Usage of two simultaneous accelerometers

[clovismarcondes]

Hi guys,

I´m working on an academic project that I have the intention to use two accelerometers (MMA8452Q) to get the deformation of a body in movement. The first accelerometer will stay over a soft surface that can suffer deformations and the other one will stay at another part (rigid) and will only detect accelerations from movement of the entire body. If I could assure they where aligned I could make the difference between the 2 vectors and so I could get the deformation acceleration of the body even in movement. But they are not aligned so I thought I could rotate one vector over the other one, to get the values on the same coordinate system and get the difference. Is it possible? How to make this on a dynamic system with the body in movement and the accelerometers changing their alignments?

[reyes]

Hi Clovis Marcondes,

Yes, it is totally possible to manually rotate the sensor so you can get the same coordinates from both sensors and this way you can get the difference between the measurements when a deformation is applied.

About how to make the alignment dynamically in a body on movement and the accelerometers changing their alignments, I think that this can be done by performing an offset calibration, this way you will change the zero (0) reference point, for example, if the zero (0) position in a tilt application is always at a 15° angle, thus considering this the new “zero” position, this way you can align one accelerometer to your other accelerometer.

More information about offset calibration can be found in the application note AN4069.

Have a great day,
Jose Reyes

-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------

[clovismarcondes]

Hi Reyes,

Thanks for your reply. The offset calibration seems to me like something that I have to do to compensate any problem caused by external events after the production of the accelerometers. But even both accelerometers calibrated I still have the problem that their tilt will vary during the experiments and they will be different of each other all the time.

I did not explained first but the accelerometers will be placed on a belt that will be used around someone´s torso (one on front and the other on the back). I already have a problem to calibrated them because once placed there, it´s not practical to follow the calibration instructions, I will not be able to put the accelerometers at the right positions described at the document. Despite that and considering the calibration can be done, the readings still be refering the axis of each accelerometers, so I still cannot compare them without some kind of conversion (rotation). At least that is what I think. Am I wrong?

Thanks,

Clóvis