| Products > Test Equipment |
| Functional comparison of R&S RTB2000, Siglent SDS2000X and Keysight DSOX1000 |
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| rf-loop:
--- Quote from: nctnico on April 05, 2022, 01:15:21 pm --- --- Quote from: rf-loop on April 05, 2022, 01:03:28 pm --- --- Quote from: Someone on April 05, 2022, 10:48:18 am --- --- Quote from: rf-loop on April 05, 2022, 10:22:12 am --- --- Quote from: RBBVNL9 on April 05, 2022, 09:43:22 am ---SDS - “Seq. Acq. Switch” set to off. When it is turned on, I see sets of n acquisitions (where n is the number set by the “Seq Segment” parameter” with almost 100mS in between, so a considerable drop in the number of trigger events per second. --- End quote --- This is really weird. Even If I test with this same signal with SDS1104X-E and 200us/div and Sequence. I take oneshot sequence with 50MSa/s 140k length and when I look segments time stamps they have all 3ms (3000us) delta time. So 333.33 segments in second. Then I change it to 14k memory so 5MSa/s and look 1900 segment single sequence. Every single segment in sequence time stamp delta time is 3ms. So 333.33... segment/s Then with 1GSa/s 2.8M current mem lenght (one segment length)... still all 19 segments delta time is 3ms.... 333.33... segment/s --- End quote --- I think the explanation is good, with the sequence mode in run mode: [n sequences without gaps] 100ms processing interval [n sequences without gaps] 100ms processing interval... etc Interesting it was not in a circular mode (does not support it?) where the sequences capture around forever until stop is pressed. --- End quote --- It was nice you rise this circular mode up. Siglent do not have it (least yet afaik) --- End quote --- AFAIK the history buffer should work thay way (although likely not with fast sequence mode). --- End quote --- Yes it works as continuous FIFO (always bacround). When stop there is always last segments available. But even when it (SDS1kX-E) may have up to >100kwfm/s (ksegment/s) average speed in second! (1 channel on, 50ns/div and display mode dots, measurements off). This mode quaranteed speed is extremely slow. So if it is important to be sure it do not drop out any single trig event... example with SDS1104X-E if measurements off theree can be 3.5ms pause. So quaranteed speed may example 280wfm/s (segment/s) and with measurements on example 24ms pause (with average speed example around ~70kwfm/s) means quaranteed speed around 40wfm/s. Many times in segmented mode we need some quarenteed speed to be sure any trig event is not dropped out. If this is not important then of course this mode can use as continuous segment mode (fifo mode) and after stop last segments are in buffer and every segment can analyze. |
| kcbrown:
--- Quote from: RBBVNL9 on April 05, 2022, 09:43:22 am ---SDS - Record length (parameter “MAX record length”) setting is 20k. Interestingly, any other setting (200k, 2M, 20M, 200M) does not make any difference for this measurement - Sample rate is 10.0 MSa/s (this number changes when other record lengths are selected) - “Acqu Mode” set to “Fast”. Interestingly, changing it to “Slow” does not make any difference for this measurement - “Seq. Acq. Switch” set to off. When it is turned on, I see sets of n acquisitions (where n is the number set by the “Seq Segment” parameter” with almost 100mS 100ms in between, so a considerable drop in the number of trigger events per second. - Display Type = Vectors. But setting it to dots makes no difference whatsoever. - Only Channel 1 activated. --- End quote --- I was able to reproduce this, but there's a caveat that I'll explain below. My suspicion is that you set the final memory depth after you set your timebase and that your initial memory depth was at least 20M. From what I've seen it makes all the difference in the world. Once you have your acquisition settings finalized, change the timebase and the settings will "take". Sometimes that's not necessary, while other times it is (with the timebase set as you have, going from 20M or 200M to anything less than 20M will necessitate a twiddle of the timebase to get the new waveform update rate to take hold). With the timebase set as you have (200 us/div), with a 1 kHz waveform, here's what I get for trigger output frequency (average), which presumably is a representation of the internal waveform update rate: PointsSamples/secFrequency (avg)--------------------------------------20k10M333200k100M3002M1G15320M (actual: 4M)2G30200M (actual: 4M)2G30 If I start with maximum memory depth, set up the timebase and volts/div, I get 30 Hz as described above. If I then set my memory depth to 200k, it will stay at 30 Hz until I twiddle the timebase. Twiddling other settings (including things like hitting the "normal" trigger button again) makes no difference. Only the timebase seems to actually cause the update rate to change under these conditions. |
| RBBVNL9:
@ kcbrown, Thanks a lot for replicating this, leading to what seems to be a quite important finding! So it seems a change in memory depth setting (and hence sample rate) only takes effect if the user afterwards changes the timebase settings... That would be strange and non-intuitive behaviour from the user's point of view, but it would certainly explain a lot about the low (re-)trigger rate we were observing. Hope to have some time tonight to test this myself, and also find out what this means for the poor visual observation of infrequent glitches (which I talked about in my video episode 7 at 47:27) and the ability to observe mask failures (for which I have some preliminary measurements mentioned in the comparison document V61 on page 33). So, thanks again! Excellent work! . rudi |
| kcbrown:
--- Quote from: RBBVNL9 on April 08, 2022, 06:15:39 am ---@ kcbrown, Thanks a lot for replicating this, leading to what seems to be a quite important finding! So it seems a change in memory depth setting (and hence sample rate) only takes effect if the user afterwards changes the timebase settings... --- End quote --- Not necessarily. Going from a smaller memory depth to a larger memory depth seems to make the new setting have an immediate effect on the waveform update rate (which might be a small change, as it was when going from 20k to 200k). I haven't tested other timebases and, thus, other maximum capture lengths. It may be that the issue only happens when the capture size you're going from is limited by the maximum sample rate versus the screen width in time, as it is with 20M and 200M at 200 us/div (which limit the capture size to 4M). So a bit more testing is needed to fully characterize this. I do think it's safe to say, though, that if you change the memory depth, then changing the timebase will make the new setting have the appropriate effect on the waveform update rate if that effect hasn't already taken place. --- Quote ---So, thanks again! Excellent work! . rudi --- End quote --- You are most welcome! |
| Performa01:
As has been mentioned before, the trigger engine in the SDS2000X Plus is not working properly. That it fails to apply changes in max. record length without a detour (nice finding, @kcbrown!) might add to the problems, but it's certainly not the only one. I did a test with the yet unreleased sibling of the SDS2000X Plus, the new 12 bit SDS2000X HD, since it doesn't seem to have a comparable bug. The max. record length is important. We need to limit it to 200kPts to get 333 wfms/s peak (325.86 average). At 2 Mpts the average rate is about 180 Wfms/s and at 4 Mpts it is around 100 Wfms/s. So this sounds as if it is faster than the RTB, just as was to be expected from the technical data. display mode dots or vectors doesn't make a difference, the same is true for x or sin(x)/x of course. In general, dots mode is only effective at timebase settings faster than 50 ns/div, where any interpolation errors such as Gibbs ears can be avoided and the wavform update-rate sped up at the same time. See attached two screenshots: SDS2504X HD_Signal_Square_1kHz_Mem200k This is the test signal, a ~1kHz square wave on the SDS2000X HD. Vector Mode, Sin(x)/x, "Fast" Acquisition. We certainly won't get more than 30 Wfms/s in "Slow" mode. Trig_Out_1kHz_Mem200k This is the Aux Out (triggger out) signal, monitored by another scope with the counter application including statistics. |
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