Gas detection method based on nondispersive infrared absorption spectroscopy

Abstract

This invention provides a gas detection method based on non-dispersive infrared absorption spectroscopy, comprising the following steps: (A1) Measurement light emitted from a light source passes through a chopper, the rotation speed of which changes periodically; after passing through the chopper, part of the measurement light passes through a sample cell and enters a first container filled with the gas to be measured, and part of the measurement light passes through a reference cell filled with a gas containing zero content of the gas to be measured and enters a second container filled with the gas to be measured; a conversion unit senses the periodic changes in gas pressure in the first and second containers and outputs electrical signals; zero gas and standard gas of the gas to be measured are respectively introduced into the sample cell, and the conversion unit outputs electrical signals V0(t) and V... span (t), where t is time; (A2) Fit the function F0(t) = V span (t)-V0(t); (A3) The sample gas to be tested is introduced into the sample cell, and the conversion unit outputs an electrical signal V(t); (A4) The fitting function F(t)=V(t)-V0(t)=A·F0(t)+B, where A and B are the fitting parameters; (A5) The concentration of the gas to be tested in the sample gas is obtained as C=A·C span C span This refers to the concentration of the gas being measured in the standard gas. This invention has advantages such as small detection error.

Description

Technical Field

[0001] This invention relates to absorption spectroscopy, and more particularly to a gas detection method based on non-dispersive infrared absorption spectroscopy. Background Technology

[0002] Non-dispersive infrared absorption spectroscopy (NDIR) is a detection method based on gas absorption theory. Infrared radiation emitted by an infrared light source is absorbed by a gas of a certain concentration, and the change in spectral intensity is related to the gas concentration. Therefore, the concentration of the gas can be deduced by calculating the change in spectral intensity, making it widely used in gas analysis. However, in actual measurements, there is significant overlap of absorption peaks for many gases in the infrared band, and sometimes the concentration of the gas being measured is very low. Therefore, improving the selectivity and sensitivity of the system is crucial for enhancing instrument performance. Summary of the Invention

[0003] To address the shortcomings of the existing technical solutions, this invention provides a gas detection method based on non-dispersive infrared absorption spectroscopy.

[0004] The objective of this invention is achieved through the following technical solution:

[0005] A gas detection method based on non-dispersive infrared absorption spectroscopy, comprising the following steps:

[0006] (A1) The measuring light emitted by the light source passes through the chopper wheel. The wavelength of the measuring light covers the absorption spectrum of the gas being measured. The rotational speed of the chopper wheel changes periodically, with each cycle... T Inside, the rotational speed changes sequentially in the forward and reverse directions;

[0007] After passing through the chopper, part of the measurement light passes through the sample cell and enters the first container filled with the gas to be measured. Part of the measurement light passes through the reference cell filled with zero content of the gas to be measured and enters the second container filled with the gas to be measured. The pressure of the gas in the first and second containers changes periodically.

[0008] The conversion unit senses the periodic changes in the pressure and outputs a periodically changing electrical signal;

[0009] The zero gas and standard gas of the gas to be tested are respectively introduced into the sample cell, and the conversion unit outputs electrical signals V0(t) and V1(t) respectively. span (t), where t is time;

[0010] (A2) Fit the function F0(t)=V span (t)-V0(t);

[0011] (A3) Replace the gas in the sample cell with the sample gas to be tested, and the conversion unit outputs an electrical signal V(t);

[0012] (A4) The fitting function is F(t) = V(t) - V0(t) = A·F0(t) + B, where A and B are the fitting parameters;

[0013] (A5) Based on the standard gas and the fitting, the concentration of the gas to be measured in the sample gas is obtained as C = A·C. span C span It is the concentration of the gas being measured in the standard gas.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] High detection accuracy;

[0016] This invention utilizes a chopper to modulate the measurement light. The gas being measured in the first and second containers selectively absorbs light at the absorption lines of the gas being measured in the measurement light, causing a pressure change. This effectively converts the modulated light signal into a pressure change signal, which is then detected by a conversion unit. The final gas concentration is obtained through relevant calculations.

