Oscilloscope Safety - How to use your scope safely!
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- Опубліковано 29 січ 2019
- This is a very condensed version of a video by EEVblog (and others) about potential safety problems from oscilloscopes. To view a more comprehensive video, look over to EEVblog's "How not to blow up your oscilloscope" video.
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Thank you so much! There are very few sources of information so clear and so well explained as your video. So many people adopts measures that risk security, as it is the case of neutralizing the grounding of the oscilloscope to make measurements.
A suggestion that may be helpful: Put some green heat shrink on the scopes earth ground leads - it will constantly remind you it is an earth conductor and not just another test lead as in the case with multi-meters
Great idea!
But it can be used as another test lead if you're working on an isolated circuit, IE one not earth grounded or powered by USB.
Thank you for a comprehensive video on this subject. I have seen EEVblog' s video on this subject, but he doesn't show the use a RCD/GFCI gadget, at least not on any video I have seen of his. I have seen dozens of videos on scopes, but they never showed the use of a GFCI in USA, RCD in Aus and Europe. I personally have 22 circuits and all of these have RCD's on them. They are compulsory in all new homes in Australia,,, and one cannot sell / transfer an old house without having this gadget installed.
Thank you. This is EXACTLY the info I’ve been looking for!
Glad we could help!
Excellent lecture!
i know this is a older video, but everybody on UA-cam who makes video's about Oscilloscope Safety and measuring mains voltage, left one part out of the video.
If you simple want to see the 50 or 60Hz sine wave of your mains outlet, you don't need to connect the ground lead of your scope probe.
Your mains is ground referenced, but also the tip of your scope probe is ground referenced, so you don't need to connect the ground lead,
and for extra safety, you can best removed your ground lead from your probe, that way this lead can't accidently touch something.
Simple set your scope probe at X10 setting, and only use the tip of the probe and you can touch Hot / Line / Phase / Neutral without risk.
If you want to do measurings in a circuit or device that is powered from mains, and you want measure across components in circuit, or circuits that use higher frequency then 50 or 60Hz, you will get more noise when the ground lead of the probe is not used, and this method of only using the probe tip cannot be used.
As someone trying to learn, this basic-intermediate advice is very helpful. I've read and read but to truly internalize and test my assumptions I need to eventually see. Finding information on how to do something that can be very dangerous is so difficult.
IT'S REALLY REALLY GOOD!!
Wish I watched this before I burned up my power supply 😢
Thanks for the education!!
Thank you sir.
THANK YOU!
of course! Glad it helped
Thank you. "Oscilloscopes are not multimeters!" is the perfect way to phrase this message. Although I have never conflated the two tools, thinking of it this context will prevent me from making dumb errors in judgement.
Thanks!
Thanks for your support!
Always check power line (outisde or inside devices) before contacting a oscilloscopes probe tip connectors: Always be sure where is the hot phase line where is ground line of power AC outlets / cables line also inside any opened device to be repaired.
Better measure again if unsure about it or forgotten, before risking to make any bad contact.
It would be most helpful if you could show what you can do about this.
In the olden days, one used isolation transformers, differential input Scopes made for line voltage use etc. Today many cheap scopes have low voltage psu, such as USB power via powerpack.
0:56 "The multimeter probes have a high resistance between each other" -- This is *only* true if the meter is set to voltmeter mode. *The ammeter mode will short the leads to each other!*
7:31 In household electric systems the direct connection between the neutral and ground is only done once in the first breaker panel and must not be done again in additional sub panels. If a sub panel is being added to a home it may already have a bonding screw between neutral and ground and this bonding screw must be removed for sub panel usage of a breaker panel.
Just a little detail from renovations that occasionally gets missed.
Is there a good reason for that? Why only one connection between ground and neutral?
@@louco2If you have a RCD in the main breaker panel, it would trip if you connect neutral and ground behind the breaker
@@jjjannes, thank you!
I had never thought about it before, and unless I find a scope at an estate sale it won't be an issue.
Are the digital inputs using the same ground?
