Low-temperature medium liquid level sensor

Abstract

The utility model discloses a low-temperature medium liquid level sensor, and belongs to the field of liquid level measurement. The low-temperature medium liquid level sensor comprises a measuring capacitor, a gas phase reference capacitor, a liquid phase reference capacitor, a substrate and a capacitance detection circuit, the gas-phase reference capacitor and the liquid-phase reference capacitor are respectively arranged at the upper end and the lower end of the back surface of the substrate; the measuring capacitor, the gas-phase reference capacitor and the liquid-phase reference capacitor all adopt interdigital capacitors and are all connected to the capacitance detection circuit; and the capacitance detection circuit receives real-time capacitance values of the measuring capacitor, the gas phase reference capacitor and the liquid phase reference capacitor, and calculates to obtain a liquid level value after real-time calibration. The gas-phase dielectric constant and the liquid-phase dielectric constant are measured synchronously, the measured liquid level is calibrated, and the measurement precision is improved; and an interdigital capacitor is adopted, so that the sensitivity of the liquid level sensor is improved.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of liquid level measurement, more particularly, relate to a kind of low temperature medium liquid level sensor. BACKGROUND

[0002] Low temperature propellant (such as liquid hydrogen, liquid oxygen, liquid nitrogen, liquid methane, etc.) used by spacecraft will be affected by its own physical properties (such as small density, low boiling point, easy vaporization) and adiabatic conditions and other factors during storage, transportation and use, and the storage tank will also be frequently pressurized, depressurized and other operations, which makes it very difficult to accurately understand the remaining amount of propellant in the storage tank in real time. Therefore, realizing high-precision liquid level measurement of low-temperature medium is the basic condition for controlling and protecting low-temperature propellant, and ensuring the safe flight and task execution of rocket spacecraft or hypersonic aircraft. Based on the advantages of simple structure, high measurement accuracy, fast dynamic response, stable and reliable performance, low cost, easy maintenance and suitable for liquid level measurement of various media of capacitive liquid level sensor, it is also the highest comprehensive index and the most mature measurement method, therefore, capacitive liquid level measurement method is the method commonly used in low-temperature propellant liquid level measurement system at home and abroad.

[0003] The structure of capacitive liquid level sensor mainly includes cylindrical coaxial type and coplanar type. The capacitive low-temperature liquid level sensor used in the field of aerospace usually adopts cylindrical coaxial structure, which mainly includes: inner tube and outer tube of metal material coaxially sleeved, the inner tube and the outer tube are used as two electrodes of the liquid level sensor, the inner and outer tubes are fixed coaxially by insulating pad, and the outer tube is opened or grooved to allow the low-temperature liquid to freely enter and exit. The liquid level sensor with the above cylindrical coaxial structure has the following disadvantages: (1) The sensitivity of common cylindrical coaxial structure to low-temperature liquid is less than 0.04 pF / mm. (2) Due to the influence of machining process precision, the coaxiality between the inner and outer tube capacitor plates will also cause errors in liquid level measurement results, affecting the further improvement of the linearity of the sensor. (3) The gas-liquid relative dielectric constant of low-temperature liquid is very small (liquid hydrogen: 0.23; liquid oxygen: 0.51; liquid nitrogen: 0.43; liquid methane: 0.7), the difference is generally less than 1, and it is easily affected by temperature and pressure and other environmental factors, which will cause "zero drift" and reduce the measurement accuracy during liquid level measurement. The Chinese invention patent with publication number CN110873597A discloses "fluid level sensor device with interdigital planar capacitor", which uses reference capacitor to provide estimation of dielectric constant of fluid in fluid chamber, ignores the change of gas phase dielectric constant, and uses formula to calculate the liquid level value after reference capacitor calibration. However, the gas phase and liquid phase of low-temperature medium are extremely susceptible to temperature and pressure changes, and there are impurity gases in the gas phase space of low-temperature propellant storage tank, therefore, we consider adding gas phase reference capacitor to provide estimation of dielectric constant of low-temperature medium gas phase on the basis of liquid phase reference capacitor.

[0004] In summary, the existing cylindrical coaxial structure for measuring the liquid level of low-temperature propellant has the problems of low sensitivity and low measurement accuracy due to its own structure, processing precision, environmental factors, etc. Content of the utility model

[0005] In view of the defects of the related art, the utility model aims at providing a low-temperature medium liquid level sensor, and aims at solving the problems of low sensitivity and low measurement accuracy of the existing low-temperature medium liquid level sensor.