[0017] This invention introduces a non-uniformly modulated chopper frequency, which transforms the signal into a frequency-dependent function. Since noise at a specific frequency will only appear at the corresponding frequency position on the measurement function, the output signal is fitted according to a pre-calibrated fitting function for all frequencies during the fitting process. This eliminates the glitches caused by noise at a specific frequency superimposed on the signal, resulting in a more accurate concentration and significantly improving the instrument's adaptability to the application environment. Attached Figure Description

[0018] The disclosure of this invention will become more readily understood with reference to the accompanying drawings. It will be readily understood by those skilled in the art that these drawings are merely illustrative of the technical solutions of this invention and are not intended to limit the scope of protection of this invention. In the drawings:

[0019] Figure 1 This is a schematic flowchart of a gas detection method based on non-dispersive infrared absorption spectroscopy according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the chopper speed modulation in an embodiment of the present invention. Detailed Implementation

[0021] Figure 1-2The following description illustrates optional embodiments of the invention to teach those skilled in the art how to implement and reproduce the invention. Some conventional aspects have been simplified or omitted to explain the technical solutions of the invention. Those skilled in the art should understand that variations or substitutions derived from these embodiments will be within the scope of the invention. Those skilled in the art should understand that the following features can be combined in various ways to form multiple variations of the invention. Therefore, the invention is not limited to the following optional embodiments, but is defined only by the claims and their equivalents.

[0022] Example 1:

[0023] Figure 1 A flowchart illustrating an embodiment of the gas detection method based on non-dispersive infrared absorption spectroscopy of the present invention is shown, such as... Figure 1 As shown, the gas detection method based on non-dispersive infrared absorption spectroscopy includes the following steps:

[0024] (A1) The measuring light emitted by the light source passes through the chopper wheel. The wavelength of the measuring light covers the absorption spectrum of the gas being measured. The rotation speed of the chopper wheel changes periodically. Within each period T, the rotation speed changes in the forward direction and then in the reverse direction.

[0025] After passing through the chopper, part of the measurement light passes through the sample cell and enters the first container filled with the gas to be measured. Part of the measurement light passes through the reference cell filled with zero content of the gas to be measured and enters the second container filled with the gas to be measured. The pressure of the gas in the first and second containers changes periodically.

[0026] The conversion unit senses the periodic changes in the pressure, converts them, and outputs periodically changing electrical signals;

[0027] The zero gas and standard gas of the gas to be tested are respectively introduced into the sample cell, and the conversion unit outputs electrical signals V0(t) and V1(t) respectively. span (t), where t is a discrete time point;

[0028] (A2) Fit the function F0(t)=V span (t)-V0(t), and the specific function fitting method is existing technology in this field;

[0029] (A3) Replace the gas in the sample cell with the sample gas to be tested, and the conversion unit outputs an electrical signal V(t);

[0030] (A4) The fitting function F(t) = V(t) - V0(t) = A·F0(t) + B, where A and B are the fitting parameters, and the specific fitting method is the existing technology in this field;

[0031] (A5) Based on the standard gas and the fitting, the concentration of the gas to be measured in the sample gas is obtained as C = A·C. spanC span It is the concentration of the gas being measured in the standard gas.

[0032] To convert pressure changes and obtain electrical signals within the required time period, the conversion unit further includes a conversion module and a detection module. In step (A1), the conversion module outputs electrical signals, and the detection module acquires electrical signals V0(t) and V0(t) within one period T. span (t);

[0033] In step (A3), the conversion module outputs an electrical signal, and the detection module acquires the electrical signals V1(t), V2(t), ..., V1(t) over N periods T. N (t), to obtain

[0034] In order to convert the gas pressure changes in the first and second containers into electrical signals, the conversion module is further described as a capacitor, a piezoelectric crystal, or a differential pressure sensor. The sides of the conversion module are located inside the first and second containers, respectively, to sense the periodic changes in pressure.

[0035] To improve detection accuracy, the gas to be tested in the first and second containers completely absorbs the light in the measuring light at the wavelength corresponding to the absorption spectrum of the gas to be tested.

[0036] Example 2:

[0037] An application example of the gas detection method based on non-dispersive infrared absorption spectroscopy according to Embodiment 1 of the present invention in the detection of carbon monoxide.

[0038] In this application example, such as Figure 1 As shown, the gas detection method based on non-dispersive infrared absorption spectroscopy includes the following steps:

[0039] (A1) The measuring light emitted by the light source passes through the chopper wheel. The wavelength of the measuring light covers the absorption spectrum of the gas being measured. The rotational speed of the chopper wheel changes periodically. Within each period T, the rotational speed decreases linearly in the forward direction and increases linearly in the reverse direction, with the rate of change being equal. Figure 2 As shown;

[0040] After passing through the chopper, part of the measurement light passes through the sample cell and enters the first container filled with carbon monoxide and inert gas. Part of the measurement light passes through the reference cell filled with nitrogen (with zero carbon monoxide content) and enters the second container filled with carbon monoxide and inert gas. The high concentration of carbon monoxide in the first and second containers completely absorbs the light in the measurement light at the wavelength corresponding to the absorption spectrum of the gas being measured. The pressure of the gas in the first and second containers changes periodically.

