Scope with fast waveform averaging (can your scope go faster?) - Page 1
Forum section: electronics / testgear

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: July 15, 2022, 03:18:39 pm
content: I am looking for a scope that can do fast waveform averaging. For example, if the horizontal time span is 10 microsec and trigger rate is 100 kHz, it should be able to average 32768 waveforms in less than 1 sec while skipping every other trigger. In practice it usually takes much longer. Partly it has to do with waveform update rate, but even scopes that claim fast update rate slow down when averaging is on.I am wondering if anyone has looked at this characteristic among low and medium cost scopes?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 04, 2022, 08:15:11 pm
content: I am still collecting data for how fast various scopes can perform waveform averaging. The simplest setup is to send a 1 Hz sine signal to the scope, expand to minimum timescale and shortest waveform length and then increase the number of averages until the amplitude of the waveform oscillating up and down on the screen goes down by 1/2.So far my results are:Typical low-cost scopes (Siglent, Micsig, Owon): 8 to 16 averagesKeysight EDUX:5124096 (max allowed 65536)Rigol DS6104: 8192 (max allowed 8192)Siglent SDS2000X HD: 1024 drops by 2% (max allowed 1024) -thanks to rf-loopI would be curious to collect data for other newer scopes: Keysight DSOX3000 series, R&S, etc. Thanks!

author: Marco
author_rank: Super Contributor
timestamp: August 04, 2022, 08:38:48 pm
content: I haven't looked lately, but I assume they are all still sadly pathetic, for no reason other than the firmware sucking. They have the FPGA and memory bandwidth to do better, but they just don't.A few years back ina threadon capture systems with really fast averagingGageseemed to be the cheapest which came up.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 04, 2022, 09:28:11 pm
content: Quote from: Marco on August 04, 2022, 08:38:48 pmAnother option for purpose-build digitizer with averaging ishttps://spectrum-instrumentation.com/, they claim it can do 5M waveforms per sec. They also have a software solution using CUDA GPU. Gage can only do 100k waveforms/s with FPGA.But in general I don't like digitizer approach unless absolutely necessary. It can be setup and work for a single project. Then inevitably the computer or the software gets messed up and no one wants to touch it again. In contrast, a good scope can last decades for many projects.

author: Someone
author_rank: Super Contributor
timestamp: August 04, 2022, 10:18:52 pm
content: Quote from: maxwell3e10 on August 04, 2022, 08:15:11 pmBut whats the trigger? if "auto" then its anyone guess how fast triggers are being issued and if they are uncorrelated with the 1Hz signal. Sounds like a very roundabout way to try and estimate averaging speed.There are some measured averaging rates already on the forum:https://www.eevblog.com/forum/testgear/oscilloscopes-averaging-speed/

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 04, 2022, 11:19:39 pm
content: One can add a separate trigger signal and make it 100 kHz or faster. One can also measure the trigger out frequency. But this is just the simplest setup to quickly estimate the averaging speed by eye.

author: nctnico
author_rank: Super Contributor
timestamp: August 04, 2022, 11:27:59 pm
content: Quote from: Someone on August 04, 2022, 10:18:52 pmIndeed. And it will go wrong on scopes which halt for a little while before going back into auto-trigger mode or have a low auto-trigger rate to begin with.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: August 04, 2022, 11:52:50 pm
content: Rohde & Schwarz RTO1024: 4626/s (795.5/s with secondary zoom view)You can combine with low-pass averaging for no additional performance penalty.EDIT: it's about 10000/s at shorter timebases, the above was for 10us.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 05, 2022, 02:45:18 am
content: Quote from: nctnico on August 04, 2022, 11:27:59 pmWhatever conditions that make it go faster is the best. Basic question is what is the maximum possible update rate while averaging. By increasing the number of averages one can actually see the response time by eye.One of the crucial parameters is the minimum waveform length. At 10 GS/s and 10k points it takes 1 usec to collect one waveform, even if the horizontal full scale is zoomed to 100 nsec or less. If the minimum possible waveform length is longer or sampling rate is smaller, it takes even longer.

