An automatic ultraviolet spectrophotometric water quality detection system based on closed-loop calibration sampling and a control method thereof

Abstract

The application discloses an automatic ultraviolet spectrometric water quality detection system based on closed-loop calibration sampling and a control method thereof. The system comprises a finished ultraviolet spectrometer, a control unit, a plurality of peristaltic pumps, and a floating ball liquid level sensor arranged at the top of a reaction chamber. The control unit performs peristaltic pump flow rate calibration: delivers liquid to the reaction chamber, detects whether the liquid level reaches a fixed volume by using the floating ball liquid level sensor, records the time and calculates the actual flow rate, thereby correcting the subsequent sampling time, and realizing closed-loop sampling control. The application also provides a complete automatic detection process, supports timing / manual triggering, multi-parameter expandable configuration, and detection result pushing and linkage control (such as linkage with a protein separator) based on the MQTT protocol. The application solves the problems of existing peristaltic pump sampling precision drift and the difficulty in low-cost automatic transformation of the finished ultraviolet spectrometer, and has the advantages of simple structure, low cost, high detection precision, strong expandability, and the ability to realize intelligent linkage of detection and processing.

Description

Technical Field

[0001] This invention relates to the field of water quality testing technology, and more specifically, to an automated water quality testing system based on ultraviolet spectrophotometry, particularly an online multi-parameter automatic water quality testing system and its control method that achieves high precision and low cost through closed-loop calibration sample introduction. Background Technology

[0002] Ultraviolet (UV) spectrophotometry is a classic analytical method based on the Lambert-Beer Law: when a beam of monochromatic light passes through a solution, the absorbance of the solution is directly proportional to the concentration of the absorbing substance and the optical path length. This method offers advantages such as high sensitivity, relatively simple operation, and a wide detection range, and is widely used in water quality testing to determine the content of various inorganic pollutants in water, including nitrates, nitrites, phosphates, and heavy metal ions. Traditional UV spectrophotometers are mostly benchtop laboratory instruments, requiring manual operation of a series of steps including sampling, reagent preparation, sample injection, colorimetric analysis, cuvette cleaning, and data recording.

[0003] Currently, some automated or semi-automated water quality testing devices have appeared on the market. A search of existing technologies reveals several improvement solutions: For example, Chinese patent CN119915763A discloses a smart water station water quality sampling and monitoring method and system based on ultraviolet spectroscopy, which achieves water quality detection through ultraviolet spectroscopy technology. Chinese patent CN223259562U discloses a water quality detection system, which includes ultraviolet and visible light sources, a fluorescence excitation source, and a spectral detector. In addition, some fully automated water quality detection and analysis systems have been disclosed. These systems typically include sampling modules, sample preparation modules, reagent addition modules, sample injection modules, detection modules, and cleaning modules, enabling a certain degree of automation of the detection process.

[0004] Regarding sample injection control, existing technologies also attempt to perform closed-loop calibration of peristaltic pumps. For example, one patent discloses an "automatic calibration structure for peristaltic pumps," which uses a first liquid level sensor and a second liquid level sensor (specifically a pressure sensor) installed in the sample water cup to provide feedback on the liquid level, thereby calibrating the peristaltic pump. Another patent discloses a "water quality sampling unit capable of precise measurement," which corrects the number of rotations of the sampling peristaltic pump through real-time feedback from three pipeline liquid level sensors. In terms of control architecture, existing research has used Raspberry Pi as a central control unit in the control system of multi-parameter water quality analyzers, and adopted the MQTT protocol for data transmission and device linkage.

[0005] Although existing technologies have made some progress in automating water quality testing, comprehensive analysis reveals that current solutions still have the following shortcomings: First, there is a contradiction between automation and accuracy. Existing fully automated water quality testing systems mostly employ high-precision actuators such as syringe pumps and multi-position valves. While these ensure sample injection accuracy, they are costly, complex in structure, and difficult to maintain, making them unsuitable for widespread use in small and medium-sized water treatment plants or aquaculture water monitoring. Conversely, if low-cost peristaltic pumps are used as the injection power source, the actual flow rate will drift over time due to the aging and wear of the pump tubing, leading to inaccurate sample volume and affecting the reliability of the test results. Although some existing technologies propose closed-loop calibration of peristaltic pumps, these calibration methods often rely on additional pressure sensors or multiple level sensors, increasing hardware costs and requiring complex calculations or multiple samplings, making rapid, online, and low-cost calibration difficult.

