Ultraviolet spectrum nitrate measurement method and system based on pulse number self-adaption

Abstract

The application belongs to the technical field of optical sensing and water quality analysis, and relates to a nitrate measurement method and system based on pulse number self-adaption. The measurement method comprises the following steps: under a preset fixed integration time, a calibration mapping model between nitrate concentration and single pulse net signal is established; when a water sample to be detected is detected or a sudden change of a detection signal is detected, a xenon lamp is controlled to operate in a single pulse mode, an initial detection signal and a corresponding initial net signal are obtained; based on the initial net signal, a corresponding target pulse number is determined; within the fixed integration time, the xenon lamp is controlled to emit light pulses with the target pulse number, a spectral detector is controlled to accumulate and integrate photo-generated charges generated by each light pulse, and a total detection signal is obtained after the integration ends; based on the total detection signal, an equivalent single pulse net signal is obtained; and the equivalent single pulse net signal is input into the calibration mapping model to obtain the nitrate concentration of the water sample to be detected.

Description

Technical Field

[0001] This application belongs to the field of optical sensing and water quality analysis technology, and particularly relates to a method and system for measuring nitrate using ultraviolet spectroscopy based on pulse number adaptive. Background Technology

[0002] In the field of water quality monitoring, ultraviolet spectroscopy for nitrate concentration detection has advantages such as fast response and no reagent required, and has been widely used in online monitoring scenarios. However, since the nitrate concentration in actual water bodies varies greatly, how to achieve wide-range detection while ensuring measurement accuracy has become a key issue in the design of this type of sensor.

[0003] To address the aforementioned issues, one feasible solution in the existing technology is to introduce a dynamic amplification mechanism in the signal processing stage at the receiving end. This mechanism adaptively adjusts the amplification factor based on the received signal strength, thereby extending the measurement range to some extent. However, due to inherent noise in the circuit itself, noise is amplified simultaneously with signal amplification, leading to a decrease in the signal-to-noise ratio and affecting the accuracy of the measurement results. Furthermore, complex algorithms are typically required for effective signal extraction, increasing the complexity of system implementation.

[0004] Furthermore, according to the principle of light absorption, the absorbance of the sample to be tested is directly related to the length of the light propagation path in the solution. Therefore, the measurement range can also be extended by adjusting the optical path length. For example, patent CN111537448A proposes to change the optical path length by sliding a partition to adapt to the detection needs of different concentration ranges. However, this type of method relies on mechanical moving structures, which not only places high demands on the sealing performance of the sensor, but also makes the moving parts prone to wear during long-term operation, thereby causing performance degradation or even failure, reducing the reliability and service life of the system.

[0005] On the other hand, traditional multi-integration-time adaptive methods adapt to different signal intensities by switching different integration times, thereby achieving range extension. However, since changes in integration time will cause changes in dark noise characteristics and response baseline, a calibration model needs to be established for each integration time, resulting in a large calibration workload, high data storage requirements, and complex subsequent maintenance, which limits its application in practical engineering.

[0006] In summary, how to achieve wide-range, high-precision ultraviolet spectroscopy nitrate measurement without introducing noise through signal amplification, without requiring mechanical adjustment structures, and without increasing calibration complexity has become a pressing technical problem in this field. Summary of the Invention

[0007] To address the aforementioned technical issues, this application proposes a method and system for measuring nitrate using ultraviolet spectroscopy based on pulse number adaptation. By establishing a calibration mapping relationship between the net single-pulse signal and nitrate concentration under a fixed integration time, and adaptively determining the target pulse number based on the initial net signal, multi-pulse cumulative measurement and equivalent single-pulse normalization processing are achieved within a single integration period. This enables a synergistic improvement in wide measurement range and high signal-to-noise ratio without introducing additional noise amplification or requiring mechanical adjustment structures, thereby enhancing measurement accuracy and system stability.

[0008] To achieve the above objectives, the first aspect of this application provides a method for measuring nitrate using ultraviolet spectroscopy based on pulse number adaptation, comprising the following steps: A calibration mapping model between nitrate concentration and single-pulse net signal is established under a preset fixed integration time. When testing the water sample, or when a sudden change in the detection signal is detected, the xenon lamp is controlled to operate in single-pulse mode to obtain the initial detection signal and the corresponding initial net signal. Based on the initial net signal, determine the corresponding target pulse count; Within a fixed integration time, the xenon lamp emits light pulses of the target number of pulses, so that the spectral detector accumulates and integrates the photogenerated charge generated by each light pulse, and obtains the total detection signal after the integration is completed. Based on the total detection signal, the equivalent single-pulse net signal is obtained; The equivalent single-pulse net signal is input into the calibration mapping model to obtain the nitrate concentration of the water sample to be tested.

