The Key Technology Of Measurement System Of Water Content In Oil Basing On Nuclear Magnetic Resonance

The measurement for water content in oil is important to calculate output and control quality in the oil production and chemical industry. Traditional method is distillation which is based on sampling. Being limited by the technical conditions, this method needs sampling by manual work. It is inefficient in real time sampling and usually results in big error, so it is difficult to ensure the measuring accuracy. At present, there are some automation measurement ways, such as using of capacitances, microwaves and the low-powerγ-rays, etc. Disadvantages of the instruments using these methods are that, the measurement results are influenced by other components of oil, and the instruments'structure are complex, costs are expensive, or rays sometime cause pollution, etc. Especially, since wax deposit, deposit and corrosion are easily formed in the measuring probes in fluid flow, the measurement accuracy is instable. So it is necessary to develop an automatic measuring system with simple structure, little influenced, and high accuracy for improving the quality and efficiency of the products.The basic theory of NMR (Nuclear Magnetic Resonance) is analyzed in the view of quantum mechanics and classical mechanics, and the method basing on NMR to measure water content in oil is presented. The traditional equipments of NMR are huge and have severe requirement for condition. Therefore, a mini, simple and convenient NMR device to measure water content in oil is studied and designed in this thesis.Depending on the deep study for traditional NMR equipments, the key technologies of a mini NMR are presented in this thesis. This device is consistent of some main parts ---- setting of uniform strong magnetic field, radiofrequency oscillator, resonance absorption probe, and signal reception and process. Where the uniform strong magnetic field is the basic condition to produce NMR, and it will directly influence the accuracy and sensitivity of the measuring system.After comparing several methods, a method with permanent magnet to produce uniform magnetic field is introduced in detail. The distributions of magnetic induction intensity caused by several different constructions of the permanent magnets are analyzed. A simple mechanism to adjust uniform magnetic field is designed, which is to adjust the distance of two rectangular permanent magnets expediently. A compensate electrifying windings to make the field more uniform is also used. A margin oscillator and absorptive probe matched with intensity of the uniform magnetic field were designed in the end.Then, measurement result of uniform magnetic field is given, performance experiments of the related parts are carried out.