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frequency response to rolling average

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  • frequency response to rolling average

    I'm trying to collect data from an older piece of equipment, a force plate
    with piezoelectric load cells and charge amps. I'm collecting and logging
    the data through a multi-channel A/D board and computer. Due to the
    advanced age (>20 years) of the charge amps, I'm getting a lot of noise in
    what should be a quiescent signal. The without digging into the charge
    amps (something I *really* want to avoid!), there are two ways to deal with
    the noise - a discrete component low-pass filter, or some sort of numerical
    manipulation of the data. The latter is prefered beacuse it's a lot easier
    to change the coeffecient of a variable in an algorithm than purchase and
    install a discrete component in a circuit.

    In the past, one method we have used to smooth data is a rolling average.
    Normally this was done on relatively low frequency data (the data of
    interest occured at a low frequency respective to the sampling rate), and
    the frequency spectrum had never been of interest. In the current
    experiment, I am sampling at 100Hz with an expected maximum frequency of
    motion of 10Hz, a 10:1 ratio. Additionally, this time we *are* interested
    in the frequency spectrum of the signal (the rate of postural sway in the
    subjects - wich will be below 1Hz). I'm using a Fast Fourier Transform to
    extract the frequency spectrum data.

    My questions are this: how will using a rolling average to smooth the data
    affect the frequency response of the system? How will changing the window
    size of the rolling average change the frequency response?

    Guidance or references on these questions would be greatly appreciated.
    Dan Major
    Univ. of Okla. School of Industrial Engineering
    major@ou.edu htp://www.ecn.ou.edu/~major

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