Is there an oscillisocope "what not to do" tutorial? - Page 1
Forum section: electronics / beginners

author: Renegade
author_rank: Regular Contributor
timestamp: February 02, 2016, 10:58:44 am
content: I'm looking for some information or a tutorial on what NOT to do with an oscilloscope, i.e. basic safety and things that will destroy your scope.I'm asking because as a beginner, I don't want to make any stupid mistakes out of ignorance, and right now I don't know what I don't know.I'm asking in part as I've seen "right hand rule" notes that have come rather late in EE books, when it seems like they should be right up front, and many RHR notes don't explain what it is or why. As such, I'm figuring that I'm going to run into the same kinds of "lack of information" or "information too late" for oscilloscope use.Thanks in advance for any links, pointers, or other information.

author: rolycat
author_rank: Super Contributor
timestamp: February 02, 2016, 11:03:41 am
content: Dave's video is a good place to start:http://www.eevblog.com/2012/05/18/eevblog-279-how-not-to-blow-up-your-oscilloscope/Also take a look at theoscilloscope training classvideo linked at the top of the beginners sub-forum. Alan (w2aew) has more excellent oscilloscope tutorials on hisYouTube channel.

author: Renegade
author_rank: Regular Contributor
timestamp: February 02, 2016, 11:29:42 am
content: Quote from: rolycat on February 02, 2016, 11:03:41 amI did watch that, but I should probably watch it again.From what I remember, I still had quite a few questions, like "can I stick a probe into the mains to measure it?" I wouldn't do that, but that's just to give an example of the kinds of (extreme? silly? ignorant?) questions that I still have. I still have no idea if AC can be measured safely, or how.Quote from: rolycat on February 02, 2016, 11:03:41 amThanks. I'll browse through his channel for more on the topic.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 02, 2016, 11:40:28 am
content: if you pay enough attention, everything what not to do tutorial have already been written in the manual starting page II...

author: tggzzz
author_rank: Super Contributor
timestamp: February 02, 2016, 11:53:40 am
content: I've found all the references herehttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/useful. Some relate to safety, some to improving measurements and avoiding mistakes

author: Renegade
author_rank: Regular Contributor
timestamp: February 02, 2016, 11:56:52 am
content: Quote from: Mechatrommer on February 02, 2016, 11:40:28 amI read that, but I'm still not sure if there are other cases. Maybe I'm being paranoid, but I don't want to blow up my scope and shell out for another one because I did something stupid. e.g. I don't see anything about maximum voltage or current, so can I test the electrodes on the MOT spot welder I made? I'm not about to do that, but I don't know if it's safe for my oscilloscope or not. (Rigol DS1054Z)

author: Renegade
author_rank: Regular Contributor
timestamp: February 02, 2016, 11:58:21 am
content: Quote from: tggzzz on February 02, 2016, 11:53:40 amThanks. I'll read over that.

author: rs20
author_rank: Super Contributor
timestamp: February 02, 2016, 12:02:13 pm
content: Quote from: Renegade on February 02, 2016, 11:29:42 amWhere would you clip the ground lead in that instance?

author: rolycat
author_rank: Super Contributor
timestamp: February 02, 2016, 12:11:21 pm
content: Quote from: Renegade on February 02, 2016, 11:29:42 amThe recommended (and safe) way to measure mains AC is with a high voltage differential probe. Since these tend to be expensive there are various 'bodges', with varying degrees of danger to you and/or your scope.If you just want to look at the AC waveform coming out of the mains, use a step-down transformer.