[0006] Secondly, there is a lack of systematic, low-cost solutions for retrofitting commercial UV spectrometers. In existing technologies, automated water quality testing systems are mostly newly designed integrated devices, whose optical detection modules often require custom customization. However, many mature commercial UV spectrometers already exist in laboratories. How to automate these systems in a low-cost, non-invasive manner to enable online, automated testing remains a challenge. While some solutions mention automated sample introduction devices, these typically require mechanical handling of cuvettes or the use of flow cells, resulting in complex structures and making it difficult to achieve multifunctional integration of the reaction chamber (such as simultaneous sample introduction, reaction, cleaning, and calibration).

[0007] Third, the scalability of detection parameters is limited. Existing automated water quality testing systems are usually designed for specific parameters (such as COD, ammonia nitrogen, etc.). When new ions need to be added, hardware replacement or reprogramming is often required, lacking an open and scalable architecture.

[0008] Fourth, there is a lack of intelligent linkage with downstream processing equipment. Existing water quality testing systems mostly stop at data output and fail to directly use the test results to control downstream water quality treatment equipment (such as protein separators, filtration systems, etc.), thus failing to form a closed-loop water quality management system of "detection-judgment-treatment".

[0009] In summary, the technical problem to be solved by this invention is to provide a low-cost, high-precision, easily expandable, and closed-loop linkage control-enabled automated ultraviolet spectrophotometer water quality detection system and its control method. Specifically, it aims to solve the problem of decreased sampling accuracy caused by pump tube aging when using peristaltic pumps for sampling in the prior art, as well as the problem of difficulty in low-cost automated transformation of finished ultraviolet spectrophotometers. At the same time, it achieves full automation of the detection process, scalability of multiple parameters, and intelligent linkage with back-end processing equipment. Summary of the Invention

[0010] The present invention aims to overcome the shortcomings of the prior art and provide an automated ultraviolet spectrophotometric water quality detection system and its control method that is low-cost, high-precision, easy to expand, and capable of closed-loop linkage control.

[0011] Specifically, the present invention aims to solve the following technical problems: First, it solves the problem in existing technologies where peristaltic pumps cause drift in actual flow rate due to aging and wear of the pump tubing, resulting in inaccurate injection volume and reduced reliability of test results. At the same time, it avoids the problem of excessively high system costs caused by using expensive components such as syringe pumps and multi-position valves.

[0012] Second, it addresses the lack of systematic, low-cost solutions for automating existing ultraviolet spectrometers, enabling the transformation of commonly used laboratory ultraviolet spectrometers into online automated detection instruments in a non-invasive or low-invasive manner.

[0013] Third, to address the issue of limited scalability of detection parameters in existing automated water quality testing systems, an open multi-parameter detection platform architecture is provided, which allows for the addition of new detection items simply by adding the corresponding reagents and built-in standard curves.

[0014] Fourth, address the lack of intelligent linkage between existing water quality testing systems and downstream water treatment equipment, enabling real-time feedback control of testing results on treatment equipment, thus forming a closed-loop water quality management system.

[0015] To achieve the above-mentioned objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides an automated ultraviolet spectrophotometric water quality detection system based on closed-loop calibration sample introduction, comprising: A finished ultraviolet spectrometer with a modified reaction chamber; A control unit is connected to the ultraviolet spectrometer via a serial communication port; Several peristaltic pumps are used to deliver water samples, at least one test reagent, and pure water for cleaning, respectively, and all peristaltic pumps are controlled by the control unit; A float level sensor is installed at the top of the reaction chamber to detect whether the liquid level in the reaction chamber has reached a preset fixed volume position and to generate a trigger signal. The control unit is configured to perform a peristaltic pump flow rate calibration procedure before or during the injection operation. The calibration procedure includes controlling the target peristaltic pump to deliver liquid to the reaction chamber, recording the delivery time when a trigger signal from the float level sensor is received, calculating the current actual flow rate of the peristaltic pump based on the fixed volume in the reaction chamber from the bottom to the installation position of the float level sensor and the delivery time, and updating the delivery time control parameters for subsequent injections.

[0016] Furthermore, the reaction chamber is a custom-made quartz tube reaction chamber, and its top is also provided with at least one reagent inlet, one pure water inlet, at least one water sample inlet, and one overflow port; the overflow port is located above the trigger position of the float level sensor.

