Oscilloscope Zoom Out Quirk

[2N3055]

Yet it's arguably DSO user error when any capture is required that an appropriate timebase was not previously selected.

No. I'm talking about legitimately setting the timebase to capture the thing you wanted, no user error. Then perhaps you saw something unexpected and though "gee I wonder what happened before or after that".

I understand what are you saying, but when working on, say,  CAN bus, what are the chances you will happen to capture exactly packet with error if you looking at single edge? You don't capture that way looking at that kind of data. You use larger time period, with hundreds of packets and then search and scroll and zoom in and out.

You can't say you understand what I'm saying then immediately go into an example where it's not going to be of value. That is completely opposite to my point!
I'll repeat, there is no logical argument you can make to say that this isn't a potentially useful feature in some circumstances.

I wasn't trying to nullify your point, but as an reply to your hypothetical scenario, i simply gave you real scenario that is source of my opinion. I apologize if it came out as adversarial, it was not meant to be... I'm passionate about things, same as you, and sometimes it gets better of me.
I will also repeat (i understand you cannot read everything) that I repeated few times that I can see how it can be useful and that I even do that on occasion. But I don't rely on it as a important technique.
I'm not against it per se, but I don't think it's a big deal...

[2N3055]

Doesn't capturing data outside the display window => more time to capture data => less waveform updates per second?

Yes, which is why "automatic" memory depth usually defaults to the shortest record that will fill the screen.

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.

True. If you stop it will give you exactly 40 us before trigger point, and 360 us after trigger point at 5 GS/s sample rate.

[2N3055]

So when nctnico says a scope can't do this very specific (and not fully explained) thing, just ignore it. Because with only a tiny change to any part of the application or acceptable solution, just about any scope will do the job.

Yeah, but he's not wrong.
It's an interesting and demonstrably potentially useful benefit.

But nctnico is wrong to generalise it as something other scopes can't do, because they can but in subtly different ways. Its a very narrow (and poorly/not defined) example to try and push some point like the marketing "comparisons" people keep laughing at.

The case of slow and infrequent triggers allows that type of use, and impedes/prevents acquisition of more rapid events (or they get lost in the long capture). Its a simple tradeoff (or "trap" as you might embellish it) that is chosen for the specific setting.

The inflammatory nature of this discussion has been the refusal of nctnico to acknowledge either the narrow applicability of the use case, or that it can be achieved by using a zoom window/view, or other methods.

Its a massive blow up over different methods to set the memory depth (auto vs manual vs implicit vs explicit).

At one previous discussion, he actually admitted that it is same result as using proper time base/ zoom,  but that he does this because he dislikes zoom and how it takes up screen real estate.  What he does mimics  "full screen zoom" and if manufacturers would make "full screen zoom" mode that would be it..

[EEVblog]

But since we are here I can make a list with oscilloscope brands which support recording beyond the screen (or not):
GW Instek: yes
Keysight: older models: yes, newer models: single mode only

The Keysight Megazoom IV does it in both STOP and single shot mode.

[EEVblog]

I'm not against it per se, but I don't think it's a big deal...

I agree, it's not a big deal, and I certainly wouldn't make a purchase decision based on it. It's just an interesting "feature".
Probably video worthy!

[Gandalf_Sr]

I vaguely recall that this whole subject started (and then got carved off to a new thread by Dave) because a poster said something to the effect - "this scope doesn't work the way I expect it to and therefore nobody should buy one" - and that was (rightfully IMHO) jumped upon as being unreasonable.

What has followed has been a (somewhat heated) discussion that has given me valuable information in that some scopes actually capture more data than you would actually expect and it's useful to know that when you're looking for obscure data or glitches.

I brought up the (Monty Python) argument reference because, at some point in the sketch one of the men says "An argument is a connected series of statements intended to establish a proposition" which seemed apposite at the time but, in this case, there's no clear right or wrong answer.

It seems to me that different scope manufacturers approach data capture in subtlety different ways and that leaves some people surprised (or irate) when they try out a new brand/model of scope and find that it doesn't work the way they expect it to.

Thanks to all here who've gone to such great lengths to explain in detail how data capture and memory filling actually works and how to leverage it to our advantage.

[EEVblog]

Doesn't capturing data outside the display window => more time to capture data => less waveform updates per second?

Yes, which is why "automatic" memory depth usually defaults to the shortest record that will fill the screen.

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.

Thats a "special" behaviour that is only on a minority of scopes.

