Network Design Considerations 2-11
SIMATIC TIWAY I Series 500 NIM User Manual
Local Line Cable Installation (continued)
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 rearrangement of
plant equipment.
•Since network system noise is usually picked up by its interconnecting
wiring, steps should be taken at the outset to bypass or eliminate 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 and 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.
To calculate the 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 TIWAY I trunk cable or a pair of taps separated by less than the
minimum tap node separation distance. The minimum 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 upon 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 2-4 illustrates three typical examples of tap
spacing.
Planning
Considerations
Local Line Tap
Spacing