Hochiki FIRElink-400CM - Manual (Page 46)

Page 46 of 58 FIRElink-400 Air Sampling System – Installation Manual
© 2010 Hochiki Europe (UK) Ltd 9-5-0-346/ISS4/OCT10
9.2 Connecting a Detector Network to a Command Module
120 ohm screened twisted pair such as Belden 9841 24 AWG should be used for all loop connections.
The RS485 A and B wires should be taken through a ferrite (supplied) with a single loop, illustrated for the
power wires in section 6.4 “Connecting Power Cables” on page 34. The total length of interconnecting
cable between adjacent FIRElink-400 detectors in the loop should not exceed 1.2 kilometres.
The detectors are connected using the RS485 connections on the terminal block (see sections
185619544.01.1.1 “Detector Terminal Block Connections” on page 33 and 185619544.01.1.1 “Command
Module Terminal Block Connections” on page 34). RS485 1A and 1B are the signal connections for bus
1 and RS485 2A and 2B are the signal connections for bus 2. SCREEN 1 and 2 are the screen
connections for buses 1 and 2 respectively.
For the Command Module, the RS485 1A and 1B connections may be thought of as the ‘Send’ lines, and
2A and 2B the ’Return’ lines. For each detector on the loop, the 1A and 1B connections may be thought
of as the lines from the previous detector on the loop and the 2A and 2B connections the lines to the next
detector in the loop.
1.1.1 Fault Tolerant Detector Loop Configuration
It should be pointed out that loop connections such as above are only needed for a fully fault-tolerant
network where full isolation is required between detectors. If all detectors are operating within the same
zone a series connection can be used where the output from the Command Module is taken from the Bus
2 terminals and the last detector in the loop does not require to be connected back to the command
module as shown below.
In this example, the Command Module will not be able to monitor the network for communications
problems but less wiring is required.