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

[Wuerstchenhund]

What does it mean? Well, when you're on 1ns/div, you get 40000x length worth of data than what is on your screen (10ns to 400us) if you stop it. If you are at 20us/div you get only 2x (200us to 400us).
And from that point on sample rate goes down, and game repeats, changing ratio "screen/stopped capture length" all the time. I guess table could be compiled. It's just I couldn't care less.
I'm not going to base my work based on side-effects of sample engine architecture..

So if you captured something and then thought "gee I wonder what's either side of that, and you knew your scope worked like this, you'd actually rather re-capture instead of just changing the timebase?
That's kinda, well, silly.
If your answer is yes I would, then what happens if your capture was infrequent and wasn't easy to reproduce?
Sorry but I can't see a way to successfully argue this isn't a potentially useful feature.

The thing is that if recording beyond your screen on short timebases was really such a useful feature then the question for me would be why this isn't a standard feature in scopes? It's not difficult to implement after all. Rigol has done it, although I'm sure it probably down to just using a simplistic system of managing memory than to actual intention. But they not even use it for marketing. In fact, I can't remember that any scope manufacturer has ever promoted being able to "zoom out" as one their core features. While even current marketing material still bangs on about being able to "zoom in" on details. And this when all manufacturers are looking for ways to differentiate themselves from the competition. An oversight?

I don't believe so. As I said, I've never came across of any engineer even asking for this feature - aside Nico of course.

It's so interesting it's probably worthy of a video.

II believe it is. Because while I can see where it comes from I still fail to see any advantage to this method, so a video might help. 

But since we are here I can make a list with oscilloscope brands which support recording beyond the screen (or not):

GW Instek: yes
Keysight: older models: yes, newer models: single mode only
Lecroy: no
MicSig: yes
Rigol: yes
Siglent: no
Tektronix: yes
Yokogawa: ?

Why don't you list specific models instead? This would make much more sense than a vague list of manufacturers of which most have had decades of different products which may or may not all behave the same.
 
Because if it's by manufacturers only then I guess Siglent would need a "yes" because if I remember right the very early models (CL? CML?) could be set to record beyond the screen when set to long memory (which, as with Rigol, very likely down to the primitive memory management and not really intentional).

Same thing goes for Tek, because as far as I am aware (well I'm at home now and can't check) it's only the scope models which have Auto-Magnify which fully support your method, which if I remember right is limited to the MDO Series (although the old DPO2k/3k may also have had it). Outside that, I think that there are also some models which run a full length acquisition only on the last acquisition after pressing STOP or in SINGLE, like the Keysight scopes.

And which Keysight "older models" are supposed to support this outside SINGLE mode/STOP? And what about the different Infiniiums? Or the 54700 Series?

And no mention of R&S? Can't check but I don't think they let you sample beyond the screen on short timebases either. Is it supported by the RTM1000? RTM2000? RTM3000? What about the two generations of RTO? I vaguely remember trying once to capture beyond the screen on the RTM1054 and it failed.

Since there doesn't seem to be many who specifically ask for that feature in a scope it would help if you could list some actual *models* that support it (which I'm sure you know it appears you wouldn't buy a scope which doesn't). Because my gut feeling is (can't say for sure because we don't usually test for that kind of thing, simply because no-one has ever asked for it) you will find that this is not widely supported.

[Someone]

So when nctnico says a scope can't do this very specific (and not fully explained) thing, just ignore it. Because with only a tiny change to any part of the application or acceptable solution, just about any scope will do the job.

Yeah, but he's not wrong.
It's an interesting and demonstrably potentially useful benefit.

But nctnico is wrong to generalise it as something other scopes can't do, because they can but in subtly different ways. Its a very narrow (and poorly/not defined) example to try and push some point like the marketing "comparisons" people keep laughing at.

The case of slow and infrequent triggers allows that type of use, and impedes/prevents acquisition of more rapid events (or they get lost in the long capture). Its a simple tradeoff (or "trap" as you might embellish it) that is chosen for the specific setting.

The inflammatory nature of this discussion has been the refusal of nctnico to acknowledge either the narrow applicability of the use case, or that it can be achieved by using a zoom window/view, or other methods.

Its a massive blow up over different methods to set the memory depth (auto vs manual vs implicit vs explicit).

At one previous discussion, he actually admitted that it is same result as using proper time base/ zoom,  but that he does this because he dislikes zoom and how it takes up screen real estate.  What he does mimics  "full screen zoom" and if manufacturers would make "full screen zoom" mode that would be it..

Here is the "seed" for this event:

To the OP: Regarding the Siglent: one thing to watch out for is that it uses a different memory management compared to the Tektronix you are used to; Siglent typically cuts the memory short to have just enough samples to fit the screen. This has to match your usage. For me this kind of memory management is a hard fail. All in all it still is a good idea to compare several scopes yourself.

