Parameter pool automatic calibration method and system of water quality monitoring station

Abstract

This invention discloses an automatic calibration method and system for parameter cells in a water quality monitoring station, belonging to the field of water quality optical detection technology. When the method enters the detection state, it collects absorbance data sets of the detection cell and reference cell at different frequencies. Then, based on the absorbance and the current optical path, it calculates the concentration of the target substance in the water sample, making it particularly suitable for detecting nitrate and COD content in water. To avoid the influence of refractive index changes in the sample on the detection results, when entering the calibration state, this invention calculates the minimum phase difference between the detection arm and the reference arm based on the beat frequency data, then predicts the actual phase difference and calibrates the current optical path of the detection cell. Furthermore, this invention uses historical phase difference data as a reference and employs common-mode interference light to increase the refractive index range, thereby improving the accuracy of monitoring.

Description

Technical Field

[0001] This invention relates to the field of optical detection technology for water quality, and in particular to an automatic calibration method and system for parameter pools in a water quality monitoring station. Background Technology

[0002] Spectroscopic methods utilize the absorption degree of characteristic electromagnetic radiation by molecules or ions to quantitatively analyze the analyte. This method can be used for non-contact detection of water pollution, requiring no chemical reagents and causing no secondary pollution. Chinese Patent Publication No. CN111650141A discloses a water quality monitoring method based on multi-wavelength absorbance. This method includes irradiating a water body with at least two wavelengths of visible light, receiving the visible band absorbance data generated through the water body, fitting the visible band absorbance data to obtain compensated absorbance data in the ultraviolet band corresponding to window pollution and water turbidity, irradiating the water body with a preset ultraviolet band light, receiving the measured ultraviolet band absorbance data, subtracting the compensated absorbance data from the measured ultraviolet band absorbance data to obtain the true ultraviolet band absorbance data, and calculating the water quality parameters based on the true absorbance data. According to Beer-Lambert's law, the true absorbance data A = kCL, where k is the absorption coefficient, C is the solution concentration, and L is the optical path length of the detection cell. The COD concentration of the current aqueous solution can be obtained by pre-fitting the absorbance coefficient of the COD standard solution. This patent application assumes that the sample refractive index remains constant, thus keeping the optical path length of the detection cell constant. However, in practical applications, the concentration range of the water sample to be tested varies greatly, and the refractive index may change, affecting the accuracy of the detection results. Therefore, a method is needed to improve the accuracy of water pollution monitoring by calibrating the refractive index and optical path length using existing conditions. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides an automatic calibration method and system for parameter cells in a water quality monitoring station. This method monitors the concentration of target substances in the water sample by measuring the absorbance of light at different frequencies. Furthermore, this invention predicts refractive index changes by comparing the beat frequency light intensity between the detection cell and the reference cell, thereby calibrating the current optical path length of the detection cell and improving the accuracy of the monitoring data.

[0004] The objective of this invention can be achieved through the following technical means: An automatic calibration method for parameter pools in a water quality monitoring station includes the following steps: Step 1: Pump the water sample to be tested into the detection cell set in the detection arm, and pump the reference water sample into the reference cell set in the reference arm to initialize the reference phase; Step 2: Enter the detection state. The light generator generates the first incident light. The first incident light passes through the detection cell and the reference cell and enters the first receiver and the second receiver respectively, generating the first light intensity and the second light intensity respectively. Step 3: Calculate the absorbance of the detection cell based on the first and second light intensities, adjust the wavelength of the first incident light to obtain the absorbance at different wavelengths, and calculate the concentration of the target substance in the water sample to be tested based on the current optical path. Step 4: If a calibration instruction is received, proceed to Step 5; otherwise, return to Step 2. Step 5: Enter calibration state. The light generator generates a second incident light and modulates the second incident light into interference light. The interference light enters the first receiver and the second receiver through the detection cell and the reference cell, respectively, generating the first interference signal and the second interference signal. Step 6: Calculate the minimum phase difference between the detection arm and the reference arm based on the first interference signal and the second interference signal, predict the actual phase difference in combination with the reference phase, calibrate the current optical path of the detection cell based on the actual phase difference, update the reference phase, and return to step 2.

