Danfoss VLT FC51, Руководство по конструкции, Страница: 67 / 94

8 RS-485 Installation and Set-up
8.1 RS-485 Installation and Set-up
8.1.1 Overview
RS-485 is a 2-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 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 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-equalising cables to
maintain the same earth 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 frequency converter, always use
screened motor cable.
Cable Screened twisted pair (STP)
Impedance
[
Ω
]
120
Cable length
[m] Max. 1200 (including drop lines)
Max. 500 station-to-station
Table 8.1 Cable Specifications
8.1.2 Network Connection
Connect the frequency converter to the RS-485 network
as follows (see also
Illustration 8.1 ):
1. Connect signal wires to terminal 68 (P+) and
terminal 69 (N-) on the main control board of the
frequency converter.
2. Connect the cable screen to the cable clamps.
NOTICE
Screened, twisted-pair cables are recommended to
reduce noise between conductors.
61 68 69
N P COMM. GND
130BB795.10
Illustration 8.1 Network Connection
8.1.3 Frequency Converter Hardware Set-
up
Use the terminator dip switch on the main control board
of the frequency converter to terminate the RS-485 bus.
130BB966.10
Illustration 8.2 Terminator Switch Factory Setting
The factory setting for the dip switch is OFF.
RS-485 Installation and Set...
VLT
®
Micro Drive FC 51 Design Guide
MG02K302 - Rev. 2013-12-03 65
8 8