GE Industrial Solutions EntelliPro ES - Manual (Page 143)

4.6 EP OS MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL
CHAPTER 4: COMMUNICATION
4.1.5 RS-485 connections
On the upper left side of the EntelliPro ES is a nine-pin connector for the Modbus connection. A mating connector is
included for customer connection. The pin assignments for the connector are shown in Figure 4-3 and section
2.1.1.4. If
the EntelliPro ES is to be the first or last device on the RS-485 network, it must be terminated with a terminating resistor
or RC network. Place the resistor or RC network between the appropriate + and - connections on the mating connector.
(See section 4.1.6 for details on RS-485 termination).
Figure 4-3: RS-485 connection.
Please study and follow the RS-485 grounding shielding considerations and termination rules in the following sections
to ensure the correct operation of your Modbus segments.
4.1.6 RS-485 termination considerations
Per the EIA485 standard, every RS-485 network must be terminated at both ends. If the EntelliPro ES is the first device,
place a 120
Ω, 1/2 W resistor between the + and - connectors of the RS-485 port . If the EntelliPro ES is the last device,
place the resistor between the + and – connectors of the RS-485 port . Figure 4-3 illustrates appropriate termination of
an RS-485 segment at the EntelliPro ES.
If the termination resistor power dissipation is an issue, then an RC termination should be considered to minimize the
power dissipation. A 120 ohm/1/2W and 1nF/16-25V capacitor should be used.
4.1.7 Grounding shielding considerations
Figure 4-2 illustrates correct wiring for communications and shield grounding. Follow this example to create a secure
grounding point for each device on the network. Any surge will dissipate locally without being carried up or down the
network to other devices, thus minimizing the chance for damage to devices due to surge or EMI.
NOTE: The EntelliPro ES’s shield terminal is not directly grounded. If you wish to connect the RS-485 shield to ground at
the EntelliPro ES, you must also make a connection from the shield terminal to the grounding screw on the EntelliPro ES.
Use AWG #12–14 wire for this connection.