author: NilByMouth
author_rank: Regular Contributor
timestamp: February 02, 2016, 12:12:54 pm
content: Do you understand the fundamentals of electrical circuits? That's a good place to start before you start working with high energy circuits. Being told, "do this" and "don't do that" is no substitute for understanding why.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 02, 2016, 12:27:31 pm
content: Quote from: Renegade on February 02, 2016, 11:29:42 amIt comes down to understanding what you are probing, and what are the limitations of your test equipment.Do you understand Peak-to-Peak voltage vs. the RMS value we use as the nominal voltage? Do you understand why we use 10x probes with voltage dividers?Quote from: rs20 on February 02, 2016, 12:02:13 pmAnd that seems to be the other big issue with test equipment: Know where grounds vs. measurement references are.In the special case of measuring the mains voltage, it is likely that the scope is grounded to the green-wire safety ground via the power cord. And in most (all?) locations I've heard of, the low/"neutral" side of the mains is connected to ground at some point. Here in North America, they are connected together in the circuit breaker distribution panel.Remembering that an oscilloscope (at least a mains-powered scope) isINHERENTLY GROUND-REFERENCEDseems to be something that many newbies don't understand (or don't remember, or SOMETHING!) Typical battery powered DMMs are inherently floating and "differential". But, unless you have a cute little battery-operated scope, you are in grounded territory, no matter what the local conditions seem to be.

author: Renegade
author_rank: Regular Contributor
timestamp: February 02, 2016, 02:30:59 pm
content: Quote from: NilByMouth on February 02, 2016, 12:12:54 pmI understand the basics.I like seeing "do this" and "don't do that" because I can then work backwards from them to the theory, and more easily understand why. Theory without application is sometimes a bit abstract.Quote from: Richard Crowley on February 02, 2016, 12:27:31 pmYes. RMS is 0.7071x peak, or sin(PI/4).Quote from: Richard Crowley on February 02, 2016, 12:27:31 pmIt's for attentuation, but I'm not exactly certain. I believe it's to attentuate voltage to read easier/lower.Quote from: Richard Crowley on February 02, 2016, 12:27:31 pmI should probably go back and re-study some theory regarding references.Thanks for the pointers.

author: rolycat
author_rank: Super Contributor
timestamp: February 02, 2016, 03:09:25 pm
content: Quote from: Renegade on February 02, 2016, 02:30:59 pmIt has a lot more to do with bandwidth; take a look at Dave's videohere.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: February 02, 2016, 04:07:58 pm
content: Don't drop it on your foot!If it's a DSO it will break the scope. If it's an analog scope it will break your foot.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: February 02, 2016, 04:22:07 pm
content: Quote from: Renegade on February 02, 2016, 02:30:59 pmNot sure what you mean by "theory", but it's pretty simple. The ground clip on your scope is a hard ground. Attaching that to your circuit is equivalent to sticking a pin in the ground slot on your wall socket, and clipping it onto your circuit.If your circuit is floating, meaning it has no "real" ground reference relative to the wall outlet, then it doesn't matter. If your circuit is not floating, and you clip your scope's ground lead to the wrong part of the circuit (a part that's not floating or already ground), you'll short the circuit out. You'd probably be more likely to blow up your circuit rather than damage the scope, but of course it depends on the nature of the circuit you're working on.Where you really need to pay attention is when you have a multi-channel scope. The ground clips for ALL of the channels are a hard ground, and are shorted together inside the scope. So while with a DMM you can grab 2 or 3 of them to measure voltage drops in different parts of the circuit, with a scope you have to be very careful that the ground clips for all of your leads are attached to the same voltage, or you'll short the circuit out.

author: fubar.gr
author_rank: Unknown
timestamp: February 02, 2016, 05:27:41 pm
content: An often ignored point that requires attention is max voltage vs frequency derating.Eg, try measuring the output of an FM radio amplifier and you're in for a nasty surprise, even if the voltage is seemingly within the limits of the probe and scope!

author: DutchGert
author_rank: Frequent Contributor
timestamp: February 02, 2016, 05:29:14 pm
content: Don't overload the 50Ohm input if it has one...... As a test try and figure out how and why you can overload it?

