Omron NT631 Handling the Shield on RS-422A/485 Cables, Connecting the Ground Wire, Terminals

Connecting to the Host’s RS-422A/485 Port		Section 5-2
	TRM-RDA	Function
	terminals
	Shorted	Terminal resistance is applied.
		Short only at the NT631/NT631C connected to the end of an
		RS-422A/485 cable.
	Open	Terminal resistance is not applied.
		Leave the terminals open when connecting an NT631/NT631C
		anywhere other than at the end of the RS-422A/485 cable.

Note Before connecting or disconnecting cables between devices, make sure that the power supply to all of the connected devices (NT631/NT631C, PLC, etc.) is OFF.

Reference: • The internal circuit of the NT631/NT631C is shown below.

-	RDA	Making a connection here inserts a terminator between
	Terminal resistor (120 Ω)
		+ (RDB) and - (RDA).
	TRM
+	RDB

•For details on setting the terminal resistance of the host, refer to Setting methods for each type of the communications.

5-2-8 Handling the Shield on RS-422A/485 Cables

Perform the following procedures to connect, process the shield, and connect to ground for communications systems using the RS-422A/485. Incorrect con- nection may result in communications errors with the host.

Connecting the Ground Wire

The PT has a functional ground terminal (FG: ).

1,2,3... 1. Ground according to Figure (a) for normal grounding.

•Connect the ground terminal (GR) of the devices to the functional ground

(FG: ).

Make sure that each signal line is grounded at only one point and ground to 100 Ω max.

•Short the LG terminal of the PLC to the ground terminal (GR).

•Use a wire gauge of at least 2mm2 for the ground wire.

•Refer to the manual for individual Communications Units for details on proper wiring procedures.

2.Do not ground the functional ground (FG: ) of the PT if it is mounted to the same panel as devices that generate noise, such as motors or invert- ers, as shown in Figure (b).

Preparing the Shield of RS-422A/485 Connectors

Always prepare RS-422A/485 cable shields properly. Otherwise, communica- tions errors may occur with the host.

Ground only one end of the shield when connecting the ground terminal (GR)

of the devices to the functional ground (FG: ), and grounding each signal line at only one point and to 100 Ω max, as shown in Figure (a).

Ground both ends of the shield when not grounding the functional ground (FG: ) of the PT, as shown in Figure (b).

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