The fundamentals of a Control System include measuring an error signal and then adjusting the system to reach the desired course or outcome. If the system deviates too fast and the control system is unable to adjust the course or outcome, the Control System is inadequate to manage the disturbances. 

Some basic examples of a control system include a cruise control in a motor vehicle, temperature control in a building, the chemical concentrations in drinking water, the speed of a conveyor belt in a process plant. 

Control Systems are used in domestic applications, general industry, military and virtually every modern vehicle in the world. Control Systems are very common in SCADA and Industrial Automation systems. 

Control Systems are used in Industrial Automation to regulate how devices operate in real time. In a closed-loop control system the controller (RTU, PLCS, DCS) feedback (error) signal is used to adjust the control variable such that the process is constantly trying to match the operational set point. The system described here is generally referred to as a control-loop. The controller must have a suitable dynamic response to be able to adjust the system to remain stable. If the controller is unable to adjust to a stable condition (ie with minimal hunting) the control-loop is said to be “out of control”. In very complex processes a single closed-loop control system may be insufficient to stabilize the process. Cascaded control-loops may be used in situations where there is moderate complexity and the process is “changing quickly” in respect to time, however Advanced Process Controllers may be required for slow moving processes like distilling, bio-reactors etc.