Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 102)

Publication DNET-UM072C-EN-P - July 2004
4-24 Determine Power Requirements
3. Find the voltages for each device in section 2 using the equation for
thick cable.
SUM {[(L
n
x (0.0045)) + (N
t
x (0.005))] x I
n
} < 4.65V.
A.[(200 x (0.0045)) + (1 x (0.005))] x 0.25 = 0.23V
B.[(400 x (0.0045)) + (2 x (0.005))] x 1.5 = 2.72V
C.[(800 x (0.0045)) + (3 x (0.005))] x 0.5 = 1.81V
4. Add each device’s voltage together to find the total voltage for section 2.
0.23 + 2.72 + 1.81 = 4.76V
Since the total voltage in section 2 exceeds 4.65V, the system will not operate
properly (4.76V > 4.65V).
Attempt to correct this overload by moving the power supply 91m (300ft)
toward the overloaded section. Now there are four devices in section 1 and
two devices in section 2. Once you’ve moved the power supply, try the
calculations again.
1. Find the voltages for each device in section 1 using the equation for
thick cable.
SUM {[(L
n
x (0.0045)) + (N
t
x (0.005))] x I
n
} < 4.65V.
A.[(100 x (0.0045)) + (1 x (0.005))] x 0.25 = 0.11V
B.[(400 x (0.0045)) + (2 x (0.005))] x 0.25 = 0.45V
C.[(700 x (0.0045)) + (3 x (0.005))] x 0.25 = 0.79V
D4
0.25A
D5
1.5A
D6
0.5A
Results
power
supply
section 1 section 2
335m
(1100 ft)
213m
(700 ft)
122m
(400 ft)
30m
(100 ft) 30m
(100 ft)
152m
(500 ft)
T T T T T T PT
D4 D3 D2 D1 D5 D6
0.25A 0.25A 0.25A 0.25A 1.5A 0.5A
TR TR
TR = terminating resistorT = T-Port tap
PT = PowerTap D = device
41859
0.25A
D2
0.25A
D1
0.25A
D3
D4
0.25A