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Time offset?

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Time offset?

Postby justindavis » Thu Feb 07, 2013 4:14 pm

Is there a way in software to do a time offset for one channel relative to the others to adjust for things like difference in cable lengths or skew in trace lengths? Or with the reference waveforms? Sometimes the sampled data has a slight delay relative to my reference waveforms. Perhaps with the math channels?

Thanks,

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Re: Time offset?

Postby Martyn » Fri Feb 08, 2013 7:08 am

You can't do it with channels but you can with reference waveforms.

Select the reference waveform and make it visible, find the x1.0 button at the bottom right or left of the screen associated to the reference trace, and click on it to locate the delay feature.
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Re: Time offset?

Postby Mark_O » Fri Jun 19, 2015 10:14 am

Martyn wrote:You can't do it with channels but you can with reference waveforms.

It's unfortunate, but it seems like the deeper I look into the Picoscope capabilities, the more limitations I uncover. :oops:

This capability is completely routine, even on the cheapest of standalone DSOs, where it is commonly referred to as "Channel Deskew", or "Delay Calibration". It's not at all uncommon to have to trim this setting, to bring all the active channels into time alignment. Only it's not possible at all on any Picoscope? Has the situation changed since Justin asked this question, 2 years ago?

This seems like a surprising limitation, since it is purely a Display characteristic (and already provided for Reference waveforms). I'd really like to see this capability added, possibly also as another Attribute of a Probe. Especially when evaluating pulses, temporal windowing, and logic states between 2 channels, this can be an important factor. :!:

- Mark
Last edited by Mark_O on Fri Jun 19, 2015 8:55 pm, edited 1 time in total.
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Re: Time offset?

Postby Mark_O » Fri Jun 19, 2015 10:36 am

Well, to be fair, and having given it more thought, perhaps it's not quite as important as I've made it out to be. Most ranges of PicoScopes don't sample beyond 1 GSa/sec, which is 1 ns per sample. You'd need ~25 cm of lead-length difference to shift things by one sample interval. Which you could correct just by using more closely matched test leads.

I would think this might be of some concern to those with ps6000's, sampling at 5 GSa/s, though. Or a ps9000, sampling at 20 GHz. Though your Pico Oscilloscope Range-web page says "Max Sampling 1 MS/s" in the box for that model! :oops:

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Re: Time offset?

Postby Martyn » Fri Jun 19, 2015 1:40 pm

You can deskew by creating a maths channel
Advance/Delay. Add [t] after a channel name to advance it by t seconds. For example, A[0.001] is equal to Channel A advanced by 1 millisecond, and A[–0.001] is equal to Channel A delayed by 1 millisecond.


For information the 9000 series are sampling scopes, not real time scopes, the same rules do not apply and the software is completely different.
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Re: Time offset?

Postby Mark_O » Fri Jun 19, 2015 2:22 pm

Good point about the 9000-series, Martyn. Thanks for that. That's way outside my pay-grade, so I've never paid much attention to it. :) I was just looking for anything sub-nanosecond.

Very interesting that a Maths channel can offset time, and not just an amplitude value. Certainly very flexible! But creating a redundant parallel channel just to fix a nanosec or two seems like a stretch. Now that you've pointed it out, I did find it in the Manual. But I looked pretty carefully beforehand, and never found it on my own.

Doesn't this become more of an issue though with something like the MSO models? I.e., the propagation delays are going to be quite different if you're probing the same signals in both digital and analog domains, yet you'd certainly want them to be in sync. Or do the PicoScopes compensate for that differential internally?

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