Looking for simple waveform filter

[Brian Wells, Space Research Institute]

I am using E series board using single ended input to collect 16 channels of constant value data, (ie 10volts). The data has a small amount of noise and outlying data points which I need to remove. I am attempting to implement a simple low pass filter. I attempted the Buterworth and FIR filters. The code I have attempted based upon the help examples unbundles the waveforms, filters the data, and rebundles the waveforms. This produces a discontinuous waveform when ploted. Addtionally the filtered data looks like a sine wave with an amplitude ranging between zero and the bias of the constant input data dependent upon the input parameters fo the filter. I'm looking for an example code that filters a constant signal with outlying da
ta points and small amount of noise. I cannnot use a average because the outlers are all on one side of the average value and will bias my data.
Thanks for the assistnance
Brian Wells
Space Research Institute
Auburn University, AL

[Randy_H]

Brian,

Can you try a running average using shift registers? With this, if the latest point is over x% outside of the running average, then do not include it. Since your signal is "constant," then frequency filters will probably not help you. See the attached example in LabVIEW 6.0.2. The interesting part of this example is that you need to know what your expected value is. If this is unknown, then one must do a bit of statistics (probably through histogramming) to get an initial average value.

Randy Hoskin
Applications Engineer
National Instruments
http://www.ni.com/ask