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Figure 5.5 shows the detail of a 2-wire RS485 connection.
NOTES:
For All RS485 Connections:
• Use a shielded twisted pair cable 22 AWG (0.33 mm2) or larger, grounding the shield at one end 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 be assigned a unique address: refer to Chapter 5 of the Communicator EXT User's Manual for
instructions.
• Protect cables from sources of electrical noise.
• Avoid both "Star" and "Tee" connections (see Figure 5.7).
• 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 5.6. You may also connect
the shield to earth-ground at one point.
• Termination Resistors (RT) may be needed on both ends of 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 5.6 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.
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Electro Industries/GaugeTech
Figure 5.5: 2-wire RS485 Connection
Figure 5.6: RS485 Daisy Chain Connection
Doc #: E145701
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