Measurement method and system for eliminating interference of CO2 in gas sample on CO concentration measurement

Abstract

The invention discloses a measurement method and system for eliminating interference of CO2 in a gas sample on CO concentration measurement. The method comprises: obtaining the CO2 concentration of the gas sample according to the measured CO2 level of the gas sample by using a pre-established first standard curve of CO2 level and CO2 concentration; obtaining the CO correction level of the gas sample according to the CO2 concentration of the gas sample by using a pre-established second standard curve of CO correction level and CO2 concentration; adding the measured CO test level of the gas sample to the CO correction level of the gas sample to obtain the CO level of the gas sample; and obtaining the CO concentration of the gas sample according to the obtained CO level of the gas sample by using a pre-established third standard curve of CO level and CO concentration. The invention effectively eliminates the influence of high concentration of CO2 in the gas sample on the trace CO concentration measurement.

Description

Technical Field

[0001] The present invention relates to the field of biotechnology, and in particular to a measurement method and system for eliminating the interference of CO2 in a gas sample on CO concentration measurement. Background Art

[0002] CO is a colorless, odorless, tasteless gas that is widely present in the atmosphere, mainly from automobile exhaust and incomplete combustion of mineral fuels. Air pollution is extremely harmful and directly threatens human survival, so it is often used as an indicator to monitor the pollution level in large cities. CO is also a product of human metabolism. The concentration of CO in human exhaled air is very low (trace). Human exhaled CO contains three sources: heme degradation, non-heme metabolism and exogenous inhalation. 86% of endogenous CO comes from heme degradation, and the CO produced by non-heme metabolism does not exceed 14%. 85% of the heme that produces CO comes from red blood cell degradation, and 15% comes from non-red blood cell heme. Therefore, about 70% of the endogenous CO in exhaled air comes from red blood cell degradation. Studies have shown that the life span of human red blood cells can be calculated by measuring the endogenous CO concentration, and the life span of human red blood cells has a positive reference value for the diagnosis of diseases, so it has a positive significance for the determination of trace CO concentration in the human body.

[0003] In the existing infrared spectroscopy method for measuring CO concentration, a gas filter modulation wheel is used, and the mid-infrared light passing through the nitrogen cavity is used as the test light, and the mid-infrared light passing through the CO cavity is used as the reference light. After the two lights pass through the gas pool, the light energy is detected by an infrared detector and converted into voltage. After passing through a linear amplifier circuit and a difference circuit, a voltage value related to the CO concentration in the gas pool is obtained. The voltage value is substituted into the fitted "concentration-voltage" curve to calculate the concentration of CO in the gas to be tested. In this scheme, for example, when measuring CO containing a high concentration of CO2 such as exhaled breath, CO2 will have a greater impact on the measurement. Therefore, before the measurement, the CO2 in the exhaled breath must be removed outside the measuring gas chamber, otherwise it will affect the measurement accuracy of the CO concentration. However, removing CO2 will bring more structural and cost increases and introduce other errors. Summary of the invention

[0004] The purpose of the present invention is to address the above-mentioned needs and to propose a measurement method and system for eliminating the interference of CO2 in a gas sample on the measurement of CO concentration.

[0005] The technical solution of the present invention to solve the technical problem is to construct a measurement method to eliminate the interference of CO2 in the gas sample on the CO concentration measurement, and the method comprises the following steps:

[0006] Step 1: According to the measured CO2 level of the gas sample, the CO2 concentration of the gas sample is obtained by using a pre-established first standard curve of CO2 level and CO2 concentration;

[0007] Step 2: According to the CO2 concentration of the gas sample, the CO correction level of the gas sample is obtained by using a pre-established second standard curve of CO correction level and CO2 concentration;

[0008] Step 3: Add the CO test level of the gas sample measured to the CO correction level of the gas sample obtained in step 2 to obtain the CO level of the gas sample;

[0009] Step 4: According to the obtained CO level of the gas sample, the CO concentration of the gas sample is obtained by using a pre-established third standard curve of CO level and CO concentration.

