A method and system for detecting the level of liquid nitrogen

Abstract

The application provides a kind of detection method and system for liquid nitrogen liquid level, it is related to liquid level measurement technical field, including with the first data information of liquid nitrogen environment that is obtained by real-time acquisition using pre-set target sensor;Based on the first data information and the evaporation characteristics of liquid nitrogen in the present environment, after obtaining the empirical equation corresponding to the relationship between liquid nitrogen level and time, temperature, the target state equation and observation equation are constructed;Introduce Kalman filtering algorithm, and combine the target state equation and observation equation to estimate the real-time liquid level state of liquid nitrogen.Combined with Kalman filtering algorithm, the corresponding evaporation characteristics of the environment based on the storage of liquid nitrogen is used to obtain the empirical equation corresponding to the relationship between liquid nitrogen level and time, temperature, and then the sensor liquid level meter is used to realize the accurate estimation of the continuous real-time liquid level state of liquid nitrogen.

Description

Technical Field

[0001] This invention relates to the field of liquid level measurement technology, and in particular to a method and system for detecting liquid nitrogen level. Background Technology

[0002] Liquid nitrogen is the liquid form of nitrogen gas at low temperatures. It can generate relatively low temperatures and is non-toxic, colorless, odorless, non-flammable, non-explosive, and chemically stable. In recent years, it has been widely used in scientific research, medicine, food, industrial production, and aerospace, among other fields. However, due to the special nature of the containers used to store liquid nitrogen, the remaining liquid nitrogen level cannot be visually observed, which means that liquid nitrogen cannot be replenished in a timely manner during use.

[0003] Therefore, the present invention provides a method and system for detecting liquid nitrogen level. Summary of the Invention

[0004] This invention provides a method and system for detecting liquid nitrogen level. It obtains an empirical equation relating liquid nitrogen level to time and temperature based on the evaporation characteristics of the environment in which liquid nitrogen is stored, and then combines it with a Kalman filtering algorithm to achieve accurate estimation of the continuous real-time liquid nitrogen level using a sensor level gauge.

[0005] This invention provides a method for detecting liquid nitrogen level, comprising:

[0006] Step 1: Use a pre-set target sensor to collect the first data information of the environment in which the liquid nitrogen is located in real time;

[0007] Step 2: Based on the first data information and the evaporation characteristics of liquid nitrogen under the current environment, obtain the empirical equations relating liquid nitrogen level to time and temperature, and then construct the target state equation and the observation equation.

[0008] Step 3: Introduce the Kalman filtering algorithm and combine it with the target state equation and the observation equation to estimate the liquid nitrogen level in real time.

[0009] Preferably, the target sensor refers to a temperature sensor and a pressure sensor; the first data information collected in real time includes the temperature and pressure inside the set container storing liquid nitrogen, as well as the first pressure and first temperature of the environment in which the set container storing liquid nitrogen is located.

[0010] Preferably, based on the first environmental data and the evaporation characteristics of liquid nitrogen under the current environment, after obtaining the empirical equation relating liquid nitrogen level to time and temperature, the target state equation and observation equation are constructed, including:

[0011] By combining the static evaporation formula with the Clapeyron equation and then using the relationship curves between different gas pressures and temperatures, the formula for the relationship between liquid nitrogen evaporation rate and pressure can be obtained.

[0012] Based on the first data information, the real-time evaporation rate of liquid nitrogen is obtained using the liquid nitrogen evaporation rate-pressure relationship formula;

[0013] Install a preset temperature sensing element on an arbitrarily selected container for storing liquid nitrogen, conduct a liquid nitrogen evaporation experiment, and obtain empirical equations for the relationship between liquid nitrogen level and time and the relationship between liquid nitrogen level and temperature;

[0014] Based on the empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship, the target state equation and the observation equation are constructed.

[0015] Preferably, a preset temperature sensing element is installed on an arbitrarily selected container for storing liquid nitrogen, and a liquid nitrogen evaporation experiment is conducted to obtain empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship, including:

[0016] Step 11: Fix the pre-set temperature measuring element for the set container at a preset distance from the opening of the set container;

[0017] Step 12: Select any container as the experimental container and start filling it with liquid nitrogen. Use the set measuring instrument to synchronously collect the experimental temperature and weight data inside the experimental container until the liquid nitrogen has evaporated completely.

[0018] Step 13: Based on the obtained experimental temperature and weight data, establish the temperature curve of the test point changing with time, and the weight curve of the liquid nitrogen in the container changing with time.

[0019] Step 14: After smoothing and filtering the weight curve, the first weight curve is obtained. Then, through linear fitting and corresponding percentage, the empirical equation of liquid nitrogen level-time relationship is obtained.

[0020] Step 15: Based on the obtained experimental temperature and weight data, construct a temperature-weight curve with weight as the X-axis and temperature as the Y-axis.

[0021] After converting the weight change into a percentage of liquid level, the temperature-liquid level curve is obtained.

[0022] Step 16: Select the target curve segment of stable evaporation from the temperature-level curve and analyze its variation law. Then, obtain the empirical equation of liquid nitrogen level-temperature relationship through linear fitting.

[0023] Preferably, the target curve segment of stable evaporation is selected from the temperature-liquid level curve for variation analysis, including:

[0024] The temperature-level curves are divided according to the same temperature to obtain a set of liquid levels based on the same temperature. ,in, This represents the i1th liquid level segment at the same temperature T; n1 represents the total number of liquid level segments at the same temperature T.

[0025] Simultaneously, based on the time sequence, the set of liquid levels at the same temperature is obtained. Temperature transition sets with temporal adjacency ,in, This represents a temperature array that is temporally adjacent to the i1th liquid level segment at the same temperature T. ,in, This represents the temperature of the left adjacent segment corresponding to the i1th liquid level segment; This represents the temperature of the right adjacent segment corresponding to the i1th liquid level segment;

[0026] Based on the set of liquid levels at the same temperature, determine the evaporation rate of the corresponding liquid level segment at the same temperature. ;

[0027] ;

[0028] in, This represents the last liquid level value on the i1th liquid level segment at the same temperature T. This represents the initial liquid level value on the i1th liquid level segment at the same temperature T; This represents the time length of the i1th liquid level segment at the same temperature T. This represents the correction value for the evaporation rate of the i1th liquid level segment at the same temperature T; Indicates based on the left adjacent temperature With the temperature of the corresponding i1th liquid level segment Standard liquid nitrogen evaporation rate during the conversion process; express arrive Temperature transition time; express arrive Temperature transition time; Indicates based on the left adjacent temperature With the temperature of the corresponding i1th liquid level segment The actual amount of volatiles during the conversion process; This represents the temperature based on the corresponding i1th liquid level segment. adjacent temperature to the right Standard liquid nitrogen evaporation rate during the conversion process; This represents the temperature based on the corresponding i1th liquid level segment. adjacent temperature to the right The actual amount of volatiles during the conversion process;

[0029] Based on the liquid level evaporation rate at different temperatures, a evaporation rate sequence was constructed in order of temperature magnitude;

[0030] according to Calculate the conventional evaporation rate of the i1th liquid level segment at the same temperature. and with The comparison will consider the liquid level sub-segment within the comparison range as the target curve segment for stable evaporation;

[0031] Based on the target curve segment, from all We extract consistent values ​​and construct first sequences at different temperatures, and then analyze the variation patterns based on all first sequences.

[0032] Preferably, the construction of the target state equation and the observation equation includes:

[0033] After obtaining the target state equation by analyzing the empirical equations of liquid nitrogen level-time relationship and liquid nitrogen level-temperature relationship, the observation equation is determined based on the relationship between the state variables and the observed quantities.

[0034] The formulas for the target state equation and the observation equation are shown below:

[0035] ;

[0036] In the formula, This is expressed as the estimated liquid level at time k; Let A represent the control quantity for estimating the liquid level at time k; A and B represent the estimation parameters of the liquid level state quantity. The noise at time k is represented as Gaussian white noise; Let be the liquid nitrogen level value measured by the target level gauge at time k; P represents the measurement parameter. It is represented as measurement noise, and is Gaussian white noise.

[0037] Preferably, a Kalman filtering algorithm is introduced, and the target state equation and the observation equation are combined to perform real-time liquid nitrogen level state estimation, including:

[0038] Step 21: Based on the target state equation, use the optimal estimate of k-1 to predict the state variables at time k, and use it as the first predicted value. Then calculate the covariance of the first predicted value.

[0039] Step 22: Determine the Kalman gain at time k using the covariance of the first predicted value;

[0040] Step 23: Combine the first predicted value and the measured value at time k to obtain the optimal estimate at time k;

[0041] The formula is as follows:

[0042] ;

[0043] In the formula, This is expressed as the optimal estimate at time k; This is represented as the first predicted value; This is expressed as the Kalman gain at time k; Let represent the liquid level measurement value at time k; P represents the measurement parameter.

[0044] Step 24: Update the state variables at time K. The covariance is calculated, and steps 22-23 are repeated to achieve the optimal estimate of the liquid level at time k+1, so as to form an iteration to achieve real-time estimation of the liquid level state.

[0045] This invention provides a liquid nitrogen level detection system, comprising:

[0046] Data acquisition module: Uses pre-set target sensors to acquire first data information about the environment in which liquid nitrogen is located in real time;

[0047] Equation construction module: Based on the first data information and the evaporation characteristics of liquid nitrogen under the current environment, after obtaining the empirical equations relating liquid nitrogen level to time and temperature, the target state equation and observation equation are constructed.

[0048] Liquid level estimation module: The Kalman filtering algorithm is introduced and combined with the target state equation and the observation equation to perform real-time liquid nitrogen level estimation.

[0049] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0050] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0051] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0052] Figure 1 This is a flowchart of a method for detecting liquid nitrogen level in an embodiment of the present invention;

[0053] Figure 2This is a structural diagram of a liquid nitrogen level detection system according to an embodiment of the present invention. Detailed Implementation

[0054] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0055] This invention provides a method for detecting liquid nitrogen level, such as... Figure 1 As shown, it includes:

[0056] Step 1: Use a pre-set target sensor to collect the first data information of the environment in which the liquid nitrogen is located in real time;

[0057] Step 2: Based on the first data information and the evaporation characteristics of liquid nitrogen under the current environment, obtain the empirical equations relating liquid nitrogen level to time and temperature, and then construct the target state equation and the observation equation.

[0058] Step 3: Introduce the Kalman filtering algorithm and combine it with the target state equation and the observation equation to estimate the liquid nitrogen level in real time.

[0059] In this embodiment, the target sensor refers to a temperature sensor and a pressure sensor; the first data information collected in real time includes the temperature and pressure inside the set container storing liquid nitrogen, as well as the first pressure and first temperature of the environment in which the set container storing liquid nitrogen is located.

[0060] In this embodiment, evaporation characteristics refer to the changes in the evaporation rate of liquid nitrogen under different pressures and temperatures; the target state equation refers to the equation for estimating the liquid nitrogen level, constructed based on the analysis of empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship; the observation equation describes the relationship between state variables and observed quantities, wherein the empirical equation for the liquid nitrogen level-time relationship is obtained by smoothing and linearly fitting the curve of liquid level weight change over time, and the empirical equation for the liquid nitrogen level-temperature relationship describes the relationship between liquid level and temperature; the Kalman filtering algorithm is an optimized autoregressive data processing algorithm used in conjunction with a platinum resistance temperature sensor level gauge to achieve real-time estimation of the continuous state of the liquid level, wherein the platinum resistance temperature sensor level gauge is selected based on the first data information of the environment in which the liquid nitrogen is located, combined with actual needs; the level gauge includes superconducting level gauges, improved capacitive level gauges, platinum resistance temperature sensor level gauges, etc.

[0061] The beneficial effects of the above technical solution are: by obtaining the empirical equation relating liquid nitrogen level to time and temperature based on the corresponding evaporation characteristics of the environment in which liquid nitrogen is stored, and then combining it with the Kalman filtering algorithm, the sensor level gauge is used to achieve accurate estimation of the continuous real-time liquid nitrogen level.

[0062] This invention provides a method for detecting liquid nitrogen level. Based on first environmental data and the evaporation characteristics of liquid nitrogen under the current environment, after obtaining an empirical equation relating liquid nitrogen level to time and temperature, a target state equation and an observation equation are constructed, including:

[0063] By combining the static evaporation formula with the Clapeyron equation and then using the relationship curves between different gas pressures and temperatures, the formula for the relationship between liquid nitrogen evaporation rate and pressure can be obtained.

[0064] Based on the first data information, the real-time evaporation rate of liquid nitrogen is obtained using the liquid nitrogen evaporation rate-pressure relationship formula;

[0065] Install a preset temperature sensing element on an arbitrarily selected container for storing liquid nitrogen, conduct a liquid nitrogen evaporation experiment, and obtain empirical equations for the relationship between liquid nitrogen level and time and the relationship between liquid nitrogen level and temperature;

[0066] Based on the empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship, the target state equation and the observation equation are constructed.

[0067] In this embodiment, the static evaporation formula is used to obtain the static evaporation rate of liquid nitrogen based on physical quantities such as gas flow rate, gas volume coefficient, gas-liquid volume ratio under standard conditions, experimental container volume, and internal temperature, pressure, and ambient temperature of liquid nitrogen evaporation; the Clapeyron equation is used to describe the change equation of physical quantities of the unit system during the first-order phase transition equilibrium; the liquid nitrogen evaporation rate-pressure relationship formula refers to the relationship between evaporation rate and pressure.

[0068] In this embodiment, the first data information includes the temperature and pressure inside the set container for storing liquid nitrogen, as well as the first atmospheric pressure and first temperature of the environment in which the set container for storing liquid nitrogen is located; the real-time evaporation rate refers to the evaporation status of liquid nitrogen under the current environmental conditions; the set container is a container that is pre-set to meet the storage conditions of liquid nitrogen, such as a Dewar; the preset temperature measuring element refers to a PT platinum resistance thermometer; the liquid nitrogen evaporation experiment starts from filling the set container with liquid nitrogen, and simultaneously collects temperature and weight data until the liquid nitrogen is completely evaporated, the purpose of which is to obtain an empirical equation for the correspondence between liquid nitrogen level-time and liquid nitrogen level-temperature in the set container.

[0069] In this embodiment, the empirical equation for the liquid nitrogen level-time relationship is obtained by smoothing and filtering the curve of liquid level weight change over time and then linearly fitting it; the empirical equation for the liquid nitrogen level-temperature relationship is used to describe the relationship between liquid level and temperature; the target state equation refers to the equation for estimating the liquid nitrogen level constructed based on the analysis of the empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship; and the observation equation is used to describe the relationship between state variables and observed quantities.

[0070] The beneficial effects of the above technical solution are: by analyzing the linear evaporation characteristics of liquid nitrogen under the current storage environment and the environmental conditions, the relationship between liquid nitrogen level and time and temperature is obtained, thereby effectively constructing the target state equation and observation equation.

[0071] This invention provides a method for detecting liquid nitrogen level. A preset temperature sensing element is installed on an arbitrarily selected container storing liquid nitrogen, and a liquid nitrogen evaporation experiment is conducted to obtain empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship, including:

[0072] Step 11: Fix the pre-set temperature measuring element for the set container at a preset distance from the opening of the set container;

[0073] Step 12: Select any container as the experimental container and start filling it with liquid nitrogen. Use the set measuring instrument to synchronously collect the experimental temperature and weight data inside the experimental container until the liquid nitrogen has evaporated completely.

[0074] Step 13: Based on the obtained experimental temperature and weight data, establish the temperature curve of the test point changing with time, and the weight curve of the liquid nitrogen in the container changing with time.

[0075] Step 14: After smoothing and filtering the weight curve, the first weight curve is obtained. Then, through linear fitting and corresponding percentage, the empirical equation of liquid nitrogen level-time relationship is obtained.

[0076] Step 15: Based on the obtained experimental temperature and weight data, construct a temperature-weight curve with weight as the X-axis and temperature as the Y-axis.

[0077] After converting the weight change into a percentage of liquid level, the temperature-liquid level curve is obtained.

[0078] Step 16: Select the target curve segment of stable evaporation from the temperature-level curve and analyze its variation law. Then, obtain the empirical equation of liquid nitrogen level-temperature relationship through linear fitting.

[0079] In this embodiment, the set container is a pre-set container that meets the liquid nitrogen storage conditions, such as a Dewar; the preset temperature sensing element refers to a PT100 platinum resistance thermometer; and the preset distance is pre-set based on the size of the set container.

[0080] In this embodiment, the experimental container refers to any selected container used for the liquid nitrogen evaporation experiment; the experimental weight data refers to the weight parameters of the selected container in the liquid nitrogen evaporation experiment; and the test point refers to the location where the preset temperature measuring element is installed.

[0081] In this embodiment, the first weight curve is obtained after smoothing and filtering the weight curve. The purpose of smoothing and filtering is to eliminate interference signals and obtain more accurate experimental results. The temperature-weight curve is obtained by using the obtained experimental temperature and weight data with weight as the X-axis and temperature as the Y-axis. The purpose of converting the weight change into a liquid level percentage is to more intuitively express the correspondence between temperature and liquid level. Linear fitting is a form of curve fitting used to find the optimal theoretical curve. The empirical equation for the liquid nitrogen level-temperature relationship is used to describe the relationship between liquid level and temperature.

[0082] In this embodiment, for example, there is a temperature-liquid level curve, which is divided into three segments: AB, BC, and CD. The AB and CD segments indicate that the temperature rises rapidly in an extreme time period, while the BC segment is stable. In this case, the BC segment is used as the target curve for analysis of its change pattern.

[0083] The beneficial effects of the above technical solution are as follows: by designing a liquid nitrogen evaporation experiment, experimental temperature and weight data are obtained to construct temperature curves and weight curves; after smoothing and filtering the weight curve and performing linear fitting to obtain the empirical equation of liquid nitrogen level-time relationship, the temperature-weight curve is then constructed to obtain the empirical equation of liquid nitrogen level-temperature relationship, laying the foundation for establishing the target state equation and observation equation.

[0084] This invention provides a method for detecting liquid nitrogen level, which involves selecting a target segment of the temperature-level curve for stable evaporation and analyzing its variation patterns, including:

[0085] The temperature-level curves are divided according to the same temperature to obtain a set of liquid levels based on the same temperature. ,in, This represents the i1th liquid level segment at the same temperature T; n1 represents the total number of liquid level segments at the same temperature T.

[0086] Simultaneously, the set of liquid levels at the same temperature is obtained based on the time sequence. Temperature transition sets with temporal adjacency ,in, This represents a temperature array that is temporally adjacent to the i1th liquid level segment at the same temperature T. ,in, This represents the temperature of the left adjacent segment corresponding to the i1th liquid level segment; This represents the temperature of the right adjacent segment corresponding to the i1th liquid level segment;

[0087] Based on the set of liquid levels at the same temperature, determine the evaporation rate of the corresponding liquid level segment at the same temperature. ;

[0088] ;

[0089] in, This represents the last liquid level value on the i1th liquid level segment at the same temperature T. This represents the initial liquid level value on the i1th liquid level segment at the same temperature T; This represents the time length of the i1th liquid level segment at the same temperature T. This represents the correction value for the evaporation rate of the i1th liquid level segment at the same temperature T; Indicates based on the left adjacent temperature With the temperature of the corresponding i1th liquid level segment Standard liquid nitrogen evaporation rate during the conversion process; express arrive Temperature transition time; express arrive Temperature transition time; Indicates based on the left adjacent temperature With the temperature of the corresponding i1th liquid level segment The actual amount of volatiles during the conversion process; This represents the temperature based on the corresponding i1th liquid level segment. adjacent temperature to the right Standard liquid nitrogen evaporation rate during the conversion process; This represents the temperature based on the corresponding i1th liquid level segment. adjacent temperature to the right The actual amount of volatiles during the conversion process;

[0090] Based on the liquid level evaporation rate at different temperatures, a evaporation rate sequence was constructed in order of temperature magnitude;

[0091] according to Calculate the conventional evaporation rate of the i1th liquid level segment at the same temperature. and with The comparison will consider the liquid level sub-segment within the comparison range as the target curve segment for stable evaporation;

[0092] Based on the target curve segment, from all We extract consistent values ​​and construct first sequences at different temperatures, and then analyze the variation patterns based on all first sequences.

[0093] In this embodiment, the temperature-level curve is a curve describing the relationship between the temperature at a test point and the liquid nitrogen level, with the liquid level as the x-axis and temperature as the y-axis. The test point refers to the location where the preset temperature sensing element PT100 is installed. The liquid level set consists of all liquid level segments at the same temperature, where each liquid level segment refers to an array of adjacent liquid levels at the same temperature based on the temperature-level curve. The temperature conversion set refers to the combination of the liquid level set and... A set of time-adjacent relationships; liquid level evaporation rate refers to the evaporation rate of the corresponding liquid level segment at the same temperature; the evaporation rate sequence is constructed by arranging the liquid level evaporation rates at different temperatures in order of temperature magnitude; the first sequence is constructed by extracting the same value from the corresponding evaporation rates of all liquid level segments contained in the target curve segment, and then constructing them according to different temperatures.

[0094] The beneficial effects of the above technical solution are as follows: by utilizing the liquid level set and temperature conversion set obtained by dividing and analyzing the temperature-liquid level curve according to the same temperature, the liquid level evaporation rate of the corresponding liquid level sub-segment at the same temperature can be obtained. Then, it is compared with the calculated conventional evaporation rate to obtain the target curve segment, so as to construct the first sequence of different temperatures for variation law analysis, laying the foundation for the subsequent construction of an accurate and effective empirical equation for the liquid nitrogen liquid level-temperature relationship.

[0095] This invention provides a method for detecting liquid nitrogen level, comprising constructing a target state equation and an observation equation, including:

[0096] After obtaining the target state equation by analyzing the empirical equations of liquid nitrogen level-time relationship and liquid nitrogen level-temperature relationship, the observation equation is determined based on the relationship between the state variables and the observed quantities.

[0097] The formulas for the target state equation and the observation equation are shown below:

[0098] ;

[0099] In the formula, This is expressed as the estimated liquid level at time k; Let A represent the control quantity for estimating the liquid level at time k; A and B represent the estimation parameters of the liquid level state quantity. The noise at time k is represented as Gaussian white noise; Let be the liquid nitrogen level value measured by the target level gauge at time k; P represents the measurement parameter. It is represented as measurement noise, and is Gaussian white noise.

[0100] In this embodiment, the empirical equation for the liquid nitrogen level-time relationship is obtained by smoothing and filtering the curve of liquid level weight change over time and then linearly fitting it; the empirical equation for the liquid nitrogen level-temperature relationship is used to describe the relationship between liquid level and temperature; the target state equation refers to the equation for estimating the liquid nitrogen level constructed based on the analysis of the empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship; and the observation equation is used to describe the relationship between state variables and observed quantities.

[0101] The beneficial effects of the above technical solution are: by obtaining the target state equation and observation equation based on the empirical equations of liquid nitrogen level-time relationship and liquid nitrogen level-temperature relationship, it is beneficial to achieve the optimal estimation of the liquid nitrogen level state in the future.

[0102] This invention provides a method for detecting liquid nitrogen level, which introduces a Kalman filtering algorithm and combines the target state equation and the observation equation to perform real-time liquid nitrogen level estimation, including:

[0103] Step 21: Based on the target state equation, use the optimal estimate of k-1 to predict the state variables at time k, and use it as the first predicted value. Then calculate the covariance of the first predicted value.

[0104] Step 22: Determine the Kalman gain at time k using the covariance of the first predicted value;

[0105] Step 23: Combine the first predicted value and the measured value at time k to obtain the optimal estimate at time k;

[0106] The formula is as follows:

[0107] ;

[0108] In the formula, This is expressed as the optimal estimate at time k; This is represented as the first predicted value; This is expressed as the Kalman gain at time k; Let represent the liquid level measurement value at time k; P represents the measurement parameter.

[0109] Step 24: Update the state variables at time K. The covariance is calculated, and steps 22-23 are repeated to achieve the optimal estimate of the liquid level at time k+1, so as to form an iteration to achieve real-time estimation of the liquid level state.

[0110] In this embodiment, the purpose of introducing the Kalman filtering algorithm is to avoid the situation where liquid nitrogen splashes onto the sensor level gauge due to violent boiling and uneven liquid surface during the liquid nitrogen evaporation process, resulting in false liquid levels. The target state equation refers to the equation for estimating the liquid nitrogen level, which is constructed based on the analysis of the empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship. The optimal estimate is the value of the liquid level state estimate that is closest to the true liquid level. The first prediction value is obtained by using the target state equation based on the state variables of the previous moment. The covariance is used to describe the overall error of the variable. The Kalman gain is obtained by pursuing the minimum mean square error based on the estimated value and the measured value, and then combined with the currently measured value to obtain the optimal estimate value at the current moment.

[0111] The beneficial effects of the above technical solution are: by introducing the Kalman filtering algorithm and combining the target state equation and the observation equation to perform real-time liquid nitrogen level state estimation, the interference caused by liquid nitrogen splashing onto the sensor is eliminated, thereby effectively ensuring the accuracy of liquid level state estimation.

[0112] This invention provides a liquid nitrogen level detection system, such as... Figure 2 As shown, it includes:

[0113] Data acquisition module: Uses pre-set target sensors to acquire first data information about the environment in which liquid nitrogen is located in real time;

[0114] Equation construction module: Based on the first data information and the evaporation characteristics of liquid nitrogen under the current environment, after obtaining the empirical equations relating liquid nitrogen level to time and temperature, the target state equation and observation equation are constructed.

[0115] Liquid level estimation module: The Kalman filtering algorithm is introduced and combined with the target state equation and the observation equation to perform real-time liquid nitrogen level estimation.

[0116] The beneficial effects of the above technical solution are: by obtaining the empirical equation relating liquid nitrogen level to time and temperature based on the corresponding evaporation characteristics of the environment in which liquid nitrogen is stored, and then combining it with the Kalman filtering algorithm, the sensor level gauge is used to achieve accurate estimation of the continuous real-time liquid nitrogen level.

[0117] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for detecting liquid nitrogen level, characterized in that, include: Step 1: Use a pre-set target sensor to collect the first data information of the environment in which the liquid nitrogen is located in real time; Step 2: Based on the first data information and the evaporation characteristics of liquid nitrogen under the current environment, obtain the empirical equations relating liquid nitrogen level to time and temperature, and then construct the target state equation and the observation equation. Step 3: Introduce the Kalman filtering algorithm and combine it with the target state equation and the observation equation to estimate the liquid nitrogen level in real time; Based on the initial environmental data and the evaporation characteristics of liquid nitrogen under the current environment, after obtaining the empirical equations relating liquid nitrogen level to time and temperature, the target state equation and observation equations are constructed, including: By combining the static evaporation formula with the Clapeyron equation and then using the relationship curves between different gas pressures and temperatures, the formula for the relationship between liquid nitrogen evaporation rate and pressure can be obtained. Based on the first data information, the real-time evaporation rate of liquid nitrogen is obtained using the liquid nitrogen evaporation rate-pressure relationship formula; Install a preset temperature sensing element on an arbitrarily selected container for storing liquid nitrogen, conduct a liquid nitrogen evaporation experiment, and obtain empirical equations for the relationship between liquid nitrogen level and time and the relationship between liquid nitrogen level and temperature; Based on the empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship, the target state equation and the observation equation are constructed. Construct the target state equation and observation equation, including: After obtaining the target state equation by analyzing the empirical equations of liquid nitrogen level-time relationship and liquid nitrogen level-temperature relationship, the observation equation is determined based on the relationship between the state variables and the observed quantities. The formulas for the target state equation and the observation equation are shown below: ； In the formula, This is expressed as the estimated liquid level at time k; Let A represent the control quantity for estimating the liquid level at time k; A and B represent the estimation parameters of the liquid level state quantity. The noise at time k is represented as Gaussian white noise; Let be the liquid nitrogen level value measured by the target level gauge at time k; P represents the measurement parameter. It is represented as measurement noise, and is Gaussian white noise.

2. The method for detecting liquid nitrogen level according to claim 1, characterized in that, The target sensors refer to temperature sensors and pressure sensors; the first data information collected in real time includes the temperature and pressure inside the set container storing liquid nitrogen, as well as the first pressure and first temperature of the environment in which the set container storing liquid nitrogen is located.

3. The method for detecting liquid nitrogen level according to claim 2, characterized in that, By installing a preset temperature sensing element on an arbitrarily selected container for storing liquid nitrogen, a liquid nitrogen evaporation experiment was conducted to obtain empirical equations for the liquid nitrogen level-time relationship and the liquid nitrogen level-temperature relationship, including: Step 11: Fix the pre-set temperature measuring element for the set container at a preset distance from the opening of the set container; Step 12: Select any container as the experimental container and start filling it with liquid nitrogen. Use the set measuring instrument to synchronously collect the experimental temperature and weight data inside the experimental container until the liquid nitrogen has evaporated completely. Step 13: Based on the obtained experimental temperature and weight data, establish the temperature curve of the test point changing with time, and the weight curve of the liquid nitrogen in the container changing with time. Step 14: After smoothing and filtering the weight curve, the first weight curve is obtained. Then, through linear fitting and corresponding percentage, the empirical equation of liquid nitrogen level-time relationship is obtained. Step 15: Based on the obtained experimental temperature and weight data, construct a temperature-weight curve with weight as the X-axis and temperature as the Y-axis. After converting the weight change into a percentage of liquid level, the temperature-liquid level curve is obtained. Step 16: Select the target curve segment of stable evaporation from the temperature-level curve and analyze its variation law. Then, obtain the empirical equation of liquid nitrogen level-temperature relationship through linear fitting.

4. The method for detecting liquid nitrogen level according to claim 3, characterized in that, The target curve segment for stable evaporation was selected from the temperature-liquid level curve for variation analysis, including: The temperature-level curves are divided according to the same temperature to obtain a set of liquid levels based on the same temperature. ,in, This represents the i1th liquid level segment at the same temperature T; n1 represents the total number of liquid level segments at the same temperature T. Simultaneously, based on the time sequence, the set of liquid levels at the same temperature is obtained. Temperature transition sets with temporal adjacency ,in, This represents a temperature array that is temporally adjacent to the i1th liquid level segment at the same temperature T. ,in, This represents the temperature of the left adjacent segment corresponding to the i1th liquid level segment; This represents the temperature of the right adjacent segment corresponding to the i1th liquid level segment; Based on the set of liquid levels at the same temperature, determine the evaporation rate of the corresponding liquid level segment at the same temperature. ; ； in, This represents the last liquid level value on the i1th liquid level segment at the same temperature T. This represents the initial liquid level value on the i1th liquid level segment at the same temperature T; This represents the time length of the i1th liquid level segment at the same temperature T. This represents the correction value for the evaporation rate of the i1th liquid level segment at the same temperature T; Indicates based on the left adjacent temperature With the temperature of the corresponding i1th liquid level segment Standard liquid nitrogen evaporation rate during the conversion process; express arrive Temperature transition time; express arrive Temperature transition time; Indicates based on the left adjacent temperature With the temperature of the corresponding i1th liquid level segment The actual amount of volatiles during the conversion process; This represents the temperature based on the corresponding i1th liquid level segment. adjacent temperature to the right Standard liquid nitrogen evaporation rate during the conversion process; This represents the temperature based on the corresponding i1th liquid level segment. adjacent temperature to the right The actual amount of volatiles during the conversion process; Based on the liquid level evaporation rate at different temperatures, a evaporation rate sequence was constructed in order of temperature magnitude; according to Calculate the conventional evaporation rate of the i1th liquid level segment at the same temperature. and with The comparison will consider the liquid level sub-segment within the comparison range as the target curve segment for stable evaporation; Based on the target curve segment, from all We extract consistent values ​​and construct first sequences at different temperatures, and then analyze the variation patterns based on all first sequences.

5. The method for detecting liquid nitrogen level according to claim 1, characterized in that, A Kalman filtering algorithm is introduced, and combined with the target state equation and the observation equation, real-time liquid nitrogen level state estimation is performed, including: Step 21: Based on the target state equation, use the optimal estimate of k-1 to predict the state variables at time k, and use it as the first predicted value. Then calculate the covariance of the first predicted value. Step 22: Determine the Kalman gain at time k using the covariance of the first predicted value; Step 23: Combine the first predicted value and the measured value at time k to obtain the optimal estimate at time k; The formula is as follows: ； In the formula, This is expressed as the optimal estimate at time k; This is represented as the first predicted value; This is expressed as the Kalman gain at time k; Let represent the liquid level measurement value at time k; P represents the measurement parameter. Step 24: Update the state variables at time K. The covariance is calculated, and steps 22-23 are repeated to achieve the optimal estimate of the liquid level at time k+1, so as to form an iteration to achieve real-time estimation of the liquid level state.

6. A liquid nitrogen level detection system, employing the liquid nitrogen level detection method according to any one of claims 1-5, characterized in that, include: Data acquisition module: Uses pre-set target sensors to acquire first data information about the environment in which liquid nitrogen is located in real time; Equation construction module: Based on the first data information and the evaporation characteristics of liquid nitrogen under the current environment, after obtaining the empirical equations relating liquid nitrogen level to time and temperature, the target state equation and observation equation are constructed. Liquid level estimation module: The Kalman filtering algorithm is introduced and combined with the target state equation and the observation equation to perform real-time liquid nitrogen level estimation.

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