EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: joeqsmith on July 10, 2018, 09:48:11 pm
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If you are not aware, we had a tree hit by lightning which damaged a few things. One casualty was the cable modem. I took it apart and showed some of the damage. On the front end there is a device marked as a diode. At first I thought it may be a TVS but after looking at it with a meter I thought its most likely a GDT.
One viewer stated that the device is a TVS. I'm going with some sort of gas discharge tube based on my own personal experiences. I have attached the comments. What's your guess? GDT, TVS or some other device?
https://youtu.be/40TaqXOIrHo
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Picture of the cable modem and the part we are interested in looking at.
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Close up views of the unknown device and the damage around the transformer.
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Could be a GDT. I have not found any glass TVSs yet.
http://www.alibaba.com/product-detail/2018-UL-ROHS-Surge-Absorbers-Spark_60731858896.html (http://www.alibaba.com/product-detail/2018-UL-ROHS-Surge-Absorbers-Spark_60731858896.html)
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Found one. They don't appear to be as common as the GDT.
https://www.indiamart.com/proddetail/1-5kexxx-tvs-diode-13341138330.html (https://www.indiamart.com/proddetail/1-5kexxx-tvs-diode-13341138330.html)
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Under the microscope it looks like a GDT to me.
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There appears to be no signs of damage to the part. The next step is to remove it and mount it onto a test board so we can take a few measurements.
One day I am going to buy a new Pace with some micro tweezers.
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My 1970s era VNA is all warmed up and ready. This is an 8754A that I rebuilt many years ago. It has the frequency doubler option and the S-parameter test set to go with it. It would be useless without Labview.
Shown after SOLT and w/ 50ohm standard attached, sweeping to 2.7GHz.
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Not sure about consumer market availability, but melf TVS is not rare in defensive/aerospace applications where hermetic seal is a must.
I just Googled "transient TVS glass" and "gas GDT glass". Then looked at images. Too lazy to search any other way. Do you think it's a TVS, GDT or something else?
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I suspect if it is a GDT, it will look like a very small capacitor. Here is a 10pF.
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1pF. VNA is still warming up.
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It's certainly not GDT as it has D... designator. Should be bidirectional TVS or zener if it measures open both ways. As it measures open, it should be fine. Very unlikely for TVS to fail open without transient energy which would cause explosion or hole in the package. You could attach it to a laboratory PCU through resistor and check for clamping voltage.
Also it looks just like a diode/zener in melf package.
(https://media.digikey.com/Photos/Micro%20Commercial%20Photos/DO-213AB,%20MELF.JPG)
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It's certainly not GDT as it has D... designator. Should be bidirectional TVS if it measures open both ways. As it measures open, it should be fine. Very unlikely for TVS to fail open without transient energy which would cause explosion or hole in the package.
I knew someone would not be afraid to voice their opinion. During the video, I show the meter in conductance both directions. Let me try it on the electrometer.
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Not sure about consumer market availability, but melf TVS is not rare in defensive/aerospace applications where hermetic seal is a must.
I just Googled "transient TVS glass" and "gas GDT glass". Then looked at images. Too lazy to search any other way. Do you think it's a TVS, GDT or something else?
I think it could be a GDT, but I just want to say glass TVS does exist.
Well we knew that as I found one. :-DD Are you leaning towards a GDT?
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Yes. Two smooth parallel plates encapsulated in a hermetically sealed package.
And what is between the plates is exactly like in MELF diode/zener.
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Over ranges the electrometer. Yes, it's connected. :-DD
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Yes. Two smooth parallel plates encapsulated in a hermetically sealed package.
And what is between the plates is exactly like in MELF diode/zener.
I didn't see the silicone or contact.
If you have any and dare to use microscope, you'll usually see round thing (which actually is an optical illusion due to the package) in between of the electrodes. I already posted a pic of a zener which looks very similar. Electrodes of GDT look differently to begin with and there is nothing in between of them.
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It may look round on the first glance but if you look closer there is a rectangular die.
(https://www.eevblog.com/forum/projects/identify-if-its-a-gdt-or-tvs/?action=dlattach;attach=473453)
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I measured 395pA of leakage at 50 Volts with this setup. May need to clean things a bit more...
