Products > Test Equipment
SDS1104X-E DC offset in AC coupling
Bionicbone:
I am getting used to my first ever scope, have to admit I probably would have selected AC coupling for AC :palm:
I have so much to learn, but that's the main reason for buying one.
tautech:
--- Quote from: Bionicbone on March 31, 2023, 05:50:42 am ---I am getting used to my first ever scope, have to admit I probably would have selected AC coupling for AC :palm:
I have so much to learn, but that's the main reason for buying one.
--- End quote ---
Fear not, we were all scope newbies once. ;)
What you do have that's really useful for the newbie is a easy method to grab screenshots and if you use some thought beforehand with an appropriate menu captured too !
Then bring it here and upload it whenever you see something you can't work out and many of us will jump in to help with conceivably many levels of understanding.
While this link is not for the 4ch X-E, SDS1202X-E the predecessor to SDS1104X-E, shares many but not all the same features so there is much in this thread to guide you about the feature set in your scope:
https://www.eevblog.com/forum/beginners/what-an-oscilloscope-recommended-for-a-woman-passionate-about-electronics/msg3104228/#msg3104228
Deso:
--- Quote from: Performa01 on March 30, 2023, 09:15:33 am ---When discussing topics like trigger coupling, we should first understand its uses.
Different modes of Trigger coupling give us the opportunity to filter the input signal before it is checked for the trigger condition.
DC is unfiltered, i.e. from DC up to more than the bandwidth of the scope
HF-Reject is DC to about 1.2 MHz
AC is from ~8 Hz up to more than the bandwidth of the scope
LF-Reject is ~1.2 MHz up to more than the bandwidth of the scope
So it should be clear, that DC and HF-Reject are basically the same, just with a different upper bandwidth limit, whereas AC and LF-Reject are basically the same as well, just with a different lower corner frequency.
For most use cases, DC-Trigger is fine – and you should know what you're doing when you choose something different. Why would you ever use AC trigger coupling at all?
Usually, we make that choice for the input channel coupling, and if this is AC, then the trigger is inevitably AC coupled as well. This leaves the rare cases, where we:
a) don't have a (constant) DC offset, but a low frequency signal that is mixed with the signal we want to analyze and that appears as a constantly changing offset
b) still want to use DC input coupling, so that we can observe the (changing) offset
and don't want to lose triggering at times.
I can't think of many use cases, where these conditions are met. But if you run in such a situation, the trigger filters, in particular HFRJ and LFRJ, help to achieve stable triggering even in tricky situations. Of course it would be even better if we had variable corner frequencies for this, but that would use too many resources, therefore such a feature is usually found in high-end DSOs only.
And maybe now it becomes clear why Siglent is reluctant to show the trigger level indicator in all the non-DC trigger coupling scenarios. This indicator is not stable, but might have to move quite fast – and it simply isn't fast enough for that. While the actual trigger level is adapting instantly, the trigger indicator lags behind a bit.
I know, the old Rigol DS1052 does show the trigger indicator in AC-trigger coupling mode, but many others do not. And wouldn't a fast moving trigger indicator rather be confusing while not giving any essential information? The main thing is, that with AC coupling, the trigger level is related to the signal offset, not an absolute screen position, as it would be with DC coupling.
On top of all that, trigger engines have evolved over time. Older scopes had an analog trigger, whereas modern DSOs like the SDS1104X-E have a fully digital trigger engine. The latter is far more powerful and more accurate, but not fully independent from the signal acquisition.
Hint: the EXT trigger found in all modern Siglent DSOs (except 4 channel X-E) is analog.
It might be helpful to study this document, especially reply #2, part 4 of the review:
https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/
--- End quote ---
You have done a great job with this review. Kudos to that.
I read the sds1004xe manual again and indeed found the information regarding LF and HF filtering for the trigger coupling.
--- Quote ---Usually, we make that choice for the channel input and if we select AC coupling there, the trigger will inevitably be AC coupled as well.
--- End quote ---
I agree. However it is not labeled as such and if you manually switch to Trigger AC coupling - you have no level indicator. And really 99% of the time I won't touch this menu, but it should still display/work properly for those who care.
Back to main topic - While waiting for Siglent to resolve my issue with the AC coupling offset I spotted that there is a new firmware - V6.1.37R10 (EU: Release Date 04.03.23, NA: Release Date 03.30.23 ) which added "Optimized VGA configuration".
It looks like it might help me with my compensation issues. Unfortunately, not only did it not solve my problem, but it introduced a new one - interruption of the trace updating on specific interval. The trace is freezing for a fraction of the second. During one of my VNC video capturing even the oscope itself froze for a while. This issues is visible on the scope screen too.
And my input channels offsets are behaving strange. After firmware update and reboot, I waited for 40 min to warm a bit and I did calibration. The result shows no differences from the previous firmware.
Now I turn on the scope after several hours again to capture the trace drawing issue and the offsets are different, even after proper warm-up.
At the end my short straw seems to be shorter than I expected.
Here is a video with the new FW issue
https://drive.google.com/file/d/1YZMT3PAPBnjCt5um3wm5XVQ1QbDt7Kdh/preview
pope:
What is the VGA configuration?
BillyO:
--- Quote from: pope on April 04, 2023, 03:00:54 pm ---What is the VGA configuration?
--- End quote ---
Variable Gain Amplifier. They are used in the front ends of scopes (and possibly other places)..
https://www.ti.com/lit/gpn/lmh6518
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