Is there a DSO with a quick enough screen reaction? - Page 1
Forum section: electronics / testgear

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 21, 2015, 02:02:46 pm
content: Following two recent threads:https://www.eevblog.com/forum/testgear/scope-recommendation-for-ham-radio-repair/https://www.eevblog.com/forum/testgear/recommendation-request-new-rigol-ds1054z-or-used-tektronix-2467bhd/and playing with a new MDO3104 all-singing-all-dancing scope, I've uploaded a very short videohttp://youtu.be/3rYtT1GexjIto show my biggest complaint about DSOs - the delayed screen reaction when probing a circuit. For me it is essentially a deal stopper, as this delay makes it much more difficult for me to use a DSO scope for fault-finding and quick circuit checks. So here is my question in the thread title. Or perhaps I am asking too much from DSOs and should just keep my three CRT scopes in a good shape as long as I can?CheersAlex

author: Kalvin
author_rank: Super Contributor
timestamp: December 21, 2015, 02:36:21 pm
content: How long is the capture buffer. Try to adjust it shorter so that the scope will not keep capturing data until the longer-than-necessary sample buffer is full.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 21, 2015, 02:41:25 pm
content: Quote from: joeqsmith on December 21, 2015, 02:32:12 pmThe setup is very simple - I've connected the tips of two probes together and touched +5V rail for a short time. You can see that the trace on the analogue scope reacts instantly and the screen reaction on the DSO is delayed by a very noticeable amount of time. I was hoping that a relatively expensive Tek may be better in that respect compared to some cheaper DSOs, but was quite disappointed.Quote from: Kalvin on December 21, 2015, 02:36:21 pmThe record length on the video is the default 10K samples, changing it to the minimum of 1000 does not change the perceived delay.CheersAlex

author: jitter
author_rank: Frequent Contributor
timestamp: December 21, 2015, 02:44:48 pm
content: Have you tried a Keysight scope, similar to what Dave uses? I use one of those (albeit the DSO, not the MSO) at work, and I really can't complain about responsiveness.

author: Performa01
author_rank: Super Contributor
timestamp: December 21, 2015, 02:59:37 pm
content: One of the differences between analog and digital scopes is that analog shows signal changes immediately indeed, whereas digital has to fill the sample buffer first. How fast this is depends on the timebase setting (plus some processing time). Try using a faster timebase and see what you get.

author: Fungus
author_rank: Super Contributor
timestamp: December 21, 2015, 03:03:33 pm
content: Quote from: Alex Nikitin on December 21, 2015, 02:02:46 pmIf you're seeing a delay, you're doing it wrong.These scopes work by filling up a buffer with samples. If the buffer is too big there can be a delay before it restarts, yes. What's the solution? Don't use a big buffer! Look in the menu and there will be a setting somewhere.nb. Most of them also have an "AUTO" setting that does a good job of managing the buffer size.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 21, 2015, 03:05:14 pm
content: Quote from: Performa01 on December 21, 2015, 02:59:37 pmThat doesn't help (at least on this Tek and on lesser scopes I have here), even with only 1000 points and much faster timebase the delay is about the same. I've played with settings before taking the video.CheersAlexP.S. - I would appreciate is somebody can take a similar video with better results - perhaps I am doing something wrong all these years

author: nctnico
author_rank: Super Contributor
timestamp: December 21, 2015, 03:38:24 pm
content: This is not a bug but a feature of Tektronix scopes. They show the last recorded (triggered) trace a little bit longer so you have a chance to see it.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 21, 2015, 03:46:17 pm
content: Quote from: joeqsmith on December 21, 2015, 03:37:37 pm200us/div, 10K samples, 5Ms/sQuote from: nctnico on December 21, 2015, 03:38:24 pmI have two (lesser) Agilent scopes here, with a similar (even worse) behaviour.CheersAlex

author: nctnico
author_rank: Super Contributor
timestamp: December 21, 2015, 03:50:08 pm
content: Try set the trigger level outside the signal range and test again. It should be better.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 21, 2015, 04:04:36 pm
content: Quote from: nctnico on December 21, 2015, 03:50:08 pmI've tried that too - it helps a bit on the cheaper Agilent DSO1014A but doesn't make a difference on the Tek. Moving the trigger level outside the range of the signals you would like to see is somehow counter-intuitive. Again, you need to know what you are looking for before probing things, which is not always convenient or even possible.CheersAlex

author: G0HZU
author_rank: Super Contributor
timestamp: December 21, 2015, 04:11:01 pm
content: If I set my old dumpster salvaged HP54540C DSO to 200us/div with an 8k record length the probe response to a 6V DC test signal (on or off) is effectively instant in terms of probe response. I can tap the probe point numerous times per second and it keeps up no problem. I can't say that I like the overall quality of the LCD display on this old scope but the scope and the display do seem to be very responsive in this test.This scope is 20 years old and it uses an early type of flat panel LCD display so I'd expect newer scopes to be at least as good as this big old dog.

