Study On Measurement System Of Marine Conductivity And Temperature Sensor Based On MEMS Technology

With the development of Chinese strategy of building a strong country in the sea,the performance requirements of the marine conductivity and temperature sensors for the measurement of marine elements are increasing day by day.The sensors based on MEMS(micro electronic micromachining system)technology have the advantages of low cost,high sensitivity,high resolution,high accuracy and good process consistency,and become the main development of marine scientific instruments in the future.One of the directions,in this paper,the measurement system of MEMS ocean conductivity and temperature sensor is studied as follows:Firstly,based on the principle of sensor measurement and theory of electric field,a kind of MEMS circular four electrode structure conductivity sensor probe is optimized by using the COMSOL software.When the conductivity is 5-70 m S/cm and the excitation frequency is 10Hz-100 k Hz,the measurement performance of the sensor is simulated.The results show that the measurement accuracy is improved to±0.1m S/cm after the sensor structure's optimization.Secondly,a MEMS Thin film platinum resistance temperature sensor is designed,and the strain of the sensor probe before and after the silicon nitride film is coated on the surface of the sensor probe in the ocean water depth of 1000m(the pressure is about 10MPa).The results show that the wire shape of the platinum resistance before and after the silicon nitride film is reduced from about 1nm to almost zero,which provides a theory for the stable use of the sensor probe in the deep sea environment.After that,the sensor probe measuring circuit is designed after the physical processing of the sensor,including the analog signal processing circuit of the sensor front-end mainly based on the amplifier and the digital signal acquisition circuit mainly based on MSP430 and AD7124-4.Finally,the conductivity and temperature sensor were measured for three times including calibration.Finally,the calibration fitting error of conductivity sensor was within ±0.0737 m S/cm,the calibration fitting error of temperature sensor was within±0.0120?,and the accuracy was high.Two experiments in three weeks and six weeks after calibration show that the two sensors have good stability.