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Figure 5.3 shows the detail of a 2-wire RS485 connection.
NOTES:
For All RS485 Connections:
• Use a shielded twisted pair cable and ground the shield, preferably at one location only.
• Establish point-to-point configurations for each device on a RS485 bus: connect (+) terminals to (+) terminals;
connect (-) terminals to (-) terminals.
• You may connect up to 31 meters on a single bus using RS485. Before assembling the bus, each meter must have
a unique address: refer to Chapter 5 of the
• Protect cables from sources of electrical noise.
• Avoid both "Star" and "Tee" connections (see Figure 5.5).
• No more than two cables should be connected at any one point on an RS485 network, whether the connections
are for devices, converters, or terminal strips.
• Include all segments when calculating the total cable length of a network. If you are not using an RS485 repeater,
the maximum length for cable connecting all devices is 4000 feet (1219.20 meters).
• Connect shield to RS485 Master and individual devices as shown in Figure 5.4. You may also connect the shield
to earth-ground at one point.
• Termination Resistors (R T ) may be needed on both ends for longer length transmission lines. However, since
the meter has some level of termination internally, Termination Resistors may not be needed. When they are used,
the value of the Termination Resistors is determined by the electrical parameters of the cable.
Figure 5.4 shows a representation of an RS485 Daisy Chain connection. Refer to Section 5.1.2.1 for details on
RS485 connection for the Unicom 2500.
e
Electro Industries/Gauge Tech
Figure 5.3: 2-wire RS485 Connection
Communicator EXT 3.0 User's Manual
Figure 5.4: RS485 Daisy Chain Connection
Doc# E149701
for instructions.
5-3
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