Physical Structures

Connecting individual devices in the most expedient way is the goal of any network technology. Generally, in industrial control systems three popular topologies have been successfully used. They are the star, the bus, and the ring network systems. More typical are the network systems associated with traditional distributed control systems. On a larger scale, “traditional” supervisory control and data acquisition (SCADA) systems have been used for control actions and information gathering from beyond the plant. These larger systems, distributed control and SCADA, generally may employ several topology types within the same network. Local and global networks for process control systems are made of electrical wire cable or a fiber optic cable. Coaxial cable has a central conductor surrounded by an outer tube like conductor. Coaxial cable does a very acceptable job as a communication network media. Fiber-optic communications have been used in control systems since the early 1980s.