Mains and the oscilloscope - Page 1
Forum section: electronics / beginners

author: Neukyhm
author_rank: Contributor
timestamp: March 12, 2017, 03:06:15 am
content: Hi, I'm new here, I hope you can help me with this. I already know the answer, so the reason I'm asking for this is because I want to make sure that my house won't burn.I'm a physicist, but in my college the didn't teach us how to use a oscilloscope, just how to do some easy measurements.The question is: is it safe to measure mains 220AC with A-B operation so probes ground clips are not used? (assume the probe is x10)Again, I know the answer, it is safe. I just want to make sure, you guys are more experienced than me.

author: Dubbie
author_rank: Unknown
timestamp: March 12, 2017, 03:11:25 am
content: Not really safe. To be by the book you should use a high voltage cat rated probe.Edit: across the web you may get very different responses to that given by this forum. Keep in mind that this forum has many experienced professional members and bad advice is very rarely given here. Just because others on other less rigorous forums have gotten away with bad practice does not mean you will.

author: Brumby
author_rank: Unknown
timestamp: March 12, 2017, 03:14:51 am
content: The right probes arecriticalto safety.Watching this is a good idea as well....

author: Ian.M
author_rank: Super Contributor
timestamp: March 12, 2017, 06:24:46 am
content: You are under the illusion that your AC supply is a nominally 220V RMS, 50Hz sinusoid, maybe with some flattening of the crests due to loading by SMPSUs without power factor correction.It is not.Firstly the voltage may be at the upper end of itsEU harmonised tolerance rangeas your electricity supplier has no legal obligation to act on overvoltage within that range, so instead of the 311V peak you expect, you could have up to 358V. Then you must consider transients - seehttp://ecmweb.com/contractor/looking-sources-transient-overvoltages- and up to 1KV spikes riding on the sinusoid waveform are common to the point of being expected.Connect the tip of an ordinary scope probe to your mains and there is a high probability of it being exposed to spikes well over 1KV and it breaking down catastrophically.The situation is better if you have a good quality surge suppressing power filter (with transorbs, delta connected filter caps on input and output and at least one common mode choke) + an isolating transformer between the scope probe and the wall outlet - as the filter and transorbs considerably reduce the maximum spike amplitude, clipping ones on the peaks more heavily, and the transformer adds further low pass filtering as a typical fast transient doesn't have enough energy to significantly change the flux in its core, but I'd still want a CAT II rated probe with an adequate safety margin. A 500V peak rated probe will only have a 40% margin - barely enough to be safe after such a filter + transformer.

author: DimitriP
author_rank: Super Contributor
timestamp: March 12, 2017, 06:40:39 am
content: QuoteWhen you "know", "you know". If you have to ask you don't "know".What I don't know is the reason (or lack thereof) for the fascination with probing the mains voltage.

author: BrianHG
author_rank: Super Contributor
timestamp: March 12, 2017, 06:54:08 am
content: Only if you must. Get a normal 240v to 24v ac transformer.Make surethere is no direct connection to the mains and the transformer's secondary 24v side, use one with safety approvals like a wall-wart which has 24vac, or 12vac out. Probe the signal on the 24v ac side with 1 probe normally and multiply your readings by 10. The smaller the transformer, like 2 watts or less, the better the high frequency response. It may be useful to add a resistor load on the 24v side like a 1k 2 watt resistor. (The resistor will get warm) An optional 100nf capacitor in parallel with the 1k resistor if you want to get rid of high frequency noise.You should see your 50hz sine wave.

author: tggzzz
author_rank: Super Contributor
timestamp: March 12, 2017, 09:09:54 am
content: Quote from: Neukyhm on March 12, 2017, 03:06:15 amEngineers consider two things: how X worksplushow X can fail. You have only considered how that can work.The trouble is that there can be many many subtle and surprising ways that things can fail, and it is difficult for anybody (especially a beginner) to think of them all.Back to your problem. If there isn't a simpler way of achieving your (unstated) goals, you should use the appropriate type of probe. I suggest you have a look at the safety references inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: danadak
author_rank: Super Contributor
timestamp: March 12, 2017, 10:12:47 am
content: These might help -http://www.tek.com/document/application-note/three-facets-floating-measurement-solutionshttp://www.newark.com/pdfs/techarticles/tektronix/FFM.pdfRegards, Dana.

