A portable micro-dissolved oxygen intelligent analysis system based on thin film permeation

Abstract

This invention relates to the field of water quality monitoring and analysis instrument technology, specifically a portable intelligent micro-dissolved oxygen analysis system based on membrane permeation. The system includes: electrode assemblies for a main measurement channel and a reference channel; a flow channel assembly communicating with the main measurement channel and allowing water samples to flow tangentially along the membrane surface; a current acquisition assembly for acquiring sampling currents from the two channels; an auxiliary detection assembly for acquiring temperature, flow rate, and battery voltage; and a control assembly. The control assembly calculates dissolved oxygen concentration based on temperature compensation using the sampling currents from the main measurement channel and the reference channel. It also acquires membrane state parameters based on the steady-state current ratio, response time constant ratio, and flow rate weighting of the filtered current. Output is paused when the flow rate or voltage is below a threshold. When the flow rate and voltage are normal, the system performs actions such as segmented output of compensated concentration, extending the sliding window time used for calculation, or pausing to save the current concentration according to the membrane state parameters.

Description

Technical Field

[0001] This invention relates to the field of water quality monitoring and analysis instruments, specifically a portable intelligent micro-dissolved oxygen analysis system based on membrane permeation. Background Technology

[0002] In existing dissolved oxygen detection systems, the water sample is usually tested using a single-path electrode assembly, and the dissolved oxygen concentration is calculated based on the collected current signal. To improve detection stability, some systems incorporate membrane structures and related sampling circuits in the flow channel to reduce the impact of external disturbances on the output results. However, when the water sample flow state, membrane fouling level, and power supply status change, the single-path detection results are easily affected by bubble blockage, flow fluctuations, and membrane mass transfer differences, leading to increased sampling current fluctuations. This, in turn, causes the dissolved oxygen concentration output to drift or become distorted, resulting in a deviation between the system output and the state of the water sample being tested. Summary of the Invention

[0003] The purpose of this invention is to provide a portable intelligent micro dissolved oxygen analysis system based on membrane permeation, which solves the problem of distorted output results caused by single detection paths being susceptible to bubble blockage, flow fluctuations and membrane fouling, and improves detection stability by combining data from the main measurement channel and the reference channel to determine the membrane state.

[0004] The objective of this invention can be achieved through the following technical solutions: A portable intelligent micro-dissolved oxygen analysis system based on membrane permeation includes: The electrode assembly includes a main measurement channel and a reference channel, both of which are connected to the water sample to be tested. Both the main measurement channel and the reference channel are provided with a thin film and an electrode structure including a measuring electrode and a counter electrode for outputting current signals. The flow channel assembly, connected to the electrode assembly, is used to allow the water sample to flow tangentially along the surface of the membrane; the current acquisition assembly, electrically connected to the electrode structure, is used to acquire the sampling current of the main measurement channel and the reference channel respectively; the auxiliary detection assembly is used to acquire the temperature, flow rate, and voltage of the system power supply battery of the water sample. The control component is used to calculate the dissolved oxygen concentration by performing temperature compensation based on the sampling current of the main measurement channel and the reference channel; the control component is also used to obtain membrane state parameters by weighted calculation based on the steady-state current ratio of the sampling current, the response time constant ratio, and the flow rate. The control component is configured to: pause output when the flow rate is lower than the preset flow rate threshold or the voltage is lower than the preset voltage threshold; and when the flow rate is not lower than the preset flow rate threshold and the voltage is not lower than the preset voltage threshold, execute the output of the compensated dissolved oxygen concentration, extend the preset sliding window time for calculating the relative volatility, or pause the action of saving the current concentration based on the determination result of the range to which the membrane state parameter value belongs.

[0005] Optionally, the films for both the main measurement channel and the reference channel are polytetrafluoroethylene fiber films; The main measurement channel has a film thickness of 25–75 μm and an effective area of ​​3–15 mm²; the reference channel has a film thickness of 100–250 μm and an effective area of ​​1–8 mm². The distance between the measuring electrode and the counter electrode in the main measuring channel is 0.2–1.0 mm, and the distance between the measuring electrode and the counter electrode in the reference channel is 0.2–1.0 mm.

