#10: AC / DC Coupling on an Oscilloscope
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- Опубліковано 11 гру 2024
- This video discusses the AC and DC vertical coupling modes on an oscilloscope. It shows that these settings are not really the same thing as the AC/DC settings on a multimeter, but rather they dictate how the signal is coupled to the vertical channel of the scope. In many cases, the DC coupling mode is very useful for looking at AC signals. Similiarly, the AC coupling mode can be very useful when looking at DC signals. The choice of which vertical coupling mode to use depends upon the signals and circuits that you are looking at.
Excellent! Excellent! Excellent! I'm a novice elect. hobbyist and just got a Tek 2465 scope and your video series is just what I need to understand and use the scope to its fullest potential!
Good explaining of coupling Ac and DC signal.
Basically:
DC coupling: both DC [bias] and AC ripple to show
AC coupling: AC only
This is essentially he same as the AC and DC mode on a DVM meter.
But your dem is valuable as a visual proof.
Thank you.
I can't tell you how many "light-bulb" moments I've had watching your channel, even going back 12 years now since this was published.
not only explained AC/DC coupling, but also clarified couple more concepts for me)
Once again, an incredibly understandable explanation. Thank you !
I was doing an Electronics lab and didn't know what coupling meant, this helped a lot! Thanks.
I absolutely love your videos! You are so clear, detailed and to-the-point. This is excellent teaching.
Watched so many videos about using oscilloscopes , even I know how to use it and using it on daily basis. But I always love to find something new for me. Even this is not so new for me if at all after this video I have so high feeling that I have learned something new. Really god explained and showed. I wish there is more teachers like you are at UA-cam. . Huge thumbs up from me I wish I can give more thumbs.
Didn't know of that way to look at ripple, pretty cool :)
Great video. Lab-based circuits videos are particularly helpful to me, because theory only gets you so far before the practical models that were ignored/simplified come back to haunt you. Thank you for your willingness to share your insight!
Also, if anyone has any other practical electronics channels that they'd recommend, I am open to suggestions.
Using AC coupling to look at the ripple of a DC signal from a rectifying circuit, reminded me of my Circuits and Measurements Lab. In one lab, we needed to look at the ripple from turning on the power supply, so we had to be in AC coupling and take a "snapshot" by using the RUN/STOP mode instead of AUTO.
I'm glad you like the video. There are more than 250 more on my channel. Other channels I'd recommend are The Signal Path, EEVBlog, Afrotechmods, devttys0, Mr. Carlson's Lab and Great Scott!
Mind blowingly elegantly descriptive work. I can feel brain cells growing already!
I thought, "Perfect timing." I had just started to raise the questions to the answers you gave in the video. Then I scrolled down and saw it was from eight years ago. So you are actually ahead of schedule! Thank you!
Jesus!!!! I just NOW understood why the group "AC/DC" is called that!!!!!! MY GOD!!!! I lived for 40 years without knowing this!!!! 😮
This is a group of electricians!!!!
Excellent video
Excellent video and well presented. You have a nice style of presenting that talks to novice hobbyists as well as advanced techs. Keep up the good work.
love your videos! simple, short, to the point. don't get people who dislike.
I am going through your videos again. I kind of did this once before for almost the entire videos but this time, I seem to be learning much more from them. Thank you very much!
THIS IS VERY INTUITIVE EXPLAINATION OF AC AND DC COUPLING.THANKS
So many lights buld moments watching this video, thank you!
Wow. Fantastic vid, put simply and clearly. This taught me a lot, thank you.
Thank you for illustrating the correct usage. A beginner here, now I can use my equipment to see what I want to see. Thanks
I wish I had more hands, so I could give this video... 4 thumbs up! Great vid, thanks!
Thanks Matt - much appreciated!
What Matt said.
Great video. Thanks. The first time I noticed ac ripple was on a car. I have been a mechanic for 25+ years. This was when I first started doing it. I only work on BMWs. I had one come in and every digital display was rolling put the meter on ac and got 2.5v ac output. I guess the bridge rectifier was going out. I part out a lot of them so I just grab one off the shelf dont repair them just pile them up and sell to the core man every 6 months.
I was wondering about this today, then tuned in to your channel this evening, and hey-presto the perfect explanation ! Thank you.
Thanks, for refreshing what I have forgotten since high school. Very helpful video.
