Non-contact oil level measuring device and measuring method for aviation fuel tank

Abstract

The present invention discloses a non-contact oil level measuring device for an aviation fuel tank and a measuring method. The oil level measuring device comprises a non-metallic PCB substrate layer and a metal shielding layer. The two ends of the non-metallic PCB substrate layer close to the fuel tank are respectively provided with a sensing electrode and a working electrode, and the other side of the non-metallic PCB substrate layer is provided with a metal shielding layer, and the working electrode is connected to the metal shielding layer; the side opposite to the sensing electrode and the working electrode is respectively provided with a plurality of sensing electrode fingers and working electrode fingers, the sensing electrode fingers and the working electrode fingers are arranged in a staggered manner in a fingertip-crossed shape, and a plurality of sensing electrode fingers and working electrode fingers are provided between adjacent working electrode fingers. n The invention realizes non-contact oil level measurement and has the advantages of no damage, high measurement sensitivity, high reliability and high durability.

Description

Technical Field

[0001] The invention belongs to the technical field of aviation fuel measurement, and in particular relates to a non-contact oil level measuring device and a measuring method for an aviation fuel tank. Background Art

[0002] Fuel level measurement is an important task in various transportation systems such as airplanes, cars, and ships. At present, coaxial metal tube capacitive oil level sensors are widely used in the measurement of fuel level in the fuel tanks of domestic aerospace vehicles. The coaxial metal tube capacitive oil level sensor embeds the coaxial metal tube of the sensor in the fuel tank and contacts the fuel. It uses the different dielectric constants of air and fuel to output different capacitance values ​​according to the change of liquid level. It has problems such as heavy weight and need to contact with fuel. At the same time, the sensor is installed in the fuel tank, which may introduce redundant materials, and the change of fuel quality will also affect the output capacitance accuracy of the sensor.

[0003] At present, with the development of aerospace technology, its aviation equipment is also moving towards lightweight and integration. However, the traditional coaxial metal tube capacitive oil level sensor is large in size and weight, and the degree of integration of the integrated structure is low, which cannot meet the requirements of lightweight aviation equipment. In addition, during the measurement of aviation fuel, the contact sensor needs special surface treatment due to the special use environment. Even so, the accuracy and reliability will still be significantly reduced with the increase of use time, thereby reducing the service life and causing waste of manpower and material resources. Summary of the invention

[0004] The purpose of the present invention is to provide a non-contact oil level measuring device and method for aviation fuel tanks, aiming to solve the above problems. The present invention can realize non-contact oil level measurement, and has the advantages of simple structure, high reliability, high durability, and no damage.

[0005] The present invention is mainly achieved through the following technical solutions:

[0006] A non-contact oil level measuring device for an aviation fuel tank comprises a non-metallic PCB substrate layer and a metal shielding layer, wherein two ends of the non-metallic PCB substrate layer close to the fuel tank are respectively provided with a sensing electrode and a working electrode, and the other side of the non-metallic PCB substrate layer is provided with a metal shielding layer, and the working electrode is connected to the metal shielding layer; a plurality of sensing electrode fingers and working electrode fingers are respectively provided on the opposite side of the sensing electrode and the working electrode, and the sensing electrode fingers and the working electrode fingers are staggered and arranged in a fingertip-crossed shape, and a plurality of sensing electrode fingers and working electrode fingers are provided between adjacent working electrode fingers. n There are sensing electrode fingers, and the intervals between adjacent electrode fingers are equal to form a fingertip cross sensor.

[0007] In order to better implement the present invention, further, the sensing electrode finger and the working electrode finger have the same size, and the length of the electrode finger is L and the width is w ; The interval between adjacent electrode fingers is 2g.

[0008] In order to better implement the present invention, further, when L is much larger than w ,and w When g is much greater than g, the capacitance between the working electrode and the sensing electrode is:

[0009] ,

[0010] Where: g is half of the interval between adjacent electrode fingers;

[0011] ε r is the relative dielectric constant of the tank wall;

[0012] ε 0 is the dielectric constant of air;

[0013] x is the liquid level height.