[0006] Optionally, the films for both the main measurement channel and the reference channel are polytetrafluoroethylene fiber films; The main measurement channel has a film thickness of 25–75 μm and an effective area of ​​3–15 mm²; the reference channel has a diffusion gap with a thickness of 50–150 μm on the outer side of the film. The distance between the measuring electrode and the counter electrode in the main measuring channel is 0.2–1.0 mm, and the distance between the measuring electrode and the counter electrode in the reference channel is 0.2–1.0 mm.

[0007] Optionally, the flow channel assembly includes a rectifier section with a length of 20 to 50 mm and a detection section with a height of 1 to 3 mm; The top of the upstream section of the detection section is equipped with an exhaust chamber and a hydrophobic exhaust port that communicates with the outside. The exhaust chamber and the hydrophobic exhaust port are used to remove the air bubbles separated from the water sample to be tested. The detection section is provided with a mounting surface for installing the membrane, and the mounting surface is inclined at an angle relative to the direction of water sample flow; on the projection surface perpendicular to the direction of water sample flow, the main measurement channel and the reference channel are offset from each other by at least 1 mm.

[0008] Optionally, the flow channel assembly also includes a limiting step and a metal clamping ring disposed on the outside of the film, wherein the metal clamping ring presses the edge of the film against the limiting step by a threaded tightening structure.

[0009] Optionally, the current acquisition component includes two independent signal chains, which are respectively connected to the main measurement channel and the reference channel; Each signal chain includes, in sequence, a transimpedance amplifier circuit with a connecting electrode structure, a low-pass filter, and an analog-to-digital converter; The sampling frequency of the main measurement channel is set to 20–100 Hz; the sampling frequency of the reference channel is set to 5–20 Hz.

[0010] Optionally, the control component sequentially performs three-point median filtering and low-pass filtering with a cutoff frequency of 1–5 Hz on the acquired sampled current, and inputs the filtered current into a preset 10–30 s sliding window to calculate the relative fluctuation rate of the main measurement channel. Relative volatility to the reference channel ,in: ; ; In the formula, To correspond to the standard deviation of the current within the sliding window, and This corresponds to the average current within the sliding window. To prevent the preset current minimum value compensation constant from being zero in the denominator; The control component is configured to simultaneously satisfy... , , and At that time, the system is deemed to satisfy the steady-state output conditions determined based on calibration experiments; among which, The flow rate of the water sample to be tested. The temperature of the water sample to be tested. For time.

[0011] Optionally, when the system starts up, the range switches, or the rate of change calculated based on two adjacent dissolved oxygen concentrations exceeds 10%, the control component selects a data segment with a length of at least 10 seconds after the start time to fit the current change curves of the main measurement channel and the reference channel. ; In the formula, For steady-state current, For time, The response time constant is obtained by the control component through fitting; and the response time constant of the reference channel And calculate the ratio of response time constants. ; The interval obtained by standardizing the clean membrane in a standard solution When the response time is within the acceptable range, the relationship between the main measurement channel and the reference channel is considered normal.

[0012] Optionally, the control component calculates the membrane state parameters using the following formula. : ; In the formula, This is the ratio of steady-state currents. The main measurement channel steady-state current, The reference channel steady-state current; To clean the current ratio obtained by calibration of the thin film in a standard solution, To clean the ratio of the time constants obtained by calibration of the membrane in a standard solution, To calibrate the flow rate, For traffic, , , ; The control component executes the following priority judgment logic: First priority: When traffic... If the flow rate is deemed insufficient, the dissolved oxygen concentration update will be paused. Second priority: when At that time, based on the membrane state parameters Perform segmented judgment: when At that time, output the compensated dissolved oxygen concentration; when If the membrane is found to be slightly contaminated, the time of the preset sliding window is extended to 30-60 seconds, and the output dissolved oxygen concentration data is marked as abnormal and needs to be cleaned. when If the membrane is deemed severely contaminated or damaged, maintain the most recent effective concentration and suspend updating the current concentration data.

