CN215339820U - Dissolved oxygen meter calibration test system - Google Patents
Dissolved oxygen meter calibration test system Download PDFInfo
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- CN215339820U CN215339820U CN202121735407.0U CN202121735407U CN215339820U CN 215339820 U CN215339820 U CN 215339820U CN 202121735407 U CN202121735407 U CN 202121735407U CN 215339820 U CN215339820 U CN 215339820U
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Abstract
The utility model discloses a dissolved oxygen meter calibration test system which comprises a thermostatic bath, a sealed water tank, an air inlet pipe, a dissolved oxygen meter, a thermometer, a pressure gauge, an exhaust pipe and a circulating pump. The system injects a gas with known oxygen concentration into the demineralized water in the sealed water tank to enable the demineralized water to reach a saturated state, and the demineralized water is subjected to a calibration test on a dissolved oxygen meter under a flowing state. The system and the method ensure the stability of the saturated oxygen content in the desalted water in a dynamic circulation mode, the method is more accurate and simple, meanwhile, the fluctuation of the dissolved oxygen in the calibration and test processes is avoided, and the measurement accuracy of the dissolved oxygen meter is improved.
Description
Technical Field
The utility model relates to the field of detection of dissolved oxygen in water, in particular to a dissolved oxygen meter calibration test system.
Background
The dissolved oxygen meter measurement technology is mainly divided into an optical method and a polarographic method. The optical method dissolved oxygen measurement technology utilizes the characteristic that dissolved oxygen generates quenching effect on fluorescence, and obtains the concentration of the dissolved oxygen by detecting the change of fluorescence intensity.
The polarographic dissolved oxygen measuring technology is based on the Clark electrode measuring principle of a gold cathode and a silver anode, when a water sample is measured, an oxygen permeable membrane prevents electrode electrolyte from directly contacting the water sample, molecular oxygen can enter the electrode electrolyte from the oxygen permeable membrane, the oxygen is reduced to generate current under a certain polarization voltage, and the current is in direct proportion to the concentration of the dissolved oxygen. According to the standard of HJ 506-2009 electrochemical probe method for measuring dissolved oxygen in water (hereinafter abbreviated as "HJ 506"), the calibration of the dissolved oxygen meter comprises two methods: one is zero oxygen calibration, preparing a zero oxygen water standard solution by using sodium sulfite, and placing a dissolved oxygen electrode into the oxygen-free water standard solution for zero error detection; the other method is saturated oxygen calibration, wherein air is continuously introduced into distilled water to form a saturated oxygen standard solution, and then a dissolved oxygen electrode is placed into the saturated oxygen standard solution to carry out value error detection.
Both of these calibration methods have some problems in practical operation, for example, for a dissolved oxygen meter measured by polarography, the polarization of the electrode may consume a part of oxygen, resulting in the oxygen concentration in the standard solution being lower than the nominal value, and affecting the accuracy of calibration. In addition, according to the chemical equilibrium principle, the concentration of oxygen in reactants cannot be reduced to zero when the sodium sulfite is used for preparing the zero-oxygen water standard solution, trace oxygen still exists during equilibrium, and the time required for equilibrium is more than 2 hours, so that the calibration time is long and the accuracy cannot be guaranteed.
SUMMERY OF THE UTILITY MODEL
Aiming at the problems in the prior art, the utility model provides a system capable of accurately, conveniently and effectively calibrating and testing a dissolved oxygen meter.
The utility model is realized by the following technical scheme:
a dissolved oxygen meter calibration test system comprises a dissolved oxygen meter, a thermostatic bath and a sealed water tank;
the inside of the sealed water tank is filled with demineralized water, the sealed water tank is provided with an air inlet and an air outlet, and the air inlet is used for injecting gas into the sealed water tank during calibration test;
the sealed water tank is arranged in the thermostatic bath, an outlet of the sealed water tank is connected with an inlet of the dissolved oxygen meter, an outlet of the dissolved oxygen meter is connected with an inlet of the sealed water tank, and a detection device is arranged in the sealed water tank and used for detecting the temperature and the pressure inside the sealed water tank.
Preferably, the sealed water tank is connected with an inlet of the dissolved oxygen meter through a circulating pump.
Preferably, the detection device is a pressure gauge and a thermometer arranged on the sealed water tank.
Preferably, the gas is pure nitrogen or air.
Preferably, the air inlet and the air outlet are respectively provided with an air inlet pipe and an air outlet pipe;
the outlet of the air inlet pipe is positioned below the liquid level of the demineralized water, and the inlet of the air outlet pipe is positioned above the liquid level of the demineralized water.
Compared with the prior art, the utility model has the following beneficial technical effects:
the utility model discloses a dissolved oxygen meter calibration test system which comprises a constant temperature tank and a sealed water tank arranged in the constant temperature tank, wherein the sealed water tank is circularly communicated with a dissolved sample meter, the desalted water is saturated by introducing gas with set oxygen concentration into the desalted water in the sealed water tank, and the desalted water is used for carrying out calibration test on the dissolved oxygen meter in a flowing state. The system ensures the stability of the saturated oxygen content in the desalted water in a dynamic circulation mode, the method is more accurate and simple, meanwhile, the fluctuation of the dissolved oxygen in the calibration and test processes is avoided, and the measurement accuracy of the dissolved oxygen meter is improved.
