Omron OMNUC W Series Manual page 109

6 DeviceNet Communications
6.3.1 Providing the Communications Power Supply
Terminating
resistor
(DeviceNet special cable)
Node
0.1 A
6
Example
The following example shows a Network that requires power to be supplied for 240 m on
thick cable. The power supply is located in the center of the network. Because the power
supply is in the center, the maximum current will flow both to the left and to the right,
enabling the supply of at least twice the maximum current as when the power supply is
placed on the end of the network. The current consumption for individual nodes is as fol-
lows:
Trunk line
3 m max.
Communications
Node
Node
0.25 A 0.2 A
120 m
Total power supply length on left = Total power supply length on right = 120 m
Total current consumption on left: 0.1 + 0.25 + 0.2 = 0.55 A
Total current consumption on right: 0.15 + 0.25 + 0.15 = 0.55 A
Maximum current for the left side of the thick cable (see previous table) = approx. 2.5 A
Maximum current for the right side of the thick cable (see previous table)
= approx. 2.5 A
(using straight line approximation between 100 to 150 m)
Because the total current flow (0.55 A) is less than the maximum current (approx. 2.5 A)
on both the left and the right sides, the power supply can be placed at the center of the
network and provide power to all nodes.
(DeviceNet special cable)
Node
power supply
0.15 A
120 m
: Trunk line
: Power supply cable
6-12
Terminating
Trunk line
resistor
Node
Node
0.25 A 0.15 A