[0013] The beneficial effects of this invention are: This invention sets up a main measurement channel and a reference channel, both of which are connected to the water sample to be tested. By combining the membrane and electrode structure to collect the current changes after oxygen molecules pass through, the formal measurement and the control judgment can be separated, thereby improving the comparability and stability of the dissolved oxygen output results. By making the water sample flow tangentially along the membrane surface and setting up a rectification section, a detection section, an exhaust chamber and a hydrophobic exhaust hole, the air bubbles separated in the water sample can be removed in time, reducing the obstruction and disturbance of the sampling current caused by the air bubbles staying on the membrane surface, and reducing the concentration drift caused by changes in the flow state. Attached Figure Description

[0014] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic flowchart of a portable intelligent analysis method for trace dissolved oxygen based on membrane permeation provided in an embodiment of this application. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] Please see Figure 1 A portable intelligent micro dissolved oxygen analysis system based on membrane permeation includes: an electrode assembly, including a main measurement channel and a reference channel, both of which are connected to the water sample to be tested; both the main measurement channel and the reference channel are provided with a membrane and an electrode structure including a measuring electrode and a counter electrode, for outputting a current signal; and a flow channel assembly, connected to the electrode assembly, for causing the water sample to be tested to flow tangentially along the surface of the membrane. The current acquisition component, electrically connected to the electrode structure, is used to acquire the sampling current of the main measurement channel and the reference channel, respectively; the auxiliary detection component is used to acquire the temperature, flow rate, and voltage of the system power supply battery of the water sample to be tested. The control component is used to calculate the dissolved oxygen concentration by performing temperature compensation based on the sampling current of the main measurement channel and the reference channel; the control component is also used to obtain membrane state parameters by weighted calculation based on the steady-state current ratio of the sampling current, the response time constant ratio, and the flow rate. The control component is configured to: pause output when the flow rate is lower than the preset flow rate threshold or the voltage is lower than the preset voltage threshold; and when the flow rate is not lower than the preset flow rate threshold and the voltage is not lower than the preset voltage threshold, execute the output of the compensated dissolved oxygen concentration, extend the preset sliding window time for calculating the relative volatility, or pause the action of saving the current concentration based on the determination result of the range to which the membrane state parameter value belongs.

[0017] In this embodiment, the electrode assembly refers to two parallel mass transfer channels arranged along the same water sample path. The main measurement channel is used to output the formal concentration value, and the reference channel is used to provide the control current and control response process. Both channels include a thin film, a measuring electrode, and a counter electrode. The thin film is used to allow oxygen molecules to pass through and enter the electrode reaction zone, and the electrode structure is used to convert the oxygen mass transfer change into the current change. The flow channel assembly allows the water sample to flow tangentially along the membrane surface, making the water flow state near the membrane surface as stable as possible and reducing the residence of air bubbles on the membrane surface. The current acquisition component collects the sampling current after the output of each channel electrode and sends the sampling current to the control component. The control component first corrects the sampling current based on the temperature detection results, and then calculates the dissolved oxygen concentration from the current of the main measurement channel. Temperature compensation is a function of the control components to correct the conversion relationship between current and concentration based on the difference between the current water sample temperature and the calibration conditions, so that the concentration results corresponding to the same current are consistent at different temperatures. Specifically, the temperature compensation calculation is corrected using the Arrhenius equation, and the correction formula is as follows: ; Then the compensated current from the main measurement channel The dissolved oxygen concentration can be calculated using the following formula: ; In the formula, The current water sample temperature The sampling current below, To calibrate the temperature, both were calculated by adding 273.15 to the collected Celsius values; As the apparent activation energy, Let be the ideal gas constant. For the natural constant An exponential function with base 0; The dissolved oxygen concentration, calculated after temperature compensation for the main measurement channel, is expressed in mg / L. The sampling current is after temperature compensation, in amperes (A). To calibrate the sensitivity coefficient, the unit is mg·L. −1 ·A −1 ; This is the zero-point offset, in mg / L. During operation, the auxiliary detection component continuously provides the water sample flow rate, battery voltage, and water sample temperature; the control component first determines whether the flow rate is lower than the preset flow rate threshold, such as 300 mL / min, or whether the voltage is lower than the preset voltage threshold, such as the minimum safe operating voltage of the system power supply battery, such as 3.3V. If any normal condition is not met, the output of the current concentration result will stop; only when the flow rate and voltage are within the normal range will the control component continue to process the filtered current data and determine the subsequent actions based on the segmented threshold of the membrane state parameters. The membrane state parameters are synthesized by weighting the steady-state current ratio, the response time constant ratio, and the flow rate, reflecting whether the mass transfer in the two channels is consistent and whether the flow field is stable. If the membrane state parameters are in the normal range, the compensated dissolved oxygen concentration is output; if they are in the slightly abnormal range, the sliding window time is extended before making a judgment; if they are in the severely abnormal range, the current concentration is paused and saved to avoid taking the abnormal current as a valid result.

