MT3401E.doc rev.0
21/05/13
Pagina 14 di 86
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 illustrates the connection on the bus of gas detectors and remote
IN/8 or OUT/16 modules to the control panel.