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I can imagine they may have an insulator inside to set the gap. It may all be bonded as one part prior to encapsulation.
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Notice on this GDT (yes it's a GDT) how the gap is formed.
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Quacks like a duck. I'm sticking with some sort of GDT. Next, I need to see where it starts to conduct and how it behaves.
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Eh, I don't know if I would bother. You get the best GDT that will fit in the circuit. There is no good reason you can't solder in a better one. Get one with the lowest working voltage you can unless there is some kind of layered protection, which I doubt.
The only GDT parameter would be if it is used in combination with another shunt device with similar voltage, where you would have some kind of impedance (inductor) between the GDT and the other element.
Protection systems = cost. You can always do better.
You could have GDT - > inductive impedance for firing -> Thyristor -> blocking/opening -> fast diodes
If you don't have a thyristor and a TISP or such, you can probably put anything you want there. Clearly the one they put was not up to the job if it exploded. Bourns probably sells faster GDT then what they decided to put in there. You want to minimize the amount of energy going into the semiconductor stuff, thats the only job of the GDT.
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I see them as GDT used in car radios. Very hard to find.
Pic is a Ford, also seen in Kia car radios.
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Quacks like a duck. I'm sticking with some sort of GDT. Next, I need to see where it starts to conduct and how it behaves.
GDT with D... designator, silicon die inside, does not look anything like GDT and has leakage current. Yeah, :palm:. I'd say quacks like a horse.
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Quacks like a duck. I'm sticking with some sort of GDT. Next, I need to see where it starts to conduct and how it behaves.
GDT with D... designator, silicon die inside, does not look anything like GDT and has leakage current. Yeah, :palm:. I'd say quacks like a horse.
:-DD Well at least no one thinks its a MOV.
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Eh, I don't know if I would bother. You get the best GDT that will fit in the circuit. There is no good reason you can't solder in a better one. Get one with the lowest working voltage you can unless there is some kind of layered protection, which I doubt.
The only GDT parameter would be if it is used in combination with another shunt device with similar voltage, where you would have some kind of impedance (inductor) between the GDT and the other element.
Protection systems = cost. You can always do better.
You could have GDT - > inductive impedance for firing -> Thyristor -> blocking/opening -> fast diodes
If you don't have a thyristor and a TISP or such, you can probably put anything you want there. Clearly the one they put was not up to the job if it exploded. Bourns probably sells faster GDT then what they decided to put in there. You want to minimize the amount of energy going into the semiconductor stuff, thats the only job of the GDT.
I have no plans to attempt to repair this modem or modify the new one. The goal for this thread is only to identify what technology was in use. What you you think this device is?
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https://youtu.be/QWDTsfXJHyw
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Quacks like a duck. I'm sticking with some sort of GDT. Next, I need to see where it starts to conduct and how it behaves.
GDT with D... designator, silicon die inside, does not look anything like GDT and has leakage current. Yeah, :palm:. I'd say quacks like a horse.
Looks like a duck and swims like a duck. :-DD The TVS believers go silent.....
It appears the GDT starts to conduct at roughly 160 volts.
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The TVS believers go silent.....
:palm:
Looks like a duck and swims like a duck. :-DD
In a rocket.
It appears the GDT starts to conduct at roughly 160 volts.
It's either 160V zener or TVS. GDS cannot "start conducting". It either does not conduct or breakdown occurs and voltage across it drops dramatically.
http://www.citel.us/gas_discharge_tubes_overview.html (http://www.citel.us/gas_discharge_tubes_overview.html)
The gas discharge tube may be regarded as a sort of very fast switch having conductance properties that change very rapidly, when breakdown occurs, from open-circuit to quasi-short circuit (arc voltage about 20V).
EDIT: I watched your video. Dunno maybe it's just Zener which was broken open as it was glowing, probably because of your generator. But there is obviously a rectangular die inside it. Although after your experiments it might look different.
(https://www.eevblog.com/forum/projects/identify-if-its-a-gdt-or-tvs/?action=dlattach;attach=474158;image)
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The TVS believers go silent.....
:palm:
Looks like a duck and swims like a duck. :-DD
In a rocket.
It appears the GDT starts to conduct at roughly 160 volts.
