Nitrate sensor and application thereof

Abstract

A nitrate sensor includes a housing 1 containing a composite packaged light source 2, an emission intensity detection component 3 (a photodiode chip), and a control circuit mainboard 4. A flow cell is

Description

TECHNICAL FIELD The present application belongs to the technical field of water quality detection, and specifically relates to a nitrate sensor and application thereof. BACKGROUND Nitrate concentration is one of the key parameters in water quality monitoring. Spectrophotometry, due to high sensitivity and high selectivity thereof, is widely applied to detection of nitrates in water. The principle of spectrophotometric nitrate detection relies on the strong absorption peak of nitrates in the ultraviolet range of 200-230 nm for quantitative analysis. At present, spectrophotometric devices for nitrate detection mostly use xenon lamps as light sources, requiring complex light splitting structures. These devices are typically large, power intensive, and poor adaptability to complex scenarios, making difficult to implement detection of nitrates at low cost and low power consumption. Light-emitting diodes (LEDs) have the advantages such as good monochromaticity, small volume, low energy consumption, and long lifespan, making them a suitable light source of a spectrophotometric water quality monitoring device. With present development of wide bandgap AlGaN materials, deepultraviolet LEDs (UVC-LEDs) can achieve a relatively high milliwatt (mW)-level optical output power in the wavelength range of 240-290 nm. The minimum wavelength of a current commercial deep ultraviolet LED may reach 230 nm, which basically satisfies the wavelength requirement of a light source for nitrate detection. However, the output power of a 230 nm LED is extremely low (microwatt, p,W-level), and an operation amplifier resistance of 100 MQ or higher needs to be used, which may also amplify dark current signals, and further affect the sensitivity and accuracy of detection. One approach to enhancing output optical power intensity is to integrate multiple LED chips on the same circuit board. However, during LED chips packaging process, the emission intensities are likely to be uneven, leading to inaccuracy of detection results. In the related art, for example, a Chinese patent of invention with an application No. CN201780082058.7 discloses a lens design of multiple LED light sources in an integrated package, and the starting point of the invention is that when multiple RGB-LED light sources are integrated and packaged, uneven distribution of chips results in that the emissions of RGB pixel light sources do not completely overlap. In addition, a 230 nm LED light source is likely to have an unstable emission intensity or significant light attenuation, affecting the stability and reliability of a detection system. Therefore, an in-situ optical intensity monitoring structure needs to be designed to enable the real-time intensity detection of an LED light source. In the related art, for example, a Chinese patent of invention with an application No. CN201910932111.9 discloses a portable fast water quality detector and a water quality detection method, an LED light source intensity detection module of which is arranged on a side perpendicular to an LED light source and is used for detecting the emission intensity of the LED light source in real time. Because the divergence of an optical path of an LED is weak after the LED is condensed by a lens, a detection structure arranged perpendicular to the LED may cause that an ultraviolet detection chip is parallel to the optical path, and a beam angle changes with different optical power, which easily causes in-situ measurement errors of emission intensities. In addition, monitoring the intensity of a single-beam light source by using a reflection structure is also a solution. In the related art, for example, a Chinese patent of invention with an application No. CN201910002162.1 discloses a water quality monitoring apparatus based on a composite packaged LED light source, where in the design of an optical path, the emission intensities of a light source are separately detected by a proportional beam splitter, and the emission intensities after absorption by a sample are detected after reflection of light by a reflective optical sheet. The proportional beam splitter divides an original optical path into a measurement optical path and a reference optical path, with the beam splitting proportion ranging from 10 / 90 to 90 / 10. However, the design of a reflective structure in detection of emission intensities increases structural complexity of a detection system, and may further cause light loss in a measurement optical path. In addition, dissolved organic matter (DOM) in and the turbidity of water samples have absorption and scattering effects in an ultraviolet range, affecting the accuracy of spectrophotometric nitrate detection. In the related art, for example, a Chinese patent of invention with an application No. CN202022391284.5 discloses a water quality analyzer for dissolved organic matter and nitrate nitrogen, which uses a dual-wavelength LED method to detect nitrate nitrogen in water, where a UVC-LED with a peak wavelength of 235+10 nm is used for detecting nitrates, a UVC-LED with a peak wavelength of 275+10 nm is used for detecting DOM in water. The concentration of nitrate nitrogen is obtained through calculation according to Abs235+10 and Abs275+10, effectively correcting the interference of DOM on detection, and significantly improving the accuracy of nitrate detection. However, since the concentration and composition of DOM vary across different water sources, the dualwavelength spectrophotometric method needs specific calibration according to the result of a laboratory test for the nitrate concentrations, increasing the operation complexity. SUMMARY 1. Problems to be solved In view of the problems of LED-based spectrometry in the stability of a light source and the accuracy of test results in detection of nitrates, the present application is intended to provide a nitrate sensor and application thereof. By using an arrangement manner in an nxn matrix form, LED chips with multiple wavelengths and a single emission intensity detection photodiode chip are packaged in a composite manner. The intensity of an emission light source is enhanced, and in-situ monitoring of the emission intensity is achieved. During testing of a detector, multiple measurement signals are collected, and outliers of measurement caused by turbidity are excluded by a sorting and comparison algorithm. The absorbance of the DOM at the wavelength for detection of nitrates is fitted according to the measured absorbances, and the absorbances of the nitrates are further corrected. The operation and maintenance steps of the detector are simplified, and the accuracy of results of the absorbances of the nitrates measured by spectrometry is ensured. 2. Technical solution To solve the above problems, the technical solution adopted in the present application is as follow: The present application provides a nitrate sensor, including: a housing, a composite packaged light source, a emission intensity detection component, and a control circuit mainboard, where a flow cell is formed between the composite packaged light source and the emission intensity detection component and configured to allow a to-be-tested water sample to pass through; the composite packaged light source, the emission intensity detection component, and the control circuit mainboard are arranged in the housing, and the housing is mainly configured to protect the composite packaged light source, the emission intensity detection component, and the control circuit mainboard; the composite packaged light source is configured to emit ultraviolet light at particular wavelengths in the direction of the flow cell, including LED chips and a photodiode chip packaged on same substrate; the LED chips are arranged in the form of an nxn matrix, with the centrosymmetric LED chips in the matrix emitting ultraviolet light at the same wavelength. The LED chips at least include LED chips that emit ultraviolet light at wavelength of 230+10 nm and 275±10 nm; the multiple LED chips that emit ultraviolet light at the same wavelength can improve the intensities of ultraviolet light at particular wavelength; the photodiode chip is arranged at the center of the matrix and configured to detect the emission intensities of the LED chips in situ; the emission intensity detection component includes a