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20. Systems Fitted With Serial Comm.’s
Systems Fitted With the Serial Communications Option
All NEX7250 units can be supplied with a bi directional serial output card and RS485 serial port,
which can be used to transmit or receive serial alarm data to and from 3
rd
party devices on a
channel-by-channel basis or in master /slaves configurations between annunciators.
20.1 Connections
It is recommended that the RS485 communications output be wired in twin twisted pair cable, which
has both an inner and outer screen. The inner screen should be connected to the communications
0V line and one end of the outer screen should be taken to an instrument earth. It is also
recommended that the communication cable is run in separate trunking to cables carrying high
current or high voltages. The unit is provided with a communication watchdog relay, which is
normally energised and will de-energise if a communications fault occurs. Note
:-
(Rx) and (Tx) refers
to data transmission to the P725 annunciator i.e. Rx refers to data received in the annunciator and
TX refers to data transmission out of the annunciator.
Communications Card Fitted In Typical Medium Cell
INPUT
CA2
CH*
R
COM RELAY
NO
NC
SCR
B
A
RP
Tx
Rx
2
C
1
C
INPUT 1
INPUT 2
CHANNEL 2
CHANNEL 1
A
B
RX
TX
Note:- Full details of communication are provided later in the manual.
20. Systems Fitted With Serial Comm.’s
