Products > Test Equipment
Oscilloscope Zoom Out Quirk
EEVblog:
--- Quote from: nfmax on May 10, 2020, 11:58:10 am ---I think zoom windows are a bit of a distraction here.
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I agree. No need to complicate the operational understanding here.
nfmax:
--- Quote from: Wuerstchenhund on May 10, 2020, 12:04:21 pm ---Take the Rigol DS1000z. We now established that, if you set the memory to manual then it will always record the full selected memory size, no matter what. Great, right? :-+
But here's the thing: on the DS1000z at least, you can't always access that data. In RUN mode, if you switch to zoom mode, you can still only zoom *in* on the signal on screen, but not zoom *out* to look at off-screen data.
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On the DSO1014A (a Rigol design), with Zoom off, in Run mode, but with no triggers happening, you can use the horizontal scale & position knobs to move the displayed trace around within the offscreen captured data, and change the displayed duration. If you then turn Zoom on, you get a zoomed view of the currently displayed part of the captured data, even if it was originally off screen. The horizontal scale & position knobs change mode to operate as zoom and pan within the displayed window. Turn off Zoom and you can move to a different part of the captured data, rinse & repeat.
This could actually be quite useful: I didn't know you could do this! Do the more recent Rigols work in the same way? I'll check the X3000T as well now, I'm intrigued.
Wuerstchenhund:
--- Quote from: nctnico on May 10, 2020, 12:22:49 pm ---
--- Quote from: Wuerstchenhund on May 10, 2020, 12:04:21 pm ---Personally, it also doesn't fit me because it sounds a bit arbitrary (like blindly poking around in some circuitry), as I tend to think about what I want to measure and what I expect to see, and then setup the scope accordingly. But that's just me (although most of our engineers are the same "think before you do" types). But hey, whatever fits you best.
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But you don't know what you don't know. If you are looking for a bug you start with a blank slate. So how are you going to setup your scope if you don't know what you are looking for?
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You never start from a blank slate. For a start, you need to have some idea as to what the spectral content of the signal is, because that determines your scope BW.
You also need to have some idea as to the voltage levels, as you need this to select suitable probes and prevent damage to your scope and your human body.
Furthermore, you normally should have some rough idea what the UUT (i.e. a PCB) does, which gives you some hints as to what kind of signals (AC? DC? Discretes? Serial comms? Parallel comms?) you can expect to find. If you don't know then you have a closer look to get an idea what this thing actually is (although I believe it's pretty rare you're asked to probe something of which you don't know what it is).
Now when you identified what that thing on your bench does and you have an idea what kind of signals you expect, what the voltage levels are, and the approx frequency band, but still don't know what exactly the signal will be, you set your deep memory scope to a long timebase (as long as it makes sense, i.e. as long as the period of the slowest signal you could reasonably expect to see) and start capturing.
You'll quickly see if it's just DC, some AC, or if the signal looks more complex (like a Discrete or serial comms packet). If it's the latter then you can use zoom to look closer, get the different parameters for some of the level shifts, and if you don't already recognize a specific pattern then use the measurements to compare with the in-spec parameters for the type of signals that could reasonably be found on this UUT.
Or you try the serial decoders and see if they come up with sensible data.
In any case, a methodological, stepped investigative approach is usually the best approach.
Besides, I doubt it's very common for an engineer to get some UUT you really know nothing about and get told "measure something" ;)
But in any case, capturing long makes it easy to quickly assess different parts of the signal.
--- Quote ---If you already know what a signal looks like there is no use measuring it.
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So in your view things like interference or spec compliance (which usually needs to be demonstrated by measurements) doesn't exist?
There are many reasons why you want to measure signals, even if you know how it looks like.
--- Quote ---And there are also cases where it is just quicker to capture something visually rather than setting up a complex trigger condition. Remember my way of working stems from saving time & effort.
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You stated this repeatedly but I'm sorry it doesn't make sense (and as we already established, there is no difference in trigger config between your method and the standard äcquire long and zoom in" method). You're not saving time and effort, all you do is to go to extreme lengths to avoid using the zoom function, and as a result you make do with various limitations, all which can be avoided with the standard method.
The only "time saving" I could possible see is that, with your method, you don't spend time thinking about what you actually want to do, but which bites you in the backside later because of the additional things you need to do to when you find out that you ran into a dead end, and you have to reconfigure your tools to get the information you want, all which the standard method would very likely have given you anyways.
But at the end of the day, and from a professional angle, even if your method would save 10 button presses over the standard method, it wouldn't matter one bit. First of all, we don't sit next to our engineers with stop watches, so this isn't captured, and even if an engineer would have to to this 100x a day the impact on any timelines and schedules would be neglegible. Our engineers get the bucks to do engineering (i.e. to work on cutting edge technology), and how they do this is up to them (aside from standard and specs we don't dictate methodology engineers use for scoping, although there are regular exchanges to discuss test methodology to find out what we can do better). So far, no-one has ever asked for something like you describe. Go figure.
Wuerstchenhund:
--- Quote from: nctnico on May 10, 2020, 12:40:20 pm ---
--- Quote from: Wuerstchenhund on May 10, 2020, 12:24:23 pm ---I agree, this is just a case of a poor UI on a particular scope, not a problem that's inherent to zoom as a function.
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It is not; I'm using all DSOs like this.
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You can't, because clearly not all scopes even allow you to use your method.
--- Quote ---Like several others you are trying to argue less is somehow more while grasping at straws no thicker than a hair trying to ridcule me. Just give up.
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So you're arguing that if the zoom window on a scope is too small that this is something other than a UX/screen size problem?
Wuerstchenhund:
--- Quote from: nfmax on May 10, 2020, 01:31:14 pm ---On the DSO1014A (a Rigol design), with Zoom off, in Run mode, but with no triggers happening, you can use the horizontal scale & position knobs to move the displayed trace around within the offscreen captured data, and change the displayed duration. If you then turn Zoom on, you get a zoomed view of the currently displayed part of the captured data, even if it was originally off screen.
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Well, it's a work-around. You first change the actual timebase ("zoom out") which then becomes the new in-screen signal part, and then use zoom to "zoom in"to that new "in-screen" data.
What you are doing is essentially using the standard method ("capture long and zoom in") but add another step (capture short but also outside the screen, then change to a long timebase) which, essentially, adds nothing over if you just had captured long and then zoomed in in the first place :-DD
And your scope must still be on hold, i.e. not get re-triggered, or your method doesn't work.
--- Quote ---The horizontal scale & position knobs change mode to operate as zoom and pan within the displayed window. Turn off Zoom and you can move to a different part of the captured data, rinse & repeat.
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I think that would work on the DS1000z as well, but as I said it all adds up with extra steps with no actual benefit.
--- Quote ---This could actually be quite useful: I didn't know you could do this! Do the more recent Rigols work in the same way? I'll check the X3000T as well now, I'm intrigued.
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Again, it's not really useful ifyou think about it, but if you prefer this method why not ;)
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