Inductive Proximity Sensor Working Principle

Hello Geeks,  here we will discuss about the inductive proximity sensor working principle, their wide spread applications in industries and their use for commercial purposes. This blog focuses on the technology behind the inductive proximity sensors and detailed specifications. 

What is an Inductive Proximity Sensor?

The inductive proximity sensor detects the metallic object which is present next to their active side. This sensor operates under the electrical principal of inductance where a fluctuating current induces an electromotive force(EMF) in a target object. These non-contact proximity sensors detect ferrous targets, ideally mild steel thicker than one millimetre. They consist of four major components: a ferrite core with coils, an oscillator, a Schmitt trigger, and an output amplifier. This sensor has 2 main versions and they are,

• 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

MUST READ:

• Types of Proximity Sensor
• Capacitive Proximity Sensor
• How Proximity Sensor Works?

Working Principle of Inductive Proximity Sensor

The oscillator creates a symmetrical, oscillating magnetic field that radiates from the ferrite core and coil array at the sensing face. When a ferrous target enters this magnetic field, small independent electrical currents (eddy currents) which are induced on the metal’s surface.

An inductive proximity sensor has the frequency range from 10 to 20 Hz in ac, or 500 Hz to 5 kHz in dc. Because of magnetic field limitations, inductive sensors have a relatively narrow sensing range like from fractions of millimetres to 60 mm on an average.

Due to this, load will be caused on the sensor that decreases the electromagnetic field amplitude. If the metal object moves towards the proximity sensor,  the eddy current will increase accordingly. Thus, the load on the oscillator will increase, which decreases the field amplitude.

The schmitt trigger block monitors the amplitude of the oscillator and at particular level (predetermined level) the trigger circuit switches on or off the sensor. If the metal object or target is moved away from the proximity sensor, then the amplitude of the oscillator will increase.

The above image shows the waveform of the inductive proximity sensor oscillator in the presence of the target and in the absence of the target.

Nowadays, inductive proximity sensors are available with different operating voltages. These inductive proximity sensors are available in AC, DC, and AC/DC modes (universal modes). The operating range of the proximity sensor circuits is from 10V to 320V DC and 20V to 265V AC.

Advantages of Inductive Proximity Sensors

• 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 rate
• No moving parts, ensuring a longer service life

Disadvantages of Inductive Proximity Sensors

• 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 affects on the performance of the sensor.

Applications of Inductive Proximity Sensors

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

Hope this article will help you to understand the complete inductive proximity sensor working principle.

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