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- 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 138 PID OUTPUT FUZZIFIED WATER LEVEL CONTROL IN MIMO COUPLED TANK SYSTEM Vishal Vasistha (Mechanical, National Institute of Technology Surathkal, India) ABSTRACT The PID controllers are widely used in industry control applications due to their effectiveness and simplicity. This project presents PID controller design for MIMO coupled water tank level control system that is second order system. PID Controller output is fuzzified to control water level in coupled tank system. Simulation has been done in Matlab (Simulink library) with verification of mathematical model of controller. PID controller design and program has been prepared in LabVIEW. At the place of proportional valve, combinations of solenoid valves are used. The NI DAQ card is used for interfacing between hardware and LabVIEW software. Experiment is fully triggered by LabVIEW. Simulated results are compared with experimental results. Keywords: PID, MIMO, Fuzzification, Coupled Tank, Control system etc. 1. INTRODUCTION 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. 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. INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 4, July - August (2013), pp. 138-153 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
- 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 139 Figure 1.1: Block diagram of the couple-tank control apparatus 2. PROBLEM STATEMENT AND OBJECTIVE 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). 3. MATHEMATICAL MODELLING 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. Figure 3.1: Schematic diagram of coupled tank system A simple nonlinear model is derived based on figure 3.1. Let H1and H2 be the fluid level in each tank, measured with respect to the corresponding outlet. Considering a simple mass balance, the rate of change of fluid volume in each tank equals the net flow of fluid into the tank. Thus for each of tank 1 and tank 2, the dynamic equation is developed as follows:
- 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 140 ܣଵ ൌ ቀ ௗுభ ௗ௧ ቁ ܳଵ െ ܳଵ െ ܳଷ ….. (3.1.1) ܣଶ ൌ ቀ ௗுమ ௗ௧ ቁ ܳଶ െ ܳଶ ܳଷ ….. (3.1.2) Where H1, H2 = height of fluid in tank 1 and tank 2 respectively A1, A2 = cross sectional area of tank 1 and tank 2 respectively Qo3 = flow rate of fluid between tanks Qi1, Qi2 = pump flow rate into tank 1 and tank 2 respectively Qo1, Qo2 = flow rate of fluid out of tank 1 and tank 2 respectively Each outlet drain can be modelled as a simple orifice. Bernoulli’s equation for steady, non viscous, incompressible shows that the outlet flows in each tank is proportional to the square root of the head of water in the tank. Similarly, the flow between the two tanks is proportional to the square root of the head differential. ܳைଵ ൌ ߙଵ√ܪଵ ….. (3.1.3) ܳைଶ ൌ ߙଶ√ܪଶ ….. (3.1.4) ܳைଷ ൌ ߙଷඥሺܪଵ െ ܪଶሻ ….. (3.1.5) Where ߙଵ, ߙଶ,ߙଷ are proportional constants which depend on the coefficients of discharge, the cross sectional area of each orifice and the gravitational constant. Combining equation (3.1.3), (3.1.4) and (3.1.5) into equations (3.1.1) and (3.1.2), a set of nonlinear state equations