author: w2aew
author_rank: Super Contributor
timestamp: February 02, 2016, 07:06:12 pm
content: Quote from: rolycat on February 02, 2016, 03:09:25 pmor, my video here (only about 15 minutes long):

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 02, 2016, 09:39:10 pm
content: if you check the manual and scope front panel, input max 300V, pay attention to that... hence with 10X probe, you can poke 3KV no damage to the scope, but no point since your graticule cant show that magnitude and its not safe near the limit, you got >3KV spike you are screwed. so with 10X probe, stick with mains rated you'll be safe, dont mind the current, 1MegOhm will pass nothing, its also written, pay attention to that as well. about the ground clip, its in the manual... i once ignored the manual and it tripped the circuit breaker luckily, experience will teach, not much you'll understand here until you actually do it. as other have added, dont put it in the swimming pool, errr, its also in the manual...

author: cobbler
author_rank: Unknown
timestamp: February 02, 2016, 11:00:45 pm
content: Quote from: w2aew on February 02, 2016, 07:06:12 pmThanks Allen... in the beginning of video you explained why it is not good to use DMM leads because they are not coax, etc..I have been using the scope a lot using proper scope probes and noticed that often the ground clip does not even need to be connected to get somewhat accurate waveforms to appear on the screen.What are the scenarios where not having the ground clip connected will drastically destroy the accuracy of the waveform being displayed? Or make it unsafe to a low voltage circuit?Also, sometimes I connect the ground clip from ch2 to ground on the circuit, and use the +probe tip on Ch1 to poke around... it seems to work fine and makes poking around much easier. What are the scenarios where the accuracy will be off terribly using this method?Thx, great thread here..

author: w2aew
author_rank: Super Contributor
timestamp: February 03, 2016, 03:40:47 am
content: Quote from: cobbler on February 02, 2016, 11:00:45 pmScenarios where you're dealing with low frequency signals that are reasonably large, the loooooong ground connections that you get when- not connecting the ground (ground return is through the mains), or- when you use CH2 ground and probe with CH1 (ground return is through the CH2 ground terminal)don't make much difference because the inductance of the ground path doesn't degrade things much (because of low frequency content).Things will change when you start dealing with high frequency signals, or signals with higher frequency content (very fast logic edges, etc.)Also, make SURE that you properly compensate your 10X probes - this can make a BIG difference, even at low frequencies:Going back to your original query - how to NOT damage your scope. There really are only a handful of things that can really damage the scope that you need to be careful about:- GROUND: Nearly all scopes have chassis ground referenced inputs. ALL of the inputs have a COMMON ground connection. This is the biggest difference to consider compared to a DMM. With a scope, you have to be SURE that the ground connection on the scope is common with the GROUND of your circuit under test. Dave's video on "how not to blow up your scope" covers this in exhaustive detail.- OVERLOAD: Always use 10X probes unless you have a specific reason not to, and take care to have a good expectation of the magnitude of the signals you're about to probe. When in doubt, start at a high V/Div setting, then work your way down. Obey the maximum voltage ratings on your inputs and on your probes.If you take care of these two items, it will be EXTREMELY unlikely that you'll damage anything on your scope.

author: cobbler
author_rank: Unknown
timestamp: February 03, 2016, 08:43:48 am
content: Quote from: w2aew onTodayat 09:40:47 AMOk thx

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 03, 2016, 09:20:17 am
content: Quote from: Richard Crowley on February 02, 2016, 12:27:31 pmNo. Please no. This is not the case, at least not in the part of the world where I live. And this is not a notion that should be planted in the head of a novice. I'd say that up until the time where somebody understand *exactly* how their local power distribution works, they should consider the neutral to be exactly as dangerous as the so-called "live" conductor.Quote from: Richard Crowley on February 02, 2016, 12:27:31 pmI teach, parttime. This is something that I try to explain. Doesn't seem to work. I have considered to electrocute them all (just a little!) to peg home the notion but it would seem that's against the rules.

