Abstract:
An anti-saturation device for a ground magnetic resonance signal amplifying circuit has a receiving coil connected with a band-pass filter circuit through a pre-amplifying circuit and a programmable amplifying circuit. The programmable amplifying circuit is connected with an AD acquisition card through the band-pass filter circuit. The band-pass filtering circuit is connected with a computer through the AD acquisition card, and the AD acquisition card is connected with an emitting system through the computer. An automatic amplification factor adjusting module is embedded into a nuclear magnetic resonance detector, and can also directly replace a receiving amplification circuit of the nuclear magnetic resonance detector to work independently.

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
       [0001]    This application is the U.S. non-provisional application claiming priority to Chinese Patent Application No. 201610340100.8, filed May 20, 2016. Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to a nuclear magnetic resonance groundwater detector, and in particular to an anti-saturation device and an anti-saturation method for a magnetic resonance signal amplification circuit. 
       BACKGROUND 
       [0003]    The nuclear magnetic resonance (MRS) groundwater detection technology is developed for detecting groundwater directly and non-destructively in the field of geophysics at present. After the groundwater is excited by an alternating magnetic field, a nuclear magnetic resonance signal is generated. The signal is an exponentially decaying sine wave signal, which is also referred to as a free induction decay (FID) signal. The FID signal is usually in a nano-volt (nV) level, which may be detected after thousands or tens of thousands of times amplification. The signal is also apt to be interfered by an electromagnetic noise from the external environment. The interference noises of different test areas are different, and even in the same test area, the electromagnetic interference noises are also different at different times. In an amplification device for a conventional nuclear magnetic resonance detection system, an amplification factor is set only once based on experience before working. However, it will take two hours to complete a test at a test point. The environmental noise changes greatly, especially in an area having strong noise interference. Therefore, the amplifying circuit is apt to be saturated, thus failing to acquire valid data. For this reason, it is difficult to achieve a desired result by using the same amplification factor when testing in different regions or in the same region but at different times. The amplifier having a fixed amplification factor is apt to be saturated, resulting in signal distortion especially in the case of complex environments with serious noise interference. Therefore, in order to prevent the saturation of the amplifier while meeting the FID signal amplification requirements, it is of great significance to design an anti-saturation device for a ground magnetic resonance signal amplifying circuit. 
       SUMMARY 
       [0004]    One object of the present disclosure is to provide an anti-saturation device for a ground magnetic resonance signal amplifying circuit to overcome the above drawback in the conventional technology. 
         [0005]    The other object of the present disclosure is to provide an anti-saturation method for the anti-saturation device for the ground magnetic resonance signal amplifying circuit. 
         [0006]    The above object is achieved through the following technical solution: 
         [0007]    An anti-saturation device for a ground magnetic resonance signal amplifying circuit includes: a receiving coil  1 , a pre-amplifying circuit  2 , a programmable amplifying circuit  3 , a band-pass filter circuit  4 , an analog-digital (AD) acquisition card  5 , a computer  6 , a micro control unit (MCU) control circuit  7 , a level transition and electrical isolating circuit  8  and an emitting system  9 , where the receiving coil  1  is connected with the band-pass filter circuit  4  through the pre-amplifying circuit  2  and the programmable amplifying circuit  3 ; the programmable amplifying circuit  3  is connected with the AD acquisition card  5  through the band-pass filter circuit  4 ; the band-pass filter circuit  4  is connected with the computer  6  through the AD acquisition card  5 ; the AD acquisition card  5  is connected with the emitting system  9  through the computer  6 ; the computer  6  is connected with the level transition and electrical isolating circuit  8  through the MCU control circuit  7 ; and the level transition and electrical isolating circuit  8  is connected with the programmable amplifying circuit  3 . 
         [0008]    The AD acquisition card  5  includes an analog-digital converter (ADC) module  10 , a level transition and electrical isolating circuit  11 , a field programmable gate array (FPGA) module  12 , a random access memory (RAM) module  13 , a read only memory (ROM) module  14 , a network interface  15  and a serial communication interface (SCI)  16 , where the ADC module  10  is connected with the FPGA module  12  through the level transition and electrical isolating circuit  11 ; the RAM module  13  is connected with the ROM module  14  through the FPGA module  12 ; the FPGA module  12  is connected with the network interface  15  and the SCI  16 . 
         [0009]    The computer is connected with the network interface  15  and the SCI  16 . 
         [0010]    An anti-saturation method for the anti-saturation device for a ground magnetic resonance signal amplifying circuit, includes: 
         [0011]    step a: setting a programmable amplification factor, and an preset upper limit value V H  and a preset lower limit value V L  for overall signals manually based on an ambient noise intensity at a to-be-detected location before a nuclear magnetic resonance water detection system starts working; 
         [0012]    step b: performing acquisition in an acquisition time of 256 ms with 6400 sampling points, and calculating, by the computer  6 , a maximum absolute value V max  among absolute values of 6400 acquisition points based on all signals collected by the AD acquisition card  5 ; 
         [0013]    step c: transmitting the V max  to the MCU control circuit  7  by the computer  6 , where the amplification factor for the present time is denoted as A i ; comparing, by the MCU control circuit  7 , the V max  with the preset upper limit value and the preset lower limit value; and calculating the amplification factor for the next adjustment as: A i+1 =3.2*A i /V max , to reduce the amplification factor, in a case that the V max  is greater than the preset upper limit value V H , and increase the amplification factor in a case that the V max  is less than the preset lower limit value V L . Since the amplification factor of the programmable amplifier may be selected from an arithmetic sequence from 2000 to 32000 with an equal difference of 2000, totaling 16 discrete integer point amplification factors, an adjusted magnification factor for next adjustment is selected to be the integer amplification factor which is nearest to and not greater than the amplification factor A i+1 . For example, if A i+1 =5130, the actual amplification factor for the next time is selected as 4000 times. 
         [0014]    step d: setting the amplification factor of the programmable amplifying circuit  3  as the adjusted magnification factor, by the MCU control circuit  7  through the level transition and electrical isolating circuit  8 , where the set amplification factor serves as the amplification factor for acquired signals for the next time; 
         [0015]    step e: transmitting, by the MCU control circuit  7 , a complete instruction to the computer  6  after setting the amplification factor setting; and controlling, by the computer  6 , the emitting system  9  to perform a next excitation; and 
         [0016]    step f: repeating the step b to e until stopping acquisition. 
         [0017]    Advantageous effects of the present disclosure are as follows. An automatic amplification factor adjusting module is embedded into a nuclear magnetic resonance detector, and may also directly replace a receiving amplification circuit of the nuclear magnetic resonance detector to work independently. Optimal amplification factors are set through the anti-saturation device in a complex environment with severe noise interference, so that the issues that signals are distorted or the amplification factor is not sufficient as only one amplification factor is used can be solved. Since the whole amplification factor adjusting process is automatically performed, the ground water exploration efficiency is improved. The anti-saturation method is simple to implement, has a small calculation amount, and requires a low amplification factor adjusting speed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a structure diagram of an anti-saturation device for a ground magnetic resonance signal amplifying circuit; 
           [0019]      FIG. 2  is a structure diagram of an AD acquisition card  5  in  FIG. 1 ; 
           [0020]      FIG. 3  is a time-domain diagram of signals acquired in a first acquisition according to an embodiment; and 
           [0021]      FIG. 4  is a time-domain diagram of signals acquired in a second acquisition according to an embodiment. 
       
    
    
       [0022]    Reference numbers in the Figures are described as follows:  1 , receiving coil;  2 , pre-amplifying circuit;  3 , programmable amplifying circuit;  4 , band-pass filter circuit;  5 , AD acquisition card;  6 , computer;  7 , MCU control circuit;  8 , level transition and electrical isolating circuit;  9 , emitting system;  10 , ADC module;  11 , level transition and electrical isolating circuit;  12 , FPGA module;  13 , RAM module;  14 , ROM module;  15 , network interface; and  16 , SCI interface. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Hereinafter, the present disclosure will be described in detail in conjunction with drawings and embodiments. 
         [0024]    An anti-saturation device for a ground magnetic resonance signal amplifying circuit includes: a receiving coil  1 , a pre-amplifying circuit  2 , a programmable amplifying circuit  3 , a band-pass filter circuit  4 , an analog-digital (AD) acquisition card  5 , a computer  6 , a micro control unit (MCU) control circuit  7 , a level transition and electrical isolating circuit  8  and an emitting system  9 . The receiving coil  1  is connected with the band-pass filter circuit  4  through the pre-amplifying circuit  2  and the programmable amplifying circuit  3 . The programmable amplifying circuit  3  is connected with the AD acquisition card  5  through the band-pass filter circuit  4 . The band-pass filter circuit  4  is connected with the computer  6  through the AD acquisition card  5 . The AD acquisition card  5  is connected with the emitting system  9  through the computer  6 . The computer  6  is connected with the level transition and electrical isolating circuit  8  through the MCU control circuit  7 . The level transition and electrical isolating circuit  8  is connected with the programmable amplifying circuit  3 . 
         [0025]    The AD acquisition card  5  includes an analog-digital converter (ADC) module  10 , a level transition and electrical isolating circuit  11 , a field programmable gate array (FPGA) module  12 , a random access memory (RAM) module  13 , a read only memory (ROM) module  14 , a network interface  15  and a serial communication interface (SCI)  16 . The ADC module  10  is connected with the FPGA module  12  through the level transition and electrical isolating circuit  11 . The RAM module  13  is connected with the ROM module  14  through the FPGA module  12 . The FPGA module  12  is connected with the network interface  15  and the SCI interface  16 . 
