Handheld meter robustness testing

[rsjsouza]

Who would ever have thought a meter with latching relays would every make it to market.  There's no test for it.      Have they lost their way?   Seems so.

I'm not clear on the problem--there have been meters in the past that have used latching relays without issues that I know of.  Are you saying they are inherently problematic or that they aren't being used correctly?

Being mechanical, relays are naturally more fragile than solid state parts for a handheld device (no issue with bench units), therefore there are chances of accelerated degradation or failure in an equipment used in a mechanically unstable environment - IIRC the standard does not have a mechanical test (although don't quote me on that). Unfortunately, I don't think there is data that shows drop tests on both types (solid state and relay) to quantify any degradation, either short or long term.

One additional problem that Joe has shown in top of the line meters (thus compliant) is that standards do not seem to be doing their part to account for magnetic susceptibility on their tests.

(Prior I had a brainfart moment and mentioned some silliness about the power consumption, to which Trader and HKJ corrected me).

[joeqsmith]

While large government bodies can be very costly and entertaining,  they are not always very responsive.  My view on these safety standards is more about trade and less about protecting the consumer.   The more shit I look at with approvals, the more diluted my view of them becomes.   

I like to ride motorcycles and proper safety gear is important.   We have DOT which is a large government agency but there is also the private, non-profit Snell certification. 

The following quotes are take from: https://smf.org/faq
 

William "Pete" Snell was the "Racer of the Year" when he died needlessly in a 1956 Sports Car Club of America racing event. His then state-of-the-art helmet, made of leather and pressed cardboard paper, didn’t protect him. The following year, in memory of Pete, a number of his friends, colleagues, and fellow racers, including Dr. George Snively, formed the Snell Memorial Foundation, now known as Snell Foundation. Its purpose was to set helmet performance standards to encourage the development and use of truly protective helmets.

DOT and ECE are law of the land for motorcycle helmets sold in the US and in European Union countries. Although government standards are required, they also are the minimal standards. Snell Standards demand the highest premium protection that current technology and materials can offer. Snell Standards are voluntary. Many of the best helmet manufacturers decide to design and make helmets to Snell Standards because many consumers seek out Snell certified helmets.

I only use Snell rated helmets.   

I don't frequently work in what I would consider a high risk electrical environment where equipment safety, PPE, training, kept me out of trouble or  I may be interested in seeing a similar independent safety group for my industry as well.   What I am interested in is finding meters that can survive some small transients without damage, unlike my first Fluke.  Because there really isn't much data on this and most reviews I saw were people opening boxes and blabbing,   here we are... 

[nightfire]

The CAT ratings are safety standards, it just has to fail safe.
I don'y recall if that's for every test in the standard, but it's the basic gist of the high energy testing.

IIRC, the meter must continue to indicate the presence of hazardous voltages, although it doesn't have to be accurate.  This makes sense, or alternatively (not in the standards AFAIR, just my opinion) at least it should fail completely (no display) rather than indicate 0.000V.  Imagine I hang my meter up at a machine I want to test and hook it up, it says 240VAC.  I walk over to the service panel and turn off the wrong breaker, but there is a big transient that blows open the inputs on the meter--but doesn't cause any physical damage.  I come back and my meter reads 0VAC--so I go to work.  This is an argument against fused leads and also is the basis for the 'test before touch' protocol that requires that the meter be proved immediately before and after testing.

In germany, safety regulations do also not allow to check for the absence of voltage with a DMM, you are to use a 2-pole voltage tester instead. (Well known brand here is "Duspol")
Reasons:
- Due to operator error, you could misplug the cables and end up in the low-impedance input of the DMM, which causes accidents
- due to the high impedance in todays multimeters, they can measure some "stray voltage" on the wires because of some capacitic effects on long cables. A 2-pole voltage tester has buttons where you can put a low impedance on that circuit so to see if the voltage remains or under load goes down

[Fungus]

In germany, safety regulations do also not allow to check for the absence of voltage with a DMM, you are to use a 2-pole voltage tester instead. (Well known brand here is "Duspol")
Reasons:
- Due to operator error, you could misplug the cables and end up in the low-impedance input of the DMM, which causes accidents
- due to the high impedance in todays multimeters, they can measure some "stray voltage" on the wires because of some capacitic effects on long cables. A 2-pole voltage tester has buttons where you can put a low impedance on that circuit so to see if the voltage remains or under load goes down

Don't forget to take along a proving unit to see if your fancy electronic gadget is working or not.

