EEVblog

In this tutorial Dave describes what AC trigger coupling is on an oscilloscope and why it can be useful. Not only on old analog CRT oscilloscopes, but modern digital scopes as well.
How and why is it different to AC channel input coupling?
Also, use of the 50% trigger control, and how the venerable DS1052E is still more usable than the new DS1054Z.
Previous video on Rigol DS1054Z and DS2000 Jitter Problem
• EEVblog #683 - Rigol D...
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[@johnmalone9382]

Two years of electrical engineering and I struggled with this. 20 minutes of video and it sat down straight for me. Thanks Dave.

[@DIYerGuy]

Outstanding Dave! The scope companies need to educate users more. They generally give you a manual (if even that) and it tells you what the controls are, what they do, and that's it. It's an entirely different matter to explain how to use particular controls in a way that a) makes sense, and b) has a practical application. Dave, your explanation was excellent and underscores that you have to know what you're getting with a scope and how to use it to take full advantage. This kind of stuff they don't teach in engineering school. Dave, you are an invaluable resource to electronics. Love your videos!

[@jrobmccoy]

This video couldn't have come at a better time! My brother and girlfriend just (as in 3 days ago) surprised me with a Rigol DS1102E for my birthday. Watching your previous videos, I had a good understanding of how a scope worked so I was able to easily able to get a waveform displayed and stable. On one of my projects though I, for the life of me, couldn't get the trigger to act how I wanted it to. AC coupled it and BOOM! Cleanly triggered scope trace. Love the vids Dave, keep it up.

[@NullStaticVoid]

cool. I had been using AC triggering only for audio signals. Which worked well because audio is ac. Now I have a better grasp of triggering in general. Thanks.

[@davecc0000]

[how can i give 10 thumb-ups? ] Triggering must be the most complex aspect of learning to use a scope. Any time you can spend explaining this function (e.g., in any video in the course of probing a signal, spend a few seconds showing alternate (right & wrong) ways the trigger might be used) removes another layer of confusion even for the "old dogs" who hadn't thought about that. Dave you are the Great Demystifier of all things electrickery. Keep 'em coming!

[@Ziplock9000]

I find the inter relations between sample size, dynamic range, bandwidth, memory depth,hi Res mode to be the most complex

[@ece3912]

A lot of high-end analog scopes also have a "Trigger View" button, which is useful a couple of ways. First of all, it shows you exactly what's going into the trigger circuit, *after* all of the coupling and filtering, so you can get a better idea of what's going on with complex signals. Also, I sometimes used it as a convenient way to view a third signal (external trigger input) on a 2-channel scope.

[@wolf9413ify]

是全台%

[@ve2zzz]

The most brilliant trigger feature i saw on a Tektronix scope is the "Trig view" button which works like the "beam finder" function, but for trigger input.

[@PeterWalkerHP16c]

+ve2zzz The Hitachi CROs have a similar feature. They increased the brightness of the trace at that point to mark out trigger and zoom areas. All analogue - amazing!

[@FutureJPL]

I just wanted to stop by and say thanks. I ended up using an older analog O-Scope for a circuits class I took two years ago. The professor never really explained triggering at all, and I can remember getting frustrated when the darn scope wouldn't trigger! Now I feel a whole lot smarter, thanks for the video Dave!

[@TheMotoRebel]

Great video Dave. Anyone who says they don’t use AC trigger coupling probably didn’t understand why they’d want to use it.

[@frollard]

When I was looking at the circuit (first 5 minutes) I had no idea why it mattered... ...then the practical...boom, like a tonne of bricks; of course that's a valuable feature! I now understand scopes so much better! I always understood the vertical domain but the time range/triggering always messed me up! Thanks!

[@EEVblog]

frollard Cool, glad it clicked for you!

[@tubical71]

EEVblog May it´s time for you, Dave, to take us by the hand and do a fundamental scope series....As you´ve just begun with it in here....soooo...?? ;)

[@tbbw]

Yeah i'm one of those too that fiddled with the knob too much it seems.

