Introduction
High-tech power companies around the world are conducting research to identify economical ways to simplify a power plant's automatic protection and warning system, but without sacrificing reliability. One of the main components of such a system is a computing device that can handle protocol conversion, data acquisition, monitoring, and control.
Since the computing device must also be able to withstand the rigors of an industrial environment, a natural choice would be to use one or more Industrial PCs. However, the cost of this option could be high, since each IPC must be fitted with two network cards and at least one multiport serial board.
Another option is MOXA's UC-7420 embedded
computer, a front-end embedded computer that comes with
8 RS-232/422/485 serial ports, dual Ethernet ports, wireless
LAN capability, and an industrial strength no fan, no hard
drive design. The UC-7420's pre-installed Linux operating
system makes it easy to install software, and the Flash
expansion
slot lets users add additional memory space as needed.
Single LAN System
A single LAN system can be used
for non-critical systems that do not require redundancy.
In this example, Ethernet-enabled protection devices
located around the plant are connected directly to the
plant's LAN. The UC-7400's serial ports connect to various
sensors and meters, and one of the UC-7420's Ethernet
ports connects to the LAN. The user application program
installed
in
the UC-7420 is set up for protocol conversion, data acquisition
from the attached serial ports, and monitoring and control
of the protection devices. Additional programming and
data recording are handled by the main host.
Dual-LAN System
One of the UC-7420's key features
is its dual-LAN ports, which can be used to create a
redundant system to enhance system reliability. As shown
in the diagram, the system includes a "Main host" and
a "Backup host," and can include one or more
UC-7420 units installed at various locations around the
plant to collect serial data, process the data, and then
retransmit the data through the embedded computer's LAN
ports. The UC-7420 units can also communicate directly
with the protection devices. For example, the embedded
computer
could be programmed to issue alerts if one of the protection
devices receives an abnormal reading. During normal operation,
signals transmitted by the embedded computers are transmitted
over both the black and orange lines, and consequently
reach the main host, backup host, and all protection
devices via two separate routes.
The system could fail in
one of several different ways. For example, even if Switch
A fails, the Main host crashes, and one of the Ethernet
cables gets disconnected, each embedded computer will still
be able to communicate with each protection device and
with
the
backup
host. By designing redundancy into the system software,
the Backup host can be set up to take over automatically
until the Main host is back up and running.
Benefits
- No fan, no hard drive design for longer MTBF
- CompactFlash slot
for adding gigabytes of storage space
- Multiple connection options for greater networking versatility
- Programmability gives system integrators infinite possibilities
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