Ignore anyone complaining about content being to long. youtube is littered with videos that dont' actually explain anything in any useful detail. You rock! I am a software guy for 30 years, between you, Mike, Bruce Simpson, Jeri Ellsworth and the young guys like Kevin Darrah and Jeremy Blum I am actually understanding the hardware that powers what I have been doing for a living since the 80's!
Dave, you may think 20MHz is an arbitrary frequency, but it is also the point where poor probing methods with long inductive probe ground leads start to cause extra ringing on fast logic causing measurement errors. So for clarity 20MHz is for convenience when risetime induces false ringing from poor probing skills and gets a better textbook looking trace. For ideal trace remove probe tip and ground clip and only use tip and probe ring to a pair of test pins or wires of similar spacing for convenience or use the coiled ground spring accessory . This gives the best results using a 10:1 probe. Generally signals much less than 30MHz are used for this mode but logic rise times faster than 100ns ( most are) will get an overshoot proportional to the ground probe length and transition frequency resulting in ringing.. Tony EE since 1975
@@Sunnyskyguy the probe tip and ground wire are handy when you are just looking for logic levels and you don't care about the shape being a perfect square
Excellent video. Instrumentation and measurement and understanding the limits of your equipment and sources of errors are very important and often a poorly understood area. Nothing like a real demonstration to highlight the concepts and pitfalls. Good stuff Dave.
Dave, I really like your channel. Outstanding quality topics, content, judgement and sharing of your understanding and tricks. Thank you for sharing your excellence and passion.
Dave, really awesome. Well worth the time. Thanks for going through this one. I can't tell you how much the EEVBlog comes up here at work lately. Too many geeks with not enough to do? ;) ... Love it.
It has to do with the coax usually having 50 Om impedance as well. Basically, the coax is a tramission line, and when you trasmit a signal over coax, it is vitally important to have it terminated with a matching impedance load. Otherwise, you get the signal all messed up.
There is another aspect of power supply noise that is little thought of. I was involved with a huge project at a large computer site in 2010 that had to have the power supplies replaced on 5000 installed servers. The switching power supplies also generate noise back onto the ac feed line. When you had 5000 servers with no isolation, all generating noise, the electrical noice would shut down the site UPS systems. The replacement power supplies,all 10,000 of them fresh in from China,now had toroid coils on the ac line. Guess the server vendor didn't save 20 cents per server after all ?
Hey nice video. Though one more way to get rid of high frequency noise is to use a 0.1 micro farad disc cap on the probe tip. Infact you can solder it onto the probe tip and then leave a little bit of lead say 3mm extra to act as the points to probe the power supply. This is one of the standard methods
I got some Lambda LQ/LQD series linear bench PSUs recently, circa 1983 (warranty seals were unbroken haha!).. their ripple + noise specs are 0.15mV RMS, 1mV pkpk. Temp coeff. is ±(0.005% + 10μV) /°C. Line/load regulation is 0.005% + 0.5mV. Current regulation is 1mA/2.5mA (line/load), at full voltage range. Just fantastic. I verified those figures with my scope, still fully within specs. Zero overshoot with maximum load. They employ a custom Lambda branded IC for V/I regulation. I've sourced a replacement for one from China, gonna see if the specs change after I put it in.. I suspect it's not an original part from 31 years ago. :P
I got a whole lecture on noise and distortion when i studied EE, we did a huge amount of mathematical theory and a lot of fourier transform, 3rd order interseption points and stuff like that back than, but we did *not* measure a thing even at the coresponding laboratory lecture...sad...sad.
Another trap for a "young-player" might be that when one is playing around with the scobe probes and a power-supply, and they are both grounded via earth (3-pin mains) it may set the mains/installation fuse off or the "FI-switch" or both may in addition to a defective scope or PS. That´s why i´m running my scopes over a isolation transformer, in my case a 230V/230V to power up the scope. The tranny decouple its 230V output from earth.
There is a lot of good info here. I got that exact ds2202 and I'll have to check some of the linear PS i have. I will certainly learn something, most likely the probing. Great video.