[@astrogirl1usa]

Dave, my son and I have only recently started watching you, maybe a week now. Would you consider having a weekday devoted to tutorials for 'novices', such as my 17 year old? Btw, he really, really likes your videos, but is not much on commenting. I can tell he likes your posts, because watching you is the first thing he does, after getting food, when he gets home. :) Thanks for the videos!

[@HLSDK]

Astrogirl1usa I started as a hobbyist when I was about your son's age. Videos can be fun but putting together kits, researching, and slaving away above a hot soldering iron got me the engineering degree I have now. Best of luck to him, I hope he builds some cool projects. If only Dave were around when I was in highschool!

[@dave-d]

Mr Eeev strikes again! Take a bow Sir. Thank you.

[@lasersbee]

Great Scope Trigger explanation.. I've been using my analog and digital scopes with AC and DC input coupling as you describe for years and tweaking the trigger control to see what I want to see and now I know exactly how/why it works... Thanks again Dave.

[@ubuandeyelbme]

Mind blown... I needed this video more than you can know. Thanks, Dave!

[@DanielReyes1]

Aside from the Op Amp tutorial, this was the best video for me. Thank you Dave!!!

[@VikasVJois]

Nice video Dave. You always surprise us with something most of us do not know. I admire your depth of knowledge

[@eternalblue2119]

Still making great,informative videos after making 684. Awesome!

[@Xrispy24]

Very good job at demonstrating the practical use of AC trigger coupling.

[@colonelk3000]

As a bloke with very basic electronics knowledge, that was an excellent and clear video. Every day is a school day, thanks :-)

[@gamingSlasher]

Unusually clear and to the point. Very good explanation of basic oscilloscope features.

[@Guggel1966]

Very, very good explanation. Love your informative videos, Dave. I'm just a real novice hobbyist in electronics, but I've learned a lot from you!

[@TheDigitalAura]

Yet another awesome video Dave, that really helped clear a few things up. I have a DS1074Z and until I saw this didn't ever see a use for AC trigger coupling. Let's just hope Rigol can get their act together and fix this now.

[@dinkc64]

you're the best, Dave! thanks for yet another informative learning experience.

[@donmoore7785]

This is a great video. I have been using my Keysight scope for the last 3 weeks since I bought it - my first digital scope - and developed exactly the habit you mentioned. I am constantly adjusting the trigger level. It never occurred to me to switch the trigger coupling. Another video that makes you think. Nice job.

[@hansdj6647]

This was a very good explanation of why to use AC trigger coupling. But I did not hear anything about the disadvantages, because if AC trigger coupling only has advantages over DC trigger coupling, I would expect manufacturers having dropped DC trigger coupling feature.

[@Erudotic]

Wow! You're Just saved me a lot of future knob-twidling! And in the process explained one of the last mystery-switches on my beautiful antique scope. A treasure it is and has helped me so much ever since I got it. Wouldn't trade it for a digital for the World!

[@anthonyroby296]

This was 20 minutes well spent. Afer messing around recently trying to capture some waveforms, and confusing myself in the process, next time I think I'll be much more efficient now I know what these settings really do. Great explanation!

[@BrettW]

Very well explained. Loving the 50FPS as well.

[@n1elkyfan]

I would love to see a fundamentals of oscilloscope series

[@YuvalGilad]

Fantastic explanation as always!

[@truckerallikatuk]

Great explanation Dave! Thanks!

[@Bluelagoonstudios]

Still working with my "pimped" Rigol DS1052E and for audio work at home, this scope is more than enough. But my scope at work is a Rhode & Schwarz for measurements for FM transmitters. And it's an older type and weight tons. That scope has a user manual from a few hundred pages, after 15 years I know this scope's capabilities. That's a long time to figure that one out.

[@hankus253]

Great lesson Dave.

[@tpolarbeart]

Thanks they never taught about this in school so simple to understand.

[@Silverdeamon92]

Thanks for sharing this. So much more informative

[@ElectronicsGate]

Thanks. I have learnt something new for me and really useful.

[@SHOOTURESELF2]

Really liking this 50 fps, thumbs up Dave.

