PID output fuzzified water level control in MIMO coupled tank system

Master's Thesis, 2013

35 Pages, Grade: Good



1.1 Overview

A lot of industrial applications of liquid level control are used now a day’s such as in food processing, nuclear power generation plant, industrial chemical processing and pharmaceutical industries etc. The current work uses solenoid valves as actuators including of two small tanks mounted above a reservoir which functions as storage for the water. Each of both small tanks has independent pumps to pump water into the top of each tank. At the base of each tank, two flow valves (one as regular disturbance and other as leakage) connected to reservoir. In addition, capacitive-type probe level sensors have been used to monitor the level of water in each tank.

The PID Controller is usually used as temperature, motion and flow controllers. It is available in analog and digital forms. PID Controller controls the water flow rate through solenoid valves to maintain the required levels in both tanks. The NI DAQ card is used as the interface between hardware and software. MATLAB 2012a (Simulink) has been used to get the simulation result of the system performance and LABVIEW 2010 to implement the designed controller. Fig. 1.1 shows the block diagram of the coupled tank control apparatus with controller.

illustration not visible in this excerpt

Figure 1.1: Block diagram of the couple-tank control apparatus.

1.2 Problem Statement

In spite of the simple structures, PID controllers are proven to be sufficient for many practical control problems. An abundant amount of research work has been reported in the past on the tuning of PID controllers. "PID" means Proportional-Integral-Derivative, referring to the three terms operating on the error signal to produce a control signal. Since many control systems using PID control have proved satisfactory, it still has a wide range of applications in industrial control.

In this project, several useful PID Controller design techniques are be presented, and implementation issues for the algorithms are also be discussed. The PID Controller was designed to control the liquid level in both the tanks. In this project, the simulation of proportional, integral and derivative actions are explained in detail, and variations of the basic PID structure are also introduced.

Finally, we need continuous data from the plant as the feedback, so to overcome this problem NI DAQ card have been used as the interfacing device between the hardware and software.

1.3 Objective

There are several objectives that must be achieved in order to make this project successful;

i. To develop a PID Controller output fuzzified logic for controlling the liquid level in both the tanks of coupled tank system.
ii. To validate the result from simulation (using MATLAB 2012a) through experimental set up (implementation using LabVIEW 2010).

1.4 Scope of project

This current work is all about how to designed the controller and simulate it using MATLAB 2012a. Then, implement PID Controller by developing GUI using LabVIEW 2010 software on coupled tank liquid level system. After that, both results are compared.

MATLAB 2012a has been used to simulate and verified the mathematical model of the controller. LabVIEW 2010 has been used to implement the graphical user interface for PID Controller.

The communication between DAQ card, LabVIEW 2010 and Coupled tank liquid level system has to be determined, in term of address to give or receive analog or digital signal.

1.5 Summary

This chapter is about the explanation for overall project. The objective and the scope of the project has to be given in order to give an insight about the idea of the project.


2.1 Overview

This chapter discusses the article those talks about different method of designing controllers.

2.2 Article

[1] Jutarut Chaorai-ngern, Arjin Numsomran, Taweepol Suesut, Thanit Trisuwannawat and Vittaya Tipsuwanporn.,2005, ” PID Controller Design using Characteristic Ratio Assignment Method for Coupled-Tank Process”,

This paper presents the PID controller design for coupled tank process using characteristic ratio assignment (CRA).The simulation results can be illustrated the validity of their approach by MATLAB.

[2] Muhammad Rehan, Fatima Tahir, Naeem Iqbal and Ghulam., 25-26 March 2008,  “ Modelling, Simulation and Decentralized Control of a Nonlinear Coupled Tank System”,

This paper presents a coupled three tank system is taken as a plant and has been modelled mathematically using Bernoulli’ s law, simulate with Matlab/Simulink and decentralized using control and estimation tool manager from Simulink model and mathematical model.

[3] M. Khalid Khan, Sarah K. Spurgeon, 10 February 2005 “ Robust MIMO water level control in interconnected twin-tanks using second order sliding mode control”,

This paper presents a coupled twin-tank system as a plant and water level is controlled by second order sliding mode control and simulation by Matlab Simulink.

[4] Liu Jinkun., 2004, MATLAB simulation of advanced PID control.

This paper gives detailed explanation about Matlab simulation of PID controller.

2.3 Summary

This chapter is about the explanation for some articles that refer to get the information or some knowledge that applies to make the project run successfully. There are several articles that explain about same controller that has been used in this project but applied at different plant or different method of designing, and also different controller but applied at same plant.


3.1 Overview

This chapter discusses about the method that has been used to complete this project. The coupled twin-tank liquid level system has been used in this project as a plant. In this project, several useful PID Controller design techniques are presented. The PID Controller and PID controller output fuzzification has been designed to control the liquid level in both tanks to obtain the desired level. In this current work, NI DAQ card has been used as the interfacing between the hardware and software.

3.2 Project Flow Chart

illustration not visible in this excerpt

Figure 3.1: Flow chart for software and hardware development

Fig. 3.1 shows about the overall progress for both software and hardware development that has been discussed later. This project has been divided to two parts to make sure this project runs smoothly. The first part is a software part, which covers modelling the controller. The controller is designed and simulated using MATLAB 2012a and then implemented in LabVIEW 2010 as GUI with fuzzified logic. The second part covers for the hardware part. In this part, the coupled tank liquid level system has been assembled to make sure it runs properly. Then, a communication between plant and controller has been made using NI DAQ card. The DAQ card is analyzed and these operations need to refer the manual to make the interfacing between plant and controller.

After that, both parts are integrated to test the whole system. At this part, the results that implemented using LabVIEW 2010 is compared with the experiment result that simulated using MATLAB 2012a. Troubleshooting has been performed to obtain better results in case of some error occurs.

3.3 Mathematical Modelling of Coupled Tank System

Before the process of designing controller begin, it is vital to understand the mathematics of how the coupled tank system behaves. In this system, nonlinearity in the dynamic model has been observed.

illustration not visible in this excerpt

Figure 3.2: Schematic diagram of coupled tank system


Excerpt out of 35 pages


PID output fuzzified water level control in MIMO coupled tank system
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ISBN (eBook)
ISBN (Book)
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PID, MIMO, Fuzzification, Coupled Tank, Control system
Quote paper
M.Tech. Vishal Vasistha (Author), 2013, PID output fuzzified water level control in MIMO coupled tank system, Munich, GRIN Verlag,


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