Method for calculating zero point and k coefficient of Coriolis mass flowmeter under low-temperature liquid nitrogen working condition

Abstract

The invention provides a method for calculating a zero point and a k coefficient of a Coriolis mass flowmeter under a low-temperature liquid nitrogen working condition, and relates to the field of Coriolis mass flowmeter calibration. According to the flow error calculation function, an objective function is determined, and the objective function is the minimum flow error; under the liquid nitrogen working condition, the flow measured by the Coriolis mass flow meter to be calibrated and the standard device at the multiple test flow points is obtained; solving the target function according to the flow measured by the Coriolis mass flowmeter to be calibrated and the standard at the plurality of test flow points to obtain a k coefficient of the Coriolis mass flowmeter to be calibrated and the flow when the time difference is 0; according to the k coefficient of the Coriolis mass flow meter to be calibrated and the flow when the time difference is 0, the time difference zero point of the Coriolis mass flow meter to be calibrated is obtained, and the method has the advantage that calibration of the Coriolis mass flow meter under the low-temperature liquid nitrogen working condition is achieved.

Description

Technical Field

[0001] The invention relates to the field of Coriolis mass flowmeter calibration, and in particular to a method for calculating a zero point and a k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen working conditions. Background Art

[0002] The Coriolis mass flow meter needs to be calibrated in different media and at different temperatures, mainly because the calibration parameters of the Coriolis mass flow meter will change in different media or at different temperatures. Water calibration is suitable for application scenarios that require measuring liquid mass flow, such as chemical, petroleum, pharmaceutical and other industries; gas calibration is suitable for application scenarios that require measuring gas mass flow, such as the measurement of gas media such as natural gas and air.

[0003] In the prior art, the corresponding medium and temperature are selected for calibration according to the application scenario of the Coriolis mass flowmeter. First, the Coriolis mass flowmeter is zeroed, and then the calibration calculation is performed at the maximum flow point. If a liquid nitrogen test is performed at minus 170 degrees, the liquid nitrogen stops flowing and easily turns into a gas. If the Coriolis mass flowmeter is zeroed at this time, a large error will occur at the zero point, so the time difference zero point cannot be obtained by the on-site zeroing method. Since manual zeroing is not possible, the k coefficient cannot be obtained by calculation.

[0004] Therefore, it is necessary to provide a method for calculating the zero point and k-factor of a Coriolis mass flowmeter under cryogenic liquid nitrogen conditions, so as to realize the calibration of the Coriolis mass flowmeter under cryogenic liquid nitrogen conditions. Summary of the invention

[0005] The present invention provides a method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen working conditions, comprising: establishing a flow error calculation function; determining an objective function according to the flow error calculation function, wherein the objective function is to minimize the flow error; under liquid nitrogen working conditions, obtaining the flow rates measured by a Coriolis mass flowmeter to be calibrated and a standard at multiple test flow points; solving the objective function according to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points to obtain the k-factor of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0; obtaining the time difference zero point of the Coriolis mass flowmeter to be calibrated according to the k-factor of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0.

[0006] Furthermore, the flow error calculation function is: Where ER is the flow error, Q Si is the flow rate measured by the standard instrument at the i-th test flow point, n is the total number of test flow points, k S is the k coefficient of the Coriolis mass flowmeter to be calibrated, Δti is the time difference value measured by the Coriolis mass flowmeter to be calibrated at the i-th flow test point, Δt0 is the time difference zero point of the Coriolis mass flowmeter to be calibrated, and ΔQ S0 It is the error of the flow measurement value of the standard instrument caused by the zero time difference.

[0007] Furthermore, the multiple test flow points include at least a maximum flow, a minimum flow, 25% of the maximum flow, 50% of the maximum flow, and 75% of the maximum flow.

[0008] Furthermore, determining the multiple test flow points includes: under liquid nitrogen conditions, obtaining test data of multiple sample Coriolis mass flow meters at multiple candidate flow points; determining multiple candidate flow point combinations based on the multiple candidate flow points; screening the multiple candidate flow point combinations based on the test data of multiple sample Coriolis mass flow meters at the multiple candidate flow points to determine the optimal candidate flow point combination; and determining the multiple test flow points based on the optimal candidate flow point combination.

[0009] Furthermore, the objective function is solved according to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points to obtain the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, including: setting the partial derivative of the flow error calculation function with respect to the k coefficient of the Coriolis mass flowmeter to be calibrated to 0 and the partial derivative of the flow error calculation function with respect to the time difference zero point of the Coriolis mass flowmeter to be calibrated to 0, and obtaining the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0. An intermediate calculation formula for flow rate; using variable substitution, according to the intermediate calculation formula for the k-factor of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, a target calculation formula for the k-factor of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained; according to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points and the target calculation formula for the k-factor of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, the k-factor of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained.

[0010] Furthermore, the intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is: Among them, Q S0 It is the flow rate of the Coriolis mass flowmeter to be calibrated when the time difference is 0.

[0011] Further, the variable substitution is used to obtain the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 according to the intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, including: Substituting the k coefficient of the Coriolis mass flowmeter to be calibrated and the intermediate calculation formula of the flow rate when the time difference is 0, the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained as follows: Among them, Q Ai is the flow value measured by the Coriolis mass flowmeter to be calibrated at the i-th flow test point, Q A0 k is the zero flow rate measured by the Coriolis mass flowmeter to be calibrated, A is the initial k-factor of the Coriolis mass flowmeter to be calibrated.

[0012] Furthermore, the time difference zero point of the Coriolis mass flowmeter to be calibrated is calculated according to the following formula:

[0013] Furthermore, the initial k coefficient of the Coriolis mass flowmeter to be calibrated is a random number within a preset value range.

[0014] Furthermore, the method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions also includes: obtaining test data of multiple sample Coriolis mass flowmeters at multiple test flow points under liquid nitrogen conditions; and determining the initial k-factor of the Coriolis mass flowmeter to be calibrated based on the test data of the multiple sample Coriolis mass flowmeters at multiple test flow points.

[0015] Compared with the prior art, the method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions provided by the present invention has at least the following beneficial effects:

[0016] 1. Under low-temperature liquid nitrogen conditions, due to the special physical properties of liquid nitrogen (such as extremely low temperature and easy change from liquid to gas), the traditional on-site zeroing method will produce large errors. The time difference zero point calculated by this method can more accurately determine the zero point of the flowmeter, thereby improving the accuracy of the measurement. The k coefficient is an important parameter of the flowmeter, which determines the measurement accuracy of the flowmeter. Under low-temperature liquid nitrogen conditions, by solving the objective function (i.e., the minimum flow error) to obtain the k coefficient, it can ensure that the measurement error of the flowmeter at different flow points is minimized, thereby improving the overall measurement accuracy. This method is not only applicable to liquid nitrogen, but can also be extended to the flow measurement of other cryogenic liquid media (such as liquefied natural gas, liquid oxygen, etc.). By adjusting the calibration parameters and calculation methods, accurate measurement of different media can be achieved.

[0017] 2. By obtaining test data at multiple candidate flow points, the diversity and comprehensiveness of the data can be ensured. This helps to more accurately reflect the performance of the flow meter at different flow rates, thereby improving the accuracy of the calibration. By screening multiple candidate flow point combinations and determining the optimal candidate flow point combination, it can be ensured that the flow point combination used for calibration can minimize errors. This helps to obtain more accurate zero points and k-factors, thereby improving measurement accuracy. By screening the optimal candidate flow point combination, the number of unnecessary tests can be reduced, thereby simplifying the calibration process. This helps save time and resources and improves calibration efficiency. The optimized test flow point combination ensures that sufficient information is obtained within a limited number of tests to accurately calculate the zero point and k-factor. This helps to shorten the calibration cycle and improve calibration efficiency.

[0018] 3. Under liquid nitrogen conditions, a wealth of data samples can be obtained by testing multiple sample Coriolis mass flowmeters at multiple candidate flow points. These data cover the working conditions of the flowmeter at different flow rates and temperatures, providing a solid data basis for determining the initial k-factor. Determining the initial k-factor based on the test data of multiple sample Coriolis mass flowmeters can comprehensively consider the impact of metering errors at different flow points and temperatures. Through data analysis and optimization algorithms, errors can be reduced and the accuracy of the initial k-factor can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] This specification will be further described in the form of exemplary embodiments, which will be described in detail by the accompanying drawings. These embodiments are not restrictive, and in these embodiments, the same number represents the same structure, wherein:

[0020] Figure 1 It is a flow chart of a method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen working conditions according to some embodiments of this specification;

[0021] Figure 2 is a schematic diagram of test results of an existing Coriolis mass flowmeter calibration method according to some embodiments of this specification;

[0022] Figure 3 It is a schematic diagram of the test results of the method for calculating the zero point and k-factor of the Coriolis mass flowmeter under low-temperature liquid nitrogen conditions shown in some embodiments of this specification. DETAILED DESCRIPTION

[0023] In order to more clearly illustrate the technical solutions of the embodiments of this specification, the following is a brief introduction to the drawings required for the description of the embodiments. Obviously, the drawings described below are only some examples or embodiments of this specification. For ordinary technicians in this field, this specification can also be applied to other similar scenarios based on these drawings without creative work. Unless it is obvious from the language environment or otherwise explained, the same reference numerals in the figures represent the same structure or operation.

[0024] Figure 1 is a flow chart of a method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to some embodiments of this specification, such as Figure 1 As shown, the method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions may include the following steps:

[0025] Step 110, establishing a flow error calculation function.

[0026] In some embodiments, the flow error calculation function may be:

[0027]

[0028] Wherein, R is a positive integer greater than 1.

[0029] Taking the following flow error calculation function as an example, the method of calculating the zero point and k-factor of the Coriolis mass flowmeter under low-temperature liquid nitrogen conditions is explained:

[0030]

[0031] Where ER is the flow error, Q Si is the flow rate measured by the standard instrument at the i-th test flow point, n is the total number of test flow points, k S is the k coefficient of the Coriolis mass flowmeter to be calibrated, Δt i is the time difference measured by the Coriolis mass flowmeter to be calibrated at the i-th flow test point, Δt0 is the time difference zero point of the Coriolis mass flowmeter to be calibrated, and ΔQ S0 It is the error of the flow measurement value of the standard instrument caused by the zero time difference.

[0032] Step 120, determining an objective function based on the flow error calculation function, wherein the objective function is to minimize the flow error.

[0033] Step 130, under liquid nitrogen conditions, obtain the flow rates measured by the Coriolis mass flowmeter and the standard instrument to be calibrated at multiple test flow points.

[0034] As an example only, the operating temperature range of the liquid nitrogen operating condition may be -196° C. to -209° C. The operating pressure range of the liquid nitrogen operating condition may be 0.3 MPa to 0.8 MPa.

[0035] In some embodiments, the plurality of test flow points include at least a maximum flow, a minimum flow, 25% of the maximum flow, 50% of the maximum flow, and 75% of the maximum flow.

[0036] In some embodiments, determining a plurality of test flow points includes:

[0037] Under liquid nitrogen conditions, obtain test data of multiple sample Coriolis mass flowmeters at multiple candidate flow points;

[0038] Determine a plurality of candidate flow point combinations according to the plurality of candidate flow points, wherein each candidate flow point combination may include at least three candidate flow points;

[0039] Screening multiple candidate flow point combinations based on test data of multiple sample Coriolis mass flowmeters at multiple candidate flow points to determine an optimal candidate flow point combination;

[0040] According to the optimal candidate flow point combination, multiple test flow points are determined.

[0041] Specifically, for each candidate flow point combination, the flow measured by the sample Coriolis mass flowmeter at each candidate flow point included in the candidate flow point combination is obtained, and the k coefficient and time difference zero point of the sample Coriolis mass flowmeter corresponding to the candidate flow point combination can be calculated according to steps 110-150.

[0042] For each sample Coriolis mass flowmeter, the k coefficient mean and the time difference zero point mean corresponding to the sample Coriolis mass flowmeter can be calculated according to the k coefficient and the time difference zero point corresponding to the candidate flow point combination of the sample Coriolis mass flowmeter.

[0043] For each candidate traffic point combination, the priority value of the candidate traffic point combination can be calculated according to the following formula:

[0044]

[0045] Among them, S j is the priority value of the jth candidate traffic point combination, a 11 and a 12 is the weight, a 11 and a 12 is greater than 0, and a 11 +a 12 =1, k S，m，j is the k coefficient of the mth sample Coriolis mass flowmeter corresponding to the jth candidate flow point combination, k S，m，j，averageis the mean value of the k coefficient of the mth sample Coriolis mass flowmeter corresponding to the jth candidate flow point combination, Δt 0，m，j is the time difference zero point of the mth sample Coriolis mass flowmeter corresponding to the jth candidate flow point combination, Δt 0，m，j，average is the zero-point mean of the time difference of the mth sample Coriolis mass flowmeter corresponding to the jth candidate flow point combination, M is the total number of sample Coriolis mass flowmeters, N j is the total number of candidate flow points included in the jth candidate flow point combination.

[0046] The candidate flow point combination with the largest priority value is taken as the optimal candidate flow point combination, and the candidate flow points included in the optimal candidate flow point combination are taken as test flow points.

[0047] Step 140, solving the objective function according to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points, to obtain the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0.

[0048] In some embodiments, step 140 includes:

[0049] Let the partial derivative of the flow error calculation function with respect to the k coefficient of the Coriolis mass flowmeter to be calibrated be 0 and the partial derivative of the flow error calculation function with respect to the time difference zero point of the Coriolis mass flowmeter to be calibrated be 0, and obtain the intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow when the time difference is 0, that is,

[0050]

[0051] By adopting variable substitution, according to the intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained;

[0052] According to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points and the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 are obtained.

[0053] In some embodiments, the k-factor of the Coriolis mass flowmeter to be calibrated and the intermediate calculation formula for the flow rate when the time difference is 0 are:

[0054]

[0055] Among them, Q S0 The flow rate of the Coriolis mass flowmeter to be calibrated when the time difference is 0.

[0056] In some embodiments, variable substitution is adopted to obtain a target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 according to an intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, including:

[0057] Will Substituting the k coefficient of the Coriolis mass flowmeter to be calibrated and the intermediate calculation formula of the flow rate when the time difference is 0, the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained as follows:

[0058]

[0059] Among them, Q Ai is the flow value measured by the Coriolis mass flowmeter to be calibrated at the i-th flow test point, Q A0 k is the zero flow rate measured by the Coriolis mass flowmeter to be calibrated, A is the initial k-factor of the Coriolis mass flowmeter to be calibrated.

[0060] In some embodiments, the coefficient of the Coriolis mass flowmeter to be calibrated is a random number within a preset value range. As an example only, the preset value range can be manually defined or obtained by fitting large data.

[0061] In some embodiments, the method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions also includes: obtaining test data of multiple sample Coriolis mass flowmeters at multiple test flow points under liquid nitrogen conditions; and determining the initial k-factor of the Coriolis mass flowmeter to be calibrated based on the test data of multiple sample Coriolis mass flowmeters at multiple test flow points.

[0062] Specifically, the initial k coefficient of the Coriolis mass flowmeter to be calibrated can be determined according to the following formula:

[0063] S11, randomly generating a test k coefficient from a preset value range;

[0064] S12, for each sample Coriolis mass flowmeter, calculate the k coefficient corresponding to the sample Coriolis mass flowmeter according to steps 110 to 150 and the current test k coefficient;

[0065] S13, for each sample Coriolis mass flowmeter, according to the k coefficient corresponding to the sample Coriolis mass flowmeter, obtain the theoretical flow rate at the test flow point and the actual measured flow rate of the standard instrument, and calculate the test difference;

[0066] S14, determining whether the test difference is less than the test difference threshold, if so, using the current test k-factor as the initial k-factor of the Coriolis mass flowmeter to be calibrated, if not, executing S14;

[0067] S15. Generate an optimized test k coefficient according to the test difference and the current test k coefficient, update the current test k coefficient to the optimized test k coefficient, and execute S12.

[0068] For example, the optimized test k coefficient may be calculated according to the test difference and the current test k coefficient using the k coefficient optimization function.

[0069] Step 150, obtaining the time difference zero point of the Coriolis mass flowmeter to be calibrated according to the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0.

[0070] In some embodiments, the time difference zero point of the Coriolis mass flowmeter to be calibrated is calculated according to the following formula:

[0071]

[0072] The following describes the beneficial effects of the method for calculating the zero point and k-factor of a Coriolis mass flowmeter under cryogenic liquid nitrogen conditions in combination with test data.

[0073] Figure 2 is a schematic diagram of test results of an existing Coriolis mass flowmeter calibration method according to some embodiments of this specification, Figure 3 Schematic diagram of test results of a method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to some embodiments of this specification, such as Figure 2 and Figure 3 As shown in the figure, under low-temperature liquid nitrogen working conditions, due to the special physical properties of liquid nitrogen (such as extremely low temperature and easy change from liquid to gas), the existing Coriolis mass flowmeter calibration method will produce large errors. The time difference zero point calculated by this method can more accurately determine the zero point of the flowmeter, thereby improving the accuracy of the measurement.

[0074] The time difference zero point and k factor calculated by the method of calculating the zero point and k factor of the Coriolis mass flowmeter under the above-mentioned low-temperature liquid nitrogen working condition can avoid the measurement error and quantization error introduced by Δt, and can also directly measure the zero point and k factor of the Coriolis mass flowmeter under any working condition without zeroing.

[0075] Finally, it should be understood that the embodiments described in this specification are only used to illustrate the principles of the embodiments of this specification. Other variations may also fall within the scope of this specification. Therefore, as an example and not a limitation, alternative configurations of the embodiments of this specification may be considered consistent with the teachings of this specification. Accordingly, the embodiments of this specification are not limited to the embodiments explicitly introduced and described in this specification.

Claims

1. A method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions, characterized in that: include: Establish flow error calculation function; Determine an objective function according to the flow error calculation function, wherein the objective function is to minimize the flow error; Under liquid nitrogen working conditions, obtain the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points; Solving the objective function according to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points to obtain the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0; The time difference zero point of the Coriolis mass flowmeter to be calibrated is obtained according to the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0.

2. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 1, characterized in that: The flow error calculation function is: Where ER is the flow error, Q Si is the flow rate measured by the standard instrument at the i-th test flow point, n is the total number of test flow points, k S is the k coefficient of the Coriolis mass flowmeter to be calibrated, Δt i is the time difference value measured by the Coriolis mass flowmeter to be calibrated at the i-th flow test point, Δt0 is the time difference zero point of the Coriolis mass flowmeter to be calibrated, and ΔQ S0 It is the error of the flow measurement value of the standard instrument caused by the zero time difference.

3. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 1 or 2, characterized in that: The multiple test flow points at least include a maximum flow, a minimum flow, 25% of the maximum flow, 50% of the maximum flow, and 75% of the maximum flow.

4. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 1 or 2, characterized in that: Determining the multiple test flow points includes: Under liquid nitrogen conditions, obtain test data of multiple sample Coriolis mass flowmeters at multiple candidate flow points; Determine a plurality of candidate flow point combinations according to the plurality of candidate flow point combinations; Screening the plurality of candidate flow point combinations according to test data of the plurality of sample Coriolis mass flowmeters at the plurality of candidate flow point combinations to determine the optimal candidate flow point combination; The multiple test flow points are determined according to the optimal candidate flow point combination.

5. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 2, characterized in that: The objective function is solved according to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points to obtain the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, including: Assuming the partial derivative of the flow error calculation function with respect to the k coefficient of the Coriolis mass flowmeter to be calibrated to be 0 and the partial derivative of the flow error calculation function with respect to the time difference zero point of the Coriolis mass flowmeter to be calibrated to be 0, an intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained; Using variable substitution, according to the intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, a target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained; According to the flow rates measured by the Coriolis mass flowmeter to be calibrated and the standard at multiple test flow points and the target calculation formula for the flow rate when the k coefficient of the Coriolis mass flowmeter to be calibrated and the time difference is 0, the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 are obtained.

6. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 5, characterized in that: The intermediate calculation formula for the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is: Among them, Q S0 It is the flow rate of the Coriolis mass flowmeter to be calibrated when the time difference is 0.

7. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 6, characterized in that: The variable substitution is adopted to obtain the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 according to the intermediate calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0, including: Will Substituting the k coefficient of the Coriolis mass flowmeter to be calibrated and the intermediate calculation formula of the flow rate when the time difference is 0, the target calculation formula of the k coefficient of the Coriolis mass flowmeter to be calibrated and the flow rate when the time difference is 0 is obtained as follows: Among them, Q Ai is the flow value measured by the Coriolis mass flowmeter to be calibrated at the i-th flow test point, Q A0 k is the zero flow rate measured by the Coriolis mass flowmeter to be calibrated, A is the initial k-factor of the Coriolis mass flowmeter to be calibrated.

8. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 7, characterized in that: The time difference zero point of the Coriolis mass flowmeter to be calibrated is calculated according to the following formula:

9. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 7, characterized in that: The initial k coefficient of the Coriolis mass flowmeter to be calibrated is a random number within a preset value range.

10. The method for calculating the zero point and k-factor of a Coriolis mass flowmeter under low-temperature liquid nitrogen conditions according to claim 7, characterized in that: Also includes: Under liquid nitrogen conditions, obtain test data of multiple sample Coriolis mass flowmeters at multiple test flow points; Based on the test data of the multiple sample Coriolis mass flowmeters at multiple test flow points, an initial k-factor of the Coriolis mass flowmeter to be calibrated is determined.

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