I had to laugh. He measures 20 mV pk-pk, and he says it's garbage. I just got my first O-scope running and measuring a cheap SMPS, a Chinese 13.8 V, 25 A power supply made for powering RC battery chargers. I get 1 V pk-pk ringing at 62 kHz, and adding about 10 A load I now get an almost 2 V pk-pk ringing 5 µs in front of the 1 V pk-pk ringing. From looking at the trace under load, the bigger ringing appears to be the supply switching "on" and the smaller ringing the supply switching "off". Anyhow, THAT is a garbage signal. Fun stuff. Works great powering simple 12 V loads like lights or battery chargers though.
hi nice video dave. Though in my company which made power supply for defense institutions and special custom built power supply. The way we would measure ripple is to use a single probe but solder a 104 disc cap on the tip ( 0.1 micro farad) on the tip. off course no use the ground lead that is serious a big ******* antenna.
"How do we talk you into doing more Fundamental Fridays?" Make more Fridays. TGIF. If everyone thanks god for Fridays, how come there's only 1 Friday per week?
Hi, I haven't gone through all your videos. But I wish you could make some videos on different kinds of sensors and motors or even robotics control. That would be an interesting topic.
I dont understand 24:04 when he adds the "50Ohms Terminators"... I only know terminators that act as an end cap, but he uses obliviously something else ? His terminators have in- and outputs??? I am confused.
16:50 ....but...but "digital scopes are just better!" LOLing at your DSO vs CRO videos. The testing equipment manufacturers really took a step back when they abandoned analog scopes; measuring noise was a big part of a CRO's bread & butter.
You've done two; I've watched both of them a couple of times. Your claim in the second one that "they're just better" (referring to digital scopes) at showing and analyzing noise is refuted by your comments at the time index referenced in my previous post here. A two-channel CRO does the business with just throwing a couple switches; with a DSO you need to use three channels, adjust persistence and muck around with channel phase inversion and, in some cases, buy (or hack) a software option for an analysis package. You do concede in the first analog vs digital scope video (and in all your $50 eBay scope videos) that every EE should have an analog scope as entry-level gear, which goes to the point of my previous post: given their utility, there's no good reason not to still make oscilloscopes that are analog from the front end to just in front of the display driver, with no digital storage or software analysis (today's and tomorrow's EEs still know how to use a calculator, right?) Translating CRT beam deflection for an LCD driver should be trivial. ...which gives me an idea, so thank you for challenging me on this. A true analog scope with an LCD might be a cool open-source project. Most of the CRO designs came out of patent a long time ago.
+Shiwei Luan The ground wire forms an inductor coil and the noise it picks up is some electromagnetic interference generated by other devices in the room - in this case mostly PWM-controlled LED lights.
Something I notice is that using buck converters that let me regulate current, such as battery chargers (XL4015), I had way more noise when I demanded a current near to the limit I put on. Lets say I set my power supply to deliver up to 1.2A, when I put a load that demanded 1A y had some noise, but if I limit the current up to 2A with the same load, at the same conditions, the noise was smaller than before ._.
spectrum analyser is a great way to see what noise looks like. since i am poor i use my audio interface with software doing fourier transform. can see all the harmonic lovelies
Follow up this video from Afrotechmods 's DC-DC Buck Converter. And keep following up Dave and your videos are awesome! I can learn EE start just my a little knowledge of EE in high school (in Thailand) to starting some basic of Reverse Engineering! Well you're rock, Dave.
Dave used a 50 ohm terminator on the oscilloscope. What is a 50 ohm terminator and what are they used for? I need my fundamental Fridays to be even more fundamental.
+00Skyfox Read about "transmission line termination" to really understand it. In short - a terminator is simply a resistor that prevents signal from reflecting at the end of the transmission line back to the signal source which would interfere with your measurement. BTW, not all scopes have a built-in terminator.
For the past month, i have been taking hundreds of measurements the wrong way for my university project. Even the professors or the research assistants didn't tell me any of this. How I wish I saw this video one month earlier. 😭😭😭
Well, most don't do much of any hands on work. They get their grunt TAs lead all the testing, and even then, the TAs will rely on a lab technician with the electronics know how like Dave here.There are a few professors that do lab work, don't get me wrong. But most academics are snobs that won't bother with the dirty tedious work of testing and debug. Most electrical engineers just plain never learn this stuff because most of the EE jobs out there don't have an emphasis on this kind of testing. You see plenty of digital design, fpga and software coding positions, but they don't get exposed to dealing with these front end realities.
