SDS1104X-E Unexpected Behaviour - Page 1
Forum section: electronics / testgear

author: BillyO
author_rank: Super Contributor
timestamp: November 23, 2022, 10:39:22 pm
content: 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

author: Martin72
author_rank: Super Contributor
timestamp: November 23, 2022, 10:42:10 pm
content: Short video would be nice...

author: pope
author_rank: Frequent Contributor
timestamp: November 23, 2022, 10:42:40 pm
content: Interesting. I'll check mine when I get a chance.

author: BillyO
author_rank: Super Contributor
timestamp: November 23, 2022, 10:52:49 pm
content: Quote from: Martin72 on November 23, 2022, 10:42:10 pmWhat video format and size does the site permit?

author: 2N3055
author_rank: Super Contributor
timestamp: November 23, 2022, 10:54:34 pm
content: Quote from: BillyO on November 23, 2022, 10:39:22 pmCan you, please, explain what baseline, offset and position mean to you?How did you set Vertical reference settings in Utility menu? (manual pg 220.)

author: Martin72
author_rank: Super Contributor
timestamp: November 23, 2022, 10:58:14 pm
content: Quote from: BillyO on November 23, 2022, 10:52:49 pmDon´t know, me I´ve just upload vids to youtube, then linked here.

author: BillyO
author_rank: Super Contributor
timestamp: November 23, 2022, 11:04:32 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 23, 2022, 11:21:10 pm
content: How are you setting the 'offset'?

author: tautech
author_rank: Super Contributor
timestamp: November 23, 2022, 11:21:19 pm
content: C'mon Billy, screenshots please !A picture = 1000 words.

author: BillyO
author_rank: Super Contributor
timestamp: November 23, 2022, 11:24:35 pm
content: Quote from: bdunham7 on November 23, 2022, 11:21:10 pmWith the "Offset" control. How would you set it?

author: BillyO
author_rank: Super Contributor
timestamp: November 23, 2022, 11:25:49 pm
content: Quote from: tautech on November 23, 2022, 11:21:19 pmLink added to a video in first post

author: tautech
author_rank: Super Contributor
timestamp: November 23, 2022, 11:33:00 pm
content: Quote from: BillyO on November 23, 2022, 11:25:49 pmSettings change required:This video is privateEditVisible now.

author: bdunham7
author_rank: Super Contributor
timestamp: November 23, 2022, 11:44:05 pm
content: Quote from: BillyO on November 23, 2022, 11:24:35 pmThere 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.

author: 2N3055
author_rank: Super Contributor
timestamp: November 24, 2022, 03:47:32 pm
content: Quote from: BillyO on November 24, 2022, 03:14:10 pmWell, 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,

author: bdunham7
author_rank: Super Contributor
timestamp: November 24, 2022, 03:59:28 pm
content: Quote from: 2N3055 on November 24, 2022, 03:47:32 pmI 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.

author: BillyO
author_rank: Super Contributor
timestamp: November 24, 2022, 04:00:58 pm
content: 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 below25% duty square wave, DC, centeredAC, centeredAC, displaced down 1V using "Position" controlDC, displaced down 1V using "Position" controlAC, displaced down 1V using "Offset" controlDC, displaced down 1V using "Offset" control

author: 2N3055
author_rank: Super Contributor
timestamp: November 24, 2022, 04:02:20 pm
content: Quote from: BillyO on November 24, 2022, 04:00:58 pmIt probably was the opposite, added later to FW and not to manual...

author: 2N3055
author_rank: Super Contributor
timestamp: November 24, 2022, 04:12:12 pm
content: Quote from: bdunham7 on November 24, 2022, 03:59:28 pmSo 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...

author: BillyO
author_rank: Super Contributor
timestamp: November 24, 2022, 04:31:52 pm
content: Quote from: 2N3055 on November 24, 2022, 04:12:12 pmYes, 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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 24, 2022, 04:44:59 pm
content: Quote from: BillyO on November 24, 2022, 04:31:52 pmAlthough 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.

author: BillyO
author_rank: Super Contributor
timestamp: November 24, 2022, 05:02:49 pm
content: Quote from: bdunham7 on November 24, 2022, 04:44:59 pmThere 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?Quote from: bdunham7 on November 24, 2022, 04:44:59 pmProbably the best way forward.

