Products > Test Equipment
Oscilloscope Zoom Out Quirk
nfmax:
--- Quote from: SilverSolder on May 11, 2020, 01:45:09 am ---
--- Quote from: nfmax on May 10, 2020, 04:18:37 pm ---
--- Quote from: nfmax on May 10, 2020, 01:31:14 pm ---
--- 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.
--- End quote ---
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.
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I can confirm the X3000T works in the same way, in Stop/Single mode. If there is off-screen captured data, you can use the horizontal controls in ordinary mode to bring it on screen, then use the zoom mode to zoom in on the displayed part.
One more wrinkle: you only get off-screen data from the 'magic' last capture in Stop/Single mode if the ADC sample rate is 5GHz (with one channel of each pair active). Presumably, if the sample rate is any lower, all the available memory is in use anyway.
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You might get "off screen data" again if you increase the horizontal speed by 1 step compared with using 1 channel. (That is how it works on the 54622D.)
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I didn't check but I think you are right, that is how Megazoom works. The guiding principles seem to be:
* Memory control is automatic, and the scope will always use as much of the available memory as it can, subject to not compromising the waveform update rate
* If memory is available, it is used first to provide the highest possible sample rate (this is what I mean by 'designed to zoom in')
* If the ADC is running at maximum speed, memory is used to provide off-screen capture (like it was in the very earliest days of DSOs with more than one screensworth of memory), but this only happens on transition to Stop/Single modeYou will only get off-screen capture at the faster X scale settings. The switchover point depends on the memory size & ADC speed. The MZ4 scopes like the X3000T have a relatively short memory and a fast ADC (4Mpoints/5gsps), so the switchover happens at much faster X scale than it did with the 54645D which @nctnico mentioned he was using when he developed his technique (1Mpoints/200Msps). With the latest MXR scope the balance is swinging back the other way - 400Mpoints/16Gsps. As soon as I can borrow one of these I will check its behaviour & report back ;).
However, instead of using 'spare' memory for off screen capture, I rather like the Siglent technique of keeping a history of previous acquisitions you can go back and look at - I'm always too slow pressing Stop when soemthing happens!
nfmax:
--- Quote from: tautech on May 10, 2020, 11:03:20 pm ---
While it is true many lost cost DSO's with Zoom mode only provide a 50/50 split of the display do indeed limit usability while upper entry level DSOs provide a much better split ratio where buyers of which are more accustomed to not needing so much visual reference of the primary timebase when in fact they want a larger zoomed timebase which is what they primarily work with.
--- End quote ---
You don't need to use the zoom function (split window view) at all if you don't want to. In the absence of triggers, or in Stop/Single mode, the horizontal scale & position controls will let you zoom in & out to the full extent of the captured data.
Someone:
--- Quote from: nfmax on May 11, 2020, 07:50:17 am ---
--- Quote from: tautech on May 10, 2020, 11:03:20 pm ---While it is true many lost cost DSO's with Zoom mode only provide a 50/50 split of the display do indeed limit usability while upper entry level DSOs provide a much better split ratio where buyers of which are more accustomed to not needing so much visual reference of the primary timebase when in fact they want a larger zoomed timebase which is what they primarily work with.
--- End quote ---
You don't need to use the zoom function (split window view) at all if you don't want to. In the absence of triggers, or in Stop/Single mode, the horizontal scale & position controls will let you zoom in & out to the full extent of the captured data.
--- End quote ---
Yes, but using a zoom window you can see both long and short time details at the same time without having to adjust or move anything. If you have more flexibility in how to allocate traces and screen space to such windows then all the better.
Both useful approaches depending on the specific circumstances.
tautech:
--- Quote from: nfmax on May 11, 2020, 07:50:17 am ---
--- Quote from: tautech on May 10, 2020, 11:03:20 pm ---
While it is true many lost cost DSO's with Zoom mode only provide a 50/50 split of the display do indeed limit usability while upper entry level DSOs provide a much better split ratio where buyers of which are more accustomed to not needing so much visual reference of the primary timebase when in fact they want a larger zoomed timebase which is what they primarily work with.
--- End quote ---
You don't need to use the zoom function (split window view) at all if you don't want to.
--- End quote ---
Of course not however it gives the fullest pre and post trigger capture which in the case of a deep memory DSO could be 100+ Mpts before and after the trigger.
nfmax:
--- Quote from: tautech on May 11, 2020, 08:41:06 am ---
--- Quote from: nfmax on May 11, 2020, 07:50:17 am ---
--- Quote from: tautech on May 10, 2020, 11:03:20 pm ---
While it is true many lost cost DSO's with Zoom mode only provide a 50/50 split of the display do indeed limit usability while upper entry level DSOs provide a much better split ratio where buyers of which are more accustomed to not needing so much visual reference of the primary timebase when in fact they want a larger zoomed timebase which is what they primarily work with.
--- End quote ---
You don't need to use the zoom function (split window view) at all if you don't want to.
--- End quote ---
Of course not however it gives the fullest pre and post trigger capture which in the case of a deep memory DSO could be 100+ Mpts before and after the trigger.
--- End quote ---
Maybe that is the case on Siglent scopes, but on InfiniVision scopes it is nothing more than a different view of the same data, after capture. You can always set the trigger delay to whatever you need, before or after the trigger event. The actual trigger event doesn't even have to be included in the capture at all, if that is what you want.
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