7 RS-485 Installation and Set-up
7.1 RS-485
7.1.1 Overview
RS-485 is a two-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.
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 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 important, including at high frequencies. Thus,
connect a large surface of the shield to ground, for
example, with a cable clamp or a conductive cable
connector. It may be necessary to apply potential-
equalizing cables to maintain the same ground potential
throughout the network - particularly in installations with
long cables.
To prevent impedance mismatch, always use the same
type of cable throughout the entire network. When
connecting a motor to the adjustable frequency drive,
always use shielded motor cable.
Cable Shielded twisted pair (STP)
Impedance
[Ω]
120
Cable length
(ft [m])
Max. 4,000 ft [1200 m] (including drop lines)
Max. 1,650 ft [500 m] station-to-station
Table 7.1 Cable
7.1.2
Network Connection
Connect the adjustable frequency drive to the RS-485
network as follows (see also Figure 7.1):
1. Connect signal wires to terminal 68 (P+) and
terminal 69 (N-) on the main control board of the
adjustable frequency drive.
2. Connect the cable shield to the cable clamps.
NOTICE!
Shielded, twisted-pair cables are recommended to
reduce noise between conductors.
61 68 69
N
P
COMM. GND
130BB795.10
Figure 7.1 Network Connection
RS-485 Installation and Set... Design Guide
86 Danfoss A/S © Rev. 2014-01-14 All rights reserved. MG18C522
77
To Next Page
Loading...
Need help?
General