EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: BillyO on November 23, 2022, 10:39:22 pm
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I discovered a bug in the Siglent SDS1104X-E. I actually discovered it a while ago (when I found the offset in AC coupling mode on all 4 channels) but it's now becoming a bit annoying.
Offset and position do exactly the same thing. They shouldn't. Position should set the base-line (it does), offset should adjust the offset from base-line. It doesn't, it just changes the base-line just like the position control does. I am not sure if this was introduced in the latest software/firmware as that's what I'm using and have never used anything else.
Is there an official way to log a bug report?
Edit: Video added.
https://youtu.be/UzVjM4AltRc (https://youtu.be/UzVjM4AltRc)
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Short video would be nice...
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Interesting. I'll check mine when I get a chance.
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Short video would be nice...
What video format and size does the site permit?
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I discovered a bug in the Siglent SDS1104X-E. I actually discovered it a while ago (when I found the offset in AC coupling mode on all 4 channels) but it's now becoming a bit annoying.
Offset and position do exactly the same thing. They shouldn't. Position should set the base-line (it does), offset should adjust the offset from base-line. It doesn't, it just changes the base-line just like the position control does. I am not sure if this was introduced in the latest software/firmware as that's what I'm using and have never used anything else.
Is there an official way to log a bug report?
Can you, please, explain what baseline, offset and position mean to you?
How did you set Vertical reference settings in Utility menu? (manual pg 220.)
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Short video would be nice...
What video format and size does the site permit?
Don´t know, me I´ve just upload vids to youtube, then linked here.
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Baseline is where you put the trace with the vertical position control. The vertical position is, well the vertical position. Where you set the trace to be vertically on teh screen. It is marked with a triangular flag on the left. Offset is where the trace actually is. If offset=0 then the trace will be at the set position. If offset=10mV then the trace will be 10V above where the set position is. If the offset=-20mV then the trace will be 20mV below the set position.
I will try the two options mentioned on page 220 right now and get back. However, this does not sound like the problem unless their English is wanting.
Edit: Changing from fixed position to fixed offset had no effect.
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How are you setting the 'offset'?
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C'mon Billy, screenshots please !
A picture = 1000 words.
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How are you setting the 'offset'?
With the "Offset" control. How would you set it?
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C'mon Billy, screenshots please !
A picture = 1000 words.
Link added to a video in first post
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C'mon Billy, screenshots please !
A picture = 1000 words.
Link added to a video in first post
Settings change required:
This video is private
Edit
Visible now.
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With the "Offset" control. How would you set it?
There are some 'offset' settings for rmath functions (DC offset in integration for example) but I've never seen or used the offset setting in the channel menu until I turned mine on just now and looked. Indeed, there it is, and it is obviously just a replication of the position knob. Why that is there, I've no idea. My SDS2354X+ appears not to have such a setting, or at least I couldn't find it right away.
There was an uncommon feature of certain CROs that would actually allow you to put a separate (from the position controls) DC bias on the inputs, often much more than the position controls could achieve. None of that is really necessary with a typical DSO, the position knob effectively does both.
Edit: for those that don't see it right away, it is on page 2 of the channel menu.
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This whole "BUG!!" is between chair and oscilloscope. Please repair this thread title. Please first try to learn basic fundamentals and after real knowledge and experience start naming things as "bugs".
Here you can of course ask how to use oscilloscope. But please, before it, try to even read the user manual first, even though it's boring.
What an amazing A-#ole! First, I don't think you have any idea what I'm talking about. Next, unless you have something constructive to add .. STFU!
I have read the manual. Have you? As bdunham7 mentions, it's found in the 2nd page of the channel menu and it is not even mentioned in the manual.
The "bug" might simply be the fact that they have two controls that do the same thing but are labeled differently. Or it's not meant to exist. That's fine. Fix the "bug" by calling them both "position" or both "offset" or just removing it. However, not being a Finnish twat, where I come from the words "position" and "offset" mean different things, especially in context of each other.
The title stays the same. Now, vittuun!