[@richardnanis]

Thanks Dave! A really great explanation - finally even I got it ! :-)

[@aladaris]

Best video in a while! (Not saying the others are bad!!)

[@VolksTrieb]

Dave. Your the man!

[@rikvdmark]

Very useful an educational! Thank you!

[@MrTridac]

I like these whiteboard/bench tutorials. Reminds me of my job training. Scribble some equations on the board and then off to the bench blasting caps.

[@Tool-Meister]

Good for you Dave. I used to teach these same concepts to customers when I worked for Tektronix in the 70’s. Peak-to-peak Auto was a new development about that time. It appeared one the 7000 series then into the portables like 465 & 475. Customers thought it was magic when it was only “clamped” A/C mode.

[@questionmark9684]

Hi Dave, Excellent video, thank you! Now my digital scope is on AC coupling, until I specifically need DC coupling. Cheers Mark

[@scott2e]

Well explained!

[@VasilisMathas]

Thanks for the usefull info you give to us

[@gearstil]

I learned something new and useful!

[@tubical71]

Good one, Dave!! I think a lot of people are sadly no longer familiar with analog domain (=CRT) Scopes.

[@davidbeauchesne7399]

Thanks so much for this video.

[@sir7586]

that's useful.. it's like finding the very last link in the puzzle) Thanks

[@DumbledoreMcCracken]

Well done!

[@kmacriver]

Great job

[@boeesen]

Thanks for an informative video. Do you have a video on how and when to use external trigger?

[@louf7178]

This could be on the Home Shopping Network ... for oscilloscopes ... and they would sell. And now I know more about them, too.

[@hdmalpas]

I live and learn Dave. Nice video.

[@PelDaddy]

Of course the example could be solved by using Auto P-P triggering, or by adjusting the trigger manually as you demonstrate. Thanks for sharing.

[@Mystickneon]

Thank you!

[@joblessalex]

You just fixed the hackerspaces scopes. Thanks!

[@davecc0000]

Explain pleez. Inquiring minds want to know!

[@joblessalex]

The scopes were all on DC coupling and old analog.... Switched to AC, and they work all the time.

[@cmguitar50]

Thanks, Dave - I like!

[@TheBdd4]

Dave, THANKS! I grew up on analog scopes and now use digital scopes but never used AC Triggering. I sure will from now on thanks to you. :) Also, looking at the LIKES/DISLIKES I can't understand why someones would dislike this presentation...was it the RIGOLIANS?

[@FalcoGer]

Thank you.

[@dwDragon88]

50 FPS looks good Dave, thanks.

[@excavatoree]

Fundamentals Wednesday - Instrumentation. Thanks, Dave. A link to this video should be on your Wiki somewhere - Oscilloscopes, Use of test equipment, or something.

[@38911bytefree]

Brilliant.

[@ElectroplatedToaster]

First.. could we (and Dave who started it long ago) refrain from separating the buffs from the youngsters? The buffs will die out, the young people (so much talent!) will replace us and I want Dave to have a future audience! Hell, I wish _I_ was younger :-) On my Tek 465 (and the dust collecting predecessors) I always used AC triggering since otherwise I'd often completely lost the trace (as Dave showed). Time for "Beam Find" button, fiddle, then switch to DC trigger, and then tune the trigger level to find that over/under-shoot or weird signal level once a us I was really suspecting/searching for. That is not the case with DSO's, the "beam" is always present (well, in auto trigger, which I often start in) and it saves a lot of time for me. This episode's perfectly clean sinusoidal or square waves are not in my "problem space" (which is digital logic or known/expected analog signal levels with suspected over-under shoots or glitches) and does not really persuade me to switch to AC triggering as default. Perhaps Dave could show a more complicated scenario were AC triggering on a DSO is beneficial over DC coupling? For the record: If Rigol has a selling feature, it should (of course) work, and Dave has and is helping the hobbyists (and professionals) a LOT! Kudos.

[@shmehfleh3115]

This is one of those videos I wish I would've seen years ago. I couldn't ever quite get my scope to trigger the way I thought it should, and I just wrote it off as a bad scope. Well sure as shit, it was set to DC coupling. Even my brand spanking new digital scope was set to DC triggering by default.

