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| Oscilloscope Zoom Out Quirk |
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| 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:
--- 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. --- 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 |
| Wuerstchenhund:
--- Quote from: EEVblog on May 09, 2020, 12:09:51 am --- --- Quote from: 2N3055 on May 08, 2020, 04:32:26 pm ---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.. --- End quote --- 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. --- End quote --- 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. --- Quote ---It's so interesting it's probably worthy of a video. --- End quote --- 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. :-+ --- Quote from: nctnico on May 09, 2020, 08:33:33 am ---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: ? --- End quote --- 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:
--- Quote from: 2N3055 on May 09, 2020, 08:56:58 am --- --- Quote from: Someone on May 09, 2020, 02:35:24 am --- --- Quote from: EEVblog on May 09, 2020, 12:02:53 am --- --- Quote from: Someone on May 08, 2020, 11:59:42 pm ---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. --- End quote --- Yeah, but he's not wrong. It's an interesting and demonstrably potentially useful benefit. --- End quote --- 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). --- End quote --- 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.. --- End quote --- Here is the "seed" for this event: --- Quote from: nctnico on May 06, 2020, 08:30:42 pm ---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. --- End quote --- 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:
--- Quote from: Someone on May 09, 2020, 09:45:38 am --- Nothing in there about it being a very specific workflow for a corner case and other ways to do the same thing. --- End quote --- 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 ! |
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