Author Topic: Handheld meter robustness testing  (Read 1364968 times)

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Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4925 on: April 24, 2024, 06:54:34 pm »
Thanks.

Interesting, they went back to a single dimple contact rather than the double dimple.  Plating appears the same.  I've seen them change these contacts over and over again.  I wonder why they can't settle on a design.  I take it you don't have a set of calipers to measure the PCB thickness.   If you lift off the switch contact holder from the brass hex shaft, is there a shim under it? 

PCB has some changes.  New clamp design.  I wonder why they changed it and it it improved its electrical robustness.  With it being Dave's meter, I am surprised he doesn't show off the changes and explain the reasons for them.   Maybe he did and I wasn't paying attention.   

***
Just an FYI, I had bought two of these to review.  Showing the board of the unit that was damaged during the grill starter.  Notice the changes. 
« Last Edit: April 24, 2024, 06:58:33 pm by joeqsmith »
 

Offline ploxiln

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Re: Handheld meter robustness testing
« Reply #4926 on: April 24, 2024, 07:11:09 pm »
I do have a cheap digital caliper ... just not very experienced, and being a bit cautious/ginger - the reading depends a bit on how much pressure I apply to the jaws. It's probably actually 1.5 mm, that's what I get when applying more pressure.

I don't have a great setup for the close-ups, anyway, some more switch detail ...
 

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4927 on: April 24, 2024, 07:34:51 pm »
Measuring mine under the large HRC fuse where there is no copper I measure 1.40mm.  Measuring in that same are with copper on both sides, I measure 1.49mm.  The shim thickness on this meter measures 1.05mm.  Dave had said the shim was made to correct for the wrong thickness of the PCB.  I was expecting yours to measure over 2mm.   May have been a story? 

Shown is one of the double dimple wipers from my meter after the 50,000 (full rotation) life cycle test.

***
Looking at your PCB, the switch contacts appear identical to mine.  I know my meter when set to the LowZ mode does not have enough spacing to prevent it from flashing over at the levels I typically test at.  Looking at this meter, it doesn't appear that I tried that with the higher energy generator as the PCB doesn't appear damaged.
« Last Edit: April 24, 2024, 07:45:25 pm by joeqsmith »
 
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Offline armandine2

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Re: Handheld meter robustness testing
« Reply #4928 on: April 25, 2024, 06:55:12 pm »
I do have a cheap digital caliper ... just not very experienced, and being a bit cautious/ginger - the reading depends a bit on how much pressure I apply to the jaws. It's probably actually 1.5 mm, that's what I get when applying more pressure.

I don't have a great setup for the close-ups, anyway, some more switch detail ...

Verniers cheap or not can be awkward to get at the right angle, I find, best to use a micrometer.
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Offline Hydrawerk

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Amazing machines. https://www.youtube.com/user/denha (It is not me...)
 
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Offline Hydrawerk

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Re: Handheld meter robustness testing
« Reply #4930 on: May 11, 2024, 01:07:52 pm »
This has a different case!
Amazing machines. https://www.youtube.com/user/denha (It is not me...)
 

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4931 on: June 03, 2024, 12:23:20 pm »
Neon sign transformer vs DMM

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4932 on: December 15, 2024, 01:00:43 am »
After watching Dave's recent video on "How to Discharge Capacitors SAFELY using a Multimeter!",  and thinking about home appliance repairs using this technique.   I've constructed a microwave oven simulator.  Most microwaves appear to be around 1uF at 2kV. 

https://www.cde.com/resources/catalogs/940C.pdf

https://www.reddit.com/r/AskElectronics/comments/9h7g39/how_dangerous_are_microwave_capacitors/




Offline floobydust

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Re: Handheld meter robustness testing
« Reply #4933 on: December 15, 2024, 02:28:49 am »
I'd churned through the math for a cap discharger that could take on microwave oven caps.
I got around 4J not that much really (2.5kV and 1.3uF) and two of 1k8 50W in series for 3k6 and 0.7A pk 1.7kW for maybe 25msec which I think is OK for wirewounds.
You have to be careful of the voltage rating of the resistors. Arcol HS-25 and HS-50 seem pretty good. Would not use the junk Aliexpress power resistors, they have air gaps in the potting and likely would arc from resistor element to the housing.

Mr. Carlson's Lab made a cap discharger tool, I believe 4 of 1k 50W in series.
https://ab1dq.com/2019/01/01/mr-carlsons-lab-high-voltage-capacitor-discharge-tool/
 

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Re: Handheld meter robustness testing
« Reply #4934 on: December 15, 2024, 04:49:33 am »
After watching Dave's recent video on "How to Discharge Capacitors SAFELY using a Multimeter!",  and thinking about home appliance repairs using this technique.   I've constructed a microwave oven simulator.  Most microwaves appear to be around 1uF at 2kV. 

If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.
 

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4935 on: December 15, 2024, 05:01:03 am »
If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.

 :-DD :-DD    First, you know damn well I am indeed that dumb....   Let's see what happens.

