||A Highly Accurate Ultrasonic Measurement System
Using Vernier Caliper Phase Meter
||Department of Electrical Engineering
two-frequency continuous wave
vernier caliper phase meter
direct digital frequency synthesizer
ultrasonic distance measurement system
ultrasonic temperature measurement system
phase locked loops
超音波量測實驗是在溫控箱中進行，在溫控箱中安裝兩個頻率範圍為 40 ± 2 kHz的超音波感測器，並以單晶片微電腦控制兩個連續波信號的發射及相位偵測，計算並紀錄相位差的資訊，再將相關資料送到 PC 計算出距離或溫度值並進行校正。在距離量測系統中，發射及接收端的超音波感測器是安裝在溫控箱的同一邊，以增加系統的實用性。實驗結果顯示，當量測範圍為 50 到 200 mm 時，準確度可達 ± 0.1362 mm，解析度為 40 kHz 信號波長的 0.04%。溫度量測系統則是在溫控箱中，以面對面方式安裝兩個相距1 m的超音波感測器。實驗結果顯示，當量測範圍為 0 到 80 ℃ 時,本系統的準確度可達到 ±0.2 ℃，解析度為 0.01%。
Precise measurements of distance and temperature are very important in scientific research and industrial applications. Ultrasonic transducer, a superior choice for distance and temperature measurement, has the advantages such as fast response and contactless operation. Many techniques are available for ultrasonic measurement system mainly includes the time-of-flight (TOF) method and the phase-shift method (PSM). In comparison to the TOF method, the PSM is more accurate and overcomes the delay inertia phenomenon and amplitude attenuation problems, but the range of measurement is limited by a full wavelength. This limitation can be overcome by using such a technique as the multiple-frequency continuous-wave (MFCW) PSM, in which the frequency differences of multiple signals can be decreased to expand the ranges of measurement much greater than one wavelength.
The main aim of this dissertation is to discuss a measurement system based on two frequency continuous wave (TFCW) ultrasonic phase shift method to measure distance and average temperature in air. Two signals with different frequency are generated and sequentially transmitted to the receiver. The phase shift between the transmitted and received signals are then detected and used to compute the distance or temperature data. Especially, the phase shift is measured via a vernier caliper phase meter (VCPM) to improve the accuracy and resolution of the system. A highly accurate TFCW ultrasonic distance measurement system (UDMS) for use in air is described in the first part of this dissertation. In the system, two VCPMs are used to measure the phase-shift data. The phase meter circuit developed to emulate the vernier caliper to measure the phase shift is able to eliminate the measuring errors and produce higher-resolution results without increasing the clock frequency. In the second part of this dissertation, we present an improved system structure for TFCW ultrasonic temperature measurement. The system is based on the transmission of a TFCW signal that is generated by two direct digital frequency synthesizers (DDFSs). The advantages of the DDFS include fine frequency step, smooth frequency transition, and fast switching speed. The phase shift between the transmitted and received signals is also measured by a VCPM. The phase shift data is recorded to determine the speed of ultrasound. The changes in the speed of ultrasound are then calculated and used to determine the average temperature of bulk air.
In the test embodiment, two 40 ± 2 kHz ultrasonic transducers are placed in the temperature-controlled chamber. A single-chip microprocessor is used to control the two frequency continuous wave phase-shift measurement and send the data to a personal computer for the calibration and examination of distance or temperature measurement. In the UDMS, two ultrasonic transducers are placed at the same side of the chamber for practicality. The experimental results show that the accuracy of the system is ± 0.1362 mm and the distance resolution is 0.04% of the wavelength corresponding to the 40 kHz ultrasonic wave at a range of 50-200 mm. Furthermore, in the UTMS, two ultrasonic transducers are placed face to face with a fixed distance (1 m) between them. The experimental results show that the proposed measurement system reaches a high accuracy of ±0.2℃ within a temperature range from 0 to 80℃, with a resolution of 0.01%.
