A method and device for measuring ammonia concentration

Abstract

The present invention discloses a method and device for measuring ammonia concentration. The method includes: dividing a plurality of different concentration range intervals according to a pre-determined target component concentration range; selecting corresponding absorption spectral lines and gas cell optical path lengths for each concentration range interval, and then building an optical path detection system with a plurality of gas cells, wherein the plurality of gas cells are filled with ammonia to be measured; controlling the operation of the optical path detection system to obtain a detection signal associated with the ammonia to be measured, and then using an optimization algorithm to invert the concentration information of the ammonia to be measured in combination with the detection signal. By setting a plurality of gas cells to assist in the measurement of different ammonia concentration ranges, the present invention can greatly reduce measurement errors, and the entire ammonia testing process is simple and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of gas concentration measurement, and particularly to a method and device for measuring ammonia concentration. Background Art

[0002] Ammonia is widely used in the denitrification processes of agricultural fertilizer production, cold storage, cold chain logistics, and high-temperature industrial fields (such as metallurgy, building materials, power generation, etc.), and has become an indispensable part of daily life and industrial production. With the rapid industrialization and urbanization processes in recent years, air pollution phenomena represented by haze and photochemical smog occur frequently. The excessive escape of ammonia in industrial production will cause it to react with water vapor and nitrogen oxides in the atmospheric environment to form ammonium nitrate particles, which will then form suspended aerosols. At the same time, the excessive escape of ammonia will cause corrosion and blockage of denitrification equipment; in addition, the excessive leakage of ammonia during transportation, storage, and use will damage the human respiratory system and skin, and seriously endanger human life safety. Therefore, how to achieve strict measurement of ammonia is crucial for environmental protection, industrial safety production, and human safety. However, currently common ammonia concentration measurement devices often achieve measurement by selecting an absorption spectral line and a gas cell with a fixed length, and have disadvantages such as a narrow measurement range and low measurement accuracy. Summary of the Invention

[0003] The present invention provides a method and device for measuring ammonia concentration to solve one or more technical problems existing in the prior art, and at least provide a beneficial option or create conditions.

[0004] An embodiment of the present invention provides a method for measuring ammonia concentration, and the method includes:

[0005] Dividing a plurality of different concentration range intervals according to a pre-determined target component concentration range;

[0006] Selecting corresponding absorption spectral lines and gas cell optical path lengths for each concentration range interval, and then building an optical path detection system with a plurality of gas cells, wherein the plurality of gas cells are filled with the ammonia to be measured;

[0007] Controlling the operation of the optical path detection system to obtain a detection signal associated with the ammonia to be measured, and then using an optimization algorithm to invert the concentration information of the ammonia to be measured in combination with the detection signal.

[0008] Further, the absorbance peak value of the absorption spectral line corresponding to each concentration range interval at normal temperature and pressure is greater than 0.001 and less than 2.0.

[0009] Further, the implementation process of selecting the corresponding gas cell optical path length for each concentration range interval includes:

[0010] On the condition that the absorbance peak value of the absorption spectral line corresponding to each concentration range interval is greater than 0.001 and less than 2.0, the optical path length of the gas cell corresponding to each concentration range interval is selected by querying the spectral database.

[0011] Further, the optical path detection system includes a function generator, a laser controller, a laser, a collimator, a photodetector and a plurality of gas cells; wherein, the function generator is used to generate a drive signal, the laser controller is used to set the operating temperature and operating current of the laser according to the drive signal, the laser is used to emit a laser signal, the collimator is used to collimate the laser signal to obtain parallel light, the plurality of gas cells are used to prompt the ammonia gas to be measured to absorb the parallel light to obtain a measured optical signal, the photodetector is used to convert the measured optical signal into a measured electrical signal, and the measured electrical signal is the detection signal.

[0012] Further, when the optical path detection system adopts the direct absorption spectroscopy technology, the implementation process of inversely inferring the concentration information of the ammonia gas to be measured by using the optimization algorithm in combination with the detection signal includes:

[0013] Establish a simulation model of the optical path detection system, and obtain a reference detection signal associated with the ammonia gas to be measured and its corresponding reference spectral absorbance through simulation analysis;

[0014] Analyze the detection signal and the drive signal by using the Beer-Lambert law to obtain the measured spectral absorbance;

[0015] Determine the first relational expression between the spectral absorbance and the ammonia concentration. When the difference between the measured spectral absorbance and the reference spectral absorbance reaches the minimum, substitute the measured spectral absorbance into the first relational expression for inverse deduction operation to obtain the concentration information of the ammonia gas to be measured.

