Thirty years ago I worked for a company by the name of IRD Mechanalysis.
Their business was vibration detection, monitoring and analysis for
preventive maintenance of heavy machinery.
At that time they were a subsidiary of H H Robinson Company, a
construction company based in Pittsburgh PA.
We built our own crystal-transducers to work with the monitoring equipment.
I never worked in the analysis end of the business, so I cannot tell you
where the frequencies indicating "good" and "bad" lie. Each device is
different. A problem with each component was indicated by a different
frequency.
The only aviation use I am aware of was to dynamically balance props.

Jim Weir wrote:
I've come across a marvelously cheap vibration sensor that I want to convert
into an engine vibration instrument for a Kitplanes article. The electronics
for me is relatively trivial...the mechanics of vibration are a little harder to
fathom.

From a mechanical engineering point of view on a horizontally opposed engine,
there are (as with most things) three axes of freedom -- fore and aft, side to
side, and up and down (longitudinal, lateral, vertical).

The sensor I have reads two axes, and my hit is that fore-aft is the least
interesting vibration mode of the engine. The question is whether to have a
two-channel meter (which complexes up both the design AND the panel space), a
single meter switchable between lateral and vertical) or a single meter with the
two axes summed together.

Comments and thoughts from the technonerds amongst us appreciated.

(It has nothing, repeat NOTHING to do with the fact that such a meter might have
detected a crack in that cylinder WAY BEFORE it departed the engine on the way
home from Oshkosh {;-) )


Jim


Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com