Poll

Are you interested in seeing more handheld meters tested?

This testing is pointless! Please STOP damaging these meters!
3 (6.4%)
 Yes, I would like to more meters tested.
44 (93.6%)

Total Members Voted: 47

Author Topic: Handheld meter electrical robustness testing.  (Read 597948 times)

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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3675 on: December 31, 2019, 06:03:17 pm »
Let's not confuse "electrical robustness" with safety. I have yet to see a failure mode on these meters that will hurt the user.

Giving misleading readings is the only safety issue I've seen so far - how difficult would it be to design a meter with a universal HV warning? (AC, AC, DC+AC) Some indicator telling the user if it's safe or not even if the meter can't correctly display the reading.
Good point.

I would hope that after all these years that you would never expect my transient tests to ever cause a meter to fail in such a way that it would hurt a user.  I would also hope by now no one would think this was ever a goal.   

I recently repaired a meter that is UL marked.  You will not find a single MOV in the meter.  It was easily damaged with the rectified 220V waveform.   Yet it has a UL mark.  The meter may very well be safe but it's certainly not what I would consider electrically robust.   

Because my hobbies don't involve any high voltage, high energy sources but I do from time to time work with sources of high voltage and low energy,  I am more interested in the EMC rather than the safety standards.  This TPI with it's very weak front end would not survive my normal use.

*****
Just to note, this company clearly is not concerned if the meter survives.  This is a different stance than what Fluke has stated and demonstrated they take  by having their meters survive.   I have often stated that for safety that I would guess that it is more about the mechanics of the meter and the case of the TPI branded SUMMIT meter appears to be one of the more solid ones I have looked at.

The fact that UL would certify the meter leads me to believe that it is not required that a meter survive.   Seeing the Gossen with it's latching relays that can easily change state and cause the meter to not display a hazardous voltage and the 121GW where it seems the firmware can also cause the meter not to display a hazardous voltage,  maybe this is also not a requirement as both of these meters are also certified.   
« Last Edit: December 31, 2019, 06:11:45 pm by joeqsmith »
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Offline Cliff Matthews

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Re: Handheld meter electrical robustness testing.
« Reply #3676 on: January 01, 2020, 04:57:32 am »
With 2 minutes left in the decade.. Happy New Year Joe! and everyone else!
 
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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3677 on: January 06, 2020, 12:51:26 pm »
Happy New Year!   Hoping Australia's fires are under control soon.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Online rsjsouza

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Re: Handheld meter electrical robustness testing.
« Reply #3678 on: January 08, 2020, 08:12:27 pm »
Maybe it has already been discussed before in this thread, but I am wondering why there are no cheap Fluke clones with good electrical robustness. Most of the techniques are in plain sight. Just copy the board with big clearances, large fuses and MOVs. It may cost a few more dollars for parts, but the margin for "professional" multimeters is much larger.

Because:
a) There's no need, sales of unsafe meters are doing just fine.
b) Certification costs money and you're not going to sell many meters without certification marks.
c) Once a meter is certified you're not allowed to change a single component supplier or any part of your production line without going through re-certification.

I suspect (c) is a real problem for Chinese meter makers.
Fungus, "c" is only valid if you apply for their "listed" program (UL, TÜV, Intertek, etc.). The listing requires annual inspection to the manufacturing plant audits and process reviews. Most Chinese low cost meters do not go through that, but that does not solely explain lack of safety: several japanese brands (Samwa, Hioki) have excellent quality and reputation and also do not have markings.

I have been involved with projects where "c" was required but wouldn't think this was required for a DMM.  For example, say your JEDEC 4007 from company X is no longer offered, I doubt you would be required to stop production until you get your new diode certified.   Have anything to back up this statement? 
I don't have anything to back your statement about "production stop due to the lack of certification". This is an exception that would probably be negotiated between the cert agency and the manufacturer. 

My experience with the marking process and audits is related to a few products (not DMMs) we were releasing in the past few years. We didn't fall for the siren songs from the cert agency (ies) as the markings didn't add value to our products, therefore I don't know how the exception would be dealt. 

