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EEVblog => EEVblog Specific => Topic started by: EEVblog on February 07, 2015, 01:50:53 am

Title: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 01:50:53 am
Dave shows why Uni-T multimeters generally suck in this teardown (and a little bit of a review) of the $180 UT71E 0.025% accuracy multimeter with power measurement capability.
He also opens the UT71A, UT61E, and compares the input protection and rating with a Brymen BM257.

http://uni-trend.com/UT71E.html (http://uni-trend.com/UT71E.html)
MAX6190 Voltage Reference: http://datasheets.maximintegrated.com/en/ds/MAX6190-MAX6198.pdf (http://datasheets.maximintegrated.com/en/ds/MAX6190-MAX6198.pdf)
OP1177 Opamp: http://www.analog.com/static/imported-files/data_sheets/OP1177_2177_4177.pdf (http://www.analog.com/static/imported-files/data_sheets/OP1177_2177_4177.pdf)
Cyrustek ES51922 DMM chipset: http://www.cyrustek.com.tw/spec/ES51922.pdf (http://www.cyrustek.com.tw/spec/ES51922.pdf)
Holtek HT1621 LCD driver: http://www.ywslcm.com/Upload/tbDownload/2013-4-13_9_37_49.pdf (http://www.ywslcm.com/Upload/tbDownload/2013-4-13_9_37_49.pdf)
AD636 True RMS Converter chip: http://www.analog.com/static/imported-files/data_sheets/AD636.pdf (http://www.analog.com/static/imported-files/data_sheets/AD636.pdf)

EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck) (https://www.youtube.com/watch?v=i2Tkm21dI1g#ws)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mariush on February 07, 2015, 02:11:15 am
The weird ass adapter looks like it has the classic European mains sockets (well, most of Europe)

Only viewed the first 6 minutes so far but it seems you're unfair comparing and saying it sucks because it doesn't match the metrahit which is 4 digit in cost.

agree with the fuse choice...

4:50 : you can't wiggle those round metal things once the case is closed, the case would press on the metal keeping it in place.



Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 02:28:18 am
Only viewed the first 6 minutes so far but it seems you're unfair comparing and saying it sucks because it doesn't match the metrahit which is 4 digit in cost.

If a multimeter can measure power, then damn straight I'm disappointed if it can't measure that over all its ranges.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: iloveelectronics on February 07, 2015, 02:38:29 am
Dave, Uni-T has improved in their recent releases. Have a look at the newer 139, 171 and 181 series, they are built much better (to my untrained eyes anyway):

https://www.eevblog.com/forum/testgear/new-trms-uni-t-ut139c-dmm-is-available-now/msg289221/#msg289221 (https://www.eevblog.com/forum/testgear/new-trms-uni-t-ut139c-dmm-is-available-now/msg289221/#msg289221)
https://www.eevblog.com/forum/testgear/uni-t-ut171a-pictures-and-first-impressions/ (https://www.eevblog.com/forum/testgear/uni-t-ut171a-pictures-and-first-impressions/)
https://www.eevblog.com/forum/testgear/uni-t-ut171b-teardown/ (https://www.eevblog.com/forum/testgear/uni-t-ut171b-teardown/)
https://www.eevblog.com/forum/testgear/uni-t-ut181a-pictures/ (https://www.eevblog.com/forum/testgear/uni-t-ut181a-pictures/)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 07, 2015, 02:43:13 am
This was the first multimeter I posted about here in 2010. It arrived at 0.4% accuracy. After getting some "help"from Uni-T I got it working OK. If you want to know to see the schematic I have uploaded one. It appears that the UT71E is the worst deal amongst the UT7X series. There are some here who think the UT71D is a good deal. The UT71E is the same as the Voltcraft VC940, and the UT71D the Voltcraft VC960.

Uni-T has stepped up their game with their latest meters. The UT171X series, UT181, and the UT139C are much better for input protection.

It was because of my disappointment with the UT71E that I started down the rabbit hole of multimeter quality and safety.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Smokey on February 07, 2015, 02:43:57 am
Did you really actually buy that meter yourself like you implied in the video?  Are you saying you bought a piece of test gear from a company you know makes crap without even looking at the specs first?  Why would you even consider spending money on this if you know you already had far superior tools like the Gossen?  You couldn't get someone to give/loan you one for videos? 
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Chrisdlb on February 07, 2015, 03:15:09 am
Irrefutable evidence that Uni-T metres are shit, provided by dave, but yet still for some reason, people try to defend them!  :palm:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 07, 2015, 03:20:06 am
Irrefutable evidence that Uni-T metres are shit, provided by dave, but yet still for some reason, people try to defend them!  :palm:

Irrefutable that the old models of Uni-T are almost all shit. They really have improved things on some new models.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: george graves on February 07, 2015, 03:32:36 am
I'd expect a review of more then one Uni-T meter before claiming that all "Uni-T Meters Suck".  Sucks compared to what?  A meter costing 10x as much?  |O

I think the inner multimeter snob conosur in Dave came out a bit too much in this video. 

These are tools.  Tools cost money(that not everyone has).  Tools have limits.....knowing the limits of your tools is the more important thing.




Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: alter Ratz on February 07, 2015, 03:52:20 am
Hi all,

What I personally really hate about the UNI-T meters is that they are REALLY slow (not only continuity but also range switching). Has this gotten better with the new models?

Best regards,
Bernhard
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: sakujo7 on February 07, 2015, 04:50:48 am
Putting "CAT IV 600V" on a meter that clearly cannot meet that spec is just... :wtf:. Being overly optimistic about accuracy is one thing, but you do NOT mess with safety ratings.

It's a shame, because some of their meters (eg. the 61E) work reasonably well for the price point for low-voltage only. (I own one and occasionally use it for this purpose).

A suggestion for anyone still buying one: scrape off the Cat III/IV labels.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 04:56:40 am
 few things to note:
-UT71C/D/E is only 0.025% on the 400mV range. It's 0.05% up to 400V. The 400mV range probably bypasses some of those trimmers because the input impedance is different also (2.5Gohm vs 10Mohm).
I've had a UT71D for 3+years and a Fluke 87V for 2+years and both of them have always (and still do) agree within 5 counts on DC.
-To be fair the screw hole via going through the current trace doesn't reduce the trace width too drastically because of the plating inside the via and the meter is only rated for 5A continuous anyway. 10A rating is <10seconds with 15minute cooldown.
-The datasheet linked on youtube is for the ES51922 instead of the ES51966 which is a 44000/440000 count meter chip http://www.cyrustek.com.tw/spec/ES51966.pdf (http://www.cyrustek.com.tw/spec/ES51966.pdf)
-See if you can get a true 40,000 counts of resolution on resistance or current out of the UT71 ;) (spoiler: there is some kind of lower res + averaging funny business going on).

It's not that bad for the price really. Terrible as an everyday meter, good cheap companion to something like a Fluke 87 for electronics work.



Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Nerull on February 07, 2015, 05:02:52 am
"We've got ourselves a voltage reference, Maxim, If it's genuine." "I'm sure it is"

Why bother speculating it might not be genuine with one breath and then with the very next breath claim to be sure it is? What's going on?

Are you familiar with the term 'sarcasm'?

Quote
I don't personally care for the full-on shitcanning style you like using from time to time but I know it is popular.

It looks to me you started out with the intention of hammering the crap out of UNI-T and then as time went on you started to do a review and you got a bit more objective.

I'm no fanboy and if UNI-T claim some standard and then fail to meet it they deserve all the criticism you can heap on them. But for viewers like me who aren't intimately familiar with CAT ratings and PCB design to meet them it would be better if you toned down the noise and increased the explanation. The information IS there but you make it harder to distil it out.  The most useful part was when you started comparing with other examples of how things can be done better. A complete novice, who is more likely to consider a cheaper meter, would have an even harder time than I did filtering out the noise.

I kept wondering WHY you bought it in the first place. It sounded like you made a mistake and then wanted to throw a brick through UNI-T's front window.

The Uni-T pretends its rated for measurements directly on the outputs of a power transformer to a building, where there are no breakers to protect you and available current is north of 10000 amps (the limit for Class 3). If this meter were used on such a circuit improperly or experienced a spike it would quite literally explode in your hand and stands at least a half-decent chance of taking you with it. The rating is a complete lie, and if they're willing to lie about basic safety what else is wrong?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: feetwet on February 07, 2015, 05:12:05 am
I just wanted to say the EE man is back. It's nice to see Dave back in his rare form. I thought the review of the Uni-T UT71E was spot on. Nice work Dave.  :-+

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gonzoid on February 07, 2015, 05:15:28 am
https://www.youtube.com/watch?v=7fFjiLU5bF0# (https://www.youtube.com/watch?v=7fFjiLU5bF0#)
Quote
"Well, it's not a fluke. It's... you know what I mean."
Perfect timing to post this video. Advertisement at its finest!!  :-DD :wtf:

What I personally really hate about the UNI-T meters is that they are REALLY slow (not only continuity but also range switching). Has this gotten better with the new models?
If you happen to have one of the UT71 series, you can press and hold the blue button while powering on the meter to enable its 4000 counts mode, which is way faster.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 07, 2015, 05:39:38 am
Putting "CAT IV 600V" on a meter that clearly cannot meet that spec is just... :wtf:. Being overly optimistic about accuracy is one thing, but you do NOT mess with safety ratings.
And that would likely be why Uni-T has no official distributors and meters are only available through third-party sellers on places like Amazon, Craigslist, eBay, etc.

If Uni-T had official ties outside China, that would expose them to lawsuits for wrongful death or injuries attributable to failure to meet their safety rating claims if there has been any.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 05:46:56 am
If Uni-T had official ties outside China, that would expose them to lawsuits for wrongful death or injuries attributable to failure to meet their safety rating claims if there has been any.
Well they sort of do. Uni-T meters are sold under the "Tenma" brand through Farnell/Element14 for example. If anyone knows if the Tenma variants are built safer I'd be interested to know.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gonzoid on February 07, 2015, 06:15:43 am
Well they sort of do. Uni-T meters are sold under the "Tenma" brand through Farnell/Element14 for example. If anyone knows if the Tenma variants are built safer I'd be interested to know.
Appart for the case color, they don't seem to be any different according to the photos on http://sigrok.org/wiki/UNI-T_UT71x_series (http://sigrok.org/wiki/UNI-T_UT71x_series)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 06:20:00 am
I just don't get the pricing on these product's, either the middle men are
making a truck load [...]
And the same can't be said for particular Fluke and Agilent products? It's worth whatever people are prepared to pay for it, and people do buy them so what's the issue?

The UT71D which is basically what Dave reviewed minus the power measurement capability can be found for ~US$130 including international shipping. That doesn't seem like a half bad deal to me for a ~0.05% meter with USB datalogging and 10,000 points memory.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 07, 2015, 06:30:24 am
Well they sort of do. Uni-T meters are sold under the "Tenma" brand through Farnell/Element14 for example. If anyone knows if the Tenma variants are built safer I'd be interested to know.
I know there are variants of the UT61E which actually have MOVs. My UT61E is one of the no-MOV variant.

I just don't get the pricing on these product's, either the middle men are making a truck load [...]
And the same can't be said for particular Fluke and Agilent products?
At least, Fluke and Agilent are not carrying fake safety ratings.

Pop the back on most Uni-T multimeters and you quickly realize that safety ratings on them are blatantly criminally fake, which is a shame when minor PCB layout changes are often all that would be required to make them considerably safer - along with proper fuses which many models lack.

The lack of precision parts in something that claims to be a precision instrument is not exactly reassuring either, even if it has been trimmed into the next time zone to bring it somewhere within specs.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 06:58:01 am
Pop the back on most Uni-T multimeters and you quickly realize that safety ratings on them are blatantly criminally fake, which is a shame when minor PCB layout changes are often all that would be required to make them considerably safer - along with proper fuses which many models lack.
While I hope no one buys one of these meters hoping to use it on high energy circuits, you'd be kidding yourself to think that Uni-T are the only ones who put dubious ratings on their meters. Also depending where you live it may not be illegal to sell a meter that displays a CAT rating but has not been compliance tested.

Input protection is a non-issue for people who only plan to dick around on the bench with low power electronics anyway so many of us are willing to overlook the safety claims because Uni-T meters present a unique combination of features/value that very few others provide.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: bitshape on February 07, 2015, 07:02:28 am
Thanks for the nice Ranteview Dave!  :clap:


And really; buying a decent multimeter is not impossible, even for a Fluke in fluking-expensive Europe:

I bought a Fluke 287 for €270,- (incl.vat), and it was almost never used before and even with the original (half-empty) batteries in it. After buying I filled it with a set of rechargeable Eneloop-AA and it is still my best portable meter on the bench.
And some time later an new and unused 'open box' Fluke 28II for €200,- (incl.vat), and seriously, nothing wrong with it. This meter has now got a fresh set of Energizer Lithium-AA's for the long run. :-+

Thus it is possible for everyone to buy something safe & decent (read: not a €190,-* (http://www.batronix.com/shop/multimeter/multimeter-ut71e.html) Uni-Trash) for a 'decent' price, only if you are patient and regularly look on some closing-business-auction-sales and your local/online marketplace.

* Uni-T UT71E  incl.vat & delivery
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 08:16:00 am
"We've got ourselves a voltage reference, Maxim, If it's genuine." "I'm sure it is"
Why bother speculating it might not be genuine with one breath and then with the very next breath claim to be sure it is? What's going on?

Welcome to non-scripted off-the-cuff video blog. I press record and something comes out.

Quote
I don't personally care for the full-on shitcanning style you like using from time to time but I know it is popular.

IIRC you don't seem to care for much of what I do at all, you seem to be always criticising  ::)

Quote
It looks to me you started out with the intention of hammering the crap out of UNI-T

You are wrong.
I was hoping this meter with it's rare power measurement function would actually be OK.

Quote
I'm no fanboy and if UNI-T claim some standard and then fail to meet it they deserve all the criticism you can heap on them. But for viewers like me who aren't intimately familiar with CAT ratings and PCB design to meet them it would be better if you toned down the noise and increased the explanation.

I've done videos on this stuff before, go watch them, I can't repeat everything in every single video every single time.

Quote
I kept wondering WHY you bought it in the first place. It sounded like you made a mistake and then wanted to throw a brick through UNI-T's front window.

Stated above.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 08:20:10 am
I'd expect a review of more then one Uni-T meter before claiming that all "Uni-T Meters Suck".

I have yet to find a single Uni-T meter that is well engineered and manufactured.
Prove me wrong, please.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 08:28:50 am
Tools have limits.....knowing the limits of your tools is the more important thing.

What do you say about tools that claim to have a particular safety rating on the front, but fail to meet that spec?
By your reckoning everyone is supposed to open their meter and critically analyse the design to see if it meets the specs  :palm:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 08:33:42 am
Did you really actually buy that meter yourself like you implied in the video?

Yes.

Quote
Are you saying you bought a piece of test gear from a company you know makes crap without even looking at the specs first?

Not in minute detail, no.
I thought I saw evidence it might be a goer, it wasn't.

Quote
Why would you even consider spending money on this if you know you already had far superior tools like the Gossen?

In case you weren't aware, I run an electronics video blog. One of things I do is test equipment reviews.
There is also another reason which I won't elaborate on.

Quote
You couldn't get someone to give/loan you one for videos?

Maybe, but it was a spur of the moment thing.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 08:40:58 am
While Dave's review was entertaining, fairness wasn't high up on the agenda. Dave couldn't even find the precision resistor network on a very simple board design.
Nobody will dispute the very basic input protection and the slow continuity test on those meters. If you can live with that, the meter has some redeeming aspects. It offers a host of features for the electronics hobbyist at a very affordable price.
The Cyrustek 40,000 count dual slope ADC, while not the fastest, is pretty good (also used in the FLIR meter) and drift, which I monitored over 2 years, is minimal. Calibration can be done through the RS232 with connection to calibrator or, cheaply, manually with the trimpots. I haven't had to adjust mine yet, unlike the 61E.
While I also own Fluke and Gossen DMMs, I value my UNI-T meters for specific tasks, like datalogging and peak detection, for instance.
Here is my 71D review, if you haven't seen it yet: https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/ (https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Chupacabras on February 07, 2015, 08:41:06 am
The weird ass adapter looks like it has the classic European mains sockets (well, most of Europe)

Well, one of the good things about this meter is that it has PROPER mains adapter. Not that weird overseas one...
Cheers from Europe ;)

Actually, Dave could do some video blog rant about pros and cons of mains sockets from different parts of the world.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 08:47:53 am
While Dave's review was entertaining, fairness wasn't high up on the agenda.
Have to say i agree...

Next week on EEVBlog, "Why Fluke multimeters SUCK"
(https://farm8.staticflickr.com/7437/16274896800_745922f29b.jpg)
"Look at that offset on the current range, what a flaming pile of turd!"
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: george graves on February 07, 2015, 08:54:10 am
What do you say about tools that claim to have a particular safety rating on the front, but fail to meet that spec?
By your reckoning everyone is supposed to open their meter and critically analyse the design to see if it meets the specs  :palm:

A fool and his life are soon parted with?  Darwin award?  Who in their right mind would work with +300V from a Chinese multimeter?  Granted, in the US, we only really have 120, so for us, it's really not much of an issue.   :bullshit:

I have yet to find a single Uni-T meter that is well engineered and manufactured.
Prove me wrong, please.

I can't.  You prove ME wrong.  ;)  What Uni-T meters have you looked at?  You asserted that "they are all crap".  I was merely asking "Ok back that statement up!!?!?"

Dave, Uni-T has improved in their recent releases. Have a look at the newer 139, 171 and 181 series, they are built much better (to my untrained eyes anyway):

https://www.eevblog.com/forum/testgear/new-trms-uni-t-ut139c-dmm-is-available-now/msg289221/#msg289221 (https://www.eevblog.com/forum/testgear/new-trms-uni-t-ut139c-dmm-is-available-now/msg289221/#msg289221)
https://www.eevblog.com/forum/testgear/uni-t-ut171a-pictures-and-first-impressions/ (https://www.eevblog.com/forum/testgear/uni-t-ut171a-pictures-and-first-impressions/)
https://www.eevblog.com/forum/testgear/uni-t-ut171b-teardown/ (https://www.eevblog.com/forum/testgear/uni-t-ut171b-teardown/)
https://www.eevblog.com/forum/testgear/uni-t-ut181a-pictures/ (https://www.eevblog.com/forum/testgear/uni-t-ut181a-pictures/)

They really have improved things on some new models.





Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Barny on February 07, 2015, 09:06:49 am
Actually, Dave could do some video blog rant about pros and cons of mains sockets from different parts of the world.
Thats a good idea.

@Dave:
I think you have to take the this estimating-iron to your friend with the special test-gear like the Fluke in your intro video.

@George Grave
If its about safety-rating it had to meet its specs.

If not, its crap.
There is no excuse like in Kindergarten: "But other multimeter does ist too."

A fool and his life are soon parted with?  Darwin award?  Who in their right mind would work with +300V from a Chinese multimeter?  Granted, in the US, we only really have 120, so for us, it's really not much of an issue.   :bullshit:
Dont take your crap powerlines as an excuse.
Have you thought about oscilatorcircuits?
You'll get several 1000V out of an 1,5V batery.


The only positive thing i've seen is a little bit of blast-protection of the case when it blows up
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 09:10:06 am
While Dave's review was entertaining, fairness wasn't high up on the agenda. Dave couldn't even find the precision resistor network on a very simple board design.

Because it's not there.
Please point out where the precision ceramic hybrid resistor network typically found in such accuracy class instruments actually is. Perhaps I did miss it, in which case please show it to me.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 09:11:24 am
Dont take your crap powerlines as an excuse.
Have you thought about oscilatorcircuits?
You'll get several 1000V out of an 1,5V batery.
It isn't exactly going to make a meter with M205 glass fuses explode like a grenade though is it? Worst case bzzt and the meter stops working.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: george graves on February 07, 2015, 09:14:33 am
@Dave:
I think you have to take the this estimating-iron to your friend with the special test-gear like the Fluke in your intro video.


That I would like to see that.  See if it can withstand 600v.



Dont take your crap powerlines as an excuse.
Have you thought about oscilatorcircuits?
You'll get several 1000V out of an 1,5V batery.

Our crappy power line?  You mean the one powered by freedom?   :)  :box:

Yea, I know you could get a +1000V volts out of a AA battery, but there would never be enough energy there, right?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mikeselectricstuff on February 07, 2015, 09:17:01 am
No reason you can't have trimmers on a high accuracy bit of kit, as long as their adjustment range is properly limited with external resistors , e.g. +/=0.05% adjust range  on a 0.25% spec
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 09:18:05 am
While Dave's review was entertaining, fairness wasn't high up on the agenda. Dave couldn't even find the precision resistor network on a very simple board design.

Because it's not there.
Please point out where the precision ceramic hybrid resistor network typically found in such accuracy class instruments actually is. Perhaps I did miss it, in which case please show it to me.
8 Precision metal film resistors 1W TCA5C6 (4x2.5M and 1M11, 101K, 10K1, 1K01) (0.05% resistance tolerance and 10ppm/C)
Lift the skirt on the metal shield can.
The meter has lots of issues, but voltage accuracy is not one of them.
(https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/?action=dlattach;attach=93285;image)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 09:18:13 am
A fool and his life are soon parted with?  Darwin award?  Who in their right mind would work with +300V from a Chinese multimeter?  Granted, in the US, we only really have 120, so for us, it's really not much of an issue.   :bullshit:

It seems I have to correct you almost every time you speak George  :palm:
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.
If you knew anything about mulitmeter protection and CAT rating then you would have known that. Clearly, you don't.

I can't.

Thanks for admitting that.

Quote
You prove ME wrong.  ;) 

I don't have to because I don't give a toss about you say.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Huluvu on February 07, 2015, 09:21:15 am
As far as I understood from the cut outs of the Standard EN 61010-1 the Cat Ratings before 2004 could have had exclusions for the Ratings.
It looks like the valid Standard before 2004 (released in 1995) you can exclude everything you want from the requirements.
As an example this would mean that you may only validated Volts AC measurement on your Multimeter and exclude every other Measuring part from it.
--> using for e.g. 250V Fuses instead of the required 600V or 1000V Fuses.

For sure this would not explain why Uni-T can still produce and distribute Meters like Dave's Version to the Market.
Even it would not explain why there is not the expected creepage and clearance on the Volts Input section ....

It would be interesting if there is any different on the current selling Europe Versions which are directly purchased from Europe Market.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 09:23:17 am
8 Precision metal film resistors 1W TCA5C6 (4x2.5M and 1M11, 101K, 10K1, 1K01) (0.05% resistance tolerance and 10ppm/C)
Lift the skirt on the metal shield can.
(https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/?action=dlattach;attach=93285;image)

There are 4 x 1W axial metal film resistor under that can that also contains trimmers? Doesn't look like there is enough room to me. And based on the underside photo of pins protruding, they would have to be mounted vertically. 1W resistors are not small.
But ok, if you say so, I'll have a look next time I'm in the lab.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Barny on February 07, 2015, 09:24:10 am
Dont take your crap powerlines as an excuse.
Have you thought about oscilatorcircuits?
You'll get several 1000V out of an 1,5V batery.
It isn't exactly going to make a meter with M205 glass fuses explode like a grenade though is it? Worst case bzzt and the meter stops working.
That was only an example, because he thought that 115V/120V are on the save site when he uses this meters.

PS:
If the involved capacitor is big enough, the bzzt will get a nice booom.

If I remember right, the multimeter which get blown in daves intro video was with the usage of the energy of an AA Cell.

@Gorge:
I knew.
Your powerlines runns with feedom and hope instead of electricity.
And you deliver your freedom with 700 bullets per minute to the whole word.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 09:25:59 am
Don't need to warm up the iron, I have a picture:
I'll grant you it is a crude design, but it seems to work.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 09:30:41 am
Don't need to warm up the iron, I have a picture:

That is not the same model nor layout as the UT71E.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Negative-Bias on February 07, 2015, 09:31:18 am
I don't get into all this stuff, fascinating watching all the views .pictured is my multimeter which I've owned from New,low count so what I got it cal checked at work,passed straight off perfect measurements,the cal dept want me to sell it to them "No Chance". Used daily how about these bit's of quality Dave :-+
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 09:39:27 am
While Dave's review was entertaining, fairness wasn't high up on the agenda.
Have to say i agree...
Next week on EEVBlog, "Why Fluke multimeters SUCK"

I gave the UT71E a fair go by actually getting it and doing a review and teardown. But review not going to happen now, I won't waste my time.
It's not my fault that it failed to deliver. Which is something that Uni-T does time and time again seemingly without fail.
My comment about them sucking is based on evidence, in case you missed it.
Just because some people don't like me pointing it out doesn't mean I'm not being fair.
Unfair would be to not review any more Uni-T meters because they have always failed to impress. But I didn't, so once against, evidence that I gave them a fair go by actually doing this.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 09:41:45 am
Don't need to warm up the iron, I have a picture:

That is not the same model nor layout as the UT71E.
That's a 71B, AFAIK, they are all the same under that metal can (71D for sure). I don't own the 71E, so check when you have time, but I'd be very surprised if they are not there. The meter wouldn't work without them.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 07, 2015, 09:45:15 am
That's a 71B, AFAIK, they are all the same under that metal can (71D for sure). I don't own the 71E, so check when you have time, but I'd be very surprised if they are not there. The meter wouldn't work without them.

You can see on the photo I posted they are not the same. Clearly less parts and huge isolation slots on the UT71E.
Perhaps they have moved to SMD parts though, I have to open the can.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 09:53:56 am
Perhaps. You have one of the latest board revisions with 'improved' clearances and space for HRC fuses. I doubt it though. Let us know later.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: meerweten on February 07, 2015, 09:56:15 am
seems like ut updated their design of the ut61 model (i recently replaced my old dvm870 with the ut61D)

in my case there are crapy chinees HRC fuses :p , can't remembet the voltage rating on them

do i claim its a good meter?
For my use and budget it might be, still want to have a fluke, just can't afford it :'(
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: hamdi.tn on February 07, 2015, 10:09:32 am
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 10:11:13 am
fwiw, the 71D I have (purchased early 2012) has through-hole resistors like Wytnucls' visible through the perforations in the can.
(https://farm8.staticflickr.com/7330/16276790247_d6aea9ff58.jpg) (https://farm8.staticflickr.com/7330/16276790247_4a8028026a_o.png)

While Dave's review was entertaining, fairness wasn't high up on the agenda.
Have to say i agree...
Next week on EEVBlog, "Why Fluke multimeters SUCK"

I gave the UT71E a fair go by actually getting it and doing a review and teardown. But review not going to happen now, I won't waste my time.
I already posted this to youtube, but i will repost the same here again. You used statements like "out of spec according to the agilent" and then "juuuuust going to squeeze in" when both times it was well within the claimed % of reading + counts claimed in the Uni-T's manual. You also claimed that "0.3%+8" spec for resistance measurement was poor, when a Fluke 87V is "0.2%+10" in 20000 count mode and costs significantly more. This makes your review biased imo. An unbiased review would have checked that the multimeter was within specification and moved on without making derogatory comments about it. The claimed specs of the UT71 are exceedingly good for the asking price and even you were able to confirm that it meets them out of the box.

The spec for the Amps range on a Fluke 87V is 0.2%+20 and as i have shown mine is 15 counts out with the inputs shorted (or open, makes no difference). It was like this the day i took it out of the box brand new. That makes it closer to being out of it's claimed spec than the Uni-T you tested was. Not every meter is going to be "0.0%+0" out of the box and Fluke is no exception so don't start moaning about a Uni-T that is 10 counts out when the claimed spec is up to 25 counts out.

Your claims that the meter can't have long term stability because it uses trimmer pots are also unfounded rumour unless you have tested it yourself or can point us to a reputable source that has characterised the drift of this particular multimeter, or has data on the expected drift of the trimmers/components used and calculates the overall expected drift with the circuit implementation that Uni-T has used.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: miguelvp on February 07, 2015, 10:21:34 am
I got my UT71B for just $35 at clearance from mortoncontrols, I never planned to use it for anything other than my little projects and for that price and 20000 counts it suits my needs.

I knew from the get go that the CAT ratings where not to be trusted but for the price and because I didn't want to spend too much and get something better than my crappier GB GDT-200A and adding data logging and everything else for that price it was on par of what I wanted for my under 24V measurement needs.

My biggest complain for my purposes is that the volume is quite high and if I disable the buzzer then it takes away the (slow) continuity test sound, other than that I'm happy with it for the discounted price, if it was the full price (around $100+) then no way I would have gotten it.



Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: 0b01010011 on February 07, 2015, 10:35:07 am
If Uni-T had official ties outside China, that would expose them to lawsuits for wrongful death or injuries attributable to failure to meet their safety rating claims if there has been any.
Well they sort of do. Uni-T meters are sold under the "Tenma" brand through Farnell/Element14 for example. If anyone knows if the Tenma variants are built safer I'd be interested to know.
I have a Tenma 72-7730a, 20000 count (UT71B equivalent?) bought from Farnell Australia, and this has the much larger ceramic HRC fuses - similar to the Brymen meter Dave showed.  If anyone's interested in pictures I'm happy to try and get some sorted tomorrow.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gonzoid on February 07, 2015, 10:37:56 am
seems like ut updated their design of the ut61 model (i recently replaced my old dvm870 with the ut61D)
Interestingly enough, their new catalog (here (http://www.uni-trend.com/uploads/soft/Catalog/2015--catalog-EN.pdf)) pretends both the UT61 and UT71 series are compliant with CAT.III 1000V and CAT.IV 600V ratings (specified by UL 61010-1, EN 61010-1, EN 61010-2-030 and EN 61326-1), but only the UT61 page is displaying logos from ETL/Intertek (https://en.wikipedia.org/wiki/ETL_SEMKO) and TÜV/GS (https://en.wikipedia.org/wiki/Technischer_%C3%9Cberwachungsverein), implying only those models may have been approved.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: open loop on February 07, 2015, 10:46:06 am
Dave,

We have the Tenma branded version of these meters at Work, don't ask why - long story. Next time you are in the lab check out the battery consumption of these meters and then do a Blab rant about the battery consumption.

These meters are not terrible but not great either, ok if you are doing low energy work. (Next breath) I like to see your mains on the "ohms range" test.



Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: george graves on February 07, 2015, 10:58:49 am
OK.  I'll trust your knowledge Dave.  You know a TON more then I do.  Absolutely, 100%.  Done and done. Never questions that. You win.   |O

But, "What Uni-T meters have you looked at?  You asserted that "they are all crap".  I was merely asking "Ok back that statement up!!?!?"

What other Uni-T meters have you had hands on with?  Fair question.  NO?

I'm betting that if you did another multimeter round up, that was up-to-date with the times, that a UNI-T would be a front runner in the $100-$150 range.  no?

For me....as a "amateur" I think I'm in a nice spot.  A 87-5 that I totally trust, and two UNI-T UT-61E's, and a 3478A.  An ebay DMM voltage reference standard.

I'm NOT an Uni-T fan boy - far from it.  I would gladly trade them in for something better.  But as a 2nd, 3rd, 4th meter, they are awesome.

Personally, I think what I have is over kill for 99.9% of people.  What am I missing?  We can't all have voltage standards and current sources.  You missed the point about price vs performance on this review IMHO.

There are a ton of people that are starting out, and need a decent meter, and will never measure +300 volts.  So, perhaps, a mention of that in the review would be warranted?



Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: fubar.gr on February 07, 2015, 10:59:20 am
My 71E has a different 10A shunt:

(http://fubar.gr/wp-content/uploads/2014/04/IMG_20140414_175015.jpg)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 11:03:39 am
Tenma (Element14) sells the UNI-T UT71B and 71D under their brand. The meters come with 1000V HRC fuses to comply with the latest European safety regulations. (No independent testing AFAIK)
It would be interesting to examine the PCB to see if MOVs and PTCs have been installed.
Battery consumption is average (7mA) and should give 100hrs of normal use.
Mains on the Ohm's range has been done before. No drama, the meter has 1000V crowbar circuits on the relevant ranges.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: PeterL on February 07, 2015, 11:04:54 am
I really can't understand how people can be so forgiving about this CAT-rating lie on meters like these. Sure most of the time safety is not an issue because of the nature of the circuits we are probing.
But if you buy you're meter for those circuits, you would be happy with a meter that said 'Not CAT rated!!'

