How to trigger on missing pulse? - Page 1
Forum section: electronics / testgear

author: Sören_Marodören
author_rank: Contributor
timestamp: April 06, 2024, 09:00:01 pm
content: Hi,In my system I have short pulses (<0.1 uS) that comes at approx 20 kHz indicating every "frame" that is ok.In case of a frame error, the pulse for that frame is skipped.How can I setup an Oscilloscope to trig on this missing pulse so I can see what caused it?I have been thinking on making a timer circuit that get reset by the pulse. If it is not reset, the timer will generate its own pulse (Like a pacemaker.)But, shouldn't it be possible to do this kind of measurements with a modern digital oscilloscope like Keysight DSOX 3/4000 or R&S MXO4?Can a signal generator be used as the timer mentioned above?Cheers,/Sören

author: egonotto
author_rank: Super Contributor
timestamp: April 06, 2024, 09:21:35 pm
content: Hello,in Siglent SDS2000X HD you can use dropout trigger or Nth Edge Trigger. In the R&S MXO5 you can use interval triggers. In Agilent InfiniiVision 5000/6000/7000 Series Oscilloscopes you can use the Nth Edge Burst Trigger.Best regardsegonotto

author: noisyee
author_rank: Contributor
timestamp: April 07, 2024, 06:31:09 am
content: Yes off cause, most modern scope have advanced trigger can handle the task. Just translate the event to something the scope can understand.E.g. a missing pulse of a periodic pulse sequence can be regard as an unexpected long negative "pulse"(I know it's not what we call a pulse, but scope seems don't mind), or an unexpected long interval of two edge, or a time out event...Pulse Trigger (Some called Width Trigger, or even Glitch Trigger if you don't mind it's not a glitch at all), Interval Trigger, Timeout Trigger can do the trick.

author: Aldo22
author_rank: Super Contributor
timestamp: April 07, 2024, 08:22:04 am
content: Quote from: noisyee on April 07, 2024, 06:31:09 amOut of curiosity, I tried this out on my cheap Hantek DSO2000.I think the settings are correct as the OP specifies (in the picture on the right)?That seems to work.If that's what the OP means, then it's relatively simple.EDIT: For the OP, "Width" would of course have to be greater than 50μs in your case. I don't have a pulse generator that pulses irregularly. So it still triggers at the 49μs in the picture, but at over 50μs it would no longer trigger, or only if a pulse is missing, which is the point of the question afaiu.

author: Psi
author_rank: Super Contributor
timestamp: April 07, 2024, 08:30:05 am
content: yep, most scopes have an option for trigger low / high time 'less than' / 'greater than'.So you just trigger on a low time pulse longer than the typical time between your pulses.I do recall that the Rigol 1052 had some issues with this. It didn't always work quite right.But pretty much all modern scopes the the option for triggering on a pulse longer than a set value and it normally works ok.

author: Aldo22
author_rank: Super Contributor
timestamp: April 07, 2024, 09:47:32 am
content: I have to admit that I don't fully understand all these trigger variants.I copied a few variants that appear as options for this question from the Hantek manual into an image (excerpts, attachment).Are there any more in-depth explanations about this? Link?

author: David Hess
author_rank: Super Contributor
timestamp: April 07, 2024, 02:08:46 pm
content: Quote from: Sören_Marodören on April 06, 2024, 09:00:01 pmThat is the most straightforward way, although the trigger occurs after the missing pulse which may or may not be acceptable. See below.QuoteMost modern DSOs, even lower cost ones, support triggering on a missing pulse, however this may limit the trigger rate depending on how it is implemented. Older DSOs may support it, or could use their trigger on mask violation to do it.QuoteSome signal generators, at least some old function generators, can phase lock to an external signal allowing them to reproduce the phase and frequency of the input at their output. Then a simple logic gate could compare the input to the output and trigger when the input pulse is missing. This would have the advantage of triggering on the missing pulse immediately instead of after a timeout period.

author: nctnico
author_rank: Super Contributor
timestamp: April 07, 2024, 03:21:16 pm
content: Quote from: Sören_Marodören on April 06, 2024, 09:00:01 pmThat is no problem at all. You can setup a trigger for the situation where the time between two edges is too long (where you specify how much time is 'too long'). No need to make extra circuits.

author: Sören_Marodören
author_rank: Contributor
timestamp: April 07, 2024, 08:04:48 pm
content: Thanks for the idea to use unexpected long negative "pulse" for triggering.I set up my DSOX3014A for pulse width triggering and had it to look for hegative pulses > 54 µs.And Bingo, there I could see the gap stedy on hte screen. See attached screen shot.Now I shall see what the rest of my design do during that gap...