Portable handheld oscilloscopes vs EEVblog #279 - Page 1
Forum section: electronics / beginners

author: VSV_electron
author_rank: Regular Contributor
timestamp: April 05, 2023, 05:35:07 am
content: In his famous #279 EEVblog episode Dave clearly explained how not to blow an oscilloscope (or maybe just the ground alligator lead of the probe in the lucky scenario).When doing that video the man implied a desktop scope with the BNC connectors bound to the mains ground through the power chord.What would remain in that video if the scope in question was one of the now commonly used on the amateur electronics workbench and quite popular portable battery powered oscilloscopes?Since these devices are floating with no common ground reference it would be safe to use them in any of the 4 scenarios that Dave considered.However those portable scopes still have some weak points, haven't they? How should that famous video be reworked for the battery powered handheld scopes to keep it at the top of the YT search?What are the dangers for the portable scope itself and for its operator when it's used incorrectly and what those dangerous scenarios are?One of the YTubers in his video on the subject has a warning to never disconnect the common ground from an oscilloscope since in that floating state a scope can be easily damaged with simply touching it with a bare finger - that's what he suggests.Since the portable scopes are not grounded are they inherently more vulnerable to ESD failures as such?

author: theHWcave
author_rank: Regular Contributor
timestamp: April 05, 2023, 08:36:57 am
content: Yes, there are a few dangers. I am using a OWON HDS272 portable scope (2 channel) for the scary stuff and also have a RIGOL 1054Z bench scope. Of the top of my head:Old dangers that still apply on battery powered scopes:forgettiing that 2nd, 3rd .. channel all use the same ground (even if not connected to "ground")scope inputs are generally not suitable for direct 240VAC mains and neither are cheap 1:10 probeson a floating scope, touching any exposed metal & BNC connectors when 1 channel is connected to measure something that may have direct mains connectionNew dangers for battery powered scopes:forgetting that if its connected to charger or PC its no longer floating(to be continued)

author: Ian.M
author_rank: Super Contributor
timestamp: April 05, 2023, 10:43:03 am
content: Yep. Unless the handheld scope and its matched probe have CAT ratings backed by verifiable certificates from a 1st world safety testing and standards organisation (e.g. U.L, VDE etc.), its a potential electrocution hazard if its connected to any circuit that isn't isolated from the AC mains. It may appear to be safely insulated, but without those certificates or personally destructively tearing down an identical one, you have no way of knowing if its got adequate creepage and clearance distances between metal parts connected to the the live chassis and the operator's hand. Now add some conductive dirt buildup down the sides of buttons, or in the case seam etc. and sweaty hands, and its a potential booby trap waiting to kill someone.

author: alm
author_rank: Super Contributor
timestamp: April 05, 2023, 02:36:03 pm
content: Quote from: theHWcave on April 05, 2023, 08:36:57 amThis is a danger specific for battery powered scopes, since on normal mains-connected scopes the BNC shell will be connected to PE, and hence safe to touch, although connected to a circuit it might destroy the circuit or trip a breaker. For this reason, a not so great made mains-connected scope is safer, because all exposed metal will be connected to PE, so it's unlikely to shock the user. While a battery-powered scope without isolated or at least insulated inputs could very easily shock a user through an uninsulated BNC connector, USB connector or DMM/scope probes (if DMM and scope channels are not isolated either).That's why early Fluke Scopemeters used insulated BNC connectors and insulated Multi-Contact / Staubli IsoProbe probes, and modern Scopemeters (and other decent battery-powered scopes) use fully isolated channels.

author: VSV_electron
author_rank: Regular Contributor
timestamp: April 05, 2023, 02:50:53 pm
content: Quote from: theHWcave on April 05, 2023, 08:36:57 amThat's interesting. I would expect that a wall charger that connects to a battery powered scope supplies floating voltage to the device since there is normally no ground in the low voltage side DC connector. Isn't it floating then?

author: theHWcave
author_rank: Regular Contributor
timestamp: April 05, 2023, 05:24:57 pm
content: Quote from: VSV_electron on April 05, 2023, 02:50:53 pmYes, maybe I was a bit unspecific there. The danger depends of course on the charger... However, since many battery powered scopes are using USB to charge (and/or connect to PC), it is likely that some users may use dodgy USB chargers with highly questionable isolation distances. Who knows the build quality of their chargers? Hence I use the rule: before measuring, unplug the scope from everything else. I think its a good habit to never seeing a USB lead and probes connected to your scope at the same time. Maybe extreme, but better safe...

author: VSV_electron
author_rank: Regular Contributor
timestamp: April 05, 2023, 06:13:00 pm
content: Quote from: theHWcave on April 05, 2023, 05:24:57 pmI see what you mean. Maybe that's indeed a good practice in respect to the "USB socket" as a general rule. Sort of getting into a good foolproof habit: "I see the USB connection - it gives warning". And maybe then... "Well, I know what it is - it won't scare me off!"

author: Jwillis
author_rank: Super Contributor
timestamp: April 05, 2023, 08:39:27 pm
content: USB charger are required by regulation to be isolated . But as they say " Don't turn it on. Take it apart".

author: alm
author_rank: Super Contributor
timestamp: April 05, 2023, 08:56:43 pm
content: Quote from: Jwillis on April 05, 2023, 08:39:27 pmWhich regulation says that USB chargers should be isolated? How about desktop computers, are they violating this regulation? Or grounded laptop chargers? Does the regulation also specify isolation between multiple outputs on a multi-output charger? What voltage does the regulation say the shield on USB A and C plug is rated for?Using USB cables for something that might be floating hundreds of volts above ground sounds like a recipe for disaster to me. I'd leave the flap covering the USB connector unconditionally closed while measuring anywhere near dangerous voltages (like on the same PCB that might also carry mains).