| With the liquefied natural gas (LNG) being widely used in automobile fuel, the need of LNG cryogenic storage tank liquid level measuring device is gradually increasing. The main purpose of this paper is to solve problem that measures the current low level of liquefied natural gas fuel automobile fuel tank. Cryogenic storage tank liquid level measuring device can not only measure the height of liquid level of liquid, but can also get the data about remaining fuel calculated by residual fuel tank. The measuring and warning level are the important parts of automatic controlling system of vehicle fuel. By discovering reliable device to measure the fuel level and liquid volume, it can allow the drivers clearly know the situation about remaining fuel in the fuel tank. Specifically speaking, that is to develop three modules including sensor, transmitter, display, as well integrated them into the automatic transmitter instrument. Besides, through a large number of experimental verification and post optimization, a safe and reliable, economic and durable fuel liquid level measuring device can be obtained. The project chooses capacious liquid level measurement scheme, which has the best performance in different measurement schemes, as well as quite reasonable price. So we prefer the scheme of the capacious measuring principle.Due to the liquefied natural gas (LNG) belongs to the ultra low-temperature liquid; therefore the liquid sensor detection needs to deal with the ultra low-temperature working situation. Sensor selection is based on 304 stainless steel for the coaxial capacitance sensor material. Based on 204 stainless steel as substrate material in inner and outer shaft, and plate inert materials on the stainless steel in order to protect the sensor. Between two axis use Teflon as the insulating material. Such kind of sensor has stable performance, as well as uniform variation of capacitance, cryogenic, which is suitable to be chosen as the suitable sensor of the paper.The signal from the capacious sensor transmission needs to be captured and processed, which requires the design of relevant transmitter measuring circuits. The project project uses STM32 chip and type 7555 timer, embedded technology will change in capacitance sensor and be converted into a pulse signal output. Then through the software algorithm the pulse width can be measured and calculate the capacitance value. Finally calculate the liquid height and fuel allowance. The experimental results prove that the measuring circuit can be stable to transform the sensor switching capacitance signal precisely into pulse signal and convert it into the liquid level value to display.The touch screen was adapted to display data. Industrial touch screen is the ideal choice among the touch screens, which has several advantages such as high and low temperature resistance, oil resistance, scratch resistance, static electricity and it also has many good functions such as the effect to display data and situation, operate and simulate image and so on. The program can be written into PC by SD card. The instructions and data in lower computer was transmitted by RS232 to the touch screen, the touch keystroke signal was feed-backed to the control unit. The simple and convenient and practical man-machine interface has also been designed with touch screen manual.The actual debugging and the experiment proves that the experiment device has accurate effects, stable and reliable experimental performance. |
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