14-10-2017, 09:44 AM
A control system manages, orders, directs or regulates the behavior of other devices or systems using control loops. It can range from an individual heating controller that uses a thermostat that controls a domestic boiler to large industrial control systems that are used to control processes or machines.
For continuously modulated control, the feedback control system is used to automatically control a process or operation. The control system compares the value or status of the process variable (PV) controlled with the desired value or set point (SP), and applies the difference as a control signal to carry the variable process output the plant at the same value as the control signal. For sequential and combinatorial logic, software logic is used, as in 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 boiler on / off. The process variable is the build temperature).
In a closed-loop control system, the control action of the controller depends on the desired and actual process output values. In the case of boiler analogy, this will use a thermostat to control the temperature of the building and therefore will feed back a signal to ensure that the output of the 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.
For continuously modulated control, the feedback control system is used to automatically control a process or operation. The control system compares the value or status of the process variable (PV) controlled with the desired value or set point (SP), and applies the difference as a control signal to carry the variable process output the plant at the same value as the control signal. For sequential and combinatorial logic, software logic is used, as in 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 boiler on / off. The process variable is the build temperature).
In a closed-loop control system, the control action of the controller depends on the desired and actual process output values. In the case of boiler analogy, this will use a thermostat to control the temperature of the building and therefore will feed back a signal to ensure that the output of the 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.