Author Topic: Oscilloscope-non alternating between channels type  (Read 1287 times)

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Offline simon christo

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Oscilloscope-non alternating between channels type
« on: April 30, 2019, 03:49:17 am »
Hi again.Regarding my Oscilloscope question, I meant a type that if it says 2Gs/s per channel it is always that no matter how many channels you are on.Thanks Simon.
 

Online DaJMasta

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Re: Oscilloscope-non alternating between channels type
« Reply #1 on: April 30, 2019, 04:07:21 am »
Probably better to keep it in the same thread, but there are lots of scopes that do this, but it depends on the architecture.  It's common to have two ADCs and interleave the inputs so that you run all four channels at half sample rate or two channels at full sample rate, but not every scope does it, and if you need 2GS/s on all four channels, you can either look for a scope that has 4 ADCs and does not change the sample rate with number of channels, or you just look for a scope with a high enough sample rate that halving it still meets your requirement (like getting a 5GS/s scope that still does halve sample rate with all channels enabled).

I wrote that thinking a 4 channel scope, but the same principle applies to choosing a two channel scope.
 

Offline simon christo

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Re: Oscilloscope-non alternating between channels type
« Reply #2 on: May 01, 2019, 03:16:24 am »
Hi there again.OK, how many scopes can trigger on any or all channels and display all channels on a single shot?
My Oscilloscope is a rebadged UNI-TREND (40Mhz 500MS/s) and it does'nt display all channels on a single shot.
I'd say if it can't display ALL channels on a single shot, then it definetly will have troubles showing a REAL-TIME
signal on NORM or AUTO mode.
   I can see it would be possible to 'interleave' the signal at the output of the A-D converter, but this would
require quite a lot of 'Sample and Hold' memory - but it would be quite possible.Anyway my TENMA won't do it.
This is why I'm looking for a better CRO.What I'm really asking is whether the CRO can trigger of ANY or ALL the inputs
(which ever is first), and then display ALL the traces simultaneously on the fastest timebase at the same sweep.
I'd be interested if any of the latest SCOPES can do this using 1 ADC's for 2 channels or 2 ADC's for 4 channnels
as I would say it could be possible.But as I've said before, my TENMA does a complete full screen sweep, and then
another full screen sweep, making it totally not suitable for testing for High-Speed Real-Time signals between
channels.Thanks again.Simon.
 

Offline maginnovision

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Re: Oscilloscope-non alternating between channels type
« Reply #3 on: May 01, 2019, 03:20:49 am »
I'm so confused. Your scope will only display a single channels waveform if you do single shot?
 

Offline extide

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Re: Oscilloscope-non alternating between channels type
« Reply #4 on: May 01, 2019, 03:38:16 am »
So typically a scope can only trigger from one source at a time, but when that trigger happens it will capture and display data from all of the enabled channels at the same time. In fact I haven't ever heard of a scope that would trigger from multiple sources at the same time and thinking about it I don't think that would be a very useful feature anyways.
 

Offline simon christo

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Re: Oscilloscope-non alternating between channels type
« Reply #5 on: May 01, 2019, 09:08:50 am »
Yes that's right, my CRO displays only one trace for a single shot.It only can trigger from ALL or either input, depending on the settings.
This is why I want to make sure it can trigger and display simultaneously all the traces interlaced.Thanks Simon.
 

Offline StillTrying

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Re: Oscilloscope-non alternating between channels type
« Reply #6 on: May 01, 2019, 10:48:40 am »
Yes that's right, my CRO displays only one trace for a single shot.It only can trigger from ALL or either input, depending on the settings.

Could ALL stand for Alternate, even though misspelt and makes little sense on a DSO. :-//

Triggering off either channel should show both traces in single captures.

I can see it would be possible to 'interleave' the signal at the output of the A-D converter, but this would
require quite a lot of 'Sample and Hold' memory - but it would be quite possible.Anyway my TENMA won't do it.

Normally on a 500Msa/s scope the ADC is internally 2 250Msa/s ADCs, they're interleaved to make 1 CH up to 500Msa, for 2 CH each has its own 250Msa ADC. Perhaps it not normal. :)

TENMA 72-8225  It's a pain when the vital info is in another thread!
« Last Edit: May 01, 2019, 11:02:21 am by StillTrying »
CML+  That took much longer than I thought it would.
 