Now for the meter reviewed here I think it's even worse, as it's unique selling point is meauring Watt's, not microWatt's, not milliWatt's but Watt's. They even provide a nice adapter encouraging you to hook it up to 230V mains. Also the price is high enough that you would expect some level of quality imho.

And about this being a Chinese meter, well WE know, but not everyone does. Uni-T sure doesn't sound Chinese to me, and it looks like a decent western product to.

But all that still doesn't matter. It says CAT-rated, so it should be CAT-rated. And if anyone could just put a CAT rating on their device, well than this whole rating is just worthless, as we simply cannot thrust this. I think that's something the entire sector should care about.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Owen on February 07, 2015, 11:13:18 am
Can someone explain why Brymen is putting a 10 A fuse @ 600V(ac) in a dmm that's rated for 8 A and 1000 V CATII? And why is Brymen doing this on the mA range (620 mA @500V), too?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rolycat on February 07, 2015, 11:16:22 am
The "improved safety" on the UT61 series largely seems to consist of fitting those 250V ceramic fuses.

As can be seen in Dave's video, they are marked 'BS1362', which is the British Standard for the fuses fitted to all UK mains plugs. Uni-T use them because they are manufactured in the millions, and are consequently very cheap. They are supposed to be HRC fuses, but there are a lot of dangerous fakes around these days. Example here (https://www.youtube.com/watch?v=KVJVswLbqaA).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 11:20:47 am
No, there is a GS approved version of the UT61 with proper HRC fuses and a lower CAT rating.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mikeselectricstuff on February 07, 2015, 11:21:57 am
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gonzoid on February 07, 2015, 11:22:23 am
Tenma (Element14) sells the UNI-T UT71B and 71D under their brand. The meters come with 1000V HRC fuses to comply with the latest European safety regulations. (No independent testing AFAIK)
It would be interesting to examine the PCB to see if MOVs and PTCs have been installed.
I have a Tenma 72-7730a, 20000 count (UT71B equivalent?) bought from Farnell Australia, and this has the much larger ceramic HRC fuses - similar to the Brymen meter Dave showed.  If anyone's interested in pictures I'm happy to try and get some sorted tomorrow.
This meter is documented on the sigrok wiki: http://sigrok.org/wiki/Tenma_72-7730 (http://sigrok.org/wiki/Tenma_72-7730)
A PCB revision from 2005 is pictured, it has minimum protection with only glass fuses, one PTC and one unpopulated location for MOV/GDT.
Show us some pictures, the more documented revisions, the better!  ;)


Calibration can be done through the RS232 connection or, cheaply, manually with the trimpots. I haven't had to adjust mine yet, unlike the 61E.
[...]
Here is my 71D review, if you haven't seen it yet: https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/ (https://www.eevblog.com/forum/testgear/uni-t-ut71d-review/)
I've quickly re-read your thorough review, but cannot find any mention of a calibration procedure through RS232. You meant the "hidden menu" procedure, right? ???
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: jeremy on February 07, 2015, 11:25:55 am
Um, how has no-one noticed the trace going nowhere? 5:44 in the video. Unless this board has plugged vias, which I seriously doubt. Or my eyes are deceiving me, which is more likely.

It's also visible in other peoples pictures in this thread.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 11:28:55 am
I'm going by the Tenma multimeter manual, which mentions the 1000V fuses ratings and dimensions. Opening up a recent meter is the only way to find out for sure.
There is no menu as such for calibration. Just a calibration mode for the meter and a published paper procedure, with a calibrator hooked up.
In fact, now that I think about it, the calibration procedure doesn't need the RS232 connection which is not bi-directional. The software is in the meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 07, 2015, 11:29:53 am
Different price categories, different capabilities. I cannot afford a $1000 multimeter and I do not need one (I'd rather buy a function generator). I do not need the 0.001% accuracy either. If I measure the B+ voltage of a radio and get 280V when the spec is 275V I will consider it OK and move to other areas to try to find the fault.

If I ever buy a more expensive meter than my current one, it will have to be able to measure AC voltage at up to 30kHz (to make tape deck calibration easier).

And yes, I do sometimes stick my not-sure-if-really-rated meter to mains to measure voltage. Though if I am repairing a switching power supply (like a PC PSU) I use a 2kVA isolation transformer and my Rigol DS1052E scope.

As for safety - I'd think that robbing a bank to buy the real CAT rated meter is way more dangerous than using the cheap meter and not robbing anyone.

I really can't understand how people can be so forgiving about this CAT-rating lie on meters like these.
Because it does not really matter to me, the meter can say CAT6 rated and I wouldn't really care. OTOH, if the spec said that AC voltage measurement frequency response is up to 30kHz and in reality it was 1kHz I would not be happy at all.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 11:42:51 am
Um, how has no-one noticed the trace going nowhere? 5:44 in the video. Unless this board has plugged vias, which I seriously doubt. Or my eyes are deceiving me, which is more likely.

It's also visible in other peoples pictures in this thread.
Probably an isolation trace, but I'll let Dave answer that one. (The trace goes to ground with a via)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 11:54:05 am
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.
Things are changing for the better, UNI-T and CEM are having most of their meters sent for independent testing nowadays. I suspect that the UT71s will be discontinued shortly, with safer meters having been released recently.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: electr_peter on February 07, 2015, 11:58:13 am
Mains adapter is suited only for EU, but it is incredibly useful. It is actually very difficult (in practice) to quickly and safely rewire mains plug for both voltage and current measurements with any multimeter. It is possible to have one time setup with alligator clips, but it is kind of annoying and tricky to do so. I have made special adapter box just for that.
However, UT71E accuracy and resolution are only marginally better than simple cheap (~10-20€) mains power adapter - so what is the point of power measurement feature? It is useful only for high power AC and DC circuits, not for electronic circuits or battery drain measurements.

Blatant lie on CAT ratings is not excusable. While safety aspect for some forum users is not that important, you have to remember why CAT ratings were instituted at all. If meter in I or V mode is put on mains, internal low resistance arc can occur (both from blown glass fuse or arc-over) resulting in massive currents flowing through leads -> heating+fire+explosion+flying molten metal -> not fun at all. It is absolutely non obvious that this could happen ("Hey, I just going to check the voltage") and it is somewhat rare/exotic/unexpected event, so this safety issue is often neglected.

Some meters from UNI-T have good value for money. UT71E does not seem to be in that category in my opinion.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: PeterL on February 07, 2015, 12:07:32 pm
I cannot afford a $1000 multimeter and I do not need one
I never said you had to spend $1000 on a multimeter. In fact, I don't spend that much on a meter either.

And I think I already stated in other words that we do not all need a meter with high CAT ratings.

I just think just like Mike said it would be a lot better if the meter didn't have these CAT III/IV ratings on it.

And again, this particulair meter just shout's "Connect me to a mains outlet" and "Let's measure the current consumption of you're vacuumcleaner, or other high power and/or inductive device". Lying about a CAT rating feels like horribly bad to me here.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 12:17:37 pm
The cat rating lies are unforgivable.
For people that say "it's OK, I don't use it on high energy circuits", well you know, that too is inexcusable too IMVHO.
Just because you are informed (and choose to forgive) uninformed users are at risk, and defending this company is putting more and more lives at risk.
I care more for my fellow man that anyone's profit margin.

Now, having variants on meters, some that may and some that may not meet cat ratings may even make this situation worse.
We all know that print is easier to forge/achieve that manufacture of good quality, and again it clouds this issue with the uninformed.

Stop with cognitive bias, and stop with selfism "I'm alright Jack" BS.
This company should be nailed to the wall.
I noticed that Maplin in UK sells UnitT meters, wonder if all these meet their cat ratings:
http://www.maplin.co.uk/c/components/component-testers/multimeters#Brand:Uni-Trend&sort=&page=1&productsPerPage=12 (http://www.maplin.co.uk/c/components/component-testers/multimeters#Brand:Uni-Trend&sort=&page=1&productsPerPage=12)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: SilverSolder on February 07, 2015, 12:24:55 pm
Lying about the CAT rating is a big mistake by Uni-T, even if the meters work fine otherwise.

It is like a car manufacturer lying about having crash tested their product.  Not really acceptable, is it?




Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 12:40:18 pm
Maplin, as an importer, is responsible for making sure their recent meters comply with the latest IEC regulations. Old stocks are exempted for a while.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 12:45:45 pm
Maplin, as an importer, is responsible for making sure their recent meters comply with the latest IEC regulations. Old stocks are exempted for a while.

Thanks Wytnucls.
So that could be another example of this dangerous shite escaping onto the market through ambiguity and profiteering.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 12:52:53 pm
Absolutely. There is a reporting system in Europe to counter the practice. Flawed products have to be removed from the market. Not sure about subsequent fines. (RAPEX)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 12:57:57 pm
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!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: zapta on February 07, 2015, 01:00:29 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rsjsouza on February 07, 2015, 01:09:24 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Hootch on February 07, 2015, 01:15:42 pm
It seems that there are different versions of this multimeter available. My UT71E has two HRC-fuses.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: max_torque on February 07, 2015, 01:16:14 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: ptp170 on February 07, 2015, 01:23:07 pm
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..
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 01:23:55 pm
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!  ;D
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 01:25:43 pm
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 (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)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 01:41:03 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Maxlor on February 07, 2015, 01:43:03 pm
As for independent testing, here's the relevant page: http://etlwhidirectory.etlsemko.com/WebClients/ITS/DLP/products.nsf/4c8700f3b75987a08525777700583333/bb3d3302a13f93f086257ddd000985fc?OpenDocument (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 (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 (http://www.cem-instruments.com/en/pro/nsort15-2.html)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: timb on February 07, 2015, 01:46:02 pm
LOL "RAPEX"


Sent from my Smartphone
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mikro on February 07, 2015, 01:57:55 pm
That is some poor manufacturing. Is there a solder bridge on that trimmer, which soldering side is shown at  12:33?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 02:05:56 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 07, 2015, 02:08:35 pm
LOL "RAPEX"
RAPid EXchange
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 07, 2015, 02:10:52 pm
Mains adapter is suited only for EU
Schuko has nothing to do with the EU.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 07, 2015, 02:15:14 pm
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
(http://www.worldstandards.eu/WordPress/wp-content/uploads/electricity-type-K-socket-300x300.jpg)
nor this (same issue)
(http://www.worldstandards.eu/WordPress/wp-content/uploads/electricity-type-L-socket-single-199x300.jpg)
and definitely not this
(http://www.worldstandards.eu/WordPress/wp-content/uploads/electricity-type-G-socket-300x298.jpg)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: PChi on February 07, 2015, 02:18:35 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: ctz on February 07, 2015, 02:28:49 pm
Here's the innards of a Tenma 72-7730A (€93), which is Farnell's whitelabelling of a UT71B (€105).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 02:29:36 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mij59 on February 07, 2015, 02:29:51 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 07, 2015, 03:59:09 pm
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/ (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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: JoeLaBidouille on February 07, 2015, 04:07:59 pm
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.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: parbro on February 07, 2015, 04:13:50 pm
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/ (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?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Nerull on February 07, 2015, 04:14:35 pm
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.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: jaxbird on February 07, 2015, 04:23:56 pm
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.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 04:28:46 pm
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.
Ethics of improper CAT ratings aside, you aren't going to find a meter which has the same features for any where near the same price. If you can overlook the pitfalls suddenly $180 doesn't look so bad when you consider that a 40000+ count datalogging meter like the Fluke 289 will set you back $540 and a power multimeter like the Gossen Metrahit Energy will hit you (no pun intended) for an eye watering $1200.

The current going price for a UT71E from a chinese seller on ebay is US$169.90 including international shipping and there is a Australian seller who has them for US$147.22 including national postage.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 04:30:48 pm
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/ (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.
It is old news. There are better UNI-T meters now, but they don't do Watts anymore, which Dave was after. I don't know what is written on the box, but the manual clearly stipulate that test voltage must fall between 50V and 250V AC only.
The best and cheapest meter for that type of measurement including energy, would be a second-hand 310,000 count Gossen 29S, with 0.1uW resolution, which usually sells for less than 400 Euros in Germany.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Hootch on February 07, 2015, 04:46:03 pm
Bought my UT71C from Reichelt, same fuses as yours, it came with some kind of compliance note, don't remember what it was about.

Yes indeed, my dmm is also from Reichelt. As you mentioned, there was a note. After a little search, I found it finally:

"Manual amendment
In order to meet new CE Standards, the following amendments are made:

Alligator Clamp - Removed

Safety Measuring Cable - Removed"

Nothing about fuses...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: allikat on February 07, 2015, 04:51:19 pm
Re the Uni-61E:
Quote
BS 1362 specifies sand-filled ceramic-bodied cylindrical fuses, 1" (25.4 mm) in length, with two metallic end caps of 1/4" (6.3 mm) diameter and roughly 1/5" long. The standard specifies breaking time versus current characteristics only for 3 A or 13 A fuses.

For 3 A fuses: 0.02–80 s at 9 A, < 0.1 s at 20 A and < 0.03 s at 30 A.
For 13 A fuses: 1–400 s at 30 A, 0.1–20 s at 50 A and 0.01–0.2 s at 100 A.
Source: https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets_-_British_and_related_types (https://en.wikipedia.org/wiki/AC_power_plugs_and_sockets_-_British_and_related_types)

Even if those fuses meet spec, are they good enough protection for your meter?  I mean, they claim to be BS1362 fuses, but are the wrong colour!
Quote
BS 1362:1973, allows any fuse rating up to 13 A, with 3 A (coloured red) and 13 A (coloured brown) as the preferred (but not mandated) values when used in a plug. All other ratings are to be coloured black.
Source: Same wiki page as above.

I know how they do these meters for the price, the same way a lot of junk electronics companies do. By bloody lying and using parts off the back of whatever's passing at the time.

By the way, the CE marking usually means "China Export", and it's an intentionally similar to the CE European conformity marking.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: AF6LJ on February 07, 2015, 05:03:02 pm
Having seen those Uni-T meters at hamfests I was really wondering how good they were, now I need some Eye Bleach. GAAACHH What a pile of damp Cat Crap.
I guess I will still be looking for a new decent meter, my Beckman (Labeled as such and not Wavetek) RMS-225 I was given by Beckman to evaluate 24 years ago will have to fill the bill for some time before I retire it.

It is amazing the crap they pass off as test equipment these days.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 07, 2015, 05:04:35 pm
Even if those fuses meet spec, are they good enough protection for your meter?  I mean, they claim to be BS1362 fuses, but are the wrong colour!
Quote
BS 1362:1973, allows any fuse rating up to 13 A, with 3 A (coloured red) and 13 A (coloured brown) as the preferred (but not mandated) values when used in a plug. All other ratings are to be coloured black.
Source: Same wiki page as above.

And the 1A and 10A fuses shown in the UT61E are.. black!

By the way, the CE marking usually means "China Export", and it's an intentionally similar to the CE European conformity marking.

No, it means nothing of the sort.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 05:05:11 pm
The fact that the chip is 20k count but the meter claims to be 40k count is pretty damming. Fake parts too... So unnecessary, there are quality low cost parts from Chinese manufacturers that will do the job, no need for a fake label on them.

Dave, maybe you should look at getting some equipment for testing installation at the rated voltages that manufacturers claim. See if you can get the magic smoke out.

I was worried when you removed that jumper, could have cleared calibration data or something. Seems okay though.

No need for the "one hung low" either, but otherwise an interesting and enlightening tear down.
It pays to read previous posts. Post #12 will tell you that Dave was wrong, the count of the Cyrustek chip on the 71E is actually 40,000, not 20,000.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 07, 2015, 05:12:04 pm
By the way, the CE marking usually means "China Export", and it's an intentionally similar to the CE European conformity marking.

That's an urban myth, similar to the one about the Japanese town of Usa.

You are correct about the fuses though.

The fuses are black. How is he correct?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 07, 2015, 05:18:18 pm
All this talk about the uni T meters has got me looking at other meters as I was thinking of getting another meter, so does anyone know anything about the Megger AVO410. I was thinking of getting one.
http://www.tester.co.uk/megger-avo410-digita-multimeter-cativ-600v (http://www.tester.co.uk/megger-avo410-digita-multimeter-cativ-600v)

Or am I doomed to getting a yellow peril (Fluke)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 05:23:51 pm
Perhaps not relevant to the thread, but your Megger is an Appa 73 meter. You're doomed.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 07, 2015, 05:27:24 pm
Which also appears to be an Ideal meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 05:39:00 pm
The fact that the chip is 20k count but the meter claims to be 40k count is pretty damming.
Dave made an oopsy - he pulled up the datasheet for the ES51922 instead of the ES51966 which is actually what is in the meter. It's a 44000/440000 count meter chip http://www.cyrustek.com.tw/spec/ES51966.pdf (http://www.cyrustek.com.tw/spec/ES51966.pdf)
There is however a catch - on resistance and current (at least when set to amps) the resolution does seem to be lower than 40000 because i've noticed that it has a tendency to snap to certain increments. It is perhaps operating in 4000 or 4400 actual counts with some averaging going on.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: lapm on February 07, 2015, 05:39:31 pm
Edit relating 20.000 count crap...

Also if they lie about cat ratings, what else do they lie about? Or what else hidden treasures that meter has hidden inside it...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 07, 2015, 05:39:58 pm
Ok now im seriously curious how they get 40.000 counts out of 20.000 count chip set...

You should really read the last few posts.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Grapsus on February 07, 2015, 05:40:57 pm
I don't get it why so many people think that Dave was somehow unfair with this meter and Uni-T in general. What is all this justification stuff ? Are you trying to make yourself feel better about having wasted 180$ and bought a crappy and dangerous meter ? There is a lot of alternatives : 1W resolution mains power meters can be bought for 20$ in any PC shop and for 150$ you can have a used 20000 counts Fluke.

The PCB is a horrible mess, it has every possible 5$-meter cost reduction trick except for a few precision parts to meet the announced precision. Look at every photo posted here, there is silkscreen for a spark gap "SG1" but it is always missing. Aside from cost reduction it looks like the designers just don't give a shit about their product, a screw hole in a 10A track, seriously ?!

Yes, from a single teardown like this we can deduce that Uni-T is a company that reduces costs, plays tricks on its customers and puts them in danger by claiming unmet security standards. Therefore all their products should be considered as dangerous crap until proven otherwise. And if they don't like this negative bias they are welcome to make good quality stuff for several years as others have done to earn their reputation.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 05:52:27 pm
I don't get it why so many people think that Dave was somehow unfair with this meter and Uni-T in general. What is all this justification stuff ? Are you trying to make yourself feel better about having wasted 180$ and bought a crappy and dangerous meter ? There is a lot of alternatives : 1W resolution mains power meters can be bought for 20$ in any PC shop and for 150$ you can have a used 20000 counts Fluke.
The ~$170 E variant is a bit of a gimmick but the cheaper versions without the power measurement have some merit. You aren't going to find a 40000 count datalogging meter with USB for $130 from anyone else. Hell most of the other manufacturers charge you that just for the USB cable.

I don't know why people find this so hard to understand. It's like all the car manufacturers selling V8 sports cars for $50,000. Then some chinese company comes along and sells a V8 sports car that is just as powerful for $7000 but the catch is that it has no seatbelts and the fit and finish is a bit naff. Suddenly everyone is like "Oh my God! you can't sell a car without seatbelts!". But who cares, it's $7000. Install them yourself if you are so inclined.

If all you want is a 20000 count multimeter without any bells and whistles then yeah buy an old second hand 87...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 06:04:55 pm
On the 71D, 10,000 data memory, accessible on the meter or the PC. 30,000 on my Gossen 30M, but I have to buy the Gossen cable and software to see any of it (350$). That's after you paid 900$ for the meter, 60$ for the bag and 140$ for the 5V wall wart, otherwise you have 16 hours of battery life. Oh, it's only CAT II 600V, with 100mA max. And it comes with a bodged cap on the DC to DC converter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 07, 2015, 06:47:05 pm
There is a real point of contention here when we look at the UT71E. It is clearly, obviously, intended to be used on high energy circuits as it has an attachment and function that are required to be connected to a high energy circuit in order to use them. The design and execution of the meter is clearly, obviously, not up to the task in a safe manner. On this point alone, the UT71E is a piece of junk that is not suited to its task and could cause someone serious injury.


The majority of Uni-T meters are cheaply built and have less than minimal input protection. Some of the latest multimeters have much improved input protection and I am comfortable recommending the UT139C at least.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Grapsus on February 07, 2015, 06:49:56 pm
I don't know why people find this so hard to understand. It's like all the car manufacturers selling V8 sports cars for $50,000. Then some chinese company comes along and sells a V8 sports car that is just as powerful for $7000 but the catch is that it has no seatbelts and the fit and finish is a bit naff. Suddenly everyone is like "Oh my God! you can't sell a car without seatbelts!". But who cares, it's $7000. Install them yourself if you are so inclined.

Well in civilized countries it is a crime to knowingly sell cars that don't meet the required safety standards.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 06:50:46 pm
I don't get it why so many people think that Dave was somehow unfair with this meter and Uni-T in general. What is all this justification stuff ? Are you trying to make yourself feel better about having wasted 180$ and bought a crappy and dangerous meter ? There is a lot of alternatives : 1W resolution mains power meters can be bought for 20$ in any PC shop and for 150$ you can have a used 20000 counts Fluke.
The ~$170 E variant is a bit of a gimmick but the cheaper versions without the power measurement have some merit. You aren't going to find a 40000 count datalogging meter with USB for $130 from anyone else. Hell most of the other manufacturers charge you that just for the USB cable.

I don't know why people find this so hard to understand. It's like all the car manufacturers selling V8 sports cars for $50,000. Then some chinese company comes along and sells a V8 sports car that is just as powerful for $7000 but the catch is that it has no seatbelts and the fit and finish is a bit naff. Suddenly everyone is like "Oh my God! you can't sell a car without seatbelts!". But who cares, it's $7000. Install them yourself if you are so inclined.

If all you want is a 20000 count multimeter without any bells and whistles then yeah buy an old second hand 87...

How would you make that meter meet the CAT ratings?
A new PCB design and quality components?
How much would all that time, effort and parts cost in the end?
Be easier to buy a quality meter and paint Uni-t on the front, but then why would you.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: c4757p on February 07, 2015, 06:51:06 pm
I don't know why people find this so hard to understand. It's like all the car manufacturers selling V8 sports cars for $50,000. Then some chinese company comes along and sells a V8 sports car that is just as powerful for $7000 but the catch is that it has no seatbelts and the fit and finish is a bit naff. Suddenly everyone is like "Oh my God! you can't sell a car without seatbelts!". But who cares, it's $7000. Install them yourself if you are so inclined.

I think you're saying this seriously, but many of us would consider such a statement to have a high likelihood of being satirical...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 07:00:13 pm
So we are all agreed that its a moral dilemma that the incorrect cat rating text is printed on the front panel of the meter and in the literature and that the meter doesn't actually represent horrible value for money? Good, I thought so too.


There is a real point of contention here when we look at the UT71E. It is clearly, obviously, intended to be used on high energy circuits as it has an attachment and function that are required to be connected to a high energy circuit in order to use them. The design and execution of the meter is clearly, obviously, not up to the task in a safe manner. On this point alone, the UT71E is a piece of junk that is not suited to its task and could cause someone serious injury
There is a disclaimer that the mains attachment is only to be used up to 250vac. Also to probe a household mains outlet only requires cat II. Whether or not the meter would pass cat II is a secondary matter but it certainly does not need to be catIV
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 07:09:32 pm
It is criminal and life threatening, can't put a price on the latter.
So it represents the poorest of value for money.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 07, 2015, 07:13:33 pm
I haven't read through all 9 pages yet because the teardown of the extremely DANGEROUS PIECE OF SHIT led me straight away to a case I read about where an electrician and a fire official were killed due to arc  flash.
They died because of Chinese shit manufacturing with safety as a no-thought. The meter the electrician used to check all 3 phases exploded and the result as I said...
Please read this trade journal regarding this story. NEVER use cheap meters across a circuit that can literally vapourize you in an instant. Make sure that it is of the proper CAT rating for the job and from a reputable manufacturer with real approvals. Sorry if this has been said and linked before, but I can't see someone getting hurt by equipment like this.
the link: http://ecmweb.com/arc-flash/case-deadly-arc-flash (http://ecmweb.com/arc-flash/case-deadly-arc-flash)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: boffin on February 07, 2015, 07:21:46 pm
I'm guessing Dave ended up with a Chinese knock-off of a Chinese cheap brand.  The PCB is likely just a copy, but the components/fuses are the cheapest knockoff they could find.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 07:27:09 pm
Cool story, I think we have got the point that you shouldn't probe a 3 phase power plant with one of these by now.

The point I'm trying to get across is that for someone who just plays with bench power supplies, USB and battery powered devices, the Uni-t meters represent good value for money. I for one am not going to lose sleep over owning a meter with the incorrect rating printed on the front panel if I don't need a rating in the first place.


The combination of the mains power dongle and a meter that claims cat ratings which it obviously does not meet is a bit of a faff. However, that does not mean you should paint all uni-t meters with the same brush and that is exactly what Dave and others have done.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 07, 2015, 07:35:05 pm
Cool story, I think we have got the point that you shouldn't probe a 3 phase power plant with one of these by now.
The meter is mislabeled is my main point. One day in a pinch, or in a frenzied hurry, some unsuspecting fool will grab a meter and check the mains at home or at work, not realizing that given the right circumstances, the meter may kill them. Glass fuses with minimal spacing are not proper fuses for Arc-Flash protection. I certainly wouldn't leave the thing plugged in doing an unattended survey.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Grapsus on February 07, 2015, 07:40:05 pm
I don't know why people find this so hard to understand. It's like all the car manufacturers selling V8 sports cars for $50,000. Then some chinese company comes along and sells a V8 sports car that is just as powerful for $7000 but the catch is that it has no seatbelts and the fit and finish is a bit naff. Suddenly everyone is like "Oh my God! you can't sell a car without seatbelts!". But who cares, it's $7000. Install them yourself if you are so inclined.

I think you're saying this seriously, but many of us would consider such a statement to have a high likelihood of being satirical...

I think there might be a cultural difference at play here. For example in western Europe or North America people trust regulations because those imply responsibility. Therefore in those countries you don't expect a large pothole on a highway because you know that somebody is responsible for maintaining the road in good condition. On the other hand, for example in Russia or India, I saw that people only count on themselves and assume that regulations are bullshit, so a one-meter pothole on the highway would not surprise them as much. Since Dave is from a country that is from the first kind, you can't expect him not to be shocked and say something like "wow ! a 40000 count data-logging meter for only 180 bucks, thank you Uni-T ! notice that it might blow your head off, but that's ok, we all know that CAT ratings are bullshit so just be careful when you probe a high energy circuit, after all, you're the only one responsible for your safety".
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 07:42:50 pm
Cool story, I think we have got the point that you shouldn't probe a 3 phase power plant with one of these by now.
The meter is mislabeled is my main point. One day in a pinch, or in a frenzied hurry, some unsuspecting fool will grab a meter and check the mains at home or at work, not realizing that given the right circumstances, the meter may kill them.
Absolutely. I would like to see uni-t remove the cat markings from the offending meters because they are wrong. That said it is moronic to discount the entire line of uni-t meters for low energy usage (which, let's face it, is 99% of electronics use) just because they have false markings on them.


To the people who are dwindling on the fact that you can pay $180 for a meter and get very little in the way of safety - is it really that hard to believe that if you can buy a $180 fluke and get a lot of safety but very few features, you could also part with the same amount of cash for a multimeter that has a tonne of features and very little safety? Regardless of claimed ratings I think its fair to point out that its unreasonable to expect a tonne of features and fluke level safety/quality for the price point. If it was, then fluke would be out of business long ago.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 07, 2015, 07:55:41 pm
Well for 180 $ or here in europe for the same in euro :scared: it is really far away of a good value  :-- :--. For the same money you will get a second hand gossen or fluke with lightyears away better quality in construction , accuracy and input protection .  Even it has 40000 counts resolution this is not a tool . It is a dangerous toy where the packagaging and the carrying bag is more expensive in the production price than the meter itself .
Just keep your eyes open to get a good and cheap multimeter . It s easy to find this at ebay or sometimes on the fleamarket where my old shitty crappy looking norma D 3012 came from ( made in Austria , not in Australia ) . It is a 25000 counts multimeter and the accuracy almost meet the specifications except at 1 V it has 0.04 % instead of 0.02 % accuracy . But for me it is more than enough and anyway this puppy is roundabout 30 years old and it is not a trms meter . And at that time there were no cat ratings for multimeters . But for low energy measurements it is more than good enough and it will work many times longer than this cheap UNI-T s . I m going to make a teardown soon of this multimeter and put some pics here in the forum . By the way , I paid 15 Euro for this multimeter at the fleamarket  ;D
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 08:05:20 pm
Cool story, I think we have got the point that you shouldn't probe a 3 phase power plant with one of these by now.


No you haven't got the point, and I am begging to think you are trolling here, and will report you for doing so soon.

It does not have "this is a dangerous piece of shit" written on the front does it?
If it did then there would be perhaps a case for this to be sold.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 08:06:34 pm
What does a Brymen cost in dollar equivalent?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Rick Law on February 07, 2015, 08:08:44 pm
...

I think there might be a cultural difference at play here. For example in western Europe or North America people trust regulations because those imply responsibility

....

Speak for your self, my friend.  There is nothing in our current administration (USA) that I trust. 
In fact, I assume for the most part the opposite is true.  The Constitution of The USA is written with the premise and the for reason that government cannot be trusted.

Case and point, the administration has been singing praises to themselves about the "low unemployment" and LinkedIn Pulse (their email alerts) latest "Pulse" is "The Big Lie: 5.6% Unemployment" written by Jim Clifton, CEO at Gallup.

Private labs such as UL carries far more weight to me than anything the USA government can say.

I fault UNI-T in carrying false labels.  This in my view is fraudulent.  I think UNI-T is good enough that it has a market without falsely claiming compliance.  It has a role even as a non CATx compliant meter.

I would like it better if UNI-T simply erase the label.  Since in some cases, the PCB already made provision, UNI-T can print on the box "Upgradable to CATx ???V compliant by authorized service agent".

Rick
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 08:12:36 pm
It does not have "this is a dangerous piece of shit" written on the front does it?
If they replaced the cat text with that, would your perceived value of the product be better, worse or unchanged? I'm curious to know.

Numerous people have claimed that they consider it poor value for money solely based on the false cat rating so I'm curious if people would consider it better value if it made no claim to being safe at all

People don't seem to have an issue with sub $50 meters which make dubious claims about safety, so how is this one any different? Its more expensive but it also brings a tonne of features to the table.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 08:20:34 pm
A Brymen is much better value for money, and not that far off in price.

Do you have a UniT meter TMM ?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 08:24:58 pm
A Brymen is much better value for money, and not that far off in price.

Do you have a UniT meter TMM ?
I own a UT71D and a Fluke 87V...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 08:28:46 pm
A Brymen is much better value for money, and not that far off in price.

Do you have a UniT meter TMM ?
I own a UT71D and a Fluke 87V...

How do you feel about the quality of that Uni-t?
Have you opened it up?

A Brymen 857A is about $160 (from TME), plus some for delivery, but hey it is UL listed and built like a tank.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 07, 2015, 08:40:47 pm
I thought the datalogging cable for the Brymen was expensive and it doesn't have internal datalogging memory? It probably works out to be close to double what I paid for the uni-t.

The quality of the uni-t is 'good enough' imo. Its not fluke-level but it doesn't feel like cheap junk either. The only thing that really sucks is the poor quality voltage/com jacks.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 08:45:24 pm
The discussion about fuses is moot. If you're worried about glass fuses, buy the 1KV version. The real CAT rating is unknown; hopefully it is at least CAT II 600V, which would be sufficient for most of us. My Gossen has that rating and it doesn't even have a fuse on the mA range, just a polyswitch.
Independent testing is the only way to tell for sure what the CAT rating is. I wish IEC would stipulate that as a requirement, like they do for some other instruments. In the meantime, be safe and stay away from the meter if you have to test high energy circuits.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 08:51:38 pm
The discussion about fuses is moot. If you're worried about glass fuses, buy the 1KV version. The real CAT rating is unknown; hopefully it is at least CAT II 600V, which would be sufficient for most of us. My Gossen has that rating and it doesn't even have a fuse on the mA range, just a polyswitch.
Independent testing is the only way to tell for sure what the CAT rating is. I wish IEC would stipulate that as a requirement, like they do for some other instruments. In the meantime, be safe and stay away from the meter if you have to test high energy circuits.

