CN105136245A - Triangular capacitive sensor and liquid level measuring system - Google Patents

Abstract

The invention provides a triangular capacitive sensor and a liquid level measurement system, which are used for liquid level measurement in LNG vehicle-mounted bottles. The triangular capacitive sensor includes: a first triangular plate, a second triangular plate and a rectangular plate installed in the inner cavity of the LNG vehicle bottle, the effective areas of the first triangular plate and the second triangular plate are equal and arranged symmetrically ; The plates of the first triangular pole plate and the second triangular pole plate are located in the same plane, the respective longest sides of the first triangular pole plate and the second triangular pole plate are opposite and arranged in parallel, the first triangular pole plate and the second triangular pole plate The shortest sides of the pole plates are respectively parallel to the liquid level in the inner chamber of the LNG vehicle bottle; the plate surface of the rectangular pole plate is arranged parallel to the plate surface of the first triangular pole plate, and the plate surface of the rectangular pole plate is parallel to the first triangular pole plate and the first triangular pole plate. The plate faces of the second triangular plate are opposite to each other. The above technology of the present invention can accurately measure the liquid level without being affected by the dielectric constant of LNG.

Description

Triangular Capacitive Sensor and Level Measurement System

technical field

The invention relates to liquefied natural gas technology, in particular to a triangular capacitive sensor and a liquid level measurement system used for liquid level measurement in a liquefied natural gas vehicle bottle.

Background technique

From January 1, 2016, the fourth phase of mandatory national standards for fuel consumption of passenger vehicles will be implemented, and natural gas passenger vehicles will be included in the accounting for the first time. According to the "carbon balance method", the energy consumption of natural gas vehicles has an advantage of 15%-20% compared with traditional gasoline vehicles, which will further enhance the enthusiasm of car companies to develop and apply natural gas vehicles. In the next ten years, my country will usher in a golden age for the development of natural gas for vehicles. According to the national plan, by 2020, the output of natural gas vehicles (liquefied natural gas (LNG) vehicles and compressed natural gas (CNG) vehicles) in China will reach 2.2 million units per year, of which passenger cars and trucks will reach 200,000 units (LNG vehicles about 50%), and 1 million passenger cars (LNG vehicles account for about 20%).

LNG vehicle bottle is an important part of LNG vehicle fuel system, and its liquid level measurement technology has received extensive attention from all walks of life. During the measurement process, various safety devices must be installed to ensure the safe and reliable operation of LNG vehicle bottles in various capacities. Therefore, a high-performance liquid level measurement system is designed to achieve accurate measurement and real-time detection of cryogenic liquids. It is very necessary.

The traditional liquid level measurement system mainly includes the sensor device installed in the LNG vehicle bottle, the sensor device is externally connected to the signal transmitter, the signal transmitter is connected with the liquid level display, and the sensor used in the LNG vehicle bottle is usually a single round The cylindrical triangular capacitive sensor is located in the vehicle bottle; the signal transmitter transmits and processes the collected signal and is located at the head of the vehicle bottle; the liquid level display is mainly for the real-time display of the liquid level signal transmitted by the signal transmitter , located in the cab. Through these three components, the liquid level in the LNG vehicle bottle will be displayed in real time and be mastered by the driver.

However, this traditional LNG vehicle-mounted bottle liquid level measurement system is based on the assumption that the dielectric constant of the measured medium and air is constant, and its detection method has the following disadvantages: the quality of liquefied natural gas will vary depending on the place of origin, temperature These differences will lead to changes in the dielectric constant of liquefied natural gas, which will have a greater impact on the capacitance of the triangular capacitive sensor, which will cause the traditional detection method to accurately detect the LNG vehicle bottle. The liquid level of the liquefied natural gas in the medium brings a lot of inconvenience to the normal filling, transportation and use of the LNG vehicle bottle. In addition, there are currently two commonly used methods to eliminate the influence of the dielectric constant on the basis of the traditional cylindrical triangular capacitive sensor, that is, irregularly calibrate the measured medium and introduce a reference capacitance to obtain the dielectric constant of the measured medium. These two methods not only greatly increase the amount of computation, but also occupy more container space.