Well, frankly, you have colorful personality yourself...
So let us all calm down and let's figure this out..
Position and offset are actually interchangeable in this context for reasons to be discussed. And it is why I asked what do you mean by this two terms. And I didn't mean by it to be explained as to what is meaning of these two english words (know that, thank you anyways) but as to what meaning you ascribe to them in context of the scope...
I don't have SDS1000X-E so I didn't know about this distinction. Touch screen scopes from them don't have it. And I agree with RF, it is not a bug. It might be confusing design choice or misnomer but not a bug.
What I presume it has it because offset/position in DC and AC mode will differ. Maybe they wanted to have separate control for the two.
Experiment: apply 25% duty cycle 0 to 1V squarewave to scope input.
Put it in DC mode. What you see?
Center it on the screen with vertical position knob (physical one on the channel).
Change channel to AC mode. What do you see?
Now try moving it up and down with vertical position knob (physical one on the channel).
Go out in DC mode? What you see?
Center it again.
Go back in AC mode.
Now try moving it up and down with offset function ( one in the menu ).
Go out in DC mode? What you see?
Do you see any difference in behaviour now?
Would you be so kind and try this? I am also curious what would the results be.
Best,
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Do you see any difference in behaviour now?
I tried it and as I expected it made no difference. In the AC-coupled mode, the baseline was displaced to -250mV as you'd expect, but the controls work the same way--if you select 'OFFSET' the multipurpose knob has the exact same effect as the position knob. In the AC mode, the difference between the channel marker and the baseline of the waveform is always -250mV, in DC mode it always lines up.
The only thing different about the offset vs position is that if you push the multipurpose knob, you get the option of entering the value numerically, albeit painfully slowly with the turn/click method.
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Yes, I can be .. colorful .. especially when someone introduces themselves with a personal insult. :--
Enough of that for now.
I'll try what you suggest, but I think a key point is that there is no mention of this control in the manual. Almost like it was there for beta test purposes but was not removed for the final product.
I'll report back on my findings.
Edit: Findings below
25% duty square wave, DC, centered
AC, centered
AC, displaced down 1V using "Position" control
DC, displaced down 1V using "Position" control
AC, displaced down 1V using "Offset" control
DC, displaced down 1V using "Offset" control
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Yes, I can be .. colorful .. especially when someone introduces themselves with a personal insult. :--
Enough of that for now.
I'll try what you suggest, but I think a key point is that there is no mention of this control in the manual. Almost like it was there for beta test purposes but was not removed for the final product.
I'll report back on my findings.
It probably was the opposite, added later to FW and not to manual...
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Do you see any difference in behaviour now?
I tried it and as I expected it made no difference. In the AC-coupled mode, the baseline was displaced to -250mV as you'd expect, but the controls work the same way--if you select 'OFFSET' the multipurpose knob has the exact same effect as the position knob. In the AC mode, the difference between the channel marker and the baseline of the waveform is always -250mV, in DC mode it always lines up.
The only thing different about the offset vs position is that if you push the multipurpose knob, you get the option of entering the value numerically, albeit painfully slowly with the turn/click method.
So it was not remembering different settings in AC and DC mode ..
Then it is really only an alias for vertical position button but to be accessed from menu.
I presume it is there because of remote control via HTTP interface...
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Then it is really only an alias for vertical position button but to be accessed from menu.
I presume it is there because of remote control via HTTP interface...
Yes, as I said in the beginning, it does the same thing but gives it a different name.
Makes no sense for the HTTP interface as it requires several more steps to access it. The position control is easier to get to and easier to use, even through the webserver interface.
My previous post has been updated with the results of your suggestions.
So, my position on this is it is either a bug in the terms I previously described and should be corrected to provide a means to adjust offset of waveform from position, or it should just be removed. It serves absolutely no purpose I can find as it stands.
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So, my position on this is it is either a bug in the terms I previously described and should be corrected to provide a means to adjust offset of waveform from position, or it should just be removed. It serves absolutely no purpose I can find as it stands.