Thank you very much! :) I got exam the day after tomorrow, your videos helped me a lot!
This was very well explained, thank you so much! Especially liked the example with the transistor/bias voltage.
You are the man! all your videos are very informative i have been watching them for a month now, you are helping make sense of a lot of things. I have learned so much in the past week my brain hurts. And just got my first scope today and i am excited to start playing..
KD2GOE
Thanks for the nice comments. Good luck with the new scope, and be sure to let me know if you need a video on something to help you out!
@w2aew Great reply, thanks a lot. Here is another example:
Say if I have a sine wave on my scope, I hit the ground to set the baseline. The if I switch the coupling from AC to DC...well, of course it has no effect.
If I set a baseline and hook my scope up to a square wave, then swith the AC/DC coupling back and forth it changes things up. The DC coupling will show the total wave above the baseline (gnd-peak positive-gnd). Ac coupling will split the square wave......DOH.
You are an excellent instructor! Thank you!
You are a master of electronics. Thanks for the great video
Have had several also scopes but I've never known of what the purpose of DC ground and AC coupling were. Thank you
Very well explained, thank you for taking the time in explaining AC DC Coupling
Briefly in response to the previous question by revising the ground wiring of the alternator, battery and chassis connections you could avoid the ripply alternator current travelling through the chassis.
However the vehicle 12v supplies will still have some ripple on them...
You could research ultra-capacitors, they have very large capacitances and very low ESR.
Very informative. Your videos are a great resource!
Thank you for this video and all the insights. I like the examples. Very useful!
Justified reason to use a "dual" trace scope! Well done! RW - KC2RDU
Quite informative! Hopefully this explains why I wasn't seeing what I was hoping for with some DAC produced waveforms...
Good explaing of coupling Ac and DC signal
So I think the internal capacitor simply "charges up" to the DC bias voltage and the scope's horizontal line now uses that charged up voltage as it's new zero reference point. Is that a good description of how it works?
Yes, the capacitor removes the DC content of the signal so that the signal centers around it's average value.
Great video, Alan. And I love that Simpson meter!
Thank you for the great video! Can you explain about GND coupling? what is the purpose of the GND coupling in an oscilloscope?
GND is used to pre-charge the AC coupling capacitor for AC-coupling mode.
Really well explained. Thanks
Very clear and very helpful, Thanks!
Learned something new!
Great videos allen, thanks kindly!
Thanks, I'm doing a Linear Lab for a common emitter amp, and I thought the same as you just confirmed.
I've a number of additional videos on transistor amplifiers, including how biasing affects the class of operation, the basic configurations of CE, CC, and CB amps, and even one that looks at the frequency response characteristics of the common emitter amplifier.
great video. very informative.
Great review, I needed it.
Great video! Thanks so much.
I have one question sir. Why the half wave got shifted to the negative side from 0 level voltage (@2:20)? Even if we consider around 1 volt drop across diode, should it be appearing above the 0 volt level ? If it is shifting to downwards, does that mean diode is conducting for that small fraction of voltage with opposite polarity? Where did I go wrong? Please help me.
Because the scope was AC coupled, so the signal settled around it's average value.
@@w2aew yayyy I got the reply...Thank you sir for replying 😊🙏🙏🙏✌️. So the initial level we are setting is not "zero" level it is better to say the "average" level. Am I correct sir??
@@deepakjanardhanan7394 When using AC coupling, yes.
@@w2aew Thank you sir 🙏🙏😊.
w2aew, when the AC voltages on TV circuits and Arcade games are reversed polarity the display images fonts and images will have a "wavey" look. From 12VAC, 7VAC, 5VAC if the AC voltages are reversed polarity out of phase the image fonts and images are wavey, Any reasons why? How can I use a DMM meter to know if my VAC voltages are In phase or out of phase, how can I know using a DMM meter set to measure AC voltages?
Thank you, that was very useful.
Thanks for this informative video! Helped me a lot.
This is just what I need to start using my scope. I have a pile of power supplies that are not working or at least not well. I am going to need to get a isolation transformer first I think. Thanks Louis/w0it
Off topic, but I've got a question about impedance matching. For maximum power transfer, the impedances of the source, transmission lines, and load have to match. But does the source impedance have to match in order to avoid return loss/reflections? A 25Ω source into a 50Ω load leaves power on the table, but will any power reflect back to the source in an arrangement where there is no (or electrically short) transmission line, or the transmission line and load are matched (but again, not to the source)? My intuition thus far says that it shouldn't matter, with power supplies and audio amps being examples, but I wanted to know for sure by asking someone much more experienced than I am, especially where RF is concerned.
