The one basic quality of DCS is to distribute its functions into relatively small sets of semiautonomous subsystems, and they are connected using a high-speed communication network. The distribution of functions has several advantages over more classical process computer architectures, including:
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Lower exposure to component or subsystem failure and better isolation to facilitate maintenance and upgrades
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Better partitioning of application requirements for different process areas
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Improved modularity for application development
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Facilitation of geographical distribution, which reduces installation costs (reduced wiring) and provides more localized operational supervision while offering global access to information and control capabilities
The DCS automate the process by integrating advanced regulatory control, logic and sequential control. The “control” aspect of the modern DCS has expanded to include information that is capable of supporting such manufacturing enterprise applications as:
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activity-based cost accounting
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production scheduling and dispatching
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preventative or predictive maintenance scheduling
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validation of employee job certification and readiness
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information exchange with business, logistics, and transportation applications
The systems aspect of a DCS organizes the command structure and information flow between its constituent parts to act as a single automation system that unifies the various subsystems, including:
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process signal input and conditioning
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process actuator signal output
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regulatory, combinatorial, and sequence logic and procedural and supervisory control
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human readable process displays of current values, alarms, trends, and calculations
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human actions including setpoint changes, manual overrides and alarm handling
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application subsystems such as process optimization and manufacturing support
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information-storage subsystems
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communications subsystems