Gas discharge tubes can be very complex devices and have a number of specifications. Normally the voltage spec that you see is the DC specification, in other words, the firing voltage if the voltage is slowly ramped up (2kV/second is on rate used); however, the impulse voltage -- the voltage at which the tube fires with a fast pulse (anywhere from 100V/us to 10kV/us) is normally much higher.
One of the objectives in gas tube design is to get the DC and impulse voltages to be as consistent as possible, and as close together as possible (actually very difficult). Gas mixtures, doping, electrode geometry, etc. are all critical to the design. Some gas is sensitive to light, some work better in the light and for a while, some were doped with radioactivity to help control the firing point under different voltage impulse conditions. Hope this helps.... Nothing's ever simple. Best Regards, Mike Hopkins Thermo KeyTek. -----Original Message----- From: Robert Macy [mailto:[email protected]] Sent: Wednesday, February 20, 2002 7:18 PM To: Chris Maxwell; [email protected] Cc: EMC-PSTC Internet Forum Subject: Re: Use of PCB Traces as Fuse and Voltage suppressor Our experience with gas discharge tubes was that they worked according to spec in the lab. fired perfectly around 400V like they're supposed to, but down inside of the PVC oil tank holding the 150KV isolation transformer they liked to fire at 600V+ Guess they needed photon energy to make the gas trigger or something. - Robert - Robert A. Macy, PE [email protected] 408 286 3985 fx 408 297 9121 AJM International Electronics Consultants 619 North First St, San Jose, CA 95112 -----Original Message----- From: Chris Maxwell <[email protected]> To: [email protected] <[email protected]> Cc: EMC-PSTC Internet Forum <[email protected]> List-Post: [email protected] Date: Wednesday, February 20, 2002 2:15 PM Subject: RE: Use of PCB Traces as Fuse and Voltage suppressor > >Hi Bogdan, > >I'm sorry if you thought that my previous message was an endorsement for >using necked down PCB traces as a fuse. I understand and share the >sentiment that it is an unpredictable and probably not even cost >effective solution. > >I was wondering why anyone would shape a PCB trace in such a way (two >triangles pointing at each other with a thin trace between the points). >A "fuse" is probably not the likely intention. A reasonable explanation >may be a "cut jumper". The triangles make the trace visible; while the >thin trace provides an easy spot for the trace to be cut with an exacto >knife---- which permanently removes the "jumper". Another reason >(suggested by a colleage) are alignment marks used by the PCB fab house >to help align layers. > >Just to be sure... I'm not suggesting the above as design ideas. I'm >just trying to figure out why anyone would do such a thing. > >One solution to the original problem that I haven't seen suggested is >the good old "air discharge tube", "gas-discharge tube", "gas tube" >...whatever you want to call them. Of course, they aren't free (about >$1 each). They are more predictable than open air terminals, they are >UL/CSA recognized and they can handle some massive breakdown currents. >They are available from Bourns and Sankosha USA... probably some other >manufacturers as well. > >Chris > > > >> -----Original Message----- >> From: bogdan matoga [SMTP:[email protected]] >> Sent: Wednesday, February 20, 2002 4:19 PM >> To: [email protected]; Chris Maxwell; [email protected] >> Subject: Use of PCB Traces as Fuse and Voltage suppressor >> >> Gabi: >> I believe that there is a basic rule which is not published anywhere: >> when you design something, then do it right. >> When transient suppressors are needed, then use the correct component, >> which will not depend on Paschen's Law and give predictable >> performance. >> >> Same for "necked down" fuses. >> When you want performance, then do it right. The above original >> suggestions are perfect for Mickey-Mouse-engineering. >> Bogdan. >> > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list" ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: [email protected] Dave Heald: [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
