Protecting an oscilloscope and probes from nuclear detonation? - Page 1
Forum section: electronics / beginners

author: nzo
author_rank: Regular Contributor
timestamp: September 11, 2015, 08:35:56 pm
content: Hi all,Just been watching Dave's video:EEVblog 279 - How NOT To Blow Up Your Oscilloscope!Is it unrealistic of me to imagine designers and manufacturers to advance their scope technology to a point where their products and the gear they are connected to can be considered safe from the scenarios outlined by Dave?Other than protected probes priced from US$300.00 up and some equally expensive USB isolators, it appears that not much thought and innovation has gone into gear safety or newbies who may not be aware of the risks involved in inadvertently hooking probe earth to a dangerous point on the gear being tested.When you got your first scope, were you aware of the risks Dave talks about? Did you learn the (bang!) hard way? How do you minimise those risks when you work with a scope?Thanks for your input, if any.

author: jolshefsky
author_rank: Regular Contributor
timestamp: September 11, 2015, 09:00:28 pm
content: Like any tool, understanding how to use it is unrelated to whether you are able to purchase it.

author: Chris C
author_rank: Frequent Contributor
timestamp: September 11, 2015, 09:02:40 pm
content: Every built-in protection tends to increase cost, and decrease performance. Would you buy a scope that's twice as rugged, but twice the cost, and with half the performance?Quote from: nzo on September 11, 2015, 08:35:56 pmAware, yep. Bang, nope. To minimize the risks, understand your scope and the device under test. Be aware that all potentials are relative, and ground can mean different things. If you're in the habit of testing things that may have unusual grounding schemes, plug the device under test into an isolation transformer. You will find them in every TV repair shop.I've run across a few things where the chassis or other large metal areas that would normally be grounded, are instead directly connected to AC hot or other high voltage; usually signified by a big red warning sticker. In those cases, since I don't have an isolation transformer, I use only battery powered test equipment.

author: DimitriP
author_rank: Super Contributor
timestamp: September 11, 2015, 09:06:29 pm
content: Some people read the manual beforebang, err... before hand.Altogether now, out loud:

author: helius
author_rank: Super Contributor
timestamp: September 11, 2015, 09:27:12 pm
content: The Tek 547 and its comrades will survive a nuclear detonation, if that's what matters to you.You should still avoid shorting out the ground lead, but they are a little more rugged there as well.

author: free_electron
author_rank: Super Contributor
timestamp: September 11, 2015, 09:42:02 pm
content: in case of a nuclear detonation you have other issues than worrying about your diff probe being fried...

author: Ampere
author_rank: Regular Contributor
timestamp: September 11, 2015, 09:50:58 pm
content: Quote from: DimitriP on September 11, 2015, 09:06:29 pmSome of us are stuck with second-hand analog scopes whose manuals have disappeared long before we owned them.Thankfully, I never had a reason to connect the ground leads to anywhere but ground so I've managed to avoid the, but I'm sure it would have happened eventually. I'm tempted to print out this safety notices excerpt and tape it to the top of my scope just in case.

author: tautech
author_rank: Super Contributor
timestamp: September 11, 2015, 10:27:44 pm
content: The industry standard documents are:http://www.tek.com/document/primer/xyzs-oscilloscopes-primer-1And much further study here:http://www.tek.com/search/apachesolr_search/floating%20measurementsParticularly this one:http://www.tek.com/document/fact-sheet/fundamentals-floating-measurements-and-isolated-input-oscilloscopes

author: DimitriP
author_rank: Super Contributor
timestamp: September 11, 2015, 10:43:02 pm
content: Quote from: Ampere on September 11, 2015, 09:50:58 pmI'm going to let you realize what you just said on your own

author: vk6zgo
author_rank: Super Contributor
timestamp: September 12, 2015, 02:31:59 am
content: Quote from: nzo on September 11, 2015, 08:35:56 pmWhen you place your earth(ground) clip on a point that is at Mains Active potential,it goes "Bang!!",draws excessive current through the DUT Mains fuse & blows it.Alternatively, it trips the bench circuit breaker,either through over current,or because the Residual Current Device (RCD) trips from Earth current.It may,perhaps blow the fuse or drop the breaker/RCD at the building fuse box.Of course,if you live in the UK,there is also the fuse in the power plug.All these things are happening just as they are designed to----Active connected to Earth causes the supply to be disconnected,ensuring safety.Or,at least,this happens in countries where all power sockets are equipped with an Earth connection.Historically,Oscilloscopes were mainly used in Engineering establishments of various types where such "safety" Earths were more the rule than the exception.Oscilloscopes were built into metal cases,with the "ground" clip solidly connected to this case,as was the Earth connection from the Mains.These could usually sustain such an incident with no damage other than a burn mark on the clip.Modern 'scopes are made of plastic,with the connection between the ground clip & Mains Earth being via a PCB track.These can,& sometimes do,act as a fuse,& become open,removing the protection offered by the Mains Earth.In working with voltages of Mains levels,the best trick is to set up the probe connections with the DUT unpowered.That's why there is a "hook" on the end of your probe!The worst case scenario then is you may (& only "may") injure your 'scope & not yourself.If you do have a "Bang" happening,check continuity between your ground clip & the Earth pin of your power cord before proceeding further.