[0006] To achieve the above-mentioned purpose, the utility model provides a low-temperature medium liquid level sensor, comprising: a measurement capacitor, a gas-phase reference capacitor, a liquid-phase reference capacitor, a substrate and a capacitor detection circuit.

[0007] The measurement capacitor is arranged on the front surface of the substrate, the gas-phase reference capacitor is arranged on the upper end of the back surface of the substrate, the liquid-phase reference capacitor is arranged on the lower end of the back surface of the substrate, the upper end of the gas-phase reference capacitor is aligned with the upper end of the measurement capacitor, and the lower end of the liquid-phase reference capacitor is aligned with the lower end of the measurement capacitor.

[0008] The measurement capacitor, the gas-phase reference capacitor and the liquid-phase reference capacitor all adopt interdigital capacitors and are all connected to the capacitor detection circuit.

[0009] The measurement capacitor is used for measuring the liquid level of the low-temperature medium in the storage tank where the low-temperature medium liquid level sensor is located.

[0010] The gas-phase reference capacitor is used for measuring the gas-phase dielectric constant of the low-temperature medium in the storage tank where the low-temperature medium liquid level sensor is located.

[0011] The liquid-phase reference capacitor is used for measuring the liquid-phase dielectric constant of the low-temperature medium in the storage tank where the low-temperature medium liquid level sensor is located.

[0012] The capacitor detection circuit is used for accepting the real-time capacitance values of the measurement capacitor, the gas-phase reference capacitor and the liquid-phase reference capacitor, and calculating the real-time calibrated liquid level value.

[0013] Optionally, the measurement capacitor is a horizontally crossed comb-shaped electrode or a vertically crossed comb-shaped electrode.

[0014] Optionally, the electrode width and the electrode spacing are equal, and the value range is between 0.05mm and 0.4mm; when the measurement capacitor is made of a PCB process, the electrode width and the electrode spacing are 0.1mm; when the measurement capacitor is made of an FPC process, the electrode width and the electrode spacing are 0.05mm.

[0015] Optionally, each interdigital capacitor comprises two comb electrodes, respectively an excitation electrode and a sensing electrode, the excitation electrode is connected to a positive voltage, and the sensing electrode is connected to a negative voltage or ground.

[0016] Optionally, an equal-potential shielded positive electrode is arranged outside the excitation electrode, and an equal-potential shielded negative electrode is arranged outside the sensing electrode; the shielded positive electrode and the shielded negative electrode surround the interdigital capacitor.

[0017] Optionally, a shielded electrode plane is arranged in the substrate, and the shielded electrode plane is located between the measurement capacitor and the gas-phase reference capacitor and the liquid-phase reference capacitor, and is used to shield the electric field interference between the two.

[0018] Optionally, when the measurement capacitor is manufactured by using a PCB process, the thickness of the substrate is greater than 0.2 mm; and when the measurement capacitor is manufactured by using an FPC process, the thickness of the substrate is greater than 0.1 mm.

[0019] Optionally, the capacitor detection circuit and the measurement capacitor are integrated on the same substrate.

[0020] Compared with the prior art, the above technical scheme conceived by the utility model can achieve the following beneficial effects:

[0021] 1. The low-temperature medium liquid level sensor provided by the utility model has the advantages that: by arranging the gas-phase reference capacitor and the liquid-phase reference capacitor, the gas-phase dielectric constant and the liquid-phase dielectric constant of the low-temperature medium are synchronously measured when the measurement capacitor measures the liquid level of the low-temperature medium, so that the measured liquid level is calibrated, and the measurement precision is improved; the measurement capacitor, the gas-phase reference capacitor and the liquid-phase reference capacitor all adopt interdigital capacitors, and have the characteristics of simple structure and strong adaptability, compared with the cylindrical coaxial capacitor liquid level sensor, the interdigital capacitors can directly contact the liquid, do not need to guide the liquid through the liquid hole, do not need to fix the inner and outer electrodes by using the electrode support frame, have a higher inherent frequency, have a shorter dynamic response time, and have the beneficial effects of improved sensitivity.

