The working principle and design of contact oil level measuring transmitter

Background of the invention

Capacitive oil level sensor uses the capacitance formed by filling the liquid medium between the positive and negative probes to change linearly with the liquid level, and converts the change in capacitance (that is, the change in liquid level) into a standard electrical signal output. Generally, the sensing part of a general capacitive oil level measurement sensor is a coaxial container. When the oil enters the container, it causes a change in the capacitance between the sensor tube and the sensing electrode. This change is carried out by the conversion of the temperature compensation circuit. Linearity and temperature compensation, output 4-20mA or 0-5V standard signal for display instrument. Since analog components such as bidirectional switches and operational amplifiers in the circuit are easily affected by changes in the working environment temperature, the output of the circuit has a large temperature drift. Such a temperature drift value has a relatively large impact on the accuracy of measuring the fuel level quality of the aircraft. Therefore, it needs to be compensated. The general situation is that the law of the output voltage of the capacitance measuring circuit changing with the temperature is obtained from the experiment, and the temperature drift of the circuit is compensated by the single-chip technology to reduce the temperature drift.

In the prior art, the capacitive sensor for measuring the fuel level of an aircraft has the following shortcomings: (1) The sensor does not have a fuel temperature measurement component, so it cannot compensate for the error caused by the fuel level measurement due to the change of the fuel temperature. (2) The positioning method between the sensor tubes is generally composed of multiple concentric positioning pins with vertical space, which has the problems of poor process manufacturability and low positioning. (3) Fuel contaminants are often deposited on the sheath plates installed at both ends of the sensor, which causes the capacitance value of the sensor to be seriously out of tolerance, resulting in a larger parasitic capacitance value. (4) After the cable in the fuel tank is connected to the signal terminal of the sensor, there is no effective stress buffer device. In the environment of the aircraft, the swing of the wire will produce a large impact on the lug or the wiring ring connected to the terminal. , Easily lead to loose connection.

Invention content

The purpose of the utility model is to address the above-mentioned shortcomings of the prior art, and provide a concentric positioning with high accuracy, strong shock resistance, capable of reducing the parasitic capacitance value in the dry capacitance value of the sensor, and compensating for the fuel caused by the temperature change of the fuel. Oil level measurement error, contact oil level measuring transmitter that solves the above problems in structure and function.

The technical solution adopted by the utility model to solve its technical problems is: a contact type oil level measuring transmitter, including an oil level height measuring module 4 composed of three coaxially assembled metal pipe bodies and fixed at the oil level The temperature compensation module 9 at the bottom of the height measurement module is characterized in that the outer metal pipe body 10 serves as a shielding outer pipe and a fixed support for the entire sensor. The output of the middle metal pipe body 11 and the inner metal pipe body 12 is proportional to the oil immersion height. Proportional oil level signal capacitance value C, and the three metal pipes consist of three evenly distributed in space. The inner liner 13, outer liner 15 and pin 14 separated from the upper and lower positions are positioned radially, and the bottom end is guided by The rod 5 and the aluminum tray 7 are coaxially fixed with a temperature compensation module 9. The temperature compensation module 9 is fixed at the center of the bottom end of the metal pipe through the aluminum tray 7 and the guide rod 5. The wiring sleeve 16 connects the capacitance of the oil level measurement module 4 The value C and the resistance value R of the temperature compensation module 9 are output through the guide rod 5 in the tube body, which will be converted into current signals IC and IR proportional to the capacitance C and the resistance value R, and the socket connected through the shielded wire (17) (19) Transfer to the fuel measurement control system.

