MT4412E Rev.3 15/10/2019 Page 15 of 30
Detectors with RS485 output
Gas detectors provided with RS485 serial communication are connected directly to the RS485
bus of the MULTISCAN 8+ central unit. The STG/IN8-S input module and STG/OUT16-S output
module are also connected to the RS485 bus.
4 conductors are needed for this type of connection: 2 for the RS485 serial and 2 for the power
supply of devices. For this reason, we suggest that two different wires or a single wire is used.
with the features described below.
-) The RS485 serial bus must be connected with an EIA RS 485 connection wire: No. 2 wires with
0.22/0.35 mm2 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 cable is a BELDEN 9841 or similar wire (EIA RS485
data transmission wire). Only connect detectors (and IN and OUT modules) in a "cascading"
manner. Avoid tree or star connections since they reduce interference immunity.
-) The power supply to the detectors (and IN and OUT modules on the bus) must be connected
with a 2-core wire with adequate section based on the number of connected devices, their
distance from the power supply and each device’s consumption (please see the technical manual
enclosed with gas detectors for this purpose).
Note: each detector connected on the RS485 line must have its own univocal address between 1
and 255 (247 for the ModBus protocol). Please see the gas detector technical manual for address
settings.
The diagram below shows the connection of IN and OUT detectors and remote modules on the
RS485 bus of the central unit
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