Isn't it also about the meters ability to protect itself (MOVs etc)?
Lightages found that his Uni-t couldn't and died, he made a vid about it.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 08:58:39 pm
MOVs are not a requirement, although it is probably wise to install.
The 71E didn't die, the 61E did. But it wasn't a CAT rating test at all. By the way, it doesn't matter if the meter dies, as long as the damage is contained.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: electr_peter on February 07, 2015, 08:58:57 pm
On the 71D, 10,000 data memory, accessible on the meter or the PC. 30,000 on my Gossen 30M, but I have to buy the Gossen cable and software to see any of it (350$). That's after you paid 900$ for the meter, 60$ for the bag and 140$ for the 5V wall wart, otherwise you have 16 hours of battery life. Oh, it's only CAT II 600V, with 100mA max. And it comes with a bodged cap on the DC to DC converter.
Gossen 30M with 1 200 000 counts, stable reference and 4 wire measurement is not in the same league for price comparison. It is like comparing rotten apples and gold plated oranges.
Agilent/Keysight sell IR->USB interface for ~30$ USD. UNI-T IR->USB adapter is the same for all their meters I thinks - same adapter for 61, 70, 81 series at least. Gossen are on very expensive side for some reason with their adapters and SW.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: IshtarTor on February 07, 2015, 09:04:00 pm
It does not have "this is a dangerous piece of shit" written on the front does it?
If they replaced the cat text with that, would your perceived value of the product be better, worse or unchanged? I'm curious to know.

Numerous people have claimed that they consider it poor value for money solely based on the false cat rating so I'm curious if people would consider it better value if it made no claim to being safe at all

People don't seem to have an issue with sub $50 meters which make dubious claims about safety, so how is this one any different? Its more expensive but it also brings a tonne of features to the table.

In any case, I would go for one of the newer models, which are both good value AND safe. And it's better if you buy it in Europe rather than in China, as chinese resellers may put crappy fuses instead of the correct ones. Or buy fuses as well.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 09:10:06 pm
MOVs are not a requirement, although it is probably wise to install.
The 71E didn't die, the 61E did. But it wasn't a CAT rating test at all. By the way, it doesn't matter if the meter dies, as long as the damage is contained.

Yes, sorry about the model confusion, confusing to say the least (though UniT are not alone here!).
Not a question of user safety, more a question of the value, if the meter is electrically "fragile", not so much a bargain if it "joins the choir invisible" when something nasty happens.
Every time it needs replacing it effectively doubles in cost (if replaced with the same model).
Again, this is not a point about user safety, and not about high energy circuits, just unexpected high volts or perhaps wrong range selected (charged cap when in ohms mode sort of thing).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 09:14:13 pm
All ranges are protected by crowbar circuits up to 1000V.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Candid on February 07, 2015, 09:20:15 pm
There seeme to be many different board designs. These are some pictures of my 71E that I bought some weeks ago. Only the MOVs have been added by me the rest is original. The board was already designed for adding MOVs so I only had to solder them in.

I just removed the metal can so you can see what there is under it in the 71E with maybe the newest board design. I got it from reichelt.de in germany.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Candid on February 07, 2015, 09:21:29 pm
And under the metal can.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Candid on February 07, 2015, 09:22:30 pm
Last Picture.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 07, 2015, 09:24:59 pm
All ranges are protected by crowbar circuits up to 1000V.

Thanks again Wyt!

Lights vid is unclear as it is after the fact, wonder what the threshold for damage is?
Not specifically UniT, and as suggested before, be nice to see a range of meters incrementally hit with high voltages.
Find out at what point the damage occurs for each model, as it is part of the bang for buck (ooo bad punnage).
Again, not high energy, just high volts (high energy is another type of issue and vid altogether!).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 07, 2015, 09:28:48 pm
Interesting. So, there have been a few changes under the can. Part of the resistor network has gone surface mount (resistor network, voltage divider). The 4x2.5MOhms resistors in series are still through hole.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 07, 2015, 10:11:20 pm
Modifying a multimeter with added MOVs or a spark gap does not make it safer, not necessarily. The design of the circuit board, the placement of the components, and the actual values are to be taken as a whole. It is possible that the current limiting resistors on the input jacks are not up to the task and putting an MOV in there is just adding a miniature bomb ready to go off if the current goes through it. I sincerely think that they aren't there as a cost cutting measure, but they could have been omitted to prevent a bigger problem that wasn't anticipated in the original design.

Labeling a meter with a specific safety rating incorrectly is wrong and no one can defend that. What is the harm? Well how about the person who is buying his first meter and watches some youtube video about meter ratings and sees that the UT71E is rated for CATIV 600V and then proceeds to use it on the meter connection to his house and gets seriously burned? This is not a problem? Sure the meter might be good value for the money, but only if you know that the ratings are a lie and know what you are buying.

No one can argue that meter with exactly the same specs is not a better meter if it has the correct CAT rating on it instead of a bogus one. No one can argue that a meter with a bogus rating is being sold truthfully. No one can argue that everyone has the time to take apart every meter on the market before they buy one and have them all tested individually for safety. That is what the standards are supposed to be for and why people die and get burned when they trust the CAT rating on a meter stuck on there by greedy assholes, culturally related or not. Thanks to off brand thieves and liars, people die. It is that simple.

That is why I started the thread about meters that don't appear to meet their CAT ratings, so that there was a reference and some guides for people to check. I have not updated it for a long time but it seems it needs to be again. How a sticky that is there for all to read with warnings about Uni-T meters has been missed, including by Dave, I don't know.

So Uni-T makes some shit meters, and some blatantly unsafe ones. DON"T BUY THEM. If they make safer ones, them buy them and send them a message that people don't want the bad ones. Unfortunately education and culture do play a part in this and where I live quality seems to be a joke and to ask for service is an insult. Mastech, Victor, Vichy, etc, all have deservedly bad reputations but then you get people here and other forums complaining about meter snobs who don't understand the needs of the less fortunate who don't have the money. Again what is the point of these discussions? EDUCATION. The poor and underprivileged need the same education so at least when the buy junk, they know, and they know the risks and limitations.

I have yet to see a Mastech I would recommend, nor a Vichy, most Digiteks no, and if I do recommend anything for anyone from the really budget class I make it a point to educate that the bogus CAT ratings are a joke and they should keep the probes out of the wall socket. Yes, not everyone has $100 to spend on a meter, some not even $50. This is exactly who needs to know what they are buying and why they need to be careful where they use it.

As far as the UT61E I had. It fried at 2500VDC. This was above the rated input but not above the impulse it is supposed to protect the user from. Maybe around 10mA passed through from the test and it caused nice sparks to jump around the selector dial. If it had been a 500A pulse the meter probably would have exploded. If you can see the spark at <10mA image the arc at 500A!!!

Again, say what you want about a meter having "value" even if it doesn't meet its safety rating. Go tell that to the people's friends and family who died in the story linked to earlier.

<Edited for grammar and spelling>
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 07, 2015, 10:30:51 pm
You just about summed it up Lightages. Sounds about right to me.. :box: < It's a knockout!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 07, 2015, 10:35:11 pm
Sure the meter might be good value for the money

But...that's the point. It isn't. $180 isn't a cheap meter by any standard. $180 for a meter where every single component is a cheap clone, several major design flaws, fake safety rating, marginal performance (the chip is a 20000 count device yet the meter claims 40000 count) isn't "good value". There are plenty of good meters at that price range, this one shouldn't be among them.

So Uni-T makes some shit meters, and some blatantly unsafe ones. DON"T BUY THEM. If they make safer ones, them buy them and send them a message that people don't want the bad ones.

Does it work like that? If people see other people using Uni-T meters they might assume it's a good brand. It isn't. The meter in this video was intentionally built to rip people off and make the maximum amount of profit. There's no other explanation IMHO.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 07, 2015, 10:36:31 pm
a meter where every single component is a cheap clone

Er, they are?

Quote
marginal performance (the chip is a 20000 count device yet the meter claims 40000 count)

No, the chip is a 44,000 count device.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 07, 2015, 10:41:19 pm
No, the chip is a 44,000 count device.

Watch the video again at time 17:15

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 07, 2015, 10:42:55 pm
No, the chip is a 44,000 count device.

Watch the video again at time 17:15

Watch the video again and look at the chip. Dave was wrong, it is an ES51966, which is a 44,000 count chip. It is clearly visible at 15:45.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 07, 2015, 10:44:42 pm
And let's not forget that Dave couldn't actually use the "Watts" function because they didn't supply the right plug for Australia.

(Probably just as well given the 1mm clearance between the input voltage line and GND. Would you connect it to something like a washing machine with a big motor?)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 07, 2015, 10:45:31 pm
Watch the video again and look at the chip. Dave was wrong, it is an ES51966, which is a 44,000 count chip. It is clearly visible at 15:45.

Ok, you win. I was just going by what the video said.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 07, 2015, 10:54:23 pm
a meter where every single component is a cheap clone

Er, they are?

Well, maybe not 100% of them. But far too many. When you're charging $180 the very least you could do is buy real part.

PS: I bet you're fun at parties...

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: hamdi.tn on February 07, 2015, 11:07:07 pm
some ppl gone too far with this killer meter , i used a Uni-t dirt cheap meter in main , in 3 phase main it work ok , and still alive  :phew:
i don't think that anyone here needed this video to actually be aware of how this meter quality is crap compared to any other high range brand, but again you know what you buying with your money, you know the risks related to it.
And i think some ppl here tend to forget that all of us started as hobbyist ... mean that you only have a limited amount of money to put it in one place, and a uni-t meter will surely be enough for the task and for the budget.
However lying about safety is certainly wrong and immoral, and they should correct that ...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 07, 2015, 11:32:24 pm
Value is all about matching price to expectations.

Would you not feel ripped off if you spent $180 on a meter then opened it up and saw what we saw in this video?




Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: sparx on February 07, 2015, 11:49:06 pm
some ppl gone too far with this killer meter , i used a Uni-t dirt cheap meter in main , in 3 phase main it work ok , and still alive  :phew:
i don't think that anyone here needed this video to actually be aware of how this meter quality is crap compared to any other high range brand, but again you know what you buying with your money, you know the risks related to it.
And i think some ppl here tend to forget that all of us started as hobbyist ... mean that you only have a limited amount of money to put it in one place, and a uni-t meter will surely be enough for the task and for the budget.
However lying about safety is certainly wrong and immoral, and they should correct that ...

Just because you survived, doesn't mean that somebody else may connect it to 240v mains and it cause damage/injury/death.


Compare it to a vehicle, I get in my car and drive nearly every day. I'm sitting near enough on top of gallons of high power fuel with a relatively low flashpoint. I trust that the manufacturer has performed safety testing, and engineered in safety to the design. Same with the tyres and every other component.

When a manufacturer starts labelling equipment with markings/certifications which it does not have then they are undermiming those certifications/markings and what they mean, potentially resulting in future distrust in the markings as they will start to mean nothing! At least in that case I may be able to chase a global, massive, vehicle manufacturer for damages. I doubt you'd get a penny out of Uni-T.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Nerull on February 08, 2015, 12:14:14 am
Brymens are in the same price point, have almost all of the same features (except the near-useless watt range), and aren't built like shit.

No, a comparison between a Uni-T and a Gossen or brand-new Fluke isn't fair, but those aren't the only meters in the market. The Uni-T fails to compete with other meters in *its* price range.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Leadfootin on February 08, 2015, 12:35:59 am
If you want to know about our "safety rating" agencies, go to restorecsa.com which highlights some of the issues with CSA and it's ratings.

The articles will show you why not to trust any stated rating from one of these agencies.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: AlphZeta on February 08, 2015, 12:45:44 am
For those who are not familiar with CAT rating requirements, from Wikipedia:

...The required values can vary from 0.04 mm for single insulation CAT II, 50 V, to 28 mm for double insulation CAT IV, 1000 V. The exact values are defined in the international standards.[1] Such standards should be followed rigorously during the design process of the appropriate equipment.

So yes, the fact it does not meet CAT IV standard is pretty clear.

But I wouldn't go so far as to discredit this meter altogether. Having the ability to measure power is one of its main selling point and most electricians only do mains related work and would not need an accuracy higher than 0.1 W.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rageoftheblacksmith on February 08, 2015, 01:14:18 am
Hello Dave and everybody else.
I'm writing here because i own a couple of UNI-T instruments but i am not a fanboy, neither am i trying to justify the money i spent on those things.

In the past i had to rely on a 830 and a 2905 chinese multimeters; i ain't posting pics because i suppose you all know what i am talking about.
In an emergency (woodworking workshop, very important machine stopped running) i had to search for the 400V 3-phase power with the 830; in another emergency i had to do the same (MIG welding machine) with the 2905. I was lucky, i'm still alive and both meters still pretend to work.

Back to recent times, my old no-brand LCR meter died and i wanted to replace it, so i went searching on ebay and i found this UNI-T LCR meter and i bought one.
When i got it in the mail i started testing it and i was pretty happy with it, the perceived quality was good so i decided to buy a multimeter from the same manufacturer and i got myself a 71D.

Unfortunately i wasn't on eevblog forum then and i found no information on UNI-T being bad; i can't afford a Fluke at the moment and i wonder if there is any intermediate segment between no-brand cheap shit, UNI-T down and The Real Instruments up. I thought i had a good deal with my UNI-T meters but now Dave says "don't buy that crap", more or less.

I've been thinking of buying an oscilloscope and, well, i would have gone for a UNI-T one but now i am not so sure.

Hope i wasn't boring you people, greetings and wishes,
rageoftheblacksmith.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 08, 2015, 01:21:17 am
There really needs to be a requirement here for people to state where they live before asking for any recommendations. This comes up over and over and over again. Where do you live? It is hard to tell you the best place to buy or what to buy if we have no idea where you are!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rhdf on February 08, 2015, 01:32:43 am
And that would likely be why Uni-T has no official distributors and meters are only available through third-party sellers on places like Amazon, Craigslist, eBay, etc.

If Uni-T had official ties outside China, that would expose them to lawsuits for wrongful death or injuries attributable to failure to meet their safety rating claims if there has been any.

Well, In Sweden they are sold by  At least 2 "big" chains. "Clas Ohlson", who sells some models as "UNI-T Clas Ohlson Edition" No idea whats special with that edition, but the package states "imported by Clas Ohlson".
The other one is "Kjell & Co" They seems to sell them "unbranded"
( non of them has the 71E model, only the 61D as "top model") But ~600 SEK is "OK" for hobbyists instead of the cheapest FLUKE for double the price
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: AG6QR on February 08, 2015, 01:36:16 am
I've got an older Triplett meter (1101) which has engraved in the plastic case "NOT FOR USE ON HIGH ENERGY CIRCUITS".  It has a glass fuse inside, lacks proper input protection to pass CAT standards, but it meets my expectations.  It is what it is, and like Dave's first Micronta meter that he displayed in the Radio Shack video, it is capable of safely doing useful work within its limitations.

The UNI-T, on the other hand, clearly claims it meets CAT standards, but it doesn't.  The circuit board looks like it was even designed to hold proper fuses, but assembled without them.  The company obviously made a conscious decision to cut costs at the expense of safety, and they did it while maintaining the claim on the front of the meter that it meets CAT standards.  And they package the meter with the device to invite you to plug it into mains.

That's slimy and untrustworthy.  If I can't trust the company behind the meter, I won't really trust the readings from the meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rolycat on February 08, 2015, 01:37:01 am
There really needs to be a requirement here for people to state where they live before asking for any recommendations. This comes up over and over and over again. Where do you live? It is hard to tell you the best place to buy or what to buy if we have no idea where you are!
A poll (https://www.eevblog.com/forum/chat/%28poll%29-setting-the-country-in-new-user-profiles/) a year ago showed a substantial majority in favour of requiring users to specify a country during registration. This can be a 'black flag' for those paranoid about revealing personal information on the net.

However, Dave does not appear keen.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 08, 2015, 01:39:45 am
Value is all about matching price to expectations.

Would you not feel ripped off if you spent $180 on a meter then opened it up and saw what we saw in this video?
Although it was not really a variable in my purchase decision for my UT61E, I certainly would not be happy that a device clearly labeled as Cat-IV like the 71E might only meet Cat-II and only up to 250V. Intentionally misleading people into believing the device is much safer than it actually is certainly does not earn positive marks from me and should not earn any from anyone.

If you are going to design a piece of equipment that only meets 250V Cat-II safety, do the world a favor and mark it as 250V Cat-II before you kill someone.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rageoftheblacksmith on February 08, 2015, 01:40:32 am
Where do you live? It is hard to tell you the best place to buy or what to buy if we have no idea where you are!

Sorry, Lightages, i didn't think that my location was important. I live in Italy and most of the chinese stuff i buy online comes either from Hong Kong or from stocks in the UK.
I wouldn't buy anything from the U.S.A. because stuff coming from there always seems to be involved in customs trouble.
Should i ever decide to buy a Fluke there should be no problem because they are supposed to be made in Germany, right?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 08, 2015, 01:47:33 am
I'll say it again eh?
Brymen meters if you are in EU.

There's a few places to get them, TME, and our own Lightages or Franky(Iloveelectronics)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 08, 2015, 02:02:36 am
What Yago said!

Look at these, much safer, better built, and more reliable:
http://www.tme.eu/en/details/bm257/portable-digital-multimeters/brymen/bm257s/# (http://www.tme.eu/en/details/bm257/portable-digital-multimeters/brymen/bm257s/#)
http://www.tme.eu/en/details/bm829/portable-digital-multimeters/brymen/# (http://www.tme.eu/en/details/bm829/portable-digital-multimeters/brymen/#)
http://www.tme.eu/en/details/bm857a/portable-digital-multimeters/brymen/# (http://www.tme.eu/en/details/bm857a/portable-digital-multimeters/brymen/#)
http://www.tme.eu/en/details/bm869/portable-digital-multimeters/brymen/bm869s/# (http://www.tme.eu/en/details/bm869/portable-digital-multimeters/brymen/bm869s/#)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rageoftheblacksmith on February 08, 2015, 02:11:04 am
Thank you Yago and Lightages for the information.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: iampoor on February 08, 2015, 02:52:03 am
The problem with buying these meters that lie about the safety ratings is that it encourages the manufacture to keep on making them!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: zapta on February 08, 2015, 03:11:25 am
There really needs to be a requirement here for people to state where they live before asking for any recommendations. This comes up over and over and over again. Where do you live? It is hard to tell you the best place to buy or what to buy if we have no idea where you are!

I just adding that they live in my town and give advise accordingly.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 08, 2015, 05:13:10 am
If they replaced the cat text with that, would your perceived value of the product be better, worse or unchanged? I'm curious to know.

Numerous people have claimed that they consider it poor value for money solely based on the false cat rating so I'm curious if people would consider it better value if it made no claim to being safe at all

People don't seem to have an issue with sub $50 meters which make dubious claims about safety, so how is this one any different? Its more expensive but it also brings a tonne of features to the table.

If you are buying a meter with an expectation that it meets the claimed safety rating then yes it would be poorer value for money if it failed to meet them. Value is all about matching price to expectations. It isn't a measure of features per dollar.
Hmm. What i am having trouble understanding is how people are willing to accept that the chinese UT61 series for $60 is a good deal but the UT71 series for $130 isn't. Both promise cat IV and fail to deliver. The extra features justify the price hike over a UT61. I must have missed the memo that after a multimeter exceeds a certain $ point it MUST be safe, regardless of how useful it's features are otherwise, or it must be crucified on EEVBlog forums.

I'll admit the 71E seems to represent worse value compared to it's cheaper A/B/C/D brothers. A mains power dongle is obviously of limited usefulness when the input protection is of a low standard. That said, it's not reason alone to lump all of one brand of meters together and declare universally "Uni-T Meters Suck".
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: IshtarTor on February 08, 2015, 05:48:08 am
For those who are not familiar with CAT rating requirements, from Wikipedia:

...The required values can vary from 0.04 mm for single insulation CAT II, 50 V, to 28 mm for double insulation CAT IV, 1000 V. The exact values are defined in the international standards.[1] Such standards should be followed rigorously during the design process of the appropriate equipment.

So yes, the fact it does not meet CAT IV standard is pretty clear.

But I wouldn't go so far as to discredit this meter altogether. Having the ability to measure power is one of its main selling point and most electricians only do mains related work and would not need an accuracy higher than 0.1 W.
Except that you DON'T want to use this on mains.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 08, 2015, 06:41:24 am
Except that you DON'T want to use this on mains.
Why not? I don't think that the meter needs a lot of cats to be able to function when connected to the mains. And if you are worried about the meter blowing up somehow (wouldn't the probe melt first if you shorted the mains) just place it further away from you.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: AG6QR on February 08, 2015, 07:00:13 am
For those who are not familiar with CAT rating requirements, from Wikipedia:

...The required values can vary from 0.04 mm for single insulation CAT II, 50 V, to 28 mm for double insulation CAT IV, 1000 V. The exact values are defined in the international standards.[1] Such standards should be followed rigorously during the design process of the appropriate equipment.

So yes, the fact it does not meet CAT IV standard is pretty clear.

But I wouldn't go so far as to discredit this meter altogether. Having the ability to measure power is one of its main selling point and most electricians only do mains related work and would not need an accuracy higher than 0.1 W.
Except that you DON'T want to use this on mains.

I agree that it's a piece of crap that shouldn't be used.  But let me play devil's advocate for just a moment...

We all plug in various devices into mains -- lamps, power supplies, radios, computers, kitchen appliances, etc.  The only things which I commonly use that have proper HRC fuses are multimeters.  I've seen some junk inside of consumer goods that make that awful UNI-T look fantastically safe in comparison.  Yet most consumers survive their appliances.  Most general consumer goods that most of us plug in to mains are generally safe, yet they don't have CAT ratings, and they're not as rigorously designed as a top quality industrial multimeter.  What's the difference?

One difference is that meters are often being held in your hand as you stick them in the socket, so any explosion is right next to you.  Another is that meters may sometimes be used for probing around in the main power distribution panel, where very large currents are available.  But a big difference is that it's up to us, the users, to connect the meters to mains properly every single time.   And most meters have both a high impedance mode, for voltage measurement, and a low impedance mode, for current measurement.  The mistake that is too easy to make, and potentially deadly when made with a poor quality meter, is to probe a high energy voltage source when your probes are plugged into the current terminals.  There aren't many other devices which we regularly connect to mains that have this potential for deadly user error.

That mains dongle that comes with the UNI-T meter would seem to prevent the human error of mixing up the voltage and current probing.  That's worth something, in my book.

That dongle would seem to turn the Uni-T meter into a specialized mains power consumption meter that is almost as idiot proof as the P3 Kill-a-Watt meter (common in the USA).  The Kill-a-Watt does not claim a CAT rating. 

But even with the dongle, the UNI-T doesn't stack up well against the dedicated power meter.   The UNI-T costs nine times as much, has a worse resolution of 1 watt versus 0.1 watt for the P3 Kill-a-Watt meter, and the Uni-T doesn't measure cumulative energy over time, while the Kill-a-Watt does.  The Kill-a-Watt is a $20.00 specialized device for measuring power and energy consumption of mains-powered devices, not a general purpose multimeter.  Still, if you want a power meter for mains power, you could do worse than buying a Kill-a-Watt for that particular task, while buying a general purpose multimeter that doesn't make a false CAT claim for your other tasks.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 07:06:28 am
it's not reason alone to lump all of one brand of meters together and declare universally "Uni-T Meters Suck".

Why not? This obviously intentional - somebody in management signed off on this meter and presumably gave the order to swap the expensive HRC fuses for cheap glass ones (to increase profit!)

Why would you buy anything from a company which does that?

Its only selling feature is the "Watts" function but that only works for large Wattages so it's useless (almost).

But I wouldn't go so far as to discredit this meter altogether. Having the ability to measure power is one of its main selling point and most electricians only do mains related work and would not need an accuracy higher than 0.1 W.

Why would an 'electrician' buy that multimeter when these things cost about $30?

(http://g-ecx.images-amazon.com/images/G/01/electronics/detail-page/Image_A.jpg)

You shouldn't be using a multimeter for finding live mains wires, use one of these instead (much faster/safer/easier!):

(http://www.fluke.com/NR/rdonlyres/BED0D7ED-88C9-47C6-A358-C31BC49F0433/0/F1aca_II_03a_328px_x_220px.jpg)

You can buy both of those, get a proper multimeter for electronics work (eg. the Brymen BM257) and still have change from $180. No need to keep Unit-T in business ripping people off.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 08, 2015, 07:14:53 am
Why would an 'electrician' buy that multimeter when these things cost about $30?

(http://g-ecx.images-amazon.com/images/G/01/electronics/detail-page/Image_A.jpg)
Do tell me more about it 40000 count datalogging functionality and Cat IV safety. Oh wait.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 07:18:52 am
let me play devil's advocate for just a moment...

The mistake that is too easy to make, and potentially deadly when made with a poor quality meter, is to probe a high energy voltage source when your probes are plugged into the current terminals.  There aren't many other devices which we regularly connect to mains that have this potential for deadly user error.

This is precisely what CAT ratings are for. One of the things a CAT rating tells you is that you can connect the meter to power with any combination of leads or range-selector setting and it won't kill you. If it fails, it will fail safely (should blow a fuse at most - no internal fires allowed).

The Kill-a-Watt does not claim a CAT rating. 

The Kill-a-Watt doesn't allow you to move leads around or select a low-impedance path through it.

That mains dongle that comes with the UNI-T meter would seem to prevent the human error of mixing up the voltage and current probing.  That's worth something, in my book.

Except that Dave couldn't actually use it in the country where he bought the meter - more evidence that they simply don't care about customers and don't deserve anybody's business.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 08, 2015, 07:19:54 am
Well this electrician would be sucidal to use this " multimeter " for power measurements on mains . Anyway if you look at the specs the multimeter is suited for 5 A continously and more than 5 A for 10 seconds . That means you can use it from 0.1 until 1150 Watts at cos phi 1 . Measuring power for 10 sec maximum is absolutely useless . This " multimeter " is a really bad joke and for 165 Euro ist is an absolutely rip off . The input jacks are shit , the clearance inside is shit , the fuses are shit , the overvoltage protection is shit , the trace to the com jack is shit , well it is in specs , but that doens t catch the world on fire . It is a dangerous slapped together piece of shit labelled with the wrong cat rating , sold for an astronomical price . normally it has to be banned from the market and been destroyed by the authority . Even if there are several versions on the market with better input protection and fuses , the board contruction has not enough clearance to meet the cat IV regulation . You can put in 100000 movs and ptc s and anything else but this " multimeter " never never never will meet the cat IV rating , no way !!!!!!
It is a good example of crap design and planned obsolescence . One small transient and the " multimeter " is dead and if you send it back they will tell you that you used it out of the voltage rating and don t send you a new one for free and that s it . Even if you don t use it on mains , the jacks never never would give good contact after more than 1000 connections with the probes and the contacts of the range switch will be worn out quickly , so this multimeter tightly may survive the guarantee  time and after that it is fit only for a knacker s yard
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 08, 2015, 07:27:51 am
The Kill-a-Watt doesn't allow you to move leads around or select a low-impedance path through it.
To be fair, neither does the UT71E when used in conjunction with the supplied mains dongle.

Except that Dave couldn't actually use it in the country where he bought the meter - more evidence that they simply don't care about customers and don't deserve anybody's business.
Pretty sure the meter Dave obtained is analogous to a grey import, regardless of what the 'distributor' would have him believe.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 08, 2015, 07:54:46 am
Well by the way , electricians don t use the wall wart wattmeters because they are not accurate enough . In many of the VDE 701/702 insulation testers there is a built in function tester for the test item and this also measures power . But these testers are really special and cost a damn lot of money . For example the Fluke 2600-2 cost roundabout 1700 bucks .
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 08:07:55 am
Quote from: TMM
Except that Dave couldn't actually use it in the country where he bought the meter - more evidence that they simply don't care about customers and don't deserve anybody's business.
Pretty sure the meter Dave obtained is analogous to a grey import, regardless of what the 'distributor' would have him believe.

It will be interesting to see if Uni-T responds to this video, it could seriously affect their sales.

(I'm betting they won't, pretty much everything inside the meter is indefensible...)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 08, 2015, 08:29:01 am
Quote from: TMM
Except that Dave couldn't actually use it in the country where he bought the meter - more evidence that they simply don't care about customers and don't deserve anybody's business.
Pretty sure the meter Dave obtained is analogous to a grey import, regardless of what the 'distributor' would have him believe.

It will be interesting to see if Uni-T responds to this video, it could seriously affect their sales.

(I'm betting they won't, pretty much everything inside the meter is indefensible...)
They have actually responded to the design of the UT71 before https://www.eevblog.com/forum/reviews/uni-t-multimeter-ut71d-unboxing-and-teardown/15/ (https://www.eevblog.com/forum/reviews/uni-t-multimeter-ut71d-unboxing-and-teardown/15/)

I think Dave owes it to us to tear down a UT139, UT181 or UT171 series before making blanket statements about the entire brand.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: classical on February 08, 2015, 08:43:09 am
i can't afford a Fluke at the moment and i wonder if there is any intermediate segment between no-brand cheap shit, UNI-T down and The Real Instruments up. I thought i had a good deal with my UNI-T meters but now Dave says "don't buy that crap", more or less.
For my use as hobbyist I also bought a BM857A from TME. Delivery to Germany was very quick and without issues. Nice meter with very good value (at least when I bougt it). But regarding TME you have to add the VAT!
I also have access to a BM869 which in some aspects it is a better meter and the dual display can be very helpful e.g. measuring ripple or flickering of a lamp. So you alsways have correponding U=~ and U~ values in one sample. When I bougt the BM857 it was a bit cheaper than today and the difference to the BM257 was too low to think about it.
I also have access to a BM525 which is very fine for standalone data logging.
I've been thinking of buying an oscilloscope and, well, i would have gone for a UNI-T one but now i am not so sure.
watch Daves reviews on Rigol 1054Z https://www.youtube.com/watch?v=W2qdtQkBKhc (https://www.youtube.com/watch?v=W2qdtQkBKhc)
If this is too expensive look for a Rigol 1052e on sale or second hand.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 08, 2015, 08:52:27 am
What i am having trouble understanding is how people are willing to accept that the chinese UT61 series for $60 is a good deal but the UT71 series for $130 isn't. Both promise cat IV and fail to deliver.
Mt UT-61C bought from Reichelt in Germany is silk screened "CATIII 300V" and "CATII 600V". It also displays silk screened TÜVRheinland and GS logos. The TÜV logo for some reason says ID:0000000002, though.


(https://www.eevblog.com/forum/product-reviews-photos-and-discussion/uni-t-ut61e-multimeter-teardown-photos/?action=dlattach;attach=29867;image)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: iampoor on February 08, 2015, 08:53:17 am
Quote from: TMM
Except that Dave couldn't actually use it in the country where he bought the meter - more evidence that they simply don't care about customers and don't deserve anybody's business.
Pretty sure the meter Dave obtained is analogous to a grey import, regardless of what the 'distributor' would have him believe.

It will be interesting to see if Uni-T responds to this video, it could seriously affect their sales.

(I'm betting they won't, pretty much everything inside the meter is indefensible...)
They have actually responded to the design of the UT71 before https://www.eevblog.com/forum/reviews/uni-t-multimeter-ut71d-unboxing-and-teardown/15/ (https://www.eevblog.com/forum/reviews/uni-t-multimeter-ut71d-unboxing-and-teardown/15/)

I think Dave owes it to us to tear down a UT139, UT181 or UT171 series before making blanket statements about the entire brand.

