SYSTEMP – Installation Operation Manual (IOM SYSTEMP rev.N)

Table Of Contents
78
11.1 RS485 SERIAL COMMUNICATION BOARD CONNECTION (Modbus RTU - BACnet MS/TP)
The SySmart
3
microprocessors can be connected to a supervision and/or BMS (Building Management System) network,
which adopts the Modbus RTU (Standard) or BACnet MS/TP (Accessory) protocol through a dedicated RS485 serial board.
Using this type of board it is also possible to connect the gateways necessary to interface the SySmart
3
with networks that
use dierent protocols to those available as accessories.
To create a connection to the RS485 board, simply connect the units from the terminals on it (see wiring diagram for further
information):
A Unit 1
B Unit 2
C BMS / Supervision system/Gateway
D RS485 output terminals
E RS485 input terminals
F RS485 connection cable
In order to guarantee correct serial communication between the network-connected units, it may be necessary to insert a
120 Ω terminating resistor.
SySmart
3
microprocessors tted with suitable micro switches for activating suitable 120 Ω terminating resistors if set to ON.
Set micro switch RS485LT2 (1) to ON to activate the 120 Ω
terminating resistor
The type of cable to be used for the connection must have the following features:
Main features of serial communication cable
Type Data transmission cable
Application EIA RS485 Interface
Shielding Tinned copper braid - Cover at least 65%
Cross-section and number of conductors 2 x 0.35 mm
2
- AWG 22 + 1 x 0.35 mm
2
- AWG 22
Stranding Twisted pairs
Nominal loss (1 MHz) dB/100m 1.64
Maximum DC resistance for conductor at 20°C Ω/km 49
Insulation resistance at 20°C MΩ*km 5000
Mutual capacitance c-c / c-s nF/km 40 - 70
Inductance mH/km 0.7
Impedance Ohm 120 +/- 0.12
Maximum length m 100
Example
A
D
B
C
F
D E
F