Author Topic: Uni-T Multimeter UT71D unboxing and teardown  (Read 25581 times)

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Offline ElectroElvis

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Uni-T Multimeter UT71D unboxing and teardown
« on: February 09, 2012, 08:35:37 am »
Hello evryone,

today i got my new multimeter i have been waiting for :D I am very pleased with it, its build quality and all in all it feels great in hands. I havent had a time to test it a little just opened it took some photos and put it back together to get to room temperature.

There are few flaws i noticed right in begining, for instance (for now) continuity test is dissapointment :) it needs like 1 second to start producing "beep". Few of them i also wrote in following link.

I also uploaded a lot of pictures from unboxing to opening the multimeter and looks of inside. Hope you all enjoy it, any comments are very welcome.


http://electroelvis.wordpress.com/2012/02/09/multimeter-uni-t-ut71d-teardown/

To admins: hope i dont violet any rools by posting link to pictures in my "site", if i do please notify me.

Thanks

Elvis

Offline Richard W.

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #1 on: February 09, 2012, 07:34:55 pm »
The UT71D is about 150€ here in germany. I expected better quality for that price.

those fuses :o
those CAT ratings  :o 
those horrible Mini-MELF resistors  :o
those resistors next to the PTC  :o
those soldering on R44 and R45 :o (the lower half of the board seems to be soldered manually)
and why the hell is a screw in the pcb trace to the COM jack?  :o

If i were you, i'd return it. honestly.
 

alm

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #2 on: February 09, 2012, 07:38:38 pm »
Thanks for posting the teardown. Most of the soldering looks decent, but I'm not impressed by the protection devices, just one PTC and two glass fuses. I would be hesitant to use this for mains or other dangerous circuits. Don't worry about this with batteries, wall warts or bench power supplies.

I'm surprised they use those MELF packages, I thought most people hated them both for production and prototyping (Most End up Lying on Floor).

Don't worry about the link. Dave doesn't mind links to other electronics blogs at all, as long as it's relevant.
 

Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #3 on: February 09, 2012, 08:34:02 pm »
Yes i bought it from germany for 149€+ shipping.

I dont intend to stick that to mains for saftey reasons and the main reasons is i have no business with mains. What I am looking for is to measure circuits powered by either 9V battery or 12V 2A max power supply :) It will all depend how i will shrink my idea in future.

I could return it and what would i get another half hand made meter like other uses did with UT61x series. Its a compromise between price and quality. I would definitly be angra if somthing like that woulc be on a 500€ meter but on this i can live with it :)

Thanks for comments, i will post video or two and some testing with caps, resistors...

Elvis

Offline Bored@Work

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #4 on: February 09, 2012, 09:07:15 pm »
I would still have a word with the supplier. You got a meter where the manufacturer intentionally fitted sub-standard parts, the 250V fuses, and left out parts, like the spark gap. This is nasty, because the meter is apparently designed to be fitted with HRC fuses. The manufacturer decided so save a few Jiao at the cost of user's health and safety.

The thing is, it doesn't adhere to its CAT rating. Today you might think this is ok. But you never know where this meter will end up. In the future someone might happen to use it, not knowing what you know about it. Or you might happen to forget for a moment that the CAT rating is a scam.
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Offline grumpydoc

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #5 on: February 09, 2012, 09:34:27 pm »
Quote
...is apparently designed to be fitted with HRC fuses....

Yes - the PCB is clearly laid out to accept the HRC fuses. My UT61E is the same, as anyone "upgraded" theirs?

Also is there any reason not to put a 1000v MOV in place of the "spark gap"?

 

Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #6 on: February 09, 2012, 10:04:27 pm »
Quick test of Multimeter and what i meant with "SLOW" :D

To posters above, i sended e-mail to my seller and Uni-T waiting for responses.

