宽波束时差法超声波流量计的研究与设计
摘要
时差法超声波流量计以其测量精度高、应用方便等优点近年来被广泛应用于工业生产中。但是采用传统的窄波束发射技术时，接收信号范围小，探头安装困难，测量时声束位置受温度影响大，易产生偏移，给测量带来不便；而采用宽波束发射技术可以很好地解决这些问题。因此宽波束时差法超声波流量计的研究无论对于工业生产还是测量技术的提高，都是一项极有意义的研究课题。
宽波束发射技术的理论基础是Lamb波理论。但是经典的Lamb波理论仅适用于单层媒质薄板，而现有的多层媒质Lamb波理论也不适用于管道流量测量的特殊情况，因此本课题根据流量测量和管道结构的特点，建立了管道宽波束声路的物理模型，在固体弹性力学和经典Lamb波理论的基础上推导出了管道Lamb波的频率方程，据此分析了管道中的声场分布，并给出了在管道中激发Lamb波的方法，从而建立了一整套管道Lamb波理论。实验数据初步证明了该理论的合理性。
多脉冲测量技术是实现宽波束测量的前提。本系统在硬件上采用了开窗技术、波形存储器等一系列具有独创性的设计方案，以TMS320F240 DSP为核心，辅以单片机、CPLD等其它电路，实现了一套完整的多脉冲测量系统。本系统不仅具有瞬时流速、流量、累积流量等显示功能，还具有电流输出和OCT输出功能，其软件稳定性好、效率高，操作灵活方便。
数据处理方面，本系统采用了先低通滤波后中值滤波(FLLM算法)、滚动滤波、均值滤波四重滤波，能自动判断流体的流态，并掘此采用不同的数据处理方法，使测量结果的稳定性和实时性都得到提高。流体流速稳定时，测量结果波动的峰峰值不超过3ns，流速跳变时能在2秒钟内跟上流速的变化，精度可以达到1％。
本文在实验的基础上建立了静态误差产生原因的模型，提出并实现了静态误差的软件自动校正，克服了以往硬件手动调零的诸多缺点，使仪表一致性和稳定性得到很大提高。经过校正，静态时测量的绝对误差小于0.01m／s。
最后，本文还提出了一种新的计时方法，可以用低频计时时钟测量高频信号，并给出了一种用PLL实现的方案。
Ultrasonic transit-time flowmeters are widely used in industry because of their high resolving power and expedience, but the range of receiving signal is limited when the traditional narrow-beam technique is adopted and the position of receiving beam is sensitive to the environment temperature, so that there are difficulties in process of installation and measurement. Wide-beam technique is a solution to the trouble. Therefore, research of wide-beam ultrasonic transit-time flowmeter is significative not only to industry but to measurement technology.
A pipe-Lamb-wave theory is put forward in this paper according to the characteristic of pipe flux measurement. After a physical model of wide-beam path in pipes is designed, the frequency equations for Lamb-wave in pipes are derived in detail. Furthermore, a method of how to engender the Lamb-wave in pipes is proposed.
Hardware and software of a wide-beam ultrasonic transit-time flowmeter are designed in this paper. Open-window means and signal-memory are two kinds of original technique in hardware design. Because of its high-speed and the capability for signal-processing, a TMS320F240 DSP is chosen as the core of hardware. A MCU, CPLDs and other circuits and chips are included as its auxiliaries. Besides the velocity and flux display, a current and a OCT output signal are available. The whole system is stead-going and the operation is convenient and intelligent.
Four different filters are introduced in signal-processing and the system can adopt different algorithm according to the different flux-state automatically and in time, so that the system has an excellent performance in stability and real-time capability. A model of zero-error is constructed on base of several experimentations, according to which, a new dynamic zero-error compensate method replaces the traditional hardware compensate means in this system. After the signal-processing and compensate, the final measure result is smooth, real-time and accurate.
At last, a new timing method is introduced in this paper, it can timing a high-frequency signal with a low-frequency clock. A realization scheme is presented accordingly.
