GAI-Tronics 12579-003 Monitored Relay Module (MRM) - Manual (Page 10)

Pub. 42004-716L2C
Model 12579-003 Monitored Relay Module Page 10 of 16
f:\standard ioms - current release\42004 instr. manuals\42004-716l2c.doc
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Mode 4: IAC Line Supervision
In Mode 4, outputs can be used to control several dc-powered signaling devices by connecting/
disconnecting power to these devices. In addition, this loop is monitored for open circuits, wire-to-wire
short circuits (across + and −), and ground faults. If any of these three conditions are detected by the
MRM, the MRM indicates that a fault has occurred. Please note that monitoring of the loop only occurs
while the loop is inactive (signaling devices are off).
Figure 8. IAC Line Supervision – DC-Powered Beacons
It is recommended that Mode 4 only be used with dc-powered signaling devices. In Mode 4, one
blocking diode must be provided for every signaling device connected to the loop. Note that some
signaling devices already include a blocking diode in the unit - in this case, no additional blocking diode
is required. The end-of-line device is a 20 k
, 2-watt, 5% tolerance resistor. Please observe all polarities
as indicated in Figure 8 above.
N OTE : The blocking diodes, the wire jumpers, and the 20 k
, 2-watt, 5% tolerance resistor are not
included with the MRM. These components are included in a kit (12509-004), which must be ordered
separately.
*N OTE : The MRM does not contain any current-limiting for the signaling device power. It is
recommended that an external fuse be provided for each output circuit with the appropriate voltage and
current ratings. The selected fuse should be of the slo-blo variety.