According to the calibration method of the present invention, it can be known from Henry's law that the solubility of oxygen in demineralized water is proportional to the equilibrium pressure of oxygen above the surface of the demineralized water. By utilizing the law, gas with known oxygen concentration is continuously introduced into the desalted water under the constant temperature and pressure state, so that the gas space above the liquid level of the desalted water is filled with the gas, the desalted water is saturated, and the dissolved oxygen concentration of the desalted water is equal to the oxygen concentration of the gas. The demineralized water is then continuously flowed into the dissolved oxygen meter, which can be calibrated and tested. In the whole calibration test process, gas is continuously introduced into the demineralized water, so that the oxygen concentration of the demineralized water at the inlet of the circulating pump is ensured to be stable and unchanged.
And further, injecting air or pure nitrogen into the sealed water tank to enable the demineralized water to reach a saturated oxygen state or a zero oxygen state, and calibrating the dissolved oxygen meter by the demineralized water in the saturated oxygen state or the zero oxygen state to realize the saturated oxygen calibration and the zero oxygen calibration of the dissolved oxygen meter.
Drawings
FIG. 1 is a schematic diagram of a dissolved oxygen meter calibration test system according to the present invention.
In the figure: the device comprises a thermostatic bath 1, a sealed water tank 2, an air inlet pipe 3, a dissolved oxygen meter 4, a thermometer 5, a pressure gauge 6, an exhaust pipe 7 and a circulating pump 8.
Detailed Description
The present invention will now be described in further detail with reference to the attached drawings, which are illustrative, but not limiting, of the present invention.
Referring to fig. 1, a dissolved oxygen meter calibration test system includes a dissolved oxygen meter 4, a thermostatic bath 1, and a sealed water tank 2.
Inside the sealed water tank 2 is filled with demineralized water, and the sealed water tank 2 is arranged in the thermostatic bath 1, and the temperature of the demineralized water in the sealed water tank 2 can be adjusted through the thermostatic bath 1.
An air inlet pipe 3 and an air outlet pipe 7 are arranged on the sealed water tank 2, the outlet of the air inlet pipe 3 is positioned below the liquid level of the demineralized water, and the inlet of the air outlet pipe 7 is positioned above the liquid level of the demineralized water.
The detection device is a thermometer 5 and a pressure gauge 6 which are arranged on the sealed water tank 2, the thermometer 5 is used for measuring the temperature of the desalted water of the sealed water tank 2, and the pressure gauge 6 is used for measuring the pressure of the gas side of the sealed water tank 2.
The measurement principle of the dissolved oxygen meter calibration test system provided by the utility model is as follows:
adjust the demineralized water temperature through thermostatic bath 1, under constant temperature and pressure state, to the demineralized water among sealed water tank 2 let in pure nitrogen gas or air, make it reach the saturated condition, can obtain the oxygen concentration of demineralized water according to henry's law, utilize circulating pump 8 to let in the demineralized water dissolved oxygen table 4 and calibrate and test, it can maintain the oxygen concentration in the demineralized water and keep unchangeable to continuously let in gas, has guaranteed the accuracy of calibration test result.
The method of the present invention for calibrating a test system for dissolved oxygen meter will be described in detail below, including two methods, zero oxygen calibration test and saturated oxygen calibration test.
As is known from henry's law, the solubility of oxygen in demineralized water is proportional to the equilibrium pressure of oxygen above the surface of the demineralized water. By using this law, a gas (for example, pure nitrogen gas or air) having a known oxygen concentration is continuously introduced into the demineralized water at a constant temperature and pressure to fill the gas space above the surface of the demineralized water and to reach a saturated state in the demineralized water, and the dissolved oxygen concentration of the demineralized water is equal to the oxygen concentration of the gas. The demineralized water is then continuously flowed into the dissolved oxygen meter, which can be calibrated and tested. In the whole calibration test process, gas is continuously introduced into the demineralized water, so that the oxygen concentration of the demineralized water at the inlet of the circulating pump is ensured to be stable and unchanged. The following describes two calibration test schemes of zero oxygen and saturated oxygen for the dissolved oxygen meter.
Example 1
A zero oxygen calibration test method of a dissolved oxygen meter calibration test system comprises the following steps:
step 1, adjusting the constant temperature tank 1 to adjust the demineralized water in the sealed water tank 2 to a preset temperature.
The above-mentioned preset temperature is 25 + -2 deg.C, that is, the demineralized water is heated to 25 deg.C.
And 2, continuously introducing pure nitrogen into the sealed water tank 2 from the inlet of the air inlet pipe 3 until the nitrogen is filled in the space above the liquid level of the desalted water, wherein the air space above the liquid level of the desalted water in the sealed water tank 2 is in a positive pressure state, air cannot enter the sealed water tank until the nitrogen is discharged from the air outlet pipe 7, so that the desalted water reaches a zero-oxygen state under the conditions of constant temperature and constant pressure, namely the dissolved oxygen content of the desalted water is less than 1 microgram/L, and the desalted water is visible to be in a zero-oxygen state.
And 3, inputting the desalted water in the zero-oxygen state into a dissolved oxygen meter by using a circulating pump 8, and obtaining a measured value of the dissolved oxygen meter.
And 4, when the measured value in the step 3 is 0, judging that the dissolved oxygen meter is accurately measured without calibration, and when the measured value is not 0, calibrating the dissolved oxygen meter, adjusting the measured value of the dissolved oxygen meter to 0, and completing the calibration of the dissolved oxygen meter.
Compared with the HJ 506 standard method, the zero-oxygen calibration test method can obtain faster stabilization time and smaller indication error, and has stable data and good reproducibility. The results of the comparison of the two zero calibration test methods are shown in table 1.
Table 1 comparison of the effects of two zero calibration test methods
Example 2
A saturated oxygen calibration test method of a dissolved oxygen meter calibration test system comprises the following steps:
and step 1, adjusting the constant temperature tank 1 to adjust the demineralized water in the sealed water tank 2 to a preset temperature.
And 2, continuously introducing gas with known oxygen concentration into the sealed water tank 2 from the inlet of the gas inlet pipe 3 to enable the gas to fill the gas space above the liquid level of the desalted water in the sealed water tank 2, then discharging the gas from the exhaust pipe 7, and finally enabling the desalted water to reach an oxygen saturation state under the conditions of constant temperature and constant pressure.
The gas with known oxygen concentration is air, and the dissolved oxygen concentration c 'in the desalted water in an oxygen saturation state'sCan be calculated from the following formula:
in the formula: c's-solubility of oxygen in water at a temperature t and a gas pressure p (kpa), (mg/L);
cs-theoretical concentration of dissolved oxygen in water at temperature t and pressure 101.325kPa, (mg/L);
p-atmospheric pressure at test, (Pa);
pw-pressure of saturated water vapour at temperature t, (kPa).
The values of temperature t and pressure p can be obtained by means of a thermometer 5 and a pressure gauge 6, cs、pwConstant at the corresponding temperature, so the dissolved oxygen concentration c 'in the demineralised water'sCan be obtained by calculation. For example, p can be found by measuring t at 25 ℃ with a thermometer and p at 101.325kPa with a pressure gauge under normal temperature and pressurewAt 3.17kPa, csA dissolved oxygen concentration c 'in the oxygen-saturated desalted water of 8.26 mg/L'sIt was 8.26 mg/L.
And 3, conveying the desalted water in the oxygen saturation state to the dissolved oxygen meter 4 by using a circulating pump 8, obtaining a measured value of the dissolved oxygen meter, and continuously inputting air in the measuring process.
and when the measured value is different from the standard value, calibrating the dissolved oxygen meter 4 according to the standard value, adjusting the measured value of the dissolved oxygen meter 4 to the standard value, and completing the calibration of the dissolved oxygen meter.
Dissolved oxygen table 4 was subjected to on-line inspection and calibration in a flowing state. Compared with the HJ 506 standard method, the method can obtain faster stabilization time and smaller indication error, and has stable data and good reproducibility. The results of a comparison of the two saturated oxygen calibration measurements are shown in table 2.
TABLE 2 comparison of the effects of two saturated dissolved oxygen calibration test methods
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (5)
1. A dissolved oxygen meter calibration test system is characterized by comprising a dissolved oxygen meter (4), a thermostatic bath (1) and a sealed water tank (2);
the inside of the sealed water tank (2) is filled with demineralized water, the sealed water tank (2) is provided with an air inlet and an air outlet, and the air inlet is used for injecting gas into the sealed water tank (2) during calibration test;
sealing water tank (2) sets up in thermostatic bath (1), and the exit linkage dissolved oxygen meter (4) entry of sealing water tank (2), dissolved oxygen meter (4) export and sealing water tank (2) access connection are provided with detection device in sealing water tank (2) for detect the inside temperature and the pressure of sealing water tank (2).
2. A dissolved oxygen meter calibration test system according to claim 1, wherein the sealed water tank is connected to the inlet of the dissolved oxygen meter (4) by means of a circulation pump (8).
3. A dissolved oxygen meter calibration test system according to claim 1, wherein the detection means are a pressure gauge (6) and a temperature gauge (5) arranged on the sealed water tank (2).
4. The system of claim 1, wherein the gas is pure nitrogen or air.
5. The dissolved oxygen meter calibration test system according to claim 1, wherein an air inlet pipe (3) and an air outlet pipe (7) are respectively arranged on the air inlet and the air outlet;
the outlet of the air inlet pipe (3) is positioned below the liquid level of the demineralized water, and the inlet of the exhaust pipe (7) is positioned above the liquid level of the demineralized water.
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| CN113466423A (en) * | 2021-07-28 | 2021-10-01 | 西安热工研究院有限公司 | Dissolved oxygen meter calibration test system and method |
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| CN113466423A (en) * | 2021-07-28 | 2021-10-01 | 西安热工研究院有限公司 | Dissolved oxygen meter calibration test system and method |
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