Efficient Regulation Method for Water Body Oxygen Concentration for Sensor Automatic Calibration Control

Abstract

The present invention discloses an efficient method for adjusting the water body oxygen concentration for sensor automatic calibration control, belonging to the field of water quality environment monitoring. Specifically, first, the oxygen concentration increase rate coefficient adjusted by pure oxygen, the oxygen concentration decrease rate coefficient adjusted by pure nitrogen, and the oxygen concentration change coefficient adjusted by the mixed gas are obtained respectively. Subsequently, based on the difference between the current value of the water body oxygen concentration measured by the dissolved oxygen sensor and the target value to be adjusted, pure oxygen or pure nitrogen is used for rough adjustment, and mixed gases with different nitrogen-oxygen ratios are used for fine adjustment, and the continuous bubbling of the mixed gas is maintained before the data recording at this concentration point is completed. The present invention utilizes the correlation rules between the stable oxygen concentration and the bubbling duration and the nitrogen-oxygen ratio in different bubbling methods summarized from a large number of experiments, making the oxygen concentration adjustment result have high reproducibility and predictability, without the need for manual observation and judgment, and thus the whole process of sensor calibration can be realized with programmed control.

Description

Technical Field

[0001] The present invention belongs to the field of water quality environmental monitoring, and particularly relates to an efficient method for regulating the water body oxygen concentration for automatic calibration control of sensors. Background Art

[0002] Dissolved oxygen (DO) is one of the most important water quality environmental monitoring parameters. Compared with the traditional iodometric titration method, the dissolved oxygen sensor can in-situ and online measure the oxygen content in the water body, which can greatly improve the efficiency of water quality environmental monitoring. During long-term use, the dissolved oxygen sensor will have varying degrees of data drift and needs to be calibrated regularly. With the increasing application of current dissolved oxygen sensors, it poses a great challenge to the calibration work of the sensors. The calibration of the sensor mainly includes two aspects: creating a calibration environment and obtaining a reference value. The regulation and control of the water body oxygen concentration is an important part of creating a calibration environment, and to a large extent, it can directly determine the efficiency and precision of the calibration method.

[0003] The existing methods for regulating the water body oxygen concentration can be divided into three categories: (1) Adding a strong reducing agent to reduce the oxygen concentration: adding sodium sulfite reagent to quickly remove the dissolved oxygen in the water body; (2) Preparing dissolved oxygen solutions with different concentration gradients in advance: introducing different volumes of high-purity oxygen or saturated air into anaerobic water, or introducing different volumes of nitrogen or adding different masses of sodium sulfite reagent into oxygen-saturated water to form a series of prefabricated solutions with concentration gradients; (3) Introducing gas into the water body to change the concentration: introducing a certain amount of oxygen, nitrogen or a mixed gas into the water body of the calibration device to change the dissolved oxygen content in the water body.

[0004] The above three methods can all play a role in regulating the water body oxygen concentration, but none of them are applicable to the automatic calibration control of dissolved oxygen sensors. The main reasons include: (1) Poor reproducibility: affected by factors such as reagent storage and air oxidation, the sodium sulfite regulation method has strong randomness, and it is difficult to stabilize at the same concentration value after adding the same dose; (2) Poor predictability: when the initial concentrations are inconsistent, the gas bubbling regulation method cannot predict how much gas needs to be introduced for a given regulation target, and can only rely on manual observation and judgment; (3) Low efficiency of precise regulation: due to the lag of reagent reaction and gas dissolution, when aiming at a specific precise regulation target, it is difficult to ensure that the concentration after stabilization is consistent with the target value even relying on manual judgment.

[0005] Therefore, establishing an anticipatable and efficient method for regulating the water body oxygen concentration helps to quickly adjust and stably maintain the sensor calibration environment. Using it for the calibration work of dissolved oxygen sensors is expected to greatly improve the calibration efficiency and calibration accuracy of the sensors. Summary of the Invention

[0006] The object of the present invention is to overcome the disadvantages of low efficiency and poor reproducibility of existing water body oxygen concentration adjustment means, and to provide an efficient method for adjusting the water body oxygen concentration for sensor automatic calibration control, which can meet the requirements of the dissolved oxygen sensor automatic calibration method for the calibration environment creation ability.

