Installation And Set-Up - Danfoss VLT AQUA Drive Design Manual

VLT ® AQUA Drive Design Guide
7. RS-485 Installation and Set-up
7.1. RS-485 Installation and Set-up
7.1.1. 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 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 very important, also at high
frequencies. This can be achieved by connecting a large surface of the shield to ground, by means
of a cable clamp or a conductive cable gland, for example. 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 net-
work. When connecting a motor to the adjustable frequency drive, always use shielded motor
cable.
Cable: Shielded twisted pair (STP)
Impedance: 120 Ohm
Cable length: Max. 3,396 ft [1,200 m] (including drop lines)
Max. 1,640 ft [500 m] station-to-station
7.1.2. Network Connection
Connect the adjustable frequency drive to the RS-485 network as follows (see also
diagram):
1.
2.
Connect signal wires to terminal 68 (P+) and terminal 69 (N-) on the main control board
of the adjustable frequency drive.
Connect the cable shield to the cable clamps.
NOTE
Shielded, twisted-pair cables are recommended in order to reduce noise between
conductors.
MG.20.N2.22 - VLT ® is a registered Danfoss trademark.
7. RS-485 Installation and Set-up
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