Why the series 50 ohm resistances at the far end of the differential measurement coax in additon to the parallel 50 ohm? Edit: Nevermind, I see the low impedance power supply needs a series resistor on its end to match the coax. Great video, by the way. I learned a lot. Thanks, Dave.
@@robegatt there is no need for the source impedance to match the characteristic impedance of a unidirectional transmission line. The source impedance only represents energy loss in this scenario. Bidorectional transmission line is another story. There you need to also match the source impedance.
@@vonnikon there is nothing like "uniderctional transmission line" ! If the source impedance is missing you have the signal bouncing back at the source right at the beginning of the line.
Wow! That was low tech but for me that was very interesting. I have that same Rigol scope and power supply. I also have that DC programmable load. I had no idea that load could put that noise on the there. Very interesting. I know my equipment a lot better now. Thumbs up!
Absolutely excellent tutorial. I am going to have to troubleshoot the power supply of my VTVM, and my thinking is to make the probes you demonstrated for my Tek 475 scope. I have another option that I wanted to ask you about, however. It happens that I have an old Tek 545b scope with a differential plug-in. My question is, what is the best way to hook it to the power supply, or am I just as well off to use your adaptors and the later model 475 scope. Thanks, Bob
Why would using two separate probes in subtract mode reject common mode noise whereas s single ened connection would not? Single ended connection still takes difference between signal and ground so if noise is common to both, it should cancel out right?
hi i got a tecktronix analog with ac coupling on that ,can i measure 450v dc supply with 1 x probe or i must use 10 x probe ,can i see ripple on my scope with 10 x probe .What value is acceptable for ripple!thanks
I think it is not much worse than today ones. Back then ripple was also a problem. Current PSUs are only much more efficient than the old ones. And the caps are of course crap, because they wanna save the last bottom microcent.
Hi Dave, Al video but can't find the information I need. I need to measure some powersuppy noise. (cheap or RC equipment) Yoi made the probes at 32min. I think this will do but do you have a tutorial or pictures from this how you made it. Type of coax (impedance) . Resistor and the capacitor you used? Mabve buying a BNC cable Cutting it in 2 pieces to start with. Thank you in advance or any follower that replies.
He wasn't measuring DC, he was measuring noise and ripple, which are both AC components riding on the DC. 5V DC would have over-driven the scope on the mV ranges, and so AC coupling was needed to bring the signals back down to 0V average.
Because you can't measure the small amplitude AC signals in the presence of a larger DC voltage. The ADC in the scope doesn't have the resolution. e.g. a 5V DC supply and 8 bit ADC gives you 19.5mV per bit. So 20mV noise will only appear as 1 bit flipping on an off - useless. Same for the analog scope where you won't be able to see the small noise on the DC signal
I also have LED retrofit T9 tubes here. 6 of them in my living room 6500K. I'm not able to recieve FM radio anymore, when I have them on, altough the lamp fittings are grounded and even the reflectors are grounded. Problem is that the tubes are lacking of input common mode choke and filtering. The LIVE and NEUTRAL wires are acting as big chunky antennas... I think it's time to make coaxial mains cables, because of cheap thinking china products... And the tubes were quite expencive and the overall quality is very good. It seems just lacking the input filtering... Too much copper wire for the choke and additional inducter plus some caps...
***** then put a filter in the input and let us know, you can get one of those filter modules that PSUs use from old PSUs (some of them have IEC C14 receptacle integrated) or just use the filtering board from a computer PSU as well
I have some filter circuits from the formery electronic ballasts of these fittings. But the circuit does not fit into the tubes, nor does it fit into the fitting anymore... :/
Where can I buy a ripple suppressor for my LED power supply? I'm getting a strange strobe effect on certain outlets, but I don't want to have to buy another regulated power supply. Anyone know?