[0018] In a preferred embodiment of the present invention, the films of both the main measurement channel and the reference channel are polytetrafluoroethylene fiber films; The main measurement channel has a film thickness of 25–75 μm and an effective area of ​​3–15 mm². The thin film thickness of the reference channel is 100–250 μm, and the effective area is 1–8 mm². The distance between the measuring electrode and the counter electrode in the main measuring channel is 0.2–1.0 mm, and the distance between the measuring electrode and the counter electrode in the reference channel is 0.2–1.0 mm.

[0019] In this embodiment, the main measurement channel and the reference channel use the same type of polytetrafluoroethylene fiber membrane, so that the two channels have the same permeation mechanism for oxygen molecules, and different mass transfer responses are formed by the difference in thickness and area; the main measurement channel uses a thin film with a first preset thickness and a first effective area to obtain a first response time; The reference channel uses a thin film with a second preset thickness and a second effective area to obtain a second response time, wherein the first preset thickness is less than the second preset thickness, the first effective area is greater than the second effective area, and the first response time is less than the second response time; the electrode spacing of the two channels is controlled within the same range to keep the electrode reaction areas comparable and reduce additional deviations. In actual operation, when the water sample to be tested enters the two channels along the flow path, oxygen molecules pass through the membrane in sequence and undergo electrochemical reactions in the electrode area; due to the difference in membrane thickness and area between the main measurement channel and the reference channel, there will be identifiable differences in the rate of current change and steady-state current level between the two. Based on the differences, the control component calculates the ratio of steady-state current to the ratio of response time constant to determine whether there is contamination, bubble blockage, or abnormal flow on the membrane surface. In a preferred embodiment of the present invention, the films of both the main measurement channel and the reference channel are polytetrafluoroethylene fiber films; The main measurement channel has a film thickness of 25–75 μm and an effective area of ​​3–15 mm². The outer side of the thin film in the reference channel has a diffusion gap with a thickness of 50–150 μm; The distance between the measuring electrode and the counter electrode in the main measuring channel is 0.2–1.0 mm, and the distance between the measuring electrode and the counter electrode in the reference channel is 0.2–1.0 mm.

[0020] In this embodiment, the reference channel has a diffusion gap on the outside of the film; the diffusion gap is located on the outside of the film and is used to allow oxygen molecules to enter the film surface after traveling a predetermined distance; This structure lengthens the oxygen mass transfer path of the reference channel, thereby increasing the response time constant of the reference channel and making the steady-state current change smoother; the reference channel is used to reflect changes in the flow field and film surface state. During operation, the main measurement channel outputs the formal measurement current according to the first response time, while the reference channel forms a second response time process that is longer than the first response time due to the diffusion gap. After the control component collects the current of the two channels, it calculates the steady-state current ratio and the response time constant ratio respectively, and compares them with the calibration values. If the reference channel deviates abnormally due to changes in the diffusion gap and the mass transfer path outside the membrane, the control unit will incorporate this deviation into the membrane state parameters, affecting whether to continue outputting the current concentration.

[0021] In a preferred embodiment of the present invention, the flow channel assembly includes a rectifier section with a length of 20 to 50 mm and a detection section with a height of 1 to 3 mm; The top of the upstream section of the detection section is equipped with an exhaust chamber and a hydrophobic exhaust port that communicates with the outside. The exhaust chamber and the hydrophobic exhaust port are used to remove the air bubbles separated from the water sample to be tested. The detection section is provided with a mounting surface for installing the membrane, and the mounting surface is inclined at an angle relative to the direction of water sample flow; on the projection surface perpendicular to the direction of water sample flow, the main measurement channel and the reference channel are offset from each other by at least 1 mm.

