DEVELOPMENT OF A FIBRE OPTIC ANEMOMETER (FOA) Nor Hayati Saad 1, Zuriati Janin 2, Shah Alam, Selangor, Malaysia

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1 ABSTRACT DEVELOPMENT OF A FIBRE OPTIC ANEMOMETER (FOA) Nor Hayati Saad 1, Zuriati Janin 2, 1 Faculty of Mechanical Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia norhayatisaad@salam.uitm.edu.my 2 Faculty of Electrical Engineering, Universiti Teknologi MARA, Shah Alam, Selangor, Malaysia zuriaty@salam.uitm.edu.my A Fibre Optic Anemometer is an instrument used to measure the wind speed and direction. The final reading of the instrument was wind speed in the unit of meter per second and direction in degree ( o ) unit and displayed through the computer. The main interfacing hardware of the instrument was Peripheral Interface Controller, PIC16F873 and the interfaced program was developed by using Microsoft Visual Basic 6.0. The fibre optic technology was applied as a sensor element to measure the wind speed using light beam interruption principle and wind direction using light beam reflection principle. Specifically the paper discusses the step involved in development of the instrument including the conceptual design of the instrument, development of electronics system, interfacing hardware and software and instrument calibration. The advantages of the fibre optic as the sensor element have improved the performance of the anemometer. The final output of the research which is the Fibre Optic Anemometer instrument; is useful, can be further improved, fabricated professionally and can be implied in any long distant monitoring system such as high tower or weather stations. 1. INTRODUCTION The most applications of the anemometer are in the aerospace area, weather stations, measuring the wind speed for certain high building and so on. From the survey that had been conducted, the specific application of the anemometer in eight weather stations in Malaysia is to measure the surface air. An example, KLIA Weather Station used the anemometer to measure the surface air, which is the basic and important information for aircraft to taking off and landing. Currently, some of the weather stations already used the fibre optic, though only as a data transmission cable. However, they faced few problems; In fact, the cost is expensive and the speed and direction of wind were measured separately. The anemometer is not made locally, but is imported. This research will lead to an improvement of anemometer instrumentation used specifically to measure wind speed and detect the wind direction. 2. OBJECTIVE OF THE RESEARCH i) To design and develop a portable anemometer to measure wind velocity and detect the wind direction. ii) To develop a measuring instrument and handle signals using fibre optics technology. iii) To provide an interface between the measuring instrument and a computer for acquiring data in a computer.

2 3. RESEARCH METHODOLOGY i) Desk research. ii) Development of the conceptual design of the complete physical body of the instrument and mechanical system in capturing the wind speed and direction signal. iii) Design and fabrication of the mechanical system of FOA. It involves the part for capturing and measuring the wind speed such as slotted disc, shaft, and disc with different depth of hole (to detect the direction of the wind), the casing of the instrument and the stand to hold the instrument. iv) Build-up, assemble, install and mounting the electronics part of sensor elements in the mechanical system. v) Development of an interface system between the measuring equipment and the computer. vi) Equipment calibration. 4. DEVELOPMENT PHASE OF THE INSTRUMENT, RESULT AND DISCUSSION Figure 1 shows the building block of the Fibre-Optic Anemometer instrumentation. The development of the instrument involved four main phases, design and fabrication of mechanical system; development of the electronics system including the Fibre Optic Sensor and signal conditioning circuitry; interfacing hardware and software development; and finally the instrument calibration. INPUT Mechanical System - Primary Sensing Element: Capturing Wind Speed Signal Capturing Wind Direction signal Electronics System: Sensor -Signal Conditioning -Analogue/Digital Conversion Interfacing Hardware and Software: Data Transmission Signal Analysis Instrument Calibration: Output Figure 1. Building Blocks of the FOA Instrumentation

3 4.1 Development of the Mechanical System The final dimension of the developed FOA is 271 mm x 550 mm in length and weight is about 1.04 kg. The weight is included the main physical elements of the FOA and the casing of the instrument. Figure 2 shows the exploded part of the instrument; (1) Vane head, (2) Shaft 1 (wind speed measurement), (3) Disc 1 slotted disc, (4) Vane body, (5) Back Vane, (6) Vane tail, (7) Vane feet, (8) Shaft 2 (wind direction measurement), (9) Main body direction measurement, and (10) Disc 2 with different depth of holes (multiple blind-holes disc). There were four essential steps involved in the development of mechanical system [Nor Hayati, Zuriati Janin, 2005]; (i) conceptual design of the mechanical system (ways in capturing the wind speed and direction signal); (ii) mounting and positioning the mechanical and related electronics components; (iii) design the casing and the platform of the instrument; and (iv) fabrication, assembling and instrument calibration Figure 2. Exploded drawing of the Fibre Optic Anemometer 4.2 Development of the Electronics System As illustrated in Figure 3, the instrumentation involved two stages which were development of the system for capturing the input signal and development of the signal conditioning circuitry to convert the input signal to output signal before it can be interfaced to the interfacing hardware. The system for capturing the wind speed signal and wind direction signal are portrayed in Figure 4 and 5 consequently. Referring to Figure 4, when the wind blows, the propeller will spin and concurrently rotate the shaft. The signal of the rotational propeller was measured using the light chopping concept. If the light beam is interrupted, no signal will be transmitted from the light source to the photo detector. The photo detector does not receive any signal to be transmitted to the signal conditioning system; the electronic system will assume the system is off with output 0. Otherwise if the light beam passes through the disc slot, the photo detector will receive the signal and transmit to the signal conditioning system. The electronic system will translate

