Rs-485 Serial Communication - Danfoss VLT FC 102 Operating Instructions Manual

Electrical Installation

4.8.6 RS-485 Serial Communication

Up to 32 nodes can be connected as a bus, or via drop
cables from a common trunk line to 1 network segment.
Repeaters can divide network segments. Each repeater
functions as a node within the segment in which it is
installed. Each node connected within a given network
must have a unique node address, across all segments.
•
Connect RS-485 serial communication wiring to
terminals (+)68 and (-)69.
•
Terminate each segment at both ends, using
either the termination switch (bus term on/off,
see Illustration 4.13) on the frequency converters,
or a biased termination resistor network.
•
Connect a large surface of the screen to ground,
for example with a cable clamp or a conductive
cable gland.
•
Apply potential-equalising cables to maintain the
same ground potential throughout the network.
•
Use the same type of cable throughout the entire
network to prevent impedance mismatch.
Cable Screened twisted pair (STP)
120 Ω
Impedance
Max. cable 1200 (including drop lines)
length [m] 500 station-to-station
Table 4.4 Cable Information
®
VLT HVAC Drive Operating Instructions
MG11AJ02 - Rev. 2013-07-31
4 4
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