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A Complete Guide on Inductive Proximity Sensor

A proximity sensor is a non-contact sensor that detects the presence of an object (also known as the “target”) when it enters the sensor’s field of view. The sensor may detect a target via sound, light, infrared radiation (IR), or electromagnetic fields, depending on the type of proximity sensor. Phones, recycling factories, self-driving cars, anti-aircraft systems, and assembly lines all employ proximity sensors. There are several different types of proximity sensors, and each detects targets in a different way. 

In this blog, we discuss the Inductive proximity sensor working principle, its advantages, disadvantages,& its applications in industries, and their use for commercial purposes. 

What is an Inductive Proximity Sensor?

An Inductive proximity sensor can detect metal targets approaching the sensor, without physical contact with the target. Inductive Proximity Sensors are classified into the following three types based on the operating principle: the high-frequency oscillation type using electromagnetic induction, the magnetic type using a magnet, and the capacitance type using the change in capacitance.

This sensor operates under the electrical principle of inductance where a fluctuating current induces an electromotive force(EMF) in a target object. These non-contact proximity sensors detect ferrous targets, preferably mild steel with a thickness of less than one mm. A ferrite core with coils, an oscillator, a Schmitt trigger, and an output amplifier are the four major components. There are two primary versions of this sensor:

  • Unshielded: Electromagnetic field generated by the coil is unrestricted, allowing for wider and greater sensing distances
  • Shielded: Electromagnetic field generated is concentrated in the front, where sides of the sensor coil are covered up

Inductive sensors cannot detect plastic, cardboard, or other non-metallic materials since only metallic objects have inductive properties. However, different metals have varying inductive qualities, therefore the sensing distance will be affected by the type of metal being sensed. For example, ferromagnetic materials like steel have the longest sensing distances, whereas non-ferrous metals like aluminum or copper have far shorter sensing distances. Inductive proximity sensors are best suited to short-range applications since the inductive effect diminishes as the distance between the sensor and the object to be detected increases.

Inductive proximity sensors work efficiently in dirty environments because pollutants do not obstruct the sensor’s capacity to detect metallic objects. They can withstand dirt, dust, and smoke in the environment between the sensor and the thing to be detected, for example.

Features of Proximity Sensor:

  • Non-Contact Detection

Unlike a limit switch, it detects an object without any mechanical contact. Hence, there is no likelihood of the sensing object or the sensor getting damaged by contact.

  • Usable in severe environment

Reliable sensing is possible even in adverse conditions where it can come in contact with water, etc. Most of the sensors have IP67 protection and oil-resistant construction.

  • High precision

It is suitable for precise object positioning because of its very high repeatability.

  • Short response time

Stable detection is possible even with fast traveling objects because of its high response frequency (3.3 kHz max.).

  • Long life

Due to its non-contact output, it has a long life and requires practically no maintenance.

  • Short sensing range

Although there are several methods for improving the sensing range, such as increasing the detection coil size, using non-shielded sensor heads, etc., the sensing range is still smaller than that of photoelectric sensors.

  • Only metal detection

It cannot detect non-metals in which current cannot flow, since detection is based on thermal loss due to induced current.

(Also, metals such as ferrite, which do not allow current flow, cannot be detected.)

Working Principle of Inductive Proximity Sensor

Inductive proximity sensors consist of an oscillator circuit and a coil that generates a symmetrical, oscillating magnetic field at the sensing face, which radiates from the ferrite core and coil array. Small independent electrical currents (eddy currents) are induced on the surface of a ferrous object when it enters this magnetic field. The eddy currents have the effect of dampening the amplifier’s oscillations. The presence of a metallic object is detected by the reduction in oscillations.

diagram of working principle of inductive proximity sensor

The frequency range of an inductive proximity sensor is 10 to 20 Hz in ac or 500 Hz to 5 kHz in dc. Inductive sensors have a relatively small detecting range, ranging from fractions of millimeters to 60 mm on average, due to magnetic field limits.

 As a result, the sensor will be loaded, lowering the electromagnetic field amplitude. The eddy current will grow as the metal object travels closer to the proximity sensor. As a result, the load on the oscillator increases, lowering the field amplitude.

The Schmitt trigger block monitors the oscillator’s amplitude and switches on or off the sensor when it reaches a certain level (predetermined level). The amplitude of the oscillator increases as the metal object or target moves away from the proximity sensor.

Advantages of Inductive Proximity sensor

  • It can withstand harsh environmental conditions.
  • It has longer life.
  • Contactless detection
  • Environment adaptability- resistant to common conditions seen in industrial areas such as dust and dirt
  • Capable and versatile in metal sensing
  • High switching ratio 
  • No moving parts, ensuring a longer service life
  • It has very predictable results and performance.

Disadvantages of Inductive Proximity sensor

  • Lack in detection range, averaging a max range of up to 60 mm
  • Can only detect metal objects
  • External conditions like extreme temperatures, cutting fluids, or chemical effects on the performance of the sensor.

Applications of Inductive Proximity Sensors

  • Machine tools, assembly line, automotive industry
  • Detection of metal parts in harsh environments
  • High-speed moving parts

Conclusion

Hope this blog helps you to understand the basics of Inductive proximity sensors, their working, applications, and advantages and disadvantages. We, MATHA ELECTRONICS will come back with more informative blogs.

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