[0022] In this embodiment, the flow channel assembly consists of a rectification section and a detection section; the rectification section is used to regulate the flow velocity of the water sample entering the system into a more stable flow pattern, and the detection section is used to allow the water sample to complete oxygen mass transfer detection near the membrane surface; an exhaust chamber and a hydrophobic exhaust hole are provided upstream of the detection section so that air bubbles in the water sample can accumulate at the top of the flow channel and be discharged through the exhaust hole. The mounting surface is tilted so that the bubble moves away from the detection area along the upper path; the main measurement channel and the reference channel are staggered on the projection surface to prevent the same bubble from blocking both channels at the same time and to maintain the distinguishability of the data from the two channels. The water sample to be tested first passes through the rectification section and then enters the detection section; if the water sample contains air bubbles, the air bubbles will enter the exhaust chamber at the top of the upstream of the detection section and be discharged through the hydrophobic exhaust hole. The water sample passes tangentially across the membrane surface and enters the membrane reaction zone of the main measurement channel and the reference channel. Since there is a gap between the two channels on the projection plane, the effect of a single local bubble on the two channels is not completely consistent. The control component can use this to determine whether there is bubble interference and include it in the membrane state parameters.

[0023] In a preferred embodiment of the present invention, the flow channel assembly further includes a limiting step and a metal clamping ring disposed on the outside of the film, wherein the metal clamping ring presses the edge of the film onto the limiting step by a threaded tightening structure.

[0024] In this embodiment, the limiting step is used to define the installation position of the membrane. The metal clamping ring presses the edge of the membrane onto the limiting step through a threaded tightening structure, limiting the deformation of the membrane edge when the water sample pressure fluctuates; so as to keep the effective permeable area of ​​the membrane in a stable state and reduce the impact of changes in the thickness of the outer space on the current output. When the water sample pressure changes, if the membrane deforms, it will change the oxygen diffusion path and the mass transfer conditions near the electrode, resulting in current fluctuations. After the membrane edge is fixed by the limiting step and the clamping ring, the mass transfer conditions of the main measurement channel and the reference channel are more likely to be kept consistent, and the ratio of steady-state current and the ratio of response time constant calculated by the control component are also more stable.

[0025] In a preferred embodiment of the present invention, the current acquisition component includes two independent signal chains, which are respectively connected to the main measurement channel and the reference channel. Each signal chain includes, in sequence, a transimpedance amplifier circuit with a connecting electrode structure, a low-pass filter, and an analog-to-digital converter; The sampling frequency of the main measurement channel is set to 20–100 Hz; the sampling frequency of the reference channel is set to 5–20 Hz.

[0026] In this embodiment, two independent signal chains correspond to the main measurement channel and the reference channel, respectively, and acquire current independently to avoid crosstalk caused by sharing a single path; each signal chain first converts the weak current into voltage through a transimpedance amplifier circuit, then removes high-frequency noise through a low-pass filter, and finally converts the analog quantity into a digital quantity through an analog-to-digital converter and sends it to the control component. The main measurement channel uses a first sampling frequency to acquire the current process when the concentration is changing; the reference channel uses a second sampling frequency lower than the first sampling frequency to suppress fluid pulsation interference and reduce the amount of sampling data. During operation, the sampling data from the main measurement channel is primarily used for concentration conversion, while the sampling data from the reference channel is primarily used for stability assessment. After receiving two digital currents, the control component first performs filtering and window calculations on each, and then uses the results to determine the steady-state current ratio, response time constant ratio, and membrane state parameters.

[0027] In a preferred embodiment of the present invention, the control component sequentially performs three-point median filtering and low-pass filtering with a cutoff frequency of 1-5Hz on the acquired sampling current, and inputs the filtered current into a preset sliding window of 10-30s to calculate the relative fluctuation rate of the main measurement channel. Relative volatility to the reference channel ,in: ; ; In the formula, To correspond to the standard deviation of the current within the sliding window, and This corresponds to the average current within the sliding window. To prevent the preset current minimum value compensation constant from being zero in the denominator; The control component is configured to simultaneously satisfy... , , and At that time, the system is deemed to satisfy the steady-state output conditions determined based on calibration experiments; among which, The flow rate of the water sample to be tested. The temperature of the water sample to be tested. For time.