This is a very good video. Do you know much about ECMO machines? If you have an idea, a video on how they work would be good, or at least the oxygenator, how the membrane exchanges the CO2 and the O2 and the pump.
I have not had much exposure to ECMO machines. I will look into them, it sounds like it would be an interesting topic. Thanks for the tip!
Hi @Engineering Technology for Healthcare, I have just found this video and your channel, you have condensed the information nicely (I have subscribed). Could please inform us of what BMET is / stands for, I have searched the web but can only find references to Bermingham University or a blood test? Thank you and have a good day.
Glad you enjoyed it! I have a video that describes the field ua-cam.com/video/XKOLF7sANk8/v-deo.html
But in general it stands for Biomedical Engineering Technology - the field focuses on the repair and maintenance of medical equipment.
@@HTMWorkshop, thank you for the swift reply and the information, looking forward to your next video. 👍
This material is based upon work supported by the National Science Foundation under grant number 1700649. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of the National Science Foundation.
Wish you hadn't said that. I never trust anything the government is involved with. They want us all dead.
Is it safe to say never apply power to the ground lead? Would this cover all situations? And if you were worried could you just wire in an inline glass fuse?
My oscilloscope is on a circuit protected by a combination GFCI and AFCI (arc fault) circuit breaker. It tripped immediately when I accidently connected the ground probe to a hot voltage source. That saved everything!
Yeah - you can also power it with an isolated supply instead of line voltage…that is another good safety feature
@@HTMWorkshop isolation transformers are also tied back to earth ground in the board hence, the neutral path as well. Most isolation transformers are not ‘isolated’ so you can still blow up your oscilloscope or electrocute yourself.
Did you capture the spike before the power went out?
@@robertsmith2956Unfortunately, no. It would have been interesting to see the waveform pattern the AFCI looks for.
@@HTMWorkshopThe use of an isolation transformer is a standard practice that has been around for a long time. The issue with it is that you lose your ground reference and circuit ground may be substantially different from earth ground. The newer electrical circuit breakers may mitigate the need for an isolation transformer or cover you in one of those Oops situations.
Early cardiac monitors are connected to an oscilloscope (to display the ECG waveform).
Ha, yes early cardiac monitors used to be made from the same companies that made o-scopes like Tektronix.
So the paddles are connected to earth ground. That could be a shocker for the patient in the next bed.
Even if you did do that -- it would just flip the breaker in the house panel. But I get your point: be cautious where you put the ground leads.
Yeah... ummmm NOT ALWAYS
ALSO some people do not have an RCD but merely ceramic fuses
other people have Faulty RCD's
Excellent info! How would I safely use a oscilloscope to see the pure sine wave of a 12v Inverter that has a earth ground? Thanks!
I don’t see any issues at 12v -just make sure you connect the ground of your scope to the ground of your inverter
Cheers for that Dude! If the scope is USB powered by a 2 pin 5v charger - does that do away with the mains issue - leaving only the potential difference possibility?
Correct - your scope is isolated on usb. Makes it much safer
Great video thanks. But as a total vovice where is it safe to connect a scope? Will it damage a scope on say 30volts? My scope says max input voltage of 300v? Rohde & Schwarz RTB 2002 (Not that I would ever use that voltage) Any chance you could expand a bit and do a video where it is safe to connect on a cicuit board? (obviouslly not the mains input)
Hi, 30 V should be very safe. Just make sure you connect the alligator clip to ground on your circuit board then you can probe around pretty safely on the board (safe for you and the scope...safe for the device depends on what the device is and where you probe). Not a bad idea on doing a video with some tips on circuit testing. Here is decent video ua-cam.com/video/JAELtZ1MrwY/v-deo.html from Rigol
@@HTMWorkshop Thanks for your reply very helpful.
Careful. The 300V limit applies only to the voltage between the measuring lead and the ground lead of a single scope probe. You can’t connect the ground leads of two scope probes to different voltages, because they are shorted together. Connecting one ground lead to 0V and a second ground lead to 30V in the circuit will cause enough current to flow to destroy something.
It would be nice to explain if the situation changes with battery operated oscilloscopes.
