New TRMS Uni-T UT139C DMM is available now

[edavid]

If you are going to be using a clamp meter it implies that you will be working on high energy circuits.

Why do you say that?  I only use mine on household circuits.

Actually household circuits, if you are referring to house wiring, are considered high energy. If I remember correctly, the distribution panel and any circuits within 10 meters of the panel.

Do you have a citation for that?  I don't think it's true here in the US.

[naughtilus]

For the Uni-T UT139C we need the SIBA 7012540.0.630 (page 620), which is 700VAC, 630mA, 50kA, ceramic w/filler and 6.3mm x 32mm.

Found these sources doing a google search: DIYtrade.com and 11467.com (no affiliation). Indicatively prices are under $8 for 100 unit lot on these, which is not bad for a difficult to find fuse I reckon. Any group buys organized before on this forum or maybe Franky is interested offering this type of fuse for his ebay store (where I got my 139C originally)? Franky, do you do pre-orders where we give you money and when there is at least 100 of us you buy a lot and send us the fuses? Small amount per person at stake and we are all bound eventually to blow the voltage fuse considering this is somewhat of an electricians DMM, not for bench work really. I bought it to poke the mains at home.

Thoughts?

[Lightages]

If you are going to be using a clamp meter it implies that you will be working on high energy circuits.

Why do you say that?  I only use mine on household circuits.

Actually household circuits, if you are referring to house wiring, are considered high energy. If I remember correctly, the distribution panel and any circuits within 10 meters of the panel.

Do you have a citation for that?  I don't think it's true here in the US.

Actually, a US company says so! The most concise explanation comes from Fluke. It isn't a very rigorous explanation but it does confirm my assertion.

http://www.fluke.com/fluke/m2en/training/safety/

Look for ABCs of multimeter safety.

This is why I almost always suggest a properly rated meter for even casual bench users. The temptation to use it on home wiring is too much.

[edavid]

Actually, a US company says so! The most concise explanation comes from Fluke. It isn't a very rigorous explanation but it does confirm my assertion.

http://www.fluke.com/fluke/m2en/training/safety/

Look for ABCs of multimeter safety.

That document does not define "high energy".

Anyway, it says that CAT III is three-phase distribution, so doesn't that mean that single-phase house wiring would be CAT II?

[naughtilus]

I have three-phase outlets (400V) in my house. Those would be CAT III most likely.

[Lightages]

Do I need to read everything and repeat for everyone? 

''Within a category, a higher working voltage”
(steadystate voltage) is associated with a
higher transient, as would be expected. For
example, a CAT III 600 V meter is tested
with 6000 V transients while a CAT III 1000 V
meter is tested with 8000 V transients."

"CAT III Three-phase distribution, including • Equipment in fixed installations, such as switchgear and polyphase motors.
single-phase commercial lighting • Bus and feeder in industrial plants.
• Feeders and short branch circuits, distribution panel devices.
• Lighting systems in larger buildings.
• Appliance outlets with short connections to service entrance."

[naughtilus]

Transients... pffft. Just roll the dice man!  O0

[Wytnucls]

A three-phase outlet is considered CAT III, as is a single-phase outlet within 10 meters of the distribution panel.

[Lightages]

Obviously "High Energy" is a relative term. I think that anyone with experience with electricity would agree that Class III would be classed as "High Energy". This, especially, when compared to bench electronics energy levels.

[naughtilus]

Basically everything in my house is CAT III since everything is within 10m radius from the distribution boards.

The Uni-T UT139C + Fluke TL71 leads seems good enough for measuring single phase <240Vac at home and <24Vdc/1A for hobby projects. Not sure if I wanna poke in the 3-phase outlet though... I'd call it CAT II and CAT III-ish.

[Lightages]

Basically everything in my house is CAT III since everything is within 10m radius from the distribution boards.

The Uni-T UT139C + Fluke TL71 leads seems good enough for measuring single phase <240Vac at home and <24Vdc/1A for hobby projects. Not sure if I wanna poke in the 3-phase outlet though...

Yes! You understand now. I am glad someone will know their risks and won't be blindly poking probes where they could be a hazard. Now you know the risks and can asses them to your liking instead of just thinking you are safe.

[naughtilus]

Also it seems leaving the protective caps on the leads increases their CAT rating. This is most likely because by reducing the exposed metal tips area, chances of arc flash occurring during a large transient when you pull out the tips are greatly reduced. HV cutouts between the inputs and fuses also seems to help prevent this. Plasma ball in your face can't be fun. 

That Fluke ABC pdf is a fun read. Thanks for sharing LA.

[Wytnucls]

Basically everything in my house is CAT III since everything is within 10m radius from the distribution boards.

The Uni-T UT139C + Fluke TL71 leads seems good enough for measuring single phase <240Vac at home and <24Vdc/1A for hobby projects. Not sure if I wanna poke in the 3-phase outlet though... I'd call it CAT II and CAT III-ish.

For three-phase outlets in Europe, the voltage to consider for IEC CAT III environment is between neutral and any phase (230V 50Hz), not the voltage between two phases (400V 50Hz).
There is a big jump in transient energy test between CAT II and CAT III/CAT IV, as the voltage source impedance is reduced from 12 Ohms to 2 Ohms.
If the UT139C lives up to its CAT rating, it's all good up to 600V in a CAT III environment. Of course, without independent testing, that CAT rating is not to be trusted.

[naughtilus]

For three-phase outlets, the voltage to consider for IEC CAT III environment is between neutral and any phase (230V 50Hz), not the voltage between two phases (400V 50Hz).

So 400V between phases for a domestic plug within 10m distance of the dist. board is what category?

BTW. How's for safety? Or   The future Photonicinduction?