[0014] In order to better implement the present invention, further, the maximum electric field penetration depth of the fingertip crossing sensor is:

[0015] ,

[0016] Where: g is half of the spacing between adjacent electrode fingers.

[0017] In order to better implement the present invention, further, n is equal to 3 or 5; 3 or 5 sensing electrode fingers are arranged between adjacent working electrode fingers.

[0018] In order to better realize the present invention, further, the metal shielding layer is a metal copper-clad layer, and metal copper-clad layers are respectively arranged on both sides of the non-metallic PCB substrate layer to form a double-sided copper-clad PCB substrate; the metal copper-clad layer on the side of the double-sided copper-clad PCB substrate close to the fuel tank is etched to form a sharp cross sensor.

[0019] In order to better implement the present invention, further, it also includes a shielded wire, and the working electrode and the sensing electrode are connected to the host computer through the shielded wire respectively.

[0020] The present invention is mainly achieved through the following technical solutions:

[0021] A non-contact oil level measurement method for an aviation fuel tank is based on the above-mentioned non-contact oil level measurement device for an aviation fuel tank, and comprises the following steps:

[0022] Step S1: installing the oil level measuring device on the outer wall of the oil tank, connecting the working electrode and the sensing electrode to the external power excitation and acquisition circuit respectively, and connecting the metal shielding layer outside the non-metallic PCB substrate layer to the working electrode;

[0023] Step S2: generating an electric field in the fingertip crossing sensor by voltage excitation;

[0024] Applying voltage excitation to the working electrode and the sensing electrode respectively, so that the working electrode is connected to a high potential AC excitation relative to the sensing electrode, and a fringe electric field is generated between the working electrode and the sensing electrode;

[0025] Step S3: The capacitance value C output by the oil level measuring device 1,n Calculate the liquid level.

[0026] The beneficial effects of the present invention are as follows:

[0027] (1) The present invention sets an IDT sensor near one side of the oil tank, and generates a fringe electric field by applying a potential difference between the working electrode and the sensing electrode. The fringe electric field penetrates the oil tank wall to sense the oil level change in the composite oil tank. When the oil level changes, the capacitance between the working electrode and the sensing electrode also changes as a function. The signal is connected to the host computer through a shielded wire for oil level signal transmission. The present invention realizes non-contact oil level measurement and has the advantages of no damage, high reliability and high durability.

[0028] (2) The present invention is a non-contact capacitive oil level measurement method, which can be used to measure the liquid level of non-metallic thin-walled oil tanks. It is non-destructive to sensors and has high reliability and durability. The present invention has high measurement sensitivity, and the output capacitance is linearly related to the liquid level change. The present invention has a simple structure and is light in weight. It only requires working electrodes and sensing electrodes crossed by fingertips to form a capacitor. Its working environment is not limited by the special structure of the oil tank. Compared with the embedded coaxial metal tube capacitive oil level sensor, it is more than 70% lighter. The present invention is suitable for integrated oil tanks and contributes to the integrated development of aviation equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a structural schematic diagram of the non-contact oil level measuring device for aviation fuel tanks of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the IDT sensor with structure 1-1-1 in Example 1;

[0031] Figure 3 Schematic diagram of the electric field distribution generated between the working electrode and the sensing electrode in Example 1;

[0032] Figure 4 Schematic diagram of electric field penetration of IDT sensor;

[0033] Figure 5 It is a simulation diagram of the capacitance value Ceq1-n-1 changing with w / 2g and n;

[0034] Figure 6 It is a simulation diagram showing the maximum electric field penetration depth changes with w / 2g and n;

[0035] Figure 7 Schematic diagram of a parallel plate capacitor based on a 1-5-1 structure IDT sensor in Example 2.