[0009] In some embodiments, the setting of the fixed integration time simultaneously satisfies both the anti-saturation condition and the timing tolerance condition, wherein: The anti-saturation condition is as follows: when measuring pure water samples, the xenon lamp is controlled to emit a single pulse, the output signal of the spectral detector is within the linear response region, and a preset safety margin is retained; The timing tolerance condition is: ,in, This represents the maximum number of pulses allowed under safety margin constraints. For single pulse width, This is the minimum interval between adjacent pulses.

[0010] In some embodiments, the method for establishing the calibration mapping model is as follows: Prepare a nitrate standard solution covering the target concentration range; Under a fixed integration time, a single pulse measurement was performed on each nitrate standard solution, the corresponding spectral response signal was acquired and dark noise correction was performed to obtain the net response signal of each nitrate standard solution. Based on the net response signal, characteristic wavelength signals characterizing the absorption properties of nitrate ions are extracted. A calibration mapping model is constructed based on the characteristic wavelength signals of each nitrate standard solution and their corresponding concentration data.

[0011] In some embodiments, the method for determining the target pulse number is as follows: Initial net signal With the preset optimal signal range Compare; when < At that time, according to the formula Determine the number of target pulses and limited ≤ This ensures that the total pulse duration is contained within a fixed integral time; where round indicates rounding to the nearest integer. when Located in the preset optimal signal range Within the time frame, provided that the timing tolerance conditions are met, the target pulse count is determined. Set to an integer greater than 1; when > At that time, the target pulse count Set to 1.

[0012] In some embodiments, the measurement method further includes a xenon lamp aging monitoring and automatic compensation step, specifically including: A reference optical path is set up to extract a portion of the light energy from each emitted pulse of light as a reference signal; The reference signal is acquired in real time to obtain the reference optical signal; The reference optical signal is accumulated and processed, and the degree of attenuation of the xenon lamp output energy is determined based on the deviation between the accumulated processing result and the initial calibration reference. ; Based on the degree of attenuation The number of target pulses is compensated and corrected to ensure that the accumulated light energy within each fixed integration time is maintained within a preset energy range. The compensation and correction formula is as follows: ,in, Indicates rounding up; The target pulse count is updated after light source aging compensation. When the degree of decay When the preset attenuation threshold is reached, a xenon lamp replacement prompt is triggered, and the initial calibration reference is reset after the xenon lamp replacement is completed.

[0013] In some embodiments, the method for obtaining the equivalent single-pulse net signal is as follows: Total detection signal Based on the target pulse count after compensation and correction Normalization was performed, and dark signals were subtracted. The equivalent net single-pulse signal is obtained. This can be expressed as a formula: .

[0014] In some embodiments, the method for accumulating and integrating photogenerated charges is as follows: Obtain the xenon lamp trigger pulse sequence and its corresponding integral gating signal; The integration is initiated first in response to the rising edge of the integration gate signal, and then the xenon lamp is triggered to emit light pulses to generate photogenerated charge, and the photogenerated charge is collected during the integration process; The collection of photogenerated charge is terminated in response to the falling edge of the integral gating signal, and charge transfer and readout are performed. Based on the target number of pulses, the xenon lamp trigger pulse sequence and integral gating signal are synchronously controlled so that the photogenerated charge generated by each pulse is accumulated within the same fixed integral time.

[0015] In some embodiments, the measurement method further includes an automated verification step for the effectiveness of nitrate concentration, specifically including: Step S1: Compare the nitrate concentration with the effective working range of the calibration mapping model. If it exceeds the effective working range, generate a corresponding anomaly marker; if it is within the effective working range, proceed to step S2. Step S2: Determine the equivalent single-pulse net signal according to the preset signal quality criteria. If the preset signal quality criteria are not met, trigger the retest process; if they are met, proceed to step S3. Step S3: Statistically compare the nitrate concentration with the historical valid measurement results. If the deviation between the two exceeds the preset deviation threshold, execute the initialization process of resetting the pulse count to 1 and remeasure. If the deviation does not exceed the preset deviation threshold, proceed to step S4. Step S4: Based on the residuals of the calibration mapping model, the level of dark noise signal, and the pulse energy fluctuation, the expanded uncertainty and the corresponding confidence interval of this measurement result are obtained.