photodiode chip which is configured to detect the emission intensities of ultraviolet light emitted by the composite packaged light source after the ultraviolet light is absorbed by a to-be-tested water sample in the flow cell and convert optical signals into electrical signals; and the control circuit mainboard is configured to control switch-on and switch-off of LED chips in the composite packaged light source, and convert the emission intensities detected by the emission intensity detection component into electrical signals, and the like. Further, in the composite packaged light source, n=2-5. Further, in the composite packaged light source, n=2, 3, 4, or 5. Further, in the composite packaged light source, the LED chips further include one or more of LED chips that emit ultraviolet light at wavelengths of 320+10 nm and 365+10 nm. Further, in the composite packaged light source, n=2, and the LED chips include LED chips that emit ultraviolet light at wavelengths of 230+10 nm and 275+10 nm, the numbers of which are 2, respectively. Further, in the composite packaged light source, n=3, the LED chips include LED chips that emit ultraviolet light at wavelengths of 230+10 nm, 275+10 nm, and 320+10 nm, the number of the LED chips that emit ultraviolet light at wavelength of 230+10 nm is 4, and the numbers of the LED chips that emit ultraviolet light at wavelengths of 275+10 nm and 320+10 nm are 2, respectively. Further, in the composite packaged light source, n=3, and the LED chips include LED chips that emit ultraviolet light at wavelengths of 230+10 nm, 275+10 nm, 320+10 nm, and 365+10 nm, the numbers of which are 2, respectively. Further, in the composite packaged light source, connection pins of the LED chips are led out in a packaging manner of a shared anode and independent cathodes, and are separately connected to the respective driver circuits, to implement independent switch control. Further, the LED chips of the composite packaged light source are all controlled by independent constant current circuits, and can emit strobe light in sequence according to a set collection frequency. Further, the photodiode chip includes a GaN- or SiC-based semiconductor photodiode chip. Still further, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. Further, a quartz lens is packaged above the LED chips of the composite packaged light source. Further, the control circuit mainboard includes independent driver circuits of LED chips, a signal amplification circuit, and a micro processing chip, which are used to control the switchon of the LED chips, detect photoelectric signals, and process the signals. Further, the nitrate sensor further includes: a cleaning brush, arranged between the composite packaged light source and the emission intensity detection component, and configured to ensure cleaning of a light path structure during testing. The present application provides application of the nitrate sensor in detection of nitrates in a water sample. Further, the application includes the following steps: in-situ detection and correction of emission intensities: measuring the emission intensities of the LED chips and the emission intensities detected in the detection component in pure water, as well as the emission intensities of the LED chips and the emission intensities detected in the detection component during testing of a water sample, and obtaining corrected emission intensities through two groups of emission intensity signals; sorting and screening of emission intensity signals: controlling, by using pulse modulation and frequency setting, the LED chips that emit ultraviolet light at the same wavelength to emit strobe light for multiple times, sorting the obtained emission intensity signals, using a maximum value as a emission intensity representative value at the wavelength, and further obtaining absorbance values by calculation; and correction of the detected absorbance of nitrate: correcting the absorbance values obtained at detection wavelengths of 230 nm and 275 nm; or obtaining an organic matter correction coefficient by calculation with the absorbance values obtained at wavelengths other than 230 nm, so as to obtain an interference absorbance of organic matter on the detection of nitrates and corrected absorbances for the detection of nitrates. Further, the in-situ detection and correction of emission intensity include: first, measuring the emission intensities of the composite LED chips packaged in an nxn matrix form in a light source component, and the corresponding emission intensities detected in the detection component in pure water, i.e., a blank sample, as F(i, o) and I(x, o) respectively, X representing the emission wavelength of an LED; and measuring the emission intensities of the composite LED chips having a same emission wavelength and packaged in an nxn form in the light source component, and the emission intensities detected in the detection component when a to-be-tested water sample fills a flow cell, as I'(x, t) and !(%, t) respectively; I’(x, o> / f(x, t) being the in-situ J* attenuation degree of the emission light source, and I correct^) = x being the (At) corrected emission intensity detected in the detection component. Further, the sorting and screening of emission intensity signals include: controlling, by using pulse modulation and frequency setting, the LED chips with same emission wavelength to emit strobe light simultaneously for multiple times to obtain multiple emission intensity signals, sorting the obtained emission intensity signals in descending order, and using a maximum value as a emission intensity representative value when the LED having the wavelength is used for testing, to avoid interference of sudden decrease of optical signals caused by the turbidity of or particles in the sample flow cell during testing; and calculating the absorbance value of a to-be-tested water sample during emission of each LED by formula (1): Al = “Ig Acorrect(Z,t)A _ _ \ ^2,0) / V(A 0)^) / Further, the correction of the detected absorbances of nitrates includes: calculating a correction coefficient 5' for the detection of nitrates by formula (3), Xi and X? representing two different wavelengths of LEDs; substituting 5' into formula (3) to obtain the interference absorbance A 230 on the detection of nitrates at a wavelength of 230 nm, Xi being any wavelength other than 230 nm of an LED; and obtaining the corrected absorbance ACOrrected for the detection of nitrates by ACOrrected=A230-A230, and converting the corrected absorbance values into the nitrate concentration in water based on a linear relationship between the concentrations of the nitrates and the corrected absorbances, _ tn (^21 / ^22) (2) A’23O = A^230^ (3). Further, in the correction of the detected absorbances of nitrates, one or more correction coefficients 5' may be obtained by calculation, and are obtained by calculation with the absorbances obtained at at least two wavelengths other than 230 nm; and when there are two or more correction coefficients S, an average value is obtained and used as a correction coefficient for the detection of nitrates, and the absorbance data obtained at 230 nm is substituted for correction calculation. Further, the application includes: filtration of abnormal absorbances, including: storing absorbance values in a built-in memory; after a series of absorbance values are stored in the memory, selecting a particular number (m) of pieces of absorbance data in a time sequence at the detection wavelength of X as a monitoring array [A(i.i), A(U), ..., A(x,m)]; writing the monitoring array into a register, and shifting and replacing the register data with time; for each point in a window, calculating a median Mi of all data points in the window and a median absolute deviation (MAD), MADx being a median of an absolute value of a difference between the median and each point in the window; setting a threshold T=pxMAD; and comparing a deviation |A(i,m)-Mi| between each point in a monitoring window and the median with a preset threshold T: if |A(x.m)-Mi|<T, reserving the value, and if |A(x.m)-Mx|>T, considering the value as an outlier, and replacing the outlier with the median value Mi. Further, p=3. 