filtering performance

[sdsi]

Hi!

I would like to filter data acquired at 100 Hz with Labview 7.1.
If I use the default filter box (configuration : 2nd order butterworh filter with a band pass of [5 Hz - 30 Hz] ),
the filtering process seems to be done at a frequency lower than 100 Hz.
If I use the IIR module, the VI performance are improved but it does not reach 100 Hz.

What are the performance of the filtering box?
Thx

[johnsold]

It is not clear exactly what filter performance you are looking for. If your data is sampled at 100 Hz, then the Nyquist criterion specifies that any signal components above 50 Hz cannot be accurately represented. In fact if there are components above 50 Hz in the signal fed to the data acquisition device, the sampled signal is irretrievably corrupted. Also make sure that your filter knows what the sample rate was. If your data is of type waveform, the timing data is included. If your data is an array of values, you must specify the sample period or frequency. How you do that depends on which filter VI you are using.

Lynn