[0017] Furthermore, the control unit is a Raspberry Pi running a Linux operating system and uses the Python programming language to implement the control logic; the control unit communicates with external servers or user terminals via the MQTT protocol and pushes the detection results via DingTalk or email.

[0018] Furthermore, the control unit is also configured to automatically execute the peristaltic pump flow rate calibration process before each water quality test, or to execute the peristaltic pump flow rate calibration process at preset time intervals.

[0019] Furthermore, the control unit is also configured to perform the following detection process: In response to a timed trigger or user command, the corresponding water sample peristaltic pump and reagent peristaltic pump are controlled to deliver a predetermined volume of water sample and detection reagent into the reaction chamber according to the calibrated flow rate and preset injection time. The ultraviolet spectrometer is controlled to measure the absorbance value of the solution after the reaction at a preset wavelength; Based on the built-in standard curve, the absorbance value is converted into the concentration value of the ion being measured, and the detection result is output or stored. The system controls the injection of pure water into the reaction chamber using a peristaltic pump and controls the evacuation to complete the automatic cleaning of the reaction chamber.

[0020] Furthermore, the system also includes a linkage control module: the control unit compares the detected ion concentration value with a preset threshold, and when the concentration value exceeds the threshold, it sends a control command to an external water treatment device (e.g., a protein separator) via the MQTT protocol to adjust the working mode of the external water treatment device (e.g., switch to a high discharge mode).

[0021] Secondly, the present invention also provides an automated ultraviolet spectrophotometric water quality detection method based on closed-loop calibration sample introduction, applied to the system described in the first aspect above, comprising the following steps: Step S1: The peristaltic pump flow rate calibration process is executed by the control unit, including: controlling the target peristaltic pump to deliver liquid into the reaction chamber, using a float level sensor set on the top of the reaction chamber to detect whether the liquid level has reached the fixed volume position, recording the delivery time, and calculating the current actual flow rate of the peristaltic pump based on the fixed volume and the delivery time. Step S2: Based on the calibrated flow rate, control the water sample peristaltic pump and the reagent peristaltic pump to deliver a predetermined volume of water sample and detection reagent into the reaction chamber, respectively; Step S3: Control the ultraviolet spectrometer to measure the absorbance value of the solution after the reaction; Step S4: Convert the absorbance value into the concentration value of the analyte ion according to the built-in standard curve; Step S5: Control the pure water peristaltic pump to automatically clean the reaction chamber.

[0022] Furthermore, the peristaltic pump flow rate calibration process in step S1 is executed automatically before each test, or automatically according to a user-defined time period.

[0023] Furthermore, in step S3, before measuring the absorbance value, a zero-point calibration step is also included: controlling the peristaltic pump for cleaning to inject pure water into the reaction chamber, and measuring the absorbance value of the pure water as a blank reference.

[0024] Furthermore, the method also includes step S6: comparing the concentration value obtained in step S4 with a preset threshold, and when the threshold is exceeded, sending a linkage control command to the external water treatment equipment via the MQTT protocol to change its operating status.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves low-cost, high-precision automated sample injection. It creatively employs a closed-loop calibration scheme of "peristaltic pump + float level sensor at the top of the reaction chamber + fixed-volume feedback," eliminating the need for additional high-precision syringe pumps or multi-position valves. Using only a simple float level sensor and a fixed-volume reaction chamber, it can perform real-time calibration of flow rate drift caused by pipe aging and wear in the peristaltic pump. This calibration method features low hardware costs, simple and reliable calibration logic, and fast calibration speed, ensuring volume accuracy for each injection and significantly improving the accuracy and repeatability of test results. Compared to existing calibration schemes using pressure sensors or multiple level sensors, this invention has a simpler structure, lower cost, and is easier to implement in miniaturized equipment.

[0026] 2. This invention enables low-cost, non-invasive, automated retrofitting of existing UV spectrometers. By connecting the control unit to the existing UV spectrometer via serial communication and customizing the reaction chamber (integrating the inlet, overflow port, and level sensor), the functionality of the existing UV spectrometer is expanded, giving it online automated detection capabilities. Users do not need to purchase expensive integrated automated analyzers; they only need to add control units and actuators to their existing laboratory equipment to achieve a fully automated upgrade, demonstrating significant industrial application value.

