antialiasing filtering problem, no hardware filter

[pellet8]

I have an NI compactRIO 9205 analog input module, sampling at 250 KS/s for 32 channels. There is no hardware antialiasing filtering. I need to use the frequency component between 1 to 1000 Hz, but I'm afraid the signal has been contaminated by aliasing. Is there any way I can do antialiasing filtering in software and resample the data at 1 kHz?

Thanks.

[AstroGlen]

In short, no.

But you might be able to make some assumptions about your signal and work from there... Like is your signal purely periodic? In which case you might be able to dis-regard some of the non-harmonic frequency components.

[Coq_Rouge]

Like Astroglen says. You should evaluate your acquired signal. Then ask your self what you have measured and why. Then doing data acquisition your signal will always have some unwanted contamination. Like 50 or 60 Hz from the mains as one example. But if you do a FFT you will able to determine if your signal to noise ratio is adequate or not. Also some digital filtering may help. But remember that the closer to the Nyquist frequency you get, your digital filter will be less efficient. If you feel it would be any help. Post a picture of your FFT.  

[pellet8]

Thank you for the reply.

My signal is chaotic in nature. I'm using the chaotic theory to analyse it and find patterns. Any suggestions on the best way to test how severe the signal contamination is?

On another thought, is there any product that I can attach to the input of the 9205 modul and antialiasing filter before it is sampled?

I haven't started my VI development yet. Still trying to decide the architect. I have the FPGA module and the 9012 processor. Ideally, I would like to do all the filtering on the FPGA and the 9012 can do some other calculation. It won't use much computer processor time, so it can work on something else. However, I don't know the processing limit on the FPGA and 9012, because I could potentially end up with 100 channels all sampling at 7kHz. I don't know if this is even doable without the use of computer power.

Any suggestions?

[AstroGlen]

I think that many DAQ board designs usually include either a static pre-designed IC filter such as:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=MAX292CPA%2B-ND

or a custom one. Here is a good website for designing your own:

http://www.dspguide.com/ch3/4.htm