Addressable Gas Detection System Manual
Addressable System Manual
12
Issue 2, January 2015
Two serial bus modules are fitted as standard. A further two may be added to the
spare slots located on the reverse side of the main board (item 9 on Figure 2.1.1).
Serial bus module locations are shown on the image below.
Rear side view of main board
2.2.1)
Gas detector positioning
Detectors must be placed near any potential gas leaks or where potential stagnation may
occur following gas leaks from different points.
To detect explosive gas with specific weight heavier than air's, detectors must be placed
about 30 cm from the floor. Vice versa, to detect gas with specific weight lighter than air's,
detectors must be placed about 30 cm from the ceiling.
To detect toxic gas or oxygen, we suggest you place detectors about 150 cm from the floor
in areas were individuals to be protected frequently sojourn.
For correct positioning, also keep in mind that any dispersed gas clouds move according to
air currents (doors, windows, air conditioning, etc.).
The detector must be protected against direct contact and immersion in water.
Furthermore, it is best to install detectors in easily accessible positions for periodic
maintenance purposes.
In any case, please refer to gas detector manuals for correct positioning.
2.2.2)
Detector connections
Detectors with RS485 output
Detectors with RS485 digital outputs are directly connected to the RS485 bus.
4 wires are required in this type of connection: 2 for the RS485 serial bus and 2 for
device power supply. For this reason we suggest you use two different wires or a
single wire with suitable features as described below.
The RS485 serial bus must be connected with an EIA RS 485 connection wire: No. 2
wires with 0.22/0.35 mm
2
section with shield (TWISTED PAIR). Nominal capacity
between conductors < 50 pF/m, nominal impedance 120 ohm. Total line length with
this type of connection must not exceed 1,000 metres. An example of a
recommended wire is a BELDEN 9841 or similar wire (EIA RS485 data transmission
wire). Only connect detectors (and IN and OUT modules) in cascade. Avoid tree or
delta connection since they reduce interference immunity.
Serial bus
modules 1
and 2
Serial bus
module 3 and 4
spare positions