[0027] 3. The invention achieves fully automated testing, reducing manual intervention and consumable consumption. It automates the entire process from equipment calibration, water sample extraction, reagent addition, reaction, test reading, data processing to reaction chamber cleaning, supporting both timed and manually triggered testing. The entire process eliminates the need for manual pipetting, colorimetric analysis, and data recording, avoiding human error and reagent contamination. Furthermore, it eliminates the need for disposable consumables such as pipettes and centrifuge tubes, reducing testing costs.

[0028] 4. It possesses open, multi-parameter scalability. The control unit of this invention has a built-in configurable detection process and standard curve library. For different detection ions (such as nitrates, phosphates, etc.), no additional reaction operations, such as digestion, are required. Simply add the corresponding detection reagents and call or input the corresponding standard curve parameters to add new detection items without modifying the hardware structure. This open architecture gives the system excellent flexibility and scalability, enabling it to adapt to constantly changing detection needs.

[0029] 5. Intelligent linkage between detection and treatment is achieved. This invention pushes detection results to the user terminal in real time via the MQTT protocol and can automatically send linkage control commands to external water treatment equipment (such as protein skimmers) based on preset thresholds, realizing closed-loop water quality management of "detection-judgment-treatment". Compared with existing technologies that only focus on data output, this invention can actively intervene in the water treatment process, improving the intelligence and automation level of water quality management. Attached Figure Description

[0030] To make the technical solution of the present invention clearer and easier to understand, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following drawings are only used to schematically illustrate the preferred embodiments of the present invention, and their specific structure, size, proportion and layout should not be construed as any limitation on the present invention.

[0031] Figure 1 : A schematic diagram of the overall structure of the automated ultraviolet spectrophotometric water quality detection system in Embodiment 1 of the present invention; Figure 2 : A partial cross-sectional view of the reaction chamber in Embodiment 1 of the present invention; Figure 3 Schematic diagram of the peristaltic pump flow rate calibration principle in Embodiment 1 of the present invention; Figure 4 : Flowchart of the overall control of automated water quality testing in Embodiment 1 of the present invention; Figure 5 : A schematic diagram of the control linkage between the system and external water treatment equipment in Embodiment 2 of the present invention. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It should be noted that the specific embodiments described below are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] Example 1: Basic Automated Testing System Please see Figures 1 to 4 Embodiment 1 of the present invention provides an automated ultraviolet spectrophotometer water quality detection system based on closed-loop calibration sample introduction. The system mainly includes: a finished ultraviolet spectrometer 1, a control unit 3, several peristaltic pumps 4 (including a water sample peristaltic pump, a reagent peristaltic pump and a pure water peristaltic pump for cleaning), a float level sensor 5 set on the top of the reaction chamber 2, and a series of connecting pipelines.

[0034] The finished UV spectrometer 1 can be any commercially available laboratory UV-Vis spectrophotometer with a serial communication interface (such as RS232, RS485, or USB virtual serial port). This embodiment uses a Shanghai Puli-UV20 UV-Vis spectrophotometer. The cuvette rack originally used to hold standard cuvettes inside the spectrometer 1 has been removed and replaced with the custom-modified reaction chamber 2 of this invention. The reaction chamber 2 is custom-made from quartz glass tubing, possessing excellent UV transmittance. Its lower end is sealed, and its upper end is open and fitted with a sealing cap. The optical path length of the reaction chamber 2 (i.e., the path length of UV light through the solution) is matched to the optical path design of the UV spectrometer 1, preferably 20mm. The control unit 3 is connected to the communication interface of the UV spectrometer 1 via a serial communication cable, sending commands such as measurement wavelength setting, measurement start, and data reading to the spectrometer 1, and receiving absorbance or energy values ​​returned by the spectrometer 1. The control unit 3 is also connected to the drive modules of each peristaltic pump 4 and the signal output terminals of the float level sensor 5 via general purpose input / output interfaces (GPIO). The control unit 3 is preferably a Raspberry Pi single-board computer running a Linux operating system, with control programs written in Python. Of course, in other embodiments, the control unit 3 can also be an Arduino, STM32 microcontroller, or other embedded controller, as long as it has sufficient computing power and interface resources. The control unit 3 also has a built-in or external real-time clock module to support timing detection functions. Furthermore, the control unit 3 is connected to the Internet via a network module (such as WiFi or Ethernet) and communicates with remote servers or user terminals (such as WeChat mini-programs, DingTalk robots, and email servers) using the MQTT protocol.