author: Ian.M
author_rank: Super Contributor
timestamp: February 03, 2016, 09:21:26 am
content: This *ONLY* applies to analog CROs. (or hybrid DSOs in pure analog mode)If you are using XY mode, NEVER leave a static spot on the screen, unless the intensity (brightness) can be and is turned down far enough that it is no brighter than a normal trace, with no signs of 'blooming' round it. If the H shift control has enough range to bring the spot onto the screen when the timebase is untriggered, and it doesn't have effective blanking before triggering, don't do that either!Avoid intensity levels that cause the trace to 'bloom' and if you have to turn up the intensity to view an expanded trace or to look for glitches on a fast edge, turn it back down to normal immediately after making the measurement.Why? Phosphor burn. If a static high intensity line is displayed for long enough, it can damage the phosphor coating, so the light output is permanently reduced, or in some cases with a very high intensity static spot, even crack the faceplate of the tube due to local heating. Pure DSOs are generally immune even if they use a CRT, because the raster scan used doesn't concentrate the energy on one spot even in XY mode.

author: Brumby
author_rank: Unknown
timestamp: February 03, 2016, 12:31:12 pm
content: A basic rule for old-school CROs - is to only have the brightness turned up enough for you to see the trace clearly. Screen burn in is one reason - and the other is that a brighter trace is usually thicker. A nice, thin trace makes for better observation and more accurate measurement.

author: tggzzz
author_rank: Super Contributor
timestamp: February 03, 2016, 02:47:14 pm
content: Quote from: Richard Crowley on February 02, 2016, 12:27:31 pmImportantly that is COMPLETELY WRONG in many locations around the world. And, ISTR, not even the case everywhere in the USA. The OP is in Canada.Getting that wrong can lead to, um, extreme surprise and disappointment.I can seefourwiresoutside my house. The lowest (which you are most likely to touch) is the common return and the higher three are each a different phase. I can see my neighbours are on a different phase to me, unsurprisingly.

author: newbrain
author_rank: Super Contributor
timestamp: February 03, 2016, 03:45:52 pm
content: Quote from: tggzzz on February 03, 2016, 02:47:14 pmQFT. In Rome, Italy, most apartments are on two phases of a 127V three-phase system (220V phase to phase), so there's no neutral distributed, only protective earth (with own per building earth, TT system) for residential users.

author: Brumby
author_rank: Unknown
timestamp: February 04, 2016, 02:19:50 am
content: How do you get the 127v from just 2 phases without a neutral?

author: Renegade
author_rank: Regular Contributor
timestamp: February 04, 2016, 03:46:09 am
content: Thank you so much to everyone who has helped.I'll have a fair bit to get through to make sure that I understand these things on a deeper level than I do now.Quote from: w2aew on February 03, 2016, 03:40:47 amThanks for those.Quote from: w2aew on February 03, 2016, 03:40:47 amI've watched it 3 or 4 times. I watched it a long before I knew jack about squat, and barely understood anything.But even after watching it a few more times, he gets into extreme detail without giving the "idiot's" version. You summed it up easier there for a newb.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 04, 2016, 04:50:55 am
content: Quote from: tggzzz on February 03, 2016, 02:47:14 pmIf I look out the window,I see a big twisted cable which has 3 phases & Neutral coming in from the pole.My Stove runs off two phases,there is a thumping great 3 ph outlet that I've never used in the carport,& the lights & power are distributed across the phases in ways I don't know.What I do know is that Neutral & Protective Earth are connected at the house Power line entry point.OK,I know that not all systems use the MEN setup like in Oz,but I was pretty sure they all connected Neutral to Earth somewhere in the system.OK,all bets are off with USA 240v sockets,as both sides are "hot".