[0016] In some embodiments, the preset signal quality criterion includes a signal-to-noise ratio (SNR) criterion, wherein the SNR is the ratio of the standard deviation of the corresponding pixel in the equivalent single-pulse net signal to the standard deviation of the dark noise signal; when the SNR is not lower than a preset SNR threshold, it is determined that the preset signal quality criterion is met. The effective working range is the closed interval formed by the minimum and maximum concentrations of the standard solution used when establishing the calibration mapping model.

[0017] A second aspect of this application provides a pulse-number adaptive ultraviolet spectroscopy nitrate measurement system for implementing the measurement method described in the first aspect of this application, comprising: The timing control module is used to control the xenon lamp to emit a corresponding number of light pulses within a fixed integration time according to the target number of pulses; The spectral detector module is used to accumulate and integrate the photogenerated charge within a preset fixed integration time and output the initial detection signal or the total detection signal. The data processing module is configured to: determine the initial net signal based on the initial detection signal, and determine the target pulse count accordingly; determine the equivalent single-pulse net signal based on the total detection signal and the target pulse count, and determine the nitrate concentration of the water sample to be tested accordingly.

[0018] Compared with the prior art, the advantages and positive effects of this application are as follows: This application establishes a calibration mapping relationship between the single-pulse net signal and nitrate concentration under a fixed integration time, and adaptively determines the target pulse number based on the initial net signal. It completes multi-pulse cumulative measurement and equivalent single-pulse normalization processing within a single integration period, so that the detection signal can be adaptively kept within a reasonable range. This results in stable and high signal-to-noise ratio measurement results under different concentration conditions, and effectively expands the measurement dynamic range and improves the measurement accuracy. Attached Figure Description

[0019] Figure 1 This is a flowchart of the ultraviolet nitrate measurement method based on pulse number adaptation in the embodiments of this application. Detailed Implementation

[0020] The present application will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, this application provides a pulse-number adaptive ultraviolet spectroscopy method for nitrate measurement, comprising the following steps: A calibration mapping model between nitrate concentration and single-pulse net signal is established under a preset fixed integration time. When testing the water sample, or when a sudden change in the detection signal is detected, the xenon lamp is controlled to operate in single-pulse mode to obtain the initial detection signal and the corresponding initial net signal. Based on the initial net signal, determine the corresponding target pulse count; Within a fixed integration time, the xenon lamp emits light pulses of the target number of pulses, so that the spectral detector accumulates and integrates the photogenerated charge generated by each light pulse, and obtains the total detection signal after the integration is completed. Based on the total detection signal, the equivalent single-pulse net signal is obtained; The equivalent single-pulse net signal is input into the calibration mapping model to obtain the nitrate concentration of the water sample to be tested.

[0023] The aforementioned ultraviolet nitrate measurement method based on pulse number adaptation in this application achieves a quantitative correlation between the measurement results and the basic response signal by constructing a calibration mapping model between nitrate concentration and single-pulse net signal under fixed integration time conditions. A single-pulse mode is introduced at the initial detection stage or during signal abrupt changes to obtain the initial net signal, and the target pulse number is adaptively determined accordingly, thereby dynamically adjusting the excitation intensity based on the actual concentration level of the water sample. By accumulating and integrating multiple pulse signals within a single integration period, the signal-to-noise ratio and detection stability under weak signal conditions are improved. Furthermore, the nonlinear effects caused by multi-pulse superposition are eliminated through inversion calculation of the equivalent single-pulse net signal, ensuring the consistency and comparability of the measurement results with the calibration model. Ultimately, this achieves high-precision, wide dynamic range detection of nitrates within different concentration ranges, significantly improving the adaptability, stability, and detection accuracy of the measurement method.

[0024] In some embodiments, the setting of the fixed integration time simultaneously satisfies both the anti-saturation condition and the timing tolerance condition, wherein: The anti-saturation condition is as follows: when measuring a pure water sample, the xenon lamp is controlled to emit a single pulse, the output signal of the spectral detector is within the linear response region, and a preset safety margin is retained. The timing tolerance condition is as follows: ,in, This represents the maximum number of pulses allowed under safety margin constraints. For single pulse width, This is the minimum interval between adjacent pulses.

[0025] It should be noted that the linear response region is the working range in which the output signal of the spectral detector maintains an approximately linear relationship with the incident light intensity; the safety margin is a signal buffer reserved below the upper limit of the linear response region to avoid entering a nonlinear or saturated state under conditions of multi-pulse accumulation or signal fluctuation.