Thanks,

Elvis

Offline Neilm

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #7 on: February 09, 2012, 10:28:29 pm »
I can't make out the test lead rating, but judging by how much bare metal there is I don't think that the test leads meet the requirements of IEC61010. The new version of IEC61010 was released a few years ago which banned test leads with lots of bare metal. I believe that the transition period for these ended about a year ago.

Glass fuses have not been allowed under 61010 for many years.

If I had bought this in the UK, I would report it to Trading Standards and / or a notified body. (I would also have a chat with a guy I know who is on TC66 - the committee that is responsible for 61010).

The resistors by the PTC could be for voltage monitoring purposes. They could be high integrity resistors - I can't tell from the picture.

Also is there any reason not to put a 1000v MOV in place of the "spark gap"?

No reason at all. Indeed, a MOV will provide more consistent performance than a spark gap.

those horrible Mini-MELF resistors 
What is wrong with Mini-MELF? I have just designed a product that uses them - they are rated at 1W with the ability to handle pulses of over 10kV :o Admittedly, it only does that it potted / coated but I did test them and they are quite happy with it. With the correct pads and nozzle on the pick and place machine they can be placed as easily as any other component. Just don't lift the board up before it is soldered.

Neil
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Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #8 on: February 09, 2012, 11:03:10 pm »
Very big Pros for seller he responded to my e-mail within half an hour :) here is first part of his explanation:


Fuses are for current measurement.
Like in manual written





And the marking on PCB is 71A and not 71D.

No problem, same pcb with other components for A, B, C, D

Offline Bored@Work

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #9 on: February 09, 2012, 11:11:26 pm »
Fuses are for current measurement.

That answer misses the point.
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Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #10 on: February 09, 2012, 11:17:17 pm »
And here is answer for that SCREW in middle of PCB trace :D pretty funny one hehe:


Version written next to 71A is: V20051010-6

did have a other pcb layout

But same class fuses.

But also class fuses without a white filling can have UL registration.

Because of:

what is the SCREW doing in middle of PCB trace?

Its really a special design!

But the VIA is connected to all layers, also cupper filled.
So the resistor lost is verysmall or same like a  trace before andafter the via


@Neilm: In manual it says it is IEC 61010 CAT III 1000V, CATIV 600V overvoltage and double insulation standard COMPLIED heh can you belive it
« Last Edit: February 09, 2012, 11:19:21 pm by Elvis O. »
 

alm

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #11 on: February 09, 2012, 11:35:14 pm »
BaW: Don't be so hard on them. At least the statement is true, that's a start. Of course it's completely irrelevant and utterly useless, but getting correct statements out of tech support is already better than I'd expect. Getting relevant information out of them is completely hopeless.

@Neilm: In manual it says it is IEC 61010 CAT III 1000V, CATIV 600V overvoltage and double insulation standard COMPLIED heh can you belive it
Ask them how those glass 250 V fuses perform when the meter is exposed to a 8 kV transient from a 2 ohm source impedance, i.e. 4 kA short circuit current, as specified for CAT III 1000 V. What's their max. interrupt current?

That UL certificate has got to be phony or for a different model with all components mounted, there's no way this meter meets IEC 61010.

What's the current rating of those (presumably) 0.025" square pin headers that carry the current from the current jacks to the main PCB? Probably something like 1 A per pin? Three pins seems a little wimpy for carrying up to 10 A, and more in case of an overload until the fuse blows (presuming it doesn't arc).
 

Offline FenderBender

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #12 on: February 10, 2012, 02:22:34 am »
MELF resistors?  ::) Umm...

It doesn't look too bad other than the shite input protection. Even my $18 (~15euro) Home Depot meter has ceramic fuses.