Contents of the invention

A brief overview of the invention is given below in order to provide a basic understanding of some aspects of the invention. It should be understood that this summary is not an exhaustive overview of the invention. It is not intended to identify key or critical parts of the invention nor to delineate the scope of the invention. Its purpose is merely to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

In view of this, the present invention provides a triangular capacitive sensor and a liquid level measurement system for liquid level measurement in LNG vehicle-mounted bottles, to at least solve the problem that the existing liquid level measurement technology cannot accurately detect the liquid level of liquefied natural gas in LNG vehicle-mounted bottles. bit problem.

According to one aspect of the present invention, a triangular capacitive sensor for liquid level measurement in an LNG vehicle-mounted bottle is provided, the triangular capacitive sensor comprising: a first triangular plate, a second triangular plate and a rectangular plate, The effective areas of the first triangular pole plate and the second triangular pole plate are equal and arranged symmetrically; when in use, the first triangular pole plate, the second triangular pole plate and the rectangular pole plate are as follows Installed in the inner cavity of the LNG vehicle-mounted bottle: the plates of the first triangular plate and the second triangular plate are located in the same plane, and the respective surfaces of the first triangular plate and the second triangular plate are The longest sides are opposite and arranged in parallel, and the shortest sides of the first triangular pole plate and the second triangular pole plate are respectively parallel to the liquid level in the inner chamber of the LNG vehicle-mounted bottle; the plate surface of the rectangular pole plate is parallel to the The plates of the first triangular plate and the second triangular plate are arranged in parallel, and the plates of the rectangular plate are opposite to the plates of the first triangular plate and the second triangular plate.

Further, an insulating layer is provided on the outer walls of the first triangular plate and the second triangular plate.

Further, the respective plate surfaces of the first triangular pole plate and the second triangular pole plate are arranged in such a way as to be perpendicular to the liquid level in the inner chamber of the LNG vehicle-mounted bottle.

Further, the shapes of the first triangular plate and the second triangular plate are the same right-angled triangle, and the lengths of the right-angled sides of the right-angled triangle are H and D respectively; in use, the length is The right-angled side of H is set vertically to the liquid surface, while the right-angled side whose length is D is set parallel to the liquid surface, and H and D are respectively positive numbers.

Further, the distance between the respective longest sides of the first triangular plate and the second triangular plate is in the range of (0 mm, 5 mm].

Further, H is equal to the diameter of the circular section of the LNG vehicle-mounted bottle liner.

Further, D is equal to 80mm; the value of H is one of the following: 500mm; 600mm; 650mm.

In addition, according to another aspect of the present invention, a liquid level measurement system for measuring the liquid level in an LNG vehicle-mounted bottle is also provided, the liquid level measurement system includes: an inner cavity of an LNG vehicle-mounted bottle, A triangular capacitive sensor in the inner cavity of the bottle, a signal transmitter connected to the triangular capacitive sensor, and a liquid level indicator connected to the signal transmitter; wherein, the triangular capacitive sensor is right The triangular capacitive sensor described in any one of requirements 1-6; the first triangular plate and the second triangular plate in the triangular capacitive sensor are connected to the signal transmitter through two test probes, The two test probes measure the respective capacitance signals of the first triangular plate and the second triangular plate, and the signal transmitter converts the capacitance signals transmitted by the two test probes into a DC voltage signal, the liquid level height is calculated through the signal processing module arranged in the signal transmitter, and the calculated liquid level height is displayed in real time through the liquid level display.

