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

[miguelvp]

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.

[0b01010011]

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.

[gonzoid]

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) 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 and TÜV/GS, implying only those models may have been approved.

[open loop]

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.

[george graves]

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.   

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?

[fubar.gr]

My 71E has a different 10A shunt:

[Wytnucls]

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.

[PeterL]

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.

[Owen]

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?

[rolycat]

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 .

[Wytnucls]

No, there is a GS approved version of the UT61 with proper HRC fuses and a lower CAT rating.

[mikeselectricstuff]

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.

[gonzoid]

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
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/

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?

[jeremy]

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.

[Wytnucls]

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.

[Pentium100]

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.

[Wytnucls]

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)

[Wytnucls]

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.

[electr_peter]

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.

[PeterL]

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.

[Yago]

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

[SilverSolder]

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?

[Wytnucls]

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.

[Yago]

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.

[Wytnucls]

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)