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Functional comparison of R&S RTB2000, Siglent SDS2000X and Keysight DSOX1000

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Someone:

--- Quote from: RBBVNL9 on April 04, 2022, 07:32:01 pm ---Can anyone enlighten me? Why does the RTB have periodic interruptions? And, more importantly, why is the SDS so slow to re-trigger ?!?
Do I overlook relevant device settings?
--- End quote ---
Double check the memory depth you have set, it often has a large effect on the update rate. Not sure if the SDS 2000X will approach "perfection", older models were similar to what you see:
https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg3169060/#msg3169060
(no idea if there is a set of measured data for the 2000X, so hard to search through the mountains of information on this forum).
If you look very carefully over a long period even on the Keysight there will be some gaps in the triggers (or use a pulse width trigger to catch it!).

Edit, found some measured values for the 2000X:
https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg3133558/#msg3133558
Not fully explained the methodology, but suggests better performance is possible in some configuration/situation.

RBBVNL9:
Thanks egonotto, Someone and PeDre for taking the time to respond so swiftly. Some quick replies:


--- Quote ---Double check the memory depth you have set, it often has a large effect on the update rate.
--- End quote ---
I tried each memory depth setting available in the SDS (see my post) but none of made a difference in seeing this pattern. But will do some more attempts later. (This setting did make a difference for the RTB though.)


--- Quote ---If you look very carefully over a long period even on the Keysight there will be some gaps in the triggers (or use a pulse width trigger to catch it!).
--- End quote ---
That might be the case. But as can be seen from the PicoScope screen print, the Keysight DSOX’s average of 333.3 trigger out pulses per second was very stable; over 109 observations (of each ~150 pulses) there is an extremely low standard deviation. So, if it misses triggers, it’s not many. Indeed, a pulse width trigger (or mask test) could reveal this.


--- Quote ---Edit, found some measured values for the 2000X:
--- End quote ---
Like in the post of Martin72 you refer to, I am indeed finding similar, very low waveform update rates on the SDS (orders of magnitude lower than advertised). That is the reason why I started to do these trigger experiments…


--- Quote ---This has been asked before, here is Rich's answer:
--- End quote ---
Thanks for forwarding Rich’s answer. Before posting, I did a search on the forum but it’s not always easy to find what you are looking for, even if it’s there  :-| But anyway, questions answered!


--- Quote ---RTB and SDS take time to execute the samples. Meanwhile they do not sample.
--- End quote ---
Yes, seems so. Perhaps the reason the DSOX is doing so well here is that it dedicated these tasks to different hardware resources so it can keep on triggering even when it’s buffering and plotting on the screen. 


--- Quote ---RTA behave little wilder.
--- End quote ---
Can you perhaps elaborate on what you mean here?

Bottom line: While it’s now clear to me what the RTB is doing, the bigger concern here is the SDS. After a trigger, it misses something like 10 possible triggers before its ‘arming’ again. For a trigger signal as slow as 1 kHz, this is quite strange. Perhaps, like Martin72 suggests, there might be a serious bug here that is still waiting to be fixed?

Someone:

--- Quote from: RBBVNL9 on April 05, 2022, 06:23:20 am ---
--- Quote from: egonotto on April 05, 2022, 12:41:00 am ---RTB and SDS take time to execute the samples. Meanwhile they do not sample.
--- End quote ---
Yes, seems so. Perhaps the reason the DSOX is doing so well here is that it dedicated these tasks to different hardware resources so it can keep on triggering even when it’s buffering and plotting on the screen.
--- End quote ---


--- Quote from: RBBVNL9 on April 05, 2022, 06:23:20 am ---Bottom line: While it’s now clear to me what the RTB is doing, the bigger concern here is the SDS. After a trigger, it misses something like 10 possible triggers before its ‘arming’ again. For a trigger signal as slow as 1 kHz, this is quite strange. Perhaps, like Martin72 suggests, there might be a serious bug here that is still waiting to be fixed?
--- End quote ---
I do not think it is a bug, but just the way they work. As you say above these different scopes have different hardware separation of the work, DSOX puts most things in ASIC/FPGA which makes it fast but less flexible (examples: cannot reduce memory depth, or turn off interpolation, even though that would make it faster). Probably Siglent do much more of the display drawing in CPU/software for more flexibility/cheaper product (example benefit: colourised intensity view).

RBBVNL9:

--- Quote ---I do not think it is a bug, but just the way they work.
--- End quote ---

Well, even if these devices do work differently, Siglent does publish a waveform update rate. And if the actual update rate is orders of magnitude lower than what is published (see the posts of Martin72 and Performa01 referred to above, which are indeed in line with my own measurements, see my video Episode 7 at 47:27) then I think it is correct to speak of a bug... 

2N3055:

--- Quote from: RBBVNL9 on April 05, 2022, 06:23:20 am ---
Bottom line: While it’s now clear to me what the RTB is doing, the bigger concern here is the SDS. After a trigger, it misses something like 10 possible triggers before its ‘arming’ again. For a trigger signal as slow as 1 kHz, this is quite strange. Perhaps, like Martin72 suggests, there might be a serious bug here that is still waiting to be fixed?

--- End quote ---

Hi.

Could you check something on Siglent? If you go into Acquistion  menu, do you have Slow or Fast mode set there? You need to be in the dot mode also..

A small suggestion, if I may. To avoid confusion, may I suggest a wording specificum: a time that scope needs to be ready for a new trigger event can be called retrigger time.  We can also use a term rearm time or even a blind time to signify time that scope is "blind" to new events while trigger engine is being rearmed for another go.  I say that because saying that "scope is missing triggers" can be misconstrued as scope being ready for trigger but it didn't recognize it properly.
Difference is that first one is operating specification of the scope and the other one (missed triggers) is defect, a bug.

A bit of pedantry, I know, but nevertheless not unimportant sometimes.

As Someone correctly said, phosphor emulation works by virtue of sampling short bursts of acquisitions synchronised with screen refresh rate. Keysight also does it on certain timebase settings. Even KS 3000T that is clocked at more than 1 milion triggers per second does it at some settings.
But this is nothing new, really. This is pretty much only thing KS does better in Infiniivision scope series (Megazoom IV based). Whole architecture is based around this feature. With all the compromises that stem from it, like very small memory, use of decimated buffers for all measurements, all time interpolation with no user control etc. These are pretty much speciallistic scopes made to emulate something similar to analog CRT scope triggering performance as primary design goal.

Both R&S and Siglent, with their long memory architecture are closer to "analytic" scope type, where you capture longer sequences and then analyse it. In fact, we can argue that these scopes with long memory can achieve "zero" blind time for bursts of, say, 100ms. This way of thinking, though, does need for user to actually adjust way how they are using scopes, because it is slightly different to how you would use CRT scopes many people are used to.
That is why I always keep repeating that, for instance, KS 1000X series are not very capable scopes (they have very limited capabilities compared to even scopes many times cheaper) but are good for people that don't need advanced features (user wants to to only look at waveform on the screen and maybe use cursors and basic measurements) and that want as good as possible CRT emulation.

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