Some people do not understand the concept of a scope. A scope is not a multimeter. The ground lead of the probe (and the ground connection on the unit itself) is connected to the earth of the power grid in your house or lab. If you connect the ground lead of the probe to anything which has a voltage directly coming from the grid , bad things will happen. Your probe may explode and you could get hurt or worse. It is a good idea to install and use an isolation transformer to protect your gear and yourself.
I just finally got my first actual scope (largely based on your reviews and input) and it's embarrassing how excited I am about this!😄 I've only ever used them in school before and I look forward to not blowing it up
@@els1f Have you had a chance to use it yet? I also have one but i am not familiar with some of the controls and i still have the issue on how to connect the scope to the isolation transformer and what happens when you hook up the component to be tested to the wall outlet since now you are back to the same problem because you have to hook up the ground clip to the component in ordet to troubleshoot it.
I get it! Took me several days to even turn on my Rigol DSO814. Finally fired it up last night and am working on using it with a Vellman Oscilloscope trainer. It’s going real slow and making me feel a little stupid but I’m learning and happy. I’m still worried about blowing it up but will stay away from high voltage for a while.
Really helpful for scope newbies. Bought a Rigol DS1102Z-E as a christmas gift to myself :D Recently I aquired two old analog Hameg scopes (HM 412-1 & HM 512-6). Interestingly, these old scopes are not connected to mains earth. The instruction manual warns you about getting shocked from the scopes casing if you connect the scopes GND to a high potential.
A few points: first, many if not all modern scopes with two or more inputs can be set to differential mode: it might be a switch or menu selection with "Sum" and "Difference" or "Add" and "Subtract". In this configuration, the ground clips on the probes need not be used. This is especially useful for plain old telephone lines: the wires are long and pick up large common mode noise, so if either tip or ring are grounded horrible buzzing noise is introduced. Sometimes performance suffers, and there certainly are limits to it: you can't expect to investigate noise between a pair of 1000V circuits or circuit points especially if they are ground referenced. Floating an AC line powered scope also has similar limitations: elevate the chassis high enough and it will arc from ground of the scope to line or neutral through power supply elements or nearby circuit traces. Sometimes the limits to maximum common-mode voltage are expressed on the front panel, but should be spec'd in the manual. Second, most if not all isolation transformers bridge ground across the windings by default: thus they just don't do what most people expect. Also, Ethernet connectors are fairly well isolated: if you had problems I bet you used a less common shielded STP cable: they always sound like a great idea but are usually just a big hassle, as both ends need to be well grounded. Thanks for reminding me that although dangerous internal faults in a modern scope are highly unlikely, the chances of elevating the scope chassis through the circuit under test by human error or otherwise should be carefully considered. In general, anything outside of plain vanilla should be planned carefully, with consideration of the limitations of each device in the chain and "what if" scenarios, and verified that each piece does what you expect: assume nothing.
I hooked a scope probe to a floating chassis TV once and melted an expensive Tektronix scope probe. I learned to use the 1:1 isolation transformer that day.
Thanks - this is a great point! I need to update this video and talk about the advantages of battery powered scopes. Also Isolated or differential probes are a great subject!
My Rigol DSO814 is way over my head but I’m enjoying learning. Still on step one of the Velleman Oscillator Trainer. Just understanding the probes 1x and 10x function is complex right now. Yes I understand 1x vs 10x but applying it is different. The menus and language are so new to me right now but how exciting to be learning.
When I was a noob, I wanted to measure the ac ripple on one of my dc power supplies, and like a dummy, I connected my clip to the neg banana plug on the power supply instead of ground, and pos to pos banana. Well I blew the breaker, and blew channel A of my cheapie Hantek. Scared the crap out of me. I though that my channel A would be gone forever but months later I was able to locate an open smd series resistor with the help of a friend. Boy was I lucky! I heard you can also use A-b by discconecting your gators and conect channe B to board ground or whaterver it is you are working on but never tried that, thats not totally safe either. Good info all around!
Wow - thanks for the great feedback! One helpful note is to go slow and before connecting any ground - do it with power off - and then bring power up slow if you can. If you see a lot of current or the probe ground wire starts to heat up - then bring power back down. Another safe way i sto to use an ohm meter to measure the ground to your scope ground to be sure that they are the same potential (before connecting your scope ground).
Someone mentioned residual current protection. Would another way be to use an rcbo to interrupt when you do misplace the ground probe? Of course isolation transformer would be a better option to let you you continue on measuring. But a 10$ breaker would be a good protector and stop damage from occuring.
oh thank you, I'm quite cautious about that but I assumed the usb of the scope had a built-in isolator. Kinda weird to me that a scope company would not care about creating a ground loop.
Newby question - I think I did exactly what you are saying NOT to do in this video. In trying to get a sine wave going I attached just the ground lead of the probe to a 120V outlet (which is attached to the scope) and got a big POP! Orange flare sparks and everything. The scope seems to still be working - as in it didn't turn off. Did I damage anything internally to the oscilloscope? I'll never do that again. lol.
Great story Phil!! Yes, that was a short;) Was the ground clip actually connected or were you just touching it? That kind of short would most likely melt down your scope probe lead, but if it happened fast enough - it could just fuse open the ground lead in the probe if it were not attached as well as it should. The ground lead goes to the shield of the bnc cable which is a pretty good connection back to your scope - and then to the ground connection of the scope's ac input power. Most likely the scope is just fine. The probe is probably fine too if you can put it on the cal signal and it has a square wave and you can compensate it as usual. Let us know what you find;)
Yes, thank for the video, well done. You didn't mention GFCI's in Australia we call them RCD's and they trip beyond 15mA in about 10 ms. So if by chance you connected the BNC ground to to neutral on your workpiece, and your probe to hot (active) on your workpiece, there would be a differential current and the RCD/GFCI would trip,,,, wouldn't it??? presuming that you are not using an I/T on your work piece 120/240vac board.
Thanks cookie boi - I appreciate your feedback! Yes, if the scope probe ground is connected to the Neutral then it could trip the RCD/GFCI, if there is an imbalance that causes enough current to flow. It really doesn't; matter if the scope tip is touching anything it is just a matter of the current flowing on the ground lead.