which describe the system dynamics of the coupled tank are derived. ܣଵ ቀ ௗுభ ௗ௧ ቁ ൌ ܳଵ െ ߙଵ√ܪଵ െ ߙଷඥሺܪଵ െ ܪଶሻ . ….. (3.1.6) ܣଶ ቀ ௗுమ ௗ௧ ቁ ൌ ܳଶ െ ߙଶ√ܪଶ ߙଷඥሺܪଵ െ ܪଶሻ ….. (3.1.7) For a set of inflows ܳଵ and ܳଶ, the fluid level in the tanks is at some steady state level ܪଵ and ܪଶ. Consider a small variation in each inflow, ݍଵ in ܳଵ and ݍଶ in ܳଶ. Let the resulting perturbation in level be ݄ଵ and ݄ଶ respectively. From equations (3.1.6) and (3.1.7), the equation becomes: For Tank 1- ܣଵ ݀ሺܪଵ ݄ଵ ሻ ݀ݐ ൌ ሺܳଵ ݍଵሻ െ ߙଵඥሺܪଵ ݄ଵሻ െ ߙଷඥሺܪଵ െ ܪଶሻ ሺ݄ଵ െ ݄ଶሻ ….. (3.1.8)
- 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 141 For Tank 2- ܣଶ ݀ሺܪଶ ݄ଶሻ ݀ݐ ൌ ሺܳଶ ݍଶሻ െ ߙଶඥሺܪଶ ݄ଶሻ ߙଷඥሺܪଵ െ ܪଶሻ ሺ݄ଵ െ ݄ଶሻ ….. (3.1.9) Subtracting equations (3.1.6) and (3.1.7) from equation (3.1.8) and (3.1.9), the equations obtained are, ܣଵ ൬ ݄݀ଵ ݀ݐ ൰ ൌ ݍଵ െ ߙଵሼඥሺܪଵ ݄ଵ ሻ െ ඥܪଵ ሽ െ ߙଷሼඥሺܪଵ െ ܪଶ ݄ଵ െ ݄ଶሻ െ ඥሺܪଵെܪଶሻሽ ….. (3.1.10) ܣଶ ቀ ௗమ ௗ௧ ቁ ൌ ݍଶ െ ߙଶሼඥሺܪଶ ݄ଶ ሻ െ ඥܪଶ ሽ ߙଷሼඥሺܪଵ െ ܪଶ ݄ଵ െ ݄ଶሻ െ ඥሺܪଵെܪଶሻሽ ….. (3.1.11) For small perturbations, ඥሺܪଵ ݄ଵ ሻ ൌ ටܪଵ ቀ1 ுభ ଶுభ ቁ ….. (3.1.12) Therefore, ඥሺܪଵ ݄ଵ ሻ െ ඥܪଵ ൎ ݄ଵ 2ඥܪଵ Similarly, ඥሺܪଶ ݄ଶ ሻ െ ඥܪଶ ൎ ݄ଶ 2ඥܪଶ And ඥሺܪଶ െ ܪଵ ݄ଶ െ ݄ଵ ሻ െ ඥܪଶ െ ܪଵ ൎ ݄ଶ െ ݄ଵ 2ඥሺܪଶ െ ܪଵሻ Simplify equation (3.1.10) and (3.1.11) with these approximations becomes, ܣଵ ቀ ௗభ ௗ௧ ቁ ൌ ݍଵ െ ఈభ ଶඥுభ ݄ଵ െ ሼߙଷ/2ඥሺܪଵ െ ܪଶሻሽ ሺ݄ଵ െ ݄ଶሻ ….. (3.1.13) ܣଶ ቀ ௗమ ௗ௧ ቁ ൌ ݍଶ െ ఈమ ଶඥுమ ݄ଶ ሼߙଷ/2ඥሺܪଵ െ ܪଶሻሽ ሺ݄ଵ െ ݄ଶሻ ….. (3.1.14)
- 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 142 In equations (3.1.13) and (3.1.14), note that the coefficients of the perturbations in level are functions of the steady state operating points ܪଵand ܪଶ. Note that the two equations can also be written in the form- ܣଵ ቀ ௗభ ௗ௧ ቁ ൌ ݍଵ െ ݍଵ െ ሼߙଷ/2ඥሺܪଵ െ ܪଶሻሽ ሺ݄ଵ െ ݄ଶሻ ….. (3.1.15) ܣଶ ቀ ௗమ ௗ௧ ቁ ൌ ݍଶ െ ݍଶ ሼߙଷ/2ඥሺܪଵ െ ܪଶሻሽ ሺ݄ଵ െ ݄ଶሻ….. (3.1.16) Where q୭ଵ and q୭ଶ represent perturbations in the outflow at the drain pipes. This is appropriate in the case where outflow is controlled by attaching an external clamp for instance. Each value of ߙଵ, ߙଶ, ߙଷ, ܣଵ, ܣଶ, ܪଵand ܪଶ can be obtained from mathematical modelling equations- ܪଵ = 20, ܪଶ = 17 ߙଵ = 53.436 ߙଶ = 53.436 ߙଷ = 53.436 ܣଵ = 600 ܣଶ = 600 By using the Parameters value and equations (3.1.13), (3.1.14), we can get the following equations in the form of manipulating variables ݍଵ, ݍଶ and process variables ݄ଵ, ݄ଶ – ௗభ ௗ௧ ൌ 1.67݁ሺെ3ሻ ݍଵ െെ 9.96݁ሺെ3ሻ ݄ଵ െെ 0.0257 ሺ݄ଵ െ ݄ଶሻ ….. (3.1.15) ௗమ ௗ௧ ൌ 1.67݁ሺെ3ሻ ݍଶ െ 0.0108 ݄ଶ 0.0257ሺ݄ଵ െ ݄ଶሻ ….. (3.1.16) ቆ ݄ଵ ሶ ݄ଶ ሶ ቇ ൌ ቂ െ0.03566 0.0257 0.0257 െ0.0356 ቃ ൬ ݄ଵ ݄ଶ ൰ 1.67݁ሺെ3ሻ 0 0 1.67݁ሺെ3ሻ ൨ ൬ ݍଵ ݍଶ ൰ ൬ ݕଵ ݕଶ ൰ ൌ ቂ 1 0 0 1 ቃ ൬ ݄ଵ ݄ଶ ൰ ቂ 0 0 0 0 ቃ ൬ ݍଵ ݍଶ ൰ ….. (3.1.17)
- 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 143 Above equation (3.1.17) is the transfer function of coupled tank system in the form of state- space matrices, where ݄ଵ ሶ = derivative of state variable for tank 1 ݄ଶ ሶ = derivative of state variable for tank 2 ݄ଵ = state variable for tank 1 ݄ଶ = state variable for tank 2 ݍଵ = input variable for tank 1 ݍଶ = input variable for tank 2 ݕଵ = output variable for tank 1 ݕଶ = output variable for tank 2 4. SIMULATION RESULTS (MATLAB) This topic presents the designing of PID Controller to control coupled