Although you could provide a limited 'digital trim' as your offset, I don't think there's much utility in having some separate offset trim. It would be potentially confusing if you misunderstand it or forget that it is not set to zero. As far as removing the menu item, that might break something as there may be some internal reason that it is there. I would just chalk it up to a not-so-polished UI and ignore it.
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I don't think there's much utility in having some separate offset trim.
There is actually. I can think of 2 (maybe rare) use cases, but important if you need it. Maybe Mr. loop, with all his superior knowledge of metrology, could expand on that?
I would just chalk it up to a not-so-polished UI and ignore it.
Probably the best way forward.
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I got a siglent spectrum analyzer at work, not a fan of the interface on that, a working machine is one thing, communicating in another language (that of the user) is a different skill set.
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There is actually. I can think of 2 (maybe rare) use cases, but important if you need it. Maybe Mr. loop, with all his superior knowledge of metrology, could expand on that?
On a CRO or other scope where the vertical position has to operate within reasonable limits, the addition of an adjustable DC bias on the input that allows you to offset the input by many divisions worth does have some uses, like looking at PSU ripple and more. This was an uncommon feature on CROs. But a DSO like the Siglent SDS1104X-E already has this feature built-in and incorporated into the vertical amplifier system. Even if you did have some second offset system in the vertical amp, it would just add to or subtract from the first one. The only other 'offset' I can think of that you could do is some sort of digital trim, but that would have to be pretty limited. What use case do you have that isn't met by the system in the 1104X-E?
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What use case do you have that isn't met by the system in the 1104X-E?
Well, there is the case that kind of brought this back for me. Looking at and making some measurements on a very low frequency not quite square wave signal. Using AC coupling naturally distorted the waveform. It would have been handy to use DC coupling and apply an offset to bring the signal back to where it should be.
The other use case is the problem I had before where there was a considerable offset in the vertical ranges below 10mV/div.
Yes, both are rare and both can be worked around, but an offset adjustment would make quick work of that.
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Well, there is the case that kind of brought this back for me. Looking at and making some measurements on a very low frequency not quite square wave signal. Using AC coupling naturally distorted the waveform. It would have been handy to use DC coupling and apply an offset to bring the signal back to where it should be.
Do you mean a signal with a large DC bias? Or something else?
The other use case is the problem I had before where there was a considerable offset in the vertical ranges below 10mV/div.
This would be like trim or zeroing, I suppose it might come in handy on occasion. But it wouldn't be stable. I can't think of a single DSO that implements this directly. You can do it with a MATH function, but that would be a lot of effort.
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Do you mean a signal with a large DC bias? Or something else?
Well, large is relative, but in this case I'd say yes. The DC offset was 10V while the AC component was 4V. However, the variance of interest was less than .5V. I just built a small summing circuit to take the DC component out then adjust the measurements accordingly. So it was easy enough to work around although a bit of a pain. A better measurement solution would have been a fast response chart recorder. They have offset adjustments as a matter of rule, but they are also not within my reach. Another solution would be to get a data logging DMM.
Anyway, I think we're drifting off topic a bit and obviously nobody cares. I'll treat this "Offset" adjustment as though it were an appendix. Not very useful, but hanging around nonetheless .. and that's just fine. :palm:
It's kind of like having a control in your car that is labeled "Brake adjustment" but when you use it to make an adjustment it just applies the brakes. :-//
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Well, large is relative, but in this case I'd say yes. The DC offset was 10V while the AC component was 4V. However, the variance of interest was less than .5V. I just built a small summing circuit to take the DC component out then adjust the measurements accordingly. So it was easy enough to work around although a bit of a pain. A better measurement solution would have been a fast response chart recorder. They have offset adjustments as a matter of rule, but they are also not within my reach. Another solution would be to get a data logging DMM.
If you have a 4Vp-p AC signal with a +10V DC bias, you just set the position (or offset) to -10V and the vertical scale to 500mV/div and it should appear life-sized on your screen. That gives you a whole division to look at your 0.5V variance.