But, what about making an inst. amp. design to use with measuring diff. values ? Maybe you can sketch a design with specific parts for us to have it use on our scopes... Please :)
How do I know if my ripple capacitors can handle the ripple current? I have some surplus caps that I am using for ripple suppression, they are rather large and I am scared they will blow up if I have too much ripple current. It's on a 110vAC 60hz input with rectified ripple of 4-6v p/p. The Current load is 150amp for a DC motor load. Caps are 250v 2000uF each but that's about all the specs I have on them.
Im also thinking about the 50 terminators, why did that change the situation as much? I mean the shield was already grounded so the core should not pick up so much noise, right?
It is not only shielding, is also about impedance. If your ground is of "high" impedance ther will be a voltage drop. If your signal leed had an intrinsic impedance you´ll "only" get a voltage divider. If you have a ground impedance in your wire it is the same but little more: It is a voltage divider as well as an antenna for all kinds of fields. Magnetic and electric as well.
6 years on and your 'deep dive' stuff is still pure gold, I wonder if the UNI's around the world use this in their curriculum..they should..cheers.
8 years later, came here to say this. Evergreen content for sure!
9 years later and the sentiment is still the same! Rock on! 🎉
10 years still good stuff 😊
Ignore anyone complaining about content being to long. youtube is littered with videos that dont' actually explain anything in any useful detail. You rock! I am a software guy for 30 years, between you, Mike, Bruce Simpson, Jeri Ellsworth and the young guys like Kevin Darrah and Jeremy Blum I am actually understanding the hardware that powers what I have been doing for a living since the 80's!
Dave, you may think 20MHz is an arbitrary frequency, but it is also the point where poor probing methods with long inductive probe ground leads start to cause extra ringing on fast logic causing measurement errors.
So for clarity 20MHz is for convenience when risetime induces false ringing from poor probing skills and gets a better textbook looking trace.
For ideal trace remove probe tip and ground clip and only use tip and probe ring to a pair of test pins or wires of similar spacing for convenience or use the coiled ground spring accessory . This gives the best results using a 10:1 probe.
Generally signals much less than 30MHz are used for this mode but logic rise times faster than 100ns ( most are) will get an overshoot proportional to the ground probe length and transition frequency resulting in ringing..
Tony EE since 1975
@@Sunnyskyguy the probe tip and ground wire are handy when you are just looking for logic levels and you don't care about the shape being a perfect square
no book could have given such memorable clarity on these pitfalls.... excellent video Dave and the best part is its a free video )))
Totally agree with Jens Andree. These kind of videos actually makes a difference in the world for a lot of people. Thx Dave....more of this stuff :)
For me one of the best videos from the EEVBlog series. Cannot really understand why two guys gave a thumbs down...
actually they are four by now....i presume they do not give a damn on noise as they only play music *loud* ;)
Thanks Dave, keep up the Fundamentals videos. I can't wait to get out to my lab and try this with my own scope..
Excellent video. Instrumentation and measurement and understanding the limits of your equipment and sources of errors are very important and often a poorly understood area. Nothing like a real demonstration to highlight the concepts and pitfalls. Good stuff Dave.
Wonder if you could do a video on ground loops? Thanks great channel!
th-cam.com/video/wopmEyZKnYo/w-d-xo.html
Dave, I really like your channel. Outstanding quality topics, content, judgement and sharing of your understanding and tricks. Thank you for sharing your excellence and passion.
Thanks for doing the fundamentals. These are my favorite videos.
I've been wondering for months what a CRO probe was. True, I didn't look it up, but still wondered. Cathode Ray Oscilloscope (CRO) probe.
Brilliant!
Dave, really awesome. Well worth the time. Thanks for going through this one. I can't tell you how much the EEVBlog comes up here at work lately. Too many geeks with not enough to do? ;) ... Love it.
Why the 50ohm terminators made so much diference?
Yes Mr Johns. Make a short video explaning about 50 ohm termination. Pliiiiiizzzz , with sugar on . Please ?
In this example it gave the signals a reference since the PSU is a floating supply.
It also acted as a voltage divider because the probes have about 300 ohms of resistance
Because without it the PSU output is at a high impedance.
