7 RS-485 Installation and Setup
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 unit 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 very important, including at high frequencies. This
can be achieved by connecting a large surface of the
screen to ground, for example by means of 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 instal-
lations where there are long lengths of cable.
To prevent impedance mismatch, always use the same
type of cable throughout the entire network.
Cable: Screened twisted pair (STP)
Impedance: 120 Ohm
Cable length: Max. 1200 m (including drop lines)
Max. 500 m station-to-station
7.1.2 Network Connection
Connect the unit to the RS-485 network as follows (see
also diagram):
1.
Connect signal wires to terminal 68 (P+) and
terminal 69 (N-) on the main control board of the
unit.
2.
Connect the cable screen to the cable clamps.
NOTE
Screened, twisted-pair cables are recommended in order to
reduce noise between conductors.
130BB022.10
61
68
69
Illustration 7.1 Network Terminal Connection
130BB021.10
12 13 18 19 27 29 32 33 20 37
Remove jumper to enable Safe Stop
61 68 69
39 42 50 53 54 55
Illustration 7.2 Control card terminals
7.1.3 RS-485 Bus Termination
Use the terminator dip switch on the main control board
of the unit to terminate the RS-485 bus.
RS-485 Installation and Set...
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