Edwards LaserSense HSSD-2

Chapter 2: Installation and assembly
32 LaserSense HSSD-2 Aspirating Smoke Detector Installers Handbook
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 RS-485 A and B wires should be taken through a ferrite
(supplied) with a single loop (see Figure 16 ) . The total length of interconnecting
cable between adjacent detectors in the loop should not exceed 1.2 kilometres.
The detectors are connected using the RS-485 connections on the terminal block
(see figure 14 and 15) RS-485 1A and 1B are the signal connections for bus 1
and RS-485 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 RS-485 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.
Fault-tolerant detector loop configuration
Figure 21 shows the configuration for a fault-tolerant network.
Figure 21: Fault tolerant detector loop configuration
(1) Command module
(2) Detector 1
(3) Detector 2
(4) Detector 127
Nonfault-tolerant serial configuration
It should be pointed out that loop connections such as in “Fault-tolerant detector
loop configuration” 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