[0036] Among them: 1-metal shielding layer, 2-non-metal PCB substrate layer, 3-sensing electrode, 4-working electrode, 5-shielded wire. DETAILED DESCRIPTION

[0037] Embodiment 1:

[0038] A non-contact oil level measuring device for an aviation fuel tank, such as Figure 1 As shown, it includes a double-sided copper-clad PCB substrate and a shielded wire 5. The double-sided copper-clad PCB substrate includes metal copper-clad layers on both sides and a non-metallic PCB substrate layer 2 in the middle, wherein the metal copper-clad layer on one side is etched with a fingertip cross pattern by a copper etching solution to form an interdigital (IDT) sensor. The interdigital sensor includes a working electrode 4 and a sensing electrode 3, and the metal copper-clad layer on the other side needs to be connected to the working electrode 4 so that the generated magnetic field is only directed from the working electrode 4 to the sensing electrode 3; the working electrode 4 and the sensing electrode 3 are connected to an external power supply and a host computer through a shielded wire 5. The oil level measuring device is attached to the outer wall of the composite oil tank, and the interdigital (IDT) sensor is located on the inner side of the oil level measuring device.

[0039] like Figure 1 and Figure 2 As shown, a plurality of sensing electrode fingers and working electrode fingers are arranged at intervals on the opposite sides of the sensing electrode 3 and the working electrode 4, and the sensing electrode fingers and the working electrode fingers are arranged in a staggered manner in a fingertip cross shape. The structure of the IDT sensor is 1-1-1, and the 1-1-1 structure means that one working electrode finger, one sensing electrode finger and one working electrode finger are arranged in sequence from front to back.

[0040] like Figure 3As shown, by applying +3.3V voltage excitation to the working electrode 4 and -3.3V voltage excitation to the sensing electrode 3, the working electrode 4 of the IDT sensor is connected to a high potential AC excitation relative to the sensing electrode 3, and the 1-1-1 structure of the IDT sensor constitutes a parallel plate capacitor, and a fringe electric field is generated between the working electrode 4 and the sensing electrode 3. The formation of the field penetration depth and the capacitance value depends on the geometric structure of the sensor, the height of the measured medium and the excitation intensity. Since the geometric structure and the excitation intensity do not change, the generated capacitance is only related to the change in the liquid level. Therefore, the present invention realizes the liquid level measurement of the composite oil tank without contacting the measured liquid.

[0041] Embodiment 2:

[0042] This embodiment is optimized on the basis of the embodiment 1. Two crucial parameters of the present invention are the "electric field penetration depth" and the "capacitance value" between the working electrode 4 and the sensing electrode 3. The former determines whether the induced electric field can penetrate the side wall of the oil tank to complete the sensing function, and the latter determines the sensing sensitivity and signal-to-noise ratio.

[0043] like Figure 2 and Figure 3 As shown in the figure, the spacing between adjacent working electrode fingers and sensing electrode fingers in the IDT sensor is equal, and the gap between the electrode fingers is 2g. The length of the electrode finger is L, the width is w, and the wavelength is r, where the wavelength r is the spacing between two adjacent electrode fingers on the same side. IDT sensor and relative dielectric constant ε r The thickness of the tank wall is T and the electrodes are excited by a potential of ±V. Due to this potential, the electric field lines pass through the tank wall from the positive electrode to the negative electrode.

[0044] like Figure 4 As shown, (a) is the thickness of the tank wall T is less than the field penetration depth h 1 Schematic diagram of electric field penetration when (b) is when the thickness of the tank wall T is greater than the field penetration depth h 1 Schematic diagram of electric field penetration when the maximum height of the electric field is h 1 . Assume that the width of the electrode is much larger than the gap between the electrodes (w>>2 g). Expand the two coplanar semi-infinite parallel plate electrodes with a gap of 2g. The two-dimensional electrode field distribution can be easily solved with the help of the conformal mapping technique of the inverse cosine transform. Using the results of the conformal mapping solution, the approximate expression of the capacitance can be obtained.

[0045] For the IDT sensor with a 1-1-1 structure, under the conditions of L>>w and w>>g, the capacitance between the working electrode 4 and the sensing electrode 3 can be expressed as:

[0046] (1)

[0047] (2)

[0048] By recursive formula, it can be extended to the 1-n-1 structure IDT sensor. Under the conditions of L>>w, w>>g, the capacitance value between the working electrode 4 and the sensing electrode 3 can be expressed as:

[0049] (3)

[0050] where ε 0 is the dielectric constant of air; Q is the total charge on a single electrode, x is the liquid level height. From the functional relationship, we can know that C 1，n (That is, the capacitance value Ceq1-n-1) can be determined by the fingertip structure (the value of n) and the fingertip width and gap ratio (w / 2g).

