MT4061E Rev.2
15/10/2019
Pagina 14 di 45
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 cable
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 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 following diagram explains the bus connection of gas detectors and remote
STG/IN8-S or STG/OUT16-S modules to the control panel.