author: David Hess
author_rank: Super Contributor
timestamp: March 12, 2017, 10:53:31 am
content: Quote from: Neukyhm on March 12, 2017, 03:06:15 amYes, it is generally safe but if it is something that you do regularly, better probes and maybe a better oscilloscope with appropriate safety ratings should be considered. The peak voltage from 240VAC is lower than many probe and oscilloscope input ratings and with a x10 probe, it helps that the two are in series. At least my older oscilloscope can handle 400 to 500 volts peak directly connected to their inputs. Failure do to a severe overload will probably be limited to a blown input.The common mode range of A-B mode is poor (you will be stuck at 50V/div) so the sensitivity will be limited. A dedicated differential probe will have much higher sensitivity.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 12, 2017, 12:59:41 pm
content: Bend the tines of a two forks and attach them together using a pickle. Stick the tines into your outlet forming a series circuit with the pickle. If the pickle burns evenly at both contact points you have an AC waveform, and at least 100 volts. This is the UL approved way to test this and meets ISO9001 standards.

author: rstofer
author_rank: Super Contributor
timestamp: March 12, 2017, 03:47:59 pm
content: Quote from: Neukyhm on March 12, 2017, 03:22:58 pmI too have an issue with measuring high voltages with a scope. I don't even own the appropriate PPE (Personal Protective Equipment) like gloves.Maybe x100 probes are a help. They will certainly help protect the scope and they will probably have an appropriate safety rating.A-B measurements have been a scope feature for generations. It would be worth reading the User Manual for limitations.It is my understanding that Residual Current Devices are common in Europe and that they protect the entire panel. That certainly reduces the shock hazard. In the US, we have Ground Fault Circuit Interrupters on branch circuits to various specified locations but they don't protect the entire panel and they trip at a very low number of mA. But they are only used for outlets in wet or outdoor locations, not my spare bedroom.Then there is the 'oops' bit. How much energy is available on the circuit? In the US, it will generally be less than 10,000A for residential services and probably lower than 5000A. This is further limited by the branch circuit wire size but still, there can be a heck of an arc.All in, I prefer to stay below 50V and more likely below 12V. I'm especially fond of 5V. And, no, I have no interest in SMPSs. If I need one, I'll just buy it.

author: tggzzz
author_rank: Super Contributor
timestamp: March 12, 2017, 06:52:22 pm
content: Quote from: Neukyhm on March 12, 2017, 03:22:58 pmOh, for heaven's sake! Why don't you ask the question you want answered, rather than encourage everybody to waste their (remaining) life giving useful answers to things that don't interest you.How would you feel if I asked "is it OK to eat whelks" , and then said "listen, whelks are just an example of seafood I want to eat"?

author: julian1
author_rank: Frequent Contributor
timestamp: March 12, 2017, 08:50:09 pm
content: I had a similar sense of trepidation about the A-B thing. Eventually I decided it made no sense not to buy the correct tool for the job - instead of relying on a workaround. A high-voltage differential probe, that's battery powered provides the necessary isolation. About $200 second-hand on ebay.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 12, 2017, 08:55:43 pm
content: Quote from: tggzzz on March 12, 2017, 06:52:22 pmWhat if I have a friend who may or may not have access to high voltages and may or may not own an oscilloscope, and say the probes accidentally touch the hot and the neutral...

author: Ian.M
author_rank: Super Contributor
timestamp: March 12, 2017, 09:10:37 pm
content: Odds are, in North America, you'll get away with it, Unless there is a floating neutral,. your domestic mains is under 200V peak (neglecting spikes) so for a typical 500V rated probe, that still leaves you 300V margin to handle spikes. Its not ideal ore perfectly safe, you should use a proper Cat II rated probe, and you *REALLY* shouldn't probe before the appliance fuse.Clipping the probe ground to neutral is another matter - that's just dumb, and can melt the ground clip lead, the probe coax lead or even melt traces off the PCB inside your scope. A GFCI breaker will trip but probably wont save you because it interrupts the live(s) not the neutral, and the problem is the potential difference between neutral and ground, usually caused by either poor bonding at the panel or heavy loads on the circuit.

