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Rapid Trigger Mode--Questions

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Rapid Trigger Mode--Questions

Postby Mark_O » Tue Jun 16, 2015 7:00 am

The PS6 manual has a side note that RTM is only usable "on the fastest timebases". But says nothing about what those limitations are. This degree of vagueness is more than a little confusing. Especially for a powerful function in an engineering tool.

Would it be possible to clarify a bit just what the constraints are on RTM? Thanks.

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Re: Rapid Trigger Mode--Questions

Postby Martyn » Thu Jun 18, 2015 8:02 am

Rapid Trigger is available at timebases of 1ms/div or faster, equivalent to 10ms across the screen or less.

When operating in this mode the memory inside the scope is segmented, to capture multiple blocks of data, in response to multiple triggers, before returning the complete set to the application. The time gap between segments can be as little as 1us, depending on the scope settings and trigger signal.

Slower timebases will either have too much data in each block, if the sample interval is small, or have a sample interval that would not offer any benefit from the use of rapid trigger.
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Re: Rapid Trigger Mode--Questions

Postby Mark_O » Thu Jun 18, 2015 10:53 am

Thanks very much, Martyn. That is a good explanation. Definitely worthy of inclusion in a future update of the documentation. :wink: I'm glad to hear RTM is usable as low as 1ms/div. "only on the fastest timebases" was suggestive of being a significantly higher rate. And thus more restrictive. But it's really not.

You mentioned inter-segment gaps being as small as 1us, and I was wondering what that gap might be in a situation where one was using a 32M buffer, split into something close to the maximum 10k segments (so ~3200 Sa/seg), with each segment around 1ms in duration (100us/div)? I.e., something around 312ns per sample, or 3.2 MSa/s.

So how large would the gap between segments be there?

And looking at it another way, would it make any difference if it was 100% pre-trigger data (the trigger came at the very end of the acquisition), how much time would one lose after segment n triggered, before segment n+1 started acquiring again? (I know that scenario isn't always possible, but assume it was for this example.)

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Re: Rapid Trigger Mode--Questions

Postby Mark_O » Sun Jun 28, 2015 10:00 pm

Waking this back up again, since it's been 10 days with no response...

You mentioned inter-segment gaps being as small as 1us, and I was wondering what that gap would be in a situation where one was using a 32M buffer, split into something close to the maximum 10k segments (so ~3200 Sa/seg), with each segment around 1ms in duration (100us/div)? I.e., something around 312ns per sample, or 3.2 MSa/s.

So how large would the gap between segments be there?

Also, would it make any difference if it was 100% pre-trigger data (the trigger came at the very end of the acquisition), how much time would one lose after segment n triggered, before segment n+1 started acquiring again?

(In that case, it's not a matter of the trigger rearming in time, but just data being acquired for the next burst.)

These are actually questions involving the segmentation engine of considerable importance to me. And nothing I have found documented provides any information that would be able to answer them.

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Re: Rapid Trigger Mode--Questions

Postby Mark_O » Sun Jul 19, 2015 11:40 pm

Now that we finally have some solid information on how slowly re-arm times degrade with slower sample rates (which is a good thing), here:

post57021.html#p57021

let's return to this topic again, after a month has gone by. The remaining question that still hasn't been addressed, I would like to understand more fully is very simple:

>> does it make any difference if the trigger position is shifted back?

I.e., after one acquisition completes, we know about the re-arm time before it can trigger again, on the next segment. But would shifting the trigger point back, to the 100% pre-trigger position, provide any additional margin? Because the scope would only start capturing again, but not need to deal with the trigger immediately.

My guess is that there would be no difference at all. I.e., it could trigger just as easily on the first sample it was prepared to see in the next segment, as it could on the last. There is a fixed "dead time", which impacts both acquisition and triggering equally. But it would be good to have that confirmed, or refuted.

Thanks!

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Re: Rapid Trigger Mode--Questions

Postby Martyn » Tue Aug 04, 2015 10:20 am

The position of the trigger will not have an effect on the re arm time, this time is related to the writing of the last sample value to the current memory segment, stopping the collection, preparing to use the next segment, re enabling the trigger, and then restarting the collection.
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