[Wytnucls]

Three phase outlet, regardless of distance is CAT III, requiring a meter rated CAT III 600V minimum, being lowest voltage for CAT III.

[naughtilus]

Thanks.   

[mos6502]

Looks like the boards went through a few revisions. I've attached pics of the PCB of the meter I got some three weeks ago. The first in this thread was marked 190612-1, mine is 190612-4, so presumably it's the fourth revision. As you can see, they added another MOV. The board also looks better made than the the old one, all the components are straight and the soldering looks excellent.

[mematyi]

Hello there!
I just got this meter, and well it is quite good for the price. Mine is also the 4.th revision.
I wonder if anyone read the chip's datasheet? It says that there are serial output.
There are also connections on the PCB for communicating(sda,scl) and for calibration 
Apparently the "cal" traces do not lead to the mcu, but the RMS chip if i am correct

[Ichabod]

DTM0660L IS HYCON HY12P65 Digital Multi-function Meter (DMM) ICs
http://www.hycontek.com/e-page2-HY12P.html

But i ask me where UNI-T takes the other 1000 Counts     - on HYCON stands 5000 only!

[Electro Fan]

I don't get it, why would you buy this instead of a UT61E?

On a related question, why wouldn't the manufacturer read the half a zillion posts about the UT61E and their other models and either modify or add one or a few models that better address the user feedback? 

Seems like they have the ability to make many different models - why not put the most popularly requested features into one or two really, really well-received combinations? 

No doubt, the UT61E has done pretty well - but it could be even more successful.

As it is you can choose model A with this and this but not that and that, or you can get model B with that and that but not this and this.  I could understand it if they only made one or two models but when they have a bunch of models why not add a backlight here and a whatever there? 

The manufacturer would probably say "we've studied the market and segmented the market by user types and use-cases and we've determined that the profile of a person who buys a UT61E is someone who has $45 not $48 and they don't value having a backlight".  On the other hand, we have found the profile of a UTXYZ customer and they have even less money but they like to see their digits in the dark."

The answer is that in most companies the Marketing department that does "outbound" marketing communications rather than the "inbound" determination of market requirements and opportunities.  Meanwhile Engineering is generally too busy and often doesn't have the skill set, experience, budget, or charter (at least one of the above is missing) to sort through the signals and noise in the market, and the Sales people get listened to even less than the customers.  As a result you get a hodgepodge of "almost" products in a product family all scattered around the targets rather than hitting any of the targets squarely.  Of course since the targets change over time (due to changes in technology and competition as well as use cases) it's an evolutionary process but the low hanging fruit is to thoughtfully incorporate user feedback regarding current products.  It sure does seem like the DMM market could benefit from better product planning rationalization.

Having said all that, it's probably easier to be a critical customer than a successful product marketing manager.

[Lightages]

I have come to the conclusion that multimeter manufacturers really don't spend much time worrying about customer feedback. They seem to design in the dark and think they are designing to lead the consumer. The exception seems to be Uni-T. They seems to just make a whole pile of different models with as many variations as possible and hope tat something sells. If they were actually trying design for what people want, then they could cut down their range of models to 1/10 of what they have now.

[adrianf88]

Hey there everyone, a few months ago i was looking at the 139c as my next buy but i just couldn't source it locally. I know Franky is an ebay seller that everyone recommends around here, and i was going to buy it from him. But after i bought several items from ebay and recieved them all banged up by the local mail and customs office and by no fault of the seller i decided to wait for it to be available locally

A few days ago i finally found it in a store in my city and next thing tomorrow after i leave work i plan on buying it.

But seeing that its price is a 1/5 of my monthly salary i do feel like i should bury my impulses and think about it for a minute or two.

My questions are:

How reliable is it for bench operation only?
How much drift should i expect after 1 year? What about 5?
Can i calibrate it once it drifts?
When something eventually goes poof! and releases the magic ghost, how likely am i to find the necessary parts and documentation for the repair?

Thank you all for your time in advance!

[joeqsmith]

>How reliable is it for bench operation only?
Difficult to know what you do on your bench. 

>How much drift should i expect after 1 year? What about 5?
Good question.  The two I have purchased only lasted a few hours after removing them from the box.    

>Can i calibrate it once it drifts?
I assume you mean align it and I would doubt it.

>When something eventually goes poof! and releases the magic ghost, how likely am i to find the necessary parts and documentation for the repair?
These meters are what I would consider disposable.  The two I damaged took out the control IC and I was unable to do anything with them.   Some of the meters I have tested had enough protection to at least save the main controller.   These I have been able to repair.   

The PCB shown appears to be the same as what I had ran.  Notice the two unpopulated clamps.   I do wonder if the controller IC would have survived if these were populated but those four diodes cost money!

[adrianf88]

What i do on the bench is mainly hobby type stuff, amps, led's, repair broken stuff around the house (monitors, tv, etc) stuff like that.

What did you do to them that they only lasted 2 hours?

I know the term calibrate, i have 0 ideea what you mean by align.

Well, do you have any ideea what diodes were supposed to go there? If so, we can add them on our own.

[joeqsmith]

If you are playing with line voltage stuff and you have some sort of clamp and breaker, the meter itself should be alright if you know what your doing. 

The two I had were purchased for the purpose of attempting to see how robust they were.   They were both tested to failure and were not repairable. 

In my own neck of the woods, Calibration is going to be verifying that the equipment is within the manufactures tolerances using some traceable means.    If the equipment is out of calibration, we would have it Aligned to bring it back into tolerance.   

I would guess they would have used the same parts that were used for the other clamp but I would NOT recommend that ANYONE would EVER attempt to make ANY changes to a meter they plan to use for ANY high energy work!!!