宽波束发射技术的理论基础是Lamb波理论。但是经典的Lamb波理论仅适用于单层媒质薄板，而现有的多层媒质Lamb波理论也不适用于管道流量测量的特殊情况，因此本课题根据流量测量和管道结构的特点，建立了管道宽波束声路的物理模型，在固体弹性力学和经典Lamb波理论的基础上推导出了管道Lamb波的频率方程，据此分析了管道中的声场分布，并给出了在管道中激发Lamb波的方法，从而建立了一整套管道Lamb波理论。实验数据初步证明了该理论的合理性。
多脉冲测量技术是实现宽波束测量的前提。本系统在硬件上采用了开窗技术、波形存储器等一系列具有独创性的设计方案，以TMS320F240 DSP为核心，辅以单片机、CPLD等其它电路，实现了一套完整的多脉冲测量系统。本系统不仅具有瞬时流速、流量、累积流量等显示功能，还具有电流输出和OCT输出功能，其软件稳定性好、效率高，操作灵活方便。
数据处理方面，本系统采用了先低通滤波后中值滤波(FLLM算法)、滚动滤波、均值滤波四重滤波，能自动判断流体的流态，并掘此采用不同的数据处理方法，使测量结果的稳定性和实时性都得到提高。流体流速稳定时，测量结果波动的峰峰值不超过3ns，流速跳变时能在2秒钟内跟上流速的变化，精度可以达到1％。
本文在实验的基础上建立了静态误差产生原因的模型，提出并实现了静态误差的软件自动校正，克服了以往硬件手动调零的诸多缺点，使仪表一致性和稳定性得到很大提高。经过校正，静态时测量的绝对误差小于0.01m／s。
最后，本文还提出了一种新的计时方法，可以用低频计时时钟测量高频信号，并给出了一种用PLL实现的方案。
Ultrasonic transit-time flowmeters are widely used in industry because of their high resolving power and expedience, but the range of receiving signal is limited when the traditional narrow-beam technique is adopted and the position of receiving beam is sensitive to the environment temperature, so that there are difficulties in process of installation and measurement. Wide-beam technique is a solution to the trouble. Therefore, research of wide-beam ultrasonic transit-time flowmeter is significative not only to industry but to measurement technology.
A pipe-Lamb-wave theory is put forward in this paper according to the characteristic of pipe flux measurement. After a physical model of wide-beam path in pipes is designed, the frequency equations for Lamb-wave in pipes are derived in detail. Furthermore, a method of how to engender the Lamb-wave in pipes is proposed.
Hardware and software of a wide-beam ultrasonic transit-time flowmeter are designed in this paper. Open-window means and signal-memory are two kinds of original technique in hardware design. Because of its high-speed and the capability for signal-processing, a TMS320F240 DSP is chosen as the core of hardware. A MCU, CPLDs and other circuits and chips are included as its auxiliaries. Besides the velocity and flux display, a current and a OCT output signal are available. The whole system is stead-going and the operation is convenient and intelligent.
Four different filters are introduced in signal-processing and the system can adopt different algorithm according to the different flux-state automatically and in time, so that the system has an excellent performance in stability and real-time capability. A model of zero-error is constructed on base of several experimentations, according to which, a new dynamic zero-error compensate method replaces the traditional hardware compensate means in this system. After the signal-processing and compensate, the final measure result is smooth, real-time and accurate.
At last, a new timing method is introduced in this paper, it can timing a high-frequency signal with a low-frequency clock. A realization scheme is presented accordingly.
引文
[1] 祝海林，邹昱．管道流量非接触测量——方法与技术．北京：气象出版社，1999．Page(s)1-65
[2] 金长善．超声工程．哈尔滨：哈尔滨工业大学出版社，1989．Page(s)1-194
[3] R.W.米勒编著，孙延祚译．流量测量工程手册．北京：机械工业出版社，1990．Page(s)1-694
[4] 同济大学声学研究室．超声工业测量技术．上海：上海人民出版社，1977．Page(s)1-256
[5] 姚新益．超声波流量计的特点及误差分析．计量技术，1999，8：Page(s)40-42
[6] 刘存，魏永广．时差法流量测量的温度补偿．仪器仪表与分析检测，1998，1：Page(s)35-37
[7] R. Motegi, S. Takeuchi, T. Sato. Widebeam Ultrasonic Flowmeter. Ultrasonics Symposium, 2000:Page(s)331-336
[8] Henry M. Morris. Ultrasonic flowmeter uses wide beam technique to measure flow. Control Engineering, 1980,7:Page(s)99-101
[9] 于大安．超声检测的物理基础，基础自动化，1995，6：Page(s)53-57
[10] 杜功焕，朱哲民，龚秀芬．声学基础．南京：南京大学出版社，2001．Page(s)513-541
[11] 应崇福．超声学．北京：科学出版社，1990．Page(s)52
[12] 彭应秋．声学基础．南昌：南昌航空工业学院，1989．Page(s)1-144
[13] 王祖荫．声发射技术基础．济南：山东科学技术出版社出版，1990．Page(s)33-56
[14] 王耀俊，宁伟，朱为勇．层状复合介质中的Lamb波．物理学进展，1996，9，Vol．16，No．3 and 4：Page(s)：363-376
[15] 宁伟，王耀俊．三层复合结构中的漏Lamb波：理论与实验．声学学报，1996，9，Vol．21，No．5：Page(s)767-772
[16] 宁伟，王耀俊．三层固体复合介质中Lamb波的传播．声学学报，1996，8，Vol．21，No．4：Page(s)414-420
[17] 朱哲民，李剑，邹薇．有液层负载时薄板中类Lamb波的传播．声学学报，1996，3，Vol．21，No．2：Page(s)174-181
[18] 邹薇，朱哲民，杜功焕．纯纵体波模式Lamb波的研究．声学学报，1996，8，Vol．21，No．4：Page(s)409-413
[19] 赵晓亮，朱哲民，杜功焕．薄板中类Lamb波在负载流体中引起的声流的研究．声学学报，1999，9，Vol．24，No．5：Page(s)463-469
[20] TI.TMS320F/C24x DSP Controllers Reference Guide: CPU and Instruction Set. Texas Instruments, 1999,6:Page(s)1-389
[21] TI.TMS320F/C24x DSP Controllers Reference Guide: Peripheral Library and Specific Devices. Texas Instruments, 1999,6:Page(s)1-474
[22] TI.TMS320C1x/C2x/C2xx/cC5x Assembly Language Tools:User's Guide. Texas Instruments, 1995:Page(s)1-483
[23] TI. Code ComposerUser's Guide. Texas Instruments, 1999,10:Page(s)1-234
[24] Cypress Semiconductor Corporation. 32K×8 Static RAM CY7C199. 2001, 7: Page(s)1-16
[25] 串行E~2PROM．武汉力源电子股份有限公司产品资料．1997：Page(s)1-3
[26] TI. 10-Bit Digital-to-Analog Converters: TLC5615C, TLC5615I. Texas Instruments,2000,3:Page(s)1-18
[27] Analog Devices. 4-2OmA Transmitter: AD694. Analog Devices: Page(s)1-12
[28] 叶晓东，朱兆达．中值滤波的快速算法．南京航空航天大学学报，1997，4：Page(s)159-162
[29] The MathWorks, Inc. MATLAB Function Reference, Revised for Release Ⅱ.1999,1:Page (s) 591-592
[30] 姚国民．超声波流量计中的数据处理．声学技术，1998，1：Page(s)35-37
[31] 张毅刚，付平，王丽．采用数字相关法测量相位差．计量学报，2000，7：Page(s)216-221
