control system

A control system is a set of mechanical or electronic devices that regulates other devices or systems by way of control loops. Typically, control systems are computerized.

Control systems are a central part of industry and of automation. The types of control loops that regulate these processes include industrial control systems (ICS) such as supervisory control and data acquisition (SCADA) and distributed control systems (DCS).

Control systems are used to enhance production, efficiency and safety in many areas, including:

• Agriculture
• Chemical plants
• Pulp and paper mills
• Quality control
• Boiler controls and power plant
• Nuclear power plants
• Environmental control
• Water treatment plants
• Sewage treatment plants
• Food and food processing
• Metal and mines
• Pharmaceutical manufacturing
• Sugar refining plants

There are two main types of control loops: Open loops, which operate with human input, and closed loops, which are fully autonomous. Some loops can be switched between closed and open modes. When open, a switchable loop is manually controlled and when closed it is fully automated.

Programmable logic controllers (PLCs), programmable automation controllers (PACs), remote terminal units (RTUs), control servers, intelligent electronic devices (IEDs) and sensors are some of the elements of control loops that are in turn a part of control systems. The control loops that make up control systems are generally made themselves of a sensor, a controller and a final control element. The sensor reads the process variable or a related measurement. The controller receives the signal from the sensor and then forwards it to instrumentation, to remote terminal units and to final control elements where the process variable is adjusted, to be kept constant at what is known as a set point.