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- Опубликовано: 3 окт 2024
- Don't be caught out by embarrassing premature triggering!
Dave demonstrates how and why your oscilloscope may trigger before it's supposed to, and how to solve it.
Forum: www.eevblog.co...
#Oscilloscope #Tutorial #Triggering
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These are amazing videos. So much information and experience to be gleaned from these. Thank you Dave and hope you and the fam have a great weekend!
Been there, seen that. In the late '60s I was on a team building a drone navigation/autopilot system based on Omega Navigation technology. (GPS gear was too expensive and bulky.) This was in the USA but the company, which had been strictly building analog telemetry radio links, was bought out be an Italian company that built the airframe. They wanted the USA electronics knowhow. The owner of this company insisted that all the new test equipment be made by HP, so our scopes were, of course, HP scopes.
We had a big sheet of plywood with all our prototype electronics bolted down to it to simulate the airframe and there was three separate systems avionics boxes mounted there with the electrical cabling connecting them together. We had the whole system working together and were still testing and updating the software.
One day we started working in the morning but everything had become unreliable. Stuff would work for a while and then the software in one system or the other would crash. We were baffled for quite a while. We kept asking the various teams what they might have changed that could affect all the systems this way. Nobody knew. We kept thinking it was noise in the power system. Finally the right person heard the story and said, "Oh, we changed out all the fans to brushless motor type.
We hooked the scope to the power line but it looked just fine, smooth as silk. One of the engineers said that HP scopes weren't fast enough to see the noise that might be there. Well we got a Tektronix rep to bring in a 'scope, a 465 to be precise. We hooked it up the same way we had connected the HP scope and ... nothing. But then we turned off all the lab lights and turned up the the brightness on the scope and there it was, a sharp little glitch riding on the power.
Needless to say, we bought some of those scopes. The fix was pretty easy, just added some filtering on the power. I don't remember the details of the fix but I sure remember that 'scope.
I just want to be the first person to say, "Okay boomer" in reply to this comment. Peace.
Great story, thanks for sharing.
Chineese takeaway oopsie protection. Never change Dave. 😂
This is also a good example of why you should be aware of the sampling rate at the current timebase, and that using peak detect acquisition can help to see this sort of glitches.
This is something I think is often forgotten (I do sometimes forget this for sure), that the signal that enters the scope is split up in 2 paths.
One is just for triggering and such stuff, and the other goes trough the processing circuitry and is what we actually see on the screen.
Real men have "chinese takeaway oopsie protection" :)
Absolutely!😂🤣😂🤣
That's the best addition to my tech jargon board for a while indeed :)
I watch most Eevblog videos while doing something else so I don't pay 100% attention. Where does he say that?
New title: “why doesn’t my scope trigger correctly?”
Not bad!
I went with the very mature, Premature!
EEVblog - LOL
this video needs a trigger warning!
I hate it when things happen Premature.
Good video - useful to be aware of this potential triggering.
Also don't forget you have the filter enabled, how much time will one waste trying to troubleshoot a bandwidth issue. Ask me how I know...
Great video, good to see back to basics again.
I don't think I need to ask how you know!
Very interesting. I wouldn't have thought the trigger and display circuitry were separated like that, but it makes sense now that I think about it.
Always use peak acquiring mode to capture the glitches, instead of faster timebase or memory depth
And this is why there's no excuse for a scope not have external trigger input! All it costs is 1 BNC and 1 relay and just goes straight into the trigger circuit.
2:50 "Waveform extended to the maximum!" Fan-freaking-tastic! lmao
I seem to remember some scopes, may have been before digital units used to have a button for trig view which put up an extra display beam to specifically show what it was triggering on.
The application note AN47 written by Jim Williams has a really useful chapter about all kinds of probing techniques including a "organic" probe. If you like this video, you'll probably love the AN47.
I needed this info a week ago when I was getting premature triggering.
I usually set the trigger level to just below the expected signal level.
Not the avoid this sort of issue, but for things like tri-state logic.
Perhaps you could make a simple test jig to re-create this issue, something the EE students could do in the lab with a signal generator and and inductor.
Wouldn't have helped much in this case, some of those induced transients are well above the signal level.