[0005] In this invention, the first incident light is broadband light and the second incident light is infrared light.

[0006] In this invention, in step 2, after entering the detection state, the first incident light is selected by the dichroic separator to be a single wavelength light. The single wavelength light is separated into a first refracted light and a first reflected light by the first beam splitter. The first refracted light passes through the detection cell and enters the first receiver, and the first reflected light passes through the reference cell and enters the second receiver.

[0007] In this invention, in step 3, the absorbance of the first incident light at different wavelengths forms an absorbance matrix B, the absorption coefficients of different components to the first incident light form a transformation matrix K, and the concentration vector C is calculated by combining B=εCK. The concentration of the target substance is extracted from the concentration vector C, and ε is the current optical path of the detection cell.

[0008] In this invention, the first absorbance matrix after the end of the previous calibration state is extracted, the variance between the current absorbance matrix and the first absorbance matrix is ​​calculated, and the calibration instruction is generated when the detection duration is greater than a first threshold or the variance is greater than a second threshold. After the calibration state ends, the detection duration is initialized.

[0009] In this invention, in step 5, the second incident light is separated into a second reflected light and a second refracted light by a second beam splitter, the second reflected light is modulated into a third incident light, and the second refracted light and the third incident light are combined into common-mode interference light by a third beam splitter.

[0010] In this invention, in step 6, the first interference signal and the second interference signal are mixed based on the orthogonal reference signal to obtain orthogonal components, the phase angle of the first interference signal and the second interference signal is calculated, the minimum phase difference Δω' is calculated, and the integer j that makes |j2π+Δω'-ω0| take the minimum value is calculated. The actual phase difference Δω=j2π+Δω'.

[0011] In this invention, the refractive index η of the detection cell is first calibrated according to the actual phase difference Δω, η=η0+Δωλ0 / (2πL), where η0 is the refractive index of the reference water sample, λ0 is the wavelength of the interference light, and L is the geometric width of the detection cell. Then, the current optical path ε=ηL of the detection cell is calculated, and finally, the reference phase ω0=Δω is updated.

[0012] A system for implementing the automatic calibration method for the parameter pool of the water quality monitoring station includes: The testing pool is configured to store water samples to be tested. The reference pool is configured to store reference water samples; The light generator is configured to generate either a first incident light or a second incident light; An optical path assembly is configured to construct an optical path for receiving a first incident light or a second incident light; The detection arm is configured as the optical path for constructing the detection cell; The reference arm is configured as the optical path for constructing the reference cell; The first receiver is configured to generate a first light intensity or a first interference signal for the detection cell; The second receiver is configured to generate a second light intensity or a second interference signal for the reference cell; The data processing unit is configured to predict the concentration of the target substance based on the first light intensity, the second light intensity, and the current optical path. The calibration unit is configured to calibrate the current optical path based on the first interference signal and the second interference signal; The optical path controller is configured to switch the optical path components to detection or calibration states.

[0013] In this invention, the optical path assembly includes at least a first beam splitter, a dichroic separator, a second beam splitter, a third beam splitter, and an acousto-optic modulator. When the first beam splitter and dichroic separator are engaged, the system enters a detection state; when the first beam splitter, the second beam splitter, the third beam splitter, and the acousto-optic modulator are engaged, the system enters a calibration state.

[0014] The present invention discloses an automatic calibration method and system for parameter cells in a water quality monitoring station. Its advantages include: First, the method collects absorbance data sets of the detection cell and reference cell at different frequencies, then calculates the concentration of the target substance in the water sample, making it particularly suitable for detecting nitrate and COD content in water. Since the current optical path affects absorbance, the present invention calculates the phase difference of light passing through the detection cell and reference cell using beat frequency data from the detection arm and reference arm, thereby calibrating the actual refractive index of the detection cell. Then, based on the refractive index and the geometric width of the detection cell, the current optical path is calibrated, improving monitoring accuracy. Furthermore, the present invention uses historical phase difference data as a reference and employs common-mode interference to increase the range of refractive index. The present invention can quickly switch optical path states through optical path components, improving calibration convenience and enabling online continuous monitoring. Attached Figure Description