4 the condition as on with the output 1. The light chopping processes will produce a series of pulses signal. The speed of the propeller was calculated based on the produced pulses. As portrayed in Figure 5, the disc with different depth of holes was used to detect the direction of the wind and mounted at the end of the rotated shaft. The system used light beam reflection to detect the direction of the wind. The reflected light beam will be transmitted via the fibre optic cable and reach at the photo detector. The photo detector examines the received signal and sends to the signal conditioning system. The signal conditioning system translates the output signals in form of the different level of the voltage; due to the various light intensity received based on the different depth of the disc holes. Figure 6 and 7 show the final signal conditioning circuit for measuring the wind speed and detecting the wind direction. The signal conditioning circuit consisted of combination of six circuit types: i) Driver, (ii) Amplification, (iii) Filtering, (iv) Current to voltage converter, (v) Buffer, and (vi) Frequency to voltage converter circuit [Nor Hayati, Zuriati Janin, 2005]. Mechanical Electronic System Input Signal Input Signal System - capturing the wind Speed signal System - capturing the wind direction signal Signal conditioning circuitry For wind speed measurement: Signal Amplification Signal Filtering Buffer & Amplification Signal Conversion Signal conditioning circuitry For wind direction detection: Signal Amplification Signal Filtering Buffer & Amplification Signal Conversion Output signal: 1) Wind speed signal, 2) Wind direction Signal Interfacing Hardware & Software Figure 3. Development phase of the electronic system of FOA Propeller Slotted Disc1 Air Flow Shaft 1 Driver circuitry LED Fibre Optic Signal conditioning circuit Photodetector Output signal Figure 4. System for capturing the wind speed signal of the FOA

5 Air Flow Propeller Fibre Optic Photodetector Output signal Shaft 1 Shaft 2 Signal conditioning circuit Driver circuitry Fibre Optic LED Multiple blind-hole discs (Disc with different depth of holes) Figure 5. System for capturing the wind Direction signal of the FOA Figure 6. Signal Conditioning circuitry for speed measurement Figure 7. Signal Conditioning circuitry for Direction measurement

6 4.3 Interfacing Hardware and Software Development The hardware consisted of several components, which were: DC power supply, Serial Port, RS232 Interface IC, PIC16F873. PIC16F873 microcontroller was used as the control device for the whole system. Figure 8 shows the schematic diagram of the hardware interface device. Basically, a range of 4.5V to 5.0V DC was fed to the hardware Interface device. This voltage was used as the power supply for the RS232 interface IC and PIC16F873. The serial port used in the hardware interface device consisted of 9 pins. It was referred to the port that has been connected to the COM port of the personal computer for the data transmission. Figure 8. Schematic Diagram of the Hardware Interface Device START Create user interface Write Visual Basic code to perform actions when user interact with the hardware Run the program and test for errors Correct Errors Error? END No Yes Figure 9. Process Flow of the Display Software Development

7 Frequency (Hz) The simple programming using Microsoft Visual Basic 6.0 was developed in order to display the result on the computer. There were four types of Visual Basic code; sub procedure, function procedure, variables and constant. Their main functions were to execute in responding to an event, write the arguments, store the values and declare the same value of variables to constant, respectively. Refer to Figure 9 for the process flow of the display development. Figure 10 shows the example of the FOA display result. Figure 10. The result of the Visual Basic programming 5. INSTRUMENT CALIBRATION The instrument was calibrated in wind tunnel. The speed of the wind tunnel was varied from a minimum speed to a maximum speed and the output voltage that corresponds to the speed of the FOA was measured using digital voltmeter. The pattern of the output can be seen using the oscilloscope. 5.1 Results for Wind Speed Calibration As the speed of the propeller increased, the width of the output PWM (Pulse Width Modulation) also increased, as well as the output voltage (Figure 11). The speed of the propeller was equal to the output PWM. The final relationship is shown in Figure 12. Input frequency versus output voltage output voltage (Vo) Figure 11. Relationship between Input Frequency and Output voltage

