Omron OMNUC W Series Manual page 110

Step 2: Calculating the Best Location of the Actual Nodes
Go to Step 2 if the best location for the power supply cannot be determined from the graphs.
The second method calculates the best location for each actual node and does not estimate
the worst possible configuration for the power supply.
Basically, in the DeviceNet network the permissible maximum voltage drop within the sys-
tem can be specified at 5 V for a power supply line (+V or -V), by calculating the specifica-
tions for the voltage of the communications power supply (24 V DC) and the input voltage
of the communications power supply of each device (11 to 25 V DC).
Of the permissible maximum voltage drop within the system (5 V), the permissible voltage
drop in the trunk lines and drop lines are 4.65 V and 0.35 V respectively. The following
explains the formula in case the communications power supply and the internal circuit
power supply are provided individually.
For details about voltage drop and the formula when the communications power supply and
the internal circuit power supply are the same, refer to the DeviceNet Operation Manual
(W267-E1- ).
Formulas
Try to calculate the best location for each node using the condition formula below. If the best
location for each node can be determined using the formula, the specifications for the power
supply to each node can also be met. Do not exceed the maximum current capacity of the
cable (Thick cable: 8 A and thin cable: 3 A).
× ×
S +
(Ln Rc Nt 0.05)
Ln: The distance between the power supply and the nodes (not including the lengths of the
drop lines)
Rc: Maximum cable resistance per cable
(Thick cable: 0.015 W/m, thin cable: 0.069 W/m])
Nt: The number of T-branch Taps between each node and the power supply
In: The consumption current required for the communications power supply for each node
0.005 Ω = The contact resistance of the T-branch Taps
Note If nodes are placed on both sides of the power supply, calculate in each direction and make sure the
following conditions are satisfied.
Voltage drop (V) on left trunk line
Voltage drop (V) on right trunk line
6.3 Precautions for Communications Line Design
× ≤
In 4.65 V
≤
4.65 V
≤
4.65 V
6-13
6