I'll admit I didn't guess the answer at first, but I actually had the reverse problem a few months ago at work.... I had HF reject turned on, and my scope (Keysight DSOX3034T) wasn't triggering for the transients I was trying to capture. I didn't consider them to be that high frequency(We're talking 10s of kHz) but the integral over the trigger point would've been relatively small, so apparently the trigger level didn't stay high enough long enough to grab the transient, yet I knew it was occurring because I was still experiencing a failure mode I had already characterized..
I might've ended up adding an RC filter to the input, but at the frequencies we're talking, a 5 degree phase shift is not insignificant (200Hz for the main signal)
Dave, if you use a pol filter on your camera you can almost totally avoid the reflection on your scope screen or other reflective surfaces.
Wow this brings make memories as back in the eighties I was building a digital scope for my final project and it did glitch. As a poor student the cost of the fast static ram was so expensive that can remember taking out with extreme!!!!!!!!! care in my lab time.
This is one of the reasons I sometimes hate to think in terms of memory depth when I set up an aquisition. Just keep an eye on the sampling rate if you know what kind of content you expect(or don't expect) and the maximum timebase will be limited by the amount of memory available. If you do it the other way around and just set the maximum memory you will be tempted to increase your timebase at the expense of sampling rate and then wonder why you miss glitches. In other terms: never acquire events on a single timebase/sampling rate; always explore your signal: increase de sampling rate, move the horizontal refference, zoom out, zoom in.
Nice video!
Some time, i have also some trouble with common mode interference, i put many ferrite on probe cable and make great difference in reading and triggering.
High DV/DT and high DI/DT circuit is always a chalenge to probe.
Really love your explanation. Loved this video.......thank you....
Thanks Dave. I am a newbie, this helped me to look with greater accuracy at some glitches I am currently looking at.
😁
Thanks Dave, i've learned so much of this one :-)
This is a good topic. Perhaps Dave or others could look into how ground strap layout changes could reduce the area/space in which induced field is entering, thus causing the EM noise, maybe wrapping the ground strap around the probe or taping it down.
It also leads to possible discussions on improved PCB layout design for probing points in these types of boards, eg. having a ground point very close the the probe point and using a spring-type ground "lead" attached to the probes tip ring. Of course that does not help in probing around other points on the board that are not official probe points...
Cheers Dave,
Warning! The High Frequency Reject method may not work for all kinds of premature triggering issues, especially if you are probing out of your league.
Might need some pre trigger protection on your probe.
Trigger on some handy circuit before the actual target to clear the pipes
I would also try Peak Detect Aquisition Mode. Maybe it would catch this spike.
Long ago I worked for a company that made systems normally sold into 60 Hz markets. When we won a large 50Hz order, the customer insisted on a long-term 50 Hz test run to ensure completely normal operation. We chose to use a large diesel generator whose output was extremely noisy, some of which made it through the system's power supplies.
We soon learned to keep HF Reject permanently on.
Fun, informative, educational, as (almost :)) always!
I think there ought to be an alternative trigger mode that is based on the digitized data from the ADC instead of a separate analog trigger circuit, perhaps should even be the default mode and then use the analog trigger if you want to find spikes and things that are too fast for the sampling.
Also the HF reject should adjust its limiting bandwidth according to the sampling rate, and I think it does in some scopes.
The teaspoon in the football field. Such a runt pulse in a long time base.
20 or 200MHz probe BW limit is your friend in many cases :) Even Mr. Nyquist approves when the sample rate > 40 or 400MS/s
Very useful !!!
Cool video, something to look out for. I will be doing exactly this once I get my arse into gear.
Can't think of a good use for noise reject? You actually showed a good use for it earlier in the video: 2:27 and 4:14 :)
Here in the lab the noise of the led lights is so big that it is almost impossible to trigger in small signals when they are on
It always helps to keep a lab clean enough to be able to receive SW Radio. Why use the cheapest LED drivers in an electronic lab ? That's nonsense.
olha lá o menino gregory...
A slightly off topic question: How would you contrast your Keysight MSOX3054T vs a
MSO of similar performance from Rigol, say the Rigol MSO/DSM7000 500 MHz, the MSO8000 600 MHz, or even the MSO5000 350MHz? The screen on your Keysight looks TERRIFIC but I’ve never seen either the 7000 or 8000 series side-by-side with the Keysight. I hope you’ll comment or point us to existing EEVBlog episodes I’ve overlooked. Keep up the great work and content. I’ve known engineers as talented as you but none so willing to share and mentor others!