I have a scope that I've hardly used because I'm scared 💩less of blowing it up. I think (sometimes) the best way is running everything from an isolation transformer and use a differential probe?..... Unfortunately I haven't found any bags of money.
LOL - I don't blame you;) I know people who use what I call cheater plugs to isolate the ground from the scope. This isn't a recommended practice as any floating metal on your scope can potentially bite you. Just be careful to be sure all your scope probes are referenced to the same voltage potential. If probing a circuit connected to and AC circuit, be sure to have all the probes connected to ground.
it's not the voltage that will kill you considering that when you get a static shock it's probably 2kv BUT pico amps or less. It's current that will kill you. .5 amps across the heart will do it.
Yes, that's why car ignition systems don't kill. (in my 50 years (in the trade) of messing with spark plug leads)... I've never see a fatality.. However late model cars in the last 20 years can certainly give you a good bite and wake you up on a Monday morning.
½ amp will (probably) kill you!!! Currents between 100 and 200 mA (0.1 to 0.2 amp) are more than enough to be lethal. GFCI's are by design set to trip at 5 mA for protection of personnel. But do not get hung up on amperage alone. Although it's probably the biggest factor in electrocution, it's not the only one... Besides current: PATH taken thru the body And TIME exposed to the current. Remember- "Being electrocuted Hertz the whole time, until you die" Sincerely, a Master Electrician
Sir. I love your videos on scopes and hope you produce more. I''ve recently watched a vidoe from the, "bald engineer," in which he was showing how to use a scope. He did something that I thought couldn't be done. He connected the probe to an AC wire to show a since wave, the ground wire wasn''t visible in the shot. Is that right. I myself am working strictly with DC and ardiunos. I even disconnect the arduino from the pc and use an undrounded wall afdapter to power it when using my scope !
Thanks for this awesome vid.. Thumbs up. Quick question : what kind of isolation transformer can you suggest? I am having trouble identifying the correct class of equipment. Thx!
Great warning!! :-) If I did understand correctly, you talked about only using one earth from one probe while not using earth on the other, an that could give noise, why if all probes do use the same ground in the scope-side? Would an other solution be to connect all the ground leads together at one point?
You can use one scope probe ground clip and leave the other off, but that can introduce noise. This is because the probe has a filter element that wants to pick up the current for it from the probing point, and if it is left open it has to bet it up from the other probe then across the scope then down to its probe. So, it is better to use both grounds - just be sure that they are referenced to the same potential with each other (the ground clips)., And, if you are on a circuit that is on the prime power, then they need to be on the earth ground potential. I've seen digital engineers and techs disconnect the ground leads on the probes and use a ground lead from the scope to the ground of the circuit and probe that way. And that's fine if they are looking for digital on/off voltages (not fast), but at times they get really noisy measurements.
@@KissAnalog When you use the ground clip, you effectively create a Faraday cage at ground potential for nearly the entire length of the probe and cable. That keeps your signal clean.
This is one of the most complex and complicated issues in electronics (for me). I've read so many do's and don'ts and now I'm more confused than ever. So, how do you hookup your workbench? Do you ONLY plug the DUT (Device Under Test) to the isolation transformer? I think that's what they recommend for working on old Ham radios that don't have a power transformer - that have a "live" or "hot" chassis. Or, do you ONLY plug your test instruments into the isolation transformer and have the DUT plugged into house power? Or, do you plug everything into the isolation transformer? I think I've read that that can be dangerous, too. In any case, I guess it's a good idea to have a GFCI (Ground Fault Circuit Interrupter) (like used in bathrooms) multiple outlet bar to have the fastest shutdown of power if an imbalance in circuit power is detected. Another question I have is - do I need (would it be useful to have) one of those Siglent SDS1202's to troubleshoot a bunch of old Tektronix 465 oscilloscopes I have? I think I'm looking for an excuse to buy one. My rationale is that I don't know how functional or accurate any of those old 465's are and the Siglent would be new and better able to give me super accurate readings, wouldn't it? Maybe? Or would I be better off spending my money on other things?
It is the same to me. I still have not received a clear answer about the question on how to hook up everything and what goes to what? I have two O'scopes but am adraid to use them not knowing how to hook them up.
man, as always, a wise question contains half the answer. i think you have the necessary base, just keep your eyes open, measure twice, before connecting, you'll be fine. added automatic protection is always nice, i rather it trip 50 times instead of killing me once
btw im not better than you, im still too overcautios around my gear, and despite that i recently burned and old motherboard and a new powerbank circuit
@@AlexanderBukh Another question i have is. The old receivers/component don't have a ground plug so they are not hooked up to mains earth and it should be ok to hook up the O'scope probes to the component being tested. That question has not been answered.
Another way is to use a non grounded scope such as a Fluke scopemeter or in my case a Micsig tablet for automotive use with all the options great scope and safe in that regard
Thank you! Yes that is so true. A battery powered scope is a great way to help provide a safer way to take measurements. And it can help get cleaner measurements too;)
By using an isolation transformer on the DUT, you isolate the chassis ground of the work, from the earth ground of the O-Scope. By isolationing the scope itself, If you accidently hook up to high voltage in the work, now you've tied your scope lead back to theBNC connectors of the scope, giving them high voltage as well.@@KissAnalog
Valuable video but how on "Earth" can connecting the computer via ethernet port connect the earth back to the oscilloscope? Is ethernet port not inherently isolated?
Great question! The shield on the ethernet port is grounded on the scope - so ohm your connection to your computer to verify. This has been a surprise to others...
as for the "pc connection": for the USB-port I'm with you - the shield is usually connected all the way thru - as for a RJ45 ether jack? at least from my personal experience most (as in more than 50%) of both the plug as well as the socket are made from plastic and only the up to 8 pins are actual connected also ethernet connections are usually galvanic isolated - so although the ethernet cable itself carries the information it's floating in respect to "machine" it's hooked into - so there won't be any galvanic connection between a scopes ethernet port and a pc one tldr: in difference to a usb connection an ether connection should not cause a ground loop as neither the 8 conductors nor the outer shield is galvanic connected all the way thru (hence shielded cables are kind of a scam as the shield is floating as its not connected to anything) but I'm open to get corrected
Thanks for the feedback! I've been in labs where the user didn't check the USB connection to the computer - and it caused a problem. Best way to check is to just use your ohm meter with power turned off.