Given the OP had another Siglent scope and had mentioned using an MDO3000 in the past its possibly a bit alarmist. Nothing in there about it being a very specific workflow for a corner case and other ways to do the same thing.

[tautech]

Nothing in there about it being a very specific workflow for a corner case and other ways to do the same thing.

Add, universally....that works will all DSO's.

Heavens, what are we attempting to teach future engineers......walk into most any EE establishment and tell them they should be zooming out captures as part of their workflow.....expect to get laughed out of the place !

[Someone]

But since we are here I can make a list with oscilloscope brands which support recording beyond the screen (or not):

GW Instek: yes
Keysight: older models: yes, newer models: single mode only
Lecroy: no
MicSig: yes
Rigol: yes
Siglent: no
Tektronix: yes
Yokogawa: ?

Why don't you list specific models instead? This would make much more sense than a vague list of manufacturers of which most have had decades of different products which may or may not all behave the same.
 
Because if it's by manufacturers only then I guess Siglent would need a "yes" because if I remember right the very early models (CL? CML?) could be set to record beyond the screen when set to long memory (which, as with Rigol, very likely down to the primitive memory management and not really intentional).

Same thing goes for Tek, because as far as I am aware (well I'm at home now and can't check) it's only the scope models which have Auto-Magnify which fully support your method, which if I remember right is limited to the MDO Series (although the old DPO2k/3k may also have had it). Outside that, I think that there are also some models which run a full length acquisition only on the last acquisition after pressing STOP or in SINGLE, like the Keysight scopes.

And which Keysight "older models" are supposed to support this outside SINGLE mode/STOP? And what about the different Infiniiums? Or the 54700 Series?

And no mention of R&S? Can't check but I don't think they let you sample beyond the screen on short timebases either. Is it supported by the RTM1000? RTM2000? RTM3000? What about the two generations of RTO? I vaguely remember trying once to capture beyond the screen on the RTM1054 and it failed.

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).

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?).

[Someone]

Doesn't capturing data outside the display window => more time to capture data => less waveform updates per second?

Yes, which is why "automatic" memory depth usually defaults to the shortest record that will fill the screen.

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.

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

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

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.

[Someone]

Bumping around a couple of different manufacturers manuals, something looked rather similar....

guess the two brands!

[Wuerstchenhund]

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'.

[EEVblog]

There are many more scopes on the market than Keysight Megazoom units.

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.

[Wuerstchenhund]

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).

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

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?).

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]

It doesn't let me go beyond the screen.

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]

There are many more scopes on the market than Keysight Megazoom units.

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.

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:

Doesn't capturing data outside the display window => more time to capture data => less waveform updates per second?

Yes, which is why "automatic" memory depth usually defaults to the shortest record that will fill the screen.

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.

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

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

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.

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.

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:

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.

[Someone]

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'.

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]

It doesn't let me go beyond the screen.

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.

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'.

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.

[Wuerstchenhund]

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'.

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

Maybe it was fixed (broken? ) in one of the recent firmware updates.

[2N3055]

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'.

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

Maybe it was fixed (broken? ) in one of the recent firmware updates.

Unfortunately, I don't have DS1000Z anymore to check... But what I remember it did behave like Someone says..

[Wuerstchenhund]

DS1000z behaves differently if you set it to AUTO or if you manually fix acquisition length. 

I tried both, didn't made a difference. I could not zoom out beyond the screen data.

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.

Maybe that's it, I used the zoom function.

I'll try later with just going to STOP and just twiddling the timebase knob.

Update: I tried just changing the timebase, and with the memory set to manual it did indeed show the full 24Mpts. I did note some artifacts which aren't in the signal, though, so I'm not sure if this behavior is intentional

[SilverSolder]

I didn't realize this was so contentious?  -  on my old Agilent 54622D megazoom,  I take it completely for granted that you can zoom both in and out (provided the horizontal speed is high enough) and I use it all the time when exploring new waveforms where it is hard to say what is going to be the best timebase - I thought this is just one of the many awesome convenience advantages of a digital scope! 

[Wuerstchenhund]

I didn't realize this was so contentious?  -  on my old Agilent 54622D megazoom,  I take it completely for granted that you can zoom both in and out (provided the horizontal speed is high enough) and I use it all the time when exploring new waveforms where it is hard to say what is going to be the best timebase - I thought this is just one of the many awesome convenience advantages of a digital scope! 

I no longer have a 54622D but I don't think it worked any different than all the InfiniVision scopes - they only use the max available memory on short timebases if you're either in SINGLE or on the last acquisition after pressing STOP.

It's *not* about just changing the timebase to change the time period displayed on screen.