[0010] Furthermore, the method further comprises:

[0011] The exhaled air and the ambient background gas are respectively used as the gas samples and the CO concentrations in the exhaled air and the ambient background gas are measured through the steps 1 to 4 respectively. The endogenous CO concentration in the exhaled air is obtained by subtracting the CO concentration in the ambient background gas from the CO concentration in the exhaled air.

[0012] Furthermore, the method further comprises:

[0013] Collect the subject's exhaled breath and the ambient air of the place where the subject was before the exhaled breath was collected;

[0014] Insert the collected exhaled air into the air inlet of the measurement system, and after sampling according to the set sampling method, measure the CO2 level and CO test level in the exhaled air respectively;

[0015] Insert the collected ambient background gas into the air inlet of the measurement system. After sampling according to the set sampling method, measure the CO2 level and CO test level in the ambient background gas respectively.

[0016] Furthermore, the first standard curve is obtained by the following experimental method:

[0017] Insert a high concentration of CO2 standard gas into the air inlet of the measurement system to clean the air chamber. Measure the actual CO2 level value P before and after the air intake. 1-CO2 and P 2-CO2 , P 2-CO2 Subtract P 1-CO2 Get the net value of CO2 level after deducting the background (2-1)-CO2 The CO2 level as a CO2 standard gas with a high concentration;

[0018] Insert a low-concentration CO2 standard gas into the air inlet of the measurement system to clean the air chamber. Measure the actual CO2 level value P before and after the air intake. 3-CO2 and P 4-CO2 , P 4-CO2 Subtract P 3-CO2 Get the net value of CO2 level after deducting the background P (4-3)-CO2 The CO2 level as a CO2 standard gas with a lower concentration;

[0019] According to P (2-1)-CO2 , P (4-3)-CO2 and the CO2 concentration of the CO2 standard gas corresponding to each of them, and fitting to obtain the first standard curve.

[0020] Furthermore, the third standard curve is obtained by the following experimental method:

[0021] Insert a high concentration of CO standard gas into the air inlet of the measurement system to clean the air chamber. Measure the actual CO level value P before and after the air intake. 1-CO and P 2-CO , P 2-CO Subtract P 1-CO Get the net value of CO level after deducting the background value P (2-1)-CO The CO level as a CO standard gas with a high concentration;

[0022] Insert a low-concentration CO standard gas into the air inlet of the measurement system to clean the air chamber. Measure the actual CO level value P before and after the air intake. 3-CO and P 4-CO , P 4-CO Subtract P 3-CO Get the net value of CO level after deducting the background value P (4-3)-CO The CO level as a CO standard gas with a relatively low concentration;

[0023] According to CO level P (2-1)-CO and CO level P (4-3)-CO and the CO concentration of their respective corresponding CO standard gases, and the third standard curve is obtained by fitting.

[0024] Furthermore, the second standard curve is obtained by the following experimental method:

[0025] Insert a mixed standard gas of CO2 and CO with a high CO2 concentration into the air inlet of the measurement system to clean the air chamber. Measure the actual CO test level value P before and after the air intake. 5-CO and P 6-CO , P 6-CO Subtract P 5-CO Get the CO test level net value P (6-5)-COAs the CO test level of the standard gas for the mixed standard gas of CO2 and CO with a high CO2 concentration;

[0026] Insert a mixed standard gas of CO2 and CO with a low CO2 concentration into the air inlet of the measurement system to clean the air chamber. Measure the actual CO level value P before and after the air intake. 7-CO and P 8-CO , P 8-CO Subtract P 7-CO Get the CO test level net value P (8-7)-CO CO test level as a standard gas for a CO2 and CO mixed standard gas with a low CO2 concentration;

[0027] According to the known CO concentration values ​​in the two mixed standard gases with higher and lower CO2 concentrations, the third standard curve is checked to obtain the theoretical CO level value P of the mixed standard gas with higher CO2 concentration. (6-5)’-CO The theoretical value of CO level P of the mixed standard gas with a lower CO2 concentration (8-7)’-CO ;

[0028] P (6-5)’-CO Subtract P (6-5)-CO Get the CO correction level P of the mixed standard gas with a higher CO2 concentration 校1-CO , P (8-7)’-CO Subtract P (8-7)-CO Get the CO correction level P of the mixed standard gas with lower CO2 concentration 校2-CO ;

[0029] According to P 校1-CO and P 校2-CO and their corresponding CO2 concentrations, and a second standard curve is obtained by fitting.

