Serial Communication - Danfoss VLT FC 103 Instruction Manual

Installation

2.4.7 Serial Communication

RS-485 is a two-wire bus interface compatible with multi-
drop network topology, i.e., nodes can be connected as a
bus, or via drop cables from a common trunk line. A total
of 32 nodes can be connected to one network segment.
Repeaters divide network segments. Note that 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.
Terminate each segment at both ends using either the
termination switch (S801) of the adjustable frequency
drives or a biased termination resistor network. Always use
shielded twisted pair (STP) cable for bus cabling, and
always follow good common installation practice.
Low-impedance ground connection of the shield at every
node is important, including at high frequencies. Thus,
connect a large surface of the shield to ground, for
example with a cable clamp or a conductive cable
connector. It may be necessary to apply potential-
equalizing cables to maintain the same ground potential
throughout the network. Particularly in installations with
long cables.
To prevent impedance mismatch, always use the same
type of cable throughout the entire network. When
connecting a motor to the adjustable frequency drive,
always use shielded motor cable.
Cable Shielded twisted pair (STP)
120 Ω
Impedance
Max. cable 4,000 ft [1,200 m] (including drop lines)
length (ft [m]) 1,650 ft [500 m] station-to-station
Table 2.10 Cable Information
MG16E222
Instruction Manual
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
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