Control System

Open Loop & Closed Loop Control System

A control system is a device, or set of devices, that manages, commands, directs or regulates the behavior of other devices or systems. Industrial control systems are used in industrial production for controlling equipment or machines.
There are two common classes of control systems:-
1. open loop control systems :-  In open loop control systems output is generated based on inputs.

2. closed loop control systems:-  In closed loop control systems current output is taken into. consideration and corrections are made based on feedback. A closed loop system is also called a feedback control system. The human body
is a classic example of feedback systems

Linear control systems use linear negative feedback to produce a control signal mathematically based on other variables, with a view to maintain the controlled process within an acceptable operating range.The output from a linear control system into the controlled process may be in the form of a

cascade control systems: (a) temperature control of a stirred tank reactor, (b) governor of a DC motor with motor current control

directly variable signal, such as a valve that may be 0 or 100% open or anywhere in between.this is not feasible and so, after calculating the current required corrective signal, a linear control system may repeatedly switch an actuator, such as a pump, motor or heater, fully on and then fully off again, regulating the duty cycle using pulse-width modulation.

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