Method and equipment for measuring dissolved oxygen in ppb-grade water by fluorescence method

Abstract

The invention belongs to the technical field of measurement of dissolved oxygen in water, and particularly discloses a method and equipment for measuring dissolved oxygen in ppb-level water through a fluorescence method.The method comprises the steps that S1, a dissolved oxygen sensor system is configured, the dissolved oxygen sensor system comprises a detection head assembly and a main control panel assembly, S2, the detection head assembly is preset in a water standard sample, the method comprises the following steps: S1, collecting photoelectric, temperature and atmospheric pressure information by a detection head assembly, and transmitting the photoelectric, temperature and atmospheric pressure information to a main control panel assembly, S3, converting the collected photoelectric, temperature and atmospheric pressure information by the main control panel assembly, and converting a collected current signal into a voltage signal by the main control assembly, and S4, outputting the voltage signal. And S5, after the remote upper computer receives the signals, a mathematical model is used for carrying out data analysis, and the concentration of the dissolved oxygen in the water is calculated, the design of exciting light and reference light with the same frequency and the same initial phase is adopted, and the measurement error is effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of dissolved oxygen measurement in water bodies, and in particular to a method and equipment for measuring dissolved oxygen in ppb-level water using a fluorescence method. Background Art

[0002] At present, there are three commonly used methods for detecting dissolved oxygen: iodine titration, electromechanical method and fluorescence method. Among them, the fluorescence method is convenient and fast to determine dissolved oxygen, has a fast response during measurement, can get rid of the constraints of the laboratory, realize on-site measurement, and does not consume oxygen or cause pollution during the measurement process. The fluorescence method for measuring dissolved oxygen is based on the principle of fluorescence quenching effect. The concentration of dissolved oxygen is inferred by measuring the degree of reduction in the luminescence intensity of fluorescent substances in the presence of oxygen. After being excited by a specific wavelength (such as blue light), the fluorescent substance will emit fluorescence (such as red light). Oxygen molecules can absorb the energy of the excited state of the fluorescent substance, resulting in fluorescence quenching, that is, the fluorescence intensity is weakened. The degree of fluorescence quenching is inversely proportional to the concentration of dissolved oxygen, that is, the higher the concentration of dissolved oxygen, the weaker the fluorescence intensity.

[0003] Although fluorescence measurement has many advantages, it also has some disadvantages and shortcomings. Existing dissolved oxygen sensors are often complicated to install and use, complex to network, difficult to replace and maintain after damaged components, and high maintenance costs, making it difficult to promote them on a large scale in the aquaculture Internet of Things. Summary of the invention

[0004] The object of the present invention is to provide a method and device for measuring dissolved oxygen in ppb level water by fluorescence method, so as to solve the problems raised in the above background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a method for measuring dissolved oxygen in ppb-level water by fluorescence method, comprising:

[0007] Step S1, configuring a dissolved oxygen sensor system, the dissolved oxygen sensor system comprising a detection head assembly and a main control board assembly;

[0008] Step S2, presetting the detection head assembly in a water standard sample, collecting photoelectric, temperature, and atmospheric pressure information by the detection head assembly, and transmitting the information to the main control board assembly;

[0009] Step S3, the main control board component converts the collected photoelectric, temperature, and atmospheric pressure information, and the main control component converts the collected current signal into a voltage signal;

[0010] Step S4, the main control board component transmits the collected and converted voltage signal output to the remote host computer;

[0011] Step S5, after receiving the signal, the remote host computer uses a mathematical model to perform data analysis and calculate the dissolved oxygen concentration in the water.

[0012] Preferably, in step S1, the configured dissolved oxygen sensor system needs to be experimentally calibrated before actual use to obtain a relationship model between the output of the dissolved oxygen sensor system and the oxygen partial pressure, and the configured dissolved oxygen sensor system is placed in multiple groups of different standard samples with known oxygen partial pressures, and then the output value of the dissolved oxygen sensor system is recorded, including the phase difference and the fluorescence intensity, and the collected data is analyzed, and a mathematical method is used to fit the relationship between the output value and the oxygen partial pressure.

[0013] Preferably, in step S5, after completing the dissolved oxygen concentration calculation, the dissolved oxygen sensor system needs to be stored, and the detection head assembly needs to be cleaned before storage. Clean water is used for cleaning to ensure the cleanliness of the surface of the detection head assembly to avoid dirt remaining on the detection head assembly and causing measurement errors during subsequent use. Desiccant is placed during storage to ensure a dry environment for the storage space and the dissolved oxygen sensor system.

[0014] In a second aspect, the present invention provides a device for measuring dissolved oxygen in ppb-level water by fluorescence method, including a dissolved oxygen sensor system, which is divided into a detection head component and a main control board component, wherein the detection head component includes an LED driving module, a photoelectric processing module and a temperature measurement module, and the main control board component mainly includes a power management module, a DAC driving module, an AD acquisition module, an MCU main control core, and a wireless communication module;

[0015] The LED driving module is used to drive the LED light emitting diode to generate reference light and excitation light pulse light waves. The excitation light is blue light with a central wavelength of 450nm. The excitation light irradiates the fluorescent film to generate red fluorescence. The reference light is red light with a central wavelength of 700nm. The reference light and the red fluorescence are rectangular pulse waveforms with the same frequency and initial phase, and the optical path and circuit structure are consistent.

[0016] The photoelectric processing module uses a photodiode to receive the red fluorescence and reference light signal generated on the oxygen sensitive film, and converts the light signal into an electrical signal; the photoelectric processing module is connected to an I / V conversion module, which realizes the conversion of the current signal into the voltage signal, and amplifies the voltage signal by a certain multiple;

[0017] The temperature measurement module uses a single-bus device digital temperature sensor to measure the ambient temperature through a one-wire structure to provide temperature compensation for dissolved oxygen concentration calculation;

[0018] Power management module, providing stable power for the system;

[0019] DAC driver module: uses the 10KHz sine wave signal generated by the MCU to drive the LED to emit light;

[0020] AD acquisition module: collects fluorescence signals and excitation light signals and stores them;

[0021] MCU main control core: processes the signal collected by the AD acquisition module, performs fast Fourier transform FFT to calculate the phase difference between the excitation light and the fluorescence signal, and substitutes the temperature value into the dissolved oxygen concentration calculation model to obtain the dissolved oxygen concentration value;

[0022] Wireless communication module: sends data such as dissolved oxygen concentration, temperature and node information to the remote host computer;

[0023] Preferably, the dissolved oxygen sensor system is further provided with an atmospheric pressure acquisition module, and the atmospheric pressure acquisition module uses a digital barometer to obtain the atmospheric pressure of the standard sample area.

[0024] Preferably, the oxygen sensitive membrane is prepared by coating a polyester sheet with a reflux solution of a mixture of polydimethylsiloxane and tetraethoxysiloxane and tetraphenylplatinum porphyrin and curing the mixture.

[0025] Preferably, the LED driving module adopts two symmetrical LED circuits, one for driving the excitation light blue LED to irradiate the oxygen sensitive membrane to produce fluorescence, and the other for driving the reference light red LED, to ensure the structural symmetry of the two driving circuits and reduce measurement errors.

[0026] Preferably, the wireless communication module uses LoRa long-distance transmission technology, the frequency band where LoRa is located is a global free frequency band, and the networking method adopts a star topology. A LoRa gateway can connect to multiple LoRa nodes and receive multiple signals.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts the design of excitation light and reference light with the same frequency and initial phase to effectively reduce the measurement error; the present invention sets the MCU main control core to adopt the FFT algorithm to improve the measurement accuracy and response speed; designs the temperature measurement module to realize temperature compensation and improve the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a system design diagram of a device for measuring dissolved oxygen in ppb level water using a fluorescence method according to the present invention.

