Ultrasonic probe constant-temperature pure water calibration method based on model

Abstract

A model-based ultrasonic probe constant-temperature pure water calibration method is characterized in that a calibration data core point is a curved surface model of urea concentration C = f (T, V), and the curved surface model is formed by integrating and summarizing experimental data and fitting sampling data points of an ultrasonic urea concentration sensor by using a least square method; comprising the following steps: step 1, an electric appliance preparation stage, step 2, a solution preparation stage, step 3, a calibration acquisition stage, step 4, a calibration calculation stage, step 5, a calibration fitting stage, and step 6, a calibration storage stage. On the basis of integration and summarization of a large amount of experimental data, sampling data points of the ultrasonic urea concentration sensor are fitted into the urea concentration curved surface model through the least square method, length consistency calibration of the urea ultrasonic probe in the constant-temperature pure water environment can be achieved, and the method is high in practicability, high in calibration data precision and high in accuracy. The defects of uncontrollability, PID calibration complexity, environment corrosivity and the like of calibration environment by using a urea solution with the concentration of 32.5% in the industry are avoided.

Description

Technical Field

[0001] This invention relates to the field of automotive sensor technology, specifically a model-based method for constant temperature pure water calibration of ultrasonic probes. Background Technology

[0002] Currently, domestic methods for measuring liquid concentration mainly include chemical analysis, chromatography, infrared absorption spectroscopy, and optical refractive index method. Chemical analysis is often performed at a crucial stage of production, using specific chemical reactions to analyze sampled liquids. This method offers extremely high precision but is time-consuming, resource-intensive, inefficient, and cannot be performed online, thus failing to meet the needs of vehicle applications. Chromatography provides comprehensive liquid concentration measurement, enabling high-precision, full-component solution analysis. However, its high component costs, complex structure, and demanding manual maintenance limit its widespread adoption in China. Infrared absorption spectroscopy is a mature method. Its advantages include short measurement time, simultaneous measurement of multiple components, and preservation of the original liquid composition, making it a relatively good method. However, it suffers from large instrument size, demanding testing environment requirements, complex and expensive instrument maintenance, and a narrow range of applications. Optical methods utilize the different refractive indices of light in solutions of varying concentrations to detect liquid concentration. Optical methods offer extremely high precision but are highly dependent on the testing environment; even small fluctuations in light intensity can significantly affect the results, resulting in poor stability.

[0003] In recent years, significant progress has been made in the research of ultrasonic urea concentration detection. Ultrasonic detection technology has matured and become a reliable detection method. Ultrasonic detection technology has advantages such as short detection time and no pollution, making it a rapidly developing and widely used detection technology. When ultrasound propagates in a medium, factors such as the concentration, viscosity, and temperature of the medium all affect the physical propagation characteristics of the ultrasound to varying degrees. Currently, ultrasonic detection technology has been successfully applied in the field of automotive urea concentration detection. Based on the above theoretical status and the consistency issues exposed by mass production, when the concentration, viscosity, and temperature of the urea solution are constant, the largest variation parameter is the processing accuracy of the ultrasonic probe's external structural components. In mass production, the distance between the emitting and reflecting surfaces of the ultrasonic probe often varies, resulting in a certain deviation in the concentration measured by different ultrasonic probes under the same calibration data, thus affecting the calculation of urea concentration.

[0004] Currently, the industry in my country mostly uses a 32.5% concentration standard urea solution for product consistency calibration. This method has certain drawbacks: considering the evaporation characteristics of urea solution itself, its concentration may deteriorate in durability; secondly, the ultrasonic probe length calibration strategy mostly adopts PID closed-loop difference fitting, which takes a long time and has relatively slow production efficiency; and because urea solution is alkaline and ammoniated, it is also corrosive to the electronic equipment of the production line. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a model-based method for calibrating ultrasonic probes in constant-temperature pure water.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a model-based method for constant temperature pure water calibration of an ultrasonic probe, wherein the core point of the calibration data is the urea concentration C=f(T,V) surface model, which is based on the integration and summarization of experimental data and fitted to the sampling data points of the ultrasonic urea concentration sensor using the least squares method.

[0007] Specifically, the following steps are included: Step 1: Electrical preparation stage, connect the display and control smart screen, power supply, and ultrasonic urea concentration sensor; Step 2: Solution preparation stage, the ultrasonic urea concentration sensor is placed in a stable 40℃ constant temperature bath; Step 3: Calibration and data acquisition stage, the ultrasonic urea concentration sensor acquires solution temperature data and ultrasonic wave propagation speed data within the solution; Step 4: Calibration calculation stage, calculate the default value ΔC of urea concentration based on the C=f(T,V) surface model; Step 5: In the calibration and fitting stage, if there is a calibration deviation, calculate the ultrasonic probe length deviation according to ΔC and the velocity-time formula, and obtain a reasonable ultrasonic probe length S1; Step 6: Calibration and storage stage. When the default value △C=0, the ultrasonic probe length S=S0 is stored directly. When the default value △C≠0, △S is calculated using the speed-time formula, S=S0+△S, and the ultrasonic probe length S is stored.

[0008] Furthermore, in step one, a smart display screen supporting CAN communication is used. The smart display screen with CAN communication has CAN bus message monitoring function and simulated message sending function, supports automotive-grade SAE J1939 communication protocol, supports macro instruction script editing and calling, and uses DC power supply to power the smart display screen and urea quality sensor. This invention can realize the probe length consistency calibration of urea ultrasonic probe in a 40℃ constant temperature pure water environment without the need to use 32.5% standard urea solution, avoiding many drawbacks such as the uncontrollability of the mainstream calibration environment in the industry, the complexity of PID calibration, and environmental corrosivity.

[0009] Furthermore, in step two, the 40°C constant temperature pure water environment needs to be controlled using a constant temperature bath.

[0010] Furthermore, in step three, the urea quality sensor collects solution temperature data using an NTC thermistor, and the ultrasonic propagation speed data in a 40℃ constant temperature pure water environment is calculated using the speed-time formula v=s / t.

[0011] Furthermore, the expression for the urea concentration C=f(T,V) surface model in step four is summarized as follows: C=a1+a2T+a3T2+a4V+a5V2+a6T·V.

[0012] Furthermore, in step four, the default value △C = C0 - 0% reflects the deviation of the current concentration measurement.

[0013] Furthermore, in step five, the calculation method is to substitute △C into the C=f(T,V) surface model to calculate the propagation speed deviation △V, and then calculate △S based on S=V·t to obtain the ultrasonic probe length S1.

[0014] Furthermore, in step six, the length S of the ultrasonic probe is saved to the ROM memory of the MCU.

[0015] Based on the above settings, this invention integrates and summarizes a large amount of experimental data, and uses the least squares method to fit the sampling data points of the ultrasonic urea concentration sensor into a urea concentration surface model. This enables the length consistency calibration of the urea ultrasonic probe in a constant temperature pure water environment. This method is highly practical, has high calibration data accuracy, and avoids many drawbacks of the industry's use of 32.5% concentration urea solution for calibration, such as the uncontrollability of the environment, the complexity of PID calibration, and environmental corrosivity. Attached Figure Description

[0016] The present invention will now be further described with reference to the accompanying drawings.

[0017] Figure 1 This is a flowchart of the calibration method of the present invention; Figure 2 This is a schematic diagram of the constant temperature pure water calibration device of the present invention; Figure 3 This is a schematic diagram of the urea concentration C=f(T,V) surface model of the present invention; Figure 4 This is a scatter plot of temperature T versus velocity V at a concentration of 32.5%. Figure 5 This is a schematic diagram of a cubic polynomial fitting of temperature T and velocity V in a 32.5% solution. Detailed Implementation

[0018] like Figure 1-5 As shown, a model-based method for calibrating an ultrasonic probe in constant temperature pure water is presented. The core data point of the calibration is the urea concentration C=f(T,V) surface model. This surface model is based on the integration and summarization of experimental data and is fitted to the sampling data points of the ultrasonic urea concentration sensor using the least squares method.

[0019] Includes the following steps: Step 1: Electrical preparation stage. Connect the display and control smart screen, power supply, and ultrasonic urea concentration sensor. The display and control smart screen that supports CAN communication is used. The display and control smart screen with CAN communication has CAN bus message monitoring function, analog message sending function, supports automotive-grade SAE J1939 communication protocol, supports macro instruction script editing and calling, and uses DC power supply to power the display and control smart screen and urea quality sensor. Step 2: Solution preparation stage. The ultrasonic urea concentration sensor is placed in a stable 40℃ constant temperature bath. In this step, the 40℃ constant temperature pure water environment needs to be controlled by a constant temperature bath. Step 3: Calibration and data acquisition stage. The ultrasonic urea concentration sensor acquires solution temperature data and ultrasonic wave propagation speed data in the solution. In this step, the urea quality sensor acquires solution temperature data using NTC thermistor method. The ultrasonic wave propagation speed data in a 40℃ constant temperature pure water environment is calculated using the speed-time formula v=s / t. Step 4: Calibration Calculation Stage. The default value ΔC of urea concentration is calculated based on the C=f(T,V) surface model. The expression for the urea concentration C=f(T,V) surface model in this step is summarized as follows: C=a1+a2T+a3T2+a4V+a5V2+a6T·V; The default value is △C = C0 - 0%, and the calculation result reflects the deviation of the current concentration measurement. Step 5: Calibration and fitting stage. If there is a calibration deviation, calculate the ultrasonic probe length deviation according to ΔC and the velocity-time formula, and obtain a reasonable ultrasonic probe length S1. The calculation method in this step is to substitute ΔC into the C=f(T,V) surface model to calculate the propagation velocity deviation ΔV, and then calculate ΔS according to S=V·t to obtain the ultrasonic probe length S1. Step 6: Calibration and storage stage. When the default value △C=0, the ultrasonic probe length S=S0 is stored directly. When the default value △C≠0, △S is calculated using the speed-time formula, S=S0+△S, and the ultrasonic probe length S is stored. In this step, the ultrasonic probe length S is saved to the ROM memory of the MCU.

[0020] Working principle of this invention: As described in the background section, the industry currently uses a 32.5% concentration standard urea solution for product consistency calibration. This approach has certain drawbacks: considering the evaporation characteristics of urea solution, continuous testing during production can lead to a decrease in the durability of the equipment's medium concentration; secondly, the ultrasonic probe length calibration strategy often uses PID closed-loop difference fitting, and combined with experimental data, it can be found that the urea concentration calibration fitting curve at room temperature has a small downward deviation, thus the method has a certain degree of calibration accuracy problem due to the influence of ambient temperature; and because urea solution is alkaline and ammoniated, it also has a certain degree of corrosiveness to the electronic equipment on the production line.

[0021] The key feature of this invention, a model-based method for constant-temperature pure water calibration of an ultrasonic probe, lies in: using a surface model of urea concentration C=f(T,V) fitted from a large amount of experimental data as a basis, and employing the least squares method to fit the sampling data points of the ultrasonic urea concentration sensor to form a functional relationship formula: C(T,V)=a+bT+cV+dT+eT·V+fV², the surface fitting result is as follows... Figure 3 As shown.

[0022] Based on the C=f(T,V) surface model mentioned above, the ultrasonic probe speed under 0% urea concentration (pure water) medium has a high degree of matching with the fitted surface at 40℃, and has efficient calibration conditions.

[0023] Related experiments: The results and calibration times of pure water calibration and standard urea solution calibration are compared, as shown in the table below;

[0024] The inconsistency between the distance between the emitting and reflecting surfaces of the ultrasonic probe can affect the concentration accuracy of the actual product measurement. This distance s is defined as a constant (assuming distance s = 36.10 mm). The following uses different methods to calibrate the concentration consistency of the 10 samples. The specific test results are shown in the table below.

[0025] Method a: Standardize with a 32.5% urea solution at room temperature. Method b: Pure water calibration, 40℃ constant temperature bath Advantages of pure water calibration 1. Precise and stable benchmark: Pure water is a 0-concentration standard medium with highly stable physicochemical properties. It is free from problems such as urea crystallization, concentration drift, and impurity interference, and can provide a unique and reliable zero-point calibration benchmark, thereby improving the initial accuracy and long-term consistency of sensor concentration detection from the source.

[0026] 2. Costs are significantly reduced; there is no need to purchase, prepare, or store standard urea solution, saving costs on consumables, transportation, sealing, and waste liquid treatment; pure water is readily available and extremely low in cost, resulting in significant cost reduction during large-scale production.

[0027] 3. Significantly improved calibration efficiency; eliminates the pipeline purging and cleaning processes required in traditional urea calibration, simplifies the calibration process, shortens the calibration time per unit, adapts to high-speed automated production lines, and significantly improves production efficiency.

[0028] 4. Safe and environmentally friendly, compliant with automotive standards; the pure water is non-toxic, non-corrosive, and non-volatile, with no safety hazards or waste liquid discharge pressure during the production process, meeting the environmental protection and automotive-grade production requirements of the workshop.

[0029] 5. Hardware compatibility and easy implementation: No need to modify the existing hardware architecture such as ultrasonic probes and CAN bus communication; it can be directly compatible with the current mainstream sensor structure, resulting in low investment and quick implementation in production line transformation.

[0030] 6. Better product consistency; there is no difference in composition between batches of pure water, and the calibration results have high repeatability, which can effectively improve the factory qualification rate and batch consistency of sensors.

[0031] This invention has market and protection value. Commercial vehicle SCR after-treatment systems are a rigid demand. The method of this invention can form a core technology knowledge barrier in the production process, effectively enhance product competitiveness, and has high licensing and industrialization value.

[0032] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A model-based method for constant-temperature pure water calibration of an ultrasonic probe, characterized in that, The core data for calibration is the urea concentration C=f(T,V) surface model. This model is based on the integration and summarization of experimental data and is fitted to the sampling data points of the ultrasonic urea concentration sensor using the least squares method. The process includes the following steps: Step 1: Electrical preparation stage, connect the display and control smart screen, power supply, and ultrasonic urea concentration sensor; Step 2: Solution preparation stage, the ultrasonic urea concentration sensor is placed in a stable 40℃ constant temperature bath; Step 3: Calibration and data acquisition stage, the ultrasonic urea concentration sensor acquires solution temperature data and ultrasonic wave propagation speed data within the solution; Step 4: Calibration calculation stage, calculate the default value ΔC of urea concentration based on the C=f(T,V) surface model; Step 5: In the calibration and fitting stage, if there is a calibration deviation, calculate the ultrasonic probe length deviation according to ΔC and the velocity-time formula, and obtain a reasonable ultrasonic probe length S1; Step 6: Calibration and storage stage. When the default value △C=0, the ultrasonic probe length S=S0 is stored directly. When the default value △C≠0, △S is calculated using the speed-time formula, S=S0+△S, and the ultrasonic probe length S is stored.

2. The model-based ultrasonic probe constant-temperature pure water calibration method as described in claim 1, characterized in that: In step one, a smart display screen that supports CAN communication is used. The smart display screen with CAN communication has CAN bus message monitoring function, simulated message sending function, supports automotive-grade SAE J1939 communication protocol, supports macro instruction script editing and calling, and uses DC power supply to power the smart display screen and urea quality sensor.

3. The model-based ultrasonic probe constant-temperature pure water calibration method as described in claim 1, characterized in that: In step two, the 40℃ constant temperature pure water environment needs to be controlled using a constant temperature bath.

4. The model-based ultrasonic probe constant-temperature pure water calibration method as described in claim 1, characterized in that: In step three, the urea quality sensor collects solution temperature data using an NTC thermistor, and the ultrasonic propagation speed data in a 40℃ constant temperature pure water environment is calculated using the speed-time formula v=s / t.

5. The model-based ultrasonic probe constant-temperature pure water calibration method as described in claim 1, characterized in that: The surface model of urea concentration C=f(T,V) in step four is summarized as follows: C=a1+a2T+a3T2+a4V+a5V2+a6T·V.

6. The model-based ultrasonic probe constant-temperature pure water calibration method as described in claim 1, characterized in that: In step four, the default value △C = C0 - 0% is used, and the calculation result reflects the deviation of the current concentration measurement.

7. The model-based ultrasonic probe constant-temperature pure water calibration method as described in claim 1, characterized in that: The calculation method in step five is to substitute △C into the C=f(T,V) surface model to calculate the propagation speed deviation △V, and then calculate △S based on S=V·t to obtain the ultrasonic probe length S1.

8. The model-based ultrasonic probe constant-temperature pure water calibration method according to claim 1, characterized in that: In step six, the length S of the ultrasonic probe is saved to the ROM memory of the MCU.

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