Siglent SDS1202X-E compensation issue (and other manufacturers ?) - Page 1
Forum section: electronics / testgear

author: tkonekt
author_rank: Newbie
timestamp: October 13, 2017, 08:52:00 am
content: Hello everyone,I just received my Siglent SDS1202X-E oscilloscope, and I have a small query that appears immediately after trying to set my probe compensation.I wonder if I have to make a material return !As soon as it was first used, I set the compensation of the probes with the internal square wave generator, everything goes well, this setting is very very sensitive on probes... (Of course, probes and software are set to x10 mode except software for CH2 probe...).By changing the vertical resolution step by the steps proposed by the system (up voltage input via knob), I constat that I have an over-compensation that appears when internal scale relays come into action.Thinking that there may be a software problem, I updated the system (version 5.1.3.8R2 to 5.1.3.13) and then made the fundamental automatic calibration. The problem still there.Do you have the same type of problem? (regardless of the brand of your oscilloscope)I find it a bit aberrant to must make a probe compensation when I change vertical level of adjustment, we speak nevertheless here measuring instrument already calibrated, isn't it ?What do you think ? Is this issue part of the tolerances of input ?Thank you for your adviceSorry for my English, I hope you'll understand my jabber

author: tkonekt
author_rank: Newbie
timestamp: October 13, 2017, 07:53:12 pm
content: Maybe variable capacitance showed in analog input stage onEEVblog #985 - Siglent SDS1202X-E Oscilloscope Teardownare used to compensate this different relays action modes, what do you think about that ?

author: tautech
author_rank: Super Contributor
timestamp: October 13, 2017, 08:05:45 pm
content: You will get some little drift as the unit warms up, this is not uncommon with any scope.The trimming sensitivity is related to the range of trimming available for the probe, probes with a narrow adjustment range will be less sensitive.I use a slower timebase and increased amplitude like in your 6th image to compensate probes and I have found one faulty probe in a new X-E before dispatch to a customer. Your's look OK.

author: nctnico
author_rank: Super Contributor
timestamp: October 13, 2017, 08:14:57 pm
content: Judging from the pictures the oscilloscopes internal compensation isn't right so you have to return it for service/repair. A square wave should look like a square wave at every V/div setting.

author: tkonekt
author_rank: Newbie
timestamp: October 15, 2017, 01:05:12 pm
content: A friend test this strange report with a Rigol DS1054Z, no issue seems occur... Relays scale are not ont same level.Screenshot source1: 500mV/Div2: 2V/Div3: 5V/Div

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2017, 05:20:24 pm
content: The screendumps of your friend's scope look the way they should look.

author: StillTrying
author_rank: Super Contributor
timestamp: October 15, 2017, 05:38:04 pm
content: I think it looks normal for fuzzy vision. There's only about 25 voltage levels per vertical division, so a drift of 1 level looks worse than it is.

author: nctnico
author_rank: Super Contributor
timestamp: October 15, 2017, 07:21:00 pm
content: Quote from: StillTrying on October 15, 2017, 05:38:04 pmIn that case you'd see the effect stronger in pictures 1&2 than in picture 3 because the sensitivity in pictures 1&2 is higher. However in pictures 1&2 it isn't there but in picture 3 it is clearly visible.

author: tkonekt
author_rank: Newbie
timestamp: October 15, 2017, 09:49:28 pm
content: I just do another test in "Fine ajustement" mode of V/Div in two way :1st (Pict 1&2) -> I go down (with vertical scale knob), until I hear a 'clic' of relay', I set the compensation then I go just above (0,02V/Div)2nd (Pict 3&4) -> The opposite, I go just above the 'clic' relay and do readjustment of compensation then go below .Result ...We can see another issue, reading voltage is wrong on overcompensed curve, but it's normal, mesurement works !...

author: StillTrying
author_rank: Super Contributor
timestamp: October 15, 2017, 10:18:25 pm
content: "I just do another test in "Fine ajustement" mode of V/Div in two way :"Good test, in that case I agree the frequency response of the different Y sensitivities are off a bit.

