two traces on SDS1104X-E wth? - Page 1
Forum section: electronics / testgear

author: nemail2
author_rank: Regular Contributor
timestamp: December 03, 2018, 11:38:00 pm
content: HeyI was doing some measurements recently, using my SDS1104X-E and when using Slope "Alter" for triggering, I get two traces in "Normal" trigger mode. In single shot mode, there's only one trace.What on earth is that? I have tested this on channel 1 and channel 3.I was measuring the 12V supply voltage of a self-made LED stripe dimmer during PWM dimming of around 3m LED stripe @ 3A (rolled up on the spool so it was a "little" bit of an inductor), @lowest duty cycle.Thanks for any help for a newbie :-)edit: oh yeah, I just saw that the channels were in AC coupling mode but the trigger was in DC. would that be an issue?

author: ataradov
author_rank: Super Contributor
timestamp: December 03, 2018, 11:44:21 pm
content: It looks like you have both rising and falling edges enabled for the trigger. If I'm interpreting those up and down arrows correctly in the trigger settings. And slope is set to "Alter" too.

author: DaJMasta
author_rank: Super Contributor
timestamp: December 03, 2018, 11:46:06 pm
content: In normal mode, every input signal that the scope can catch that matches the trigger condition is displayed in the window unless your persistence settings are zero, so if you have signals that are different but can trigger, they will appear overlayed on the screen. Also works if you have multiple points in the same signal that can satisfy the trigger condition.

author: nemail2
author_rank: Regular Contributor
timestamp: December 04, 2018, 12:08:07 am
content: thanks!im curious: when would one use this functionality, for example?

author: DaJMasta
author_rank: Super Contributor
timestamp: December 04, 2018, 12:27:26 am
content: You see more of what's going on with them overlayed, a screen's refresh rate is probably 60Hz or less, but the waveform captures per second of a even an entry level scope will be thousands, having slight persistence and this display mode means you can see a lot more of those captures and compare for inconsistencies or glitches.You're sort of asking the wrong question, though, standard oscilloscope triggers work in this way, so this isn't really a feature, it's just a result of the standard way an edge trigger works. If you think it's detrimental, there are other trigger types available that won't catch such a glitch, or you can set the trigger point to a part of the waveform that only will capture the one "version" of this waveform. As mentioned, just constraining the trigger to a falling edge exclusively, instead of rising or falling edge as it is right now, you'll only get the one waveform. I think for most basic use cases, a single direction edge trigger is a good default.

author: tautech
author_rank: Super Contributor
timestamp: December 04, 2018, 03:36:04 am
content: Quote from: nemail2 on December 04, 2018, 12:08:07 amIt's really useful for eye diagrams.Otherwise an edge trigger is used for most work, rising mostly but occasionally falling. Leave trigger on DC coupling.For looking at a small AC on top of DC, AC input coupling is the way to go and sometimes setting the probe and input attenuation to 1x allows for the sensitivity you might need. Otherwise leave it on 10x.BTW, screenshots are just a few 10's of kb when you use the blue Print button and save them onto a USB stick.Just give the scope a few seconds to recognize the stick and you're good to go.

author: rf-loop
author_rank: Super Contributor
timestamp: December 04, 2018, 07:46:33 am
content: Quote from: DaJMasta on December 04, 2018, 12:27:26 amSiglent SDS1000X-E series screen refresh interval is bit over 40.32ms (~24.8Hz)When it do its maximum there can be up to over 4600 wfm overlaid in one screen.If Acquisition mode is selected "Fast" (it is default).Siglent have two acquisition modes (selection is in Acquire menu page 2). Fast and Slow. Rarely occasionally also slow mode may be useful.Of course "Fast" mode result depends current wfm/s speed depending many settings.If user select Acquisition mode "Slow" then it is forced to maximum one acquisition for one TFT update so that every tft refresh have maximum just exactly one waveform or less (as in old school DSO).QuoteYes. And most scopes, also Siglent, have this as factory default (if user have not programmed "default button" for his own defaults then pressing this "default" return most of settings to factory default.If user select some other trigger minimum need is that he know how they work or just for learn how they work. Education is... some times fun and some times frustrating as in OP case show.-----I can also see some confusion is OP messageOP:QuoteIf you do not know then keep Trigger coupling DC. Select Input coupling as you need for DC or AC.Select Trigger coupling to AC only if you really need it (and in this case you also know how it works and why) It need understand that trigger engine after ADC do not care anything how your input coupling is. Trigger engine see only digitized signal after ADC and nothing else. And trigger DC/AC is just related to this signal what it can see. All what it can see is ADC output. In some cases if you need input coupling DC for watching DC level drifting etc but want trigger to example signal what riding on this moving DC (example in systems where power(DC) and data (signal riding on this DC) is delivered in same wire and this DC may have some drifting. In this case you separate this signal from this DC for trigger using Trigger coupling AC... or if you need bit higher corner frequency what AC coupling then it can also do with trigger coupling LF reject (what is also as "AC" coupling)Without more experience and knowledge and in normal simple use. Just keep Trigger coupling DC for avoid confusions. Select input coupling as need DC or AC.