PicoScope SDK trigger jitter significantly higher than PicoScope 6

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larry.cao
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PicoScope SDK trigger jitter significantly higher than PicoScope 6

Post by larry.cao » Wed Nov 28, 2018 4:02 am

I am using Labview to acquire a periodical signal and the results turned up that the edges of my signals "shifting left and right" through repeating acquisitions, indicating that the trigger jitter was significantly higher.

When I watch the same signal in PicoScope 6, this didn't happen.

I recorded a video in google drive where all settings can be seen.
https://drive.google.com/open?id=12x6rG ... MYHAk6QtOs

Martyn
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Re: PicoScope SDK trigger jitter significantly higher than PicoScope 6

Post by Martyn » Mon Dec 03, 2018 7:58 am

This is the adjustment that PicoScope 6 makes to ensure that all traces go through the diamond, so that when you step back through you don’t get jitter.

It is best described using an example

Consider a rising edge trigger at 1V with 9 pre trigger samples, at sample 9 the voltage is 0.999V so the scope hasn’t triggered, at sample 10 the voltage is 1.004V and the scope has triggered. Now in the next buffer at sample 9 the voltage is 0.996V so the scope hasn’t triggered, at sample 10 the voltage is 1.000V and the scope has triggered. If you plot these then they will not sit on top of each other and won’t pass through the trigger point at 1V on sample 10.

What we do is some simple straight line interpolation triangle maths to work out exactly where between sample 9 and sample 10 we pass through the 1V point and then we adjust the time axis with this knowledge.

To help the API has two functions to assist with this TriggerTimeOffset for BlockCapture, and TriggerTimeOffsetBulk for RapidBlockCapture, which will give you this adjustment for each captured block of data.

This is purely an aesthetic function to please the human eye, the captured data in LabVIEW is real.
Martyn
Technical Support Manager

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