Handheld meter robustness testing

[bdunham7]

CAT ratings have many grey areas. It's easy to invent worst-case scenarios for any category.

If it is going to wear the label, then it should be suitable for all the situations that the label covers, not just your home panel.

I'm not going to pretend to understand them but I'll happily point out that a CAT III 600V rating isn't automatically a CAT IV 300V rating even though they both say "6000V @ 2 Ohms" in the cute little chart.

I don't know whether that's true or not regarding the standards, even if certain manufacturers opt to not put a CAT IV label on where you might expect that they could.

The way I understand it is that the standards only say that the meter has to fail in a safe manner.

ie. the PTC can explode during the first transient and it still gets the rating if no shrapnel penetrates the case.

as discussed elsewhere:

"After the voltage of 4.4.2.101 has been applied to the METER, the METER shall continue to be
able to indicate the presence of HAZARDOUS LIVE voltages up to the maximum RATED voltage.
NOTE The METER is not required to maintain its normal accuracy. A maximum deviation of 10 % is acceptable."

[AndrewBCN]

...
It seems you feel that the transients I apply cause the PTCs to switch.   I have no idea why you would feel this way, but I've made whole videos on this subject.   You could also look at the datasheets for various PTCs and see what are the effects of various package sizes.
...

I apologize for misunderstanding, Joe. It's just that what seems obvious to you, because you are so familiar with the subject, honestly flies way over my head most of the time. 

[Fungus]

as discussed elsewhere:

"After the voltage of 4.4.2.101 has been applied to the METER, the METER shall continue to be
able to indicate the presence of HAZARDOUS LIVE voltages up to the maximum RATED voltage.
NOTE The METER is not required to maintain its normal accuracy. A maximum deviation of 10 % is acceptable."

I note you've missed out the next part of that text, which says:

"Conformity is checked by inspection while applying the maximum RATED voltage of each voltage measurement range capable of MAINS voltage measurements."

The PTCs aren't on the "voltage measurement" part of a multimeter circuit, they're on the much lower-impedance "ohms/continuity/etc" part of the circuit.

Ref: https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/100/

[joeqsmith]

as discussed elsewhere:

"After the voltage of 4.4.2.101 has been applied to the METER, the METER shall continue to be
able to indicate the presence of HAZARDOUS LIVE voltages up to the maximum RATED voltage.
NOTE The METER is not required to maintain its normal accuracy. A maximum deviation of 10 % is acceptable."

I note you've missed out the next part of that text, which says:

"Conformity is checked by inspection while applying the maximum RATED voltage of each voltage measurement range capable of MAINS voltage measurements."

The PTCs aren't on the "voltage measurement" part of a multimeter circuit, they're on the much lower-impedance "ohms/continuity/etc" part of the circuit.

Ref: https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/100/

 

Fungus goes to school...

[AVGresponding]

as discussed elsewhere:

"After the voltage of 4.4.2.101 has been applied to the METER, the METER shall continue to be
able to indicate the presence of HAZARDOUS LIVE voltages up to the maximum RATED voltage.
NOTE The METER is not required to maintain its normal accuracy. A maximum deviation of 10 % is acceptable."

I note you've missed out the next part of that text, which says:

"Conformity is checked by inspection while applying the maximum RATED voltage of each voltage measurement range capable of MAINS voltage measurements."

The PTCs aren't on the "voltage measurement" part of a multimeter circuit, they're on the much lower-impedance "ohms/continuity/etc" part of the circuit.

Ref: https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/100/

But, aren't they prior to the range switch, and therefore part of the circuitry in play when in the volts ranges?

[bdunham7]

And where do you think CAT III is?

On the safest side of a distribution panel with circuit breakers in it.

So just to follow that up with a 'correction', or at least an acknowledgement that your statement has basis in fact, the very old UK 61010-2-033 that I got my hands on does indicate that CAT II is at least two breakers away from the transformer, CAT III a least one and CAT IV perhaps none.  No limit on size mentioned, available fault currents listed as 10kA, 50kA and >50kA respectively.  This is not the way I've seen is described in (much) later literature, but I don't have a later standard to look at. 

Edit: What I have also appears to just be addenda and revisions, and I'm lacking 61010-1 which they refer to extensively....so I really don't have much.

[bdunham7]

I note you've missed out the next part of that text, which says:

"Conformity is checked by inspection while applying the maximum RATED voltage of each voltage measurement range capable of MAINS voltage measurements."