[0035] The float level sensor 5 is one of the key components for achieving closed-loop calibration in this invention. The sensor 5 includes a hollow float and a reed switch (or Hall effect switch) sensing element. The float level sensor 5 is fixedly installed on the sealed cover at the top of the reaction chamber 2, with its sensing probe extending vertically into the interior of the reaction chamber 2. When the liquid level in the reaction chamber 2 rises to a preset fixed volume position, the float rises with the liquid level to the sensing point, triggering the reed switch to close or the Hall effect switch to output a high level, thereby generating an electrical trigger signal sent to the control unit 3. The internal volume of the reaction chamber 2 corresponding to this trigger position (the volume from the bottom inner surface of the reaction chamber 2 to the trigger position) is a fixed value calibrated at the factory, denoted as S0 (unit: milliliters, preferably 15-33.0 mL). The calibration method for this fixed volume S0 can be as follows: with the reaction chamber 2 empty, inject a known volume of water into the reaction chamber 2 using a high-precision injection pump until the float sensor is triggered, record the injected volume, and repeat multiple times to obtain the average value. This calibration value is fixed in the storage medium of the control unit 3 at the factory.

[0036] In addition, the float level sensor 5 has another function: to quickly provide feedback on the liquid level in case the peristaltic pump 4 malfunctions and cannot be shut down. If the continuous triggering lasts for more than 1 minute, the power supply to the entire machine will be cut off to avoid greater equipment damage.

[0037] The most core innovation of this invention lies in the closed-loop calibration mechanism for the peristaltic pump flow rate. During long-term use, the pump tubing of the peristaltic pump 4 experiences elastic fatigue, wear, and even slippage, causing a drift in the actual volume of liquid delivered at the same rotational speed and operating time. To address this issue, this invention proposes an online calibration method based on the fixed volume S0 and the float level sensor 5. Please refer to [link / reference needed]. Figure 3 The calibration process is illustrated as follows: When calibration is required (e.g., after system initialization, before each test, or at a preset cycle such as every 24 hours), the control unit 3 first starts the peristaltic pump 4 (e.g., a water sample peristaltic pump) to be calibrated at a preset speed, beginning to deliver liquid (e.g., pure water or a water sample) into the reaction chamber 2. Simultaneously, a timer inside the control unit 3 starts timing. Liquid is continuously injected into the reaction chamber 2, and the liquid level continues to rise. When the liquid level reaches the trigger position of the float level sensor 5, the float rises, and sensor 5 sends a trigger signal to the control unit 3. Upon receiving this signal, the control unit 3 immediately stops the peristaltic pump 4 and records the time t (in seconds) elapsed from start to stop. At this time, the control unit 3 calculates the time according to formula V... actual = S0 / t, calculate the actual flow velocity V of the peristaltic pump 4 at the current speed. actual (Unit: ml / s). Subsequently, the control unit 3 will inject the preset target injection volume V. target (For example, if a 2 mL water sample needs to be drawn) Divide by the actual flow rate Vactual The corrected running time t is obtained. corrected = V target / V actual In subsequent sample injection tests, control unit 3 will follow the corrected time t. corrected The operation of the peristaltic pump 4 is controlled to ensure the accuracy of each injection volume. It should be noted that this calibration process applies not only to the water sample peristaltic pump but also to all reagent peristaltic pumps and cleaning pumps. To improve calibration efficiency, only the water sample pump and the core reagent pump with the highest injection accuracy requirements can be calibrated. In a preferred embodiment, the control unit 3 is configured to automatically perform a flow rate calibration of all relevant peristaltic pumps before the start of each detection process, thereby eliminating instantaneous flow rate fluctuations caused by factors such as temperature changes and fatigue from continuous operation. In another embodiment, to save time and reagents, calibration can be performed according to a user-defined time cycle (e.g., every 6 hours, daily, or weekly). Furthermore, if the user wishes to perform flow rate calibration immediately, a corresponding manual switch can be set.

