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Filtering out 20-200Hz vibration from MMA8652FC

Question asked by Tim Tanner on Nov 25, 2015
Latest reply on Nov 27, 2015 by Anthony Duhamel

Hi,

 

We are planning to use the MMA8652FC in a system where there is large amplitude vibration in the range 20-200Hz. We are interested in measuring accelerations from DC to 1Hz and rejecting the vibration.

The data sheet and application notes mention low pass filtering as part of the tap detection function but it is not very clear if this will do what we want or whether the filtering will be adequate.

With frequency components up to 200Hz we will presumably need to sample at 400Hz or greater to avoid aliasing? We don't want 400Hz ODR so some sort of oversampling will be required.

There is a table of HP_FILTER_CUTOFF setting options but nothing about setting the low pass filter.

Q1. Can I assume that the cut-off frequencies mentioned in Table 10 are also the low pass cut-off frequencies?

Q2. What is the roll off of the LP filter? We probably need 40dB of attenuation at 20Hz. Will this limit the cut-off frequency to less than 1Hz?

 

Kind regards,

 

Tim.

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