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!
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.