核磁共振信号全波采集系统的设计与实现
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摘要
水是人类赖以生存的最重要的自然资源之一。为解决中国的水危机,用高新技术探测地下水已成为当务之急。地面核磁共振找水方法是在近二十多年里发展起来的直接找水的物探新方法。
核磁共振信号采集系统是核磁共振找水仪的关键部件,它的性能直接影响到整个仪器的勘探效果和准确度。现有的采集系统拾取的是核磁共振信号的包络,由51单片机控制16位A/D采集,从采集速度、采集精度以及采集所得到的信息量上都存在一定的局限性。针对核磁共振信号的特点和仿真分析,本文提出核磁共振信号全波采集的设计方案,即以ARM7作为数据控制核心,实现高速采集和大容量存储;用CPLD控制A/D采集的读时序,完成数据锁存、地址译码和电平转换功能;用高速并行模数转换器AD7760对核磁共振信号进行高精度全波形采集;DDS可变频率发生器给AD7760提供所需的频率,该频率可编程控制,从而达到变采样率的目的。核磁共振信号全波采集系统设计完成后经过了一系列测试,测试结果表明全波采集方法是有效可行的。
Water is one of the most valuable natural resources for the survival of mankind. To solve the water crisis, high-tech investigation for groundwater has become an urgent task. Twenty years on, the only direct detection for groundwater is the ground geophysical methods MRS. It uses the proton magnetic moment which displays under the earth magnetic field. Along the earth magnetic field vertical direction, we add an alternating magnetic field in to stimulate the underground hydrogen proton; the proton magnetic moment is able to deviate the earth magnetic field direction to form the macroscopic magnetic moment. After the excitation field stops, the macroscopic magnetic moment can restore to and produces the weak signal along the earth magnetic field direction. With the signal, we can gather the information about the water content, the depth and the porosity of the underground water. As the signal is so weak (only nV), the method is easily disturbed by the noise. And the frequency is (1.278~2.556 kHz). So a high performance acquisition system is required. This paper is to design an acquisition system that fits MRS signal. MRS signal acquisition system is the key unit of the MRS instrument. Its performance decides the whole instrument’s exploration ability.
Group of MRS Instruments (Jilin University) has already developed the MRS underground water investigation instrument JLMRS-I for shallow groundwater investigations (down to approximately 150 m depth). The existing acquisition system detects the envelope of MRS signal. This system uses 51 Single-chip to control 16-bit A/D to sample MRS signal. But it has the shortage in storage capacity, acquisition speed, accuracy and the amount of information collected. In view of the particularity of MRS signal and the inadequacies of current system, this paper proposes a new program: ARM7+CPLD+ AD7760+DDS. MRS signal full-wave acquisition system is given out based on the program. It is consisted by signal conditioning circuit, A/D circuit, CPLD circuit, ARM circuit, DDS circuit, communication circuit and PC software.
Signal conditioning circuit uses low noise, high speed op amp (OP37). It transfers single-ended signal to differential signals, ensuring the integrity and stability of MRS signal.
A/D circuit selects the high-precision, high sampling rate, 24-bit parallel A/D (AD7760). Its reference voltage is 2.5V which is provided by low noise, high accuracy ADR431. For AD7760’s digital circuitry and FIR Filter is 2.5 V Power Supply, so its digital pins are connected to the bank of CPLD which is 2.5V power supply.
CPLD has four banks. Each bank can be powered by different voltage to work as voltage-level translator. Also it has the functions: AD7760’s reading timing control, data latches, address decoding and so on.
ARM circuit completes the minimum system design. It is the core control part of the entire acquisition system. ARM circuit supports emulation and debugging via a JTAG serial port.
This paper has completed the design of peripheral circuits for AD9850. The frequency could be programmed according to the Lamor frequency and the noise of the local by writing cotrol words to AD9850.
Communication circuit provides the RS-485 interface circuit. After all the data stored in 64k static RAM, the data then could be sent to the PC to process via the communication circuit.
PC software is designed based on MATLAB GUI. After receiving data from serial port, the PC software draws a graph, and also shows the sampling frequency, sampling time and other information. The software is simple and easy to operate.
Through the experiments and improvement, MRS signal full-wave acquisition system’s performance is improving continuously. The results showed that the system can work stablely and reliablely.
