Würth mini multimeter - Page 1
Forum section: electronics / testgear

author: meeder
author_rank: Regular Contributor
timestamp: March 25, 2015, 07:58:09 pm
content: A company which build medical devices gives the following multimeter to it's engineers.It is the Würth 0715 53 390 mini multimeter, it features four settings uA, mA, V and a combined resistance, diode test and continuity test (which is dead slow).Besides that it features a built in flashlight and a non-contact voltage detector (the only safe bit about this multimeter).This thingy is supposed to be CAT III rated at 1000V, I am not sure how they will ever get that into a package this small.On the right side however it states that it can take 600V with a resettable fuse. Besides the battery cover it is not possible to open the unit in a non-destructive way.The test leads are rated CAT III 1000 and CAT IV 600VThe backside doesn't reveal anything usefulTo see how small it really is I took a picture together with some well known meters so you can judge the sizeThe Würth website shows a "nice" image of someone using this meter but I would never go near these kinds of voltages with a toy like this (the display reads 386V).Upon talking to people from that company they just shrugged and told me "it is safe to 1000V"... Yeah right...Granted, the devices the engineers work on are mostly 24V but there is a pretty beefy mains section as well to power a compressor, PC and a robot controller.Has anyone seen this thing before or has anyone taken one apart?

author: Lightages
author_rank: Unknown
timestamp: March 25, 2015, 08:02:57 pm
content: That looks like a pretty cool pocket meter. I would love to see one. I agree though, CATIII/1000V seems very optimistic.

author: meeder
author_rank: Regular Contributor
timestamp: March 25, 2015, 08:16:12 pm
content: Just found out that Mastech sells the same thing (little bit different, with some more functions and 4000 counts instead of 2000 counts) with part number: MS8232B and they claim CAT III 600V which is closes to the truth I guess but when you look at pocket meters from more reputable manufacturers they mostly claim CAT II 600V.And yes, Extech sell the same thing as well as the Extech DM220. Extech also claim CAT III 1000V and CAT IV 600V and what is strange is that Würth claims 2000 counts and Extech claims 4000 counts and the Extech looks exactly the same as the Würth.

author: Balaur
author_rank: Unknown
timestamp: March 25, 2015, 08:17:04 pm
content: It's an Extech DM220 that has been rebadged extensively.I have the same under the name of Chauvin-Arnoux CA703. Expensive and worthless. Slow and starts by default in AC (which make sense since it's an electrician multimeter)Made me avoid Chauvin-Arnoux products like plague. Which is too bad because they have some 100+ years history and they originated not that far from my city.Oh well, if you pretend to have all that experience and you are that proud of your history, attach your name to worthier stuff!

author: retiredcaps
author_rank: Super Contributor
timestamp: March 25, 2015, 08:38:52 pm
content: CEM Instruments is likely the original manufacturer.http://www.cem-instruments.com/en/pro/pro-497.html

author: meeder
author_rank: Regular Contributor
timestamp: March 25, 2015, 08:51:22 pm
content: That clears the 2000 vs 4000 counts spec as well. The Würth is probably the CEM DT-118 and the Extech DM220 is probably the CEM DT-118B.

author: PeterFW
author_rank: Frequent Contributor
timestamp: March 25, 2015, 09:05:59 pm
content: Quote from: Lightages on March 25, 2015, 08:02:57 pmThe next best price i could find was 50€ but for 60€ i get a fluke 101 with leads that can be replaced if damaged, capacitance/frequency measurement and a carry case.But without current measuring capability... there is allways something

author: Fungus
author_rank: Super Contributor
timestamp: March 25, 2015, 09:08:59 pm
content: Fluke 101 seems a much better bet if you're not worried about measuring amps.

author: meeder
author_rank: Regular Contributor
timestamp: March 25, 2015, 09:09:14 pm
content: I have seen prices from around €20 for the CEM branded version.

author: Fungus
author_rank: Super Contributor
timestamp: March 25, 2015, 09:24:48 pm
content: Quote from: meeder on March 25, 2015, 09:09:14 pmWith voltage detector and flashlight?All that's missing is a transistor tester...

author: meeder
author_rank: Regular Contributor
timestamp: March 25, 2015, 09:26:23 pm
content: Quote from: Fungus on March 25, 2015, 09:24:48 pmIt's IP54 as well!

author: Lightages
author_rank: Unknown
timestamp: March 25, 2015, 09:59:38 pm
content: Oh well, rebadged CEM is usually crap.

author: dannyf
author_rank: Super Contributor
timestamp: March 25, 2015, 10:41:25 pm
content: QuoteSo you think you have bought your meter from a fraudulent company?

author: meeder
author_rank: Regular Contributor
timestamp: March 25, 2015, 10:46:02 pm
content: Quote from: dannyf on March 25, 2015, 10:41:25 pmNo I didn't buy it, it is a company handing out these things to their engineers that are out in the field. Nothing fraudulent about that.

author: macboy
author_rank: Super Contributor
timestamp: March 27, 2015, 01:06:22 pm
content: Quote from: blueskull on March 25, 2015, 10:37:50 pmConsider this: It only has a 200 mA range. So with 200 mA and a 2 V burden voltage, it would have a 10 ohm shunt (estimated; no spec in the datasheet). That would limit current to "just" 100 A if set to mA range but probing a 1000 V circuit. With series impedance that high, safety is significantly improved even on low impedance circuits like CAT III or IV. Current of 100 A should be breakable by more conventional means than a HRC fuse. A typical handheld meter with a 10 or 20 A range will have a shunt with milliohms of resistance (The Fluke 87V has 0.030 Ohm for example). This does not limit the current so well with 1000 V across it. Use of HRC fuses is then the only reasonable option.