The PTCs aren't on the "voltage measurement" part of a multimeter circuit, they're on the much lower-impedance "ohms/continuity/etc" part of the circuit.

No, I didn't miss that.  However, on the UNI-T we are trashing, one of the PTCs is in series with the voltage circuit and since there is no surge resistor, when the 2 MOVs clamp it will be roasted just as badly as if it were in series with another low-impedance circuit.  If that UNI-T can actually read mains voltage after being subject to 10 strokes of whatever transient most closely matches the CAT III/600V 6kV/2ohm IEC model, I'll buy one.

[AndrewBCN]

...
If that UNI-T can actually read mains voltage after being subject to 10 strokes of whatever transient most closely matches the CAT III/600V 6kV/2ohm IEC model, I'll buy one.

Either you should set aside the equivalent to 15€ or you can lose all faith in independent certification companies. Because Intertek has indeed tested the UT125C. I found the UT125C in their directory, here:

https://ramuk.intertekconnect.com/WebClients/ITS/DLP/products.nsf/4c8700f3b75987a08525777700583333/1d393ddebcfb5489862586280014abff?OpenDocument

[joeqsmith]

But, aren't they prior to the range switch, and therefore part of the circuitry in play when in the volts ranges?[/b]

He knows they are or I fear his cognitive functions are in decline.   Both very possible.  If the latter,  someone should take away his meters before he hurts himself.

[Fungus]

The PTCs aren't on the "voltage measurement" part of a multimeter circuit, they're on the much lower-impedance "ohms/continuity/etc" part of the circuit.

No, I didn't miss that.  However, on the UNI-T we are trashing, one of the PTCs is in series with the voltage circuit and since there is no surge resistor, when the 2 MOVs clamp it will be roasted just as badly as if it were in series with another low-impedance circuit.  If that UNI-T can actually read mains voltage after being subject to 10 strokes of whatever transient most closely matches the CAT III/600V 6kV/2ohm IEC model, I'll buy one.

I haven't looked closely at this particular Uni-T but generally multimeters have a separate 10MOhm voltage input and a 10kOhm+PTC resistance/continuity input.

[bdunham7]

Either you should set aside the equivalent to 15€ or you can lose all faith in independent certification companies. Because Intertek has indeed tested the UT125C. I found the UT125C in their directory, here:

I would happily spend the $22 to have my faith renewed in the certification process and gain a reliable meter that I don't need in the process.  Unfortunately I'm anticipating being disappointed by the Intertek Shenzen branch--or somebody, anyway.

[bdunham7]

I haven't looked closely at this particular Uni-T but generally multimeters have a separate 10MOhm voltage input and a 10kOhm+PTC resistance/continuity input.

I'm not sure what you mean by the last part but in this case, have a look at the nice hi-res photos you'll see that once the input gets to 2X the knee voltage of those MOVs, the only finger in the dam other than the long, winding trace back to the COM lead is those PTCs--and they aren't in series.

[joeqsmith]

The PTCs aren't on the "voltage measurement" part of a multimeter circuit, they're on the much lower-impedance "ohms/continuity/etc" part of the circuit.

No, I didn't miss that.  However, on the UNI-T we are trashing, one of the PTCs is in series with the voltage circuit and since there is no surge resistor, when the 2 MOVs clamp it will be roasted just as badly as if it were in series with another low-impedance circuit.  If that UNI-T can actually read mains voltage after being subject to 10 strokes of whatever transient most closely matches the CAT III/600V 6kV/2ohm IEC model, I'll buy one.

I haven't looked closely at this particular Uni-T but generally multimeters have a separate 10MOhm voltage input and a 10kOhm+PTC resistance/continuity input.

Keep those stories coming.  We're here all night folks. 

[Fungus]

Keep those stories coming.  We're here all night folks.

I'm having a moment, aren't I?

[AndrewBCN]

Either you should set aside the equivalent to 15€ or you can lose all faith in independent certification companies. Because Intertek has indeed tested the UT125C. I found the UT125C in their directory, here:

I would happily spend the $22 to have my faith renewed in the certification process and gain a reliable meter that I don't need in the process.  Unfortunately I'm anticipating being disappointed by the Intertek Shenzen branch--or somebody, anyway.

You can anticipate whatever you want but facts are facts:

1. Intertek has certified the UNI-T UT125C.
2. Shenzhen (please note the correct spelling) is a modern, prosperous city of nearly 13 million, including thousands of permanently resident foreigners. https://en.wikipedia.org/wiki/Shenzhen
3. Intertek has countless offices in China, 13 of which are located in Shenzhen. https://www.intertek.com/contact/asiapacific/china/

[joeqsmith]

Keep those stories coming.  We're here all night folks.