[0026] The fixed integration time setting method described in this application simultaneously introduces anti-saturation conditions and timing tolerance conditions to collaboratively constrain and optimize the integration window, ensuring stable and reliable signal acquisition capabilities under different operating conditions. Specifically, by controlling the spectral detector output within the linear response region and reserving a safety margin under single-pulse testing conditions for pure water samples, detector saturation and nonlinear distortion caused by strong signal input are effectively avoided. Furthermore, by constructing a timing matching relationship between the fixed integration time and the maximum number of pulses, pulse width, and pulse interval, the multi-pulse excitation process can be fully accommodated within a limited integration period, achieving effective accumulation of multi-pulse signals. Based on this, while considering dynamic range expansion and signal quality control, multi-pulse integration measurements are stably completed, thereby significantly improving the linear reliability, timing consistency, and overall measurement accuracy of the spectral detection process.

[0027] In some embodiments, the method for establishing the calibration mapping model is as follows: Prepare a nitrate standard solution covering the target concentration range; Under a fixed integration time, a single pulse measurement was performed on each nitrate standard solution, the corresponding spectral response signal was acquired and dark noise correction was performed to obtain the net response signal of each nitrate standard solution. Based on the net response signal, characteristic wavelength signals characterizing the absorption properties of nitrate ions are extracted. A calibration mapping model is constructed based on the characteristic wavelength signals of each nitrate standard solution and their corresponding concentration data.

[0028] Specifically, the calibration mapping model adopts a partial least squares regression model based on net signal full-band information.

[0029] The aforementioned pulse-adaptive ultraviolet spectroscopy nitrate measurement method described in this application achieves accurate acquisition and dark noise correction of the spectral response signals of each standard solution by preparing a nitrate standard solution covering the target concentration range and performing single-pulse measurement under fixed integration time conditions, thereby obtaining a reliable net response signal. By extracting the characteristic wavelength signal characterizing the absorption properties of nitrate ions and combining it with the concentration data corresponding to each standard solution, an accurate calibration mapping model is constructed to achieve quantitative conversion from signal to concentration. On this basis, by adopting a partial least squares regression (PLS) model based on the full-band information of the net signal, the full-spectrum information is fully utilized to improve the modeling accuracy and noise resistance, thereby significantly improving the quantitative accuracy, adaptability, and stability of the nitrate measurement method in different concentration ranges, meeting the needs of high-precision and rapid in-situ detection of water samples.

[0030] In some embodiments, the method for determining the target pulse number is as follows: Initial net signal With the preset optimal signal range Compare; when < At that time, according to the formula Determine the number of target pulses and limited ≤ This ensures that the total pulse duration is contained within a fixed integral time; where round indicates rounding to the nearest integer. when Located in the preset optimal signal range Within the time frame, provided that the timing tolerance conditions are met, the target pulse count is determined. Set to an integer greater than 1; when > At that time, the target pulse count Set to 1.

[0031] The adaptive determination method for the target pulse count described in this application dynamically adjusts the xenon lamp pulse excitation intensity by comparing the initial net signal with a preset optimal signal range. When the initial net signal is lower than the lower limit of the optimal range, the target pulse count is calculated proportionally and rounded to determine the target pulse count, while limiting the maximum number of pulses to ensure that the total pulse duration is contained within a fixed integration time. When the initial net signal is within the optimal range, the target pulse count is set to an integer greater than 1, provided that the timing containment condition is met, to optimize the signal-to-noise ratio and measurement stability. When the initial net signal is higher than the upper limit of the optimal range, the target pulse count is set to 1 to avoid the detector entering a nonlinear or saturated state. Based on this, adaptive cumulative integration of the spectral detection signal is achieved, thereby significantly improving the dynamic response capability, signal linearity reliability, and overall measurement accuracy of the nitrate measurement method.

[0032] In some embodiments, the method for detecting signal mutation is as follows: the difference between the total detection signal obtained by the current measurement and the total detection signal obtained by the previous measurement is calculated, and when the absolute value of the difference exceeds a preset mutation threshold, it is determined to be a signal mutation.

