I opened up my DMMs - Page 1
Forum section: electronics / testgear

author: LeoTech
author_rank: Regular Contributor
timestamp: February 09, 2018, 08:15:53 pm
content: Hey community,So, during my time on this forum and as a viewer of Dave's content I have seen a lot of complaining about the 'quality' of lower priced DMMs, so as i own two lower priced multimeters I decided to open them up and have a look. Well actually, the original reason for opening these was to see if I could re-calibrate them, but anywho...The first i opened was a ISO-tech IDM 72, and to be honest: It wasn't good quality, but way better than expected. (See attached picture)Although the fuse wasn't in its own compartment, it was indeed pretty decent, compared to the other DMMs. Besides that, it was pretty neat, and seemed well designed. Some cables have even heat shrink attached.The second DMM was a TE.Electronic MS8264, it seemed really well designed as well, taking price point into account, although i couldn't locate the fuse, hmmm......The input terminals were attached well to the PCB, and it even had a shunt resistor!Both PCBs were neatly laid out, and the components used seemed 'good quality' and the manufacturing showed no 'rushed stages' nor any errors.So, although I completely agree on the fact that these are not 'perfect', they are still pretty decent, compared to what people normally say about these lower priced DMMs. Although i highly doubt that they are CAT III rated.I would like to know what you people think about these? Because I would say that they are good enough for the average hobbyist and maker for taking quantitative measurements? Or is it just me who miss-judges these, and has way to less experience in the field to argue/comment on this?LeoAttachment:https://www.dropbox.com/s/tka9lnex2a6ys9e/ISO-tech%20IDM%2072.JPG?dl=0

author: PedroDaGr8
author_rank: Super Contributor
timestamp: February 09, 2018, 09:34:16 pm
content: The MS8264 is a Mastech piece of crap, if it hasn't undergone revisions it uses a polyfuse (yellow thing bottom right) as its fuse. That and a couple wimpy PTCs round out its safety protection. No separation between high current or high voltage traces and other parts of the meter, not thought to anything but quick and cheap. This thing wouldn't even pass CAT I standards, let alone CAT III. This is a very low budget meter and represents near the bottom of the barrel for Mastech stuff, the only step down would be the 830B type multimeters.The Iso-tech IDM 72 on the other hand is a solidly build meter. Nice beefy input protection, well designed layout, safety and accuracy in mind clearly. The OEM appears to be APPA as it looks VERY similar to several of their meters. I am not sure which one it is based on though or if it was custom designed by APPA for RS.

author: Electro Detective
author_rank: Super Contributor
timestamp: February 09, 2018, 09:54:39 pm
content: Cheap meters in pairs (to verify they work and work properly) have their place and many usesWhere they can fail miserably, is when going into high voltage or high current situations,where there may be an underlying fault condition, or user error setting up the meter, or a probe prod slip up etcThe better meters may blow a fuse or internal link, or go south as the manufacturer planned, and bite you in the pocketthe cheap meters may end up costing you an arm and a leg in many respects

author: Fungus
author_rank: Super Contributor
timestamp: February 09, 2018, 10:40:39 pm
content: Quote from: LeoTech on February 09, 2018, 08:15:53 pmHow much did it cost? It looks quite solid to me.

author: joeqsmith
author_rank: Super Contributor
timestamp: February 10, 2018, 02:17:17 am
content: ISO-tech IDM 72, traces running between the switch pads. I wonder if they get cut like that cheap AN8002. Cap tacked in place above R11? What's up with the unmarked cap in the center? Shared current input. I don't see a second fuse. Maybe a polyfuse with some shrink over it?Switch pads looks beefy. Looks like they used TH parts for the clamps. I wonder how they would hold up. I wonder if SPG1 is the high energy clamp. I've never seen this package style before.

