EEVblog Electronics Community Forum

Products => Test Equipment => Topic started by: josephny on November 04, 2015, 01:54:22 pm

Title: Newbie w/1054Z
Post by: josephny on November 04, 2015, 01:54:22 pm

Can someone explain why there is about a 5 second delay in display response when the sweep reaches the right side of the display before updating the display?

I'm sure I'm doing something wrong, but I can't figure it out.

Thank you!
Title: Re: Newbie w/1054Z
Post by: Fungus on November 04, 2015, 02:22:59 pm
It depends on your settings, in particular the memory size.

If you tell the 'scope to fill up all your RAM with recorded signal then that takes a long time at lower frequencies (the DS1054Z has a lot of memory for a 'scope). Result: You won't see the trace come back on screen for quite a while.

(nb. You can scroll the display to the left to see the entire signal buffer).

Fiddle with the settings under "Acquire->Mem Depth" and see what happens.

Title: Re: Newbie w/1054Z
Post by: alsetalokin4017 on November 05, 2015, 03:52:17 pm
Yep. We kind of need to know all the scope's settings in order to be able to help out much.
Title: Re: Newbie w/1054Z
Post by: max666 on November 06, 2015, 01:07:11 am
I guess technically you just found a bug, but it's not a big one.

Like blueskull already said, this behaviour of the 1054Z is normal if you have the trigger mode set to "Normal" or "Single", but it doesn't make sense in "Auto" (if you set a large time base).
So what's going on? If you set the time base to 1 s/div the 1054Z doesn't go into roll mode yet, even though it kinda looks like the roll mode (but the roll mode doesn't have trigger). And if you have your trigger point in the middle of the screen, then at 1 s/div this means you have 6 s to the left (pre-trigger) and 6 s to the right (post-trigger). In "Normal" mode the scope will wait and fill up memory for those 6 s to the left before it does anything, because that's pre trigger information it needs so it can display a complete 6 s of waveform to the left of the trigger point when a trigger occurs. After it got 6 s it continuous to capture pre-trigger information and is now armed to accept a trigger. Once a trigger occurs the last 6 s of waveform get displayed and the remaining 6 s to the right are drawn as they come. So that's perfectly fine behaviour, because Rigol doesn't want to display incomplete waveforms, so you gotta wait until you got all the pre-trigger first.
Now in "Auto" it doesn't make sense (for such a large time base), because during the 6 s of pre-trigger capture the scope can't be triggered, and once it got 6 s worth of information it will very quickly do an auto display of the waveform anyway, so why not draw the pre-trigger capture instantaneously as well. I would say this is only an issue for the small window of time bases, where the scope doesn't switch to roll mode yet and on the other side where the update rate isn't bigger than the display refresh rate yet.

So if this annoys you I would suggest to either switch to roll mode in the horizontal menu, or move the trigger point to the left of the screens, so there is no pre-trigger capture.
Title: Re: Newbie w/1054Z
Post by: ebastler on November 06, 2015, 06:52:43 am
I guess technically you just found a bug, but it's not a big one.

No, not a bug in my view. What I expect from a scope in "Auto" mode is:
In order to meet requirement 1, I think the scope must collect the pre-trigger trace first (which takes time at slow time bases). Only after this has happened, and when the trigger event is "due" but not occuring, the scope can fall back to the untriggered mode and display the trace.

As you said, roll mode avoids this. Setting a trigger condition which is alway met (so that you effectively revert to "untriggered", rather than "auto" mode) should also work, if you don't like the rolling trace.
Title: Re: Newbie w/1054Z
Post by: Howardlong on November 06, 2015, 08:00:49 am
I agree, it's not a bug, that's how DSOs work. If you move the horizontal trigger point further left, hopefully that will self-explain what is happening.

Think about it: you have a trigger point, how can the scope know how to display what's pre-trigger before the trigger's happened? Once we have invented the time machine, we'll be in a position to deal with that of course!
Title: Re: Newbie w/1054Z
Post by: max666 on November 06, 2015, 02:36:46 pm
Ok, you are right, it's not a bug, because the scope is actually doing what it's supposed to do.
But furthermore I did some crude testing and the scope isn't actually doing what I thought it would do. I thought after it has collected 6 s of pre-trigger, the auto mode would immediately force a display refresh, since there hasn't been an update of the display in 6 s. But that would be silly, because you never get a chance of a synchronous waveform that way. The scope is actually waiting a reasonable amount of time, after it has collected the pre-trigger, for a trigger event to occur and only after that it does an auto display update.
Title: Re: Newbie w/1054Z
Post by: alsetalokin4017 on November 06, 2015, 04:44:11 pm
Yep, not a bug, the scope is behaving as it should do. 

Remarkable!    :clap: