IFAC PapersOnLine 50-1 (2017) 13480–13485 ScienceDirect Available online at www.sciencedirect.com 2405-8963 © 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Peer review under responsibility of International Federation of Automatic Control. 10.1016/j.ifacol.2017.08.2327 © 2017, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved. Keywords: Control education using laboratory equipment, disturbance rejection, output feedback control, analytic design, PID controllers 1. INTRODUCTION Water tanks systems as well as PI/PID controllers play an important role for introductory courses in control, ˚ Astr¨ om & ¨ Osterberg (1986); Yurkevich & Naidu (2012). Even in a single tank system, fluid level control problem allows for a nontrivial discussion concerning the PI controller settings, Blachuta et al. (2017). A more challenging cascaded tank system shown in Fig.1.a consists of two tanks placed one over another. Such systems have been used for more than Fig. 1. Schematic diagrams of tanks systems; a 1 ,a 2 and a 12 - cross-sectional areas of corresponding orifices 30 years in the Control Lab of the Lund Institute of Technology, ˚ Astr¨ om & ¨ Osterberg (1986), contributing to education of thousands of students in the domain of automatic control. It is also produced commercially by Canadian company Quanser Consulting Inc. Apkarian (1999). Such setup allows, in a very intuitive way, for an ⋆ The research has been supported by the Department of Automatic Control Grant No. BK-213/RAu1/2016 important message: use the PI controller for the first order plant, and PID for the second order one. Perhaps even more popular is another system called Cou- pled Tanks Apparatus, Bastida et al. (2013); Hussein & Mishr (2014); Laubwald (2015), presented in Fig.1.b–c. There are many companies, eg. British TecQuipment 1 , Australian LabShare 23 , or Singaporean Kent Ridge In- struments 45 that manufacture laboratory rigs based on that concept. While their design attained the highest tech- nical level, including the possibility of remote internet access, Ko at al. (2001), the theory of coupled tanks systems with a backward impact published in several papers and laboratory guides is rather shallow and does not explain specific phenomena to be observed in these installations. The main difference between these two sys- tem types, revealed in Grygiel et al. (2016b), is that in normal operation conditions, like those displayed in Fig.1, the cascaded tanks system in (a) has two identical time constants T 1 = T 2 while in the coupled one in (b) there is T 1 = 20T 2 , and its properties are similar to those of the single tank system. This, however, is not the case when this ratio attains its maximal value of about 6 in the system depicted in Fig.1.c, when using PID controller is still hardly justified, but the behavior of the closed loop system with the PI controller differs much more from that of the first order one. 1 Datasheet of CE105 Coupled Tanks Apparatus. http://www. tecquipment.com/Datasheets/CE105_0115.pdf 2 User Guide. Coupled Tanks Rig Laboratory, http://www. labshare.edu.au/ 3 User Guide. Modelling of the Coupled Tank System and Design of Controllers for control of a Coupled Tank System,http://www. labshare.edu.au/ 4 Control apparatus of coupled-tank. Web based virtual laboratory, http://vlab.ee.nus.edu.sg/ ~ vlab/vlab/control/introduction. html 5 Coupled-Tank Control Apparatus PP-100, http://www.kri.com. sg/ctank.html Department of Automatic Control, Silesian University of Technology 16 Akademicka St., Gliwice, PL 44-101, Poland (e-mail: marian.blachuta@polsl.pl). Abstract: In this paper dynamics of a single as well as of two builds of double tanks systems are studied in more depth than usually. A normalization which makes mathematical description independent of a particular system dimensioning is proposed. A new approach to PI/PID controller design, aimed at attaining higher dynamical accuracy, is presented for considered systems. An influence of particular dynamics of the coupled tanks apparatus on controller settings and control system behavior is studied. Conclusions concerning a teaching significance of these systems and design methods applied are drawn. Robert Bieda, Marian Blachuta and Rafal Grygiel A New Look at Water Tanks Systems as Control Teaching Tools ⋆