tank system using MATLAB R2012a software. This software is used to create the Simulink diagram for PID Controller and performance for each parameter for PID Controller is also simulated. The performances of PID Controller are evaluated in terms of overshoot, rise time and steady state error. Then, the gain for each parameter also has been tuned in this software and the validity for each parameter is compared using the reference value (set point). Fig. 4.1 shows the MATLAB Simulink block for PID Controller combines with plant. Figure 4.1: Block Diagram of PID Controller combines with plant Figure 4.2: State-space matrices values in Matlab
- 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 144 Figure 4.3: Block Diagram of inside PID Figure 4.4: Block Diagram of inside PID Controller 1 Controller 2 Based on the transfer function for equation (3.1.17), state-space matrices values are fed in Matlab, shown in fig. 4.2, Fig. 4.3 and 4.4 are the controllers for both the tanks in this system. This controller is design based on equation of PID Controller, ݑሺݐሻ ൌ ܭ ݁ሺݐሻ ܭ ݁ሺݐሻ݀ݐ ܭௗ ݀݁ ݀ݐ ሺݐሻ ݑሺݐሻ ൌ ܭ ሾ݁ሺݐሻ 1 ܶ ݁ሺݐሻ݀ݐ ܶௗ ݀݁ ݀ݐ ሺݐሻሿ ….. (4.1.1) Where ܭ = ܭ / ܶ : ܭௗ = ܭ . ܶௗ Simulation result has been established for different type of controller used for tank-1 water level control. The equation for coupled tank system refers the equation (3.1.17). Fig 4.5 shows tank 1 level control for different controllers’ response comparison. From fig. 4.6 it is clear that for P controller rise time is more compare to other controllers. PI controller has overshoot while P and PD controllers give undershoot. Comparing with other controllers, PID has less rise time and more stable (no overshoot/undershoot), so PID controller is most effective than any other controller. Figure 4.5: Tank 1 level response for different Figure 4.6: Tank 1 level response for different Controllers controllers in terms of rise time and overshoot/undershoot 0 1 2 3 4 5 6 7 8 9 10 0 5 10 15 20 25 Time (seconds) H1 Tank 1 Leval Response for Different Controllers SET POINT P PI PD PID 0.7 0.75 0.8 0.85 0.9 0.95 19.5 19.6 19.7 19.8 19.9 20 20.1 20.2 Time (seconds) H1 Tank 1 Level Response for Different Controllers SETPOINT P PI PD PID
- 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 145 Figure 4.7: Tank 1 level response for different controllers in terms steady state error (S.S.E.) The simulation result for different type of controllers used for tank-2 water level control is very much similar to simulation results shown above for tank-1, only difference of different water levels maintained in tanks. 5. EXPERIMENTAL RESULTS (LABVIEW) This section shows the experimental result as the PID Controller output fuzzified logic controls liquid level at tank 1 and tank 2. The performance result for level liquid that is controlled by PID Controller has been discussed. Figure 5.1: Tank-1 maintained level using Figure 5.2: Tank-2 maintained level using PID Controller PID Controller Fig. 5.1 and 5.2 shows the result when PID Controller is controlling water level in tank-1and tank-2 at coupled tank system. The set points (20 cm for tank-1 and 17 cm for tank-2) are set for both the tanks. The proportional