It has to do with the coax usually having 50 Om impedance as well. Basically, the coax is a tramission line, and when you trasmit a signal over coax, it is vitally important to have it terminated with a matching impedance load. Otherwise, you get the signal all messed up.
Measuring the ripple is so much easier using a True RMS multimeter. Set it to AC voltage, read the result, done. However, using a scope is more fun.
It's everyday friday here! thanks Dave for your lessons!
Great lectures. Definitely talented instructor.
But how do you get rid of noise??
There is another aspect of power supply noise that is little thought of. I was involved with a huge project at a large computer site in 2010 that had to have the power supplies replaced on 5000 installed servers. The switching power supplies also generate noise back onto the ac feed line. When you had 5000 servers with no isolation, all generating noise, the electrical noice would shut down the site UPS systems. The replacement power supplies,all 10,000 of them fresh in from China,now had toroid coils on the ac line. Guess the server vendor didn't save 20 cents per server after all ?
You, Sir, are a gift from heaven!
Hey Dave, where can you buy the probe BNC adaptor for the rigol scope. Do you have a part number. Cheers
Awesome explanation of all the concepts!
An awesome video that I have been watching since years again and again! Thanks Dave! :)
Those measurement tips and tricks were sooooooooooooo informative. Thanks for sharing this content!
Excellent because it shows the tips&tricks of ripple and noise measurement.
That HP calculator induced memories. Highschool programming, iterating math & stuff.
Brilliant video. So useful. Perhaps I shouldn't be so disappointed with my digital scope after all! Thank you.
Thank you, thank you, thank you! Starting out in electronics and your video's help so much!
Hey nice video. Though one more way to get rid of high frequency noise is to use a 0.1 micro farad disc cap on the probe tip. Infact you can solder it onto the probe tip and then leave a little bit of lead say 3mm extra to act as the points to probe the power supply. This is one of the standard methods
I got some Lambda LQ/LQD series linear bench PSUs recently, circa 1983 (warranty seals were unbroken haha!).. their ripple + noise specs are 0.15mV RMS, 1mV pkpk. Temp coeff. is ±(0.005% + 10μV) /°C. Line/load regulation is 0.005% + 0.5mV. Current regulation is 1mA/2.5mA (line/load), at full voltage range. Just fantastic. I verified those figures with my scope, still fully within specs. Zero overshoot with maximum load. They employ a custom Lambda branded IC for V/I regulation. I've sourced a replacement for one from China, gonna see if the specs change after I put it in.. I suspect it's not an original part from 31 years ago. :P
I got a whole lecture on noise and distortion when i studied EE, we did a huge amount of mathematical theory and a lot of fourier transform, 3rd order interseption points and stuff like that back than, but we did *not* measure a thing even at the coresponding laboratory lecture...sad...sad.
Great vid Dave. Thanks
Dave Jones, the EE Professor
I miss Dave's videos like this
Another trap for a "young-player" might be that when one is playing around with the scobe probes and a power-supply, and they are both grounded via earth (3-pin mains) it may set the mains/installation fuse off or the "FI-switch" or both may in addition to a defective scope or PS. That´s why i´m running my scopes over a isolation transformer, in my case a 230V/230V to power up the scope. The tranny decouple its 230V output from earth.
I've also isolated my scope. Solved a lot of my mains noise problems.
Fundamentals Friday FTW!
That was heavy (but fun). I have found if an auditing Piezo sounds 'normal', were golden. If the screech is too Bjork or Yoko then I find a Dave.
Excellent, informative, and eye and mind opening!!! Thank You!!!
There is a lot of good info here. I got that exact ds2202 and I'll have to check some of the linear PS i have. I will certainly learn something, most likely the probing. Great video.
Terrific video, Dave. I went into this thinking I would not learn a thing. I was wrong.
I had to laugh. He measures 20 mV pk-pk, and he says it's garbage. I just got my first O-scope running and measuring a cheap SMPS, a Chinese 13.8 V, 25 A power supply made for powering RC battery chargers. I get 1 V pk-pk ringing at 62 kHz, and adding about 10 A load I now get an almost 2 V pk-pk ringing 5 µs in front of the 1 V pk-pk ringing. From looking at the trace under load, the bigger ringing appears to be the supply switching "on" and the smaller ringing the supply switching "off".