[0007] The specific technical solutions adopted by the present invention are as follows:

[0008] The present invention provides an efficient method for adjusting the water body oxygen concentration for sensor automatic calibration control, specifically as follows:

[0009] S1: Pour a part of water into a sealed calibration container, completely immerse the detection area of the dissolved oxygen sensor to be calibrated in the water, start the dissolved oxygen sensor, and display and save its output data in real time throughout the process.

[0010] S2: Introduce pure oxygen with a fixed flow rate into the calibration container for a certain period of time. After waiting for the output data of the dissolved oxygen sensor to stabilize, introduce pure oxygen with a fixed flow rate for another certain period of time and wait for the output data of the dissolved oxygen sensor to stabilize again. Repeat several times to continuously increase the oxygen concentration in the water, obtain several sets of corresponding data of the stable water body oxygen concentration value and the cumulative oxygen injection duration, and obtain the oxygen concentration increase rate coefficient adjusted by pure oxygen according to the recorded data.

[0011] S3: Introduce pure nitrogen with a fixed flow rate into the calibration container for a certain period of time. After waiting for the output data of the dissolved oxygen sensor to stabilize, introduce nitrogen with a fixed flow rate for another certain period of time and wait for the output data of the dissolved oxygen sensor to stabilize again. Repeat several times to continuously reduce the oxygen concentration in the water, obtain several sets of corresponding data of the stable water body oxygen concentration value and the cumulative nitrogen injection duration, and obtain the oxygen concentration decrease rate coefficient adjusted by pure nitrogen according to the recorded data.

[0012] S4: Continuously introduce a mixed gas with a certain nitrogen-oxygen ratio into the calibration container. After waiting for the output data of the dissolved oxygen sensor to stabilize, change the nitrogen-oxygen ratio of the mixed gas and wait for the output data of the dissolved oxygen sensor to stabilize again. Change the nitrogen-oxygen ratio of the mixed gas several times to continuously change the oxygen concentration in the water, obtain several sets of corresponding data of the stable water body oxygen concentration value and the nitrogen-oxygen ratio of the mixed gas, and obtain the oxygen concentration change coefficient adjusted by the mixed gas according to the recorded data.

[0013] S5: Judge according to the difference between the current value of the water body oxygen concentration measured by the dissolved oxygen sensor and the target value to be adjusted. Use pure oxygen or pure nitrogen for rough adjustment by using the results obtained in steps S2 and S3, use mixed gases with different nitrogen-oxygen ratios for fine adjustment by using the results obtained in step S4, and keep the mixed gas continuously injected before completing the data recording at this concentration point.

[0014] Preferably, steps S2 to S4 are repeated 4 to 6 times respectively.

[0015] Preferably, during the measurement of steps S2 to S4, the experimental conditions are kept the same and unchanged; the experimental conditions include the water volume, temperature, position of the dissolved oxygen sensor, and position of the air injection port in the calibration container.

[0016] Preferably, during the measurement of steps S2 to S4, the gas flow rate into the calibration container is controlled by a mass flow controller.

[0017] Preferably, the specific method for obtaining the oxygen concentration increase rate coefficient adjusted by pure oxygen in step S2 is as follows:

[0018] S21: Subtract the initial oxygen concentration value from the oxygen concentration value measured by the dissolved oxygen sensor in the stable state after each group is filled with pure oxygen to obtain the increase value of the water body oxygen concentration ΔDO at each stable state 氧 ;

[0019] S22: Fit the increase value of the water body oxygen concentration ΔDO at each stable state 氧 with the cumulative duration of pure oxygen injection corresponding thereto to obtain the following fitting formula:

[0020] ΔDO 氧 = A1·t (1)

[0021] In the formula, ΔDO 氧 is the increase value of the water body oxygen concentration; t is the cumulative duration of pure oxygen injection, with the unit of s;

[0022] Obtain the oxygen concentration increase rate coefficient A1 adjusted by pure oxygen through the obtained fitting formula.

