Process control is extensively used throughout industry to enable mass production and control of continuous processes such as oil refining, paper manufacturing, chemical production, food processing and power generation. Process control allows the automation of these complex processes to be remotely monitored by a small staff of operating personnel.
Typically in a large distributed system such as the Substation Monitoring and Control System shown above, a Master Data Centre will monitor and control systems operating in a number of remote stations--often located miles away. For many years Serial Communications has been used to control and collect data from equipment via embedded or host computer systems. The traditional way to configure these systems is to run long, bulky, shielded serial (RS-232 or RS-485) cables between multiple Remote Terminal Units (RTUs) and a local host PC at the substation. The RTUs process sensor inputs and transmit that information to the local PC. That PC is then connected via phone line or radio tower to the Master Data Centre. The result is a system that transmits data and enables remote monitoring, but does not enable the RTU itself to be remotely controlled.
Network-enabling the process control system leverages the serial equipment currently in place, significantly reduces the cost of deploying additional RTUs (because Ethernet cable can be run for about one tenth the cost of shielded serial cable), and will allow remote access and control of each RTU from any PC or server on the network, regardless of operating system. Further, the device server can also be connected to other monitoring equipment such as energy meters, which can then also be remotely monitored and controlled.
Device servers offer the additional versatility of being invisible to software applications. Thus they are compatible with all industrial protocols, because they function simply as pass-through devices. The device server does not interpret proprietary signals, it simply encapsulates any RS-232/422/485 serial signal in a TCP/IP packet, transports it over Ethernet, then strips away the TCP/IP information, leaving the PC or server to interpret the serial data using any supported language or protocols. This means a single device server can be used with any combination of equipment using any number of different protocols.
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