Anyhow, THAT is a garbage signal. Fun stuff. Works great powering simple 12 V loads like lights or battery chargers though.
good video, I didn't understand it all, I'm a repair tech not an engineer, but I did learn a lot. thx Dave
hi nice video dave. Though in my company which made power supply for defense institutions and special custom built power supply. The way we would measure ripple is to use a single probe but solder a 104 disc cap on the tip ( 0.1 micro farad) on the tip. off course no use the ground lead that is serious a big ******* antenna.
Wohoo! :D
I have waited for these videos :)
Thanks Dave!
great video ! helped me a lot. got here because of exactly the kind of spikes seen in this video from a dual rail power supply i built.
hey, that brick converter you used is used as a 5v / 2A BEC for quadcopters.Differential probes are shit expensive :(
Yep, they can cost more than your scope.
Amazing video! Learning a lot... much more than at school!
How do we talk you into doing more Fundamental Fridays? I absolutely love these segments.
"How do we talk you into doing more Fundamental Fridays?"
Make more Fridays. TGIF. If everyone thanks god for Fridays, how come there's only 1 Friday per week?
ionyou I wasn't aware that Dave put out a "Fundamentals Friday" video every Friday. When did this happen?
Hi, I haven't gone through all your videos. But I wish you could make some videos on different kinds of sensors and motors or even robotics control. That would be an interesting topic.
I dont understand 24:04 when he adds the "50Ohms Terminators"... I only know terminators that act as an end cap, but he uses obliviously something else ? His terminators have in- and outputs??? I am confused.
nice video. it would be interesting if you discuss about power supply transient response as well in your next video
you don't need 400uV vertical sensitivity, you need a good pre-amplifier, and you can measure down to microvolts; that's how Linear does it
Really insightful. Thank you Dave!
Very helpful Dave, just what I need right now!
I was hoping you would test the power supply you designed to see how it compares to the Rigol.
Great explanation well done
16:50 ....but...but "digital scopes are just better!" LOLing at your DSO vs CRO videos. The testing equipment manufacturers really took a step back when they abandoned analog scopes; measuring noise was a big part of a CRO's bread & butter.
Wrong. I've done a video on analogue vs digital scope noise if you want to educate yourself
You've done two; I've watched both of them a couple of times. Your claim in the second one that "they're just better" (referring to digital scopes) at showing and analyzing noise is refuted by your comments at the time index referenced in my previous post here. A two-channel CRO does the business with just throwing a couple switches; with a DSO you need to use three channels, adjust persistence and muck around with channel phase inversion and, in some cases, buy (or hack) a software option for an analysis package.
You do concede in the first analog vs digital scope video (and in all your $50 eBay scope videos) that every EE should have an analog scope as entry-level gear, which goes to the point of my previous post: given their utility, there's no good reason not to still make oscilloscopes that are analog from the front end to just in front of the display driver, with no digital storage or software analysis (today's and tomorrow's EEs still know how to use a calculator, right?) Translating CRT beam deflection for an LCD driver should be trivial.
...which gives me an idea, so thank you for challenging me on this. A true analog scope with an LCD might be a cool open-source project. Most of the CRO designs came out of patent a long time ago.
Hey Dave! Thanks for this amazing, content filled video! I has one question, what do the 50 ohm terminators do exactly?
Found this to be enormously helpful- thanks!!
Hugely instructive as usual Dave! Cheers!
These videos are great. You would have a blast at the Dayton Hamvention.
This is exactly what I needed, thanks for explaining Dave!
Hi Pro, at 14:37, could you explain why the ground wire of probe picks up noise? Thank you.
+Shiwei Luan The ground wire forms an inductor coil and the noise it picks up is some electromagnetic interference generated by other devices in the room - in this case mostly PWM-controlled LED lights.
You should try the noise testing with an old DECT phone next to it.