8 Output Voltage (Vo) Output Voltage versus Speed Speed (rps) Figure 12. Relationship between output voltage and speed 5.2 Results for Wind Direction Calibration The second testing was done to calibrate and test the light intensity signal circuit. The calibration result was shown in Figure 13. The relationship between the distance of a source of light and its apparent intensity was governed by the inverse square law approximately because of the mechanical part such as blind-holes disc and mounting part of the light source to the photodiode. It only appears to do so as a result of being sensed at a different distance; the farther away it was sensed, the larger the area the photons are spread over and the fewer are sensed. In other words, it can be said that the intensity of light decreases as the depth of blind-holes disc increases. Wind Direction Testing Result Output Voltage Wind Direction ( ) Distance (mm) Figure 13 Relationships between Wind Direction & Distance

9 6. CONCLUSION The developed Fibre Optic Anemometer (FOA) is a portable instrument used to measure the wind velocity and detect the wind direction. This research has led to an improvement of anemometer instrumentation used specifically to measure wind speed and detect the wind direction concurrently. The advantages of the fibre optic as the sensor element will improve the performance of the anemometer. The output of this research is useful to be implied in long distant monitoring system such as high tower. In general the combination of wind speed measurement and wind direction detection will simplify and minimise the size of the anemometer. 7. FUTURE RECOMMENDATION Further researches can be made to improve the instrument: i) The modification on the mechanical system design can be made to improve its accuracy and sensitivity in measuring the wind speed and direction. ii) The proper fibre optic sensor with a dome must be fabricated especially to ensure that more light immersion is converged into the receiver. iii) The signal conditioning has an improvement pulses signal after being filtered. However the signal can be improved much better if a better filtering technique is applied and it is required a detail study on the filtering techniques. iv) The more advanced and sophisticated software and program can be used for signal interfacing to the computer, such as Lab View; so that the result of the measurement can be displayed more conveniently. By using the software more function can be added such as graph and chart plotting. REFERENCES 1. D.A Krohn, Fibre optic sensors fundamentals and applications, Instrument society of America, David R. Goff, Fibre Optic Reference Guide: A Practical Guide to the Technology, second edi., Focal Press, Ekedahl, Micheal and Newman, William, Programming with Microsoft Visual Basic 6.0: An Object Oriented Approach, Course Technology, International Thomson Publishing company, Cambridge, Gerald D Byrne, Stephen W James, Ralph P Tatam, A Bragg Grating Based Fibre Optic Reference Beam Laser Doppler Anemometer, Institute of Physics Publishing, Measurement Sci. Technology, 12 (2001)

10 5. J Knuhtsen, E Olldag, P Buchhave, Fibre-Optic Laser Doppler Anemometer with Bragg Frequency Shift Utilising Polarisation-Preserving Single-Mode Fibre, Journal Physics, E: Sci. Instrem., Vol.15, N.H. Saad, Z Janin, A.R. Mahamad Sahab, Instrumentation of Digital-Propeller- Anemometer, 2003 Asian Conference on Sensor, Renaissance Hotel, Kuala Lumpur, Institute of Electrical and Electronic Engineers (Malaysia Section), IEEE Cataloguing no. 03EX729C, ISBN: , Library of Congress No.: , pp , July Nor Hayati Saad, Zuriati Janin and Ruhaidawati Mohd Ali Piah, Computer- Interfacing Development for Propeller Anemometer, International Conference on Control, Automation and Systems, The Shangri-La Hotel, Bangkok, Thailand, August, Nor Hayati Saad, Zuriati Janin, Development of a Fibre Optic Anemometer, Short Term Grant Research report, Faculty of Mechanical Engineering, UiTM Shah Alam, (2005). 9. Nor Hayati Saad, Zuriati Janin, Heldinna Nyotem, Signal Conditioning System for Propeller-Anemometer, Proceedings of the 6 th International Conference on Electronics Materials and Packaging (EMAP 2004), Penang, Malaysia, ISBN: X, pp , 5 7 December 2004 ACKNOWLEDMENT The authors would like to convey very deep gratitude and appreciations to all supporters and individuals involved: Institute of Research, Development and Commercialisation (IRDC), UiTM for sponsoring the research; The Technicians: Fluid Mechanics Lab., Automation Lab., Computer Lab., Faculty of Mechanical Engineering; and Instrument Lab., Faculty of Electrical Engineering, for the use of equipments and laboratory. Thank you so much. Your efforts and contributions are very much appreciated.