Designing an accelerometer

[EngineeringDaN]

I posted another thread here talking about two instrument designs using strain gauges. One was for measuring torque, and the other for acceleration.

I would like to go ahead with designing an accelerometer using a full strain gauge bridge. The basic idea I have in mind is similar to this:

http://instrumentationandcontrollers.blogspot.com/2012/10/strain-gauge-accelerometer.html

Now I have two different applications in mind. One is to measure the vibration of an engine or motor spinning a propeller or even possibly the vibration due to speakers. The second application is to measure the acceleration of an electric motor accelerating a propeller from zero to max rpm.

I have a problem with both applications. Since measuring vibrations will result in the mass moving back and forth, how can I display the strain caused by this vibration to show the frequency ? I am guessing that the one thing you would want from measuring the extent of vibration is the frequency, but how do I go about converting this change in output voltage from the strain gauge to show a frequency graph ?

The problem with the second application, measuring the acceleration of a motor and mounted propeller, is that if I mount the motor on the accelerometer the resultant strain would be due to both acceleration and pulling force of the motor. The propeller would accelerate from zero to max rpm, then spin at its maximum causing no further acceleration but still causing a force which will strain the gauges. Is there any possible way to isolate the acceleration ?

Any advice or possible ideas for small scale application of a strain gauge accelerometer would be highly appreciated.

 

[timthereaper]

Question: why would you want to design an accelerometer rather than just buy one? They're fairly cheap and worth the investment if you're serious about completing your project.