How to avoid aliasing

[vedran]

Hi,

I have NI-DAQ 6024E and i have some analog signals (continuous) on an few inputs (voltage). I heard of possibility of aliasing problems in this case. can somebody tell me something more about that and how to avoid it.

thanx in advance

Vedran Divkovic

Message Edited by vedran on 05-03-2005 03:11 AM

[AlexxxR]

Hi Vedran,

an aliasing effect is not depending on the Hardware. It´s depending to the sample rate and the frequency of the aquired signal.

Check out this link for further informations:
http://zone.ni.com/devzone/nidzgloss.nsf/10ce50b61f969f5a86256879000d3a01/54d6f1a8731445688625686a00793d73?OpenDocument

And look at the attached Picture to understand Aliasing-Effect.


Hope this helps

Alex

[E Murphy]

Hi Vedran:
You will need to sample just a bit above twice the maximum frequency in your signal. Otherwise you need an antialiasing filter (5th to 7th or more order) with a cut off frequency at half the sampling frequency. You could have, for example, a filter with cut off at 10 kHz, sample at 20 kHz and then use a digital filter (software) to set other bandwidths if you are displaying the data as frequency spectrums (you can do an FFT in Excel, it is one of the "analysis tools")
Regards
Eduardo Murphy