Thanks - great question! If you use your multimeter you will see that the earth ground is connected to the alligator (ground) clip. So, yes you can connect those, and yes the voltage is within the rating of the probe (check the voltage rating of the probe to be sure),
Much as I watch these I'm still confused. I'm in a late 1920's house with 2 wired outlets, where the only tie to earth is at the breaker box where (I suppose) neutral is wired to a water pipe. I surmise THIS represents ground, where neutral and Earth are at the same potential, But that's as far as my brain goes if even correct. I can't understand what that means or how to use it safely? All my three prong devices go either into the adapter (cheater) plugs or into a surge strip which itself goes into an adapter plug. Any helpful tips?
And as followup to my own question I'm thinking it's ok to treat Neutral as Ground....as long as all plugs are oriented correctly especially the final plug to wall, that the outlet is wired correctly so that the Neutral side of the plug is genuinely going into the Neutral side of the wall outlet. Sound ok?
Great question! If you do not have the ground at your wall, well then it is actually maybe safer for your scope;) You don't have to worry as much about placing the ground of your scope probe to ground when you are looking at AC power - since you don't have a ground. But, you still need to be sure that each channel that you use has the ground on the scope probes at the same potential. Make sense?
Thanks. I have less lucid moments and more lucid where things come together. At the moment I'm somewhat in between. I've been wondering just that - if I'm kind of isolated by virtue of plugging the 3rd prong grounded chassis into nothingness. I'm thinking it's not the same though if I plug in an ancient 2 prong appliance but that's a moot point here. So far I've had no need to run both channels but I'll keep that advice in mind should it come up. Funny thing is ever since I broke but repaired a German Rangefinder camera at about 12yo, I've had the confidence to feel I could repair anything...so long as I can see it's mechanism. Electricity...well those who understand components will say it is also a mechanism but to me it's an elusive invisible monster that's always intimidated me. At 64 tho I'm finally developing a grasp, just enough to have troubleshooted a few of my tube amps and father's old radios. Thank you. Oh another funny....all that equipment lined up and you didn't have the 99cent cheater plug to show and tell in your video...(just kidding).
i run an isolation transformer on the equipment I’m testing...are you advising to run isolation on scope instead?? also...would you advise 10: 1 or 100:2 probes..I’really paranoid about o-scope safety etc...thanks
That really depends on what kind of equipment. I think running an isolation transformer on either is a big step. Just remember to keep all scope channels and any metal contact on the scope chassis - like the USB port at the same potential. I mostly use 10:1, but if I were running higher voltages than I'd use 100:2. My diff probes are actually 20:1 and 50:1 as lowest settings. Thanks for the great questions.
Did something similar on my siglent 1104ex “3” channel…when testing an amplifiers 20-20k sweep I without fireworks or any signs blew channel ones input. I got no pops nor the oscope turning off. Everything is just so on the 2,3,4 channels. But the next time I turned on the scope my readings were off on channel one, i try to compensate for this ridiculous looking wave that I cannot compensate with the probe, it looks like an old picture of a 50s saucer dish UFO on its side. Ive factory restarted and put it back to factory but I realized I must have shorted out my input on channel one. I have the 1104ex and its my first real digital scope so I still have 3 channels that work perfectly but I would like to repair the input on channel one someday soon. I really need a differential probe. Can you make a more nuts and bolts explanation of this topic. Its really my biggest downfall in my oscope knowledge. I get certain fundamentals but when putting in real time practice with bridged, stereo, and other variations of where and what to hook up or to use ground leads. I hoped me f’ing it up would have taught me the lesson so I am currently irritated I could never grasp the concept on how applications will vary depending on you wanna introduce yourself into the circuit.
Thanks for the great question Blake! Can you give me more details on what signal that you were looking at when this happened? Did you have a scope probe connected? Was it in x10 or x1 position?
@@KissAnalog |- is the closest on here I can think of to give the wave shape. So, imagine a square wave that has double volt overshoot at the start of the wave and then immediately comes down in a slope down to “calibration” volts and it is a repeat over and over and does not change with the probe screw adjustment being turned either all the way down nor backed out all the way. Hope that helps. Ill send it to you if you wanna use it in a video to help others and myself with a fix. Alas, I was using the probe is 10x as well as 10x in the trigger settings. I was accepting a 10th of the signal basically.
I have issues with not fully understanding why if a device has a floating voltage it can not cause current to flow as there may still be a potential difference between the ground and teh floating voltage. This is also causing me problems in feeling safe about attaching my pc to serial ports on alarm/telecom equipment as they are not driven by relays or optoisolators. Could someone please explain why this floating voltage does not matter.
I hope that you realize that it is possible to damage your test equipment, the device you're working on, or even yourself (maybe fatally) in far less time than it would take to hit either of your emergency buttons.
I recently bought Hantek 5102p Oscilloscope after years of wait to buy a scope. I have kind of a stupid doubt and don't know who can I ask it to. Suppose if I have an arduino running which outputs 5volt pwm signal at 50% duty cycle and 1kHz frequency. If I connect probes of both the channel to the very same pin of arduino that is outputting 5V pwm. Will it cause any kind of damage to my scope? A simpler way to put that question would be, "Can I connect same signal to two Probes of two different channels simultaneously?"
That is a fantastic question! I'll bet there are many others wondering the same thing - so cheers to you for asking;) No there is no problem there. What you want to be sure of is that the ground wire (usually with alligator type jaws) is connected to the same potential. You can check this with power off. Just do an ohm check with a multimeter to verify that the grounds are connected where you think they are. Then connect both probes to the same potential (ground/return), then you can place the scope tips where you want to see the voltage (voltage difference form the tip to the ground). Thank you for asking!
Nikki Marie The scope probe returns are all tied together on the scope so be careful to connect the grounds at the probe tips at the same potential on the circuit that you are probing. Make sense?
@@KissAnalog My home was built in 1947 and has no earth ground wire in outlets, however my power cords are all tied together to a floating ground. As a temporary solution my equipment rack has grounding studs and I can tie a real earth ground to that at least so i think but thats all off topic.
