LCS 1b - Feedback control and control loop

In the first part of this lecture we have learned that control systems are very important and control finds its application in almost all modern industrial processes. In this second part we shall talk about some basic concepts of control systems. In all the control systems that we have discussed on previous slides one thing is common in all the control systems that is feedback and feedback in the control system whether it is automatic control or manual and these control systems can be represented in a block diagram as shown in the figure on this loop. In this diagram the process to be controlled is represented by a block it has an input and an output. When we talk in terms of control systems output is the variable that is to be controlled and input is the variable through which we control the output. Output is measured by some sensor and then the measured value is compared with the desired output. This is called feedback. Based upon the difference between desired output and actual output an algorithm called controller decides which what action should be taken. Actuator is the component in the control system which converts the command generated by the controller into a physical actuation. We have too much terminologies on this slide but don't do not worry we explain these on the next slide with the examples that we have already discussed. Consider again the our first example of liquid level system. If we talk in terms of control the process consists of cylindrical tank with inflow and outflow of liquid. The output is the variable to be controlled which in this case is the level of the liquid inside the tank. What is the control input? You remember input is the variable through which we can control the output. In this case the control input is the opening of the valve. The eyes of the person are sensors which measure the actual liquid level in the tank. Inside the brain of the operator the actual level is compared with the desired level and some decision is taken in the brain. So the controller in this case is in the brain of the operator. The decision taken by the brain has to be converted into some physical actuator signal which is done by the hands of the operator. So actuator in this case are the hands of the operator. Let's explain the same thing with two more examples. In upper diagram is a physical system which consists of a rotating disc. We want to control the speed of the We can show the system in black diagram. The process to be controlled is the rotating disc. What is the output in this system? The output is the variable that is to be controlled. In this case it is the angular speed of the disc. What sensor is used to measure the speed? Yes it is tachometer. The desired speed is set by the arrangement consisting of a battery and variable resistor. The difference between desired and actual speed called error signal is computed. There is a dc amplifier which amplifies the error signal. It acts as a controller. The amplified error signal is then converted into physical actuation signal by a dc motor in this system. Therefore the dc motor is the actuator in this particular system. Now look at the hard disk. We want to control the position of the head. Now you can easily match different components of the black diagram with the system. Most of the contents presented in this lecture are from the book by Dorff. The book is very good in the sense that it presents some interesting real life applications. Now a very important thing for you is the course contents and other discussions. You are already familiar with me. I am Muhammad Abid. You may contact me in my office in room number SE302. Sometimes I pronounce it 302. My office extension is 3440. My email address and webpage is also written on this slide. The prerequisite for this course is basic knowledge of differential equations and Laplace transform. Course material will be shared through canvas this time. It is also placed on my folder on data server. Complete course contents and lecture breakdown is also shared on canvas. Our textbook is control systems engineering by Norman Nice. This is a very good book in my opinion for understanding the mathematical modeling of physical processes and for learning some basic concepts. We shall also use books by Ogata particularly for frequency domain analysis and design of control system. The third book is by Dorff. This book is interesting because it presents very good examples of real physical systems. We shall use MATLAB and Simulink for analysis and design of control systems. Here is marks distribution. Normally there are two sessional exams, one and one terminal exam. However, this time I think there will be one midterm exam. There will be regular assignments and quizzes. Terminal exam carries a weightage of 50 marks. For linear control system labs, the schedule will be announced by the course coordinator. I shall share the lab manual on canvas and on the data server. Marks distribution for lab, you will have to submit a well-written lab report. The detailed format of report is shared in the lab manual. There will be evaluations during lab sessions. There will be one open-ended lab and FIWARE exam. In the next lecture, we shall talk about mathematical modeling of physical systems.