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 04, 2016, 05:00:24 am
content: Quote from: tggzzz on February 03, 2016, 02:47:14 pmCanada and US are the same in this regard. The neutral is always directly connected to earth in the panel and out on the pole. I've worked on some very old installations dating back to the 20s and have not seen otherwise.

author: Brumby
author_rank: Unknown
timestamp: February 04, 2016, 05:03:06 am
content: Quote from: vk6zgo on February 04, 2016, 04:50:55 am... but they have a neutral/earth at the mid-point, do they not?

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 04, 2016, 05:13:03 am
content: Quote from: Brumby on February 04, 2016, 05:03:06 amYes, they do. But large loads typically don't even use the "neutral"/center-tap. So supply circuits to those loads typically have two "hot" leads and a green-wire safety ground, but no "neutral" reference.Note that my original statement about neutral/ground/oscilloscope reference was specifically pointed at the OP from North America where neutral and ground are bonded together at the local distribution point (the circuit breaker panel, etc.) And as an explanation of why one could appear to measure the mains power voltage without any explicit ground/reference connection.Yes, from numerous previous discussions, we all realize that power mains distrbution (including neutral/ground protocol) varies widely from place to place on the planet. Perhaps someone should start a thread discussing this as a primary topic and letting us all see the different practices in our individual jurisdictions.

author: zapta
author_rank: Super Contributor
timestamp: February 04, 2016, 05:19:22 am
content: ElectroBoom had recently a video that touched on this topic

author: newbrain
author_rank: Super Contributor
timestamp: February 04, 2016, 07:28:21 am
content: Quote from: Brumby on February 04, 2016, 02:19:50 amYou don't...In the sense that the neutral is not directly distributed to normal residential users.PE scheme is usually, AFAIK (and wikipedia seems to agree) TT (terra-terra=ground-ground), so each building has its own earth electrode.If there are no major problems, ground potential is close to neutral (which is grounded somewhere in distribution), and you can measure about 127V from each phase to PE and 220V=127*2*sin(60) across.Older buildings are slowly being brought up to standard wrt PE, the one I used to live had PE distributed to all flats only in 2006. The more recent one I'm in now when in Italy always had PE, but the phases from the meters cabinet are all wired with yellow-green cable.The two-phase distribution is not so common in other parts of Italy, the certified electrician we called when renovating was quite puzzled, as he had only recently moved to Rome. To me it was the way it's always been, even in several other houses I've lived in.

author: Brumby
author_rank: Unknown
timestamp: February 04, 2016, 11:36:22 am
content: So are you saying that they are relying on the conductivity of the dirt/soil/water table from the premises back to the distribution point for the neutral?

author: Ian.M
author_rank: Super Contributor
timestamp: February 04, 2016, 11:55:18 am
content: Europe is 220V 50Hz land, and historically, the further south and east you go, the dodgyer the pre-EU electrical wiring regs were and the slower the uptake/implementation of modern safety standards. You can blame the Moors, Catholic church and Ottoman empire for many generations of encouraging a culture of fatalism. If it isn't God's will for you to die today, the wiring wont kill you!

author: Brumby
author_rank: Unknown
timestamp: February 04, 2016, 11:58:50 am
content: I was just thinking that if the physical earth under your feet was an active part of the electrical distribution network, it could make for some 'interesting' experiences.

author: Ian.M
author_rank: Super Contributor
timestamp: February 04, 2016, 12:09:37 pm
content: Yep, and you've got them in the Outback:https://en.wikipedia.org/wiki/Single-wire_earth_return

author: Brumby
author_rank: Unknown
timestamp: February 04, 2016, 12:23:45 pm
content: Hadn't thought about it much before - but it makes sense, so long as the ground impedance was low enough. Which, for the appropriate voltage, it obviously is.

