Control System

OBJECTIVES

1. Able to list the application of control system
2. Able to describe open-loop and closed-loop control system.
3. Able to determine transfer function of a system.
4. Able to perform block diagram reduction to obtain overall transfer function of a system.
5. Able to compare analog and digital control.
6. Able to describe the objective of control system design.

Control System

• Control means to regulate, direct, command, or govern.
• A system is a collection, set, or arrangement of elements (subsystems).
• A control system is an interconnection of components forming a system configuration that will provide a desired system response.

Input & Output

• The input is the stimulus, excitation, or command applied to a control system.
• The output is the actual response resulting from a control system.
• The output may or may not be equal to the specified response implied by the input.

Application

• Control system applications are found in;
• robotics
•  space-vehicle systems
• aircraft autopilots and controls
•  ship and marine control systems
•  intercontinental missile guidance systems
• automatic control systems for hydrofoils
• surface-effect ships
• high-speed rail systems

Examples of Control Systems

Examples of man-made control systems:
Washing machine, radio antenna, rockets/missiles, robots, room air condition.


Examples of God-created control systems : entry of
light through the human eye, holding and carrying things using hand.


Open-loop Control System



A control system where the control (regulating) action is independent of the output.
The output from the system has no effect on the input signal to the plant or process.
Advantage: relatively simple, cheap and generally has a good reliability.


Disadvantages:


Often inaccurate since there is no correction for errors in the output which might result from disturbances.
There is no changing of the control action to account for any disturbances which change the output variable.



Elements of Open-loop Control System

Control element
→This determines the action to be taken as a  result of the input of the required value signal to the system
Correction element
→This has an input from the controller and gives an output of some action designed to change the variable being controlled.
Process
→This is the process of which a variable is being controlled.