Nikki Marie OK, so all your equipment chassis are tied together. That sounds good. Because equipment with three wire power cords typically have capacitors tied to chassis. This puts some charge on the chassis, so bonding them together is a safer situation as it holds them at the same potential. It sounds like you have it figured out. ;)
You know i've seen this video before and daves, but clearly I clearly didn't get the memo, was just working on a power supply and tried probing post rectifying then tried to set up second channel to look at the first and overlap, about a minute later heard a small pop and smelt some burning :). After watching the video I still didn't understand so I went over and probed the shields with my meter which confirmed they were combined together then I realized what had happened. rectified 0v gnd then i tried putting 28v ac in on the same ground (Facepalm). Can't complain though, live and you learn, scope seems ok for now. If i could go back and time id let it happen again hahehhehehe
@@KissAnalog no, it wasn't working before, it was a lucky day to get one flash from the old phosphorus display, I was in the back shorting wires to get a beam, then I looked up to see smoke billowing out the vent, leaving a horrible stench, I think I killed my oscilloscope, but I am too scared to plug it in given the house down the street burning down from a coffee maker.
Wow - well it sounded like it was on its way out already. If the caps and some circuitry needs to be replaced - it might be worth it to repair and have fun doing it. If the CRT is going bad - then that might be tough to find a replacement.
I don't understand what all the talk all over the internet about this is, surely it's simple, the ground/earth lead on the probe should ALWAYS be connected to EARTH! FULL STOP!?!
TH-cam: John Ward. Isolation Transformers Explained. You DO NOT plug your ‘scope into an isolation transformer. About 10 minutes into the video I’m no expert, but he explains exactly why.
Thanks for your feedback. I've seen John Ward's video - and he makes good points - but there is no clear and simple solution to everyone. The problem is - that there is so much confusion on what an isolation transformer is - and what it isn't - and the different types. I'm happy to debate these topics with anyone;)
Early in your vid, you said that you can isolate a scope using a cheater plug. That is NOT the case! The neutral/common (white) wire is common to all outlets. How is that possible? Think about it. If you CAREFULLY removed the breaker panel cover (not recommended) you would see that all the white conductors are screwed into a common bus, as all the bare ground wires are. If you completely disconnect the mains breaker, you could then safely probe neutral to ground with an ohmmeter. Why would you have to disconnect the mains, you ask. Think about it logically. There is a low resistance from neutral to ground and back again. Simple Ohm's law: low impedance, high current. The solution is to modify an isolation transformer by opening the case and disconnecting the green chassis wire from the secondary winding and insulating it with heat shrink. Just remember that the secondary winding is now truly floating and completely isolated. Your 'Scope is now 'protected.' You, not so much!
Thanks Richard for this great question! Using the transformer as you described is the better way to isolate. The cheater plug works to though, and I’ve seen a lot of power guys use this method in the lab. You are correct, at the service entrance the neutral is bonded to the earth or safety ground. It is isolated because at the scope the chassis is no longer tied to safety ground, so your probes ground has no DC connection to the input power. The scope has an isolated power supply so there is no connection from chassis/scope ground to input power, so it’s isolated.
Thanks for the feedback - but ohm your ethernet jack to your ground - and you may be surprised. Ethernet often uses an isolation transformer to transfer the signals to the internal circuitry - but test your shield in your cable...
Why do you say this? I have actually worked on those things. I have lots of videos showing differential probes. Just not sure how you get to that conclusion watching this video???
Sorry about that! I'm always trying to to better and this was one of my early videos. But, I do have a tendency to chat - so maybe you might want to skip my channel. Sorry again...
Newbie question. on a 2 channel handheld dmm oscilloscope, how do you take 2 separate voltage measurements simultaneously while the probe grounds are not isolated by design? I can only assume you cannot? I don't see the the use in a two channel where they cannot Operate independently.
You are right - it is limiting when you need to have two isolated returns. That’s when you need a differential probe;) see this link and thanks for this great question! th-cam.com/video/892RcsIUAtU/w-d-xo.html
Some people do not understand the concept of a scope. A scope is not a multimeter. The ground lead of the probe (and the ground connection on the unit itself) is connected to the earth of the power grid in your house or lab. If you connect the ground lead of the probe to anything which has a voltage directly coming from the grid , bad things will happen. Your probe may explode and you could get hurt or worse. It is a good idea to install and use an isolation transformer to protect your gear and yourself.
1959Berre you are right - thank you for your help
As a noob it sounds as if (disregard your safety) it is better to not have ground on any gear in the lab at all?
I wouldn’t go that far;)
@@KissAnalog Many years ago I do a short circuit with the scope ground, now I use a cheater plug on each scope.
Cheers.
Ricardo B LOL I actually do too! I am afraid to suggest that as a fix because of potential issues;)
I just finally got my first actual scope (largely based on your reviews and input) and it's embarrassing how excited I am about this!😄 I've only ever used them in school before and I look forward to not blowing it up
LOL that’s awesome! Ask any questions and we will try to help you!
@@KissAnalog Thanks a lot 🙂👍
@@els1f Have you had a chance to use it yet? I also have one but i am not familiar with some of the controls and i still have the issue on how to connect the scope to the isolation transformer and what happens when you hook up the component to be tested to the wall outlet since now you are back to the same problem because you have to hook up the ground clip to the component in ordet to troubleshoot it.
I get it! Took me several days to even turn on my Rigol DSO814. Finally fired it up last night and am working on using it with a Vellman Oscilloscope trainer. It’s going real slow and making me feel a little stupid but I’m learning and happy. I’m still worried about blowing it up but will stay away from high voltage for a while.
Really helpful for scope newbies. Bought a Rigol DS1102Z-E as a christmas gift to myself :D Recently I aquired two old analog Hameg scopes (HM 412-1 & HM 512-6). Interestingly, these old scopes are not connected to mains earth. The instruction manual warns you about getting shocked from the scopes casing if you connect the scopes GND to a high potential.
