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Remove gravity from accelerometer

Hello,

 

I am using a 3axis acceleromter ADXL345 and I want to frequencies between 0.5-25 Hz.  I want to do some filtering first in order to get rid of the gravity factor and the dv offset as well as some noise. I have read multiple articles on the internet but none seems to be very clear. Can someone give me some quick tips to guide me with my task?

 

Thank you in advance

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Where were you N years ago when I was mentoring a group of Master-level students trying to design an instrument to measure muscle twitches due to nerve stimulation in order to monitor the level of post-operative muscle paralysis?

 

This is a two-fold problem.  One problem (which, I'm astounded by and disappointed to say, the students never realized) is a "Calibration" question -- how do you translate Voltage (in Volts) to Acceleration (in m/sec/sec, or in g's)?  [Our accelerometers were analog, and the voltage offset and gain for the three channels were specified, plus-or-minus 10%, in other words, the accelerometers were uncalibrated).  The other question (which, again, sadly, I had to coax out of them) was "under what conditions will you have an acceleration of 1g, and how will it be "distributed" among the three axes of the accelerometer?"

 

The answer to the two questions is similar, and the thought that goes into it will also answer the questions that you pose -- you should be able to figure it out for yourself.  It's only high-school Physics, after all ...

 

Bob Schor

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