[0033] In some embodiments, the method further includes a xenon lamp aging monitoring and automatic compensation step, specifically including: A reference optical path is set up to extract a portion of the light energy from each emitted pulse of light as a reference signal; The reference signal is acquired in real time to obtain the reference optical signal; The reference optical signal is accumulated and processed, and the degree of attenuation of the xenon lamp output energy is determined based on the deviation between the accumulated processing result and the initial calibration reference. ; Based on the degree of attenuation The number of target pulses is compensated and corrected to ensure that the accumulated light energy within each fixed integration time is maintained within a preset energy range. The compensation and correction formula is as follows: ,in, Indicates rounding up; The target pulse count is updated after light source aging compensation. When the degree of decay When the preset attenuation threshold is reached, a xenon lamp replacement prompt is triggered, and the initial calibration reference is reset after the xenon lamp replacement is completed.

[0034] The xenon lamp aging monitoring and automatic compensation method described in this application achieves real-time monitoring of the light source output by setting a reference optical path in the xenon lamp output optical path and using a portion of the energy of each pulse as a reference signal. It quantifies the attenuation degree δ of the xenon lamp output energy by accumulating and processing the reference optical signal and performing deviation analysis with the initial calibration benchmark. Based on the attenuation degree, it automatically compensates and corrects the target pulse number, ensuring that the accumulated light energy within each fixed integration time remains within a preset energy range. When the attenuation degree reaches a preset threshold, it triggers a xenon lamp replacement prompt and resets the initial calibration benchmark after lamp replacement. Based on this, it achieves dynamic correction of the measurement signal by light source aging, thereby significantly improving the long-term stability, repeatability, and quantitative accuracy of the spectral nitrate measurement method.

[0035] In some embodiments, the method for obtaining the equivalent single-pulse net signal is as follows: Total detection signal Based on the target pulse count after compensation and correction Normalization was performed, and dark signals were subtracted. The equivalent net single-pulse signal is obtained. This can be expressed as a formula: .

[0036] The method for obtaining the equivalent net single-pulse signal described in this application normalizes the total detection signal collected within a fixed integration time and subtracts the dark signal to correct the single-pulse signal, thereby obtaining the equivalent net single-pulse signal.

[0037] In some embodiments, the xenon lamp is a pulsed xenon flash lamp; the spectral detector is a linear CCD or a back-illuminated CMOS image sensor with no less than 512 effective pixels and a spectral resolution better than 1 nm.

[0038] In some embodiments, the method for accumulating and integrating photogenerated charges is as follows: Obtain the xenon lamp trigger pulse sequence and its corresponding integral gating signal; The integration is initiated first in response to the rising edge of the integration gate signal, and then the xenon lamp is triggered to emit light pulses to generate photogenerated charge, and the photogenerated charge is collected during the integration process; The collection of photogenerated charge is terminated in response to the falling edge of the integral gating signal, and charge transfer and readout are performed. Based on the target number of pulses, the xenon lamp trigger pulse sequence and integral gating signal are synchronously controlled so that the photogenerated charge generated by each pulse is accumulated within the same fixed integral time.

[0039] The method for accumulating and integrating photogenerated charges described in this application decouples the integration start time from the xenon lamp trigger time in a timely manner, and prioritizes the start of integration at the rising edge of the integration gate signal, effectively avoiding interference from the transient xenon lamp ignition on the initial stage of integration, thereby improving the stability and signal-to-noise ratio of photogenerated charge acquisition; by triggering the xenon lamp to emit light pulses within the integration window and simultaneously completing the generation and collection of photogenerated charges, efficient matching of the light signal and the integration process is achieved; by uniformly terminating charge collection and performing charge transfer and readout at the falling edge of the integration gate signal, the temporal consistency and data integrity of the readout process are guaranteed; based on this, by synchronously controlling the xenon lamp trigger pulse sequence and the integration gate signal, the photogenerated charges generated by multiple pulses are accumulated within the same fixed integration time, thereby significantly improving the detection sensitivity and measurement repeatability of weak signals, meeting the application requirements of high-precision spectroscopic detection or trace substance analysis.

[0040] In some embodiments, the method further includes an automated verification step for the effectiveness of nitrate concentration, specifically comprising: Step S1: Compare the nitrate concentration with the effective working range of the calibration mapping model. If it exceeds the effective working range, generate a corresponding anomaly marker; if it is within the effective working range, proceed to step S2. Step S2: Determine the equivalent single-pulse net signal according to the preset signal quality criteria. If the preset signal quality criteria are not met, trigger the retest process; if they are met, proceed to step S3. Step S3: Statistically compare the nitrate concentration with the historical valid measurement results. If the deviation between the two exceeds the preset deviation threshold, execute the initialization process of resetting the pulse count to 1 and remeasure. If the deviation does not exceed the preset deviation threshold, proceed to step S4. Step S4: Based on the residuals of the calibration mapping model, the level of dark noise signal, and the pulse energy fluctuation, the expanded uncertainty and the corresponding confidence interval of this measurement result are obtained.

[0041] Specifically, the preset signal quality criterion includes a signal-to-noise ratio (SNR) criterion, wherein the SNR is the ratio of the standard deviation of the corresponding pixel in the equivalent single-pulse net signal to the dark noise signal; when the SNR is not lower than a preset SNR threshold, it is determined that the preset signal quality criterion is met, wherein the preset SNR threshold is 20dB.

[0042] Specifically, the effective working range is the closed interval formed by the minimum and maximum concentrations of the standard solution used when establishing the calibration mapping model; the preset deviation threshold is 30%.

[0043] The automatic verification method for nitrate concentration validity described in this application achieves the reliability and traceability of measurement results through multi-level signal and measurement result verification. First, the nitrate concentration to be measured is compared with the effective working range of the calibration mapping model. If it exceeds the range, an anomaly marker is generated to indicate data abnormality; otherwise, the next verification stage is initiated. Subsequently, the equivalent single-pulse net signal is evaluated according to preset signal quality criteria. If the quality requirements are not met, a retest process is triggered to ensure data reliability. If the signal quality is acceptable, the current measurement result is statistically compared with historical valid measurement data. If the deviation exceeds a preset threshold, an initialization process to reset the pulse count to 1 is executed, and the measurement is repeated to eliminate possible cumulative errors. Finally, based on the calibration model residual, dark noise level, and pulse energy fluctuation, the expanded uncertainty and corresponding confidence interval of the current measurement result are calculated, thereby significantly improving the reliability, dynamic stability, and high-precision detection capability of the nitrate concentration measurement method.

[0044] The purpose of this application is also to provide a pulse-number adaptive ultraviolet spectroscopy nitrate measurement system for implementing the above-mentioned measurement method, including: The spectral detector module is used to accumulate and integrate the photogenerated charge generated by a single pulse or multiple light pulses within a preset fixed integration time, and output the initial detection signal or the total detection signal. The timing control module is used to generate a xenon lamp trigger pulse sequence and an integral gating signal, and to control the xenon lamp to emit a corresponding number of light pulses within the fixed integration time according to the target number of pulses, wherein the xenon lamp is controlled to operate in single-pulse mode during the initial detection phase. The data processing module is configured to: perform dark noise correction on the initial detection signal in single-pulse mode to obtain an initial net signal; determine the target pulse count based on the initial net signal; perform dark noise correction on the total detection signal and calculate the equivalent single-pulse net signal in combination with the target pulse count; input the equivalent single-pulse net signal into the calibration mapping model to obtain the nitrate concentration of the water sample to be tested.

[0045] The aforementioned ultraviolet spectral nitrate measurement system based on pulse number adaptation achieves high-precision and wide dynamic range measurement of nitrate concentration through modular design. Specifically, the spectral detector module accumulates and integrates single-pulse or multi-pulse photogenerated charges within a preset fixed integration time, outputting an initial detection signal or a total detection signal to obtain reliable raw spectral data. The timing control module generates a xenon lamp trigger pulse sequence and an integration gating signal, and controls the xenon lamp to emit a corresponding number of light pulses within a fixed integration time based on the target pulse number. In the initial detection stage, a single-pulse mode is used to obtain the initial signal, providing a basis for adaptive adjustment. The data processing module corrects the initial detection signal for dark noise to obtain an initial net signal, and determines the target pulse number accordingly. Simultaneously, it corrects the total detection signal for dark noise and normalizes it to the target pulse number, calculating an equivalent single-pulse net signal. Finally, this signal is input into a calibration mapping model to obtain the nitrate concentration of the water sample. Based on this, continuous, stable, and traceable measurement of nitrate concentration in water samples is achieved, significantly improving the system's measurement accuracy, signal linearity reliability, and dynamic adaptability.

[0046] To verify the effectiveness of the pulse-number-adaptive ultraviolet spectroscopy nitrate measurement method proposed in this application, nitrate standard solutions with concentrations of 0.5 mg / L, 5 mg / L, 20 mg / L, and 80 mg / L were prepared, covering a wide dynamic range from low to high concentrations. The integration time was fixed at 50 ms, the maximum allowable number of pulses was set to 16, and the optimal signal range was set to 30%–70% of full scale.

