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| Siglent SDS1104X-E anomaly on what should be a simple task. |
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| 2N3055:
--- Quote from: py-bb on November 05, 2022, 12:42:08 pm ---You posted a link to this from one of my threads and I agree your situation is terrible, the pictures show a stark contrast. What do you think of a Rigol DS1052E? I'm after a digital one to capture things that don't repeat and I'm not asking for recommendations as such, I'm asking "is it afflicted by the same deal breaking problem?" Or was yours somehow defective? The probes perhaps? Thanks --- End quote --- There is no problem. Whole signal should fit on a screen. If you have something going off the screen then your signal is out of dynamic range of that particular input settings. That means you're overdriving something and will be at mercy of overdrive recovery. To be honest, there will be a little area of the screen where it still works but it is not 5 screens high more like 10%. So simple rule that works all the time: your whole signal amplitude should fit vertically on screen. |
| bdunham7:
--- Quote from: py-bb on November 05, 2022, 12:42:08 pm ---Or was yours somehow defective? The probes perhaps? --- End quote --- It wasn't defective, it simply has a characteristic of having much, much slower overdrive recovery than the other scopes I compared it to. It has been stated by others that this is simply the nature of modern DSO input amplifiers, but I haven't taken the time to compare any others nor do I actually have access to many to try. AFAIK nobody has tried my fairly simple signal test on any fancier scopes. It is possible that older designs may not have this issue even in cheapo scopes, but I don't know. Yes, keeping the signal on the screen fixes the issue, or at least almost does (there was a thread about this same scope showing a small dip on a very slow square wave and I think that is probably also related to the damping of the input amplifier somehow) but keeping it on the screen also reduces the resolution of your view of the signal that you actually want to see. |
| 2N3055:
I'm sorry I don't know the links of top of my head (and won't be searching for it), but modern DSO scopes have more limited dynamic range than old CRT scopes. Members here did find that some old Tek DSO had a bit better overdrive behaviour but not much. I tried with Keysight 3000T, people tried with R&S scopes and they all have overdrive recovery distortions (R&S RTB2000 and RTM3000 quite nasty ones too). Also I remember RTB2000 had squarewave droop on some timebases on some scopes, it was on here few weeks ago.. --- Quote from: bdunham7 on November 06, 2022, 05:43:36 am ---AFAIK nobody has tried my fairly simple signal test on any fancier scopes. It is possible that older designs may not have this issue even in cheapo scopes, but I don't know. --- End quote --- Would you be so kind and remind me as to what test you mean? Thanks. |
| bdunham7:
--- Quote from: 2N3055 on November 06, 2022, 10:37:34 am ---Would you be so kind and remind me as to what test you mean? Thanks. --- End quote --- This one here: https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/msg3451402/#msg3451402 --- Quote ---Members here did find that some old Tek DSO had a bit better overdrive behaviour but not much. --- End quote --- My Tek 2221A CRO/DSO hybrid did fine, but my Tek TPS2024 also seems to recover quickly enough to not have issues with this test. Since the recent poster asked about the Rigol 1052E, I have to wonder if it might actually be OK here--it has the same analog trigger circuitry (well, not quite) and pitifully small memory as the TPS2024. Looking at the thread again and in light of the more recent discussion regarding the 'dip' on a 10Hz square wave, I think there is visible distortion even on the first screenshot with the signal fully on the screen. I think there is more than just overdrive recovery going on there. Edit: One additional data point--I just tried the SDS2104X+ on this test, it works fine down to 200mV/div, (15 divisions off the top of the screen) but fails below that. |
| 2N3055:
--- Quote from: bdunham7 on November 06, 2022, 02:24:17 pm --- --- Quote from: 2N3055 on November 06, 2022, 10:37:34 am ---Would you be so kind and remind me as to what test you mean? Thanks. --- End quote --- This one here: https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-anomaly-on-what-should-be-a-simple-task/msg3451402/#msg3451402 --- Quote ---Members here did find that some old Tek DSO had a bit better overdrive behaviour but not much. --- End quote --- My Tek 2221A CRO/DSO hybrid did fine, but my Tek TPS2024 also seems to recover quickly enough to not have issues with this test. Since the recent poster asked about the Rigol 1052E, I have to wonder if it might actually be OK here--it has the same analog trigger circuitry (well, not quite) and pitifully small memory as the TPS2024. Looking at the thread again and in light of the more recent discussion regarding the 'dip' on a 10Hz square wave, I think there is visible distortion even on the first screenshot with the signal fully on the screen. I think there is more than just overdrive recovery going on there. Edit: One additional data point--I just tried the SDS2104X+ on this test, it works fine down to 200mV/div, (15 divisions off the top of the screen) but fails below that. --- End quote --- Thanks fo the link. Yes these kinds of tests were done, and I cannot remember where exactly I posted this (there were dozens of these discussions on same topic over years) but pretty much all modern scopes (designed in the last 10ish years) will have same problem. R&S RTB2000/RTM3000 has really bad response to overdrive, my Keysight 3000T also. There is a bit of range outside screen but maybe 10-20% (it will vary on input range , sometimes a bit more) and only way to do it right is to keep it on the screen. Inside signal path uses low voltage rails and if you apply 1 volt to input of amplifier with 20X gain that drives amp into clipping. Simple as that. Even old CRT scopes had same problem, but they had very high voltages inside and therefore large dynamic headroom. Also they have been optimized for such use because with analog scopes you had to look at signal differently... Vertical offset works to nullify large DC from signal that has large DC with some AC on top. In which case you subtract DC part and amplifier gets only the rest. You could do that with AC coupling, but DC coupling with offset retains absolute voltage values for correct measurements. Different scopes have different DC offset ranges. One thing I like about SDS2000X HD is extended offset in comparison to other scopes in class.. Useful for work on power circuits, well complemented with 12 bit, low noise and analysis package.. |
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