
B-64044EN/01 CONNECTION 1.CONNECTING THE DeviceNet
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This expression cannot be used when the same power supply is used
for communication and the NC, so make another review.
• Conditional expression (summation of voltage drops by main
lines)
Σ (Ln × Rc + Nt × 0.005) × ln ≤ 5V
Ln: Distance between the power supply and the nodes
(excluding the branch length)
Rc: Maximum cable resistance (0.015 Ω/m for thick-wire cables
or 0.069 Ω/m for thin-wire cables)
Nt: Number of taps between nodes and the power supply
In: Current consumption required by the communication units
of nodes
0.005 Ω = Contact resistance of a tap
When nodes are placed on only one side of the power supply (sample
configuration 1)
Terminator
Power supply for
communication
Terminator
Node
Power
tap
50mA
Node
5
nodes
Node
40mA
40mA
Node
30mA
Node
8
nodes
Node
30mA
30mA
Node
50mA
Node
10
nodes
Node
50mA
50mA
1m
30m
50m
<Group 1>
50mA+40mA×5=250mA
<Group 2>
30mA×8=240mA
<Group 3>
50mA×10=500mA
Power supply for
communication
Branch line:
thin-wire cable
Main cable:
thick-wire
Calculate the voltage drop for each group.
Group 1: (1×0.015+1×0.005)×0.25=0.005V
Group 2: (30×0.015+2×0.005)×0.24=0.1104V
Group 3: (50×0.015+3×0.005)×0.50=0.3825V
Sum of the voltage drops = 0.005 + 0.1104 + 0.3825 = 0.4979 V ≥
4.65 V
Therefore, the conditional expression is not satisfied in this case.