 

Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #13 on: February 16, 2012, 08:43:51 am »
A little indepth preview of some stupid flaws of this multimeter:

And here is in written form what i noticed: http://electroelvis.wordpress.com/2012/02/16/multimeter-ut71d-from-uni-t-flaws/
« Last Edit: February 16, 2012, 08:52:03 am by Elvis O. »
 

Offline vtl

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #14 on: February 16, 2012, 08:50:12 am »
For the peak hold and minmax you need to manual range it with the RANGE button, otherwise it gives you the OL, at least thats how it works on the UT61E. Quite annoying how it doesnt range in those modes though
 

Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #15 on: February 16, 2012, 08:55:07 am »
@vtl: thank you for telling me that, i tried and it works. I find 2 problems with that anyway. First one is why it doesnt say that anywhere? And other one is it still gives some random values even in manual range mode.

Offline vtl

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #16 on: February 16, 2012, 09:09:34 am »
On the UT61E the display indicates both 'manual' and 'auto' on the LCD segments, which makes it quite clear. But it seems 'auto' just disappears on your UT71 when its manual ranging. It is not indicated in the UT61E manual either. The first time i tried it I was wondering why it was beeping at me when it exceeded the counts, but figured it was in manual ranging.
 

Offline cybergibbons

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #17 on: February 16, 2012, 02:01:22 pm »
@Neilm: In manual it says it is IEC 61010 CAT III 1000V, CATIV 600V overvoltage and double insulation standard COMPLIED heh can you belive it
Ask them how those glass 250 V fuses perform when the meter is exposed to a 8 kV transient from a 2 ohm source impedance, i.e. 4 kA short circuit current, as specified for CAT III 1000 V. What's their max. interrupt current?

That UL certificate has got to be phony or for a different model with all components mounted, there's no way this meter meets IEC 61010.

Right - I have the same meter, and I can't recall what it looks like inside, but I believe it has glass fuses and has the same CAT markings. I bought it from Farnell - do you think if I approach them, under UK law, they will do anything about it?
 

alm

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #18 on: February 16, 2012, 04:49:39 pm »
They may give you a refund if you make a fuss. Assuming you find a knowledgeable CSR who actually understands what you're talking about.
 

Offline Bored@Work

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #19 on: February 16, 2012, 08:07:43 pm »
If it has a UL mark, making a few photos of the inside and contacting UL might bring some fun. Same for other safety marks. Contacting the relevant authorities for electrical safety where you bought it might or might not bring some fun, too.

Contacting the seller? They probably give a toss. They have the stuff in stock and disposing of the stock, sending it back and dealing with Uni-T to get reimburse is a lot of hassle. Selling it is easy.
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Offline Neilm

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #20 on: February 16, 2012, 08:47:21 pm »
If it has a UL mark, it should have the certificate number. If so - you can look it up on the UL website. (I know you can for components, so I assume it will be the same for completed instruments).

@cybergibbons: I don't know what they would say - It is possible they won't have a clue about what you are on about. I would have a chat with trading standards and ask them.


Ask them how those glass 250 V fuses perform when the meter is exposed to a 8 kV transient from a 2 ohm source impedance, i.e. 4 kA short circuit current, as specified for CAT III 1000 V. What's their max. interrupt current?

That UL certificate has got to be phony or for a different model with all components mounted, there's no way this meter meets IEC 61010.

What's the current rating of those (presumably) 0.025" square pin headers that carry the current from the current jacks to the main PCB? Probably something like 1 A per pin? Three pins seems a little wimpy for carrying up to 10 A, and more in case of an overload until the fuse blows (presuming it doesn't arc).

I don't know about an 8kV transient on 1kV with a 2 ohm impedance - the tester at work is not man enough to deliver the required current. Actually, the mains transformer on site isn't man enough to meet the full spec.
Testing with that on a very cheap Chinese meter was fun. Small explosion and fire - the test leads turned out to be better fuses.

Neil
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Offline ElectroElvis

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #21 on: February 28, 2012, 08:54:55 pm »
With a little delay i got answer to my question about functions and fuses. I asked directly to HQ of Uni-T and here is what they came up with. Let me just remind you that Manual does not have any "usefull" information inside as you also could see in my video i made.