A few points: first, many if not all modern scopes with two or more inputs can be set to differential mode: it might be a switch or menu selection with "Sum" and "Difference" or "Add" and "Subtract". In this configuration, the ground clips on the probes need not be used. This is especially useful for plain old telephone lines: the wires are long and pick up large common mode noise, so if either tip or ring are grounded horrible buzzing noise is introduced. Sometimes performance suffers, and there certainly are limits to it: you can't expect to investigate noise between a pair of 1000V circuits or circuit points especially if they are ground referenced. Floating an AC line powered scope also has similar limitations: elevate the chassis high enough and it will arc from ground of the scope to line or neutral through power supply elements or nearby circuit traces. Sometimes the limits to maximum common-mode voltage are expressed on the front panel, but should be spec'd in the manual. Second, most if not all isolation transformers bridge ground across the windings by default: thus they just don't do what most people expect. Also, Ethernet connectors are fairly well isolated: if you had problems I bet you used a less common shielded STP cable: they always sound like a great idea but are usually just a big hassle, as both ends need to be well grounded. Thanks for reminding me that although dangerous internal faults in a modern scope are highly unlikely, the chances of elevating the scope chassis through the circuit under test by human error or otherwise should be carefully considered. In general, anything outside of plain vanilla should be planned carefully, with consideration of the limitations of each device in the chain and "what if" scenarios, and verified that each piece does what you expect: assume nothing.
I hooked a scope probe to a floating chassis TV once and melted an expensive Tektronix scope probe. I learned to use the 1:1 isolation transformer that day.
Thanks Brett! I think if you spend enough time in the lab - that many of us have had this happen - or begin to happen;) Great feedback!
Good advice for Saelig customers too! Isolated probes or battery-powered scopes like Micsig might be helpful in some situations!
Thanks - this is a great point! I need to update this video and talk about the advantages of battery powered scopes. Also Isolated or differential probes are a great subject!
My Rigol DSO814 is way over my head but I’m enjoying learning. Still on step one of the Velleman Oscillator Trainer. Just understanding the probes 1x and 10x function is complex right now. Yes I understand 1x vs 10x but applying it is different. The menus and language are so new to me right now but how exciting to be learning.
When I was a noob, I wanted to measure the ac ripple on one of my dc power supplies, and like a dummy, I connected my clip to the neg banana plug on the power supply instead of ground, and pos to pos banana. Well I blew the breaker, and blew channel A of my cheapie Hantek. Scared the crap out of me. I though that my channel A would be gone forever but months later I was able to locate an open smd series resistor with the help of a friend. Boy was I lucky! I heard you can also use A-b by discconecting your gators and conect channe B to board ground or whaterver it is you are working on but never tried that, thats not totally safe either. Good info all around!
Wow - thanks for the great feedback! One helpful note is to go slow and before connecting any ground - do it with power off - and then bring power up slow if you can. If you see a lot of current or the probe ground wire starts to heat up - then bring power back down. Another safe way i sto to use an ohm meter to measure the ground to your scope ground to be sure that they are the same potential (before connecting your scope ground).
Someone mentioned residual current protection. Would another way be to use an rcbo to interrupt when you do misplace the ground probe? Of course isolation transformer would be a better option to let you you continue on measuring. But a 10$ breaker would be a good protector and stop damage from occuring.
oh thank you, I'm quite cautious about that but I assumed the usb of the scope had a built-in isolator. Kinda weird to me that a scope company would not care about creating a ground loop.
Thanks - I agree! I was caught off guard when I learned this! I'm surprised that there isn't an isolated connection - like optical input.
Newby question - I think I did exactly what you are saying NOT to do in this video. In trying to get a sine wave going I attached just the ground lead of the probe to a 120V outlet (which is attached to the scope) and got a big POP! Orange flare sparks and everything. The scope seems to still be working - as in it didn't turn off.
Did I damage anything internally to the oscilloscope?
I'll never do that again. lol.
Great story Phil!! Yes, that was a short;) Was the ground clip actually connected or were you just touching it? That kind of short would most likely melt down your scope probe lead, but if it happened fast enough - it could just fuse open the ground lead in the probe if it were not attached as well as it should. The ground lead goes to the shield of the bnc cable which is a pretty good connection back to your scope - and then to the ground connection of the scope's ac input power. Most likely the scope is just fine. The probe is probably fine too if you can put it on the cal signal and it has a square wave and you can compensate it as usual. Let us know what you find;)
Yes, thank for the video, well done. You didn't mention GFCI's in Australia we call them RCD's and they trip beyond 15mA in about 10 ms. So if by chance you connected the BNC ground to to neutral on your workpiece, and your probe to hot (active) on your workpiece, there would be a differential current and the RCD/GFCI would trip,,,, wouldn't it??? presuming that you are not using an I/T on your work piece 120/240vac board.
Thanks cookie boi - I appreciate your feedback! Yes, if the scope probe ground is connected to the Neutral then it could trip the RCD/GFCI, if there is an imbalance that causes enough current to flow. It really doesn't; matter if the scope tip is touching anything it is just a matter of the current flowing on the ground lead.
I have a scope that I've hardly used because I'm scared 💩less of blowing it up.
I think (sometimes) the best way is running everything from an isolation transformer and use a differential probe?..... Unfortunately I haven't found any bags of money.
LOL - I don't blame you;) I know people who use what I call cheater plugs to isolate the ground from the scope. This isn't a recommended practice as any floating metal on your scope can potentially bite you. Just be careful to be sure all your scope probes are referenced to the same voltage potential. If probing a circuit connected to and AC circuit, be sure to have all the probes connected to ground.
it's not the voltage that will kill you considering that when you get a static shock it's probably 2kv BUT pico amps or less. It's current that will kill you. .5 amps across the heart will do it.
Thanks for this great feedback! You are right - it is only about 0.5 amps that can kill. It really doesn't take much.
Yes, that's why car ignition systems don't kill. (in my 50 years (in the trade) of messing with spark plug leads)... I've never see a fatality.. However late model cars in the last 20 years can certainly give you a good bite and wake you up on a Monday morning.
½ amp will (probably) kill you!!!
Currents between 100 and 200 mA (0.1 to 0.2 amp) are more than enough to be lethal. GFCI's are by design set to trip at 5 mA for protection of personnel. But do not get hung up on amperage alone. Although it's probably the biggest factor in electrocution, it's not the only one... Besides current:
PATH taken thru the body
And
TIME exposed to the current.
