[Closed] Low frequency response of IIS3DWB

[MAnil.1]

I have been characterizing the sub 200Hz characteristic of the IIS3DWB, and we are aware that it is somewhat an uncharted territory.

But I was somewhat surprised by my observation when I compared a piezoelectric sensor attached to an IIS3DWB, vibrated together. The piezoelectric sensor is single axis, and I use only the z axis to take the measurement. (The vibrating coil is not perfect, might also have perpendicular components.)

The ratio of the signal that I get from both sensors are like the following. (Had to diminish the amplitude for IIS3DWB not to saturate.)

It seems that there is a resonant peak at about 70 Hz, (the cone also has a resonance there, but I look at relative outputs, and I wonder whether this is an issue.)

And there is a high-pass characteristic, where at the lowest frequencies the signal dies out.

 

I wonder:

• How does IIS3DWB measure gravitational acceleration if low frequencies have a cutoff even without the digital filter
• Is there a structural reason for a low frequency resonance?
• I am using an audio speaker cone to vibrate the assembly, can magnetic field be the culprit here?

[MAnil.1]

My follow up question: How can IIS3DWB estimate gravity as 1000 milli-g as the amplitude of the signal goes to zero at f=0Hz?

[Eleon BORLINI]

Hi @Community member Anil​ ,

Can you please check whether the FDS bit of the CTRL8_XL (17h) register is enabled? See datasheet, p. 16.

 

It looks as the HPF is enabled in the ODR/4 configuration.

By default, you should be able to clearly see the 1g acceleration along z axis when in flat position.

-Eleon

[MAnil.1 · Accepted solution]

Eleon, thank you for your response.

I realized that my measurement was far from ideal, therefore I will close this issue.

[Eleon BORLINI]

Thank you for your update @Community member Anil​!

I agree with you that, especially for the characterization of the vibrometer, a repeatable and stable setup is mandatory.

-Eleon