Housing for accelerometer

[Kvon .1]

The target of our educational project was creating a vibration sensor based on a MEMS-accelerometer. We found that housing itself of completed device and method of placing PCB in housing has a significant effect on instrument readings. This effect is observed in form of non-linear frequency response, for example, in the frequency range up to 300 Hz, the readings of our device and the control device practically coincided but in the higher-frequency range, there were areas of signal attenuation and subsequent areas of its amplification. This effect may be explained to resonance effects cased with housing properties and its pouring by compound.

So we have the following questions:

1) Can the accelerometer location in the rather compact PCB be significant, and is it correct that the better accuracy can be obtained by placing the accelerometer in the center of the PCB?

2) Could the placement of components other than the accelerometer in the PCB layout play an important role in sensor readings, given that there are no very bulky components and they are all relatively evenly distributed across the board?

3) Are there any recommendations for designing housings for devices with MEMS accelerometers?

4) Can pouring of the housing with compound significantly affect the readings of the accelerometer?

[Eleon BORLINI]

Hi @Kvon .1​ ,

during the characterization of the vibration of an inertial sensor, in order to disentangle the effects caused by the spurious vibration modes of the board on which the accelerometer / IMU is mounted, we typically use a design like the STEVAL-MKI209V1K, or industrial adapter.

1) In case the board is different from the one above, its effect has to be taken into account, but one can try to understand whether the contribution to the vibration checking the typical frequency response usually reported in the datasheet.

2) If the other components are not dissipating too much heat, or are much bigger than the, they might affect a little the performances of the IMU in terms of temperature and bending dependence, but both effects can be compensated at firmware of software level.

3) You can check the design suggested above; if it is not feasible, you should prefer an area of the board which is less sensitive to the pcb spurious vibrations (e.g. placing it in a node of the vibrating mode).

4) This should not affect the IMU reading, especially if the compound is not liquid. But the compound vibration will be anyway detected by the accelerometer.

Let me please know if I well understood the point.

-Eleon