[0029] Figure 2 This is a design diagram of a transmission node of a wireless communication module in a device for measuring dissolved oxygen in ppb level water using a fluorescence method according to the present invention.

[0030] Figure 3 It is the solubility of oxygen under different atmospheric pressure and water temperature conditions in the atmospheric pressure range of 50.5~110.5Kpa and temperature of 0~40℃. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] In the description of the present invention, it should be noted that the terms "vertical", "up", "down", "horizontal", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0033] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] See also Figure 1-2 The present invention provides a technical solution: a method and device for measuring dissolved oxygen in ppb-level water by fluorescence method,

[0035] In a first aspect, the present invention provides a method for measuring dissolved oxygen in ppb-level water by fluorescence method, comprising:

[0036] Step S1, configuring a dissolved oxygen sensor system, the dissolved oxygen sensor system comprising a detection head assembly and a main control board assembly;

[0037] Step S2, presetting the detection head assembly in a water standard sample, collecting photoelectric, temperature, and atmospheric pressure information by the detection head assembly, and transmitting the information to the main control board assembly;

[0038] Step S3, the main control board component converts the collected photoelectric, temperature, and atmospheric pressure information, and the main control component converts the collected current signal into a voltage signal;

[0039] Step S4, the main control board component transmits the collected and converted voltage signal output to the remote host computer;

[0040] Step S5, after receiving the signal, the remote host computer uses a mathematical model to perform data analysis and calculate the dissolved oxygen concentration in the water.

[0041] Furthermore, in step S1, the configured dissolved oxygen sensor system needs to be experimentally calibrated before actual use to obtain a relationship model between the output of the dissolved oxygen sensor system and the oxygen partial pressure. The configured dissolved oxygen sensor system is placed in multiple groups of different standard samples with known oxygen partial pressures, and then the output values ​​of the dissolved oxygen sensor system are recorded, including phase difference and fluorescence intensity. The collected data are analyzed, and a mathematical method is used to fit the relationship between the output value and the oxygen partial pressure.

[0042] Furthermore, in step S5, after completing the dissolved oxygen concentration calculation, the dissolved oxygen sensor system needs to be stored. Before storage, the detection head assembly needs to be cleaned with clean water to ensure the cleanliness of the surface of the detection head assembly to avoid dirt remaining on the detection head assembly and causing measurement errors during subsequent use. Desiccant is placed during storage to ensure a dry environment for the storage space and the dissolved oxygen sensor system.

[0043] In a second aspect, the present invention provides a device for measuring dissolved oxygen in ppb-level water by fluorescence method, including a dissolved oxygen sensor system, which is divided into a detection head component and a main control board component, wherein the detection head component includes an LED driving module, a photoelectric processing module and a temperature measurement module, and the main control board component mainly includes a power management module, a DAC driving module, an AD acquisition module, an MCU main control core, and a wireless communication module;

[0044] The LED driving module is used to drive the LED light emitting diode to generate reference light and excitation light pulse light waves. The excitation light is blue light with a central wavelength of 450nm. The excitation light irradiates the fluorescent film to generate red fluorescence. The reference light is red light with a central wavelength of 700nm. The reference light and the red fluorescence are rectangular pulse waveforms with the same frequency and initial phase, and the optical path and circuit structure are consistent.

[0045] The photoelectric processing module uses a photodiode to receive the red fluorescence and reference light signal generated on the oxygen sensitive film, and converts the light signal into an electrical signal; the photoelectric processing module is connected to an I / V conversion module, which realizes the conversion of the current signal into the voltage signal, and amplifies the voltage signal by a certain multiple;

[0046] The temperature measurement module uses a single-bus device digital temperature sensor to measure the ambient temperature through a one-wire structure to provide temperature compensation for dissolved oxygen concentration calculation;

[0047] Power management module, providing stable power for the system;

[0048] DAC driver module: uses the 10KHz sine wave signal generated by the MCU to drive the LED to emit light;

[0049] AD acquisition module: collects fluorescence signals and excitation light signals and stores them;

[0050] MCU main control core: processes the signal collected by the AD acquisition module, performs fast Fourier transform FFT to calculate the phase difference between the excitation light and the fluorescence signal, and substitutes the temperature value into the dissolved oxygen concentration calculation model to obtain the dissolved oxygen concentration value; it should be noted that the dissolved oxygen concentration calculation model is:

[0051]

[0052] Where: ′ (O) s is the mass concentration of dissolved oxygen in the water sample at temperature t℃ and atmospheric pressure PKPa, mg / L; ρ(O) s is the mass concentration of dissolved oxygen in the water sample at temperature t℃ and standard atmospheric pressure, mg / L, see Appendix Figure 3 ; 101.325 is standard atmospheric pressure, KPa; P w is the pressure of saturated water vapor at temperature t℃, KPa.

[0053] Wireless communication module: sends data such as dissolved oxygen concentration, temperature and node information to the remote host computer;

[0054] Furthermore, the dissolved oxygen sensor system is further provided with an atmospheric pressure acquisition module, and the atmospheric pressure acquisition module uses a digital barometer to obtain the atmospheric pressure of the standard sample area.

[0055] Furthermore, the oxygen sensitive membrane is prepared by coating a polyester sheet with a reflux solution of polydimethylsiloxane and tetraethoxysiloxane mixed with tetraphenyl platinum porphyrin and solidifying the mixture.

[0056] Furthermore, the LED driving module adopts two symmetrical LED circuits, one for driving the excitation light blue LED to irradiate the oxygen sensitive film to generate fluorescence, and the other for driving the reference light red LED, so as to ensure the structural symmetry of the two driving circuits and reduce the measurement error.

[0057] Furthermore, the wireless communication module uses LoRa long-distance transmission technology. The frequency band of LoRa is a global free frequency band. The networking method adopts a star topology. One LoRa gateway can connect to multiple LoRa nodes and receive multiple signals.

[0058] Working principle: The present invention provides a method and device for measuring dissolved oxygen in ppb-level water by fluorescence method. Excitation light is irradiated on the oxygen sensitive membrane to generate red fluorescence inversely proportional to the dissolved oxygen concentration. The photodiode receives the fluorescence and reference light signals and converts them into electrical signals. After the electrical signals are converted by I / V, they are processed by MCU for FFT to calculate the phase difference between the excitation light and the fluorescence signal. The dissolved oxygen concentration is obtained by combining the temperature measurement value and using the dissolved oxygen concentration calculation model. The result is sent to a remote host computer through a wireless communication module. The present invention adopts the design of excitation light and reference light with the same frequency and initial phase to effectively reduce the measurement error. The present invention sets the MCU main control core to adopt the FFT algorithm to improve the measurement accuracy and response speed. The temperature measurement module is designed to realize temperature compensation and improve the measurement accuracy.

[0059] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for measuring dissolved oxygen in ppb-level water by fluorescence method, characterized in that: include: Step S1, configuring a dissolved oxygen sensor system, the dissolved oxygen sensor system comprising a detection head assembly and a main control board assembly; Step S2, presetting the detection head assembly in a water standard sample, collecting photoelectric, temperature, and atmospheric pressure information by the detection head assembly, and transmitting the information to the main control board assembly; Step S3, the main control board component converts the collected photoelectric, temperature, and atmospheric pressure information, and the main control component converts the collected current signal into a voltage signal; Step S4, the main control board component transmits the collected and converted voltage signal output to the remote host computer; Step S5, after receiving the signal, the remote host computer uses a mathematical model to perform data analysis and calculate the dissolved oxygen concentration in the water.

2. The method for measuring dissolved oxygen in ppb-level water by fluorescence method according to claim 1, characterized in that: In step S1, the configured dissolved oxygen sensor system needs to be experimentally calibrated before actual use to obtain a relationship model between the output of the dissolved oxygen sensor system and the oxygen partial pressure. The configured dissolved oxygen sensor system is placed in multiple groups of different standard samples with known oxygen partial pressures, and then the output value of the dissolved oxygen sensor system is recorded, including the phase difference and the fluorescence intensity. The collected data is analyzed, and a mathematical method is used to fit the relationship between the output value and the oxygen partial pressure.

