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Distributed Control Systems. Being A Lecture Note of Process. Dynamics and Control (CHE 532). Engr. Prof. Abdulwahab GIWA.
Typology: Lecture notes
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Introduction
Figure 1. A typical distributed control system (DCS) (Source: Seborg, 2004)
run application software such as databases, spreadsheets, financial software, and simulation software via an OPC (object linking and embedding for process control) interface. These stations can be used for e-mail and as webservers, for remote diagnosis, configuration, and even for operation of devices that have an IP (Internet Protocol) address. Application stations can communicate with the main database contained in on-line mass storage systems.
disk drives that are used to store active data, including on- line and historical databases and non-memory resident programs. Memory resident programs are also stored to allow loading at system start-up.
( 5 ) Engineering Workstations: They are similar to operator stations but can also be used as programming terminals to develop system software. This arrangement reduces compatibility problems between the development and application environments for the system software. Typically, users may also develop their own application programs on these workstations.
( 6 ) Operator Stations: These typically comprised colour graphics monitors with special keyboards to perform dedicated functions. The control processes from the workstations are supervised by operators. These stations may also be connected directly to printers for alarm logging, printing reports, or process graphics.
( 8 ) Fieldbuses/Smart Devices: An increasing number of field- mounted devices are available that support digital communication of the process input/output (I/O) in addition to, or in place of, the traditional 4 - 20 mA current signal. These devices possess greater functionality, resulting in reduced setup time, improved control, combined functionality of separate devices, and control-valve diagnostic capabilities. Digital communication also allows the control system to become completely distributed where, for example, a PID control algorithm could reside in a valve positioner or in a sensor/transmitter.
( 9 ) Real-Time Clocks: Generally, process control systems must respond to events in a timely manner and should have the capability of real-time control. As such, some DCSs are connected to atomic clock signals for maintenance of accuracy.
