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 555025 times)

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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3450 on: November 10, 2019, 08:08:49 pm »
Part 2, looking at the differences between the prototype and production hardware.   I seem to have missed FB4.

https://www.youtube.com/watch?v=Ayd9Lz9xZXQ&feature=youtu.be
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Offline tautech

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Re: Handheld meter electrical robustness testing.
« Reply #3451 on: November 10, 2019, 08:48:09 pm »
Riveting watching as always Joe.  :clap:
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Offline malagas_on_fire

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Re: Handheld meter electrical robustness testing.
« Reply #3452 on: November 10, 2019, 09:44:45 pm »
Good to watch the collected differences. That SD Holder card really needed some reinforcement, a little blob of glue as said in the video.

What about the glitch on the rotary switch? Gone?
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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3453 on: November 11, 2019, 01:10:41 am »
Fuck me! 

Looking at the changes on the Rev V.02 units, its obvious they have upped their game.   So I just spent $600+ on old stock that I will pretty much bet is not going to survive to the same levels this new meter will.   Look at the size of those transistors compared with the parts in mine.   

I opened up the second meter just to make sure as it was a later SN.  No luck,  the two meters that were shipped are both the old design.   

So I've burned down a fair bit of time, plus the cash.   I am going to have to give it some thought on how to proceed.   
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Offline EEVblog

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Re: Handheld meter electrical robustness testing.
« Reply #3454 on: November 11, 2019, 08:00:56 am »
The latest is V.02.1910 which has the transistors integrated. Although they are not in the wild yet.
 

Offline kf4hzu

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Re: Handheld meter electrical robustness testing.
« Reply #3455 on: November 11, 2019, 10:28:47 am »
Do these changes only impact input protection?
 

Offline exe

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Re: Handheld meter electrical robustness testing.
« Reply #3456 on: November 11, 2019, 10:56:39 am »
It would be cool to know the differences between revisions and what they mean to user. So, I really appreciate what Joe does.

I wonder if it's possible to improve some parameters (at least in some ranges) by fine-tuning components. May be it's time for me to remove the dust from my DMM and read the datasheet...

PS Afaik Dave said "we are not going to spin a different pcb revision, we'll fix problems in software". Turned out either my memory is bad, or they changed their mind.
 

Offline malagas_on_fire

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Re: Handheld meter electrical robustness testing.
« Reply #3457 on: November 11, 2019, 10:57:43 am »
Do these changes only impact input protection?

Hope in the positive way to protect more that input.
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Online Dr. Frank

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Re: Handheld meter electrical robustness testing.
« Reply #3458 on: November 11, 2019, 11:57:50 am »
Fuck me! 

Looking at the changes on the Rev V.02 units, its obvious they have upped their game.   So I just spent $600+ on old stock that I will pretty much bet is not going to survive to the same levels this new meter will.   Look at the size of those transistors compared with the parts in mine.   

I opened up the second meter just to make sure as it was a later SN.  No luck,  the two meters that were shipped are both the old design.   

So I've burned down a fair bit of time, plus the cash.   I am going to have to give it some thought on how to proceed.


Hey Joe!

This transistor clamping circuit on the additional PCB is obviously the circuit, which Dave had explained in his videos #1157 and 1158.

I criticized though, that this does not work at all to protect the pin15 of MUX 4053, U9 for the Ohm circuit.

https://www.eevblog.com/forum/blog/eevblog-1157-transistor-zener-clamp-circuit/msg2043757/#msg2043757

The circuit is able to protect symmetrical inputs, at +/- 6V clamp voltage, or +/- 20..25V, if special npn types are used.

This use case is asymmetric, as it has to be protected at -0.5V / + VDD ~ 4...16V.

I've never got a response from Dave, but obviously this not working circuit was implemented in certain HW versions of the 121GW.
It would be interesting, if in the most recent version, the BC diode of both transistors were properly used to protect the Ohm circuit, by using them as direct replacement of the original 1N4007.