         [0026]    The computer  6  is connected with the network interface  15  and the SCI interface  16 . 
         [0027]    An anti-saturation method applied in the anti-saturation device for a ground magnetic resonance signal amplifying circuit includes steps a to f. 
         [0028]    In step a, a programmable amplification factor, and an preset upper limit value V H  and a preset lower limit value V L  for overall signals are set manually based on an ambient noise intensity at a to-be-detected location before a nuclear magnetic resonance water detection system starts working. 
         [0029]    In step b, acquisition is performed in an acquisition time of 256 ms with 6400 sampling points, and a maximum absolute value V max  among absolute values of 6400 acquisition points is calculated by the computer  6  based on all signals collected by the AD acquisition card  5 . 
         [0030]    In step c, the V max  is transmitted to an MCU control circuit  7  by the computer  6 , the amplification factor for the present time is denoted as A i , the V max  is compared with the preset values in the MCU, and the amplification factor for the next adjustment is calculated as: A i+1 =3.2*A i /V max , to reduce the amplification factor in a case that the V max  is greater than the preset upper limit value V H , and increase the amplification factor in a case that the V max  is less than the preset lower limit value V L . Since the amplification factor of the programmable amplifier may be selected from an arithmetic sequence: 2000, 4000, 6000 . . . 30000, 32000 with an equal difference of 2000, totaling 16 discrete integer amplification factors, an adjusted magnification factor is selected to be the integer amplification factor which is nearest to and not greater than the amplification factor A i+1 . For example, if A 1+1 =5130, the actual amplification factor for the next time is selected as 4000 times. 
         [0031]    In step d, the amplification factor of the programmable amplifying circuit  3  is set as the adjusted magnification factor, by the MCU control circuit  7  through the level transition and electrical isolating circuit  8 . The set amplification factor serves as the amplification factor for acquired signals for the next time. 
         [0032]    In step e, a complete instruction is transmitted by the MCU control circuit  7  to the computer  6  after the amplification factor is set, and the emitting system  9  is controlled by the computer  6  to perform a next excitation. 
         [0033]    In step f, the step b to e are repeated until stopping acquisition. 
         [0034]    As shown in  FIG. 1 , the anti-saturation device for a ground magnetic resonance signal amplifying circuit includes a receiving coil  1 , a pre-amplifying circuit  2 , a programmable amplifying circuit  3 , a band-pass filter circuit  4 , an AD acquisition card  5 , a computer  6 , an MCU control circuit  7 , a level transition and electrical isolating circuit  8  and an emitting system  9 . The receiving coil  1  is connected with the band-pass filter circuit  4  through the pre-amplifying circuit  2  and the programmable amplifying circuit  3 . The programmable amplifying circuit  3  is connected with the AD acquisition card  5  through the band-pass filter circuit  4 . The band-pass filter circuit  4  is connected with the computer  6  through the AD acquisition card  5 . The AD acquisition card  5  is connected with the emitting system  9  through the computer  6 . The computer  6  is connected with the level transition and electrical isolating circuit  8  through the MCU control circuit  7 . The level transition and electrical isolating circuit  8  is connected with the programmable amplifying circuit  3 . 
         [0035]    As shown in  FIG. 2 , the AD acquisition card  5  includes an ADC module  10 , a level transition and electrical isolating circuit  11 , an FPGA module  12 , an RAM module  13 , an ROM module  14 , a network interface  15  and an SCI interface  16 . The FPGA module  12  is connected with the ADC module  10  through the level transition and electrical isolating circuit  11 . The RAM module  13  is connected with the ROM module  14  through the FPGA module  12 . The FPGA module  12  is connected with the network interface  15  and the SCI interface  16 . 
         [0036]    The computer  6  is connected with the network interface  15  and the SCI interface  16 . 
         [0037]    The ground magnetic resonance signals are induced by the receiving coil  1 , and are inputted to the AD acquisition card  5  through the pre-amplifying circuit  2 , the programmable control amplifying circuit  3  and the band-pass filter circuit  4 . The ADC module  10  is controlled by the FPGA module  12  to transmit the acquired ground magnetic resonance signals to the computer  6 . The computer  6  processes the signals to obtain the maximum evaluation value. The evaluation value is transmitted to the MCU control circuit  7  to compare the evaluation value with the preset values. The amplification factor is reduced in a case that the evaluation value is greater than the preset upper limit value, and is increased in a case that the evaluation value is less than the preset lower limit value. The above process is repeated by setting the amplification factor of a next excitation based on the data collected for the present time, until the end of work. 
         [0038]    An anti-saturation method applied in the anti-saturation device for a ground magnetic resonance signal amplifying circuit includes steps a to f. 
