Field Instrumentation

What is a proximity switch and what is it used for? How do proximity switches work

What is a proximity switch and what is it used for? How do proximity switches work

A proximity switch is used to determine how close an object is, or the proximity of an object. The proximity of an object is determined by using certain means such as magnetic, electric, or optical. So these switches can be used to check the presence of an object. These switches are widely useful for many security processes. These switches can be used to check the motor rotation speed. Proximity switches can detect the approach of a metallic device part with the help of a magnetic or electromagnetic field. Normal proximity switches use a permanent magnet so it can create a sealed switch mechanism if an object’s mechanical part come close to it. There are certain types of proximity sensors that can act as a metallic detector and this type can be considered as the complex proximity switches. The complex proximity switches operate by energizing a coil of wire by using electric current, the magnitude of the current is monitored electronically. The monitoring section would trip if a metallic part gets close to the coil.

How capacitive proximity switches are different from inductive switches

The sensing material is different in both of these switches and the inductive switches can only be used to detect the metallic objects or the objects that have a metallic part in it while the capacitive switches can be used to check certain materials such as wood. Paper, cardboard…

Why do we need proximity switches

Proximity switches are used in many industrial applications, in many industrial processes certain physical quantities must be monitored, and in order to do that switches are used. So proximity switches are used these switches are used to sound the alarms, so while an alarm is sounded means some of the physical quantity is not at its normal level. These proximity switches are also used to shut down equipment if any of its variables have reached dangerous levels. Proximity switches are also used in automation and security-related applications.

What are the types of proximity switches and how does it work

  1. Inductive proximity switch
  2. Ultrasonic proximity switch
  3. Optical proximity switch
  4. Capacitive proximity switch

1.Inductive proximity switches

Inductive proximity switches can detect the presence of a metallic object without any contact with the object. The switching speed of inductive proximity switches is very high and that’s a reason why it is widely used in the automation field. This type of proximity switches has a coil driven by an oscillator. An electromagnetic field is created by the oscillator that would reach the active section of the switch. So if the metal part comes close to this part, then the electromagnetic field is reduced and the switch would turn on or off. By using inductive proximity sensors we can determine the metallic object, position of the metallic part in a machine, it can also detect small metallic parts such as screws and rotation speed of the device that can be checked if the rotational part is metal. It only detects conductive material and operating distance up to 50mm. it also has high noise immunity

2.Ultrasonic proximity switches

Ultrasonic proximity switches are used in the automation field and these also contact-free sensors. These sensors are used for distance measurement, not only these devices can detect object but it can also measure the distance from the object to the device. This device is used whenever we need to measure distances through the air. This type of proximity switch is very reliable. The ultrasonic proximity switches transmit ultrasonic pulses. So these pulses would be reflected by the objects and these echoes are received by the proximity switch and distance is calculated. These devices can sense up to 10 meters


  • Level measurement and position detection
  • Limit detection and thickness measurement
  • Stack height measurement

3.Optical switch (Photoelectric proximity switch)

An optical switch is a type of proximity switch and this device has a photocell and a light source. The device would react to changes in the received quantity of light, the light beam emitted from the emitter diode is interrupted or reflected by the object to be detected. This device is also used for safety purposes so by using this device we can check dangerous areas before personnel entry. These sensors are really compact and economical. These sensors have great flexibility


  • Conveyor systems and packing machines
  • Mechanical engineering
  • Paper, textile and plastic processing
  • In printing machines
  • Access control

4. Capacitive Proximity switches

Capacitive proximity switches can measure conductive and non-conductive material and it is a non-contact sensor. The detection of the object is done according to a shift in capacitance. This device can detect objects in solid, powder, or liquid state. So this type of proximity switch can detect wood, oil, water, plastic, and ceramic. Capacitive proximity switches can detect objects through certain non-metallic objects. In this proximity switch, two electrodes are used, so when an object reaches the active section of the switch it would be in place of the electrical field of the electrodes and changes the coupling capacitance.


  • Level indication
  • Object counting
  • Automation control
  • Level control in plastic or glass containers


post-graduate in Electronics & communication.

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