Something I notice is that using buck converters that let me regulate current, such as battery chargers (XL4015), I had way more noise when I demanded a current near to the limit I put on. Lets say I set my power supply to deliver up to 1.2A, when I put a load that demanded 1A y had some noise, but if I limit the current up to 2A with the same load, at the same conditions, the noise was smaller than before ._.
spectrum analyser is a great way to see what noise looks like. since i am poor i use my audio interface with software doing fourier transform. can see all the harmonic lovelies
Dave, excellent tutorials, can you explain how to measure the any oscilloscope noise floor ?
Follow up this video from Afrotechmods 's DC-DC Buck Converter. And keep following up Dave and your videos are awesome! I can learn EE start just my a little knowledge of EE in high school (in Thailand) to starting some basic of Reverse Engineering! Well you're rock, Dave.
Thanks for sharing, Dave
Hi Dave,
Can't you set the oscilloscope in 1MOhm resistance and measure it using two probe technique, without attenuation?
Dave used a 50 ohm terminator on the oscilloscope. What is a 50 ohm terminator and what are they used for? I need my fundamental Fridays to be even more fundamental.
+00Skyfox Read about "transmission line termination" to really understand it. In short - a terminator is simply a resistor that prevents signal from reflecting at the end of the transmission line back to the signal source which would interfere with your measurement. BTW, not all scopes have a built-in terminator.
this was amazingly informative. another ripper dave this has been really useful. great scientific reasoning
For the past month, i have been taking hundreds of measurements the wrong way for my university project. Even the professors or the research assistants didn't tell me any of this. How I wish I saw this video one month earlier. 😭😭😭
Well, most don't do much of any hands on work. They get their grunt TAs lead all the testing, and even then, the TAs will rely on a lab technician with the electronics know how like Dave here.There are a few professors that do lab work, don't get me wrong. But most academics are snobs that won't bother with the dirty tedious work of testing and debug. Most electrical engineers just plain never learn this stuff because most of the EE jobs out there don't have an emphasis on this kind of testing. You see plenty of digital design, fpga and software coding positions, but they don't get exposed to dealing with these front end realities.
Another great video, thanks Dave!
Many thanks Dave
Can you measure this using a bench DMM using maths or AC setup ? That would be a useful video. Is it really as easy as RMS AC ?
Why the series 50 ohm resistances at the far end of the differential measurement coax in additon to the parallel 50 ohm? Edit: Nevermind, I see the low impedance power supply needs a series resistor on its end to match the coax. Great video, by the way. I learned a lot. Thanks, Dave.
No, your original question is valid.
There is no need for the source resistors. They will just add undesired attenuation.
@@vonnikonnope, it's a transmission line
@@robegatt there is no need for the source impedance to match the characteristic impedance of a unidirectional transmission line.
The source impedance only represents energy loss in this scenario.
Bidorectional transmission line is another story. There you need to also match the source impedance.
@@vonnikon there is nothing like "uniderctional transmission line" ! If the source impedance is missing you have the signal bouncing back at the source right at the beginning of the line.
@robegatt try it!
It works perfectly fine.
Plenty of transmission lines use a low source impedance. 10/100MBit Ethernet to name a popular example.
Woo Dave 666 videos on your main channel!
Keep up the great work!
Wow! That was low tech but for me that was very interesting. I have that same Rigol scope and power supply. I also have that DC programmable load. I had no idea that load could put that noise on the there. Very interesting. I know my equipment a lot better now. Thumbs up!
Absolutely excellent tutorial. I am going to have to troubleshoot the power supply of my VTVM, and my thinking is to make the probes you demonstrated for my Tek 475 scope. I have another option that I wanted to ask you about, however. It happens that I have an old Tek 545b scope with a differential plug-in. My question is, what is the best way to hook it to the power supply, or am I just as well off to use your adaptors and the later model 475 scope.
Thanks,
Bob
Love the tuts Dave.
You make a good lecturer
Why would using two separate probes in subtract mode reject common mode noise whereas s single ened connection would not?
Single ended connection still takes difference between signal and ground so if noise is common to both, it should cancel out right?
hi i got a tecktronix analog with ac coupling on that ,can i measure 450v dc supply with 1 x probe or i must use 10 x probe ,can i see ripple on my scope with 10 x probe .What value is acceptable for ripple!thanks
It was quite educative video, thanks for sharing. I wonder what is the noise level in 20+ years old computer power supply?
