2-2-10 Grounding Methods - Omron DEVICENET Operation Manual

Network Configuration

2-2-10 Grounding Methods

Proper Grounding
Practices
Example A
Power Supply Tap
V+
CAN H
Shield (S)
CAN L
V−
V+ V− FG
Communications
power supply
42
Configuration A:
Shared communications
and internal circuit
power supply
Correct
Configuration B:
Shared communications
and internal circuit
power supply
Incorrect
Note The low voltage limit for the internal circuit power supply is higher than the low
voltage limit for the communications power supply. To meet the voltage speci-
fications for the internal circuit power supply, be sure to follow the specifica-
tions listed in SECTION 3 Communications Power Supply Methods.
Ground the DeviceNet shield wire to 100 Ω max. at one and only one point in
the network. Grounding more than one point can cause ground loops and
noise in the network.
Generally, the communications power supply's FG terminal is grounded to
100 Ω max. and connected to the V- terminal and the Power Supply Tap's
shield (S) terminal, as shown in example A below. It is also acceptable to con-
nect the communications power supply's FG terminal and the V- terminal and
ground the network from the Power Supply Tap's shield (S) terminal, as shown
in example B below.
In either case, ground the network as close to the center of the network as
possible.
V+
CAN H
Shield (S) DeviceNet
cable
CAN L
V−
V+ V− S
Ground to
100 Ω max.
When there are two or more communications power supplies in the network,
determine which power supply is closest to the center of the network. Connect
Communications Internal circuit
power supply power supply
24 VDC
−
V− V+ +
Communications Internal circuit
power supply power supply
24 VDC
−
Vv V+ +
Example B
Power Supply Tap
V+
CAN H
Shield (S)
CAN L
V−
V+ V− S
V+ V− FG
Communications
power supply
Section 2-2
Communications Internal circuit
power supply power supply
24 VDC
−
V− V+ +
Communications Internal circuit
power supply power supply
24 VDC
−
V− V+ +
V+
CAN H
DeviceNet
Shield (S)
cable
CAN L
V−
Ground to
100 Ω max.