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Document 15949 Rev. E 4/12/95 P/N 15949:E
3.3 The Isolator Module
The loop isolator module (ISO-X) is used to protect critical elements of the communications
loop from faults on other branches or sections of the loop. The ISO-X continuously monitors
the circuit connected to Terminals 3 (-) and 4 (+). Upon power up, an integral relay is latched
on. The ISO-X periodically pulses the coil of this
relay. A short circuit on the loop resets the relay.
The ISO-X sees this short and disconnects the
faulted branch by opening the positive side of the
loop (Terminal 4). This effectively isolates the faulted
branch from the remainder of the loop. Once the
fault is removed, the ISO-X automatically reapplies
power to the communications loop branch. Figure
3-12 illustrates the use of an ISO-X on a
non-redundant communications loop. For employ-
ing ISO-Xs on a redundant or isolated-redundant
communications loop, see Figure 3-8.
Note: During a fault condition, the System 5000
will register a trouble condition for each zone mapped to the isolated loop branch.
Figure 3-12: Isolating Non-Redundant Communications Loops
Shorts on this branch of an isolated non-redundant communications loop will be isolated
from all devices installed both upstream of the ISO-X and on the continuation of the loop
(shown as dotted line).
commloop5
T-Tapped Branch off the Communications Loop
Continuation of the Communications Loop
Communications
Loop
M500XJ
1
2
3
4
comloop4
ISO-X
Loop In (-)
Loop In (+)
Loop Out (-)
Loop Out (+)
ISO-X
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