         [0039]    In step a, a programmable amplification factor, and an preset upper limit value V H  and a preset lower limit value V L  for overall signals are set manually based on an ambient noise intensity at a to-be-detected location before a nuclear magnetic resonance water detection system starts working. 
         [0040]    In step b, acquisition is performed in an acquisition time of 256 ms with 6400 sampling points, and a maximum absolute value V max  among absolute values of 6400 acquisition points is calculated by the a computer  6  based on all signals collected by the AD acquisition card  5 . 
         [0041]    In step c, the V max  is transmitted to an MCU control circuit  7  by the computer  6 , the amplification factor for the present time is denoted as A i , the V max  is compared with the preset values in an MCU, and the amplification factor for the next adjustment is calculated as: A i+1 =3.2*A i /V max , to reduce the amplification factor in a case that the V max  is greater than the preset upper limit value V H , and increase the amplification factor in a case that the V max  is less than the preset lower limit value V L . Since the amplification factor of the programmable amplifier may be selected from an arithmetic sequence: 2000, 4000, 6000 . . . 30000, 32000 with an equal difference of 2000, totaling 16 discrete integer amplification factors, an adjusted magnification factor is selected to be the integer amplification factor which is nearest to and not greater than the amplification factor A i+1 . For example, if A 1+1 =5130, the actual amplification factor for the next time is selected as 4000 times. 
         [0042]    In step d, the amplification factor of the programmable amplifying circuit  3  is set as the adjusted magnification factor, by the MCU control circuit  7  through a level transition and electrical isolating circuit  8 . The set amplification factor serves as the amplification factor for acquired signals for the next time. 
         [0043]    In step e, a complete instruction is transmitted by the MCU control circuit  7  to the computer  6  after setting the amplification factor, and the emitting system  9  is controlled by the computer  6  to perform a next excitation. 
         [0044]    In step f, the step b to e are repeated until stopping acquisition. 
       Embodiment 
       [0045]    The application of the anti-saturation device for the ground magnetic resonance signal amplifying circuit is described with an example of detecting, in the North Lake Wetland Park in Changchun, with a nuclear magnetic resonance groundwater detection system having a transmitting coil and a receiving coil both of a size of 50 m*50 m, and arranged with the anti-saturation device. 
         [0046]    In step a, an initial amplification factor of 20000 times, an preset upper limit value V H =4V and a preset lower limit value V L =0.5V are set manually through the computer  6  based on an ambient noise intensity at a to-be-detected location before the nuclear magnetic resonance water detection system starts working. 
         [0047]    In step b, acquisition is performed in an acquisition time of 256 ms with 6400 sampling points, and a maximum absolute value V max  among absolute values of 6400 acquisition points is calculated by the computer  6  based on all signals collected by the AD acquisition card  5 . 
         [0048]    In step c, the V max  is transmitted to an MCU control circuit  7  by the computer  6 , the amplification factor for the present time is denoted as A i , the V max  is compared with the preset values in an MCU, and the amplification factor for the next adjustment is calculated as: A i+1 =3.2*A i /V max , to reduce the amplification factor in a case that the V max  is greater than the preset upper limit value V H , and increase the amplification factor in a case that the V max  is less than the preset lower limit value V L . Since the amplification factor of the programmable amplifier may be selected from an arithmetic sequence: 2000, 4000, 6000 . . . 30000, 32000 with an equal difference of 2000, totaling 16 discrete integer point amplification factors, an adjusted magnification factor is selected to be the integer amplification factor which is nearest to and not greater than the amplification factor A i+1 . For example, if A i+1 =5130, the actual amplification factor for the next time is selected as 4000 times. 
         [0049]    The result of the first data acquisition is shown in  FIG. 3 . V max =4.5V is calculated by the anti-saturation device automatically. Since V max &gt;V H , i.e., V max  is greater than the upper limit of the preset value, the amplification factor need to be reduced. As A i+1 =3.2*A i /V max =14222, the actual amplification factor of the programmable amplifier is set as 14,000 times. 
         [0050]    In step d, the amplification factor of the programmable amplifying circuit  3  is set as the adjusted magnification factor, by the MCU control circuit  7  through the level transition and electrical isolating circuit  8 . The set amplification factor serves as the amplification factor for acquired signals for the next time. 
         [0051]    In step e: the MCU control circuit  7  transmits a complete instruction to the computer  6  after setting the amplification factor, and the computer  6  controls the emitting system  9  to perform a next excitation. 
         [0052]    The result of the second data acquisition is shown in  FIG. 4 , in which the maximum absolute value V max =3.7V, and V L &lt;V max &lt;V H , which means the signals is between the upper preset value and lower preset value, not only meeting the requirement for amplifying signals but also avoiding the amplifier saturation problem in the case of single amplification factor. 
         [0053]    In step f: the step b to e are repeated until stopping acquisition.