基于模拟正交矢量锁定放大的SNMR信号采集系统

Design of SNMR FID Signal Collection System Based on Analog Orthogonal Vector Lock-in Amplifier

为了对地下水信息进行反演，确定地下水水量、地层结构等信息，根据乘法型正交矢量锁定放大器的基本原理，设计了基于模拟正交矢量锁定放大的SNMR（Surface Nuclear Magnetic Resonance）信号采集系统。系统利用CPLD（Complex Programmable Logic Device）和D／A转换器，使地下水核磁共振信号和参考信号相乘，实现信号正交功能，提取出自由感应衰减（FID：Free Induction Decay）信号，获得地面核磁共振找水探测的各关键参数。模拟正交法软硬件设计简单，进一步改善了信噪比。该地面核磁共振找水仪采集系统在探寻地下水源中已得到验证，采样频率可根据各地Lamor频率的不同在250～1000Hz范围内进行程控调整。

In order to inverse to obtain undergeound water structure information of stratum, according to muhiplieative information, determine quantity of groundwater and orthogonal vector lock-in amplifier principle, SNMR （ Surface Nuclear Magnetic Resonance） signal collection system based on analog orthogonal vector lock-in amplifier has been designed. Taking advantage of CPLD （Complex Programmable Logic Device） and D/A converter, SNMR signal and reference signal multiplies to achieve signal orthogonal functions. The free induction decay FID （Free Induction Decay） signal is extracted and then the water parameters of SNMRdetecting are obtained. The hardware and software of the analog orthogonal method are simple and the SNR （Signal-to-Noise Ratio） is advanced. After field tests, the SNMR FID signal collection system using the analog orthogonal is tested in the practice detecting groundwater. According to different Lamor frequency, sampling frequency can be adjusted at 250 - 1 000 Hz by programming.