核磁共振信号采集系统是核磁共振找水仪的关键部件,它的性能直接影响到整个仪器的勘探效果和准确度。现有的采集系统拾取的是核磁共振信号的包络,由51单片机控制16位A/D采集,从采集速度、采集精度以及采集所得到的信息量上都存在一定的局限性。针对核磁共振信号的特点和仿真分析,本文提出核磁共振信号全波采集的设计方案,即以ARM7作为数据控制核心,实现高速采集和大容量存储;用CPLD控制A/D采集的读时序,完成数据锁存、地址译码和电平转换功能;用高速并行模数转换器AD7760对核磁共振信号进行高精度全波形采集;DDS可变频率发生器给AD7760提供所需的频率,该频率可编程控制,从而达到变采样率的目的。核磁共振信号全波采集系统设计完成后经过了一系列测试,测试结果表明全波采集方法是有效可行的。
Water is one of the most valuable natural resources for the survival of mankind. To solve the water crisis, high-tech investigation for groundwater has become an urgent task. Twenty years on, the only direct detection for groundwater is the ground geophysical methods MRS. It uses the proton magnetic moment which displays under the earth magnetic field. Along the earth magnetic field vertical direction, we add an alternating magnetic field in to stimulate the underground hydrogen proton; the proton magnetic moment is able to deviate the earth magnetic field direction to form the macroscopic magnetic moment. After the excitation field stops, the macroscopic magnetic moment can restore to and produces the weak signal along the earth magnetic field direction. With the signal, we can gather the information about the water content, the depth and the porosity of the underground water. As the signal is so weak (only nV), the method is easily disturbed by the noise. And the frequency is (1.278~2.556 kHz). So a high performance acquisition system is required. This paper is to design an acquisition system that fits MRS signal. MRS signal acquisition system is the key unit of the MRS instrument. Its performance decides the whole instrument’s exploration ability.
Group of MRS Instruments (Jilin University) has already developed the MRS underground water investigation instrument JLMRS-I for shallow groundwater investigations (down to approximately 150 m depth). The existing acquisition system detects the envelope of MRS signal. This system uses 51 Single-chip to control 16-bit A/D to sample MRS signal. But it has the shortage in storage capacity, acquisition speed, accuracy and the amount of information collected. In view of the particularity of MRS signal and the inadequacies of current system, this paper proposes a new program: ARM7+CPLD+ AD7760+DDS. MRS signal full-wave acquisition system is given out based on the program. It is consisted by signal conditioning circuit, A/D circuit, CPLD circuit, ARM circuit, DDS circuit, communication circuit and PC software.
Signal conditioning circuit uses low noise, high speed op amp (OP37). It transfers single-ended signal to differential signals, ensuring the integrity and stability of MRS signal.
A/D circuit selects the high-precision, high sampling rate, 24-bit parallel A/D (AD7760). Its reference voltage is 2.5V which is provided by low noise, high accuracy ADR431. For AD7760’s digital circuitry and FIR Filter is 2.5 V Power Supply, so its digital pins are connected to the bank of CPLD which is 2.5V power supply.
CPLD has four banks. Each bank can be powered by different voltage to work as voltage-level translator. Also it has the functions: AD7760’s reading timing control, data latches, address decoding and so on.
ARM circuit completes the minimum system design. It is the core control part of the entire acquisition system. ARM circuit supports emulation and debugging via a JTAG serial port.
This paper has completed the design of peripheral circuits for AD9850. The frequency could be programmed according to the Lamor frequency and the noise of the local by writing cotrol words to AD9850.
Communication circuit provides the RS-485 interface circuit. After all the data stored in 64k static RAM, the data then could be sent to the PC to process via the communication circuit.
PC software is designed based on MATLAB GUI. After receiving data from serial port, the PC software draws a graph, and also shows the sampling frequency, sampling time and other information. The software is simple and easy to operate.
Through the experiments and improvement, MRS signal full-wave acquisition system’s performance is improving continuously. The results showed that the system can work stablely and reliablely.
引文
[1]潘玉玲,张昌达,刘天佑.一种新的找水方法—核磁共振找水[J].物探化探译丛,1995,(5):343-347.
[2]潘玉玲.地面核磁共振找水理论和方法[M].中国地质出版社,2000.