It's either 160V zener or TVS. GDS cannot "start conducting". It either does not conduct or breakdown occurs and voltage across it drops dramatically.
http://www.citel.us/gas_discharge_tubes_overview.html (http://www.citel.us/gas_discharge_tubes_overview.html)
The gas discharge tube may be regarded as a sort of very fast switch having conductance properties that change very rapidly, when breakdown occurs, from open-circuit to quasi-short circuit (arc voltage about 20V).
Sure, there is an area where it will start to conduct. A GDT it not a perfect switch.
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Scott asked to see it under a microscope. Same setup as before.
https://youtu.be/A7sEDzuB_gU
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Notice on this GDT (yes it's a GDT) how the gap is formed.
Yeah, and every of them look completely different. 3 pictures, which of them look more similar?
(https://www.eevblog.com/forum/projects/identify-if-its-a-gdt-or-tvs/?action=dlattach;attach=473159;image)
(http://arabtronics.net/image/cache/catalog/10/MELF-500x500.jpg)
(https://www.eevblog.com/forum/projects/identify-if-its-a-gdt-or-tvs/?action=dlattach;attach=473465;image)
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Die looks like it's glowing with occasional discharge occurring on the side. I certainly have seen glowing BJT dies.
Scott asked to see it under a microscope. Same setup as before.
https://youtu.be/A7sEDzuB_gU
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I assume you TD the video when you just watched it. :-DD :-DD The glow upsets you?
I can imagine they may have an insulator inside to set the gap. It may all be bonded as one part prior to encapsulation.
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I assume you TD the video when you just watched it. :-DD :-DD The glow upsets you?
I can imagine they may have an insulator inside to set the gap. It may all be bonded as one part prior to encapsulation.
I watched it embedded here, didn't visit youtube. Why the hell GDT would have insulator in the middle? To destroy it's performance and ensure that arc runs across the insulator and outer glass thus damaging them? If you look on the actual GDT picture you provided, it's specially made to ensure that there is a gap between electrodes and outer glass.
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Some larger examples
(https://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/Gasableiter.jpg/220px-Gasableiter.jpg)
(https://sc02.alicdn.com/kf/HTB10xnTJVXXXXXWXpXXq6xXFXXXB/2-Electrode-Spark-Gap-Gas-Discharge-Tube.jpg_350x350.jpg)
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I assume you TD the video when you just watched it. :-DD :-DD The glow upsets you?
I can imagine they may have an insulator inside to set the gap. It may all be bonded as one part prior to encapsulation.
I watched it embedded here, didn't visit youtube. Why the hell GDT would have insulator in the middle? To destroy it's performance and ensure that arc runs across the insulator and outer glass thus damaging them? If you look on the actual GDT picture you provided, it's specially made to ensure that there is a gap between electrodes and outer glass.
Yes that's another style. The one GDT I show also has material between the gap. I suspect its a ceramic rod that is coated and the gap was laser etched. Pure guess on my part.
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Finally, a little fun. How do they compare with some sort of transient. So, to be clear this is not an IEC combo generator. It loosely follows the voltage profile. It has a 2 ohm source and can deliver about 20J into a dead short is all.
This the axial through hole GDT. Scale is 500V/div. Notice how the GDT is very slow. I've show this before in a video. It basically allows the voltage to reach some pretty big numbers. No surprise.
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Now let's have a look at the GDT from the modem. Again we can see how slow it is . Even slower than the axial part. I've shown how fast TVSs switch before.
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I watched it embedded here, didn't visit youtube.
I need to apologize for calling you out but the timing was perfect. :-DD
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I checked what higher voltage TVSs I had on hand. This is a 1V5KE150A. IPPm for this device is 7.2A and the clamping voltage at IPPm is 207V. I'm exceeding the peak current by a fair amount but the pulse is short. Notice this is 2us/div where the other two were at 50us.
