Contemporary Control Systems PCI20U Adapters - Manual (Page 5)

TD030700-0I
G
5
FIELD CONNECTIONS
The PCI20U is available in several transceiver options. Each transceiver,
which is matched to a particular cable type, is identified by a suffix appended
to the model numbers. The capabilities of each transceiver differs.
Figure 2 — A hub is required to extend bus segments.
-CXB
Coaxial Bus
For hubless systems, the -CXB transceiver can be used. NIMs are
interconnected with RG-62/u cables and BNC Tee connectors. Each -CXB
NIM represents a high-impedance connection in both the powered and
unpowered states. Therefore, passive termination must be applied to both
ends of a bus segment. Use BNC-style 93 (nominal) ohm resistors at each
end. The maximum segment length is 1000 feet and the maximum number of
NIMs that can be connected to a segment is eight.
To extend a bus segment beyond 1000 feet, an active hub is required. If the
hub port is of the -CXS type, connection can be made if a few simple rules
are followed. Only connect this type of hub at the end of a segment. Do not
connect the hub to the middle of a segment since the hub port is not of the
high impedance type. Do not terminate the end which attaches to the hub
port since a -CXS port effectively terminates the end of a bus segment.
Simply remove the BNC Tee connector and terminator from the segment end
and attach the cable directly to the hub port. The opposite segment end still
requires termination if no hub connection is being made.
-CXS
Coaxial Star
In a coaxial star system, NIMs and hubs are interconnected in a point-to-point
fashion using coaxial cable. A NIM can connect to one other NIM or
can
connect to an unused port on a hub. Hub-to-hub connections are allowed.
In a two-node system, simply connect the two -CXS NIMs together using
RG-62/u coaxial cable. The length of cable cannot exceed 2000 feet.
If more than two NIMs are used on a network, either an active or passive hub
is required. With passive hubs, a maximum of four NIMs can be
interconnected.
Unused ports on the passive hub must be terminated with a
93 ohm (nominal)
resistor.
The maximum length allowed between a passive hub port and a NIM
is 100 feet.