Well if you can produce a Power Density Spectrum, it might be useful for
engine condition monitoring. On my helicopter, I have a two channel device
with a photo sensor to give me some idea the crank angle (if I'm checking
engine balance) or rotor position if I'm doing a rotor balance. However, I
put a scope probe on the out put of the accelerometer and can't find an
intelligent signal. I'm told that my processor does a tracking filter based
on the RPM derived from the photo sensor output. The sensors that I'm using
are the piezoelectric type and the processor integrates their output to
derive an "inches per second" or ips reading. I find the vibration analyzer
both mandatory and frustrating. I will surely follow any KitPlanes article
you produce with your sensors. Good luck.

"Jim Weir" wrote in message
...
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