What is the long term stability of an accelerometer calibration?

[payschulzehorn]

Hello together!

After mounting a MMA8451Q accelerometer usually there has to be a calibration to measure the individual sensor or the mounting deviations.

After what kind of maintenance intervall shall the measurement be repeated?

Has the MMA8451Q a drift over months or years?

with regards

[david_diaz]

Hello Pay,

Thank you for writing.

Indeed, immediately after the device is mounted, there will be a change in its accuracy: the Zero-g Level Offset.

This change is caused due to the stress on the package during the reflow process and cannot be avoided, however, we have a document that could help you with some tips and mounting guidelines to minimize this stress and another document that could help you to perform a Zero-g offset calibration on the MMA8451 accelerometer, please find these documents on the links below:

AN4069, Offset Calibration of the MMA8451, 2, 3Q:

http://www.nxp.com/files/sensors/doc/app_note/AN4069.pdf

AN4077, MMA845xQ Design Checklist and Board Mounting Guidelines:

http://www.nxp.com/files/sensors/doc/app_note/AN4077.pdf

I hope this information will be useful for you.

If I misunderstood your question, feel free to let me know.  I will be glad to help.

Have a great day.

David Diaz.

[daviduhen]

The data sheet for the MMA8652FC simply states...

"Offset is to some extent a result of stress on the MEMS sensor, and therefore the offset can slightly change after mounting the sensor onto a printed circuit board or after exposing it to extensive mechanical stress." 

I understand the need to compensate for stresses related to PCB mounting and the magnitude of the offset is listed in the datasheet. Does NXP have any test data to share on drift after a shock event or repeated shock events?  It would be useful to know what level of mechanical stress will cause a significant, permanent offset to occur.

[payschulzehorn]

Hello David,

After the zero-g offset calibration has been undertaken the sensor data are ready for the application.

In the technical data sheet of the MMA8451Q is stated in section 3.2, that the pyhsical principle of the sensor is a MEMS (micro electrical mechanical system). A source on the internet is explaining that a MEMS is measuring the earth gravitational vector by the extension of some elastic elements ( e.g. a micro spring ).

What is the long term stability of the elastic elements and their extension measurement within the MMA8451Q?

with my regards

Pay