3. Beneficial effects Compared with the prior art, the present application has the following beneficial effects: (1) The nitrate sensor and the application thereof provided by the present application have an advantage that multiple 230nm LED chips are packaged in a composite manner, and the emission intensities of the 230 nm LEDs are enhanced. The LED chips with multiple wavelengths are packaged simultaneously, so that detection of absorbances at multiple wavelengths can be implemented. The LED chips are arranged in an nxn matrix form symmetrical manner, and the uniformity of emission of the light source is ensured. The emission intensity detection chip is arranged at the center of the nxn matrix form matrix, and can implement in-situ detection of the emission intensity of the light source and correct the emission intensity of the detection part. (2) The nitrate sensor and the application thereof provided by the present application have an advantage that the emission intensities detected by the LEDs at the same wavelength are sorted in descending order to obtain the maximum value, the interference of the turbidity of water in a flow cell on the detection of absorbances by spectrometry is eliminated, and the accuracy of the testing results is ensured. (3) The nitrate sensor and the application thereof provided by the present application have an advantage that the characteristics of a to-be-tested water sample are used as a correction basis for the absorbances of nitrates, that is, an interference absorbance of DOM in water at the wavelength of 230 nm is calculated and fitted by using the absorbance at a wavelength other than 230 nm, and further the absorbance values of the nitrates measured at 230 nm are corrected. An operation in a conventional method is omitted, that an interference coefficient of organic matter can be calibrated according to nitrate data of a water sample containing an agent measured by ion chromatography to correct the absorbances of nitrates, and operation and maintenance processes of a device are simplified, and the nitrate sensor of the present application is automatically adapted to detection of water of different sources. (4) The nitrate sensor and the application thereof provided by the present application have an advantage that for an application scenario of long-term measurement of a detector, combination of shifting of register data with a filter can effectively reduce accidentally generated outliers without excessively smoothing the data, thereby reserving useful signal characteristics. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic structural diagram of a nitrate sensor provided in the present application. FIG. 2 is a schematic diagram of a composite packaged light source provided in the present application. FIG. 3 is a schematic diagram of a composite packaged light source provided in the present application. FIG. 4 is a comparison between an original absorbance value obtained and an absorbance value processed by a filter algorithm when a detector is applied to detection of nitrates in effluent water of a municipal sewage plant. Description of reference numerals: 1-housing; 2-composite packaged light source; 3-luminous intensity detection component; 4-control circuit mainboard; 5-cleaning brush; 201-quartz lens; 221-224-LED chips; 225-photodiode chip; 231-238-LED chips; and 239-photodiode chip. DETAILED DESCRIPTION The present application will be further described in conjunction with specific embodiments. It should be noted that terms such as "upper," "lower," "left," "right," and "middle" mentioned in the specification are merely for ease of description, and are not intended to limit the implementable scope. Changes or adjustments in relative relationships without a substantial change in technical content shall also be considered as the implementable scope of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs. The term "and / or" used herein includes any and all combinations of one or more related items listed. If a specific condition is not indicated in embodiments, a common condition or a condition recommended by a manufacturer is followed. The reagents or instruments used without specific manufacturers are commercially available conventional products. As used herein, the term "about" is used for providing flexibility and imprecision associated with a given term, measurement, or value. Those skilled in the art can easily determine the flexibility degree of a specific variable. As used herein, the term "at least one of..." is intended to be synonymous with "one or more of...". For example, "at least one of A, B, and C" explicitly includes only A, only B, only C, and combinations thereof. Concentration, quantity, and other numerical data can be presented in the form of a range herein. It should be understood that the form of a range is used merely for convenience and brevity, and should be flexibly interpreted as not only including numerical values explicitly stated as range limits, but also including all individual numerical values or sub-ranges within the range, as if each numerical value and sub-range is explicitly stated. For example, a numerical range of about 1 to about 4.5 should be interpreted as not only including the explicitly stated limit values of 1 to about 4.5, but also including individual numbers (such as 2, 3, and 4) and sub-ranges (such as 1 to 3 and 2 to 4). The same principle is applicable to a range describing only one numerical value, for example, "less than about 4.5" should be interpreted as including all the aforementioned values and ranges. Furthermore, regardless of the breadth of the range or features described, this interpretation should apply. As used herein, a "sensor" refers to a detection apparatus that can sense the measured information and convert the sensed information into electrical signals or other required forms of information to be outputted according to certain rules, in order to meet the requirements such as information transmission, processing, storage, display, recording, and control. As used herein, "LED light attenuation" refers to the phenomenon where the emission intensity of an LED becomes lower than its original emission intensity after a period of lighting, and the lower part is the light attenuation of the LED. As used herein, an "LED" refers to a light-emitting diode, which is a commonly used light emitting device that releases energy through electron-hole recombination and emit light, can efficiently convert electrical energy into light energy, and has a wide range of applications in modern society, such as lighting, flat panel displays, and medical devices. As used herein, "emission intensity" refers to the radiated power per unit area. As used herein, a "photodiode chip," also known as a "detector chip," refers to a semiconductor device that converts light energy into electrical energy via photoelectric effect, detecting optical signals through the photoelectric effect, and converting the optical signals into electrical signals. The photoelectric effect refers to the phenomenon that electrons in a material absorb photon energy under light irradiation, and if the absorbed energy exceeds the material's work function, the electrons will eject from the material to form photoelectrons and produce a positively charged hole. When a photodiode is working, a reverse voltage is applied to two poles thereof. Without light irradiation, due to the reverse high resistance characteristic of the diode, only a small dark current exists in the circuit; and with light irradiation, the hole produced by the photoelectric effect are driven towarsd the negative pole of the external voltage, and the photoelectrons will go to the positive pole of the external voltage, thereby increasing the reverse current in the diode and achieving detection of optical signals. Embodiment 1 This embodiment provides a nitrate sensor, which is used for detecting nitrates in surface water, domestic sewage, or other water samples. The nitrate sensor provided in this embodiment is shown in FIG. 1, and includes: a housing 1, a composite packaged light source 2, a emission intensity detection component 3, and a control circuit mainboard 4. A flow cell is formed between the composite packaged light source 2 and the emission intensity detection component 3 and configured to allow a to-be-tested water sample to pass through. The composite packaged light source 2, the emission intensity detection component 3, and the control circuit mainboard 4 are arranged in the housing 1, and the housing 1 is mainly configured to protect the composite packaged light source 2, the emission intensity detection component 3, and the control circuit mainboard 4. The composite packaged light source 2 includes LED chips and a photodiode chip packaged on a same substrate. The LED chips are distributed in the form of an nxn matrix, the centrosymmetric LED chips in the matrix emit ultraviolet light at the same