[0015] Figure 1 This is a flowchart of an automatic calibration method for the parameter pool of a water quality monitoring station according to the present invention; Figure 2 This is a schematic diagram of the optical path for detecting the state of the present invention; Figure 3 This is a schematic diagram of the first incident light passing through the optical path assembly of the present invention; Figure 4 This is a schematic diagram of the current optical path of the detection cell in this invention; Figure 5 Absorbance curves of nitrate aqueous solutions with different molar concentrations; Figure 6 This is a schematic diagram of the optical path during the calibration state of the present invention; Figure 7 This is a schematic diagram of the second incident light passing through the optical path assembly of the present invention; Figure 8 Refractive index fitting plots for COD solutions with different molar concentrations; Figure 9 This is a block diagram of the system for implementing the automatic calibration method for the parameter pool of the water quality monitoring station according to the present invention; Figure 10 This is a schematic diagram of the optical path controller of the present invention; Figure 11 This is a schematic diagram of the horizontal layout of the system for implementing the automatic calibration method of the parameter pool of the water quality monitoring station according to the present invention.

[0016] The attached figures are labeled as follows: Detection cell 11, Reference cell 12, Moving prism 13, Fixed prism 14, Light generator 21, First receiver 22, Second receiver 23, First beam splitter 31, Dichroic separator 32, Second beam splitter 33, Third beam splitter 34, Acousto-optic modulator 35, Collimating lens 36, Light intensity monitor 37, First pump 41, Second pump 42, First tank 43, Second tank 44, Third tank 45. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Example 1

[0018] This invention uses ultraviolet-visible spectroscopy to obtain the absorbance of water bodies, and then combines this with Lambert-Beer's law to detect water pollution indicators such as nitrate content and COD. Furthermore, it automatically calibrates the current optical path parameters based on the phase difference between the detection cell and the reference cell, thereby improving the accuracy of water pollution monitoring. Figures 1 to 8 The present invention provides an automatic calibration method for the parameter pool of a water quality monitoring station, comprising the following steps.

[0019] Step 1: Pump the water sample to be tested into the detection cell located within the detection arm, and pump the reference water sample into the reference cell located within the reference arm, initializing the reference phase. The detection arm constructs the optical path of the detection cell, and the reference arm constructs the optical path of the refracting reference cell. In water pollution monitoring, the reference water sample is, for example, pure water. The reference water sample is used to construct the same external environment as the water sample to be tested, to compensate for errors caused by the external environment. The reference phase is the fundamental phase difference between the detection cell and the reference cell confirmed during equipment commissioning. Ideally, the optical parameters of the detection cell and the reference cell are the same, and the geometric lengths of the detection arm and the reference arm are also the same; in this case, the reference phase ω0 = 0 is initialized.

[0020] Step 2: Entering the detection state, the light generator generates the first incident light. This first incident light passes through the detection cell and reference cell, respectively, and then enters the first and second receivers, generating the first and second light intensities, respectively. The first incident light is broadband light. When monitoring relevant parameters such as nitrate, COD, BOD, and TOC in water, ultraviolet-visible light with a wavelength range of 10nm-780nm is used. (Refer to...) Figures 2 to 4 After entering the detection state, the first incident light is selected as a single wavelength by a dichroic separator. This single wavelength is then separated into a first refracted light and a first reflected light by a first beam splitter. The first beam splitter separates lasers of different frequencies. According to the beam splitter's principle, the first refracted light and the first reflected light have the same frequency but differ in rotation by 45°. The first refracted light passes through the detection cell and enters the first receiver, while the first reflected light passes through the reference cell and enters the second receiver. Specifically, a moving prism changes the optical path of the first refracted light, guiding it to the first receiver. A fixed prism changes the optical path of the first reflected light, guiding it to the second receiver. The moving and fixed prisms determine the geometric lengths of the detection arm and the reference arm. If the geometric lengths of the detection arm and the reference arm are unequal, the initial value of the reference phase can be adjusted accordingly during equipment debugging.