Further, the signal processing module is used for: denoting the capacitance value of the first triangular plate as C ₁ , denoting the capacitance value of the second triangular plate 220 as C ₂ , and calculating the The ratio ΔC of the capacitance value of the second triangular plate to the slight change in the capacitance value of the second triangular plate, wherein, According to the ratio ΔC of the capacitance value of the first triangular plate to the capacitance value of the second triangular plate, and the plate surface of the first triangular plate and the second triangular plate The height H, determine the liquid level height h _x : $h_x=\frac{h}{1+\mathrm{\Δ}C}.$

Thus, applying the triangular capacitive sensor for liquid level measurement in the LNG vehicle-mounted bottle of the present invention can test the two triangular plates (i.e. the first triangular plate 210 and the second triangular plate 220) respectively by two test probes. The capacitance value is measured synchronously, and by differential processing the measured capacitance signal, the height of the liquid level is only related to the ratio of the micro-changes of the two capacitances, and has nothing to do with the dielectric constant of LNG, which eliminates the principle of The influence of the measured medium. Thus, for the situation of different dielectric constants, the triangular capacitive sensor of the present invention can accurately measure the liquid level in the LNG vehicle-mounted bottle, thereby realizing accurate measurement of the liquid level without being affected by the dielectric constant of LNG. Measurement.

In addition, by setting an insulating layer such as polytetrafluoroethylene on the outer wall of the triangular plate, it can effectively avoid the wall-hanging effect caused by impurities in the LNG, thereby improving the measurement accuracy of the triangular capacitive sensor and reducing the The probability of occurrence of sensor failure is reduced.

The liquid level measurement system of the present invention has the above effects of the triangular capacitive sensor of the present invention.

These and other advantages of the present invention will be more apparent through the following detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

Description of drawings

The present invention can be better understood by referring to the following description given in conjunction with the accompanying drawings, wherein the same or similar reference numerals are used throughout to designate the same or similar parts. The accompanying drawings, together with the following detailed description, are incorporated in and form a part of this specification, and serve to further illustrate preferred embodiments of the invention and explain the principles and advantages of the invention. In the attached picture:

Fig. 1A is a schematic structural view showing an example of applying the triangular capacitive sensor of the present invention in an LNG vehicle-mounted bottle;

Fig. 1 B is the view of triangular capacitive sensor shown in Fig. 1 A along A-A ' direction;

Fig. 2A is a schematic diagram showing a structure of the triangular capacitive sensor shown in Fig. 1A, and Fig. 2B is a schematic diagram showing another structure of the triangular capacitive sensor shown in Fig. 1A;

FIG. 3 is a flow chart illustrating the process of liquid level measurement using the triangular capacitive sensor shown in FIG. 1A .

It will be appreciated by those skilled in the art that elements in the figures are illustrated for simplicity and clarity only and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of the embodiments of the present invention.

Detailed ways

Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual implementation are described in this specification. It should be understood, however, that in developing any such practical embodiment, many implementation-specific decisions must be made in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and those Restrictions may vary from implementation to implementation. Moreover, it should also be understood that development work, while potentially complex and time-consuming, would at least be a routine undertaking for those skilled in the art having the benefit of this disclosure.

Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure and/or processing steps closely related to the solution according to the present invention are shown in the drawings, and the Other details not relevant to the present invention are described.

An embodiment of the present invention provides a triangular capacitive sensor for liquid level measurement in a vehicle-mounted LNG bottle. The triangular capacitive sensor includes: a first triangular plate, a second triangular plate and a rectangular plate, the first The effective areas of a triangular pole plate and the second triangular pole plate are equal and arranged symmetrically; in use, the first triangular pole plate, the second triangular pole plate and the rectangular pole plate are installed on the In the cavity of the LNG vehicle-mounted bottle: the plates of the first triangular plate and the second triangular plate are located in the same plane, and the respective longest sides of the first triangular plate and the second triangular plate are Relatively and in parallel, the shortest sides of the first triangular plate and the second triangular plate are respectively parallel to the liquid level in the inner cavity of the LNG vehicle-mounted bottle; the plate surface of the rectangular plate is parallel to the first A triangular pole plate is arranged parallel to the planes of the second triangular pole plate, and the planes of the rectangular pole plate are opposite to the planes of the first triangular pole plate and the second triangular pole plate.

Below, a description of an example of the triangular capacitive sensor for liquid level measurement in an LNG vehicle-mounted bottle of the present invention will be given with reference to FIGS. 1A, 1B and 2A, 2B.

