Types and Applications of Proximity Switches

Proximity switch, also known as contactless proximity switch, is the ideal electronic switching sensor, when the metal detector is close to the induction area of the switch, the switch can be no contact, no pressure, no spark, and issue electrical instructions, widely used in machine tools, metallurgy, chemical, textile and printing industries, in the automatic control system can be used as a limit, counting, positioning control and automatic protection links, etc. Proximity switch is a position switch that does not need to be operated by mechanical direct contact with moving parts. When the object is close to the switch sensing surface to the operating distance, the switch can be operated, thereby driving the DC electrical appliance or providing control instructions to the PLC device.

Proximity switch is a switch type sensor (that is, contactless switch), which has the characteristics of stroke switch and micro-switch, and has sensing performance, and reliable action, stable performance, fast frequency response, long application life, strong anti-interference ability, and waterproof, corrosion resistance, etc., products have eddy current, capacitive, hall, photoelectric, pyro electric, and other forms.

1. Inductive proximity switch

This switch is sometimes called eddy current proximity switch, which uses conductive objects to generate eddy current inside the object when they approach the electromagnetic field proximity switch. This eddy current reacts to the proximity switch and changes the internal circuit parameters of the switch, thereby identifying whether conductive objects move closer and controlling the switch on or off. The object that the proximity switch can detect must be an electrical conductor.

2. Capacitive proximity switch

The measurement of this kind of switch is usually a plate that constitutes a capacitor, and the other plate is the shell of the switch. This shell is usually grounded or connected with the shell of the equipment during the measurement process. When an object moves close to the switch, regardless of whether it is a conductor, the dielectric constant of the capacitor will change due to its proximity, so that the capacitance will change. The state of the circuit connected to the measuring head also changes, so that the switch can be controlled to turn on or off, the object detected by the close switch is not limited to the conductor, the liquid or powder that can be insulated.

3. Hall proximity switch

Hall component is a magnetically sensitive switch, the use of Hall components made of the switch, called Hall switch, when the magnetic object moves close to the Hall switch, the Hall component on the switch detection because of the Hall effect and the switch internal circuit state changes, thereby identifying the presence of nearby magnetic objects, and then control the switch on and off, the detection object of this close switch must be magnetic objects.

The switch made of photoelectric effect is called photoelectric switch, the light emitting device and photoelectric device are installed in the same detection head in a certain direction, when the reflective surface (detected object) is close, the photoelectric device receives the reflected light in the signal output, so that the object can be sensed.

5. Pyro electric proximity switch

The switch made of components that can sense temperature changes is called the pyro electric proximity switch. This switch is to install the pyro electric parts on the detection surface of the switch. When an object with a different ambient temperature is close to it, the output of the pyro electric appliance changes, so that an object can be detected.

6. Other forms of proximity switches

When the observer or system changes the distance of the wave source, the frequency of the approaching wave will shift, which is called Doppler Effect. Sonar and radar are made by using the principle of this effect. Ultrasonic proximity switch and microwave proximity switch can be made by using Doppler Effect. This can identify whether objects are approaching.

Accurately reflect the position and stroke of the moving mechanism, even if it is used for general stroke control, its positioning accuracy, operating frequency, service life, convenience of installation and adjustment and the ability to apply to harsh environments are not comparable to the general mechanical stroke switch.

1. Movement (detection) distance

The operating distance refers to the spatial distance from the reference position (close to the sensing surface of the switch) to the detection surface when the detection body moves according to a certain square, and the rated operating distance refers to the nominal value of the operating distance close to the switch.

2. Set the distance

Refers to the setting distance of the proximity switch in actual work, generally 0.8 times the rated operating distance, the installation distance between the measured object and the proximity switch is generally equal to the rated operating distance, to ensure reliable work, after installation must also be adjusted, and then tightened.

3. Reset distance

After approaching the switch action, the distance from the measured object when it is reset again is slightly greater than the operating distance.

4. Back difference value

The greater the absolute value of the return differences between the operating distance and the reset distance, the stronger the anti-interference ability to the outside interference and the jitter of the measured object.

5. Response frequency

According to the regulations, within a time interval of 1 second, the maximum number of approaching switch action cycles, when the repetition frequency is greater than this value, the proximity switch has no response, response time t: the difference between the time when the proximity switch detects the object and the time when the proximity switch appears the level state flip.