[0028] In this embodiment, the control component performs three-point median filtering and low-pass filtering on the sampled current; the three-point median filtering is used to remove single-point abrupt changes, and the low-pass filtering is used to reduce high-frequency fluctuations; after filtering, the control component inputs the current into a sliding window of a preset length for statistical analysis; The window length is dynamically determined within 10 to 30 seconds based on the stability of the water sample flow rate and velocity. When the difference between the water sample flow rate and the calibration flow rate is less than the preset difference, the window length is set to the first preset time length. When the difference between the water sample flow rate and the calibration flow rate is greater than or equal to the preset difference, or when the fluid pulsation amplitude is greater than the preset pulsation threshold, the window length is taken as the second preset time length, which is greater than the first preset time length; the mean and standard deviation are calculated within the window, and then the relative volatility of the main measurement channel and the relative volatility of the reference channel are obtained according to the formula; The standard deviation is determined by the degree of dispersion of each sampling point within the same sliding window relative to the mean current of that window. The main measurement channel and the reference channel are calculated using the filtered data from their respective signal chains. The minimum compensation constant is taken as a positive number less than the minimum resolvable unit of the absolute value of the normal current, and the same value taking rule is used in both channels, so as to avoid the denominator being zero when the window mean is close to zero, while not changing the volatility judgment in the normal current range. The stability of the current within a set time is determined by the relative volatility. Only when the relative volatility of the main measurement channel and the reference channel simultaneously meets the threshold, and the changes in flow rate and temperature also meet the threshold, does the control component determine that the system is in a steady-state output condition. Among them, a relative fluctuation rate of no more than 1% in the main measurement channel indicates that the formal measurement current is in a stable state, and a relative fluctuation rate of no more than 2% in the reference channel indicates that the control current is not significantly affected by fluid pulsation. When the flow rate is between 400 and 800 mL / min and the temperature change rate does not exceed 0.5℃ / min, it indicates that the current mass transfer and temperature conditions are within the calibration allowable range. At this time, the system will then call the temperature-compensated calibration relationship to output the dissolved oxygen concentration. Otherwise, it will continue to wait until the data in the window meets the steady-state conditions.

[0029] In a preferred embodiment of the present invention, when the system starts up, the range is switched, or the rate of change calculated based on two adjacent dissolved oxygen concentrations exceeds 10%, the control component selects a data segment with a length of at least 10 seconds after the start time to fit the current change curves of the main measurement channel and the reference channel. ; In the formula, For steady-state current, For time, The response time constant is obtained by the control component through fitting; and the response time constant of the reference channel And calculate the ratio of response time constants. ; The interval obtained by standardizing the clean membrane in a standard solution When the response time is within the acceptable range, the relationship between the main measurement channel and the reference channel is considered normal.

[0030] In this embodiment, the control component initiates a transient fitting process when the system starts up, the range is switched, or the rate of change between two concentration calculations exceeds a threshold. The data segment after the start time is a continuous current data segment collected after the self-triggering condition is met, and its length must at least meet the fitting requirements. The data segment is directly extracted from the raw data after low-pass filtering before entering the 10-30s sliding window to retain the true transient physical characteristics. Before fitting, linear interpolation is used to align the discrete sampling point dimension of the reference channel to the array length of the main measurement channel according to the timestamp. The control component substitutes this data segment into a first-order exponential model and fits the current change curves of the main measurement channel and the reference channel respectively to obtain their respective response time constants. The start time of the fitted data segment is uniformly taken as the moment when the trigger condition is first met, and the end time is taken as the moment when the continuous data segment reaches the preset length; in the same fitting, the two channels use the same start and end time range, and the filtered current data of the corresponding channel is used. During the fitting process, the steady-state current is taken as the average current value of the stable interval at the end of the data segment, and the response time constant is taken as a positive parameter that minimizes the deviation between the model curve and the sampled current. When there are insufficient effective sampling points or the fitted response time constant is not positive, the fitting result is invalid, and the previous effective response time relationship judgment result is maintained. The response time constant characterizes the rate at which the current reaches a steady state; the control component then calculates the ratio of the response time constants of the two channels and compares it with the calibration range of the clean membrane in the standard solution; The calibration range is determined by repeatedly collecting multiple transient response processes of the clean membrane under temperature and flow conditions, and covers the normal variation range of the calibrated ratio; When the ratio is within the range, it indicates that the response relationship between the two channels remains normal; when it exceeds the range, it indicates that the mass transfer conditions of the channels have changed. For trigger conditions such as system startup, range switching, or concentration change rate exceeding 10%, the same data segment selection rules, the same fitting model, and the same ratio range are used for judgment. The fitted result... As the sole response time input in subsequent membrane state parameter calculations; In a preferred embodiment of the present invention, the control component calculates the membrane state parameters using the following formula. : ; In the formula, This is the ratio of steady-state currents. The main measurement channel steady-state current, The reference channel steady-state current; To clean the current ratio obtained by calibration of the thin film in a standard solution, To clean the ratio of the time constants obtained by calibration of the membrane in a standard solution, To calibrate the flow rate, For traffic, , , ; The control component executes the following priority judgment logic: First priority: when traffic... If the flow rate is insufficient, suspend updating the dissolved oxygen concentration; second priority: when At that time, based on the membrane state parameters Perform segmented judgment: when At that time, output the compensated dissolved oxygen concentration; when If the membrane is found to be slightly contaminated, the time of the preset sliding window is extended to 30-60 seconds, and the output dissolved oxygen concentration data is marked as abnormal and needs to be cleaned. when If the membrane is deemed severely contaminated or damaged, maintain the most recent effective concentration and suspend updating the current concentration data.