As shown in Figures 1A and 1B, the triangular capacitive sensor 2 of the present invention comprises a first triangular pole plate 210, a second triangular pole plate 220 and a rectangular pole plate 230, the first triangular pole plate 210 and the second triangular pole plate 220 The effective areas are equal and arranged symmetrically.

When in use, the first triangular pole plate 210 and the second triangular pole plate 220 are installed in the LNG vehicle-mounted bottle cavity 1 shown in FIG. 1A in a diagonal parallel state, that is, the first triangular pole plate 210 and the second The respective longest sides of the two triangular pole plates 220 are opposite and arranged in parallel, and the shortest sides of the first triangular pole plate 210 and the second triangular pole plate 220 are respectively parallel to the liquid level in the LNG vehicle-mounted bottle cavity 1; the rectangular pole plates The plate surface of 230 is arranged parallel to the plate surfaces of the first triangular pole plate 210 and the second triangular pole plate 220, and the plate surface of the rectangular pole plate 230 is opposite to the plate surfaces of the first triangular pole plate 210 and the second triangular pole plate 220 .

It should be noted that the liquid level mentioned below all refers to the liquid level in the inner chamber 1 of the LNG vehicle bottle.

Wherein, the plate surfaces of the first triangular plate 210 and the second triangular plate 220 are located in the same plane S ₀ . There is no covering between the two surfaces of the first triangular plate 210 and the second triangular plate 220 .

According to an implementation manner, the plane S ₀ where the first triangular plate 210 and the second triangular plate 220 are located is vertical to the liquid surface. That is, the plate faces (ie, triangular faces) of the first triangular plate 210 and the second triangular plate 220 are arranged vertically to the liquid surface. In this way, in the subsequent measurement process, the plate height used when calculating the liquid level height is the height of the plate surface (i.e., the triangular surface), such as H shown in Figure 2A, to avoid the tilting of the plate surface The problem of inaccurate final measurement due to inaccurate height calculation improves measurement accuracy and calculation efficiency.

According to an implementation manner, the distance between the respective longest sides of the first triangular plate 210 and the second triangular plate 220 may range in value from (0 mm, 5 mm], for example, the distance may be 1 mm.

The capacitance values of the first triangular plate 210 and the second triangular plate 220 are measured synchronously by two test probes (not shown in FIG. 1A ). When the liquid level height in the LNG vehicle bottle inner chamber 1 changes, the two capacitance signals measured simultaneously by the first triangular plate 210 and the second triangular plate 220 are transmitted to the circuit shown in Figure 1A through the above two test probes. In the signal transmitter 3, the change trends of the measurement results of the two capacitance signals are opposite. The change of the liquid level makes the capacitance of the two triangular plates change accordingly, that is to say, the two plates respectively convert the liquid level signal of LNG into a capacitance signal. In the signal transmitter 3, by performing differential processing on the two capacitance signals, the height of the liquid level is only related to the ratio of the micro-changes of the two capacitances, and has nothing to do with the dielectric constant of the LNG, so as to realize the dielectric constant of the LNG. Constant independent level measurement. Therefore, the liquid level height of LNG can be accurately measured without being affected by the dielectric constant of LNG.

It should be noted that the "capacitance value of the first triangular plate 210" refers to the capacitance value of the capacitor formed by the first triangular plate 210 and the rectangular plate 230, and the "capacitance value of the second triangular plate 220" is Refers to the capacitance value of the capacitor formed by the second triangular plate 220 and the rectangular plate 230 .

According to an implementation manner, as shown in FIG. 2B , the shapes of the first triangular plate 210 and the second triangular plate 220 are the same right triangle. The lengths of the sides of this right triangle are H and D, respectively. When in use, the right-angled side with a length of H is arranged vertically to the liquid surface (making H=the height of the plate surface at this time), and the right-angled side with a length of D is arranged parallel to the liquid surface. Wherein, the hypotenuse of the first triangular plate 210 is opposite to the hypotenuse of the second triangular plate 220 .