[3] Varian, R.H., Ground liquid prospecting method and apparatus[J]: 1962, US Patent 3,019,383.
[4] A. Legchenko, M. Ezersky, C. Camerlynck, A. Al-Zoubi, K. Chalikakis, and J-F. Girard. Locating water-filled karst caverns and estimating their volume using magnetic resonance soundings [J]. Geophysics, 2008, 73(5): 51–61.
[5] Jean Roy, Alain Rouleau, Michel Chouteau, Michel Bureau. Widespread occurrence of aquifers currently undetectable with the MRS technique in the Grenville geological province, Canada [J]. Journal of Applied Geophysics, 2008, 66(3-4): 82-93.
[6] David O Walsh. Multi-channel surface NMR instrumentation and software for 1D/2D groundwater investigations [J]. Journal of Applied Geophysics, 2008, 66(3-4): 140-150.
[7]袁照令,潘玉玲,万乐,李振宇,董浩斌,张兵.核磁共振找水方法的应用效果[J].地球科学—中国地质大学学报,2000,25(2):132-158.
[8]尹成勇,潘玉玲.核磁共振技术在找水中的应用[J].地下水,1996,18(4):158-160.
[9]潘玉玲,万乐,袁照令,李振宇.核磁共振找水方法的现状和发展趋势[J].物探与化探2000,19(1):105-108.
[10]王应吉,林君,荣亮亮,高东旭,贾晓晨.地面核磁共振找水仪放大器设计[J].仪器仪表学报,2008,29(8),1627-1632.
[11]潘玉玲,李振宇,张兵,万乐.应用地面核磁共振法找水[J].地球学报,2002(23):95-98.
[12]邹家衡.核磁共振找水方法[J].铀矿地质,1999,15(1):62-64.
[13]王为民等.近代物理及实验[M].地质出版社,1988,6.
[14]何振亚,自适应信号处理[M],北京:科学出版社,2002.
[15]沈福民,自适应信号处理[M],西安:西安电子科技大学出版社,2001.
[16]周立功等编.深入浅出ARM7(下册)[M].广州致远电子有限公司.
[17]周立功等编.μCOS-II微小内核分析与程序设计-基于LPC2300[M].广州致远电子有限公司.
[18] http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/ad9850/products/product.html.
[19] http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7760/products/product.html.
[20]周立功等编.深入浅出ARM7(上册)[M].广州致远电子有限公司.
[21]朱范德.直接数字频率合成(DDS)技术在ADC系统中的应用[J].现代电子技术.2002,(01).
[22]沈兰荪.数据采集技术[M].合肥:中国科学技术大学出版社,1990:2-3.
[23] http://www.analog.com/ADR431.
[24]许强.嵌入式系统微处理器芯片设计与展望[J].中国科技信息,2005,24(2):69-70.
[25]周立功等编. ARM嵌入式系统应用技术笔记(下册)[M].广州致远电子有限公司.
[26]周立功等编. ARM嵌入式系统应用技术笔记(上册)[M].广州致远电子有限公司.
[27]周立功等编.嵌入式SoC智能平台(ESoC)开发指南—基于LPC2300[M].广州致远电子有限公司.
[28]郑泽胜,嵌入式系统及实时软件开发,www.pocketlx.com.
[29]吴继华,王诚.Altera FPGA/CPLD设计(高级篇篇)[M].北京:人民邮电出版社,2005.
[30]王诚,吴继华等.Altera FPGA/CPLD设计(基础篇)[M].北京:人民邮电出版社,2005.07.
[31]潘松,黄继业编.EDA技术与VHDL[M].清华大学出版社,2005.07.
[32]肖忠祥.数据采集原理[M].西安:西北工业出版社,2001.02.
[33]谭浩强著C程序设计[M].北京:清华大学出版社,2003.07.
[34]戴佳,戴卫恒. 51单片机C语言应用程序设计实例精讲[M].电子工业出版社,2006.04.
[35]康华光.电子技术基础模拟部分[M].高等教育出版社,1982.10.
[36]何桥,段清明,邱春玲.单片机原理及应用[M].中国铁道出版社,2005.
[37]王金山.核磁共振波谱仪与实验技术[M].机械工业出版社,1982.06.
[2]潘玉玲.地面核磁共振找水理论和方法[M].中国地质出版社,2000.