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I did actually try that, but it seemed to bugger up the mean and RMS measurement values. Perhaps that's a real bug.
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https://www.eevblog.com/forum/blog/eevblog-1223-whats-all-this-ac-rms-stuff-anyhow/ (https://www.eevblog.com/forum/blog/eevblog-1223-whats-all-this-ac-rms-stuff-anyhow/)
The scope's RMS measurement will give you AC+DC TRMS, for the AC TRMS you use the STDEV measurement. For a 'mean', I'd have to know what mean you mean want but there's probably a way to do it.
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There is actually. I can think of 2 (maybe rare) use cases, but important if you need it. Maybe Mr. loop, with all his superior knowledge of metrology, could expand on that?
On a CRO or other scope where the vertical position has to operate within reasonable limits, the addition of an adjustable DC bias on the input that allows you to offset the input by many divisions worth does have some uses, like looking at PSU ripple and more. This was an uncommon feature on CROs. But a DSO like the Siglent SDS1104X-E already has this feature built-in and incorporated into the vertical amplifier system. Even if you did have some second offset system in the vertical amp, it would just add to or subtract from the first one. The only other 'offset' I can think of that you could do is some sort of digital trim, but that would have to be pretty limited. What use case do you have that isn't met by the system in the 1104X-E?
This use case is dealt with by selecting how the position of the screen reacts to changing the V/div, it can go around the centre of the screen or around 0V these do not coincide when you look at a voltage far from ground reference.
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https://www.eevblog.com/forum/blog/eevblog-1223-whats-all-this-ac-rms-stuff-anyhow/ (https://www.eevblog.com/forum/blog/eevblog-1223-whats-all-this-ac-rms-stuff-anyhow/)
The scope's RMS measurement will give you AC+DC TRMS, for the AC TRMS you use the STDEV measurement. For a 'mean', I'd have to know what mean you mean want but there's probably a way to do it.
You'd expect that for the RMS, but that wasn't the case.
The "mean" I wanted was the one provided for in the SD1104X-E measurements. The one that ideally would be 0V for a perfect AC square wave.
There was a way to do what I wanted and get the results I needed, buy summing my signal with -10V and using the scope with DC coupling. It was simple enough to do and gave results that made sense.
As an example if I do simulation here on the bench using a 1KHz square wave @ 4Vp-p with a 10V DC component, trying the method you suggest gives me a VRMS of 0.22V and a mean of -30mV. Using the method I used I get VRMS of 2.03V and a mean of 6.7mV, which is what I get if I use AC coupling, which I can in this case due to the 1KHz I'm using for just that purpose.
I don't think the scope's internal measurements can cope with the position being set so far off the screen. Something is being clipped.
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As an example if I do simulation here on the bench using a 1KHz square wave @ 4Vp-p with a 10V DC component, trying the method you suggest gives me a VRMS of 0.22V and a mean of -30mV. Using the method I used I get VRMS of 2.03V and a mean of 6.7mV, which is what I get if I use AC coupling, which I can in this case due to the 1KHz I'm using for just that purpose.
I don't think the scope's internal measurements can cope with the position being set so far off the screen. Something is being clipped.
My AWG won't do a 10V DC bias with a 4Vp-p square wave (max output is 10V), so I set it up with 8VDC + 4Vp-p square wave, the result should be the same. If somehow you do this and it works at 8V and not at 10, I'll float the AWG and bridge two channels. But I don't think 8V vs 10V will matter.
So I set up my SDS1104X-E as follows:
Offset/position: -8.00V
CH1: 1V/div, measurements RMS, STDEV and MEAN.
Horizontal 500us/div.
The results I get are ~8V MEAN, 2.00V STDEV and 8.21V RMS. The SDS1104X-E doesn't have a formula editor for math and there's no obvious way to have the math channel do CH1 minus 8 volts, so you'd have to mentally subtract the offset from the mean to get the mean you want. Since you were originally looking at very low frequency stuff, I tried slowing the signal down to 0.1Hz and using a slow enough acquisition speed. I get the same result. Those numbers exactly match what a very accurate TRMS meter gives me for both AC and AC+DC, as well as matching the calculated expectations pretty closely as well. The AC and mean should be obvious, the AC+DC is the square root of 68.