author: Karel
author_rank: Super Contributor
timestamp: December 21, 2015, 04:22:58 pm
content: No problem here with a Rigol DS6104, timebase 200uS/div, 14Mpts, 5Gsa/sec.It reacts instantly.The tek can do 280,000 waveformupdates/second, so I guess there must be something wrong with your setup.

author: G0HZU
author_rank: Super Contributor
timestamp: December 21, 2015, 04:27:56 pm
content: I did a side by side comparison of the HP54540C DSO against my Tek 465 analogue CRO and the Tek 'wins' if I scratch the probe across the test circuit because it can respond super fast to an intermittent connection here. But the DSO does OK too. It's not as fluid as the CRO but it updates the screen fairly quickly.But in terms of a basic on/off probe test the HP54540C is quick enough to appear instant for this type of test. I think it is fast enough such that my camera won't do it justice. Much, much faster than the MDO3000 in the video in the first post.

author: dom0
author_rank: Super Contributor
timestamp: December 21, 2015, 04:28:51 pm
content: Throughput =/= latency(The accuracy =/= precision of IT)

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 21, 2015, 04:32:14 pm
content: A decent digital scope has negligible latency. Even cheap ones rarely have enough to be a problem or annoyance.Something to bear in mind is that some scopes have enough memory that by setting a sufficient big time offset you will see a delay, becase that's exactly what you told it to do.I'm guessing that MDO hasn't been set up right to minimise latency.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: December 21, 2015, 04:37:05 pm
content: If you don't compare it to an analogue scope the reaction may look quick. And if you touch something very quickly you may even see nothing on a DSO and a clear result on a CRT scope. I may try to video that too.CheersAlex

author: Howardlong
author_rank: Super Contributor
timestamp: December 21, 2015, 04:38:34 pm
content: Quote from: nctnico on December 21, 2015, 03:38:24 pmTotally agreed. It's to do with therefreshupdate rate when in Auto trigger when no trigger is applied. It's a Tek DSO trait.It is covered here:

author: Howardlong
author_rank: Super Contributor
timestamp: December 21, 2015, 04:43:44 pm
content: Quote from: Karel on December 21, 2015, 04:22:58 pmOnly in FastAcq mode... where you lose a whole bunch of other scope functionality. I've yet to find a practical use for it myself.

author: G0HZU
author_rank: Super Contributor
timestamp: December 21, 2015, 06:04:14 pm
content: When the auto trigger level is set below the signal range on my little Tek TDS2012 the response time is extremely fast on 250us/div. Much too fast for a typical camera to capture. The LeCroy scopes in joeqsmith's video look slower in comparison (probably due to the camera/youtube/my_monitor) but maybe I'm cheating by setting the trigger level like this.If I set the auto trigger inside the signal range then the display response time of the TDS2012 becomes less consistent and usually it pauses and displays and holds the first triggered sweep for a fraction of a second. There is a lot of lag after the probe is removed in this mode too.But by sliding the trigger point out of range it becomes instant for both on and off.

author: georges80
author_rank: Frequent Contributor
timestamp: December 21, 2015, 06:18:42 pm
content: Agilent msox2024a has pretty well instant update of probe touch/release in auto trigger mode - faster than my eyes/neurons... even at 1ms/divisionJust set the timebase appropriately (faster).cheers,george.

author: woodchips
author_rank: Frequent Contributor
timestamp: December 21, 2015, 06:42:01 pm
content: After reading the many threads here about a DSO being a complete replacement for analogue, and discovering that I really am a dinosaur, what does the waveform update rate mean?I assumed that if it can do, say, 100,00 waveform updates per second then that the latency discussed here doesn't exist?Adjusting the time/div setting seems irrelevant to me, with analogue then the trace simply rises to the peak irrespective of when in the scan the probe is touched to the 5V line. Does it mean that a DSO has to complete a scan before any of it will appear on the screen?Got three DSOs, but dropped one and still not mended, not certain where the other two are but both pretty old, 10+ years, so might not be good examples to try.

