Answer / kevin hackart

THE END-OF-LINE RESISTOR IS USED IN MOST ALARM SYSTEMS AS A
CABLE FAULT MONITORING DEVICE, EG.CABLE CUT BY INTRUDER.
THE MAIN CIRCUIT USES A SPECIFIED RESISTANCE AND THE MOMENT
THAT VALUE ALTERS OR DISAPPEARS IT TRIGGERS THE ALARM. ALSO
WHAT COULD BE USEFUL IN FIRE ALARMS IS IF THE CABLE IS
BURNT OFF OR HEATED THUS CHANGING THE RESISTANCE FURTHER
DOWN THE LINE IT WILL ALSO TRIGGER THE ALARM AND COVER FOR
A FAULTY DETECTOR. MAINLY THE RESISTOR IS FOR TAMPERING AS
MOST SYSTEMS USE A NORMALLY CLOSED LOOP AND SO IT IS EASY
FOR SOMEONE TO JUST SHORT OUT THAT CIRCUIT WITH A PIECE OF
WIRE, A SPECIFIC RESITANCE MAKES IT TOUGHER TO BE BYPASSED.

Answer / pratheesh

I dont know excatly the use of end off line resistor in
Fire alarm system.

But in communication system(Profibus) we use end off
line resistor. In this system, all the communication
devices connected to the same bus in parallel. The bus
having only 2 wires and all the devices connected to
this same 2 wires in parallel.. And each communicator
devices have one address in that bus. Thats how the
server identifies the signals from that particular
device. So the extreme end of this bus cannot be kept
open. By providing an End Off Resistance, server can
know that this is the end of the bus and there is no
devices from that particular point.

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