Subject: Re: More:Inductance to Voltage
Date: Sun, 6 Oct 2002 15:30:41 +1000
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Read up on resonance.
I am assuming that your "7.9 mH inductive proximity sensor" is just a coil
on an iron or ferrite core, nothing fancy.
When the inductive reactance (which increases with frequency) and the
capacitive reactance (which decreases with frequency) are equal, the cap
and the inductor form a "parallel resonant circuit", which has a very high
This is the electrical equivalent of a weight bouncing up and down on a
spring, or a tuning fork, or a pendulum (the maths are identical for all
You will most likely find that your inductive sensor becomes very much more
sensitive to metalic objects at resonance. OTOH, the effect will probably be
less repeatable than non-resonance. As I recall it, you wanted to get a
measure of distance, so non-repeatability may be a problem.
You are unlikely to damage your inductor, but core saturation may cause loss
of sensitivity. The 400mV rating of the coil sounds like a saturation thing.
"Bruce Kingsley" wrote in message
> I don't understand why the inductor acts this way:
> A 1Khz sine wave signal is feed into a 1k ohm resistor, then to a 7.9 mH
> inductive proximity sensor. As capacitors are added across the inductor,
> amplitude grows. Why? I would have figured the capacitor would have
> the amplitude. The inductor is designed for a 400 mV signal, but when the
> capacitors (2 uf) are added the signal grows to almost 1 volt. Am I
> endangering the inductor?
> Bruce Kingsley