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FEEDBACK

The term of feedback refers to the direction in which the measured output signal is

returned to the control elements. It also means whereby a signal related to the

actual condition being achieved is fed back to modify the input signals to a process.

In other word, feedback is an important feature of a closed loop control system is

that a control system output signal fed back to the input stage, providing information

to the controller about the current output state and facilitating an appropriate control

action. It is not possible to have fully functional automatic or even manual control

system without a feedback signal.

Basics Principle of Feedback

Fig. 1: Basic principle of feedback

The feedback circuit connected to the process output is a distinguishing feature of

this system. The origin of the feedback signal is a sensor attached to the process

output. The feedback circuit returns a signal to the controller. The controller is fed by

a summing circuit that compares the set point input and feedback signals. The input

or process energy source is responsible for establishing the setpoint value of the

system. The setpoint value is adjusted by the operator according to the needs of thesystem. The actual value of the process output is determined by the sensor. If the

Process Energy Source Actuator or FinalControl Elements Process Output

Sensor

Feedback

Path

ControllerManual Setpoint

Adjustment

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actual value output is the same as setpoint value, the controller indicates system

balance. The actuator or final control remains unchanged. If the actual output

deviates from the setpoint value, signals applied to the controller will no longer be in

balance. This causes a correction signal to be developed by the controller. The

corrective signal is directed to after the actuator or final control element. This type ofresponse causes the system to be self correction.

Positive Feedback

Positive feedback has the property that signals tend to reinforce themselves, and

grow larger. In a positive feedback system, noise from the system is added back to

the input, and that in turn produces more noise. Positive feedback, since plus sign is

assigned to the feedback signal. It also tends to increase the event that caused it,

such as in a nuclear chain-reaction. It is also known as a self-reinforcing loop.

Negative Feedback

Negative feedback is almost always the most useful type of feedback. Since a minus

sign is assigned to the feedback signal, it calls negative feedback. Which is also

tends to reduce the input signal that caused it, is also known as a self-correcting or

balancing loop.

Using of Feedback

The use of feedback is shown to be for the purpose of reducing the error between

the reference inputs and the system output.

Signal Block Diagram

What is a signal block diagram? A useful ways of representing a system and also

Block Diagrams are a useful and simple method for analyzing a system graphically.

It consist 4 formal block diagram to represent the element and connections:

1. System element

2. Information flows

3. Summing junction

4. Take-off point

Why we need a signal block diagram?

The block diagram is typically used for a higher level, less detailed description aimed

more at understanding the overall concepts and less at understanding the details of

implementation. Useful tool in designing new process and in improving existing

process. Why we need it? Because to design a new process or improve the existing

process. Moreover, it is easily to adapt and understand in process or to control.

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Signal Block Diagram of a Closed-loop Control System