author: TK
author_rank: Super Contributor
timestamp: October 15, 2017, 10:23:57 pm
content: Time to return it and buy a real scope

author: tautech
author_rank: Super Contributor
timestamp: October 15, 2017, 10:28:46 pm
content: Quote from: tkonekt on October 15, 2017, 09:49:28 pmThanks for clear examples of this issue. I'll report it to the team at the factory right this minute.

author: TK
author_rank: Super Contributor
timestamp: October 15, 2017, 10:33:39 pm
content: Quote from: tkonekt on October 15, 2017, 09:49:28 pmPicture 1 & 3 should measure the same, 1.2V or 1.22V, but they are different.

author: tkonekt
author_rank: Newbie
timestamp: October 16, 2017, 08:29:20 am
content: I forgot to specify, but I have the issue problem with both channels, even by interchanging the probes ...Someone would have this oscilloscope to do the same test to be sure if I'm an isolated case ?I proceed to the material return for refund, however I do not know where to turn now, I think I'm going to move to another manufacturer ...Quote from: tautechThanks tautech to report this issue at the factory, because I'm not good enough in english to explain that in one shot ...

author: tautech
author_rank: Super Contributor
timestamp: October 16, 2017, 07:23:16 pm
content: Quote from: tkonekt on October 16, 2017, 08:29:20 amOne last thing I'd ask you to check, is firmware version 5.1.3.13 seen on the System page ?(just to confirm it's properly installed)

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2017, 07:54:06 pm
content: Quote from: tkonekt on October 16, 2017, 08:29:20 amTell us what you want to use your scope for. What kind of circuits do you repair and/or build?

author: etron
author_rank: Newbie
timestamp: October 16, 2017, 08:10:39 pm
content: My scope has the same issue, firmware version 5.1.3.13. And as in your case it's on both channels with either probe. So you're not an isolated case.Wonder if this is a hw or sw issue..?Anyone else?

author: tautech
author_rank: Super Contributor
timestamp: October 16, 2017, 08:27:49 pm
content: Quote from: etron on October 16, 2017, 08:10:39 pmWelcome to the forum.I'm quite sure it's SW as it's only visible at certain points when using the Fine V/div adjustment.Unlike old analog Fine V/div implementation where it's done with a divider, in this case where it's both on the boundary of a relay shift and the amplitude is changed within IC's, a firmware fix is the likely remedy.We'll know soon when I get some feedback from the factory.I've emailed a # of contacts at Siglent to ensure they are fully aware of it and implement a prompt fix.

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2017, 08:46:56 pm
content: Quote from: tautech on October 16, 2017, 08:27:49 pmI strongly doubt it can be fixed by firmware. Simplified: in an oscilloscope front-end you need multiple capacitive/resistive dividers to get different attenuations and each needs to be adjusted to get a flat frequency response. If you get that wrong (for example due to too high component variations) you get the effects visible in the screendumps. The problem occuring when the relay is switching from one range to another is a tell-tale sign the problem is in the hardware. I have quite a bit of hands-on experience with these kind of circuits.

author: tkonekt
author_rank: Newbie
timestamp: October 16, 2017, 09:00:33 pm
content: My first tests was with V 5.1.3.8R2 Firmware, then with lastest V5.1.3.13 available at the moment.You may find that I have done the firmware upgrade quickly, look at the "Startups times" value between the two picturesI think the problem is more on the input stage than the firmware itself.I took THE good decision of the day : return to retailer and I asked it a refund (to take my time to choose a new trademark device).I can not conceive to keep a device for which I know there is a defect that I could see only two minutes after starting it.I am relatively disappointed by this Siglent model which looked promising on datasheet...The subject is not closed, I would like to see if other users have encountered the same issue, and especially if certain one finally opened the beast to correct it, for example add extra-cap to the existing cap compensation, or other things, because I'm sure it's hardware issue near of the relay (scale selector) on input, and I would have done it if the oscilloscope had at least one year..

author: kcbrown
author_rank: Frequent Contributor
timestamp: October 16, 2017, 09:15:40 pm
content: Quote from: nctnico on October 16, 2017, 08:46:56 pmIs it not possible to specify the components in question specified with sufficient precision and accuracy to make such adjustments unnecessary? If not, then what is responsible for causing adjustment to be necessary in the first place?If such adjustments have to be made on a per-scope basis then how are they typically made in applications such as this? With variable resistors/capacitors? By selecting custom values at assembly time?In any case, if the values are adjusted on a per-scope basis then that suggests a quality control problem at Siglent.