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 04, 2016, 12:35:40 pm
content: Quote from: Brumby on February 04, 2016, 11:36:22 amYes, in some cases. Here in the US, it is quite common to see distribution at the residential street level (the final leg of the journey) as a single high-voltage line into the "pole pig" transformer, and a ground wire travelling down the pole to a ground rod which is the return of the circuit.The secondary of the transformer is typically 220VCT. And the Center-Tap is typically grounded both at the pole, and then again at the final destination termination point (the customer's meter connection).http://www.utterpower.com/household_power.htm

author: newbrain
author_rank: Super Contributor
timestamp: February 04, 2016, 01:31:47 pm
content: Quote from: Brumby on February 04, 2016, 11:36:22 amIn a way, yes. As said,TT, and RCDs ("differentials", as they are called in Italian) are now compulsory.The conductivity needs only be high enough to trigger the RCD. If it's too low, the network becomes in practice an IT one, and the RCD is useless (the 220V is effectively "floating" so, quite dangerous, but not that much more...).But, this true only for some localities (Rome and Ostia): I think it happened due to an easier conversion form the preexisting 110V distribution: to convert a line to 220V just attach another phase in stead of the previous neutral and slightly over-volt the street transformer...PE? What PE?Quote from: Brumby on February 04, 2016, 11:58:50 amAnd that used to happen, when there were no RCDs and PE was often (the horror!) the water pipe...

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 04, 2016, 05:34:09 pm
content: Quote from: Brumby on February 04, 2016, 11:58:50 amThere is a legendary tale in telephone circles related to that. In early days, and especially in rural areas, telephone lines were sometimes ground-return, but almost all of them were "selective ring" party-lines. Many of the "selective ring" schemes used a local ground reference for the ring voltage which approaches 100VAC at different frequencies (ring frequency being one of the selective-ring schemes).Anyway, there was a customer complaint from a rural customer that there was a strange problem with their telephone ringer. Apparently when a call came in, the phone never rang for several cycles until their dog barked, and then the phone rang.They sent a repairman out and he climbed a pole and clipped on his butt-set and dialed the customer's number. Sure enough several ring cycles and nothing happened. Then their old dog got up and barked a couple times and peed on the metal rod he was chained to. And then the phone rang.Apparently the dog was chained to the telephone ground rod which had gradually increased impedance and no longer had enough conductance to the earth. So when the ring current came down the line, it shocked the dog through his chain, he got up and barked in complaint, and then peed on the ground rod, temporarily lowering the impedance enough to pass sufficient ring current. Maybe old telco lore, but maybe true.FYI: Butt-set:

author: Richard Crowley
author_rank: Super Contributor
timestamp: February 04, 2016, 05:49:36 pm
content: There have also been cases where people experimented with communicating through ground currents.The magazine "Popular Electronics" in the January, 1968 featured an article about this history of ground communication and adding a suggested experiment to try CW or voice communication.http://www.americanradiohistory.com/Popular-Electronics-Guide.htm1968, January, p.45 "The Mystery of Radio Waves That Travel Along or Beneath the Surface of the Earth"

author: Renegade
author_rank: Regular Contributor
timestamp: February 04, 2016, 07:13:35 pm
content: Quote from: Richard Crowley on February 04, 2016, 05:34:09 pmI had no idea that a thread on oscilloscope no-nos would end up in dog pee when I first posted it...

author: zapta
author_rank: Super Contributor
timestamp: February 04, 2016, 09:06:03 pm
content: Quote from: Richard Crowley on February 04, 2016, 05:49:36 pmThe story I remember is that they used to close telegraph loops using the railroad as return line and one day they realized that it kept working when the rails were disconnected for repair.

author: Brumby
author_rank: Unknown
timestamp: February 04, 2016, 11:15:25 pm
content: Quote from: Renegade on February 04, 2016, 07:13:35 pmI think this arm of the thread has gone off at somewhat of a tangent to the original topic - but it is an interesting one that deserves it's own thread (as has been suggested somewhere else on the forum, I believe).I might like to suggest this topic is split from:https://www.eevblog.com/forum/beginners/is-there-an-oscillisocope-'what-not-to-do'-tutorial/msg858591/#msg858591into it's own topic - something along the lines of "Power distribution and earthing".