author: Kappes Buur
author_rank: Regular Contributor
timestamp: March 13, 2017, 09:30:36 am
content: See the adventure of ElectroBoom probing an AC circuit

author: Ian.M
author_rank: Super Contributor
timestamp: March 13, 2017, 11:29:12 am
content: An excellent example of how *NOT* to do it. e.g. 2:00 - 2:08 - floating a scope with scotch tape!/////////////// CAUTION /////////////// CAUTION //////////////// CAUTION //////////////// CAUTION ///////////////////

author: grumpydoc
author_rank: Super Contributor
timestamp: March 13, 2017, 11:33:24 am
content: Quote from: Ian.M on March 13, 2017, 11:29:12 amI think ElectroBoom specialises in "HowNOTto do it" videos. My main worry is that fact might not be obvious to everyone.

author: Ian.M
author_rank: Super Contributor
timestamp: March 13, 2017, 11:40:46 am
content: Yes. We could make good use of a full width animated gif 'caution' black and yellow hazard tape 'smiley' for use above and below all ElectroBoom and some other videos!Alternatively, if Dave installs the SMF hilight tag mod:http://custom.simplemachines.org/mods/index.php?mod=3825we could simply do what I tried to above.

author: BrianHG
author_rank: Super Contributor
timestamp: March 13, 2017, 11:57:34 am
content: Quote from: Kappes Buur on March 13, 2017, 09:30:36 amIt would have been funnier if after each time he had an explosion, the scope should have been blanked out, and after the next scene cut, you would see the scope on his desk to the right & a new one in use in front of him until that one is destroyed...

author: grumpydoc
author_rank: Super Contributor
timestamp: March 13, 2017, 11:58:46 am
content: Quote from: Ian.M on March 13, 2017, 11:40:46 am seems to work (in preview, anyway)./\/\/\/\/\/ CAUTION /\/\/\/\/\/\/

author: Ian.M
author_rank: Super Contributor
timestamp: March 13, 2017, 12:07:32 pm
content: Quote from: BrianHG on March 13, 2017, 11:57:34 amRigol's Legal department should sent him a cease and desist letter requiring him to obscure all Rigol branding and model numbers on any equipment shown in his videos!Mehdi Sadaghdaris obviously a graduate of the 'Elect-a-Pope' school of engineering. He reminds me of 'Klaus' the fork-lift driver.

author: rsjsouza
author_rank: Super Contributor
timestamp: March 13, 2017, 12:17:34 pm
content: Quote from: Neukyhm on March 12, 2017, 03:22:58 pmMains is a different beast when compared to, say, a local high voltage power source whose characteristics such as maximum voltage/current and source impedance are well known.Mains has a low impedance that can yield currents at the order of kA as mentioned by rstofer, which will be only relevant if a breakdown or an arc happens between the power source and the test equipment (oscilloscope, probes, etc.). The chances of such event occur are defined by either a transient or an accidental mistake.A transient is extremely hard to predict and can reach spikes at the order of kV which can easily exceed the probe safety specifications. Given the very low impedance of the source, any arc will be quite an event.Accidental mistakes can be (but not limited to) either shorting the probes or inadvertently switching the probes from 10:1 to 1:1 (several regular oscilloscope probes have this tiny switch on them).Probing a high voltage power supply is different than mains, given the fact that, even if it has a similar impedance as mains, it still has an advantage as spikes may not exist or be well characterized - thus eliminating the element of surprise.All in all, kudos to you to double-check your procedure on this forum. In a very distant past I measured the voltage of the three-phase 60A bus bars feeders to my house and no surprises happened, but I was ignorant of all these factors at the time and did not take any precaution other than checking the maximum voltages of the 10:1 probes.

author: madires
author_rank: Super Contributor
timestamp: March 13, 2017, 01:49:30 pm
content: Quote from: Neukyhm on March 12, 2017, 03:06:15 amIf someone is experienced with scopes and high voltage measurements, knows the limitations of the poor man's differential probe (A-B), and stays within specs of the probes and the scope, the answer would be "not recommended, but it will work at you own risk". In your case I'd strongly recommend proper differential probes rated for the voltages you want to measure plus a generous safety margin. Don't buy cheap knock-offs, buy a well known brand from a well known distributor. Yes, they are expensive, but your life is more valuable.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 14, 2017, 03:00:01 am
content: Mr Carlsons lab does a great example of how to plug a scope into the mains and how to do it right.I know in america (not spain) since you have 120VAC you don't know what leg of the 220 your outlet is plugged into, that's why people always say its a 50/50 shot if you blow up your scope.https://youtu.be/XBsQ3sZ45Fk

author: mtdoc
author_rank: Super Contributor
timestamp: March 14, 2017, 05:53:49 am
content: Nice video but...Quote from: raspberrypi on March 14, 2017, 03:00:01 amNo - The issue has nothing to do with which leg (L1 or L2 in the North American split phase 120/240V system) the particular branch circuit you are plugged into is utilizing.

