 I am Milka Jagle, working as an assistant professor in the Department of Mechanical Engineering, Vulture Institute of Technology, SolarPort. Today we are going to learn PID controllers, learning outcome. At the end of this session, students will be able to know the various controllers used in the control systems, that is proportional, integral and derivative controllers. So today we are going to see what is controller, proportional controller, integral controller, derivative controller, limitations of PI and D controllers and what is PID controller. As we have studied previously, a controller is a device which when introduced in the feedback or forward path controls the steady state and transient response as per the requirement. So this is a block diagram of closed-look control system. You see the input is given to the controller. The input of the processor is nothing but control signal which is the output of controller. Here there are various types of controllers used in the place of controller. So let us see, this is the types of controllers used in the control system. First is a simple on-off controller, second proportional controller, third integral controller, derivative controller, proportional plus integral controller, proportional plus derivative controller, proportional integral derivative controller. So let us see what is proportional controller. This is also indicated by capital P. Proportional controller is a controller in which output generated by the controller is directly proportional to the error signal. In proportional controller, the controller simply multiplies the error by the proportional gain that is Kp to get the controller output. Kp is the proportionality constant. Here if you see in the diagram the error is multiplied by Kp and we get a controlled output. So next integral controller it is also known as I controller. It is the function of error signal so it is called as integral controller. To eliminate the offset generated by the proportional controller, the proportional controller is replaced by proportional plus integral controller. If the integral control action is added to the controller as long as there is error signal, a signal is developed by the controller. In place of controller there are two controllers used proportional and integral controller. The input reference input is given to the controller and we get the controlled output which is the output of both proportional and integral controller. Next derivative controller. In this the output of controller is differential function of error signal. Such type of controller is also known as derivative controller. The control action is also called as rate action and anticipator. Derivative control action responds to the rate at which the error is changing that is derivative of the error. Derivative controller is not used alone because it provides no output when the error is constant. You see in the diagram derivative controller is used either along with proportional integral controller or the only proportional controller. So here are few limitations of PID controllers. Disadvantage of proportional controller is it generates offsets error as we have already discussed proportional controller generates the offset error. The disadvantage of integral control system is its response to the error signal is low as the error is integrates for every signal. Disadvantage of derivative controller system is it provides the step for each value of error signal and as the error signal is minimized the error gets constant and the output of the controller is 0. Due to the disadvantages of PID controllers these controllers are not used individually but they are used by the combination of PI or PD or PID controllers. So let's see what is PID controller PID stands for proportional integral and derivative. As the name implies it has three controllers first proportional second integral and third derivative. PID is a control loop feedback mechanism proportional corrects instances of error integral corrects accumulation of the error and the derivative corrects present error versus the error in the last time it was checked. So here are few diagrams for PID controllers. So you see the in place of controller the combination of PI and D controller is used and we get a controlled output. So let's see the characteristics of PI and D controllers. Integral controller will have the effect of reducing the rise time and will reduce but never eliminate the steady state error. Integral controller will have the effect of eliminating the steady state but it may make the transient response worse. Derivative controller will have the effect of increasing the stability of the system reducing the overshoot and improving the transient response. These are the references a book by Bakshi and automatic control engineering book by Francis Raven. Thank you.