[0023] Preferably, the specific method for obtaining the oxygen concentration decrease rate coefficient adjusted by pure nitrogen in step S3 is as follows:

[0024] S31: Subtract the initial oxygen concentration value from the oxygen concentration value measured by the dissolved oxygen sensor in the stable state after each group is filled with pure nitrogen to obtain the decrease value of the water body oxygen concentration ΔDO at each stable state 氧 ;

[0025] S32: Fit the decrease value of the water body oxygen concentration ΔDO at each stable state 氧 with the cumulative duration of pure nitrogen injection corresponding thereto to obtain the following fitting formula:

[0026] ΔDO 氮 = B1·t (2)

[0027] In the formula, ΔDO 氮 is the decrease value of the water body oxygen concentration; t is the cumulative duration of pure nitrogen injection, with the unit of s;

[0028] The oxygen concentration reduction rate coefficient B1 adjusted by pure nitrogen is obtained through the obtained fitting formula.

[0029] Preferably, the specific method for obtaining the oxygen concentration change coefficient adjusted by the mixed gas in step S4 is as follows:

[0030] The oxygen concentration value DO of the water body measured by the dissolved oxygen sensor in the stable state after each group of mixed gas is introduced is fitted with the corresponding nitrogen-oxygen ratio of the mixed gas to obtain the following fitting formula:

[0031] DO = C2·x 2 + C1·x + C0 (3)

[0032] In the formula, DO is the oxygen concentration value of the water body, and x is the nitrogen-oxygen ratio of the mixed gas;

[0033] The oxygen concentration change coefficients C2, C1, and C0 adjusted by the mixed gas are obtained through the obtained fitting formula.

[0034] Preferably, step S5 is specifically as follows:

[0035] S51: When the target value is greater than the current value and the difference between the two is greater than 50 μmol·L -1 At this time, first adjust with pure oxygen, and the bubbling duration is calculated by substituting the difference into formula (1); after the adjustment of pure oxygen bubbling is completed, adjust with the mixed gas, and the nitrogen-oxygen ratio of the mixed gas is calculated by substituting the target value into formula (3);

[0036] S52: When the difference between the target value and the current value is less than 50 μmol·L -1 , directly adjust with the mixed gas, and the nitrogen-oxygen ratio of the mixed gas is calculated by substituting the target value into formula (3);

[0037] S53: When the target value is less than the current value and the difference between the two is greater than 50 μmol·L -1 At this time, first adjust with pure nitrogen, and the bubbling duration is calculated by substituting the difference into formula (2); after the pure nitrogen bubbling is completed, adjust with the mixed gas, and the nitrogen-oxygen ratio of the mixed gas is calculated by substituting the target value into formula (3).

[0038] The present invention has the following beneficial effects compared with the prior art:

[0039] 1) The present invention is a method for regulating the oxygen concentration in water bodies predictably, which provides the basic conditions for the automatic control of the calibration of dissolved oxygen sensors. In the existing chemical reagent and air-blowing methods, manual operation and judgment are required during the process. The present invention utilizes the correlation laws between the stable oxygen concentration, the air-blowing duration, and the nitrogen-oxygen ratio in different air-blowing methods summarized from a large number of experiments, making the oxygen concentration regulation results highly reproducible and predictable, without the need for manual observation and judgment, and thus the whole process of sensor calibration can be programmed and controlled.

[0040] 2) The method proposed by the present invention can achieve precise regulation and control of the oxygen concentration in water bodies. Due to the hysteresis of reagent reactions and gas dissolution, it is difficult for the existing methods to accurately control the final stable concentration value even with manual judgment. The present invention can achieve precise regulation and stable maintenance of the oxygen concentration through the pre-established fitting relationship between the stable oxygen concentration value and the nitrogen-oxygen ratio, and can set the most reasonable concentration point according to the actual needs of calibration. At the same time, the present invention is not affected by factors such as air-blowing duration and device airtightness, and has good practicability. Description of the Drawings

[0041] Figure 1 The fitting formula for the cumulative air-blowing duration and the increased value of oxygen concentration in the pure oxygen regulation method in the embodiment;

[0042] Figure 2 The fitting formula for the cumulative air-blowing duration and the decreased value of oxygen concentration in the pure nitrogen regulation method in the embodiment;

[0043] Figure 3 The fitting formula for the nitrogen-oxygen ratio and the oxygen concentration value in the mixed gas regulation method in the embodiment;

[0044] Figure 4 The application verification results of the oxygen concentration regulation in the sensor calibration in the embodiment. Detailed Embodiments

[0045] The present invention will be further described and explained below in conjunction with the drawings and specific embodiments. The technical features of each embodiment in the present invention can be combined accordingly without conflict.