I'm having a moment, aren't I?

I suspect you have been looking at too many low end meters like the UNI-T,  ANENG....    Your statement about "...generally multimeters have a separate 10MOhm voltage input.." could be correct as I suspect there are more low end meters being introduced and sold.    We love our cheap, disposable products which drives the market and I just don't want to admit it. 

***
You won't see me posting anytime soon about how electrically robust (or mechanically) Dave's 121GW meter is but it's input circuit uses the more common approach I find in the meters that do well against my tests.   

[Fungus]

I suspect you have been looking at too many low end meters like the UNI-T,  ANENG....    Your statement about "...generally multimeters have a separate 10MOhm voltage input.." could be correct

Yeah, the only ones I've sat and traced out (a couple of years ago) were cheapies and the voltage input went straight to the 10MOhm resistor chain with a separate branch where the 10K resistor and (single) PTC was.

I've just watched this again and I'm all edumacated now:



The meter in that video^ (Fluke 27) has two input branches, one with only a resistor before it goes off to the ADC. 

[joeqsmith]

I suspect you have been looking at too many low end meters like the UNI-T,  ANENG....    Your statement about "...generally multimeters have a separate 10MOhm voltage input.." could be correct

Yeah, the only ones I've sat and traced out (a couple of years ago) were cheapies and the voltage input went straight to the 10MOhm resistor chain with a separate branch where the 10K resistor and (single) PTC was.

I've just watched this again and I'm all edumacated now:
...

The meter in that video^ (Fluke 27) also has two input branches, one with just a resistor before it goes off to the ADC. 

On the UT61e I had attached, you have that 1k connected directly to the input.   The other side to a 10M.  The 10M has various capacitors which gives the meter a very wide AC response.   Of course, there's a downside to it.

Dave's 121GW uses a couple of PTCs in series to act as a load for AC mains testing.  There's nothing else to limit it.   The funny thing with this meter is the mechanical switch does not have enough clearance and it will arc over the contacts at a fairly low voltage.  It's been certified by Intertek so it must be safe. 

[joeqsmith]

The meter in that video^ (Fluke 27) has two input branches, one with only a resistor before it goes off to the ADC. 

I've never looked at the 27.  No doubt Fluke has changed their secret sauce over the years.  Their front end designs have certainly evolved since my first DMM, the 8000A.   Even the Fluke 77 I looked at was an improvement over my first meter but it can't come close to the level of robustness seen with their later generations.  I think I ran that old, abused Fluke 189 up to 6kV without any problems.  They have certainly gained my respect. 

And if we want to talk about the mechanical robustness, to this day, I have not seen a switch that handled that life cycle test like the Fluke 17B+.  Looking at how the 87V was cutting into the PCB and how it was chattering, I  think they have learned a few tricks there as well.

****
This is the sort of thing general customers don't see or consider.  This kind of innovation that improves reliability and reduces downtime is one reason why Fluke is where they are today.

****
It's easy enough for you to verify what you are watching on YT.  See the attached service manual.   

https://www.testmart.com/webdata/mfr_pdfs/FLU/27______smeng0100.pdf

[bdunham7]

3. Intertek has countless offices in China, 13 of which are located in Shenzhen. https://www.intertek.com/contact/asiapacific/china/

They may have a lot of offices, but I'm sure they can keep count.  It wouldn't speak well for their organizational skills otherwise.  How is this relevant to the issue at hand?

2. Shenzhen (please note the correct spelling) is a modern, prosperous city of nearly 13 million, including thousands of permanently resident foreigners.

I think the Chinese spell it " 深 圳 " but there may not be agreement on that either.  AFAIK, there is no 'correct' spelling otherwise as it is just an attempt at phonetical representation of sounds that don't easily match up to any English pronunciations.  Don't know about French.  These representations seem to change over the years in some attempt to more correctly represent how they are pronounced by the Chinese.  So "Mao Tse Tung" is now "Mao Zaedong" and perhaps someday the current leader "Xi" will become "Sjhee" or something.  I haven't heard enough native Chinese speakers pronounce the name of the city to have an opinion on which representation is best, but apparently "Shenzhen" is the most popular at the moment.  How is this relevant to the issue at hand?