author: Performa01
author_rank: Super Contributor
timestamp: August 05, 2022, 07:28:17 am
content: Quote from: maxwell3e10 on August 04, 2022, 08:15:11 pmSiglent SDS6000 manages 8192 averages at about 62% of the original amplitude (600 mVpp). Similar to the SDS2000X HD, there is still almost no amplitude drop with only 1024 averages. See screenshot with 1 s display persistence:SDS6204_Avg8192_1Hz_600mVppI don't have one here, but I strongly disagree that the current low end Siglents will have slow averaging. Even the cheapest SDS1202X-E has the averaging acquisition mode implemented in hardware, so its speed should be in the same ballpark as SDS2000X HD. The SDS2000X Plus is the only modern Siglent DSO, which explicitely lacks the Average acquisition mode and has it as a math function exclusively - which is slow, of course.EDIT: SDS1000X-E series actually doesn't seem to have hardware support for averaging.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 05, 2022, 01:47:18 pm
content: I retested a few scopes again, couldn't see much difference between auto trigger and normal trigger with >100 kHz rate.On Keysight EDUX1002 I now get up to 4096 averages before the waveform amplitude drops by a bit more than 1/2 (see picture, initial signal is nearly full vertical scale).On Siglent SDS1104X-E I get very slow averages even if the number is set to 4. Not sure if it has the latest firmware or maybe some other setting is making it slow, perhaps someone else should check.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: August 05, 2022, 03:08:16 pm
content: Ohh, 10us wasn't a part of the requirement? In that case, the RTO is faster, see above.

author: switchabl
author_rank: Frequent Contributor
timestamp: August 05, 2022, 10:43:20 pm
content: On a Keysight 2000X series scope I can get up to 13.3k wfms/s in averaging mode (dependent on the timebase setting but not the number of averages), down from 220k wfms/s in normal mode. This is measured with a frequency counter connected to the trigger output.The -3dB frequency of a moving average filter is approx. fs* 0.443 / N (for large N). So that works out at around 5800 averages in your methodology. Depending on the actual implementation, things may be a bit more complicated (don't believe it is actually purely a FIR filter, so the frequency response may be somewhat different).

author: JehTeh
author_rank: Contributor
timestamp: August 06, 2022, 04:03:25 am
content: I might not be running this test right, but I was bored and had a few minutes this evening around the house - my Rigol MSO8204 just falls under the halfway mark at 32768 averaged samples. At 8k, no drop at all and at 16k it just starts to fall off.This is at 200ps/div though - I did not play around much with longer time base settings.1Hz square wave on channel 1, 1Vpp. I had the external trigger on 1MHz though but I don't think she will actually trigger that often...I don't know if there is a built in display on the Rigol for wfms/s (which would be nice) and I didn't feel like dragging its baby brother I have on the shelf out for checking trigger rate, but I think in this configuration it should be running basically full speed.32k samples16k samples8k samples

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 06, 2022, 11:16:39 am
content: Welcome to the forum! This looks like the fastest so far! But I am not sure if square wave input would give the same result as sine wave. Could you check if it's similar with 1 Hz sine wave input?Also I noticed it says the waveform has only 20 pts. Does the scope give you an option to limit number of waveform points to only what is on the screen?

author: JehTeh
author_rank: Contributor
timestamp: August 06, 2022, 03:32:12 pm
content: I tried again with a 1Hz sine wave - it does get a bit worse, you can see the 16K averages and 32K averages attached. 16K is a bit over half, 32k is roughly 1/4 FS.The only other difference to the last test is I just moved the GPSDO 10M reference to the EXT trigger in, so we have a 10M instead of 1M external trigger for this, but I don't think that will matter.On auto memory depth at 200ps/div it sets 20pts - if I manually select the lowest option for memory depth in the averaging window (1k) it does not appear to change the measurement by much if at all (maybe the tiniest bit smaller with more data).The last two attachments are at 32k samples 100ns/div. Auto memory sets 10kpts, signal is basically gone, manually setting 1k points we are right around 1/4 FS still, just the smallest bit less than at 200ps/div.

