Research On Online Oil Water Content Detection Device Based On Resonance Technology

With the rapid development of the economy and industry,the use of oil fluids is indispensable in all fields.Water content is an important factor in testing the quality of oil,especially for high-performance hydraulic systems,fuel systems and lubrication systems in industrial machinery,automobiles,submarines,aircraft and other equipment,which have the most stringent requirements for water content,which needs to be below 0.01%.Therefore,it is of great importance to be able to detect the slight water content of fluids online in real time in the industrial production,transmission and operation of machinery.The online detection of water content in fluids has great potential for development.Microwave resonance method is a popular online non-destructive testing method for lubricants in recent decades.In this paper,the relationship between the dielectric constant of oil and resonant frequency under the resonant cavity perturbation method is investigated,and a microwave resonant cavity technology-based online oil water content detection device is designed for measuring the water content of oil.The oilwater mixed dielectric model and the operating mode of the resonant cavity are analysed;according to the actual measurement requirements,semi-closed end faces are designed for both sides of the cylindrical resonator in order to ensure a high Q value of the resonant cavity and liquid fluidity.The shape and dimensions of the cylindrical resonant cavity end faces,probe position and length,cavity dimensions and other parameters,metal materials and the actual detection conditions were optimised using HFSS simulation software to obtain a 3D model of the resonant cavity that meets the resolution requirements.The testing system of the oil moisture content online testing device includes hardware design and software driving.In the hardware part,the microcontroller controls the output 0～15V controllable voltage of the DA converter and connects the output voltage to the load VCO to realise the sweep function;meanwhile the microwave signal output from the resonant cavity is converted to voltage value under the action of the logarithmic detector and the microcontroller collects the voltage value of the relevant parameters.The software programming enables the driving and data acquisition functions of the whole testing equipment,and realises the monitoring and processing of the data information of each part.To improve the measurement accuracy,a temperature sensor is set up to analyse the effect of temperature changes on the measurement results.Finally,the oil fluids with different water contents were measured separately to achieve water content detection accuracy on the order of one ten thousandth and one thousandth of a percent.The simulation and experimental comparison showed that the sensitivity of this oil fluid water content detection system can reach 100 ppm or even lower.The linearity of the fitted equation is 0.9989 for trace water content measurements and 0.99587 for low water content measurements,and the maximum error of the system is 0.33 MHz.Temperature compensation has also been provided.The online moisture detection device not only provides high sensitivity for moisture measurement,but also has the advantages of wider detection range,economical and practical,small size,easy installation and cleaning.