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Note for Control System Engineering - CSE By JNTU Heroes

  • Control System Engineering - CSE
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  • Jawaharlal Nehru Technological University Anantapur (JNTU) College of Engineering (CEP), Pulivendula, Pulivendula, Andhra Pradesh, India - JNTUACEP
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Control Systems UNIT-1 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, or is that means by which any quantity of interest in a system is maintained or altered in accordance with a desired manner. Any control system consists of three essential components namely input, system and output. The input is the stimulus or excitation applied to a system from an external energy source. A system is the arrangement of physical components and output is the actual response obtained from the system. The control system may be one of the following type. 1) man made 2) natural and / or biological and 3) hybrid consisting of man made and natural or biological. Examples: 1) An electric switch is man made control system, controlling flow of electricity. input : flipping the switch on/off system : electric switch output : flow or no flow of current 2) Pointing a finger at an object is a biological control system. input : direction of the object with respect to some direction system : consists of eyes, arm, hand, finger and brain of a man output : actual pointed direction with respect to same direction 3) Man driving an automobile is a hybrid system. input : direction or lane system : drivers hand, eyes, brain and vehicle output : heading of the automobile. Classification of Control Systems Control systems are classified into two general categories based upon the control action which is responsible to activate the system to produce the output viz. 1) Open loop control system in which the control action is independent of the out put. 2) Closed loop control system in which the control action is some how dependent upon the output and are generally called as feedback control systems. Open Loop System is a system in which control action is independent of output. To each reference input there is a corresponding output which depends upon the system and its operating conditions. The accuracy of the system depends on the calibration of the system. In the presence of noise or disturbances open loop control will not perform satisfactorily. ECE/ 5 2

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Control Systems input Actuating signal nput output Controller System EXAMPLE - 1 Rotational Generator The input to rotational generator is the speed of the prime mover ( e.g steam turbine) in r.p.m. Assuming the generator is on no load the output may be induced voltage at the output terminals. Induced Voltage Speed of the Rotational Generator Prime mover Inputs Output Fig 1-2 Rotational Generator EXAMPLE - 2 Washing machine Most ( but not all ) washing machines are operated in the following manner. After the clothes to be washed have been put into the machine, the soap or detergent, bleach and water are entered in proper amounts as specified by the manufacturer. The washing time is then set on a timer and the washer is energized. When the cycle is completed, the machine shuts itself off. In this example washing time forms input and cleanliness of the clothes is identified as output. Cleanliness of clothes Time Washing Machine Fig 1-3 Washing Machine EXAMPLE - 3 WATER TANK LEVEL CONTROL To understand the concept further it is useful to consider an example let it be desired to maintain the actual water level 'c ' in the tank as close as possible to a desired level ' r '. The desired level will be called the system input, and the actual level the controlled variable or system output. Water flows from the tank via a valve Vo , and enters the tank from a supply via a control valve V Actual Water level c W at er in level r Valve VO C Water out WATER TANK Fig 1-4 b) Open loop control Fig -1.4 a) Water level control ECE/ 6 3

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Control Systems A closed loop control system is one in which the control action depends on the output. In closed loop control system the actuating error signal, which is the difference between the input signal and the feed back signal (out put signal or its function) is fed to the controller. Reference i n p u t Forward path Error detector Actuating / error  signal Control elements Controlled output System / Plant controller Feed back elements Feed back signal Fig -1.5: Closed loop control system EXAMPLE - 1 - THERMAL SYSTEM To illustrate the concept of closed loop control system, consider the thermal system shown in fig6 Here human being acts as a controller. He wants to maintain the temperature of the hot water at a given value ro C. the thermometer installed in the hot water outlet measures the actual temperature C0 C. This temperature is the output of the system. If the operator watches the thermometer and finds that the temperature is higher than the desired value, then he reduce the amount of steam supply in order to lower the temperature. It is quite possible that that if the temperature becomes lower than the desired value it becomes necessary to increase the amount of steam supply. This control action is based on closed loop operation which involves human being, hand muscle, eyes, thermometer such a system may be called manual feed back system. Human operator Thermometer Desired hot Steam Hot water ro c old water CoCC Muscles water. temp + Steam Actual Water temp Brain of operator (r-c) + and Valve Thermometer Drain Fig 1-6 a) Manual feedback thermal system b) Block diagram EXAMPLE -2 HOME HEATING SYSTEM The thermostatic temperature control in hour homes and public buildings is a familiar example. An electronic thermostat or temperature sensor is placed in a central location usually on inside ECE/ 7 4

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