Why dont you do the teardown? I think its a pretty safe bet to say that Dave wont be giving Uni-T any more Simoleans after this video.  >:D
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 08, 2015, 09:13:30 am
What is inside the power adapter for the meter, it could have its own shunts etc and not pass the full current and voltage to the meter, not that I will be buying one. I did however buy a UT61E on the recommendation's from this forum 2 years ago. I have now just joined the yellow peril brigade and ordered a Fluke 115 for work on power circuits this is to replace my old dinosaur AVO. I was thinking of an AVO410 but why buy a re-badge Chinese meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 08, 2015, 09:16:05 am
Well it is a little better than the 71E but still  :scared: :scared: :scared: . Look at the clearance between the 10A fuse and the shunt resistor . Must be 2 or 3 mm clearance . They still have to do their homework at UNI-T  :-- :-- :palm:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 08, 2015, 09:23:13 am
Well it is a little better than the 71E but still  :scared: :scared: :scared: . Look at the clearance between the 10A fuse and the shunt resistor . Must be 2 or 3 mm clearance . They still have to do their homework at UNI-T  :-- :-- :palm:

Could be a safety feature, acts as a spark gap shunting a HV surge to ground before it goes through the meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: poorchava on February 08, 2015, 09:28:43 am
I am using UT71A as one of my 2 main meters (the other one being a Fluke 87). In general I'm pretty satisfied with the accuracy I must say.  Other thing is that I don't do a great deal of mains connected stuff,  so the clearances and such are of little interest to me (and if I have to measure mains,  I use fluke anyway).

Brymen might be a better deal,  but the uni-t is not bad either,  if the safety ratings are not that big of a deal.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 08, 2015, 09:36:40 am
What is inside the power adapter for the meter, it could have its own shunts etc and not pass the full current and voltage to the meter, not that I will be buying one. I did however buy a UT61E on the recommendation's from this forum 2 years ago. I have now just joined the yellow peril brigade and ordered a Fluke 115 for work on power circuits this is to replace my old dinosaur AVO. I was thinking of an AVO410 but why buy a re-badge Chinese meter.

For sure there will absolutely nothing inside the adaptor except the parallel wiring to the V and Com and in serial to the A jack . If it would the price for the UT 71e would be 350 $ at that price policy of Uni-T . There needn t to be a shunt resistor or transformer in the adaptor , it is a superduper safe multimeter with cat IV rating  :-DD
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 09:45:50 am
Anyone notice the solder joint adjacent to the ADC pin 1 @ 8:55? It looks marginal at best.

Yes, I was wondering about that.

It looks to me like all the through-hole parts that come from underneath the board are hand-soldered. Look (for example) at the flux residue around the two joints to the left of the PTC at 5:50 (the ones labelled '+' and '-'). Definitely has a hand-soldered look to it.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 08, 2015, 09:46:37 am
What i am having trouble understanding is how people are willing to accept that the chinese UT61 series for $60 is a good deal but the UT71 series for $130 isn't. Both promise cat IV and fail to deliver.
Mt UT-61C bought from Reichelt in Germany is silk screened "CATIII 300V" and "CATII 600V". It also displays silk screened TÜVRheinland and GS logos. The TÜV logo for some reason says ID:0000000002, though.


(https://www.eevblog.com/forum/product-reviews-photos-and-discussion/uni-t-ut61e-multimeter-teardown-photos/?action=dlattach;attach=29867;image)
Yes, but most people who have purchased the UT61E have the chinese version with no MOVs/SGs and purchased it with the knowledge that it shouldn't be used on high energy circuits.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 08, 2015, 10:00:24 am
What i am having trouble understanding is how people are willing to accept that the chinese UT61 series for $60 is a good deal but the UT71 series for $130 isn't. Both promise cat IV and fail to deliver.
Mt UT-61C bought from Reichelt in Germany is silk screened "CATIII 300V" and "CATII 600V". It also displays silk screened TÜVRheinland and GS logos. The TÜV logo for some reason says ID:0000000002, though.


(https://www.eevblog.com/forum/product-reviews-photos-and-discussion/uni-t-ut61e-multimeter-teardown-photos/?action=dlattach;attach=29867;image)
Yes, but most people who have purchased the UT61E have the chinese version with no MOVs/SGs and purchased it with the knowledge that it shouldn't be used on high energy circuits.

Who are these "most people"?
Are you referring to the members of EEVBlog, because that is far from the numbers of these meters sold I'd GUESS.
Or do yo have number of meters sold and the education and experience of all buyers.

I already pointed out that the Brymen 857a(and you may get the improved 857S) is the same price from TME as the UniT is (I logged to get the gross price).
Why on earth would anyone even take the risk of any misleading posts about dangerous UniT here, when 857A is available.
Didn't someone here hack the Brymen data logging code too (I seem to remember a thread)?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 08, 2015, 10:09:15 am
Who are these "most people"?
Are you referring to the members of EEVBlog, because that is far from the numbers of these meters sold I'd GUESS.
Or do yo have number of meters sold and the education and experience of all buyers.
The general impression that it get from reading posts on the internet, which has about as much merit as Dave's blanket statement that Uni-T has a bad reputation. Dave is actually violating Australian defamation law and would have a big problem if he made a similar statement about an Australian company.

I already pointed out that the Brymen 857a(and you may get the improved 857S) is the same price from TME as the UniT is (I logged to get the gross price).
Why on earth would anyone even take the risk of any misleading posts about dangerous UniT here, when 857A is available.
I've already pointed that out but just incase you have already forgotten - the Brymen meter with the datalogging cable costs over US$200 to my door. A UT71D which has a similar feature set, plus internal datalogging memory is around US$130. If safety was a concern i would absolutely not buy the Uni-T. If i only needed to use it for low energy circuits I would consider the tradeoffs of the Uni-T for a considerable price saving.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 08, 2015, 10:21:57 am
Yes, you did and I didn't forget.
I'll try and find that thread, at the moment got the mother of migraines.

I just put safety first, always.

Edit found this, might be worth a look:
https://gitorious.org/sigrok/libsigrok/commit/e493ec2aac301aae16b9aa42cb7574a857285c6f
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 08, 2015, 10:43:01 am
Having just read through this thread and the Fluke data sheets Dave posted I have come to the conclusion that it is not just the CE marks you cannot trust but the CAT ratings as well even on a known brand like fluke as looking on the web I see what are more than likely fake Flukes.
Therefore the only safe route is to buy a meter made by an ISO 9001 registered company through another ISO 9001 registered company.
Before the ISO 9001 came along I used to do work for BNFL at Sellafield, I made low grade waste bins an sea water gate actuator levers as a sub contractor, I would buy Orlikon welding rods which were Lloyd's registered and still had to send a packet or two of each shipment to Lloyd's for testing as even back then in the early 80's there was fake products being sold and no documentation path.
So the only route to be taken to ensure absolute safety is but from an ISO registered stockist with all the associated extra costs.   
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: 0b01010011 on February 08, 2015, 10:44:50 am
Inside the Tenma 72-7730A ordered about October 2014 from Farnell Australia.

The original 500mA HRC fuse was unbranded similar to how the 10A one is, but I blew that one during a moment of stupidity and had to replace it.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 08, 2015, 10:52:48 am
i'm glad i didn't buy the uni-turd meter :D i bought a Brymen 869S instead.... i(t was just 40Euro more expensive) took it apart just to see the input protection.. there is a significant difference... note the big-ass fuses, input resistors and several movs.

(https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-(why-uni-t-meters-suck)/?action=dlattach;attach=135013)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Horstelin on February 08, 2015, 11:10:14 am
I own a voltcraft VC940 (which is a labeled UNI-T 71E). I got it as a Christmas gift from my dad 2 years ago. He (like Dave) basicly bought it because of the Power measurement functions and since he doesn't know one's stuff in electrical engineering he had no idea even about what CAT ratings are.

My meter broke after I had used the power measurement function on a Wifi Printer which draws ~5-10 W. It's bricked, only shows +88.888 on the Display. I have found several persons on the internet who had the same problem (Mainly in German forums).

Of course, my dad did not keep the receipt so 180€ down the drain.

Guys stop defending UNI-T in respect to the 71E, it clearly isn't properly engineered enough to be connected to mains. Nevertheless they still sell it with an adaptor to connect it to the mains. And there are no shunt resistors whatsoever in that adaptor, everything is directly connected to the meter.

Still makes me mad that the store my dad bought it from seems to sell overpriced crap to people who have no idea what they are doing.

Cheers,  Urs
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 08, 2015, 11:20:07 am
Having just read through this thread and the Fluke data sheets Dave posted I have come to the conclusion that it is not just the CE marks you cannot trust but the CAT ratings as well even on a known brand like fluke as looking on the web I see what are more than likely fake Flukes.

To my knowledge there has never been a fake Fluke meter.
Some have come close, like "Fuke" and others that try to look similar, but have never seen a fake that looks exactly like a real fluke.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 08, 2015, 11:23:28 am
It will be interesting to see if Uni-T responds to this video, it could seriously affect their sales.

It won't do diddly squat. People who want a cheap meter will always buy a cheap meter.
And may people simply don't care about proper input protection, and if you don't then, well, that's entirely your choice.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 08, 2015, 11:28:42 am
I think Dave owes it to us to tear down a UT139, UT181 or UT171 series before making blanket statements about the entire brand.

If you read my video description I do say "generally suck".
Those "professional" ones (as they call them?) do look decent at first glance.
But if Uni-T do make a couple of decent meters, the fact remains that it seems that the majority of meters they make a built down to a price and cut so many corners.
I have no doubt Uni-T are capable of making a decent meter if they really want, but they just fail to do it so often people come to expect that from them.
They have very much earned the reputation they have ended up with.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: FrontSideBus on February 08, 2015, 11:46:16 am
I must admit, I was recently after a decent electronics multimeter. Previously I've been using an AC/DC clamp meter and while it was good for basics measurements, I wanted something more precise.
I was looking at some of the "high-end" Uni-T meters and thought about it for a while but after reading several very, very mixed reviews I saved a bit of money and got an ex Australian Defence Force Tektronix DMM916 sent over to the UK from a surplus dealer in AU, champion.
I'm glad I did that now after seeing this video!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: firewalker on February 08, 2015, 11:50:55 am
I believe the subject is over analyzed. The are using fake ratings. That's it. If they were stating the truth, no one could say anything.

Alexander.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: R_Gtx on February 08, 2015, 11:55:30 am
Why is everybody confusing the CAT rating, which on all meters applies only to the V-R-.. input ranges with overload protection, which is applicable to the I inputs. Yes, HRC fuses are preferable, but they are not in the high impedance input so do not impact on that inputs CAT rating.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 08, 2015, 12:09:54 pm
Having just read through this thread and the Fluke data sheets Dave posted I have come to the conclusion that it is not just the CE marks you cannot trust but the CAT ratings as well even on a known brand like fluke as looking on the web I see what are more than likely fake Flukes.

To my knowledge there has never been a fake Fluke meter.
Some have come close, like "Fuke" and others that try to look similar, but have never seen a fake that looks exactly like a real fluke.
I was looking today on E bay and saw quite a few 87's that were supposedly like new with protection film still on etc the probes did not look right and they were asking a third of the price as a buy now that other used were selling at auction for.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 12:18:38 pm
Why is everybody confusing the CAT rating, which on all meters applies only to the V-R-.. input

Nope. The CAT rating says that you can connect the maximum rated input (eg. 600V AC) to any input with the range selector set to any position.

Yes, HRC fuses are preferable

Here's a case of an exploding multimeter that killed two people and badly injured another because of ... a glass fuse:

http://ecmweb.com/arc-flash/case-deadly-arc-flash (http://ecmweb.com/arc-flash/case-deadly-arc-flash)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: eV1Te on February 08, 2015, 12:23:39 pm
... I've already pointed that out but just incase you have already forgotten - the Brymen meter with the datalogging cable costs over US$200 to my door. A UT71D which has a similar feature set, plus internal datalogging memory is around US$130. If safety was a concern i would absolutely not buy the Uni-T. If i only needed to use it for low energy circuits I would consider the tradeoffs of the Uni-T for a considerable price saving.

A long time ago I did use a Uni-T meter to measure the incoming mains line to my building, after seeing this video I am happy nothing went wrong because I was unaware of these safety issues!

Maybe you know that your meter is only good for low voltage measurements, but you might lend it to a family member or a friend that then uses it for another purpose.

I would not have a problem with Uni-T if they labeled their multimeters as Cat-II 300V.
Title: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: timb on February 08, 2015, 12:46:27 pm
For portable data logging, I bought three of those $25 Digitek meters. Comes with not-as-cheap feeling probes, RTD and the USB cable. It's even CAT II rated.

For lab use, I don't know why anyone would bother with this $180 piece of garbage when you can get something like a used 5.5 digit Keithley 197A benchtop meter for $100 on eBay and a GPIB to USB adapter for $50. (They're small, lightweight and even have provisions for a battery pack!)


Sent from my Smartphone
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Owen on February 08, 2015, 12:52:22 pm
Nope. The CAT rating says that you can connect the maximum rated input (eg. 600V AC) to any input with the range selector set to any position.

And why is Brymen using 0.63A/500V and 10A/600V fuses in their BM257? Because they specified three different CAT ratings for their volt and amp ranges: mA -> CATIII 500 V(ac) 300 V(dc), A -> CATIII 600 V(ac) 300 V(dc), V -> as it's shown on the multimeter. I don't like that either. No I'm not a fanboy of Brymen and/or Uni-T, but that's why i bought an Agilent/Keysight U1272A and i love it.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: eV1Te on February 08, 2015, 12:53:55 pm
I started reading a bit more in this thread, but not all the posts so maybe someone has brought this up before.

It seems that a few people does not know what happens when you accidentally short a high energy power line with a multimeter and then pull away the probes so that you get an arc that can span between the phases. The initial short might be due to a transient in the power line that arcs inside the DMM or the operator might have used the current setting instead of voltage with incorrect fuses in the DMM.


Here is a controlled experiment of what happens if you get this type of short from a faulty DMM (not a real person in the video)
Demonstration of HS 20kA Arc in 100A Disconnect 15 Cycles (https://www.youtube.com/watch?v=hA-w0QAaxRU#)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 08, 2015, 01:37:21 pm
Nope. The CAT rating says that you can connect the maximum rated input (eg. 600V AC) to any input with the range selector set to any position.

And why is Brymen using 0.63A/500V and 10A/600V fuses in their BM257? Because they specified three different CAT ratings for their volt and amp ranges: mA -> CATIII 500 V(ac) 300 V(dc), A -> CATIII 600 V(ac) 300 V(dc), V -> as it's shown on the multimeter. I don't like that either. No I'm not a fanboy of Brymen and/or Uni-T, but that's why i bought an Agilent/Keysight U1272A and i love it.

Could only guess that the meter is only capable of measuring up to 8 Amp, and displays an over range.

One thing that is sure, is that it will interrupt dangerous currents safely, as it has been tested so by the UL.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 08, 2015, 02:17:35 pm
Which is why I posted the link on page 9 to the EC&M article about arc flash. I read this at the time in the print version of the magazine and took it to heart. See, I foolishly did the same thing where I worked when a 750KVA transformer blew one of its phases. I used a trusted meter, a Fluke and probed the 480V 3 phase 400A distro box with no cover on it now. It was all "hurry up find out we're losing money!"  Because all of the "engineers" in the plant had their thumbs up their ass, I decided to take action.They were having a debate by staring at the open box wondering how electricity flowed, so I was pro-active.
Yes nothing happened, but after reading that story I will never probe a high energy circuit with any multimeter, especially when it is in distress. It's not worth the gamble.
My point is again is that this meter is a blatant lie in regards to the CAT ratings on the face and inside as well. It is a disaster waiting to happen.
It seems that a few people does not know what happens when you accidentally short a high energy power line with a multimeter and then pull away the probes so that you get an arc that can span between the phases.
Here is a controlled experiment of what happens if you get this type of short from a faulty DMM (not a real person in the video)
Demonstration of HS 20kA Arc in 100A Disconnect 15 Cycles (https://www.youtube.com/watch?v=hA-w0QAaxRU#)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 08, 2015, 03:33:05 pm
We need to send some meters to Photoinduction so that he can test them including a Fluke as I suspect that his HV supply will see a Fluke off as well but how soon and at what voltage would be interesting.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 08, 2015, 04:10:42 pm
Who are these "most people"?
Are you referring to the members of EEVBlog, because that is far from the numbers of these meters sold I'd GUESS.
Or do yo have number of meters sold and the education and experience of all buyers.
The general impression that it get from reading posts on the internet, which has about as much merit as Dave's blanket statement that Uni-T has a bad reputation. Dave is actually violating Australian defamation law and would have a big problem if he made a similar statement about an Australian company.
I do not see how Dave could be liable for defamation for pointing out how Uni-T disregarded safety with blatantly false Cat-III/IV ratings. That would be a violation of trade (misrepresentation, misleading advertising) and occupational safety laws in many countries. Uni-T rightfully deserves to get named and shamed for it.

It is not defamation when the "defamatory" comments are undeniable facts.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 08, 2015, 04:27:35 pm
In answer to Brymen has used lower rated fuses than the CAT voltage rating in their older meters, it was allowed by the regulations at the time. They still had designed the circuit board correctly and used full HRC fuses capable of breaking the appropriate pulse current specified in the CAT rating tests. The only difference was that the fuse was a lower rated voltage.

This is no longer allowed by the latest regulations so Brymen has revised all their meters that they produce to match the latest requirements. The BM257 is now known as the BM257s and has fuses matching the voltage rating of the rest of the meter. To be clear, the fuses have always been capable of the interruption current needed for the CAT rating on the meter. The difference between the old Brymens and the UT71E is night and day for safety.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mariush on February 08, 2015, 04:32:29 pm
Dave, you should update the blog post (or main website) and change the link and text for the correct cyrustek IC.  Maybe also put a note on the video to correct what you said - you say in video they're using 20k count dmm chip instead of 40k.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Nerull on February 08, 2015, 04:33:40 pm
Who are these "most people"?
Are you referring to the members of EEVBlog, because that is far from the numbers of these meters sold I'd GUESS.
Or do yo have number of meters sold and the education and experience of all buyers.
The general impression that it get from reading posts on the internet, which has about as much merit as Dave's blanket statement that Uni-T has a bad reputation. Dave is actually violating Australian defamation law and would have a big problem if he made a similar statement about an Australian company.

 :-DD :-DD :-DD
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: c4757p on February 08, 2015, 04:42:56 pm
As much as I thought that most of the opinions he gave in this video were silly (exception being the safety standards bit), anyone bleating about it being illegal to give such opinions really ought to just shut up and let this viewpoint die. They're opinions for fuck's sake. "Dave's blanket statement that Uni-T has a bad reputation" is an opinion, unless there's some objective notion of what makes up a "bad reputation".
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 08, 2015, 05:31:10 pm
I once shorted out the mains outlet with a really cheap meter (with unfused 10A range). The meter survived, part of the probe pin vaporized though.

And I do not have access to a 10kV line or even a 100A line. Maybe shorting out 400V 100A line could make the meter explode...

Also, most of the devices connected to the mains (except multimeters) have glass fuses rated for 250V. If that fuse is good enough for a radio, PC or an amp, why a multimeter containing the same fuse should not be connected to the mains?

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 08, 2015, 05:39:36 pm
I once shorted out the mains outlet with a really cheap meter (with unfused 10A range). The meter survived, part of the probe pin vaporized though.

And I do not have access to a 10kV line or even a 100A line. Maybe shorting out 400V 100A line could make the meter explode...

Also, most of the devices connected to the mains (except multimeters) have glass fuses rated for 250V. If that fuse is good enough for a radio, PC or an amp, why a multimeter containing the same fuse should not be connected to the mains?

you have a circuitbreaker/fuse (usually 6/10/16Amp here in Europe) in the line which is providing the power to that radio.... but in the distribution panel you have lines with 100+ Amp fuses..... that's why there are CAt II, III, IV ratings.. CAT II is good enough to poke around in the house - and a glass fuse is kind of OK for CAT II.  CAT IV must have "giant" HRC fuses to be able to disconnect the circuit safely when the meter is used in the distribution panel.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: classical on February 08, 2015, 05:42:36 pm
Also, most of the devices connected to the mains (except multimeters) have glass fuses rated for 250V. If that fuse is good enough for a radio, PC or an amp, why a multimeter containing the same fuse should not be connected to the mains?
Please read http://en.wikipedia.org/wiki/Measurement_category (http://en.wikipedia.org/wiki/Measurement_category) for CAT definition.
A mains outlet is different from the mains inlet into your house. within your house you have additional breaker which are lower rated and help a lot.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 08, 2015, 05:43:23 pm
It is a good argument that glass fuses in any equipment connected to the mains is a bad idea. In fact, in England, all equipment connected to mains is supposed to have a specifically designed ceramic fuse.

But the main difference is with a multimeter is that you are intentionally connecting a direct short across two test points. This is much different than providing a backup protection for a piece of equipment that normally runs without shorts.

If you have a multimeter that is rated CATI/250V, then glass fuses are acceptable. If you have a meter rated for CATIII then they are not acceptable.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: classical on February 08, 2015, 05:44:17 pm
Also, most of the devices connected to the mains (except multimeters) have glass fuses rated for 250V. If that fuse is good enough for a radio, PC or an amp, why a multimeter containing the same fuse should not be connected to the mains?
Please read http://en.wikipedia.org/wiki/Measurement_category (http://en.wikipedia.org/wiki/Measurement_category) for CAT definition.
A mains outlet is different from the mains inlet into your house. within your house you have additional breaker which are lower rated and help a lot.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Jay_Diddy_B on February 08, 2015, 05:53:16 pm
I once shorted out the mains outlet with a really cheap meter (with unfused 10A range). The meter survived, part of the probe pin vaporized though.

And I do not have access to a 10kV line or even a 100A line. Maybe shorting out 400V 100A line could make the meter explode...

Also, most of the devices connected to the mains (except multimeters) have glass fuses rated for 250V. If that fuse is good enough for a radio, PC or an amp, why a multimeter containing the same fuse should not be connected to the mains?



The issue is fault currents. Essentially the closer you are the source of the electrical power the higher fault currents. Fuse and breakers are given a interrupting capacity. The danger is that if the fuse cannot interrupt the current a plasma will form which is conductive and by-pass the fuse.

CAT 1 is for circuits that are not directly connected to the mains.

CAT II is for sub-circuits. The wall outlets in your house would normally be included in this category.

CAT III would be the distribution panel in your house. An outlet close the panel may be CAT III

CAT IV is for industrial applications, power entry into building etc.

Most of the catastrophic accidents occur when a multi-meter with inadequate safety is used.

The danger with a DMM is might be set on the wrong range, for example the current range and then connected to a supply with very high fault currents. This can trigger a plasma, like arc welding, and is called an arc-flash event.

A small fuse can protect some appliances because they are connected to circuits with lower fault current ratings.

Jay_Diddy_B
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 06:05:46 pm
I once shorted out the mains outlet with a really cheap meter (with unfused 10A range). The meter survived, part of the probe pin vaporized though.

The issue is fault currents. Essentially the closer you are the source of the electrical power the higher fault currents. Fuse and breakers are given a interrupting capacity. The danger is that if the fuse cannot interrupt the current a plasma will form which is conductive and by-pass the fuse.

This is why HRC fuses are filled with sand - to prevent that plasma from forming.

Glass fuses can also explode with enough force to bend the metal of the fuse holder out of shape and touch other parts of the meter internally (this is why flukes have blast walls all around the fuse area even though they use HRC fuses!)

Here's a cautionary tale of an exploding multimeter that killed two people and badly injured another. The suspected reason? It had glass fuses in it.

http://ecmweb.com/arc-flash/case-deadly-arc-flash (http://ecmweb.com/arc-flash/case-deadly-arc-flash)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 08, 2015, 06:05:59 pm
It is a good argument that glass fuses in any equipment connected to the mains is a bad idea. In fact, in England, all equipment connected to mains is supposed to have a specifically designed ceramic fuse.

Which is not internal to the equipment and has nothing to do with protection of the equipment. Nor is it present on any equipment connected via means other than a BS1363 plug or a fused connection unit designed to replace said plug. There is a substantial amount of this equipment in the home.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 08, 2015, 06:11:03 pm
my 2cents for those who don't know....

HRC fuse has sand in it, and it's bigger.... that's the whole point - if the fault current (in kilo-Amps range) is blowing a fuse, the wire in the fuse is instantly vaporized - the sand will simply extinguish the arc by cooling the plasma (former wire) very quickly - combined with the longer distance for the arc it yields a very good disconnect capability.

small glass fuse - once the wire is vaporized - the air / gas in the fuse is not able to cool the plasma (former wire) quick enough and the plasma becomes a short - letting even more current to flow, heating up even further till the whole multimeter explodes, PCB traces are vaporised - providing even more plasma to conduct across the wires - this will go like avalanche - it will go like that till wires are melted and the distance between the wires will be large enough to extinguish the arc.

however with small fault currents the glass fuse is just ok - because it can't heat up so rapidly (less energy blows the fuse).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 08, 2015, 06:12:23 pm
It is a good argument that glass fuses in any equipment connected to the mains is a bad idea. In fact, in England, all equipment connected to mains is supposed to have a specifically designed ceramic fuse.

Which is not internal to the equipment and has nothing to do with protection of the equipment. Nor is it present on any equipment connected via means other than a BS1363 plug or a fused connection unit designed to replace said plug. There is a substantial amount of this equipment in the home.

I stand corrected. I thought that all equipment was required to have the BS1363 fuse.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 08, 2015, 06:13:45 pm
I once shorted out the mains outlet with a really cheap meter (with unfused 10A range). The meter survived, part of the probe pin vaporized though.

And I do not have access to a 10kV line or even a 100A line. Maybe shorting out 400V 100A line could make the meter explode...
If you want/need to poke around inside a breaker box, the fuse/breaker bus-bars can carry 100-200A depending on what the entrance breaker/fuses are, more if you account for surge ratings. If you probe the mains entrance terminals, then you have a completely unprotected connection directly to the local low-voltage distribution transformer which can provide a short-circuit current well over 1kA, enough to make your probe leads explode if nothing else blows first.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 08, 2015, 06:16:58 pm
It is a good argument that glass fuses in any equipment connected to the mains is a bad idea. In fact, in England, all equipment connected to mains is supposed to have a specifically designed ceramic fuse.

Which is not internal to the equipment and has nothing to do with protection of the equipment. Nor is it present on any equipment connected via means other than a BS1363 plug or a fused connection unit designed to replace said plug. There is a substantial amount of this equipment in the home.

I stand corrected. I thought that all equipment was required to have the BS1363 fuse.

Absolutely not. Not only does it have nothing at all to do with the equipment (it protects the cable) the fuse (A BS1362 fuse..) is only required to protect said cables from the excessive continuous current available on a 30/32A ring final circuit. This means: Every switch, every light fitting, every smoke alarm, any equipment over 13A (and most over 10A), and anything not fitted for a BS1363 plug (substantial amounts of industrial and commercial equipment, most hardwired equipment) has no contact with a BS1362 fuse.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 08, 2015, 06:41:13 pm
If you want/need to poke around inside a breaker box, the fuse/breaker bus-bars can carry 100-200A depending on what the entrance breaker/fuses are, more if you account for surge ratings. If you probe the mains entrance terminals, then you have a completely unprotected connection directly to the local low-voltage distribution transformer which can provide a short-circuit current well over 1kA, enough to make your probe leads explode if nothing else blows first.

In which case the multimeter is good enough. The power to my house comes from an outside panel with the meter and a 3x16A breaker. I do not have access to that panel, it belongs solely to the power company. The breaker panel inside my house is thus current limited by the breaker. So, unless I break the law and either open the panel with the meter or break into a substation, I probably would not be able to make the meter explode by accident.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 08, 2015, 06:54:25 pm
Huh, I posted a question in here a few minutes ago... oops.

I was asking about the length of cable run from the high energy source providing an inductance that resists the initial current surge.
So the closer you are to the high energy source the higher the danger.
This also being part of CAT ratings and fuse requirements.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: yaputya on February 08, 2015, 07:04:37 pm
The weird ass adapter looks like it has the classic European mains sockets (well, most of Europe)

It's the standard Euro plug alright - called a pig's nose for obvious reasons. The socket is recessed about 2cm with the two holes at the bottom and two springs on the sides for earth, they look pretty strange compared to the flat Aussie type. Also they are not polarised, so Active and Neutral can be on either pin. The socket probably supports the plug mechanically much better than Aussie ones though.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 08, 2015, 07:14:17 pm
The weird ass adapter looks like it has the classic European mains sockets (well, most of Europe)

It's the standard Euro plug alright - called a pig's nose for obvious reasons. The socket is recessed about 2cm with the two holes at the bottom and two springs on the sides for earth, they look pretty strange compared to the flat Aussie type. Also they are not polarised, so Active and Neutral can be on either pin. The socket probably supports the plug mechanically much better than Aussie ones though.

actually it's the Schuko socket  - one of the standard sockets in Europe ;)  the other standard is the French type - but both of the sockets are accepting the Euro-plug.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: plexus on February 08, 2015, 07:16:51 pm
I appreciated the review. The board looks ok but yes it was a weird to see all the trimmers and lack of precision parts. seems like they are dialing in the precision. the challenge with that is linearity. but the lack of claimed rating infrastructure nullifies consideration for the product. add in its $190 (is that AUS?) and well you can do well better or even just spend the money on a quality meter with less features.

Thanks to dave for pointing out the features vs quality on this meter. too many companies are padding up the feature set and comprimising quality. the quality aspect is harder to tell unless you open it up and test it.

I don't feel dave was out of line on his comments about this meter. it should irritate you when companies try and pass off a POS like this by padding it with crappy features and charge so much for it. its a shame we have to dig into these things to validate the claims so thanks to dave for doing that for us.

FAIL
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 08, 2015, 07:52:11 pm
In which case the multimeter is good enough. The power to my house comes from an outside panel with the meter and a 3x16A breaker. I do not have access to that panel, it belongs solely to the power company. The breaker panel inside my house is thus current limited by the breaker. So, unless I break the law and either open the panel with the meter or break into a substation, I probably would not be able to make the meter explode by accident.
In my case, the building has 100A cartridge fuses for my apartment and while investigating the relatively low outlet voltage, I went in the utility room to measure line voltage directly at the service disconnect / entrance fuse box to rule out building wiring. I did the same thing at my previous apartment but that was to file a complaint with the power company for weak/floating neutral which killed both of my CRT monitors. AFAIK, those fuses are intended to be user-serviceable, so no law is broken by me accessing those terminals.

A few years ago, one of my friends called me in the middle of the night because his mother called him about power freaking out in her apartment with lights flickering wildly on half the circuits whenever the fridge started. It turned out there was a 20-50V drop across one of the 100A entrance fuses. After removing the fuse, it read open (>100Meg) on the ohm range - I definitely was not expecting that from a fuse that can still pass enough current to (sort of) run a fridge and some lights.

Those are the sorts of occasions where someone might end up probing a effectively unprotected circuits without being in an industrial environment.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 08, 2015, 08:05:10 pm
AFAIK, those fuses are intended to be user-serviceable, so no law is broken by me accessing those terminals.
Different places, different rules. The panel with the meter and a breaker near my house has a seal on it. Also, breakers are used everywhere instead of fuses (fuses can be found in old installations only). This was done probably because nobody replaced blown fuses - just put a piece of wire on the fuse after it blew.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 08, 2015, 09:05:49 pm
Also, breakers are used everywhere instead of fuses (fuses can be found in old installations only). This was done probably because nobody replaced blown fuses - just put a piece of wire on the fuse after it blew.