[0016] Further, when the optical path detection system adopts the wavelength modulation spectroscopy technology, the implementation process of inversely inferring the concentration information of the ammonia gas to be measured by using the optimization algorithm in combination with the detection signal includes:

[0017] Establish a simulation model of the optical path detection system, and obtain a reference detection signal associated with the ammonia gas to be measured and its corresponding reference harmonic signal intensity through simulation analysis;

[0018] Analyze the detection signal and the drive signal by using the principle of wavelength modulation spectroscopy to obtain the measured harmonic signal intensity;

[0019] Determine the second relationship between the harmonic signal intensity and the ammonia concentration. When the gap between the measured harmonic signal intensity and the reference harmonic signal intensity reaches the minimum, substitute the measured harmonic signal intensity into the second relationship for inverse calculation to obtain the concentration information of the measured ammonia gas.

[0020] In addition, an embodiment of the present invention further provides an ammonia concentration measuring device, which includes an optical path detection system and a data processing system;

[0021] The optical path detection system includes a function generator, a laser controller, a laser, a collimator, a photodetector, and a plurality of gas cells, and the measured ammonia gas is introduced into the plurality of gas cells; wherein, the function generator is used to generate a driving signal, the laser controller is used to set the operating temperature and operating current of the laser according to the driving signal, the laser is used to emit a laser signal, the collimator is used to collimate the laser signal to obtain parallel light, the plurality of gas cells are used to cause the measured ammonia gas to absorb the parallel light to obtain a measured optical signal, and the photodetector is used to convert the measured optical signal into a measured electrical signal;

[0022] The data processing system includes a data acquisition card, a data processor, and a data display; wherein, the data acquisition card is used to collect the driving signal and the measured electrical signal and then transmit them to the data processor, the data processor is used to inversely calculate the concentration information of the measured ammonia gas by using an optimization algorithm, and the data display is used to display the concentration information of the measured ammonia gas.

[0023] Further, the plurality of gas cells are suitable for gas detection in different concentration range intervals, and the absorption spectrum line corresponding to each concentration range interval and the optical path length of the gas cell should satisfy a preset constraint condition, and the preset constraint condition is that the absorbance peak value of the absorption spectrum line under the influence of normal temperature and pressure and the optical path length of the gas cell is greater than 0.001 and less than 2.0.

[0024] Further, the laser adopts a distributed feedback semiconductor laser, and the center frequency of the laser is 1513 nm and its spectral line width is less than 3 MHz.

[0025] Further, the output beam diameter of the collimator is 3 mm, and the effective photosensitive surface diameter of the photodetector is 3 mm.

[0026] The present invention has at least the following beneficial effects: by dividing a plurality of different concentration ranges according to a predetermined target component concentration range, and selecting a corresponding absorption spectrum line and a gas cell optical path length for each concentration range, a plurality of gas cells are formed to assist in the measurement of different ammonia concentration ranges, thereby significantly reducing the measurement error, and the entire ammonia testing process is simple and efficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0028] Figure 1 is a flow chart of a method for measuring ammonia concentration in an embodiment of the present invention;

[0029] Figure 2 It is a schematic diagram of the structural composition of an ammonia concentration measuring device in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] It should be noted that, although the functional modules are divided in the system schematic diagram and the logical order is shown in the flowchart, in some cases, the steps shown or described may be performed in a different order than the module division in the system or the order in the flowchart. The terms "first", "second", etc. in the specification, claims and the above drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0032] Example

[0033] Please refer to Figure 1 , Figure 1 1 is a flow chart of a method for measuring ammonia concentration provided by an embodiment of the present invention, the method comprising the following steps:

[0034] S110, dividing a plurality of different concentration ranges according to a predetermined target component concentration range;

[0035] S120, selecting a corresponding absorption spectrum line and a gas cell optical path length for each concentration range, and then constructing an optical path detection system with a plurality of gas cells, wherein the ammonia gas to be detected is introduced into the plurality of gas cells;

[0036] S130. Control the operation of the optical path detection system to obtain a detection signal associated with the ammonia gas to be measured, and then use an optimization algorithm to invert the concentration information of the ammonia gas to be measured in combination with the detection signal.