wavelength, and the LED chips at least include LED chips that emit ultraviolet light at wavelength of 230+10 nm and LED chips that emit ultraviolet light at wavelength of 275+10 nm. The multiple LED chips that emit ultraviolet light at the same wavelength can improve the intensities of ultraviolet light at particular wavelength. The photodiode chip is arranged at the center of the matrix and configured to detect the emission intensities of the LED chips in situ. In this embodiment, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. The emission intensity detection component 3 includes a photodiode chip which is configured to detect the emission intensities of ultraviolet light, which are emitted by the composite packaged light source 2, after a to-be-tested water sample absorbing in the t. In this embodiment, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. The control circuit mainboard 4 is configured to control switch-on and switch-off of the composite packaged light source 2, convert the emission intensities detected by the emission intensity detection component 3 into electrical signals, and the like. In this embodiment, the composite packaged light source 2 has a structure shown in FIG. 2, and includes: an LED chip 221, an LED chip 222, an LED chip 223, an LED chip 224 and a photodiode chip 225 packaged on the same substrate. The LED chip 221, the LED chip 222, the LED chip 223, and the LED chip 224 are distributed in the form of an nxn (n=2) matrix, and the photodiode chip 225 is arranged at the center of the matrix. The LED chip 221 and the LED chip 224 are centrosymmetric and emit ultraviolet light with same wavelength of 230+10 nm The LED chip 222 and the LED chip 223 are centrosymmetric and emit ultraviolet light with same wavelength of 275+10 nm. The composite packaged light source further includes a quartz lens 201 packaged above the LED chips and configured to condense light, and the beam angle is approximately 7°. In this embodiment, connection pins are led out in a packaging manner of a shared anode and independent cathodes, and are separately connected to the respective driver circuits, to implement independent switch control. In other embodiments, the nitrate sensor may further include a cleaning brush 5. The cleaning brush 5 is configured to clean light windows on both sides of the flow cell to keep the light windows clean and reduce interference of other factors. Embodiment 2 This embodiment provides application of the nitrate sensor in Embodiment 1, for the detection of nitrates in surface water, domestic sewage, or other water samples. The application includes the following steps: S1: Detection of pure water Sil: A pure water sample is allowed to flow through the flow cell formed between the composite packaged light source 2 and the emission intensity detection component 3. S12: The LED chip 221 and the LED chip 224 that emit ultraviolet light with same wavelength of 230+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(230,0) and 1(230,0), respectively. S13: The LED chip 222 and the LED chip 223 that emit ultraviolet light with same wavelength of 275+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are 1'(275,0) and 1(275,0), respectively. S2: Detection of a water sample S21: A water sample is allowed to flow through the flow cell formed between the composite packaged light source 2 and the emission intensity detection component 3. S22: Pulse modulation and frequency are set, the LED chip 221 and the LED chip 224 that emit ultraviolet light with same wavelength of 230+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at detection wavelength of 230 nm. The emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(230,t) and 1(230,t), respectively. S23: Pulse modulation and frequency are set, the LED chip 222 and the LED chip 223 that emit ultraviolet light with same wavelength of 275+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at detection wavelength of 275 nm. The emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(275,t) and I(275,t), respectively. S3: Calculation of nitrate concentration S31: The absorbances at different detection wavelengths are calculated by formula (1), Ax = -ig (1) where X refers to a detection wavelength; Ax refers to the absorbance at the detection wavelength of X; / (^0) refers to the emission intensity detected by the photodiode chip in the composite packaged light source when pure water is detected at the detection wavelength of X; 7(2,0) refers to the emission intensity detected by the emission intensity detection component when pure water is detected at the detection wavelength of X; 7(2,t) refers to the emission intensity detected by the photodiode chip in the composite packaged light source when a water sample is detected at the detection wavelength of X; and 7(2,t) refers to the emission intensity detected by the emission intensity detection component when a water sample is detected at the detection wavelength of X; The absorbance values of the to-be-tested water sample at the detection wavelengths of 230 nm and 275 nm are respectively as follows: 1 V(230,0)^230,t) / 275 6 v(27S,0) / ('27S t); S32: Correction of the absorbance of a water sample The absorbance of a water sample is corrected by formula (2): ^corrected -^230 k X. ^275 (2) where k is a correction coefficient, obtained by calculation with the concentrations of nitrates of a water sample and the corresponding absorbances measured by ion chromatography. S33: The corrected absorbance values are converted into the nitrate concentration in water based on a linear relationship between the nitrate concentration and the corrected absorbances. Embodiment 3 This embodiment provides a nitrate sensor, which is used for detecting nitrates in surface water, domestic sewage, or other water samples. The nitrate sensor provided in this embodiment is shown in FIG. 1, and includes: a housing 1, a composite packaged light source 2, a emission intensity detection component 3, and a control circuit mainboard 4. A flow cell is formed between the composite packaged light source 2 and the emission intensity detection component 3 and configured to allow a to-be-tested water sample to pass through. The composite packaged light source 2, the emission intensity detection component 3, and the control circuit mainboard 4 are arranged in the housing 1, and the housing 1 is mainly configured to protect the composite packaged light source 2, the emission intensity detection component 3, and the control circuit mainboard 4. The composite packaged light source 2 includes LED chips and a photodiode chip packaged on a same substrate. The LED chips are distributed in the form of an nxn matrix, the centrosymmetric LED chips in the matrix emit ultraviolet light with same wavelength, and the LED chips at least include LED chips that emit ultraviolet light with wavelength of 230+10 nm and LED chips that emit ultraviolet light with wavelength of 275+10 nm. The multiple LED chips that emit ultraviolet light with same wavelength can improve the intensities of ultraviolet light at a particular wavelength. The photodiode chip is arranged at the center of the matrix and configured to detect the emission intensities of the LED chips in situ. In this embodiment, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. The emission intensity detection component 3 includes a photodiode chip which is configured to detect the emission intensities of ultraviolet light, which are emitted by the composite packaged light source 2, after a to-be-tested water sample absorbing in the flow cell. In this embodiment, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. The control circuit mainboard 4 is configured to control switch-on and switch-off of the composite packaged light source 2, convert the emission intensities detected by the emission intensity detection component 3 into electrical signals, and the like. In this embodiment, the composite packaged light source 2 has a structure shown in FIG. 3, and includes: an LED chip 231, an LED chip 232, an LED chip 233, an LED chip 234, an LED chip 235, an LED chip 236, an LED chip 237, an LED chip 238, and a photodiode chip 239 packaged on the same substrate. The LED chip 231, the LED chip 232, the LED chip 233, the LED chip 234, the LED chip 235, the LED chip 236, the LED chip 237, and the LED chip 238 are distributed in the form of an nxn (n=3) matrix, and the photodiode chip 239 is arranged at the center of the matrix. The LED chip 231 and the LED chip 238 are centrosymmetric and emit ultraviolet light with same wavelength of 275+10 