EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)

[Yago]

Absolutely. There is a reporting system in Europe to counter the practice. Flawed products have to be removed from the market. Not sure about fines.

Bet Maplin wouldn't agree to open up a meter and see what's inside!

[zapta]

It's not about what line voltage you use, it's about the energy capacity behind it, and the ability for high energy overvoltage transients to happen.

Any way of testing it? This will add spice to your videos, having cheap meters going in flames.

[rsjsouza]

I agree with others that lying about CAT ratings and even voltage limits is inexcusable.

One thing that strikes me is the hodge podge of processors in this meter. If Lightages' schematics are accurate, the Cyrustek is the main meter, the MSP430FE425 is the wattmeter and the MSP430F149 does... LED and button management?!? These two MSPs are capable of much more, and I can't help but wonder that over the years and versions the original design simply became a collage of circuits and devices that increased the overall price of the BOM, which conversely required cost cutting measures on other areas such as the input protection.

[Hootch]

It seems that there are different versions of this multimeter available. My UT71E has two HRC-fuses.

[max_torque]

It wouldn't be half as bad if they were just honest about the safety ratings- most people just don't need CatIV, but manufacturers seem obsessed with a "me-too" game of dishonestly copying competitors' specs and markings.

This x10 ^^^^


The issue for me is the blatant lying on the safety ratings on the meter case.  Now, i'm sure that You, or I, with lots of electronics experience would rightly, and with prior knowledge, take one look at such a meter and go "NO WAY" to using it on anything high voltage, but for every one of us, there are 100million other people who are not lucky enough to know or have learnt any better.
  For them, this IS a significant safety issue.  For example, anyone could say buy one of these meters secondhand anywhere, get it home, and go "hmm, i wonder if i can measure the mains voltage in my house" and take a look at the front, see the words "600V" and think, hey, excellent, this meter is perfect for that.

This is why CAT ratings were introduced, to help none expert users choose test equipment that is properly rated for the task.


So, once this basic issue is found, i couldn't care less if the inside of the meter is machined from solid gold, and uses unicorn horn hybrid un-obtainium trimmers or what ever!

 So, Uni-T, fix the basics, and THEN we can discuss if the meter is "value for money" or not.

[ptp170]

Absolutely. There is a reporting system in Europe to counter the practice. Flawed products have to be removed from the market. Not sure about fines.

Bet Maplin wouldn't agree to open up a meter and see what's inside!

Maplins remove and edit reviews people make on their website so not a chance in hell they're going to be honest about self reviewing multimeters!

One chap got really annoyed about a jump start battery pack so did a YouTube video on it.. quite funny as he includes the ridiculous quotes that Maplins used when 'justifying' themselves..

[Wytnucls]

It seems that there are different versions of this multimeter available. My UT71E has two HRC-fuses.

Yep. You have the more expensive 1KV European version. No independent testing though, so who knows if it meets the regulations.
And your MELF resistors are straight! 

[Wytnucls]

The RAPEX system doesn't work all that well. Only a handful of meters have been withdrawn so far:

http://ec.europa.eu/consumers/safety/rapex/alerts/main/index.cfm?event=main.search

(Type multimeter in the search area and tick all the relevant years)

[Wytnucls]

I agree with others that lying about CAT ratings and even voltage limits is inexcusable.

One thing that strikes me is the hodge podge of processors in this meter. If Lightages' schematics are accurate, the Cyrustek is the main meter, the MSP430FE425 is the wattmeter and the MSP430F149 does... LED and button management?!? These two MSPs are capable of much more, and I can't help but wonder that over the years and versions the original design simply became a collage of circuits and devices that increased the overall price of the BOM, which conversely required cost cutting measures on other areas such as the input protection.

Actually, the basic design hasn't changed much at all. Bean counters probably had their say when it came to final component selection.

[Maxlor]

As for independent testing, here's the relevant page: http://etlwhidirectory.etlsemko.com/WebClients/ITS/DLP/products.nsf/4c8700f3b75987a08525777700583333/bb3d3302a13f93f086257ddd000985fc?OpenDocument

Of course, the 71 series is not there

Curiously, I see the 61 series on there, when just on account of the british fuses in Dave's (and mine) it'd fail the testing. It must be the newer improved version.