Happy new year, BTW!
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3679 on: January 09, 2020, 03:09:29 am »
Maybe it has already been discussed before in this thread, but I am wondering why there are no cheap Fluke clones with good electrical robustness. Most of the techniques are in plain sight. Just copy the board with big clearances, large fuses and MOVs. It may cost a few more dollars for parts, but the margin for "professional" multimeters is much larger.

Because:
a) There's no need, sales of unsafe meters are doing just fine.
b) Certification costs money and you're not going to sell many meters without certification marks.
c) Once a meter is certified you're not allowed to change a single component supplier or any part of your production line without going through re-certification.

I suspect (c) is a real problem for Chinese meter makers.
Fungus, "c" is only valid if you apply for their "listed" program (UL, TÜV, Intertek, etc.). The listing requires annual inspection to the manufacturing plant audits and process reviews. Most Chinese low cost meters do not go through that, but that does not solely explain lack of safety: several japanese brands (Samwa, Hioki) have excellent quality and reputation and also do not have markings.

I have been involved with projects where "c" was required but wouldn't think this was required for a DMM.  For example, say your JEDEC 4007 from company X is no longer offered, I doubt you would be required to stop production until you get your new diode certified.   Have anything to back up this statement? 
I don't have anything to back your statement about "production stop due to the lack of certification". This is an exception that would probably be negotiated between the cert agency and the manufacturer. 

My experience with the marking process and audits is related to a few products (not DMMs) we were releasing in the past few years. We didn't fall for the siren songs from the cert agency (ies) as the markings didn't add value to our products, therefore I don't know how the exception would be dealt. 

Happy new year, BTW!

I'm a little lost.  Fungus made the statement in regards to meters which I don't believe they would be held to C.  Are you asking under what circumstances we were or just merely pointing out that I did not provide any details?   

I have been involved with getting products certified for safety by UL before but nothing to do with meters.  There was nothing that would have prevented us from changing vendors during production.   

Cases where this may come up is with something a bit more critical.  Something using Rad qualified parts for example.    A story comes to mind from many years ago that made the news.   There was a company making some of the electronics for one of our missiles.  The company wasn't able to purchase some of the MilStd IC's and so they swapped in some commercial parts so they could continue production.  The customer requires the baby papers and so once they received the actual parts, they supplied the accompanied paper work.   They then stored on-site the actual parts.   Someone in the company knew what was happening and what the end product was and contacted the customer.    I want to say that was in the 80's.

****
It seems I saw it on 60 minutes.  Doing a search, I came up with the attached from "Proposed Legislation Regarding Whistleblower Protection: H.R. 2579 ..., Volume 4":   
« Last Edit: January 09, 2020, 04:24:33 am by joeqsmith »
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Online rsjsouza

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Re: Handheld meter electrical robustness testing.
« Reply #3680 on: January 10, 2020, 06:51:46 pm »
I'm a little lost.  Fungus made the statement in regards to meters which I don't believe they would be held to C.  Are you asking under what circumstances we were or just merely pointing out that I did not provide any details? 
I guess the lines were crossed somehow. I was a bit confused and understood that you were asking me to provide documental proof about an assertive I haven't made. Nevermind. It is still early in the year... :P

It seems I saw it on 60 minutes.  Doing a search, I came up with the attached from "Proposed Legislation Regarding Whistleblower Protection: H.R. 2579 ..., Volume 4":
Quite interesting story. The snippet of document you sent has a striking resemblance with the whole 737MAX brouhaha: "Today consultants and private contractors not only build projects, they regulate them."
Vbe - vídeo blog eletrônico http://videos.vbeletronico.com

Oh, the "whys" of the datasheets... The information is there not to be an axiomatic truth, but instead each speck of data must be slowly inhaled while carefully performing a deep search inside oneself to find the true metaphysical sense...
 