author: Marco
author_rank: Super Contributor
timestamp: March 27, 2015, 05:37:46 pm
content: A quick search for 1000V PTCs doesn't show anything which could withstand 1000V without adding way too much resistance.In theory they could use something like a combination of MOSFETs and TVS I guess, but I think it more likely that the 1000V rating is bullshit on the current range.

author: macboy
author_rank: Super Contributor
timestamp: March 27, 2015, 05:45:53 pm
content: Quote from: blueskull on March 27, 2015, 03:03:54 pmMeasuring a voltage source on current range is one fault mode; assuming that a multi-kV surge occurs simutaneous to that would be a double-fault type of scenario. Anything can fail when you compound fault after fault after fault... Any Class 2 electronics can have a metal case that is double insulated from mains voltages. But what if both levels of insulation fail simultaneously? You can die of course. That doesn't mean that all Class 2 electronics are unsafe. What about Class 1 with a grounded case, but a lifted ground... same thing. If you consider multiple simultaneous failure modes, many things 'can' be unsafe.Personally I wouldn't use a meter like that on anything but low voltage DC on the bench, but I am playing devil's advocate here and presenting the argument that lack of HRC fuse does not instantly imply unsafe in all cases. The fact is that we don't know what the protection looks like. But we know that it doesn't have anything like that ~ 0.03 Ohm path for "oops" current that most other meters have when accidentally left set up for measuring current.

author: Marco
author_rank: Super Contributor
timestamp: March 27, 2015, 06:45:51 pm
content: Quote from: blueskull on March 27, 2015, 03:03:54 pmAFAICS a HRC fuse is not what's needed to make a meter safe for this kind of voltage on ACV/DCV. With 10 MOhm input resistance 2.3 kV puts a measly half Watt into the meter ... hardly worth sacrificing a fuse for.

author: meeder
author_rank: Regular Contributor
timestamp: March 27, 2015, 07:51:12 pm
content: Well I managed to get my hands on one and I found a way to take it apart in a non-destructive way. There was single hidden screw which held everything together.I have attached some pictures of the inside to this message.

author: Lightages
author_rank: Unknown
timestamp: March 27, 2015, 08:06:27 pm
content: Except for the PTC "fuse", that looks like a reasonably built pocket meter. Does it meet its CAT ratings? I don't think so and specifically under the new rules absolutely no. The "fuse" needs to be rated at least 1000V too. Keep the limitations in mind and I think it a nice pocket meter.

author: meeder
author_rank: Regular Contributor
timestamp: March 27, 2015, 08:17:23 pm
content: I told them that it was fine on the low power 12V and 24V rails but that they should not use it at the 230V mains rails.The thing is that most of their engineers are mechanical guys who sometimes don't even know what they are doing when using a multimeter so the risk of someone having it in the mA range when trying to measure a voltage is quite high.I suggested to get a Fluke T90 or something equivalent for testing mains voltages, it has a nice simple LED indicator and is reasonably foolproof.

author: retiredcaps
author_rank: Super Contributor
timestamp: March 27, 2015, 08:37:52 pm
content: Thanks for sharing some teardown pictures.For input protection, it has 2 PTCs, one green looking like MOV, and possibly one power resistor?The last picture definitely shows it is a CEM DT-118L. As such, it has the traditional crappy CEM solder quality with respect to the probes, tact switches and usage of cheap Chong brand electrolytic capacitors.

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: March 27, 2015, 08:52:02 pm
content: am shocked ... didn't expect company like wurth to give such low price multimeter to their engineer.

author: meeder
author_rank: Regular Contributor
timestamp: March 29, 2015, 09:57:02 pm
content: Quote from: hamdi.tn on March 27, 2015, 08:52:02 pmno, Würth isn't doing it.

author: max666
author_rank: Frequent Contributor
timestamp: March 29, 2015, 10:34:49 pm
content: I don't mind some Würth rebadging

author: fubar.gr
author_rank: Unknown
timestamp: March 30, 2015, 06:07:44 pm
content: I have a similar Wurth meter. It is almost identical to that, but has no current measurement capability, only voltage.I'll post some teardown photos tomorrowQuote from: meeder on March 27, 2015, 07:51:12 pmWhere's that screw?

author: meeder
author_rank: Regular Contributor
timestamp: April 01, 2015, 09:04:07 am
content: Quote from: fubar.gr on March 30, 2015, 06:07:44 pmOn the backside there is the black plastic insert where you can store the probes. If you get that piece out (at first I though it was glued but it wasn't) you get to the screw.You have to remove the sticker on the front because it keeps the two halves together (I lifted it up to just below the seam and I could stick it back without damage).

author: fubar.gr
author_rank: Unknown
timestamp: April 01, 2015, 09:17:40 am
content: Thanks!BTW, since it is rated as CATIII 1000V, why does it say 600V max on its side?

author: meeder
author_rank: Regular Contributor
timestamp: April 01, 2015, 10:43:24 am
content: Quote from: fubar.gr on April 01, 2015, 09:17:40 amBecause the "fuse" is rated 600V. The same as the UNI-T's which only have 250V fuses (ceramic if you are lucky, glass if not).I wouldn't go near mains voltages with both though