Omron OMNUC W Series Manual page 106

Note 1. Configuration is recommended for a single power supply to several nodes.
2. If power supply specifications cannot be met with a single power supply when the current
capacity of the thick cable exceeds 8 A even after the power supply location is modified, use
more than one communications power supply.
3. In configuration , the power can be supplied bi–directionally to the trunk line as long as each
current capacity is 8 A or less when using thick cable. Accordingly, it is possible to have a
configuration with a total maximum current capacity of up to 16 A.
4. Consider changing to thick cable to meet specifications if the current capacity of the thin cable
exceeds 3 A when using thin cable for the trunk line.
Setting the Location of the Power Supply
Determine whether or not the current can be supplied normally by finding the current capac-
ity required by each node and the voltage drop in the cables to be used to provide power.
Calculate the values below in advance.
• The current capacity required by each node
• The distance between the power supply and each node
Calculating the Location of the Power Supply
There are two methods to find the best location of the communications power supply on the
trunk line.
• Simple calculation from a graph
• Calculation by formula (Calculating the voltage drop from resistance and current con-
sumption of the communications cables)
Each drop line must satisfy the equation in Basic Concept on page 6-6, which represents the
relationship between the drop line length and the current capacity for the drop line.
Note 1. From the graph, a hypothetical power supply location can be determined if the conditions
calculated in the graph are met by estimating the worst configuration (that has the maximum
voltage drop as shown in the diagram below).
Communications
power supply
2. Even if the power supply specifications cannot be met using the graph, the conditions can be
met and a hypothetical power supply location determined by using the formula.
3. When the communications power supply and the internal circuit power supply are the same, use
the formula to calculate a hypothetical power supply location because it cannot be determined
by using the graph.
6.3 Precautions for Communications Line Design
6-9
6
Node
Node
Node
Node