Another remark: the use of the 1N4007, as well as a TVS at that point both affect negatively the calibration of the 5M and 50M Ohm ranges by their leakage currents. Only without them, these ranges may work linearly.

Frank
 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3459 on: November 11, 2019, 01:08:16 pm »
...
This transistor clamping circuit on the additional PCB is obviously the circuit, which Dave had explained in his videos #1157 and 1158.
...
Another remark: the use of the 1N4007, as well as a TVS at that point both affect negatively the calibration of the 5M and 50M Ohm ranges by their leakage currents. Only without them, these ranges may work linearly.

Frank,  1158 shows the mezzanine boards that are used on the ones I just purchased.   These are not the same parts that are used on the current revision, nor is it the same PCB. 

I remember your posts about the leakage.  I've never ran any experiments as I didn't think it would be helpful to run on the prototype with the other changes I had made but would not be at all surprised.   

I can't comment on how any of these changes effect the electrical robustness of the meter.  If I wanted to analyze the most recent revision, I would need a current schematic for starts.  Still, like the UT181A, the has a decent front end design, the layout needs some help.  That's why I run the tests. 

PS Afaik Dave said "we are not going to spin a different pcb revision, we'll fix problems in software". Turned out either my memory is bad, or they changed their mind.

I just paid for two brand new meters and received the floor sweepings that are now apparently 2 PCB revisions old.   I wasn't told anything about them being old stock when I made the purchase or I wouldn't have placed the order.   I got fucked once.  It won't happen again. 

I seem to remember Dave posting something to that effect.  Searching, here is one about the the switch.  The brand new, out of the box meter certainly had some intermittent problem. 
https://www.eevblog.com/forum/testgear/new-eevblog-branded-multimeter-coming/msg1405035/#msg1405035

I wasn't able to find those posts about the revision and firmware.     

As far as how to proceed.  We have two old meters that do not represent the current production.   Sure I can test them but like the prototype, if they do poorly, the response will be we addressed that in the new revision.   

I can't see wasting too much time on the details.  For example, Frank mentions the non-linearity.  The new meter will behave differently.

If the new design addresses the shim, cycling the switch may not prove useful.   Then again, I am up to seeing how it holds up without spit shinning the contacts.  It could prove entertaining but keep in mind that the fall back is always going to be, we addressed that in the next revision. 

I still plan to keep the one meter as a virgin, if anything just for a reminder of business practices.   As for the second meter, feel free to comment on what you would like to see done with it.   I'm not at all apposed to just saying fuck all and run the transient tests to failure and cycling the switch just for the entertainment.   
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Online gnavigator1007

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Re: Handheld meter electrical robustness testing.
« Reply #3460 on: November 11, 2019, 01:42:30 pm »
While I'd be interested in seeing every single version tested and compared, it doesn't really matter that much and is obviously impractical for a hobbyist to do so. Who knows how many more board revisions there will be in the future. In my mind, it's still the current version if that is what is being sold.
 

Offline dcac

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Re: Handheld meter electrical robustness testing.
« Reply #3461 on: November 11, 2019, 03:03:04 pm »
The latest is V.02.1910 which has the transistors integrated. Although they are not in the wild yet.

Will this PCB have the 'correct' thickness so no shim is needed?
 

Offline dcac

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Re: Handheld meter electrical robustness testing.
« Reply #3462 on: November 11, 2019, 03:12:53 pm »
Fuck me! 

Looking at the changes on the Rev V.02 units, its obvious they have upped their game.   So I just spent $600+ on old stock that I will pretty much bet is not going to survive to the same levels this new meter will.   Look at the size of those transistors compared with the parts in mine.   

I opened up the second meter just to make sure as it was a later SN.  No luck,  the two meters that were shipped are both the old design.   

So I've burned down a fair bit of time, plus the cash.   I am going to have to give it some thought on how to proceed.


Hey Joe!

This transistor clamping circuit on the additional PCB is obviously the circuit, which Dave had explained in his videos #1157 and 1158.

