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From: firstname.lastname@example.org (john jardine)
Subject: Re: Inductance to Voltage Converter
Date: 28 Sep 2002 11:29:45 -0700
NNTP-Posting-Date: 28 Sep 2002 18:29:45 GMT
"Bruce Kingsley" wrote in message news:...
> I'm looking for an accurate, stable circuit for converting Inductance to
> Voltage for monitoring an Inductive sensor position. Here's the facts:
> 1) The inductor sensor (2-wire) varies 7 mH to 9 mH based on target's
> (ferrous) distance.
> 2) Excitation must be 1kHz @ 400mV.
> 3) DC Output desired is a clean 0 to 10 VDC.
> 4) The sensor is known as an Inductance Proximity Sensor.
> Thanks to all.
(Assuming the 400mV is 'rms', ie 1120mV pp)
Feed the 1kHz signal to maybe a 150 ohm feed resistor and then to the
sensor and from there back to 0v. Pick off the ac voltage at the end
of the resistor that feeds the sensor. This will be from about 110mVac
(7mH) to 138mVac (9mH). Feed straight into a single op-amp 'precision
rectifier' set for a gain of about x10 and then to an op-amp set with
a small DC gain to give the 0 to 10V DC signal. (Add a static DC
offset to it's gain set resistors to give the 7mh=0V output). (also
needs 2 preset trimmers to calibrate the 0.0v zero and 10.0v fsd
The sensor is used as a simple ac potential divider. There is very
little to drift or cause instability. Be careful about making the feed
resistor too high a value as there may be added signal losses due to
cable capacitance on the run out to the sensor position. Look also to
hanging a couple of small caps across the signal wires if there is
significant pickup interference.
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