User guide

System Hardware
System Description, AutroSafe Integrated Fire & Gas Detection System, 116-P-ASAFE-IFG/XE Rev. B, 2005-10-27,
Autronica Fire and Security AS
Page 35
4.8.3.5 Why loop-back?
The BSD-321 requires a RS-485 loop-back connection. Loop-back is
used to give increased system safety. While one channel on the BSD-
321 is transmitting, the other is receiving making it possible to verify
that the internal operation of the BSD-321 is correct. By using RS-485
loop connection dual communication paths to the detectors are
obtained in addition.
Loop-back
Loop-back of RS-485 can be done either locally on BSD-321 or
remotely with loop to/from detector. Switches S1 and S2 must be set
accordingly for correct termination.
Local loop-back:
• Set S2-6 OFF (Disable EOL resistor for port 1)
• The detector at the other end of the RS-485 bus must enable its
EOL resistor
Remote loop-back:
• Set S2-6 ON (Enable EOL resistor for port 1). None of the
detectors must have EOL resistors
4.8.4 Earthing
If shielded cable is used for the AutroFieldBus, the shield should be
connected to the CT terminals (both in and out, terminals 3 and 11).
Shielded cable is required used for the RS485 cable, the shielding
should be connected to the instrument earth (IE) for serial 0 or serial
1, respectively.
Any armouring should be connected to protective earth (PE).
See “System shielding and earthing” for further information.