Mains measurement with PicoScope 5000 - Page 1
Forum section: electronics / testgear

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 02:44:43 pm
content: I am in the market for a scope that I can use for a number of purposes, from serial bus to VFD output. I am looking at thePicoScope 5244D, but the manual mentions that it is not for mains use.But shouldn't a quality CAT II 1:100 probe be able deal with this issue, measuring nothing more than 600Vac. Am I missing something here?

author: 2N3055
author_rank: Super Contributor
timestamp: April 16, 2020, 02:58:08 pm
content: Quote from: Damascus on April 16, 2020, 02:44:43 pmYes, you are missing at least two dozen discussions on that topic on this very forum.Search for it...google "site:eevblog.com measuring mains with scope"

author: rvalente
author_rank: Frequent Contributor
timestamp: April 16, 2020, 02:59:37 pm
content: For messing with a VFD and other high energy stuff please, get yourself an isolated scope or, at least, a differential probe.Because it is safer and you'll need to probe with different grounds.Although, if you're really looking forward with PICO I would additionally to the the differential probe get a USB isolator, its a must.Checking briefly the PICO I've seen its non isolated usb 3.0 so I believe the isolator would not be cheaper and easy to findDo you need the set of fetures from the pico? For VFDs I would get a used hand held scope (because they are the cheapest channel isolated, I've myself a THS720A, its pretty old, slow and very very low memory depth, but its isolated and CAT rated).I would suggest looking for a used U1610A or U16xx series, Siglent also have a isolated channels and are cheaper than the THS3000Ooohh, the TPS2000 is also channel isolated as long as I remember, low density memory but, safe.

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 03:56:59 pm
content: I can isolate a PICO, just run the pc on battery.I want the serial decoding features not available with handheld.

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 03:59:38 pm
content: Quote from: 2N3055 on April 16, 2020, 02:58:08 pmFunny, I didn't see one about the note in the Pico manual.

author: rvalente
author_rank: Frequent Contributor
timestamp: April 16, 2020, 04:06:03 pm
content: Quote from: Damascus on April 16, 2020, 03:56:59 pmI believe this would be very limiting and prone to error but, its a way.Just out of curiosity, why are you willing to pay 2K USD on the pico?Is it because of the vertical resolution (is it true resolution or over sampling?)

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 04:09:15 pm
content: Portability, 200MHz, serial decoding in software (manchester)

author: rvalente
author_rank: Frequent Contributor
timestamp: April 16, 2020, 04:11:22 pm
content: Great!So have your doubt been resolved?

author: engrguy42
author_rank: Frequent Contributor
timestamp: April 16, 2020, 04:30:28 pm
content: I agree. No need to waste time searching the forum. Simple answer:Get a differential probe.They have meghoms of input resistance, and generally also an optoisolator to isolate the USB.Disconnecting case grounds is a bad idea.

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 04:43:53 pm
content: Quote from: engrguy42 on April 16, 2020, 04:30:28 pmThis is my issue. Why? I've used a handheld 199C on mains before, without differential probes, and no case ground to disconnect if I wanted to.What's the difference between floating a Pico and using a handheld that Pico would make a statement 'not for mains'.

author: engrguy42
author_rank: Frequent Contributor
timestamp: April 16, 2020, 04:49:21 pm
content: I'm not familiar with a Pico, but if it has a metal case with an earthing prong connected to the mains then that earthing is there for your protection.If it has a plastic case with no accessible metal, and no 3-prong mains connection and no USB to earth connection, then maybe you don't need it. For example, if it's handheld like a plastic multimeter, and powered by battery, for example, then yeah, you probably don't need a differential probe.But I'm assuming since the mfr said don't use it on mains they have a reason.

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 04:57:51 pm
content: From what I see, it has rubber standoffs, powered by USB(2 chan), and a seprate ground tab. Almost as if it is designed to be floated.

author: rvalente
author_rank: Frequent Contributor
timestamp: April 16, 2020, 04:58:56 pm
content: Quote from: engrguy42 on April 16, 2020, 04:49:21 pmProbably the equipment was not tested/rated for CAT because there is a low degree or no protection at allIMHO: Anyway, I've never been a fan of instruments without screens and buttons. If its for field use the last thing I want is another brick attached and dependeble of my computer. You can't easily bring a PC + device to a cabinet to troubleshoot a VFD and this equipment is not adequate for field service.Anyway with 2 grand as budget I would get anything but a pico scope, maybe If i needed the 16 bit precision, but for what?

author: engrguy42
author_rank: Frequent Contributor
timestamp: April 16, 2020, 05:05:18 pm
content: Quote from: Damascus on April 16, 2020, 04:57:51 pmTry emailing the mfr and see if they agree with you.

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 05:11:18 pm
content: Quote from: rvalente on April 16, 2020, 04:58:56 pmIn my business, all I do is bring a PC and test gear to cabinets inside and outside in all weather conditions - that's what it's for. And that Pico fits in a computer bag real easy. Show me something with 200MHz and Manchester code that you would buy.

author: engrguy42
author_rank: Frequent Contributor
timestamp: April 16, 2020, 05:26:52 pm
content: Do you honestly expect people here to tell you "yeah, ignore the manufacturer's recommendations" and plug your probe into the mains?? Seriously?All because your company doesn't want to spend $180 on a differential probe?

author: Damascus
author_rank: Newbie
timestamp: April 16, 2020, 05:37:55 pm
content: No, I expected some intelligent and informed feedback by people experienced and knowledgeable in the field.As opposed to answers from people with no experience or idea of the equipment they are talking about. This is you.This place is worse than stack overflow. Adios.

author: 2N3055
author_rank: Super Contributor
timestamp: April 16, 2020, 05:38:11 pm
content: Quote from: Damascus on April 16, 2020, 03:59:38 pmThat is why you have me.Seriously, do the search. This is already long topic with no answers. It's done to death here, together with all the reasons, and which are good probes etc.I wrote about it many times, and won't repeat myself. Also many users here feel like that , and don't even want to write explanation why. It's tiresome repeating stuff all the time.Also you seem to post here because you wanted us to confirm you're right with your opinion, not to have right answer. Don't float Picoscopes. You and Pico might survive it, but not every time, all the time. PC has exposed GND on all connectors, Pico has exposed GND on all BNCs. Most importantly, all BNC on Pico are connected together.Best scope for that kind of work is one with isolated channels (from scope and each other)Using High voltage diff probes makes all those problems go magically avay, on all scopes, all the time.Pico is superb for that work, because of custom probes.As far as Picoscopes, i love them, have two. They have many possibilities other scopes don't..All the best,

author: engrguy42
author_rank: Frequent Contributor
timestamp: April 16, 2020, 05:48:45 pm
content: First of all, "worse than Stackoverflow"Wow. That's hitting WAY below the belt.Secondly, a great philosopher once said, "People believe what they want to believe. Facts are irrelevant".Let's just hope in this case it doesn't result in a foolish, unnecessary injury.

author: rvalente
author_rank: Frequent Contributor
timestamp: April 16, 2020, 06:06:58 pm
content: Why sometimes people (usually with very low posting counts) come here to ask stuff as this is a consulting place, where answers must be given accordingly to what they want to read?I can't get this nonsense... anyway, i'm off here.