latched (bipolar), and dual signal output. The Hall switch has the characteristics of no electric shock, low power consumption, long service life and high response frequency. The interior is sealed by epoxy resin, so it can work reliably in all kinds of harsh environments. Hall switches can be used in proximity switches, pressure switches, odometers, etc. as a new type of electrical accessories.


The function of the Hall switch is similar to that of the reed switch, but it has a longer life, faster response and no wear, and the polarity of the magnet should be paid attention to during installation.


The internal schematic diagram and the transfer characteristics and wiring diagram of the input/output are as follows:



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Proximity switch selection

1, the choice of proximity switch type


Inductive type is used for detecting metal first, and capacitive type is preferred for detecting non-metal, and magnetic proximity switch for detecting magnetic signal is selected.


2, the choice of proximity switch appearance


Cylindrical thread shapes are often used, which can be selected according to actual needs.


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Cylindrical thread shaped proximity switch


3, the choice of detection distance


According to the needs of the selection, the general manufacturer's instructions will indicate the detection distance.


4, the signal output selection


The AC proximity switch outputs an AC signal, and the DC proximity switch outputs a DC signal. Pay special attention: the current of the load must be less than the output current of the proximity switch, otherwise a conversion circuit should be added.


5, the choice of switching frequency


The switching frequency refers to the number of times the proximity switch switches from "on" to "off" per second. The DC proximity switch can reach 200Hz, and the AC proximity switch can only reach 25Hz.


6, the choice of rated voltage


The AC proximity switches are preferably AC 220V and AC 36V; the DC proximity switches are preferably DC 12V and DC 24V. In general, the proximity switch has a wide selection of voltages. As shown below: