A dynamic weighing compensation method for cryogenic fluids with self-calibration function

Abstract

The present invention discloses a low-temperature fluid dynamic weighing compensation method with a self-calibration function. A resistance strain gauge bridge is installed outside the measured pipeline of a low-temperature fluid flow standard device to measure the deformation of the measured pipeline during the calibration process. During the flow calibration process, the input rated voltage of the resistance strain gauge bridge is E i , by measuring the rated resistance of the two bridge arms of the resistance strain gauge bridge and the voltage between the resistance strain gauge E 0 , get the external force exerted by the tested pipeline on the tank direct connection pipeline in the vertical direction F y , the external force F y The invention adopts a force measurement self-calibration device to regularly calibrate the resistance strain gauge bridge; through the result of the resistance change difference of the resistance strain gauge of the Wheatstone bridge, the measurement of the measured pipeline deformation is optimized, and the external force measurement accuracy of the pipeline deformation is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of cryogenic fluid metering, and in particular relates to a cryogenic fluid dynamic weighing compensation method with a self-calibration function based on vacuum sleeve strain measurement, which is used to optimize the dynamic weighing accuracy of the cryogenic fluid. Background Art

[0002] Green energy such as hydrogen energy has become the main force of the energy technology revolution. Taking hydrogen energy as an example, the storage form of cryogenic liquid is much more energy dense than that of high-pressure gas, which is convenient for storage and transportation and has obvious advantages in large-scale industrial development. In the key links such as the preparation, storage, transportation, application and trade settlement of cryogenic fluids, the accuracy of flow measurement is crucial and directly related to the production safety, smooth operation and trade fairness of the entire industry chain.

[0003] The measurement of cryogenic fluid flow is inseparable from the measurement of mass. The weighing of cryogenic fluid is different from that of conventional fluids such as water and oil. Due to its low temperature characteristics, the system needs to be designed for thermal insulation. Taking the flow standard device as an example, the conventional water flow standard device adopts the static mass method. During flow measurement, the commutator is used to realize the flow of fluid into the weighing tank. The tank is not connected to the pipeline, and the liquid in the tank is exposed to the air. The measurement process of the cryogenic fluid flow standard device needs to ensure the insulation of the system, and all pipelines need to be wrapped with vacuum sleeves. When the cryogenic fluid flow standard device performs flow measurement, if the non-disconnected weighing of the pipeline and the tank can be selected, that is, the dynamic mass method, the efficiency of the entire test process will be greatly improved. However, during the dynamic mass method measurement process, the external force generated by the liquid flow in the pipeline on the tank will introduce additional uncertainty to the flow measurement. Therefore, there is an urgent need for a dynamic weighing compensation method for cryogenic fluids to meet the needs of value traceability and transmission of flow measurement of cryogenic fluids such as liquid hydrogen. Summary of the invention

[0004] In view of the above-mentioned shortcomings, the present invention proposes a low-temperature fluid dynamic weighing compensation method with a self-calibration function, which can optimize the measurement accuracy and reliability of the low-temperature fluid dynamic weighing.

[0005] In order to achieve the above object, the technical solution of the present invention is as follows:

[0006] A method for dynamic weighing compensation of cryogenic fluid with self-calibration function comprises the following steps:

[0007] Step 1: Install a resistance strain gauge bridge outside the measured pipeline of the low-temperature fluid flow standard device to measure the deformation of the measured pipeline during the calibration process;

[0008] Step 2: Before the test, the resistance strain gauge bridge is calibrated using the force measurement self-calibration device; the input rated voltage E of the resistance strain gauge bridge is i ;

[0009] Step 3: Start the power source, open the first commutator, close the second commutator, and after the cryogenic fluid is drawn out from the first storage tank, the system will self-circulate, pre-cool the system pipeline, and wait for the system flow to stabilize;

[0010] Step 4: Start the test. After the system self-circulation flow rate is stable, close the first commutator and open the second commutator. The cryogenic fluid is drawn from the first tank and flows into the second tank. After the flow rate is stable, record the starting time t1 and the initial mass m1 of the second tank at this time.

[0011] During the flow calibration process, the rated resistance of the two bridge arms of the resistance strain gauge bridge and the voltage E0 between the resistance strain gauge are measured;

[0012] Step 5: After the verification is completed, the first commutator is opened and the second commutator is closed. The system recirculates automatically and the cut-off time t2 and the final mass m2 of the second storage tank at this time are recorded;

[0013] According to the voltage E0, the external force F exerted by the measured pipeline on the direct-connected pipeline of the tank in the vertical direction is obtained. y , that is, the external force that needs to be compensated for dynamic weighing of the tank;

[0014] Step 6. Calculate the calibration flow Q as:

[0015]

[0016] Where g is the acceleration due to gravity.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. It can effectively improve the dynamic weighing measurement accuracy and meet the flow measurement needs of cryogenic fluids using the MT method;

[0019] 2. The correction results of dynamic weighing of cryogenic fluid flow standard device can be directly traced back to the mass unit, which has high feasibility and accuracy;

[0020] 3. The present invention adopts a force measurement self-calibration device, which can regularly calibrate the resistance strain gauge, greatly improving the system reliability;

[0021] 4. The scheme of the present invention is simple, low in cost and easy to promote;

[0022] 5. The present invention is applicable to dynamic weighing compensation of flow standard devices of various cryogenic fluids;

[0023] 6. The present invention eliminates the measurement error caused by temperature by arranging two resistance strain gauges on the same pipeline;

[0024] 7. The measurement of pipeline deformation is optimized by the differential result of the resistance change of the resistance strain gauge of the Wheatstone bridge, which further improves the accuracy of the external force measurement of pipeline deformation, that is, improves the accuracy of measuring the external force of the pipeline on the storage tank, and improves the measurement accuracy of the low-temperature fluid flow standard device based on the dynamic mass method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the detection section and axial filling tank of the cryogenic fluid flow standard device;

[0026] Figure 2 It is a schematic diagram of the detection section and radial filling tank of the cryogenic fluid flow standard device;

[0027] Figure 3 The schematic diagram of the pipeline under test is shown in Figure 1.

[0028] Figure 4 It is a schematic diagram of the cross section of the pipeline under test;

[0029] Figure 5 It is a schematic diagram of the Wheatstone bridge of the resistance strain gauge on the measured pipeline;

[0030] Figure 6 It is a schematic diagram of a force measurement self-calibration device;

[0031] Figure numerals: 1, first storage tank, 2, second storage tank, 3, cryogenic pump, 4, refrigerator, 5, flow meter to be tested, 6, first commutator, 7, second commutator, 8, measuring support seat, 9, pipeline to be tested, 10, pipeline directly connected to storage tank, 11, resistance strain gauge bridge, 12, force measurement self-calibration device, 901, cryogenic pipeline, 902, vacuum sleeve, 903, first calibration hook, 1101, first resistance strain gauge, 1102, second resistance strain gauge, 1103, first rated resistance, 1104, second rated resistance, 1201, standard weight, 1202, weight tray, 1203, weight drive assembly, 1204, frame, 1205, center hanger, 1206, moving beam, 1207, motor, 1208, second calibration hook. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0033] The present invention uses a high-precision resistance strain gauge to measure the strain of the vacuum sleeve of the measured pipeline, and compensates for the measurement error of the dynamic mass method of the low-temperature fluid flow standard device. A Wheatstone bridge consisting of two resistance strain gauges and two fixed value resistors is set on the measured pipeline, wherein the first resistance strain gauge measures the tensile deformation of the pipeline, and the second resistance strain gauge measures the compressive deformation of the pipeline. The result of the difference in the resistance change of the two resistance strain gauges is related to the voltage E0 between the rated resistance of the two bridge arms and the resistance strain gauge, and the external force on the measured pipeline is characterized thereby.

[0034] Example

[0035] Figure 1 and Figure 2 All of them are schematic diagrams of the detection section of the cryogenic fluid flow standard device. Figure 1 The middle axial filling of the second tank 2 and Figure 2 The second storage tank 2 is applicable to the mid-radial filling.

[0036] The cryogenic fluid flow standard device of the present invention comprises a first storage tank 1, a power source, a main pipeline, a measurement support seat 8, a measured pipeline 9, a storage tank direct-connected pipeline 10, a resistance strain gauge bridge 11, a second storage tank 2, a weighing unit and a force measurement self-calibration device 12.

