Uni-T Multimeter UT71D unboxing and teardown

[cybergibbons]

More to the point - if I connect common to the line, one end of the current circuit, which isn't CAT rated, is going to be at a high potential. Surely it's really quite awkward to design something with one half CAT rated and the other not?

[alm]

Just connect the common jack to 1000 VDC and the current jack to ground. This way you observe the voltage ratings for both inputs .

[cybergibbons]

I've sent them the following back. I only have a much older copy of the standards unfortunately.

Unfortunately, I don't think that resolves the issue.

EN-61010-1, the older revision of the standard states in section 16.2:
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Multifunction meters and similar equipment shall not cause a hazard in any possible combination of rated input voltages, and settings of function and range controls.

The maximum rated voltage specified for any function is applied to each pair of terminals in turn, in every combination of function and range controls.

During and after the tests, no hazard shall arise.
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I believe EN 61010 -2-030:2010 is even tighter and deals with possible misuse, which surely must include leaving the probes in the current range when trying to measure voltage.

If I apply the maximum rated voltage for the voltage function to each pair of terminals, including the current terminals, I'm sure a hazard will arise.

Your product page also just states the CAT rating without any qualification - nearly every other multimeter on the market has the same ratings for all terminals. The manual isn't available online for me to look at - until you look into it, it isn't clear that this is a UT-71D from Unitrend.

I'm also going to pre-empt the manufacturer - I bet they say the CAT rating is only marked for the voltage terminals on the meter. Every other meter with adequate protection on the current terminals is marked the same - look at the Fluke 87V, Amprobe AM-140-A etc.

It's clear from the layout of the board that they intended to use larger fuses that could provide the required level of protection. Why this was changed, I don't know.

I really don't think that this meter is safe or complies with the standards marked on it.

[cybergibbons]

A response from that:

1.    In EN61010-1:2001, no any clauses request the maximum interrupting current of the fuses must comply with a rated value, and as you mentioned, in clause 16.2: “Multifunction meters and similar equipment shall not cause a hazard in any possible combination of rated input voltages, and settings of function and range controls”, so we had evaluated no hazards when the maximum rated voltage specified for any function is applied to each pair of terminals in turn (See attached page 53 & 54 of test report), except that, the enclosure and product construction had been designed to reinforced insulation, thereby the products complied with EN61010-1:2001.

2.     Except the misuse tests basic on clause 16.2  which had been evaluated no hazards, the current terminals must be designed to have adequate clearance and creepage distance to guarantee product safety when rating maximum voltage applied on them. 

[Erwin Ried]

@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.

I bought this meter for about 120 usd, I found it very nice compared to my earlier experiences with ultra cheap ones. I saw that info also in the manual. About the hold button, I am pretty sure the hold function usually works that way, but you have log capabitilies anyway.

The only thing that bugs me is the BEEP, it is anoying and loud, and the only option is to disable it completelly (even if you want it in the continuity test)

[Mitsch]

Hello,
I bought the multimeter and wanted to change those really cheap glass fuses.
After I opened the multimeter I was really surprised. My UT71D shipped with really big "Holly" fuses, see attachment.

Regards,
Michael

[nidlaX]

Note how the PCB is marked 71A(1KV FUSE) instead of the vanilla 71A model.

Time to go add some fuse holders and fuses to my 71B...