As control systems become more complex, they require more effective communication schemes between the system components. Some machine and process control systems require that programmable controllers be interconnected, so that data can be passed among them
easily to accomplish the control task.
Other systems require a plantwide communication system that centralizes functions, such as data acquisition, system monitoring, maintenance diagnostics, and management production reporting, thus providing maximum efficiency and productivity.
Local Area Networks
The term local area network (LAN) is used to describe a communication network designed
to link computers and their peripherals within the same building or site. A LAN is a high-speed, mediumdistance communication system.
For most LANs, the maximum distance between two nodes in the network is at least one mile, and the transmission speed ranges from 1 to 20 megabaud. Also, most local networks support
at least 100 stations, or nodes.
A special type of LAN, the industrial network, is one which meets the following criteria:
? capable of supporting real-time control.
? high data integrity (error detection).
? high noise immunity.
? high reliability in harsh environments.
? and suitable for large installations.