[0021] Step 3: Calculate the absorbance of the detection cell based on the first and second light intensities. Adjust the wavelength of the first incident light to obtain absorbance at different wavelengths. Combine this with the current optical path length to calculate the target concentration of the water sample. The first incident light is a broadband light with multiple wavelengths. The dichroic analyzer disperses the composite light and selects high-purity monochromatic light. A set of absorbances is obtained for each wavelength of the first incident light. The absorbances of the first incident light at different wavelengths form the absorbance matrix B. As described in Example 2, this invention updates the transformation matrix K based on the current optical path length and the absorption coefficients of different components to the first incident light. Combine this with B=εCK to calculate the concentration vector C, and extract the target concentration from the concentration vector C. ε is the current optical path length of the detection cell.

[0022] Step 4: If a calibration command is received, proceed to Step 5; otherwise, return to Step 2. This invention requires determining the moment to enter the calibration state based on the detection duration and fluctuations in the detection data. The first absorbance matrix after the end of the previous calibration state is taken, and the variance between the current absorbance matrix and the first absorbance matrix is ​​calculated. The variance is used to measure the fluctuation of the detection data between the current moment and the first detection after calibration. A clock unit is set up to record the detection duration after calibration; the detection duration is initialized after each calibration state ends. The calibration command is generated when the detection duration exceeds a first threshold or the variance exceeds a second threshold. The first and second thresholds are related to the system accuracy. The first threshold is, for example, 4 hours, and the second threshold is, for example, 5 × 10⁻⁶. -4 .

[0023] Step 5: Enter calibration mode. The light generator generates a second incident light, which is modulated into interference light. The interference light passes through the detection cell and reference cell, respectively, and enters the first and second receivers, generating the first and second interference signals, respectively. (Refer to...) Figure 6 The second incident light is separated into a second reflected light and a second refracted light by a second beam splitter. The second reflected light is modulated into a third incident light. The second refracted light and the third incident light are then combined by a third beam splitter to form a common-mode interference light. The second incident light is infrared light (wavelength 1550nm) with a frequency of, for example, 193THz. The third incident light is frequency-modulated near-infrared light with a frequency of, for example, 193THz + 80MHz. The frequency of the interference light in this case is, for example, 80MHz. Combining ultra-high frequency incident light into interference light increases the wavelength and expands the detection range. Furthermore, common-mode interference light can significantly suppress common-mode noise and improve calibration speed.

[0024] Step 6: Calculate the minimum phase difference between the detection arm and the reference arm based on the first and second interference signals. Combine this with the reference phase to predict the actual phase difference. Based on this phase difference, calibrate the current optical path of the detection cell, update the reference phase, and return to Step 2. On a macroscopic scale, both the first interference signal I1(t) and the second interference signal I2(t) at this frequency are trigonometric functions of time t. Due to the refraction of the target object within the detection cell, the first interference signal I1(t) and the second interference signal I2(t) have the same amplitude but different phases. The refractive index and current optical path of the detection cell can be calibrated based on the phase difference. This invention uses an orthogonal reference signal to perform a mixing operation on the first interference signal to obtain a first orthogonal component. The phase of the first interference signal is calculated based on the first orthogonal component, the phase of the second interference signal is calculated based on the second orthogonal component, and then the minimum phase difference is calculated.

[0025] Furthermore, since the phase of the trigonometric function ranges from 0 to 2π, the calculated phase difference is the minimum phase difference. The actual phase difference Δω needs to be obtained from the reference phase ω0. The refractive index of the detection cell is calibrated based on the actual phase difference, and then the current optical path ε is calculated. It should be noted that since the reference arm and the detection arm are in the same detection environment, the phase difference is related to the current optical path ε of the detection cell. At this point, the total optical path of the detection arm is ε - L + ε0, where L is the geometric width of the detection cell and ε0 is the optical path of the reference arm. After calibration, the reference phase ω0 is updated based on the actual phase difference Δω, ω0 = Δω. Example 2

[0026] Common pollutants in water bodies absorb light signals, thereby changing their absorbance, and different pollutants absorb light signals of different frequencies to varying degrees. Figure 5 The absorbance curves of nitrate aqueous solutions with different molar concentrations are shown, with the molar concentration increasing sequentially from bottom to top. This embodiment further discloses the preferred method of the present invention for calculating the concentration of the target substance based on the absorbance of broadband light.

[0027] Step 301: Calculate the absorbance of the detection cell based on the first and second light intensities. The absorbance b corresponding to wavelength n. n =lg(I n2 / I n1 ), I n1 For the first light intensity, I n2 This is the second light intensity. Ideally, the refractive index of the reference cell is close to 1.3. Due to the extremely high frequency of the light wave, the first and second receivers measure the average light intensity on a macroscopic scale.

[0028] Step 302: Select N groups of first incident light wavelengths, and form an absorbance matrix B based on the absorbance of the first incident light at different wavelengths. B = [b1b2... b... n ... b N Typically, 10 to 20 characteristic wavelengths of absorption by the target analyte are selected. For example, COD and nitrates usually show significant absorption at wavelengths of 220 nm, 240 nm, 250 nm, and 270 nm.

[0029] Step 303: Extract the transformation matrix K, composed of the absorption coefficients of different components for the first incident light. The absorption coefficient describes the degree to which light is absorbed by the medium as it propagates through it; it is a characteristic constant of the substance. The absorption coefficient can be obtained experimentally; for example, the absorption coefficient of nitrate ions at a wavelength of 220 nm is 9000 L·mol⁻¹. -1 ·cm -1 Potassium dichromate has an absorption coefficient of 4500 L·mol⁻¹ at a wavelength of 350 nm. -1 ·cm -1The absorption coefficient of permanganate ions at a wavelength of 525 nm is 2500 L·mol⁻¹. -1 ·cm -1 The water sample to be tested is assumed to contain M main components. For component m, the absorption coefficient of the nth wavelength of the first incident light is k. mn Then the transformation matrix K is an M×N matrix.

[0030] Step 304: Calculate the concentration vector C using B=εCK, where C=BK T (KK T ) -1 / ε, where ε is the current optical path length of the detection cell. Then, the target analyte concentration is extracted from the concentration vector C. Specifically, let C = [C1 C2… C… m … C M The matrix can be converted into a system of equations: b1=ε(k 11 C1+k 21 C2+...+k m1 C m +...+k M1 C M ); b2=ε(k 12 C1+k 22 C2+...+k m2 C m +...+k M2 C M ); ...; b n =ε(k 1n C1+k 2n C2+...+k mn C m +...+k Mn C M ); ...; b N =ε(k 1N C1+k 2N C2+...+k mN C m +...+k MN C M ).

[0031] Since N≠M, the least squares method can be used to solve for each concentration value of the concentration vector. Example 3

[0032] This embodiment further discloses a preferred method for calibrating the current optical path of the detection cell in this invention.

[0033] Step 601: The first interference signal can be expressed as I1(t) = I 01 +A1cos(ft+Φ1), the second interference signal can be expressed as I2(t)=I 02 +A2cos(ft+Φ2). I 01 with I 02 Let A1 and A2 be the direct current values ​​of the first and second interference signals, respectively, and let f be the frequency of the interference light, t be the time, Φ1 be the phase angle of the first interference signal, and Φ2 be the phase angle of the second interference signal. After removing the direct current, the first interference signal is I1(t) = A1cos(ft + Φ1), and the second interference signal is I2(t) = A2cos(ft + Φ2).

[0034] Step 602: Perform mixing operations on the first and second interference signals based on the orthogonal reference signals. Create orthogonal reference signals R1(t) and R2(t) with the same frequency as the interference light, R1(t) = cos(ft), R2(t) = sin(ft). Multiply the first interference signal with the orthogonal reference signals to obtain two sets of mixing quantities: I1(t)R1(t) = A1cos(ft + Φ1)cos(ft) = A1[cos(2ft ​​+ Φ1) + cosΦ1] / 2, I1(t)R2(t) = A1cos(ft + Φ1)sin(ft) = A1[sin(2ft + Φ1) - sinΦ1] / 2. Similarly, the second interference signal is multiplied by the orthogonal reference signal to obtain two sets of mixing quantities: I2(t)R1(t)=A2cos(ft+Φ2)cos(ft)=A2[cos(2ft+Φ2)+cosΦ2] / 2, I2(t)R2(t)=A2cos(ft+Φ2)sin(ft)=A2[sin(2ft+Φ2)-sinΦ2] / 2.