[0037] In the embodiment of the present invention, the concentration range of the target component mentioned in step S110 is 0.1 ppm - 100%, and the several different concentration range intervals actually include four concentration range intervals of 0.1 ppm - 100 ppm, 100 ppm - 2000 ppm, 2000 ppm - 10000 ppm, and 10000 ppm - 100%. Of course, it can also be divided into four concentration range intervals with different values, and the present invention does not limit the specific number of the divided concentration range intervals.

[0038] In step S120, the implementation process of selecting corresponding absorption spectral lines and gas cell optical path lengths for each concentration range interval includes: First, technicians select the absorption spectral lines required for ammonia measurement according to experience, so that the absorbance peak value of the absorption spectral line corresponding to each concentration range interval is greater than 0.001 and less than 2.0 at normal temperature and pressure, and the absorption spectral line corresponding to each concentration range interval has strong sensitivity to temperature and there is no excessive interference from adjacent absorption spectral lines around it; Second, on the condition that the absorbance peak value of the absorption spectral line corresponding to each concentration range interval is greater than 0.001 and less than 2.0, the corresponding gas cell optical path length is selected for each concentration range interval by querying the spectral database, where the spectral database is the HITRAN database.

[0039] In the embodiment of the present invention, the optical path detection system mentioned in step S120 is composed of a function generator, a laser controller, a laser, a collimator, a photodetector, and several gas cells. The number of the several gas cells is set to four, and each gas cell corresponds to one of the concentration range intervals, as Figure 2 shown; among them, the laser uses a distributed feedback semiconductor laser, its central frequency is 1513 nm and its spectral line width is less than 3 MHz, the output beam diameter of the collimator is 3 mm, the effective photosensitive surface diameter of the photodetector is 3 mm, and any one of the gas cells can use a White cell or a Herriott cell or a single-pass cell.

[0040] In the specific implementation process, the function generator is used to generate a driving signal, the laser controller is used to set the operating temperature and operating current of the laser according to the driving signal, the laser is used to emit a laser signal, the collimator is used to collimate the laser signal to obtain parallel light, the plurality of gas cells are used to cause the ammonia gas to be measured to absorb the parallel light to obtain a measured optical signal, and the photodetector is used to convert the measured optical signal into a measured electrical signal, and the measured electrical signal is the detection signal; wherein, a beam splitter is actually arranged at the outlet of the collimator, so that the parallel light emitted by the collimator can be split into four beams by the beam splitter to respectively pass through four gas cells, and at this time the photodetector can simultaneously receive four measured optical signals for combination.

[0041] In an embodiment of the present invention, when the optical path detection system adopts the direct absorption spectroscopy technique, the scanning frequency of the laser is set to 100 Hz, the amplitude is 70 mV, the offset is 250 mV, and the phase is 270°, and the specific implementation process of step S130 includes the following:

[0042] Step A1: Establish a simulation model of the optical path detection system, and obtain a reference detection signal associated with the ammonia gas to be measured and its corresponding reference spectral absorbance through simulation analysis;

[0043] Step A2: Analyze the detection signal and the driving signal by using the Beer-Lambert law to obtain the measured spectral absorbance, where the Beer-Lambert law is expressed as: α v =-ln(I t / I0) v , α v is the measured spectral absorbance, I t is the detection signal, I0 is the driving signal, and v is the center frequency of the laser;

[0044] Step A3: Determine the first relationship between the spectral absorbance and the ammonia concentration. When the difference between the measured spectral absorbance and the reference spectral absorbance reaches the minimum, substitute the measured spectral absorbance into the first relationship for inverse calculation to obtain the concentration information of the ammonia gas to be measured.