Good point - It would be nice to have ua-cam.com/video/rOK7PPUpVjM/v-deo.html
a different video on how isolated power works. I do have a video on hospital isolated power but which is related but yeah your right the ground completely changes if you use an isolated or batter powered scope (or USB powered scope). We only cover traditional bench-top scopes here but that is a good idea.
Manufacturers are now making oscilloscope with dmm and waveform generator modes
I have seen waveform generators in oscopes but not Dmm... that is a strange combination
@@HTMWorkshop hantek 2d42, hantek2d72 have oscilloscope, dmm and pulse generator
@@adeyemibabatunde1814 Oh yeah I have seen those before - I always thought of those as DMM with a oscope function.
Well , very simple . Use an isolated battery pack supply for your oscilloscope, just like the DMM . As long as the DC ground is totally separated from the earth/neutral AC , you should be golden !!!!
Sorry, no. The scope ground leads are still shorted together. To illustrate, suppose the oscilloscope is powered by a battery as you suggest. Suppose the circuit is also powered by a battery to isolate it from the 120V or 220V mains. Suppose one part of the circuit is a resistor connected across the battery and the rest of the circuit is arbitrarily anything else. If you accidentally connect a scope ground lead to one side of the resistor and another scope ground lead to the other side of the resistor, the short between the ground leads will short out the circuit battery. A lot of current will flow. As the presenter mentioned, the scope ground lead may vaporize. The ground lead circuitry inside the scope may vaporize (goodbye scope) on a cheaper scope. If the scope ground leads and scope can somehow handle the short, the battery won’t. It will overheat and catch fire. If that circuit battery is a higher capacity lithium battery, it will be a very exciting fire.
Thank you so much ( I'm 3 years too late ), but if you still active do you have any suggestions for what hardware I could start learning the oscilloscope? I was thinking USB power bricks or just order bunch of components from web and go to town. I'm hands on learner that's why I am asking.
If you already have an o-scope you could check out our new kit we are selling on simulating ECG waveforms. The kit is here htm-workshop.com/product/ecg-simulator/. And the learning resources are here htm-workshop.com/ecg-simulator-educational-resources/. Instead of using a patient monitor you would just view the signal using the o-scope. I have also used this kit amzn.to/3yU0sHK which has a nice instructions and many activities but Im not sure how good it is for practice with an o-scope.
@@HTMWorkshop that's awsome, just buyed that ECG simulator. Thank you so much 😊
@@cptsmoke0001 Great! However, I did not see any new orders over the weekend but it may just take a second. If you have issues you can email contact@htm-workshop.com for help with product orders. Our website was just updated so if there is something wrong on our end, I'll make sure you get a discount.
If you are addressing this to hobbyists you should have mentioned the use of isolation transformers. That is how you avoid damaging your scope. The transformer isolates the circuit under test from the power supply ground.
That is a good idea - I think a video on how to pair a scope and isolation transformer makes a lot of sense. I do have another video on this channel about isolated power ua-cam.com/video/rOK7PPUpVjM/v-deo.html
Nope. You will still get into trouble. The connection to mains ground is very much a problem, but another problem is the different scope leads are shorted together. If you connect two ground leads to different voltages, you will vaporize something.
my osci isnt connected to ground, only 220V AC. would that still be a problem probing voltages with the ground pin?
Then you should be ok…if your scope is isolated from ground you can circumvent the issue
As a novice in oscilloscopes I isolate myself from this issue by having a cheap USB scope that is connected to my laptop that runs on batteries. Also I make sure other parts of the laptop are not connected to the circuit I'm disturbing with the probe (something like arduino board connected to the same laptop via USB and I'm probing something that's connected to that board).
Yes using a usb isolated supply is a good solution - those o scopes usually have a lower bandwidth but for most applications they work great
Don't forget that most laptop chargers have the negative part of the DC jack straight connected to earth of the mains inside the charger.
So if your laptop charger is plugged in during your measurings, your cheap UBS scope is grounded and still can be destroyed.
@@BjornV78 Sure, laptop must be on battery at the moment
So just to clarify, you are saying to plug the oscilloscope into the gfci outlet?
