Engineering Documentation

Table Of Contents
Chapter 4 Equipment Controllers
BACnet DXR2 Room Automation Station
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143 | 231
Fig. 87: Lab DXR2 network – Daisy chain
Not recommended
Single DXR2 failure could affect multiple rooms (depends on device location)
Sensor Bus Communication (SCOM) Connection
SCOM provides dedicated digital sensor communication.
Star topology for 24Vac wiring (incl. 0..10V signal)
Diameter of 24Vac wire is a limiting factor for the distance between controller and
sensor
SCOM must be wired in Line topology.
SCOM is an RS-485 communication any cable for BACnet/MSTP could be used
(e.g. Belden 9925). It is also allowed to use a 2 x 2-wire twisted pair to wire back
and forth for cable saving purpose and for installing the terminators in the
controller enclosure (e.g. J-Y(St)Y 2x2x0.8 or KNX cable)
Consider 120 Ohm terminators on the two ends in case the total SCOM length is >
30m /100ft
Additional terminals needed at the controller for SCOM and 24 Vac wiring
3 cables are connected to the sensor (2 Knock-outs available at the DXA.S04P1-
B)
Fig. 88: SCOM connection for DXR2.x17C...