I criticized though, that this does not work at all to protect the pin15 of MUX 4053, U9 for the Ohm circuit.

https://www.eevblog.com/forum/blog/eevblog-1157-transistor-zener-clamp-circuit/msg2043757/#msg2043757

The circuit is able to protect symmetrical inputs, at +/- 6V clamp voltage, or +/- 20..25V, if special npn types are used.

This use case is asymmetric, as it has to be protected at -0.5V / + VDD ~ 4...16V.

I've never got a response from Dave, but obviously this not working circuit was implemented in certain HW versions of the 121GW.
It would be interesting, if in the most recent version, the BC diode of both transistors were properly used to protect the Ohm circuit, by using them as direct replacement of the original 1N4007.

Another remark: the use of the 1N4007, as well as a TVS at that point both affect negatively the calibration of the 5M and 50M Ohm ranges by their leakage currents. Only without them, these ranges may work linearly.

Frank

From what I can tell from the pictures they now seem to be using two STN83003

https://www.st.com/resource/en/datasheet/stn83003.pdf

has a Emitter-base breakdown voltage 14V to 18V.

 

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Re: Handheld meter electrical robustness testing.
« Reply #3463 on: November 11, 2019, 03:15:50 pm »
I just paid for two brand new meters and received the floor sweepings that are now apparently 2 PCB revisions old.   I wasn't told anything about them being old stock when I made the purchase or I wouldn't have placed the order.   I got fucked once.  It won't happen again. 

I am sorry to hear you got caught on the crossfire of revisions. I was looking forward for that series but, yes, I agree with you that your regular tests will not be greatly useful at this point in time. Perhaps get ahold of a modern schematics and try to implement in the new meter, à la UT61E improved protection exercise?

If only the revisions had an externally visible marker... Instead, cue the serial number merry-go-round. I wonder if UEI was avoiding an Osborne effect? If so, the cat is out of the hat. (but I confess I wasn't following the evolution that close anyways to know if this is old news).

Although any manufacturer states that "the products are subject to changes without prior notice", this reeks of a Uni-T UT61E stunt.
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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3464 on: November 11, 2019, 06:16:57 pm »
While I'd be interested in seeing every single version tested and compared, it doesn't really matter that much and is obviously impractical for a hobbyist to do so. Who knows how many more board revisions there will be in the future. In my mind, it's still the current version if that is what is being sold.

It appears they have been selling the newer revision for at least a few months but Dave is holding onto old stock.   You would think UEI would want that old stock replaced. 

From my testing with the prototype, besides the mechanical problems, this is the weakest link.   As I mentioned in that last video, I wouldn't hang my hat on the fact that the prototype 121GW withstood levels beyond what an 87V that obviously had a problem. 

Of course Dave/UEI and the internet masses may suggest these changes make no difference but people like me will ask why they continue to focus on that section of circuitry.   


I just paid for two brand new meters and received the floor sweepings that are now apparently 2 PCB revisions old.   I wasn't told anything about them being old stock when I made the purchase or I wouldn't have placed the order.   I got fucked once.  It won't happen again. 

I am sorry to hear you got caught on the crossfire of revisions. I was looking forward for that series but, yes, I agree with you that your regular tests will not be greatly useful at this point in time. Perhaps get ahold of a modern schematics and try to implement in the new meter, à la UT61E improved protection exercise?

If only the revisions had an externally visible marker... Instead, cue the serial number merry-go-round. I wonder if UEI was avoiding an Osborne effect? If so, the cat is out of the hat. (but I confess I wasn't following the evolution that close anyways to know if this is old news).

Although any manufacturer states that "the products are subject to changes without prior notice", this reeks of a Uni-T UT61E stunt.

I have no doubt that I could modify the production meter to survive but I think that takes us even further from meaningful data.   The best thing would be to get an actual meter.   I can't see this happening.  It seems we have a jumbled up grab bag of meters.  Like a child, blindly reaching into a grab bag of candy,  you pull something out.  It's not such a great business practice.   
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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3465 on: November 15, 2019, 01:13:22 am »
A few updates.   First, it appears that the new hardware does not require the shim.   I've asked the person posting if they could measure the PCB thickness and will post any updates as they become available. 

