Omron DEVICENET -, Operation Manual

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27
Network Configuration Overview Section 2-1
Note The branch line length is not just the distance between T-branch Taps or the
distance from a node to a T-branch Tap on the branch line; it is the total dis-
tance from the trunk line to the end of the branch.
Definition of Total
Branch Line Length
The total branch line length is the sum of all branch lines in the network.
In the example above, the total branch line length is 40 m. The maximum total
branch line length is 39 m for 500-kbps communications, so a baud rate of
250 kbps or 125 kbps must be used in this network.
(Total branch line length) = (1) + (2) + (3) + (4) + (5) + (6) + (7) + (8) + (9) +
(10) + (11) + (12) + (13)
= 2 + 3 + 1 + 2 + 2 + 6 + 2 + 2 + 1 + 1 + 6 + 6 + 6
= 40 m
Current Capacities of
the Cables
The current capacity of the trunk line is 8 A when a Thick Cable is used, 3 A
when a Thin Cable is used, and 5 A when a Special Flat Cable is used. To
estimate the current through the trunk line, add up the current consumption of
all the nodes in each direction from the communications power supply. The
total current consumption must be no more than 8 A when a Thick Cable is
used, 3 A when a Thin Cable is used, and 5 A when a Special Flat Cable is
used.
With branch lines, the current carrying capacity of the branch line is inversely
proportional to the length of the line. The current capacity of a branch line is
4.57/L (A) where L is the length of the branch line (m). Verify that the total cur-
4 m
1 m 1 m
1 m
2 m
Branch line
(6 m max.)
Node
T-branch
Tap
Node 1
Example 1 Example 2
Node 2
Node 3 Node 4
Trunk
line
Trunk line
T-branch
Tap A
These lengths
are not branch
line lengths.
Branch line
length
T-branch Tap A to Node 1: 5 m
T-branch Tap A to Node 2: 6 m
T-branch Tap A to Node 3: 5 m
T-branch Tap A to Node 4: 6 m
All branch lines are 6 m or less.
(5) 2 m
(3) 1 m
(1) 2 m
(4) 2 m
(2) 3 m (6) 6 m
(7) 2 m
(8) 2 m
(10) 1 m
(9)
1 m
(11) 6 m (12) 6 m (13)
6 m
Terminator
Node
Terminator
Node
Node Node Node Node Node
Node
Node
Node
Node
Total branch line length
is the total of all of
these branch lines.
(40 m in this case)