Allen-Bradley GuardPLC 1753, Safety Reference Manual

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Publication 1753-RM002C-EN-P - September 2008 111
Appendix
B
Use in Central Fire Alarm Systems
All GuardPLC systems with analog inputs can be used for control and
indicating equipment in accordance with DIN EN 54-2 and NFPA 72.
The user program must fulfill the functional requirements established
for central fire alarm systems by the standards cited above.
The required maximum cycle time of 10 seconds (DIN EN 54-2) for
central fire alarm systems can be achieved with GuardPLC systems,
whose cycle times can be measured in milliseconds. Similarly, the
required 1 second safety time (error response time) can also be
achieved, if necessary.
The fire alarms are connected using the open-circuit principle with
line control for the detection of short-circuits and line breaks. The
digital and analog inputs of the GuardPLC 1800 and the analog inputs
of the GuardPLC 2000 1755-IF8 module can be used. See the
application example below.
Wiring of Fire Alarms - Example
M = Fire alarm
R
EOL
= Terminating resistor on the last sensor of the loop
R
L
= Limitation of the maximum permitted current in the loop
R
shunt
= Measuring resistor
IMPORTANT
DeviceNet Safety I/O modules are not appropriate for safety
systems.
Sensor Supply
Analog Input
R
shunt
M
1
M
2
M
3
M
n-1
M
n
R
EOL
Reference Pole
(L-, I-)
R
L
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