The source impedance will not affect return loss or reflections at the load end. If the load is matched to the transmission line, there will be little/no reflection, and the source impedance won't matter.
@@w2aew Thanks for helping me out, and confirming my intuition! I appreciate that you still reply to comments on these old videos to help out relatively inexperienced guys like myself. God bless!
Very good info. Thanks
Another good one. Q:What happens to the transistor during a prolonged saturation state in actual circuit applications?
Great video. Thanks for the education
Thank ya, I need more
I'm wondering if you could do a video on pros/cons of connecting up different components in series vs. parallel. E g. Signal gen is your source. You want to see output on 1. Freq counter, 2. VOM, 3. Oscilloscope all simultaneously.
So do you connect all three in series i.e. (daisy chained?) Or, feed all three in parallel from a three-way splitter from the sig gen(?)
Note that even when you connect your counter, scope, etc. to each other using things like BNC-tee connections, they are still in PARALLEL with the signal source and load - they are not in series. When your signal frequencies are low (below about 1MHz, and definitely below 100kHz), the way you connect won't really have an affect. When you go higher in frequency, where transmission line effects start being important (above 1-10MHz or so), then it does matter. You can use BNC-tee connections, but mount the Tee(s) directly at the instrument connector (no coax) so that the stub length of the connection from the main line to the instrument is as short as possible. You can get away with this up to a few hundred MHz. Above that, then everything needs a proper termination and the splitter is the way to go.
@@w2aew Ok thanks I think I see what you mean.
Nice. Thanks for explaining why.
Ghost voltages are due to wires coupling or other interferences in the circuit. My question is how do you know when you're measuring a ghost voltage or how do you even know if you have a ghost voltage? Can the oscilloscope determine a real voltage from a ghost voltage?
If you load the circuit, a ghost voltage will go away. This is the principle behind the classic "Wiggy" tester.
Fantastic! I need a scope! Do you have any idea of why the filter capacitors in tube amps have such an effect on the sound. Many of the reissue guitar amplifiers has higher uF values after the rectification, compared to the originals from the 60's, 70's. And with higher uF values the "cleaner" DC makes the amp sound more sterile/harsh. User patfurlan has a lot of videos of filtering caps mods, for example the fender champ.
Great stuff! Keep em coming please!
Excellent as always,,, thanks.
@w2aew Thanks a lot for the video. What if you have a very basic scope that displays the signal with no on- screen voltmeter to show polarity of Peak pos and neg, and you have ZERO knowledge of what type of signal you have displayed on your meter....say a square wave that may be ac (peak pos-through ground-peak neg )or DC (peak pos-gnd-peak pos). How do you identify AC or DC in this situation???? Changiing coupling does not tell a lot in this situation.
Very interesting thanks for the vid.
nice video. thanks a lot. i still have confusion. if i am feeding an AC signal superimposed on some positive dc and coupling mode is dc, i should get dc, right?(please correct if i am wrong.) but, here we see a sine in dc coupling in case of transistor. how does that happen? please explain. thank you.
I'm glad I found this video. Though I got lost after 6.:30. Can oscilloscope also affect the voltage? Or does it only "see" and show the current/voltage as is and all the buttons are just to make it fit the screen?
I'm considering to buy an osciloscope (currently just have a multimeter) but I'm bit too poor and too "scared". These aren't cheep toys.
The scope only sees the voltage, it doesn't affect it (ideally). It is true that the resistive and capacitive loading of a scope probe can affect some circuits. But, usually you'd consider a scope as a "monitor" and not an active part of the circuit.
@@w2aew Thank you! Glad to know
Excellent videos, thank you so much!
does the a/c coupling setting on scope essentially add a capacitor to the circuit to further reduce dc ripple?
thanks
john
No, it doesn't. AC coupling inserts a capacitor in *series* with the signal in order to remove the DC component so that only the AC portion of the signal is displayed on the scope.
You are such a good teacher. Thank you. I am still green as can be, do you have a vid explaining dc bias a little more? Thanks again.
