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Triggering, noise rejection questions

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Triggering, noise rejection questions

Postby MarkWyman » Tue Aug 30, 2005 3:11 am

Hi all,

I suppose I am spoiled by some pretty pricey equipment, but I am having a heck of a time getting reliable slope direction detection on analog waveforms with the 3206. HF noise is causing the trigger to trip in either direction, rendering some of the "phosphor" modes useless.

Is there a way to trigger on a low-pass filtered waveform apart from using external circuitry? I see one of the modes for display alows a filtered waveform to reduce noise, is it possible to use this for triggering while using the unaltered waveform for display?

Thank you

-Mark
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Postby MarkWyman » Tue Aug 30, 2005 8:40 pm

Quiet on this board, isn't it?
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Postby Michael » Thu Sep 01, 2005 10:19 am

Hello Mark,

Thank you for your post.

You would need to condition the signal for noise before the scope. The trigger function is basic and stability can be subject to noise particularly at higher frequencies.

You would need to play with the trigger advance/delay to get the most out of the scope buffer.

Best regards,
Michael
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Postby MarkWyman » Fri Sep 02, 2005 1:02 am

Thanks for the info... Perhaps that is a suggestion for the future, a simple low-pass filter built into the picoscope software for triggering dependant on the sample rate, one of those infamous:

aveHolder = (aveHolder - (AveHolder >> n)) + newSample
aveSample = (aveHolder >> n)

little highly efficient equations. Where N can be the power of two numbers of points of averaging.

I haven't had time to look at your programming API, but I am highly interested in writing some custom scope displays as I have a little programming background, and a desire to learn a little 3D programming skills (using the Direct X interface). I am hoping to add a third dimension to the scope display and use it to display historical events that can be reviewed. Default much like the digital accumulator display, only rotatable. However that winds up being a bit useless if I cannot make the trigger reliable enough due to noise. I would hate to have to apply analog filters depending on the signal I wish to observe.

One last question, are the Fourier transforms performed in the PicoScope or on the PC? My scope display gets very slow depending on the maximum frequency selected, but my PC's % of processor remains very low. Wouldn't it be more efficient to off-load this processing onto the PC?

Thanks for humoring me. I love the concept of this product, which is why I purchased it.

-Mark W
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Postby Sarah » Tue Sep 06, 2005 8:28 am

Hi

Thank you for your post.

The FFT happens in the software. All you get back from the oscilloscope are raw readings which you then have to process youself, hence the calculation of FFT is all software based.

Hope this helps

Best Regards
Sarah
 


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