Remember-
"Being electrocuted Hertz the whole time, until you die"
Sincerely, a Master Electrician
Should always isolate the DUT not the test equipment. But sometimes we do things because we have to.....
Thanks for your feedback! I have worked in many labs that float scopes - not that it is recommended for safety reasons...
Sir. I love your videos on scopes and hope you produce more. I''ve recently watched a vidoe from the, "bald engineer," in which he was showing how to use a scope. He did something that I thought couldn't be done. He connected the probe to an AC wire to show a since wave, the ground wire wasn''t visible in the shot. Is that right. I myself am working strictly with DC and ardiunos. I even disconnect the arduino from the pc and use an undrounded wall afdapter to power it when using my scope !
Thanks for this awesome vid.. Thumbs up. Quick question : what kind of isolation transformer can you suggest? I am having trouble identifying the correct class of equipment. Thx!
Great warning!! :-)
If I did understand correctly, you talked about only using one earth from one probe while not using earth on the other, an that could give noise, why if all probes do use the same ground in the scope-side?
Would an other solution be to connect all the ground leads together at one point?
You can use one scope probe ground clip and leave the other off, but that can introduce noise. This is because the probe has a filter element that wants to pick up the current for it from the probing point, and if it is left open it has to bet it up from the other probe then across the scope then down to its probe. So, it is better to use both grounds - just be sure that they are referenced to the same potential with each other (the ground clips)., And, if you are on a circuit that is on the prime power, then they need to be on the earth ground potential. I've seen digital engineers and techs disconnect the ground leads on the probes and use a ground lead from the scope to the ground of the circuit and probe that way. And that's fine if they are looking for digital on/off voltages (not fast), but at times they get really noisy measurements.
@@KissAnalog Thanks a lot for your clear and great answer!!
@@KissAnalog When you use the ground clip, you effectively create a Faraday cage at ground potential for nearly the entire length of the probe and cable. That keeps your signal clean.
This is one of the most complex and complicated issues in electronics (for me). I've read so many do's and don'ts and now I'm more confused than ever. So, how do you hookup your workbench? Do you ONLY plug the DUT (Device Under Test) to the isolation transformer? I think that's what they recommend for working on old Ham radios that don't have a power transformer - that have a "live" or "hot" chassis. Or, do you ONLY plug your test instruments into the isolation transformer and have the DUT plugged into house power? Or, do you plug everything into the isolation transformer? I think I've read that that can be dangerous, too. In any case, I guess it's a good idea to have a GFCI (Ground Fault Circuit Interrupter) (like used in bathrooms) multiple outlet bar to have the fastest shutdown of power if an imbalance in circuit power is detected. Another question I have is - do I need (would it be useful to have) one of those Siglent SDS1202's to troubleshoot a bunch of old Tektronix 465 oscilloscopes I have? I think I'm looking for an excuse to buy one. My rationale is that I don't know how functional or accurate any of those old 465's are and the Siglent would be new and better able to give me super accurate readings, wouldn't it? Maybe? Or would I be better off spending my money on other things?
It is the same to me. I still have not received a clear answer about the question on how to hook up everything and what goes to what? I have two O'scopes but am adraid to use them not knowing how to hook them up.
man, as always, a wise question contains half the answer. i think you have the necessary base, just keep your eyes open, measure twice, before connecting, you'll be fine.
added automatic protection is always nice, i rather it trip 50 times instead of killing me once
btw im not better than you, im still too overcautios around my gear, and despite that i recently burned and old motherboard and a new powerbank circuit
@@AlexanderBukh Another question i have is. The old receivers/component don't have a ground plug so they are not hooked up to mains earth and it should be ok to hook up the O'scope probes to the component being tested. That question has not been answered.
@@SDsailor7 i would say consider them floating, use isolating transformer or/and extra carefulness
Another way is to use a non grounded scope such as a Fluke scopemeter or in my case a Micsig tablet for automotive use with all the options great scope and safe in that regard
Thank you! Yes that is so true. A battery powered scope is a great way to help provide a safer way to take measurements. And it can help get cleaner measurements too;)
Isolating the unit your are checking is the safe way..
Thanks Sampler One. You are right;) and thanks for the great feedback.
And how do you isolate the unit you are checking?
Never float your scope, only the DUT!
Thanks for your feedback - but why do you say that?
By using an isolation transformer on the DUT, you isolate the chassis ground of the work, from the earth ground of the O-Scope. By isolationing the scope itself, If you accidently hook up to high voltage in the work, now you've tied your scope lead back to theBNC connectors of the scope, giving them high voltage as well.@@KissAnalog
Valuable video but how on "Earth" can connecting the computer via ethernet port connect the earth back to the oscilloscope? Is ethernet port not inherently isolated?
Great question! The shield on the ethernet port is grounded on the scope - so ohm your connection to your computer to verify. This has been a surprise to others...
as for the "pc connection": for the USB-port I'm with you - the shield is usually connected all the way thru - as for a RJ45 ether jack?
at least from my personal experience most (as in more than 50%) of both the plug as well as the socket are made from plastic and only the up to 8 pins are actual connected
also ethernet connections are usually galvanic isolated - so although the ethernet cable itself carries the information it's floating in respect to "machine" it's hooked into - so there won't be any galvanic connection between a scopes ethernet port and a pc one
tldr: in difference to a usb connection an ether connection should not cause a ground loop as neither the 8 conductors nor the outer shield is galvanic connected all the way thru (hence shielded cables are kind of a scam as the shield is floating as its not connected to anything)
but I'm open to get corrected
Thanks for the feedback! I've been in labs where the user didn't check the USB connection to the computer - and it caused a problem. Best way to check is to just use your ohm meter with power turned off.
A shielded Ethernet cable would likely propagate earth ground, does no my desktop PC. Those cables are not that uncommon, but can be avoided.
Hey! great video! I got a question...
Can I attach the ground clip (the black alligator clip) of the probe to Earth Ground and the probe to live?
Thanks - great question! If you use your multimeter you will see that the earth ground is connected to the alligator (ground) clip. So, yes you can connect those, and yes the voltage is within the rating of the probe (check the voltage rating of the probe to be sure),
@@KissAnalog Thanks a lot man!