I thought the traditional 'fix' was a .22 bullet ... they're about the same size as a standard fuse.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 08, 2015, 09:19:39 pm
I thought the traditional 'fix' was a .22 bullet ... they're about the same size as a standard fuse.
Except that a bullet is way more difficult to find than the fuse, not to mention a piece of wire. It was easier to find bullets during and immediately after WW2, but WW2 happened a log time ago.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 08, 2015, 09:27:08 pm
There is a good case for banning DVM's in high energy environments and having meters that only read volts and separate meters for amps of the clamp variety, looking through the Fluke range I notice that they do have meters without the amp range.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: jancumps on February 08, 2015, 10:11:30 pm
AFAIK, those fuses are intended to be user-serviceable, so no law is broken by me accessing those terminals.
Different places, different rules. The panel with the meter and a breaker near my house has a seal on it. Also, breakers are used everywhere instead of fuses (fuses can be found in old installations only). This was done probably because nobody replaced blown fuses - just put a piece of wire on the fuse after it blew.
We're not discussing your apartment here. We're talking about a meter that claims it is safe to be used at points where you personally  are not allowed to go in your apartment.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 08, 2015, 10:33:08 pm
Slightly off topic,
There is a great invention to thwart dodgy Chinese electronics plugged in to the mains socket, be they glass or ceramic fused, from burning down your house, and it's the:
AFCI http://en.wikipedia.org/wiki/Arc-fault_circuit_interrupter (http://en.wikipedia.org/wiki/Arc-fault_circuit_interrupter)
With these, they detect an arc in its infancy and trip the breaker. I don't know if they are used in the EU & Australia, but they sure do work in here in the US.
Many states specify the use of them in "living areas" as being a mandatory installation. I just got done updating all the wiring from 1939 and up, in my "new" home, and put them on all branch circuits regardless of the mandatory locations.
All wiring was gutted out for scrap and MC armoured cable installed. The MC cable http://www.afcweb.com/product-category/mc-metal-clad-cables/ (http://www.afcweb.com/product-category/mc-metal-clad-cables/) keeps the critters from chewing on the Romex and see line one above. A little pricy on the refit, but safety first.
The original wiring had seen too many do-it-yourselfers without the simplest of knowledge, including a single circuit that was fed from 2 different breakers in a "loop" configuration. :clap:
My point is if it can be done in a shoddy manner, it will be. China as of late the greatest offender. At least there's a remedy for it in the AFCI. :blah:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: jancumps on February 08, 2015, 10:43:49 pm
At least they are protected by your mains fuse. The UNI-T is supposed to work upstream of that tripper, where there is no fuse to protect you from harm :)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Corporate666 on February 08, 2015, 11:24:56 pm
A fool and his life are soon parted with?  Darwin award?  Who in their right mind would work with +300V from a Chinese multimeter?  Granted, in the US, we only really have 120, so for us, it's really not much of an issue.   :bullshit:

Fluke meters are made in China too.  And I don't think "Uni-T" is a particularly Chinese sounding name... certainly not like Tenma or the ones that don't even have a name on them.

And I don't think it's unreasonable to expect something labeled to a spec to meet that spec - it's a foundation of marketing and truth in advertising.

In cases where something doesn't meet its spec or isn't of the quality the name or price suggest, how does the consumer find out about that?  They either open it up themselves (in which case they have already purchased it, likely can't then return it and may not be qualified to know what they are looking at).  Or they look to a reviewer who does know what he/she is talking about to review the product.

Sort of like Dave.  :o
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Hydrawerk on February 09, 2015, 12:52:40 am
UT70A is quite OK for me. It was designed in 2002 or so. But it has some minor problems. https://www.eevblog.com/forum/testgear/uni-t-ut70a-gone-weird/msg255397/#msg255397 (https://www.eevblog.com/forum/testgear/uni-t-ut70a-gone-weird/msg255397/#msg255397)
https://www.youtube.com/watch?v=lBJJrkUiD7Q (https://www.youtube.com/watch?v=lBJJrkUiD7Q)
Also if you want to replace battery, you have to loosen three screws. For changing the fuse you must loosen seven screws. It is badly designed. The input protection is also rather poor.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 09, 2015, 01:00:04 am
I thought the traditional 'fix' was a .22 bullet ... they're about the same size as a standard fuse.
You would have a hard time replacing one of these:
http://uk.farnell.com/cooper-bussmann/non-100/fuse-100a-250v-one-time/dp/2112064 (http://uk.farnell.com/cooper-bussmann/non-100/fuse-100a-250v-one-time/dp/2112064)
with a bullet - the gap between terminals for the 100A/250V type is almost 6" / 15cm.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Monkeh on February 09, 2015, 01:10:02 am
I thought the traditional 'fix' was a .22 bullet ... they're about the same size as a standard fuse.
You would have a hard time replacing one of these:
http://uk.farnell.com/cooper-bussmann/non-100/fuse-100a-250v-one-time/dp/2112064 (http://uk.farnell.com/cooper-bussmann/non-100/fuse-100a-250v-one-time/dp/2112064)
with a bullet - the gap between terminals for the 100A/250V type is almost 6" / 15cm.

In Soviet Russia, bullet much bigger than fuse. 12.7mm and 14.5mm rounds aren't that uncommon.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Muttley Snickers on February 09, 2015, 04:15:44 am
These are safer once calibrated, I have the required tool.   :-DD


Muttley
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Smokey on February 09, 2015, 05:34:53 am
My point is if it can be done in a shoddy manner, it will be. China as of late the greatest offender. At least there's a remedy for it in the AFCI. :blah:
(https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-(why-uni-t-meters-suck)/?action=dlattach;attach=135133;image)

That is a serious Violation!!  That rock isn't approved to be used as a chair!!  That rock is going to give that guy back problems!!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 05:42:23 am
One major flaw of the 71E, which was overlooked until recently, is the lack of an intermediate amps range (4A).
The true RMS converter doesn't work properly under 10% of range, which means there is a dead zone between 400mA and 1A on this meter. It overreads by 10~15% of measurement.
That's a show stopper on a meter where AC current and power measurement is a major feature.
If the majority of your AC measurements are under 400mA or above 1A, you're OK, otherwise buy something else.
All meters in the 71 range are affected and so is the 61E, with an even larger dead zone of 220mA~1A AC.
Sadly, the new UT181A probably also has a dead zone between 600mA and 1A. UT171 models are OK.

I'm surprised that 71E owners didn't pick this up sooner.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 09, 2015, 07:10:39 am
I'm surprised that 71E owners didn't pick this up sooner.
As others have said: if Uni-T is willing to fool around something as serious as safety ratings on a meter that is clearly intended to be connected directly to mains, what else might they be less than honest, if not outright liars, about?

People who buy "inexpensive" Uni-T meters might not have something significantly better or more reputable to compare against. My UT61E is currently my "best" meter and my only True (?) RMS one. One of the first things I did when I got my DS1054Z was a sanity check on that: see if I could get them to agree on the RMS value of voltage across a 0.1 ohm low-side sense resistor powering a 23W CFL lamp, a PC power supply, other stuff I had lying around and a mix of them to produce oddball current waveforms. I could get them to agree within 1% by changing the sampling rate and memory depth on the scope, which is about as good as it is going to be with the DS1000z's DC offset issue.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 09, 2015, 08:19:48 am
There are other "more reputable" meters that have blindspots in their ranges too - Agilent U1232A is one.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 09, 2015, 09:22:39 am
I thought the traditional 'fix' was a .22 bullet ... they're about the same size as a standard fuse.
You would have a hard time replacing one of these:
http://uk.farnell.com/cooper-bussmann/non-100/fuse-100a-250v-one-time/dp/2112064 (http://uk.farnell.com/cooper-bussmann/non-100/fuse-100a-250v-one-time/dp/2112064)
with a bullet - the gap between terminals for the 100A/250V type is almost 6" / 15cm.
That is a 20mm cannon shell size fuse.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Maister on February 09, 2015, 09:23:35 am
This is really interseting:
I have the UT61E which you are showing towards the end of the video. Mine is only rated 300V CAT III and not 600V CAT IV.
Despite that mine has a better input protection: A bigger HRC fuse for the 10 amps (690V, I1=80kA), 4 MOVs, and 3 PTCs.

Here are the photos of my UT61E:
https://dl.dropboxusercontent.com/u/11083462/DSCN1240.JPG
https://dl.dropboxusercontent.com/u/11083462/DSCN1241.JPG
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Stonent on February 09, 2015, 09:28:21 am
Um, how has no-one noticed the trace going nowhere? 5:44 in the video. Unless this board has plugged vias, which I seriously doubt. Or my eyes are deceiving me, which is more likely.

It's also visible in other peoples pictures in this thread.

They put in an antenna for better Dave reception.  It didn't work.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 09:36:50 am
There are other "more reputable" meters that have blindspots in their ranges too - Agilent U1232A is one.
That's pretty obvious with the lack of a mA range on the meter and plenty warning text : 'DC/AC current range of 0.6 mA to 300 mA is not measureable on the U1232A and U1233A models'.
More insidious on the 71E. Even Dave, with his vast experience, didn't latch onto that. Mentions of glass fuses always elicit more gasps from the audience.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 09, 2015, 09:38:47 am
More insidious on the 71E. Even Dave, with his vast experience, didn't latch onto that. Mentions of glass fuses always elicit more gasps from the audience.

I wasn't reviewing the meter, it was a teardown. I had barely touched it.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Stonent on February 09, 2015, 09:41:46 am
What Yago said!

Look at these, much safer, better built, and more reliable:
http://www.tme.eu/en/details/bm257/portable-digital-multimeters/brymen/bm257s/# (http://www.tme.eu/en/details/bm257/portable-digital-multimeters/brymen/bm257s/#)
http://www.tme.eu/en/details/bm829/portable-digital-multimeters/brymen/# (http://www.tme.eu/en/details/bm829/portable-digital-multimeters/brymen/#)
http://www.tme.eu/en/details/bm857a/portable-digital-multimeters/brymen/# (http://www.tme.eu/en/details/bm857a/portable-digital-multimeters/brymen/#)
http://www.tme.eu/en/details/bm869/portable-digital-multimeters/brymen/bm869s/# (http://www.tme.eu/en/details/bm869/portable-digital-multimeters/brymen/bm869s/#)

http://www.brymen.com.tw/product-html/index.html (http://www.brymen.com.tw/product-html/index.html)

The Byrmen homepage is straight out of 1996, complete with the animated Under Construction man digging.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 09, 2015, 09:43:42 am
This is really interseting:
I have the UT61E which you are showing towards the end of the video. Mine is only rated 300V CAT III and not 600V CAT IV.
Despite that mine has a better input protection: A bigger HRC fuse for the 10 amps (690V, I1=80kA), 4 MOVs, and 3 PTCs.
Here are the photos of my UT61E:
https://dl.dropboxusercontent.com/u/11083462/DSCN1240.JPG
https://dl.dropboxusercontent.com/u/11083462/DSCN1241.JPG

That goes to show the insane variability in Uni-T products. Madness.
Shame, because your meter is very decent indeed.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 09, 2015, 09:45:33 am
http://www.brymen.com.tw/product-html/index.html (http://www.brymen.com.tw/product-html/index.html)
The Byrmen homepage is straight out of 1996, complete with the animated Under Construction man digging.

They must spend their money UL testing instead of a web designer.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 09, 2015, 09:47:43 am
That goes to show the insane variability in Uni-T products. Madness.

couldn't it be that we have fake UNI-T meters out there ?  :-// or did just UNI-T hired a new management pushing the costs down heavily ?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 09:54:12 am
No fake meters, just some safer versions for specific markets, under pressure from importers.
The company went public recently, is probably flush with cash and is upping their game a bit, with proper independent testing and safer meters in the works. But China is China, so there is always someone on the line looking for shortcuts to save some pennies (fens).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Stonent on February 09, 2015, 10:06:04 am
http://www.brymen.com.tw/product-html/index.html (http://www.brymen.com.tw/product-html/index.html)
The Byrmen homepage is straight out of 1996, complete with the animated Under Construction man digging.

They must spend their money UL testing instead of a web designer.

I just looked at the source code to their page, and it really is about that level of skill, including BLINK tags.  Those were deprecated back in Internet Explorer 4 I think.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 09, 2015, 10:55:27 am
Just opened my UT61B bought for 58€ in a brick and mortar shop (40 less than the next cheapest: the Brymen i really wanted including postage) last northern hemisphere summer.
I seems to have the input protection and proper fusing. It's quite ok and well built for the price.
And if the 61B(GS) 200107-7 code mean that the PCB was designed then? If that's the case, they've been able to do so since at least 2001!

Ah well, i'll get a Fluke when I grow up.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 09, 2015, 11:06:04 am
There are other "more reputable" meters that have blindspots in their ranges too - Agilent U1232A is one.
That's pretty obvious with the lack of a mA range on the meter and plenty warning text : 'DC/AC current range of 0.6 mA to 300 mA is not measureable on the U1232A and U1233A models'.
More insidious on the 71E. Even Dave, with his vast experience, didn't latch onto that. Mentions of glass fuses always elicit more gasps from the audience.
Does it say that anywhere other than buried deep within the Users Guide? I could forgive someone for thinking that a U1232A would have a decent mA range contained within the A range just as it has mV ranges contained within it's V range.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 09, 2015, 11:07:49 am
I have the UT61E which you are showing towards the end of the video. Mine is only rated 300V CAT III and not 600V CAT IV.
Despite that mine has a better input protection: A bigger HRC fuse for the 10 amps (690V, I1=80kA), 4 MOVs, and 3 PTCs.
Where did you buy it?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: 3roomlab on February 09, 2015, 11:15:33 am
This is really interseting:
I have the UT61E which you are showing towards the end of the video. Mine is only rated 300V CAT III and not 600V CAT IV.
Despite that mine has a better input protection: A bigger HRC fuse for the 10 amps (690V, I1=80kA), 4 MOVs, and 3 PTCs.

Here are the photos of my UT61E:
https://dl.dropboxusercontent.com/u/11083462/DSCN1240.JPG
https://dl.dropboxusercontent.com/u/11083462/DSCN1241.JPG

oh my, is that a new revision? or an older but better design?
my version certainly is lacking :P
maybe i could add MOVs as a precaution  :-//

edit :: my over 10yr old APPA 62T which is about USD60 looks to be of even better quality. but i couldnt make out what is the component SPG2 ?  "spark gap" ? a different kind of "MOV" ? the placement of this SPG2 is indeed in a position where someone would find the MOV ... :D ... and a single SIBA... USD60 approx ... unfortunately, this model is no longer around. anyone seen any new APPA? maybe this factory could be the new best favourite for low cost and safe DMM ? (D51/D50 looks like additional space for TVS ?)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 09, 2015, 11:21:59 am
It's quite ok and well built for the price.
And if the 61B(GS) 200107-7 code mean that the PCB was designed then? If that's the case, they've been able to do so since at least 2001!

The problem is that the management of that company feel it's OK to lie to customers and rip them off.

There's alternatives out there. Uni-T don't really deserve anybody's business until there's nothing but well built meters in their lineup and they've recalled all the bad ones from stores.

OK, they're not going to do that but they should at the very least remove the CAT-IV labels and market them for what they are.

Plus HRC fuses and proper track clearances aren't that expensive to do. That's pretty much all it would take to bump the safety up by an order of magnitude.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 11:22:44 am
Just opened my UT61B bought for 58€ in a brick and mortar shop (40 less than the next cheapest: the Brymen i really wanted including postage) last northern hemisphere summer.
I seems to have the input protection and proper fusing. It's quite ok and well built for the price.
And if the 61B(GS) 200107-7 code mean that the PCB was designed then? If that's the case, they've been able to do so since at least 2001!
It looks like you have a GS version modified with the old original BS1362 fuses in place and all MOVs removed. Not good.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 09, 2015, 11:34:13 am
It's quite ok and well built for the price.
And if the 61B(GS) 200107-7 code mean that the PCB was designed then? If that's the case, they've been able to do so since at least 2001!

The problem is that the management of that company feel it's OK to lie to customers and rip them off.

There's alternatives out there. Uni-T don't really deserve anybody's business until there's nothing but well built meters in their lineup and they've recalled all the bad ones from stores.

OK, they're not going to do that but they should at the very least remove the CAT-IV labels and market them for what they are.

Plus HRC fuses and proper track clearances aren't that expensive to do. That's pretty much all it would take to bump the safety up by an order of magnitude.
Right now, my only alternative are the yellow hard plastic 5€ jobbies from the hardware store... I don't want those, even for free.
Your video only reinforced that belief ;)

Anyway you look at it, I'm not getting another UNI-T unless/until they clear up their rating and the manufacturing issues.
As a client I should get what it  says on the box, not gamble that I might...
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 09, 2015, 11:51:57 am
Does it say that anywhere other than buried deep within the Users Guide? I could forgive someone for thinking that a U1232A would have a decent mA range contained within the A range just as it has mV ranges contained within it's V range.

I thought it was pretty obvious from the front panel. It doesn't say mA/uA or mA/A like most meters do.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 09, 2015, 11:53:04 am
Just opened my UT61B bought for 58€ in a brick and mortar shop (40 less than the next cheapest: the Brymen i really wanted including postage) last northern hemisphere summer.
I seems to have the input protection and proper fusing. It's quite ok and well built for the price.
And if the 61B(GS) 200107-7 code mean that the PCB was designed then? If that's the case, they've been able to do so since at least 2001!
It looks like you have a GS version modified with the old original BS1362 fuses in place and all MOVs removed. Not good.
That opens up a few questions:
- Can I solder some on?
- What should be they be rated at?
- Should someone start a thread on "How to make your UT61 less crap for a couple of Euros" (by someone competent, I'm not).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 09, 2015, 11:57:07 am
Does it say that anywhere other than buried deep within the Users Guide? I could forgive someone for thinking that a U1232A would have a decent mA range contained within the A range just as it has mV ranges contained within it's V range.

I thought it was pretty obvious from the front panel. It doesn't say mA/uA or mA/A like most meters do.
It also doesn't say mV or have a dedicated switch position for it, but it does measure mV.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 09, 2015, 12:16:41 pm
Right now, my only alternative are the yellow hard plastic 5€ jobbies from the hardware store... I don't want those, even for free.
Your video only reinforced that belief ;)

Thanks!  :-+
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Horstelin on February 09, 2015, 12:20:26 pm
This is really interseting:
I have the UT61E which you are showing towards the end of the video. Mine is only rated 300V CAT III and not 600V CAT IV.
Despite that mine has a better input protection: A bigger HRC fuse for the 10 amps (690V, I1=80kA), 4 MOVs, and 3 PTCs.

Here are the photos of my UT61E:
https://dl.dropboxusercontent.com/u/11083462/DSCN1240.JPG (https://dl.dropboxusercontent.com/u/11083462/DSCN1240.JPG)
https://dl.dropboxusercontent.com/u/11083462/DSCN1241.JPG (https://dl.dropboxusercontent.com/u/11083462/DSCN1241.JPG)

My UT61D (which I bought from Reichelt.de) seems to have the same input protection:

(http://abload.de/thumb/img_20150209_13101261cau1x.jpg) (http://abload.de/img/img_20150209_13101261cau1x.jpg) (http://abload.de/thumb/img_20150209_12582381fqz8a.jpg) (http://abload.de/img/img_20150209_12582381fqz8a.jpg) (http://abload.de/thumb/img_20150209_12594375d2uk5.jpg) (http://abload.de/img/img_20150209_12594375d2uk5.jpg)

At least the GS and TÜV logos they print on there seem to be real

Cheers
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mullecy on February 09, 2015, 12:38:57 pm
In terms of specs the vc870 seems close to the Uni-T UT71E but seems better constructed:
https://www.eevblog.com/forum/testgear/conrad-voltcraft-vc870/ (https://www.eevblog.com/forum/testgear/conrad-voltcraft-vc870/)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 01:21:53 pm
Safer, yes. A lot of features are lacking: No AC+DC, 1kHz AC bandwidth only, 0.1% accuracy instead of 0.025%, no internal memory, optional PC connection, no peak hold and no current input jack aural warning.
Still, a pretty good meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mullecy on February 09, 2015, 01:36:53 pm
Safer, yes. A lot of features are lacking: No AC+DC, 1kHz AC bandwidth only, 0.1% accuracy instead of 0.025%, no internal memory, optional PC connection, no peak hold and no current input jack aural warning.
Still, a pretty good meter.

not really: it has true-rms, pc connection, and warnings if your probes are not in the right connectors...
if you want 0.025% and true rms ac+dc, take the vc880 for 30E more (but no W measure)

I don't say it's the best dmm but It's OK for lots of usages.
Which dmm would you buy for less than 200E if you had to choose one ?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pasky on February 09, 2015, 02:28:57 pm
I think that's the first time I've seen someone recommend a VC model multimeter over something else.   :P

EDIT: Nevermind, had no idea that was a Voltcraft.  Thought it was the cheap Chinese Vichy (sp?) multimeter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 02:40:50 pm
Safer, yes. A lot of features are lacking: No AC+DC, 1kHz AC bandwidth only, 0.1% accuracy instead of 0.025%, no internal memory, optional PC connection, no peak hold and no current input jack aural warning.
Still, a pretty good meter.

not really: it has true-rms, pc connection, and warnings if your probes are not in the right connectors...
if you want 0.025%, take the vc880 for 30E more (but no W measure)

I don't say it's the best dmm but It's OK for lots of usages.
Which dmm would you buy for less than 200E if you had to choose one ?
Assuming you live in Europe, a second-hand Gossen 26S, which I did buy. An 18S would be pretty good too.
The Fluke 185 is my favorite, but they don't come up for sale very often.
Incidentally, the VC870 and 880 have the same blind spot as the 71E on AC current.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mullecy on February 09, 2015, 03:28:17 pm
Fluke 185 and 2nd hand meters... not easy to find...  :-//

I updated my reply: 880 has truerms ac+dc and has better accuracy and frequency response (1kHz 0.5%, 10kHz 1%, 100kHz 5%, instead of 1kHz 1% for the 870)... I start to feel that I should have bought this one instead of 870...

The problem is to have good performance, availability (if you can't actually buy it?) but also safety : what good is a 200E meter if you can't even check mains with it? At that price point, a bad input protection is unacceptable and raise the question of designers professionalism and the brand honesty: who really verify that the meter actually meets ALL announced performances ? (verifying VDC is easy but doing it ALL is a lot of work that 99.99% users will skip)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: janaf on February 09, 2015, 03:49:33 pm
Small detail that annoys me with the UNI-T meters is that COM terminal is marked with red color text. At least on my UT71D. I have seen the same on pics of other UNI-T models too.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Maister on February 09, 2015, 04:32:30 pm
I have the UT61E which you are showing towards the end of the video. Mine is only rated 300V CAT III and not 600V CAT IV.
Despite that mine has a better input protection: A bigger HRC fuse for the 10 amps (690V, I1=80kA), 4 MOVs, and 3 PTCs.
Where did you buy it?

My girlfriend bought it from www.reichelt.de (http://www.reichelt.de) (Germany) :) (X-Mas present for me :) )
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TASK on February 09, 2015, 04:39:04 pm
Hi.

Im new here. Im frequently watching EEVlog videos. And a just saw that video on Uni-T. Iam as "hobbyist" (hope its writed good: D) sometimes need multimeter. Because i collect old audiotechnics from our national Czechoslovakian firm TESLA. So few years ago i bought Uni-T UT39C for like 45$ something like that. And i just bring you my fotoreport, sorry for not so good quality, i shot it in fast time.

Album:
http://task-ava.rajce.idnes.cz/UNI-T_UT39C (http://task-ava.rajce.idnes.cz/UNI-T_UT39C)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 09, 2015, 04:41:02 pm
I don't think that Amprobe are any better. I have a AM240  There is only one PTC on the input and that is for the Volts ohms low amps and resistance etc. the high amps (if you call 10 amps high) has nothing except the fuse. Amprobe are frequently sold as being made by Fluke which of course they are not it is just the same group holding.
The only saving grace is the cat rating is only claimed to be cat III 600V
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 07:45:13 pm
Just opened my UT61B bought for 58€ in a brick and mortar shop (40 less than the next cheapest: the Brymen i really wanted including postage) last northern hemisphere summer.
I seems to have the input protection and proper fusing. It's quite ok and well built for the price.
And if the 61B(GS) 200107-7 code mean that the PCB was designed then? If that's the case, they've been able to do so since at least 2001!
It looks like you have a GS version modified with the old original BS1362 fuses in place and all MOVs removed. Not good.

That opens up a few questions:
- Can I solder some on?
- What should be they be rated at?
- Should someone start a thread on "How to make your UT61 less crap for a couple of Euros" (by someone competent, I'm not).
Sorry, forgot about your questions. Yes you can and because it is a GS board, it is easy. Just find out the specs from someone who owns one. Usually 1KV MOVs unless in series.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Rutger on February 09, 2015, 07:56:53 pm
I would agree that this is a bad meter, here is why I think so;

1) The design engineer planned to put better components on the board, but Management told them to cut the cost and they had to compromise of safety and on accuracy.
What other compromises are hiding in this meter??
2) A meter in this price class should have precision resistors and not pots that can drift over time and start to corrode.
3) I bet you that the drift of this meter is terrible, with time & temp & moisture this meter will go out of spec really quick.
4) Lying about a rating is just dangerous and wrong and a lawsuit is waiting to happen.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 09, 2015, 08:14:28 pm
4) Lying about a rating is just dangerous and wrong and a lawsuit is waiting to happen.
But who are you going to sue? While I have little doubt lying about safety compliance could potentially lead to wrongful death or injury lawsuits in most civilized coutries, you cannot sue Uni-T directly since it has pretty much zero official presence outside China. You would have to sue the seller who probably happens to be just a random somebody who imported seemingly decent multimeters and sold them for a few quick bucks, like so many other cheap yet dangerous Chinese electronics.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: janaf on February 09, 2015, 08:24:13 pm
In the EU, as far as I know, it's the First importer / seller of a CE marked product who carries the responsability for the CE marking. Now how you prove who's first? But it may be something to think of if you import and sell, as manufacturers in China seem to slap on CE marks on everything.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 09, 2015, 08:29:27 pm
In the EU, as far as I know, it's the First importer / seller of a CE marked product who carries the responsability for the CE marking. Now how you prove who's first? But it may be something to think of if you import and sell, as manufacturers in China seem to slap on CE marks on everything.

In UK, manufacturer or seller.
So Maplins could be in the firing line!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 09, 2015, 08:34:03 pm
Where did you buy it?

My girlfriend bought it from www.reichelt.de (http://www.reichelt.de) (Germany) :) (X-Mas present for me :) )
I had a hunch that it was from Reichelt. I wonder if they are the only ones selling these GS + TÜV marked meters or if other German shops also have them. Or put another way: Are they a special version made for Reichelt? I also wonder why they aren't branded differently or at least as another series to differentiate them from the lesser versions.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 09, 2015, 08:36:52 pm
I would agree that this is a bad meter, here is why I think so;

1) The design engineer planned to put better components on the board, but Management told them to cut the cost and they had to compromise of safety and on accuracy.
What other compromises are hiding in this meter??
2) A meter in this price class should have precision resistors and not pots that can drift over time and start to corrode.
3) I bet you that the drift of this meter is terrible, with time & temp & moisture this meter will go out of spec really quick.
4) Lying about a rating is just dangerous and wrong and a lawsuit is waiting to happen.
1. Possibly
2. It has precision resistors.
3. Hardly any drift over 2 years of monitoring (71D and 71B bench use).
4. The glass fuse version can't be sold in Europe anymore. If UNI-T has provided papers to EU importers documenting compliance with IEC regulations, the importer is not liable, unless the meters carry the importer's label.
To sue or report the meter as unsafe, the best way would be to point out the creepage distances below the required 8mm for CAT III 1000V.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 09, 2015, 10:55:27 pm
Safer, yes. A lot of features are lacking: No AC+DC, 1kHz AC bandwidth only, 0.1% accuracy instead of 0.025%, no internal memory, optional PC connection, no peak hold and no current input jack aural warning.
Still, a pretty good meter.

not really: it has true-rms, pc connection, and warnings if your probes are not in the right connectors...
if you want 0.025% and true rms ac+dc, take the vc880 for 30E more (but no W measure)

I don't say it's the best dmm but It's OK for lots of usages.
Which dmm would you buy for less than 200E if you had to choose one ?

I bought the Brymen 869s  : 0.02% on low DC voltage ranges, true rms, AC + dc, very fast continuity tester (fastest i ever had) , and it has proper input protection (photo posted earlier in this hread) . it was 210Euro including 20% VAT (bought from TME).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TheNewLab on February 10, 2015, 01:09:14 am
I am surprised at so many pages on this DMM review. I am not sure to be amused or perturbed about all the flaming. Ya, Dave, even  jumped into the fray!

So, I am dropping my 2 cents in. I've been watching Dave, since he was doing this in his garage. This review is just his style..Fluke is always the gold standard. I have no idea when Gossen got into the Electrical test gear market. Their light meters have been around as far back as the ...1960's?? They are great meters.
Their 3 color light meters were great and many pros swear by their reliability.

The UNI-T is Chinese made. Talk inside China say the company wants to compete in the same market with Fluke. Obviously not yet. Remember The grab bag episode where Dave received an analog multimeter? I believe it was made by the Beijing Research..blah blah! HA! HA! loved it.

Regarding CAT ratings. many companies are still behind the curve on the new standards issued recently. And certification? UL is the only outfit what is independent and tests the product to earn the UL trademark  I wish the EU would put some teeth behind the CE certification. Someone to cross check UL.

Now for what I would like to see!!

1.) with battery compartment closed drop it a few times! better yet slam it on the floor a few times! Let's see if the battery compartment pops open..
2.) Try out some Chinese fake Ceramic fuses and pump say 15 to 20 amps through that baby and see what happens. Maybe this one is not such a good idea. how about 8 to 10 amps and just let it simmer.
3.) How about sending it over to Martin Lorton and he can freeze it then bake the DMM!  I could not stop laughing when he did that test early on...I love that guy!

I would guess Dave, that with that review, the meter will just get tossed into some dusty box, or in a dumpster.. So why not have some fun?
- Extech did a video slamming their DMM into a wall.
-The Lightware  company filled up their camera case with Hasselblad equipment and drove a truck over the case repeatedly.

Finally, one thing I would like to see is someone actually adjusted the trimmer pots on a multimeter with those cheap ones to see if it could be brought into a tighter spec, then see if it stays there. When I look at the inside of such multimeter. I have this incredible urge to just experiment with each trimmer and see what each one actually adjusts.

OK, that is my personal rant about the UNI-T 71E review!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TheNewLab on February 10, 2015, 01:18:13 am
Oh, Perhaps I should add I am clearly an amateur hobbyist. That obvious?  I do have a kind of twisted, mischievous streak in me.
I also have the Uni-T  D71D. I am very happy with it. the precision is way beyond what I need. It matches my two Amprobe meters. also way more accurate than what I need. 
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: f4eru on February 10, 2015, 01:22:57 am
>> I have this incredible urge to just experiment with each trimmer and see what each one actually adjusts.

These are uncal pots :)))
Each and every one of these pots will put the meter out of cal, coz it's just barely in spec with no aging/ temp/whatever.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Rick Law on February 10, 2015, 03:45:38 am
May be because I am not an engineer, what I see is the UniT meters being built as an OEM platform:
- Glass fuse sitting on HRC fuse foot-print
- MOV marking and component holes
...

So what they were making is a platform for an OEM-buyers to refine this OEM manufacturer's meter into the OEM-Buyer's own.  Say I am the DMM maker seeking OEM, it is a platform for me to specific one with MOV, with HRC fuse, with this goodie or that goodie to differentiate my XX71 meter and make it more suitable for my selected market; whereas, Joe elsewhere may specify the most basic for BigCrap71Extreme model for his market.

It obviously worked some, as reported in this forum, some other makers do put they brand name (and enhancements) over what would otherwise be a bare UniT meter.  But it obviously didn't work well enough.  It fell so far below target that they need to market it under their own name, which OEM manufacturer are generally reluctant to do - to compete with their own customers in general is a no no.  As "an OEM platform" also explains their somewhat crazy product line-up.  Perhaps 71ABCD and E were not expected to be sold under the same brand name.  Instead, the 71A under brand name X might have been competing with 71B under a different brand name.

If indeed they begun life as viewing themselves as OEM manufacturer, it follows that they prepared their manufacturing (finishing) for those who would have specified enhancements that qualifies the meter for certain labels (CE, whatever) per OEM customer's enhancements.  But when they started selling it under their own brand, they decided to "just enable all" the labels - which of course is not a good thing to do.

While it worked (as OEM manufacturer) to some degree, they don't have a big enough OEM manufacturing market;  Yet they are not quite prepared to be on their own as their own brand name.  The more they sell it under their own brand, the less they are a desirable as OEM manufacturer.  They were at a catch 22.  Now they reached a point where perhaps they are no longer look at as OEM manufacturer but a DMM maker that also OEM's.

So, they have to alter their behavior - start earning a name for themselves under their own name plate.  Clean up their own product lines, begin marketing themselves...  most of all, decide which niche they want fit in (or dominate).

