 I am Priyanka Bansore and today we are going to discuss about one of the application of closed loop control system that is liquid level control system. These are the learning outcomes of this video lecture. At the end of this session students will be able to first describe the application of closed loop control system and second explain the working of liquid level control system. These are the contents we will be covering in this session. Now before moving towards pause this video for few seconds and you have to recall closed loop control system. A closed loop system is a system in which the controlling action is somehow dependent on the changes in the output. You can observe in the block diagram of closed loop system here R of t is the reference input and B of t is the feedback signal. Feedback signal is compared with the reference input means B of t is compared with the R of t with the help of error detector and it gives an error signal that is E of t is equal to R of t plus or minus B of t when the feedback is positive we can add with reference input and when the feedback is negative we can subtract with the reference input. Then this error signal is modified by the controller and decides the proportional manipulated signal that is M of t for the process to be controlled. This manipulation is such that error will approach to 0 and then this signal actuates the actual system and it produces a controlled output that is C of t. Let us see the application of closed loop system that is liquid level control system. So, first we will see what is liquid level controller. It is used to control or to maintain the liquid level in a tank. In many industries like chemical there is a restriction on liquid level of a container. So in such cases with the help of level controller we can maintain the level of the liquid at desired value. So, there are the two methods to control the water level or to control the fluid level. So first method manual. So in first method we can adjust the level of water manually and second automatic method in that automatically we can adjust the level of water. We will discuss in detail about the manual control system. So manual control system is a system in which human operator is necessary. A manual system is like a book keeping system in which records maintenance is done by hand without using a computer or any automatic system. So here the purpose of this system is to maintain the liquid level in the tank. Liquid level in the tank that is represented by small h as close to the desired liquid level and desired liquid level is represented by capital H. So the output flow rate is varied by opening the wall. So you can see in that figure in manual method a human control the liquid level that is close to the desired level using a site tube. Using site tube human or operator compares the present level by the desired level and adjust the wall accordingly by adjusting the fluid flow out. So simply with the help of human we can adjust the liquid level of the tank and with the observation of human we can adjust the wall accordingly. So here Q in is the input of the tank with the help of that we fill the tank and Q out is the output of the tank which is used for water out. There are some conditions Q out depends on the liquid level and if Q out is equal to Q in it means h is constant. If Q out is greater than Q in means tank is empty and if Q out is less than Q in then tank overflows. So with the help of these conditions we can level the adjust of the tank manually. So here there are some drawbacks of the manual method. First one error due to human but obviously then second error due to time wasted in opening and closing of the walls and the last there is a need of automatic system because if we want to increase the accuracy at that time we require the automatic system. Let us see automatic control system. Automatic control system is a system in which human operator is not at all required. In automatic method the human is replaced by the controller due to that the accuracy is increased automatically then it is a combination of both software and hardware which is designed and programmed to work automatically without the need of any human operator. Let us see advantages of automatic method. So first one error is reduced by controller because here human is replaced by the controller. So automatically error is reduced then second automatic method is more reliable as compared to the manual. So it is more stable and the last it is costly as compared to manual but accuracy and stability is better than the manual method. We will see application of automatic control system that is liquid level control system. It is an example of closed loop system it consists of dashboard, water tank, motor, power amplifier then walls V1 and V2 and potentiometer is used as an error detector. So V1 is manually wall and V2 depends on control action of voltage. Here small h is the liquid level and capital H is the desired liquid level. So in that figure reference input is the capital H and control output is nothing but small h that is liquid level ok. Then potentiometer is use an error detector, power amplifier and the motor drive are the feedback element are working as a feedback element and float is the feedback path element. We will discuss actual process of the liquid level control system. This control system can maintain the liquid level that is H and control output of the tank within accurate tolerance of the desired liquid level. Even though output flow rate through the wall V1 is varied and wall V1 is controlled by opening of wall V2. Then you can see in the figure this potentiometer is nothing but here it is use an error detector. So it has the two slider arms A and B. First the liquid level is sense by the float which is connected to the slider arm B on a potentiometer and another slider arm A of potentiometer is corresponding to the desired liquid level that is capital H. So when the liquid level rises or falls the potentiometer as an error detector gives an error voltage and this error voltage is proportional to the change in liquid level. Means if the liquid level is this or falls automatically error voltage is generated and this error voltage is directly proportional to the change in liquid level. This error voltage is produced due to arm A and B and this error voltage is applied to the power amplifier. It actuates the motor through this power amplifier which in turn to decrease or increase the opening of the wall V2 in order to restore the liquid level. Then motor drive and wall V2 are connected through the mechanical link that is in short control system automatically corrects any deviation between the actual and the desired liquid level in the tank. These are the references of this video lecture. Thank you.