[0041] The conversion unit includes a capacitor and a detection module. The two sides of the capacitor are located in the first container and the second container, respectively. It senses the periodic changes in pressure in the two containers, converts them into periodic changes in capacitance value, and outputs them.

[0042] The zero gas and standard gas of the gas to be tested are respectively introduced into the sample cell, and the detection module collects the electrical signals V0(t) and V1(t) within one period T. span (t), where t is a discrete time point;

[0043] (A2) The function F0(t) = V is fitted using a higher-order polynomial. span (t)-V0(t), and the specific fitting method is existing technology in this field;

[0044] (A3) Replace the gas in the sample cell with the sample gas to be tested, and the detection module collects electrical signals V1(t), V2(t), ..., V1(t) over N periods T. N (t), to obtain

[0045] (A4) The fitting function F(t) = V(t) - V0(t) = A·F0(t) + B, where A and B are the fitting parameters, and the specific fitting method is the existing technology in this field;

[0046] (A5) Based on the standard gas and the fitting, the concentration of the gas to be measured in the sample gas is obtained as C = A·C. span C span It is the concentration of the gas being measured in the standard gas.

[0047] Example 3:

[0048] The application example of the gas detection method based on non-dispersive infrared absorption spectroscopy in carbon monoxide detection according to Embodiment 1 of the present invention differs from Embodiment 2 in that:

[0049] The conversion module uses a piezoelectric crystal. When the pressure changes in the first and second containers are applied to the two sides of the pressure crystal, the squeezed piezoelectric crystal outputs a changing electrical signal.

Claims

1. A method for detecting a gas based on non-dispersive infrared absorption spectroscopy, the method comprising the following steps: (A1) a measurement light emitted by a light source passes through a chopper wheel, the wavelength of the measurement light covers the absorption line of the measured gas, the rotation speed of the chopper wheel changes periodically, in each period T, the rotation speed changes forward and reversely in turn; part of the measurement light after passing through the chopper wheel enters a first container filled with the measured gas after passing through a sample cell, part of the measurement light after passing through the chopper wheel enters a second container filled with the measured gas after passing through a reference cell with zero content of the measured gas, the pressure of the gas in the first and second containers changes periodically; a conversion unit senses the periodic change of the pressure and outputs a periodic change of an electric signal; The zero gas and the standard gas of the measured gas are respectively introduced into the sample cell, and the conversion unit respectively outputs an electrical signal V0(t) and V span (t) in one period T, t is time; (A2) fitting a function F0(t) = V span (t) - V0(t); (A3) Replacing the gas in the sample cell with a sample gas to be measured, the conversion unit outputs the electrical signals V1(t), V2(t) ··· V N (t) for N periods T, obtaining ; (A4) a fitting function F(t)=V(t)-V0(t)=A·F0(t)+B, A and B are fitting parameters respectively; (A5) According to the standard gas and the fitting, the concentration C of the measured gas in the sample gas is obtained as C = A·C span , C span is the concentration of the measured gas in the standard gas.

2. The method of claim 1, wherein the non-dispersive infrared absorption spectroscopy technique is selected from the group consisting of: a) a non-dispersive infrared absorption spectroscopy technique that uses a single beam of infrared radiation; and b) a non-dispersive infrared absorption spectroscopy technique that uses a dual beam of infrared radiation. The conversion unit comprises a conversion module and a detection module, in step (A1), the conversion module outputs electrical signals respectively, the detection module collects electrical signals V0(t), V span (t) respectively; In step (A3), the conversion module outputs electrical signals, and the detection module collects electrical signals V1(t), V2(t) ··· V N (t).

3. The gas detection method based on non-dispersive infrared absorption spectroscopy according to claim 2, characterized in that, the conversion module is a capacitor or a piezoelectric crystal or a differential pressure sensor, the side of the conversion module is in the first and second containers respectively, and the periodic change of the pressure is sensed respectively.

4. The gas detection method based on non-dispersive infrared absorption spectroscopy according to claim 1, characterized in that, The forward change and the reverse change are both linear.

5. The gas detection method based on non-dispersive infrared absorption spectroscopy according to claim 1, characterized in that, In step (A2), a polynomial fitting function F0(t) is used.

6. The gas detection method based on non-dispersive infrared absorption spectroscopy according to claim 1, characterized in that, The measured gas in the first and second containers completely absorbs the light of the measurement light with the wavelength corresponding to the absorption line of the measured gas.

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