Offline nctnico

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Re: Oscilloscope-non alternating between channels type
« Reply #7 on: May 01, 2019, 11:36:46 am »
So typically a scope can only trigger from one source at a time, but when that trigger happens it will capture and display data from all of the enabled channels at the same time. In fact I haven't ever heard of a scope that would trigger from multiple sources at the same time and thinking about it I don't think that would be a very useful feature anyways.
Not true and not true. The feature is called alternate triggering and can be found on some DSOs (GW Instek for sure). It is handy to show signals which have different frequencies but still have some relation. But you have to realise that the oscilloscope will make seperate acquisitions for each channel so the data on the screen is not from the same time.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline simon christo

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Re: Oscilloscope-non alternating between channels type
« Reply #8 on: May 02, 2019, 02:27:11 am »
I've got my eyes on a Keysight, Tektronix or Rhodes & Shawz.I should be happy with that sort of selection.Thanks Simon.
 

Offline extide

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Re: Oscilloscope-non alternating between channels type
« Reply #9 on: May 02, 2019, 03:36:36 am »
Not true and not true. The feature is called alternate triggering and can be found on some DSOs (GW Instek for sure). It is handy to show signals which have different frequencies but still have some relation. But you have to realise that the oscilloscope will make seperate acquisitions for each channel so the data on the screen is not from the same time.

Interesting, I guess that makes sense. Good to know!
 

Online tautech

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Re: Oscilloscope-non alternating between channels type
« Reply #10 on: May 02, 2019, 03:42:40 am »
I'm so confused. Your scope will only display a single channels waveform if you do single shot?
This the most elementary requirement of a DSO and even a $500 4ch 1 GSa/s DSO should have absolutely no trouble with this.
Yes that's right, my CRO displays only one trace for a single shot.It only can trigger from ALL or either input, depending on the settings.
This is why I want to make sure it can trigger and display simultaneously all the traces interlaced.Thanks Simon.
Here's some live traces, 2 & 3 ON but no signal and ch4 35ns pulse at 1MHz and ch1 30 MHz sine.



Push Single result:


Bread and butter eazy peezy stuff.  ;)
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Online ebastler

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Re: Oscilloscope-non alternating between channels type
« Reply #11 on: May 02, 2019, 04:18:15 am »
Could ALL stand for Alternate, even though misspelt and makes little sense on a DSO. :-//
Triggering off either channel should show both traces in single captures.

Ah yes, that must be it. That TENMA/UDT scope does indeed support ALTernate triggering.

@simon christo: As others have stated, you are probably mixing up the trigger selection with the actual capture and display of the traces. You have to select one of the channels for triggering (trigger on wither CH1 or CH2), but then the scope will capture both traces. This applies in single-trigger as well as recurring trigger mode.

Your scope also has the capability of alternate triggering (which is unusual for a digital scope). In that mode, it will first wait for a trigger event on CH1, then capture CH1, then wait for a trigger event in CH2, then capture CH2. If you select ALTernate triggering in single-shot mode, the scope will probably capture only one of the traces indeed -- so alternate triggering in single-shot mode is a meaningless combination.

There is no option to tell the scope "wait for a trigger event on either CH1 or CH2, then capture both traces". I am not aware of a general-purpose scope which can do that. You always have to select one of the channels to define the trigger event.
 

Offline rf-loop

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Re: Oscilloscope-non alternating between channels type
« Reply #12 on: May 02, 2019, 05:57:18 am »


There is no option to tell the scope "wait for a trigger event on either CH1 or CH2, then capture both traces". I am not aware of a general-purpose scope which can do that. You always have to select one of the channels to define the trigger event.

Many scopes have logic gate in trigger system and you can connect channels to this gate input and gate output generate trigger.

If there is example 4 channels connected to some signal sources and user want trig if channel A or B or C or D meet trigger level and then it capture all channels simultaneously.
What modern digital oscilloscope can not do it? 

Just right trigger mode (depending scope, in Siglent it is "Pattern") and select trigger gate OR and select what channels are connected to this OR gate, this gate output generate trigger.

Typically there can select  OR, NOR, AND and NAND gate and also gate inputs can invert depending needs. (This is available of course for normal analog channels as also LA channels if scope have these.)
If practice and theory is not equal it tells that used application of theory is wrong or the theory itself is wrong.
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Offline StillTrying

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Re: Oscilloscope-non alternating between channels type
« Reply #13 on: May 02, 2019, 08:58:13 am »
I think rf-loop has figured it. :)

If you want either channel's trigger to capture a 1 shot you need a scope with the trigger OR logic.