Therefore, the ultrasonic measurement system presented in this dissertation can expand the range of measurement by using DDFS to control the frequency difference of the transmitted signal precisely. The resolution of phase measurement can be improved by increasing the main and vernier scales of the VCPM. Comparing with the system using MFCW phase shift method, the measurement range of our system can easily be expanded just by using two signals, instead of increasing the number of transmitting signals. Therefore, the system complexity can be decreased and the total measuring time of the system can be saved. In conclusion, the main advantages of our ultrasonic measurement systems include high resolution, high accuracy, low cost, and ease of implementation.
LIST OF TABLES XI
LIST OF FIGURES XII
CHAPTER 1 INTRODUCTION 1
1.1 ULTRASONIC DISTANCE MEASUREMENT 1
1.2 ULTRASONIC TEMPERATURE MEASUREMENT 4
CHAPTER 2 METHODS 7
2.1 TFCW PHASE SHIFT METHOD AND DISTANCE COMPUTATIONS 7
2.2 TFCW-BASED ULTRASONIC SYSTEM AND TEMPERATURE COMPUTATIONS 12
2.3 DIRECT DIGITAL FREQUENCY SYNTHESIZER 15
2.4 VERNIER CALIPER PHASE METER 17
CHAPTER 3 SYSTEM IMPLEMENTATION AND EVALUATION 20
3.1 ULTRASONIC DISTANCE MEASUREMENT SYSTEM 20
3.1.1 HARDWARE DESCRIPTION 21
3.1.2 SOFTWARE DESCRIPTION 24
3.1.3 EXPERIMENTAL SETUP 26
3.1.4 EXPERIMENTAL RESULTS 27
3.2 ULTRASONIC TEMPERATURE MEASUREMENT SYSTEM 32
3.2.1 HARDWARE DESCRIPTION 33
3.2.2 SOFTWARE DESCRIPTION 35
3.2.3 EXPERIMENTAL SETUP 37
3.2.4 EXPERIMENTAL RESULTS 38
CHAPTER 4 DISCUSSION 41
CHAPTER 5 CONCLUSIONS 43
M. Parrilla, J. J. Anaya, and C. Fritsch, “Digital signal-processing techniques for high accuracy ultrasonic range measurements,” IEEE Trans. Instrum. meas., vol. 40, pp. 759-763, Aug. 1991.
D. Marioli, C. Narduzzi, C. Offelli, D. Petri, E. Sardini, and A. Taroni, “Digital time-of-flight measurement for ultrasonic sensors,” IEEE Trans. Instrum. meas., vol. 41, pp. 93-97, Feb. 1992.
C. Cai, and P. P .L. Regtien, “Accurate digital time-of-flight measurement using self-interference,” IEEE Trans. Instrum. meas., vol. 42, pp. 990-994, Dec. 1993.
G. Tardajos, G. G. Gaitano, and F. R. M. de Espinosa, “Accurate, sensitive, and fully automatic method to measure sound velocity and attenuation,” Rev. Sci. Instrum., vol. 65, pp. 2933-2938, Sep. 1994.
F. Figueroa, and E. Barbieri, “An ultrasonic ranging system for structural vibration measurements,” IEEE Trans. Instrum. meas., vol. 40, pp. 764-769, Aug. 1991.
M. S. Young, and Y. C. Li, “A high precision ultrasonic system for vibration measurements,” Rev. Sci. Instrum., vol. 63, pp. 5435-5441, Nov. 1992.
F. E. Gueuning, M. Varlan, C. E. Eugene, and P. Dupuis, “Accurate distance measurement by an autonomous ultrasonic system combing time-of-flight and phase-shift methods,” IEEE Trans. Instrum. meas., vol. 46, pp. 1236-1240, Dec. 1997.
C. C. Tong, J. F. Figueroa, and E. Barbieri, “A method for short or long range time-of-flight measurements using phase-detection with an analog circuit,” IEEE Trans. Instrum. meas., vol. 50, pp. 1324-1328, Oct. 2001.
