Omron DEVICENET Operation Manual page 120

Step 2: Evaluating the Configuration with Calculations
Example Configuration 2
Terminating
Resistor
Branch lines:
Thin cable
Group 3:(30 × 0.015 + 3 × 0.005) × 0.30 = 0.1395 V
Group 4:(40 × 0.015 + 4 × 0.005) × 0.15 = 0.093 V
Total voltage drop = 0.0039 + 0.0651 + 0.1395 + 0.093 = 0.3015 V ≤ 4.65 V
In this case, formula 1 is satisfied, so the power supply can supply just the
communications power.
2. Calculate the voltage drop when the communications power supply pro-
vides both communications power and internal circuit power (formula 2.)
Group 1:(1 × 0.015 + 1 × 0.005) × 0.545 = 0.0109 V
Group 2:(20 × 0.015 + 2 × 0.005) × 0.84 = 0.2604 V
Group 3:(30 × 0.015 + 3 × 0.005) × 1.1 = 0.5115 V
Group 4:(40 × 0.015 + 4 × 0.005) × 0.85 = 0.527 V
Total voltage drop = 0.0109 + 0.2604 + 0.5115 + 0.527 = 1.3098 V ≥ 0.65 V
In this case, formula 2 is not satisfied, so the power supply cannot supply
the communications power and internal circuit power.
In this example, the power supply is near the middle of the trunk line. The
trunk line is thick cable and the branch lines are thin cable.
System 1
20 m
Trunk line:
10 m
Thick cable
4-point Analog
Master Input Unit
Node Node
16-point 4-point Analog
Output Unit Input Unit
Node Node
. .
7
. .
. Units .
16-point 4-point Analog
Output Unit Input Unit
Node Node
Group 1 Group 2
45 mA + 30 mA × 7 = 255 mA 30 mA × 10 = 300 mA
90 mA × 7 = 630 mA 80 mA × 10 = 800 mA
1. Calculate the voltage drop when the communications power supply pro-
vides communications power only (formula 1.)
a) System 1 (Left Side)
Group 1:(20 × 0.015 + 2 × 0.005) × 0.255 = 0.0791 V
Group 2:(10 × 0.015 + 1 × 0.005) × 0.3 = 0.0465 V
Total voltage drop = 0.0791 + 0.0465 = 0.1256 V ≤ 4.65 V
In this case, formula 1 is satisfied on the left side.
b) System 2 (Right Side)
Group 3:(10 × 0.015 + 1 × 0.005) × 0.15 = 0.0233 V
Group 4:(30 × 0.015 + 2 × 0.005) × 0.15 = 0.069 V
Total voltage drop = 0.0233 + 0.069 = 0.0923 V ≤ 4.65 V
In this case, formula 1 is satisfied on the right side.
2. Calculate the voltage drop when the communications power supply pro-
vides both communications power and internal circuit power (formula 2.)
a) System 1 (Left Side)
Power
Supply
System 2
30 m
10 m
16-point
Input Unit
Node
16-point
Input Unit
Node
10
Units
.
.
16-point
.
Input Unit
Node
Group 3
30 mA × 5 = 150 mA
70 mA × 5 = 350 mA
Section 3-5
Terminating
Resistor
2-point Analog
Output Unit
Node
2-point Analog
Output Unit
Node
5 5
Units Units
.
.
2-point Analog
.
Output Unit
Node
Group 4
30 mA × 5 = 150 mA
140 mA × 5 = 700 mA
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