The following hierarchy is of importance in the process control to handle all startup and shutdown tasks. First among them is process control level which includes the systems for operation, monitoring, engineering and diagnostics. Then comes process level where server, and processing units are connected to process control level by a terminal bus employing the technique of plant bus to the automation level for data exchange. Next is automation level which consists of programmable logic controllers which provide operating idleness. The direct process interface to the I & C is provided by individual control level. Analog and binary signal transmitters, actuators like motors and electrically actuated valves etc. comes in field level which is connected to the individual control level by copper wires. Fiber optic technology is used in bus system which includes terminal bus and plant bus sections.
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