[bdunham7]

In germany, safety regulations do also not allow to check for the absence of voltage with a DMM, you are to use a 2-pole voltage tester instead. (Well known brand here is "Duspol")
Reasons:
- Due to operator error, you could misplug the cables and end up in the low-impedance input of the DMM, which causes accidents
- due to the high impedance in todays multimeters, they can measure some "stray voltage" on the wires because of some capacitic effects on long cables. A 2-pole voltage tester has buttons where you can put a low impedance on that circuit so to see if the voltage remains or under load goes down

What would those regulations say about a DMM that doesn't have current ranges and is fully protected on the ranges that it does have (takes care of first problem) and has a Lo-Z function?

[Fungus]

In germany, safety regulations do also not allow to check for the absence of voltage with a DMM, you are to use a 2-pole voltage tester instead. (Well known brand here is "Duspol")
Reasons:
- Due to operator error, you could misplug the cables and end up in the low-impedance input of the DMM, which causes accidents
- due to the high impedance in todays multimeters, they can measure some "stray voltage" on the wires because of some capacitic effects on long cables. A 2-pole voltage tester has buttons where you can put a low impedance on that circuit so to see if the voltage remains or under load goes down

What would those regulations say about a DMM that doesn't have current ranges and is fully protected on the ranges that it does have (takes care of first problem) and has a Lo-Z function?

When is a multimeter not a multimeter?

https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-113

[2N3055]

In germany, safety regulations do also not allow to check for the absence of voltage with a DMM, you are to use a 2-pole voltage tester instead. (Well known brand here is "Duspol")
Reasons:
- Due to operator error, you could misplug the cables and end up in the low-impedance input of the DMM, which causes accidents
- due to the high impedance in todays multimeters, they can measure some "stray voltage" on the wires because of some capacitic effects on long cables. A 2-pole voltage tester has buttons where you can put a low impedance on that circuit so to see if the voltage remains or under load goes down

What would those regulations say about a DMM that doesn't have current ranges and is fully protected on the ranges that it does have (takes care of first problem) and has a Lo-Z function?

When is a multimeter not a multimeter?

https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-113

Well that is exactly what I was explaining in that other topic. Bullet prof devices exist. They come with heavy limits.
If very limited functionality is sufficient for job at hand, they are perfect devices for the task.

[bdunham7]

When is a multimeter not a multimeter?
https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-113

Well, it is still plenty 'multi' since it does VDC, VAC, (both with ranges down to 6.000V) Ohms, Capacitance, Diode and a bit of continuity.  But you don't have to go to that extreme either:

https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-116

[Fungus]

https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-116

That one's only CAT III 600V. The 113 is CAT IV 600V - Flukes highest rating!

If I'm an "electrician" I'm taking the 113.

(it's also much cheaper!  )

[Per Hansson]

Hey Joe thanks for your videos! Just watched your new video about the UT61E+ as it was recommended to me (see, you do get recommended by Youtube!)
I'm just curious if you would be willing to make a very simple input test: give the meter 230VAC on the ohms range.
That easily killed the old model, even when it was the "GS" typerated version with beefier input protection.
You can see my thread on it linked below, I managed to kill mine twice already this way
I do realize after you changed the input protection now it might fare better, but still an interesting test I'd say, as it is an easy mistake to do.
https://www.eevblog.com/forum/repair/uni-t-ut61e-diode-mode-repair/msg3622382/#msg3622382

[joeqsmith]

Hey Joe thanks for your videos! Just watched your new video about the UT61E+ as it was recommended to me (see, you do get recommended by Youtube!)
I'm just curious if you would be willing to make a very simple input test: give the meter 230VAC on the ohms range.
That easily killed the old model, even when it was the "GS" typerated version with beefier input protection.
You can see my thread on it linked below, I managed to kill mine twice already this way
I do realize after you changed the input protection now it might fare better, but still an interesting test I'd say, as it is an easy mistake to do.
https://www.eevblog.com/forum/repair/uni-t-ut61e-diode-mode-repair/msg3622382/#msg3622382

I read your previous posts.  One test I run is a taking a 220VAC, run it through bridge and apply that to the meter with it set to every mode.  Sadly, you will not find where I ran a UT61E beyond the one I modified for the purpose of surviving my tests.   The plan is to put the 61E+ through the normal tests but just not document any of the results due to it being slightly modified. 

