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

FC 300 Design Guide
9. RS-485 Installation and Set-up
9.1. RS-485 Installation and Set-up
9.1.1. Overview
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.
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
converters 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
frequencies. 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, par-
ticularly in installations where there are long lengths of cable.
To prevent impedance mismatch, always use the same type of cable throughout the entire net-
work. 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
9.1.2. Network Connection
Connect the frequency converter to the RS-485 network as follows (see also dia-
gram):
1.
2.
Connect signal wires to terminal 68 (P+) and terminal 69 (N-) on the main control board
of the frequency converter.
Connect the cable screen to the cable clamps.
NB!
Screened, twisted-pair cables are recommended in order to reduce noise between
conductors.
MG.33.B9.02 - VLT ® is a registered Danfoss trademark
9. RS-485 Installation and Set-up
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