[0035] Step 603: Filter the mixed quantity to obtain orthogonal components. Filter out the second harmonic components cos(2ft+Φ1), sin(2ft+Φ1), cos(2ft+Φ2), and sin(2ft+Φ2) of the mixed quantity, then negate the sinusoidal quantity to obtain the first co-directional component Q1, the first orthogonal component Q2, the second co-directional component Q3, and the second orthogonal component Q4. Q1=(A1 / 2)cosΦ1, Q2=(A1 / 2)sinΦ1. Q3=(A2 / 2)cosΦ2, Q4=(A2 / 2)sinΦ2.

[0036] Step 604: Calculate the phase angles of the first and second interference signals based on the orthogonal components, and then calculate the minimum phase difference Δω'. Φ1=arctan(Q2 / Q1), Φ2=arctan(Q4 / Q3), Δω'=Φ1-Φ2.

[0037] Step 605: Calculate the actual phase difference. Since the phase angles Φ1 and Φ2 obtained in step 604 are less than 2π, Δω' is less than 2π. If high concentration pollution occurs, the actual phase difference may exceed 2π. Due to the diffusion characteristics of water pollution, the refractive index difference of the water samples obtained at adjacent sampling times is small. This invention uses the reference phase ω0 to estimate the actual phase difference more accurately. This invention calculates the integer j that minimizes |j2π+Δω'-ω0|, then the actual phase difference Δω = j2π+Δω'.

[0038] Step 606: Calibrate the current optical path of the detection cell. First, calibrate the refractive index η of the detection cell based on the actual phase difference Δω. η = η0 + Δωλ0 / (2πL), where η0 is the refractive index of the reference water sample. When the reference water sample is pure water, η0 is usually taken as 1.33. Figure 8 This section presents refractive index fitting plots for COD (benzene, phenol, polycyclic aromatic hydrocarbons) solutions with different molar concentrations. λ0 represents the interference wavelength. When the frequency of the second incident light is f1 and the frequency of the third incident light is f2, the interference frequency f = |f1-f2|, and the interference wavelength λ0 = 1 / f = 1 / |f1-f2|. L represents the geometric width of the detection cell. The current optical path ε is then calibrated based on the refractive index η, where ε = ηL. Finally, the reference phase ω0 is updated based on the actual phase difference Δω, where ω0 = Δω. Example 4

[0039] like Figures 9 to 11 This embodiment discloses a system for implementing an automatic calibration method for the parameter pool of the water quality monitoring station, comprising: a detection pool 11, a reference pool 12, a light generator 21, an optical path assembly, a detection arm, a reference arm, a first receiver 22, a second receiver 23, a data processing unit, a calibration unit, and an optical path controller.

[0040] The detection cell 11 is configured to store the water sample to be tested. The reference cell 12 is configured to store a reference water sample. The detection cell 11 and the reference cell 12 have the same geometric length, and the detection arm and the reference arm have the same structure. The detection arm is configured to construct the optical path of the detection cell 11. The reference arm is configured to construct the optical path of the reference cell 12. The detection arm and the reference arm create the same detection environment to reduce errors caused by the detection environment. To facilitate equipment calibration, a movable prism 13 and a fixed prism 14 can be set in the detection arm and the reference arm respectively, and the geometric length of the detection arm can be changed by moving the position of the movable prism 13.