I don't remember if Dave ran that test or not but it is something he has done in the past.  You could also check some of the unboxing videos.  Maybe someone has already done it with a virgin meter.     

****
Skimming Dave's review, he did not appear to run it this time for what ever reason.   

[Per Hansson]

Thanks for your reply Joe, maybe Dave will see this thread and run the test on his.
I think it would be valuable, especially if it fails such an easy test as easily as mine does 

[AndrewBCN]

@Joe
Hi Joe, and first, keep safe and more importantly a big THANK YOU for keeping this thread going and your fascinating testing & analysis of dozens of DMMs over the last 6 years and counting!
I have read of course the rules that you set in your first post in this thread and I hope I am not disrespecting them if I have a request for you: would it be possible for you to test this unassuming, low cost (around $15 including shipping) UNI-T UT125C DMM? What makes it different from others in the same price range is that it is apparently independently certified to conform to UL STD 61010-1, -2-030, -2-033 and -031 and rated CAT III 600V.
It's a tiny thing, comparable in size to the Brymen BM27 which you have tested, only much thicker and mechanically sturdier. Now whether it would pass your gas grill lighter test is an unknown.
I am attaching two pics of the UT125C, a top view and an internal view which shows the PTCs and MOVs and protection diodes in its input path. Curiously there is also a spark gap but the component above it is not present, so I wonder if the spark gap has any use in this case.

Thanks again for your fascinating work!

[joeqsmith]

@Joe
Hi Joe, and first, keep safe and more importantly a big THANK YOU for keeping this thread going and your fascinating testing & analysis of dozens of DMMs over the last 6 years and counting!
I have read of course the rules that you set in your first post in this thread and I hope I am not disrespecting them if I have a request for you: would it be possible for you to test this unassuming, low cost (around $15 including shipping) UNI-T UT125C DMM? What makes it different from others in the same price range is that it is apparently independently certified to conform to UL STD 61010-1, -2-030, -2-033 and -031 and rated CAT III 600V.
It's a tiny thing, comparable in size to the Brymen BM27 which you have tested, only much thicker and mechanically sturdier. Now whether it would pass your gas grill lighter test is an unknown.
I am attaching two pics of the UT125C, a top view and an internal view which shows the PTCs and MOVs and protection diodes in its input path. Curiously there is also a spark gap but the component above it is not present, so I wonder if the spark gap has any use in this case.

Thanks again for your fascinating work!

There are a few problems I see running this meter.  First, its a brand known to fail.  13 products so far and all have performed poorly.  You're not seriously expecting a different outcome are you?   

Another problem I see is how the meter shares the inputs with the current function.  The problem there is depending how the meter is designed, the fuse may blow after each transient.   For two functions, that's  20 transients for each level, or 20 fuses.    I have seen meters like this before and point them out but have not ran them for this reason. 

Then there's what you are calling a spark gap.  It sure does look like that's the intent with the plated edges.  I would hope that gap is not directly across the inputs. If it is and has a UL safety cert, it would just further erode my confidence in these large bodies. 

Have you tried to find pictures of the bottom side?  You may be able to trace out the front end.

I have a UT90A that has a few spark gaps but I doubt very much these were by design.  They breakdown at such a low voltage, I could never permanently damage it.  Not doubt there are some idiots who would say that meter is very robust.      After constructing the half cycle generator, I made another attempt to end it.     

[Fungus]

I am attaching two pics of the UT125C, a top view and an internal view which shows the PTCs and MOVs and protection diodes in its input path. Curiously there is also a spark gap but the component above it is not present, so I wonder if the spark gap has any use in this case.

The thing I'm not seeing in the Uni-T is the big surge-rated resistor.

ie. I'd like to see one of these in the front end:

[bdunham7]

I would hope that gap is not directly across the inputs. If it is and has a UL safety cert, it would just further erode my confidence in these large bodies.

That's a serious issue that some might be reluctant to discuss.  I recently had a UL-certified device (UV pool sanitizer) cause many thousands of dollars of damage and nearly burn my house down because it arced internally and started a fire.  It turns out the product had a known defect and was recalled, but I didn't know about that.  Now there are many ways in which a UL listing or label can be useless--it may be entirely faked, the product may not have been submitted for the testing one might expect, the exemplar submitted may not match the product as manufactured.....or other things even more disturbing.  In any case, my confidence in a testing lab label on its own, on a product from an unknown or not well reputed company, is not very high.