[0038] After calibration, the system can then execute the formal automated water quality testing process. Please refer to the relevant documentation. Figure 4The process includes the following steps: First, the control unit 3, in response to a preset timed task (e.g., 8:00 AM and 2:00 PM daily) or a manual trigger command sent by the user via a mini-program, begins the detection. The control unit 3 controls the corresponding water sample peristaltic pump to extract a predetermined volume (e.g., 10.0 mL) of water sample from the water source to be tested, according to the calibrated actual flow rate and corrected running time, and delivers it to the reaction chamber 2 via the injection pipeline. Next, the control unit 3 controls the corresponding reagent peristaltic pump (e.g., for phosphate detection, two test reagents are required, so there may be two corresponding peristaltic pumps here), to extract a predetermined volume of test reagent according to the calibrated parameters, and inject it into the reaction chamber 2 as well. The water sample and reagent are mixed in the reaction chamber 2. A miniature magnetic stirring rotor (not shown in the figure) can be installed at the bottom of the reaction chamber 2, or mixing can be achieved through the swirling effect during liquid injection. The system waits for a preset reaction time (e.g., 10 minutes) to allow the colorimetric or chemiluminescent reaction to proceed fully. After the reaction time is up, the control unit 3 sends a command to the UV spectrometer 1 via serial port to set the detection wavelength (e.g., 880nm for phosphate detection, and dual wavelengths of 220nm and 275nm for nitrate detection). It is important to emphasize that before measuring the sample absorbance, to eliminate background absorption from the reaction chamber 2 and pure water, the control unit 3 performs a zero-point calibration step: it controls the peristaltic pump to inject pure water into the reaction chamber 2 to a fixed volume S0, measures the absorbance of the pure water at that wavelength as a blank reference (i.e., zero reference), and then drains the chamber. Subsequently, the absorbance of the reacted sample solution is measured. The absorbance value measured by the UV spectrometer 1 is returned to the control unit 3 via serial port. The control unit 3 internally stores standard curves for different detected ions, i.e., the relationship equation between concentration C and absorbance A, for example, C = k A + b, where k and b are coefficients obtained through standard solution calibration. Control unit 3 substitutes the measured absorbance into the standard curve equation for the corresponding ion to calculate the concentration of the analyte. The calculated result is stored in a local database by control unit 3 and also pushed to a user-specified receiving end via the MQTT protocol, such as a DingTalk group robot, email address, or WeChat mini-program. If the detection result exceeds the user-preset alarm threshold (e.g., nitrate concentration exceeding 1 mg / L), control unit 3 will also proactively send an alarm push.

[0039] After the test is completed, the system automatically enters the cleaning process. Control unit 3 controls the peristaltic pump to inject a large amount of pure water into reaction chamber 2 and controls the peristaltic pump to drain the waste liquid. Preferably, the cleaning process may include multiple injection-drain cycles, for example, 2 to 3 times, with each injection of pure water being 1 times the fixed volume S0, to thoroughly rinse away residual reagents and reaction products. At this point, a complete automated testing process is finished. The system enters standby mode, awaiting the next timed trigger or manual command.

[0040] Example 2: Extended system with linkage control function Based on Embodiment 1 above, this embodiment further provides a linkage control function to achieve intelligent feedback of detection results to downstream water treatment equipment. Please refer to [link / reference needed]. Figure 5 This embodiment is particularly suitable for water quality management in recirculating aquaculture systems or landscape water bodies, which are typically equipped with a protein skimmer (protein foam separator) as the core water treatment device. When the concentration of nutrients (such as nitrates and phosphates) in the water increases, it is necessary to increase the operating power of the protein skimmer or adjust its air-to-water ratio to promote the removal of organic matter. In this embodiment, the control unit 3 stores a preset concentration threshold (which can be remotely set by the user via a mini-program). When the detected concentration of a certain ion (e.g., phosphate concentration) exceeds the threshold, the control unit 3 does not merely push an alarm message, but further generates a linkage control command. This command is sent to the control system of the protein skimmer via the MQTT protocol through a local area network or the Internet. After receiving the command, the control system of the protein skimmer automatically switches its operating mode from "standard mode" to "high discharge mode," for example, increasing the water pump speed by 20%, increasing the air intake, and extending the operating time. In this way, the water quality detection system is no longer just a passive monitoring tool, but becomes a key node in the "sensing-decision-execution" closed loop of actively participating in water quality regulation. In other embodiments, the external water treatment equipment may also be a sand filter, an algae reactor, an ultraviolet disinfection device, etc.