[0037] The outlet of the first storage tank is connected to the power source; the downstream of the power source is connected to the system main line; the measuring support seat is located between the main line and the measured pipeline; the measured pipeline is connected to the direct-connected pipeline of the tank, and a force measurement self-calibration device and a resistance strain gauge bridge are arranged on the measured pipeline; the resistance strain gauge is arranged on the measured pipeline between the force measurement self-calibration device and the measuring support seat; the other end of the direct-connected pipeline of the tank is connected to the second storage tank, and the second storage tank is placed on the weighing unit.

[0038] The power source may be a high-pressure gas source, a cryogenic pump 3 , etc., but is not limited to these equipment.

[0039] The main pipeline, the tested pipeline and the tank direct-connected pipeline are all in direct contact with the cryogenic fluid, and are wrapped with a vacuum sleeve on the outside.

[0040] The measuring support seat is a fixed point of the pipeline, ensuring that the pipeline has no displacement at this point.

[0041] The force measurement self-calibration device uses a standard weight to provide a standard force to calibrate a resistance strain gauge, and a hook is used to connect the force measurement self-calibration device and the calibration measuring point.

[0042] The verification measuring point is located downstream of the resistance strain gauge bridge on the measured pipeline.

[0043] The resistance strain gauges are located at the top and bottom of the outer surface of the vacuum sleeve when viewed from the cross section of the measured pipeline.

[0044] A Wheatstone bridge is constructed by resistance strain gauges, and a number of resistance strain gauges are set on each bridge arm. The larger the number of resistance strain gauges, the higher the measurement sensitivity will be.

[0045] By measuring the strain of the vacuum sleeve of the measured pipeline, the external force on the pipeline is calculated according to the change in the resistance value of the resistance strain gauge, thereby equivalently measuring the vertical mass force exerted by the pipeline on the second storage tank. This mass force is eliminated from the measurement results of the weighing unit, optimizing the dynamic weighing measurement accuracy of the cryogenic fluid flow standard device.

[0046] The force measurement self-calibration device equipped in the system can calibrate the resistance strain gauge regularly, realize dynamic monitoring of the system's metrological characteristics, and improve the system's measurement accuracy.

[0047] Furthermore, when the system is self-calibrated, the force measurement self-calibration device works to calibrate the resistance strain gauge. According to the measured value of the resistance strain gauge and the actual weight mass, check whether the resistance strain gauge has caused the measurement accuracy to decrease due to factors such as creep and fatigue.

[0048] Specifically, Figure 1 As shown, when axial filling is adopted, the resistance strain gauge bridge 11 is calibrated by the force measurement self-calibration device 12 before the system is calibrated; the cryogenic fluid is stored in the first storage tank 1, and the cryogenic pump 3 provides power for the system to pump the cryogenic fluid into the test section. The refrigerator 4 further cools the cryogenic fluid to ensure that the cryogenic fluid in the system is in a full liquid state, and the full liquid cryogenic fluid flows through the detection pipeline to be tested by the flow meter 5. Before the start of the calibration, the first commutator 6 is opened, the second commutator 7 is closed, and the cryogenic fluid is drawn out from the first storage tank 1 and then recirculated in the system; after the start of the calibration, the first commutator 6 is closed, the second commutator 7 is opened, and the cryogenic fluid is drawn out from the first storage tank 1 and flows into the second storage tank 2. After the flow rate stabilizes, the starting time t1 and the initial mass m1 of the second storage tank are recorded. The upstream of the system tested pipeline 9 is fixed by the measuring support seat 8, and the downstream connected tank direct connection pipeline 10 is connected to the second storage tank 2. A resistance strain gauge bridge 11 is attached to the outside of the tested pipeline 9. During the detection phase, the low-temperature fluid flows through the tested pipeline 9, and the resistance strain gauge bridge 11 measures the deformation of the tested pipeline 9 during the detection process. During the flow calibration process, the low-temperature fluid flows through the tested pipeline 9. According to the rated resistance of the two bridge arms of the resistance strain gauge bridge 11 on the tested pipeline 9 and the voltage E0 between the resistance strain gauges, the external force applied by the tested pipeline on the direct-connected pipeline of the storage tank in the vertical direction is obtained, that is, the external force that needs to be compensated for the dynamic weighing of the storage tank. At the end of the calibration, the first commutator 6 is opened, the second commutator 7 is closed, and the system re-circulates, recording the cutoff time t2 and the end mass m2 of the second storage tank.

[0049] like Figure 3 and Figure 4As shown, the upstream of the measured pipeline 9 is fixed by the measuring support seat 8, and the resistance strain gauge bridge 11 is arranged between the force point of the force measurement self-calibration device 12 and the measuring support seat 8 of the measured pipeline. The measured pipeline 9 can be regarded as a cantilever beam structure, and the deformation of the pipeline is measured by the resistance strain gauge bridge 11. Since the end of the measured pipeline 9 is the point with the maximum deflection, the equivalent pressure in the vertical direction can be deduced from the maximum deflection, that is, the force that needs to be compensated for the dynamic weighing of the storage tank.

[0050] The interior of the tested pipeline 9 is a cryogenic pipeline 901, and its periphery is wrapped by a vacuum sleeve 902. From the cross section of the tested pipeline, the first resistance strain gauge 1101 is pasted on the top of the outer side of the cross section of the vacuum sleeve 902, and the second resistance strain gauge 1102 is pasted on the bottom of the vacuum sleeve 902. A first calibration hook 903 is set at the calibration measuring point of the tested pipeline 9.

[0051] like Figure 5 As shown, a Wheatstone bridge is constructed by forming a Wheatstone bridge through two high-precision resistance strain gauges, a first resistance strain gauge 1101 and a second resistance strain gauge 1102 and two rated resistors, a first rated resistor 1103 and a second rated resistor 1104.

[0052] The first resistance strain gauge 1101 is pasted just above the measured pipeline 9 to measure the tensile strain of the pipeline, and the second resistance strain gauge 1102 is pasted just below the measured pipeline 9 to measure the compressive strain of the pipeline. The first resistance strain gauge 1101 and the second rated resistor 1104 are in the same branch, and the second resistance strain gauge 1102 and the first rated resistor 1103 are in the same branch. Since the resistance strain gauges work in the same environment, the stress changes caused by temperature can be offset. The rated voltage E is given at the end of the bridge. i , measure the voltage E0 between the rated resistance of the two bridge arms and the resistance strain gauge, and obtain the differential value of the resistance change of the two resistance strain gauges.

[0053] The first resistance strain gauge generates tensile strain, and the second resistance strain gauge generates compressive strain, and the absolute values ​​of their strains are the same. Therefore, the resistance value of the resistance strain gauge changes, where:

[0054] ΔR1=SR(ε+ε T ),ΔR2=SR(-ε+ε T )

[0055] Where: R1 is the nominal value of the first resistance strain gauge; R2 is the nominal value of the second resistance strain gauge; S is the sensitivity of the resistance strain gauge; ε and ε T are the stresses caused by deformation and temperature, respectively.

[0056] The resistance strain gauge and the rated resistance have the same initial resistance, that is, R1=R2=R3=R4=R.

[0057] The voltage E0 between the rated resistance of the two bridge arms and the resistance strain gauge is given by the rated voltage E at the bridge end point. i The force on the pipeline deformation can be differentially corrected based on the resistance strain gauge bridge:

[0058]

[0059] Where ΔR is the difference between the resistance values ​​of the two strain gauges.

[0060] The measured pipeline is similar to a cantilever beam structure. For the cantilever beam structure, the strain ε is proportional to the external moment M, that is:

[0061]

[0062] Where: E is the elastic modulus of the vacuum jacket of the measured pipeline; I is the moment of inertia of the cross-sectional area of ​​the vacuum jacket of the measured pipeline about the neutral axis.

[0063] The maximum deflection is where the tested pipeline is directly connected to the tank:

[0064]

[0065] Where M y is the moment at the maximum deflection; L is the maximum length of the cantilever beam, that is, the distance from the measuring support to the end of the measured pipeline.

