My scope scan mode is broken, can it be fixed? SDS1102CNL - Page 1
Forum section: electronics / testgear

author: hlj.pycad
author_rank: Contributor
timestamp: May 31, 2023, 03:24:07 am
content: It works totally fine from 2.5ns/div to 50ms/div timebase in which it runs in trigger mode.When the timebase is above 50ms/Div, says 100ms/Div, scan mode kick in. The scope captured many nonsense points make the scan mode useless... Selfcalibration pass fine.It's 1K Hz square wave captured in 100ms/Div timebase, then zoom-in, you can see only a small portion of the zoom in captured waveform show what it is, most of the the data were non-sense dots.Which parts of my scope is possible broken? And can it be fixed?

author: ataradov
author_rank: Super Contributor
timestamp: May 31, 2023, 03:59:43 am
content: This scope has 40 kpts of memory, there is no way it can save high frequency the data as long time scales, the sampling rate will have to drop.This is not a bug, just a limitation of the instrument you need to deal with, or get one with more sample memory.

author: hlj.pycad
author_rank: Contributor
timestamp: May 31, 2023, 04:10:51 am
content: thanks for you reply. One thing I don't understand is, 50ms/div should be 200% sample rate compare to 100ms/div, it shouldn't be any problem for capturing a 1K square wave, and you can see in the image, some part of the captured waveform was really nice. My scope is modified, it's a SDS1102CML in fact, I solder a 2Mpts SRAM on it and turn on long memory mode.And I tried a 10Hz sine wave by a JDS6600 DDS, it like a ladder wave in my scope in scan mode. It's not high frequence, so I think my scope scan mode is broken... or I am missing some other knowledge about scope scan mode.

author: ataradov
author_rank: Super Contributor
timestamp: May 31, 2023, 04:16:16 am
content: Figure out what the actual sample rate is used in that mode. Some scopes would let you separately configure the memory depth, otherwise they select the slowest that is good enough to fill the screen.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 31, 2023, 05:21:34 am
content: Quote from: ataradov on May 31, 2023, 04:16:16 amThis was the problem with the early DSOs, which reduced the sample rate at large values of time/div, so far that it dropped below the higher frequency components of a PAL analog video waveform, the resultant aliasing making the display unusable.The first one I encountered couldn't even show a line (horizontal) waveform, whereas the later ones were better, showing a "sort of" accurate line rate signal, but a field rate signal was a total mess.As the OP's signal isn't near as complex as a video waveform, I'm surprised that a modern DSO can't display it.

author: ataradov
author_rank: Super Contributor
timestamp: May 31, 2023, 05:41:08 am
content: I know for sure that Rigol DS1054DZ will default to lower sample rate to just accommodate the display at the current time/div setting, no zooming in. I'm not entirely sure what is the logic behind that - you have the memory, use it.And there is a separate option to disable automatic selection and force it into the mode you like. I had to do that when I needed to capture full video frames and it worked without any issues. I bet this scope does the same, the question is whether it has the override setting.

author: tautech
author_rank: Super Contributor
timestamp: May 31, 2023, 07:12:53 am
content: Quote from: hlj.pycad on May 31, 2023, 04:10:51 amDoes it know it's now a CML ?Is the deep memory available in the menu ?What does Sys Info report ?

author: hlj.pycad
author_rank: Contributor
timestamp: May 31, 2023, 09:17:39 am
content: QuotePositive. it's called "long memory". I can export 1M points valid file from EasyScopeX for both channel after it's enable.

author: hlj.pycad
author_rank: Contributor
timestamp: June 01, 2023, 02:30:34 am
content: this one is automatic scale the sampling rate, no user setting is allowed.I just check the sampling rate at 100ms/Div, it's 25KSa/s regardless the "Long Memory" option is enabled or not, in other words, deep memory is temporarily disabled in scan mode.But again, it's did well when the part of record waveform is good, as in the picture. 25kSa/s is suffucient for the job

author: ataradov
author_rank: Super Contributor
timestamp: June 01, 2023, 02:41:32 am
content: 25KSa/s is enough to sample 1 kHz signal reasonably well. I'm not sure I would trust those dots though. Try a more complicated signal (even a sine would work) and see how it behaves.