DC bias is just a term that is used to describe the DC voltage that exists at any point in a circuit. Unlike digital circuits where voltages are typically high or low, analog circuits are often operated "in between". The DC bias voltages determine the circuits operating point - kind of like idling in your car.
Awesome tutorial! Thanks so much for the clear explanation =)
what causes a circuit to have ghost voltages? what do you mean by this wiggy tester? How would an electronic technician know if the voltage is real or a ghost voltage, how can you tell the differences?
A ghost voltage is simply a voltage that is picked up on a high-impedance line due to coupling through the air to some other power source (like an antenna). As soon as a load is placed on this ghost voltage, it will collapse. The Wiggy tester uses a solenoid as a load on the AC line so that ghost voltages won't be seen. Here's an example of a Wiggy: www.amazon.com/Square-D-WIGGY-VOLTAGE-TESTER/dp/B000BVXW1C
Does analog Oscopes have a Persistence time adjustment? and what signals when measuring would you want to use the Persistence time? I know its used to measure AM modulation signals on digital Oscopes but most Analog Oscopes didn't have a persistence time adjustment so I don't know how they were measuring AM modulation waveform without the persistence time adjustment like on digital Oscopes
Only a very few specialized analog scopes had variable persistence phosphor. The vast majority of analog scope do not have variable persistence. You don't need a persistence adjustment on an analog scope to view/measure AM signals
@@w2aew But what was the persistence adjustment on analog scoped used for to measure what types of waveforms and signals?
@@waynegram8907 On those rare scopes that had a persistence adjustment, it was used for waveform storage so that you could examine signal-shot or rare events. It was the pre-cursor to digital storage scopes.
@@w2aew but what is the persistence time used for on digital oscopes to measure what type of waveforms and signals? the persistence time on digital oscopes is 250ms, 500ms, 1second, 2second, 5 second, I don't know what these are used for. Is the persistence time used for trying to look for "glitches"?
@@waynegram8907 Mainly, yes.
Great video what do you use for the AC power source?
When measuring AC 60hz how can you measure how many zero crossing events happen in one second using an Oscilloscope? its suppose to have 120 zero crossing events but how do you view this on an Oscilloscope
If you set the scope to 100ms/div, then you'll have 1 second of time across the screen - then pause the scope and count the cycles - you should see 60 cycles, and since you have two zero-crossings per cycle, there's your 120 zero-crossing events.
@@w2aew Does Digital Oscilloscopes have an Event List or a Menu to display all the zero crossing events?
@@waynegram8907 Some do, some don't.
@@w2aew Can you make a video showing how to set up the event listing to list all the zero crossing events because you have to set the upper level and lower level window of the events
🍎🌺🌺 you are 🌺🌺🌹 very clear 🌺 really an engineer 🌻🌼
Very educational.
I don't really understand why there is AC/DC coupling on the channel and the trig section too.
Check out my video #11 on the triggering controls and their usage.
Www.ua-cam.com/video/OFGm-Pel4Hg/v-deo.html
Great Vid, I watched it and learned a lot. Thank You! However, I am not quite sure what would happen if you DC coupled the trig with an AC coupled channel. Why application could I use that for?
I'm sure that this combination might come in handy for some applications, but probably not very often.
Thank You man!
excellent! thanx a lot mate!
you are phenomenal. Thanks!
good work!
Great! Thank you.
Hi, I am a bit confused. When in AC coupling mode, should'nt the DC get blocked? So when you switched to AC mode, how come you are seeing it ride on the DC? Sorry if this is a dumb question.
When switched to AC coupling, the DC offset observed on the scope is simply due to the Vertical Position knob on the scope.
oh i see...thanks for the reply. Really liked the video. Learnt alot.
Nice Tek scopes? Which all do you have?
I've got a 465B, 485, 2465 and 2467. Most came to me in some need of repair...
AC/DC coupling is done by caps, this is to my understanding ?
+jon123423 Yes - AC coupling inserts a capacitor in series between the front panel connector and the scope input.
Thank You
thank you so much
thank you very much.
really good !
Why is DC power more Energy Efficient than AC power?
It isn't. Power *TRANSMISSION* using AC compared to DC is more efficient because you can easily transform to higher voltages, which means lower current for the same power level, thus minimizing resistive losses.