Hi from italy dave
Hi
Why not use sequence mode in this case? Seems like capturing the waveforms from each trigger would have been more straightforward...
Wow. That must be a one narrow pulse that it cannot be seen with a 10ns/div timebase. I wonder what phenomenon is responsible for generating it. ...maybe some Diode Step Recovery effect.
I love the chinese takeout oopsy protection 10/10
Maybe little tip, but if your scope doesn't have a HF reject option (or it'snot good enough), you can just easily make one yourself from some passives on the external trigger.
Just add a low pass filter?
@@cameronwebster6866 yes exactly
BTW, When I was a Field Sales Engineer for Tektronix people would ask if we made 12” or even longer Probe ground leads. I’d say sure we do. Do want to buy some for someone you don’t like much?
"got your noise!" should be the electronics engineer equivalent of "got your nose!"
There's absolutely no excuse for integrating a noisy and unreliable switching power supply when there's room enough for integrating a real (linear) power supply.
My fully digital Hantek does not suffer from these kinds of bugs, since it does not incorporate the inferior analogue trigger circuitry of yesteryear.
Get a scope that triggers in the digital domain.
Nice oscilloscope
One of the constant "features" of digital sampling. I love the advantages but you have to remember the limitations too.
Nice Shirt!
Lovin' the plastic microwave proof container over the PS
An ooPSie protection for the PS, probably made in PS (polystyrene) plastic.
couple of more Dave videos, and I'll be electronics engineer
I am new to electronics, can you please make a video about waveform capture on oscilloscope (I don't know anything about trigger)
I thought they had tablets for you to take for that problem Dave...😂🤣😂🤣😂🤣😂
TRIGGERED!
+1 for probing tips video
i am offended about all this triggering ITS CURENT F*UCKING YEAR
And here I am stuck with an old analog Hitachi scope from the early 80's with no capture at all. Gotta stop being cheap and get on board with this newfangled digital stuff. 8)
Nonetheless, you've given me a lot of good info on how to use my CRT scope better. I love all your videos. Thanks!
old analog scopes use a roll of coax inside to delay the signal after the trigger.
now dave before you give it away; is it something with pretrigger time
also (not related) i just found one change with youtubes ad system: they asked if i want to see midroll ads or watch 3 ads right before the thing. lol.
but there is a way to get around it without adblockers i found out;
lets just say that you will learn to love construction side cones (disguise is neccessary here)
WHAT? YT actually asked you that?
@@EEVblog yeah just was to slow to screencap that but if your not responding it just defaults to showing preroll
@@EEVblog yes i managed to capture it there you go: (gotta translate that from german your self though)
imgur.com/RFEvd5w.png
Sounds like something you might want to talk to your Doctor about.
lol!
14:14 So what's the neat little trick for people with only two hands to aid with probing? :)
im too stupid to understand but i like it
Why not use the peak instead of normal capture mode to see what your missing?
I tried this, and now my oscilloscope is upset with me, calling me all sorts of political names ):
I guess triggering it wasn't such a great idea...
I was curious as to weather or not it was the mains switch being turned on that created the false trigger. Well, in part due to the long ground lead.
Geee you sure get some really nice toys... thanks...:)
I am sure there are few million people who need a filter to reduce their false trigger levels lol
The problem is the fact that your using 2 different scope probes, one has a different propagation delay causing as much as 5 minutes of skew ... ... well at least thats what my old professor made it seem like when he marked me down for using probes that were not "matched" than probing i2c at 120khz :P
and yes, im being a smart ass
Wouldn't that mean the waveforms are just apart horizontally by a few ns? One of my probes is 1m longer than the other. By my estimations that is less than one tenth of a division on max zoom of my 20MHz scope. You may be being a smartass but I'd say the professor was wrong to mark you down. You probably had more error from the probe compensation being subperfect.
When an oscilloscope is more easily triggered than a snowflake...
Nothing more embarrassing than premature triggering!
What is that HDMI like connector labeled Sbus on that Siglent?
Why can't we just trigger digitally from ADC output?
