Tuesday, November 2, 2010

LAN Communication System for PLCs





In any complex assembly process the need for rapid information flow is critical. Conditions at any point in the process may impact the entire process. This need for information flow often requires that intelligent devices such as PLCs, intelligent sensors, drives, computers, and operator interface systems be interconnected by one or more local area networks (LAN).

A LAN is a communication system designed for private use in a limited area. LANs are used in office areas as well as in manufacturing environments; however, LANs used in industrial applications must be unsuitable for office-grade equipment. Industrial environments typically have a high level of electrical noise and a greater range of temperature and humidity than found in office environments.

Specifications for industrial LANs vary considerably depending upon the requirements of the application. Issues such as the amount of data to be communicated, the rate at which data must be communicated, the number of devices to be connected, the reliability and noise immunity required, compatibility with other networks, and cost are examples of important considerations. In general, it is not possible for one network type to maximize all characteristics. For instance, a network that can communicate a large amount of data in a short time is likely to be more expensive than a network that has more limited requirements. Therefore, many factories use multi level structure for communication.



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