Rs485 Installation And Set-Up; Rs485; Overview - Danfoss VLT DriveMotor FCP 106 Programming Manual

RS485 Installation and Set-...

3 RS485 Installation and Set-up

3.1 RS485

3.1.1 Overview

RS485 is a 2-wire bus interface compatible with multi-drop network topology. 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 1 network segment.
Repeaters divide network segments, see Illustration 3.1.
Illustration 3.1 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 (S800) 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-equalizing cables to
maintain the same ground potential throughout the
network - particularly in installations with long cables.
MG03N202
Programming Guide
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
Impedance [Ω]
Cable length
[m]
Table 3.1 Cable Specifications
Danfoss A/S © 11/2015 All rights reserved.
Screened twisted pair (STP)
120
Maximum 1200 (including drop lines)
Maximum 500 station-to-station
3 3
15