| The water is the basic unit of constituting the living things;the basic conditions for occurrence,growth and reproduction of life;the one of the most important natural resources that human depend on. With the social development and population growth,human demand for water is increasing. To solve the water crisis of the world, making use of high-tech to investigate,explore,develop and use of groundwater has become imperative. Nuclear magnetic resonance method (NMR) is currently the only direct methods to find water in the field of geophysics.Nuclear magnetic resonance method(NMR) for groundwater is to use the nuclear magnetic resonance phenomenon that the hydrogen protons in the groundwater will generate,which first launch the alternating electromagnetic field,then collect the free precession signal. According to the amplitude of the FID signal,the depth and thickness of the ground aquifer can be obtained by inversion explanation. The amplitude of the free precession signal is impacted by the excitation pulse. To detecting deep aquifers,we only increase the emission current,which is also the main function of the hydroscope power supply.The contents of this paper are one part of the"nuclear magnetic resonance instrument research and development",which is one of the projects on"Eleventh five-Year"national scientific and technological support projects"scientific instruments and equipment research and development".The main contents are hydroscope power and its control unit design,whose implementation will improve hydroscope machine's efficiency and accuracy.Based on the well-known for principles of NMR and its instrument's work process,the importance of power supply design is recognized,and many books about power supply design are read. Then the idea of nuclear magnetic resonance instrument power supply design is conceived,and the working principle and process for each part of the nuclear magnetic resonance instrument power supply are described in detail in the paper.Firstly,the paper introduces the theory and practical usage of the storage units,and determines the selection of a large capacitor as the energy storage unit. Then the energy storage mode is determined by making simulation analysis on constant voltage and constant current charging respectively. After comparing their advantages and disadvantages,the constant current charging mode is chosen.Secondly,the constant current source module is designed,the constant current source DC-DC inverter is designed. From selecting the power devices,to designing RC snubber circuit and PWM control drive circuit,and to one-way full-bridge rectifier circuit,each part is designed carefully. And taking the stability of the power work into account,some protection and filter circuits are designed specially.After designing the current source,the monitoring unit circuit should be conceived. The power monitoring unit is designed based on STC12C5408AD which comes with 8 10-bit A/D converter, to ensure the accuracy of the voltage. The RS232 and RS485 communication interface are designed to increase the communication distance.At the end of the paper,each part of the circuit is measured. Many sets of nuclear magnetic resonance instrument power supply are finally assembled. After a number of indoor and field experiments to power supply, the data reaches its original target design. Many deficiencies such as layout messy,bulky,heavy,low efficiency and short distance communication existing in the original power supply,can be solved.
|
PDF Full Text Request