Rockwell Automation DeviceNet Media Design Installation Guide User 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

x (0.0045)) + (N

x (0.005))] x I

} < 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

x (0.0045)) + (N

x (0.005))] x I

} < 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

0.25A

1.5A

0.5A

Results

power
supply

section 1

section 2

335m
(1100 ft)

213m
(700 ft)

122m
(400 ft)

30m
(100 ft)

152m
(500 ft)

0.25A

1.5A

0.5A

TR = terminating resistorT = T-Port tap
PT = PowerTap D = device

41859

0.25A