gain is set equal to 1.2, integral time is set equal to 50 min and derivative time is set equal to 0.1 min to provide the desired response. After the Start/Run button is clicking, the controller starts to run and send desired voltage to solenoid valves combinations at tank-1 and tank-2. The value of desired voltage controls manipulating variable (flow rate) through solenoid valves combinations. As level is going to be maintained in both the tanks, it is shown on waveform chart at front panel. 9.695 9.7 9.705 9.71 9.715 9.72 9.725 19.94 19.95 19.96 19.97 19.98 19.99 20 20.01 20.02 20.03 Time (seconds) H1 Tank 1 Leval Response for Different Controllers SETPOINT P PI PD PID
- 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 146 6. LABVIEW GUI’S This topic presents the designing of PID Controller to control coupled tank system using LabVIEW 2010 software. This software is used for getting the implement result for the project by develop a GUI for PID Controller. Before the GUI for PID Controller is programmed, algorithm for PID Controller is needed. So that, to find the algorithm the set point is compared to the process variable to obtain the error. Error = SP– PV Then, convert equation (4.1.1) becomes, ݑሺݏሻ ൌ ܭ ሺ1 1 ܶ ݏ ܶௗ ݏሻ ݑ ൌ ܭ ሾ݁ݎݎݎ ݁ݎݎݎ ݊݁ݓ െ ݁ݎݎݎ ݈݀ ܶ ሺ݁ݎݎݎ ݊݁ݓ െ ݁ݎݎݎ ݈݀ሻ כ ܶௗ ሿ ..… (6.1.1) Fig. 6.1 and 6.2 show the first GUI that has been created. This GUI is created based on the algorithm for PID Controller that had been stated on equation (6.1.1). Figure 6.1: The GUI for PID Controller 1 Figure 6.2: The GUI for PID Controller 2 Fig. 6.3 shows the second GUI for any one tank sensor analog input measurement that been created. GUI for another tank sensor is same as first one. NI module 9221 is used for analog input measurement. This GUI is the first GUI that runs once the program is started. This GUI is created to
- 10. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 147 detect the DAQ card that been used. The Run button appears after GUI detects the DAQ card and clicked to proceed to next step. Figure 6.3: The GUI for DAQ card analog Figure 6.4: The GUI for DAQ card digital input detection output detection Fig 6.4 shows the third GUI for any one tank digital output measurement that has been created. GUI for another tank digital output measurement be same as first one. NI modules 9474 and 9472 have been used for digital output measurement. This GUI is created to detect the DAQ card that been used. The Run button appears after GUI detects the DAQ card and clicked to proceed to next step. 7. DAQ CARD The NI cDAQ with NI A/I and A/O Modules has been used as the data acquisition input output card for the experimental implementation. Fig. 7.1 shows the DAQ card functions to communicate between controller and plant. Figure 7.1: NI DAQ card connection The designed controllers are sending the required signal to solenoid valves at the coupled tanks. These signals must flow through the DAQ card. Then, the DAQ card sends these signals to solenoid valves in the coupled tanks system. Each coupled tank which consists of sensor and actuator is in a continuous closed loop to send back the signal to the controller for next iteration.