[0045] In the above step A3, first establish the first optimization function as:

[0046]

[0047] And determine the first relationship between the spectral absorbance and the ammonia concentration as:

[0048]

[0049] Secondly, when it is determined that the constraint condition of the first optimization function is satisfied between the measured spectral absorbance and the reference spectral absorbance, substitute the measured spectral absorbance into the first relational expression for back-calculation to obtain the concentration information of the measured ammonia gas;

[0050] In the formula, minf refers to the first optimization function, which is used to determine that the gap between the measured spectral absorbance and the reference spectral absorbance reaches the minimum. n is the number of wave peaks, and the number of wave peaks included in the detection signal is the same as the number of wave peaks included in the reference detection signal. is the k-th measured spectral absorbance peak value included in the detection signal. is the k-th reference spectral absorbance peak value included in the reference detection signal. P is the atmospheric pressure, L is the optical path length of the gas cell, and S i (T) is the absorption line intensity, and φ v refers to the line shape function with respect to the center frequency of the laser. X NH3 is the concentration information of the measured ammonia gas.

[0051] It should be noted that in the embodiment of the present invention, the central wave number v of the laser can also be controlled to have a small offset to obtain v1. At this time, the first reference detection signal associated with the measured ammonia gas and its corresponding first reference spectral absorbance are re-obtained through the above step A1, and the optical path detection system is re-controlled to operate to obtain the first detection signal associated with the measured ammonia gas, and then the first measured spectral absorbance is re-obtained through the above step A2. Therefore, the first optimization function mentioned in the above step A3 can also be set as:

[0052]

[0053] Or:

[0054]

[0055] Or:

[0056]

[0057] Among them, is the k-th first measured spectral absorbance peak value included in the first detection signal. is the k-th first reference spectral absorbance peak value included in the first reference detection signal. is the integration result of the k-th measured spectral absorbance peak value included in the detection signal. is the integration result of the k-th reference spectral absorbance peak value included in the reference detection signal.

[0058] In an embodiment of the present invention, when the optical path detection system adopts wavelength modulation spectroscopy technology, the scanning frequency of the laser is set to 100 Hz, the amplitude is 70 mV, the bias is 250 mV, the phase is 270°, and the modulation frequency of the laser is set to 50000 Hz, the amplitude is 30 mV, the bias is 0, and the phase is 270°. The specific implementation process of step S130 is as follows:

[0059] Step B1: Establish a simulation model of the optical path detection system, and obtain a reference detection signal associated with the ammonia gas to be measured and the intensity of its corresponding reference harmonic signal through simulation analysis;

[0060] Step B2: Analyze the detection signal and the drive signal using the principle of wavelength modulation spectroscopy to obtain the intensity of the harmonic signal to be measured, where the principle of wavelength modulation spectroscopy is a prior art;

[0061] Step B3: Determine the second relationship between the intensity of the harmonic signal and the ammonia concentration. When the difference between the intensity of the harmonic signal to be measured and the intensity of the reference harmonic signal reaches the minimum, substitute the intensity of the harmonic signal to be measured into the second relationship for inverse calculation to obtain the concentration information of the ammonia gas to be measured.

[0062] In step B3 above, first establish the second optimization function as:

[0063]

[0064] And determine the second relationship between the intensity of the harmonic signal and the ammonia concentration as:

[0065]

[0066] Secondly, when it is determined that the intensity of the harmonic signal to be measured and the intensity of the reference harmonic signal satisfy the constraint conditions of the second optimization function, substitute the intensity of the harmonic signal to be measured into the second relationship for inverse calculation to obtain the concentration information of the ammonia gas to be measured;

[0067] In the formula, min F refers to the second optimization function, which is used to determine that the difference between the intensity of the harmonic signal to be measured and the intensity of the reference harmonic signal reaches the minimum. m is the harmonic order, and the harmonic order included in the detection signal is the same as that included in the reference detection signal. is the peak value of the k-th harmonic signal intensity to be measured included in the detection signal, that is, the value obtained by normalizing the first harmonic of the second harmonic at the position of the k-th absorption peak included in the detection signal. is the peak value of the k-th reference harmonic signal intensity included in the reference detection signal, that is, the value obtained by normalizing the first harmonic of the second harmonic at the position of the k-th absorption peak included in the reference detection signal. S2f / 1f is the intensity of the harmonic signal to be measured, i0 is the normalized linear intensity modulation amplitude, P is the atmospheric pressure, L is the optical path length of the gas cell, S i (T) is the intensity of the absorption line, X NH3 is the concentration information of ammonia to be measured, φ refers to the line shape function, v is the center frequency of the laser, a is the modulation depth of the laser, and θ is the set angle parameter for performing the integration calculation.

