Online calibration system for low-temperature Coriolis mass flowmeter

Abstract

The invention discloses an online calibration system for a low-temperature Coriolis mass flowmeter, and relates to the technical field of flowmeter calibration. The method comprises the following steps: drawing a characteristic line in a constructed rectangular plane coordinate system, calculating a cold drop slope, a heat rise slope and a trend slope ratio, analyzing the trend slope ratio and a cold and hot trend line slope of a temperature performance value, constructing a data pair by using the trend slope ratio and the cold and hot trend line slope type, and matching a corresponding temperature correction coefficient through a database. Then the ratio of the temperature correction value to the temperature reference value and the ratio of the environment correction value to the environment reference value are calculated respectively, the sum of the temperature weight and the environment weight is combined to obtain a density adjustment index, a corresponding density adjustment coefficient is matched, and the measured density is corrected; the problems that in the prior art, the temperature data cannot be accurately evaluated, the density cannot be effectively corrected, and the trend change of the temperature is ignored when the temperature data is evaluated, so that the calibration accuracy cannot be guaranteed are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of flowmeter calibration, and particularly relates to an on-line calibration system for a cryogenic Coriolis mass flowmeter. Background Art

[0002] A Coriolis mass flowmeter is an instrument that uses the Coriolis force generated when a fluid flows through a vibrating tube, which is proportional to the mass flow rate, to measure the mass flow rate. In industries such as chemical engineering and energy, Coriolis mass flowmeters are commonly used for accurate measurement of the mass flow rate of fluids.

[0003] However, the existing on-line calibration systems for Coriolis mass flowmeters still have the following deficiencies in the actual application process: When facing cryogenic media, their density will change significantly due to temperature changes. When the temperature rises, the molecular thermal motion intensifies, the volume expands, and the density decreases; when the temperature drops, the volume shrinks and the density increases. However, the existing systems often cannot accurately evaluate the temperature data and effectively correct the density, and the trend change of temperature is ignored when evaluating the temperature data, resulting in the accuracy of calibration not being guaranteed; In addition, in a low-temperature environment, the surface of the vibrating tube is prone to frosting. The additional mass of the frost will change the vibration characteristics of the vibrating tube, causing the measured value of the flowmeter to deviate from the true flow rate. However, the existing systems lack effective monitoring of the frosting situation and targeted secondary correction measures, resulting in a decrease in measurement accuracy and being unable to meet the requirements of high-precision measurement of cryogenic fluid flow in industrial production.

[0004] Therefore, an on-line calibration system for a cryogenic Coriolis mass flowmeter is introduced. Summary of the Invention

[0005] In view of this, the present invention provides an on-line calibration system for a cryogenic Coriolis mass flowmeter to solve the problems raised in the above background art.

[0006] The object of the present invention can be achieved by the following technical solutions: An on-line calibration system for a cryogenic Coriolis mass flowmeter, comprising: A calibration setting module: preset r calibration points. After reaching each calibration point, record the temperature data of the cryogenic medium upstream and downstream of the vibrating tube and the ambient temperature of the outer wall of the vibrating tube within the set measurement window, and transmit them to the calibration calculation module; A calibration calculation module: receive the temperature data of the cryogenic medium upstream and downstream of the vibrating tube and the ambient temperature of the outer wall of the vibrating tube within the set measurement window, and conduct a comprehensive evaluation, and correct the density of the cryogenic medium based on the evaluation result; Calibration and optimization module: It monitors the vibration acceleration signal of the vibration tube in real time, converts it into displacement amplitude through integration, comprehensively analyzes the displacement amplitude to obtain a warning amplitude index. If the warning amplitude index within a certain sliding window is greater than the set threshold, it triggers a frosting warning and then executes corresponding steps to perform secondary correction on the density of the low-temperature medium.

[0007] In some embodiments, it receives the temperature data of the low-temperature medium upstream and downstream of the vibration tube within the set measurement window and conducts a comprehensive evaluation. Specifically: Extract the temperature data of the low-temperature medium upstream and downstream of the vibration tube within the set measurement window, calculate the mean value of the temperature data upstream and downstream at the same time point, and obtain the temperature performance value of the low-temperature medium at each time point within the set measurement window; For the temperature performance values at each time point, take the average value to obtain the comprehensive temperature value of the low-temperature medium within the set measurement window; multiply the analyzed temperature correction coefficient by the comprehensive temperature value to obtain the temperature correction value.

[0008] In some embodiments, the specific analysis process of the temperature correction coefficient is as follows: Input the temperature performance values at each time point into a pre-constructed rectangular coordinate system. The horizontal axis represents the set measurement window, and the vertical axis represents the temperature performance values at each time point; Plot the numerical points corresponding to the temperature performance values at each time point in the rectangular coordinate system, and connect adjacent numerical points to obtain a characteristic line; Calculate the slope of the characteristic line and the angle between the characteristic line and the horizontal line; when the angle between the characteristic line and the horizontal line is an acute angle, mark the slope of this characteristic line as the cold drop slope; when the angle between the characteristic line and the horizontal line is an obtuse angle, mark it as the heat rise slope; sum up the values of all cold drop slopes to obtain the total cold drop value and mark it as Z1, sum up the values of all heat rise slopes and take the absolute value to obtain the total heat rise value and mark it as Z2; Use the total cold drop value Z1 as the numerator and the total heat rise value as the denominator to calculate the ratio, and obtain the trend slope ratio Z3; Connect the numerical point with the earliest order and the numerical point with the latest order in the rectangular coordinate system to obtain a line segment and mark this line segment as the cold and heat trend line. Calculate the slope of the cold and heat trend line and the angle with the horizontal line. When the angle between the cold and heat trend line and the horizontal line is an acute angle, mark the slope of this previous line as the cold trend slope, and the value of the cold trend slope is represented by the symbol L1; when the angle between the cold and heat trend line and the horizontal line is an obtuse angle, mark the slope of this cold and heat trend line as the heat trend slope, and the absolute value of the heat trend slope is represented by the symbol L2; Identify the slope types of the cold and hot trend lines, which include cold trend slope and hot trend slope, and construct a data pair with the trend slope ratio Z3, expressed as (Z3, Le), where e is equal to 1 or 2; input the constructed data pair into a pre-constructed database for matching to obtain the temperature correction coefficient.

[0009] In some embodiments, the constructed data pair is input into a pre-constructed database for matching, specifically: Extracting reference data pairs corresponding to the data pairs from a pre-built database, each reference data pair including the slope type of the hot and cold trend lines and the data pair value range, and each reference data pair corresponding to a set of temperature correction coefficients; The slope type of the hot and cold trend lines of the constructed data pairs is matched with the slope type of each group of reference data pairs. After the match is successful, the data pair value ranges of the constructed data pairs and each group of reference data pairs are further matched, that is, the Z3 and Le of the constructed data pairs are matched with the Z3 value range and Le value range of the reference data pairs respectively. After the match is successful, the temperature correction coefficient is extracted.

[0010] In some embodiments, the density of the cryogenic medium is corrected based on the evaluation result, specifically:

[0011] The ambient temperature of the outer wall of the vibrating tube within the set measurement window is extracted, and the average value is calculated to obtain the ambient correction value; the temperature correction value is ratioed to the set temperature reference value, that is, the temperature correction value is used as the numerator and the temperature reference value is used as the denominator to obtain the temperature reference ratio; the ambient correction value is ratioed to the set ambient reference value, that is, the ambient correction value is used as the numerator and the ambient reference value is used as the denominator to obtain the ambient reference ratio; Multiply the temperature reference ratio and the environment reference ratio by the set temperature weight and environment weight respectively, and then sum them to obtain the density adjustment index; pre-construct the index value ranges of each group corresponding to the density adjustment index, and each index value range corresponds to a density adjustment coefficient; The obtained density adjustment index is matched with the value range of each group of indexes to determine the density adjustment coefficient, and the initial measured density value of the cryogenic medium is multiplied by the density adjustment coefficient to obtain the density of the cryogenic medium after correction.

[0012] In some embodiments, the comprehensive analysis of the displacement amplitude to obtain the warning amplitude index is specifically: The mean A and standard deviation B of the displacement amplitude data in the sliding window are calculated using formulas (1) and (2) respectively. The formulas are expressed as follows: ; where i represents the number of each time point, n is the total number of time points, represents the displacement amplitude at each time point; Using the mean value A as the denominator and the standard deviation B as the numerator, a ratio calculation is performed to obtain the warning amplitude index.

[0013] In some embodiments, after triggering the frosting warning, corresponding steps are executed to perform secondary correction on the density of the cryogenic medium. Specifically: S1: Obtain the thermal image of the vibrating tube at the current time point when the frosting warning is triggered, set a low-temperature threshold, and mark the area in the thermal image that is lower than the low-temperature threshold as the frosting area. S2: Identify the boundary of the frosting area, and obtain the area and location of the frosting area; if the number of frosting areas is one, execute step S3, and if the number of frosting areas is greater than one, execute step S4.

[0014] In some embodiments, when the number of frosting areas is one, step S3 is executed. The specific process of step S3 is as follows: S3: Calculate the average value of the temperatures of each temperature distribution point in the frosting area to obtain the frosting temperature value. Denote the area outside the frosting area in the thermal image as the normal area, and calculate the average value of the temperatures of each temperature distribution point in the normal area to obtain the normal temperature value; subtract the frosting temperature value from the normal temperature value to obtain the frosting temperature difference. Based on the frosting temperature difference and combined with the physical properties of the cryogenic medium, calculate the frosting thickness d. The formula is expressed as ; where is the heat flux, is the thermal conductivity of the frost layer, is the frosting temperature difference; According to the frosting area and thickness d, calculate the additional mass m of the frost. The formula is expressed as m = pe × S × d; where S represents the frosting area and pe is the density of the frost. Equivalent the additional mass m of the frost to the density increment of the cryogenic medium, and perform secondary correction on the mass flow rate measured by the Coriolis flowmeter. The result of the secondary correction is expressed as ; where represents the mass flow rate value directly measured by the Coriolis mass flowmeter, represents the mass flow rate measurement value after secondary correction; respectively represent the reference density of the cryogenic medium and the density increment of the cryogenic medium.

[0015] In some embodiments, when the number of frosting areas is greater than one, step S4 is executed. The specific process of step S4 is as follows: S4: Number each frosting area, denoted by k, k = 1, 2,..., f, where f is the total number of frosting areas; For each frosting area, obtain the centroid coordinates , similarly, in step S3, calculate the additional mass of frosting; divide the vibrating tube into each constituent region, map the centroid coordinates of each frosting region to the corresponding constituent region, and calculate the sum of the additional mass of frosting within each constituent region to obtain the regional mass sum; Mark the regional mass sum within each constituent region as Cg, where g is the number corresponding to each constituent region. Extract each group of experimental cases from the pre-constructed database. Each group of experimental cases includes the simulated frosting region, regional mass sum, and density increment of each constituent region; Screen out the experimental cases with the same current medium type from each group of experimental cases as the cases to be matched. Use the Euclidean distance formula to calculate the distance bt between the regional mass sum Cg within the current each constituent region and the regional mass sum of each group of cases to be matched; The formula is expressed as ; where N is the total number of constituent regions, and Sg represents the regional mass sum of each constituent region within the case to be matched; Compare the distance bt of each group of cases to be matched with the set distance reference value. Screen out the cases to be matched with a distance less than the distance reference value and extract the density increment. After averaging the extracted density increments of each group, use it as , and similarly in step S3, perform secondary correction on the mass flow rate measured by the Coriolis flowmeter.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The present invention draws characteristic lines in the constructed plane rectangular coordinate system, calculates the cold drop slope, heat rise slope, and trend slope ratio, analyzes the trend slope ratio of the temperature performance value and the slopes of the cold and heat trend lines, constructs data pairs with the trend slope ratio and the cold and heat trend line slope types, matches the corresponding temperature correction coefficient through the database, then calculates the ratios of the temperature correction value to the temperature reference value and the environmental correction value to the environmental reference value respectively, combines the temperature weight and the environmental weight to sum to obtain the density adjustment index, and then matches the corresponding density adjustment coefficient to correct the measured density, solving the problems in the prior art that it is impossible to accurately evaluate temperature data and effectively correct the density, and the trend change of temperature is ignored when evaluating temperature data, resulting in the lack of guarantee of the calibration accuracy; The present invention collects vibration signals through an acceleration sensor, calculates the warning amplitude index, triggers a frosting warning when the index exceeds the threshold, and marks the frosting region in combination with an infrared thermal image to realize real-time monitoring of frosting; For a single frosting region, the present invention calculates the frosting temperature difference, thickness, and additional mass, equivalent to the density increment, calculates the corrected flow rate through the formula, and eliminates the interference of the additional mass of frosting on the vibration characteristics; The present invention maps multi-frost regions to each component region according to centroid coordinates, calculates the regional mass sum, matches experimental cases of the same medium in the database through Euclidean distance, and extracts the average density increment for secondary correction to avoid errors caused by the same total mass but different distributions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In the following description of exemplary embodiments with reference to the drawings, more details, features, and advantages of the present application are disclosed. In the drawings: Figure 1 is a block diagram of the principle of the present invention; Figure 2 is a graph showing the change trend of the temperature performance value in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The following will describe several embodiments of the present application in more detail with reference to the drawings so that those skilled in the art can implement the present application. The present application can be embodied in many different forms and purposes and should not be limited to the embodiments described herein. These embodiments are provided to make the present application comprehensive and complete and to fully convey the scope of the present application to those skilled in the art. The embodiments do not limit the present application.

[0019] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present application belongs. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the relevant art and / or the context of the present specification, and will not be interpreted in an idealized or overly formal sense unless clearly defined herein.

[0020] Please refer to Figure 1 - Figure 2 as shown, a low-temperature Coriolis mass flowmeter on-line calibration system includes a calibration setting module, a calibration calculation module, and a calibration optimization module; The calibration setting module is used to preset r calibration points according to the actual working conditions. After reaching each calibration point, the temperature data of the low-temperature medium upstream and downstream of the vibrating tube and the ambient temperature of the outer wall of the vibrating tube within the set measurement window are recorded and transmitted to the calibration calculation module; Supplementary note, select at least 3 calibration points (such as 10%, 50%, 90% of the range) to cover the common flow range; the stable measurement time for a single calibration point is not less than 5 minutes to ensure the stability of the low-temperature medium state (temperature, pressure) and flow; The temperature is collected by high-precision platinum resistors arranged upstream and downstream of the vibrating tube; an infrared temperature sensor is arranged on the outer wall of the pipeline to collect the ambient temperature; The calibration calculation module is used to receive the temperature data of the cryogenic medium upstream and downstream of the vibrating tube within the set measurement window and the ambient temperature of the outer wall of the vibrating tube, and conduct a comprehensive evaluation. Based on the evaluation results, the density of the cryogenic medium is corrected; It should be noted that the density of the cryogenic medium is sensitive to temperature; When the temperature of the cryogenic medium rises, the molecular thermal motion intensifies, the volume expands, and the density decreases; when the temperature decreases, the volume shrinks and the density increases; Specifically: Extract the temperature data of the cryogenic medium upstream and downstream of the vibrating tube within the set measurement window, calculate the average value of the temperature data upstream and downstream at the same time point, and obtain the temperature performance value of the cryogenic medium at each time point within the set measurement window; For the temperature performance values at each time point, take the average value to obtain the comprehensive temperature value of the cryogenic medium within the set measurement window; input the temperature performance values at each time point into the pre-constructed rectangular coordinate system, where the horizontal axis represents the set measurement window and the vertical axis represents the temperature performance values at each time point; Plot the numerical points corresponding to the temperature performance values at each time point in the rectangular coordinate system, and connect the adjacent numerical points to obtain a characteristic line; Calculate the slope of the characteristic line and the angle between the characteristic line and the horizontal line; when the angle between the characteristic line and the horizontal line is an acute angle, mark the slope of the characteristic line as the cold drop slope; when the angle between the characteristic line and the horizontal line is an obtuse angle, mark it as the heat rise slope; sum up the values of all the cold drop slopes to obtain the total cold drop value and mark it as Z1, sum up the values of all the heat rise slopes and take the absolute value to obtain the total heat rise value and mark it as Z2; Use the total cold drop value Z1 as the numerator and the total heat rise value as the denominator for ratio calculation to obtain the trend slope ratio Z3; Connect the numerically first point and the numerically last point in the rectangular coordinate system to obtain a line segment and mark this line segment as the cold and heat trend line, calculate the slope of the cold and heat trend line and the angle with the horizontal line. When the angle between the cold and heat trend line and the horizontal line is an acute angle, mark the slope of this previous line as the cold trend slope, and the value of the cold trend slope is represented by the symbol L1; when the angle between the cold and heat trend line and the horizontal line is an obtuse angle, mark the slope of this cold and heat trend line as the heat trend slope, and the absolute value of the heat trend slope is represented by the symbol L2; Identify the slope types of the cold and heat trend lines, where the slope types include the cold trend slope and the heat trend slope, and construct a data pair with the trend slope ratio Z3, denoted as (Z3, Le), where e is equal to 1 or 2; Extracting reference data pairs corresponding to the data pairs from a pre-built database. Each reference data pair includes the slope type of the hot and cold trend lines and the data pair value range. Each reference data pair corresponds to a set of temperature correction coefficients. The temperature correction coefficient range is set to 0.895-1.136. Supplementary note: if the slope type of the hot and cold trend lines is a cold trend slope and the value of Z3 is large, the probability of matching 1.136 is higher. The specific setting is made by technicians based on experimental data; Match the slope type of the hot and cold trend lines of the constructed data pair with the slope type of each reference data pair. After the match is successful, further match the data pair value ranges of the constructed data pair with each reference data pair, that is, match the Z3 and Le of the constructed data pair with the Z3 value range and Le value range of the reference data pair respectively. After the match is successful, extract the temperature correction coefficient; multiply the temperature correction coefficient by the temperature comprehensive value to obtain the temperature correction value; In addition, when the temperature change trend is gradually decreasing, the temperature comprehensive value is further adjusted downward to make the correction value more in line with the actual temperature change. For example, if the temperature comprehensive value is -160℃ and the trend is continuously decreasing, it is adjusted to -162℃ to compensate in advance for the impact of subsequent temperature drop on density. If the temperature trend is gradually increasing, the opposite is true; Extract the ambient temperature of the outer wall of the vibration tube within the set measurement window, calculate the average value and obtain the environmental correction value; Calculate the ratio of the temperature correction value to the set temperature reference value, that is, the temperature correction value is used as the numerator and the temperature reference value is used as the denominator to obtain the temperature reference ratio; Calculate the ratio of the environmental correction value to the set environmental reference value, i.e., the environmental correction value is used as the numerator and the environmental reference value is used as the denominator, to obtain the environmental reference ratio; Multiply the temperature reference ratio and the environment reference ratio by the set temperature weight and environment weight respectively, and then sum them to obtain the density adjustment index; the sum of the temperature weight and the environment weight is one, and the temperature weight is greater than the environment weight; Supplementary note: the vibration tube is assumed to work in a low temperature environment; Pre-construct the index value ranges for each group of density adjustment indices, and each index value range corresponds to a density adjustment coefficient. The density adjustment coefficient range is set between 0.954 and 1.127. The larger the density adjustment index, the higher the probability of matching 1.127. The obtained density adjustment index is matched with the value range of each group of indexes to determine the density adjustment coefficient, and the initial measured density value of the cryogenic medium is multiplied by the density adjustment coefficient to obtain the density of the cryogenic medium after correction; The calibration and optimization module is used to utilize the deployed acceleration sensors to monitor the vibration acceleration signal of the vibration tube in real time, convert it into displacement amplitude through integration, comprehensively analyze the displacement amplitude to obtain the warning amplitude index. If the warning amplitude index within a certain sliding window is greater than the set threshold, a frosting warning is triggered and corresponding steps are executed to perform secondary correction on the density of the low-temperature medium; Supplementary note: Install acceleration sensors (sensitivity ≥ 100mV / g, frequency response 0.1~1000Hz) at both ends or in the middle of the vibration tube to collect the vibration acceleration signal of the vibration tube, and convert it into displacement amplitude (unit: μm) through integration; Continuously sample at a frequency above 100Hz to ensure capturing high-frequency vibration details; Use a sliding window (such as 500 data points, duration 5 seconds) to calculate the real-time amplitude; The specific process of calculating the warning amplitude index is as follows: Calculate the mean value A and standard deviation B of the displacement amplitude data within the sliding window respectively using formulas (1) and (2). The formulas are expressed as: ; where i represents the number of each time point, and n is the total number of time points, represents the displacement amplitude of each time point; Use the mean value A as the denominator and the standard deviation B as the numerator to perform ratio calculation to obtain the warning amplitude index; After triggering the frosting warning, execute the corresponding steps, specifically: S1: Use a low-temperature infrared thermal imager deployed around the flowmeter to cover the entire surface of the vibration tube, obtain the thermal image of the vibration tube at the current time point when the frosting warning is triggered, set the low-temperature threshold, and mark the area in the thermal image that is lower than the low-temperature threshold as the frosting area; S2: Identify the boundary of the frosting area, obtain the area and location of the frosting area; If the number of frosting areas is one, execute step S3, if the number of frosting areas is greater than one, execute step S4; S3: Calculate the average value of the temperatures of each temperature distribution point within the frosting area to obtain the frosting temperature value. Denote the area outside the frosting area in the thermal image as the normal area, and calculate the average value of the temperatures of each temperature distribution point within the normal area to obtain the normal temperature value; Subtract the frosting temperature value from the normal temperature value to obtain the frosting temperature difference; Based on the frosting temperature difference and combined with the physical properties of the low-temperature medium, calculate the frosting thickness d. The formula is expressed as ; where is the heat flux, is the thermal conductivity of the frost layer, is the frosting temperature difference; According to the frosting area and thickness d, calculate the additional mass m of frosting. The formula is expressed as m = pe × S × d; where S represents the frosting area, pe is the density of the frost, and take 500kg / m , , , , , , , , , 3 , , , , , ; The frosting additional mass m is equivalent to the density increment of the cryogenic medium, and the mass flow rate measured by the Coriolis flowmeter is corrected twice. The result of the second correction is expressed as ; where represents the mass flow rate value directly measured by the Coriolis mass flowmeter, represents the measured value of the mass flow rate after the second correction; respectively represent the reference density of the cryogenic medium and the density increment of the cryogenic medium; Supplement explanation, when the cryogenic medium pipeline is frosted, the additional mass of the frost will change the vibration characteristics of the vibrating tube, making the measured value of the flowmeter deviate from the true flow rate. By quantifying the equivalent density increment, the measurement result is corrected to improve the accuracy of flow measurement in the low-temperature environment; S4: Number each frosting area, denoted by k, k = 1, 2,..., f, where f is the total number of frosting areas; Obtain the centroid coordinates for each frosting area , and calculate the frosting additional mass in the same way as in step S3; Divide the vibrating tube into each constituent area; for example, the tube top, tube bottom, and tube middle; map the centroid coordinates of each frosting area to the corresponding constituent area, and calculate the sum of the frosting additional masses within each constituent area to obtain the area mass sum; Supplement explanation, if the frosting areas k = 1, 2 are located at the tube top and k = 3 is located at the tube bottom, then the area mass sum of the tube top area = m1 + m2, and the area mass sum of the tube bottom area = m3; Mark the area mass sum within each constituent area as Cg, where g is the number corresponding to each constituent area. Extract each group of experimental cases from the pre-constructed database. Each group of experimental cases includes the simulated frosting area, area mass sum, and density increment of each constituent area; Screen out the experimental cases with the same current medium type from each group of experimental cases as the cases to be matched. Use the Euclidean distance formula to calculate the distance bt between the area mass sum Cg within the current each constituent area and the area mass sum of each group of cases to be matched; The formula is expressed as ; where N is the total number of constituent areas, and Sg represents the area mass sum of each constituent area within the case to be matched; Compare the distance bt of each group of cases to be matched with the set distance reference value, screen out the cases to be matched with a distance less than the distance reference value and extract the density increment, and take the average value of the extracted density increments of each group as and perform a second correction on the mass flow rate measured by the Coriolis flowmeter in the same way as in step S3; Supplementary description: When there are multiple frosting regions, through numbering, centroid positioning, and region mapping, the additional mass of each region is incorporated into the sum calculation of the corresponding component regions. For example, the sum of the masses of multiple frosting regions at the top of the tube and the sum of the masses of a single region at the bottom of the tube are processed separately, avoiding the correction errors caused by "the same total mass but different distributions" in the case of multi-region frosting, and improving the adaptability of the system to complex frosting patterns; using the Euclidean distance to screen cases with the same current medium to ensure that the physical properties of the matching cases are consistent with the actual working conditions, reducing the correction deviation caused by medium differences; The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the present invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. An online calibration system for a low-temperature Coriolis mass flowmeter, characterized in that Including: Calibration setting module: Preset r calibration points. After reaching each calibration point, record the temperature data of the cryogenic medium upstream and downstream of the vibrating tube within the set measurement window and the ambient temperature of the outer wall of the vibrating tube, and transmit them to the calibration calculation module; Calibration calculation module: Receive the temperature data of the cryogenic medium upstream and downstream of the vibrating tube within the set measurement window and the ambient temperature of the outer wall of the vibrating tube, and conduct a comprehensive evaluation, and correct the density of the cryogenic medium based on the evaluation result; Calibration optimization module: Monitor the vibration acceleration signal of the vibrating tube in real time, convert it into displacement amplitude through integration, conduct a comprehensive analysis of the displacement amplitude to obtain a warning amplitude index. If the warning amplitude index within a certain sliding window is greater than the set threshold, trigger a frosting warning and then execute corresponding steps to perform a secondary correction on the density of the cryogenic medium.

2. The on-line calibration system of a low-temperature Coriolis mass flowmeter according to claim 1, characterized in that, The receiving of the temperature data of the cryogenic medium upstream and downstream of the vibrating tube within the set measurement window and the comprehensive evaluation are specifically as follows: Extract the temperature data of the cryogenic medium upstream and downstream of the vibrating tube within the set measurement window, calculate the mean value of the temperature data upstream and downstream at the same time point, and obtain the temperature performance value of the cryogenic medium at each time point within the set measurement window; For the temperature performance values at each time point, take the average value to obtain the comprehensive temperature value of the cryogenic medium within the set measurement window; Multiply the analyzed temperature correction coefficient by the comprehensive temperature value to obtain the temperature correction value.

3. The on-line calibration system of a low-temperature Coriolis mass flowmeter according to claim 2, characterized in that, The specific analysis process of the temperature correction coefficient is as follows: Input the temperature performance values at each time point into a pre-constructed rectangular coordinate system, where the horizontal axis represents the set measurement window and the vertical axis represents the temperature performance values at each time point; Plot the numerical points corresponding to the temperature performance values at each time point in the rectangular coordinate system, and connect adjacent numerical points to obtain a characteristic line; Calculate the slope of the characteristic line and the angle between the characteristic line and the horizontal line; When the angle between the characteristic line and the horizontal line is an acute angle, mark the slope of this characteristic line as the cold drop slope; When the angle between the characteristic line and the horizontal line is an obtuse angle, mark it as the heat rise slope; Sum up the values of all the cold drop slopes to obtain the total cold drop value and mark it as Z1, sum up the values of all the heat rise slopes and take the absolute value to obtain the total heat rise value and mark it as Z2; Use the total cold drop value Z1 as the numerator and the total heat rise value as the denominator for ratio calculation to obtain the trend slope ratio Z3; Connect the numerical point with the earliest order and the numerical point with the latest order in the rectangular coordinate system to obtain a line segment and mark this line segment as the cold and heat trend line, calculate the slope of the cold and heat trend line and the angle with the horizontal line. When the angle between the cold and heat trend line and the horizontal line is an acute angle, mark the slope of this previous line as the cold trend slope, and the value of the cold trend slope is represented by the symbol L1; When the angle between the cold and heat trend line and the horizontal line is an obtuse angle, mark the slope of this cold and heat trend line as the heat trend slope, and the absolute value of the heat trend slope is represented by the symbol L2; Identify the slope type of the cold and heat trend line. The slope type includes the cold trend slope and the heat trend slope, and construct a data pair with the trend slope ratio Z3, expressed as (Z3, Le), where e is equal to 1 or 2; Input the constructed data pair into a pre-constructed database for matching to obtain the temperature correction coefficient.

4. An on-line calibration system for a low-temperature Coriolis mass flowmeter according to claim 3, characterized in that, The matching of the constructed data pairs to the pre-constructed database is specifically as follows: Extract each group of reference data pairs corresponding to the data pairs from the pre-constructed database. Each group of reference data pairs includes the slope type of the cold and hot trend lines and the data pair value range, and each group of reference data pairs corresponds to a group of temperature correction coefficients respectively; Match the slope type of the cold and hot trend lines of the constructed data pairs with the slope types of each group of reference data pairs. After successful matching, further match the data pair value ranges of the constructed data pairs and each group of reference data pairs, that is, match Z3 and Le of the constructed data pairs with the Z3 value range and Le value range of the reference data pairs respectively. After successful matching, extract the temperature correction coefficients.

5. An on-line calibration system for a cryogenic Coriolis mass flowmeter according to claim 4, characterized in that, The correction of the density of the low-temperature medium based on the evaluation result is specifically as follows: Extract the ambient temperature on the outer wall of the vibrating tube within the set measurement window, and obtain the ambient correction value after averaging; perform a ratio calculation between the temperature correction value and the set temperature reference value, that is, use the temperature correction value as the numerator and the temperature reference value as the denominator to obtain the temperature reference ratio; perform a ratio calculation between the ambient correction value and the set ambient reference value, that is, use the ambient correction value as the numerator and the ambient reference value as the denominator to obtain the ambient reference ratio; Multiply the temperature reference ratio and the ambient reference ratio by the set temperature weight and ambient weight respectively, and then sum to obtain the density adjustment index; pre-construct each group of index value ranges corresponding to the density adjustment index, and each group of index value ranges corresponds to a density adjustment coefficient respectively; Match the obtained density adjustment index with each group of index value ranges to determine the density adjustment coefficient, and multiply the initial measured density value of the low-temperature medium by the density adjustment coefficient as the density of the corrected low-temperature medium.

6. The on-line calibration system for a cryogenic Coriolis mass flowmeter according to claim 5, characterized in that, The comprehensive analysis of the displacement amplitude to obtain the warning amplitude index is specifically as follows: Calculate the mean value A and the standard deviation B of the displacement amplitude data within the sliding window by using formulas (1) and (2) respectively. The formulas are expressed as follows: where i represents the number of each time point, n is the total number of time points, represents the displacement amplitude of each time point; Perform a ratio calculation with the mean value A as the denominator and the standard deviation B as the numerator to obtain the warning amplitude index.

7. An on-line calibration system for a low-temperature Coriolis mass flowmeter according to claim 6, characterized in that, After triggering the frost warning, execute the corresponding steps to perform secondary correction on the density of the low-temperature medium, specifically as follows: S1: Obtain the thermal image of the vibrating tube at the current time point when the frost warning is triggered, set a low temperature threshold, and mark the area in the thermal image that is lower than the low temperature threshold as the frost area; S2: Identify the boundary of the frost area, and obtain the area and location of the frost area; if the number of frost areas is one, execute step S3, if the number of frost areas is greater than one, execute step S4.

8. An on-line calibration system for a cryogenic Coriolis mass flowmeter according to claim 7, characterized in that, If the number of frost areas is one, execute step S3. The specific process of step S3 is as follows: S3: Calculate the average value of the temperatures of each temperature distribution point within the frost area to obtain the frost temperature value. Denote the area outside the frost area in the thermal image as the normal area, and calculate the average value of the temperatures of each temperature distribution point in the normal area to obtain the normal temperature value; Subtract the frost temperature value from the normal temperature value to obtain the frost temperature difference; Based on the frosting temperature difference and combined with the physical properties of the cryogenic medium, the frosting thickness d is calculated, and the formula is expressed as ; where is the heat flux,[[]] is the thermal conductivity of the frost layer,[[]] is the frosting temperature difference; According to the frost area area and thickness d, calculate the additional mass m of the frost, and the formula is expressed as m = pe × S × d; where S represents the frost area area, and pe is the density of the frost; The frosting additional mass m is equivalent to the density increment of the cryogenic medium, and the mass flow rate measured by the Coriolis flowmeter is corrected twice. The result of the second correction is expressed as ; where represents the mass flow rate value directly measured by the Coriolis mass flowmeter, represents the mass flow rate measurement value after the second correction; respectively represent the reference density of the cryogenic medium and the density increment of the cryogenic medium.

9. The on-line calibration system of a low-temperature Coriolis mass flowmeter according to claim 8, characterized in that, If the number of frost areas is greater than one, execute step S4. The specific process of step S4 is as follows: S4: Number each frosting area, denoted by k, where k = 1, 2,......, f, and f is the total number of frosting areas; Obtain the centroid coordinates for each frosting area , and similarly calculate the additional frosting mass in step S3; divide the vibrating tube into each constituent area, map the centroid coordinates of each frosting area to the corresponding constituent area, and calculate the sum of the additional frosting mass within each constituent area to obtain the regional mass sum; Mark the sum of the regional masses in each component area as Cg, where g is the number corresponding to each component area. Extract each group of experimental cases from the pre - constructed database. Each group of experimental cases includes the simulated frosting areas, the sum of the regional masses, and the density increment of each component area; Select the experimental cases with the same medium type as the current one from each group of experimental cases as the cases to be matched, and use the Euclidean distance formula to calculate the distance bt between the regional mass sum Cg in each current component region and the regional mass sum of each group of cases to be matched; the formula is expressed as ; where N is the total number of component regions, and Sg represents the regional mass sum of each component region within the case to be matched; Compare the distance bt of each group of cases to be matched with the set distance reference value, screen the cases to be matched with a distance less than the distance reference value and extract the density increment, and take the average value of the extracted density increments of each group as , and similarly to step S3, perform secondary correction on the mass flow rate measured by the Coriolis flowmeter.

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