how to filter external signal digitally using labview

[suni]

Can somebody help me how to use digital filter in DAQmx?

[stanthetiger]

Hi suni,

DAQmx does not contain any digital filter. However, LabVIEW does contain many different pre-made signal processing VIs that you can use (ie. Bessel Filter, Butherwork Filter, etc...)

Here's some useful resources that you can take a look at

LabVIEW 8.5 Help: Signal Processing VIs
LabVIEW 8.5 Help: Filter VIs

NOTE: LabVIEW Base Develoment System does not contain the Signal Processing VIs. You would need Full, Professional or DevSuite.

Regards,
Stanley Hu
National Instruments
Applications Engineering
http://www.ni.com/support

[suni]

Hi

I used daq assist to enter the external signal and digital notch filter.vi to as filter. The filtered signal was not anntenuated initial. Can you tell me how to fix it? I attached the graph i got . 

Thanks 

[stanthetiger]

Hi suni,

This is expected behavior. Depending on the filter topology (Butterworth, Chebyshev, Elliptic, Bessel, etc...) you would be getting different response. The order of the filter will also affect how well the filter behaves. A higher order filter would give you a better filter, but it would be more processor intensive.

Regards,
Stanley Hu
National Instruments
Applications Engineering
http://www.ni.com/support

[suni]

Hi
Thanks for the reply. Can you tell me how to output this filtered signal form the daq card so i can used it to control the servo? Thanks

[stanthetiger]

Hi suni,

If you're using one of our data acquisition devices, you can use the DAQmx palette to output the signal to the daq card. For first time users, I would suggest using the DAQ Assistant.

Here's a really useful Developer Zone article that can help you get started with data acqusition with DAQmx.

Regards,
Stanley Hu
National Instruments
Applications Engineering
http://www.ni.com/support

[suni]

Hi

I want to display the filtered signal on the scope so I  see what it look likes after the digital to analog conversion. I want to do this in real time. Can somebody tell me how to do that?

[stanthetiger]

Hi Suni,

You can connect an analog output channel from your DAQ device to your scope. Using DAQmx, you can then output the signal to the analog output channel.

Regards,
Stanley Hu
National Instruments
Applications Engineering
http://www.ni.com/support