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2017, 09:39:15 pm
content: The sensitivity and requirement for adjustments depend entirely on the design. It could be an error in the bill of material so they mounted a +/-20% X5R capacitor instead of a 1% NPO/COG capacitor but that is pure speculation. You can only answer these questions after reverse engineering the input stage of the SDS1202X-E.

author: etron
author_rank: Newbie
timestamp: October 16, 2017, 10:36:58 pm
content: There are two trim caps on each input stage as seen in Dave's teardown:EEVblog #985 - Siglent SDS1202X-E Oscilloscope Teardownso you'd think this would be fixed during calibration (by Siglent or Saelig?).The reason I wondered if sw could be the culprit is that both channels are out by the same amount despite being individually tune-able (via the trim caps). I would have expected a sloppy calibration to have affected the inputs at least somewhat differently. And my results are also the same as tkonekt's.Would be great to hear from other owners.

author: nctnico
author_rank: Super Contributor
timestamp: October 16, 2017, 11:49:26 pm
content: There is a test you can do: use a direct connection between the calibrator output and the input (or use a function generator with a square wave output). If the effect is gone then the problem is likely that the input capacitance of the scope isn't constant and throwing off the adjustment for the 1:10 probe. If the effect persists then it is likely a factory calibration error or out of spec component.

author: rf-loop
author_rank: Super Contributor
timestamp: October 17, 2017, 07:03:32 am
content: Quote from: nctnico on October 16, 2017, 11:49:26 pmSignal from generator.SDS1203X-E analog front end have 3 different vertical bands.Test signals to scope input. Gen out - Suhner RG223/U 1m - Tek 011-0049 - SDS1kX-E input.Attached images:Vertical band 1. 0.4V Sqr Scope vertical 100mV/div, probe multiplier 1xVertical band 2. 0,8V Sqr Scope vertical 200mV/div, probe multiplier 1xVertical band 3 8.0V Sqr, Scope vertical 200mV/div, probe multiplier 1xOf course square is not flat because frequency response from 0Hz to 200MHz is not flat. I do not know any single scope where this frequency response is flat, not even if scope price is same as house.In this test small change in input capasitive reactance between V bands do not affect so much it can detect. Most part of difference between ideal square wave come from frequency response flatness.Situation with these probes when probe is set for 10:1 (10x) is bit different.There can see some LF compensation error.In this case my opinion is that it is possible that square wave is disturbed due to small change in oscilloscope 1Mohm input (capasitive) reactance change. V bands 2 and 3 have not so much difference between each others but V band 1 change capasitance more. Change is perhaps even some 1pF's and it affect to this probe Low Freq compensation. {Siglent development team need take this into consideration}Every V band (I, II and III) have separate pathway what are selected by relays. There is not adjustment for null these capasitive input reactance differences between vertical bands.I do not want speculate if different probes are less sensitive for this small reactance change.If want, it can also say that this error do not violate given specifications for frequency response error limits or level error limits, not even close. But cosmetically...., well - it can be better also my nose can be more beautiful. Ideal pure square waves can find only in kids school books.All what human see in oscilloscope display is sum of errors added to unknown truth. After get real long time wide range experience people can live with errors mixed with unknown and still he can do his jobs.I have not any even minor difficulties to do my works with Tektronix 2465, HP old digita or some more new digitals and also including this SDS1202X-E. I have not any single equipment what do not tell me wrong things. All frequencies are off, all voltagfes and currents are off, my clock os off. My straight line is not straigth, my micrometer is wrong, my temperatures are wrong. I not know anything what is right. I have brains for live with all these errors and they do not stop or other way fail my work. If my brain or heart go to too big errors, then my works fails.Vertical Band IVertical Band IIVertical Band III