author: soundtec
author_rank: Regular Contributor
timestamp: February 10, 2018, 07:26:08 am
content: That looks like a nice bit of kit ,Its kinda funny alright that some who never went near anything more than 50 volts in their life cringe and complain about meter safety.With the best will and highest safety precautions possible you cant ever account for mishaps due to lack of knowledge.High Voltage is my bread and butter ,valve/tube amps are my thing ,I only ever managed to blow up one meter ,it was my first ,an Altai analog ,it never was a great meter for tube amp voltages either way ,but I fixed a lot of amps with it none the less .Eyes, ears and multimeter see most faults sorted for me , I have to admit Ive caught a dose of the metrology bug since joining up here and grabbed myself a 10,000 count plus meter ,way way more accurate than I need really .I do enjoy the multimeter destruction testing vids ,the contributors name escapes me just now ,just minor design changes which cost no more than a thought can make a world of difference in preventing internal flashover/arching.Anyroad ,respect the power (of electricity) and keep one hand in your arse pocket while probing high voltage rock n roll .Kindest.Oppps, speak of high voltage and Joe shows up ,has there been a meter that the test rig has failed to kill yet Joe ?

author: soundtec
author_rank: Regular Contributor
timestamp: February 10, 2018, 07:44:28 am
content: I do see some slight hairyness between the switch pads now you mention it alright , I just ordered in a Unitity 171b ,hopefully it gets Joe's 'hard to kill' seal of approval .

author: LeoTech
author_rank: Regular Contributor
timestamp: February 10, 2018, 10:48:09 am
content: Quote from: Fungus on February 09, 2018, 10:40:39 pmWell, i actually got if for free, so I do not know the price, and even a quick google search doesn't seem to help at all, wonder why?But if I recall correctly it was about 50 USD or so.Quote from: soundtec on February 10, 2018, 07:26:08 amYeah I thought the same, because as far as I know, most hackers and hobbyist never exceed this - including myself - so for me it is more than good enough in terms of safety - for now, where as precision is another argument.Leo

author: joeqsmith
author_rank: Super Contributor
timestamp: February 10, 2018, 04:12:47 pm
content: Quote from: soundtec on February 10, 2018, 07:26:08 amMore like speak of cheap meters and Joe shows up. My spreadsheet is still on-line. Several meters could not be damaged with ESD, the AC line test or the newer generator. These include:Brymen BM235, BM869s, BM319s, BM839Fluke 101, 107, 115, 17B+Gossen Metrawatt M248BHIOKI DT4252RadioShack 2200087UNI-T UT15CTo your question, to date the meters that have never been damaged are the Fluke 101, Fluke 115, Brymen BM235 and the Gossen Metrawatt M248B. Of course, the Gossen has a lot of other problems. The HIOKI DT4252 was never damaged electrically but the plastic barrier was having some problems. The Fluke 107 was exposed to the highest levels of any meter I looked at which is why it was damaged. The spreadsheet is really a better place to look.

author: Electro Detective
author_rank: Super Contributor
timestamp: February 10, 2018, 06:40:34 pm
content: Quote from: soundtec on February 10, 2018, 07:26:08 amThose 'some' people stranded in the50 volts zonemay one day encounter a 500v charged capacitor or two (in series lol) and find cause to 'cringe n complain about meter safety'or a friend borrows their meter to test a car battery, or 240 volt mains... with the leads still in the current sockets from an Arduino Adventure

author: soundtec
author_rank: Regular Contributor
timestamp: February 10, 2018, 07:41:31 pm
content: Thanks Joe ,Do most companies send you meters for free or do you have to pay for it out of your own pocket ?The test videos remind me a bit of something called the Milgram experiment,but for multimeters instead of people.I certainly have gotten zapped by undischarged 500volt caps a few times ,no fault of the meter, luckily not across the chest either which would be way more serious.The nerves would be a bit jangled after such events alright , Ive heard it said by some that the reflex action when you get shocked can be even more dangerous that the shock itself .Anyways be carefull out there ,