Basic of Control System

   

Control System: A control system is an arrangement of physical components connected or related in such a manner as to command, direct, or regulate itself or another system.

v A control system is that means by which any quantity or interest is maintain according to desired manner.

vIn a Control System analysis we are not think about what is inside the system we only think what behaviors of system is.

vThe events or group of elements are called plants and the one who control the plants is called Controller. Controller performs two jobs.

1.      Error Detection

2.      Control Action

v    vWhen feedback is present than controller performs Error Detection + Control Action

v    vWhen feedback is not present than only Control action is performed.

Input: The input is the stimulus, excitation or command applied to a control system, typically from an external energy source usually in order to produce a specified response from a control system. It is nothing but a desired output.

Output: The output is the actual response obtained from a control system. It may or may not be equal to the specified response implied by the input.

System:  A system is an arrangement of physical components connected or related in such a way as to form an entire unit. System means of transfer of (one form of energy to other)or exchange of signal.

Example of Control system:

1.           An Electric switch in which flipping the switch ON and OFF may be considered as the input and Output is the flow or nonflow of electricity.

2.           A thermostatically controlled heater where input to the system is reference temperature and output is the actual temperature.

3.           Automatic Washing machines in which the amounts of detergent, bleach, water, temperature of the water and time for wash and spin cycle are considered as input whereas the percentage of cleanliness is the output.

There are two types of control system: Open-loop and Closed-loop systems

Open- loop Control System: An open loop control system is one in which the control action is independent of the output. In other word these are the systems in which present output depends upon present input only.

In such system there is absence of error detecting elements.

Some important features of open-loop control system are:

1.         The ability to perform accurately is determined by their calibration. To calibrate means to establish the input - output relation to obtain desired system accuracy.

2.      They are not usually troubled with problems of instability.

3.       Simple to design and cheaper.

Example of Open - loop Control system: Fan, Torch, Traffic System, Most automated toasters, Washing machine coffee server, 

Close – loop control system: The close-loop control systems are more commonly also known as feedback control system. These are the systems in which present output depends on present input as well as previous output.

Feedback: The Feedback is that property of a closed-loop system which permits the output to be compared with the input to the system so that the appropriate control action may be formed as some function of the output and input.

More general, feedback is said to exist in a system when a closed sequence of cause-and-effect relations exists between system variables.

Characteristics of FEEDBACK:

1.      Increased Accuracy.

2.      Tendency towards oscillation or instability.

3.       Reduced sensitivity.

4.       Reduced effects of nonlinearities.

5.       Reduced effects of external disturbances or noise.

6.       Reduced Bandwidth.                                                                                        

Some important features of close-loop control system are:

1. Accurate and Reliable

2. Output is less affected by Noise

3. The Effect of Non linearity is less

4. The Effect of parameter variation is less

5. Complex to design and costly

6. There is problem of stability

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Example of closed - loop Control system: An autopilot mechanism and the airplane it controls, Controlled AC, Microwave, Any commanding or sensing system, Human Reciprocity  System, Smoking, Human driving system, walking in Room