TABLE OF CONTENTS The majority of modern control systems today are programmable electronic systems (PESs). They are typically supplied with display systems, printers, and communication links. PESs include the following systems:
direct digital control (DDC)
distributed control systems (DCSs)
programmable controllers (PLCs) and personal computers (PCs)
microprocessor-based standalone PID controllers
Before the introduction of PESs, standalone indicators, controllers, recorders, annunciators, and the like were used for monitoring and control. Such standalone devices are still used for small applications, but for large applications they would be expensive and relatively difficult to modify. In addition, these standalone devices have limited features that are not acceptable in today's control requirements, take up a large amount of space in the control room, and have limit capacity for field-to-control room data exchange.
When implementing PESs, plant personnel should always keep the following key items in mind:
The simplest solution that meets the project requirements is generally the best approach.
The operator, who is really the end user, should be involved from the time the equipment is selected, through the design and implementation phases, and including graphics design and color selection. In addition, the operator must be well trained in how to use the system.
A successful implementation depends crucially on the quality of engineering and equipment.
A PES is made of hardware and software. The hardware consists of input modules (accepting analog, discrete, or digital signals), control modules (which perform the logic), output modules (which send out analog, discrete, or digital signals), communication components, and operator...
