Rs-485 Installation And Set-Up - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

RS-485 Installation and Set-up

RS-485 Installation and Set-up
Overview
RS-485 is a two-wire bus interface compatible with multi-drop network topology, i.e. nodes can be con-
nected as a bus, or via drop cables from a common trunk line. A total of 32 nodes can be connected to
one network segment.
Network segments are divided up by repeaters. Please 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 frequency con-
verters or a biased termination resistor network. Always use screened twisted pair (STP) cable for bus
cabling, and always follow good common installation practice.
Low-impedance ground connection of the screen at every node is very important, including at high fre-
quencies. This can be achieved by connecting a large surface of the screen to ground, for example by
means of a cable clamp or a conductive cable gland. It may be necessary to apply potential-equalizing
cables to maintain the same ground potential throughout the network, particularly in installations where
there are long lengths of cable.
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: 120 Ohm
Cable length: Max. 1200 m (including drop lines)
Max. 500 m station-to-station
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