[0022] 2. The low-temperature medium liquid level sensor provided by the utility model has the advantages that: by adjusting the values of the electrode width and the electrode spacing, when the values of the electrode width and the electrode spacing are both 0.1 mm, the sensitivity of the comb electrode arranged in a horizontal cross mode can reach 0.37 pF / mm, and the sensitivity of the comb electrode arranged in a vertical cross mode can reach 0.26 pF / mm, and the sensitivity is improved by one order of magnitude compared with the cylindrical coaxial structure.

[0023] 3. The low-temperature medium liquid level sensor provided by the utility model has the advantages that: by using the PCB / FPC manufacturing process, the interdigital capacitor has higher repeatability and consistency, and the linearity of the interdigital capacitor in measuring the liquid level is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1It is a low temperature medium liquid level sensor schematic diagram provided by the utility model;

[0025] Figure 2 It is another low temperature medium liquid level sensor schematic diagram provided by the utility model;

[0026] Figure 3 It is a low temperature medium liquid level sensor side view provided by the utility model;

[0027] Figure 4 It is a finger capacitor geometric size schematic diagram provided by the utility model, wherein, (a) part corresponds to Figure 1 (b) part corresponds to Figure 2 ;

[0028] Table 1 is the sensitivity of the cylindrical coaxial liquid level sensor of common geometric size;

[0029] Figure 5 It is a schematic diagram of the sensitivity of the interdigital capacitor changing with electrode width and electrode spacing.

[0030] The reference signs in the above-mentioned drawings are as follows:

[0031] 1, measurement capacitance, 2, gas phase reference capacitance, 3, liquid phase reference capacitance, 4, substrate, 5, shielded positive electrode, 6, shielded negative electrode, 7, shielded electrode plane. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the utility model more clear and obvious, the utility model is further described in detail below in combination with the drawings and examples.It should be understood that the specific examples described herein are only used to explain the utility model, and are not used to limit the utility model.In addition, the technical features involved in each embodiment of the utility model described below can be combined with each other as long as they do not conflict with each other.

[0033] The content involved in the above-mentioned examples will be described below in combination with a preferred example.

[0034] The embodiment discloses a low temperature medium liquid level sensor, because the dielectric constant of gas phase and liquid phase in the storage tank is different, the capacitance value between the two comb electrodes is different, so that the measurement of low temperature medium liquid level is realized.

[0035] As Figures 1-3As shown, the liquid level sensor described in this embodiment includes a measuring capacitor 1, a gas phase reference capacitor 2, a liquid phase reference capacitor 3, a substrate 4, and a capacitance detection circuit (not shown). The measuring capacitor 1 is disposed on the front side of the substrate 4, the gas phase reference capacitor 2 is disposed on the upper part of the back side of the substrate 4, and the liquid phase reference capacitor 3 is disposed on the lower part of the back side of the substrate 4. The upper end of the gas phase reference capacitor 2 is aligned with the upper end of the measuring capacitor 1, and the lower end of the liquid phase reference capacitor 3 is aligned with the lower end of the measuring capacitor 1. The measuring capacitor 1, the gas phase reference capacitor 2, and the liquid phase reference capacitor 3 are all interdigitated capacitors and are all connected to the capacitance detection circuit. The measuring capacitor 1 is used to measure the liquid level of the cryogenic medium in the tank where the cryogenic medium level sensor is located. The gas phase reference capacitor 2 is used to measure the gas phase dielectric constant of the cryogenic medium in the tank where the cryogenic medium level sensor is located. The liquid phase reference capacitor 3 is used to measure the liquid phase dielectric constant of the cryogenic medium in the tank where the cryogenic medium level sensor is located. The capacitance detection circuit is used to receive the real-time capacitance values ​​of the measuring capacitor 1, the gas phase reference capacitor 2, and the liquid phase reference capacitor 3, and calculate the real-time calibrated liquid level value.

[0036] Among them, such as Figure 1 and Figure 2 As shown, the storage tank for the cryogenic medium is placed vertically. The cryogenic medium exists in both gaseous and liquid states within the tank. A gaseous reference capacitor 2 is positioned on the upper back of the substrate 4 to facilitate the measurement of the gaseous cryogenic medium, obtaining its gaseous dielectric constant. A liquid reference capacitor 3 is positioned on the lower back of the substrate 4 to facilitate the measurement of the liquid cryogenic medium, obtaining its liquid dielectric constant. The upper end of the gaseous reference capacitor 2 is aligned with the upper end of the measuring capacitor 1, ensuring that the gaseous dielectric constant sensed by the gaseous reference capacitor and the measuring capacitor are consistent, while also serving as a high liquid level warning. The lower end of the liquid reference capacitor 3 is aligned with the lower end of the measuring capacitor 1, ensuring that the liquideous dielectric constant sensed by the liquid reference capacitor and the measuring capacitor are consistent, while also serving as a low liquid level warning.