Offline floobydust

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Re: Handheld meter robustness testing
« Reply #4936 on: December 15, 2024, 05:14:40 am »
Are we taking bets?  :popcorn:
 
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Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4937 on: December 15, 2024, 05:19:24 am »
I'd churned through the math for a cap discharger that could take on microwave oven caps.
I got around 4J not that much really (2.5kV and 1.3uF) and two of 1k8 50W in series for 3k6 and 0.7A pk 1.7kW for maybe 25msec which I think is OK for wirewounds.
You have to be careful of the voltage rating of the resistors. Arcol HS-25 and HS-50 seem pretty good. Would not use the junk Aliexpress power resistors, they have air gaps in the potting and likely would arc from resistor element to the housing.

Mr. Carlson's Lab made a cap discharger tool, I believe 4 of 1k 50W in series.
https://ab1dq.com/2019/01/01/mr-carlsons-lab-high-voltage-capacitor-discharge-tool/

1 joule  is enough to damage some meters.   My small transient generator can provide 15J which is normally lost to heat internally, in the output wave shaping circuit.  It puts out an unloaded 100us FWHH exponentially decaying waveform.   The microwave oven, there is no wave shaping.  I had some idiot posting how I was connecting these meters directly to capacitors when testing them.  In this case, that is exactly what we would be doing.

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4938 on: December 15, 2024, 05:32:40 am »
Are we taking bets?  :popcorn:

I still have the remaining low cost meters that I had planned to test.   These were all viewer requests and are still new in the box.   I doubt very much that these would survive but we can certainly have a look...

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4939 on: December 15, 2024, 09:07:09 pm »
Initial checkout



Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4940 on: December 23, 2024, 10:22:56 pm »
Using the meters that survived my low voltage transient tests to discharge my simulated microwave oven capacitor.   



Offline janiorib

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Re: Handheld meter robustness testing
« Reply #4941 on: December 24, 2024, 03:19:58 am »
If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.

 :-DD :-DD    First, you know damn well I am indeed that dumb....   Let's see what happens.
My screwdriver is my friend :-/O
 

Offline Fungus

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Re: Handheld meter robustness testing
« Reply #4942 on: December 24, 2024, 04:39:55 am »
My screwdriver is my friend :-/O

I was always told "you're always safe if you're not the easiest path to ground".
 

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4943 on: December 24, 2024, 07:44:48 pm »
If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.

 :-DD :-DD    First, you know damn well I am indeed that dumb....   Let's see what happens.
My screwdriver is my friend :-/O

Directly shorting with a screwdriver may exceed the capacitor's peak current and dv/dt ratings.     

Offline bdunham7

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Re: Handheld meter robustness testing
« Reply #4944 on: December 24, 2024, 09:42:59 pm »
If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.

Actually a I think a properly implemented Lo-Z range on a CATIII/1kV or higher meter probably ought not have any issues with a 2kV 1µF capacitor.  That's only 2J total energy.  As joeqsmith has figured out, almost any meter that survives even moderate transient tests should be fine. 

But what about bigger capacitors?  >:D

I was looking at a Fluke schematic for the 189-II/289 and I think it could survive 2kV for quite a while on the Lo-Z range because the two 910V MOVs in series are not exposed to the full voltage.  The Lo-Z uses two YS4020 (the Godzilla of PTCs) in series plus the 1k surge resistor.  When you put 2kV across the input the voltage is divided between the three but then the PTCs quickly heat up and the voltage is then 1kV across each of them.  The only thing that looks like it would be stressed at all is Z1, the planar ceramic 1M input resistor with a 1W rating indicated on the schematic.  At 2kV, assuming that Z1 would be dropping the vast majority of the voltage,  you'd have 2mA and 4W.  So I think the meter could take 2kV for as long as Z1 can dissipate 4W.  If you look at the datasheet for the YS4020, you'll see that it trips in about 50ms at 1A.  At 2kV the initial current will be less than that since the total resistance is 3.2k.  As a bad approximation you could say that the two PTCs could bleed off roughly 50mC before tripping and if that reduces the capacitor voltage to 1kV or less, then the rest can bleed off over time without harming anything.  This implies a 100µF capacitor.  I recommend not using a screwdriver for that!

Note:  I drew in RT2 where I think it goes on an actual 289.  The schematic is from the 189-II/AN manual.



https://www.mouser.com/datasheet/2/18/amphenoladvancedsensors_YS4020-1157120.pdf

« Last Edit: December 24, 2024, 09:51:23 pm by bdunham7 »
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4945 on: December 25, 2024, 12:34:43 am »
But what about bigger capacitors?  >:D

And higher voltages?  :scared: 

One thing to consider is that beyond the capacitance and voltage, when I transient test the meters with the low voltage generator,  the edge rates are very slow.  I suspect the grill starter damages so many UNI-T meters in part because of the edge rate.  To get the UT61E to survive, I gave up some of the meter's AC bandwidth.   When you jam a meter across a capacitor like this, you may create a fairly fast edge.   