[@danman32]

I feel it still could make sense having the trigger level marker even with AC coupling. When you zero the trigger level, it should put the marker at the absolute average of the AC component of the signal. In other words, in the middle of the wave. It is digital after all, the SW should be able to figure it out.

[@brig.4398]

I was lucky enough to get an owner's manual for the scope I got from ebay so I just set the switches to that position. anyway thinks for the explanation and it's interesting to see how those digital scopes compare.

[@kl1nk0r]

One question: On your first diagram, you tap of the channels before their correspondent AC/DC input selection switches. But if I set up my scope to use AC input coupling and use the exact same channel for triggering, then the triggering will be AC coupled as well, won't it? Thus in my opinion the taps at the channels to the triggering unit should go just behind the input coupling switches.

[@proluxelectronics7419]

Nice explanation, It's a lot easier to see how the displayed trigger levels work on new digital scopes. How is the +/- trigger referenced, Is it to the DC offset or scope ground?

[@bobmccarthy8637]

I have an old ---- but very HiTec for its times, ---- LeCroy 7200A with 7242B L2 option Plug-ins [500Mhz @ 2Gs/s], which has a wonderful feature of "Auto Triggering" on any triggering input. An even though it is truly a 'digital scope' in the sense that it uses two series 250Mhz ADCs, I much prefer to consider it an 'analogue' scope (for a few reasons I'll not get into here). However, my point here is why isn't Rigol (or many of the other premier manufactures) using such technology in their scopes. It seems only natural to have such a feature for, as you say, "probing unknown circuits," to which I wholeheartedly agree with your premise on having at minimum a "50%" trigger function, or at least one that the user can "preset"??? Whereas I welcome all comments on this and any input as to some of the main manufacturers' year' of incorporation of such feature[s].

[@twocvbloke]

I've never used sillyscope (heard that term used enough times though!!) myself, so it's an education on what the coupling functions do... :)

[@toddbellows5282]

I wish I had Dave for professor back in college.

[@ANTHONYBRUNO03]

good explanition

[@KX36]

I love the interface on the 2225. Wish the modern DSOs had more physical switches for common functions instead of menus inside menus...

[@schwinn434]

Well, when do u use DC trigger coupling?

[@OK2BCK]

much appreciated

[@Scruffybiggems]

wow really like the fps much smoother

[@powder-phun949]

Dave! I need your help! Could you explain to me why the mean value of the signal in the measurment tab changes slightly when i adjust vertical position of it? I discovered that on both tectronix scopes i have access to. It happens even when the scope is in stop mode. Is it normal? It probably ruined my measurments.

[@explorerpragun431]

Whats the value of ac coupling capacitor

[@vwestlife]

I only have an analog scope, so I thought AC trigger coupling would always be the norm!

[@tubical71]

Me, as well. Modern DSO have so much more, but when it comes to XY-display for example almost all DSOs give up very easly while even a 10mhz analog scope display averything just fine. So keep your analog scope. As it comes very handy someday....

[@FrozenHaxor]

Wasn't this one recorded in somewhat higher framerate? The image is definitely smoother and more... "live".

[@MyCrazyGarage]

Its 50 FPS

[@benderrodriquez]

Which button do I press to activate the Trigger warning?

[@IsaacC20]

Does Dave have a video that explains triggering? I understand it as a scope feature that "stops" a "moving trace" when the magnitude of the trace exceeds the magnitude set by the trigger level. Why does the trace move in the first place? This video did teach me about DC/AC input coupling (in addition to AC trigger coupling) though. Big thanks!

[@Ziplock9000]

It moves because it's change in voltage over time. X axis is time

[@tubical71]

I´m fooling around with my lates find a "VUKO VKS 220-16" basically a hameg 203-4a with an added "transient-recorder" 8kByte/ch. Luckly i got the whole documentation with all the scematics as well. They´re dated 16.84 until 28.84. AC triggering is working just fine;)

[@stevekhanou3412]

Can any one PLEASE tell me whats the difference between switching your trigger source from input signal and AC line ? And what do you see in the oscilloscope screen ? thank you!

