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5: Communication Installation
Electro
Industries/GaugeTech
The Leader In Power Monitoring and Smart Grid Solutions
Electro
Industries/GaugeTech
The Leader In Power Monitoring and Smart Grid Solutions
• Protect cables from sources of electrical noise.
• Avoid both “Star” and “Tee” connections (see Figure 5.6).
• 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 5.5. You
may also connect the shield to earth-ground at one point.
• Termination Resistors (RT) may be needed on both ends of longer length transmis-
sion 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 5.5 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.
Figure 5.5: RS485 Daisy Chain Connection
Twisted pair, shielded (SH) cable
R
T
+
-
SH
R
T
+
-
SH
+
-
SH
+
-
SH
Slave device 1
Slave device 2
Last Slave device N
Master device
Earth Connection, preferably at
single location
Twisted pair, shielded (SH) cable
Twisted pair, shielded (SH) cable
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