author: georges80
author_rank: Frequent Contributor
timestamp: December 21, 2015, 06:48:12 pm
content: ^ if you set the timebase slow then the waveform WILL appear in realtime like a heartbeat monitor.There's really no issue with a modern DSO. I got rid of my CRT boat anchor scopes a LONG time ago and can't think of anytime that I've wanted one back.There are quite a few folk that still live in the dinosaur era that imagine that an analogue/crt based scope gives them some benefit... same folk that need to have 4 or more of those scopes on their bench at all times (waiting to mutate to an 8 armed octopus I guess)cheers,george.

author: joeqsmith
author_rank: Super Contributor
timestamp: December 21, 2015, 06:57:24 pm
content: Quote from: G0HZU on December 21, 2015, 06:04:14 pmAll three DSOs were set to auto. In the first two, trigger was set to mid. Last, trigger was set outside (which is what I had assumed the OP was doing). Trying to run some different conditions for OP. I think your idea to scrape the probe is good but really, I was not sure what the OP was attempting to do.I drug out my Tektronix eval board. Found the manual on-line for it. Pages 8&9 talk about screen update rates. How times have changed.http://www.pa4tim.nl/wp-content/uploads/2010/11/Tek-Scope-Evaluation-Board-24-P.pdf

author: G0HZU
author_rank: Super Contributor
timestamp: December 21, 2015, 07:36:42 pm
content: QuoteOnly four? I've seen some benches where there are double this amountAt my place of work, I haven't seen anyone use an analogue scope for many years but we do still have several of them on the TE racks.I rescued a couple of fully working Hameg HM1004-3 and HM1007 CRO scopes from a trip to the company skip/dumpster last week along with the big old HP54540C DSO.http://www.hameg.com/hm1004-3.0.htmlhttp://www.hameg.com/downloads/man/HM1007_english.pdfI'm hoping to offer them to a local radio club (if they want them)I do like using my old Tek 465 CRO from time to time and it still commands a permanent place on my workbench. But I suspect that it will finally be retired when I decide to buy a modern and versatile DSO.

author: free_electron
author_rank: Super Contributor
timestamp: December 21, 2015, 08:38:15 pm
content: typicla problem for scoes that use a software trigger mechanism. fill the buffer -> crunch data to find trigger event -> display.this can sometimes be 'fixed' by setting the time mark to the left of the screen ( as opposed ot the center ). in that case the scope does not have to show the pre-trigger buffer and refresh rate goes up

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: December 21, 2015, 09:06:07 pm
content: Hi, Daniel from Keysight here. Sorry if I'm repeating information from other replies."Screen reaction" = "waveform update rate"Update rate is basically how quickly the scope can re-arm and display a signal. Most scope vendors now specify this (especially when we started making a big deal about it).There are a few things that will effect your update rate:1. Time per division setting. (Or sweep speed). Obviously a time/div setting of 1s/div will give you a significantly slower update rate, because you are only updating every dozen seconds or so.2. Memory depth setting. For some vendor's scopes, the longer the memory depth setting the slower the update rate. I feel obligated to say this isn't true for our Keysight InfiniiVision scopes, they always capture full memory depth and won't tank the update rate doing so.3. Trigger mode. Again, depending on the vendor, the difference between what we call "auto" and "normal" trigger modes can have an effect. Especially when using a non-triggerable waveform like you used in your example.4. Other features turned on. For processor based architectures, turning on other features will slow your update rate. For example turning on digital channels, serial decoding, measurements, math waveforms, etc. will significantly slow down your update rate. This isn't the case for ASIC based scopes (see my obligatory pitch below). I've seen other vendor's scopes with update rates in the mHz because of other features being turned on.Obligatory pitch: As far as our Keysight scopes go, the 2000 X-Series have a 50,000 wfms/s update rate and the 3 and 4k scopes have a 1,000,000 wfms/suncompromisedupdate rate. Because we use in-house designed ASICs for our scopes, we are able to do a processes in parallel with plotting. So, turn on digital channels, measurements, cursors, decoding etc. and it won't change your update rate.