nm, the LED chip 232 and the LED chip 237 are centrosymmetric and emit ultraviolet light with same wavelength of 230+10 nm, the LED chip 234 and the LED chip 235 are centrosymmetric and emit ultraviolet light with same wavelength of 230+10 nm, and the LED chip 233 and the LED chip 236 are centrosymmetric and emit ultraviolet light with same wavelength of 320+10 nm. The composite packaged light source further includes a quartz lens 201 packaged above the LED chips and configured to condense light, and the beam angle is approximately 7°. In this embodiment, connection pins are led out in a packaging manner of a shared anode and independent cathodes, and are separately connected to the respective driver circuits, to implement independent switch control. Embodiment 4 This embodiment provides application of the nitrate sensor in Embodiment 3, for the detection of nitrates in surface water, domestic sewage, or other water samples. The application includes the following steps: S1: Detection of pure water Sil: A pure water sample is allowed to flow through the flow cell formed between the composite packaged light source 2 and the emission intensity detection component 3. S12: The LED chip 232, the LED chip 234, the LED chip 235, and the LED chip 237 that emit ultraviolet light with same wavelength of 230+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(230,0) and 1(230,0), respectively. S13: The LED chip 231 and the LED chip 238 that emit ultraviolet light with same wavelength of 275+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are 1'(275,0) and 1(275,0) respectively. S14: The LED chip 233 and the LED chip 236 that emit ultraviolet light with same wavelength of 320+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are 1'(320,0) and 1(320,0), respectively. S2: Detection of a water sample S21: A water sample is allowed to flow through the flow cell formed between the composite packaged light source 2 and the emission intensity detection component 3. S22: Pulse modulation and frequency are set, the LED chip 232, the LED chip 234, the LED chip 235, and the LED chip 237 that emit ultraviolet light with same wavelength of 230+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at detection wavelength of 230 nm. The emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(230,t) and I(230,t), respectively. S23: Pulse modulation and frequency are set, the LED chip 231 and the LED chip 238 that emit ultraviolet light with same wavelength of 275+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at a detection wavelength of 275 nm. The emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(275,t) and 1(275,t), respectively. S24: Pulse modulation and frequency are set, the LED chip 233 and the LED chip 236 that emit ultraviolet light with same wavelength of 320+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at a detection wavelength of 320 nm. The emission intensities detected by the photodiode chip 225 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(320,t) and 1(320,t), respectively. S3: Calculation of nitrate concentration S31: The absorbances at different detection wavelengths are calculated by formula (1), V(A, 0)^0 / (1) where X refers to a detection wavelength; refers to the absorbance at the detection wavelength of X; refers t° the emission intensity detected by the photodiode chip in the composite packaged light source when pure water is detected at the detection wavelength of X; Z(^o) refers to the emission intensity detected by the emission intensity detection component when pure water is detected at the detection wavelength of X; refers to the emission intensity detected by the photodiode chip in the composite packaged light source when a water sample is detected at the detection wavelength of X; and refers to the emission intensity detected by the emission intensity detection component when a water sample is detected at the detection wavelength of X. The absorbance values of the to-be-tested water sample at the detection wavelengths of 230 nm, 275 nm, and 320 nm are respectively as follows: -^230 — — -^275 = — 1g ^(230,¢ / (230,0)^, 3(230,o / (23O,¢) / Z(275,¢ / (275,0)\ 3(275,0 / (275,¢) A = lg 320 AO If. jf / ’ V(320,0)^(320,t) / S32: Calculation of a correction coefficient A correction coefficient for the detection of nitrates is calculated by formula (3): c_In (-^320 / -^275) zo\ ^275--^320 S33: Calculation of an interference absorbance An interference absorbance on the detection of nitrates is calculated by formula (4): ^230 = A275e-s(230"275) or A^30 = A32oe-S(23°-32O) (4) S34: Correction of the absorbance of a water sample Corrected absorbances for the detection of nitrates are calculated by formula (5): Acorrected=A230~A2^Q (5) S35: The corrected absorbance values are converted into the nitrate concentration in water based on a linear relationship between the concentrations of the nitrates and the corrected absorbances. Table 1 shows after water samples of three sewage plants tested, the comparison results of an absorbance Acorrected corrected by formula (3), formula (4), and formula (5), and an absorbance Acorrected corrected by the same correction coefficient set by a conventional method, based on absorbances A275 and A320 detected at wavelengths of 275 nm and 320 nm. Before a water sample tested by conventional test method , a correction coefficient is calculated based on the concentration of nitrate nitrogen concentration in a water sample and the corresponding absorbance measured by ion chromatography, with the absorbance at the wavelength of 230 nm corrected based on the correction coefficient. In this embodiment, the correction coefficient for the tested wavelength of nitrates is k=2.22, and the corrected absorbance Acorrected' is obtained by Acorrected -A230 -kxA275- It can be seen from the results that, if a uniform correction coefficient is used for correcting the absorbances of nitrates detected, the differences in organic matter between different water samples are ignored, while the coefficient corrected in the method of the present patent is self-corrected based on the absorbance of organic matter contained in water samples, thereby ensuring the accuracy of a correction test. Table 1 Comparison of original and corrected absorbances IC measurement Absorbance data Dual-wavelength absorbance correction method Method of this embodiment Sample N03'-N concentration (mg / L) A230 A275 A320 N03'-N k Acorrected' concentration Deviation (mg / L) 5 N03--N Acomaed concentration Deviation (mg / L) A 10.48 0.269 0.044 0.017 2.02 0.181 11.27 7.62% 0.0211 0.156 9.74 -7.04% B 11.10 0.277 0.042 0.016 0.192 11.94 7.58% 0.0216 0.165 10.28 -7.37% C 8.64 0.229 0.035 0.014 0.159 9.89 14.46% 0.0194 0.146 9.08 5.04% Embodiment 5 This embodiment provides a nitrate sensor, which is used for detecting nitrates in surface water, domestic sewage, or other water samples. The nitrate sensor provided in this embodiment is shown in FIG. 1, and includes: a housing 1, a composite packaged light source 2, a emission intensity detection component 3, and a control circuit mainboard 4. A flow cell is formed between the composite packaged light source 2 and the emission intensity detection component 3 and configured to allow a to-be-tested water sample to pass through. The composite packaged light source 2, the emission intensity detection component 3, and the control circuit mainboard 4 are arranged in the housing 1, and the housing 1 is mainly configured to protect the composite packaged light source 2, the emission intensity detection component 3, and the control circuit mainboard 4. The composite packaged light source 2 includes LED chips and a photodiode chip packaged on a same substrate. The LED chips are distributed in the form of an nxn matrix, the centrosymmetric LED chips in the matrix emit ultraviolet light with same wavelength, and the LED chips at least include LED chips that emit ultraviolet light with wavelength of 230+10 nm and LED chips that emit ultraviolet light having a wavelength of 275+10 nm. The multiple LED chips that emit ultraviolet light with same wavelength can improve the intensities of ultraviolet light at particular wavelength. The photodiode chip is arranged at the center of the matrix and configured to detect the emission intensities of the LED chips in situ. In this embodiment, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. The emission intensity detection component 3 includes a photodiode chip which is configured to detect the luminous intensities of ultraviolet light, which are emitted by the composite packaged light