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12 RS-485 Installation and Set-up
12.1 Installation and Set-up
12.1.1 Overview
RS-485 is a 2-wire bus interface compatible with multi-drop network topology, that is, 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, see
Illustration 12.1 .
Illustration 12.1 RS-485 Bus Interface
NOTICE
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 frequency converters or a
biased termination resistor network. Always use screened
twisted pair (STP) cable for bus cabling, and follow good
common installation practice.
Low-impedance ground connection of the screen at every
node is important, including at high frequencies. Thus,
connect a large surface of the screen to ground, for
example with a cable clamp or a conductive cable gland. It
may be necessary to apply potential-equalising cables to
maintain the same earth 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 frequency converter, always use
screened motor cable.
Cable Screened twisted pair (STP)
Impedance [
Ω
] 120
Cable length
[m] Max. 1200 (including drop lines)
Max. 500 station-to-station
Table 12.1 Cable Specifications
RS-485 Installation and Set...
VLT
®
AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
176 MG33BF02 - Rev. 2013-12-20
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