PSN-L Email List Message

Subject: Re: detector design
From: Ron Thompson rlthompson@.................
Date: Sun, 09 Sep 2001 10:36:22 -0230

An attempt to make a text sketch of the concept.

                           ---- CENTRE TAPPED COIL----
|                             |
                           |                    GND

T                                                   T
M                          X
O                           |
V                           A
I                            N
N                           T
V                            R
A                            X
N                            |
E                            A
|                            N
|                            T

|                                                    |

This is, I believe, in simple form the basic idea of the detector.  It
should work well in the MHz range, within the limits of 4000
series CMOS logic circuits.

The exciter (Transmitter) puts an RF voltage on the two
TX antennae through the centre tapped coil, so the two
TX antennae are always 180 out of phase with each other.

The moving vane capacitively couples to the TX antennae, and
when the vane is dead centre between the antennae it is in
a null field and has 0 volts RF on it, and no voltage is
capacitively coupled to the RX antennae.

Move the vane to one side or the other and it is out of the
null position.  The vane now has a voltage on it, and the
phase of the voltage, with respect to the oscillator reference
will be in phase or 180 degrees out of phase, depending upon
which side the vane moved to.  The vane capacitively
couples to the two RX antennae.

The RX antennae are connected together and go into a high
gain, low noise amplifier and the 0 or 180 degree phase shift,
with respect to the oscillator, gives left / right (or up / down)
information while RX signal amplitude gives vibration
amplitude information.

Phase differentiation then is only 0 or 180.  It should work,
I believe, in the MHz range, where wire lengthes and
propagational delays will not be critical.

Tom Leiper wrote:

> If you really want a super-sensitive and novel way of detection,
> why don't you review the archives for a post I did last year which
> described a method whereby two oscillators are permeably (and
> oppositely) tuned by a moving core, and very sensitive frequency
> changes are, in effect, measured with cheap presettable counters.
> If fact, I think I even biased the coils with dc feedback to make it
> a force-balance instrument at the same time. I have not had the
> time to build it, but I know it will work.
> And so there is more grist for our ever grinding mill...
> Tom

    This sounds like what I had in mind initially.  I'd be glad to take
a look at it.  Is there an easy way to identify your file?

    Thanks for the interest,



Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]

Larry Cochrane <cochrane@..............>