[0051] like Figure 5 As shown, (a) is a schematic diagram of MATLAB simulation of capacitance value Ceq1-n-1, w / 2g and n, and (b) is a curve diagram of capacitance value and w / 2g when n=1, 3, 5, and 11. From the MATLAB simulation results, it can be seen that the capacitance value Ceq1-n-1 gradually increases with w / 2g and gradually decreases with n. In order to facilitate the analysis of the function change trend, the simulation results are simplified by taking typical values ​​of n=1, 3, 5, and 11.

[0052] For the tank wall thickness T,

[0053] (4)

[0054] According to the critical condition, when the tank wall thickness and the maximum electric field penetration depth are equal, for the 1-1-1 structure IDT sensor, the maximum electric field penetration depth can be expressed as:

[0055] (5)

[0056] According to the recursive formula, the maximum electric field penetration depth can be expressed as:

[0057] (6)

[0058] From the functional relationship, we can know that the maximum electric field penetration depth h n It is determined by the fingertip structure (the value of n), fingertip width, and gap ratio (w / 2g). Figure 6 As shown in the figure, (a) is a MATLAB simulation diagram of the maximum electric field penetration depth, w / 2g and n, and (b) is a curve diagram of the maximum electric field penetration depth and w / 2g when n=1, 3, 5, and 11. From the MATLAB simulation results, it can be seen that the field penetration depth hn It increases with the increase of w / 2g and n. To facilitate the analysis of the function change trend, the simulation results are simplified by taking typical values ​​of n=1, 3, 5, and 11.

[0059] like Figure 5 and Figure 6 As shown, the simulation analysis results confirm the accuracy of formula (3) and formula (6). The total equivalent capacitance and penetration depth need to be considered comprehensively during design, and a moderate n value should be selected to design the IDT sensor. To facilitate the analysis of the function change trend, the simulation results are simplified by taking typical values ​​of n=1, 3, 5, and 11. The IDT sensor with a 1-1-1 structure exhibits good signal strength, that is, the output capacitance is large, but the penetration depth is low, while the IDT sensor with a 1-11-1 structure exhibits good field penetration depth as the number of sensing electrodes 3 increases, but the output capacitance is lower than that of the IDT sensor with a 1-1-1 structure. Therefore, IDT sensors with a 1-3-1 or 1-5-1 structure may be the best choice for medium signal strength and penetration depth. Users can choose a suitable structure according to their individual needs. In this example, the emphasis is on penetration depth, so the 1-5-1 structure IDT sensor is taken as the optimal structure. As shown Figure 7 As shown, the 1-5-1 structure of the IDT sensor now constitutes 10 different parallel plate capacitors, such as Figure 3 As shown, a fringe electric field is generated between the working electrode 4 and the sensing electrode 3 .

[0060] Embodiment 3:

[0061] A non-contact oil level measurement method for an aviation fuel tank is implemented based on the above-mentioned non-contact oil level measurement device for an aviation fuel tank, and comprises the following steps:

[0062] Step 1: Install the oil level measuring device on the outer wall of the composite oil tank, connect the working electrode 4 and the sensing electrode 3 to the external power source excitation and acquisition circuit, connect the metal shielding layer 1 to the working electrode 4, and use voltage excitation to make the IDT sensor generate an electric field. At this time, the capacitance formed in the oil level measuring device has a fixed capacitance C formed by the air gap between the IDT sensor and the composite oil tank wall. a , the fixed capacitance C formed by the composite tank wall w The capacitance C formed by the air in the fuel tank T , C a and C w These two capacitors will be connected with capacitor C T connected in series and work as fixed bias capacitors;

[0063] Step 2: Through the change of the liquid level in the tank, the capacitor in the tank is composed of a portion of air formed capacitor C A The capacitance C formed by the fuel at a certain height H , CT =C A +C H ;

[0064] Step 3: The liquid level height can be calculated by the output capacitance value, the total capacitance C 1,n = C T +C a +C w .