[0068] Embodiment

[0069] Please refer to Figure 2 , Figure 2 which shows an ammonia concentration measuring device, the device includes an optical path detection system and a data processing system; wherein, the optical path detection system includes a function generator, a laser controller, a laser, a collimator, a photodetector and a plurality of gas cells, and the plurality of gas cells are filled with ammonia to be measured; the data processing system includes a data acquisition card, a data processor and a data display.

[0070] In an embodiment of the present invention, the plurality of gas cells are suitable for gas detection in different concentration range intervals, and a preset constraint condition should be satisfied between the absorption line corresponding to each concentration range interval and the optical path length of the gas cell, and the preset constraint condition is that the absorbance peak value of the absorption line under the influence of normal temperature and pressure and the optical path length of the gas cell is greater than 0.001 and less than 2.0.

[0071] Preferably, the number of the plurality of gas cells is set to four, and any one of the gas cells can adopt a White cell or a Herriott cell or a single-pass cell, as Figure 2 shown, wherein, the first gas cell is suitable for gas detection in the concentration range interval of 0.1 ppm - 100 ppm, the second gas cell is suitable for gas detection in the concentration range interval of 100 ppm - 2000 ppm, the third gas cell is suitable for gas detection in the concentration range interval of 2000 ppm - 10000 ppm, and the fourth gas cell is suitable for gas detection in the concentration range interval of 10000 ppm - 100%; of course, the above-mentioned four concentration range intervals can also be set to other values, and the present invention does not limit the specific number of gas cells, that is to say, the present invention does not limit the specific number of concentration range intervals either.

[0072] In an embodiment of the present invention, preferably, the laser adopts a distributed feedback semiconductor laser, its center frequency is 1513 nm and its line width is less than 3 MHz, the output beam diameter of the collimator is 3 mm, and the effective photosensitive surface diameter of the photodetector is 3 mm.

[0073] In an embodiment of the present invention, the implementation process of the optical path detection system is as follows: A driving signal is generated by the function generator, the working temperature and working current of the laser are set by the laser controller according to the driving signal, a laser signal is emitted by the laser, the laser signal is collimated by the collimator to obtain parallel light, the parallel light is absorbed by the ammonia gas to be measured through the plurality of gas cells to obtain a measured optical signal, and the measured optical signal is converted into a measured electrical signal by the photodetector; wherein, a beam splitter is actually arranged at the outlet of the collimator, so that the parallel light emitted by the collimator can be split into four beams by the beam splitter to respectively pass through four gas cells, and at this time, the photodetector can simultaneously receive four measured optical signals for combination.

[0074] In an embodiment of the present invention, the implementation process of the data processing system is as follows: The driving signal and the measured electrical signal are collected by the data acquisition card and then transmitted to the data processor, the concentration information of the ammonia gas to be measured is inverted by the data processor using an optimization algorithm, and the concentration information of the ammonia gas to be measured is displayed by the data display; wherein, the specific implementation process of the data processor is the same as the implementation process of step 130 mentioned in the above ammonia concentration measurement method, and will not be elaborated here.

[0075] Although the description of the present application has been quite detailed and several embodiments have been particularly described, it is not intended to be limited to any of these details or embodiments or any particular embodiment, but should be regarded as effectively covering the intended scope of the present application by referring to the appended claims and considering the broad possibilities of interpretation of these claims in light of the prior art. In addition, the present application is described above in terms of embodiments foreseeable by the inventors for the purpose of providing a useful description, and non-substantive modifications to the present application that are not currently foreseeable may still represent equivalent modifications of the present application.

