SensorsのトピックRe: MMA8452Q Self Test

MMA8452Q Self Test

stanfordhudson — Tue, 03 Feb 2026 21:52:58 GMT

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

Re: MMA8452Q Self Test

TomasVaverka — Wed, 23 Apr 2014 11:26:56 GMT

Hello Stanford,

The reason why the Z axis self-test output does not correspond to the typical value specified in the datasheet is that the self-test is not factory trimmed. Generally, the test is considered successful if the minimum magnitude of change (50 counts for all axes at ±4g mode) is achieved.

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct" or “Helpful”. Thank you.

Re: MMA8452Q Self Test

stanfordhudson — Wed, 23 Apr 2014 15:53:29 GMT

Thank you Tomas for the response. I am assuming by magnitude you mean the magnitude of the XYZ vector?

(sqrt(x^2+y2+z^2)).

Would this then be the correct procedure:

1. Measure xyz in Active mode.

2. Compute magnitude (mag0=sqrt(x^2+y2+z^2))

3. Measure xyz in Self Test mode.

4. Compute magnitude (mag1=sqrt(x^2+y2+z^2)).

5. Test pass if abs(mag1-mag2)>=50.

Thanks, Stan

Re: Re: MMA8452Q Self Test

TomasVaverka — Thu, 24 Apr 2014 08:37:46 GMT

Hi Stan,

Sorry for not being clear enough, the procedure does not require calculating the XYZ vector, just simply compute the difference between the acceleration output of all axes with self-test enabled and disabled as follows:

X_ST = X_{ST_ON}− X_{ST_OFF}

Y_ST = Y_{ST_ON}− Y_{ST_OFF}

Z_ST = Z_{ST_ON}− Z_{ST_OFF}

and if these self-test changes are higher than 50 counts at ±4g mode, the test is considered to pass.

As you are doing correctly, it is recommended to take several samples (e.g. 10) for each axis and average them.

I hope it helps.

Regards,

Tomas

Re: MMA8452Q Self Test

danielwerder — Fri, 08 Jul 2016 06:21:54 GMT

Hi Tomas,

I have a question about Self Test range.
About datasheet are XYZ will be deflected by +45, +64 and +420.

Are there no tolerance (min, max) values?

BR,
Daniel

Re: MMA8452Q Self Test

TomasVaverka — Fri, 08 Jul 2016 07:54:16 GMT

Hi Daniel,

We do not specify the limits as the self-test output is not trimmed.

Regards,

Tomas

Re: Re: MMA8452Q Self Test

bobpaddock — Tue, 09 Aug 2016 12:13:10 GMT

How well does this work out if the device is moving, in uncontrolled ways, while self-test is being done?

Re: MMA8452Q Self Test

chrislin_wpi — Mon, 13 Feb 2017 04:18:03 GMT

Dear Tomas,

Do you mean each axis (Xst,Yst and Zst) higher than 50 counts at ±4g mode, it's pass?

_{And how about ±2g mode?}

_{Best Regards}

_{Chris Lin}

Re: MMA8452Q Self Test

TomasVaverka — Mon, 13 Feb 2017 08:27:42 GMT

Dear Chris,

It is 100 counts at ±2g mode.

Best regards,

Tomas