[0041] Example 3: Scalable Multi-Parameter Detection Platform Under the system architecture of this invention, the detection parameters are not fixed in the hardware, but are flexibly expandable through software configuration. The storage medium of the control unit 3 stores a detection item configuration table. This configuration table defines a set of parameters for each detectable ion (or chemical indicator), including but not limited to: detection item name (e.g., "nitrate"), detection wavelength (e.g., 220nm and 275nm), type and injection volume of the reagent used, water sample injection volume, reaction waiting time, standard curve equation coefficients (k and b), result unit (mg / L), alarm threshold, etc. When a user needs to add a new detection item (e.g., detecting ferrous ions in water), no modification to the system's hardware structure is required. The user only needs to perform the following operations: 1) Prepare the corresponding detection reagent according to known national or industry standards; 2) Connect the reagent bottle to the peristaltic pump corresponding to an idle reagent inlet of the system; 3) Send a configuration command to the control unit 3 through the user terminal (app), entering the above configuration parameters for the new item; 4) After receiving the configuration, the control unit 3 stores the parameters of the new item in the configuration table. Subsequently, the system can automatically perform timed or manual testing on the new project according to the configuration. This open, scalable architecture, requiring no hardware modifications, allows the invention to adapt to constantly changing testing needs, greatly enhancing the product's lifecycle value and market competitiveness. Furthermore, the system also supports automatic calibration: users prepare a series of standard solutions of known concentrations, the system automatically injects the samples, measures the absorbance, and the control unit 3 automatically fits and stores the coefficients of the standard curve equation based on the measurement results, eliminating the need for manual calculations and further reducing the operational threshold.

[0042] Example 4: Further Optimization of the Calibration Process To improve calibration accuracy and extend pump tubing life, this embodiment provides several preferred calibration implementation methods. First, multi-flow-rate calibration. In conventional implementations, the system typically performs calibration only at a single preset rotational speed. However, experiments show that the flow rate drift characteristics of a peristaltic pump may differ at different rotational speeds. Therefore, the control unit 3 can be configured to perform calibration at multiple different rotational speeds (e.g., low, medium, and high speeds) on the same peristaltic pump, recording the actual flow rate at each speed and fitting a "rotational speed-flow rate" correction curve. During subsequent injection, the control unit 3 interpolates the corrected running time from this curve based on the required injection rate. This method further improves accuracy in variable flow rate injection scenarios. Second, temperature-compensated calibration. The elasticity of the pump tubing is significantly affected by ambient temperature. The system can be equipped with a temperature sensor (not shown in the figure) connected to the control unit 3. During each calibration, the control unit 3 simultaneously records the ambient temperature and establishes a "temperature-flow rate drift coefficient" compensation model. When the system operates in an environment different from the calibration temperature, the control unit 3 can automatically compensate and correct the calibrated flow rate based on the current temperature, thereby eliminating the influence of temperature on injection accuracy. Third, adaptive periodic calibration. The control unit 3 can record the flow rate value obtained from each calibration and analyze its trend over time (e.g., pump tubing aging curve). When the flow rate change rate is detected to exceed a preset threshold (indicating severe wear of the pump tubing), the system automatically shortens the calibration cycle and sends a maintenance reminder to "replace the pump tubing." These optimized features all fall within the scope of this invention, and no similar teachings have been found in the retrieved prior art.

[0043] Example 5: Alternative solutions for reaction chamber structure While the foregoing embodiments describe a top-mounted float level sensor structure for reaction chamber 2, other types of level detection methods can be used in some implementations to achieve fixed-volume feedback. For example, a non-contact photoelectric level switch can be installed at a fixed height on the outer wall of reaction chamber 2, determining whether the level has been reached by detecting changes in the reflection or refraction of light at the liquid surface. This non-contact approach avoids contact between the sensor and the detection solution, eliminating the risk of cross-contamination and corrosion, and is suitable for detection systems with strong corrosiveness. Furthermore, the bottom drainage method for reaction chamber 2 can rely on an independent peristaltic pump, or it can employ gravity-fed drainage controlled by an electromagnetic valve, or switch the sample inlet line to the drainage line using a three-way valve, utilizing the forward and reverse rotation of the same peristaltic pump to achieve both inlet and outlet drainage. These simple structural variations, as long as their core function (fixed-volume level feedback) is essentially the same as that of this invention, should be considered to fall within the scope of protection of this invention.

[0044] In summary, this invention solves the long-standing technical problem of peristaltic pump injection accuracy drift by introducing the core technical feature of "interior fixed-volume liquid level feedback in the reaction chamber + closed-loop calibration of the peristaltic pump" at extremely low hardware cost. Simultaneously, by combining a Raspberry Pi IoT architecture, a configurable multi-parameter detection platform, and intelligent linkage control, a complete automatic water quality detection solution with significant technological advancements and industrial application value is formed. Various modifications, combinations, or equivalent substitutions made by those skilled in the art based on the technical solutions disclosed in this invention without creative effort do not depart from the spirit and scope of this invention.