- 11. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 148 8. SOFTWARE PART Figure 8.1: Front Panel of PID output fuzzified control water level coupled tank system Figure 8.2: Block diagram (LabVIEW) of PID output fuzzified control water level coupled tank system 9. HARDWARE PART Figure 9.1 NI 9474 Digital Output DAQ module
- 12. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 149 Measurement Type Digital Isolation Type Ch-Earth Ground Isolation Output-Only Channels 8 Current Drive Single 1 A Maximum Output Range 5 V , 30 V Length 9 cm Width 2.3 cm I/O Connector Screw terminals Operating Temperature Range -40 o C to 70 o C Storage Temperature Range -40 o C to 85 o C Table 9. A Specifications Summary NI 9474 Figure 9.2 NI 9221 Analog Input DAQ module Measurement Type Analog Isolation Type Ch-Earth Ground Isolation Single-Ended Input Channels 8 Current Drive Single 1 A Voltage Range -60 V , 60 V Length 9 cm Width 2.3 cm I/O Connector 25-pin D-Sub , Screw terminals Operating Temperature Range -40 o C to 70 o C Storage Temperature Range -40 o C to 85 o C Resolution 12 bits Sample Rate 800 kS/s Table 9.B Specifications Summary NI 9221
- 13. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 150 Figure 9.3 Solenoid valve Model 2W160-15 Working medium Air,water,oil,gas Acting type Direct acting Type Normal close CV value 4.8 Mm/aperture of flow rate 16 Material of body Brass Working pressure Water 0-0.7 MPa Table 9.C Solenoid Valve Specifications Figure 9.4 Vegetronix Moisture Sensor Probe Parameter Range Model VH400 Input Voltage 3.3V to 20 VDC Power on to Output Stable 400 ms Operational Temperature -40 o C to 85 o C Output Voltage Range 0 to 3V Typical Power < 7Ma Sensitive to Volume No Sensitive to Salt No Frequency of operation 80 MHz Internal Voltage Regulator Yes Table 9.D Specifications Summary VH400
- 14. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 151 10. FUZZIFICATION LOGIC PART 10.1 Fuzzification logic for tank-1 If (V<=0.3) {P=0; Q=0; R=0 ;} If (V<=0.8 && V>0.3) {P=1; Q=0; R=0 ;} If (V<=1.2 && V>0.8) {P=1; Q=1; R=0 ;} If (V<=2.5 && V>1.2) {P=0; Q=0; R=1 ;} If (V<=3 && V>2.5) {P=0; Q=1; R=1 ;} If (V>3) {P=1; Q=1; R=1 ;} 10.2 Fuzzification logic for tank-1 If (V<=0.5) {P=0; Q=0; R=0 ;} If (V<=1 && V>0.5) {P=1; Q=0; R=0 ;} If (V<=2.5 && V>1) {P=1; Q=1; R=0 ;} If (V<=4.5 && V>2.5) {P=0; Q=0; R=1 ;} If (V>4.5) {P=1; Q=1; R=1 ;} 11. COMPARISON BETWEEN SIMULATION AND IMPLEMENTATION RESULT The objective of comparing the result of PID Controller that control liquid level at both the tanks on coupled tank between the simulation and implementation result is to investigate to find the better result of PID Controller. Design techniques of simulation and implementation have been explored and their performance is evaluated base on percentage overshoot, settling time and steady state error. It is shown that, the simulation result achieve the set point voltage as show in fig. 4.1 and 4.4. The simulation result showed the steady state error value is nearly 0%. The settling time is the time for response to reach and stay within the set point and for simulation result is very less around 1 second. The simulation result does not have any percentage overshoot. Therefore, the implementation result does not achieve the set point exactly as it required. As it shows in fig. 4.7 and 4.8, the steady state error value exists there, even it’s very small. In the implementation result, there are no percentage overshoot but some settling time because the plot does not achieve the set point exactly.