[0037] Calculating the liquid level value based on the measured capacitance value is well known in the art. In this embodiment, a gas phase reference capacitor 2 and a liquid phase reference capacitor 3 are added, and their measured capacitance values ​​are used to correct the capacitance value measured by the measuring capacitor 1. In this embodiment, the real-time calibrated liquid level value H is calculated based on the following equation:

[0038]

[0039] Where C is the real-time capacitance value of the measured capacitance, C G C is the capacitance value of the measuring capacitor in a gaseous cryogenic medium. RL C is the real-time capacitance value of the liquid phase reference capacitor. RGH is the real-time capacitance value of the gas-phase reference capacitor r H is the height of the gas-phase reference capacitor and the liquid-phase reference capacitor.

[0040] The main method to improve the sensitivity of the liquid level sensor with a cylindrical coaxial structure in the prior art is to reduce the gap between the inner and outer tube capacitor plates. According to the European standard EN10220, the geometric dimensions of the inner and outer tubes are selected among common geometric dimensions to measure liquid hydrogen, for example, as shown in Table 1, the sensitivity values are all less than 0.04 pF / mm. At the same time, the gap between the inner and outer tube capacitor plates of the narrow gap type is too small, which can cause capillary phenomenon and affect the free flow of the liquid, which will cause additional systematic errors in the measurement error. Therefore, the gap between the inner and outer tubes cannot be too small, and is generally 2-3 mm.

[0041] Table 1

[0042]

[0043] In the present embodiment, the measurement capacitor is a horizontally crossed comb-shaped electrode or a vertically crossed comb-shaped electrode.

[0044] In the example of Figure 4 , the measurement capacitor 1 is a horizontally crossed comb-shaped electrode or a vertically crossed comb-shaped electrode. Figure 4 In the example of (a), the horizontally crossed comb-shaped electrode has a total width L, an electrode width w, and an electrode gap g. Figure 4 In the example of (b), the vertically crossed comb-shaped electrode has a total width L, an electrode width w, and an electrode gap g. Figure 5 In the example of , the smaller the electrode width w and the electrode gap g, the greater the sensitivity. When the electrode width and the electrode gap are in the range of 0.05 mm-0.4 mm, the sensitivity of the horizontally crossed comb-shaped electrode and the vertically crossed comb-shaped electrode is greater than that of the cylindrical coaxial structure with common geometric dimensions.

[0045] The value range is between 0.05mm and 0.4mm. According to the accuracy requirement of the PCB / FPC manufacturing process, the PCB manufacturing process is used to manufacture the measurement capacitor, the electrode width and the electrode spacing are 0.1mm, the sensitivity of the horizontally-crossed comb-shaped electrode can reach 0.37pF / mm, the sensitivity of the vertically-crossed comb-shaped electrode can reach 0.26pF / mm, compared with the sensitivity of the cylindrical coaxial structure, the sensitivity is improved by one order of magnitude; the FPC manufacturing process is used to manufacture the measurement capacitor, the electrode width and the electrode spacing are 0.05mm, the sensitivity of the horizontally-crossed comb-shaped electrode can reach 1.16pF / mm, the sensitivity of the vertically-crossed comb-shaped electrode can reach 0.73pF / mm, compared with the sensitivity of the cylindrical coaxial structure, the sensitivity is improved by one order of magnitude; by using the PCB / FPC manufacturing process, the repeatability and consistency are high, and the linearity of the interdigital capacitor for measuring the liquid level is greatly improved.

[0046] Compared with the liquid level sensor of the cylindrical coaxial structure, the two kinds of comb-shaped electrodes greatly improve the sensitivity, and the gap between the comb-shaped electrodes is smaller, so that the measurement accuracy is also improved.

