EEVblog #685 - What Is Oscilloscope AC Trigger Coupling?

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

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[johnmalone]

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.

[davecc]

[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!

[ece]

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.

[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.

[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!

[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!

[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.

[vezzz]

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.

[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.

[Xrispy]

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

[DanielReyes]

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

[Guggel]

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!

[donmoore]

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.

[colonelk]

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

[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!

[dave-d]

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

[eternalblue]

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

[gamingSlasher]

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