I think it is not much worse than today ones. Back then ripple was also a problem. Current PSUs are only much more efficient than the old ones. And the caps are of course crap, because they wanna save the last bottom microcent.
Top notch and informative video, thanks
Hey. Why you do not suggest to disconnect probes from power supply to check if noise is picked up by probes themselves?
Great Dave! I have learned a lot with this video. Thanks
Hi Dave,
Al video but can't find the information I need.
I need to measure some powersuppy noise. (cheap or RC equipment)
Yoi made the probes at 32min.
I think this will do but do you have a tutorial or pictures from this how you made it.
Type of coax (impedance) . Resistor and the capacitor you used?
Mabve buying a BNC cable
Cutting it in 2 pieces to start with.
Thank you in advance or any follower that replies.
Please explain why you have the oscilloskop on AC coupling when measuring a DC signal..?
He wasn't measuring DC, he was measuring noise and ripple, which are both AC components riding on the DC. 5V DC would have over-driven the scope on the mV ranges, and so AC coupling was needed to bring the signals back down to 0V average.
Ripple and noise, are AC signals...
Because you can't measure the small amplitude AC signals in the presence of a larger DC voltage. The ADC in the scope doesn't have the resolution. e.g. a 5V DC supply and 8 bit ADC gives you 19.5mV per bit. So 20mV noise will only appear as 1 bit flipping on an off - useless.
Same for the analog scope where you won't be able to see the small noise on the DC signal
Thanks for the comments guys. I find it all very interesting even though I sometimes don't understand everything.
EEVblog i
is there a way you can shield the PS for your lights with proper grounding?, the ammount of RF noise that thing is putting out is insane!
I also have LED retrofit T9 tubes here. 6 of them in my living room 6500K. I'm not able to recieve FM radio anymore, when I have them on, altough the lamp fittings are grounded and even the reflectors are grounded. Problem is that the tubes are lacking of input common mode choke and filtering. The LIVE and NEUTRAL wires are acting as big chunky antennas... I think it's time to make coaxial mains cables, because of cheap thinking china products... And the tubes were quite expencive and the overall quality is very good. It seems just lacking the input filtering... Too much copper wire for the choke and additional inducter plus some caps...
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then put a filter in the input and let us know, you can get one of those filter modules that PSUs use from old PSUs (some of them have IEC C14 receptacle integrated) or just use the filtering board from a computer PSU as well
I have some filter circuits from the formery electronic ballasts of these fittings. But the circuit does not fit into the tubes, nor does it fit into the fitting anymore... :/
Any recommendations for the Caps on the Homebrew probes? Will just a small value ceramic do the job??
what would be an appropriate test setup, to see if the noise is making it onto the output of my rf amplifier? Spec An? Oscope?
Where can I buy a ripple suppressor for my LED power supply? I'm getting a strange strobe effect on certain outlets, but I don't want to have to buy another regulated power supply. Anyone know?
Try a ferrite bead. They are designed to lower supply ripple
Great great video Dave!!!! Many thanks!!!
I really liked this one! Thumbs up and more of this please.
But, what about making an inst. amp. design to use with measuring diff. values ? Maybe you can sketch a design with specific parts for us to have it use on our scopes... Please :)
How do I know if my ripple capacitors can handle the ripple current? I have some surplus caps that I am using for ripple suppression, they are rather large and I am scared they will blow up if I have too much ripple current. It's on a 110vAC 60hz input with rectified ripple of 4-6v p/p. The Current load is 150amp for a DC motor load. Caps are 250v 2000uF each but that's about all the specs I have on them.
I wonder if there is any digital scope that can do diff IN ANALOG HARDWARAE like analog scopes do?
Im also thinking about the 50 terminators, why did that change the situation as much? I mean the shield was already grounded so the core should not pick up so much noise, right?
It is not only shielding, is also about impedance. If your ground is of "high" impedance ther will be a voltage drop. If your signal leed had an intrinsic impedance you´ll "only" get a voltage divider. If you have a ground impedance in your wire it is the same but little more: It is a voltage divider as well as an antenna for all kinds of fields. Magnetic and electric as well.