[0030] Furthermore, the method further comprises: when the intercept of the fitted second standard curve is not zero, correcting the second standard curve by the following method:

[0031] A mixed standard gas of CO2 and CO with different CO2 concentrations is used as the sample gas, and the known CO concentration value of the sample gas is the nominal value;

[0032] The sample gases are measured in order of CO2 concentration from high to low, and the CO concentration values ​​of the sample gases are obtained by executing the steps 1 to 4 as experimental measurement values. When the difference between the experimental measurement value of a certain sample gas and the nominal value reaches a preset upper limit of the deviation allowable value, the CO2 concentration corresponding to the sample gas is used as the CO2 concentration lower limit to be found;

[0033] Connect the coordinates formed by the CO2 concentration lower limit value and the CO correction level queried on the second standard curve whose intercept is not zero according to the CO2 concentration lower limit value and the coordinate origin, and use this connecting line to replace the section from the CO2 concentration lower limit value to the CO2 concentration zero of the fitted second standard curve whose intercept is not zero, so as to obtain a corrected second standard curve applicable to all CO2 concentration values.

[0034] Furthermore, the method further comprises: the sampling mode of the measuring system during measurement comprises: negative pressure sampling, or / and direct sampling by air pump, or / and sampling by air cylinder;

[0035] The negative pressure injection specifically comprises:

[0036] The measuring gas chamber is vacuumed according to a set vacuuming treatment mode, so that the pressure in the measuring gas chamber reaches a set pressure threshold before sampling, wherein: the pressure threshold before sampling is less than the atmospheric pressure, and the vacuuming treatment mode includes directly vacuuming the measuring gas chamber and cleaning the measuring gas chamber once or multiple times before vacuuming;

[0037] Perform one or more injections according to the set injection times, wherein each injection is based on the internal and external pressure difference of the measuring chamber formed by vacuuming, so that the sample to be tested connected to the air inlet end of the measuring chamber automatically enters the measuring chamber.

[0038] On the other hand, the present invention also constructs a measurement system for eliminating the interference of CO2 in a gas sample on CO concentration measurement, characterized in that the system includes a CO measurement gas chamber that meets specific technical parameter requirements, a CO2 measurement gas chamber, an injection unit, a cleaning unit, and a main control unit that executes the measurement method described in any of the preceding items.

[0039] Furthermore, the CO measurement gas chamber comprises: an infrared gas chamber body, an infrared generator and an infrared detector arranged on the infrared gas chamber body, and an optical path system arranged between the infrared generator and the infrared detector, wherein the optical path system comprises a narrow-band filter, and the infrared light emitted by the infrared generator is detected by the infrared detector after passing through the optical path system;

[0040] Wherein, a constant temperature module is arranged in the infrared detector, the narrow-band filter is arranged at any position on the optical path between the infrared light source and the infrared detector, and the infrared detector detects the light passing through the narrow-band filter;

[0041] The specific technical parameter requirements of the narrowband filter are: the central wavelength of the transmittance infrared light is 4.705 μm±0.095 μm, the infrared light transmittance at the central wavelength is greater than or equal to 30%, and the half-height width is not greater than 0.25 um.

[0042] The measurement method and system for eliminating the interference of CO2 in a gas sample on the measurement of CO concentration of the present invention have the following beneficial effects: the present invention does not directly obtain the CO concentration by converting the CO test level, but obtains the CO2 concentration by using the measured CO2 level, and then obtains the CO correction level, and then obtains the CO level of the exhaled air and the ambient background gas according to the CO test level and the obtained CO correction level. The CO level is calibrated, so based on the calibrated CO level, the obtained CO concentration is more accurate, and the influence of the high concentration of CO2 in the exhaled air on the measurement of the trace CO concentration is effectively eliminated, and the difficulty of removing CO2 before measuring the trace CO in the exhaled air by the infrared spectroscopy method is overcome, and the problem of removing CO2 when measuring CO containing a higher concentration of CO2 by the infrared spectroscopy method is perfectly solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0044] Figure 1 A flow chart showing a method for measuring trace CO concentration in alveolar gas according to the present invention;