In practical applications, for example, a capacitor composed of two parallel rectangular plates can be used, one of the two parallel rectangular plates is cut along the diagonal, and the other rectangular plate remains unchanged, wherein The cut plate is divided into two symmetrical right-angled triangle plates, the hypotenuses of the two right-angled triangles are opposite, and there is a small distance (for example, 1mm) between the two hypotenuses, so that the two right-angled The triangular plate serves as the first triangular plate 210 and the second triangular plate 220 , and the other rectangular plate serves as the rectangular plate 230 in the triangular capacitive sensor 2 .

Wherein, the actual lengths of H and D are determined according to the actual size of the inner cavity 1 of the LNG vehicle-mounted bottle. For example, H can be equal to the cavity height of the inner chamber 1 of the LNG vehicle-mounted bottle (that is, the diameter of the circular section of the LNG vehicle-mounted bottle liner), and D is smaller than H, which can save material costs while ensuring accurate measurement.

According to an implementation manner, in a container with a volume of 450 L of an LNG vehicle-mounted bottle, H is 650 mm in diameter of the inner liner of the LNG vehicle-mounted bottle; D is 80 mm. H is the diameter of the inner liner of the vehicle bottle, which can accurately measure the height of the liquid level. For example, for a 240-liter gas cylinder, H=500mm; for a 275-liter gas cylinder, H=500mm; for a 340-liter gas cylinder, H=600mm.

Wherein, the distance between the first triangular plate 210 and the rectangular plate 230 and the distance between the second triangular plate 220 and the rectangular plate 230 are equal, for example, both are 5 mm or 10 mm.

If D is set too large, the plate will take up the volume of LNG; if D is set too small, the plate will not be stable and difficult to process. Therefore, when D is set to 80mm, it is beneficial to the stability of the pole plate and the processing of the pole plate, and will not occupy too much volume of liquefied natural gas.

In addition, according to an implementation, an insulating layer (such as a polytetrafluoroethylene insulating layer) is provided on the outer walls of the first triangular pole plate 210 and the second triangular pole plate 220, so as to improve the performance of the triangular capacitive sensor 2 of the present invention. measurement accuracy and success rate.

In practical applications, when the LNG vehicle bottle is filled with liquid, there will always be impurities in the LNG, and the impurities are easily attached to the plate, which will make the measurement results inaccurate. Therefore, by disposing an insulating layer on the outer walls of the first triangular plate 210 and the second triangular plate 220 , the influence caused by hanging on the wall can be avoided, and the accuracy and success rate of the triangular capacitive sensor measurement can be improved.

For example, polytetrafluoroethylene insulation layer can be used as the above insulation layer. Compared with other materials, this insulation layer has the following advantages: high temperature resistance - the working temperature can reach 250 ° C; low temperature resistance - good mechanical toughness, even The temperature drops to -196°C, and only maintains 5% elongation; corrosion resistance - insoluble in most chemical liquids, such as strong acids and alkalis; weather resistance - extremely long aging life High lubrication - extremely high friction coefficient Low; Non-adhesive - does not stick to anything; Electrical Insulation - Excellent insulation.

The above-mentioned triangular capacitive sensor used for liquid level measurement in LNG vehicle-mounted bottles of the present invention can carry out liquid level measurement in the following manner: Utilize two test probes to test the capacitance value of the first triangular pole plate 210 and the capacitance value of the second triangular pole plate 220 respectively Real-time synchronous measurement of the capacitance value, the capacitance value of the first triangular plate 210 is recorded as C ₁ , and the capacitance value 220 of the second triangular plate is recorded as C ₂ ; the ratio ΔC of the slight change between C ₁ and C ₂ is calculated: Calculate the liquid level h _x of the LNG vehicle bottle: Where H is the height of the plate surfaces of the first triangular plate 210 and the second triangular plate 220 . Wherein, "the liquid level height of the LNG vehicle-mounted bottle" is also the liquid level height in the inner chamber 1 of the LNG vehicle-mounted bottle.

