Design And Experimental Study Of Capacitive Oil Level Detection System

Liquid level measurement have a wide range of applications in the fields like petrochemical, food and health.In the industrial production, liquid level of the container usually need to be measured.The devices like glass tube,float level gauge are applied as the traditional level measurement,but have low precision and large measurement error.Therefore,the high precision level measurement is of great significance to improve product quality, production efficiency and optimize control.In this paper, after adequate comparative analysis to the development and status of level measurement technology, a liquid level detection system based on capacitive type measurement methods is designed. The capacitance sensor that change media is selected as the basic principle of the level measurement. The dielectric constant changes of the measured medium will have an impact on the accuracy of the measuring in the capacitive sensor. To solve this issue, the structure and principle of traditional coaxial cylinder type capacitor have been improved and the compensation plate is increased to compensate the dielectric constant changes of the measured medium.Several methods of detect tiny capacitance are compared and analyzed. The capacitance-digital converter chip PCap01 that based on the V/F conversion principle is selected as the core device of tiny capacitance detection. The factors that caused the measurement error in the sensor are analyzed. The materials of the plate and base of the sensor are determined. The structure and assembly method of the sensor are designed. STM32F103c8t6 is selected as the microcontroller.On the basis of the minimum system, the hardware circuits that include capacitive sensing, signal processing, transmission and result display are designed, and the PCB is produced. The softwares are designed for the needs of parts of system.After design of the system, calibration experiment is done and measurement experiments show that the improvement of the structure of the sensor can effectively compensate the dielectric constant changes.The results show that, within the range of 0-270mm of measurement plate, the absolute error is less than 0.8mm, the relative error of each measurement point within the range is up to 3.38%, meeting the requirement of fuel level detection and the system is suitable for level measurement of various non-conductive liquids, such as the oil of the oil drums and vehicle fuel tanks,etc.