[32] 黄建军，刘存．改进超声波流量计性能的研究．仪器仪表学报，2001，8：Page(s)87-88
[2] 金长善．超声工程．哈尔滨：哈尔滨工业大学出版社，1989．Page(s)1-194
[3] R.W.米勒编著，孙延祚译．流量测量工程手册．北京：机械工业出版社，1990．Page(s)1-694
[4] 同济大学声学研究室．超声工业测量技术．上海：上海人民出版社，1977．Page(s)1-256
[5] 姚新益．超声波流量计的特点及误差分析．计量技术，1999，8：Page(s)40-42
[6] 刘存，魏永广．时差法流量测量的温度补偿．仪器仪表与分析检测，1998，1：Page(s)35-37
[7] R. Motegi, S. Takeuchi, T. Sato. Widebeam Ultrasonic Flowmeter. Ultrasonics Symposium, 2000:Page(s)331-336
[8] Henry M. Morris. Ultrasonic flowmeter uses wide beam technique to measure flow. Control Engineering, 1980,7:Page(s)99-101
[9] 于大安．超声检测的物理基础，基础自动化，1995，6：Page(s)53-57
[10] 杜功焕，朱哲民，龚秀芬．声学基础．南京：南京大学出版社，2001．Page(s)513-541
[11] 应崇福．超声学．北京：科学出版社，1990．Page(s)52
[12] 彭应秋．声学基础．南昌：南昌航空工业学院，1989．Page(s)1-144
[13] 王祖荫．声发射技术基础．济南：山东科学技术出版社出版，1990．Page(s)33-56
[14] 王耀俊，宁伟，朱为勇．层状复合介质中的Lamb波．物理学进展，1996，9，Vol．16，No．3 and 4：Page(s)：363-376
[15] 宁伟，王耀俊．三层复合结构中的漏Lamb波：理论与实验．声学学报，1996，9，Vol．21，No．5：Page(s)767-772
[16] 宁伟，王耀俊．三层固体复合介质中Lamb波的传播．声学学报，1996，8，Vol．21，No．4：Page(s)414-420
[17] 朱哲民，李剑，邹薇．有液层负载时薄板中类Lamb波的传播．声学学报，1996，3，Vol．21，No．2：Page(s)174-181
[18] 邹薇，朱哲民，杜功焕．纯纵体波模式Lamb波的研究．声学学报，1996，8，Vol．21，No．4：Page(s)409-413
[19] 赵晓亮，朱哲民，杜功焕．薄板中类Lamb波在负载流体中引起的声流的研究．声学学报，1999，9，Vol．24，No．5：Page(s)463-469
[20] TI.TMS320F/C24x DSP Controllers Reference Guide: CPU and Instruction Set. Texas Instruments, 1999,6:Page(s)1-389
[21] TI.TMS320F/C24x DSP Controllers Reference Guide: Peripheral Library and Specific Devices. Texas Instruments, 1999,6:Page(s)1-474
[22] TI.TMS320C1x/C2x/C2xx/cC5x Assembly Language Tools:User's Guide. Texas Instruments, 1995:Page(s)1-483
[23] TI. Code ComposerUser's Guide. Texas Instruments, 1999,10:Page(s)1-234
[24] Cypress Semiconductor Corporation. 32K×8 Static RAM CY7C199. 2001, 7: Page(s)1-16
[25] 串行E~2PROM．武汉力源电子股份有限公司产品资料．1997：Page(s)1-3
[26] TI. 10-Bit Digital-to-Analog Converters: TLC5615C, TLC5615I. Texas Instruments,2000,3:Page(s)1-18
[27] Analog Devices. 4-2OmA Transmitter: AD694. Analog Devices: Page(s)1-12
[28] 叶晓东，朱兆达．中值滤波的快速算法．南京航空航天大学学报，1997，4：Page(s)159-162
[29] The MathWorks, Inc. MATLAB Function Reference, Revised for Release Ⅱ.1999,1:Page (s) 591-592
[30] 姚国民．超声波流量计中的数据处理．声学技术，1998，1：Page(s)35-37
[31] 张毅刚，付平，王丽．采用数字相关法测量相位差．计量学报，2000，7：Page(s)216-221
[32] 黄建军，刘存．改进超声波流量计性能的研究．仪器仪表学报，2001，8：Page(s)87-88