5 RS485 Installation and Set-up
5.1 Introduction
5.1.1 Overview
RS485 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 5.1 RS485 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 ground potential throughout the
network, particularly in installations with long cables.
To prevent impedance mismatch, 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 5.1 Cable Specifications
RS485 Installation and Set-...
Design Guide
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