Parker H Series, Installation & Service Instructions Manual

Page: 233 / 344

Publication DNET-UM072C-EN-P - July 2004
Determine Power Requirements 4-21
Use the Equation
A supply that is not end-connected creates two sections of trunk line. Evaluate
each section independently.
SUM {[(L
n
x (R
c
)) + (N
t
x (0.005))] x I
n
} < 4.65V
Term Definition
L
n
L
=
The distance (m or ft) between the device and the power supply, excluding the drop line distance.
n = The number of a device being evaluated, starting with one for the device closest to the power supply and increasing
by one for the next device. The equation sums the calculated drop for each device and compares it to 4.65V.
R
c
Thick cable
Metric 0.015
Ω
/m
English 0.0045
Ω
/ft
Thin cable
Metric 0.069
Ω
/m
English 0.021
Ω
/ft
Flat Cable
Metric 0.019
Ω
/m
English 0.0058
Ω
/ft
N
t
The number of taps between the device being evaluated and the power supply. For example:
when a device is the first one closest to the power supply, this number is 1
when a device has one device between it and the power supply, this number is 2
when 10 devices exist between the evaluated device and the power supply, this number is 11.
For devices attached to a DeviceBox tap or DevicePort tap, treat the tap as one tap. The currents for all devices attached
to one of these taps should be summed and used with the equation only once.
(0.005)
The nominal-contact resistance used for every connection to the trunk line.
I
n
I = The current drawn from the cable system by the device.For currents within 90% of the maximum, use the nominal
device current. Otherwise, use the maximum rated current of the device. For DeviceBox taps or DevicePort taps, sum the
currents of all the attached devices, and count the tap as one tap.
n = The number of a device being evaluated, starting with one for the device closest to the power supply and increasing
by one for the next device.
4.65V The maximum voltage drop allowed on the DeviceNet trunk line. This is the total cable system voltage drop of 5.00V
minus 0.35V reserved for drop line voltage drop.