Embodiments of the present invention also provide a liquid level measurement system for measuring the liquid level in an LNG vehicle-mounted bottle, the liquid level measurement system comprising: an inner cavity of an LNG vehicle-mounted bottle, a triangular shaped tube arranged in the inner cavity of the LNG vehicle-mounted bottle A capacitive sensor, a signal transmitter connected to the triangular capacitive sensor, and a liquid level indicator connected to the signal transmitter; wherein, the triangular capacitive sensor is the triangular capacitive sensor described above type sensor; the first triangular plate and the second triangular plate in the triangular capacitive sensor are connected to the signal transmitter through two test probes, and the first triangular plate is measured by the two test probes. The respective capacitance signals of the pole plate and the second triangular pole plate, the signal transmitter converts the capacitance signal transmitted by the two test probes into a DC voltage signal, through the signal processing set in the signal transmitter The module calculates the height of the liquid level, and displays the calculated liquid level in real time through the liquid level display.

In one example, as shown in FIG. 1A , the liquid level measurement system may include: an inner cavity 1 of an LNG vehicle-mounted bottle, a triangular capacitive sensor 2 arranged in the inner cavity 1 of an LNG vehicle-mounted bottle, a triangular capacitive sensor 2 connected to the A signal transmitter 3 and a liquid level indicator 4 connected to the signal transmitter 3 . Wherein, the triangular capacitive sensor 2 includes a first triangular plate 210 and a second triangular plate 220, the structures of which are the same as those described above.

Wherein, the triangular capacitive sensor 2 (i.e. the first triangular pole plate 210 and the second triangular pole plate 220) is connected with the signal transmitter 3 through two test probes (not shown in the figure), and the inner cavity of the LNG vehicle bottle The height of the liquid level in 1 is measured simultaneously (two test probes measure the respective capacitance signals of the first triangular plate 210 and the second triangular plate 220), and ensure that when the liquid level changes, the two measured values are relative The trend changes, the signal transmitter 3 converts the capacitance signals transmitted by the two test probes into the required DC voltage signal, and then uses the signal processing module (not shown) arranged in the signal transmitter 3 to calculate the liquid Level height, its processing can make the liquid level height only related to the conversion of two values, and finally the liquid level of the LNG vehicle-mounted bottle is displayed in real time through the liquid level display 4 .

According to an implementation manner, the signal processing module in the signal transmitter 3 may perform the processing of steps S320 and S330 described below in conjunction with FIG. 3 .

According to an implementation manner, an insulating layer (such as a polytetrafluoroethylene insulating layer) is provided on the outer wall of the triangular capacitive sensor 2 to improve the measurement accuracy and success rate of the above-mentioned liquid level measurement system.

The liquid level measurement system of the present invention has the functions and effects of the triangular capacitive sensor described above, and will not be repeated here.

Next, with reference to FIG. 3 , how to use the triangular capacitive sensor described above in conjunction with FIG. 1A and FIGS. 2A and 2B to measure the liquid level in the LNG vehicle bottle.

Assume that the height of the two triangular plates (ie, the first triangular plate 210 and the second triangular plate 220 ) in the triangular capacitive sensor 2 is H.

In step S310, two test probes (not shown in FIG. 1A ) are used to carry out real-time synchronous measurement of the capacitance values of the first triangular plate 210 and the second triangular plate 220 respectively, and the capacitance of the first triangular plate 210 is The value is denoted as C ₁ , and the capacitance value of the second triangular plate 220 is denoted as C ₂ .

Next, in step S320, the ratio ΔC of the slight variation between the capacitance C ₁ of the first triangular plate 210 and the capacitance C ₂ of the second triangular plate 220 is calculated, that is,

Then, in step S330, the liquid level height h _x of the LNG vehicle-mounted bottle is calculated according to the following measurement formula: $h_x=\frac{h}{1+\mathrm{\Δ}C}.$

It can be seen that the liquid level height of the LNG vehicle-mounted bottle calculated by the above-mentioned liquid level measurement process is only related to the ratio ΔC of the capacitance value _C1 of the two triangular plates in the triangular capacitive sensor ₂ and the slight change of C2, while It has nothing to do with the dielectric constant of LNG and air.

The derivation and demonstration of the above measurement formula are given below.