Much as I watch these I'm still confused. I'm in a late 1920's house with 2 wired outlets, where the only tie to earth is at the breaker box where (I suppose) neutral is wired to a water pipe. I surmise THIS represents ground, where neutral and Earth are at the same potential, But that's as far as my brain goes if even correct. I can't understand what that means or how to use it safely? All my three prong devices go either into the adapter (cheater) plugs or into a surge strip which itself goes into an adapter plug. Any helpful tips?
And as followup to my own question I'm thinking it's ok to treat Neutral as Ground....as long as all plugs are oriented correctly especially the final plug to wall, that the outlet is wired correctly so that the Neutral side of the plug is genuinely going into the Neutral side of the wall outlet. Sound ok?
Great question! If you do not have the ground at your wall, well then it is actually maybe safer for your scope;) You don't have to worry as much about placing the ground of your scope probe to ground when you are looking at AC power - since you don't have a ground. But, you still need to be sure that each channel that you use has the ground on the scope probes at the same potential. Make sense?
Thanks. I have less lucid moments and more lucid where things come together. At the moment I'm somewhat in between. I've been wondering just that - if I'm kind of isolated by virtue of plugging the 3rd prong grounded chassis into nothingness. I'm thinking it's not the same though if I plug in an ancient 2 prong appliance but that's a moot point here. So far I've had no need to run both channels but I'll keep that advice in mind should it come up. Funny thing is ever since I broke but repaired a German Rangefinder camera at about 12yo, I've had the confidence to feel I could repair anything...so long as I can see it's mechanism. Electricity...well those who understand components will say it is also a mechanism but to me it's an elusive invisible monster that's always intimidated me. At 64 tho I'm finally developing a grasp, just enough to have troubleshooted a few of my tube amps and father's old radios. Thank you. Oh another funny....all that equipment lined up and you didn't have the 99cent cheater plug to show and tell in your video...(just kidding).
i run an isolation transformer on the equipment I’m testing...are you advising to run isolation on scope instead?? also...would you advise 10: 1 or 100:2 probes..I’really paranoid about o-scope safety etc...thanks
That really depends on what kind of equipment. I think running an isolation transformer on either is a big step. Just remember to keep all scope channels and any metal contact on the scope chassis - like the USB port at the same potential. I mostly use 10:1, but if I were running higher voltages than I'd use 100:2. My diff probes are actually 20:1 and 50:1 as lowest settings. Thanks for the great questions.
This is why you use a differential probe right ?
Yes this is a big reason;)
Did something similar on my siglent 1104ex “3” channel…when testing an amplifiers 20-20k sweep I without fireworks or any signs blew channel ones input. I got no pops nor the oscope turning off. Everything is just so on the 2,3,4 channels. But the next time I turned on the scope my readings were off on channel one, i try to compensate for this ridiculous looking wave that I cannot compensate with the probe, it looks like an old picture of a 50s saucer dish UFO on its side. Ive factory restarted and put it back to factory but I realized I must have shorted out my input on channel one. I have the 1104ex and its my first real digital scope so I still have 3 channels that work perfectly but I would like to repair the input on channel one someday soon. I really need a differential probe. Can you make a more nuts and bolts explanation of this topic. Its really my biggest downfall in my oscope knowledge. I get certain fundamentals but when putting in real time practice with bridged, stereo, and other variations of where and what to hook up or to use ground leads. I hoped me f’ing it up would have taught me the lesson so I am currently irritated I could never grasp the concept on how applications will vary depending on you wanna introduce yourself into the circuit.
Thanks for the great question Blake! Can you give me more details on what signal that you were looking at when this happened? Did you have a scope probe connected? Was it in x10 or x1 position?
@@KissAnalog |- is the closest on here I can think of to give the wave shape. So, imagine a square wave that has double volt overshoot at the start of the wave and then immediately comes down in a slope down to “calibration” volts and it is a repeat over and over and does not change with the probe screw adjustment being turned either all the way down nor backed out all the way. Hope that helps. Ill send it to you if you wanna use it in a video to help others and myself with a fix.
Alas, I was using the probe is 10x as well as 10x in the trigger settings. I was accepting a 10th of the signal basically.
I have issues with not fully understanding why if a device has a floating voltage it can not cause current to flow as there may still be a potential difference between the ground and teh floating voltage. This is also causing me problems in feeling safe about attaching my pc to serial ports on alarm/telecom equipment as they are not driven by relays or optoisolators. Could someone please explain why this floating voltage does not matter.
Thank you so much.
You are welcome! I appreciate you!
How is your recovery going? From one to another. ❤
Great! I think I'm recovered;)
Hi Eddie, thanks for this video it was great
Thanks for watching!
I have 2 emergency stop buttons on my workbench just in case. Kills all power.
Very smart! ;) Thanks for your feedback!
I hope that you realize that it is possible to damage your test equipment, the device you're working on, or even yourself (maybe fatally) in far less time than it would take to hit either of your emergency buttons.
Good stuff to know😊
Thanks for watching!
Well done
Thank you! I appreciate you!
Ooh, a killer queen plug!
That’s awesome!
guaranteed to blow your mind 🤣 nice
Great video, but bottom line never have a scope floating. 👍
Thank you! Although it isn't recommended, I have seen a lot of scopes that are floating;)
Unless, the scope you are using is battery powered. In that case it would be like a battery powered DMM.
Thanks Peter!
This guy's shirt is awesome :D
LOL thank you!
Thanks
You bet! Thanks for supporting!
I recently bought Hantek 5102p Oscilloscope after years of wait to buy a scope. I have kind of a stupid doubt and don't know who can I ask it to.
Suppose if I have an arduino running which outputs 5volt pwm signal at 50% duty cycle and 1kHz frequency.
If I connect probes of both the channel to the very same pin of arduino that is outputting 5V pwm. Will it cause any kind of damage to my scope?
A simpler way to put that question would be, "Can I connect same signal to two Probes of two different channels simultaneously?"
That is a fantastic question! I'll bet there are many others wondering the same thing - so cheers to you for asking;) No there is no problem there.