Quote
As joeqsmith has figured out, almost any meter that survives even moderate transient tests should be fine. 

Of the meters that survived the 5.9kV 100us FWHH and 2ohm source, the only meters I did not check against the capacitor bank were the Fluke 107, Brymen BM786, BM839,  Yokogowa TY720 and UNI-T UT15C.   

The UNI-T UT15C was damaged beyond repair and recycled.   

The BM786s are early prototypes.  I had done a fair amount of rework on them.  I am very confident they would survive as they use the same front end as the 789.   

While the Yokogowa had been damaged,  the front end was fine (nightmare to repair).   This meter had no problem discharging the 1uF 2kV capacitor bank.

The Fluke 107 was damaged at 15kV.  It damaged one of the high speed clamps and looked like it had caused some damage to the PTC.  I did repair this meter (eventually replacing the PTC).  It had no problem discharging the capacitor bank.

So,  I'm going to go out on a limb and stick with my original statement that if a meter makes it though all of my testing including the low voltage transient generator,  it will survive this new test.

I was a bit surprised that the Brymen BM27s (rebranded AMPROBE PM55A) has held up so well to everything I have put that pocket meter through.  Remember, member True had four of these that all failed.  Mine arced over at 8kV but no damage was done to the electronics.  Impressive for a little pocket meter.
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/msg1787117/#msg1787117

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4946 on: December 25, 2024, 12:52:41 am »
Just to add, the capacitor bank in the low voltage generator is 0.666uF (also film).   I charge it to about 5.9kV max.  So you have about 12 Joules available, IF the meter breaks down.  Normally all that energy is given off as heat in the wave shaping circuit.   Then again, most meters never make it that far, so we are talking about much lower energy levels.

Offline floobydust

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Re: Handheld meter robustness testing
« Reply #4947 on: December 25, 2024, 02:08:26 am »
I'd include a check if the PTC resistance shifted before/after. To know if they are getting damaged from the hit. The tiny chinese ones prefer to explode and tell the world 'it was too much' lol. I haven't found a source for them.
I've killed a few multimeters with 0.01uF caps charged around 10-15kV, I thought they were discharged... this seems to arc inside on the PCB and the weirdest things get damaged.
 

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Re: Handheld meter robustness testing
« Reply #4948 on: December 26, 2024, 03:49:34 am »
If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.

Actually a I think a properly implemented Lo-Z range on a CATIII/1kV or higher meter probably ought not have any issues with a 2kV 1µF capacitor.  That's only 2J total energy.  As joeqsmith has figured out, almost any meter that survives even moderate transient tests should be fine. 

It's not just the energy at play, the higher voltage can cause arc over on switch contacts or other areas of the PCB. That's why I wouldn't recommend going over the 1000V/600V max meter rating.
Sure, many will survive of course, but if I copped some flack for daring to suggest that at a pinch you can use the ohms range of a meter to discharge a cap at 400V, then suggesting doing the same at 1000V more than the max meter voltage rating is worthy of a slap with a wet fish, right?  ;D
 

Offline joeqsmithTopic starter

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Re: Handheld meter robustness testing
« Reply #4949 on: December 26, 2024, 02:12:16 pm »
If anyone is dumb enough to discharge a 2kV 1uF capacitor using the ohms range of their meter, or even the Low Z range, then they deserve to get a blown meter.

Actually a I think a properly implemented Lo-Z range on a CATIII/1kV or higher meter probably ought not have any issues with a 2kV 1µF capacitor.  That's only 2J total energy.  As joeqsmith has figured out, almost any meter that survives even moderate transient tests should be fine. 

It's not just the energy at play, the higher voltage can cause arc over on switch contacts or other areas of the PCB. That's why I wouldn't recommend going over the 1000V/600V max meter rating.

Most of the surviving meters I have looked at I suspect would survive the IEC surge tests.   If the PCB were to breakdown, I would take that as a failure.  Not to  :horse: but again, this idea of the meter surviving, versus other views where the meter can be damaged and as long as it presents no harm to the user is fine comes from my discussions with Fluke.   I don't see a lot of risk testing the higher end meters with a 1uF 2kV cap as I have demonstrated.  But as I stated in both videos, I wouldn't recommend anyone do this.   

Sure, many will survive of course, but if I copped some flack for daring to suggest that at a pinch you can use the ohms range of a meter to discharge a cap at 400V, then suggesting doing the same at 1000V more than the max meter voltage rating is worthy of a slap with a wet fish, right?  ;D

My personal feedback about your video was that you never constrained the problem.  While you show a 400V TV as an example, you seemed to speak in general terms.  Beginners may see this as suggesting this practice is fine for any home repairs.   Suggesting if they are that dumb and blow up their meter, seemed a bit lazy of an out.   

Slapping with wet fish are fine.  I catch a lot of flack for taking what many consider are perfectly good meters and damaging them beyond repair.  I would hope a few people have learned a little about what makes for a robust meter and what brands they should consider if that is important to them. 
« Last Edit: December 26, 2024, 05:25:39 pm by joeqsmith »
 


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