If UniT is a child, I would use the word "encourageable" to describe them.  I would also tell them "honesty is the glue that make value sticks to the brand".
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: miguelvp on February 10, 2015, 04:59:41 am
On my UNI-T UT71B my MELF resistors are straight and they used the proper footprint ones. Also the clearance to the shunt is larger than the E.

Seems all the boards are different, but mine is very similar to the 71D

(https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-(why-uni-t-meters-suck)/?action=dlattach;attach=135393;image)

(https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-(why-uni-t-meters-suck)/?action=dlattach;attach=135395;image)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 10, 2015, 06:14:04 am
2.) Try out some Chinese fake Ceramic fuses and pump say 15 to 20 amps through that baby and see what happens.
Nothing exciting will happen, it will just go open circuit. Same goes for a glass fuse.

When things get exciting is when you use one to put a stop to hundreds or thousands of amps with thousands of volts behind it. The result is that the fuse cannot put a stop to current flowing and you get a big boom as the insides of your multimeter burn up.
http://en.wikipedia.org/wiki/Breaking_capacity (http://en.wikipedia.org/wiki/Breaking_capacity)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: BradC on February 10, 2015, 06:21:12 am
Nothing exciting will happen, it will just go open circuit. Same goes for a glass fuse.

When things get exciting is when you use one to put a stop to hundreds or thousands of amps with thousands of volts behind it.

I wonder if you could do some fuse tests with a TIG welder with HF start. The fuse would blow, then the HF start would chuck a couple of thousand volts through it to generate a plasma which should draw a couple of hundred amps.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 10, 2015, 06:23:35 am
Daves already done multimeter destruction before  :-+
https://www.youtube.com/watch?v=M-FZP1U2dkM (https://www.youtube.com/watch?v=M-FZP1U2dkM)

A test with longer surge duration would be fun though :D
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 10, 2015, 07:05:02 am
I noticed all these amateur high voltage/current tests are always performed on cheap dubious quality meters. Never on Fluke or equivalent equipment.
Ideally, the well documented IEC CAT III 1000V test should be replicated to show how a meter with a UL listing passes the test, while a lesser meter doesn't.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Maister on February 10, 2015, 01:51:13 pm
Where did you buy it?

My girlfriend bought it from www.reichelt.de (http://www.reichelt.de) (Germany) :) (X-Mas present for me :) )
I had a hunch that it was from Reichelt. I wonder if they are the only ones selling these GS + TÜV marked meters or if other German shops also have them. Or put another way: Are they a special version made for Reichelt? I also wonder why they aren't branded differently or at least as another series to differentiate them from the lesser versions.


You are right. It Comes with a "CE - www.reichelt.de (http://www.reichelt.de)"-sticker on :) May be a Special Version for Reichelt.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 10, 2015, 04:30:02 pm
Nothing exciting will happen, it will just go open circuit. Same goes for a glass fuse.

When things get exciting is when you use one to put a stop to hundreds or thousands of amps with thousands of volts behind it. The result is that the fuse cannot put a stop to current flowing and you get a big boom as the insides of your multimeter burn up.
But there should not be thousands of volts at the inputs of a multimeter only rated for 600Vac/1kVdc. Thousands of volts would fry any meter not intended for that range and from there, anything goes. It takes only 60-80V to maintain an arc once it has been struck - that's why standard breakers and many switches are only rated for 24-30VDC, so there really is no need for thousands of volts. If you want to make air explode, you can use a low-power, high-voltage, high-frequency transformer to create arcs and then hook up a 400V 470µF cap via a small inductor to avoid extinguishing the arc to dump current in the arc... that was one of the loudest electrically-generated bangs I had ever created.

Anything other than a nearly perfect vacuum will arc over if you give it enough voltage and blow up if you give it enough current.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: m100 on February 10, 2015, 04:35:09 pm
I was looking today on E bay and saw quite a few 87's that were supposedly like new with protection film still on etc the probes did not look right and they were asking a third of the price as a buy now that other used were selling at auction for.

Not sure what price that equates to but current retail (RS / Farnell) is GBP400 +VAT   I picked a brand new boxed one on Ebay UK about three years ago for GBP228 delivered.  Nice meter, pity about the arse about face AC/DC current selection

It costs very little to nothing extra to properly engineer something.   To engineer to a deliberately degraded quality and mark otherwise IS CRIMINAL.   The directors,  accountants (and maybe the engineers)  should be behind bars for a very long stretch.

IMHO kit that doesn't meet, and has no possibility of meeting its claimed ratings should be crushed.   It's not protectionism, it's not colourism aka Fluke yellow trademarks, it's ultimately saving lives somewhere and until the Chinese and importers and retailers (like Amazon etc) realise this then they will continue to sell substandard kit and get away with it. 

The 'China Export' mark claimed further up this thread to be an urban myth exists, we've all seen it, it's not a CE mark as the characters have the wrong form and spacing, but I wouldn't rely on any of those markings nor the CAT marking on anything but a well known brand with a long established reputation.   (By the way I've no objection in general to Chinese kit and have a number of power supplies, a hot air rework station, very low voltage test kit and a Rigol 1052)   


Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 10, 2015, 06:28:49 pm
There seems to be quite few Flukes from China at under £60-00 I cannot find the seller who had several as new Fluke meters still with screen protector on at £98-00 each either they have all gone or the add has been taken down.
Personaly I have only come across 2 deaths from electrocution one was a bulk tipper driver who raised his buck into overhead 11000 volt lines and the other was someone welding inside a silo he was killed by 86 volt OC from a welding plant. I have searched through the HSE web site and cannot find a case of someone getting killed or injured by an exploding DMM, I am thinking that this might be the kind of event that ocurs more in the US due to the way the distribution system works there, the pole tranformers are set up so that they are auto transformers using the same line for earth and neutral for both HT and LT sides.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 10, 2015, 06:54:06 pm
I have searched through the HSE web site and cannot find a case of someone getting killed or injured by an exploding DMM,

I posted an example earlier in the thread: http://ecmweb.com/arc-flash/case-deadly-arc-flash (http://ecmweb.com/arc-flash/case-deadly-arc-flash)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: AG6QR on February 10, 2015, 07:20:36 pm
Nothing exciting will happen, it will just go open circuit. Same goes for a glass fuse.

When things get exciting is when you use one to put a stop to hundreds or thousands of amps with thousands of volts behind it. The result is that the fuse cannot put a stop to current flowing and you get a big boom as the insides of your multimeter burn up.
But there should not be thousands of volts at the inputs of a multimeter only rated for 600Vac/1kVdc. Thousands of volts would fry any meter not intended for that range and from there, anything goes.

That's the point of CAT ratings.  Transients DO occur, and a CAT rated meter must be designed to handle them.  A 600V CAT IV rated meter is required to be tested to withstand 8000V transients.

http://www.testequipmentdepot.com/application-notes/pdf/safety/abcs-of-multimeter-safety_an.PDF (http://www.testequipmentdepot.com/application-notes/pdf/safety/abcs-of-multimeter-safety_an.PDF)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 10, 2015, 08:48:05 pm
I have searched through the HSE web site and cannot find a case of someone getting killed or injured by an exploding DMM,

I posted an example earlier in the thread: http://ecmweb.com/arc-flash/case-deadly-arc-flash (http://ecmweb.com/arc-flash/case-deadly-arc-flash)

I was referring to UK incidences of arc flash there seems quite a lot in the US very often with thunder storms in the story but I cannot find any in the UK government archives that was triggered by a test meter.
http://www.hse.gov.uk/ (http://www.hse.gov.uk/)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 10, 2015, 09:12:19 pm
Industrial electrical fatalities (USA):
http://esfi.org/index.cfm/page/Workplace-Electrical-Injury-and-Fatality-Statistics,-2003-2010/cdid/12396/pid/10272 (http://esfi.org/index.cfm/page/Workplace-Electrical-Injury-and-Fatality-Statistics,-2003-2010/cdid/12396/pid/10272)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: MBY on February 10, 2015, 10:04:50 pm
If Uni-T had official ties outside China, that would expose them to lawsuits for wrongful death or injuries attributable to failure to meet their safety rating claims if there has been any.
Well they sort of do. Uni-T meters are sold under the "Tenma" brand through Farnell/Element14 for example. If anyone knows if the Tenma variants are built safer I'd be interested to know.
I have checked the insides of my Voltcraft (Conrad) VC-940 a few times. I bought it maybe 4-5 years ago. Since Uni-Ts letter scheme is so confusing, I'm not sure, but I think this is the same meter as shown in Daves video (AC power measurement, 40,000 counts but no data logging [but working RS232 interface]). My unit is clearly better inside. By "better" I don't mean "good". No HRC fuses no MOVs (or only small MOVs), but no stupid screw holes in high current path (or any path I know of) and a proper TRMS circuit in a metal can. And only one 10-turn trimmer and differences in board layout.

I share the opinion that some Uni-T meters is quite good, but the 71-series is not among them. My VC 940 is prone to freezes, have terrible battery life (since I use it mainly for AC power measurement with logging I have hacked in a isolated DC-supply replacing the battery) and confusing to use in the menus.

As a AC power meter with True RMS it is quite decent (but, as Dave points out, it is only suitable for higher loads and when accuracy may not be the most important thing) and stable, as long as the load is "nice". Loads with terrible power factor or fast, inductive changes, the meter clearly has some EMC issues and can freeze.

When I think about it, this is my second VC-940. The first one was DOA.

But I very much like my VC-820, an Uni-T UT60E I believe. A terrific little meter with optic RS232 and a battery that lasts for months or years (or weeks, if you run a datalogging experiment with the meter constantly on).

Another one is my "VC-1008" (yeah, all three is from Conrad) DMM/oscilloscope which of course is a joke as far as "oscilloscope" goes, but it does one thing very well (and thats what its for): oscilloscope function on all (well, except ohms and cap range) ranges, including 10A-range. And this is mainly what I use it for, current measurements in the time domain.

So, mixed feeling about Uni-T. They are cheap, and you get what you pay for, but sometimes, just sometimes this is also exactly what you need. I really value my UT-60E/VC-820 (in contrast with Dave I really value PC-connectivity in my DMMs. Especially RS232 and with a documented protocol [no matter how retarded or overcomplicated. Uni-T meters actually sends strings with a "bitmap" relating to the display segments. Awful, but documented, so you can make your own software]).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: open loop on February 10, 2015, 11:26:40 pm
Further to my post on page 4.

I have made some measurements on the Tenma 72-7730A (Farnel version of the Uni-T U71A)

This is what I had found when looking at current measurement:

When the selector switch was at VDC the consumption was 4.5mA,
At VAC position the consumption was at 9.0mA,
At the ohms position it was at 6 to 7mA
When measuring temperature it was at 10mA
The back light in low mode seemed to add 5mA

Now I let it go to low power/auto shut off mode and then made the following measurements:

When the selector to VDC and the meter going to sleep consumed 0.578 mA
When the selector was on temperature it was using 1.167 mA

As we can see the battery life would not be great therefore we only use re-chargeable batteries in these meters. Supposing we had a 560 mA/h Duracell and a current of about 5.8 mA (assuming that we would be mostly measuring voltage and resistance)

This gives a battery life of about 97 hours so Wytnucls was spot on with 100 hours a few posts later. He also pointed out that the mains on ohms test would cause no drama, thanks for pointing that out. Anyway I never really liked this meter (it was bought before I joined the department I now work in).

I think Uni-T could save money by doing two things.

1 Do the front end of their meters properly using the quality components. This would mean only one BOM and the quality front end parts then would be bought in quantity and therefore cheaper. This would also stop there being several versions of one product.
2. Cut the number of meters in a range just have a couple in each price bracket as I can only imagine it would be way too confusing choosing a meter, like going to the restaurant with a 10 page menu for just the food.

But more importantly to save reputation rather than money.

DROP THE FAKE CAT MARKINGS  >:( and actually test the products they produce to prove it meets the CAT rating.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: MBY on February 10, 2015, 11:59:43 pm
Dave,

We have the Tenma branded version of these meters at Work, don't ask why - long story. Next time you are in the lab check out the battery consumption of these meters and then do a Blab rant about the battery consumption.

These meters are not terrible but not great either, ok if you are doing low energy work. (Next breath) I like to see your mains on the "ohms range" test.
One non-bad thing I can say about my Uni-T meters are that they DO survive the "230VAC on ohms test". My VC-940 (UT-71E(?)) is "tested" several times. Every time I forgot to turn off the auto power off function while in power meter mode, the simplest way to bring it back is to turn it off and on again, sweeping through ohms, mV and V ranges. It does squeak while mains AC on the inputs in ohms mode, but it has so far survived without problems. I also do this when it freezes.

VC-940 and Amprobe PM55A is the only two meters I ever saw freezing. Actually, in that regard, the Amprobe PM55A is much worse. I even have to "overvolt" the damn thing, squeezing two CR2025 batteries in series instead of one CR2032. That keeps it stable and does not affect it in other ways so far (apart from killing the battery economy...). 
Title: Uni-T power measurement (can create energy)
Post by: eCloud on February 11, 2015, 09:01:15 am
Dave shows why Uni-T multimeters generally suck in this teardown (and a little bit of a review) of the $180 UT71E 0.025% accuracy multimeter with power measurement capability.

For all interested in the power measurement capabilities of the UT71-E, I have attached some interesting pictures.
7.5 Watts going into my inverter circuit and (tada ....)
724 Watts coming out.

The UT71E measures 295V while only about 45 V are there.

By the way: The load is purely resistive. Cos Phi is also off.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 11, 2015, 09:11:59 am
Wow Ecloud you have cracked it with the help of UNI T. You have proved free energy from over unity. :-DD Joking of course but perhaps this sort of thing leads to some people being convinced they have.
Title: Re: Uni-T power measurement (can create energy)
Post by: Wytnucls on February 11, 2015, 10:25:55 am
Dave shows why Uni-T multimeters generally suck in this teardown (and a little bit of a review) of the $180 UT71E 0.025% accuracy multimeter with power measurement capability.

For all interested in the power measurement capabilities of the UT71-E, I have attached some interesting pictures.
7.5 Watts going into my inverter circuit and (tada ....)
724 Watts coming out.

The UT71E measures 295V while only about 45 V are there.

By the way: The load is purely resistive. Cos Phi is also off.

I don't know why people try to operate their equipment outside of the manufacturer's specifications. 50V AC is the minimum input voltage.
Does it give normal W readings when you plug your 220V kettle in the adapter? If not, the meter is obviously faulty.
Furthermore, there is no mention in the manual of using the W feature without the power adaptor, so was most likely developed for mains voltage testing.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: asp on February 11, 2015, 12:15:45 pm
So my UT71E (V20051120-6) looks different ( take a look at the bottom side ). The traces look better spaced from what I see and there is no trip pot at the top of the fuse either.

I think I ordered this directly from China (via ebay) some time ago.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Ericho on February 11, 2015, 01:35:45 pm
Quote
I share the opinion that some Uni-T meters is quite good, but the 71-series is not among them. My VC 940 is prone to freezes, have terrible battery life (since I use it mainly for AC power measurement with logging I have hacked in a isolated DC-supply replacing the battery) and confusing to use in the menus.

Yea, my VC940 freezes from time to time as well
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 12, 2015, 03:34:36 am
come to think of it, it is good if there is more tear downs of these "cheaper" gear. it will show alot of potential buyers if they should take the risks of using lesser protected gear (due to financial limitations) or just for pure show and tell so as to let people know the protection ratings is way over blown (and also whether they are worth the money)  :-+ ... MORE  ! MORE !!  :-+
That's how I see it too.

The only way to (hopefully) stop manufacturers from fraudulently mislabeling and specifying their products is to name and shame them when caught so future would-be buyers will be aware of the issues they might be buying into and factor that into the price they are willing to pay for it.

Personally, the fake cat-III/IV ratings on the UT71E (at least as-shown in the tear-down) would knock $50 off what I might be willing to pay for one solely based on principle and the lack of genuine safety rating, regardless of how low, would knock another $20 off. Questionable clearances on the PCB and missing MOVs might knock another $20 off. Lop another $10 off for being useless and grossly inaccurate for low-power measurements and one more $20 for being barely within specs on many ranges with potentially questionable long-term accuracy.

Since leaving safety ratings out altogether is cheaper and safer than faking them, I would prefer if customs seized, inspected and destroyed them outright as hazardous goods - thou shall not fake safety ratings.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 12, 2015, 05:37:14 am
The problems with mislabeled CATIV ratings apply only to a small number of people. If the meter does not blow up when connected to the mains outlet then most people are safe. If the meter does not blow up when connected inside the breaker panel of a flat (or individual house) then even more people are safe.

So, showing that a meter with the wrong rating can explode when connected inside a substation (especially if it's the 10kV part) will make most people go "well, I'll keep that in mind if I decide to break into a substation to steal the oil".
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 12, 2015, 06:28:19 am
Personally, the fake cat-III/IV ratings on the UT71E (at least as-shown in the tear-down) would knock $50 off what I might be willing to pay for one solely based on principle and the lack of genuine safety rating, regardless of how low, would knock another $20 off. Questionable clearances on the PCB and missing MOVs might knock another $20 off. Lop another $10 off for being useless and grossly inaccurate for low-power measurements and one more $20 for being barely within specs on many ranges with potentially questionable long-term accuracy.
So, with this thing built to Fluke levels of refinement you'd only pay $300? I'm sorry to say you are still very far off the mark.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 12, 2015, 06:31:58 am
The problems with mislabeled CATIV ratings apply only to a small number of people. If the meter does not blow up when connected to the mains outlet then most people are safe. If the meter does not blow up when connected inside the breaker panel of a flat (or individual house) then even more people are safe.

So, showing that a meter with the wrong rating can explode when connected inside a substation (especially if it's the 10kV part) will make most people go "well, I'll keep that in mind if I decide to break into a substation to steal the oil".

you got it wrong... that meter will not explode when you connect it to mains voltage regardless of the place (outlet in a house, distribution panel) , it's "just" 240 or 420VAC (phase-ground or phase-phase). the meter without a proper protection WILL blow up during a transient voltage on the line (kV range) again regardless of the place. another type of "blow-up" is when you accidentally short the mains with a meter on current range - again during normal operation (no transients on mains) the glass fuse will do the job , but during a transient (btw.. transients are pretty common - just shut off a motor nearby) the meter with glass fuse will blow up... the location (outlet in the house, fuse box, distribution panel) is just determining the maximum fault current and therefore determining the "amount of damage" ;)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 12, 2015, 08:41:37 am
There is no transient on the A/mA range. The fuse ruptures as soon as the meter shorts the mains supply (250V).
That's why there is no high voltage transient test done on the current ranges for a CAT rating. The test consists of applying double the voltage rating with ruptured fuses in place to check for arcing (creepage and clearances), for one minute.
New IEC regulations do require HRC fuses now, with a voltage rating equal to the highest DMM CAT rating. Glass fuses are out for ever in any new multimeter (in countries which abide by those regulations, like Europe and the USA).
If you see some meters with glass fuses for sale in a local shop, 'educate' the manager and tell him to dump them in the trash.
Small 5$ pocket multimeters with current ranges, equipped with small glass fuses or no fuse at all, are not legal either.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 12, 2015, 09:11:14 am
The problems with mislabeled CATIV ratings apply only to a small number of people. If the meter does not blow up when connected to the mains outlet then most people are safe.

No. You don't understand what the CAT ratings are for.
Even a $5 meter can measure 240V mains, that's not the point. The point is about transients that can happen on the mains and the energy behind those transients.
Lighting strikes, heavy gear switching, your neighbor doing something stupid etc. High CAT rated meters are designed to safely absorb such transients without blowing your hand off.
If you think the odds of this are low and want to take your chances, then fine, it's your life, but don't say it doesn't apply for anyone else.
These CAT ratings have been developed for a very good reason, your safety.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: electr_peter on February 12, 2015, 09:29:01 am
The problems with mislabeled CATIV ratings apply only to a small number of people. If the meter does not blow up when connected to the mains outlet then most people are safe. If the meter does not blow up when connected inside the breaker panel of a flat (or individual house) then even more people are safe.

So, showing that a meter with the wrong rating can explode when connected inside a substation (especially if it's the 10kV part) will make most people go "well, I'll keep that in mind if I decide to break into a substation to steal the oil".
I don't agree.
Technically your statement is partly true (if you measuring only low level voltages, CAT ratings are not that important), but the whole point of measuring is to find out unknown value. If you already know in advance about mains level, why do you measure it? It is because you don't know what reading will show. And this is the problem - you are measuring unknown voltage source while assuming that it should be safe (which might not be true). Reasons for potential dangers were well explained in other posts.

My point is that in almost all cases where injuries occurred (or were close calls) person measuring the voltage assumed (but did not knew exactly) that both meter and voltage levels are safe for work. See posts above - "I thought it is OK", "it is only low voltage", "I have done it before", "I will show other guys how to do it", "meter looked good enough", etc. If one always goes with such logic, one day serious accident can occur.

The other point is a lie about CAT ratings. Would you like a lift with fake maximum capacity rating/plane with false max cargo weight/building with false load rating/etc.?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: george graves on February 12, 2015, 10:56:13 am
No. You don't understand what the CAT ratings are for.
Even a $5 meter can measure 240V mains, that's not the point. The point is about transients that can happen on the mains and the energy behind those transients.
Lighting strikes, heavy gear switching, your neighbor doing something stupid etc. High CAT rated meters are designed to safely absorb such transients without blowing your hand off.
If you think the odds of this are low and want to take your chances, then fine, it's your life, but don't say it doesn't apply for anyone else.
These CAT ratings have been developed for a very good reason, your safety.

Energy.  Yes, we(I) understand that.  That's college/University freshman year stuff.  I don't think you're giving your viewers/forum peeps the credit they deserve.

Yes, CAT ratings are important.  If your working on high voltage, high energy stuff.  And those that do....know to look for it.  And would never use a Chinese DMM for work. 

For the 99.999% of that don't.  We know a chinesse multimeter is going to fib on it's CAT ratings.  Duh.

As far as a lightening strike while I measure mains voltage?  Well.  That's just plain silly.  Everyone knows during a lighting strike you need to fly a kite with a key on the line.

Should Uni_T be slapped on the wrist for faking CAT ratings?  Sure.  That sounds like a great idea for a video for you!







Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 12, 2015, 12:10:28 pm
No. You don't understand what the CAT ratings are for.
Even a $5 meter can measure 240V mains, that's not the point. The point is about transients that can happen on the mains and the energy behind those transients.
A risk people also run with electric hand mixers, curling irons, power drills, etc., etc. That said, exaggerated CAT ratings are of course despicable. I'd go as far as saying that not having a rating at all is much better than having one that is a lie.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 12, 2015, 12:12:02 pm
It would be difficult to prove that it doesn't meet its CAT rating.
It now has the right HRC fuses.
Regulations don't impose the fitting of MOVs, PTCs or high power current limiting resistors on the PCB.
They only require adequate clearances and a minimum of 8mm creepage distances (for CAT III 1000V) between, presumably, not all traces but only traces with potential high voltage differentials.
Internal damage is allowed, as long as it doesn't escape the meter and cause injury.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Pentium100 on February 12, 2015, 03:47:09 pm
If you already know in advance about mains level, why do you measure it? It is because you don't know what reading will show. And this is the problem - you are measuring unknown voltage source while assuming that it should be safe (which might not be true). Reasons for potential dangers were well explained in other posts.

I may want to measure the voltage to find out if the value is not too low. If the voltage is too high, but only slightly (270V instead of 230) then the meter will not explode. If the voltage is 800V instead of 230V then the meter might explode, but so will all devices connected to the mains. I may also want to measure just to see if the voltage is there and whether the wire is safe to touch.

A cheap way to reduce the risk might be to connect a lightbulb in series with the probes when measuring voltage. Then even if the meter is shorted, the lightbulb will limit the current to below the explosion level (and provide indication that there is a problem) while the resistance of the cold filament will not affect the voltage reading.

They have fuses in the plugs, the multimeter has a fuse but it's in your hand, and in these models there isn't enough clearance and the fuse isn't a suitable type.
I have seen a fuse in a plug once, in a British plug. The other devices do not have fuses in the plugs, including my electric shaver (which runs on 230V and not batteries).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Ericho on February 12, 2015, 05:58:03 pm
I worked on high power systems part of my career (mostly on ships) personally up to 4000kw electrical systems up to 1100v able to handle >2000A
I’ve seen the inside of a hospital twice and got plenty of near misses and burn scares.
Those accidents I got were on a 220/380 net and on a 24v dc net (both able to handle a few hundred amps)
So not the 660v 1100v stuff
Lack of respect for high power systems was always part of it. (I was young and ….. back then)
You cannot just poke anything just into anything. It ends badly, and yes explosions happen easily when equipment fails. (never seen a dmm explode thou)
Cat ratings and safety guidelines should be taken seriously. Don’t go assuming that it is not so, you may hurt yourself or someone else.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 12, 2015, 06:08:16 pm
The naysayers must understand this one statement & question:
Electricity travels at the speed of light. Do you think that your reflexes do?  :box:
Then there is no hope for you. Move along, there is nothing here to see.
Perhaps we will read about you in the local news or a trade magazine.
Please look up Arc Flash, and understand that before you can pull away or even manage a yelp, it's over.
BTW so are you.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lesterwyatt on February 12, 2015, 07:04:35 pm
The naysayers must understand this one statement & question:
Electricity travels at the speed of light. Do you think that your reflexes do?  :box:
Then there is no hope for you. Move along, there is nothing here to see.
Perhaps we will read about you in the local news or a trade magazine.
Please look up Arc Flash, and understand that before you can pull away or even manage a yelp, it's over.
BTW so are you.

Not quite the speed of light. Electricity (Electrons)travels (1/100) the speed of light. Anyhow it still moves very fast; faster than our reflexes!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: electr_peter on February 12, 2015, 08:10:35 pm
The naysayers must understand this one statement & question:
Electricity travels at the speed of light. Do you think that your reflexes do?  :box:
Then there is no hope for you. Move along, there is nothing here to see.
Perhaps we will read about you in the local news or a trade magazine.
Please look up Arc Flash, and understand that before you can pull away or even manage a yelp, it's over.
BTW so are you.
Nice said and rhymed. :-+
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 12, 2015, 08:38:33 pm
So, with this thing built to Fluke levels of refinement you'd only pay $300? I'm sorry to say you are still very far off the mark.
You got it backwards. What I meant is that with the UT71E built the way it is, I would not be willing to pay more than maybe half its current street price.

Most of the safety issues come from basic layout and mechanical design flaws that cost almost $0 to fix... or simply remove the CAT-III/IV rating claims - nobody will complain that a CAT-II multimeter is built like a CAT-II multimeter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: david77 on February 12, 2015, 09:05:23 pm
A risk people also run with electric hand mixers, curling irons, power drills, etc., etc.

They have fuses in the plugs, the multimeter has a fuse but it's in your hand, and in these models there isn't enough clearance and the fuse isn't a suitable type.

They only do in case of the BS1363 plugs. Are there any other fused mains plugs around?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 12, 2015, 09:55:32 pm
A risk people also run with electric hand mixers, curling irons, power drills, etc., etc.

People only plug those into the "CAT II" area of the house...

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Tepe on February 12, 2015, 09:57:29 pm
People only plug those into the "CAT II" area of the house...
And I assumed that that was the area that Dave's "The point is about transients that can happen on the mains" alluded to.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 12, 2015, 10:24:44 pm
A risk people also run with electric hand mixers, curling irons, power drills, etc., etc.

People only plug those into the "CAT II" area of the house...
Just a by-the-way: outlets that are within 10 meters copper distance from the breaker box may also be considered CAT-III - potentially not enough wiring inductance and resistance to limit fault current to CAT-II rating.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rsjsouza on February 12, 2015, 10:33:45 pm
A risk people also run with electric hand mixers, curling irons, power drills, etc., etc.

Don't forget there are bad and good quality appliances as well! The bad quality ones will blow up in your face/hand due to poor manufacturing, transients, etc.  :-BROKE

Not quite the speed of light. Electricity (Electrons)travels (1/100) the speed of light. Anyhow it still moves very fast; faster than our reflexes!
Don't confuse the speed of moving electrons with speed of the electronic charge. Electrons move very slowly as they hop from atom to atom, but the energy released and absorbed in the process (the electronic charge) travels at a speed comparable to the speed of light in vacuum.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 12, 2015, 11:39:35 pm
I am so tired of hearing the argument: "I stick my tongue in on the wires on the power poles out side and nothing ever happens to me!" Well I have driven the same distance as that from the Earth to the moon, twice, in my lifetime, and I have not died in a car accident. WTF does that have to do with the millions of people who have died from car accidents? Safety rules and regulations have been put in place because of those who have had problems, not those who have never had problems. If you have never had a problem it could be because of all the other people who have been injured or killed before you.

Go ahead, take the risk. I DON'T CARE IF YOU DON'T. I care about the people who are uneducated and care to learn. If you don't want to learn, then stop complaining and go away.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Hydrawerk on February 13, 2015, 12:17:09 am
Any opinion on CEM multimeters? Are they better than Unitrend? http://www.cem-instruments.com/en/pro/sort7-1.html (http://www.cem-instruments.com/en/pro/sort7-1.html)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 13, 2015, 12:28:03 am
They can be  better. They are the OEM for some meters sold by Extech, specifically the EX series. They are also the OEM for many other brands. They seem to designed fairly well but the quality control is all over the place. Dave did his $50 shootout and his $100 shootout with Extech EX series meters included. One was his best buy, the other was a piece of laughable garbage. Other people have complained about the poor build quality of the Extech EX series. Personally I would stay away from anything CEM or its re-brands.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 13, 2015, 11:02:01 am
I am so tired of hearing the argument: "I stick my tongue in on the wires on the power poles out side and nothing ever happens to me!" Well I have driven the same distance as that from the Earth to the moon, twice, in my lifetime, and I have not died in a car accident. WTF does that have to do with the millions of people who have died from car accidents? Safety rules and regulations have been put in place because of those who have had problems, not those who have never had problems. If you have never had a problem it could be because of all the other people who have been injured or killed before you.

Go ahead, take the risk. I DON'T CARE IF YOU DON'T. I care about the people who are uneducated and care to learn. If you don't want to learn, then stop complaining and go away.

Me too Light, me too.
Had a gut full of it on EEV youTube vid, people telling me I'm full of it for stating correct Cat safety must be adhered to.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 13, 2015, 12:00:35 pm
I am so tired of hearing the argument: "I stick my tongue in on the wires on the power poles out side and nothing ever happens to me!"

Me too Light, me too.

Yep. If it was child safety seat ratings there'd be a national scandal and daytime TV would be demanding action!!!

Here we say "Don't buy Uni-T meters because they're overpriced and lie about the safety ratings" and people are actually stepping up to defend them.

Yes it's true that child safety seat ratings aren't critical so long as you don't crash your car, but that's not the point, is it?

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rsjsouza on February 13, 2015, 12:10:56 pm
I am so tired of hearing the argument: "I stick my tongue in on the wires on the power poles out side and nothing ever happens to me!" Well I have driven the same distance as that from the Earth to the moon, twice, in my lifetime, and I have not died in a car accident. WTF does that have to do with the millions of people who have died from car accidents? Safety rules and regulations have been put in place because of those who have had problems, not those who have never had problems. If you have never had a problem it could be because of all the other people who have been injured or killed before you.

Go ahead, take the risk. I DON'T CARE IF YOU DON'T. I care about the people who are uneducated and care to learn. If you don't want to learn, then stop complaining and go away.
As you know, Lightages, this argument is not new nor it seems to change. As I said 1-1/2 years ago on this thread (https://www.eevblog.com/forum/testgear/cheap-mulitmeters-what-is-so-bad/msg261116/#msg261116):
"Hey, you know, I'm probably a bit biased here because I'm a pro and so I have seen or heard horrible stories and experienced some bad scenarios that convinced me that I wouldn't personally use that [insert tool], but if you are really sure you will use within it's limitations, which realistically is probably all you want, don't underestimate that accidents usually happen under stress, tiredness or distraction and this will not be fine."
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 13, 2015, 12:36:41 pm
don't underestimate that accidents usually happen under stress, tiredness or distraction and this will not be fine."

Yep.