author: Gyro
author_rank: Super Contributor
timestamp: March 14, 2017, 06:48:04 pm
content: Neutral will normally beNEARground, but depending on where they are commoned there will be a voltage between them, caused by Neutral conductor current. This will of course be a very low impedance source. It is not sensible or reasonable to expect a probe ground lead to short this current, regardless of any fault condition or not!

author: madires
author_rank: Super Contributor
timestamp: March 14, 2017, 07:21:37 pm
content: A scope is the wrong tool for that kind of measurement. Ask an electrician, he's got the right tool for that.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2017, 07:25:25 pm
content: Quote from: Neukyhm on March 14, 2017, 06:59:22 pmAnd that, ladies and gentlemen, is an excellent example of why you should determine a potential client'sactual problembefore discussing their "solution".First the question was "The question is: is it safe to measure mains 220AC with [a scope]... Again, I know the answer, it is safe.... "That mutated into "Listen, asking if I can measure mains voltage is my way to ask if I can measure hundreds of volts of anything with the oscilloscope (assuming that voltage is below probe & oscilloscope limits). It's not like I feel fascination for mains."And we now find that all he wants to do is find a gross fault in his mains installation. Nothing subtle.A scope is the wrong tool for that problem.Given what you have said so far, I strongly recommend you get a properly qualified electrician to examine your installation. Don't risk hurting other people.

author: mtdoc
author_rank: Super Contributor
timestamp: March 14, 2017, 07:45:31 pm
content: I agree with what madires and tggzzz have said. An oscilloscope is the wrong tool and it's best to consult an electrician.But - if you have a DMM (with proper CAT rating) that has a lo-Z setting you can check whether that 40V is really of any consequence. For example, seethis nice Fluke application note on ghost voltages.On the other hand if your neutral is not properly bonded to a proper earth ground, it may be real..If you're not absolutely sure you can test this safely - call an electrician.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2017, 10:51:27 pm
content: Quote from: mtdoc on March 14, 2017, 07:45:31 pmOf course, that doesn't work where the Dunning-Kruger syndrome is present.

author: DimitriP
author_rank: Super Contributor
timestamp: March 15, 2017, 12:09:47 am
content: Quote from: Neukyhm on March 14, 2017, 11:20:20 pmA quien no pide consejo, darlo es de necios.You did ask.

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2017, 12:12:54 am
content: Quote from: Neukyhm on March 14, 2017, 11:20:20 pmIt was a general statement, not specifically aimed at you.However, in your original post you did write "...Again, I know the answer, it is safe...". I do appreciate English is probably not your first language, just as Spanish is not mine.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 15, 2017, 01:39:34 am
content: Quote from: mtdoc on March 14, 2017, 05:53:49 amCare to elaborate what the issue is? Usually when you tell someone they are wrong you explain why.

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 15, 2017, 01:48:59 am
content: Quote from: Neukyhm on March 14, 2017, 06:59:22 pmMy neutral has 40 volts on it too when I put the meter between it and ground. Is this caused by coupling from the wires all running next to each other? How much current roughly would this 40 volts put out? Could I run a 5W light bulb off it or even an LED? Or would it disappear as soon as you put any load on it.

