Inductive Sensors

Inductance is a parameter that is often considered a confusing factor as it is not commonly used in daily life. But most of the times sensing techniques that involve inductance may not be explicitly termed inductive sensors. The following article discusses inductive sensors in detail.

Contents:

  1. What is an Inductance?
  2. How Inductance is used in Sensors?
  3. Commonly used Inductive Sensors
  4. Metal Detectors
  5. Inductive Proximity Sensors
  6. Types of Inductive Proximity Sensors
  7. Inductive Position Sensors
  8. Other Petty Applications

What is an Inductance?

To understand the concept of inductive sensors, it is mandatory to have a clear view of inductance. As inductance is not a very common parameter, it can be easy to mess up. What is an Inductance, how it is used in real life, and other such facts on inductance are stated below.

  • Technically, inductance can be defined as the ratio between the voltage across the conductor to the current flowing through it.
  • In other words, inductance can also be defined as the resistance created by the electromagnetic field of the conductor.
  • Normally inductance is produced in conductors that are wound in the shape of coils and are used to store energy in the form of an electromagnetic field.
  • It is also used in various electronic applications like filtering, transferring energy, blocking the current etc.

How Inductance is used in Sensors?

Just like many other applications of inductance, it can also be used in sensing various parameters. The sensors that use inductance for measurement are known as inductive sensors. The generalized working of inductive sensors is as follows:

  • Inductive sensors are similar to capacitance sensors that use the target object itself as its other half.
  • An inductive sensor consists of an inducting coil that can generate a magnetic field with high frequency.
  • When an object is placed near the sensor, an eddy current is produced in the inducting coil due to the presence of another conductor inside the magnetic field.
  • The presence of an object can be detected by checking whether there is an eddy current produced or not.
  • The presence of an object can be detected by checking whether there is an eddy current produced or not.One of the main disadvantages of inductive sensors is that they can only detect metal objects as it is necessary to induce eddy current within the coil.

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Commonly used Inductive Sensors

As mentioned earlier inductive sensors are not commonly used in real life. Even if they are used, they are not termed as inductive sensors. They may have different names and works. Sensors that use inductance as the method of analysis are explained below.

  • Metal Detectors – They are one of the most important applications of inductive sensors. Metal detectors are used in almost every public place to ensure the safety of the public.
  • Proximity sensors – Just like the capacitance proximity sensors, inductance can also be used in proximity sensors but only to detect metallic objects.
  • Position sensors – Inductive position sensors are used to find the position of a moving particle or an object using inductance.
  • Traffic light management can also be done using inductive sensors.

Metal Detectors

As the name suggests, metal detectors are used to detect whether there is a metal object is present or not in a pile of objects that are something similar to that. Metal detectors are used in public places like malls, temples and arcades to prevent violent situations to happen. The construction and working of a metal detector are as follows:

  • The metal detector consists of a coil named search coil which is used to induce an electromagnetic field around the detector.
  • The generated field then flows across the surroundings until it touches a metal object.
  • Once it reaches a metal object, the object gets energized i.e., eddy current is produced within the object.
  • The current produced inside the target disturbs the flow of the electric field of the sensor.
  • Once it is done, it means that there is a metal object within the range of the metal detector and an output device like a buzzer or a LED light gets energized.
  • Sometimes, the object is also detected by analysing the field that gets reflected from the metal object.

Inductive Proximity Sensors

Proximity sensors are one of the most important sensors in our day-to-day life. It is a versatile device that can be paired up with various input and output devices. They are used in various technological fields such as automation, instrumentation, etc. Some proximity sensors use inductance to detect the presence of an object. The concept of inductive proximity sensors is explained below.

  • Inductive proximity sensors are similar to metal detectors.
  • But metal detectors are larger when compared to inductive proximity sensors and they are the complete device that can be directly used.
  • While a proximity sensor is similar to a component of a circuit that cannot be used as an individual module.
  • The construction and working principle of the inductive proximity sensor is the same as of the metal detectors.
  • Application-wise, these proximity sensors have an application that is similar to a switch or a push-button.
  • When an inductive proximity sensor is connected to a circuit, initially the circuit remains open when energized.
  • When the proximity sensor detects a metal object, mutual inductance is produced across the sensor and the target object.
  • Due to this, the circuit becomes a closed circuit and the output devices in the circuit will be energized.

Types of Inductive Proximity Sensors

The main application of inductive sensors is the inductive proximity sensors. Though the main concept of proximity sensors is similar, it is classified into three major types. This classification is based on the operating principle of the sensors. The classification of proximity sensors is tabulated below.

Type of inductive proximity sensor Method of Operation
Oscillation proximity sensor This sensor uses a high-frequency oscillator and the electromagnetic field that is induced by the oscillator to detect the presence of the object.
Magnetic proximity sensor This sensor uses a magnet that acts like a coil in a general inductive sensor and is used only to detect metal objects as it involves a magnet.
Capacitance proximity sensor This sensor uses a capacitor along with an inductor to produce accurate results.

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Inductive Position Sensors

Inductive position sensors are used to determine the position of a moving object using inductance. They are used in industries and automobiles where an object moves constantly but within a certain loop-like structure. The construction and working of an inductive position sensor are as follows.

  • These sensors consist of a coil that is used to induce an electromagnetic field to determine the position of the target.
  • The inducting coil is then connected to a printed circuit board using conductive wires and the whole setup is placed in the path of the target.
  • When the target is at the initial position, the eddy current produced within the target will be high as it will be near the sensor.
  • When the target moves further, the intensity of the eddy current produced will be reduced.
  • By analysing the amount of disturbance of the initial magnetic field, the position of the target can be calculated.
  • An object that is connected to a belt that is moving can be monitored by using this sensor.
  • These sensors can also detect the object which is moving in a rotary motion (objects that are connected to gear like structures).
  • One of the main advantages of this sensor is that it does not have complex construction and is easy to maintain an inductance-based sensor.

Other Petty Applications

Other than the applications that are explained above, inductance can also be used in various other applications to sense, monitor and control a certain parameter. Such applications are listed below.

  • Inductive sensors are used inside the traffic light control systems. It uses inductance type loop detectors to maintain a constant time delay between the traffic lights. It can also be used in controlling traffic in junctions.
  • These sensors can be used in various automobile applications as it involves the measurement or sensing within a certain range which will always remain constant.
  • They are also used in robotics as they can be used to detect the presence of objects within a certain range.
  • In the case of automation, inductive sensors are used as the automatic switches that are energized when some metal object is detected.

Key Points to Remember

Here are some key points we need to remember about “Inductive Sensors”

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  • Inductance is a characteristic of a conductor to limit the flow of energy by storing some of the energy in the form of an electromagnetic field.
  • The sensors that use inductance for measurement or analysis of a certain parameter are known as inductive sensors.
  • Metal detectors are the main application of inductive sensors and are used in our daily life.
  • Inductive proximity sensors are devices that use inductance to detect the presence of an object and to determine the distance between the sensor and the target object.
  • Inductive proximity sensors are classified into three main types.
  • Inductive position sensors are used to find the position of a moving target that moves within a certain range.
  • Inductive sensors are also used in various fields of technology like robotics, automation, instrumentation etc.

If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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