[0046] Embodiment 1

[0047] Taking the widely used Norwegian AADI 3835 dissolved oxygen sensor in the industry as an example in this embodiment, the efficient method for regulating the oxygen concentration in water bodies for the automatic calibration control of sensors in the present invention is further described, which specifically includes the following steps:

[0048] (1) Fill a certain amount of distilled water into the calibration container, adjust the water temperature in the device to 20 °C and keep it unchanged throughout the experiment. Place the dissolved oxygen sensor to be calibrated in the container, ensure that the detection area of the sensor is immersed in water, start the sensor operation program, and display and save the sensor output data in real time throughout the process;

[0049] (2) Pass pure oxygen into the device for 15 s, 30 s, 60 s, and 120 s in sequence, with the flow rate always fixed at 1 L / min. Record the stable value of the water body oxygen concentration after each stabilization (Table 1), and obtain the oxygen concentration increase rate coefficient adjusted by pure oxygen according to the recorded data;

[0050] (3) Pass pure nitrogen into the device for 15 s, 30 s, 60 s, and 120 s in sequence, with the flow rate always fixed at 15 L / min. Record the stable value of the water body oxygen concentration after each stabilization (Table 2), and obtain the oxygen concentration decrease rate coefficient adjusted by pure nitrogen according to the recorded data;

[0051] (4) Continuously pass mixed gases with nitrogen-oxygen ratios of 4:1, 5:1, 7:1, 10:1, 15:1, and 20:1 into the device, with the oxygen flow rate always fixed at 0.6 L / min. Record the stable value of the water body oxygen concentration after each stabilization (Table 3), and obtain the oxygen concentration change coefficient adjusted by the mixed gas according to the recorded data;

[0052] As Figure 1 shown, the specific method for obtaining the oxygen concentration increase rate coefficient adjusted by pure oxygen in step (2) is:

[0053] <1> Subtract the initial oxygen concentration value from the oxygen concentration value in the stable state after each pure oxygen bubbling to obtain the increase value of the water body oxygen concentration ΔDO at each stable state 氧 ;

[0054] <2> Fit the increase value of the water body oxygen concentration ΔDO at each stable state 氧 with the cumulative duration of pure oxygen bubbling corresponding to it to obtain the fitting formula:

[0055] ΔDO 氧 = 0.9068·t (1)

[0056] In the formula, ΔDO 氧 is the increase value of the water body oxygen concentration; t is the cumulative duration of pure oxygen bubbling, with the unit of s.

[0057] The oxygen concentration increase rate coefficient A1 adjusted by pure oxygen obtained from this fitting formula is 0.9068.

[0058] As Figure 2 shown, the specific method for obtaining the oxygen concentration decrease rate coefficient adjusted by pure nitrogen in step (3) is:

[0059] <1>Subtract the initial oxygen concentration value from the oxygen concentration value in the stable state after each pure nitrogen aeration to obtain the decrease value of water body oxygen concentration ΔDO in each stable state 氧 ;

[0060] <2>Fit the decrease value of water body oxygen concentration ΔDO 氧 in each stable state with the corresponding cumulative duration of pure nitrogen aeration to obtain the fitting formula:

[0061] ΔDO 氮 = 0.8532·t (2)

[0062] where ΔDO 氮 is the decrease value of water body oxygen concentration; t is the cumulative duration of pure nitrogen aeration, with the unit of s.

[0063] The oxygen concentration decrease rate coefficient B1 adjusted by pure nitrogen is obtained from this fitting formula as 0.8532.

[0064] As Figure 3 shown, the specific method for obtaining the oxygen concentration change coefficient adjusted by the mixed gas in step (4) is: Fit the oxygen concentration value DO in the stable state after each nitrogen-oxygen ratio mixed gas aeration with the corresponding nitrogen-oxygen ratio of the mixed gas to obtain the fitting formula:

[0065] DO = 0.9191·x 2 - 32.618·x + 401.38 (3)

[0066] where DO is the water body oxygen concentration value; x is the nitrogen-oxygen ratio of the mixed gas.

[0067] The oxygen concentration change coefficients C2 is 0.9191, C1 is - 32.618, and C0 is 401.38 are obtained from this fitting formula.