source 2, after a to-be-tested water sample absorbing in the flow cell. In this embodiment, the photodiode chip includes an AlGaN-based deep ultraviolet photodiode chip. The control circuit mainboard 4 is configured to control switch-on and switch-off of the composite packaged light source 2, convert the emission intensities detected by the emission intensity detection component 3 into electrical signals, and the like. In this embodiment, the composite packaged light source 2 has a structure shown in FIG. 3, and includes: an LED chip 231, an LED chip 232, an LED chip 233, an LED chip 234, an LED chip 235, an LED chip 236, an LED chip 237, an LED chip 238, and a photodiode chip 239 packaged on the same substrate. The LED chip 231, the LED chip 232, the LED chip 233, the LED chip 234, the LED chip 235, the LED chip 236, the LED chip 237, and the LED chip 238 are distributed in the form of an nxn (n=3) matrix, and the photodiode chip 239 is arranged at the center of the matrix. The LED chip 231 and the LED chip 238 are centrosymmetric and emit ultraviolet light with same wavelength of 320+10 nm, the LED chip 232 and the LED chip 237 are centrosymmetric and emit ultraviolet light with same wavelength of 230+10 nm, the LED chip 234 and the LED chip 235 are centrosymmetric and emit ultraviolet light with same wavelength of 275+10 nm, and the LED chip 233 and the LED chip 236 are centrosymmetric and emit ultraviolet light with same wavelength of 365+10 nm. The composite packaged light source further includes a quartz lens 201 packaged above the LED chips and configured to condense light, and the beam angle is approximately 7°. In this embodiment, connection pins are led out in a packaging manner of a shared anode and independent cathodes, and are separately connected to the respective driver circuits, to implement independent switch control. Embodiment 6 This embodiment provides application of the nitrate sensor in Embodiment 5, for the detection of nitrates in surface water, domestic sewage, or other water samples. The application includes the following steps: S1: Detection of pure water Sil: A pure water sample is allowed to flow through the flow cell formed between the composite packaged light source 2 and the emission intensity detection component 3. S12: The LED chip 232 and the LED chip 237 that emit ultraviolet light with same wavelength of 230+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(230,0) and 1(230,0) respectively. S13: The LED chip 234 and the LED chip 235 that emit ultraviolet light with same wavelength of 275+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are 1'(275,0) and 1(275,0) respectively. S14: The LED chip 231 and the LED chip 238 that emit ultraviolet light with same wavelength of 320+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are 1'(320,0) and 1(320,0) respectively. S15: The LED chip 233 and the LED chip 236 that emit ultraviolet light with same wavelength of 365+10 nm are enabled to emit strobe light simultaneously, and the emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are / 365' and I365 respectively. S2: Detection of a water sample S21: A water sample is allowed to flow through the flow cell formed between the composite packaged light source 2 and the emission intensity detection component 3. S22: Pulse modulation and frequency are set, the LED chip 232 and the LED chip 237 that emit ultraviolet light with same wavelength of 230+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at a detection wavelength of 230 nm. The emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(230,t) and 1(230,t) respectively. S23: Pulse modulation and frequency are set, the LED chip 234 and the LED chip 235 that emit ultraviolet light with same wavelength of 275+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at a detection wavelength of 275 nm. The emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(275,t) and 1(275,t) respectively. S24: Pulse modulation and frequency are set, the LED chip 231 and the LED chip 238 that emit ultraviolet light with same wavelength of 320+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at a detection wavelength of 320 nm. The emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are 1'(3203) and 1(320,t) respectively. S25: Pulse modulation and frequency are set, the LED chip 233 and the LED chip 236 that emit ultraviolet light with same wavelength of 365+10 nm are enabled to emit strobe light simultaneously, and the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 detect the emission intensities respectively. At least 10 emission intensity signals are acquired, sorted in descending order, and a maximum value is used as the representative emission intensity value at a detection wavelength of 365 nm. The emission intensities detected by the photodiode chip 239 in the composite packaged light source 2 and the emission intensity detection component 3 are I'(365,t) and 1(365,t) respectively. S3: Calculation of nitrate concentration S31: The absorbances at different detection wavelengths are calculated by formula (1), Ie 8 VGUO)^), (1) where X refers to a detection wavelength; refers to the absorbance at the detection wavelength of X; refers to the emission intensity detected by the photodiode chip in the composite packaged light source when pure water is detected at the detection wavelength of X; / (^0) refers to the emission intensity detected by the emission intensity detection component when pure water is detected at the detection wavelength of X; ^(A,t) refers to the emission intensity detected by the photodiode chip in the composite packaged light source when a water sample is detected at the detection wavelength of X; and / (^t) refers to the emission intensity detected by the emission intensity detection component when a water sample is detected at the detection wavelength of X. The absorbance values of the to-be-tested water sample at the detection wavelengths of 230 nm, 275 nm, 320 nm, and 365 nm are respectively as follows: Z(365,Otsego) S32: Calculation of a correction coefficient Based on the absorbances A275 and A320 at the detection wavelengths of 275 nm and 320 nm, a correction coefficient Si for the detection of nitrates is calculated by formula (6): c _In O320M275) z275-z320 Based on the absorbances A320 and A365 at the detection wavelengths of 320 nm and 365 nm, a correction coefficient S2 for the detection of nitrates is calculated by formula (7): c _ In 01365 / ^320) / -7 > d2 — —j 25 v) A320A365 A correction coefficient S' is obtained by taking the average value of Si and S2. S33: Calculation of an interference absorbance An interference absorbance on the detection of nitrates is calculated by formula (8): A' — A p—S'(230—275) nr A' — A p—S'(230—320) m 3' — A p-S'(230-365) zo\ ^230 — n275e or -^230 — ^3206 or -^230 — ^3656 (°) S34: Correction of the absorbance of a water sample Corrected absorbances for the detection of nitrates are calculated by formula (5): Acorrected=A230~A22Q (5) S35: The corrected absorbance values are converted into the nitrate concentration in water based on a linear relationship between the concentrations of the nitrates and the corrected absorbances. Embodiment 7 This embodiment further provides a method (filter algorithm) of filtration of abnormal absorbances. The method specifically includes the following steps: Absorbance values (Embodiment 6) are stored in a built-in memory and outputted to a display for displaying. As the measurement time sequence increases, a series of absorbance values are stored in the memory. By using the absorbance data at a wavelength of 230 nm as an example, 11 pieces of absorbance data are selected as monitoring windows [A(23o,ij, A(230,2), ■ ■■, A(230,ii)], and the absolute deviations between the data points in the windows and the median M230 is calculated. A threshold T=3xMAD is set. The deviation value \A(23o,m)-M23o\ between each point in a monitoring window and the median is compared with a preset threshold T: if \A(23o,m)-M23o\<A, the value is reserved, and if \A(23o,m)-M23o\>A, the value is considered as an outlier, and the outlier is replaced with the median value M230. FIG. 4 is a comparison between an original absorbance value obtained and an absorbance value processed by a filter algorithm when a detector is applied to detection of nitrates in effluent water of a municipal sewage plant. Obvious outliers are excluded after the absorbances detected by the detector are processed, also the original data is not excessively smoothed, and the original signal characteristics are effectively reserved.