That is not ideal, an isolated power supply is what you want. A GFCI will provide some protection but it's still grounded, so I would not recommend that.
Quick question - if you were using a battery powered oscilloscope, wouldn't that isolate the o-scope from the ground? I know there are several models that may not be as accurate or as full featured, but which are adequate for purposes of say, diagnosing audio equipment issues?
yes that is a good way to do it
Yes it would
the problem occurs because the electrical box is referenced to earth.
with a battery that is not the case
I have a question: you can only check for continuity between neutral/neutral and ground/ground out but not live wire/live wire to live wire right?. I was under the impresion that you would destroy your multimeter if you try to measure continuity while power on dc or ac.
you mean with a multimeter correct? not an oscope - you should not be checking for continuity with an o-scope. If you want to check continuity with a multimeter of a live wires it is possible - could depend on the quality of the meter. But the multimeter is isolated from ground so you could check continuity of most things (there is going to be a limit but line voltage is find) but I can't say I use it for that so there may be some exceptions
No, Not necessarily but it would be a question of whether you would get the tone or not, You need to understand certain things
1. The continuity beep requires voltage to be heard
2. the test is designed to be used on AN NON ENERGIZED WIRE
so let's say the beep requires 2 V DC and you place it on a line with 50Volts
chances are it won't come through
There are however some that will, for example, i have a device called A LOOP A LINE
specifically Teletech TX916
These are telecommunications continuity testers that can push through a tone SAFELY even on an energized line
Keeping in mind it assumes TNV (Telecommunications Network Voltage) which is usually up to 54V DC but can be up to 120 on ISDN Lines (which we don't see much of nowadays)
so it does depend on your continuity tester
but in general , why are you trying to tone over an energized line in the first place.
You can test from live to live
BUT FIRST TURN THE POWER OFF
What about hand held, battery driven scopes? They are not grounded, or are they?
correct - at least in all cases of battery powered scopes I have seen.
Thank you for the info. However, you advised the novice as to what was unsafe to do but not what was proper and safe. Of the neutral, ground and hot wires -- you said to not connect probe ground to the hot. That still leaves the neutral and the ground to choose from. Can a newbie assume either is OK? (I think assumptions are never safe!) Also will you please detail the steps to determine if it is safe to connect ground to a point in a circuit when one is not sure if it is connected to hot, neutral, or ground?
Thanks again for sharing your knowledge.
You can connect the probe ground to ground, usually this means circuit ground (not live voltage ground). That does not mean you can not connect the probe to live ground or line neutral (which should be at the same potential if all is well with the wiring), but that is a pretty odd. In other words, I can't think of a reason to do that. Connecting to a circuit board or breadboard ground is absolutely allowed and exactly what you should be doing. Common ground and line ground a different concepts, so be aware when I say your circuits ground I mean common ground - which has to do with the ground for that particular circuit - it is not the same as line ground unless you connect them. Live ground is specific to your outlet/wall wiring/circuit breaker. Usually when dealing with live voltage you would not use a o scope but a multimeter. Hope that helps
@@HTMWorkshop So, basically, if my circuit has its ground connected to the live ground, then my probe ground must be connected to this? And then the test probe could be connected to one of the phases to measure the signal?
@@gabrielgrmcp The first part sounds right - yes you want to connect to common ground (which if tied to the line ground then yes same thing, since they are forced to be at the same potential - However when you say phase - are you dealing with 2 or 3 phase power? If so I don't think a scope is probably what you want to use (but maybe). If you give me the situation I may be able to help more. The issue with 3 phase power is you may be exceeding the max voltage/power the o scope can deal with
@@HTMWorkshop thanks a lot! Actually I'm dealing with 2 phase power and the sinewave I want to measure is the one my load (fan) is receiving after a triac (dimmer system) changes it. Considerating that the ground of this circuit is connected to the main ground through the chassi of the product in which this circuit is located.
@@gabrielgrmcp @Gabriel Mateus Well it is possible - just make sure that ground clip does not come into any live voltage (if you did it will be a direct short to ground and will definitely fry something). I would just make sure you check your scopes max voltage (just in case you have low voltage scope). You definitely will want to think through each step and make sure you don't provide any shorts. Goodluck!