@@w2aew But how can you measure Power transmission and Energy Efficient for AC voltages/current and DC voltages/current? is there any lab test equipment that measures Power transmission and Energy Efficient? Because they say that DC motors are More Energy Efficient compared to AC motors because DC voltage/current is more Energy Efficient. Using DC solenoid coils they are stronger compared to using AC voltage on solenoid coil because of Energy Efficient. I don't understand what they mean by Energy Efficient or how to measure energy efficient.
Now i understand it thanks
I think the scope should be labeled normal and AC. I think the way they label the switch settings is confusing.
Unfortunately, this is the way that the oscilloscope channel coupling has been labeled for more than 75 years - because it makes perfect engineering sense. It is not likely to change.
It's confusing, when I see the DC setting on a voltmeter only measures DC, yet on a scope you see both DC and AC. Anyway thx for the great videos, keep them coming.
The thing to remember is: On a voltmeter - the AC or DC setting refers to a measurement MODE or FUNCTION. On an oscilloscope, it refers to the channel COUPLING, not the measurement mode or function.
thx, now it makes sense to me..
Fire!
You are The Godfather of cool. Gratitude++ 99e99
Complete NOOB here. If you are examining a DC signal, how can an AC signal be riding on top of the DC signal? Where did the DC signal come from?! And vice versa. A signal is either AC or DC. A battery is always DC and only that. The wall socket [mains] only provides AC and only AC. What am I not understanding? Please let me know. I truly want to learn. Thank you kindly
I suppose I am using the terms somewhat loosely. When I say "AC signal riding on top of a DC signal", I'm really referring to a DC signal that is "wiggling" a bit. It is DC in the sense that the polarity is always constant, but "AC" in the sense that the level is varying. A good example is ripple on a DC power supply. Does this help?
OK, so there is NO AC signal of any kind - it's just an "expression" you guys use, to describe a not-so-perfect DC signal. Got it. Thanks for replying
@@maxwarfield6699 sometimes it is a proper signal, such as an audio signal riding on top of a DC bias signal in an amplifier for example.
'Been thinking about this one... Ok, so, when you want to see the DC quality/ripple of an AC signal - you use the DC coupling. And when you want to see if your AC signal has any kind of "clipping" or DC-like quality, then set the scope, to DC coupling - is this correct? If I got this right, it STILL doesn't explain, how a scope can perform a task, that it was never meant/programmed to do. A ripple on a DC signal, should be seen ONLY on DC coupling, as that is the base-signal. And any clipping in an AC signal, should ONLY be seen in an AC coupling because, THAT is the base-signal. If a locomotive is on tracks, that after 1KM turn left, that locomotive will not turn right, EVER, even if it had a steering wheel. Switching modes [from AC to DC, and vice versa] on a scope, would be like adding a steering wheel, to that locomotive - if the tracks turn right [AC] that is where the locomotive will end-up. And if the tracks turn left [DC] that is where, it'll end-up. If a scope does not "see" a ripple on a DC signal OR if it doesn't see, the clipping on an AC signal - to me, that just demonstrates the limitations of the scope's sensitivity. All of the above, is just my not-so-well-informed opinion, of course. And I could be wrong [I am, a complete NOOB], but I don't think so. Anyhoo, I like thinking about stuff like this. So, please feel free to school me. Cheers!
@@maxwarfield6699 Let's see if I can make this clearer... You're NOT asking the scope to do something it was never meant to do - quite the contrary!! The AC / DC Coupling control is a TOOL that is there for you to use to help view your waveforms. Period. This control has NOTHING TO DO WITH whether the signals you're looking at are AC or DC signals. Repeat that to yourself. DC Coupling allows you to see your waveforms exactly as they are, including any DC bias or offset. The AC Coupling control quite simply INSERTS A SERIES CAPACITOR in the measurement path. All this does is remove any DC bias or offset from the signal, so that the signal appears on the scope to be centered around it's own average. This can be very helpful when the variation in the signal is small and the DC bias/offset is large. Consider the following example: You have a squarewave clock signal from a 5V logic circuit. When using DC Coupling, the waveform will be a squarewave where the bottom of the waveform is at ground and the top of the waveform is at 5V. Exactly what you expect. If you switch to AC Coupling, the waveform will be centered at its average, so the bottom of the waveform will be -2.5V and the top will be +2.5V. The shape and amplitude will be exactly the same, just the DC offset is removed.
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