Claims

What is claimed is:

1. A nitrate sensor, comprising: a housing, a composite packaged light source, an emission intensity detection component, and a control circuit mainboard, wherein a flow cell is formed between the composite packaged light source and the emission intensity detection component; the composite packaged light source, the emission intensity detection component, and the control circuit mainboard are arranged in the housing; the composite packaged light source emits ultraviolet light at a particular wavelength in the direction of the flow cell; the emission intensity detection component comprises a photodiode chip; the control circuit mainboard is configured to control switch-on and switch-off of LED chips in the composite packaged light source; whereinthe composite packaged light source comprises the LED chips and a photodiode chip packaged on a same substrate; the LED chips are arranged in the form of an nxn matrix, the centrosymmetric LED chips in the matrix emit ultraviolet light with same wavelength, and the LED chips at least comprise LED chips that emit ultraviolet light with wavelength of 230 10 nm and LED chips that emit ultraviolet light with wavelength of 275±10 nm; and the photodiode chip is arranged at the center of the matrix.

2. The nitrate sensor according to claim 1, wherein n=2-5.

3. The nitrate sensor according to claim 2, wherein n=2, and the LED chips comprise LED chips that emit ultraviolet light at wavelengths of 230 10 nm and 275 10 nm with the number of LED at each wavelength is 2.

4. The nitrate sensor according to claim 2, wherein n=3, the LED chips comprise LED chips that emit ultraviolet light at wavelengths of 230 lOnm, 275 10 nm, and 320 lOnm, the number of the LED chips that emit ultraviolet light at wavelength of 230 10 nm is 4, and the numbers of the LED chips that emit ultraviolet light at wavelengths of 275 10 nm and 320 10 nm respectively are 2, respectively.

5. The nitrate sensor according to claim 2, wherein n=3, the LED chips comprise LED chips that emit ultraviolet light at wavelengths of 230 10 nm, 275 10 nm, 320 10 nm, and 365 10 nm, the numbers of which are 2 respectively.

6. The nitrate sensor according to any one of claims 1 to 5, wherein a quartz lens is packaged above the LED chips of the composite packaged light source.

7. Use of the nitrate sensor according to any one of claims 1 to 6 in detection of nitrates in a water sample.

8. A method for detecting nitrates in water samples using the nitrate sensor according to claim 7, whereinthe method comprises:in-situ detection and correction of emission intensities: measuring the emission intensities of the LED chips and the corresponding emission intensities detected by the detection component in pure water, as well as the emission intensities of the LED chips and the corresponding emission intensities detected by the detection component during testing with a water sample, and obtaining corrected emission intensities through two groups of emission intensity signals;sorting and screening of emission intensity signals: controlling, by using pulse modulation and frequency setting, the LED chips that emit ultraviolet light at the same wavelength to emit strobe light for multiple times, sorting the obtained emission intensity signals, using a maximum value as a emission intensity representative value at the wavelength, and further obtaining absorbance values by calculation; andcorrection of the detected absorbance of nitrate: correcting the absorbance values obtained at detection wavelengths of 230 nm and 275 nm; or obtaining an organic matter correction coefficient by calculation with the absorbance values obtained at wavelengths other than 230 nm, so as to obtain an interference absorbance of organic matter on the detection of nitrates and corrected absorbances for the detection of nitrates.

9. The method according to claim 8, whereinthe nitrate sensor is the nitrate sensor according to claim 3, and the method thereof comprises the following steps:S1: detection of pure waterSil: allowing a pure water sample to flow through the flow cell formed between the composite packaged light source and the emission intensity detection component;S12: enabling the LED chips that emit ultraviolet light with same wavelength of 230 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chipin the composite packaged light source and the emission intensity detected by detection component being I'(230,0) and 1(230,0) respectively; andSI3: enabling the LED chips that emit ultraviolet light having a same wavelength of 275 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detected by detection component being l'(275,0) and 1(275,0) respectively;S2: detection of a water sampleS21: allowing a water sample to flow through the flow cell formed between the composite packaged light source and the emission intensity detection component;S22: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 230 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using a maximum value as a representative emission intensity value at a detection wavelength of 230 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(230,t) and 1(230,t) respectively; andS23: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 275 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using a maximum value as arepresentative emission intensity value at a detection wavelength of 275 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(275,t) and 1(275,t) respectively; andS3: calculation of nitrate concentrationS31: calculating the absorbances at different detection wavelengths by formula (1),(1)whereinX refers to a detection wavelength;refers to the absorbance at the detection wavelength of X; / (2 o) refers to the emission intensity detected by the photodiode chip in the composite packaged light source when pure water is detected at the detection wavelength of X;^230 — — 1g (-^275 = — 1g ( / (2,o) refers to the emission intensity detected by the emission intensity detection component when pure water is detected at the detection wavelength of A.; / (2^ refers to the emission intensity detected by the photodiode chip in the composite packaged light source when a water sample is detected at the detection wavelength of X; / (2,t) refers to the emission intensity detected by the emission intensity detection component when a water sample is detected at the detection wavelength of 1; andthe absorbance values of the to-be-tested water sample at the detection wavelengths of 230 nm and 275 nm are respectively as follows: / (230, 0^(230,0)3^(230,0)^(230 / ) / ^(275 / )^(275,0)3 ^(275,0)^(275 / ) / S32: correcting the absorbance of a water sample,and specifically, correcting the absorbance of a water sample by formula (2): ^corrected — -^230 — k X / I275 (2)wherein k is a correction coefficient, obtained by calculation with the concentrations of nitrates of a water sample and the corresponding absorbances measured by ion chromatography; andS33: converting the corrected absorbance values into the nitrate concentration in water based on a linear relationship between the concentrations of the nitrates and the corrected absorbances,10. The method according to claim 8, wherein the nitrate sensor is the nitrate sensor according to claim 4, and the method thereof comprises the following steps:S1: detection of pure waterSil: allowing a pure water sample to flow through the flow cell formed between the composite packaged light source and the emission intensity detection component;S12: enabling the LED chips that emit ultraviolet light with same wavelength of 230 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detected by detection component being I'(23o,o) and 1(230,0) respectively;S13: enabling the LED chips that emit ultraviolet light with same wavelength of 275 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detected by detectioncomponent being 1(275,0) and 1(275,0) respectively; andS14: enabling the LED chips that emit ultraviolet light with same wavelength of 320 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detected by detection component being 1'(320,0) and 1(320,0) respectively;S2: detection of a water sampleS21: allowing a water sample to flow through the flow cell formed between the composite packaged light source and the emission intensity detection component;S22: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 230 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using a maximum value as a emission intensity representative value at a detection wavelength of 230 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(230,t) and 1(230,t) respectively;S23: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 275 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using a maximum value as a emission intensity representative value at a detection wavelength of 275 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(275,t) and 1(275,t) respectively; andS24: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 320 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using a maximum value as a emission intensity representative value at a detection wavelength of 320 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(320,t) and I(320,t) respectively; andS3: calculation of nitrate concentrationS31: calculating the absorbances at different detection wavelengths by formula (1),wherein the absorbance values of the to-be-tested water sample at the detection wavelengths of 230 nm, 275 nm, and 320 nm are respectively as follows:-^230 —-^275 — 1g^320 —^(230,0^(230,0)^, / (230,0) / (230,() / 7(275,0^275,0)^, / (275,0) / (275,() / / (320,() / (320,0)^, / (320,0) / (320,() / S32: calculating a correction coefficient,and specifically, calculating a correction coefficient for the detection of nitrates by formula (3):_ ln CA320M275) q) / 275- / 320S33: calculating an interference absorbance,and specifically, calculating an interference absorbance on the detection of nitrates by formula (4):a' — A p—5(230—275) nr 4' — A „—5(230—320) (4)^230 — ^275^ or n230 — ^3206 WS34: correcting the absorbance of a water sample,and specifically, calculating corrected absorbances for the detection of nitrates by formula (5):^corrected=A230~^230 (5) andS35: converting the corrected absorbance values into the nitrate concentration in water based on a linear relationship between the concentrations of the nitrates and the corrected absorbances.