[0041] The light generator 21 is configured to generate either a first incident light or a second incident light. The first receiver 22 is configured to generate a first light intensity or a first interference signal in the detection cell 11. The second receiver 23 is configured to generate a second light intensity or a second interference signal in the reference cell 12. Since the incident light has different frequency states, the light generator 21 can be a combination of various specific optical devices. In the detection state, a continuous spectrum light source, such as a deuterium lamp or a tungsten halogen lamp, is used. In the calibration state, a dual-frequency laser that generates the second and third incident lights is used, or a single laser (e.g., an Nd:YAG laser) is combined with the acousto-optic modulator 35. Similarly, due to the different light source forms, the receivers can also be switched between different devices. The first receiver 22 and the second receiver 23 can be switched between a photomultiplier tube and a PIN photodiode.

[0042] Reference Figures 2 to 7 The optical path components are configured to construct an optical path for either a first incident light or a second incident light. The optical path components include at least a first beam splitter 31, a dichroic separator 32, a second beam splitter 33, a third beam splitter 34, and an acousto-optic modulator 35. When the first beam splitter 31 and dichroic separator 32 are engaged, a detection state is entered. When the first beam splitter 31, second beam splitter 33, third beam splitter 34, and acousto-optic modulator 35 are engaged, a calibration state is entered. The first beam splitter 31, second beam splitter 33, and third beam splitter 34 can be Wollaston prisms (or polarizing beam splitters with quarter-wave plates) for polarization beam splitting. The acousto-optic modulator 35 is used to achieve optical wave modulation from 40MHz to 100MHz, modulating a portion of the second incident light into a third incident light with a specific frequency difference. In this invention, a reflector can be added to the optical path of the second receiver 23 to adjust the optical path of the first reflected light, and a reflector can be added to the optical path of the acousto-optic modulator 35 to adjust the optical path of the second reflected light. Furthermore, a collimating lens 36 and a light intensity monitor 37 can be provided at the outlet of the dichroic separator 32 for focusing monochromatic light and monitoring light intensity.

[0043] The data processing unit is configured to predict the target concentration based on the first light intensity, the second light intensity, and the current optical path. The calibration unit is configured to calibrate the current optical path based on the first interference signal and the second interference signal. The data processing unit and the calibration unit can be integrated into the MCU chip as software modules through compilation and called by the chip's main control unit. The optical path controller is configured to switch the optical path components to detection or calibration states; the optical path controller, for example, is a timing controller. Specifically, the photomultiplier tubes of the first receiver 22 and the second receiver 23, together with the dichroic separator 32, form a first switching module; the PIN photodiodes of the first receiver 22 and the second receiver 23, together with the second beam splitter 33, the third beam splitter 34, and the acousto-optic modulator 35, form a second switching module. Figure 10As shown, the optical path controller has two sets of drive modules, which drive the first switching module and the second switching module respectively to realize the switching between detection state and calibration state.

[0044] Furthermore, as a more preferred embodiment, the present invention can also construct an automatic update mechanism for the water sample to be tested, achieving continuous detection and continuous updating of the reference phase. (Refer to...) Figure 11 The first pump 41 pumps a reference water sample into the first tank 43, and the second pump 42 pumps the water sample to be tested into the second tank 44. A throttle valve regulates the flow rate and volume of the water sample entering the detection pool 11 and the reference pool 12. The third tank 45 can also pump reagents and cleaning solutions into the first tank 43 and the second tank 44. Through the periodic operation of the first pump 41, the second pump 42, and the throttle valve, the water sample to be tested is automatically updated.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An automatic calibration method for parameter pools in a water quality monitoring station, characterized in that, Includes the following steps: Step 1: Pump the water sample to be tested into the detection cell set in the detection arm, and pump the reference water sample into the reference cell set in the reference arm to initialize the reference phase; Step 2: Enter the detection state. The light generator generates the first incident light. The first incident light passes through the detection cell and the reference cell and enters the first receiver and the second receiver respectively, generating the first light intensity and the second light intensity respectively. Step 3: Calculate the absorbance of the detection cell based on the first and second light intensities, adjust the wavelength of the first incident light to obtain the absorbance at different wavelengths, and calculate the concentration of the target substance in the water sample to be tested based on the current optical path. Step 4: If a calibration instruction is received, proceed to Step 5; otherwise, return to Step 2. Step 5: Enter calibration state. The light generator generates a second incident light and modulates the second incident light into interference light. The interference light enters the first receiver and the second receiver through the detection cell and the reference cell, respectively, generating the first interference signal and the second interference signal. Step 6: Calculate the minimum phase difference between the detection arm and the reference arm based on the first and second interference signals. Predict the actual phase difference using the reference phase. Based on this actual phase difference, calibrate the current optical path of the detection cell, update the reference phase, and return to Step 2. In step 6, the first interference signal and the second interference signal are mixed based on the orthogonal reference signal to obtain orthogonal components. The phase angle of the first interference signal and the second interference signal is calculated, and then the minimum phase difference Δω' is calculated. The integer j that makes |j2π+Δω'-ω0| the minimum value is calculated. The actual phase difference Δω=j2π+Δω', and ω0 is the reference phase.