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Old paper on GDTs. I had asked someone if theirs were radioactive. This paper seems to have been written about the time they were experimenting with it.
http://www.dtic.mil/dtic/tr/fulltext/u2/a214199.pdf (http://www.dtic.mil/dtic/tr/fulltext/u2/a214199.pdf)
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Showing both GDTs on the generator running some higher currents than a few uA previously shown. I turned it all the way up on the last transient I applied to the modem's GDT.
https://youtu.be/goiBhEn4xL4
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I'd treat it like a neon lamp, give it 100VAC at 1mA and see if she glows
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I'd treat it like a neon lamp, give it 100VAC at 1mA and see if she glows
I fed it with an unfiltered, full rectified 240V signal through a 2Meg. The both drew about 50uA and glow. That's a couple of videos back. Also when it was under the microscope, it was the same setup and you can see the glow as well.
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Interesting old patent on a GDT.
When certain crystalline dielectric materials are placed in an intense electric field, electrons are emitted from the surface of the dielectric. When this is used to initiate an arc in a gas that surrounds the dielectric, the phenomenon is called "dielectric-stimulated arcing."
Cooper and Allen [1973] used dielectric-stimulated arcing to decrease the response time of spark gaps. The spread of dc firing voltages that were obtained in a batch of spark gaps was also reduced.
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From that patent, using the stepped electrode shape :
"... 0.0005" gap, a DC breakdown of about 400 volts and an impulse breakdown of about 460 volts have been obtained.
For a 0.001" gap, breakdown voltages of about 550 and 650 respectively have been obtained.
For a conventional gap of 0.002", the impulse breakdown voltage can be from 1200 volts to 2500 volts, or higher"
At that tiny a gap, no way you can make glass that precise, heed a spacer. I think it's easier to use a larger gap and radioactive elements.
I worked on lightning protection, tested at Hydro-Québec testing laboratories, (http://www.hydroquebec.com/innovation/en/testing-calibration-repair-services.html) for the pipeline industry. They usually test electric utility stuff like breakers and transformers, bushings etc. to impulse voltage of 5.4 MV, a switching impulse of 2.7 MV and a peak test voltage of 1,800 kV AC or 1,200 kV DC.
GDT's are unfortunately slow, the transient pass-through before they conduct still damages things.
It's strange to see them used in some multimeter front-ends.
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The GDTs like the MOVs, sit behind a PTC and surge rated resistor/s and you will normally have a faster clamp for the lower impedance legs. I've looked at three meters that used GDTs. The HIOKI and Gossen held up very well against my tests. Obviously, that Gossen has a lot of issues but purely from my transient testing, it was never damaged. I wasn't impressed with the Keysight at all.
My old HP 34401A bench meter also utilizes GDTs on the front end. When I pulled it apart for repairs, was the first time I have had it apart and just noticed them.
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Before tossing out both parts, I made an attempt to do a direct discharge with my half cycle generator on each part.
https://youtu.be/Yca42Ih-FPc
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Glows like a GDT, arcs like a GDT, clamps very slow like a GDT.. Did finally get it to come apart.
https://youtu.be/0thOfk4I3qs?t=2278
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I did write the person who commented on the YT video about it being a TVS. Basically, I am looking for a suggested part number. I have no doubts that a TVS could be found in this type of package but they do appear rare. Not something I would expect to see in a commercial grade modem when plastic packages are widely available.
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I did write the person who commented on the YT video about it being a TVS. Basically, I am looking for a suggested part number. I have no doubts that a TVS could be found in this type of package but they do appear rare. Not something I would expect to see in a commercial grade modem when plastic packages are widely available.
TVS/zener at least do come in this package. Find at least one GDT part number that comes in such package as well.
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I don't see a need for glass-packaged TVS as there is no gas envelope, like in a GDT.
Hermetic-packaged TVS are MIL spec. by Sensitron. (http://www.militarysystems-tech.com/files/militarysystems/supplier_docs/TVS%20Products%20Brochure.pdf)
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I don't see a need for glass-packaged TVS as there is no gas envelope, like in a GDT.
Hermetic-packaged TVS are MIL spec. by Sensitron.
(http://www.militarysystems-tech.com/files/militarysystems/supplier_docs/TVS%20Products%20Brochure.pdf)
Then why tons of diodes and zener diodes come in glass package?
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Small switching diodes in glass hermetically-sealed packages are widely available, like DO-35, DO-41, MELF etc. I don't remember ever seeing TVS in glass packages.
