How does inductive proximity sensor work?

hello-
I am looking at an inductive sensor and wondering how it works. here is what the website says (about how it works)
Inductive proximity sensors consist of an oscillator driven coil. The oscillator creates an electromagnetic field which appears at the active face of the sensor. If a metal target enters this area, the electromagnetic field is reduced and the sensor switch turns on or off

Can anyone explain further?
Thanks!

Re: Inductive sensor

Omron gives this short explanation:https://www.ia.omron.com/support/guide/48/principles.html

Detection Principle of Inductive Proximity Sensors

Inductive Proximity Sensors detect magnetic loss due to eddy currents that are generated on a conductive surface by an external magnetic field. An AC magnetic field is generated on the detection coil, and changes in the impedance due to eddy currents generated on a metallic object are detected.

Click to expand...

To my opinion, it's containing all aspects of a standard inductive proximity sensor's operations principle.

Re: Inductive sensor

They have two oscillators /an inner one with a fix frequency and other with the external coil at the same frequency , when something near the coil modify the inductance the frequency is modified and the diference between both frequencies activate the switch.

Re: Inductive sensor

Here's an article about simulation of inductive (aka eddy current) proximity sensors. It gives a good idea about the principles of operation.

Re: Inductive sensor

They have two oscillators

Click to expand...

This has been the operation principle of early metal detectors (e.g. for mine sweeping). It has been replaced by pulse techniques with higher selectivity since long.

I'm not aware of industrial proximity detectors utilizing this method, but there may be some..

Re: inductive current sensor

Nora said:

hello-
I am looking at an inductive sensor and wondering how it works. here is what the website says (about how it works)
Inductive proximity sensors consist of an oscillator driven coil. The oscillator creates an electromagnetic field which appears at the active face of the sensor. If a metal target enters this area, the electromagnetic field is reduced and the sensor switch turns on or off

Can anyone explain further?
Thanks!

Click to expand...

Hi Nora!! By the way, I was writing a small homework of inductive proximity sensors, so I have the ideas still fresh
I suposse you're talking about an inductive proximity sensor. This kind of sensors produce an ON/OFF output which represents the presence or the absence of the object at some defined distance from the object (switching distance).

The device is based in eddy currents. They are inductive because a coil is required to induce eddy currents (AC current through the coil creates an AC field which induces eddy currents on the surface of the target .) The target has to be conductive.

When the target approaches the coil, the impedance of the coil changes. The changes of impedance mean that the magnetic flux through the coil changes, and the apparent resistance seen by the coil increases (to create the eddy currents, some energy is required), so commonly, engineers say that the impedance is "loaded".

Now it is possible to build a simple LC oscillator with some feedback provided by an operational amplifier (the circuit coil in parallel with a capacitor forming a simple tank circuit). The circuit coil unloaded has just the resistance of the wire. But if the target approaches, resistance increases. This extra resistance damps the oscillation. Oscillation is "killed".
This circuit is called "killed oscillator", because the circuit simply stops its oscillations when the target approaches.
I hope the information is useful. Greetingsl
Kronprinz Adam.

Re: Help inductive proximity sensor work?

Thanks for the article about inductive proximity sensor
I already suffering some problem about it
I got a circuit but I dont know how to make the coil.
I already baught ferite core , bobbin and wires
I need to make a eight mm sensing distance
sensor can you give some help

Thanks Ajitkumar

maxim10373

This is opening a new discussion inviting details of specifications!