2. The automatic calibration method for the parameter pool of a water quality monitoring station according to claim 1, characterized in that, The first incident light is broadband light, and the second incident light is infrared light.

3. The automatic calibration method for the parameter pool of a water quality monitoring station according to claim 1, characterized in that, In step 2, after entering the detection state, the first incident light is selected by the dichroic separator to be a single wavelength light. The single wavelength light is separated into a first refracted light and a first reflected light by the first beam splitter. The first refracted light passes through the detection cell and enters the first receiver, and the first reflected light passes through the reference cell and enters the second receiver.

4. The automatic calibration method for the parameter pool of a water quality monitoring station according to claim 1, characterized in that, In step 3, the absorbance of the first incident light at different wavelengths forms an absorbance matrix B, and the transformation matrix K, composed of the absorption coefficients of different components to the first incident light, is extracted. The concentration vector C is calculated by combining B=εCK, and the concentration of the target substance is extracted from the concentration vector C. ε is the current optical path of the detection cell.

5. The automatic calibration method for the parameter pool of a water quality monitoring station according to claim 1, characterized in that, Extract the first absorbance matrix after the previous calibration state ends, calculate the variance between the current absorbance matrix and the first absorbance matrix, generate the calibration command when the detection duration is greater than the first threshold or the variance is greater than the second threshold, and initialize the detection duration after the calibration state ends.

6. The automatic calibration method for the parameter pool of a water quality monitoring station according to claim 1, characterized in that, In step 5, the second incident light is separated into the second reflected light and the second refracted light by the second beam splitter. The second reflected light is modulated into the third incident light. The second refracted light and the third incident light are combined into common-mode interference light by the third beam splitter.

7. The automatic calibration method for the parameter pool of a water quality monitoring station according to claim 1, characterized in that, In step 6, the refractive index η of the detection cell is first calibrated according to the actual phase difference Δω, η=η0+Δωλ0 / (2πL), where η0 is the refractive index of the reference water sample, λ0 is the wavelength of the interference light, and L is the geometric width of the detection cell. Then, the current optical path ε=ηL of the detection cell is calculated, and finally, the reference phase ω0=Δω is updated.

8. A system for implementing the automatic calibration method for the parameter pool of a water quality monitoring station as described in claim 1, characterized in that, include: The testing pool is configured to store water samples to be tested. The reference pool is configured to store reference water samples; The light generator is configured to generate either a first incident light or a second incident light; An optical path assembly is configured to construct an optical path for receiving a first incident light or a second incident light; The detection arm is configured as the optical path for constructing the detection cell; The reference arm is configured as the optical path for constructing the reference cell; The first receiver is configured to generate a first light intensity or a first interference signal for the detection cell; The second receiver is configured to generate a second light intensity or a second interference signal for the reference cell; The data processing unit is configured to predict the concentration of the target substance based on the first light intensity, the second light intensity, and the current optical path. The calibration unit is configured to calibrate the current optical path based on the first interference signal and the second interference signal; The optical path controller is configured to switch the optical path components to a detection state or a calibration state, wherein... The optical path assembly includes at least a first beam splitter, a dichroic separator, a second beam splitter, a third beam splitter, and an acousto-optic modulator. When the first beam splitter and dichroic separator are engaged, the system enters the detection state; when the first beam splitter, the second beam splitter, the third beam splitter, and the acousto-optic modulator are engaged, the system enters the calibration state.

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