Not doubt there are some idiots who would say that meter is very robust.

Perhaps they haven't seen a Jacob's Ladder...

[bdunham7]

The thing I'm not seeing in the Uni-T is the big surge-rated resistor.

Well, there's the fuse!

Now you tell me how the meter can meet the requirement to "continue to be able to detect and display the presence of hazardous voltages" or however it is phrased, if the fuse is blown?  Or is there some additional stuff on the other side of the circuit board?

[Fungus]

Then there's what you are calling a spark gap.  It sure does look like that's the intent with the plated edges.  I would hope that gap is not directly across the inputs. If it is and has a UL safety cert, it would just further erode my confidence in these large bodies.

You mean this?



It sure looks like it's directly across the inputs, I think the metallic blob just above "F1" is where the black lead meets the PCB. Maybe AndrewBCN can confirm if it is or not.

Even if it is: The meter is only CAT III so there's supposed to be a circuit breaker between you and the big bad power cable in which case it could be "legal" to do that.

I'm not sure what the vertical white line between the two vias on side of that gap is. It looks like maybe a current shunt could be placed there in a different version of the meter. 

[rsjsouza]

Another problem I see is how the meter shares the inputs with the current function.  The problem there is depending how the meter is designed, the fuse may blow after each transient.   For two functions, that's  20 transients for each level, or 20 fuses.    I have seen meters like this before and point them out but have not ran them for this reason. 

IMO that is one of the worst features of any DMM. Sure, you can make the case that ultra-cheap meters cannot afford an extra input jack due to size/cost, but that is a terrible design decision for anything more serious that might be subjected to transients.

The thing I'm not seeing in the Uni-T is the big surge-rated resistor.

That tends to be replaced by R46, R47 and R48. 300kΩ each.

[AndrewBCN]

Have you tried to find pictures of the bottom side?  You may be able to trace out the front end.

Yes, there are high resolution pictures of the top and bottom sides of the UT125C PCB on HKJ's website.

Top side:

Bottom side:

[joeqsmith]

The input is common to the PTCs and fuse.  The fuse goes back to the spark gap and onto the common point.  If the gap breaks over, the fuse may blow depending what I am dumping into it.  I could pull the fuse and test the two sets of functions but is that even a valid  test.   Then again, it's a UNI-T and the ESD would most likely stop the testing before we need to concern ourselves with a fuse.   In the end, is it really even worth spending any time looking at?   Don't we know how it will end? 

[joeqsmith]

While the UT61E+ uses a couple of PTCs in series to maybe double the breakdown voltage, here you have a single and nothing else to limit the current or reduce the voltage (in a controlled manor).  The 5mm parts can't handle much and I have shown many times the end result.   The outside case comes apart as it arcs over.  Once they arc, the MOVs may take the brunt of it.   But they are a long way away from the input...  Bases on all the tests I have ran on these low end meters, this just looks bad.   

[AVGresponding]

If you think that Uni-T 135C is bad (and I agree with you), just be glad you haven't had the misfortune to encounter one of these turds:

https://www.amazon.co.uk/Kewtech-KT111-Automatic-Digital-Multimeter/dp/B01N1MPAHH


A colleague of mine who tests fire alarm systems and emergency lights in schools and local authority buildings was given one of these by his line manager. It would read 10VDC when measuring a 12V SLA battery, which while on charge should be around 13.5VDC. When he asked me to check it I was appalled at the gimcrack nature of the device from what is if not a premium manufacturer, at least a respected one.

Incidentally it was sent off for calibration, and apparently it was within spec...

[Fungus]

If you think that Uni-T 135C is bad (and I agree with you), just be glad you haven't had the misfortune to encounter one of these turds:

"The ultimate electrician's digital Multimeter!"



Does "CAT III 500V" even exist as a rating? 

[bdunham7]

Yes, there are high resolution pictures of the top and bottom sides of the UT125C PCB on HKJ's website.

Can you pop the fuse out and confirm which end the positive lead is connected to?

Edit: it appears from one of HKJ's other photos that it is connected to the top (near the PTCs) as one would hope.