Claims

1. An automated ultraviolet spectrophotometric water quality detection system based on closed-loop calibration sample introduction, characterized in that, include: A finished ultraviolet spectrometer with a modified reaction chamber; A control unit is connected to the ultraviolet spectrometer via a serial communication port; Several peristaltic pumps are used to deliver water samples, at least one test reagent, and pure water for cleaning, respectively, and all peristaltic pumps are controlled by the control unit; A float level sensor is installed at the top of the reaction chamber to detect whether the liquid level in the reaction chamber has reached a preset fixed volume position and to generate a trigger signal. The control unit is configured to perform a peristaltic pump flow rate calibration procedure before or during the injection operation. The calibration procedure includes controlling the target peristaltic pump to deliver liquid to the reaction chamber, recording the delivery time when a trigger signal from the float level sensor is received, calculating the current actual flow rate of the peristaltic pump based on the fixed volume in the reaction chamber from the bottom to the installation position of the float level sensor and the delivery time, and updating the delivery time control parameters for subsequent injections.

2. The system according to claim 1, characterized in that, The reaction chamber is a custom-made quartz tube reaction chamber, and its top is also provided with at least one reagent inlet, one pure water inlet, at least one water sample inlet, and one overflow port; the overflow port is located above the trigger position of the float level sensor.

3. The system according to claim 1, characterized in that, The control unit is a Raspberry Pi running a Linux operating system and uses the Python programming language to implement the control logic. The control unit communicates with external servers or user terminals via the MQTT protocol and pushes the detection results via DingTalk or email.

4. The system according to claim 1, characterized in that, The control unit is also configured to automatically execute the peristaltic pump flow rate calibration process before each water quality test, or to execute the peristaltic pump flow rate calibration process at preset time intervals.

5. The system according to claim 1, characterized in that, The control unit is also configured to perform the following detection process: In response to a timed trigger or user command, the corresponding water sample peristaltic pump and reagent peristaltic pump are controlled to deliver a predetermined volume of water sample and detection reagent into the reaction chamber according to the calibrated flow rate and preset injection time. The ultraviolet spectrometer is controlled to measure the absorbance value of the solution after the reaction at a preset wavelength; Based on the built-in standard curve, the absorbance value is converted into the concentration value of the ion being measured, and the detection result is output or stored. The system controls the injection of pure water into the reaction chamber using a peristaltic pump and controls the evacuation to complete the automatic cleaning of the reaction chamber.

6. The system according to claim 1, characterized in that, It also includes a linkage control module: the control unit compares the detected ion concentration value with a preset threshold, and when the concentration value exceeds the threshold, it sends a control command to the external water treatment equipment through the MQTT protocol to adjust the working mode of the external water treatment equipment.

7. An automated ultraviolet spectrophotometric water quality detection method based on closed-loop calibration sample introduction, applied to the system according to any one of claims 1 to 6, characterized in that, Includes the following steps: Step S1: The peristaltic pump flow rate calibration process is executed by the control unit, including: controlling the target peristaltic pump to deliver liquid into the reaction chamber, using a float level sensor set on the top of the reaction chamber to detect whether the liquid level has reached the fixed volume position, recording the delivery time, and calculating the current actual flow rate of the peristaltic pump based on the fixed volume and the delivery time. Step S2: Based on the calibrated flow rate, control the water sample peristaltic pump and the reagent peristaltic pump to deliver a predetermined volume of water sample and detection reagent into the reaction chamber, respectively; Step S3: Control the ultraviolet spectrometer to measure the absorbance value of the solution after the reaction; Step S4: Convert the absorbance value into the concentration value of the analyte ion according to the built-in standard curve; Step S5: Control the pure water peristaltic pump to automatically clean the reaction chamber.

8. The method according to claim 7, characterized in that, The peristaltic pump flow rate calibration process in step S1 is executed automatically before each test, or automatically according to the time period set by the user.

9. The method according to claim 7, characterized in that, In step S3, before measuring the absorbance value, a zero-point calibration step is also included: controlling the peristaltic pump for cleaning to inject pure water into the reaction chamber, and measuring the absorbance value of the pure water as a blank reference.

10. The method according to claim 7, characterized in that, It also includes step S6: comparing the concentration value obtained in step S4 with a preset threshold. When the threshold is exceeded, a linkage control command is sent to the external water treatment equipment via the MQTT protocol to change its operating status.

Images