3-2
Section
Limitations on the Network Configuration
25
Note Combining Thick and Thin Cables
The most distant nodes can also be connected by a combination of thin and thick
cables. When these cables are combined, the following conditions must be met
and the maximum network length will be shorter than when only thick cables are
used. Also, when combining cables, be sure that the maximum current capacity
of the cables is not exceeded. Refer to 3-3 Sharing the Communications Power
Supply.
Baud rate
Maximum network length
500 kbps
L
THICK
+ L
THIN
100 m
250 kbps
L
THICK
+ 2.5 x L
THIN
250 m
125 kbps
L
THICK
+ 5 x L
THIN
500 m
L
THICK
: Length of the thick cable; L
THIN:
Length of thin cable
Configuration Example
Communications
power supply
Node
6 m
Node
Node
Node
Terminal block
with Terminating Resistor
Maximum network length
thin
cable
24 m
Thin cable
125 m
Thick cable
20 m
Thin cable
1 m
L
THICK
+ L
THIN
= 175
100 m
500 kbps
NG
L
THICK
+ 2.5 x L
THIN
= 125 + 2.5 x 50 = 250
250 m
250 kbps
OK
L
THICK
+ 5 x L
THIN
= 125 + 5 x 50 = 375
500 m
125 kbps
OK
The results of the above formulas indicate that 250 kbps and 125 kbps can be
used as the baud rates for this configuration example.
Even when the above conditions are met, however, the current flowing through
the cables must not exceed the permissible current capacity. ( Refer to 3-3 Shar-
ing the Communications Power Supply.)
3-2-3 Drop Line Lengths
A drop line length is measured from the point in the trunk line where the original
branch was made to the end of the branch. The maximum length of a drop line is
6 m. It is possible to make a secondary branch from a drop line.
