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In article <836@ritcsh.UUCP>, sic@ritcsh.UUCP (Eric A. Neulight) writes:
> Larry neglected to mention a third category, albeit more esoteric and
> certainly overkill for your application.  ( probably why he did not think
> it pertinent, but may as well add my little tid-bit.)
> 
> A few months back, I saw a demonstration of a commercially available
> vibration measuring device which used laser interferometry for its
> transducing.  You couldn't see or hear the vibration of the tuning fork
> they were using, but this thing picked it up from several feet.

	There are also methods for vibration measurements through reflected
wave techniques employing ultrasonics and microwaves (the more common of
the two).  Both ultrasonic and microwave techniques appeared in industry
during the 1950's, but they never saw widespread use and remained curiosity
pieces.

	Microwave measurement is particularly simple.  I can remember a
lab experiment from a EE microwaves course in which we aimed a 2K25
klystron at a tuning fork.  We could measure the frequency and displacement
of the vibration by observing the changes in repeller current on an
oscilloscope.  A simple and impressive technique, but one which just
never caught on.  I wouldn't be surprised, however, if a microwave
vibration sensor using a solid-state emitter and self-contained signal
conditining (trivial today) might cause a resurgence of interest in
this measurement technique.

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
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