3. The method for measuring dissolved oxygen in ppb-level water by fluorescence method according to claim 1, characterized in that: In step S5, after completing the dissolved oxygen concentration calculation, the dissolved oxygen sensor system needs to be stored. Before storage, the detection head assembly needs to be cleaned with clean water to ensure the cleanliness of the surface of the detection head assembly to avoid dirt remaining on the detection head assembly and causing measurement errors during subsequent use. Place a desiccant during storage to ensure a dry environment for the storage space and the dissolved oxygen sensor system.

4. A device for measuring dissolved oxygen in ppb-level water by fluorescence method, characterized in that: It includes a dissolved oxygen sensor system, which is divided into a detection head component and a main control board component. The detection head component includes an LED driving module, a photoelectric processing module and a temperature measurement module. The main control board component mainly includes a power management module, a DAC driving module, an AD acquisition module, an MCU main control core, and a wireless communication module. The LED driving module is used to drive the LED light emitting diode to generate reference light and excitation light pulse light waves. The excitation light is blue light with a central wavelength of 450nm. The excitation light irradiates the fluorescent film to generate red fluorescence. The reference light is red light with a central wavelength of 700nm. The reference light and the red fluorescence are rectangular pulse waveforms with the same frequency and initial phase, and the optical path and circuit structure are consistent. The photoelectric processing module uses a photodiode to receive the red fluorescence and reference light signal generated on the oxygen sensitive film, and converts the light signal into an electrical signal; the photoelectric processing module is connected to an I / V conversion module, which realizes the conversion of the current signal into the voltage signal, and amplifies the voltage signal by a certain multiple; The temperature measurement module uses a single-bus device digital temperature sensor to measure the ambient temperature through a one-wire structure to provide temperature compensation for dissolved oxygen concentration calculation; Power management module, providing stable power for the system; DAC driver module: uses the 10KHz sine wave signal generated by the MCU to drive the LED to emit light; AD acquisition module: collects fluorescence signals and excitation light signals and stores them; MCU main control core: processes the signal collected by the AD acquisition module, performs fast Fourier transform FFT to calculate the phase difference between the excitation light and the fluorescence signal, and substitutes the temperature value into the dissolved oxygen concentration calculation model to obtain the dissolved oxygen concentration value; Wireless communication module: sends data such as dissolved oxygen concentration, temperature and node information to the remote host computer.

5. The device for measuring dissolved oxygen in ppb level water by fluorescence method according to claim 4, characterized in that: The dissolved oxygen sensor system is also provided with an atmospheric pressure acquisition module, and the atmospheric pressure acquisition module uses a digital barometer to obtain the atmospheric pressure of the standard sample area.

6. The device for measuring dissolved oxygen in ppb level water by fluorescence method according to claim 4, characterized in that: The oxygen sensitive membrane is prepared by coating a polyester sheet with a reflux solution of polydimethylsiloxane and tetraethoxysiloxane mixed with tetraphenyl platinum porphyrin and solidifying the mixture.

7. The device for measuring dissolved oxygen in ppb level water by fluorescence method according to claim 4, characterized in that: The LED driving module adopts two symmetrical LED circuits, one for driving the excitation light blue LED to irradiate the oxygen sensitive film to generate fluorescence, and the other for driving the reference light red LED, so as to ensure the structural symmetry of the two driving circuits and reduce the measurement error.

8. The device for measuring dissolved oxygen in ppb level water by fluorescence method according to claim 4, characterized in that: The wireless communication module uses LoRa long-distance transmission technology. The frequency band where LoRa is located is a global free frequency band. The networking method adopts a star topology. One LoRa gateway can connect to multiple LoRa nodes and receive multiple signals.

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