[0045] Figure 2 It is a schematic diagram of the structure of the measuring air chamber;

[0046] Figure 3 It is a correction diagram of the second standard curve. DETAILED DESCRIPTION

[0047] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. Typical embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations on the technical solutions of the present application. In the absence of conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0048] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an element in the middle. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an element in the middle. The terms "upper", "lower", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0049] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0050] Terms including ordinal numbers such as "first" and "second" used in this specification may be used to describe various components, but these components are not limited by these terms. The purpose of using these terms is only to distinguish one component from other components. For example, without departing from the scope of the present invention, the first component may be named as the second component, and similarly, the second component may also be named as the first component.

[0051] Embodiment 1

[0052] refer to Figure 1 The method for eliminating the interference of CO2 in the gas sample on the CO concentration measurement in this embodiment comprises:

[0053] S101: according to the measured CO2 level of the gas sample, using a pre-established first standard curve of CO2 level and CO2 concentration, obtaining the CO2 concentration of the gas sample;

[0054] S102: according to the CO2 concentration of the gas sample, using a pre-established second standard curve of CO correction level and CO2 concentration, obtaining the CO correction level of the gas sample;

[0055] S103: adding the measured CO test level of the gas sample to the CO correction level of the gas sample obtained in step 2 to obtain the CO level of the gas sample;

[0056] S104: according to the obtained CO level of the gas sample, using a pre-established third standard curve of CO level and CO concentration, obtaining the CO concentration of the gas sample;

[0057] The measured CO2 level and CO test level used in the above steps S101 and S103 are measured by a measurement system. The existing measurement system can directly measure the CO2 level and CO test level. After measuring these levels, the CO2 concentration and CO concentration are directly converted according to the corresponding curves. However, this method is not reliable. For this reason, the present invention only uses the measurement system to measure the CO2 level and CO test level, and the subsequent calculation method is different from the existing measurement method. Instead, it is based on the above steps S101-S104 to achieve correction and obtain an accurate CO concentration.

[0058] In order to obtain the measured CO2 level and CO test level used in the above step S101 and step S103, the method of this embodiment further includes the following level measurement steps:

[0059] S201: Collect the exhaled breath of the subject and the ambient air of the place where the subject was before the exhaled breath was collected;

[0060] S202: inserting the collected exhaled air into the air inlet of the measurement system, and after sampling according to the set sampling method, measuring the CO2 level and the CO test level in the exhaled air respectively;

[0061] S203: inserting the collected ambient air into the air inlet of the measurement system, and after sampling according to the set sampling method, measuring the CO2 level and the CO test level in the ambient air respectively.

[0062] It is understandable that the measurement of the CO2 level only needs to be completed before step S101. Similarly, the measurement of the CO test level only needs to be completed before step S103.

[0063] The first standard curve, the second standard curve, and the third standard curve used in the above steps S101, S102, and S104 are pre-established. The establishment process of these three curves is first introduced below:

[0064] S301: using a measurement system to measure the CO2 level of the CO2 standard gas, and combining the CO2 concentration of the CO2 standard gas to obtain the first standard curve by fitting;

[0065] S302: using a measurement system to measure the CO level of the CO2 and CO mixed standard gas, and combining the CO concentration and CO2 concentration of the CO2 and CO mixed standard gas to obtain the second standard curve by fitting;

[0066] S303: Using the measurement system to measure the CO level of the CO standard gas, and combining the CO concentration of the CO standard gas to obtain the third standard curve through fitting.

[0067] The above three steps are described in detail below.

