Abstract
Almost without exception, process control computer systems have been to some extent development projects. Most have been applied to commercially operated production units, for which the improved control of the process provides adequate financial justification for the computer installation. In such cases, conflict arises between the use of the computer for the basic control of a continuously running process and the development of new programs. One solution is to provide α comprehensive conventional standby control system so that the computer can be taken off line at any time; alternatively, to limit the system to supervisory set point control . This approach is very expensive and there is α tendency for the computer to become purely α research too l, imposed upon α rather unwilling production unit. Another common approach is to use a relatively expensive computer system with backing store and full time-sharing facilities. This second method is justifiable when the process control computer is required to carry out α large amount of off-line work such as scheduling and invoicing, but is unnecessarily expensive if the computer’s principal task is process control.
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