One thing I did notice is that if I used 500mV/div instead of 1V/div, the signal is right at the edge of the screen and the scope displays measurements with ">" rather than an "=". That tells you that you are clipping, I guess. Apparently you need to keep it well on the screen for best results. What symbol did your scope show you and how did you set it up?
Clearly an actual offset bias circuit like the one you made for this would work as well, but those just don't exist AFAIK on modern DSOs and there's really no need. More advanced models can easily take that offset off of the mean in MATH if you want to display the value without having to think about it.
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Thanks for your efforts bdunham7.
I get similar results, but notice the RMS? It should be around 2V if you are just interested in the AC component.
I'll post some screen shots tomorrow.
Just for information, what versions are you at (hardware, FPGA, OS, Software/firmware)?
Mine:
Hardware: 09-06
FPGA: 2021-11-08
OS: 8.3
Firmware: 6.1.37R9
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I get similar results, but notice the RMS? It should be around 2V if you are just interested in the AC component.
I'll post some screen shots tomorrow.
Just for information, what versions are you at (hardware, FPGA, OS, Software/firmware)?
No, that's what I was nattering on about and what the DJ video I posted is about. RMS = AC+DC, STDEV = AC. And by that I mean the STDEV reading is the RMS of the AC component, if that wasn't clear.
Hardware 01-04
OS 8.2
Firmware 6.1.37R6 (I don't think any further updates apply to mine)
FPGA 2021-7-12
I wouldn't think there'd be any difference that would matter here. Post your screenshots and we'll know.
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RMS = AC+DC, STDEV = AC. And by that I mean the STDEV reading is the RMS of the AC component, if that wasn't clear.
Yeah, I do realize that the DC component is a part of the RMS value (it's not simply AC+DC though), however I am talking about the measurement I was taking. I was just interested in the RMS value of AC component. Doing the measurement this way (by changing position) rather than by removing the DC component you don't get the RMS reading of just the AC. In retrospect the STDEV didn't cross my mind. I guess it would have saved me a bit of time. :palm: Thanks for pointing that out. Now it'll always be a consideration.
I'll post my shot a bit later, but it's almost identical to yours.
Edit: Screen shot added.
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Yeah, I do realize that the DC component is a part of the RMS value (it's not simply AC+DC though)
"TRMS AC+DC" is just a common way of referring to a TRMS measurement where the DC component is not suppressed by AC coupling. It is calculated by your scope quite literally by simply taking the root of the mean of the squares of the samples. Since your square wave is 12V half the time and 8V the other half, the mean is (144 + 64)/2 or 104, the RMS is 1040.5 or ~10.2 and your measured result should match that give or take some for noise and offset.
The STDEV reading is calculated much the same way, except that the scope first calculates the MEAN value and then subtracts that from all the samples before doing the rest. Or at least that's how I expect they do it, perhaps with mathematical shortcuts to speed the process up.
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Yeah, I do realize that the DC component is a part of the RMS value (it's not simply AC+DC though)
"TRMS AC+DC" is just a common way of referring to a TRMS measurement where the DC component is not suppressed by AC coupling. It is calculated by your scope quite literally by simply taking the root of the mean of the squares of the samples. Since your square wave is 12V half the time and 8V the other half, the mean is (144 + 64)/2 or 104, the RMS is 1040.5 or ~10.2 and your measured result should match that give or take some for noise and offset.
The STDEV reading is calculated much the same way, except that the scope first calculates the MEAN value and then subtracts that from all the samples before doing the rest. Or at least that's how I expect they do it, perhaps with mathematical shortcuts to speed the process up.
Very nice. simple and concise!!
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Okay, sorry to revive this (if anyone gets upset at such things) but it seems most people that contributed to this thread did not understand or get what I was talking about.
