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: --what is a gas tube aresster how is it used in a circuit where can you
: get them of the right size. thank you. Nick R
:
Hi Nick,
A gas tube arrestor is basically a precision spark gap - one that will trigger at a relatively well-defined voltage. It is made from a two or three electrodes immersed in an air or noble gas atmosphere, and housed within a glass or ceramic envelope. It may also be constructed using slightly radioactive electrodes that provide a source of free electrons ("beta" rays) to help trigger the gap.
Arrestors are used to protect downstream circuits from being subjected to voltages that might otherwise damage or destroy them. They work by rapidly turning from an open circuit to [almost] a short circuit when an excessive voltage is applied across their terminals. Unfortunately, gas tube arrestors can take a fairly long time to fire (typically microseconds or even tens of microseconds), and in many applications, they have been replaced by solid state alternatives such as Metal Oxide Varistors (MOV's), Protection Thyristors, or zener-/avalanche transient protectors (Transorbs or equivalent).
Many parts distributors carry gas tube arrestors from a vareity of vendors, such as Digikey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=655426&k=gas tube
Following are some links with more information on gas tube arrestors and applications that you may find useful:
http://www.bourns.com/pdfs/bourns_gdt_white_paper.pdf
http://www.sankosha-usa.com/failsafe.asp
http://www.spkecl.com/manufacturer/16667/16667.html
http://www.secomtel.com/UpFiles/Attach/0/2007/5/17/135145.pdf
http://www.littelfuse.com/data/en/Application_Notes/EC6391.pdf
Bert
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