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

[ModemHead]

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.

[SNGLinks]

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

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?

[Wytnucls]

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

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.

[rollatorwieltje]

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.

[TMM]

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? 

[Wytnucls]

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.

[DanielS]

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.

[Wytnucls]

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.

[3roomlab]

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

[DanielS]

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.

[3roomlab]

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.

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 outdated?

[mux]

https://www.certipedia.com/quality_marks/0000000002?locale=en

Bogus, bullshit, lies?

[rollatorwieltje]

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 outdated?

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

[Wytnucls]

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.

[Fungus]

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:



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.

[Wytnucls]

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

[Fungus]

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.

[Wytnucls]

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.

[rob77]

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:



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 )

[WackyGerman]

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

[Wytnucls]

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.

[Maxlor]

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.

[WackyGerman]

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 ?

[Lightages]

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.

[AG6QR]

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?