Development of User Interface System for Control Laboratory Experiment

Ahmad Shahreez Hashim

Faculty of Electrical Engineering Universiti Teknologi Mara,

Shah Alam, Malaysia ahmad_shahreez@yahoo.com

Zuriati Janin Faculty of Electrical Engineering

Universiti Teknologi Mara, Shah Alam, Malaysia

zuriaty@salam.uitm.edu.my

Najidah Hambali Faculty of Electrical Engineering

Universiti Teknologi Mara, Shah Alam, Malaysia

najidah@salam.uitm.edu.my

Abstract - This paper presents the development of user interface system specifically for three tank water level process plant installed at Control Laboratory, Faculty of Electrical Engineering, UiTM Shah Alam. The system is developed in order to help students understand the experiments by visualizing data plot and simulate the process. The development of user interface system is based on the actual process plant system operation. The design includes all the necessary components and facilities necessary to function properly. The system is designed using NI LabVIEWTM and tested in term of its ability to display about the state of the process, to accept and implement the users control instructions. The application of the developed user interface system to the existing process plant system give great improvement in the way of conducting the experiments particularly, data collection. The results had proved that the developed system able to visualize the process response accurately. Keywords: LabVIEW; Human-Computer Interaction; Three-tank Water Level; Control

I. INTRODUCTION Recent technology in education field is highly dependent

on User Interface Design which also known as Human-Computer Interaction (HCI) system in order to enhance the

technical complexity to a usable ways in conveying information [1,2,3,4]. A user interface is how a human interacts with a computer and it goes beyond designing screens which consist of menus that are easier to use. A well-designed user interface is the one that is intuitive, easy to use, allows the users to maximize the efficiency and effectiveness when using it [1,2,3].

Table I shows the interaction styles of HCI system for various applications. Basically, the design of the HCI is based on the skills, experience and expectations of its anticipated users in which the elements of the design is basically the functionality, aesthetic and performance [1,2,3].

In this paper, a user interface system for three-tank water level is developed using NI LabVIEWTM. The developed system is based on the actual hardware system available at Control System Laboratory in UiTM Shah Alam. It is aim to provide an interesting and simpler ways to perform experiment. It is hoped that this work will help students understand the experiment as a whole.

TABLE I HUMAN-COMPUTER INTERACTION SYSTEM STYLES [1,2]

Interaction style Main advantages Main disadvantages Application examples

Direct manipulation Fast and intuitive interaction Easy to learn

May be hard to implement. Only suitable where there is a visual metaphor for tasks and objects.

Video games CAD systems

Menu selection Avoids user error Little typing required

Slow for experienced users. Can become complex if many menu options.

Most general-purpose systems

Form fill-in Simple data entry Easy to learn Checkable

Takes up a lot of screen space. Causes problems where user options do not match the form fields.

Stock control, Personal loan processing

Command language Powerful and flexible Hard to learn. Poor error management.

Operating systems, Command and control systems

Natural language Accessible to casual users Easily extended

Requires more typing. Natural language understanding systems are unreliable.

Information retrieval systems

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II. SYSTEM DESCRIPTION The photograph and schematic diagram of the three tank

water level system is as shown in Fig. 1 and Fig. 2 respectively. The system is a closed-loop system in which the process is operates as a single-input single output (SISO) [8,9].

The system consists of four tanks labeled as Tank 1, Tank 2, Tank 3 and Reservoir Tank. The actuator for the system is the control valve equipped with portable pump and is connected with the valve positioner (5503 PK). The valve positioner used has a linear characteristic in which a flow of 0.2 to 1.0kg/cm2 is equivalent to a signal of 4-20mA [8,9]. The differential pressure transmitter (UNE-11) is used as the device to measure the water level in Tank 3.

The main objective of the process is to maintain the water level in Tank 3 at specified level despite of the disturbance applied to the process. The measurement is taken using pressure difference reading between two points of interest in which the pressure of 10-10kPa is equivalent to 0-100% water level. The control valve system is used to permit the flow of the water into the tank. Then, the valve positioner compares the control valve position to a desired input signal and influences the valve actuator so that its position corresponds with the desired input signal.

Fig. 1 The photograph of the three-tank water level system

Fig. 2 The schematic diagram of the three-tank water level system

III. THE EXPERIMENT The experiment is conducted in which the students are

required to tune the PID parameters and observe the process response after applying the disturbance input. The tuning is done manually and it is tedious and time consuming.

Currently, there is only one process plant installed at the laboratory for a group of 10 to 15 students do the experiment. The objective of the experiment is to demonstrate how the tuning took place specifically for water level control system. Prior to this, the students are required to understand the water level control system and concept of PID control tuning. In this experiment, the tuning is accomplished using Ziegler-Nichols damped oscillation method.

The setup of the equipment normally is done by the instructor and students are required to note the changes in the output that respond to the changes in the input signal. In this experiment, the disturbance input to the process is the signal from the disturbance pump which attached at tank 2. The disturbance signal to the process is a 5 second interruption from the pump. The process response is then plotted on a paper chart recorder attached to the controller.

Normally, the experiment is only completed after 4 hours in which the plot of the process is obtained after several attempts and is time consuming since each group has to wait for the other to complete. Furthermore, students are unable to visualize the process response accurately, hence, could not able to understand the experiment as a whole. After performing the experiment, students are required to evaluate the output response plotted on the paper chart recorder. The discussion on the results obtained is then submitted as a lab report to the instructor at the end of the experiment session.

The example of the results obtained from paper chart recorder is as shown in Fig. 4, Fig. 5 and Fig. 6.