[0068] Table 1 Cumulative aeration duration and oxygen concentration increase value of pure oxygen regulation method

[0069]

[0070] Table 2 Cumulative aeration duration and oxygen concentration decrease value of pure nitrogen regulation method

[0071]

[0072]

[0073] Table 3 Nitrogen-oxygen ratio and oxygen concentration stable value of mixed gas regulation method

[0074]

[0075] After obtaining the regulation coefficients of pure oxygen, pure nitrogen, and the mixed gas through the above steps, the application verification of oxygen concentration regulation was carried out in the dissolved oxygen sensor calibration experiment. According to the measurement range of the sensor to be calibrated, the target values of calibration control were determined as 100, 150, 200, 250, 300 μmol·L -1 . According to formula (3), the nitrogen-oxygen ratios corresponding to each target value were calculated as: 23.36, 12.03, 7.51, 5.21, 3.86. Keeping the oxygen flow rate fixed at 0.6 L / min all the time, the nitrogen flow rates corresponding to each target value were: 14.02, 7.22, 4.50, 3.13, 2.32 L / min.

[0076] During the calibration process, the flow rates of nitrogen and oxygen were programmatically controlled by two mass flow controllers respectively. Taking the real-time data of the sensor to be calibrated as the current value, comparing it with the preset calibration point concentration target value, pure oxygen or pure nitrogen was used for large-range and rapid regulation, and different nitrogen-oxygen ratio mixed gases continuously introduced were used to create 5 calibration concentration points. From the verification results ( Figure 4 ), it can be seen that when using the present invention for water body oxygen concentration regulation, the fitting degree between the sensor value of the calibration point and the reference value reaches 0.9999, indicating that the present invention has extremely high precision.

[0077] The above-described embodiments are only a preferred solution of the present invention, but they are not intended to limit the present invention. Those of ordinary skill in the relevant technical field can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent replacement or equivalent transformation methods fall within the protection scope of the present invention.