[0047] In the traditional fixed single-pulse mode, the four groups of solutions were detected sequentially. The results showed that for the high-concentration sample of 80 mg / L, the signal-to-noise ratio of the spectral detector output signal was only about 8 dB, which was lower than the preset signal-to-noise ratio threshold of 20 dB, resulting in unstable measurement results with a relative error of ±18.3%. For the low-concentration sample of 0.5 mg / L, since the single-pulse signal intensity had entered the optimal signal range, the relative error of the measurement results was about ±2.1%, but the dynamic response capability in the intermediate concentration range was limited, and the overall dynamic range was less than two orders of magnitude.

[0048] When using the method proposed in this application, the system first operates in single-pulse mode to acquire the initial net signal for each concentration sample. For the high-concentration sample of 80 mg / L, the initial net signal is below the lower limit of the optimal signal range. The target number of pulses is calculated proportionally to be 12. The photogenerated charge generated by the 12 pulses is accumulated and integrated within the same fixed integration time (50 ms), improving the signal-to-noise ratio to approximately 27 dB, which meets the quality criterion. Subsequently, the nonlinear effect of multi-pulse superposition is eliminated by inverting the equivalent single-pulse net signal. After substituting into the calibration mapping model, the measurement relative error is reduced to ±1.8%. For intermediate concentration samples of 5 mg / L and 20 mg / L, the target number of pulses is adaptively determined to be 4 and 2, respectively, with the signal-to-noise ratio maintained within the optimal range and the measurement relative errors being ±1.5% and ±1.3%, respectively. For the 0.5 mg / L sample, the initial net signal exceeds the upper limit of the optimal range, and the target number of pulses is set to 1 to avoid detector saturation, resulting in a measurement relative error of ±1.9%.

[0049] The comparative experimental results are summarized as follows: In the measurements of four groups of samples with different concentrations, the relative measurement error of the method proposed in this application was controlled within ±2%, while the traditional fixed single-pulse method had an error exceeding ±18% in the low-concentration range and also suffered from insufficient dynamic range in the high-concentration range. The method proposed in this application achieves high-precision continuous detection over a wide concentration range (approximately two orders of magnitude) from 0.5 to 80 mg / L, with a dynamic range approximately four times larger than the comparative method, and a signal-to-noise ratio improved by approximately 19 dB in the low-concentration range. These results demonstrate that the pulse number adaptive strategy proposed in this application can effectively resolve the contradiction between insufficient signal-to-noise ratio and detector saturation under wide dynamic range conditions, significantly improving the adaptability, stability, and detection accuracy of the ultraviolet spectroscopy nitrate measurement method.

[0050] The above embodiments are used to explain this application, not to limit it. Any modifications and changes made to this application within the spirit and scope of the claims shall fall within the protection scope of this application.

Claims

1. A method for measuring nitrate using ultraviolet spectroscopy based on pulse number adaptation, characterized in that, Includes the following steps: A calibration mapping model between nitrate concentration and single-pulse net signal is established under a preset fixed integration time. When testing the water sample, or when a sudden change in the detection signal is detected, the xenon lamp is controlled to operate in single-pulse mode to obtain the initial detection signal and the corresponding initial net signal. Determine the target pulse count based on the initial net signal; Within a fixed integration time, the xenon lamp emits light pulses of the target number of pulses, so that the spectral detector accumulates and integrates the photogenerated charge generated by each light pulse, and obtains the total detection signal after the integration is completed. Based on the total detection signal, the equivalent single-pulse net signal is obtained; The equivalent single-pulse net signal is input into the calibration mapping model to obtain the nitrate concentration of the water sample to be tested; The calibration mapping model is established as follows: prepare nitrate standard solutions covering the target concentration range; perform single-pulse measurements on each nitrate standard solution at a fixed integration time, acquire the corresponding spectral response signals and perform dark noise correction to obtain the net response signals of each nitrate standard solution; extract the characteristic wavelength signals characterizing the absorption properties of nitrate ions based on the net response signals; and construct the calibration mapping model based on the characteristic wavelength signals of each nitrate standard solution and their corresponding concentration data. The method for determining the target pulse count is as follows: Initial net signal With the preset optimal signal range Compare; when < At that time, according to the formula Determine the number of target pulses and limited ≤ This ensures that the total pulse duration is contained within a fixed integral time; where round indicates rounding to the nearest integer. This represents the maximum number of pulses allowed under safety margin constraints. when Located in the preset optimal signal range Within the time frame, provided that the timing tolerance conditions are met, the target pulse count is determined. Set to an integer greater than 1; timing tolerance condition is: ,in, For single pulse width, This is the minimum interval between adjacent pulses; when > At that time, the target pulse count Set to 1.