If your triggers were very simple such as either of 2 logic signals going high, you could just OR them yourself with 2 diodes or 2 10ks and apply the OR'd trigger to EXTtrig.
CML+  That took much longer than I thought it would.
 

Online tautech

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Re: Oscilloscope-non alternating between channels type
« Reply #14 on: May 02, 2019, 09:28:41 am »
I forgot about Pattern triggering.........some playing with unrelated signals on a 4ch X-E.

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Online BravoV

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Re: Oscilloscope-non alternating between channels type
« Reply #15 on: May 02, 2019, 09:31:09 am »
Why I sense of lost in translation here ?  :-//

Offline StillTrying

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Re: Oscilloscope-non alternating between channels type
« Reply #16 on: May 02, 2019, 10:08:37 am »
I forgot about Pattern triggering.........some playing with unrelated signals on a 4ch X-E.

Yes but does OR triggering work in single capture mode, it should do.
I remember analogue storage tubes, but I've never needed an OR'd triggers single capture!
« Last Edit: May 02, 2019, 10:19:04 am by StillTrying »
CML+  That took much longer than I thought it would.
 

Offline rf-loop

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Re: Oscilloscope-non alternating between channels type
« Reply #17 on: May 02, 2019, 10:39:29 am »

Yes but does OR triggering work in single capture mode, it should do.
I remember analogue storage tubes, but I've never needed an OR'd triggers single capture!


Yes of course.  (in analogs most need chopping, not always nice with fast things, but then there was Tek 7844)

Here example.

Single shot.

What ever channel meet first its trigger threshold scope trigger and capture simultaneously all channels.
In this example signal in CH2 have generated single shot trig because it have first meet trigger threshold level. (all channels  have individual threshold level).



Scope in Single shot mode.
Here first signal what have meet trigger threshold is CH2 (threshold 340mV), captured all and stopped.

 Let's hope Siglent develop it bit. Now it show only one channel trigger level pointer right side of screen. I hope it show all these selected channels individual trigger level pointers. 

Note, after all channels thresholds set remember return Ch1 selected. (trigger window text "Pttn" yellow.)
« Last Edit: May 02, 2019, 11:10:32 am by rf-loop »
If practice and theory is not equal it tells that used application of theory is wrong or the theory itself is wrong.
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Online ebastler

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Re: Oscilloscope-non alternating between channels type
« Reply #18 on: May 02, 2019, 10:50:09 am »
There is no option to tell the scope "wait for a trigger event on either CH1 or CH2, then capture both traces". I am not aware of a general-purpose scope which can do that. You always have to select one of the channels to define the trigger event.
Many scopes have logic gate in trigger system and you can connect channels to this gate input and gate output generate trigger.

You are right, of course. I stand corrected on that part of my post. Stupid; I have actually used that mode...
 

Offline TK

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Re: Oscilloscope-non alternating between channels type
« Reply #19 on: May 02, 2019, 11:29:19 am »
Hi again.Regarding my Oscilloscope question, I meant a type that if it says 2Gs/s per channel it is always that no matter how many channels you are on.Thanks Simon.
The Keysight DSOX-1000X series can do 2GSa/s on both channels simultaneously

EDIT: It goes down to 1GSa/s when all 2+1 channels are activated (2 analog + 1 digital)
« Last Edit: May 11, 2019, 12:01:07 pm by TK »
 

Offline simon christo

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Re: Oscilloscope-non alternating between channels type
« Reply #20 on: May 11, 2019, 03:53:47 am »
Hi again.I'm glad we sorted out the Tenma 40 Mhz Cro question, now I'm sure that interpolated Oscilloscopes are just as good as dedicated
independent ADC's of some other Oscilloscopes.Just a small question, this Cro has the ability to store a Wave file into the Cro itself which
saves properly.But theres no way to load the waveform to display it on the Oscilloscope itself. It does however, allows the 'Setup' to be
saved and then loaded within the unit.There's a option for 'Normal' or 'Long' lengths of time, and the screen shows the time in the right
bottom corner, which displays about 10 X qiucker on playack ONLY when using the USB.But as far as the internal Storage facility, I can't
find a way to load it to display on the Oscilloscope itself.The Model No is:72-8225.

Thanks Simon.
 


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