Doubt regarding filter usage in Labview

[royalkrsna@yahoo.com]

Hello there.I've been using lab view for my project. I have a doubt.What exactly do the digital filters do?My project needs to design a bandpass filter of frequency limits .1 hz to .5 hz.And later signal process this signal to obtain frequency components.What do u suggest whether shall I resort to this labview designed filter or should i proceed with the analog circuit using op amps.The signal is a voltage one and i need to filter out that particular forementioned frequency.

[BenjaminR]

Hi,

The analog filter has a ripple rate in the pass-band, while the digital filter is perfectly flat. The flatness achievable with analog filters is limited by the accuracy of their resistors and capacitors. Even if a Butterworth response is designed (i.e., 0% ripple), filters of this complexity will have a residue ripple. On the other hand, the flatness of digital filters is primarily limited by round-off error, making them hundreds of times flatter than their analog counterparts. The digital filter is clearly the victor in both roll-off and stop-band attenuation. Even if the analog performance is improved by adding additional stages, it still can't compare to the digital filter. The digital filter's step response is symmetrical between the lower and upper portions of the step, i.e., it has a linear phase. The analog filter's step response is not symmetrical, i.e., it has a nonlinear phase.

There are still many applications where analog filters should, or must, be used. This is not related to the actual performance of the filter (i.e., what goes in and what comes out), but to the general advantages that analog circuits have over digital techniques. The first advantage is speed: digital is slow; analog is fast. The second advantage of analog over digital is dynamic range. Amplitude dynamic range is the ratio between the largest signal that can be passed through a system, and the inherent noise of the system. And the last flavor is frequency dynamic range.

In the links below you have more information about the digital filters in LabVIEW:

https://www.ni.com/docs/en-US/bundle/labview-api-ref/page/vi-lib/measure/macond-llb/digital-iir-filt...

https://www.ni.com/docs/en-US/bundle/labview-api-ref/page/vi-lib/measure/macond-llb/digital-fir-filt...

[royalkrsna@yahoo.com]

Thats very kind of u..by the information that u have provided i will resort to the digital filters.I still have few more questions?In digital filters we have both FIR and IIR ones.My project as such concerns with the continuous montoring of the input signal(voltage perhaps sine wave) from the DAQ and I need to filter out some 4 components from that and I need to signal process those obtained signals from the filters.As far as my knowledge is concerned my project doesnt need previous output values which tells me I may go for FIR filter.For the project as I forementioned can I proceed the following way. I design a band pass filter and let that signal pass through processing unit which does FFT on it and give out the necessary components and for signal processing also should I go for so called tool kit or can i give signal directly to the signal processing part.

[BenjaminR]

Hi,

Normally you have all functions what you need on the sub-palette ‘Signal Processing’. Let try to program and let me know if you have what you want. If you have some problem, do not hesitate to come here again and don’t forget to attach you Vis.

[royalkrsna@yahoo.com]

It's again very kind of u. I will do and let my doubts get clarified.Thank u.