Chinese mutlimeter drama - Page 1
Forum section: electronics / testgear

author: FlevasGR
author_rank: Regular Contributor
timestamp: March 22, 2015, 12:59:01 pm
content: Today my new multimeter (UNI-T 136B) arrived and happily i inserted a battery to test it out! It didn't go so well. First of all the screen was disconnected and i had to push the switch hard in order for it to make contact. I tried to open it up and see what is going on. Everything seemed to be okay so i closed it up.I did some test to see how it goes. Here are the results:DC VoltageFrom a cheap 5v and 3.3v power supply i have5v => 4.90v3.3v => 3.27vFrom a custom power supply i made with a 5v regulator5v => 4.97vFrom 9v wall adaptor9v => 9.34v (it's actually higher)Resistors150R => 149R1M => 1M2.2K => 2.19K1K => .99K10K => 10.01K22R => 22.2R220R => 220.2RCapacitors10uF => 10.16uF1uF => 1.1494.7uF => 4,748uFAccording to this video:the mesurents on DC are a bit off. What should i do with it? I mean its okay to be a bit off for a 15euros multimeter but the screen problem is terrible. Its not that hard to get it back to work with a press on the switch but why? It's brand new. I dont want malfunctions on my stuff. I cal always file a dispute and get my money back but i would like to work with the seller to find a solution.Ebay link:http://www.ebay.com/itm/271718053645?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

author: Lightages
author_rank: Unknown
timestamp: March 22, 2015, 01:04:12 pm
content: I am sorry to see you have troubles. This is the problem with really low end meters. Their quality control is going to be non-existent. Contact the seller and ask for a replacement. BTW, that video is mine.

author: xrunner
author_rank: Super Contributor
timestamp: March 22, 2015, 01:10:42 pm
content: When you say you "did some tests" I take it you compared the meter with a known good and calibrated meter, and not just your feelings that the readings you took didn't seem accurate enough? For example many wall adapters do not put out the voltage printed on them until a load is applied.

author: FlevasGR
author_rank: Regular Contributor
timestamp: March 22, 2015, 01:13:04 pm
content: Quote from: Lightages on March 22, 2015, 01:04:12 pmhaha the video was awesome. From the entire youtube your video made me buy this meter

author: FlevasGR
author_rank: Regular Contributor
timestamp: March 22, 2015, 01:14:52 pm
content: Quote from: xrunner on March 22, 2015, 01:10:42 pmWell, i dont have much experience so i took the 2 power supplies as granded. I dont have professional calibration equipment like the voltage standards since i'm a hobbyist but now i think i really need them!

author: xrunner
author_rank: Super Contributor
timestamp: March 22, 2015, 01:22:50 pm
content: Quote from: FlevasGR on March 22, 2015, 01:14:52 pmYou can't take them for granted. I really doubt very seriously that the 9V wall wart is putting out 9.000 volts. The meter is probably mostly correct but again you need to compare things to a standard of some sort.

author: FlevasGR
author_rank: Regular Contributor
timestamp: March 22, 2015, 01:56:15 pm
content: Quote from: xrunner on March 22, 2015, 01:22:50 pmYep, you're right! Even if the readings are well within specs the screen problem is annoying

author: amyk
author_rank: Super Contributor
timestamp: March 22, 2015, 01:56:38 pm
content: Quote from: xrunner on March 22, 2015, 01:22:50 pm+1No indication on the tolerance of the resistors and capacitors you used either. They could be far from their actual values and the meter similarly so.The UT136 is only accurate to 0.8% on the voltage ranges and between 1-1.5% for resistance, so a sufficiently accurate set of references to verify it won't cost so much (relatively speaking.)

author: mrf245
author_rank: Regular Contributor
timestamp: March 22, 2015, 02:51:33 pm
content: Maybe use a FLUKE or other higher accuracy meter to compare test reaults with your meter.Resister measure readout was fine I think.

author: dannyf
author_rank: Super Contributor
timestamp: March 22, 2015, 03:08:35 pm
content: QuoteI would do nothing. More than sufficiently good for such a cheap meter.

author: FlevasGR
author_rank: Regular Contributor
timestamp: March 22, 2015, 03:37:22 pm
content: Quote from: dannyf on March 22, 2015, 03:08:35 pmWell, you're right. But the problem with the screen remains :/

author: cosmicray
author_rank: Frequent Contributor
timestamp: March 22, 2015, 03:57:37 pm
content: Another way to get a feel for the accuracy of the meter is to measure the voltage of a flooded lead acid battery, then have someone test the specific gravity of each cell. Assuming the battery has not sulfated, there is a relationship between the specific gravy and the no-load voltage. There are some caveats to this, but it mostly holds true.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: March 22, 2015, 06:12:54 pm
content: It looks like you need one of my DMM checkersAs others said, you cannot rely on supplies as references.

author: Wytnucls
author_rank: Super Contributor
timestamp: March 22, 2015, 06:29:08 pm
content: It is a very simple meter, with a simple range switch mechanism. It shouldn't be too hard to fix the intermittent connection, unless you're all thumbs. In desperation, ask for a replacement.