Setting digital Filter for M Type DAQ card

[Cimteker]

Hi,

I had several attempts with this VI and I am still not sure if this works. Actually it does not male anyy difference if I set my filter to T or F. Does this look right? My system is PXI-6221 with my signal coing to PFI3 adn PFI8. I am counting edges, both positive and voth negative. At the end I read the result and I always get mor than expected. So I figured I need a filter. This VI is supposed to activate the filter for counter measurements on channels PFI3 and PFI8.

Thanks

CT

[BriceS]

How did you choose the value 0.00256? Are you sure that is small enough for your application? Basically, if you can provide more details about what you are trying to do and the signal you are measuring, the easier it will be for people to provide advice.

Regards,

Brice S.

Applications Engineer

National Instruments

www.ni.com/support

[Cimteker]

I am measuring an output of a Hall sensor counting edges. One counter counts positive the other negative edges. The frequency of my signal is < 1kHz. But I consistently get more values from my sensor than from the DUT that I am testing. I attribute this to noise. So I wanted to apply a filter. I experimented with 2 allowed settings (2.5 ms and 6.4 ns if I remember correctly) and it made not difference. I am thinking that maybe this is not implemented properly. I would expect at some point to get 0, as it will not allow any samples through.

Thanks

CT 

[BriceS]

One thing you should consider doing is observing the waveform to verify that it is what you're expecting and to see how much noise there is. That will tell you what value you should use for the filter.

As for how you have things wired up, it looks like you are doing it correctly (see this article: http://digital.ni.com/public.nsf/allkb/9ece7dbe7df338bd86256f8600734a41?OpenDocument ). What card are you using?

If it's still not working, it's very possible that there is something else affecting your signal other than ringing. As I said at the beginning of this post, it would be very useful to observe the waveform to see what else might be going on.

Regards,

Brice S.

Applications Engineer

National Instruments

www.ni.com/support