Claims

1. A method for measuring ammonia concentration, characterized in that, The method includes: Dividing a plurality of different concentration range intervals according to a pre-determined target component concentration range; Selecting corresponding absorption spectral lines and gas cell optical path lengths for each concentration range interval, and then building an optical path detection system with a plurality of gas cells, wherein the plurality of gas cells are filled with ammonia to be measured; Controlling the operation of the optical path detection system to obtain a detection signal associated with the ammonia to be measured, and then using an optimization algorithm to invert the concentration information of the ammonia to be measured in combination with the detection signal; Wherein, the optical path detection system includes a function generator, a laser controller, a laser, a collimator, a photodetector and a plurality of gas cells. The function generator is used to generate a driving signal. The laser controller is used to set the operating temperature and operating current of the laser according to the driving signal. The laser is used to emit a laser signal. The collimator is used to collimate the laser signal to obtain parallel light. The plurality of gas cells are used to cause the ammonia to be measured to absorb the parallel light to obtain a measured optical signal. The photodetector is used to convert the measured optical signal into a measured electrical signal, and the measured electrical signal is the detection signal; Wherein, when the optical path detection system adopts the direct absorption spectroscopy technology, the implementation process of using the optimization algorithm to invert the concentration information of the ammonia to be measured in combination with the detection signal includes: Establishing a simulation model of the optical path detection system, and obtaining a reference detection signal associated with the ammonia to be measured and its corresponding reference spectral absorbance through simulation analysis; Analyzing the detection signal and the driving signal by using the Beer-Lambert law to obtain the measured spectral absorbance; Determining a first relationship between the spectral absorbance and the ammonia concentration. When the difference between the measured spectral absorbance and the reference spectral absorbance reaches the minimum, substituting the measured spectral absorbance into the first relationship for back-calculation to obtain the concentration information of the ammonia to be measured.

2. The ammonia concentration measurement method according to claim 1, wherein The absorbance peak value of the absorption spectral line corresponding to each concentration range interval is greater than 0.001 and less than 2.0 under normal temperature and pressure.

3. The ammonia concentration measurement method according to claim 2, characterized in that The implementation process of selecting the corresponding gas cell optical path length for each concentration range interval includes: Taking the condition that the absorbance peak value of the absorption spectral line corresponding to each concentration range interval is greater than 0.001 and less than 2.0 as a condition, and selecting the corresponding gas cell optical path length for each concentration range interval by querying the spectral database.

4. An ammonia concentration measuring device, characterized in that, The device includes an optical path detection system and a data processing system; The optical path detection system includes a function generator, a laser controller, a laser, a collimator, a photodetector, and a plurality of gas cells, and the plurality of gas cells are filled with ammonia gas to be measured; wherein, the function generator is used to generate a driving signal, the laser controller is used to set the operating temperature and operating current of the laser according to the driving signal, the laser is used to emit a laser signal, the collimator is used to collimate the laser signal to obtain parallel light, the plurality of gas cells are used to cause the ammonia gas to be measured to absorb the parallel light to obtain a measured optical signal, and the photodetector is used to convert the measured optical signal into a measured electrical signal; The data processing system includes a data acquisition card, a data processor, and a data display; wherein, the data acquisition card is used to acquire the driving signal and the measured electrical signal and then transmit them to the data processor, the data processor is used to invert the concentration information of the ammonia gas to be measured by using an optimization algorithm, and the data display is used to display the concentration information of the ammonia gas to be measured; Among them, the plurality of gas cells are applicable to gas detection in different concentration range intervals, and the absorption spectrum line corresponding to each concentration range interval and the optical path length of the gas cell should satisfy a preset constraint condition, and the preset constraint condition is that the absorbance peak value of the absorption spectrum line under normal temperature and pressure and the influence of the optical path length of the gas cell is greater than 0.001 and less than 2.0; Among them, when the optical path detection system adopts the direct absorption spectroscopy technology, the implementation process of the data processor using the optimization algorithm to invert the concentration information of the ammonia gas to be measured includes: Establish a simulation model of the optical path detection system, and obtain a reference detection signal associated with the ammonia gas to be measured and its corresponding reference spectral absorbance through simulation analysis; Analyze the measured electrical signal and the driving signal by using the Beer-Lambert law to obtain the measured spectral absorbance; Determine the first relationship between the spectral absorbance and the ammonia concentration. When the difference between the measured spectral absorbance and the reference spectral absorbance reaches the minimum, substitute the measured spectral absorbance into the first relationship for back-calculation to obtain the concentration information of the ammonia gas to be measured.

5. The ammonia concentration measuring device according to claim 4, characterized in that, The laser adopts a distributed feedback semiconductor laser, and the center frequency of the laser is 1513 nm and its line width is less than 3 MHz.

6. The ammonia concentration measuring device according to claim 4, characterized in that, The output beam diameter of the collimator is 3 mm, and the effective photosensitive surface diameter of the photodetector is 3 mm.

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