[0068] Wherein, step S301 specifically includes the following sub-steps:

[0069] S301a) Insert a high concentration of CO2 standard gas into the air inlet of the measurement system to clean the air chamber, and measure the CO2 level before and after the air intake to obtain the measured value P 1-CO2 and P 2-CO2 , P 2-CO2 Subtract P 1-CO2 Get the net value of CO2 level after deducting the background P (2-1)-CO2The CO2 level as a CO2 standard gas with a high concentration;

[0070] S301b) Insert a low-concentration CO2 standard gas into the air inlet of the measurement system to clean the air chamber, and measure the CO2 level before and after the air intake to obtain the actual value P 3-CO2 and P 4-CO2 , P 4-CO2 Subtract P 3-CO2 Get the net value of CO2 level after deducting the background (4-3)-CO2 The CO2 level as a CO2 standard gas with a lower concentration;

[0071] S301c) According to P (2-1)-CO2 , P (4-3)-CO2 and the CO2 concentration of the CO2 standard gas corresponding to each of them, the first standard curve is obtained by fitting, and the expression of the first standard curve is:

[0072] Y CO2 =k1*X CO2 +b1 (1-1);

[0073] Among them, k1 and b1 are fitting constants, Y CO2 is the CO2 concentration, X CO2 is the CO2 level. (2-1)-CO2 , P (4-3)-CO2 As X in function (1-1) CO2 , taking the two CO2 concentrations as functions (1-1) in Y CO2 , k1 and b1 can be determined by fitting.

[0074] It is understandable that the first standard curve may be other functions besides the function of S301c) above. For example, in another embodiment, the first standard curve may be divided into two sections, and S301c) may be replaced by the following step S301c′):

[0075] S301c') According to P (2-1)-CO and the CO2 concentration of the corresponding CO2 standard gas, the first section of the first standard curve is obtained by fitting. (2-1)-CO2 , P (4-3)-CO2 and the CO2 concentration of the CO2 standard gas corresponding to each of them, and fitting the second section of the first standard curve,

[0076] The expression of the first paragraph is:

[0077] Y CO2 =k11*X CO2 , 0≤X CO2 ≤P (2-1)-CO2 (1-2);

[0078] The expression of the second paragraph is:

[0079] Y CO2 =k12*X CO2 +b1,X CO2 >P (2-1)-CO2 (1-3);

[0080] Among them, k11, k12 and b1 are fitting constants, Y CO2 is the CO2 concentration, X CO2 is the CO2 level. When fitting (1-2), P (2-1)-CO As X in function (1-2) CO2 , taking CO2 concentration as function (1-2) in Y CO2 , k11 can be determined by fitting. Similarly, when fitting (1-3), P (2-1)-CO2 , P (4-3)-CO2 As X in function (1-3) CO2 , taking the two CO2 concentrations as functions (1-3) in Y CO2 , k12 and b1 can be determined by fitting.

[0081] Wherein, step S303 specifically includes the following sub-steps:

[0082] S303a) Insert a high concentration of CO standard gas into the air inlet of the measurement system to clean the air chamber, and measure the CO level measured value P before and after the air intake. 1-CO and P 2-CO , P 2-CO Subtract P 1-CO Get the net value of CO level after deducting the background value P (2-1)-CO The CO level as a CO standard gas with a high concentration;

[0083] S303b) Inserting a low-concentration CO standard gas into the air inlet of the measurement system to clean the air chamber, and measuring the CO level measured value P before and after the air intake. 3-CO and P 4-CO , P 4-CO Subtract P 3-CO Get the net value of CO level after deducting the background value P (4-3)-CO The CO level as a CO standard gas with a relatively low concentration;

[0084] S303c) According to the CO level P (2-1)-CO and CO level P (4-3)-CO and the CO concentration of their respective corresponding CO standard gases, the third standard curve is obtained by fitting, and the expression of the third standard curve is:

[0085] Y CO =k3*X CO +b3;

[0086] Among them, k3 and b3 are fitting constants, Y CO is the CO concentration, X CO is the CO level.

