Cat 4 DMM with Polyfuse - Page 1
Forum section: electronics / testgear

author: zerobrain
author_rank: Contributor
timestamp: July 16, 2018, 01:46:26 pm
content: Hi,i came accross the new Owon DMM and was puzzled it uses only (!) a polyfuse for the mA current input.From my understanding this may work on a hobbyist´s workbench, but this DMM is advertised as "CAT3 and CAT4".Any ideas anybody?best regards

author: Fungus
author_rank: Super Contributor
timestamp: July 16, 2018, 02:59:55 pm
content: Which meter is it, exactly?It's notimpossiblefor it to be a low voltage CAT IV, just unlikely.It wouldn't be the first meter with a fake rating.

author: zerobrain
author_rank: Contributor
timestamp: July 16, 2018, 03:10:45 pm
content: It´s an Owon OW18B.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 16, 2018, 05:06:18 pm
content: I think Tekpower was selling that same meter. Maybe.Quote from: Fungus on July 16, 2018, 02:59:55 pmYou don't say. Why would a company ever misrepresent their product?

author: Kleinstein
author_rank: Super Contributor
timestamp: July 16, 2018, 06:14:33 pm
content: A lot of the cheap Chinese DMM have fake ratings. I don't know why, but that is what is observed.The odd thing is that for some meters (some UniT) there is a version with fake ratings and one for the EU with an at least reasonable rating that is considerable lower despite being essentially the same meter, if not higher grade fuses.It looks like there is a different meaning to CAT... in China. More like the Cat number corresponds to the number ofand. Maybe for China or India they get away with this and those cheap units find there way to others too. AT least most of the fakes are rather obvious. I am still waiting to see the a CAT V rating on a handheld.To have any trust in the CAT ratings it needs additional labels from test institutes (e.g. UL, GS, ...) - however these might be fakes too.

author: Fungus
author_rank: Super Contributor
timestamp: July 16, 2018, 08:08:31 pm
content: Quote from: Kleinstein on July 16, 2018, 06:14:33 pmCAT V? You might have to wait a while for that (at least until they invent that category)The Amprobe HD160C is CAT IV 1000V. Check out the fuse:More info:https://www.eevblog.com/forum/testgear/any-experience-with-an-amprobe-hd160c/

author: stj
author_rank: Super Contributor
timestamp: July 16, 2018, 09:43:20 pm
content: hey, the cat rating is about saving the user and not the meter.if you do something stupid - and i'v seen enough demonstrations of that recently on utube,if the meter turns to ash internally and the case contains it all, then i think it's a pass!!!every meter i'v had has imposed voltage limits on the current range that is far less than the maximum in V range - so why does the fuse - polymer,ceramic or whatever have to withstand 1000v??it doesnt, it's there to protect the tracks and shunt from overcurrent.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 16, 2018, 11:18:17 pm
content: Quote from: stj on July 16, 2018, 09:43:20 pmI've seen people post what you have just wrote about the tests that I run on them. That's how disconnected some people are. Just crazy. From a safety standpoint, it would be great to see an independent lab running meters.QuoteI think it's because the the standards require it. They are also not rated for 10KA break current and up to save the meter. It's all about safety.

author: Fungus
author_rank: Super Contributor
timestamp: July 17, 2018, 01:02:45 am
content: Quote from: stj on July 16, 2018, 09:43:20 pmBecause real people make mistakes.Real people put the leads on the wrong input jacks, etc.