11. The method according to claim 8, wherein the nitrate sensor is the nitrate sensor according to claim 5, and the method thereof comprises the following steps:S1: detection of pure waterSil: allowing a pure water sample to flow through the flow cell formed between the composite packaged light source and the emission intensity detection component;SI2: enabling the LED chips that emit ultraviolet light with same wavelength of 230 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detected by detection component being I'pso.o) and 1(230,0) respectively;SI3: enabling the LED chips that emit ultraviolet light having a same wavelength of275 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(275,0) and 1(275,0) respectively;SI4: enabling the LED chips that emit ultraviolet light having a same wavelength of 320 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detected by detection component being I'(32o,o) and 1(320,0) respectively; andSI5: enabling the LED chips that emit ultraviolet light having a same wavelength of 365 10 nm to emit strobe light simultaneously, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I365' and I365 respectively;S2: detection of a water sampleS21: allowing a water sample to flow through the flow cell formed between the composite packaged light source and the emission intensity detection component;S22: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 230 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using the maximum value as the representative emission intensity value at a detection wavelength of 230 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(230,t) and 1(230,t) respectively;S23: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 275 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using the maximum value as the representative emission intensity value at a detection wavelength of 275 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(275,t) and 1(275,t) respectively;S24: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 320 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emissionintensity signals, sorting the emission intensities in descending order, and using a maximum value as a emission intensity representative value at a detection wavelength of 320 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(320,t) and I(320,t) respectively; andS25: setting pulse modulation and frequency, and enabling the LED chips that emit ultraviolet light having a same wavelength of 365 10 nm to emit strobe light simultaneously, the photodiode chip in the composite packaged light source and the emission intensity detection component detecting the emission intensities respectively; and acquiring at least 10 emission intensity signals, sorting the emission intensities in descending order, and using a maximum value as a emission intensity representative value at a detection wavelength of 365 nm, the emission intensities detected by the photodiode chip in the composite packaged light source and the emission intensity detection component being I'(365,t) and 1(365,t) respectively; andS3: calculation of nitrate concentrationS31: calculating the absorbances at different detection wavelengths by formula (1), wherein the absorbance values of the to-be-tested water sample at the detection wavelengths of 230 nm, 275 nm, 320 nm, and 365 nm are respectively as follows:^230 — — 1g-^275 —-^320 — — 1g^365 — — 1g / (230, ¢)^230,0)3 7(230,0)^(230,t) / h275,tV(27S,0)\. 7(275,0 / (275,0 / 7(320,0^(320,0) A.7(320,0)^(320, 0 / 7(365, 0^(365,0)3. 7(365,o / (365,t) / S32: calculating a correction coefficient,specifically, based on the absorbances A275 and A320 at the detection wavelengths of 275 nm and 320 nm, calculating a correction coefficient Si for the detection of nitrates by formula (6):_ _ In (^320 / 7)275) / ,,, 0 (6)^275-^320specifically, based on the absorbances A320 and A365 at the detection wavelengths of 320nm and 365 nm, calculating a correction coefficient S2 for the detection of nitrates by formula (7):„ _ In (a36S / a32o) / -,,d2 — , , UJ^320^^365and obtaining a correction coefficient S' by taking the average value of Si and S2;S33: calculating an interference absorbance,and specifically, calculating an interference absorbance on the detection of nitrates by formula (8):4' — A 4,-^(230-275) nr A' — A ,,-S'(230-320) „r A' — A o-S’(230-365) zo\ ^230 - ^2756 or ^230 “ ^3206 or ^230 “ ^3656 I8)S34: correcting the absorbance of a water sample,and specifically, calculating corrected absorbances for the detection of nitrates by formula (5):Acorrected=A.230~A220 (5) andS35: converting the corrected absorbance values into the nitrate concentration in water based on a linear relationship between the nitrate concentration and the corrected absorbances.

12. The method according to any one of claims 8 to 11, wherein the method further comprises filtration of abnormal absorbances, the filtration of abnormal absorbances comprising:storing absorbance values in a built-in memory;after a series of absorbance values are stored in the memory, selecting a particular number (m) of pieces of absorbance data in a time sequence at the detection wavelength of A. as a monitoring array [A(x.i), Ap,2), ..., Ap,m)];for each point in a window, calculating a median Mx of all data points in the window and a median absolute deviation MAD;setting a threshold T=pxMAD; andcomparing a deviation |A(x,m)-Mx| between each point in a monitoring window and the median with a preset threshold T: if |A(x,m)-Mx|<T, reserving the value, and if |Ap,m)-Mx|>T, considering the value as an outlier, and replacing the outlier with the median value Mx.

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