Products > Test Equipment
Oscilloscope Zoom Out Quirk
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Wuerstchenhund:

--- Quote from: Someone on May 09, 2020, 10:11:15 am ---Recent R&S scopes have an auto memory depth setting, they may well be able to capture around the visible window and don't explicitly mention that the record length will be reduced for short timebases (a few forum goers have them so hopefully one checks it).
--- End quote ---

That could well be the case. Would be interesting to get some feedback from a few R&S scope owners.


--- Quote ---Tek DPO4000 certainly kept all the memory around the visible window. Which meant having to play around with the memory depth setting (lacked an auto mode?).
--- End quote ---

I'm not surprised, the MDO is, after all, just a pimped up DPO.

It could really be interesting (even just from a point of curiosity) if people could check their scopes and post the results here. I'm sure we could assemble a quite comprehensive list.
Martin72:

--- Quote ---It doesn't let me go beyond the screen.
--- End quote ---

I´m not really sure ( as a former rigol owner), but the "bigger" MSO5000 couldn´t do that too.
Maybe a actual owner could test and report it here.
Someone:

--- Quote from: EEVblog on May 09, 2020, 10:48:37 am ---
--- Quote from: Someone on May 09, 2020, 10:23:07 am ---There are many more scopes on the market than Keysight Megazoom units.
--- End quote ---
Megazoom is the entirety of Keysights range under maybe $20k or more, so it's safe to say that a Megazoom scope is the Keysight scope that most people will buy.

--- End quote ---
And now you're the one taking a general question, and narrowing it down just to highlight some specific brand/feature.... go back to the full quote tower and look at the question:


--- Quote from: EEVblog on May 09, 2020, 10:48:37 am ---
--- Quote from: Someone on May 09, 2020, 10:23:07 am ---
--- Quote from: EEVblog on May 09, 2020, 09:25:59 am ---
--- Quote from: Someone on May 09, 2020, 07:39:40 am ---
--- Quote from: EEVblog on May 09, 2020, 05:02:26 am ---
--- Quote from: Someone on May 09, 2020, 02:39:01 am ---
--- Quote from: stafil on May 09, 2020, 01:03:03 am ---Doesn't capturing data outside the display window => more time to capture data => less waveform updates per second?
--- End quote ---
Yes, which is why "automatic" memory depth usually defaults to the shortest record that will fill the screen.
--- End quote ---
Not on the Keysight. Try it. Unless you are on a slow timebase like 100ms where all the memory is used to fit the screen and it doesn't have any more to give. On 10us or under (which is where it goes to the max 5GS/s), if you press stop and then zoom out it will give you the extra data outside the display window.

--- End quote ---
Thats a "special" behaviour that is only on a minority of scopes. This has cropped up a few times:
https://www.eevblog.com/forum/testgear/new-keysight-scope-1st-march-2017/msg1125192/#msg1125192
https://www.eevblog.com/forum/testgear/new-tektronix-tbs2000-oscilloscopes/msg1282227/#msg1282227
and more recently:
https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg2895750/#msg2895750
--- End quote ---
Minority?
Surely it's the same on all Megazzom IV ASIC scopes?
1000, 2000, 3000, and 4000 series (maybe more?)
I've only tried my 3000T

--- End quote ---
There are many more scopes on the market than Keysight Megazoom units. But the point is that you don't magically get the full memory depth around a trigger, unless that happens to be a repetitive trigger falling within some (surprisingly narrow) circumstances. Rather than typing out the rather long explanation needed to explain when/how it happens I linked back to the existing posts.

For all megazoom "just works" automatic choices, some people see that as confusing or hard to force it to do exactly what they want, while others see it as eliminating unnecessary detail/traps. The memory depths are all over the place in different modes/channels/overlays. But they're always as long as practically possible, only overflowing the visible window under those "special" circumstances or by using single shot capture. As mentioned before I don't ever worry about the exact number of memory points, just check the sample rate and horizontal time will be sufficient to capture what I'm trying to look at.

--- End quote ---
Megazoom is the entirety of Keysights range under maybe $20k or more, so it's safe to say that a Megazoom scope is the Keysight scope that most people will buy.
--- End quote ---
Capturing samples outside the visible window reduces the theoretically achievable update rate, on scopes that let you control that its measurable and quite significant (https://www.eevblog.com/forum/testgear/new-tektronix-tbs2000-oscilloscopes/msg1283038/#msg1283038). The Keysight megazoom scopes do not capture all the data around the window, they only do a magic capture from run -> stop mode under quite specific circumstances.....

After pressing stop, another trigger must arrive within the next 100mS or so, but not before the several mS or so it takes to fill the pre trigger and overheads (varies depending on scope, mode, etc). Otherwise there is only the current visible window (plus a little extra margin sometimes). So many specifics and details, all of which may or may not apply to any particular use. Confusing! Not even specified or warranted behaviour. Certainly not:

--- Quote from: EEVblog on May 09, 2020, 05:02:26 am ---Unless you are on a slow timebase like 100ms where all the memory is used to fit the screen and it doesn't have any more to give. On 10us or under (which is where it goes to the max 5GS/s), if you press stop and then zoom out it will give you the extra data outside the display window.
--- End quote ---
Someone:

--- Quote from: Wuerstchenhund on May 09, 2020, 10:45:35 am ---Stuck with just three scopes at home  ;) I just tried to capture off screen with my Rigol DS1054z (firmware 00.04.04SP4) and guess what?

It doesn't let me go beyond the screen.

So it appears at least for the DS1000z the question if Nico's method would be possible should be answered with 'no'.
--- End quote ---
How bizarre, I was able to have that type of setup on an 1104Z:
https://www.eevblog.com/forum/testgear/new-tektronix-tbs2000-oscilloscopes/msg1283038/#msg1283038
2N3055:

--- Quote from: Martin72 on May 09, 2020, 10:53:40 am ---
--- Quote ---It doesn't let me go beyond the screen.
--- End quote ---

I´m not really sure ( as a former rigol owner), but the "bigger" MSO5000 couldn´t do that too.
Maybe a actual owner could test and report it here.


--- End quote ---

--- Quote from: Wuerstchenhund on May 09, 2020, 10:45:35 am ---Stuck with just three scopes at home  ;) I just tried to capture off screen with my Rigol DS1054z (firmware 00.04.04SP4) and guess what?

It doesn't let me go beyond the screen.

So it appears at least for the DS1000z the question if Nico's method would be possible should be answered with 'no'.

--- End quote ---

DS1000z behaves differently if you set it to AUTO or if you manually fix acquisition length.  One more thing to add to confusion.

But if you set to 24 MS length (1ch) it will get 24 MS every time, even if you set timebase to 5 ns/div.  But your retrigger rate will be the same as if you set timebase to 2ms/div (12divs, 24ms full screen).
Detail will be the same too, and it will do both at 1GS/s.  And with DS1000z , you don't even have to go into zoom mode. Timebase knob works even when stopped. So you capture at any timebase from 5ns/div to 2ms/div and get the same memory content and look at it with timebase knob and horizontal pos knob. Or you can use zoom if you like that.
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