I the story I posted about the exploding multimeter that killed two people and badly burned another the multimeter being used by the electrician was borrowed from the maintenance department of the shopping mall where the problem was.

If the multimeter is a known brand, looks impressive and says "CAT IV" on it... then you'd probably use it, too. Right? Even Dave probably would have used it before he opened this one up and looked inside.

Nobody should be defending Uni-T. We should be condemning them as loudly as possible for putting death-traps out in the world and making sure that everybody knows that their brand name isn't to be trusted.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 13, 2015, 01:32:07 pm
Quote
Yep.
I the story I posted about the exploding multimeter that killed two people and badly burned another the multimeter being used by the electrician was borrowed from the maintenance department of the shopping mall where the problem was.
Excuse me, the story who posted? That was me that posted that not you.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Kjelt on February 13, 2015, 02:08:02 pm
That was an impressive good "Office space" imitation there Dave at 16:33 "Hmmmmmm Yeaaaaaaa"  :-+

Compare it with the original at 0:16
https://www.youtube.com/watch?v=Fy3rjQGc6lA (https://www.youtube.com/watch?v=Fy3rjQGc6lA)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 13, 2015, 06:30:00 pm
Quote
Yep.
I the story I posted about the exploding multimeter that killed two people and badly burned another the multimeter being used by the electrician was borrowed from the maintenance department of the shopping mall where the problem was.
Excuse me, the story who posted? That was me that posted that not you.

??

I posted it here:

https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-%28why-uni-t-meters-suck%29/msg604706/#msg604706 (https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-%28why-uni-t-meters-suck%29/msg604706/#msg604706)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 13, 2015, 06:38:18 pm
Really guys? Fighting over who posted a link to a web page?  :palm:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 13, 2015, 07:05:56 pm
Really guys? Fighting over who posted a link to a web page?  :palm:

 :-DD

Not really. I looked at his posting history ( https://www.eevblog.com/forum/profile/?area=showposts;u=88216 (https://www.eevblog.com/forum/profile/?area=showposts;u=88216) ) and I can't see that he's ever posted anything related to an exploding multimeter. Certainly not in this thread.

Soooo .... No, I don't give a damn who posted what, I was just curious where this was heading.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 14, 2015, 11:09:29 pm
Really guys? Fighting over who posted a link to a web page?  :palm:

 :-DD

Not really. I looked at his posting history ( https://www.eevblog.com/forum/profile/?area=showposts;u=88216 (https://www.eevblog.com/forum/profile/?area=showposts;u=88216) ) and I can't see that he's ever posted anything related to an exploding multimeter. Certainly not in this thread.

Soooo .... No, I don't give a damn who posted what, I was just curious where this was heading.
Well I care, not fighting just some people like to say that they were first with the revelation.
If you would like to find where and where I posted it, it is here on page 9 where I excuse myself if it had been posted earlier.  https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-(why-uni-t-meters-suck)/120/?action=post;u=604114 (https://www.eevblog.com/forum/blog/eevblog-712-uni-t-ut71e-multimeter-(why-uni-t-meters-suck)/120/?action=post;u=604114) I saw that you did this before giving no credit to me for posting it and the second time I spoke up. It was spoken about for many pages prior to your discovering it no doubt on page 9, then you reposted it on page 15 "for the first time"
Perhaps your moniker suits you well.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TheEPROM9 on February 15, 2015, 12:12:41 am
Dave shows why Uni-T multimeters generally suck in this teardown (and a little bit of a review) of the $180 UT71E 0.025% accuracy multimeter with power measurement capability.
He also opens the UT71A, UT61E, and compares the input protection and rating with a Brymen BM257.

http://uni-trend.com/UT71E.html (http://uni-trend.com/UT71E.html)
MAX6190 Voltage Reference: http://datasheets.maximintegrated.com/en/ds/MAX6190-MAX6198.pdf (http://datasheets.maximintegrated.com/en/ds/MAX6190-MAX6198.pdf)
OP1177 Opamp: http://www.analog.com/static/imported-files/data_sheets/OP1177_2177_4177.pdf (http://www.analog.com/static/imported-files/data_sheets/OP1177_2177_4177.pdf)
Cyrustek ES51922 DMM chipset: http://www.cyrustek.com.tw/spec/ES51922.pdf (http://www.cyrustek.com.tw/spec/ES51922.pdf)
Holtek HT1621 LCD driver: http://www.ywslcm.com/Upload/tbDownload/2013-4-13_9_37_49.pdf (http://www.ywslcm.com/Upload/tbDownload/2013-4-13_9_37_49.pdf)
AD636 True RMS Converter chip: http://www.analog.com/static/imported-files/data_sheets/AD636.pdf (http://www.analog.com/static/imported-files/data_sheets/AD636.pdf)

EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck) (https://www.youtube.com/watch?v=i2Tkm21dI1g#ws)

One does wonder how these meters that don't meet their rating make it into the main stream market place. Bearing in mind false advertising is illegal and a lot of multimeter company's are responsible for this. To those who bash Dave in this video it is dam essential that these company's are held up and exposed for not making a product as advertised.

It is bull  :bullshit: to defend sub par products especially when the safety of peoples lives are involved.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 15, 2015, 11:09:35 am
One does wonder how these meters that don't meet their rating make it into the main stream market place. Bearing in mind false advertising is illegal and a lot of multimeter company's are responsible for this. To those who bash Dave in this video it is dam essential that these company's are held up and exposed for not making a product as advertised.

It is bull  :bullshit: to defend sub par products especially when the safety of peoples lives are involved.
You don't seem to understand how the system works.
Non-governmental IEC publishes electrical standards with occasional revisions. (IEC61010)
Revisions stipulate changes concerning input protection, but also include modifications of the testing procedures, with more stringent requirements to comply with the IEC CAT rating system.
Most countries then adopt those standards revisions as their own, from a specific date, with a grace period for manufacturers' and importers' compliance. (EN61010 for Europe, UL61010 for the US)
That grace period has expired in Europe (October 2013), but not necessarily in other countries (USA January 2018).
Some manufacturers re-submit their products (often with modifications) for independent testing, to confirm new standards compliance.
The meter Dave reviewed was first released under the previous standards, when HRC fuses were not a requirement and current range testing voltage was half of what it is now. A new version of that meter is available, with HRC fuses and revised PCB.
There is no sure way to know if a meter complies fully with regulations, unless it has gone through independent testing. In Europe, a CE marking is mandatory, with EN61010 compliance the responsibility of the manufacturer or in some cases, the importer.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 15, 2015, 01:54:40 pm
I don't give a damn who posted what, I was just curious where this was heading.
Well I care, not fighting just some people like to say that they were first with the revelation.

Maybe I didn't see your post, maybe I posted it independently. It happens.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Yago on February 15, 2015, 06:05:49 pm
I don't give a damn who posted what, I was just curious where this was heading.
Well I care, not fighting just some people like to say that they were first with the revelation.

Maybe I didn't see your post, maybe I posted it independently. It happens.

Actually I posted it first, it was about three years before the formation of this forum.
As I AM Spartacus!
:p
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 15, 2015, 07:33:31 pm
It's just that it is done with arrogance and then the quote from Fungus is:
"Not really. I looked at his posting history ( https://www.eevblog.com/forum/profile/?area=showposts;u=88216 (https://www.eevblog.com/forum/profile/?area=showposts;u=88216) ) and I can't see that he's ever posted anything related to an exploding multimeter. Certainly not in this thread." :-DD
I don't have a lot of posts only 50 or so, and most of those are for the secret ordering code. Fairly easy to find if you really looked. And with that, I'm done.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 15, 2015, 08:06:22 pm
I don't have a lot of posts only 50 or so, and most of those are for the secret ordering code. Fairly easy to find if you really looked. And with that, I'm done.

If you're accusing somebody of plagiarism, a simple reference to your original post will save a lot of confusion.

(because if they're innocent they'll have literally no idea what you're talking about)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: miguelvp on February 15, 2015, 10:25:36 pm
Posting a link is hardly plagiarism

First hit to that link:
https://www.eevblog.com/forum/testgear/dangerous-multimeter-mastech-m890g-m890g2-(aka-dc-electronics-dc03)/msg386230/#msg386230 (https://www.eevblog.com/forum/testgear/dangerous-multimeter-mastech-m890g-m890g2-(aka-dc-electronics-dc03)/msg386230/#msg386230)

But really it doesn't matter as long as the message is conveyed and no one gives a .... who posted it first.

Giving credit to someone's work is one thing, but to a link that is in the public domain? that is a bit ridiculous.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 15, 2015, 11:37:06 pm
To get back on subject:

Is there a method to test the rating of a multimeter?
Lets say I'm a small company and I'm not sure of the rating of My Uni-T, Fluke, 5$ wonders (etc) and decide to sacrifice one with an incremental test to see how many amps are needed to blow the thing up in conditions I or my employees work in.
(Without killing the intern that is).
Why? Underwriter's stamp should suffice?
Yeah, but I might have special condition: inert gas, salty air water, hydrocarbon mix above UEL (etc) that are very specific.
(These conditions are pretty common in the maritime industry)
I'd rather burn a 400$ meter than blow the hand of an employee.
Dave did a test using a High Energy 4KV capacitor unit in episode 84.
But is that kind of "pulse" (no idea how to correctly name it) a reflection of  what happens in real life?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 16, 2015, 12:11:36 am
There is no test you can do safe for you. If you want a meter that will withstand marine abuse then you probably want one that has an IP67 rating and probably one that is rated as intrinsically safe, such as the Fluke 28IIEX. Be prepared for sticker shock.

Additional:

The Fluke 27II is also IP67 and well suited for marine use. There is also the Amprobe HD160C which I find very interesting too: http://www.tequipment.net/AmprobeHD160C.html (http://www.tequipment.net/AmprobeHD160C.html)

CEM, and its rebrands like Extech EX series, has some IP67 meters too that are apparently properly rated and certified, if you get one that is properly built. There have been many reports here and on other sites of poor quality control.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: EEVblog on February 16, 2015, 09:39:39 am
You can buy insulation testing equipment. It costs more than many meters. Basically it generates very high energy pulses. You connect the DMM, stand back and see if it can survive its rated voltage/current.

It's more than that, it can be a destructive test. i.e. it has to "fail safe".
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: VK3DRB on February 16, 2015, 11:08:58 am
Actually there was a high end Fluke handheld which had data recording features that someone bought at a previous workplace around 5 years ago. The meter had to go through a slow boot up sequence when powering up, but the real horrible thing was the continuity check. Often you had to hold the leads on for a second or two before it would beep :--. Sometimes it was quick. I suspect the microcontroller code used task polling to detect continuity. FAR worse that the UNIT-T piece of crap. A $10 meter was more usable for continuity. No-one wanted to use that meter except the bloke who bought it (to save face I suspect). The Fluke should never have been sold, and Fluke should have be ashamed for pushing such a crap product. I used an Agilent 34410A instead.

I am still a fanboy of the Fluke 179 :-+. Possibly the best handheld meter ever. But to be honest, nothing beats the high end Agilent meters like the one in Dave's video if you want a bench multimeter :-+.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 16, 2015, 11:19:58 am
You can buy insulation testing equipment. It costs more than many meters. Basically it generates very high energy pulses. You connect the DMM, stand back and see if it can survive its rated voltage/current.

It's more than that, it can be a destructive test. i.e. it has to "fail safe".

If I get this, a simplified test (for real world application, not science) could be:
- Hook that insulation testing equipment up to a multimeter that set in the appropriate mode:
- Install in it's operating environment (lab simulation, or simply in real thing if not a danger), let it lie for 15 min (or the 2x the max time you spend in there).
- Start using high energy pulses from half it's rated capacity (if 500V, use 250v) with whatever Watts/Amps need be.
- Increment by 100V leaving 10minutes between pulse.
- See where she blows, let's say "X", and use X/2 as your max in that environment/usage.
Probably not perfect, but doable by almost anybody/any company.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rsjsouza on February 16, 2015, 12:12:40 pm
The Fluke should never have been sold, and Fluke should have be ashamed for pushing such a crap product.
Do you recall which model was it? Just curious...

I am still a fanboy of the Fluke 179 :-+. Possibly the best handheld meter ever.
I really like mine as well. Built like a tank and absolute peace of mind when I use it on high power circuitry. More expensive? Yes, but for something that I expect will at least survive as much as my previous meter (25 years), that translates to only about ten dollars/year.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Terabyte2007 on February 16, 2015, 12:19:36 pm

I am still a fanboy of the Fluke 179 :-+. Possibly the best handheld meter ever. But to be honest, nothing beats the high end Agilent meters like the one in Dave's video if you want a bench multimeter :-+.

I have the 34461A but was seriously considering the Fluke 8846A with 24ppm at .0024% accuracy it has a slight edge over the 34461A. BenchVue and the TFT trending display capabilities are what sold me.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: VK3DRB on February 16, 2015, 01:13:15 pm
The Fluke should never have been sold, and Fluke should have be ashamed for pushing such a crap product.
Do you recall which model was it? Just curious...

I am still a fanboy of the Fluke 179 :-+. Possibly the best handheld meter ever.
I really like mine as well. Built like a tank and absolute peace of mind when I use it on high power circuitry. More expensive? Yes, but for something that I expect will at least survive as much as my previous meter (25 years), that translates to only about ten dollars/year.

I can't recall the model, though it might have been the Fluke 287 or 289. Maybe the model was taken off the market because it was so lousy.

Yes, the 179 is expensive, but it is worth it. Whoever designed that meter deserved a medal. The specification alone makes it outstanding compared to most meters. The build quality is excellent too. Not to mention battery life.

Lower costs 179's are available from eBay occasionally. I bought one about 5 years ago as new from the USA (unwanted gift) for $US 155 delivered to my door in Australia. It is genuine, and I tested its accuracy and found it was be well within specifications. What really impressed me was it was new. Not a scratch or mark on it, complete with box and leads. New here is around $US 350 or so. Even then they are worth the money to anyone who wants to meter to provide faithful service for many years.


Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 16, 2015, 02:05:19 pm
I wonder how many DMM would stand up to being tested with a Megger S1-1568, 15KV and will test insulation to 35 Tohms.

http://www.megger.com/eu/products/ProductDetails.php?ID=2382 (http://www.megger.com/eu/products/ProductDetails.php?ID=2382)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: ModemHead on February 16, 2015, 02:53:57 pm
I can't recall the model, though it might have been the Fluke 287 or 289. Maybe the model was taken off the market because it was so lousy.
Sorry for being OT, but for the record, a Fluke 287/289 definitely has a boot-up delay, but the continuity tester is specified at <1ms response time.  The 289 I have here clocks in at around 500 usec.  Subjectively, and relative to modern DMM choices, this is "very fast".  Perhaps your colleague's unit was faulty.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: SNGLinks on February 17, 2015, 12:35:09 pm
I have a UNI-T UT60A bought recently from the UK electronics store Maplin.

It's marked CAT III 1000v and CAT IV 600v. It also has a CE mark.
http://www.maplin.co.uk/p/uni-trend-ut60a-autoranging-with-pc-interface-digital-multimeter-n80cb (http://www.maplin.co.uk/p/uni-trend-ut60a-autoranging-with-pc-interface-digital-multimeter-n80cb)

It has 2 fuses in it, both glass and marked 250v on the pcb. There seems to be space on the pcb for larger fuses.

Should I complain to Maplins and Trading Standards?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 17, 2015, 12:45:35 pm
You could, but they may claim it is old stock, to be on the legal side. New imports are definitely not allowed in the EU anymore, under current laws. Quote latest EN61010 (Oct 2010) and the requirement for HRC fuses rated for 1000V minimum for CAT III 1000V.
http://ec.europa.eu/consumers/safety/rapex/alerts/main/index.cfm?event=main.listNotifications&selectedTabIdx=1 (http://ec.europa.eu/consumers/safety/rapex/alerts/main/index.cfm?event=main.listNotifications&selectedTabIdx=1)

From Wikipedia:
There are mechanisms in place to ensure that the CE marking is put on products correctly. Controlling products bearing CE marking is the responsibility of public authorities in Member States, in cooperation with the European Commission. Citizens may contact national market surveillance authorities if the misuse of the CE marking is suspected or if a product's safety is questioned.

The procedures, measures and sanctions applying to counterfeiting of the CE marking vary according to the respective Member State's national administrative and penal law. Depending on the seriousness of the crime, economic operators may be liable to a fine and in some circumstances, imprisonment. However, if the product is not regarded as an imminent safety risk, the manufacturer may be given an opportunity to ensure that the product is in conformity to the applicable legislation before it is obliged to take the product off the market.


From the EEC:
It is the manufacturer’s responsibility to carry out the conformity assessment, to set up the technical file, to issue the declaration of conformity and to affix the CE marking to a product. Distributors must check that the product bears the CE marking and that the requisite supporting documentation is in order. If the product is being imported from outside the EEA, the importer has to verify that the manufacturer has undertaken the necessary steps and that the documentation is available upon request.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rollatorwieltje on February 17, 2015, 12:46:57 pm
I can't recall the model, though it might have been the Fluke 287 or 289. Maybe the model was taken off the market because it was so lousy.
Sorry for being OT, but for the record, a Fluke 287/289 definitely has a boot-up delay, but the continuity tester is specified at <1ms response time.  The 289 I have here clocks in at around 500 usec.  Subjectively, and relative to modern DMM choices, this is "very fast".  Perhaps your colleague's unit was faulty.
Didn't those have an issue where they would lock up or slow down when sunlight entered the IR port? Smelled like an IR receiver swamping the processor with interrupts.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TMM on February 17, 2015, 02:04:48 pm
So, with this thing built to Fluke levels of refinement you'd only pay $300? I'm sorry to say you are still very far off the mark.
You got it backwards. What I meant is that with the UT71E built the way it is, I would not be willing to pay more than maybe half its current street price.

Most of the safety issues come from basic layout and mechanical design flaws that cost almost $0 to fix... or simply remove the CAT-III/IV rating claims - nobody will complain that a CAT-II multimeter is built like a CAT-II multimeter.
My bad. So you are saying that you value this meter at $60 but if they fixed if they fixed the issues that cost "almost $0 to fix" you would happily pay $180?  :-//
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 17, 2015, 03:02:43 pm
60$ for an AC+DC 100 kHz TRMS 40,000 count meter, with a Maxim voltage reference, W measurement, multiple displays, internal memory and PC connection? You're dreaming.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 17, 2015, 05:15:39 pm
My bad. So you are saying that you value this meter at $60 but if they fixed if they fixed the issues that cost "almost $0 to fix" you would happily pay $180?  :-//
Re-read my "mark-down" post. They would need to fix more than just the blatant safety issues (by either removing their fake CAT rating or making the necessary improvements) for me to be willing to pay $180 for it... I had at least $30 of mark-downs due to initial accuracy and drift concerns and more markdowns for other flaws/omissions like the MOVs so the meter's electronics don't instantaneously fry under momentary high voltages. With only the imminent safety concerns addressed, I would still not be comfortable paying more than about $120 or so for one.

As I said multiple times before, in its "as-reviewed" form, imports of UT71E should be seized and destroyed at the border for carrying fake safety ratings.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 17, 2015, 05:44:37 pm
You have no idea whether it meets its safety rating or not. Even the version with glass fuses is still allowed in some countries, where the latest IEC regulations are not enforced yet, like the USA.
Just because it has no MOVs or beefy current limiting resistors, doesn't mean it won't pass the IEC61010 test.
There is no abnormal drift, that's a myth. PCB pots are OK; my 1,200,000 count Gossen 30M is full of them. Accuracy is within its specifications. It needs to be calibrated every year, like any meter.
Build quality is nowhere near Fluke's, but that's a given at that price.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: 3roomlab on February 18, 2015, 12:57:13 am
i think basically ... there is just so many ways a "manufacturer" can get away with "mistakes" ... and alot of low budget hobbyists have no way around it unless they have alot of spare cash to get high end gear
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: DanielS on February 18, 2015, 01:33:22 am
You have no idea whether it meets its safety rating or not. Even the version with glass fuses is allowed in some countries, where the latest IEC regulations are not enforced yet, like the USA.
Just because it has no MOVs or beefy current limiting resistors, doesn't mean it won't pass the IEC61010 test.
I'm pretty sure a 250V fuse, glass or otherwise, in a CAT-IV instrument that claims ratings above 250V does not meet CAT-IV even by the oldest relevant IEC standards. Same with the clearances that are nowhere near current specs, so likely many revisions out of date at best.

As for the missing MOVs, it is not just about safety but also about preventing the meter from getting ruined at the first minor surge or incident involving moderate voltages. Having a multimeter that won't kill you due to a minor electrical fault or user error is nice. Having a meter that will also survive said mistakes and faults with a blown fuse at worst is better.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: 3roomlab on February 18, 2015, 02:11:15 am
What i am having trouble understanding is how people are willing to accept that the chinese UT61 series for $60 is a good deal but the UT71 series for $130 isn't. Both promise cat IV and fail to deliver.
Mt UT-61C bought from Reichelt in Germany is silk screened "CATIII 300V" and "CATII 600V". It also displays silk screened TÜVRheinland and GS logos. The TÜV logo for some reason says ID:0000000002, though.


(https://www.eevblog.com/forum/product-reviews-photos-and-discussion/uni-t-ut61e-multimeter-teardown-photos/?action=dlattach;attach=29867;image)

im curious, what does it mean TUV ID 0000000002 ? a very old certification? outdated?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: mux on February 18, 2015, 08:18:01 am
https://www.certipedia.com/quality_marks/0000000002?locale=en (https://www.certipedia.com/quality_marks/0000000002?locale=en)

Bogus, bullshit, lies?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rollatorwieltje on February 18, 2015, 08:39:23 am


im curious, what does it mean TUV ID 0000000002 ? a very old certification? outdated?

http://www.certipedia.com/quality_marks/0000000002?locale=en (http://www.certipedia.com/quality_marks/0000000002?locale=en)
Looks like they printed the example code instead of the correct one...

http://www.certipedia.com/companies/30907/certificates?locale=en (http://www.certipedia.com/companies/30907/certificates?locale=en)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 09:40:21 am
I'm pretty sure a 250V fuse, glass or otherwise, in a CAT-IV instrument that claims ratings above 250V does not meet CAT-IV even by the oldest relevant IEC standards. Same with the clearances that are nowhere near current specs, so likely many revisions out of date at best.

As for the missing MOVs, it is not just about safety but also about preventing the meter from getting ruined at the first minor surge or incident involving moderate voltages. Having a multimeter that won't kill you due to a minor electrical fault or user error is nice. Having a meter that will also survive said mistakes and faults with a blown fuse at worst is better.
250V glass fuses are allowed under the previous regulations, even under CAT IV 600V. The test only required a maximum of 1000V on the amp range for 1 minute, with blown fuses in place to check for arcing. There was no requirement for 1000V HRC fuses.
Did you measure the clearances and creepage distances? Do you know where to measure them? The trace Dave pointed to, is not a high voltage one and may not matter.
If you can tell a meter doesn't meet its specs at a glance, perhaps you should work for a UL lab and save them a load of cash in unnecessary testing.
The meter is already protected up to 1000V by crowbar transistors.
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.
If you suspect your meter was hit by high voltage transients, MOVs and PTCs should be replaced, as they degrade quite a bit after each activation. Even if your meter survived.

For peace of mind, common sense dictates to only use meters with a UL or TUV listing to work on high voltage lines. Major Chinese manufacturers, at last,  are sending their meters out, for independent testing.
If I was a professional electrician, I would only use well known proven brands. If a property gets damaged because of a malfunction or misuse of a meter, lawyers are unlikely to question the quality of the equipment, if a modern Fluke was involved, for instance.
As an average citizen, I would only test connections and appliances positioned in a CAT II environment. Anything above that rating, I'd call an electrician.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 18, 2015, 12:34:05 pm
As an average citizen, I would only test connections and appliances positioned in a CAT II environment. Anything above that rating, I'd call an electrician.

Or just get one of these:

(http://www.neweysonline.co.uk/neweys/images/site/products/large/044_1008_FL04_FLUKE_1AC-II_large.jpg)

Even the Fluke branded ones are only about $20. If you're regularly sticking bits of metal into household electrical sockets to see if they're live or not then you're doing it wrong.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 01:18:26 pm
Not as reliable as a DMM:

When using the Tester, if tip does not glow, voltage could still be present.
The Tester indicates active voltage in the presence of electrostatic fields of
sufficient strength generated from the source (MAINS) voltage. If the field
strength is low, the Tester may not provide indication of live voltages. Lack of
an indication occurs if the Tester is unable to sense the presence of voltage
which may be influenced by several factors including, but not limited to:
?? Shielded wire/cables
?? Thickness and type of insulation
?? Distance from the voltage source
?? Fully-isolated users that prevent an effective ground
?? Receptacles in recessed sockets/ differences in socket design
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 18, 2015, 03:21:12 pm
When using the Tester, if tip does not glow, voltage could still be present.
The Tester indicates active voltage in the presence of electrostatic fields of
sufficient strength generated from the source (MAINS) voltage. If the field
strength is low, the Tester may not provide indication of live voltages.

If none of the wires in a socket makes it light up then you already found your problem. No need to start poking pieces of metal in there, start following the wires back towards the fuse box instead.

Poking pieces of metal into AC mains sockets should be a last resort, not a starting point.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 05:02:28 pm
These pieces of metal are CAT III 1000V CAT IV 600V 16A rated, plugged into a Gossen MetraHit 26S with blanking ports on the A/mA jacks. What's your problem? What do you think these meters were made for? Test 9V batteries?
Your hairdryer and electric shaver are much safer, of course.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rob77 on February 18, 2015, 05:29:08 pm
As an average citizen, I would only test connections and appliances positioned in a CAT II environment. Anything above that rating, I'd call an electrician.

Or just get one of these:

(http://www.neweysonline.co.uk/neweys/images/site/products/large/044_1008_FL04_FLUKE_1AC-II_large.jpg)

Even the Fluke branded ones are only about $20. If you're regularly sticking bits of metal into household electrical sockets to see if they're live or not then you're doing it wrong.

why doing it wrong ? can you explain ?

i do prefer the "phase test pen" in form of a flat-head screwdriver - it's a universal tool. if the phase test pen is not enough then a solid meter is a must. i see no real use for those fancy contact-less phase testers (o.k. those are good for someone who is overly afraid of electricity :D )
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 18, 2015, 05:32:12 pm
I'm pretty sure a 250V fuse, glass or otherwise, in a CAT-IV instrument that claims ratings above 250V does not meet CAT-IV even by the oldest relevant IEC standards. Same with the clearances that are nowhere near current specs, so likely many revisions out of date at best.

As for the missing MOVs, it is not just about safety but also about preventing the meter from getting ruined at the first minor surge or incident involving moderate voltages. Having a multimeter that won't kill you due to a minor electrical fault or user error is nice. Having a meter that will also survive said mistakes and faults with a blown fuse at worst is better.
250V glass fuses are allowed under the previous regulations, even under CAT IV 600V. The test only required a maximum of 1000V on the amp range for 1 minute, with blown fuses in place to check for arcing. There was no requirement for 1000V HRC fuses.
Did you measure the clearances and creepage distances? Do you know where to measure them? The trace Dave pointed to, is not a high voltage one and may not matter.
If you can tell a meter doesn't meet its specs at a glance, perhaps you should work for a UL lab and save them a load of cash in unnecessary testing.
The meter is already protected up to 1000V by crowbar transistors.
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.
If you suspect your meter was hit by high voltage transients, MOVs and PTCs should be replaced, as they degrade quite a bit after each activation. Even if your meter survived.



I am sorry but thats definetively not correct . The CAT IV 600 V rating rules that the test sample has to withstand a transient peak of 8000 V without danger for the user and surely included the fuses . And this will be done in ALL ranges of the multimeter , not only in current mode . So the 1000 V protection with the crowbar transistors is absolutely not relevant in this scenario because there will be for sure arcovers in the multimeter during the test because of the fuses , creepage distance and clearance of 1 mm . And for sure , the chinese manufacturer would never send their products to an undependent testing institute because that costs a great deal of money and they want to save anywhere they could . So why do you think the big brands are so expensive ? Because the multimeters have certificates and that will increase the price for the customers at the end . Well they also have better housings , designs and input protection but in comparison to a certification that is not much more expensive to realize

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 05:55:24 pm
You are wrong. There is no 8000V transient test on the fuses. The current ranges are now tested at a maximum of 2000V DC for 1 minute with ruptured fuses in place, with a source of 500VA. No arcing should be present.
There is no scenario where you will get high voltage transients on the current ranges. Your fuse will blow as soon as you short the mains, while trying to measure voltage with the probes in the amps jacks.
If you measure current in series within a mains circuit, with high voltage transients present, the voltage will be low across the meter and the fuse will rupture if the current goes high for long enough (doubtful with short transients).
On the Gossen you can't even select the current ranges with the probes in the voltage jacks for transient testing.
You are also wrong with the Chinese multimeter manufacturers. C.E.M and others have been sending their meters for independent testing for years. UNI-T is now doing the same. Brymen also manages to submit to independent testing, while keeping their prices reasonably low.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Maxlor on February 18, 2015, 06:54:56 pm
You are also wrong with the Chinese multimeter manufacturers. C.E.M and others have been sending their meters for independent testing for years. UNI-T is now doing the same. Brymen also manages to submit to independent testing, while keeping their prices reasonably low.
They do it for a select few models. It's certainly not the default, or even common.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 18, 2015, 07:02:00 pm
Ok but theoretical maybe they pass the test . this little 5x20 fuses are only rated to 250 V . Higher voltages are not allowed . But this multimeter is 1000 V CAT III  and 600 V CAT IV marked and the fuses needed to be rated to 1000 V for passing the both CAT  ratings but they don t . Even if they will make it theorectically , practical it is not a proper CAT III 1000 V/ CAT IV 600V design and never never will get any certification . And by the way , where did they send it for testing before they finally sent it to TÜV / GS with proper fuses and better overvoltage protection ? Maybe to god for blessing them in hope nobody will burn to death while using these multimeters ? :bullshit: :bullshit:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 07:09:16 pm
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.

Actually this is no quite right. a "PTC" is a Positive Temperature Coefficient resistor. It will change its resistance very rapidly in response to temperature. The higher the temperature the higher the resistance. The change in temperature will occur when too much current starts passing through the PTC resistor.  Too much current starts passing because too much voltage is seen across the PTC resistor. So the PTC is a current limiting device that protects against too much current flowing from an over voltage situation. If the voltage is higher than what the internals of the meter can withstand but does not cause too much current to flow into the meter on that input jack, then the PTC protects nothing inside the meter. These are placed in series with the input of the meter.

An "MOV" is a Metal Oxide Varistor. This device changes its resistance based on voltage. It will go from almost an open circuit to almost a short at its threshold voltage. They can also absorb relatively high currents while doing so. These will quickly clamp the voltage entering the meter and prevent a flashover across tracks further downstream towards the ICs and possible damage to the voltage sensitive devices. Preventing a flashover can also prevent an explosion or a new lower resistance path for the overload condition to continue flowing. These are placed in parallel to the input on the meter. They also degrade with each absorption event and can outright fail if too many or too high an absorption event occurs.

Sometimes a "spark gap" is used instead of an MOV. Spark gaps usually are electrodes contained inside a small container that is either evacuated of air or has a noble gas inside. They also will go from open circuit to a short as soon as the threshold voltage is reached. They change their state must faster than an MOV.

As far as fuses go, there was a loophole in the older rules that could be interpreted as allowing a lower rating on different input jacks. The new rules do not allow this. The new rules basically state that all input jacks and all functions must meet the same voltage rating.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: AG6QR on February 18, 2015, 07:11:34 pm
There is no scenario where you will get high voltage transients on the current ranges.

...

If you measure current in series within a mains circuit, with high voltage transients present, the voltage will be low across the meter and the fuse will rupture if the current goes high for long enough (doubtful with short transients).

But after the fuse ruptures, whether because of a transient spike in current or an ordinary continuous non-transient overcurrent situation, or some combination, won't the entire voltage of any subsequent transient be present across the fuse?  If not, where is the transient voltage going?

