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Oscilloscope Zoom Out Quirk

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nctnico:

--- Quote from: maginnovision on May 09, 2020, 09:23:11 pm ---
--- Quote from: nctnico on May 09, 2020, 09:02:40 pm ---
--- Quote from: maginnovision on May 09, 2020, 08:58:04 pm ---Yea, I've noticed(on the rtb) it's not uncommon to have data outside of the window even in auto memory.

--- End quote ---
I think R&S is using one of the fixed memory length selections and not an arbitrary length in auto memory mode.

--- End quote ---

It's possible they have steps in auto, I have seen odd numbers like 19.7M though. Also like egonotto most of the smaller memory sizes aren't user selectable. It seems like perhaps the auto selections are optimized for history/segmented memory modes.

--- End quote ---
That seems more likely indeed.

SilverSolder:

--- Quote from: Wuerstchenhund on May 09, 2020, 01:33:26 pm ---
--- Quote from: SilverSolder on May 09, 2020, 12:28:46 pm ---
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!  :D

--- End quote ---

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.

--- End quote ---

Agreed, you have to press STOP to catch the last triggered event of a running signal, or do a single shot.  Then, zooming out works.   (It doesn't work with signals triggered in NORMAL mode.)

The timebase has to be <=1ms on this particular scope or there is no extra data outside the screen area.  I guess the reason for that is that at 2ms, the entire memory is filled just by what is displayed on the screen.  (20ms * 200mSamples/sec = 4 Mbytes...  surprisingly, exactly the amount of RAM the scope has for analog acquisition!)

With two channels turned on...  the amount of memory is halved, effectively, so now there is no "unseen data" unless the timebase is <=2ms, instead of <=1ms.


rsjsouza:
I have used this in the past, and IIRC the old TDS3054 couldn't do it due to the puny memory it had. However I vaguely recall my old DS1102E doing a scrolling/zooming only on slower timebases, but my current DS4014 with its vast 140MS memory does that easily.

nctnico:

--- Quote from: SilverSolder on May 09, 2020, 12:28:46 pm ---
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!  :D

--- End quote ---
As a side note: it could be I have picked up this trick when using the 54622D or the (I think earlier) 54645D at one of my employers.

Someone:

--- Quote from: Wuerstchenhund on May 09, 2020, 12:05:04 pm ---
--- Quote from: 2N3055 on May 09, 2020, 11:54:36 am ---DS1000z behaves differently if you set it to AUTO or if you manually fix acquisition length. 
--- End quote ---

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


--- Quote ---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.

--- End quote ---

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

--- End quote ---
Yep, another of the corners for nctnico's atypical use case, rejection of zoom mode. You went with the obvious/logical use case!

Zoom mode adds one very important control that is missing when letting the scope expand around the visible window: you gain control of where the trigger is located within the full capture depth.

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