Dave did offer to refund the cost of the meters, including shipping.  There was no discussion about replacing them with the latest hardware.   I declined the offer and plan to move forward using the old revision.   There are a couple of reasons for this.  First, I have a fair amount of time already invested in the old hardware.  I also suspect that the vast majority of owners don't have the latest revision.   It sounds like many of the meters sold were even older hardware.    These two meters may be a better representation of what the viewers own.   

As I have stated, if any problems are uncovered during these tests I suspect the fallback plan will be to claim it was addressed on the next revision.  When I looked at the prototype that Dave supplied, it caused a fair amount of confusion with viewers.   I expect nothing less when running these meters.   While the whole revision problem could have been avoided, it isn't really my concern this time around.   

For those of you who have offered to help cover the costs, I just wanted to say again that I appreciate the gesture. 


Frank,
About your comment,  "I criticized though, that this does not work at all to protect the pin15 of MUX 4053, U9 for the Ohm circuit."   I felt you (and possibly others) may have been a little confused.   I doubt I will make any changes to the hardware this time around.  With the prototype, I had added two clamps in an attempt to protect the mux.  If you watched the videos, may have noticed the TVS located across the supply of the mux (located on top of D7&D8).     There was a second clamp that was located upstream from the resistor R82 but after the selector switch on node R_RLD.   This first clamp acts like every other higher end meter I have looked at.  It can withstand enough energy to overcome the PTCs thermal time constant.   The PTC (PTC3) along with the surge resistor (R16) limit the current through the first stage clamp.   The small resistor (R82) further limits the current.     Again, the schematics are not up to date and I really didn't dig into how these meters are designed. 

None of this is anything new as I went over it back in 2017 when I made the first series of videos for the prototype.     

I suspect that the first stage clamp was enough to protect the mux but I never tested it.  At the time my goal wasn't to optimize a production solution.  That's UEI's job and that's assuming that they even wanted to try and improve it.   Anyway, my point was that the meter may very well survive (my tests) without D7 & D8 present. 

Hope that helps. 
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Online Dr. Frank

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Re: Handheld meter electrical robustness testing.
« Reply #3466 on: November 15, 2019, 07:58:36 am »
Hello Joe,


Frank,
About your comment,  "I criticized though, that this does not work at all to protect the pin15 of MUX 4053, U9 for the Ohm circuit."   I felt you (and possibly others) may have been a little confused. 

I don't think at all, that I'm confused.
This critic is related to Daves videos #1157, especially 1158, not to any of your videos.
There, Dave clearly shows this dual transistor clamp to replace the former 1N4007, which will not work to protect the MUX.
You might investigate on that issue, simply by applying an additional voltage across the resistor under test, first higher than the supply voltage of the MUX, 2nd a negative one, and then simply checking that the voltage on this MUX pin really exceeds the Absolute Max. Ratings.

I doubt I will make any changes to the hardware this time around.  With the prototype, I had added two clamps in an attempt to protect the mux.  If you watched the videos, may have noticed the TVS located across the supply of the mux (located on top of D7&D8).     There was a second clamp that was located upstream from the resistor R82 but after the selector switch on node R_RLD.   This first clamp acts like every other higher end meter I have looked at.  It can withstand enough energy to overcome the PTCs thermal time constant.   The PTC (PTC3) along with the surge resistor (R16) limit the current through the first stage clamp.   The small resistor (R82) further limits the current.     Again, the schematics are not up to date and I really didn't dig into how these meters are designed. 

None of this is anything new as I went over it back in 2017 when I made the first series of videos for the prototype.     

I suspect that the first stage clamp was enough to protect the mux but I never tested it.  At the time my goal wasn't to optimize a production solution.  That's UEI's job and that's assuming that they even wanted to try and improve it.   Anyway, my point was that the meter may very well survive (my tests) without D7 & D8 present. 

