What is Closed Loop Control System and Open Loop Control System

Today we are going to discuss about what is Open Loop Control System & What is Closed Loop Control System. And you will also learn about different Controller Terminology such as Process Variable, Setpoint, Error Signal, and Controller Modes.

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Video content:
Open Loop Control System
It is manual control of a device or system.
It has no feedback, and it cannot correct for unwanted disturbances, and consequently, is non regulation.
A hand valve is good example of this.
Examples of open loop controls are systems that use timers; for example, a laundry machine with wash/rinse/spin cycles, or a bottle filling station controlled by a PLC.

What is Close Loop control System?
It is automatic control of a device or system, and it is self regulating. It uses negative feedback for stabilization and corrections of unwanted disturbances.
This system may have one of the three types of feedback control
Negative Feedback, Positive Feedback, Oscillation Type Feedback.
In most systems, negative feedback is the preferred method, because it provides corrective action to stabilized a process when there are unforeseen or non controllable disturbances to the system.

Controller Terminology:
Process Variable(PV)-It is physical variable being measured such as pressure, temperature, level etc.
Setpoint(SP)- It is the desired quantity or value of the product of the process in automatic control.
Error Signal-It is the difference between PV and SP signals. Direct action occurs when the error signal = PV-SP(Process Variable is greater than Setpoint Value)
Reverse Action- It occurs when the error signal = SP - PV(Setpoint is greater than Process Variable
Controller Modes- It defines the Proportional band function, the integral function,and the derivative function for a P controller, P + I controller, or a P + I + D controller.

Functions of each component Of Close Loop Control System:
What is Functions of Controller?
Controller performs a number of different functions,
(i) It compares the PV signal to the SP signal and produces an error signal
(ii)It manipulates the error signal through its P, I, and D functions
(iii)It outputs a signal to drive the process in a direction to make the error signal zero, thus making PV=SP.

Function Of Flow Control Element:
Flow control element is a mechanical device that physically changes a process in response to a change in the control system Set Point.
Pneumatic Control Valve, Motorized Control Valve, and Variable Speed Pumps are the examples of flow control element.

Another important component is measurement instrument.
Measurement instrument measures the process variable in closed loop control system.
Flow indicator transmitter, Level indicator transmitter, Pressure indicator transmitter, and temperature indicator transmitter are the example of measurement instrument.

Lastly, let's learn, what is the process disturbance, and what are the major causes of process disturbance.
First major reason of process disturbance is supply load changes.
A change in materials or energy supplied to a process are the examples of supply load change.
Another major reason which cause process disturbance, is a demand load changes. This cause by a change in materials, or energy leaving a process.
Process is also disturbed by sudden set point increment or decrement. And final major cause of process disturbance is, ambient variable changes. For example, temperature changes from hot to freezing conditions.
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