[0031] In this embodiment, the control component first takes the steady-state current of the main measurement channel and the reference channel, calculates the steady-state current ratio, and then compares it with the calibrated current ratio, the calibrated time constant ratio, and the calibrated flow rate. The membrane state parameters are obtained by multiplying the three deviation terms by their respective weights and then summing them; the calibration values ​​are obtained using the same units and calculation rules as those used during operation. , and All are positive values; The above three values ​​are checked for validity during device calibration or parameter writing. If any calibration value is zero or invalid, the membrane state parameter calculation is not performed and the output is paused. During operation, calculation is only performed when both the main measurement channel and the reference channel obtain valid steady-state current and the steady-state current of the main measurement channel is not zero. Otherwise, the judgment result of the previous effective membrane state parameters shall be used; Since each deviation term is a dimensionless relative deviation relative to its corresponding calibration value, and the sum of their weights is 1, The minimum value is 0, and the larger the value, the greater the deviation of the current mass transfer state from the clean calibration state; The control components use a priority order when making decisions; they check whether the system power supply battery voltage is lower than a preset voltage threshold based on the control logic. When the voltage is below the threshold, the output is paused and prioritized over the judgment of subsequent membrane state parameters; when the voltage is normal, the flow rate is then judged to see if it is below the lower limit. If it is below the lower limit, the update of dissolved oxygen concentration is paused. If both voltage and flow rate meet the requirements, then judge according to the membrane state parameters in segments: when they are less than the first threshold, output the compensated concentration; When the value is in the middle range, the control component extends the sliding window to 30-60 seconds before calculating and marks the output data as an anomaly to be cleaned; when the value is greater than or equal to the second threshold, the control component maintains the most recent effective concentration and pauses updating the current concentration data.

Claims

1. A portable intelligent micro-dissolved oxygen analysis system based on membrane permeation, characterized in that, include: The electrode assembly includes a main measurement channel and a reference channel, both of which are connected to the water sample to be tested. Both the main measurement channel and the reference channel are provided with a thin film and an electrode structure including a measuring electrode and a counter electrode for outputting current signals; A flow channel assembly, connected to the electrode assembly, is used to allow the water sample to be tested to flow tangentially along the surface of the membrane. A current acquisition component, electrically connected to the electrode structure, is used to acquire the sampling current of the main measurement channel and the reference channel, respectively. The auxiliary detection component is used to acquire the temperature, flow rate, and voltage of the system's power supply battery of the water sample to be tested. A control component is used to calculate the dissolved oxygen concentration by performing temperature compensation based on the sampling current of the main measurement channel and the reference channel; The control component is also used to obtain membrane state parameters by weighted calculation based on the steady-state current ratio of the sampled current, the response time constant ratio, and the flow rate. The control component is configured to pause output when the flow rate is lower than a preset flow rate threshold or the voltage is lower than a preset voltage threshold. When the flow rate is not lower than the preset flow rate threshold and the voltage is not lower than the preset voltage threshold, based on the determination result of the range to which the membrane state parameter value belongs, the actions of outputting the compensated dissolved oxygen concentration, extending the preset sliding window time for calculating the relative volatility, or pausing the saving of the current concentration are performed.

2. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 1, characterized in that, The membranes of both the main measurement channel and the reference channel are polytetrafluoroethylene fiber membranes; The main measurement channel has a film thickness of 25–75 μm and an effective area of ​​3–15 mm²; the reference channel has a film thickness of 100–250 μm and an effective area of ​​1–8 mm². The distance between the measuring electrode and the counter electrode in the main measuring channel is 0.2 to 1.0 mm, and the distance between the measuring electrode and the counter electrode in the reference channel is 0.2 to 1.0 mm.

3. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 1, characterized in that, The membranes of both the main measurement channel and the reference channel are polytetrafluoroethylene fiber membranes; The main measurement channel has a film thickness of 25–75 μm and an effective area of ​​3–15 mm²; the reference channel has a diffusion gap with a thickness of 50–150 μm on the outer side of the film. The distance between the measuring electrode and the counter electrode in the main measuring channel is 0.2 to 1.0 mm, and the distance between the measuring electrode and the counter electrode in the reference channel is 0.2 to 1.0 mm.

4. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 1, characterized in that, The flow channel assembly includes a rectifier section with a length of 20-50 mm and a detection section with a height of 1-3 mm; The top of the upstream section of the detection segment is provided with an exhaust chamber and a hydrophobic exhaust hole that communicates with the outside. The exhaust chamber and the hydrophobic exhaust hole are used to remove the air bubbles separated from the water sample to be tested. The detection section is provided with a mounting surface for mounting the membrane, and the mounting surface is inclined at an angle relative to the water sample flow direction; on the projection surface perpendicular to the water sample flow direction, the main measurement channel and the reference channel are offset from each other by a distance of at least 1 mm.

5. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 4, characterized in that, The flow channel assembly also includes a limiting step and a metal clamping ring disposed on the outside of the film. The metal clamping ring presses the edge of the film onto the limiting step through a threaded tightening structure.

6. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 1, characterized in that, The current acquisition component includes two independent signal chains, which are respectively connected to the main measurement channel and the reference channel. Each of the signal chains includes, in sequence, a transimpedance amplifier circuit, a low-pass filter, and an analog-to-digital converter connected to the electrode structure; The sampling frequency of the main measurement channel is set to 20–100 Hz; the sampling frequency of the reference channel is set to 5–20 Hz.

7. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 1, characterized in that, The control component sequentially performs three-point median filtering and low-pass filtering with a cutoff frequency of 1-5Hz on the acquired sampled current, and inputs the filtered current into a preset 10-30s sliding window to calculate the relative fluctuation rate of the main measurement channel. Relative volatility to the reference channel ,in: In the formula, To correspond to the standard deviation of the current within the sliding window, and This corresponds to the average current within the sliding window. To prevent the preset current minimum value compensation constant from being zero in the denominator; The control component is configured to: simultaneously satisfy... , , and At that time, the system is deemed to satisfy the steady-state output conditions determined based on calibration experiments; among which, The flow rate of the water sample to be tested. The temperature of the water sample to be tested. For time.

8. The portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 1, characterized in that, When the system starts up, the range switches, or the rate of change calculated based on two adjacent dissolved oxygen concentrations exceeds 10%, the control component selects a data segment with a length of at least 10 seconds after the start time to fit the current change curves of the main measurement channel and the reference channel. In the formula, For steady-state current, For time, The response time constant is used; the control component obtains the response time constant of the main measurement channel through fitting. and the response time constant of the reference channel And calculate the ratio of response time constants. ; The The interval obtained by standardizing the clean membrane in a standard solution When the response time is within the specified range, the relationship between the main measurement channel and the reference channel is determined to be normal.

9. A portable intelligent micro-dissolved oxygen analysis system based on membrane permeation according to claim 8, characterized in that, The control component calculates the membrane state parameters using the following formula. : In the formula, This is the ratio of steady-state currents. The main measurement channel steady-state current, The reference channel steady-state current; To clean the current ratio obtained by calibration of the thin film in a standard solution, To clean the ratio of the time constants obtained by calibration of the membrane in a standard solution, To calibrate the flow rate, For the traffic, , , ; The control component executes the following priority judgment logic: First priority: when the traffic If the flow rate is insufficient, the update of the dissolved oxygen concentration will be paused. Second priority: when At that time, according to the membrane state parameters Perform segmented judgment: when At that time, the compensated dissolved oxygen concentration is output; when If the membrane is found to be slightly contaminated, the time of the preset sliding window is extended to 30-60 seconds, and the output dissolved oxygen concentration data is marked as abnormal and needs to be cleaned. when If the membrane is deemed severely contaminated or damaged, maintain the most recent effective concentration and suspend updating the current concentration data.

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