Control System Lab Experiment Manual for Diploma Students ( Part -1 )

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List of Experiments-

1. To study basic open loop and close loop control systems.
2. To study the MATLAB package for simulation of control system design.
3. To obtain a transient response of first order system with unit step input.
4. To obtain a transient response of second order system with unit step input.
5. To observe the output waveform of a underdamped system with unit step input.
6. To observe the output waveform of a over damped system with unit step input.
7. To observe the output waveform of a undamped system with unit step input.
8. To observe the output waveform of a Critically damped system with unit step input.
9. To observe the output waveform of a plant controlled by P controller.
10. To observe the output waveform of a plant controlled by PI controller.
11. To observe the output waveform of a plant controlled by PID controller.

Experiment No-1

Object:- To study basic open loop and close loop control systems.

Control System :-

A control system is a combination of elements intended to act together to accomplish an objective. Control systems are classified into two general categories. Open loop and closed loop control system. The distinction is determined by the control action, which is that quantity responsible for activating the system to produce the output.

Open loop control system:-

An open loop control system is one in which the control action is independent of the output. The important features of open loop control system are:-

• Their ability to perform accurately is determined by their calibration, which implies to establish the input-output relation to obtain a desired system accuracy.
• They are not generally troubled with problems of instability.

BLOCK DIAGRAM:-

Examples of open loop control system:-

1. A man working on a road with his eyes closed is an example of open loop control system. The major components in walking are the brain, the eyes and the feet. The input may be chosen as desired work direction and the output actual work direction. The control action is determined by the eyes which detect the difference between input and output and send information to brain. Since the eyes are closed therefore the system is open loop.
2. Another example of open loop control system is an electric automatic coffee maker. One possible input for coffee maker is amount of coffee used. In addition most coffee makers have a dial which can be set for weak, medium or strong coffee. This setting usually regulates a timing mechanism. There for brewing time of coffee is another possible input and the output of any coffee maker can be chosen as coffee strength.

CLOSE LOOP CONTROL SYSTEM:-

A close loop control system is one in which the control action is some how dependent of the

output. Close loop control systems are commonly called feedback control system. Feedback is that characteristics of close loop control system which differentiates it from open loop. It is the property of closed loop system which permits the output to be compared with the input. So that appropriate control action maybe formed as a function of input and output.

Important features of feedback are:-

1. Reduced effects of non linearites and distortion.
2. Increased accuracy.
3. Increased bandwidth.
4. Reduced sensitivity of the ratio of output to input to variations in system characteristics.
5. Tendency towards oscillation or instability.

BLOCK DIAGRAM:-

Examples of closed loop control system:-

1. A man working on a road with his eyes open is an example of closed loop control system. As eyes can distinguish between the desired walk direction and actual walk direction and make the necessary correction therefore the system is closed loop.
2. Another example of closed loop control system is an automatic toaster. In which each heating element supplies same amount of heat to both sides of the bread. And toast quality can be determined by its color. The toaster is initially calibrated for a desired toast quality which needs no re-adjustment. The toaster is automatically switched off when the sensor sees the desired color with the help of feedback linkage which may be electrical or mechanical. Since the output (color of toast ) is dependent on input ( temperature setting) there for the system is closed loop.

Result:- To study basic open loop and close loop control systems.