Hope that helps.

I also do not expect that you change the actual circuit, simply check what Dave has really implemented there.. as the latest revisions have some totally different transistors, and maybe a different circuit, all that already indicates, that this version you have on your table, did not work as intended.

I expect, that the DMM will fail, when you only run your usual (destructive) tests.

Frank
 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3467 on: November 15, 2019, 12:52:45 pm »
Hello Joe,


Frank,
About your comment,  "I criticized though, that this does not work at all to protect the pin15 of MUX 4053, U9 for the Ohm circuit."   I felt you (and possibly others) may have been a little confused. 

I don't think at all, that I'm confused.
This critic is related to Daves videos #1157, especially 1158, not to any of your videos.

I was assuming that your comment stemmed from watching my recent video where I was talking about my clamps.  I didn't watch the two videos you mention other than seeing they were on the typical back to back clamp.   From your comment, it seems Dave was suggesting that this type of clamp, on it's own was going to improve the meters electrical robustness.   I wouldn't be at all surprised to see this version of hardware fail at an even lower level than the prototype using the 2X 4007s if this was the only change that was made.   

I also do not expect that you change the actual circuit, simply check what Dave has really implemented there.. as the latest revisions have some totally different transistors, and maybe a different circuit, all that already indicates, that this version you have on your table, did not work as intended.

I expect, that the DMM will fail, when you only run your usual (destructive) tests.

Frank

Assuming the mezzanine board is actually a back to back transistor clamp,  I really don't understand the purpose.   I am assuming that they have a similar clamp on R_RLD to handle the transient part.  If this is not there, I don't think there is much investigation to do outside of looking at the circuit board for additional clamps and to verify the mezzanine boards circuit.  Beyond that, I think we all know the outcome if we start to exceed the manufactures absolute ratings.   :-DD   
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Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3468 on: November 15, 2019, 04:33:19 pm »
Frank,
I watched the two videos you mentioned.  The most interesting part was seeing an old HP1704 scope as I think I had to use that same model in my early days.  In #1157, 7:00 Dave does mention the 121GW.  Really at 11:10 is where he starts to talk about the protection and replacing the diodes.    In #1158, at 7:30 its mentioned.   He never dives into great detail about their goals for the change or the problems they are trying to solve.  They also make no mention of additional changes.

I also read through the thread you linked:
https://www.eevblog.com/forum/blog/eevblog-1157-transistor-zener-clamp-circuit/msg2043757/#msg2043757

You have the new clamp referenced to the HY3131 AGND (also the TRMS ref) rather than to VSS of U9 which is where I assume they have actually connected the new clamp.  Not that it makes a difference as I believe your point is still valid.   I changed your drawing to show the paths of the couple of mods we are talking about on the prototype.  The primary clamp returns right to the common (GND) input of the DMM.  Between this, R16 and PTC3, this is where most of the energy is dissipated.   Nothing unusual as this seems to be the accepted practice for the more robust meters I have looked at.   Of course I did change out the HEF for the TI part as well.    I really didn't spend much time as I was really wanting to know what the next weakest link was going to be,  so I took a sledge hammer to the finishing nail and moved  on.   

If their goal is only to reduce the leakage, just remove D7/8 and get on with it.  But if their goal is to have the meter survive to something like that low end  AMPROBE AM510 I looked at years ago, then they will need to somehow protect that Mux and maybe implement a few other changes we talked about back in 2017.   After watching the videos and reading the thread, I am not hopeful that we are going to see any gains in the meters robustness.   



As a side note,  I did receive a new message from Dave offering to replace the meters with the more current design.  I have declined this offer as well for the reasons I mentioned earlier.   If we run into a major problem that Dave knows was addressed in newer versions of the hardware,  I just suggested he chime in.    Considering the confusion surrounding the prototype,  I am sure with all of these new variants we are going to see a lot more confusion.   While it seemed fair to pull most of the videos on the prototype to avoid this and not to cause undo harm to the reputation of the product or people involved, now that the meter is in production and these were purchased through the normal channels, I see no reason to be overly concerned about it. 