Here is a video that explains the difference between offset and position. BTW, I still think an offset control would be a handy thing to have. Siglent (and others) should consider adding it. There is even a menu item for it already in the SDS1104X-E. They just have to make it work properly.
https://www.youtube.com/watch?v=-eccL4oLVM4 (https://www.youtube.com/watch?v=-eccL4oLVM4)
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Okay, sorry to revive this (if anyone gets upset at such things) but it seems most people that contributed to this thread did not understand or get what I was talking about.
Here is a video that explains the difference between offset and position. BTW, I still think an offset control would be a handy thing to have. Siglent (and others) should consider adding it. There is even a menu item for it already in the SDS1104X-E. They just have to make it work properly.
https://www.youtube.com/watch?v=-eccL4oLVM4 (https://www.youtube.com/watch?v=-eccL4oLVM4)
What is called Vertical position in that video is also called Vertical position on SDS. That is part where front end injects DC voltage and combines it with signal.
What on Tek is called Vertical Offset, is controlled on SDS by option Reference position in Utility menu.
You can choose if screen expands around the 0V, or around Vertical offset value.
How is Reference position in Utility menu set?
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I think you are still missing my point. My point is that on the SDS there are both "Position" and "Offset" controls. "Position" on the front panel and "Offset" in the vertical menu (2nd page) However, rather than working like an offset (as in the video) it works the same as "Position".
The reference position can only be set to "Fixed Position" or "Fixed Offset" and is not adjustable. It does not do the same thing as the offset control on the Tek in the video. Mine is currently set to "Fixed Position". That's where I want it.
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The reference position can only be set to "Fixed Position" or "Fixed Offset" and is not adjustable.
It is, sorta.
With the scope controls place the portion of the waveform you wish to inspect near the 0V position and engage Fixed Offset.
Now zoom in with V/div.
Return to Fixed Position for normal use after needing large offset settings.
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Right, but you can't take out a large DC offset that may exceed the scope's input range of you zoom in too much.
In any case, I just came back from a long walk during which I was thinking about this. If Siglent have not allowed for programmable DC injection into the front end (somewhere before the ADC) it might not be possible to do this. Software can only do so much and won't be able to deal with what is physically out of range for a particular attenuation.
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Just to get a common understanding on the atatus quo:
All Siglent X- and A-Series DSOs have only an offset control. They utilize a dedicated DAC to produce a voltage that gets injected in the LF path of the input buffer, enabling the offset compensation ranges as specified in the datasheets.
The physical knobs on the scope are still labelled "Position" (if they are labelled at all), as we are used to since the old days of analog oscilloscopes. Nevertheless they control the offset - and by doing this, we can also set the trace position. Just add or subtract the required offset.
The thing is, that this also shifts the reference point, which is indicated by the small triangle at the left edge of the screen. Without offset, this reference point is always in the vertical center of the screen.
If I understand correctly, you would want to have the reference point adjustable across the screen height and the small triangle should stay there in place, regardless of the (additional) offset setting.
I can unerstand such a desire - it might come handy sometimes - yet it would require one more control element. It might be hard to decide which one is more important, offset or position. Only one control can be on the physical knob, the other one has to be tucked away in the menu system. It would be easier on the touch scopes, where we could have one control in the channel tab, which is easily accessible. I would say, offset is the important one, whereas you should not need to change the reference point that often once you've made up your mind.
Since this would be a major change in the philosophy of offset/position control and this is the first complaint about that I'm aware of, we would need really good arguments why the current solution is not sufficient.
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Since this would be a major change in the philosophy of offset/position control and this is the first complaint about that I'm aware of, we would need really good arguments why the current solution is not sufficient.
Did you look at that video? A good reason for having it is mentioned there and apparently it's reason enough for Tek to include it in at least some of their scopes.
To answer your other question. Position would take priority of course. You only have to use offset once in a while, but when you need it, it would be great to have it. Are there ways around it? Sure there are, but they are a lot of extra work. Just like there are ways around most of the math functions and being able to run automatic Bode plots.