The working principle and design of contact oil level measuring transmitter

Compared with the prior art, the utility model has the following beneficial effects: the concentric positioning accuracy is high. The three metal pipe bodies of the utility model are composed of three evenly distributed in space. The inner liner 13, the outer liner 15 and the pin 14 separated from the upper and lower positions are positioned radially; each of the three are evenly distributed on the same radial plane. The inner liner 13, the outer liner 15 and the pin 14 are assembled with another two groups at a certain interval along the axial direction, a total of nine groups are used to ensure the concentric installation of the metal pipe body. At the bottom end, a coaxial temperature compensation module 9 is fixed by a guide rod 5 and an aluminum tray 7. The structure is simple and the concentric positioning accuracy is high. The positioning method of the sensor between the tubes adopts the component positioning method of the new structure, which has good manufacturability and can solve the problem of low concentric positioning accuracy of the previous sensor. There are no movable or elastic components, impact resistance, high precision, stable performance; easy installation, high reliability, and minimal maintenance. In general, no maintenance is required. The temperature compensation module 9 passes through the aluminum tray 7 and the guide rod 5.

It can reduce the parasitic capacitance in the dry capacitance of the sensor. The utility model fixes the temperature compensation module 9 to the bottom end of the metal pipe body to compensate for the temperature drift of the output. At the same time, the aluminum bushing 8, two pipe bushings 3 and three concentric metal pipe bodies are used to protect the temperature compensation module 9 At the same time, it can play a role in lightning protection, thereby eliminating the influence of fuel pollutants on the effective capacitance of the sensor. The two inner metal pipe bodies 11 and 12 measure the oil level signal. The outer metal pipe body 10 is used to shield external interference signals and pass the capacitance value C of the oil level measurement module 4 and the resistance value R of the temperature compensation module 9 The output of the guide rod 5 in the tube body is converted into the current signal IC and IR proportional to C and R to the fuel measurement control system. The temperature compensation module 9 compensates for the fuel level measurement error and reduces the sensor dryness. The parasitic capacitance value in the capacitance value can effectively measure the temperature change of the fuel tank and eliminate the error caused by the thermal expansion and contraction of the fuel medium. The sensor adds a temperature compensation function to automatically correct errors caused by different temperatures. After temperature compensation and linear correction, it has the advantages of high precision, high stability and continuous measurement. The fuel consumption value can be obtained directly by measuring the fuel volume of the fuel tank, without any effect or impact on the oil system/pipeline. And the measured value is not affected by the temperature, specific gravity of the liquid being measured and the shape and pressure of the container. The temperature compensation module adopts a highly integrated dedicated IC chip. After temperature compensation and linear correction, it is converted into a standard signal that can be recognized by a computer. The capacitive liquid level sensor has on-site calibration function. The user can perform zero point, arbitrary cut off length, and range. Automatic calibration to adapt to various harsh or complex applications.

Improved shock resistance. The utility model uses three mutually insulated coaxial metal pipe bodies to form the oil level height measurement module 4, wherein the outer layer is used as a shielding pipe to prevent external interference signals, the inner two layers of pipes measure the oil level signal, and the bottom end is fixed with the coaxial temperature The compensation module 9 relies on measuring the change of the medium in the sensor to obtain the height and oil volume of the oil level, and implement temperature compensation and inclination compensation. The experimental results show that it can accurately measure and display with full-scale linearization, and its anti-interference ability is extremely high. Strong, can withstand the interference of high voltage electric spark of 20,000 volts for 30 seconds, and measure the results of frequency converters, high-power radios and other strong interference equipment. The two pipe bushings 3 and the adjusting washer 1 installed at the two ends of the metal pipe effectively prevent the relative axial movement between the three concentric metal pipes 10, 11, and 12 under the vibration condition of the aircraft. Sealing treatment is adopted between the guide rod 5 and the inner metal tube body 12, and the two tube bushings 3 and the aluminum bushing 8 are opened with a round hole in the middle, which can make the fuel pollutants immersed in the sensor body flow out quickly and prevent fuel pollution If the temperature measurement module is blocked or blocked, the output signal has a certain damping time, which can eliminate data fluctuations caused by vibration and bumps.

The utility model is used in an aircraft fuel measurement and control system, and has two functions: fuel oil level height signal measurement and fuel temperature measurement. It can also be used to measure the oil level of automobile fuel tanks, tank cars, railway locomotives, and oil depots. It can be installed in various occasions to accurately measure the oil level of gasoline, diesel, hydraulic oil, etc., and can also be used for high-temperature oil level measurement.