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. UC-7420's built-in 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. UC-7400's serial ports connect to various sensors and meters, and one of UC's Ethernet ports connects to the LAN. The user application program installed in the UC 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 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 UCs 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 UC 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 of Using Moxa's Embedded Computer