[3] Varian, R.H., Ground liquid prospecting method and apparatus[J]: 1962, US Patent 3,019,383.
[4] A. Legchenko, M. Ezersky, C. Camerlynck, A. Al-Zoubi, K. Chalikakis, and J-F. Girard. Locating water-filled karst caverns and estimating their volume using magnetic resonance soundings [J]. Geophysics, 2008, 73(5): 51–61.
[5] Jean Roy, Alain Rouleau, Michel Chouteau, Michel Bureau. Widespread occurrence of aquifers currently undetectable with the MRS technique in the Grenville geological province, Canada [J]. Journal of Applied Geophysics, 2008, 66(3-4): 82-93.
[6] David O Walsh. Multi-channel surface NMR instrumentation and software for 1D/2D groundwater investigations [J]. Journal of Applied Geophysics, 2008, 66(3-4): 140-150.
[7]袁照令,潘玉玲,万乐,李振宇,董浩斌,张兵.核磁共振找水方法的应用效果[J].地球科学—中国地质大学学报,2000,25(2):132-158.
[8]尹成勇,潘玉玲.核磁共振技术在找水中的应用[J].地下水,1996,18(4):158-160.
[9]潘玉玲,万乐,袁照令,李振宇.核磁共振找水方法的现状和发展趋势[J].物探与化探2000,19(1):105-108.
[10]王应吉,林君,荣亮亮,高东旭,贾晓晨.地面核磁共振找水仪放大器设计[J].仪器仪表学报,2008,29(8),1627-1632.
[11]潘玉玲,李振宇,张兵,万乐.应用地面核磁共振法找水[J].地球学报,2002(23):95-98.
[12]邹家衡.核磁共振找水方法[J].铀矿地质,1999,15(1):62-64.
[13]王为民等.近代物理及实验[M].地质出版社,1988,6.
[14]何振亚,自适应信号处理[M],北京:科学出版社,2002.
[15]沈福民,自适应信号处理[M],西安:西安电子科技大学出版社,2001.
[16]周立功等编.深入浅出ARM7(下册)[M].广州致远电子有限公司.
[17]周立功等编.μCOS-II微小内核分析与程序设计-基于LPC2300[M].广州致远电子有限公司.
[18] http://www.analog.com/en/rfif-components/direct-digital-synthesis-dds/ad9850/products/product.html.
[19] http://www.analog.com/en/analog-to-digital-converters/ad-converters/ad7760/products/product.html.
[20]周立功等编.深入浅出ARM7(上册)[M].广州致远电子有限公司.
[21]朱范德.直接数字频率合成(DDS)技术在ADC系统中的应用[J].现代电子技术.2002,(01).
[22]沈兰荪.数据采集技术[M].合肥:中国科学技术大学出版社,1990:2-3.
[23] http://www.analog.com/ADR431.
[24]许强.嵌入式系统微处理器芯片设计与展望[J].中国科技信息,2005,24(2):69-70.
[25]周立功等编. ARM嵌入式系统应用技术笔记(下册)[M].广州致远电子有限公司.
[26]周立功等编. ARM嵌入式系统应用技术笔记(上册)[M].广州致远电子有限公司.
[27]周立功等编.嵌入式SoC智能平台(ESoC)开发指南—基于LPC2300[M].广州致远电子有限公司.
[28]郑泽胜,嵌入式系统及实时软件开发,www.pocketlx.com.
[29]吴继华,王诚.Altera FPGA/CPLD设计(高级篇篇)[M].北京:人民邮电出版社,2005.
[30]王诚,吴继华等.Altera FPGA/CPLD设计(基础篇)[M].北京:人民邮电出版社,2005.07.
[31]潘松,黄继业编.EDA技术与VHDL[M].清华大学出版社,2005.07.
[32]肖忠祥.数据采集原理[M].西安:西北工业出版社,2001.02.
[33]谭浩强著C程序设计[M].北京:清华大学出版社,2003.07.
[34]戴佳,戴卫恒. 51单片机C语言应用程序设计实例精讲[M].电子工业出版社,2006.04.
[35]康华光.电子技术基础模拟部分[M].高等教育出版社,1982.10.
[36]何桥,段清明,邱春玲.单片机原理及应用[M].中国铁道出版社,2005.
[37]王金山.核磁共振波谱仪与实验技术[M].机械工业出版社,1982.06.