I'm certainly not an expert on CAT ratings or testing, but I wonder, if you expect 8000V transients to be present on your mains, how can you be sure they won't ever be imposed across a meter measuring current through those mains?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 07:18:38 pm
Current measurements use an almost 0 resistance to measure the current and are placed in series with the device being tested. Some meters might have 100ohms for a resistance, or more. So the voltage drop inside the meter is very low, even with 8000V being the source. So a transient of tens of times that voltage, or even hundreds, would be needed to make a big voltage drop in the multimeter. So the fuse only needs to be rated for the actual voltage use of the meter. Good meters have fuses rated to break 10kA.

If you connect your meter incorrectly and think you are using the meter to measure voltage and you have it connected for current, then the fuse blows and the meter isn't connected anymore. This is a very transient thing and you will have almost zero chance of making the first grave error in use and also face an 8000V+ transient on what you are connecting to.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 07:24:54 pm
CEM has at least 7 meters in my database with UL certifications, which I could verify. It is not common yet, but it will be soon as more manufacturers get shut out of some markets. Another incentive is the presence of Fluke, now that they produce cheap and safe meters in that part of the world.
Small manufacturers with low value meters may not change their ways, if people keep buying their products, without any concern for safety.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 07:38:41 pm
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.

Actually this is no quite right.
If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 18, 2015, 07:43:41 pm
There is no scenario where you will get high voltage transients on the current ranges.

...

If you measure current in series within a mains circuit, with high voltage transients present, the voltage will be low across the meter and the fuse will rupture if the current goes high for long enough (doubtful with short transients).

But after the fuse ruptures, whether because of a transient spike in current or an ordinary continuous non-transient overcurrent situation, or some combination, won't the entire voltage of any subsequent transient be present across the fuse?  If not, where is the transient voltage going?

I'm certainly not an expert on CAT ratings or testing, but I wonder, if you expect 8000V transients to be present on your mains, how can you be sure they won't ever be imposed across a meter measuring current through those mains?

Well in a case of a transient while measuring the transient also will be present across the fuse .

The 8000 V is the pretended voltage of the IEC 61010 that a multimeter has to withstand without danger the operator of the multimeter in CAT IV 600 V . Well that is not far-fetched , it is a summary of experiences from experts . Here is an example : Some electricians from a overhauling company for subways measured the voltage on the bar where the railcars of the subways are getting the feeding for control reasons . After some time one and another multimeter suddenly died . They are really wondering about that because there is roundabout 800 v dc on the rail and that should not be the problem . But the problem are the transients , they reached 9000 V and they killed the multimeters after a short time
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 07:49:03 pm
One thing that sticks out to me is that if you really want to be sure, as sure as you can be, that the manufacturer is building meters to the right standards, then you have to check a few things.

#1. Do they have a valid and current ISO900X approval and no violations? This is to ensure that they actually make things the same way every time and don't change their methods without a notification and paper trail.

#2. Do they have a proper third party certification, like UL, to show that their designs and construction methods actually meet the ratings they assert? Do they have a clause in the procedures, as listed with their ISO certification, that demand a new third party testing anytime a new part or change in design is implemented anytime it is different from the originally tested configuration?

#3. Can you find and read a record of their ISO certification and current status?

#4. Can you find a record of their third party testing/certification for compliance to the standard they mark on their meter?

#5. Is the third party certifying lab also ISO certified and can you find their records?

As you can see, the average consumer does not have the resources nor time, and probably not the education, to know what to look for or even where to look. This is assuming an educated consumer. What about all the "noobs" and people who assume too many things? This is where Dave's review and the rantings and opinions of others can help. We try to educate. It is up to the individual to assume their own risk. It is not up to the company selling them something to assume that the buyer knows the risk and understands that the product they have purchased is labelled with lies that could kill them.

In the ideal world, everyone would treat everyone with respect and help ensure each others safety.

In the real world, companies take your money and hope you don't complain or find out they have taken you money based on lies. When some companies in China started putting melamine in baby food to artificially boost the protein content test results, it didn't seem to matter to them that they were literally killing babies to make a bigger profit. The occasional injury or death from wrongly marked multimeters in a  few million users world wide probably means nothing in the big scheme of their profits. Most people probably get these injuries or problems and don't know what happened, or have no recourse.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 07:55:56 pm
Well in a case of a transient while measuring the transient also will be present across the fuse .

The 8000 V is the pretended voltage of the IEC 61010 that a multimeter has to withstand without danger the operator of the multimeter in CAT IV 600 V . Well that is not far-fetched , it is a summary of experiences from experts . Here is an example : Some electricians from a overhauling company for subways measured the voltage on the bar where the railcars of the subways are getting the feeding for control reasons . After some time one and another multimeter suddenly died . They are really wondering about that because there is roundabout 800 v dc on the rail and that should not be the problem . But the problem are the transients , they reached 9000 V and they killed the multimeters after a short time

The meters died and they were safe, Why? They did not have their meters connected incorrectly on the current jacks and tried to measure voltage. I think this validates my statement that you are HIGHLY unlikely to be make the error of connecting your meter for current and then mistakenly try to measure for voltage and then also have an 8000V transient at the same time.

Unfortunately you can not make something 100% safe. There are always risks and everyone needs to know the risks involved. Education should have told the workers that the rails were connected to inductive motors with huge capacity and that the voltage could spike from the inductive kickback. I am sure the designers of the railway system knew this, why didn't the workers? That was bad education and a bad application of test equipment due to the bad education.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 08:02:18 pm
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.

Actually this is no quite right.
If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.

PTCs do not clamp voltage, period. That is the problem with your statement. PTCs limit current.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 18, 2015, 08:06:08 pm
One thing that sticks out to me is that if you really want to be sure, as sure as you can be, that the manufacturer is building meters to the right standards, then you have to check a few things.

#1. Do they have a valid and current ISO900X approval and no violations? This is to ensure that they actually make things the same way every time and don't change their methods without a notification and paper trail.

#2. Do they have a proper third party certification, like UL, to show that their designs and construction methods actually meet the ratings they assert? Do they have a clause in the procedures, as listed with their ISO certification, that demand a new third party testing anytime a new part or change in design is implemented anytime it is different from the originally tested configuration?

#3. Can you find and read a record of their ISO certification and current status?

#4. Can you find a record of their third party testing/certification for compliance to the standard they mark on their meter?

#5. Is the third party certifying lab also ISO certified and can you find their records?

As you can see, the average consumer does not have the resources nor time, and probably not the education, to know what to look for or even where to look. This is assuming an educated consumer. What about all the "noobs" and people who assume too many things? This is where Dave's review and the rantings and opinions of others can help. We try to educate. It is up to the individual to assume their own risk. It is not up to the company selling them something to assume that the buyer knows the risk and understands that the product they have purchased is labelled with lies that could kill them.

In the ideal world, everyone would treat everyone with respect and help ensure each others safety.

In the real world, companies take your money and hope you don't complain or find out they have taken you money based on lies. When some companies in China started putting melamine in baby food to artificially boost the protein content test results, it didn't seem to matter to them that they will literally killing babies to make a bigger profit. The occasional injury or death from wrongly marked multimeters in a  few million users world wide probably means nothing in the big scheme of their profits. Most people probably get these injuries or problems and don't know what happened, or have no recourse.

Yes that s the problem . The government accepts the CE self declaration as a legal certificate but it is a carte blanche for the company to sell their products without quality control . The main thing is profit for the company and taxes for the states and they don t really care about the customers . We just have to shut up and consume .  :bullshit:
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: necessaryevil on February 18, 2015, 08:22:45 pm
Well, doesn't make a false CE clarification make a manufacturer vulnerable to lawsuit? Especially when something goes wrong? They can't say they sold a device which is not intented for the european market, and they can't claim they didn't know.

Yes, this is just in theory, of course I know CE sucks.

I have always been taught to buy tools of good quality. I did not always listen, but some stuff you have to find out for yourself. An expensive multimeter isn't really expensive if it lasts for 20 years, doesn't it?

That being said I am a huge hypocrite for owning a cheap ass multimeter. But it is on my wishlist!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 08:35:52 pm
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.

Actually this is no quite right.
If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.

PTCs do not clamp voltage, period. That is the problem with your statement. PTCs limit current.
As the 1KOhm PTC resistance increases as it heats up, the voltage drop across it increases too, so it does clamp the voltage seen by the circuit in the DMM, limiting arcing possibility.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 08:44:48 pm
The PTC will do its job of clamping the voltage above that when required.
The MOV is not a requirement, but an additional protection, to back up the PTC.

Actually this is no quite right.
If I remember correctly, the MOV is acting faster than the PTC, relieving some of the high voltage, while the PTC is busy heating up to eventually clamp the current flowing into the meter. That's what I meant as back up.

PTCs do not clamp voltage, period. That is the problem with your statement. PTCs limit current.
As the 1KOhm PTC resistance increases as it heats up, the voltage drop across it increases too, so it does clamp the voltage seen by the circuit in the DMM.

Sorry, this is a wrong way of thinking about it. The voltage drop across it increases only if it is part of series of other circuit and a current flows sufficiently to cause it to heat up.  For example, my UT61E had a PTC in the circuit, but it still allowed the 2500V to pass directly to the selector switch and it fried the main IC. There was not enough current there to cause the PTC to change its value at all.  It did not "clamp" any voltage in this case. It does not "clamp" the voltage, as you said. This could give people the wrong idea of what a PTC is. It is a resistor that varies its resistance quickly with temperature. If a PTC is not connected to anything and it is heated up, its resistance goes up. This change is independent of voltage as it is not connected to anything. This is a fundamental.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 18, 2015, 08:53:37 pm
maybe the 2500 V will arc over to the com rail on the board because of the 1 or 2 mm clearance and then some current will flow and the ptc heats up and will increase the resistance . But then the multimeter is barbequed and fit only for a knacker s yard . It s a good example for planned obsolescence combined with the shitty input jacks  :-DD
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 09:09:56 pm
The idea is not to protect the multimeter, but to protect the user. If no current flows through the PTC, serious arcing is not likely. IC damage is not a concern. A Fluke may not function properly either after an overvoltage.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: WackyGerman on February 18, 2015, 09:22:27 pm
Well I am sure at 2500 V a fluke will survive this . In most Fluke I know there are ptc s and movs and when the transient will occur the movs will decrease the resistance and so current will flow and the ptc heats up and increase the resistance . The energy is divided by the movs and the ptc and the chance that the fluke will survive is much higher than a uni t that will definitively be scrapped at 2500 V , also at 1000 V . Look at youtube . There is a video where a brymen 869 is tested with 2000 V and it survived without any problems . The 869 has 2 ptc s and 3 movs and not whimpy ones
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 09:46:20 pm
Fluke 87 damage, after accidental overvoltage (1200V):
He doesn't say if the iC was affected.

Just an update, got the service manual from Fluke. I was really suprised they have them for download.
After a thorough evaluation of the front end of the meter, I'm replacing the fusible resistor R1, both varistors RV1 and RV2, the thermistor RT1, and a cap C1 that was damaged by the varistors when they blew. Basically the entire front end protection except for the spark gap. It appears to still be a spark gap.
I bought the parts directly from fluke through thier estore. Also picked up an extra set of fuses. I thought $40 for those original replacement parts wasn't bad considering what it might cost to send it in for repair.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 09:48:43 pm
For the record, I have put 5000V through a Uni-T UT71E, a UT61E, a Brymen BM257, a BM869, a BM525, a Digitek DT2843R, and a Fluke 27/FM. All but the UT61E survived.

P.S. I should also say that this was with very limited current, like 5ma.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 09:56:39 pm
Was it on all selections or just the voltage range?
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 18, 2015, 10:01:33 pm
Hmmm, I don't remember for all of them. I will have to repeat my tests on video!  >:D

Actually I don't think I will. I don't want to potentially destroy all those meters on a test they aren't rated to survive.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 18, 2015, 10:05:09 pm
Hmmm, I don't remember for all of them. I will have to repeat my tests on video!  >:D

Actually I don't think I will. I don't want to potentially destroy all those meters on a test they aren't rated to survive.
Do it on the 71E. You won't cry if it dies...  ;)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 19, 2015, 04:21:29 am
You obviously missed the story earlier in the thread of the electrician and some people standing close who died because of a falsely rated meter. Or the story of the electrical workers who had meters dying on them mysteriously because they hadn't received proper training.Not all countries have rules about house owners not touching their electrical distribution boxes.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 19, 2015, 06:57:20 am
You obviously missed the story earlier in the thread of the electrician and some people standing close who died because of a falsely rated meter. Or the story of the electrical workers who had meters dying on them mysteriously because they hadn't received proper training.Not all countries have rules about house owners not touching their electrical distribution boxes.
Here in Belgium, I can do anything I want downstream of the meter.
But to get the installation accepted, I need to document as I go (bills, pictures and plans) and be on my toes the day of the inspection.
What worries me is that DIY superstores sell 5€ to do said work. A novice could easely short the phase before the box (240v loadsa amps in my house) and the unprotected earth...
But that being said, I find that the other end of the spectrum, like Oz, where you need a diploma to rewire a plug is ridiculous.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Quarlo Klobrigney on February 20, 2015, 10:08:15 pm
Never underestimate stupid, or at least ignorance. I am still in the process of refurbing my home, and I was tearing out a wall which had only a light switch (in use) and a 2 prong receptacle which never worked. When I got most of the wall apart, I saw a rather thick cable feeding the light switch, then exit to a smaller cable to the outlet. I assumed it was a feed to the switch, back to the light, with a carry to the outlet. Not exactly the best way, but it would work. When I opened up the mess it was all too apparent, someone wired the receptacle in parallel with the switch. :-DD :-//
Another story of the same house, after removing a breaker with a visible trace of a cable to it, I was ready to cut the cable. A surprise "hit" me as the cable was still hot. |O I followed the cable branches back still further, and found that it was fed by another breaker on the same phase, in the ON position. A loop circuit. :palm: Needless to say I check & double check never trusting what should or shouldn't  be, as it CAN be.

So, never say never, sometimes ignorance or sheer stupidity can be laughable or deadly.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 20, 2015, 11:11:49 pm
Never underestimate stupid, or at least ignorance. wavy lines wavy lines
wavy lines wavy linesAnother story of the same house, after removing a breaker with a visible trace of a cable to it, I was ready to cut the cable. A surprise "hit" me as the cable was still hot. |O I followed the cable branches back still further, and found that it was fed by another breaker on the same phase, in the ON position. A loop circuit. :palm: Needless to say I check & double check never trusting what should or shouldn't  be, as it CAN be.

So, never say never, sometimes ignorance or sheer stupidity can be laughable or deadly.
I found something similar renovating this house.
While finishing up the electricity and getting ready to plaster, I was pulling out old deactivated cables and WHITE FLASH BANG found an active that should not have been.
So out comes my trusty UNI-T, all the mains are cut at the source, a long wire is pulled between the offender and the electrical box.
And it's beeping in way too many places, in the old stuff and my new box.
Eventually, I trace it down to a series of connection boxes that are meant to feed the push button activated lights in the entrance, stairs and landing.
And to the plugs in said places.
And to the lights and plugs of the four bedrooms.
And to the lights and plugs of the bathroom.
And to the lights of the kitchen.
AND TO THE BLOODY OUTSIDE GARAGE.
ON ONE 0.8mm² wire. And that's only the phase, I have yet to discover were the neutral is hidden...
There was probably more stuff connected to it that we already had cut out.
The house was wired up like this 30 years ago by a pro (there were still his stickers and his details on the house documents) and no inspector ever noticed...
(The same inspectors that failed an inspection on the previous house for having about 1cm of nearly visible (but fully isolated, safe etc) wiring on the top/behind of the fuse box.)
So, I spent the next 8 hours making this thing "safeish" and disconnecting as much of as possible.
Some "experts" here might say "you should have done X and Y". Yeah we did, dying in a shower of sparks is not my plan, but we tested one of the two wires and it lead to a set of fuses, we disconnected them both and marked the wires as "out". But one of the two cables bi-passed the fuse in a rather sneaky way and ended up connected to the rest of the stuff.  >:(

It's a pain in the arse, but it vindicates my approach the fitting all now wiring and fuses, fuses boxes etc in the house. TRUST NO ONE.

On a side note, the internet connection over the electrical wiring has improved dramatically (in the process to of being replaced by a router and CAT6 cabling). :)

To get back on subject, if you are "just doing continuity testing" on a "professionally installed electrical wiring" and the fuses are all "off" for that area, you might still have a surprise that can blow a 5$ DMM to kingdom come.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Paul Moir on February 21, 2015, 04:43:35 am
You obviously missed the story earlier in the thread of the electrician and some people standing close who died because of a falsely rated meter...

I presume you mean the article on ecmweb?  I know it seems pedantic but the details are important, especially if you're reading a one sided story like this one.  The article describes the multimeter as advertised as an "industrial multimeter" with no IEC rating at all.  For all we know it could have been a pre-CAT meter.  The meter-induced arc flash root of this accident seems to be more with the electrician's ignorance of those ratings than the meter itself, and focusing on the meter rather than the CAT ratings misdirects the lesson.


Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 21, 2015, 04:59:02 am
The point of all of this is not one specific incident and the details. The point is that education saves lives and stopping companies from cheating on their ratings and specifications can save lives. I don't understand why people argue against education and chastising companies for false advertising.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Paul Moir on February 21, 2015, 05:25:24 am
The point is that education saves lives and stopping companies from cheating on their ratings and specifications can save lives.

I agree completely.  I just wanted to point out that it was education that was the principal cause of that root of the incident and not a false rating.  There was no rating in that case. 

Furthermore I would argue that education about the IEC CAT ratings existence is more important than pointing out bad actors who falsify (perhaps not necessarily legally, but definitely morally) their ratings.  I could accept the contrary argument that pointing out the bad actors leads to education.  :)

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Ericho on February 21, 2015, 08:34:04 am
Quote
Quote from: Ericho on February 13, 2015, 04:58:03 AM

I worked on high power systems part of my career (mostly on ships) personally up to 4000kw electrical systems up to 1100v able to handle >2000A
I’ve seen the inside of a hospital twice and got plenty of near misses and burn scares.
Those accidents I got were on a 220/380 net and on a 24v dc net (both able to handle a few hundred amps)
So not the 660v 1100v stuff
Lack of respect for high power systems was always part of it. (I was young and ….. back then)
You cannot just poke anything just into anything. It ends badly, and yes explosions happen easily when equipment fails. (never seen a dmm explode thou)
Cat ratings and safety guidelines should be taken seriously. Don’t go assuming that it is not so, you may hurt yourself or someone else.




nice to hear raw and real experiences, would you care to elaborate how your accident happen? hope its not too personal ... could be good for everyone to know  :-//

Sure, no problem. Not proud of it nor ashamed, it was a long time ago when a differend attitude towards safety was all to common.

The 24V incident:

A electricaly started 400kw emergency genset needed testing. De battery bank was empty. We made a pair of long jumper cables out of 70mm² welding cables. I connected to the full 24v bank while my second engineer was 20m away holding the non insulated connections on the other end. He tripped and connectors shorted on the aluminium floor plating. At this moment I was already 6m away from the battery bank. they exploded And the plastic shards hitting me cut me all over,, the acid in the wounds and my eyes did the rest. This was hospitalization due to lack of respect, reclesness and assuming 24v is not dangerous.

380v (or 440V) incident:

4 a clock in the morning a 350A fuse blow in a switch / fuse cabinet with a few 800kW gensets connected to it.
I opened the cabinet, wacked a new fuse in and without thinking, meashuring or closing the door I trew a genset back online, after all I was in a hurry to go back to sleep.
A half shorted amp coil behind the fuse produced a large flame and I got 1 degree burned on my arm, lost some hair to.

This is how I learned that the warning labels / CAT ratings / certificates / safety systems etc etc. are not bullshit. (more then 25 years ago).

I do understand how doing low power electronics can trick you into thinking your home 220Vac net belongs to the same category. It doesn't. It is to be considered high power and treated as such.

I own a VC940, Its ok for ow power stuff. I use basic flukes for high power stuff. I stay away with DMM's from live high voltage (> 440Vac), there are, most of the time other means to do repairs on those systems.

Brgds,
Eric


Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 21, 2015, 09:54:07 am
If you're regularly sticking bits of metal into household electrical sockets to see if they're live or not then you're doing it wrong.
why doing it wrong ? can you explain ?

Would you let a 4-year-old child do it?


i see no real use for those fancy contact-less phase testers (o.k. those are good for someone who is overly afraid of electricity :D )

"According to the Electronic Library of Construction Occupational Safety and Health (eLCOSH), exposure to electricity is still a major cause of death among construction workers. Among electricians, the most serious concern is working with or near live wires without enlisting the proper safety procedures. Electrocutions kill an average of 143 construction workers each year. Data from 1992 through 2003 indicates electrical workers suffered the highest number of electrocutions per year (586 or 34 percent of the total deaths caused by electrocution)"

http://www.ecmag.com/section/safety/alarming-statistics (http://www.ecmag.com/section/safety/alarming-statistics)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 21, 2015, 01:35:38 pm
To Enricho,

You'll be glad to hear that the STCW (Standards of Training, Certification and Watch-keeping http://www.stcw.org/ (http://www.stcw.org/) for you land lubers ARRR) is imposing a high power electricity course on top of all the electrical stuff we already have to do for the Unlimited ticket.

My school (HZS Antwerp) has finished the lab and will be starting this year.

All engineers on ships above 500 tons DWT will have to pass this course over time.

Seeing the increasing prevalence of diesel electrics and the coming usage of batteries while docked (when possible, of course), this makes sense.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 21, 2015, 06:34:54 pm
We made a pair of long jumper cables out of 70mm² welding cables. I connected to the full 24v bank while my second engineer was 20m away holding the non insulated connections on the other end. He tripped and connectors shorted on the aluminium floor plating.

Amazing how even a tiny change in protocol can make the difference between life and death.

With hindsight it's obvious that he should have connected his end of the cables first...

...although any electrical fault in the system means that you would have been two feet from the exploding battery when you connected your end!

Maybe you should connect one cable at both ends then connect the other cable to the battery while the other guy holds his end of that cable safely/securely. That way you can be as far away as possible from the boiling sulfuric acid when you make the final connection.

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: ShaunO on February 22, 2015, 05:18:10 am
Dave (and forum members),

Enjoyed the video, as well as many others. A friend recently (last 6 months) purchased a UNI-T UT61E for roughly $130 AUD. I did a mini tear-down of it to see if looked as questionable as the one you featured. I've attached some images should the be of some use to the community. Needless to say, I won't be trusting this multimeter.

Keep up the great work.

Regards,

ShaunO
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 22, 2015, 08:58:03 pm
Well I am sure at 2500 V a fluke will survive this . In most Fluke I know there are ptc s and movs and when the transient will occur the movs will decrease the resistance and so current will flow and the ptc heats up and increase the resistance . The energy is divided by the movs and the ptc and the chance that the fluke will survive is much higher than a uni t that will definitively be scrapped at 2500 V , also at 1000 V . Look at youtube . There is a video where a brymen 869 is tested with 2000 V and it survived without any problems . The 869 has 2 ptc s and 3 movs and not whimpy ones
The PTCs play no part in protecting against high voltage transients. The spurious transients don't last long enough for the current to heat up the PTC to its Curie point. You should revisit Dave's video on input protection.
The IEC 8,000V series of test pulses are 100uS long, with a steep rise time of 1.2uS and a decay to 50% of voltage after 50uS. (I seem to remember 6 pulses in a series, but I could be wrong) (Correction: Fluke notes say 20 repetitions)
PTCs can take a few seconds to heat up to 60c~80c, with a current limit of a few milliamps.
Incidentally, PTCs should never be touched with bare fingers, to prevent leaving a leakage current path behind.

http://www.vishay.com/docs/29072/29072.pdf (http://www.vishay.com/docs/29072/29072.pdf)

EEVblog #373 - Multimeter Input Protection Tutorial (https://www.youtube.com/watch?v=zUhnGp5vh60#ws)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: FrontSideBus on February 22, 2015, 10:01:46 pm
I love the way they use BS1363 plug fuses in these :)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: pinchies on February 23, 2015, 10:21:38 am
Thanks for the review Dave... but its a bit late for me!

Paid $91 for this meter (UT71E) unused and new in box on flea-bay late last year. Great meter, has both the precision, and fast update rate modes, the only thing that is really annoying is the slow continuity meter. But thats what I have another cheap ($5) meter for! Can't beat it for value, but I agree with Dave that its overselling itself (CAT 4???) when it really didn't need to. And now I can put the money saved towards a MSO!
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 11:36:44 am
From a safety point of view, there is nothing special about CAT IV.
The IEC test for CAT IV 600V is the same as CAT III 1000V. If a meter passes the 8000V 2 Ohm pulse test, it gets both ratings.
Now, as a hobbyist, you should seriously ponder if it is wise to use any meter in a CAT IV or CAT III environment. That's certified electrician territory, who should know what kind of meter to use and what protective gear to wear.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: TheEPROM9 on February 23, 2015, 03:32:05 pm
Dave (and forum members),

Enjoyed the video, as well as many others. A friend recently (last 6 months) purchased a UNI-T UT61E for roughly $130 AUD. I did a mini tear-down of it to see if looked as questionable as the one you featured. I've attached some images should the be of some use to the community. Needless to say, I won't be trusting this multimeter.

Keep up the great work.

Regards,

ShaunO

Love how the fuses are the same as you find in standard UK plugs. These are dirt cheap HRC fuses.

It is still very true that you get what you pay for.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 06:15:40 pm
It is rather unrealistic to expect 20$ 1000V HRC fuses in a 50$ meter. However, there is a GS approved version for Europe (61D), equipped with the right fuses, but it costs quite a bit more.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 23, 2015, 06:22:40 pm
A BS1363 fuse is designed to work inside a cat111 area so surely it is OK in a cat111 meter, certainly ok for a meter that is on a hobbyist bench, my scope is marked cat11 1400 volts so if that is good enough for bench work those meters should be as well. I am not trying to apologise for any meter manufacturer but a bit of realism has to be shown in these matters, and to the best of my knowledge no one has been hurt by let alone killed by a BS1363 fuse exploding, after all it is designed to work on 250 volt circuits and stop high current excursions. But then unlike the US the UK domestic circuit is not directly tied to the 11Kvolt line the transformers isolate the low from the high tension unlike the US pole pigs.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 06:43:54 pm
On the practical side, you may be right , but legally, the meter can't be sold in Europe anymore.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 23, 2015, 06:46:11 pm
Love how the fuses are the same as you find in standard UK plugs. These are dirt cheap HRC fuses.

Is there anything wrong with them?

Presumably they can prevent electrical arcing. What's the advantage over one of those big fat $15 fuses?

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 06:52:42 pm
BS1363 fuses are only rated for 240V. In Europe, the fuses must now have the same voltage rating as the highest CAT rating of the meter.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 23, 2015, 07:03:43 pm
BS1363 fuses are only rated for 250V.

OK, you need physically longer fuses for higher voltages...but do they really need to cost $15 each?

Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: gildasd on February 23, 2015, 07:09:59 pm
BS1363 fuses are only rated for 250V.
OK, you need physically longer fuses for higher voltages...but do they really need to cost $15 each?
The fuel tank on the Yacht is not going to be filled up by low priced fuses.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 07:10:52 pm
Small volumes, manufacturing tolerances and required certification may explain the cost.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: SeanB on February 23, 2015, 07:15:33 pm
The difference between the standard plug fuse and the 1kV rated one is the materials used. In both cases they use pressed tinned brass for the end caps ( or pressed tinned steel in some cases, it is immaterial in use) and a ceramic body, with a fine silica sand filling mix and a fuse element made from a wire alloy.

The difference between the plug fuse and the 1kV one is that the plug fuse uses a wire that will break at around 1.2 to 10 times the rated current ( depends on time of the pulse, temperature and such) and the arc that forms will be eventually extinguished in the sand fill in under typically 10 cycles, or around 300ms, and the deposited metal vapour and carbon inside the fuse will not explode it from overpressure and will not conduct electricity at 500VDC applied to the blown fuse.

The 1kV rated fuse uses a similar wire, with similar breaking characteristics, but it is filled with both a finer silica blend and with additive oxides such that it will stop the arc sooner, and that the fill will isolate the particles and the soot so that even at 2kV DC applied it will under no circumstances pass any current. the case is also stronger, as the higher energy available generates a much higher pressure inside the housing, and it must withstand it without exploding or emitting any vapour, and must absorb all the heat energy of the fuse operation.

Place a glass fuse directly across the mains ( in a thick housing) and you might find the end caps if you are lucky still in the fuse holder. A BS1363 fuse will blow, but should not disintegrate. The HRD fuse will blow as well without damage externally. Do the same with a 1kV line and the BS1363 fuse will explode like the glass fuse, but the 1kV one will just blow. At this voltage the glass fuse pieces will simply arc over until the holder melts.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 07:39:34 pm
The M205 glass fuse doesn't necessarily explode, unless its rating has been exceeded (100A for a 10A fuse and 35A for a 1A fuse).
The Fluke fuse enclosures are made of glass fiber:
http://mrmodemhead.com/blog/inside-a-multimeter-fuse/ (http://mrmodemhead.com/blog/inside-a-multimeter-fuse/)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: SeanB on February 23, 2015, 08:18:41 pm
True, but the most common cause for a multimeter fuse blowing is the meter being inadvertently placed across a power source with the leads set in the current range. Thus the current limiting is basically the lead resistance and the supply impedance. With mains that essentially devolves to lead resistance in most cases. More than enough to detonate a glass fuse, I have seen them explode when a power supply bridge rectifier shorts and the primary side mains fuse shatters. Secondary fuse just melted, as it was a 25A fuse ( basically a solder slug in glass).
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 08:54:55 pm
The house wall wiring impedance comes into play as well, reducing some of the current. I had trouble rupturing a couple of medium blow fuses, as the circuit breaker kept on tripping on the panel first. Eventually, I found a mains outlet where they blew with a whimper. Of course, if you're very close to the source, anything can happen. In theory, a lead impedance below 2.5 Ohm would be necessary to explode a multimeter 10A glass fuse on 250V mains and about 1 Ohm on a 110V supply.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: G7PSK on February 23, 2015, 09:33:24 pm
So if these meters with the BS 1363 fuses were rated for 250 volts RMS maximum they would be OK or not?
 
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 23, 2015, 09:40:22 pm
If a meter with the BS1363 fuses was rated at CATIII/250V, it would be legal.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 23, 2015, 09:45:37 pm
So if these meters with the BS 1363 fuses were rated for 250 volts RMS maximum they would be OK or not?
I don't think that there is a CAT rating for 250V. 300V or 150V only. Fuses also need to have a rating of 50kA or equivalent to voltage/lead impedance.
BS1362 are rated for 240V AC 6kA. There may also be an issue with the lack of a DC rating.
If I remember correctly, fuses must also be rated FF (very fast blow). The BS1362 is fast medium blow.

Bussmann fuse: http://docs-europe.electrocomponents.com/webdocs/0279/0900766b80279c60.pdf (http://docs-europe.electrocomponents.com/webdocs/0279/0900766b80279c60.pdf)
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 24, 2015, 12:56:06 am
Yes, Wytnucls is correct. I spoke too quickly.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: soren on February 24, 2015, 04:00:07 am
HRC fuses rated for 1000V are available in the 1.25" x 0.25" size from reputable manufacturers. That tells me that the 1" x 0.25" BS1362 fuse is probably good for at least 800V in practice.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Wytnucls on February 24, 2015, 04:48:48 am
What you're happy with is your personal choice.
What matters is that no meter can be legally sold in Europe fused with a BS1362 anymore, unless rated CAT II 150V perhaps.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Lightages on February 24, 2015, 12:00:25 pm
The point is that there is no 250V category, 150, 300, 500  600 and 1000V only.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: rolycat on February 24, 2015, 12:18:51 pm
The point is that there is no 250V category, 150, 300, 500 and 1000V only.
Probable typo there - that should be 150, 300, 600 and 1000V.
Title: Re: EEVblog #712 - Uni-T UT71E Multimeter (Why Uni-T Meters Suck)
Post by: Fungus on February 24, 2015, 12:30:45 pm
only 150v ?  :o
arent those rather common in 250v AC plugs? not proper even for 250v ?

The two things aren't equivalent.

Mains plug fuses are there to cut the power if there's a short-circuit inside the connected device.

Multimeter CAT ratings are about protecting people from transient power spikes.