1. Intertek has certified the UNI-T UT125C.

And Moody's certified sub-prime mortgage bonds as AAA before they weren't.  Nobody was prosecuted and Moody's still collects huge fees to rate bonds, even they they obviously were grossly negligent, IMO inherently corrupt, and very, very wrong.  The result in either case here--AAA bond rating or CAT III/600V certification--appears to be that you end up with a worthless turd with a pedigree.  We just haven't seen the UT125C blow up yet.

[joeqsmith]

CAT III is already a serious place. It is circuit just after or on fuse panel. High fault currents are still possible.
For instance you have an 200kW elevator motor, that one would be CAT III because it is behind junction box and has a fuse.

A phase-to-phase fault on a 480-V system with 20,000 amperes of fault current provides 9600000 watts of power (9,6 MW). If the fault lasts for 200 milliseconds before the overcurrent protection clears it, the released energy would be 1,92 MJ, which corresponds roughly to a stick of dynamite.

At 20000A current, at a distance of 0.5 m, light intensity might reach magnitude of about 1,8 M lux! 

Fault currents in CAT III can be up to 25kA... I assure you that is a serious arc fault accident.

Article on arc flash testing.
https://www.ecmag.com/section/safety/lets-blow-it-arc-flash-testing

The Mersen lab has two generators. Each generator is rated 10 megavolt-amperes (MVA) continuous with a short-circuit rating of 68 MVA and is powered by a 4,160-volt (V), 536-horsepower electric motor that is directly connected to the utility. When a test is conducted, the short-circuit current comes from the generator and not the electric utility.


This lab has the capability to produce up to 100,000A of short-circuit current at 480V.

What I refer to as my half cycle simulator hardly compares with the tests they conduct.   With the low energy levels I use, there is enough evidence left over to determine what went wrong.  Still a small amount of copper can create a fairly impressive pressure wave.
 

[AndrewBCN]

...
How is this relevant to the issue at hand?
...

The fact that Intertek has certified the UNI-T UT125C is certainly relevant to the issue at hand. But the baseless or irrelevant dribble you posted certainly isn't.

Apart from your "anticipating being disappointed by the Intertek Shenzen (sic) branch", do you have anything to say based on facts relevant to the issue at hand?

[Fungus]

Apart from your "anticipating being disappointed by the Intertek Shenzen (sic) branch", do you have anything to say based on facts relevant to the issue at hand?

I dunno about your Uni-T but there's a bunch of Aneng meters that are "certified" (with downloadable certification certificates!) but one look a the PCB will tell you it's lie.

eg. The Aneng Q10.

Download your CAT III 600V / Cat II 1000V certificates here: https://zotektools.com/products/zty/
 
(yes, Anengs are manufactured by Zotek)

See photos of the PCB here: https://www.eevblog.com/forum/testgear/aneng-goes-crazy-with-new-meters/msg3338126/#msg3338126

Joe: If I'm reading it right this is a meter where the input goes directly from the volts jack to the IC with only R16 and R17 in between. The PTC is on a separate circuit (after going through the range switch!)





At least they used MELFs! 

[AndrewBCN]

...
Yep. There's a bunch of Aneng meters that are "certified" with downloadable certification certificates but one look a the PCB will tell you it's lie.
...

1. "one look at the PCB" is not enough for much. If it were, we would all be experts at everything. Ah, but I forgot: you are an (self-proclaimed) expert... 
2. What exactly do you claim is a lie? The certificate (hence the lier would be Zotek) or that the meter was indeed tested and passed the tests (hence the lier would be the certification company, in this case Anbotek)? You yourself wrote just three days ago that such claims require clear evidence, but I don't think you have any evidence whatsoever to backup your claim.
3. How is the Zotek ZT-Y certification by Anbotek relevant to the UNI-T UT125C certification by Intertek? We are talking about two different products from two different companies certified by another two different companies. Where is the similarity here?

You and bdunham7 are welcome to purchase, disassemble and test the UNI-T UT125C for robustness or standards compliance anytime you see fit and report your results here or in another thread, but until then, perhaps refrain from the baseless claims and "anticipating being disappointed" sort of comments a little bit?

[joeqsmith]

Free meters!!!  It's been a while since anyone has "reached out" to me with such an offer. 

I have no intention on turning my channel into a marketing tool.   

If UNI-T or Gossen "reached out" about updates that address what we saw with their products, I would certainly invest the time to look at them a second time.   If Brymen came out with a meter that would out class the BM869s, I would certainly be interested in having a look.