Author Topic: Identify if its a GDT or TVS  (Read 7265 times)

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Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #25 on: July 11, 2018, 09:00:53 am »
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. 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #26 on: July 11, 2018, 09:32:06 am »
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?

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #27 on: July 11, 2018, 10:41:30 am »

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #28 on: July 11, 2018, 10:17:23 pm »
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.   

Online wraper

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Re: Identify if its a GDT or TVS
« Reply #29 on: July 11, 2018, 10:35:00 pm »
The TVS believers go silent..... 
:palm:
Quote
Looks like a duck and swims like a duck.   :-DD
 
In a rocket.
Quote
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
Quote
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.
« Last Edit: July 11, 2018, 10:52:41 pm by wraper »
 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #30 on: July 11, 2018, 10:50:43 pm »
The TVS believers go silent..... 
:palm:
Quote
Looks like a duck and swims like a duck.   :-DD
 
In a rocket.
Quote
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
Quote
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.   

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #31 on: July 11, 2018, 11:05:28 pm »
Scott asked to see it under a microscope.  Same setup as before.   

https://youtu.be/A7sEDzuB_gU

Online wraper

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Re: Identify if its a GDT or TVS
« Reply #32 on: July 11, 2018, 11:06:00 pm »
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?






 

Online wraper

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Re: Identify if its a GDT or TVS
« Reply #33 on: July 11, 2018, 11:09:46 pm »
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
 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #34 on: July 11, 2018, 11:12:54 pm »
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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Re: Identify if its a GDT or TVS
« Reply #35 on: July 11, 2018, 11:18:37 pm »
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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Re: Identify if its a GDT or TVS
« Reply #36 on: July 11, 2018, 11:21:21 pm »
Some larger examples



 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #37 on: July 11, 2018, 11:51:09 pm »
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. 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #38 on: July 11, 2018, 11:56:48 pm »
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.

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #39 on: July 12, 2018, 12:00:37 am »
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.   

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #40 on: July 12, 2018, 12:02:16 am »
I watched it embedded here, didn't visit youtube.
I need to apologize for calling you out but the timing was perfect.  :-DD

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #41 on: July 12, 2018, 12:48:55 am »
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.   


Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #42 on: July 12, 2018, 02:03:52 am »
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

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #43 on: July 12, 2018, 03:21:00 am »
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

Offline floobydust

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Re: Identify if its a GDT or TVS
« Reply #44 on: July 12, 2018, 05:42:28 am »
I'd treat it like a neon lamp, give it 100VAC at 1mA and see if she glows
 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #45 on: July 12, 2018, 11:30:54 am »
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. 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #46 on: July 12, 2018, 10:12:43 pm »
Interesting old patent on a GDT. 

Quote
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."

Quote
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.

Offline floobydust

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Re: Identify if its a GDT or TVS
« Reply #47 on: July 12, 2018, 10:52:36 pm »
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, 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.

 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #48 on: July 13, 2018, 11:57:09 pm »
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. 

Offline joeqsmithTopic starter

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Re: Identify if its a GDT or TVS
« Reply #49 on: July 14, 2018, 02:12:26 am »
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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