Serial Communication - GE AF-600 FP Series Design And Installation Manual

Installation
2 2
Illustration 2.22 Location of Terminals 53 and 54 Switches

2.5.9 Serial Communication

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.
Repeaters divide network segments. 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 earth (ground) connection of the screen at
every node is important, including at high frequencies.
Thus, connect a large surface of the screen to earth
(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 earth (ground)
potential throughout the network. Particularly in instal-
lations 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.
24
TM
AF-600 FP Design and Installation Guide
Cable
Impedance
Max. cable
length [m]
Table 2.10 Cable Information
130BT310.10
DET-768b
Screened twisted pair (STP)
120 Ω
1200 (including drop lines)
500 station-to-station