Online Fungus

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Re: Handheld meter electrical robustness testing.
« Reply #3681 on: January 10, 2020, 11:59:29 pm »
I'm a little lost.  Fungus made the statement in regards to meters which I don't believe they would be held to C.  Are you asking under what circumstances we were or just merely pointing out that I did not provide any details? 
I guess the lines were crossed somehow. I was a bit confused and understood that you were asking me to provide documental proof about an assertive I haven't made. Nevermind. It is still early in the year... :P

It was me who made it and it was a bit hyperbolic. Joe won't let that pass, not in this thread. :P

You can probably buy a part from a different supplier without losing your certification. Can you use a different (but similar) part? I'm not sure.
« Last Edit: January 11, 2020, 12:02:40 am by Fungus »
 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3682 on: January 11, 2020, 12:41:03 am »
The internet is filled with embellishment.  I see no reason to muddy the waters in this thread.  I guess I could try and pump up the performance of the 121GW saying it didn't blow up at 14KV.  True statement, but not helpful in any way.

Quite interesting story. The snippet of document you sent has a striking resemblance with the whole 737MAX brouhaha: "Today consultants and private contractors not only build projects, they regulate them."


Back in 2015 when the internet was in a rage about Volkswagen and their practices, I was thinking what's so news worthy about this.  Yes, history does seem to repeat often...
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 

Offline dcac

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Re: Handheld meter electrical robustness testing.
« Reply #3683 on: January 21, 2020, 09:24:15 pm »
I was amazed how fast the 121 seem to react to temperature changes. So here I have taken the green mV trace, flipped it vertically and overlayed on the two temperature traces where red being 121 internal temp and white the chamber temp.
....
Edit: correction! those two screenshots I've merged perhaps wasn't from the same sweep and therefor not in sync to begin with.




Left scale is voltage, right temperature.   White is chamber temp, Red 121's ambient, Green reported voltage.  Samples are roughly at 2Hz and lag is about 170 seconds.  Of course, the time to settle is actually well over an hour in this case..

Thanks for the extra detailed temp sweep.

After some testing it seems much of the drift could be caused by PTC3 and/or PTC4.

On my 121gw especially PTC3 is super sensitive to just lightly touching it with my finger, perhaps raising its temp no more than 3-4C. A 1.000mV reading drops almost directly 50-60uV and when I remove my finger it slowly recovers to 1mV. Touching PTC4 has the same affect but not at all as dramatically and this in fact instead seems to increase the voltage 30uV or so.

Obviously PTC’s are temperature dependent resistance devices but I really could not make any sense of how they manage to affect the reading so much given they only changes about 75 ohms with the same influence from my finger. But one thing that could affect the reading is that these type PTC’s seems to act as true thermocouples too. Measuring the voltage over them with another meter and 121gw turned of, the PTC’s easily generate 50-60uV - again from just slightly heating them with my finger. And this voltage then sits in series with whatever you’re tying to measure with the 121gw.

But it's still unclear how PTC3 can affect mV measurement at all, even if it is generating emf voltages, the main path for mV is through PTC4 and then the triple 300k (R18-20) resistors into PB0 at hy3131 where it is then measured by the ADC. But the PTC3 path ends up in RLD on hy3131 and here it's unclear how this pin is involved in mV mode, according to available documentation, it only seems to connect to the comparator mux in the 3131, the way it's configured by UEi's firmware.

But anyway, if it is the PTC’s causing the drift, at least it can explain why the 121gw reacts so quickly to ambient temperature changes as the PTC's sits very close to the meter casing, and very close to the input jack where the temperature change probably can affect them quite easily.

« Last Edit: January 22, 2020, 12:50:03 am by dcac »
 

Offline EEVblog

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Re: Handheld meter electrical robustness testing.
« Reply #3684 on: February 05, 2020, 06:02:19 am »
 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3685 on: February 05, 2020, 06:09:11 pm »
The latest spreadsheet is now available on GoogleDocs here:
https://docs.google.com/spreadsheets/d/1cXzYpIoyVm9QJUju4KXqM22CEQZP3_xwWvDyeVwxTy4/edit?usp=sharing


This spreadsheet seems out of date?

It's on-line now if you would like a copy.     
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 


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