Installation Instructions

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Siemens Desigo Desigo Room automation - Engineering, mounting and installation CM111043en_14
Smart Infrastructure SCOM sensor bus 2020-10-30
11 SCOM sensor bus
SCOM provides dedicated digital sensor communication:
· Interface type RS485 – non-insulated (reference wire is connected
to system neutral ⏊)
· Baud rate 115200
· Cable type KNX or BACnet MS/TP cable, e.g. Belden 9925
· Max. cable length 800 m (2600 ft)
· Topology Line
· Network terminators (120 Ohm, 0.5 W) are recommended at the ends of the
network between + and – if the total network length exceeds 30 m (100 ft)
· Short-circuit proof and protection against faulty wiring at max. AC 24V
· Polarity + / - must be observed
As an example, a system with sensors and damper actuators is shown.
· AC 24 V and signal cable: star topology.
Current and cable cross section limit the total distance to max. 80 m (260 ft), see
chapter 7.1.3
· SCOM: Line topology: Using 2 x twisted pair cable allows forth and back cabling
in the same cable - for cable saving purposes and for placing the network
terminators in the enclosure / installation box
· Additional terminals are needed in the controller enclosure for SCOM daisy
chain and AC 24 V wiring
Use
Connection of SCOM
devices