M. Yang, S. L. Hill, and J. O. Gray, “A multifrequency am-based ultrasonic system for accuracy distance measurement,” IEEE Trans. Instrum. meas., vol. 43, pp. 861-866, Dec. 1994.
D. Webster, “A pulsed ultrasonic distance measurement system based upon phase digitizing,” IEEE Trans. Instrum. meas., vol. 43, pp. 578-582, Aug. 1994.
S. S. Huang, C. F. Huang, K. N. Huang and M. S. Young, “A high accuracy ultrasonic distance measurement system using binary frequency shift-keyed signal and phase detection,” Rev. Sci. Instrum., vol. 73, pp. 3671–3677, Oct. 2002.
C. F. Huang, M. S. Young, and Y. C. Li, “Multiple-frequency continuous wave ultrasonic system for accurate distance measurement,” Rev. Sci. Instrum., vol. 70, pp. 1452-1458, Feb. 1999.
K. N. Huang, and Y. P. Huang, “Multiple-frequency ultrasonic distance measurement using direct digital frequency synthesizers,” Sens. Actuators A, vol. 149, pp. 42-50, Jan. 2009.
Y. P. Huang, J. S. Wang, K. N. Huang, C. T. Ho, J. D. Huang, and M. S. Young, “Envelope pulsed ultrasonic distance measurement system based upon amplitude modulation and phase modulation,” Rev. Sci. Instrum., vol. 78, pp. 065103-1~8, Jun. 2007.
L. Angrisani, A. Baccigalupi, and R. S. L. Moriello, “A measurement method based on Kalman filtering for Ultrasonic time-of-flight estimation,” IEEE Trans. Instrum. meas., vol. 55, pp. 442-448, Apr. 2006.
H. P. Lio, and M. S. Young, “New digital phase meter concept and its application,” Rev. Sci. Instrum., vol. 68, pp. 1894-1901, Apr. 1997.
K. N. Huang, C. F. Huang, Y. C. Li and M. S. Young, “High precision, fast ultrasonic thermometer based on measurement of the speed of sound in air,” Rev. Sci. Instrum., vol. 73, pp. 4022-4027, Nov. 2002.
G. S .K. Wong, and T .F. W. Embleton, “Variation of the speed of sound in air with humidity and temperature,” J. Acoust. Soc. Am., vol. 77, pp. 1710-1712, May 1985.
M. Bramanti, E. A. Salerno, A. Tonazzini, S. Pasini and A. Gray, “An acoustic pyrometer system for tomographic thermal imaging in power plant boilers,” IEEE Trans. Instrum. Meas., vol. 45, pp. 159-167, 1996.
K. D. Wilson and W. T. Dennis, “Acoustic propagation through anisotropic, surface-layer turbulence,” J. Acoust. Soc. Am., vol. 96, pp. 1080-1095, 1994.
W. Y. Tsai, H. C. Chen and T. L. Liao, “High accuracy ultrasonic air temperature measurement using multi-frequency continuous wave,” Sens. Actuator A-Phys., vol. 132, pp. 526-532, 2006.
T. S. Zhan, S. L. Wu and W. Y. Tsai, “Spontaneous and highly accurate ultrasonic temperature measurement system for air conditioner in automobiles,” J. Sci. Ind. Res., vol. 68, pp. 44-51, 2009.
P. H. Saul and M. S. J. Mudd, “A direct digital synthesizer with 100-MHz output capability,” IEEE J. Solid-State Circuit, vol. 23, pp. 819-821, 1988.
J. Tierney, C. Rader and B. Gold, “A digital frequency synthesizer,” IEEE Trans. Audio Electroacoust., vol.19, pp. 48-57, 1971.
L. Cordesses, “Direct digital synthesis: a tool for periodic wave generation (part 1),” Signal Process. Mag. IEEE, vol. 21, pp. 50-54, 2004.
A. B. Dennis, “Environmental effects on the speed of sound,” J. Audio Eng. Soc., vol. 36, pp. 8690-8710, Apr. 1988.