Omron 3G3MV-PDRT2 - Communications Line Noise Prevention; Grounding the Network

Chapter 3
3-20
Setup and Wiring
3-3 Communications Line Noise Prevention
3-3-1 Communications Line Noise
The communications line sends and receives high-speed pulse signals, and checks whether the data
is correct by checking the sequence of the signals. If the amount of noise on the communications line
is too great, the interference will alter the communications signal data, and communications will be
impossible. Communications lines are more sensitive and require higher speeds than normal I/O
lines, so be sure that noise does not interfere with communications. Use the preventative noise coun-
termeasures described here when configuring the system to ensure smooth system start up.
3-3-2 Grounding the Network
■ Grounding the Network
The DeviceNet Network must be grounded at only one location so that a ground loop is not created.
The ground should also be connected as close as possible to the center of the Network. Connect the
cable shield to the ground terminal on the communications power supply and then connect to a
ground of 100
Ω max., as shown in the following diagram.
If more than one communications power supply is connected to the same Network, ground only the
one nearest the center of the Network. Do not connect the shield wire at the other power supplies.
Note 1. Always ground the communications cable shield at one and only one location in the Network.
Note 2. Always ground to 100
Ω or less.
Note 3. Always use a separate ground. Never use the same ground as for Inverters or other drive
system devices.
CAN H
CAN L
CAN H
CAN L
FG
Power Supply Tap
Shield
Ground terminal
Communications cable
Communications
power supply
Ground (100 Ω max.)
Shield