2. The measurement method according to claim 1, characterized in that, The setting of the fixed integration time satisfies both the anti-saturation condition and the timing tolerance condition, wherein: The anti-saturation condition is as follows: when measuring pure water samples, the xenon lamp is controlled to emit a single pulse, the output signal of the spectral detector is within the linear response region, and a preset safety margin is retained.

3. The measurement method according to claim 1, characterized in that, The measurement method also includes xenon lamp aging monitoring and automatic compensation steps, specifically including: A reference optical path is set up to extract a portion of the light energy from each emitted pulse of light as a reference signal; The reference signal is acquired in real time to obtain the reference optical signal; The reference optical signal is accumulated and processed, and the degree of attenuation of the xenon lamp output energy is determined based on the deviation between the accumulated processing result and the initial calibration reference. ; Based on the degree of attenuation The number of target pulses is compensated and corrected to ensure that the accumulated light energy within each fixed integration time is maintained within a preset energy range. The compensation and correction formula is as follows: ,in, Indicates rounding up; The target pulse count is updated after light source aging compensation. When the degree of decay When the preset attenuation threshold is reached, a xenon lamp replacement prompt is triggered, and the initial calibration reference is reset after the xenon lamp replacement is completed.

4. The measurement method according to claim 3, characterized in that, The method for obtaining the equivalent single-pulse net signal is as follows: Total detection signal Based on the target pulse count after compensation and correction Normalization was performed, and dark signals were subtracted. The equivalent net single-pulse signal is obtained. This can be expressed as a formula: .

5. The measurement method according to claim 1, characterized in that, The method for accumulating and integrating photogenerated charges is as follows: Obtain the xenon lamp trigger pulse sequence and its corresponding integral gating signal; The integration is initiated first in response to the rising edge of the integration gate signal, and then the xenon lamp is triggered to emit light pulses to generate photogenerated charge, and the photogenerated charge is collected during the integration process; The collection of photogenerated charge is terminated in response to the falling edge of the integral gating signal, and charge transfer and readout are performed. Based on the target number of pulses, the xenon lamp trigger pulse sequence and integral gating signal are synchronously controlled so that the photogenerated charge generated by each pulse is accumulated within the same fixed integral time.

6. The measurement method according to claim 1, characterized in that, The measurement method also includes an automatic verification step for the effectiveness of nitrate concentration, specifically including: Step S1: Compare the nitrate concentration with the effective working range of the calibration mapping model. If it exceeds the effective working range, generate a corresponding anomaly marker; if it is within the effective working range, proceed to step S2. Step S2: Determine the equivalent single-pulse net signal according to the preset signal quality criteria. If the preset signal quality criteria are not met, trigger the retest process; if they are met, proceed to step S3. Step S3: Statistically compare the nitrate concentration with the historical valid measurement results. If the deviation between the two exceeds the preset deviation threshold, execute the initialization process of resetting the pulse count to 1 and remeasure. If the deviation does not exceed the preset deviation threshold, proceed to step S4. Step S4: Based on the residuals of the calibration mapping model, the level of dark noise signal, and the pulse energy fluctuation, the expanded uncertainty and the corresponding confidence interval of this measurement result are obtained.

7. The measurement method according to claim 6, characterized in that, The preset signal quality criteria include a signal-to-noise ratio (SNR) criterion, where the SNR is the ratio of the standard deviation of the corresponding pixel in the equivalent single-pulse net signal to the dark noise signal; when the SNR is not lower than the preset SNR threshold, the preset signal quality criteria are deemed to be met. The effective working range is the closed interval formed by the minimum and maximum concentrations of the standard solution used when establishing the calibration mapping model.

8. A pulse-number adaptive ultraviolet spectroscopy nitrate measurement system, used to implement the measurement method as described in any one of claims 1-7, characterized in that, include: The timing control module is used to control the xenon lamp to emit a corresponding number of light pulses within a fixed integration time according to the target number of pulses; The spectral detector module is used to accumulate and integrate the photogenerated charge within a preset fixed integration time and output the initial detection signal or the total detection signal. The data processing module is configured to: determine the initial net signal based on the initial detection signal, and determine the target pulse count accordingly; The equivalent net single-pulse signal is determined based on the total detection signal and the number of target pulses, and the nitrate concentration of the water sample to be tested is determined accordingly.

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