author: Howardlong
author_rank: Super Contributor
timestamp: December 22, 2015, 01:25:48 am
content: Here you go. 0.2Hz 1Vpp square wave into all scopes, at 200us/div (250us/div on the TDS2024B).Agilent DSO7104BRigol MSO1074Z-STek TDS2024BTeb MDO3014https://youtu.be/W2uEmoxQRgg

author: Someone
author_rank: Super Contributor
timestamp: December 22, 2015, 05:27:53 am
content: Quote from: Howardlong on December 21, 2015, 04:38:34 pmAuto trigger is the work of the devil, line trigger or roll mode makes it clear whats going on when you want to see untriggered signals.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 22, 2015, 09:45:29 am
content: Quote from: Someone on December 22, 2015, 05:27:53 amWhat I've never understood is why no scopes allow you to set the timeout in auto trigger mode.Also, it would sometimes be useful if it adapted the auto-trigger timeout based on incoming trigger rate, so it would effectively switch from auto and normal when incoming triggers are present, but then time out back to auto if no trigger is received for a small multiple of the last trigger rate.

author: coppice
author_rank: Super Contributor
timestamp: December 22, 2015, 10:01:29 am
content: Quote from: mikeselectricstuff on December 22, 2015, 09:45:29 amTradition.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 22, 2015, 10:12:40 am
content: Quote from: coppice on December 22, 2015, 10:01:29 amI realise that, just surprised nobody's noticed that it would be useful in some situations, and is trivial to implement.

author: coppice
author_rank: Super Contributor
timestamp: December 22, 2015, 10:45:00 am
content: Quote from: mikeselectricstuff on December 22, 2015, 10:12:40 amMusical instrument sales fall if you don't follow tradition. Why would you expect test instruments to be different?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 22, 2015, 01:25:37 pm
content: Quote from: coppice on December 22, 2015, 10:45:00 amBecause adding an additional feature isn't going to lose sales - it should default to traditional behaviour, but it would be nice to set the timeout.My Agilent MSO6034A has a timeout that appears too short sometimes, in that when it's receiving triggers at a reasonable rate, auto mode still adds additional triggers so you need to turn it off to get a stable trace.

author: w2aew
author_rank: Super Contributor
timestamp: December 22, 2015, 02:31:21 pm
content: If you're checking just DC voltage levels like this, then use Line trigger - the scope will then be triggering at the line rate (not the slower Auto trigger rate), and you won't get the apparent delay that the Auto trigger is giving you.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 22, 2015, 03:27:27 pm
content: Quote from: w2aew on December 22, 2015, 02:31:21 pmBut it won't trigger on a signal when it gets one

author: andy2000
author_rank: Frequent Contributor
timestamp: December 22, 2015, 04:02:20 pm
content: One of the few tasks that I still prefer a CRO for is aligning an older CD player. First, many older/cheaper DSOs can't easily display an RF eye pattern from the noisy signal you get from the pickup. Having an immediate response to changes in the RF eye pattern makes it much easier to optimize settings without going too far and losing focus lock. DSOs also tend to smooth out rapid variations in the RF level which can mask problems.

author: coppice
author_rank: Super Contributor
timestamp: December 23, 2015, 08:44:55 am
content: Quote from: mikeselectricstuff on December 22, 2015, 01:25:37 pmIn a typical lab, where you keep moving from instrument to instrument and have no control over them, anything that needs configuring is just another PITA.

author: rf-loop
author_rank: Super Contributor
timestamp: December 23, 2015, 12:36:59 pm
content: Quote from: w2aew on December 22, 2015, 02:31:21 pmIs it valid for modern digital side triggering digital scopes if turn off trigger holdoff?Example in Auto trig, holdoff closed, Siglent SDS1000X do around 60000 horizontal sweeps if 50ns/div and one channel in use and if signal do not have any trigger event, just free running. Using line trig it do only just 50 sweep/s if line freq is 50Hz.

author: Keysight DanielBogdanoff
author_rank: Unknown
timestamp: January 19, 2016, 06:52:51 pm
content: My checklist for looking at wfm/s update rate is:1. Fastest (smallest) time/div setting2. Stable trigger (not in "auto" trigger)3. High Hz signal (faster than the banner update rate spec, preferably by an order of magnitude)4. NO trigger holdoff. When enabled it basically adds a delay between each trigger.5. Only one channel turned onThis should get you to the banner wfm/s spec.Then, play with things like memory depth, decoding, math channels, measurements, more channels, etc.