Take the first triangular pole plate 210 and the second triangular pole plate 220 arranged as shown in Figure 2B as an example (the situation shown in Figure 2A is similar to this), the pole plate height in this case is equal to the vertical of the triangular plate surface The leg length of the layout. In addition, assuming that the outer walls of the first triangular plate 210 and the second triangular plate 220 are provided with polytetrafluoroethylene insulating layers, the distance between the surfaces of the two plates and the surface of the insulating medium is d ₀ .

The height and base width of the two pole plates (i.e. the first triangular pole plate 210 and the second triangular pole plate 220) are H and D respectively, the thickness of the insulating layer is d ₂ , the dielectric constant of air, LNG and the insulating layer are ε ₀ , ε ₁ and ε ₂ , the capacitances of the first triangular plate 210 and the second triangular plate 220 are C ₁ , C ₂ respectively, and the liquid level of the LNG vehicle bottle is h _x .

The edge effect of the electric field between the first triangular plate 210 and the second triangular plate 220 is negligible, so:

Formula one: $\begin{array}{c}{C}_1=\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2}\·\frac{{(h-h_x)}^2}{2h}\mathrm{D.}+\frac{1}{d_0/{\mathrm{\ϵ}}_1+d_2/{\mathrm{\ϵ}}_2}\&Center\; Dot;\frac{(2h-h_x)}{2h}{h}_x\mathrm{D.}\\ =\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2}\&Center\; Dot;\frac{h\mathrm{D.}}{2}+(\frac{1}{d_0/{\mathrm{\ϵ}}_1+d_2/{\mathrm{\ϵ}}_2}-\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2})\·\frac{(2h-h_x)}{2h}{h}_x\mathrm{D.}\end{array}$

Formula two: $\begin{array}{c}{C}_2=\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2}\&Center\; Dot;\frac{{(h-h_x)}^2}{2h}\mathrm{D.}+\frac{1}{d_0/{\mathrm{\ϵ}}_1+d_2/{\mathrm{\ϵ}}_2}\·\frac{{h_x}^2}{2h}\mathrm{D.}\\ =\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2}\·\frac{h\mathrm{D.}}{2}+(\frac{1}{d_0/{\mathrm{\ϵ}}_1+d_2/{\mathrm{\ϵ}}_2}-\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2})\·\frac{{h_x}^2}{2h}\mathrm{D.}\end{array}$

When the car is running, the dielectric constant and liquid level of LNG and air will change due to changes in time and environmental conditions. At the same time, when the origin of LNG is different, the dielectric constant will vary greatly. At this time, Formula 1 and Formula 2 are equivalent to a ternary quadratic equation system. In order to eliminate the influence of the dielectric constant, C ₁ and C ₂ can be differentiated with respect to h _x at the same time:

Formula three: $\frac{c_1}{{\mathrm{d\; h}}_x}=2A_2(h-h_x)$

Formula four: $\frac{c_2}{{\mathrm{d\; h}}_x}=2A_2{h}_x$

in, $A_2=(\frac{1}{d_0/{\mathrm{\ϵ}}_1+d_2/{\mathrm{\ϵ}}_2}-\frac{1}{d_0/{\mathrm{\ϵ}}_0+d_2/{\mathrm{\ϵ}}_2})\&Center\; Dot;\frac{\mathrm{D.}}{2h}$

According to Formula 3 and Formula 4, we can get:

Formula five: $\frac{c_1}{c_2}=\frac{c_1/{\mathrm{d\; h}}_x}{c_2/{\mathrm{d\; h}}_x}=\frac{h-h_x}{h_x}=\mathrm{\Δ}C$

Then the liquid level of the LNG vehicle bottle can be obtained It is only related to the ratio of slight changes of C1 and C2, but has nothing to do with the dielectric constant of LNG and air, and realizes accurate real-time measurement of liquid level. In addition, the height of the liquid level is related to the ratio of the micro-change of the capacitance, so it is suitable for the measurement of the dynamic liquid level of the LNG vehicle bottle.

While the invention has been described in terms of a limited number of embodiments, it will be apparent to a person skilled in the art having the benefit of the above description that other embodiments are conceivable within the scope of the invention thus described. In addition, it should be noted that the language used in the specification has been chosen primarily for the purpose of readability and instruction rather than to explain or define the inventive subject matter. Accordingly, many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. With respect to the scope of the present invention, the disclosure of the present invention is intended to be illustrative rather than restrictive, and the scope of the present invention is defined by the appended claims.

