Overview of Control System

A control system is a device, or set of devices, that manages, commands, directs or regulates the behavior of other device(s) or system(s). Industrial control systems are used in industrial production. The applications of control system or significance can be studied or evaluated during control system engineering as progresses.

Industrial control system (ICS): It is a general term that encompasses several types of control systems used in industrial production, including Supervisory Control and Data Acquisition (SCADA) systems, Distributed Control Systems (DCS), and other smaller control system configurations such as Programmable Logic Controllers (PLC) often found in the industrial sectors and critical infrastructures.

ICSs are typically used in industries such as electrical, water, oil, gas and data. Based on information received from remote stations, automated or operator-driven supervisory commands can be pushed to remote station control devices, which are often referred to as field devices.

Field devices control local operations such as opening and closing valves and breakers, collecting data from sensor systems, and monitoring the local environment for alarm conditions. 

Historical Perspective of Control System

Distributed Control System (DCS) systems generally refer as distributed control system design that exist in industrial process plants (e.g., oil and gas, refining, chemical, pharmaceutical, some food & beverage, water and wastewater, pulp and paper, utility power, mining, metals).

The inception of DCS system came based on need to gather widely spared data & control system in real time on high – bandwidth, low-latency data network. It is common for loop controls to extend all the way to the top-level controllers in a DCS, as everything works in real time. These systems evolved from a need to extend pneumatic control systems beyond just a small cell area of a refinery.

Programable Logic Control (PLC) evolved out of a need to replace racks of relays in ladder form. The relay racks were not particularly reliable, were difficult to rewire, and were difficult to diagnose.

PLC control tends to be used in very regular, high-speed binary controls, such as controlling a high-speed printing press. Originally, PLC equipment did not have remote I/O racks, and many couldn't even perform more than rudimentary analog controls.

Supervisory Control And Data Acquisition (SCADA) history is rooted in distribution applications, such as power, natural gas, and water pipelines, where there is a need to gather remote data through potentially unreliable or intermittent low-bandwidth/high-latency links.

SCADA systems use open-loop control with sites that are widely separated geographically. A SCADA system uses RTUs (remote terminal units, also referred to as remote telemetry units) to send supervisory data back to a control centre. Most RTU systems always did have some limited capacity to handle local controls while the master station is not available. However, over the years RTU systems have grown more and more capable of handling local controls.

The selection of control system is very critical as system engineering and its implementation can cause delay in the project completion. 

Simple thumb rule to be followed "Overview of Control System" whenever the analog input/ outputs are comparatively more, then Distributed control system to be used where as the digital inputs / outputs are more, then the Programmable logic control system is preferred. But this is not the only evaluation criteria for the system. 

The system concept and other aspects are covered in the next section.  Stay tune and keep watching our page eFunda for more information/article.

From

eFunda Team