Omron DEVICENET Operation Manual page 116

Step 1: Evaluating the Configuration with Graphs
Terminating
Node
Resistor
1.1 A
Trunk line
(5-wire cable)
Terminating
Node
Resistor
1.1 A
nected in the very center of the Network. Placing it slightly off center allows
power to be supplied properly to all nodes.
The current consumption for individual nodes is as follows:
Power Supply Tap
Trunk line
(5-wire cable)
Node Node
1.25 A 0.5 A
3 m
max.
120 m
Total power supply length on left = Total power supply length on right = 120 m
Total current consumption on left: 1.1 + 1.25 + 0.5 = 2.85 A
Total current consumption on right: 0.25 + 0.25 + 0.85 = 1.35 A
Maximum current on the left side (see table for thick cable) = approx. 2.5 A
Maximum current on the left side (see table for thick cable) = approx. 2.5 A
(using straight line approximation between 100 to 150 m)
Because the total current flow on the left side (2.85 A) is greater than the max-
imum current allowed on the left side (2.56 A), the power supply cannot sup-
ply current to all nodes properly when it is placed at the center of the network.
This problem can be corrected by moving the communications power supply
as shown in the following diagram.
Power Supply Tap
Node Node
3 m
1.25 A 0.5 A
max.
Power
Supply
100 m
Total power supply length on left = 100 m
Total power supply length on right = 140 m
Total current consumption on left: 1.1 + 1.25 = 2.35 A
Total current consumption on right: 0.5 + 0.25 + 0.25 + 0.85 = 1.85 A
Maximum current for 100 m on the left (see table for thick cable) = 2.93 A
Maximum current for 140 m on the right (see table for thick cable) = 2.1 A
(using straight line approximation between 100 to 150 m)
Because the total current flow on both the left and right sides is now less than
the allowed maximum current, the power supply can be placed as shown in
the diagram and supply current properly to all nodes.
Trunk line
(5-wire cable)
Node Node
0.25 A 0.25 A
Power
Supply
120 m
Trunk line
(5-wire cable)
Node Node
0.25 A 0.25 A
140 m
Section 3-4
Terminating
Node
Resistor
0.85 A
Trunk line
Power supply cable
Terminating
Node
Resistor
0.85 A
Trunk line
Power supply cable
95