[@KissAnalog]

There are times when it is just very difficult to get a good trigger on the signal that is being monitored, so the scope has the ability to simply use the AC power line frequency as a clock to trigger to. So, it triggers on your 60 or 50 Hz. Make sense? I have a new video that I'll be posting on KissAnalog that will explain this as well as other basic scope functions. I can't say that I'll be as good as Dave, but I'll give it my best...;)

[@InterCity134]

Curious. Now in 2020 did Rigol fix that bug of a time base offset based on the time domain choice shifting the signal in ac coupled trigger selecting yet? There is a 2014 firmware patch that vaguely needs Mentions a trigger bug but not what the bug is. Then a later firmware note suggests the specific problem. v00.04.00.00.00 2014/03/18 - Fixed bugs in triggering function v00.04.02.04.07 2014/12/31 - Fixed triggering function - Fixed storage function - Fixed bugs of jitter in the signal under the AC or low-frequency coupling

[@agonymobile]

BIG Thumbzzzz Up

[@MrJem437]

What is GND coupling?

[@izobretilnitsa]

It seems that AC coupling should be the default. In that case when and why we need DC coupling?

[@SatyajitRoy2048]

I think its better to put two lines when AC trigger is selected. Its easier to draw lines in digital scopes and when when two lines are drawn from the reference point then its easier to read whether the trigger is AC coupled or DC coupled. Its all about software.

[@ertreri]

Hi, can you provide a comment on how dangerous an anlogue osciloscope potentially concerning the emission of XRays due to the cathodic tube screen displays? I have read on the user manual of a Hameg oscilloscope that even XRays are emitted the quantity is still considered safe. On other hand, modern digital oscilloscopes are smaller and have displays do not even present this risk. Thanks.

[@caltonpizzaco]

I see you have all of that piled up on the new little bench. Is that for camera angle, or because the main bench is too loaded with a new teardown Tuesday shoot?

[@AttitudeGames]

Just like to say that the Rigol DS4000 series also has the 50% Trigger.

[@keywindgem]

Where do you get one of these T shirts :-)

[@juliand1053]

There are issues with triggering on a Rigol scope while calibrating it via remote commands. There's simply no way of capturing a healthy signal without first sending a "autoset" command and go from there. With these Rigol scopes the Aquire Menu is also weird. Maybe you will explain that one day in a video

[@Bob-bo8ik]

I have watched this a few times. What is the bug?

[@Romenadan]

Nice video Dave! Could you touch on Auto vs. Norm mode? I've always used Auto, but I only have an old clunker CRO (Goldstar OS-7040) where trigger level and holdoff are twitchy.

[@excavatoree]

Maybe it's the same Norm who used to work with Max doing automotive Air Conditioning engineering. Sorry. Seriously, I'd like to see that touched on as well.

[@ciprianwinerElectronicManiac]

Normal mode means that you only see a waveform on the screen when you're triggered on it. Auto mode means that you see the waveform even when you don't have triggered on it and the waveform will just roll from left to right or vice versa. Cheers :)

[@danedewaard8215]

Now it's so obvious! It just took a genius like yourself to get it through my thick scull and into my pea brain!!! Now I have to take a nap........

[@adamhixon]

Is there still a review of this scope coming? I'm considering it for my first scope purchase and I would enjoy seeing a detailed review by Dave. These bugs don't seem like a deal breaker to me, or maybe I'm just ignorant.

[@tubical71]

Go for an analog type.

[@EEVblog]

Adam Hixon Supporters have already seen one of the review videos. I was set to finish those up but then the bug happaned and I was waiting on Rigols response.

[@adamhixon]

EEVblog Ah, fair enough. Thanks.

[@aerospecies]

One annoying thing about one of these Rigol Scopes is that I noticed that my has more than 100mV offset. I spent half a day trying to figure out why my current sensor was not "zeroing" only to realise that the scope has a huge offset (yes 100 mV is huge for the sensitivity I wanted)

[@gotj]

A calibration may fix that, do it once it has warmed up.

[@aerospecies]

George Of The Jungle i will do that when i get to work on Monday hope it works.....