DSO too slow for sweep gen in xy mode - Page 1
Forum section: electronics / testgear

author: tkamiya
author_rank: Super Contributor
timestamp: November 05, 2018, 02:41:23 pm
content: I have a sweep generator + detector + oscilloscope in XY mode setup.The oscilloscope, so far, has to be analog kind; otherwise, it can't keep up with update except for slowest scan rate of the sweepGen.Slowness of XY mode in digital scopes are well discussed and well known issue. However, the substitute for it is not. Other than analog scope, what do I have to do this kind of thing? There is a very expensive looking scan/vga converter but I'd imagine its too expensive for hobbist budget.

author: Fungus
author_rank: Super Contributor
timestamp: November 05, 2018, 02:49:27 pm
content: The scan rate depends on your memory depth and sample rate. Try adjusting them.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: November 05, 2018, 02:59:25 pm
content: What exact settings and how many fps is slow?

author: rf-loop
author_rank: Super Contributor
timestamp: November 05, 2018, 03:55:09 pm
content: Quote from: MrW0lf on November 05, 2018, 02:59:25 pmExample Siglent SDS1004X-E do always around 25 TFT frame/s. Even when in XY mode it have in this case 66000wfm/s speed,TFT frame/s is main bottleneckin DSO/DPO's.25 TFT frame/s still make it slow(specially if compare to analog scope) if think example situation where input is for example X is 1000000Hz and Y input is 1000001Hz. Full one 360 degree one second. It means that every TFT frame have all what happen in TFT update period, in this case nearly 15 degree phase change.Here example. Scope running, snapshot 1 TFT frame. These kind of frames it update around 25fps. (frame interval ~40.3ms, ~24.8 frame/s)Behind XY display it acquire 66000 700pts waveforms every second. It works just as in YT mode behind XY display. In this case every TFT frame have around 2600 single XY plots (one plot looks like one circle or eclipse) It is reason why it can do all measurements from both channels and even trigger works. Also every single XY (one TFT frame have several overlaid as can see) is stored in history wfm buffer (FIFO)In this case every single previous 29140 XY plots.Visually when look TFT it is not so nice at all like analog scope because it works in real XY mode without TFT frame update period (or more slow if also some DSO have very low wfm/s speed behind XY draw if it use this method for XY)Of course if look this in live with eyes it looks much more smooth due to human eye (same as you pause old video) but still every TFT frame have all wfms inside 15 degree phase change (in this case).

author: tautech
author_rank: Super Contributor
timestamp: November 05, 2018, 09:02:39 pm
content: Quote from: tkamiya on November 05, 2018, 02:41:23 pmThe SDS1202X-E is not too bad.IIRC I videoed this before the last FW update and it looks better than it does when filmed.

author: tkamiya
author_rank: Super Contributor
timestamp: November 05, 2018, 09:45:31 pm
content: So.... what do you DO when you really need a fast XY representation of incoming signal? Is it so rare now that manufacturer is not concerned?In my use where sweepGen and detector is involved, I slowed the sweep rate really really low (like 20 seconds) and got something usable. But slowing down event is not always possible.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: November 05, 2018, 09:56:14 pm
content: But why need faster than lets say 25fps visual representation? Whats there to watch that cannot be just measured eg graph phase shift over time or whatever? Also if event is time limited could just shoot it in sequence mode and later play & inspect in detail.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 06, 2018, 01:28:45 am
content: Someone had asked me about running some Bowditch curves on my LeCroy 7200A that I had rebuilt.https://youtu.be/5yl97Vb0IMo?t=197

author: nctnico
author_rank: Super Contributor
timestamp: November 06, 2018, 02:06:01 am
content: Quote from: tkamiya on November 05, 2018, 02:41:23 pmIf you want to use XY on a DSO you have to set the time/div so you capture at least one full cycle in one sweep and the memory depth long enough to capture the amount of detail you want. Once you hit the maximum samplerate the only alternative to make things faster is to use less memory depth.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 06, 2018, 02:48:44 am
content: Maybe I could run some X-Y plotting software on my DSOs and use their built-in microphone jacks.Ripped a few audio tracks from YT. With the compression and noise, its not the best quality.https://youtu.be/e4JbfaadnLo

author: BrianHG
author_rank: Super Contributor
timestamp: November 06, 2018, 03:18:55 am
content: Quote from: joeqsmith on November 06, 2018, 02:48:44 amHere is a CRT's output:https://youtu.be/ZaTuFB5QXHo?t=294In the video's description links, there are sound card XY vector scope simulators. If you got a got 192khz sampling card, of have high frequency .wav files, these will emulate an analog XY vector scope.

author: joeqsmith
author_rank: Super Contributor
timestamp: November 06, 2018, 04:06:13 am
content: As I mentioned, I had watched a few of these videos and ripped the audio tracks from them to create that video. I'm sure YT makes a mess of them. I could not locate the raw audio or I would have used it. If you are aware of some audio test patterns that are free to download, just provide the link and I can give them a try on my old scopes.

author: Fungus
author_rank: Super Contributor
timestamp: November 06, 2018, 07:47:31 am
content: Quote from: tkamiya on November 05, 2018, 09:45:31 pmThe same thing you dowhenever you discover a particular requirementand a "bottom-end" 'scope like the Siglent SDS1202X-E comes up short:You spend more money on test gear.

author: rf-loop
author_rank: Super Contributor
timestamp: November 06, 2018, 09:37:40 am
content: Quote from: tautech on November 05, 2018, 09:02:39 pmWith latest FW (.23) in 1202X-E and latest FW (.26) in SDS1104/1204XE there is stillhugedifference between these models in XY mode display draw. (it looks like that 2 channel model, in contrast to 4 channel model, do not overlay multiple acquisitions to one XY TFT frame). But there is also other differences even in XY mode. Example in 2 channel model there is no XY history buffer available.

author: tkamiya
author_rank: Super Contributor
timestamp: November 06, 2018, 03:35:01 pm
content: Quote from: nctnico on November 06, 2018, 02:06:01 amWould you care to explain this for me? In XY mode, there isn't such thing as a "sweep" Do you mean to use XT mode and forget the X axis?

author: tkamiya
author_rank: Super Contributor
timestamp: November 06, 2018, 03:37:25 pm
content: Using sound card is a great idea. EXCEPT, input on X axis is a DC. (sweep)I've been looking for a large screen scope. That will solve this problem as well.

author: tkamiya
author_rank: Super Contributor
timestamp: November 06, 2018, 03:39:01 pm
content: I actually have non-bottom end scopes. I should try that. Since they are big and heavy, I haven't.Thanks everyone for ideas. Truly appreciated!Latest acquisition was a "bottom end" PC scope. Dismal failure!

author: MrW0lf
author_rank: Frequent Contributor
timestamp: November 06, 2018, 04:01:03 pm
content: Quote from: tkamiya on November 06, 2018, 03:39:01 pmWith PC scope you would want to set timebase / ack memory to minimal possible for given task, for example <10kSa.