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MMA8452Q Self Test

Question asked by Stanford Hudson on Apr 21, 2014
Latest reply on Feb 13, 2017 by Tomas Vaverka

Hello,

 

We are using an MMA8452Q and are utilizing the Self Test feature during production test. 

The datasheet indicates that when self test is activated, the XYZ axes will be deflected by +45, +64, and +420 LSBs off of the current acceleration acting on the sensor respectively.

 

Our procedure is as follows:

  Set to ACTIVE mode

  Read X,Y,Z

  Set to ST mode

  Read X,Y,Z

  Compute absolute differences in XYZ for ACTIVE and ST mode.

 

(We are doing quite a bit of averaging along the way to account for any noise that may exist in the system.)

 

We routinely get values that are 380 and below for the Z axis.  The XY are usually pretty marginal, but sometimes are dead-on.

Each accel is different.

 

Can you please give me some insight into why the Z axis is not even close to the +420 specified in the datasheet?

 

(Note that we do set the accel range to +/-4G.  The Active bit in CTRL_REG1 is cleared before we set ST.  The accel is still during the test).

 

Thanks,

Stanford Hudson

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