Nortel DMS-500 - Loop Closure; Local Talk Line Circuit

OAS alarm and Control Circuits 6-13
DMS-100 Family Alarm System Description Reference Manual BASE12
The power supplies from the OAU and standby MTM or ISM connect to the
alarm system. This connection occurs through the contacts of an SD
point-controlled relay in each office alarm circuit 3 (NT2X43) card.
Normally, only the power supplies in the OAU connect to the alarm system.
If one or two of the OAU power supplies fail, the system switches the source
for the two power supplies to the standby MTM or ISM. The system also
generates an OAU alarm. When the fault in the OAU is corrected, the alarm
system software automatically switches back to the OAU power supplies. If
one of the standby MTM or ISM power supplies fails when the OAU power
supplies are not available, the both 130 V and 20-Hz ac power supplies are
out-of-service.
OAS Version 2
In the Version 2 OAS, the 130 V power supply for the remote alarm transfer
circuit is in the card that contains the alarm transfer circuit. Only one of
these cards is present so a backup power supply is not available. The failure
of the 130 V power source causes the system to generate an alarm at the
remote office.
The 20-Hz power supply, is avalable in the Version 2 OAS only if the OAU
dead system card with unique audible (NT2X82AA, AC, AE, AF, AH or
AK) is used and is duplicated in the standby MTM or ISM. Like the Version
1 OAS, if the 20-Hz supply from the OAU fails, the system raises the OAU
alarm and switches the source for the supply to the standby MTM or ISM.
When the fault is corrected, the system automatically switches the source
back to the OAU.
Loop closure
Version 2 OAS provide loop closures to the DF for critical, major, minor,
and OAU alarms. Loop closures can be used for the following:
• to drive external alarm sending equipment
• distribution to a central maintenance center
Local talk line circuit
The local talk lines are two office telephone lines that terminate at the MAP
voice communications module logic telephone set. These lines connect so
that line 1 serves all odd aisles and line 2 serves all even aisles in the office.
The odd aisles are A, C, E, G in a continuing sequence. The even aisles are
B, D, F, H in a continuing sequence.