 Hi, as for IEC61010CAT?1000V, it is the over-voltage safety standard. In fact you cannot input such high voltage value under current ranges. Because the shunt resistance is very small, PCB will be burned when short-circuiting the input terminal and COM under such high voltage input. That is why HRC kind of fuses are not used inside.
 
 Second, concerning functions PEAK, MAX, MIN, the manual actually offers clients functions and specifications that the meter has, so are PEAK, MAX/MIN ranges, would you please check again?  As far as the range -4V---4V, the default after UT71D is powered on is 4V range, you need to select desired ranges manually. When performing Max/Min function, Max/Min values are only displayed and on second display instead of main display screen.
When test probes are disconnected, the digit bouncing is caused by the interference. Since the input impedance is 10M, so the accuracy for the meter can not be affected during measurement. so is PEAK mode
 
Regarding HOLD function, you should press down HOLD button during measurement to save readings you have got. If the button is pressed first before measurement, you cannot go on with the measurement any more,
 
 With respect to the gap between 400mA and 10A, the shunt resistance is very small and the potential will be close to zero voltage when short-circuiting between any terminal and COM. that is why no spark gap happens between these two terminals. The flat ribbon is needed inside based on circuit design, which offers misconnection alarm in current ranges. So resistance difference does exist, however the soldered resistance is the lowest, we have take this kind of issue into consideration when doing the software calibration.
 We are sorry causing you such inconveniences when using our meter. Thank you for your cooperation, please feel free to contact us if you want to know information about the meter. Thank you very much!

alm

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #22 on: February 28, 2012, 09:33:22 pm »
Hi, as for IEC61010CAT?1000V, it is the over-voltage safety standard. In fact you cannot input such high voltage value under current ranges.
So the meter conforms to IEC 61010 and is rated for CAT III 1000 V, but can not handle 1000 V? Doesn't the current version of IEC61010 require an instrument to withstand the same maximum voltage on all settings and ranges?

Because the shunt resistance is very small, PCB will be burned when short-circuiting the input terminal and COM under such high voltage input. That is why HRC kind of fuses are not used inside.
I don't understand his argument. Does he expect the PCB to act as HRC fuse? A low impedance would be even more reason for HRC fuses, not less. Our instrument is expected to blow up and kill the owner when connected to mains, so why bother with protection?
 

Offline cybergibbons

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #23 on: February 28, 2012, 10:35:06 pm »
Hi, as for IEC61010CAT?1000V, it is the over-voltage safety standard. In fact you cannot input such high voltage value under current ranges. Because the shunt resistance is very small, PCB will be burned when short-circuiting the input terminal and COM under such high voltage input. That is why HRC kind of fuses are not used inside.
 

That's a really worrying response. PCB tracks are brilliant at sustaining long, powerful, hot arcs even under moderate currents.
 

Offline cybergibbons

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Re: Uni-T Multimeter UT71D unboxing and teardown
« Reply #24 on: March 08, 2012, 04:47:45 pm »
So Farnell have come back with this from Uni-Trend:

Quote
1)     The 1000V voltage rating of the fuse is required per the standard EN61010-1:2010 / EN 61010 -2-030:2010 and enforcing date is 1st Oct 2013.

2)     The product made to compliance standard – EN61010-1:2001, we already obtained CE certificate which means that the product is OK to sell to EU market before above enforcing date.

3)     The manual already indicated overload protection voltage is 250V for the AC/DC current range, pls refer to manual page 61~62.

So - questions.

1. The manual does state overload is 250V on current. Farnell's data sheet doesn't have this information in it, and they don't provide the manual until after purchase. So how are you means to know this?

2. IEC 61010-2-30 - I'm fairly sure this says that the meter must withstand "foreseeably reasonable misuse". This to me would include using the current range mistakenly. Does anyone know? What is the deal with meters that have different CAT ratings for different inputs?

 


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