
Network Design Considerations
2-12
TIWAY 1 TI505 NIM User Manual
2.3.4 Planning
Considerations
Some
major points to consider
during the planning phase of a Local Line network are as
follows:
From
the start, allow for system growth. This means making provisions for the
attachment of additional computing devices by routing cables through all
probable
areas of future plant expansion.
Always
make the network flexible
enough to allow for re-arrangement of plant
equipment.
Since
network system noise is usually picked up by the interconnecting wiring,
try to avoid routing the communization wiring near noise sources such as
large
motor
starters, high current switches, and transformers.
If
cable redundancy is desired, the two cables should never be routed along the
same
path, since the environmental or other factors
which disable one cable will
very
likely disable the second.
A
detailed record of design and routing should be created
and maintained. This
record
should be complete enough to enable a user to trace and physically locate
all
cable paths and hardware components.
2.3.5
Local Line T
ap Spacing
To
calculate the minimum
distance between tap nodes, use the length of the dropline at
the
last tap node. A tap node consists of either a single tap on the TIW
A
Y I trunk cable or a
pair
of taps separated by less than the minimum tap node separation distance. The mini
-
mum
distance between a given tap node and the next tap
node on the network is equal to
one-half
the length of the longer drop line at the given node.
No
limit is placed on the number of NIMs that can be daisy-chained to
form a drop line off
the
main trunk as long as the resulting drop
length is no greater than 100 feet. Figure 3
illustrates
three typical examples of tap spacing.
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