author: Performa01
author_rank: Super Contributor
timestamp: August 06, 2022, 05:13:03 pm
content: Quote from: maxwell3e10 on August 05, 2022, 01:47:18 pmI had the opportunity to have a look today and unfortunately you're right. The implementation of the Average mode seems to be very different on the SDS1000X-E series.We get only a handfull of averages per second, yet the acquisition rate remains high at up to 50k triggers per second. This can serve as a warning that the trigger rate does not necessarily need to be correlated with averaging speed. Averaging looks like a true acquisition mode on the SDS1000X-E, but quite obviously is some post processing.On the SDS1000X-E, we can use Dots display mode to speed up the trigger rate, but the averaging performance will not change because of this, i.e. it is still very slow.By contrast, a SDS2000X HD or SDS6000 does not even allow Dots Display mode to be used together with Averaging Acquisition mode. Trigger rate is slower (yet well beyond 10k) but averaging performance is vastly better.BTW, what's the "Rigol DS6104" in your 2nd posting?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 06, 2022, 06:54:30 pm
content: Thanks for checking SDS1104X-E. It's interesting that trigger rate is not always indicative of average update rate.Rigol DS6104 is a (now discontinued) 1 GHz scope that I have, it's around 2010 vintage. I am hoping there is something faster now.

author: DaneLaw
author_rank: Frequent Contributor
timestamp: August 06, 2022, 07:05:28 pm
content: Quote from: maxwell3e10 on August 04, 2022, 08:15:11 pmThat is as relative as it comes.. if you have tested something specific on a given osccilioscope' then refer to that model, and not the whole brand as per se..Do recall these vendors have tons of models ranging from a few hundred bucks to numerous thousands,even Micisig varies from entry "M-model" to "ETO model" and there are numerous models in between and they seem to vary quite a bit from model to model.Same with Siglent and likely also Owon.- if you have tested a given model, and have some tangible test-data, then at least refer to it. and clock it to a given model..

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 06, 2022, 07:33:37 pm
content: I was referring to typical low cost, but popular models (Siglent 1104X-E, Micsig TO1104, Owon XDS3104), under $1k. I don't have a Rigol in this class to test. Here the standout is Keysight EDUX, which uses the hardware of higher-end models.Btw, there is no data so for on any Tektronix scopes, is there any hope for them?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 07, 2022, 06:16:51 pm
content: I played a bit more with Rigol DS6104. It's trigger out rate also has no direct relation to the number of averages, it does not change when averaging is turned on. The trigger out rate maxes out at about 180 kHz when the horizontal scale is 10 nsec/div and memory depth is set to auto, giving 700 waveform points. For shorter horizontal scale the trigger out rate goes down again.Under these conditions it can average 8192 points without significant drop in amplitude for 1 Hz sine wave. I can't increase the number of average points any more, but I can increase the input frequency to 3 Hz before the amplitude goes down to 1/2.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 10, 2022, 01:02:56 am
content: Could someone run the 1 Hz sinewave test on a Keysight DSOX3000 series scopes? I am hoping they might be faster based on 1 M waveforms/sec update speed and the fact that my puny EDUX1002A with 50,000 waveforms/s update can still do fairly close to a top Rigol.

author: Someone
author_rank: Super Contributor
timestamp: August 10, 2022, 02:00:11 am
content: Quote from: maxwell3e10 on August 10, 2022, 01:02:56 amNo, because it is a poorly designed test that doesn't measure what you think it does. We already have people posting/reporting the averaging rate in wfms/s

