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Down-Home Vibrometer

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BrianW

Well-Known Member
Joined
Jul 2, 2018
Messages
140
Location
Altus SW Oklahoma
For several years, I owned a C-150 formerly used by Spartan - Tulsa for training.
The overhaul engine in it had chrome cylinders and was remarked on for its smoothness.
I supposed that Spartan would have used vibration analysis in the course of training A&Ps.

I needed to smooth minor prop chips once or twice over the period of ownership.
I noticed that Vibrometers go for $150 - $2000 so I looked for a homebrew.
As it turns out, 3 axis accelerometers with analog outputs are now available at attractive prices.
ADXL335 ~ $15
ADXL335.jpg

So far so good. Next was the question, how to display the vibrations in X, Y, Z ?

I settled on a chinezium toy oscilloscope a DSO150 ~ $28
2020-11-06 14_25_21-Window.jpg

This device displayed the orthogonal accelerations in units of g as desired but lacked a most important facility - a second channel to display a trigger pulse, which I envisioned as a laser pointer and a phototransistor with a ruby colored plastic filter. Although I did not consider the extra cost of a two channel display was warranted for this test, I see that triggering on a sensor trained on a prop blade and adjusting the display speed suitably would indicate the crank angle for maximal amplitude. (I omit the details of connecting the accelerometer to an ethernet socket, so that a regular enet cable can be arranged to remote the sensor into the cockpit, etc.)
 
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