author: Brumby
author_rank: Unknown
timestamp: March 15, 2017, 02:23:37 am
content: With mains power, things get a little more dangerous. It's not about simple voltages any more, it is about serious energy levels. 10KV around a CRT tube will wake you up in a hurry and perhaps fry some types of component, but 230VAC mains can make things explode. Add a transient or two and things can get really dicey, really quickly and unexpectedly. Your very first post indicated you were not really aware of this, as you stated:Quote from: Neukyhm on March 12, 2017, 03:06:15 amThis line in particular ...Quote... demonstrates you didn'tknow. This is the sort of thing that makes a lot of experienced people very anxious for your safety (and why some people bring up the D-K syndrome thing).To your credit, you did have the presence of mind to bring your question here, before sticking probes into a mains environment. As a result of that, you have, indeed, learned something - and something that has the very distinct potential to save you from injury (or worse) - without exposing yourself to the real risk.To be fair to those who may have come across as overcritical, nobody here has any real idea of who you are, your background or your capabilities. You've only been a member for a couple of days - and the only thread you have posted on is this one. As time goes by and we have the chance to discuss things with you, we will develop a better understanding - but at this point in time, you are somewhat of an unknown to us.While there are a lot of things we can help you with, sometimes it is better if advice like the following is given:Quote from: mtdoc on March 14, 2017, 07:45:31 pmNot only does an electrician have the qualification for this sort of work, they also have experience. Sometimes, it is this experience that can interpret the readings and/or follow a testing path that can identify the fault - because faults in the real world are sometimes non-intuitive, untilallthe necessary information is at hand (which might take a lot of time, reasoning and measurement) ... or it has been encountered previously.We are certainly in favour of helping and educating here, but we don't want to encourage wrecklessness - and until we get to know a member a bit better, we are likely to err on the side of caution.One last word .... there is a wide scope of members here - with different backgrounds, different experience, different cultures - and, of course, different native languages. It's a global community. There are bound to be communications issues.

author: Brumby
author_rank: Unknown
timestamp: March 15, 2017, 02:26:27 am
content: Quote from: Neukyhm on March 15, 2017, 02:13:47 amYou omitted the words "IN THEORY" with your original post. If you had included those, then a whole lot of the messy part of the discussion would not have happened.If you thought we should have understood that, then you need to understand the engineering mind - it works on the basis of what is presented to it.

author: Brumby
author_rank: Unknown
timestamp: March 15, 2017, 02:32:31 am
content: Quote from: Neukyhm on March 15, 2017, 02:13:47 amThat idea is how a high voltage probe is designed - but there are a few more considerations than just simple voltage calculations....The physical layout of the divider is important, as is the substrate on which it is mounted. If using a PCB, then there has to be proper consideration given to isolation for each point. Then there is a case which will need to keep the operator safe when transients are encountered. As well, you will need to consider the voltage rating of the resistors. There are probably some other considerations that people with better knowledge on this subject could add.These issues are not trivial, especially if you don't have the practical experience. Better to buy a commercial HV probe.

author: Ian.M
author_rank: Super Contributor
timestamp: March 15, 2017, 02:38:41 am
content: Quote from: raspberrypi on March 15, 2017, 01:48:59 amPutting a load of more than a couple of mA between a 'high' neutral and ground will trip any RCD or GFCI on the circuit, unless the ground wire is broken somewhere, and in that case it will put a dangerous voltage on the exterior metalwork of all grounded equipment plugged into the same circuit.If in doubt, call in a qualified inspecting electrician.Assuming you have a CATIII or better rated DMM with fused test leads, if you really want to find out what's going on, you'll need to drive a temporary ground rod into moist ground, and bring an insulated wire from it inside to get a true Earth reference to measure against. If using thin hookup wire, you'd better put an inline fuse holder with a 250mA fuse on the end of it in case you accidentally touch it to a live terminal or other live metalwork. Do not assume that any pipework is properly grounded.By testing between the true earth wire and socket ground you can detect if the ground wiring has a problem. You can also check the voltage between true earth and neutral.CAUTION:if there is a fault, lethal voltages may exist between the true earth wire and any supposedly grounded metalwork in the room. Treat the earth wire as-if it is live until you are certain no dangerous voltage differences are present. Do *NOT* attempt this sort of testing with a CATII or lower rated meter, with unfused test leads or if you are unsure what you are doing.

author: mtdoc
author_rank: Super Contributor
timestamp: March 15, 2017, 04:14:42 am
content: Quote from: raspberrypi on March 15, 2017, 01:39:34 am*In North American split phase electrical service, there are 2 "hot" legs at the service entrance (L1 and L2) and one neutral which is bonded to earth ground.*Both L1 and L2 are 120V with respect to neutral/ground. Each individual 120V branch circuit coming off of the main service panel utilizes either L1 or L2 - but not both. (A 240V circuit utilizes both).*From the point of view of the end user of these 120V circuits at the home electrical outlets, it makes no difference which leg (L1 or L2) is supplying any particular outlet. It is only relevant to the electrician wiring the service panel and wanting to balance loads between legs.HEREis a good, concise reference for this. See figure 1.*From the point of view of oscilloscope use and safety and understanding how not to "blow up your oscilloscope" and use or miss-use of isolation transformers, the distinction or even knowledge of which leg is supplying an outlet is irrelevant and has nothing to do with any supposed "50/50 chance" of blowing up your oscilloscope.*Please watch Dave's video ("How not to blow up your oscilloscope") and the video you posted again to better understand why and how measuring mains supplied circuits (or measuring mains itself) with an oscilloscope can result in disaster without great care and understanding. It's not an easy subject to fully grasp and Dave does a much better job in his video of explaining it that I could do in a brief forum post.