- 15. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 152 12. CONCLUSION AND FUTURE RECOMMENDATION 12.1 CONCLUSION As a conclusion, PID Controller had been successfully designed to control liquid level at both the tanks on coupled tank system using simulation and implementation. The comparison has been made and simulation techniques perform better result as compared to the implementation. The advantage of simulation technique is that using block diagram is easy to run and execute the program. Therefore, there is no need to find the algorithm for PID Controller. There are some difficulties for implementation technique due to the hardware involves. Hardware such as DAQ card is needed to communicate between software and coupled tank. Because of that, the limitation for this hardware must be considered. The PID algorithm is also needed to develop the GUI for this controller. There are differences at graph plot between the simulation and implementation results because of the error happen at implementation result due to hardware limitation such as the voltage at capacitive level sensor are not equal with the voltage that set at the coding of the controller. If there is no error, the implementation result should tally as the simulation result. 12.2 FUTURE RECOMMENDATION 1. Solenoid valve can be used at coupling point. 2. Real time system can be implemented to get more accurate results. 3. Ultrasonic sensors can be used instead of capacitive probe type to get high accuracy even for 1 mm resolution also. 4. Apart from try and error method to tuning gain for each parameter, PID Controller tuning through other method such as Ziegler Nichols and Cohen Coon tuning formulae etc. 5. Issue of hardware limitation that affected the experiment result. This can be solved by placing The RC circuit can be placed between the DAQ card and coupled tank connection as a filter to get the smooth result. REFERENCE [1] Jutarut Chaorai-ngern, Arjin Numsomran, Taweepol Suesut, Thanit Trisuwannawat and Vittaya Tipsuwanporn, “PID Controller Design using Characteristic Ratio Assignment Method for Coupled-Tank Process”, Faculty of Engineering, King Mongkuts Institute of Technology Ladkrabang, Bangkok 10520, Thailand, 2005 [2] Muhammad Rehan, Fatima Tahir, Naeem Iqbal and Ghulam.,” Modelling, Simulation and Decentralized Control of a Nonlinear Coupled Tank System”, Department of Electrical Engineering, PIEAS, Second International Conference on Electrical Engineering University of Engineering and Technology, Lahore (Pakistan), 25-26 March 2008 [3] M. Khalid Khan, Sarah K. Spurgeon, “ Robust MIMO water level control in interconnected twin-tanks using second order sliding mode control”, Control and Instrumentation Group, Department of Engineering, University of Leicester, Leicester LE1 7RH, UK, 10 February 2005
- 16. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 4, July - August (2013) © IAEME 153 [4] Liu Jinkun., MATLAB simulation of advanced PID control. Beijing: Electronic Industry Press, 2004 [5] Qiang Xiong a, Wen-Jian Cai a, b,*, Mao-Jun He a, Equivalent transfer function method for PI/PID controller design of MIMO processes, Aug 28, 2012 [6] L.ShrimanthSudheer, P.Bhaskar and Parvathi.C.S., “Step Variation Studies of Arm7 Microcontroller Based Fuzzy Logic Controller for Water-In-Tank Level Control”, International Journal of Electrical Engineering & Technology (IJEET), Volume 4, Issue 2, 2013, pp. 405 - 415, ISSN Print : 0976-6545, ISSN Online: 0976-6553. [7] Gaikwad Madhukar V. and Prof. Mangulkar Madhuri N., “Seismic Performance of Circular Elevated Water Tank with Framed Staging System”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 4, 2013, pp. 159 - 167, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

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