EEVblog 1678 - BEWARE of this Oscilloscope Triggering Issue - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: April 04, 2025, 09:43:53 pm
content: Oscilloscope have a pre-arm trigger period that can cause confusion if you aren't aware of it. And how different scopes operate and indicate this in different ways.Also some potential bugs in the Keysight 3000 and HD3 series scopes.00:00 - Slow timebases can be problematic for triggering02:13 - What happens when you press the Single button? Pre-arm / pre-trigger sampling.03:02 - Keysight 3000T, where's Wally? Where is the Ready indicator?03:45 - Keysight 3000T why can I trigger without the Armed/Ready indicator?06:05 - Schrodinger's Armed Indicator07:39 - Beware of pre-arm/ pre-trigger time on slow timebases08:23 - Keysight HD3, if the Megazoom V any different?10:47 - Keysight HD3 missed trigger bug?12:59 - Keysight 3000T 20sec pre-arm delay bug?13:47 - Siglent SDS1204X HD15:24 - Rohde & Schwarz MXO416:47 - Rigol DHO81418:52 - Conclusion

author: Kleinstein
author_rank: Super Contributor
timestamp: April 05, 2025, 07:39:38 am
content: The HP scopes seem to somewhat recocnize a trigger before armed. However It does not trigger but more restart the arm period.The trig'd? text is really odd. If should be easy to change the text to a more meaingful one.The rigol scope with Run / wait T'd is already much better.The very slow time scales are a rare use case for a scope. So it is not that an important feature and no need for an extra HW LED. When slow there is no problem using the screen - ideally a popup window. At the slow speed the CPU has plenty of time and nothing interesting on the screen anyway.

author: graybeard
author_rank: Frequent Contributor
timestamp: April 06, 2025, 12:23:13 am
content: My Siglent SDS824X HD shows ARM at the top of the screen when the single sweep is pressed. That changes to READY when as soon as pre trigger buffer is full and the scope is READY to trigger.It only shows on the screen because there are no status LEDs. Your Siglent SDS1204X HD scope showed on both the screen and with the status LED.

author: bdunham7
author_rank: Super Contributor
timestamp: April 06, 2025, 02:11:10 am
content: Quote from: Kleinstein on April 05, 2025, 07:39:38 amI once used mine with a combination of slow sweep and trigger delay to capture something happening in the middle of the night, I can't remember what it was right now. I do remember being a bit surprised that I could stretch the caputure out to 1000s/div (almost 3 hours) and still get 20kSa/s. And the trigger delay maximum is 10Ms, or about 115 days. I imagine I'd want to be really sure that everything was set up right before doing a 115-day measurement!The trigger LEDs (Ready and Trig's) are a nice touch and actually useful when you are using the "knob twiddling" method of getting a trace on the screen because they're right next to the trigger level knob. For slow-motion, less important.

author: Rich1234
author_rank: Newbie
timestamp: April 06, 2025, 07:37:19 pm
content: Dave,You might want to retry your experiment with the R&S RTB2004 (with V3 firmware). It has a "Pre Trigger" display with a running percentage of amount acquired while it is in pre-trigger mode.

author: Totoro
author_rank: Contributor
timestamp: April 06, 2025, 08:58:08 pm
content: Hey Rich1234, I wanted to mention this as well. I have firmware 2.4 and same behavior as you describe.

author: golden_labels
author_rank: Super Contributor
timestamp: April 06, 2025, 10:17:34 pm
content: That makes me think: why don’t they arm the trigger instantly? We’d lose the left side of the graph, but that’s just a cosmetic problem. Obviously anybody is aware, that the scope can’t show what it didn’t observe before triggering. Just display it in dark, pale red for clarity, done.Is a patent held on that concept? Is it some non-engineer worried about UX consistency? Or just ommision among so many manufacturers?

author: EEVblog
author_rank: Unknown
timestamp: April 06, 2025, 11:54:44 pm
content: Quote from: Rich1234 on April 06, 2025, 07:37:19 pmSo it does, that's awesome. Was that change in v3?

author: Rich1234
author_rank: Newbie
timestamp: April 07, 2025, 12:04:34 am
content: Quote from: EEVblog on April 06, 2025, 11:54:44 pmAccording to @Totoro in this thread the same feature was in firmware v2.4.

author: graybeard
author_rank: Frequent Contributor
timestamp: April 07, 2025, 12:32:01 am
content: It would be even cooler if it rolled from the trigger point until it got a trigger so you could see what is happening just like in standard roll mode.This would also be a visual cue of the pre trigger buffer filling.

author: thm_w
author_rank: Super Contributor
timestamp: April 07, 2025, 09:47:33 pm
content: Quote from: Kleinstein on April 05, 2025, 07:39:38 amI agree HW LED isn't really needed, though I use slow time bases often.eg: measure current surge for device that goes through multiple powering up states over a 10s period. Then zoom in to find the peaks.Roll mode wouldn't exist if no one wanted to see long time bases, imo.