[0087] It is understandable that the third standard curve may be other functions besides the function of S303c) above. For example, in another embodiment, the third standard curve may be divided into two sections, and S303c) may be replaced by the following step S303c′):

[0088] S303c') According to P (2-1)-CO and the CO2 concentration of the corresponding CO2 standard gas, the first section of the third standard curve is obtained by fitting. (2-1)-CO , P (4-3)-CO and the CO2 concentration of the corresponding CO2 standard gas, the second section of the third standard curve is obtained by fitting,

[0089] The expression of the first paragraph is:

[0090] Y CO =k31*X CO , 0≤X CO ≤P (2-1)-CO (3-2);

[0091] The expression of the second paragraph is:

[0092] Y CO =k32*X CO +b3,X CO >P (2-1)-CO (3-3);

[0093] Among them, k31, k32 and b3 are fitting constants, Y CO is the CO concentration, X CO is the CO level. When fitting (3-2), P (2-1)-CO As X in function (3-2) CO , taking CO2 concentration as function (3-2) CO , k31 can be determined by fitting. Similarly, when fitting (3-3), P (2-1)-CO , P (4-3)-CO As X in function (3-3) CO , taking the two CO2 concentrations as functions Y in (3-3) CO , k32 and b3 can be determined by fitting.

[0094] Wherein, step S302 specifically includes the following sub-steps:

[0095] S302a) Insert a mixed standard gas of CO2 and CO with a high CO2 concentration into the air inlet of the measurement system to clean the air chamber, and measure the actual CO test level value P before and after the air intake. 5-CO and P 6-CO , P 6-CO Subtract P 5-CO Get CO test level P (6-5)-CO As the CO test level of the standard gas for the mixed standard gas of CO2 and CO with a high CO2 concentration;

[0096] S302b) inserting a mixed standard gas of CO2 and CO with a low CO2 concentration into the air inlet of the measurement system to clean the air chamber, and measuring the actual CO level value P before and after the air intake. 7-CO and P 8-CO , P 8-CO Subtract P 7-CO Get CO test level P (8-7)-CO CO test level as a standard gas for CO2 and CO mixed standard gas with low CO2 concentration;

[0097] S302c) According to the known CO concentration values ​​in the two mixed standard gases with higher and lower CO2 concentrations, the third standard curve is checked to obtain the CO level theoretical value P of the mixed standard gas with higher CO2 concentration. (6-5)’-CO The theoretical value of CO level P of the mixed standard gas with a lower CO2 concentration (8-7)’-CO ;

[0098] S302d) P (6-5)’-CO Subtract P (6-5)-CO Get the CO correction level P of the mixed standard gas with a higher CO2 concentration 校1-CO , P (8-7)’-CO Subtract P (8-7)-CO Get the CO correction level P of the mixed standard gas with lower CO2 concentration 校2-CO ;

[0099] S302e) According to P 校1-CO and P 校2-CO and their corresponding CO2 concentrations, and fitted to obtain the second standard curve;

[0100] Preferably, when the intercept of the second standard curve fitted in step S302e is not zero, the second standard curve cannot meet the theoretical requirement that "when the CO2 concentration is zero, the correction level caused by it should also be zero", that is, the second standard curve fitted is no longer applicable after the CO2 concentration drops to a certain value, and the CO2 concentration lower limit value applicable to the second standard curve fitted should be found. In this embodiment, the CO2 concentration of the second standard curve from zero to the CO2 concentration lower limit value is corrected by the following method:

[0101] 1) Use a mixed standard gas of CO2 and CO with different CO2 concentrations as the sample gas, and the known CO concentration value of the sample gas is the nominal value;

[0102] 2) Measure the sample gas in order of CO2 concentration from high to low, execute steps 1 to 4 to obtain the CO concentration value of the sample gas as the experimental measurement value, and when the difference between the experimental measurement value of a certain sample gas and the nominal value reaches the upper limit of the preset deviation allowable value, the CO2 concentration corresponding to the sample gas is used as the CO2 concentration lower limit to be found;

[0103] 3) Connect the coordinates formed by the CO2 concentration lower limit value and the CO correction level queried on the second standard curve whose intercept is not zero based on the CO2 concentration lower limit value to the coordinate origin, and use this connecting line to replace the section from the CO2 concentration lower limit value to the CO2 concentration zero of the second standard curve whose intercept is not zero, so as to obtain a corrected second standard curve applicable to all CO2 concentration values.