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 10, 2022, 03:17:31 am
content: No, it gives youexactlywhat you want, which is how fast the scope completes a given number of averages. So if you are playing with your DUT, it tells you how quickly the scope will respond to a signal change while doing the averages. Or if you want to save the data, it tells you how long to wait until you can hit the stop button.The waveforms per second (if the scope has a trigger out and one has another scope nearby to measure it) do not necessarily correspond to the number of waveforms averaged, as seen in a couple of examples above.Now, there was a test done earlier on another thread with 3000T scope:Quote from: 2N3055 on April 19, 2020, 12:03:51 amBut all it says that the scope can average at more than 10 kHz,assumingthe trigger out equals to waveforms averaged. Increasing the ns/div scale will necessarily slow it down, both because of longer acquisition time and possibly because there are more points in the waveform. Increasing the trigger rate until it is much higher than waveform/sec speed would tell what is the maximum speed.

author: Someone
author_rank: Super Contributor
timestamp: August 10, 2022, 04:27:10 am
content: Quote from: maxwell3e10 on August 10, 2022, 03:17:31 amKeysight 3000, measuring averaging speed, and that thread has posts carefully checking that the trigger output rate was an accurate representation of acquisitions (not just raw triggers as in some other scopes).The post you quoted explicitly shows how the rate on the trigger output dropped when enabling averaging compared to the "normal" acquisition mode. Averaging speed is not some constant or even a ratio of the normal speed, it will have its own characteristics and limitations, which is why it has to be tested in isolation (and for the specific use case since fast in one situation will not always be fast in others).Averaging on that particular scope is slower than "normal" acquisitions, but you only notice it when the trigger rate approaches the limit. Which is why "testing" with trigger set to auto and estimating averaging rate by adjusting thenumber??? of averages is many layers of misdirection. An (unintentionally) correlated trigger could make that average to 0 very quickly and provide extremely misleading results.

author: LaurentR
author_rank: Frequent Contributor
timestamp: August 10, 2022, 07:34:43 am
content: A quick 3000T datapoint (include disclaimer on methodology here):The 3000T 1Mwfms/s starts dropping around 20ns/div. While at 1Mwfms/s, if enabling Averaging, the wfms/s drops to 26kHz (at least according to the trigger output), regardless of the # of averages (which is 2-64k on the 3000T).Below that, there is a very variable ratio between Normal wfms/s and Averaging wfms/s (in the 1-50 range). The ratio gets smaller as longer time bases, with an asymptote at 1.At and above 20us/div, the sample rate is locked at 5GSa/s in both mode. Below 20us/div, the Normal sample rate starts dropping and the Averaging sample rate is locked at 1/4 the Normal sample rate (as reported by the scope).In all cases, the number of averages (2-64k) has no impact on wfms/s.Rough wfms/s (as measured by Trig Out - disclaimers apply):500ps/, 1ns/, 2ns/, 5ns/, 10ns/: 26.4 kHz20ns/: 34.2 kHz50ns/: 13.8 kHz100ns/: 6.9 kHz200ns/: 1.7 kHz500ns/: 1.1 kHz1us/: 1.1 kHz2us/: 1.0 kHz5us/: 950 Hz10us/: 820 Hz20us/: 650 Hz50us/: 96 Hz100us/: 96Hz200us/: 62 Hz500us/: 78 Hz1ms/: 62 Hz2ms/: 44 Hz5ms/: 18 Hz10ms/: 9 Hz20ms/: 4 Hz50ms/: 2 Hz100ms/: 1Hz

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 10, 2022, 12:43:25 pm
content: Thanks for detailed measurements. It looks like there is also a sweet spot for 20 nsec/div. What was the waveform length for these measurements? That could have an effect on the speed.In principle, running average requires only one multiplication/addition per waveform, so it's no more complicated calculation than scaling/offset that needs to be applied to every waveform to display it. Display calculations are often done on decimated data. But for low number of waveform points there should not be a big difference in number of points.To compare it to Rigol measurements (which does not have a useful Trig out signal in this case), one needs to use:Quote from: switchabl on August 05, 2022, 10:43:20 pmSo roughly speaking it looks comparable between Rigol 8000, 6000 and Keysight 3000T.Quote from: Someone on August 10, 2022, 04:27:10 amThe whole idea is that if the triggering is fast and without gaps the whole averaging completes before the slowly changing sine wave has a chance to change sign. Now, one does have to be careful if using auto trigger that it is set on a different channel or outside of waveform range, so the scope does not introduce display delay when getting a trigger on auto setting.

