How to Filter Noise

[Dennis_B.]

how do you " trigger on the polarity with a zero-crossing detector"??

[AnalogKid2DigitalMan]

Thanks for the clarification on the10x probe. I was thinking that your DAQ card was (or about to be) toast 🙂

-AK2DM

[NIquist]

With the Basic Level Trigger Detection VI.

[Kevin_Price · Accepted solution]

I very slightly modified the code you posted to add digital filtering, with a default min pulse width of 2 msec.   Give it a try.

-Kevin P

[JÞB]

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@Dennis_B. wrote:

Here are a couple screen shots. The last shows what I need to filter out.

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You didn't install the Ferrite on the USB cable correctly as shown in the Getting Started guide for your X Series DAQ product.

[Dennis_B.]

Hi Kevin,

I kept getting the attached error. I tried everything in the Ni help for this error, no oy. Do you think this might be easier by using edge counting. I can send the signal to an analog input. I tried this before but had the same issue of the DAQ counting the 20 kHz spikes. Maybe there is a way to set a minimum and maximum threshold between the zero and five volt signals. I also tried a ferrite core as suggested, no joy. This isn't an external noise issue but it was worth a try.

[Kevin_Price]

That's a timeout error which seems to suggest that the digital filter might also be suppressing your ~100 Hz signal, not just the 20 kHz noise.

To be honest, I've had little occasion to need to use digital filtering myself.  I thought I had a fairly solid understanding of how it worked, but perhaps there are some hidden gotchas?

Try taking a shipping example for edge counting and inserting a similar digital filter property node.  And be sure to navigate the property menu by way of edge counting rather than frequency measurement.   Does the 2 msec pulse width setting prevent you from getting any counts from your ~100 Hz noisy signal?   What happens as you vary the pulse width setting?

-Kevin P

[JÞB]

At the risk of repeating myself.  

The noise shown in the png's attached earlier is EXACTLY what the USB X Series device's Ferrites are provided to suppress.  If you've seen it before, it is unmistakable!  Read the getting started guide.  It even shows pictures of how to install the Ferrite correctly. 

Once the HARDWARE is properly connected we can look at other sources of trouble.

Kevin,  you should have known better than to ignore my earlier post.  😉

[Kevin_Price]

Jay,

Not ignoring, just no knowledge about the ferrite treatment and staying in my lane with other things I'd be inclined to try.  😁

-Kevin P 

[NIquist]

Just to clarify, the ferrite goes on the end of the POWER cable.  OP, make sure you follow the picture: make one loop of the cable and put it as close to the DAQ as you can.

Let us know if that clears up the signal...