Claims (9)

1. A triangle-shaped capacitive sensor for on-vehicle bottle level measurement of LNG, its characterized in that, triangle-shaped capacitive sensor includes: the device comprises a first triangular polar plate, a second triangular polar plate and a rectangular polar plate, wherein the effective areas of the first triangular polar plate and the second triangular polar plate are equal and are symmetrically arranged;

when the LNG vehicle-mounted bottle is used, the first triangular polar plate, the second triangular polar plate and the rectangular polar plate are arranged in an inner cavity of the LNG vehicle-mounted bottle in the following modes: the plate surfaces of the first triangular polar plate and the second triangular polar plate are positioned in the same plane, the longest sides of the first triangular polar plate and the second triangular polar plate are opposite and arranged in parallel, and the shortest sides of the first triangular polar plate and the second triangular polar plate are respectively parallel to the liquid level in the inner cavity of the LNG vehicle-mounted bottle; the surfaces of the rectangular polar plates are arranged in parallel with the surfaces of the first triangular polar plates and the second triangular polar plates, and the surfaces of the rectangular polar plates are opposite to the surfaces of the first triangular polar plates and the second triangular polar plates.

2. The triangular capacitive sensor of claim 1, wherein an insulating layer is disposed on an outer wall of each of the first and second triangular plates.

3. The triangular capacitive sensor of claim 1 or 2, wherein the first triangular plate and the second triangular plate are each disposed with their faces perpendicular to a liquid level in an interior chamber of the LNG vehicle bottle.

4. The triangular capacitive sensor of claim 1 or 2, wherein the first and second triangular plates are both in the shape of the same right triangle, and the lengths of the right-angled sides of the right triangle are H and D, respectively; when the liquid level meter is used, the right-angle side with the length of H is perpendicular to the liquid level, the right-angle side with the length of D is parallel to the liquid level, and H and D are positive numbers respectively.

5. The triangular capacitive sensor of claim 4, wherein the distance between the longest edges of the first and second triangular plates ranges from (0mm, 5 mm).

6. The triangular capacitive sensor of claim 4, wherein H is equal to a diameter of a circular cross section of an LNG vehicle bottle liner.

7. The triangular capacitive sensor of claim 4, wherein D is equal to 80 mm; the value of H is one of the following:

500mm；600mm；650mm。

8. a level measurement system for on-vehicle bottle level measurement of LNG, its characterized in that, level measurement system includes: the LNG vehicle-mounted bottle comprises an inner cavity of an LNG vehicle-mounted bottle, a triangular capacitive sensor arranged in the inner cavity of the LNG vehicle-mounted bottle, a signal transmitter connected with the triangular capacitive sensor and a liquid level indicator connected with the signal transmitter; wherein the triangular capacitive sensor is the triangular capacitive sensor of any one of claims 1-6;

the first triangular polar plate and the second triangular polar plate in the triangular capacitive sensor are connected with the signal transmitter through two test probes, the two test probes measure to obtain respective capacitance signals of the first triangular polar plate and the second triangular polar plate, the signal transmitter converts the capacitance signals transmitted by the two test probes into direct-current voltage signals, the liquid level height is calculated through a signal processing module arranged in the signal transmitter, and the calculated liquid level height is displayed in real time through the liquid level display.

9. The fluid level measurement system of claim 8, wherein the signal processing module is configured to:

marking the capacitance value of the first triangular polar plate as C₁And the capacitance value of the second triangular plate 220 is denoted as C₂Calculating the micro-variation ratio deltaC of the capacitance value of the first triangular polar plate and the capacitance value of the second triangular polar plate, wherein,

according to the first triangleDetermining the liquid level height H by the micro-variation ratio delta C of the capacitance value of the shape polar plate to the capacitance value of the second triangular polar plate and the height H of the polar plate surfaces of the first triangular polar plate and the second triangular polar plate_x：