17-10-2017, 11:30 AM
A control system manages, orders, directs or regulates the behavior of other devices or systems using control loops. Industrial control systems that are used to control processes or machines. The control system is used to automatically control the process. The control system compares the value or status of the variable process (PV) that is controlled with the desired value or the set point (SP) and applies the difference as a control signal to carry the variable output of the plant process to the same value the control signal. For sequential and combinational logic, software logic is used as a programmable logic controller.
There are two common classes of control action, open loop control systems and closed loop control systems. In an open loop control system, the control action of the controller is independent of the "process output". A good example of this is a central heating boiler controlled only by a timer, so that the heat is applied for a constant time, regardless of the temperature of the building. (The control action is the connection / disconnection of the boiler.
In a closed-loop control system, the control action of the controller depends on the desired and current process output values. In the case of boiler analogy, a thermostat would be used to monitor the temperature of the building and feed back to the signal to ensure that the output controller maintains the temperature of the building to that set in the thermostat.
Therefore, a closed loop controller has a feedback circuit which ensures that the controller exerts a control action to control a process variable with the same value as the "reference input" or "setpoint" (SP) . For this reason, closed loop controllers are also called reaction controllers.