What you want to be sure of is that the ground wire (usually with alligator type jaws) is connected to the same potential. You can check this with power off. Just do an ohm check with a multimeter to verify that the grounds are connected where you think they are. Then connect both probes to the same potential (ground/return), then you can place the scope tips where you want to see the voltage (voltage difference form the tip to the ground). Thank you for asking!
@@KissAnalog Thank you so so much for taking the time to explain it. :) Will try it out definitely.
I avoid buying one for now because I'm a noob at this and don't want and don't have the money to waste in burning one...
I'll have to do some videos on it for the entry level person to feel more comfortable. Thank you!
@@KissAnalog That would be awesome! :)
What if you have no earth ground at all?
Nikki Marie The scope probe returns are all tied together on the scope so be careful to connect the grounds at the probe tips at the same potential on the circuit that you are probing. Make sense?
@@KissAnalog Yes thank you.
Are you floating your scope, or the circuit that you are monitoring doesn’t have. Ground?
@@KissAnalog My home was built in 1947 and has no earth ground wire in outlets, however my power cords are all tied together to a floating ground. As a temporary solution my equipment rack has grounding studs and I can tie a real earth ground to that at least so i think but thats all off topic.
Nikki Marie OK, so all your equipment chassis are tied together. That sounds good. Because equipment with three wire power cords typically have capacitors tied to chassis. This puts some charge on the chassis, so bonding them together is a safer situation as it holds them at the same potential. It sounds like you have it figured out. ;)
You know i've seen this video before and daves, but clearly I clearly didn't get the memo, was just working on a power supply and tried probing post rectifying then tried to set up second channel to look at the first and overlap, about a minute later heard a small pop and smelt some burning :). After watching the video I still didn't understand so I went over and probed the shields with my meter which confirmed they were combined together then I realized what had happened. rectified 0v gnd then i tried putting 28v ac in on the same ground (Facepalm). Can't complain though, live and you learn, scope seems ok for now. If i could go back and time id let it happen again hahehhehehe
Thanks for this feedback! This is a great story for everyone. I think we've all done this once - at least;)
Now subscribing and hitting that bell.
Thank you - I appreciate you!
My oscilloscope started smoking, I told it to stop, by the time it did it was dead, because I unplugged it.
Oh no - how did this happen? Was it the way your probes were hooked up?
@@KissAnalog no, it wasn't working before, it was a lucky day to get one flash from the old phosphorus display, I was in the back shorting wires to get a beam, then I looked up to see smoke billowing out the vent, leaving a horrible stench, I think I killed my oscilloscope, but I am too scared to plug it in given the house down the street burning down from a coffee maker.
Wow - well it sounded like it was on its way out already. If the caps and some circuitry needs to be replaced - it might be worth it to repair and have fun doing it. If the CRT is going bad - then that might be tough to find a replacement.
I don't understand what all the talk all over the internet about this is, surely it's simple, the ground/earth lead on the probe should ALWAYS be connected to EARTH! FULL STOP!?!
Safety First
Always;)
TH-cam:
John Ward.
Isolation Transformers Explained.
You DO NOT plug your ‘scope into an isolation transformer.
About 10 minutes into the video
I’m no expert, but he explains exactly why.
Thanks for your feedback. I've seen John Ward's video - and he makes good points - but there is no clear and simple solution to everyone. The problem is - that there is so much confusion on what an isolation transformer is - and what it isn't - and the different types. I'm happy to debate these topics with anyone;)
Breaker plugs
Breakers can protect but mostly for fires. They are not fast enough to protect the initial damage to equipment.
James Hetfield goes tech :)
LOL thanks!
Early in your vid, you said that you can isolate a scope using a cheater plug. That is NOT the case! The neutral/common (white) wire is common to all outlets. How is that possible? Think about it. If you CAREFULLY removed the breaker panel cover (not recommended) you would see that all the white conductors are screwed into a common bus, as all the bare ground wires are. If you completely disconnect the mains breaker, you could then safely probe neutral to ground with an ohmmeter. Why would you have to disconnect the mains, you ask. Think about it logically. There is a low resistance from neutral to ground and back again. Simple Ohm's law: low impedance, high current. The solution is to modify an isolation transformer by opening the case and disconnecting the green chassis wire from the secondary winding and insulating it with heat shrink. Just remember that the secondary winding is now truly floating and completely isolated. Your 'Scope is now 'protected.' You, not so much!
Thanks Richard for this great question! Using the transformer as you described is the better way to isolate. The cheater plug works to though, and I’ve seen a lot of power guys use this method in the lab. You are correct, at the service entrance the neutral is bonded to the earth or safety ground. It is isolated because at the scope the chassis is no longer tied to safety ground, so your probes ground has no DC connection to the input power. The scope has an isolated power supply so there is no connection from chassis/scope ground to input power, so it’s isolated.
Ethernet is isolated
Thanks for the feedback - but ohm your ethernet jack to your ground - and you may be surprised. Ethernet often uses an isolation transformer to transfer the signals to the internal circuitry - but test your shield in your cable...
Can anyone test this out and give feedback? pursue circuit solver on the playstore!
I'd like to do a review on this - thanks!
And like.
Thank you
Obviously you have never worked on the internals af motor control systems that if you scope is NOT isolated you WILL blow the scope or the drive.
Why do you say this? I have actually worked on those things. I have lots of videos showing differential probes. Just not sure how you get to that conclusion watching this video???
This guy sounds like terry davis
Thanks - but which Terry Davis?
@@KissAnalog the programmer
LOL - I hope I don't turn out like he did...But he was brilliant!!
@@KissAnalog ikr
This is one of the worst, most rambling dis-jointed explanation I have ever heard.
Sorry about that! I'm always trying to to better and this was one of my early videos. But, I do have a tendency to chat - so maybe you might want to skip my channel. Sorry again...
Newbie question. on a 2 channel handheld dmm oscilloscope, how do you take 2 separate voltage measurements simultaneously while the probe grounds are not isolated by design? I can only assume you cannot? I don't see the the use in a two channel where they cannot Operate independently.
You are right - it is limiting when you need to have two isolated returns. That’s when you need a differential probe;) see this link and thanks for this great question!
th-cam.com/video/892RcsIUAtU/w-d-xo.html