General > General Technical Chat
How to trigger a combined signal
RAPo:
--- Quote from: nctnico on October 13, 2022, 05:59:10 pm ---Such a scope channel extender won't work for a dso because a dso can't display several traces simultaneously like a cro can (at least optically)
--- End quote ---
Did you see the video with the Rigol mso104? The crux is that the apparatus converts the 3 input signal into *one* output signal. So only one trace that embodies the input signals in its upper/middle/lower part.
Alex Eisenhut:
Is this supposed to be like "chop" mode on a CRT scope? It's usually only used for low frequency (whatever that may mean for a particular model). The scope just switches as fast as possible between inputs and puts the beam on the screen!
It triggers on whatever you want before the chop circuit AFAIK.
RAPo:
--- Quote from: Alex Eisenhut on October 14, 2022, 01:33:04 pm ---Is this supposed to be like "chop" mode on a CRT scope? It's usually only used for low frequency (whatever that may mean for a particular model). The scope just switches as fast as possible between inputs and puts the beam on the screen!
--- End quote ---
Yes it works in a similar way as far as I can tell.
--- Quote from: Alex Eisenhut on October 14, 2022, 01:33:04 pm ---It triggers on whatever you want before the chop circuit AFAIK.
--- End quote ---
No. If I look at the triggered output BNC, it shows (depending on the switch settings) the one-off original signals, the composite signal (the yellow trace) is not triggered even if I use the trig-out signal as an external trigger.
tom66:
The only way you could get a circuit like this to work is to have the scope sweeping fast enough that in the modes that use intensity grading the traces overlap. Generally that occurs once the timebase is much below one whole display frame (assuming the screen refreshes at 60Hz and 12 div horizontally, that starts to happen below 1ms/div)
However note that such modes give relatively poor performance for measurement functions etc and single shot modes will show one of the 3 different traces.
Really this does not work well with digital scopes due to how digital phosphor modes work, they behave only superficially like an analog scope does.
You still need to find some way to trigger the scope to the tracer's pulse output and you would not be able to trigger on the actual waves themselves, a quick think about how digital oscilloscopes manage pre and post trigger times will make that clear pretty quickly.
What you want to buy is an analog capture card of some kind, they often capture 16+ channels at one at low frequencies. You cannot do what you want for any reasonable real world application with a DSO. Sorry.
RAPo:
On an analogue scope, it is indeed easier.
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