So stay tuned.  I've started to work on part 3 where I plan to start comparing the 121 with some other meters I have available.   
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Offline EEVblog

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Re: Handheld meter electrical robustness testing.
« Reply #3469 on: November 16, 2019, 12:20:21 am »
As a side note,  I did receive a new message from Dave offering to replace the meters with the more current design.  I have declined this offer as well for the reasons I mentioned earlier.   If we run into a major problem that Dave knows was addressed in newer versions of the hardware,  I just suggested he chime in.

Sorry to hear you don't want to swap for the new meters, but your choice.
Bad luck timing on your part, had you asked before ordering I could have said hold off for a few weeks and I'll send you the new build.

As for the new build, FYI, it as the larger transistors integrated, a 1.60mm (measured) PCB, no shim, a plated rotary switch hole (can see this in the photo I posted), and the battery spring contacts are shorter.
Again, the new design has undergone full independent ETL testing.

Quote
Considering the confusion surrounding the prototype

There was not supposed to be any confusion surrounding the prototype, I sent it to you with the specific instructions not to do any testing with it, it was just for fun to blow up.
But you went and made a whole serious of videos about it that had confused a lot of people.

 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3470 on: November 16, 2019, 01:04:19 am »
I waited two years and you sent me old stock.  That's on you.   If you wanted to see the latest hardware reviewed,  there's an easy fix.  I would still run the old hardware but at least if there was an improvement, viewers could see it first hand.   

I've been running controlled tests on meters from the beginning.  I've never had the ability to blow up a meter.  20 Joules isn't much.   Maybe that was your perception of what I was doing but it's always been about bench marking the meters.         

To be clear, I have no problem with the time I spent looking at the prototype but that's in the past.   However, I learned a fair bit about the meter when running those tests which should help in the upcoming reviews on this older hardware.   It will be very interesting to see how it holds up after two years of development.   Should do fine, right??
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Re: Handheld meter electrical robustness testing.
« Reply #3471 on: November 16, 2019, 01:12:02 am »
But I also agree the firmware shouldn't affect so much the functionality flaws seen on the video. The slow auto range is something really obnoxious and, if this is not hardwired on the chipset, it could potentially be improved by different firmware.

Autoranging speed:

 
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Re: Handheld meter electrical robustness testing.
« Reply #3472 on: November 16, 2019, 01:19:07 am »
I waited two years and you sent me old stock.  That's on you. 

Fine. But like I said in my email if you had asked first I would have told you to hold off for a couple of weeks and I could have sent the new build that was on the way.
I do not usually pack and ship, so I had no idea you ordered these meters. If I had noticed I would have known what you had wanted them for and would have contacted you.
I can't help bad luck timing and lack of communication.
 

Offline joeqsmith

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Re: Handheld meter electrical robustness testing.
« Reply #3473 on: November 16, 2019, 01:21:50 am »
Looks like she was drifting down.  Don't include the settling time.  :-DD  Even more funny was seeing that slow Keysight lock right in and hold steady.   

BM869s, you loss a digit, of course it's a bit faster.   BM235 you loose 2 digits, and like magic its even faster.

I plan to spend a segment just on the firmware.   I'm really interested in seeing how they have changed their filters. 
How electrically robust is your meter?? https://www.youtube.com/channel/UCsK99WXk9VhcghnAauTBsbg
 
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Offline EEVblog

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Re: Handheld meter electrical robustness testing.
« Reply #3474 on: November 16, 2019, 01:27:26 am »
Looks like she was drifting down.  Don't include the settling time.  :-DD  Even more funny was seeing that slow Keysight lock right in and hold steady.   

Err, the Keysight displayed 9.7ohms at one point.
As for "drift" in the 1mOhm LSD, it's a switch, just my finger pressure can change by that amount. I checked, the Keysight "drifts" in a similar way, you just didn't happen to see it in the video.
« Last Edit: November 16, 2019, 01:32:46 am by EEVblog »
 


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