I think the difficulty is to gas-fill these with say, neon to make a GDT. Or to make these larger for more power handling, for a big die (TVS) or electrodes (GDT).
joeqsmith's part, might have been:
Mitsubishi DA53 (http://www.mmc.co.jp/adv/dev/english/contents/surge_ab/index.html)
Ruilon china (http://www.ruilon.com/plugins/Tianv_Commodity/ProductList.aspx?id=3503&s=3) RL501 series 0.5kA 2mm dia. x 4mm.
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Small switching diodes in glass hermetically-sealed packages are widely available, like DO-35, DO-41, MELF etc. I don't remember ever seeing TVS in glass packages.
I think the difficulty is to gas-fill these with say, neon to make a GDT. Or to make these larger for more power handling, for a big die (TVS) or electrodes (GDT).
joeqsmith's part, might have been:
Mitsubishi DA53 (http://www.mmc.co.jp/adv/dev/english/contents/surge_ab/index.html)
Ruilon china (http://www.ruilon.com/plugins/Tianv_Commodity/ProductList.aspx?id=3503&s=3) RL501 series 0.5kA 2mm dia. x 4mm.
They are both axial, not a MELF. Rare parts in a commercial product would make no sense at all.
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It makes sense as there is no impulse standard for cable modems that I know of. What size GDT is suitable?
GDT's meet Telecom and Mains standards such as UL1449, UL497B, FCC Part 68 etc. so they are sized large.
A tiny GDT is off the radar and has no approvals, maybe a 0.5-1kA rating.
RLM501 (http://www.ruilon.com/files/upload/pdfs/rlm501.pdf) MELF 0.5kA 2.1mm dia.
RLM102 (http://www.ruilon.com/files/upload/pdfs/rlm501.pdf) MELF 1kA 2.8mm dia.
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Yes, GDTs in a MELF package seem common. I have not heard back from the person who posted on the YT video. Waiting to see this glass MELF TVS they feel would go into a cheap modem.
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First time to see small GDT; in Sanwa PM300 DMM? https://www.eevblog.com/forum/testgear/aneng-302-pocket-meter-by-voltlog/msg1737086/#msg1737086 (https://www.eevblog.com/forum/testgear/aneng-302-pocket-meter-by-voltlog/msg1737086/#msg1737086)
In your testing, I wasn't sure if it (small GDT) could handle a Cat. III impulse.
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First time to see small GDT; in Sanwa PM300 DMM? https://www.eevblog.com/forum/testgear/aneng-302-pocket-meter-by-voltlog/msg1737086/#msg1737086 (https://www.eevblog.com/forum/testgear/aneng-302-pocket-meter-by-voltlog/msg1737086/#msg1737086)
In your testing, I wasn't sure if it (small GDT) could handle a Cat. III impulse.
The question mark does not appear to follow a question. I have never shown a category III impulse and have no way to create it. Someone had made a similar comment about my tests damaging MOVs. Perhaps you do not have an understanding how most of the meters I have looked at are designed. I suggest reading post #2411
https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/2400/ (https://www.eevblog.com/forum/testgear/hear-kitty-kitty-kitty-nope-not-that-kind-of-cat/2400/)
Sounds like Wraper is not having any luck finding a TVS that they feel would have been a replacement. I'm not surprised as it seems it would be a special part. Looking at the YT metrics, it did get a DV from someone in Latvia. :-DD :-DD Perhaps someone was upset that I was showing too much data.
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It's many questions that little GDT raises, RIP. I understand multimeter protection circuits and 61010 well enough to get equipment designs certified.
The Sanwa PM300 using a slightly larger GDT (https://www.eevblog.com/forum/testgear/pocket-multimeter-shootout/100/) with no MOV's, "The world's only CAT IV IEC61010 rated true pocket sized multimeter"
Seems strange a little GDT can pull it off, no MOV's required? Zotek and ANENG jump on board.
You and I know the let-through/follow-through current would be a catastrophe in this crappy scheme.
Looking at the PM300 approvals test report (http://www.eevblog.com/files/PM300-SHEM1610006729IT-RPT.pdf) it appears fake- 61010 ESD tested to 4kV, but no mains transient testing. The PM300 product manual (https://overseas.sanwa-meter.co.jp/items/detail.php?id=405) states that wonderful term "designed to" which is not certified to...
You think a little GDT can achieve multimeter 61010 approvals? :popcorn: