Online measurement method and system for alcoholysis degree distribution of polyvinyl alcohol

Abstract

The invention relates to the technical field of on-line analysis, in particular to a polyvinyl alcohol alcoholysis degree distribution on-line measurement method and system.The method comprises the following steps that spectral data of a polyvinyl alcohol solution is obtained, a characteristic absorption wave band in the ester group to hydroxyl group process is extracted, absorption intensity in the wave band is recorded to construct a sequence, peak positions are extracted, intensity difference is calculated, and the direction is marked; and identifying a fluctuation interval, calculating an angular velocity trend, and screening anomalies and generating an unstable section set in combination with a disturbance amplitude and a component coincidence rate. According to the method, quantitative analysis of alcoholysis degree conversion characteristics is realized through selection of characteristic absorption wavebands in spectral data and accurate identification of the change trend of the intensity difference values, the characterization precision of the alcoholysis degree of polyvinyl alcohol is improved, and more accurate trend fluctuation identification capability is provided through comparison of angular velocity difference values of absorption intensity change rates, so that the accuracy of the analysis of the alcoholysis degree of polyvinyl alcohol is improved. The analysis level of alcoholysis degree distribution details is remarkably improved, the abnormal fluctuation interval of alcoholysis degree component distribution is recognized, and the product quality difference caused by alcoholysis degree fluctuation is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of online analysis, and particularly to an online measurement method and system for the degree of alcoholysis distribution of polyvinyl alcohol. Background Art

[0002] The technical field of online analysis involves methods and devices for continuously or real-time detecting the composition, structure or properties of substances during industrial production or material processing. This technology integrates optical, electrical, chemical or mechanical sensors, and cooperates with automatic sampling, data acquisition and processing systems to achieve dynamic monitoring of key parameters of raw materials, intermediate products or final products. It is mainly applied in industries such as chemical engineering, pharmaceuticals, food, environmental monitoring, etc., to improve process control accuracy, product consistency and production efficiency, and avoid information lag problems caused by manual sampling delays. Common online analysis methods include infrared spectroscopy, Raman spectroscopy, mass spectrometry, chromatography, conductivity measurement, near-infrared analysis, etc., which have technical advantages such as rapid response, strong non-destructiveness, and high integratability.

[0003] Among them, the online measurement method for the degree of alcoholysis distribution of polyvinyl alcohol is a method for real-time obtaining the degree of alcoholysis distribution during the production or application process of polyvinyl alcohol materials. The degree of alcoholysis of polyvinyl alcohol, that is, the degree of conversion of vinyl acetate monomers into alcohol groups, is the core index determining its key performance parameters such as solubility, film-forming property, and adhesion performance. The purpose of the solution is to dynamically master the distribution of different alcoholysis degree components in polyvinyl alcohol without affecting the continuity of production, and provide an accurate basis for process adjustment, quality control and product classification. The method is applicable to the production line or use scenario of polyvinyl alcohol to improve the consistency and targeted application performance of products.

[0004] Traditional measurement methods rely on real-time measurement of the overall degree of alcoholysis level, and do not effectively focus on the fluctuation details and change trends during the conversion of ester groups to hydroxyl groups in molecules, making it impossible to timely capture local abnormal changes and subtle fluctuations in the degree of alcoholysis in the actual production environment. There is a lack of in-depth analysis and quantitative analysis means for the change trend of absorption intensity, resulting in insufficient sensitivity in trend fluctuation judgment, inability to quickly respond and accurately identify abnormal distribution of the degree of alcoholysis of polyvinyl alcohol, and difficulty in timely discovering and accurately positioning unstable component distribution phenomena in products. For example, if the subtle deviation of the degree of alcoholysis during a certain period of production cannot be timely identified, it will cause frequent product quality fluctuations, affecting the overall consistency and subsequent application performance of polyvinyl alcohol products. Summary of the Invention

[0005] The object of the present invention is to solve the deficiencies existing in the prior art, and to propose an online measurement method and system for the degree of alcoholysis distribution of polyvinyl alcohol.

[0006] To achieve the above object, the present invention adopts the following technical solution: an on-line measurement method for the degree of alcoholysis distribution of polyvinyl alcohol, comprising the following steps: S1: Obtain the spectral data of the polyvinyl alcohol solution, extract the characteristic absorption band during the conversion of the ester group in the polyvinyl alcohol molecule into a hydroxyl group, record all absorption intensities within the band range in each sampling period, and construct an ordered list according to the wavelength dimension to generate a spectral sequence of the characteristic absorption section; S2: Based on the spectral sequence of the characteristic absorption section, mark the change direction of the intensity difference between adjacent sampling points, extract the frame combination segments with opposite change directions, identify the starting and ending frame positions of the fluctuation, and generate a set of absorption peak difference fluctuation intervals; S3: Call the set of absorption peak difference fluctuation intervals, calculate the absorption peak intensity change rate vector in each time interval respectively, calculate the difference between the angular velocity change trend in the current section and the average absorption intensity change rate within the period, and generate the section absorption response offset trend information; S4: Call the section absorption response offset trend information, extract the ratio of the number of overlapping frames to the total number of frames according to the distribution interval of the alcoholysis components of the polyvinyl alcohol molecule in the corresponding time section, and construct a ratio relationship between the two parameters to generate the disturbance amplitude and component overlap information.

[0007] The present invention is improved in that the spectral sequence of the characteristic absorption section includes a wavelength sampling point index set, a multi-frame matrix of absorption intensities, an absorption channel time tag, an initial position of the peak position within the band, and a sampling period sequence mapping value; the set of absorption peak difference fluctuation intervals includes a response direction change identification sequence, a dynamic index group of absorption intensity differences, a set of peak-to-peak amplitude jump points, fluctuation starting and ending frame marking information, and absorption section structure parameters; the section absorption response offset trend information is specifically an angular velocity change symbol structure, a period difference direction vector group, an absorption trend reversal characteristic identification, a statistical value of the vector angle change within the time period, and a spectral offset trend level index; the disturbance amplitude and component overlap information includes a spectral standard deviation set, the number of overlapping frames of the component distribution within the section, a signal fluctuation and component matching coefficient, an average value of the spectral intensity change within the frame section, and an interference amplitude label index. [[ID=...]] [[ID=...]]

[0008] The present invention is improved in that the obtaining steps of the spectral sequence of the characteristic absorption section are specifically as follows: S111: Obtain the spectral data of the polyvinyl alcohol solution, identify the wavelength position and the corresponding absorption intensity value in the spectral data frame in each measurement period, organize the original band information according to the measurement time sequence to form a time sequence wavelength intensity comparison table, and generate a spectral original sampling data set; S112: Based on the original spectral sampling data set, according to the recorded spectral information, filter the wavelength ranges corresponding to the stretching vibration region of the ester carbonyl group and the stretching vibration region of the hydroxyl group in polyvinyl alcohol, extract the continuous response values of the two types of bands in each time series frame, establish a response set corresponding to the band type and the frame sequence, and obtain the target functional band response information; S113: Invoke the target functional band response information, perform an ordered arrangement on the response set in the wavelength dimension according to each type of band response value sequence and classify it according to the measurement time frame, organize the structure into a wavelength intensity order form with frame sequence labels, and generate a spectral sequence of characteristic absorption regions.

[0009] The improvement of the present invention is that the steps for obtaining the set of absorption peak difference fluctuation intervals are specifically as follows: S211: Based on the spectral sequence of characteristic absorption regions, according to the spectral frame data corresponding to each sampling time point, respectively locate the peak positions of the ester carbonyl absorption peak band and the hydroxyl absorption peak band within the frame, extract the corresponding absorption intensity values and establish a mapping relationship between the two to generate a functional peak position intensity control group; S212: According to the functional peak position intensity control group, calculate the difference between the hydroxyl absorption peak intensity and the ester absorption peak intensity, construct a time series according to the sampling time order, arrange the intensity differences corresponding to the time frames into a continuously changing structure, calculate and obtain the response change trend value of each time frame, and mark the trend change direction as a positive change direction or a negative change direction to obtain a peak difference trend change identification sequence; S213: Based on the peak difference trend change identification sequence, according to the trend change direction between consecutive frames, locate and extract the trend symbol inversion points, expand one frame on both sides of the inversion points to form a change segment combination, mark it as a response fluctuation start and end frame combination, extract the corresponding time indices in the combination and number them to establish a time period list, and generate a set of absorption peak difference fluctuation intervals.

[0010] The improvement of the present invention is that the steps for obtaining the section absorption response offset trend information are specifically as follows: S311: Invoke the set of absorption peak difference fluctuation intervals, obtain three groups of band response data of the corresponding start frame, center frame and end frame, extract the normalized absorption intensity values of the hydroxyl absorption peak and the ester carbonyl absorption peak in each frame, respectively construct a first-order difference structure with time as the sequence, obtain an intensity change path composed of three points, and generate a vector group of absorption peak compositions; S312: Form a vector group according to the absorption peaks, extract the vectors corresponding to the starting frame, the central frame, and the ending frame, calculate the angle between the two vectors through the coordinate space angle operation, divide the angle by the time interval to obtain the angular velocity corresponding to the change in absorption intensity of each segment, call the calculation results of the angular velocities in adjacent time segments for direction consistency comparison, construct trend evolution data, and calculate the offset trend value of the absorption peak response segment through operation; S313: According to the offset trend value of the absorption peak response segment, retrieve the increase and decrease changes of each trend value between adjacent two time periods, calculate the occurrence frequency of the trend offset turning points in the change direction sequence, perform cross-statistics in combination with the frequency and the angular velocity direction consistency judgment result, establish a distribution state index table between trend changes and direction stability, and generate segment absorption response offset trend information.

[0011] The improvement of the present invention is that the steps for obtaining the disturbance amplitude and component coincidence information are specifically as follows: S411: Call the segment absorption response offset trend information, extract the characteristic absorption band response values of the sampling frames from the corresponding segment according to the time segment marked as significantly changing, perform deviation square processing on the normalized intensity of the main absorption peak in each frame, and calculate the average standard deviation value within the segment to obtain the spectral disturbance amplitude parameter set; S412: Call the spectral disturbance amplitude parameter set, extract the distribution range of the alcoholysis components detected in each frame of the polyvinyl alcohol solution according to the sampling index range of each time period, count the number of frames with component coincidence in each frame within the time segment, compare it with the total number of frames in the segment to form a proportional relationship, calculate the composite index of each absorption segment through operation, sort and number according to the structural sequence of each segment, and generate the disturbance amplitude and component coincidence information; S413: According to the disturbance amplitude and component coincidence information, divide the disturbance level intervals after sorting by the exponential value, mark the segment numbers and level states correspondingly, and perform unified coding on the distribution characteristics, disturbance amplitude, and frame coincidence structure as evaluation parameters to obtain the disturbance amplitude and component coincidence information.

[0012] The improvement of the present invention is that the method further includes the following steps: S5: Call the disturbance amplitude and component coincidence information, compare it with the alcoholysis degree fluctuation benchmark index threshold, screen the frame numbers of the segments outside the deviation range, check whether there are characteristic changes of two consecutive direction reversals in the corresponding frames in the segment absorption response offset trend value, if both conditions are met, mark the time period as an abnormal fluctuation interval, and generate an alcoholysis distribution unstable marked segment set; The alcoholysis distribution unstable marked segment set specifically refers to the abnormal fluctuation segment index code, the continuous direction reversal frame label, the in-segment stability offset label, the unstable area determination logic field, and the block status identification label.

[0013] The improvement of the present invention is that the steps for obtaining the set of unstable marked sections of alcoholysis distribution are specifically as follows: S511: Invoke the perturbation amplitude and component coincidence information, compare the composite index data of each section with the set threshold of the alcoholysis degree fluctuation reference index, screen the section frame indexes with the composite index deviating from the reference threshold, establish classification labels corresponding to the deviation directions, and obtain the sequence of frame numbers with the composite index deviation; S512: According to the sequence of frame numbers with the composite index deviation, extract the angular velocity direction change labels of the corresponding frames in the section absorption response offset trend value, continuously traverse the inter-frame trend change identifiers, count the number of adjacent frame pairs with direction reversal, screen the sections with the cumulative number exceeding two groups and mark their numbers, and generate a set of sections with trend direction reversal; S513: Invoke the sequence of frame numbers with the composite index deviation and the set of sections with trend direction reversal, extract their intersection, merge and mark it as an abnormal state with the section frame number as the primary key, establish section labels, start and end frame indexes, and stability judgment identifiers, and generate a set of unstable marked sections of alcoholysis distribution.

[0014] An on-line measurement system for the alcoholysis degree distribution of polyvinyl alcohol, the system includes: The characteristic spectrum recognition module acquires the spectrum data of the polyvinyl alcohol solution, extracts the characteristic absorption band during the process of the ester group in the polyvinyl alcohol molecule being converted into a hydroxyl group, records all absorption intensities within the band range in each sampling period, constructs an ordered list according to the wavelength dimension, and generates a characteristic absorption section spectrum sequence; The fluctuation range recognition module marks the change direction of the intensity difference between adjacent sampling points based on the characteristic absorption section spectrum sequence, extracts the frame combination segments with opposite change directions, identifies the positions of the start and end frames of the fluctuation, and generates a set of absorption peak difference fluctuation ranges; The offset trend analysis module invokes the set of absorption peak difference fluctuation ranges, calculates the absorption peak intensity change rate vector in each time interval respectively, calculates the difference between the angular velocity change trend in the current section and the average absorption intensity change rate within the period, and generates the section absorption response offset trend information; The perturbation amplitude analysis module invokes the section absorption response offset trend information, extracts the ratio of the number of overlapping frames to the total number of frames according to the distribution range of the alcoholysis components of the polyvinyl alcohol molecule in the corresponding time section, and constructs a ratio relationship between the two parameters to generate the perturbation amplitude and component coincidence information; The unstable marking module invokes the perturbation amplitude and component coincidence information, compares it with the threshold of the alcoholysis degree fluctuation reference index, screens the section frame numbers within the deviation range, checks whether there are characteristic changes of two consecutive direction reversals in the corresponding frames in the section absorption response offset trend value. If both conditions are met, mark the time period as a fluctuation abnormal interval and generate a set of unstable marked sections of alcoholysis distribution.

[0015] Compared with the prior art, the advantages and positive effects of the present invention are as follows: In the present invention, through the selection of characteristic absorption bands in spectral data and the accurate identification of the change trend of intensity difference values, the quantitative analysis of the alcoholysis degree conversion characteristics is realized, the characterization accuracy of the polyvinyl alcohol alcoholysis degree is improved, and the complete time-series change characteristics are formed. By comparing the angular velocity differences of the absorption intensity change rates, the sensitivity to capture weak change trends is enhanced, the ability to identify trend fluctuations more accurately is provided, the analysis level of the details of the alcoholysis degree distribution is significantly improved. Through the precise calculation of the relationship between the disturbance amplitude and the component coincidence, the abnormal fluctuation interval of the alcoholysis degree component distribution can be identified, the positioning accuracy of the fluctuation abnormality is strengthened, the production process adjustment is more targeted, the quality control difficulty caused by the alcoholysis degree fluctuation is reduced, the consistency of the polyvinyl alcohol product and the stability of the application performance are improved, accurate real-time basis for product classification is provided, and the product quality differences caused by the alcoholysis degree fluctuation are reduced. Description of the Drawings

[0016] Figure 1 is the flowchart of the method of the present invention; Figure 2 is the flowchart for obtaining the spectral sequence of the characteristic absorption section of the present invention; Figure 3 is the flowchart for obtaining the set of difference fluctuation intervals of absorption peaks of the present invention; Figure 4 is the flowchart for obtaining the offset trend information of the section absorption response of the present invention; Figure 5 is the flowchart for obtaining the information on the disturbance amplitude and component coincidence of the present invention; Figure 6 is the flowchart for obtaining the set of unstable marker sections of the alcoholysis distribution of the present invention. Detailed Embodiments

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0018] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, in the description of the present invention, the meaning of "a plurality of" is two or more, unless otherwise specifically defined.

[0019] Please refer to Figure 1 , the present invention provides a technical solution: an on-line measurement method for the degree of alcoholysis distribution of polyvinyl alcohol, comprising the following steps: S1: Obtain the spectral data of the polyvinyl alcohol solution, extract the characteristic absorption band during the conversion of the ester group to the hydroxyl group in the polyvinyl alcohol molecule, select the ester group carbonyl stretching vibration band and the hydroxyl stretching vibration band as the comparison targets, record all absorption intensities within the band range in each sampling period and construct an ordered list according to the wavelength dimension to generate a characteristic absorption section spectral sequence; S2: Based on the characteristic absorption section spectral sequence, extract the ester group carbonyl absorption peak position and the hydroxyl absorption peak position respectively at each time sampling point, calculate the difference in absorption intensity between the two, and arrange them in chronological order to construct a response change sequence. Mark the change direction of the intensity difference between adjacent sampling points, extract the frame combination segments with opposite change directions, identify the starting and ending frame positions of the fluctuation, and generate a set of absorption peak difference fluctuation interval sets; S3: Call the set of absorption peak difference fluctuation interval sets, calculate the absorption peak intensity change rate vector respectively within each time interval according to the marked starting frame, center frame and ending frame, calculate the corresponding change angular velocity through the angle formed by three points, compare the direction consistency of the angular velocity in the front and back periods, and calculate the difference between the angular velocity change trend within the current section and the average absorption intensity change rate within the period to generate the section absorption response offset trend information; The angular velocity here refers to the change rate of the included angle formed by the vector change in the two-dimensional coordinate system of wavelength intensity, which is often used to measure the time sensitivity of the absorption change during the reaction process and represents the fluctuation speed of the absorption change direction per unit time; S4: Call the section absorption response offset trend information, analyze the standard deviation of the spectral signal in all sampling frames according to the section marked as having significant changes as an index for characterizing the spectral perturbation amplitude, extract the ratio of the number of overlapping frames to the total number of frames according to the distribution range of the alcoholysis components of the polyvinyl alcohol molecule within the corresponding time section, and construct a ratio relationship between the two parameters to generate the perturbation amplitude and component overlap information; The standard deviation of the spectral signal refers to the statistical dispersion of the absorption intensity in the characteristic band, which is widely used in the stability evaluation of on-line infrared analysis. The coincidence ratio index represents the relationship between the spectral stability and the component distribution consistency within the multi-component reaction range; S5: Call the perturbation amplitude and component coincidence information, compare it with the threshold of the saponification degree fluctuation reference index, screen the frame numbers of the sections outside the deviation range, and check whether there are characteristic changes with two consecutive direction reversals in the section absorption response offset trend value corresponding to the frame. If both conditions are met, mark the time period as an abnormal fluctuation interval and generate a set of unstable marked sections of the saponification distribution; The threshold of the saponification degree fluctuation reference index is a preset system stability judgment standard, usually derived from the section distribution and spectral fluctuation experience range under normal production conditions; The spectral sequence of the characteristic absorption section includes the wavelength sampling point index set, the multi-frame matrix of absorption intensity, the absorption channel time label, the initial position of the peak position within the band, and the sampling period sequence mapping value. The set of absorption peak difference fluctuation intervals includes the response direction change identification sequence, the dynamic index group of absorption intensity differences, the set of peak-to-peak amplitude jump points, the fluctuation start and end frame marking information, and the absorption section structure parameters. The section absorption response offset trend information is specifically the angular velocity change symbol structure, the period difference direction vector group, the absorption trend reversal characteristic identification, the statistical value of the vector angle change within the time period, and the spectral offset trend level index. The perturbation amplitude and component coincidence information includes the spectral standard deviation set, the number of component distribution coincidence frames within the section, the signal fluctuation and component matching coefficient, the average value of the spectral intensity change within the frame section, and the interference amplitude label index. The set of unstable marked sections of the saponification distribution specifically refers to the abnormal fluctuation section index code, the continuous direction reversal frame label, the stability offset label within the time period, the unstable area determination logic field, and the block status identification label.

[0020] Please refer to Figure 2 , and the specific steps for obtaining the spectral sequence of the characteristic absorption section are as follows: S111: Obtain the spectral data of the polyvinyl alcohol solution, identify the wavelength position and the corresponding absorption intensity value in the spectral data frame in each measurement cycle, sort the original band information according to the measurement time sequence to form a time-sequence wavelength intensity comparison table, and generate a spectral original sampling data set; To obtain the continuous spectral signal data of the polyvinyl alcohol solution collected by the infrared detection device, it is necessary to set a two-dimensional acquisition coordinate system with the sampling time as the horizontal axis and the wavelength as the vertical axis, and set the measurement frequency according to the time course law of the polyvinyl alcohol saponification reaction in the actual working condition in each cycle. Usually, the value is every collection Frame, identify all characteristic absorption values and corresponding wavelength points within the signal band in each frame, thereby forming a wavelength-intensity pair for a single frame. Subsequently, integrate and sort the continuous frame data according to the acquisition cycle time series numbering, and construct the response sequence of each wavelength point over continuous time. In actual implementation, if the solution reaction continues , the acquisition frequency is every frame, and a total of frames are acquired. The wavelength range is set to , and the wavelength step is , then the number of wavelength points per frame is , and groups of -dimensional vector groups need to be established. According to this group of data, a matrix structure with wavelength points as columns and time as rows is established. The example is as follows: Table 1 Schematic Table of Absorption Signal Frame Data Matrix ; As shown in Table 1, this data table records the absorption intensity values of specific wavelengths in different time frames, forming a basic matrix structure that can be used for feature extraction. Subsequently, operations such as band intercepting and target peak identification can be performed in the matrix structure. The data of this structure is the original spectral sampling data set. In this operation process, no threshold setting or weight assignment is involved, and only the numerical values are directly read and sorted and classified according to the acquisition results of the detection equipment. Therefore, no additional reference parameters need to be established, but the consistency of the wavelength sequence and the completeness of the data frames in each frame need to be ensured, otherwise a stable matrix structure sequence cannot be formed.

[0021] S112: Based on the original spectral sampling data set, according to the recorded spectral information, screen the wavelength sections corresponding to the ester carbonyl stretching vibration region and the hydroxyl stretching vibration region in polyvinyl alcohol, extract the continuous response values of the two types of bands in each time sequence frame, establish a response set corresponding to the band type and frame sequence, and obtain the target functional band response information; According to the complete wavelength response data recorded in each frame in the original spectral sampling data set, screen two types of bands in the ester carbonyl absorption region and the hydroxyl absorption region of polyvinyl alcohol. The former wavelength range is set to , corresponding to the stretching vibration absorption of the ester carbonyl, and the latter band is , belonging to the stretching vibration absorption of the hydroxyl. In each time frame, extract the absorption intensity values of all wavelength points within the above bands to form a response sequence, and establish a double-index mapping structure between the corresponding bands and frame indices. For example, in the th frame, the ester carbonyl absorption value sequence is , and the hydroxyl absorption value sequence is , corresponding to multiple wavelength points, and construct an index table to record the response structure of this frame. The data structure corresponding to the frame number and band type can be represented as a triple , finally, after all frames are aggregated, a target functional band response matrix will be formed. In this process, for each type of band, it is necessary to determine whether its response value shows an increasing, plateau, or decreasing trend within the same frame, and record the wavelength points where the median and maximum absorption values are located as the basic items for subsequent feature extraction. If the distribution concentration deviation of the response value of a certain band exceeds , that is, the difference between the maximum value and the median value exceeds , then this band is marked as a fluctuating state in the current frame, otherwise it is a stable state. This is the absorption intensity difference, which is used as a reference value to identify abnormal fluctuations. This value is set according to the measured peak fluctuation range when the alcoholysis rate is in the reaction interval. In actual measurement, for polyvinyl alcohol during alcoholysis, the average difference between the maximum and median values is . For error control, it is set to , and its allowable range is . Exceeding will be regarded as a severe disturbance.

[0022] S113: Invoke the target functional band response information. According to the response value sequence of each type of band, the response set is sorted in an orderly manner in the wavelength dimension and classified according to the measurement time frame, and the structure is organized into a wavelength-intensity order form with frame sequence labels to generate a characteristic absorption section spectral sequence.

[0023] Invoke the band response value sequence extracted from the target functional band response matrix. First, sort it in ascending order in the wavelength dimension to ensure the sequence consistency of the response data distribution in wavelength within each frame. Subsequently, the wavelength-intensity pairs are merged into the order form one by one according to the frame sequence to form a three-dimensional matrix structure. Using the frame sequence as the first dimension, the wavelength as the second dimension, and the response value as the third variable, a frame sequence-wavelength-response structure is constructed. Each frame forms a column of wavelength response vectors, and all frames are connected to form a response surface on the time axis. If the wavelength sampling point is , and the number of sampling frames is , then the constructed matrix size is , and the sequence style is as , forming a complete structural feature sequence. Extract the response evolution path of the peak wavelength point in this structure. If the average increase of the response value at a certain wavelength point exceeds in consecutive frames, and the maximum value appears in the last frame, then this point is marked as a characteristic transition point and recorded in the peak transition index table. The used in this judgment is the threshold of the response change rate, and this value is calculated by tripling the measured change mean of the absorption intensity change range per second , that is, , , and is set to As a conventional fluctuation limit, values exceeding this are marked as transition states. Finally, after all frame sequence tags, wavelength points, and normalized absorption values are assembled in a structured sequence, a wavelength intensity order form with frame sequence tags is formed and output as a spectral sequence of characteristic absorption sections.

[0024] Please refer to Figure 3 , and the steps for obtaining the set of absorption peak difference fluctuation intervals are specifically as follows: S211: Based on the spectral sequence of the characteristic absorption section, according to the spectral frame data corresponding to each sampling time point, locate the peak positions of the ester carbonyl absorption peak band and the hydroxyl absorption peak band within the frame respectively, extract the corresponding absorption intensity values, and establish a mapping relationship between the two to generate a functional peak position intensity control group; To obtain the spectral frame data corresponding to each sampling time point in the spectral sequence of the characteristic absorption section, a double mapping table between the wavelength index and the intensity value needs to be established for each frame in the sequence. First, within the frame, according to the set ester carbonyl absorption band interval and the hydroxyl absorption band interval perform a maximum value positioning operation. By comparing the absorption intensities of each wavelength point, filter out the wavelength point with the maximum intensity value and its corresponding value within the section, and define it as the absorption peak point within the current frame. For example, if in the th frame, the normalized intensity sequence of the hydroxyl absorption section is , then its maximum value corresponds to the wavelength , which is the hydroxyl peak point; the normalized intensity sequence of the ester carbonyl absorption section is , the maximum value is , the corresponding wavelength is , take it as the ester carbonyl peak point. Subsequently, record the two wavelength points and their intensity values corresponding to this frame in the structure mapping table, and establish a one-to-one mapping structure between the frame sequence and the two peaks, that is . Extract and summarize this triple for all frames to form a complete functional peak position intensity control group. In this operation process, no weight or threshold calculation is involved, only the maximum value within the frame is identified and extracted, and no feature transformation other than data normalization processing is required. The final output data structure is a double-peak structure corresponding to the one-dimensional frame sequence, formatted as: frame , where , and this control group provides the basic input for the next trend calculation.

[0025] S212: According to the functional peak position intensity control group, calculate the difference between the hydroxyl absorption peak intensity and the ester carbonyl absorption peak intensity, and construct a time series in the order of sampling time. Arrange the intensity differences corresponding to the time frames into a continuously changing structure, using the formula: ; Calculate the response change trend value for each time frame, mark the trend change direction as positive or negative, and obtain the peak difference trend change identification sequence; Among them, is the response change trend value of the time frame , is the normalized value of the hydroxyl absorption peak intensity at time frame , is the normalized value of the ester carbonyl absorption peak intensity at time frame , is the normalized value of the hydroxyl absorption peak intensity at time frame , is the normalized value of the ester carbonyl absorption peak intensity at time frame , is the normalized value of the hydroxyl absorption peak intensity at time frame , is the normalized value of the hydroxyl absorption peak intensity at time frame , is the total number of consecutive sampling frames for constructing the normalized trend; The response change trend value ΔDt is used to quantify the differential change characteristics of the absorption peaks of two key functional groups, hydroxyl and ester, within the same time frame, and assist in judging whether there is a synergistic reaction trend between the two; ΔDt is essentially a peak dynamic index at the single-point level of the time series. It not only considers the instantaneous absorption intensity difference between the hydroxyl and ester groups (reflecting spatial differences), but also considers the trend product of these two absorption peaks from the previous frame to the current frame (reflecting the consistency of the time evolution direction), belonging to a mixed-type local trend function dimension structure; The first term is the absorption intensity difference between the hydroxyl and ester groups in the current frame, representing the instantaneous response difference between functional groups.

[0026] The second term is the direction consistency weighting term: The numerator is the trend consistency product, greater than zero indicating the same direction, and less than zero indicating reverse fluctuations.

[0027] The denominator is the normalization of the sum of squares of the trend changes in the hydroxyl intensity sequence (to avoid short-term abnormal amplification), thereby realizing the standardization of trend synergy.

[0028] The larger the value, the greater the intensity difference between the two peaks, or the more consistent and intense the trend change direction, indicating that this frame is a typical reaction active frame. Approaching 0, the changes in the two functional groups are not obvious or in the opposite direction, and the reaction trend is unstable; For each set of data extracted from the control group based on the functional peak position intensity, construct the intensity difference change of each frame in the time series, and respectively call the current frame and the previous frame of the normalized intensity values of the hydroxyl and ester group absorption peaks , perform the product operation on the increase and decrease directions of the two absorption values, analyze whether the change trends of the two peaks are in the same direction, and then combine the absolute intensity difference between the two peaks of the current frame to calculate its comprehensive change trend value. The following formula is used: ; In this calculation process, the sample data is set as follows: Let , and at the same time take as the number of backtracking frames, and the normalized intensity value sequence is , then there is: The first intensity difference is ; The numerator of the second term is ; The denominator of the second term is ; Therefore, the integral expression is: ; Mark the positive and negative change directions of this value. If the trend directions of the current frame and the previous frame are the same, it is recorded as "positive change direction", and if they are opposite, it is marked as "negative change direction", and archive the marking structure into the trend change identification sequence. Each element in this sequence is . In this formula, factors such as "weight" and "coefficient" are not used, all values are directly constructed based on the peak values, and the trend judgment is calculated based on the difference direction relationship without introducing adjustment terms.

[0029] S213: Based on the peak difference trend change identification sequence, locate and extract the trend symbol reversal points according to the trend change directions between consecutive frames, and expand one frame on both sides of the reversal point to form a change segment combination, which is marked as the response fluctuation start and end frame combination. Extract the corresponding time index and number in the combination to establish a time period list, and generate the absorption peak difference fluctuation interval set.

[0030] According to the trend identification of each frame in the peak difference trend change identification sequence, locate and extract the nodes where the trend symbols of the two frames before and after in the time series are reversed. If the identification of a certain frame is positive change direction and the next frame is negative change direction, then the current frame is the reversal point. Expand one frame on both sides of the reversal point to form the frame combination segment structure, and mark this structure as the fluctuation segment. Repeatedly extract the reversal combination structure in multiple frame segments and number it to form a time index sequence, and at the same time mark the frame number range. For example , and uniformly file them into the response fluctuation segment index table, setting it as (segment number, start frame, end frame) so that subsequent structures can identify and perform segmented comparison operations on trend features. Finally, organize all the fluctuation segment identifiers and output them as the set of absorption peak difference fluctuation intervals. No threshold setting or benchmark judgment is involved in this process. The construction of all fluctuation segments only depends on the number of trend reversals and the calculation results of frame indices, belonging to the extraction of a direct operation structure.

[0031] Please refer to Figure 4 , and the specific steps for obtaining the information on the offset trend of the absorption response in the section are as follows: S311: Call the set of absorption peak difference fluctuation intervals to obtain three groups of band response data corresponding to the start frame, center frame, and end frame. Extract the normalized absorption intensity values of the hydroxyl absorption peak and the ester carbonyl absorption peak in each frame, respectively construct a first-order difference structure with time as the sequence, obtain the intensity change path composed of three points, and generate a vector group of absorption peak compositions; Call the index of each time period recorded in the set of absorption peak difference fluctuation intervals. First, it is necessary to clarify the specific numbers of the start frame, middle frame, and end frame marked in each time period, and extract the complete wavelength response data corresponding to the frame numbers from the spectral sequence of the characteristic absorption section. In this data, according to the ester carbonyl absorption band and the hydroxyl absorption band , respectively find the wavelength points with the maximum normalized intensity in each frame, and extract their intensity values as the absorption peak response values within the frame, forming binary pair structure. Set the section number as , and its frame number as . Then, construct a data sequence by extracting the response values from the three frames. For example, the hydroxyl absorption intensity of the 22nd frame , and the ester absorption intensity ; the hydroxyl absorption intensity of the 23rd frame , and the ester absorption intensity ; the hydroxyl absorption intensity of the 24th frame , and the ester absorption intensity [[ID=3t]]. Subsequently, using the time frame order as the benchmark for vector construction, calculate the first-order differences between frames of the absorption values of each molecular group. For example, the hydroxyl vector is , and the differences are and ; the ester carbonyl vector is , and the difference is and . Use the two groups of difference sequences to construct change vectors from the start frame to the center frame and from the center frame to the end frame respectively, forming , , that is, the intensity change path composed of three points, and record it in the vector group of absorption peak compositions to provide a data basis for the next analysis of angular velocity and trend direction.

[0032] S312: According to the absorption peaks, form a vector group, extract the vectors corresponding to the starting frame, the central frame, and the ending frame, calculate the angle between two segments of vectors through coordinate space angle calculation, divide the angle by the time interval to obtain the angular velocity corresponding to the change in absorption intensity of each segment, call the calculation results of the angular velocities within adjacent time sections for direction consistency comparison, construct trend evolution data, and use the formula: ; Obtain the offset trend value of the absorption peak response section through the operation; Among them, is the offset trend value of the th absorption peak response section, is the vector of the change in absorption intensity from the starting frame to the central frame in the th absorption peak response section, is the vector of the change in absorption intensity from the central frame to the ending frame in the th absorption peak response section, is the dot product of the two vectors of the change in absorption intensity in the th section, is the modulus length of the vector in the th section, is the modulus length of the vector in the th section, is the average value of the angles between all the vectors of the change in absorption intensity formed by the time frames included in the th absorption peak response section, is the standard deviation of the angles between all the vectors of the change in absorption intensity formed by the time frames included in the th absorption peak response section; The offset trend value Ψz is a section-level structural response quantity, used to quantify the degree of angular bending of the absorption peak intensity path composed of three frames in the vector space, and to measure the trend consistency and structural stability of the intensity change path.

[0033] Ψz belongs to the typical angular dimension characteristic, reflecting the non-linear offset between the directions of two vectors, and considering the difference degree between the local trend change and the overall stability of the section.

[0034] is the front-back change vector (temporal gradient of absorption intensity) composed of three-frame segments; is the angle calculation, reflecting the degree of trend turning; is the mean value and standard deviation of the angles of all three-frame vectors in this section, used to normalize this angle change; The numerator reflects the degree of trend deviation, and the denominator is used to suppress the weight of the large fluctuation section; A larger Ψz indicates that there is a trend reversal or mutation in the absorption path of the current section; Ψz approaching 0 represents stable trend changes and small angular deviations, which is a sign of stable system response; According to the three-point data structure in the vector group composed of absorption peaks, the cosine angle formula is used in the two-dimensional vector space to calculate the angle between the vectors and to determine its degree of trend bending, and then divide by the time interval to obtain the angular velocity value. Taking the , constructed in Paragraph 1 as an example, first calculate the inner product as , and the moduli are , , and then we get: ; This value represents the absorption response trend deviation degree of the section. Subsequently, all trend values in different sections are numbered and recorded according to the time sequence to form a trend sequence structure. The benefit of this formula is that by participating in the inner product, modulus length, and normalized angle dispersion parameters simultaneously, the trend deviation expression does not depend on the single-frame change rate, but reflects the structural response relationship between the combined changes in multiple directions and their deviation from the stable reference, effectively characterizing the structural offset performance of absorption reversal within the section.

[0035] S313: According to the offset trend values of the absorption peak response section, retrieve the increase and decrease changes of each trend value between two adjacent time periods, calculate the occurrence frequency of the trend offset turning points in the change direction sequence, and perform cross-statistics in combination with the judgment results of the consistency between the frequency and the angular velocity direction to establish a distribution state index table between trend changes and direction stability, and generate the offset trend information of the section absorption response.

[0036] According to the sequence of absorption response offset trend values, between two adjacent time periods, extract and record the increase and decrease change directions of the trend value . Mark the positive increase as "rising" and the negative decrease as "falling". Index and label the frame sequence of all sign reversal nodes of "rising → falling" or "falling → rising", and count their cumulative frequency in the whole sequence. For example, if there are 14 direction reversal points in 45 sections, the frequency is Meanwhile, extract the number of positive and negative switching times of the angular velocity direction change trend in each section. For example, if the direction change pattern in section z within the frame sequence segment is "positive, positive, negative, negative, positive", then count that the direction switches 2 times. Combine the above reverse frequency information, and establish a trend-direction stability cross structure by comparing the cross-occurrence positions of the two in adjacent sections, and finally uniformly record the structure index , forming complete trend and direction distribution mapping information, and outputting it as section absorption response offset trend information. No additional thresholds, weights, or coefficients are introduced in this process. All structure construction is only based on the recognition of the relationship between trend values and direction sequences, without the need to set parameters or adjustment items, ensuring that the data results come from the inherent characteristics of the response sequence.

[0037] Please refer to Figure 5 , and the specific steps for obtaining the perturbation amplitude and component coincidence information are as follows: S411: Invoke the section absorption response offset trend information. According to the time section marked as significantly changing, extract the characteristic absorption band response values of the sampling frames from the corresponding section, perform deviation square processing on the normalized intensity of the main absorption peak in each frame, and calculate the average standard deviation within the section to obtain the spectral perturbation amplitude parameter set; Invoke the time sections marked as significantly changing in the section absorption response offset trend value. First, confirm the frame range index number of each marked section, and extract the complete wavelength response structure within the corresponding frame in the spectral sequence of the characteristic absorption section. Locate the maximum normalized absorption intensity values of the ester carbonyl absorption peak and the hydroxyl absorption peak in each frame, record their values as the main absorption peak values, and establish a sequence set , where is the section number, is the frame index. Subsequently, calculate the mean difference between this main peak value in each frame and the mean value of all main peak values in this section, that is, for all normalized absorption intensity values of the absorption peaks within the frames, first calculate the average value of this section , where is the total number of frames within this section, and then perform difference square [[ID= 27]] on each frame, and take the average of all results within the entire section and then take the square root to obtain the standard deviation of this section. For example, in the section, assume there are sampling frames in total, and the normalized absorption intensity values of the absorption peaks are respectively. Calculate their mean value as , and the square deviations of each frame are respectively. The sum is , and the square root gives the standard deviation as . Record this value as the spectral perturbation amplitude parameter of the current section. After performing the above operations on all sections in sequence, summarize and form the spectral perturbation amplitude parameter set.

[0038] S412: Call the spectrum perturbation amplitude parameter set, extract the alcoholysis component distribution interval of each frame detected in the polyvinyl alcohol solution according to the sampling index range of each time period, count the number of frames with overlapping components in each frame within the time segment, and compare it with the total number of frames in the segment to form a proportional relationship, using the formula: ; The composite index of each absorption segment is obtained by calculation, and the structural sequence of each segment is combined to sort and number them, generating the perturbation amplitude and component coincidence information; in, Indicates the The composite index of the absorption segment, Indicates the In the section The normalized intensity value of the absorption peak of the frame, represents the mean absorption intensity of all sampling frames in the segment, Indicates the The number of frames with overlapping components in a segment, Indicates the The total number of sampling frames in the segment, Indicates the Theoretical overlap ratio of components within each segment; The composite index Φk is used to measure the comprehensive performance between the spectral perturbation amplitude of a certain absorption segment and the overlap between the distribution of alcoholysis components. It is a composite stability evaluation index with mixed dimensions. This index integrates,the discreteness of the spectral response reflecting the perturbation intensity,the gap between the measured coincidence rate and the theoretical stable coincidence rate (reflecting the consistency of the components); Φk serves as a coordination index between spectral stability and response consistency in the system; The numerator is the standard deviation (fluctuation amplitude) of the main absorption peak intensity within the segment; The denominator is the deviation from component consistency: is the actual component overlap rate; The ideal overlap ratio set theoretically (usually derived from experimental conditions); The larger the difference, the more serious the distribution deviation.

[0039] The larger Φk is, the more severe the fluctuation is, and the component overlap deviates from expectations, reflecting the poor stability of the section. Φk is close to 0: it indicates that the disturbance is small and the components are well matched, which represents the ideal state of the system; According to the spectrum perturbation amplitude parameter, each segment is concentrated The time frame index range is used to extract the alcoholysis component distribution information in the polyvinyl alcohol solution frame by frame, and the distribution interval within each frame is obtained. For example, in the frame, the alcoholysis component is , and there is an overlapping interval with the previous frame . Then this frame is marked as a "component overlapping frame", and the frame numbers of all frames with overlapping intervals within the section are accumulated to obtain the number of component overlapping frames . Then it is divided by the total number of frames to form a ratio. The theoretical overlapping ratio corresponding to the section is introduced. This value comes from the consistency ratio of the component intervals in the experimental stable state of polyvinyl alcohol under the set process conditions. Taking the overlapping proportion of the alcoholysis rate fluctuating in the interval under stable operating conditions as a reference, the theoretical overlapping ratio is set as . Substitute it into the formula: ; Taking the result in Paragraph 1 as an example, assume the standard deviation is , the number of frames in the section is , and the number of overlapping frames is . Then the ratio is . The denominator calculated is . The final composite index is . After summarizing all sections , they are in one-to-one correspondence with the section index structure, numbered in chronological order or according to the composite value size to form a sequence, and output as the disturbance amplitude and component overlapping information.

[0040] S413: According to the disturbance amplitude and component overlapping information, after sorting by the exponential value, divide the disturbance level intervals, correspondingly mark the section numbers and level statuses, and uniformly encode the distribution characteristics, disturbance amplitude, and frame overlapping structure as evaluation parameters to obtain the disturbance amplitude and component overlapping information.

[0041] According to the composite index corresponding to each section in the disturbance amplitude and component overlapping information, sort its value from small to large, divide the disturbance level intervals, and a reference level threshold can be set as . The corresponding disturbance levels are low, medium, and high respectively. Each section is classified and marked according to the interval where its composite index is located. For example, is classified into the medium disturbance level. Subsequently, the related attributes such as section numbers, disturbance levels, positions, overlapping rates, standard deviations, etc. are encoded to form a multi-field structure index table, and the format of this table is as , a complete feature evaluation structure is formed. The output is the perturbation amplitude and component coincidence information, which provides a quantitative reference basis for downstream stability evaluation and abnormal segment screening. This process does not involve setting new thresholds or weight terms, and all operations are completed based on the established index structure and existing numerical inputs.

[0042] Please refer to Figure 6 , and the steps for obtaining the unstable labeled segment set of alcoholysis distribution are specifically as follows: S511: Call the perturbation amplitude and component coincidence information, compare the composite index data of each segment with the set threshold of the alcoholysis degree fluctuation reference index, screen the segment frame indexes whose composite index deviates from the reference threshold, establish classification labels corresponding to the deviation directions, and obtain the sequence of frame numbers with composite index deviation; Call the composite index of each segment in the perturbation amplitude and component coincidence information As input data, it is necessary to first set the threshold of the alcoholysis degree fluctuation reference index to identify whether the current segment has a stability shift. This threshold is obtained through empirical evaluation combined with the fluctuation safety interval. In experimental statistics, when the composite fluctuation index value of polyvinyl alcohol exceeds , problems such as uneven film thickness and viscosity deviation begin to appear in the product performance. Therefore, the threshold of the alcoholysis degree fluctuation reference index is set to , and this value is used to judge whether the current segment index deviates from the reference state. For each and are compared. If or is satisfied, it is marked as the "upward deviation" or "downward deviation" type, otherwise it is regarded as "stable".

[0043] For example: If the composite index of segment number is , then the difference is , belonging to "upward deviation"; if the composite index of segment is , the difference is , belonging to "downward deviation". Finally, a corresponding set of frame numbers and deviation direction labels is formed, such as , and the structure of this set is the sequence of frame numbers with composite index deviation, which is used for subsequent trend direction judgment processing.

[0044] S512: According to the sequence of frame numbers with composite index deviation, extract the change labels of the angular velocity direction of the corresponding frames in the segment absorption response offset trend value, continuously traverse the trend change identifiers between frames, count the number of adjacent frame pairs with direction reversal, screen the segments with the cumulative number exceeding two groups and mark their numbers, and generate a set of segments with trend direction reversal; According to all segment numbers extracted from the sequence of frame numbers with composite index deviation , retrieve the angular velocity direction change information recorded in the corresponding section absorption response offset trend value in sequence, compare the direction identifier of the current frame with that of the next frame frame by frame in each deviation section, record the reversal behavior of "positive → negative" or "negative → positive", and perform cumulative statistics on the frame pairs with direction reversals. If the number of consecutive direction reversals in the same section exceeds two groups, it is determined as a trend reversal section. For example, if section contains a frame sequence of , and the direction identifiers are in sequence , then and have two reversals. Plus , if it is "- → +", it is counted as three reversals, meeting the screening criteria of being greater than 2, and is added to the set of reversal identification sections. Finally, organize the section numbers of all sections that meet the reversal conditions into a structure set, in the format of , and output it as a set of trend direction reversal sections for subsequent cross-matching with the deviation frame numbers.

[0045] S513: Call the compound index deviation frame number sequence and the set of trend direction reversal sections, extract the intersection of the two and merge and mark it as an abnormal state with the section frame number as the primary key, establish section labels, start and end frame indexes, and stability judgment identifiers, and generate an unstable label section set for the alcoholysis distribution.

[0046] Call all the section number information extracted from the compound index deviation frame number sequence and the set of trend direction reversal sections, perform set intersection calculation, perform matching and merging operations on the numbers that appear in both sets, confirm that it is a section where the stability structure is abnormal, use this intersection structure as the basis for abnormal identification, and supplement the start frame number of the section in each successfully matched section , end frame number and the original trend offset value , and set the status field to "abnormal mark". Uniformly construct the output structure table entry as . After summarizing all the matching item sets, output it as an unstable label section set for the alcoholysis distribution. This structure is the core criterion for finally determining the abnormal sections of system fluctuations. This process is only based on the combination of existing numerical calculation results and does not involve additional set parameters or assumed functions, ensuring a closed-loop closed set of data sources.

[0047] An on-line measurement system for the degree of alcoholysis distribution of polyvinyl alcohol, the system includes: The characteristic spectrum recognition module obtains the spectral data of the polyvinyl alcohol solution, extracts the characteristic absorption band during the process of the ester group in the polyvinyl alcohol molecule being converted into a hydroxyl group, records all the absorption intensities within the band range in each sampling period and constructs a sequential list according to the wavelength dimension, and generates a characteristic absorption section spectral sequence; The fluctuation range identification module marks the change direction of the intensity difference between adjacent sampling points based on the spectral sequence of the characteristic absorption section, extracts the frame combination segments with opposite change directions, identifies the starting and ending frame positions of the fluctuation, and generates a set of absorption peak difference fluctuation ranges; The offset trend analysis module calls the set of absorption peak difference fluctuation ranges, calculates the absorption peak intensity change rate vector in each time interval respectively, calculates the difference between the angular velocity change trend in the current section and the average absorption intensity change rate in the period, and generates the section absorption response offset trend information; The perturbation amplitude analysis module calls the section absorption response offset trend information, extracts the ratio of the number of overlapping frames to the total number of frames according to the distribution range of the alcoholysis components of polyvinyl alcohol molecules in the corresponding time section, and constructs a ratio relationship between the two parameters to generate the perturbation amplitude and component overlap information; The instability marking module calls the perturbation amplitude and component overlap information, compares it with the threshold of the alcoholysis degree fluctuation reference index, screens the frame numbers of the sections outside the deviation range, and checks whether there are characteristic changes with two consecutive direction reversals in the section absorption response offset trend values corresponding to the frames. If both conditions are met, the time period is marked as a fluctuation abnormal range, and a set of unstable marked sections of alcoholysis distribution is generated.

[0048] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as the technical solution content of the present invention is not departed from, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. On-line measurement method for degree of alcoholysis distribution of polyvinyl alcohol, characterized in that, It includes the following steps: S1: Obtain the spectral data of the polyvinyl alcohol solution, extract the characteristic absorption band during the process of the ester group in the polyvinyl alcohol molecule being converted into a hydroxyl group, record all absorption intensities within the band range in each sampling period, and construct an ordered list according to the wavelength dimension to generate a characteristic absorption section spectral sequence; S2: Based on the characteristic absorption section spectral sequence, mark the change direction of the intensity difference between adjacent sampling points, extract the frame combination segments with opposite change directions, identify the starting and ending frame positions of the fluctuation, and generate a set of absorption peak difference fluctuation intervals; S3: Invoke the set of absorption peak difference fluctuation intervals, calculate the absorption peak intensity change rate vector respectively within each time interval, calculate the difference between the angular velocity change trend within the current section and the average absorption intensity change rate within the period, and generate the section absorption response offset trend information; S4: Invoke the section absorption response offset trend information, extract the ratio of the number of overlapping frames to the total number of frames according to the distribution interval of the alcoholysis components of the polyvinyl alcohol molecule within the corresponding time section, and construct a ratio relationship between the two parameters to generate the disturbance amplitude and component overlap information.

2. The online measurement method for the degree of alcoholysis distribution of polyvinyl alcohol according to claim 1, wherein, The characteristic absorption section spectral sequence includes a wavelength sampling point index set, a multi-frame matrix of absorption intensities, an absorption channel time tag, the initial position of the peak position within the band, and a sampling period sequence mapping value. The set of absorption peak difference fluctuation intervals includes a response direction change identification sequence, a dynamic index group of absorption intensity differences, a set of peak-to-peak amplitude jump points, fluctuation starting and ending frame marking information, and absorption section structure parameters. The section absorption response offset trend information is specifically an angular velocity change sign structure, a period difference direction vector group, an absorption trend reversal characteristic identifier, a statistical value of the vector angle change within the time period, and a spectral offset trend level index. The disturbance amplitude and component overlap information includes a spectral standard deviation set, the number of overlapping frames of the component distribution within the section, a signal fluctuation and component matching coefficient, the average spectral intensity change within the frame section, and an interference amplitude label index.

3. The online measurement method of the degree of alcoholysis distribution of polyvinyl alcohol according to claim 2, wherein, The specific steps for obtaining the characteristic absorption section spectral sequence are as follows: S111: Obtain the spectral data of the polyvinyl alcohol solution, identify the wavelength positions and corresponding absorption intensity values in the spectral data frames in each measurement period, organize the original band information according to the measurement time sequence to form a time sequence wavelength intensity comparison table, and generate a spectral original sampling data set; S112: Based on the spectral original sampling data set, according to the recorded spectral information, screen the wavelength sections corresponding to the carbonyl stretching vibration region and hydroxyl stretching vibration region of the ester group in the polyvinyl alcohol, extract the continuous response values of the two types of bands in each time sequence frame, establish a response set corresponding to the band type and frame order, and obtain the target functional band response information; S113: Invoke the target functional band response information, perform an ordered arrangement of the response set in the wavelength dimension according to the response value sequence of each type of band and classify it according to the measurement time frame, and organize the structure into a wavelength intensity order form with a frame order label to generate a characteristic absorption section spectral sequence.

4. The on-line measurement method for the degree of alcoholysis distribution of polyvinyl alcohol according to claim 3, characterized in that, The specific steps for obtaining the set of absorption peak difference fluctuation intervals are as follows: S211: Based on the spectral sequence of the characteristic absorption section, according to the spectral frame data corresponding to each sampling time point, locate the peak positions of the ester carbonyl absorption peak band and the hydroxyl absorption peak band respectively within the frame, extract the corresponding absorption intensity values, establish the mapping relationship between the two, and generate a functional peak position intensity control group; S212: According to the functional peak position intensity control group, calculate the difference between the hydroxyl absorption peak intensity and the ester carbonyl absorption peak intensity, construct a time series in the order of sampling time, arrange the intensity differences corresponding to the time frames into a continuously changing structure, calculate the response change trend value of each time frame through operation, and mark the trend change direction as a positive change direction or a negative change direction to obtain a peak difference trend change identification sequence; S213: Based on the peak difference trend change identification sequence, according to the trend change direction between consecutive frames, locate and extract the trend symbol reversal points, expand one frame on both sides of the reversal points to form a change segment combination, mark it as the response fluctuation start and end frame combination, extract the corresponding time indices in the combination and number them to establish a time period list, and generate a set of absorption peak difference fluctuation intervals.

5. The online measurement method for the degree of alcoholysis distribution of polyvinyl alcohol according to claim 4, characterized in that The specific steps for obtaining the offset trend information of the section absorption response are as follows: S311: Call the set of absorption peak difference fluctuation intervals, obtain three groups of band response data of the corresponding start frame, center frame, and end frame, extract the normalized absorption intensity values of the hydroxyl absorption peak and the ester carbonyl absorption peak in each frame, respectively construct a first-order difference structure with time as the sequence, obtain the intensity change path composed of three points, and generate a vector group of absorption peak compositions; S312: According to the vector group of absorption peak compositions, extract the vectors corresponding to the start frame, center frame, and end frame points, calculate the angle between the two segments of vectors through coordinate space angle operation, divide the angle by the time interval, obtain the angular velocity corresponding to each segment of absorption intensity change, call the calculation results of the angular velocity in adjacent time sections for direction consistency comparison, construct trend evolution data, and calculate the offset trend value of the absorption peak response section through operation; S313: According to the offset trend value of the absorption peak response section, retrieve the increase and decrease changes of each trend value between adjacent two time periods, calculate the occurrence frequency of the trend offset turning points in the change direction sequence, perform cross-statistics in combination with the frequency and the angular velocity direction consistency judgment result, establish a distribution state index table between trend changes and direction stability, and generate the offset trend information of the section absorption response.

6. The on-line measurement method for the degree of alcoholysis distribution of polyvinyl alcohol according to claim 5, characterized in that, The specific steps for obtaining the perturbation amplitude and component overlap information are as follows: S411: Call the offset trend information of the section absorption response, according to the time section marked as prominent change, extract the characteristic absorption band response values of the sampling frames from the corresponding section, perform deviation square processing on the normalized intensity of the main absorption peak in each frame, and calculate the average standard deviation within the section to obtain a set of spectral perturbation amplitude parameters; S412: Call the spectral perturbation amplitude parameter set, extract the alcoholysis component distribution range detected in each frame in the polyvinyl alcohol solution according to the sampling index range of each time period, count the number of frames with overlapping components in each frame within the time period, compare it with the total number of frames in the period to form a proportional relationship, calculate the composite index of each absorption section, sort and number according to the structural sequence of each section, and generate the perturbation amplitude and component overlap information; S413: According to the perturbation amplitude and component overlap information, divide the perturbation level range after sorting by the exponential value, mark the section number and level status correspondingly, uniformly encode the distribution characteristics, perturbation amplitude, and frame overlap structure as evaluation parameters, and obtain the perturbation amplitude and component overlap information.

7. The on-line measurement method for the degree of alcoholysis distribution of polyvinyl alcohol according to claim 6, characterized in that, The method further includes the following steps: S5: Call the perturbation amplitude and component overlap information, compare it with the alcoholysis degree fluctuation reference index threshold, screen the section frame numbers outside the deviation range, check whether there are characteristic changes of two consecutive direction reversals in the absorption response offset trend value of the corresponding frame in the section. If both conditions are met, mark the time period as an abnormal fluctuation interval, and generate an unstable alcoholysis distribution marked section set; The unstable alcoholysis distribution marked section set specifically refers to the abnormal fluctuation section index code, continuous direction reversal frame label, in-period stability offset label, unstable area determination logic field, and block status identification label.

8. The online measurement method for the degree of alcoholysis distribution of polyvinyl alcohol according to claim 7, characterized in that, The specific steps for obtaining the unstable alcoholysis distribution marked section set are as follows: S511: Call the perturbation amplitude and component overlap information, compare it with the set alcoholysis degree fluctuation reference index threshold according to the composite index data of each section, screen the section frame indexes with the composite index deviating from the reference threshold, establish a classification label corresponding to the deviation direction, and obtain the composite index deviation frame number sequence; S512: According to the composite index deviation frame number sequence, extract the angular velocity direction change label of the corresponding frame in the section absorption response offset trend value, continuously traverse the inter-frame trend change identifier, count the number of adjacent frame pairs with direction reversals, screen the sections with more than two groups accumulated and mark the numbers, and generate a trend direction reversal section set; S513: Call the composite index deviation frame number sequence and the trend direction reversal section set, extract their intersection and merge and mark it as an abnormal state with the section frame number as the main key, establish a section label, start and end frame indexes, and stability judgment identifier, and generate an unstable alcoholysis distribution marked section set.

9. An on-line measurement system for the degree of alcoholysis distribution of polyvinyl alcohol, characterized in that, The system is used to implement the online measurement method for the alcoholysis degree distribution of polyvinyl alcohol described in any one of claims 1-8. The system includes: The characteristic spectrum recognition module obtains the spectrum data of the polyvinyl alcohol solution, extracts the characteristic absorption band during the conversion of ester groups in polyvinyl alcohol molecules into hydroxyl groups, records all absorption intensities within the band range in each sampling period, constructs an ordered list according to the wavelength dimension, and generates a characteristic absorption section spectrum sequence; The fluctuation interval recognition module, based on the characteristic absorption section spectrum sequence, marks the change direction of the intensity difference between adjacent sampling points, extracts the frame combination segments with opposite change directions, identifies the positions of the starting and ending frames of the fluctuation, and generates a set of absorption peak difference fluctuation intervals; The offset trend analysis module calls the set of absorption peak difference fluctuation intervals, calculates the absorption peak intensity change rate vector respectively within each time interval, calculates the difference between the angular velocity change trend within the current section and the average absorption intensity change rate within the period, and generates the section absorption response offset trend information; The disturbance amplitude analysis module calls the section absorption response offset trend information, extracts the ratio of the number of overlapping distribution frames to the total number of frames according to the distribution interval of the alcoholysis components of polyvinyl alcohol molecules within the corresponding time section, and constructs a ratio relationship between the two parameters to generate the disturbance amplitude and component overlap information; The instability marking module calls the disturbance amplitude and component overlap information, compares it with the alcoholysis degree fluctuation reference index threshold, screens the section frame numbers within the deviation range, and checks whether there are characteristic changes of two consecutive direction reversals in the section absorption response offset trend values corresponding to the frames. If both conditions are met, the time period is marked as a fluctuation abnormal interval, and an alcoholysis distribution instability marked section set is generated.

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