Fig. 3 Process response with PB =2

Fig. 4 Process response with PB =50

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Fig. 5 Process response with PB

The response is determined for ideal PIDwith tuning parameters shown in Table 2.response when the disturbance is applied system.

TABLE II: PID PARAMETERS SET

PID parameters Kc 1.00 (Gain) Ti 1.00 sec Td 0.00 sec

In the existing way of conducting the ex

are unable to visualize the input signal to thonly shows the output of the process. Therlack in understanding the process system athe theory learnt in the class and the experin the laboratory.

IV. PID & QUARTER DECAY RATIO T The mathematical expression of ideal P

[10-16] is as shown in (1) where e(t) is theTd is the coefficients of proportional, integactions respectively.

++= )()(

11)( sTdsTi

KcsU

On the other hand, the practical PID alg

in (2) where is the constant that lies in b[10,14].

++=((

)(11)(

sTdsTd

sTiKcsU

α

The other form of PID control algorithseries PID control structure is as shown in (

⋅+= ()(

1)()(Td

TdsTi

sTiKcsU

α

=100

D control algorithm . Fig. 5 shows the for 1.6 sec to the

TING

xperiment, students he process. The plot refore, students are

and unable to relate rimental work done

TUNING METHOD

PID control method e error, Kc, Ti, and gral and derivative

…(1)

gorithm is as shown between 0.05 to 0.2

+ 1))s

…(2)

hm also known as 3).

++

1)(1)(

sds

...(3)

The coefficients of integral presented in terms of gain as sho

TiKcKi = ...(4)

There are many established open literature [4,10,13,15]. Ththe method [10,15] by which thof one complete cycle or a rresponse. The ratio must be abodecay ratio can be calculatedresponse shown in Fig. 3.

DR =

Fig. 6 Process response f

In this method, the ultimateTu of oscillation of the conobtained. The ultimate gain experimentally determined byband, PB using (7). Then, the control is calculated using (8). and derivative time is based using (9) and (10) respectively.

[1100PB

K CU =

7.1CU

C

KK =

5.1UT

Ti =

6UT

Td =

V. MET

In this work, the user interfathat the user is allowed to interaregard to this, the user is aparameters and also observed th

and derivative actions can also own in (4) and (5).

TdKcKd .= …(5)

tuning methods available in an he quarter decay ratio (QDR) is he oscillation is reduced during ratio of the amplitude of the out or equal to 1/4 (quarter). The d using (6) from the process

AB

(6)

for QDR implementation

gain, Kcu and ultimate period, ntrol loop is experimentally

is the constant amplitude y decreasing the proportional

proportional gain of the PID On the other hand, the integral solely on the ultimate period

]%00 …(7)

7U …(8)

…(9)

…(10)

HODOLOGY face system is designed in such act with the process plant. With allowed to adjust the control e process response.

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NI LabVIEW version 9 with data logging and supervisory control (DSC); and PID toolkits is utilized in designing a user interface system. The design is based on the actual hardware system shown in Fig. 2. The buttons and menus have been designed to make it easy for the user to access the process.

In this work, the operation option ‘automatic’ must be select to automate the control valve. The set-point and PID parameters need to be entered by user. The flow of the water is designed in such that the water flows from the Reservoir Tank to Tank 1, continues to Tank 2, follows with Tank 3 and return to the Reservoir Tank. The water level in Tank 3 is measured and controlled using PID control method. Three different PID control algorithms are employed to the process plant and the response is analyzed. In this case, the PID parameters are adjusted using QDR method. Apart from that, the effect of disturbing the flow of the water to Tank 3 in second is also analyzed. The results obtained using the developed user interface system is then compared with the actual experimental work.

VI. RESULT

A. User Interface System The user interface system for three-tank water level

control system is as shown in Fig. 7 and Fig. 8. It consists of buttons and menus for PID structure selection, PID tuning parameter option, set-point range and control valve opening percentage. The programming module for PID control implementation is as shown in Fig. 9.

The example experiment results that can be obtained from

the user interface system are shown in Fig.10, Fig. 11 and Fig. 12. Fig. 10 shows the output response for open loop system with no disturbance applied to the system. It can be seen that the process experience the delay time about 60 sec. The plot for effect of disturbance to the process using three different PID control algorithms is as shown in Fig. 10, Fig. 11 and Fig. 12.

Fig. 7 Front panel of user interface system

Fig. 8 The programming of user interface system

Fig. 9 The PID control implementation for three-tank water level

Fig. 10 Output result with no disturbance

Fig. 11 shows the response for ideal PID control algorithm with the disturbance is applied to the system for 1.3 second.

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Fig. 11 Ideal PID control structure with disturbance

Fig. 12 Parallel PID control algorithm with disturbance

Fig. 11 shows the response for parallel PID algorithm with disturbance input applied to the system for 1.6 sec. The response is when the controller PB = 50%. The results displayed on the user interface system are same to the result plotted on the paper chart recorder. It shows that the developed user interface system is functioning well.

VII. CONCLUSION The design of the user interface system is dependent on the

user and system requirements. The effective user interface is determined by the simplicity of the design and ease of use.

It can be seen that by using a user interface system connected to the process plant, students able to visualize more than the output response. In fact, students able to do some simulation work and compare with the actual experiment. This will help students reduce the amount of time necessary to make connections and guessing.

ACKNOWLEDGMENTS

The authors gratefully acknowledge and thank Universiti Teknologi Mara (UiTM) for the Research Intensive Faculty (RIF) Grant (600-RMI/DANA/5/3/RIF (370/2012).

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