author: Unknown
author_rank: Unknown
timestamp: March 15, 2017, 05:17:46 am
content: Quote from: raspberrypi on March 15, 2017, 01:48:59 amWhen wired to code, the neutral is bonded to ground at the panel where utility service enters. Neutral typically rises above ground potential due to the current flowing through the resistance of the wire(s) back to where ground and neutral are bonded. For example if that were 2 ohms back and 10 volts N-G then 5 amps would be returning over the neutral. If the load were removed (0 amps draw), then neutral should be at ground potential. You are essentially just measuring the voltage across the length of the neutral wire from you to the bonding point, via the ground wire (as a long extension of your multimeter probe).40 volts seems very high for a N-G voltage. You may have bad connections (high resistance) or perhaps it is floating entirely and not bonded. I would get the attention of an electrician.

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2017, 10:26:15 am
content: In typo veritasQuote from: Brumby on March 15, 2017, 02:23:37 amThe rest of your post is spot on, too.

author: David Hess
author_rank: Super Contributor
timestamp: March 15, 2017, 11:00:14 am
content: Quote from: Ian.M on March 15, 2017, 02:38:41 amPutting more than a couple of mA between neutral or hot and any other point will trip a RCD or GFCI whether ground is connected or not. The RCD or GFCI does not require ground to work. The other point could be another phase, neutral, hot, or anything which draws a current including a different ground. The RCD or GFCI is a two wire device.

author: Ian.M
author_rank: Super Contributor
timestamp: March 15, 2017, 11:03:47 am
content: OTOH if the ground wire is broken you probably wont be able to get enough current to trip the RCD. .You cant get a L-N imbalance if the current's got nowhere to go!

author: David Hess
author_rank: Super Contributor
timestamp: March 15, 2017, 11:17:47 am
content: Quote from: Ian.M on March 15, 2017, 11:03:47 amIf that is the case, then you also cannot shock yourself except between the line and neutral which a RCD will not help with anyway. Often the problem involves the sink or tub and for that, the RCD will work just fine. At least here in the US, areas around water like the kitchen and bathroom are where RCDs are required.

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2017, 02:03:31 pm
content: Quote from: Neukyhm on March 15, 2017, 01:22:28 pmSo, before you do that you should consider the ways that could fail. And if you don't understand them all, you should reconsider.Hint: it is unlikely that a beginner will be able to simply think, and reproduce all the hard-won experience gained over the decades. Hells teeth, I doubtIcould think ofallthe ways.

author: Brumby
author_rank: Unknown
timestamp: March 15, 2017, 03:57:28 pm
content: Well, you have obviously dabbled a bit - and no doubt understand our concerns ... so I will finish by saying:Stay safe.But we are still a bit worried....

author: tggzzz
author_rank: Super Contributor
timestamp: March 15, 2017, 04:57:39 pm
content: Quote from: Neukyhm on March 15, 2017, 03:02:17 pmThere are many types of "RCD" and different installations. However, in the UK I would expect an RCD to trip if you had >30mAthroughyour bodyto ground. It wouldn't trip if the current was from live to neutral, nor if <30mA.

author: StillTrying
author_rank: Super Contributor
timestamp: March 15, 2017, 10:07:31 pm
content: Quote from: Neukyhm on March 15, 2017, 01:22:28 pmWhy did you choose a CML+ ?Did you find an online review anywhere ?

author: StillTrying
author_rank: Super Contributor
timestamp: March 16, 2017, 12:55:19 am
content: Quote from: Neukyhm on March 15, 2017, 10:51:10 pmThe jury (of about 1) is still out.https://www.eevblog.com/forum/testgear/siglent-cml-firmware/

author: tautech
author_rank: Super Contributor
timestamp: March 16, 2017, 01:07:12 am
content: Quote from: StillTrying on March 16, 2017, 12:55:19 amYours is ~3rd that I know of that has had a problem, one of which I sold.The Plus version does seem to have some issues but I am very confident Siglent will fix them in short time. They must....there are many of this model in the marketplace.SDS1102CML+ is my best seller.

