filter

[orsogna]

Hi,

have a PCI 6221 I am acquiring an analog signal using as external clock the pulse of a encoder. I recognise (by doing the FFT using an internal clock) that I have some noise at high frequency due to a asynchronous motor converter(these noise frequency are less then the sampling frequency of the encoder, so I have them in my measurements). How can I put a filter to eliminate this noise?it's a bit urgent.

thanks in advance

[GerdW]

Hi orsogna,

when you want to cancel out high frequencies you usually use a low-pass filter - either in hard- or in software...

[johnsold]

Unless the encoder is running at a constant speed, the data you collect using the encoder as sample clock will not be uniformly sampled.  That means that the time between successive samples is not the same for all samples.  With non-uniformly sampled data you cannot accurately use the FFT or the filter functions because they assume (and require) uniformly sampled data.  There is a Resample VI which can take non-uniformly sampled data and convert it to uniformly sampled data.  I think it uses interpolation techniques.

Lynn