[0066] The above formula can be used to obtain the equivalent vertical force at the maximum deflection, that is, the external force F applied by the measured pipeline to the second tank during dynamic weighing. y :

[0067]

[0068] The force measurement self-calibration device 12 included in the present invention can be used to calibrate the resistance strain gauge. The resistance strain gauge needs to be calibrated before the system is verified. According to the measured value of the resistance strain gauge and the actual weight mass, check whether the resistance strain gauge has creep or fatigue. If the sensitivity S of the resistance strain gauge is not within a reasonable range, it needs to be replaced and recalibrated with a new resistance strain gauge.

[0069] like Figure 6As shown, before the force measurement self-calibration device 12 works, the standard weight 1201 is lifted by the weight driving assembly 1203, and the force measurement self-calibration device does not generate external force on the measuring pipeline; when working, the motor 1207 drives the moving beam 1206 to move upward, and the central suspension rod 1205 is completely lifted. According to the strain calibration under different standard loading forces, the weight driving assembly 1203 transmits the required standard weight 1201 downward until the standard weight 1201 is completely placed on the weight tray 1202. A second calibration hook 1208 is provided at the upper end of the central suspension rod 1205, which is connected to the first calibration hook 903 of the measured pipeline 9. The force measurement self-calibration device applies a constant force to calibrate the measurement result of the resistance strain gauge.

[0070] The vertical external force applied by the measuring pipeline to the direct-connected pipeline of the tank, that is, the external force F that needs to be compensated for the dynamic weighing of the tank y With rated voltage E i The numerical relationship between the voltage E0 and the dynamic mass M of the cryogenic fluid flow standard device after dynamic weighing compensation is obtained. d And the calibration flow Q:

[0071] M d =m2-m1-F y / g

[0072]

[0073] The present invention is not limited to the above-mentioned implementation method. All equivalent changes and modifications made within the scope of the present invention should fall within the scope of the present invention.

Claims

1. A method for dynamic weighing compensation of cryogenic fluid with self-calibration function, characterized in that The following steps are involved: Step 1: Install a resistance strain gauge bridge outside the measured pipeline of the low-temperature fluid flow standard device to measure the deformation of the measured pipeline during the calibration process; Step 2: Before the test, the resistance strain gauge bridge is calibrated using the force measurement self-calibration device; the input rated voltage of the resistance strain gauge bridge is E i ; Step 3: Start the power source, open the first commutator, close the second commutator, and the system will self-circulate after the cryogenic fluid is extracted from the first storage tank, pre-cool the system pipeline, and wait for the system flow to stabilize; Step 4: Start the test. After the system self-circulation flow is stable, close the first commutator and open the second commutator. The low-temperature fluid flows into the second storage tank. After the flow is stable, record the starting time. t 1. Record the initial mass of the second tank at this time m 1; The rated resistance of the two bridge arms of the resistance strain gauge bridge and the voltage between the resistance strain gauge are measured. E 0; Step 5: After the test, open the first commutator and close the second commutator. The system will re-circulate and record the end time. t 2 and the final mass of the second tank at this time m 2; According to voltage E 0, get the external force exerted by the tested pipeline on the tank direct connection pipeline in the vertical direction F y ; Step 6: Calculate the calibration flow rate Q for: ； Where g is the acceleration due to gravity; In the step 1, the upstream of the measured pipeline is fixed by a measuring support seat, and a calibration point is provided downstream, and the resistance strain gauge bridge is arranged between the calibration point and the measuring support seat; In step 5, the external force F y for: ； in, L is the maximum length of the cantilever beam, that is, the distance from the measuring support to the end of the measured pipeline; S is the sensitivity of the resistance strain gauge; E is the elastic modulus of the vacuum jacket of the pipeline being tested.

2. A method for dynamic weighing compensation of cryogenic fluid with self-calibration function according to claim 1, characterized in that: The resistance strain gauge bridge comprises a plurality of resistance strain gauges and a rated resistor, and the initial resistance values ​​are set to be the same.

3. A method for dynamic weighing compensation of cryogenic fluid with self-calibration function according to claim 2, characterized in that: The resistance strain gauges are installed on the top and bottom of the outer surface of the vacuum sleeve of the measured pipeline as viewed from the cross section of the measured pipeline.

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