Hi all,
I'm designing a new telephone reset circuit for one of our products. This
time around, I'm trying to meet the telcom requirements of UL 1459, UL 1950,
GR1089-CORE and FCC Part 68 as well as the EMC requirements of EN 61326-1.
I have gone through a document provided by Teccor which provides a summary
of the telecom requirements. (by the way, this is an excellent reference
available from the site: searchpdf.adobe.com/proxies/1/68/46/48.html. )
Long and short of it is: My basic circuit consists of a phone jack with
tip and ring routed to an optoisolator which fires a reset circuit after a
certain number of rings. Fuses help to meet some of the power cross and max
current draw requirements. However, if fuses are used, there should be some
means for a customer to know that the fuse has blown. This is easy for a
phone or a modem; because, if the fuse is blown, the phone or modem won't
work.
For my product, it will keep on running just fine after blowing a tip or
ring fuse in its reset circuit. The customer may not know until months
later when they "call" the unit to remotely reset it only to find that it
won't reset. Somehow this doesn't seem acceptable.
I know of certain types of fuses that I call "GMT" or "grasshopper" fuses
that can trip an alarm when they blow. In this case, the "fuse" holds a
relay contact bent into an open position. When the fuse burns, the contact
springs over to its closed position setting off an alarm circuit.
Does anyone know of a particular brand or style of "GMT" or "grasshopper"
fuses approved for TNV circuits?
With regard to isolators:
According to GR-1089, my circuit will be required to pass a 5KV surge
"non-operationally". I'm worried about the optoisolator that I'm looking
at. They specify 8mm spacing, but only specify 4500V dielectric strength.
Do I need a full 5KV dielectric strength? If I use sidactors to protect
these devices, will they be removed or cut during the GR-1089 surge test?
Any words of wisdom?
Chris Maxwell, Design Engineer
GN Nettest Optical Division
6 Rhoads Drive, Building 4
Utica, NY 13502
PH: 315-797-4449
FAX: 315-797-8024
EMAIL: chr...@gnlp.com
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