Hi Dave ... if you put the osciloscope in peak detection i think it will show (ate list they should) show the glitch eaven whit low memory or low time base ...
it was in these mode or not ?
regards from Brasil.
Huh your second channel's purple on your siglent, silly question but how can I change that? xD
why electronician have so many scope ?
If your oscilloscope is triggering prematurely, try thinking about baseball.
That premature trigger will get you every time. 😏
A food container for safety, great idea!
Got that takeout tray going just in case anything goes BOOM! Don't want plastic or metal in your face
It's also great so you don't touch the mains
This happened to me the other day. I called all my colleagues to the lab to show them the problem I spotted with our product. It happened once in a system test last week and I had spend days trying to track down this intermittent problem. The scope was connected so I turned the system on. I set the mode to single and we waited for a moment. The scope screen suddenly showed an image of all the probed waveform, but everything was normal. Premature triggering...I was so embarrassed.
would a CRO show the same?
😲 Once again, I did not know this...
I DO NOW! Thank You
Canadian Factoid:
{TRIGGER}
A Lennoxville`s (Quebec, Canada) Burger:
Go to McDonald's, (Macca's!) order a Junior chicken burger and a double cheese Burger. Stick the Junior inside the double. You have a trigger!
Tachyons.
Got to be tachyons...
Hy Dave, how do I see that 35 minute video you were referring to?
Be a Patreon or subscribestar supporter, or forum supporter.
What is he saying at 2:40 something like byula or bulla? What does it mean? It driving me nuts.
Watch Ferris Bueller's Day Off!
😂🤣
Thanks, I can now die in peace.
LOL it drove me nuts for months I asked for help and searched the internet for "biola", "buoela" coudn't find anything i was getting crazy !!
Anybody else reading the comments, looking for the jokes about safe spaces?
Dave, that's what you get for using that new newfangled DSO rubbish. I'd have captured that easily with my Tek 7844 CRO with P11 Phosphor (blue) and my trusty Tek scope camera and Polaroid film.
I'm guessing some unimaginative viewer will regurgitate a worn-out boomer comment as they can't fit in a legend has it...
What'd that cost nowadays in film per capture? (if you can even get it?)
ottima idea la ciotola del gelato
Dave is back! I'm so happy. I thought this channel would slowly fade into nothingness and now Dave is making interesting technical videos again!
Let's do the same thing I do every time someone says this, let's look at the last 10 videos from 1310 to 1319
- 2 x Teardowns (one was HUGE)
- 1 x Debunking
- 2 x Oscilloscope tutorial type, not dissimilar to this video!
- 1 x Mailbag
- 1 x Really interesting discussion on quantum computing
- 2 x Product Reviews
+ misc videos
"Fade away into nothingness"? Sounds like the exact same mix of content I've been doing for the last decade!
I appreciate that you like this video, and may not like the others I've done recently, and that's fine, but please try and be realistic.
@@EEVblog It is long time ago since you made a comparison of equipment like your multimeter roundups. I also had the impression that topics like investment, fonds and crypto currencies got more and more of your attention.
But I'm glad to be wrong.
@@EEVblogSome ideas:
What do you think about silicon carbide MOSFETs?
What are the rules of thumb regarding high frequency digital signals (like 40MHz SPI), trace lengths, cable types and connectors if we want to connect circuit boards?
How can we ensure that our digital projects don't emit too much EMI and cause trouble?
How to select the right connector) plug type for a project?
Dude maybe you don't like his content and that is fine, but he uploads a ton and all of it is high quality... Don't know what you're talking about
@@matiastripaldi406 Maybe you are new to this channel. Then have a look into the older videos.
Premature Oscilloscope Triggering = Great name for a porn film?! 🤷♀️
Premature triggering. Know nothing about that...
*It must be an ex Uni scope you're using if it gets so easily "triggered" by barely measurable microaggressions!* 😅😅
What would happen if the ground connection was looped through a doughnut like this one? RUclips: BewyFge5MFY
DIDT DVDA? ruclips.net/video/eJUMILK7Vkc/видео.html
Problems I don't have on my hameg 604
Meh, this video is so basic... pft, it was obvious from the beginning. Dave, after all your lessons, no one falls for that one :) (just kidding - great video, especially for the newbies)