Claims

1. An efficient method for regulating the water body oxygen concentration for sensor automatic calibration control, characterized in that, The specific steps are as follows: S1: Fill a part of water into a sealed calibration container, completely immerse the detection area of the dissolved oxygen sensor to be calibrated in the water, start the dissolved oxygen sensor, and display and save its output data in real time throughout the process; S2: Introduce pure oxygen with a fixed flow rate into the calibration container for a certain period of time. After waiting for the output data of the dissolved oxygen sensor to stabilize, introduce pure oxygen with a fixed flow rate for another certain period of time and wait again for the output data of the dissolved oxygen sensor to stabilize. Repeat this several times to continuously increase the oxygen concentration in the water, obtain several sets of corresponding data of the stable value of the water body oxygen concentration and the cumulative oxygen injection duration, and obtain the oxygen concentration increase rate coefficient adjusted by pure oxygen according to the recorded data; S3: Introduce pure nitrogen with a fixed flow rate into the calibration container for a certain period of time. After waiting for the output data of the dissolved oxygen sensor to stabilize, introduce nitrogen with a fixed flow rate for another certain period of time and wait again for the output data of the dissolved oxygen sensor to stabilize. Repeat this several times to continuously reduce the oxygen concentration in the water, obtain several sets of corresponding data of the stable value of the water body oxygen concentration and the cumulative nitrogen injection duration, and obtain the oxygen concentration decrease rate coefficient adjusted by pure nitrogen according to the recorded data; S4: Continuously introduce a mixed gas with a certain nitrogen-oxygen ratio into the calibration container. After waiting for the output data of the dissolved oxygen sensor to stabilize, change the nitrogen-oxygen ratio of the mixed gas and wait again for the output data of the dissolved oxygen sensor to stabilize. Change the nitrogen-oxygen ratio of the mixed gas several times to continuously change the oxygen concentration in the water, obtain several sets of corresponding data of the stable value of the water body oxygen concentration and the nitrogen-oxygen ratio of the mixed gas, and obtain the oxygen concentration change coefficient adjusted by the mixed gas according to the recorded data; S5: Judge according to the difference between the current value of the water body oxygen concentration measured by the dissolved oxygen sensor and the target value to be adjusted. Use pure oxygen or pure nitrogen for rough adjustment by using the results obtained in steps S2 and S3, use mixed gases with different nitrogen-oxygen ratios for fine adjustment by using the results obtained in step S4, and keep the continuous injection of the mixed gas before completing the data recording at this concentration point; The specific method for obtaining the oxygen concentration increase rate coefficient adjusted by pure oxygen in step S2 is as follows: S21: Subtract the initial oxygen concentration value from the oxygen concentration value measured by the dissolved oxygen sensor in the stable state after each group is filled with pure oxygen to obtain the increase value of water body oxygen concentration ΔDO in each stable state 氧 ; S22: Fit the increase value of water body oxygen concentration ΔDO at each steady state 氧 with the corresponding cumulative duration of pure oxygen bubbling to obtain the following fitting formula: ΔDO 氧 = A1·t (1) where ΔDO 氧 denotes the increased value of water body oxygen concentration; t denotes the cumulative duration of pure oxygen injection, with the unit of s; Obtain the oxygen concentration increase rate coefficient A1 adjusted by pure oxygen through the obtained fitting formula; The specific method for obtaining the oxygen concentration decrease rate coefficient adjusted by pure nitrogen in step S3 is as follows: S31: Subtract the initial oxygen concentration value from the oxygen concentration value measured by the dissolved oxygen sensor in the stable state after each group is purged with pure nitrogen to obtain the water body oxygen concentration reduction value ΔDO at each stable state. 氧 ; S32: Reduce the water body oxygen concentration reduction value ΔDO in each stable state 氧 and fit it with the corresponding cumulative duration of pure nitrogen bubbling to obtain the following fitting formula: ΔDO 氮 = B1·t (2) Where ΔDO 氮 is the reduction value of the water body oxygen concentration; t is the cumulative duration of pure nitrogen injection, with the unit of s; Obtain the oxygen concentration decrease rate coefficient B1 adjusted by pure nitrogen through the obtained fitting formula; The specific method for obtaining the oxygen concentration change coefficient adjusted by the mixed gas in step S4 is as follows: Fit the water body oxygen concentration value DO measured by the dissolved oxygen sensor in the stable state after each injection of the mixed gas with the corresponding nitrogen-oxygen ratio of the mixed gas to obtain the following fitting formula: DO = C2·x 2 + C1·x + C0 (3) In the formula, DO is the water body oxygen concentration value, and x is the nitrogen-oxygen ratio of the mixed gas; Obtain the oxygen concentration change coefficients C2, C1, and C0 adjusted by the mixed gas through the obtained fitting formula; Step S5 is specifically as follows: S51: When the target value is greater than the current value and the difference between them is greater than 50 μmol·L -1 first, pure oxygen is used for adjustment, and the air-blowing duration is calculated by substituting the difference into formula (1); after the adjustment of pure oxygen air-blowing is completed, a mixed gas is used for adjustment, and the nitrogen-oxygen ratio of the mixed gas is calculated by substituting the target value into formula (3); S52: When the difference between the target value and the current value is less than 50 μmol·L -1 , directly use the mixed gas for adjustment, and the nitrogen-oxygen ratio of the mixed gas is calculated by substituting the target value into formula (3); S53: When the target value is less than the current value and the difference between the two is greater than 50 μmol·L -1 , first, pure nitrogen is used for adjustment, and the duration of nitrogen bubbling is calculated by substituting the difference into formula (2); after the pure nitrogen bubbling ends, a mixed gas is used for adjustment, and the nitrogen-oxygen ratio of the mixed gas is calculated by substituting the target value into formula (3).

2. The efficient regulation method for water body oxygen concentration for sensor automatic calibration control according to claim 1, characterized in that, Steps S2 to S4 are repeated 4 to 6 times respectively.

3. The efficient regulation method for water body oxygen concentration for sensor automatic calibration control according to claim 1, characterized in that During the measurement processes of steps S2 to S4, keep the experimental conditions the same and unchanged; the experimental conditions include the water volume, temperature, position of the dissolved oxygen sensor, and position of the air injection port in the calibration container.

4. The method for efficiently regulating the water body oxygen concentration for sensor automatic calibration control according to claim 1, wherein During the measurement processes of steps S2 to S4, the gas flow rate introduced into the calibration container is controlled by a mass flow controller.

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