As for C.E.M., yup, they have some meters listed too: http://etlwhidirectory.etlsemko.com/WebClients/ITS/DLP/products.nsf/4c8700f3b75987a08525777700583333/10c795564af71fa185257b58000c8b3a?OpenDocument
These are some of their simpler models, none of their more expensive models are listed. Basically, it's just the 9-digit meters here: http://www.cem-instruments.com/en/pro/nsort15-2.html

[timb]

LOL "RAPEX"


Sent from my Smartphone

[mikro]

That is some poor manufacturing. Is there a solder bridge on that trimmer, which soldering side is shown at  12:33?

[Wytnucls]

It's not about what line voltage you use, it's about the energy capacity behind it, and the ability for high energy overvoltage transients to happen.

Any way of testing it? This will add spice to your videos, having cheap meters going in flames.

Testing the amp side is fairly easy, if you have access to a beefy 2000V supply.
Test with blown fuses in place for one minute to check for arcing.
Other ranges are more difficult to test, requiring high voltage and timed pulsed delivery. The meter doesn't need to function properly afterwards. The enclosure should be able to contain the damage though and no harm done to the user. Testing with constant high voltage and low source resistance doesn't prove anything and would defeat most multimeters.
Creepage and clearance should also be measured for compliance.

[Tepe]

LOL "RAPEX"

RAPid EXchange

[Tepe]

Mains adapter is suited only for EU

Schuko has nothing to do with the EU.

[Tepe]

Mains adapter is suited only for EU

Schuko has nothing to do with the EU. It will fit neither this, at least not with a functional PE connection

nor this (same issue)

and definitely not this

[PChi]

I agree with Dave. I wasted a couple of hours probing a relatively high impedance circuit (a few hundred kohms) with a Tenma Multimeter only to find that the readings were being corrupted by mains hum. This was on a battery powered circuit so it was just random pick up by the meter. Ones based on the old 7106 / 7107 parts could be very good at rejecting hum but not the Tenma. If you are aware of the limitations the price isn't bad but you aren't buying a quality meter. All the miniature  presets don't inspire confidence in the long term stability. With test equipment the unwritten specifications are also important.

[ctz]

Here's the innards of a Tenma 72-7730A (€93), which is Farnell's whitelabelling of a UT71B (€105).

[Wytnucls]

Electromagnetic interference is quoted for 1V/m and below: Specified accuracy+5% of range. I seem to remember the Fluke 87 V was having an issue with interference too.

[mij59]

It seems that there are different versions of this multimeter available. My UT71E has two HRC-fuses.

Bought my UT71C from Reichelt, same fuses as yours, it came with some kind of compliance note, don't remember what it was about.

[Lightages]

BTW the safety issues with this meter has been known and published here for years.
https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/
and a quick search for UT71E would have brought up almost all the issues with it too. I was actually very surprised to see one in Dave's hands for a review after its history here.

[JoeLaBidouille]

In Europe, the UNI-T models are also sold under Conrad brand.
The Conrad VC920 is based on the same platform of the UT71 series.
Same PCB, same form factor... only a small difference for the color.

I took two pictures of this multimeter (red PCB)
In mine, the AD636 is a TO100 package.
At the bottom, two “thru the hole” resistors are used.

Always in UNI-T, I took a weird soldering picture of a UT61 (Conrad VC830) with a green PCB.

[parbro]

BTW the safety issues with this meter has been known and published here for years.
https://www.eevblog.com/forum/testgear/a-list-of-multimeters-that-do-not-appear-to-meet-their-claimed-safety-specs/
and a quick search for UT71E would have brought up almost all the issues with it too. I was actually very surprised to see one in Dave's hands for a review after its history here.

And yet the meters still remain for sale. What does that tell you about the ethics of UNI-T and their general regard for the customer?

[Nerull]

this way clearly a rant , can't say this is an objective review , we all know it's cheap product that do the job for low end application, as poor engineering, i think who ever built this is capable of designing a good one and uni-t is capable of manufacturing a high level multimeter BUT if everyone do that , no one will be able to buy a 15$ meter working for 4 years now.
so yeah they suck but ...they suck for a purpose.

 i think the spring is connected to the case shielding (not those for the buzzer) , so nothing wrong if it touch the shielding metal mounted in pcb.

Why is everyone throwing around the "Cheap $15 meter" excuse for a $180 meter? You can buy cheaper meters which do actually stand a chance in hell of meeting their ratings. Price isn't an excuse in this price range.

[jaxbird]

I guess Dave is happy that he is not in the US, otherwise the FTC would be all over his ass with the lack of clear disclosure etc. especially with their tightened rules for internet/youtube reviews.