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© 1996-98 Liebert Corporation
5
Rev. (08-JULY-98)
segment. A segment is defined as the network of modules between main nodes. Main nodes can be
represented by a gateway module, or a repeater (part no. REPOPT). A repeater can be used to end one
segment and begin another, all on the same CMnet.
It is recommended that only a dedicated, 22AWG to 18AWG twisted pair copper wire be used for
CMnet (EIA-485) wiring. Wire sizes smaller than 22 gauge or wires that are not twisted may cause
intermittent communication problems.
NOTE: For further explanation of communications wiring, see the Technical Handbook.
System Architecture
The Liebert Architecture is designed to support both large and small systems. Small systems (those
using less than 50 control modules) require only a single SiteGate-232 which serves the entire Control
Module Network, or CMnet (see Figure 2). The SiteGate-232 communicates with the workstation via a
EIA-232 serial communication port. A second EIA-232 port can be used for communication with
another operator workstation or a portable field computer via modem or direct EIA-232 connection.
The SiteGate-232 communicates with the CMnet through a EIA-485 port. This CMnet is a peer-to-peer
local area network which uses a "token-passing" protocol to allow all control modules to communicate
with one another with equal authority. Each control module is capable of stand-alone DDC (Direct
Digital Control), thus increasing system reliability and performance.
Mounting
Mount the SiteGate-232 in an enclosure using the four holes provided on the module's cover plate (see
Figure 3). Recommended screw size is 8. Make sure that nothing comes in contact with the back of
the printed circuit board, and leave approximately 2 inches on each side for wiring.
The SiteGate-232 is designed to be mounted inside the building envelope. All warranties are void if
mounted outside.
Figure 3: Mounting the SiteGate-232
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