Ok little lost I have a fluke 199 and it’s has no ground on the plug and normally I run it off it’s battery so now you got me wondering what would happen 🤔
Your scope is isolated if it runs on a battery and will not have the same issue (unless you ground it of course)
So the battery operated scopes will be fine?
Correct
USB power from a battery or 2 prong wall transformer should be okay since it is floating?
yes - your isolated (now you can have 2 faults before you have an issue, as opposed to a single fault)
@@HTMWorkshop Thanks.
Why isnt there a fast blow low current fuse in that ground?
Can't say for sure but my guess is it would effect measurements of sensitive high frequency circuits
Umm. Mine is.
Could you not run a safety neon in probes that will take the current in this event.
Hi Mark - I am not familiar with a safety neon - what is that?
@@HTMWorkshop Like a neon or globe used in circuits to act as a current limiter. e.g. speaker protection for audio or RF circuit etc.
@@marklowe7431 Oh I see what you are saying - you mean something that can be destroyed to save the device (like a fuse or in your example a light source with a known current maximum) - Well I guess you could use something like that to make sure you do not hurt the device but there is always a delay in how fast a device like that will work - the fuse/lamp can be used pretty well to protect a device and it may protect a person - but there is still the chance that you could get unsafe high voltage before that fuse/lamp kicks in. I can't think of many situations where you would go to the trouble of building the circuit that way but it could be used as an added safety feature.
No, you can't use a safety neon, because a neon tube acts as open circuit below the ionizing voltage, so below 50a60V you are doing measurings with a open ground connection. Your scope probe is referenced to ground, and need a low impedance ground connection to display correct measurings.
What you can do is to use a floating fuse holder in the ground lead connection of the scope probe, and use a very low mA value of fuse, like a 50mA Fact acting fuse.
Such a floating fuse holder in the ground lead is recommended by Tektronix back in the old days.
Technically it's called a Napolean connection. You heard of Napolean Blown Apart, haven't you?
So Now How I probe the high voltage circuit with oscilloscope
Depends on how high. You can buy some high voltage probes (they are pretty expensive) or you could build a voltage divider.
For ac main voltage, step down isolation transformer csn be used(e.g 240/120v ac to 6v ac)
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I wish there was an easier way to create subtitles in different languages but I am not able to write in Persian - good luck!
L oL i time i tested amps between accu poles!
Never do u hook the ground side of the ociliscope to hot ac. Wtf
DMM's have a (fuse) for a reason...Just saying. But still a descent video..😂😂 The probe part had me rotfl.. But I 'thinks that's probably why they (allow) for detachment of the ground side. So it blows straight OUT; CUT the connection. 😂😂😂
If I buy battery operated oscilloscope then there will be no problem ,I can use oscilloscope like multimeter
Actually no. Your scope ground leads are shorted together as the video points out. If you hook the ground leads to different points in the circuit, that are at different voltages, you will short the two voltages to each other. In the best case scenario, your circuit will misbehave as one or both voltages are forced to change by the short. In the worst case, you will send enough short circuit current through the ground leads to destroy the oscilloscope (e.g. burn off a ground plane trace inside the oscilloscope).
Use a cheater plug to float the scope.
Sorry mate you got that very wrong about multimeters (battery or bench). If you set your meter to measure current (usually involves moving the probe to the current socket on the meter) then if you then want to later on measure voltage - and forget to change your probe socket, you then can short out whatever volts measure which may destroy your meter. This is easily done, ask any tech who is honest enough to admit it.
Sorry mate, You must not have watched the video, because he did mention that
IT'S TRUE, i agree
Some fancy multimeters have gates that close off the current input connections when the dial is turned away from current measuring mode. Most techs are honest enough to admit they don't buy those bc we think we are too good to need it 👍
That is why my Rigol is powered via separation transformer😂
YOUR INCOMPLETE EXPLANATION IS IRRESPONSIBLE AT BEST. "PORT" ??? THEY ARE CALLED CHANNELS SIR. CHANNELS.