[0065] C a and C w Capacitor will reduce the overall sensitivity of the IDT sensor used for level measurement, so when the capacitor C T Efforts will be made to keep these capacitance values ​​high compared to the capacitance values ​​of the FET. This can be ensured by using thin-walled composite tanks and minimizing air gaps when placing the IDT sensor electrodes against the tank wall.

[0066] The present invention is suitable for the use of aviation composite fuel tanks. A potential difference is applied to the working electrode 4 and the sensing electrode 3 of the IDT sensor to generate a fringe electric field. The fringe electric field penetrates the tank wall to sense the oil level change in the composite fuel tank. When the oil level changes, the capacitance between the working electrode 4 and the sensing electrode 3 also changes as a function. The signal is connected to the host computer through the shielded wire 5 for oil level signal transmission. The present invention realizes non-contact oil level measurement and has the advantages of no damage, high reliability and high durability.

[0067] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A non-contact oil level measuring device for an aviation fuel tank, characterized in that: The invention comprises a non-metallic PCB substrate layer (2) and a metal shielding layer (1), wherein two ends of a side of the non-metallic PCB substrate layer (2) close to the oil tank are respectively provided with a sensing electrode (3) and a working electrode (4), and the other side of the non-metallic PCB substrate layer (2) is provided with a metal shielding layer (1), and the working electrode (4) is connected to the metal shielding layer (1); a plurality of sensing electrode fingers and working electrode fingers are respectively provided on the side opposite to the sensing electrode (3) and the working electrode (4), and the sensing electrode fingers and the working electrode fingers are arranged in a staggered manner in a fingertip cross shape, and n sensing electrode fingers are provided between adjacent working electrode fingers, and the intervals between adjacent electrode fingers are equal, so as to form a fingertip cross sensor; n is equal to 3 or 5; and 3 or 5 sensing electrode fingers are provided between adjacent working electrode fingers.

2. A non-contact oil level measuring device for an aviation fuel tank according to claim 1, characterized in that: The sensing electrode finger and the working electrode finger have the same size, and the electrode finger has a length of L and a width of w ; The interval between adjacent electrode fingers is 2g.

3. A non-contact oil level measuring device for an aviation fuel tank according to claim 2, characterized in that: When L is much larger than w ,and w Under the condition that g is much greater than g, the capacitance between the working electrode (4) and the sensing electrode (3) is: ， Where: g is half of the interval between adjacent electrode fingers; ε r is the relative dielectric constant of the tank wall; ε0 is the dielectric constant of air; x is the liquid level height.

4. A non-contact oil level measuring device for an aviation fuel tank according to claim 2, characterized in that: The maximum electric field penetration depth of the fingertip cross sensor is: ， Where: g is half of the spacing between adjacent electrode fingers.

5. The non-contact oil level measuring device for an aviation fuel tank according to claim 1, characterized in that: The metal shielding layer (1) is a metal copper-clad layer, and the non-metallic PCB substrate layer (2) is provided with metal copper-clad layers on both sides respectively, forming a double-sided copper-clad PCB substrate; the metal copper-clad layer on the side of the double-sided copper-clad PCB substrate close to the oil tank is etched to form a sharp cross sensor.

6. The non-contact oil level measuring device for an aviation fuel tank according to claim 1, characterized in that: It also includes a shielded wire (5), and the working electrode (4) and the sensing electrode (3) are respectively connected to the host computer via the shielded wire (5).

7. A non-contact oil level measurement method for an aviation fuel tank, based on the non-contact oil level measurement device for an aviation fuel tank according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step S1: installing the oil level measuring device on the outer wall of the oil tank, connecting the working electrode (4) and the sensing electrode (3) to the external power source excitation and collection circuit respectively, and connecting the metal shielding layer (1) outside the non-metallic PCB substrate layer (2) to the working electrode (4); Step S2: generating an electric field in the fingertip crossing sensor by voltage excitation; Applying voltage excitation to the working electrode (4) and the sensing electrode (3) respectively, so that the working electrode (4) is connected to a high-potential AC excitation relative to the sensing electrode (3), and a fringe electric field is generated between the working electrode (4) and the sensing electrode (3); Step S3: The capacitance value C output by the oil level measuring device 1,n Calculate the liquid level.

Images