Author Topic: What is this electronic symbol ?  (Read 2472 times)

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Offline pedroteck

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What is this electronic symbol ?
« on: January 13, 2015, 04:18:48 am »
Any one familiar with this PCB marking " SG " , i am confused weather its a cap or an oscillator , its connected directly to voltage test probe input of a bench DMM btw.

 

Offline c4757p

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Re: What is this electronic symbol ?
« Reply #1 on: January 13, 2015, 04:24:14 am »
Spark gap, for high voltage overload protection.
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Online T3sl4co1l

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Re: What is this electronic symbol ?
« Reply #2 on: January 13, 2015, 04:35:18 am »
FWIW, the symbol (two plates in a circle) is also sometimes used for normally-open relay contacts on ladder diagrams, or, I suppose, a capacitor that's special in some way (perhaps sealed in a vacuum, hence the circle emphasizing the envelope).  There's usually a solid dot inside the circle, denoting a gas filling (gas discharge tubes (GDTs), neon lights, etc.).  Alternatives to the straight lines include round, triangle/arrow, or 'D' shaped electrodes, emphasizing the nature or intent of the discharge (from neon glow discharge to high current spark gaps).

The "SG" designation and use definitely suggest at least an air type spark gap, in your case.

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Offline pedroteck

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Re: What is this electronic symbol ?
« Reply #3 on: January 13, 2015, 04:55:21 am »
Thanks a lot .

I see now why its near the voltage input , it acts kind of  like a MOV .
 

Offline Dr. Frank

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Re: What is this electronic symbol ?
« Reply #4 on: January 13, 2015, 08:49:50 am »
The symbol origins from a neon discharge bulb, which also ignited on a pre-determined voltage. Can be found in old FLUKE DCV calibrators, or in HP neon bulb choppers.

Same effect as a SG, maybe more precise, but for sure more expensive today.

Frank
« Last Edit: January 13, 2015, 08:53:56 am by Dr. Frank »
 

Offline pedroteck

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Re: What is this electronic symbol ?
« Reply #5 on: January 17, 2015, 01:11:09 pm »
The symbol origins from a neon discharge bulb, which also ignited on a pre-determined voltage. Can be found in old FLUKE DCV calibrators, or in HP neon bulb choppers.

Same effect as a SG, maybe more precise, but for sure more expensive today.

Frank

Maybe you have a point Dr.frank since this component belongs to an old bench dmm near the AC/DC voltage input .

The problem is that i have lost it and need to replace it with something but not quite sure with what  , if it was acting like a MOV i wold replace it with that but i need to be sure .

I remember that the component was in a plastic package ( like a small sized polyster cap) with black colour and a encircled T marking on top of it .

Like that but a little bigger ( i hope this will help more) :
« Last Edit: January 17, 2015, 01:19:55 pm by pedroteck »
 

Offline pedroteck

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Re: What is this electronic symbol ?
« Reply #6 on: January 19, 2015, 08:24:37 am »
Here is a close up view of the inside of the component case :

 


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