Products > Test Equipment
Oscilloscope Zoom Out Quirk
Someone:
--- Quote from: nctnico on May 10, 2020, 09:40:59 am ---And there is no less control over the trigger position; triggering works just fine. I don't care about how much data there is exactly at either sides of the trigger point as long as it is enough. The more memory an oscilloscope can use the lower the chance that it isn't enough.
--- End quote ---
When letting the memory depth define the size of the acquisition around the window and viewing the fast edge/information at the trigger point which you have insisted is so important to this corner case workflow, yes you have almost no control over the positioning of that extra memory.
[<------- acquisition ------- [ ---- trigger -----]------- acquisition ------->]
The trigger (while still being visible) can only be within the viewing window (not drawn to scale), roughly in the middle of the complete acquisition. If instead you use a zoomed window then the trigger can be placed anywhere within the acquisition depth while still keeping the trigger point visible:
[<-[ trigger ---------] ----------------------------- acquisition ----------->]
or
[<-------------- acquisition ----------------------------[--------- trigger]->]
etc
For someone who has gone on and on about certain scopes having less memory under different modes etc, potentially throwing away half your memory and claiming its completely under control is hypocrisy.
--- Quote from: nctnico on May 10, 2020, 09:40:59 am ---And I don't get how fast waveform updates suddenly become relevant in this thread; capturing beyond the screen has no downsides. Just set the memory shorter one way or another and you have more waveforms/s and/or history / segmented recording.
--- End quote ---
Waveform update rate is limited by letting the acquisition length expand around the visible window, to claim there is no downside in doing so is plainly ridiculous. You like having manual control of memory depth and it expanding around the screen, we keep hearing this and get it, but your justifications are nonsense, and you throw it out as some big issue when it really isn't.
--- Quote from: nctnico on May 10, 2020, 09:40:59 am ---Perhaps you should read more careful... there are at least 3 others which use an oscilloscope the same way.
--- End quote ---
Enjoy your confirmation bias, perhaps you'd find solace with the flat earthers: https://forum.tfes.org
nfmax:
--- Quote from: EEVblog on May 10, 2020, 10:56:35 am ---
--- Quote from: nctnico on May 10, 2020, 09:40:59 am ---And I don't get how fast waveform updates suddenly become relevant in this thread; capturing beyond the screen has no downsides.
--- End quote ---
It's only relevant if designing in this feature was done at the sacrifice of update rate in the design.
Obviously with Keysight having the fastest update rate and having this feature, that's obviously not a trade off that needs to be made in basic scope design.
--- End quote ---
But that only works because when you press Stop, the Keysight scopes make one last acquisition using the maximum available memory (providing a trigger arrives in time). It's a neat trick, and it does work.
KE5FX:
--- Quote from: EEVblog on May 10, 2020, 10:56:35 am ---
--- Quote from: nctnico on May 10, 2020, 09:40:59 am ---And I don't get how fast waveform updates suddenly become relevant in this thread; capturing beyond the screen has no downsides.
--- End quote ---
It's only relevant if designing in this feature was done at the sacrifice of update rate in the design.
Obviously with Keysight having the fastest update rate and having this feature, that's obviously not a trade off that needs to be made in basic scope design.
--- End quote ---
Unless they patented it.
This kind of thing is the USPTO's bread and butter. "We claim: 1. A digital oscilloscope that doesn't suck."
EEVblog:
--- Quote from: 2N3055 on May 09, 2020, 05:06:53 pm ---This shows what I'we been explaining. 3000T is capturing only screen full of data from trigger to trigger. It is only when you press stop that it will reassemble some data before begin of the screen, and it will keep capturing until it runs after memory. What I suspect is that it literally goes from RUN to STOP, by capturing one SINGLE capture on next trigger after you press STOP (Just with half of the buffer because of state of capture engine at the time, the ping-pong buffers).
I presume it behaves like that, because, if press stop now, while it's waiting for next trigger, it doesn't get any additional data:
(Attachment Link)
--- End quote ---
That sounds right. It's doing just the screen worth in Normal or Auto mode because it needs the fastest update rate possible. There is no point capturing continuous updating data outside the screen if the user can't see it.
So yes, doesn't surprise me that this only works in STOP or Single mode, because these modes are, practically by their usage definition, analysis modes were you may want to expand the timebase to view that extra data. So when the scope has been instructed perform STOP or Single mode it makes sense to then capture the entire available memory length regardless of what the user has set, because update rate no longer has any relevance.
Come to think of it this way now, there should be absolutely no reason why the likes of Siglent could not implement this easily with a firmware update. The likely reason they haven't is because they just haven't thought of it before.
To summarise, I think STOP mode or Single Mode should ultislise all available hardware memory regardless of current memory setting and at the fastest sample rate. This is clearly what Keysight have opted to do.
And perhaps that's a better description of this issue, "Capture memory depth in STOP/Single mode".
Someone:
--- Quote from: EEVblog on May 10, 2020, 10:56:35 am ---
--- Quote from: nctnico on May 10, 2020, 09:40:59 am ---And I don't get how fast waveform updates suddenly become relevant in this thread; capturing beyond the screen has no downsides.
--- End quote ---
It's only relevant if designing in this feature was done at the sacrifice of update rate in the design.
Obviously with Keysight having the fastest update rate and having this feature, that's obviously not a trade off that needs to be made in basic scope design.
--- End quote ---
Except they are mutually exclusive, the bonus full length capture of the megazoom scopes only occurs when there is another trigger after pressing stop. If you're trying to capture long record lengths of short bursts between infrequent events, pressing stop won't help.
All that extra memory around the aquisition window kills waveform update rates (a tradeoff which is completely acceptable for some uses). Here is the plot from a Tek DPO4000:
Extending the acquisition buffer each side of the trigger outside the window on the screen is shown with dotted lines toward the right. It knocks orders of magnitude off the update rate.
Although there are more intelligent memory management options, scopes are rather simple/dumb. They won't redraw/paint another trigger until the full memory depth is filled. So at 5GS/s and 10M memory depth, even a perfect zero overhead, instant trigger will only run 500 updates/s.
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