FIR help

[martinmistere]

Hi. I have to use the FIR block in labview on a sinusoidal signal with harmonics. In particular i have a fundamental at 50Hz with an amplitude of 10V and 2 harmonics one at 150Hz with an amplitude of 5V and the other at 250Hz with 3V. I need to realize a low-pass filter and i 've read the help of the block but i'ven't understood how to set the parameters of filter specifications.
What do i have to set in topology?what is a good value for taps?
Tnx for help.

[carlo>]

Hi martinmis,

I'll try to give you some hints about your FIR filter. I suppose that you're going to use the "Digital FIR Filter" function of LabVIEW. This function has two main inputs: the input signal to be filtered, obviously, and a cluster named "FIR filter specification". You have to set the parameters of this cluster according to what your filter must do; but this, doesn't concern with LabVIEW, it is instead bound to the general theory of FIR filtering signals.

The only things I can suggest you is to make a search (for example on the web) of FIR filtering theory understanding what are the best values you have to set for your parameters ("Topology", "Type" and "# taps") or trying them with the "trial and error" approach (to do this you can use the LabVIEW example "FIR Filtering and Response.vi"). Remind that, for example, the number of taps belongs to the specific number of "states-delays" of the filter whose formula is:

                                                               y(n)=c0x(n)+c1x(n-1)+...+cpx(n-p),

where "p" is the order of the filter; "x(n)" is the input signal, "y(n)" is the output signal and "ci" are the weight coefficients of the filter. And only you can set this parameters according to what you actually need.

Bye

carlo>