[0047] In the example, Figure 1 In the example, each interdigital capacitor includes two comb-shaped electrodes, which are an excitation electrode and a sensing electrode, the excitation electrode is connected to a positive voltage, and the sensing electrode is connected to a negative voltage or ground. The shielded positive electrode 5 is arranged outside the excitation electrode, and the shielded negative electrode 6 is arranged outside the sensing electrode; the shielded positive electrode and the shielded negative electrode surround the interdigital capacitor.

[0048] In the example, Figure 3 In the example, a shielded electrode plane 7 is arranged in the substrate, and the shielded electrode plane is located between the measurement capacitor 1 and the gas-phase reference capacitor 2 and the liquid-phase reference capacitor 3, and is used to shield the electric field interference between the two.

[0049] In a specific embodiment, the shielded electrode plane can not be arranged, but the thickness of the substrate needs to be greater than the sum of the electrode width w and the electrode spacing g, the PCB manufacturing process is used to manufacture the measurement capacitor, the thickness of the substrate is greater than 0.2mm, and the FPC manufacturing process is used to manufacture the measurement capacitor, the thickness of the substrate is greater than 0.1mm.

[0050] In a specific embodiment, the capacitor detection circuit and the measurement capacitor can be integrated on the same substrate.

[0051] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A cryogenic medium level sensor, characterized in that, include: Measurement of capacitance, gas phase reference capacitance, liquid phase reference capacitance, substrate and capacitance detection circuit; The measuring capacitor is disposed on the front side of the substrate, the gas phase reference capacitor is disposed on the upper side of the back side of the substrate, the liquid phase reference capacitor is disposed on the lower side of the back side of the substrate, the upper end of the gas phase reference capacitor is aligned with the upper end of the measuring capacitor, and the lower end of the liquid phase reference capacitor is aligned with the lower end of the measuring capacitor. The measuring capacitor, gas phase reference capacitor, and liquid phase reference capacitor are all interdigitated capacitors and are all connected to the capacitance detection circuit. The measuring capacitor is used to measure the level of the cryogenic medium in the storage tank where the cryogenic medium level sensor is located; The gas phase reference capacitor is used to measure the gas phase dielectric constant of the cryogenic medium in the storage tank where the cryogenic medium level sensor is located. The liquid phase reference capacitor is used to measure the liquid phase dielectric constant of the cryogenic medium in the storage tank where the cryogenic medium level sensor is located. The capacitance detection circuit is used to receive the real-time capacitance values ​​of the measuring capacitor, the gas phase reference capacitor, and the liquid phase reference capacitor, and to calculate the liquid level value after real-time calibration.

2. The cryogenic medium level sensor as described in claim 1, characterized in that, The measuring capacitance is a comb-shaped electrode arranged horizontally or vertically.

3. The cryogenic medium level sensor as described in claim 1, characterized in that, The electrode width and electrode spacing are equal, ranging from 0.05mm to 0.4mm; when the measuring capacitor is fabricated using PCB technology, the electrode width and electrode spacing are 0.1mm; when the measuring capacitor is fabricated using FPC technology, the electrode width and electrode spacing are 0.05mm.

4. The cryogenic medium level sensor as described in claim 1, characterized in that, Each interdigital capacitor includes two comb-shaped electrodes, namely the excitation electrode and the sensing electrode. The excitation electrode is connected to a positive voltage, and the sensing electrode is connected to a negative voltage or grounded.

5. The cryogenic medium level sensor as described in claim 4, characterized in that, An equipotential shielded positive electrode is disposed on the outside of the excitation electrode, and an equipotential shielded negative electrode is disposed on the outside of the induction electrode; the shielded positive electrode and the shielded negative electrode surround the interdigital capacitor.

6. The cryogenic medium level sensor as described in claim 5, characterized in that, A shielding electrode plane is provided in the substrate. The shielding electrode plane is located between the measuring capacitor and the gas phase reference capacitor and the liquid phase reference capacitor, and is used to shield the electric field interference between them.

7. The cryogenic medium level sensor as described in claim 5, characterized in that, When using PCB technology to fabricate the measuring capacitor, the substrate thickness should be greater than 0.2 mm; when using FPC technology to fabricate the measuring capacitor, the substrate thickness should be greater than 0.1 mm.

8. The cryogenic medium level sensor as described in claim 1, characterized in that, The capacitance detection circuit and the capacitance measurement circuit are integrated on the same substrate.

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