author: Simon
author_rank: Unknown
timestamp: November 24, 2022, 10:28:41 pm
content: 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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 24, 2022, 11:01:09 pm
content: Quote from: BillyO on November 24, 2022, 05:02:49 pmOn 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?

author: BillyO
author_rank: Super Contributor
timestamp: November 24, 2022, 11:27:10 pm
content: Quote from: bdunham7 on November 24, 2022, 11:01:09 pmWell, 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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 24, 2022, 11:45:34 pm
content: Quote from: BillyO on November 24, 2022, 11:27:10 pmDo you mean a signal with a large DC bias? Or something else?QuoteThis 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.

author: BillyO
author_rank: Super Contributor
timestamp: November 25, 2022, 02:00:11 pm
content: Quote from: bdunham7 on November 24, 2022, 11:45:34 pmWell, 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.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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2022, 03:28:27 pm
content: Quote from: BillyO on November 25, 2022, 02:00:11 pmIf you have a 4Vp-pAC 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.

author: BillyO
author_rank: Super Contributor
timestamp: November 25, 2022, 04:14:04 pm
content: I did actually try that, but it seemed to bugger up the mean and RMS measurement values. Perhaps that's a real bug.

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2022, 04:19:24 pm
content: 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 youmeanwant but there's probably a way to do it.

author: Simon
author_rank: Unknown
timestamp: November 25, 2022, 05:31:24 pm
content: Quote from: bdunham7 on November 24, 2022, 11:01:09 pmThis 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.

author: BillyO
author_rank: Super Contributor
timestamp: November 25, 2022, 07:36:58 pm
content: Quote from: bdunham7 on November 25, 2022, 04:19:24 pmYou'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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 25, 2022, 11:42:44 pm
content: Quote from: BillyO on November 25, 2022, 07:36:58 pmMy AWG won't do a 10V DC bias with a 4Vp-psquare wave (max output is 10V), so I set it up with 8VDC + 4Vp-psquare 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: -8.00VCH1: 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.

author: BillyO
author_rank: Super Contributor
timestamp: November 26, 2022, 03:02:29 am
content: 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: 09-06FPGA: 2021-11-08OS: 8.3Firmware: 6.1.37R9

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2022, 04:25:47 am
content: Quote from: BillyO on November 26, 2022, 03:02:29 amNo, 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 01-04OS 8.2Firmware 6.1.37R6 (I don't think any further updates apply to mine)FPGA 2021-7-12I wouldn't think there'd be any difference that would matter here. Post your screenshots and we'll know.

author: BillyO
author_rank: Super Contributor
timestamp: November 26, 2022, 04:05:03 pm
content: Quote from: bdunham7 on November 26, 2022, 04:25:47 amYeah, 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.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.

author: bdunham7
author_rank: Super Contributor
timestamp: November 26, 2022, 04:45:55 pm
content: Quote from: BillyO on November 26, 2022, 04:05:03 pm"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 1040.5or ~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.

author: 2N3055
author_rank: Super Contributor
timestamp: November 26, 2022, 07:41:44 pm
content: Quote from: bdunham7 on November 26, 2022, 04:45:55 pmVery nice. simple and concise!!

author: BillyO
author_rank: Super Contributor
timestamp: October 24, 2023, 04:54:08 pm
content: 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.

author: 2N3055
author_rank: Super Contributor
timestamp: October 24, 2023, 06:14:42 pm
content: Quote from: BillyO on October 24, 2023, 04:54:08 pmWhat 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?

author: BillyO
author_rank: Super Contributor
timestamp: October 24, 2023, 06:55:57 pm
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: October 24, 2023, 09:05:34 pm
content: Quote from: BillyO on October 24, 2023, 06:55:57 pmIt 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.

author: BillyO
author_rank: Super Contributor
timestamp: October 24, 2023, 09:11:33 pm
content: 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.

author: Performa01
author_rank: Super Contributor
timestamp: October 25, 2023, 09:25:38 am
content: 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.

author: BillyO
author_rank: Super Contributor
timestamp: October 25, 2023, 10:30:27 pm
content: Quote from: Performa01 on October 25, 2023, 09:25:38 amDid 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.