author: StillTrying
author_rank: Super Contributor
timestamp: March 16, 2017, 01:44:45 am
content: Quote from: tautech on March 16, 2017, 01:07:12 amAfter I'd gone away, I was trying to remember which thread I'd just posted that in because I remembered that I'd forgotten to say that currently the CML+ jury consists of only about 1.QuoteInnormalmodes, being able to trigger on parts of a waveform 1mV or less high is 20 times better than my aging CRO, so I won't be throwing the CML+ away just yet!

author: raspberrypi
author_rank: Frequent Contributor
timestamp: March 16, 2017, 04:04:14 am
content: I think this is where I got the 50/50 idea from:Quote

author: tautech
author_rank: Super Contributor
timestamp: March 16, 2017, 07:53:58 pm
content: Quote from: Neukyhm on March 16, 2017, 07:18:35 pmIn Utility/System info you can check the firmware version is the same as this one:http://siglentamerica.com/gjjrj-xq.aspx?id=5074&tid=15QuoteSpend some more time to become more familiar with the scope and time reading the manual on the CD.IIRC you can turn on something in the Measurements menu to get it up on the OSD.If I get a chance later I'll get one out and have a look.

author: StillTrying
author_rank: Super Contributor
timestamp: March 16, 2017, 09:37:27 pm
content: Quote from: Neukyhm on March 16, 2017, 07:18:35 pmCongratulations, it's your first bug find!Ignore me, I've got all the math functions working somehow!

author: StillTrying
author_rank: Super Contributor
timestamp: March 16, 2017, 10:39:58 pm
content: Quote from: Neukyhm on March 16, 2017, 10:11:54 pmI think you can only go by the grid/graticule divisions, (no math auto measurements).Perhaps your math waveform is hiding the "Math scale:" bit. (Edit: It is a daft place for them to have put it.)The waveforms are just my finger touching the end of the probe tips - both connected together.

author: tautech
author_rank: Super Contributor
timestamp: March 16, 2017, 11:00:48 pm
content: Quote from: Neukyhm on March 16, 2017, 10:52:23 pmI'll have a fiddle with a unit and a real simple setup, say 2 different DC voltages and various Math functions with a view to reporting your findings (when confirmed) to the factory.Probably tonight as I have a heap on today. Factory closes for the weekend at 10pm my time.

author: tautech
author_rank: Super Contributor
timestamp: March 17, 2017, 07:45:13 am
content: Simple Math test.Both channels 1V/div and and all Ref levels (0V) set to -2V, Ch1, Ch2 and Math.Math scaling set to the same as active channels: 1V/div.Supplied voltages:Ch1 5VDC, Ch2 2VDC.Math Ch1 - Ch2.The result for Math is as expected: 3 div above Ref so 3 V.The highlighted function button allows the Multifunction control to adjust the Math scaling (V/div).The uppermost function button allows the Multifunction control to adjust the Math trace Reference level.There is no Math OSD measurements in the UI.Should we ask Siglent if this can be implemented ?

author: Brumby
author_rank: Unknown
timestamp: March 17, 2017, 08:04:57 am
content: Congratulations on getting your scope up and running - but as has been said above, I would also suggest you spend some time doing that weird thing - RTFM (Read The Flippin' Manual).As for this:Quote from: Neukyhm on March 16, 2017, 07:18:35 pmI had little doubt you would survive. The chances of something going wrong are low - but they're not zero.Just do me this one little favour ... imagine what would happen if 5kV or 10kV were to hit your setup. Then, take steps to contain the aftermath ... and lastly, whenever you use it, expect that to happen.You may never have the event - but it is better to be prepared than have to deal with the consequences.I know I'm going on about this a bit - but you can't count on getting second chances. (I'll step away from the soapbox now.)

author: tggzzz
author_rank: Super Contributor
timestamp: March 17, 2017, 08:57:44 am
content: Quote from: Brumby on March 17, 2017, 08:04:57 amJust so.Engineers(i.e. not hackers or amateurs) consider how things fail to be as important as how they work.We'll see if the OP appreciates that, but so far the evidence is against it.