author: tchiwam
author_rank: Regular Contributor
timestamp: August 10, 2022, 01:03:48 pm
content: Record in a long buffer then download the wave and make the averaging yourself ?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 10, 2022, 01:08:38 pm
content: Quote from: tchiwam on August 10, 2022, 01:03:48 pmNo, that defeats the whole purpose of a scope to look at signals in real time and diagnose things based on small features in averaged signal.

author: LaurentR
author_rank: Frequent Contributor
timestamp: August 10, 2022, 03:59:36 pm
content: Quote from: maxwell3e10 on August 10, 2022, 12:43:25 pmI used a 30MHz sine wave to get enough triggers. I also tried in auto trigger with noise and saw no difference at any of the time bases.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 10, 2022, 04:38:26 pm
content: Quote from: LaurentR on August 10, 2022, 03:59:36 pm

author: Someone
author_rank: Super Contributor
timestamp: August 10, 2022, 10:20:42 pm
content: Quote from: maxwell3e10 on August 10, 2022, 01:08:38 pmAveraging without a trigger defeats the whole purpose of averaging....

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 10, 2022, 11:42:24 pm
content: Yes, in most cases that's true, when measuring a fast signal. But in this case it doesn't matter (assuming auto trigger is fast enough), because the signal is very slow. Think of it as a kind of box-car high-resolution averaging.Still curious what is the waveform length LaurentR used. I haven't used a 3000T. Does it just default to auto length equal to number of points displayed on the screen?

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 11, 2022, 05:12:05 pm
content: According to the manual, 3000T uses waveform length to fill the screen or half the working memory, it's not so clear. On my EDUX1002 it uses 50k points all the time in run mode independent of time scale and 100k points in single shot mode. In single shot mode with averaging on it is supposed to do just one set of N averages and stop.I am leaning toward Rigol 7000 series scope, it's likely to have one of the fastest averaging for a scope under $10k, new or used. Having long memory would help if one has to resort to downloading the data.

author: JehTeh
author_rank: Contributor
timestamp: August 11, 2022, 06:21:14 pm
content: On the rigol front, I was playing around more with my 8k this morning and trying to see if I could hit the 600k trigger rate, but I have been having no luck. The baby rigol watching trig out is seeing ~110k max. Interestingly whether I have averaging on or not seems to make no difference (200ps/div, 20pt 'auto' memory - all settings from 1k averages to 64k show same trigger rate).Scope is supposed to do 600k/s but I am not sure under exactly what circumstances, would be interesting to actually get it there and see if turning on averaging makes a difference.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: August 11, 2022, 07:05:45 pm
content: On Rigol 6104 I was able to hit the advertised trigger rate of 180k/sec, but interestingly not at the shortest time scale. The averaging also does not seem to affect the trigger out rate, the scope must just pick some fraction of the waveforms to average.You should be able to get from Rigol tech support the conditions to get 600k/sec since they advertise it so prominently.The datasheet has this note for waveforms update. I wonder how narrow are the conditions to get highest rate.Note: Maximum value. single-channel, 10 ns horizontal time base, input amplitude 4 div, sine wave signal with 10 MHz frequency. Others are default settings.

author: JehTeh
author_rank: Contributor
timestamp: August 11, 2022, 07:28:11 pm
content: Quickly messing around, it does indeed hit >600k wfms/s (~700 actually) at 10ns/div. Funnily enough, only there, but I have not bothered to play with it more to see where else it might be running at that rate.In this case turning on averaging brings the trigger rate back to roughly 110k/s.