[0104] That is, reference Figure 3 , we first use the following expression to fit the second standard curve, assuming that Figure 3 The curve in is expressed as:

[0105] X' CO =m*X CO2 +n (2-1);

[0106] Among them, m and n are fitting constants, X' CO is the CO correction level, X CO2 is the CO2 concentration. When fitting, P 校1-CO and P 校2-CO As X' in function (2-1) CO , the CO2 concentration of the two mixed standard gases is used as the function X in (2-1) CO2 , and then m and n can be determined by fitting. If n is not zero after fitting, it is necessary to determine the low value of CO2 concentration according to the above method, assuming that the low value of CO2 concentration is P low-CO2 , then P low-CO2Substitute X into expression (2-1) CO2 Get X' CO The specific value of is assumed to be P low-CO , find (P low-CO2 , P low-CO ) this coordinate point, we divide the curve into two segments from this coordinate point, the second segment curve remains unchanged, the first segment (0, 0) to (P low-CO2 , P low-CO ) is the section we need to correct. The corrected bold line replaces the original (0, 0) to (P low-CO2 , P low-CO ), after such correction, the final second standard curve is divided into the following two sections:

[0107] The expression of the first paragraph is:

[0108] X' CO =m'*X CO2 , 0≤X CO2 ≤P low-CO2 (2-2);

[0109] The expression of the second paragraph is:

[0110] X' CO =m*X CO2 +n,X CO2 >P low-CO2 (2-3);

[0111] Among them, expression (2-3) is actually expression (2-1) plus X CO >P low-CO2 The restriction of expression (2-2) is m', which is P low-CO2 , P low-CO Substitute X into expression (2-2) respectively CO2 , Y CO Calculated later.

[0112] Preferably, in the method, the measuring system adopts negative pressure sampling, or / and direct sampling by air pump, or / and sampling by air cylinder during measurement.

[0113] Specifically, the negative pressure injection specifically includes:

[0114] S401: vacuumizing the measuring gas chamber according to the set vacuumizing processing mode, so that the pressure in the measuring gas chamber reaches the set pressure threshold before sampling;

[0115] Wherein, the pressure threshold before injection is less than the atmospheric pressure.

[0116] The vacuum treatment method includes directly vacuuming the measuring chamber and cleaning the measuring chamber once or multiple times before vacuuming. Specifically:

[0117] 1) The direct vacuuming of the measuring air chamber includes: performing a vacuuming and exhausting step. The vacuuming and exhausting step includes: starting an air pressure control unit connected to the measuring air chamber by an air path, closing an air inlet solenoid valve, opening an air outlet solenoid valve, and closing the air outlet solenoid valve when the pressure of the measuring air chamber reaches a pressure threshold before cleaning, wherein the pressure threshold before cleaning is less than or equal to atmospheric pressure;

[0118] 2) The vacuuming treatment after cleaning the measuring gas chamber once or multiple times includes: repeatedly "performing the vacuuming and exhausting step once and then performing the cleaning step once" until the cleaning step is performed a set number of times; and then performing the vacuuming and exhausting step once more.

[0119] The vacuum exhaust step refers to the above 1). The cleaning step includes: opening the air inlet solenoid valve to allow the cleaning gas connected to the air inlet end of the measuring air chamber to automatically enter the measuring air chamber, and when the pressure of the measuring air chamber reaches the pressure threshold after cleaning, closing the air inlet solenoid valve.

[0120] Obviously, before carrying out the purge step, the purge gas must be connected to the gas inlet of the measuring cell.

[0121] S402: Perform one or more injections according to the set injection times, wherein each injection is based on the pressure difference between the inside and outside of the measuring chamber formed by vacuuming, so that the sample to be tested connected to the air inlet end of the measuring chamber automatically enters the measuring chamber. Specifically,

[0122] 1) The one injection comprises: performing one gas intake step.

[0123] The air intake step includes: opening the air intake solenoid valve to allow the sample to be tested to automatically enter the measuring chamber, and closing the air intake solenoid valve when the pressure of the measuring chamber reaches a pressure threshold after sample injection. Obviously, before performing the air intake step, the sample to be tested must first be connected to the air inlet of the measuring chamber.

[0124] 2) The multiple injections include: executing the air intake step once; and repeatedly executing “one sample exhaust step and then executing the air intake step once” until the air intake step reaches a set number of air intake times.

[0125] Wherein, the sample exhaust step includes: starting an air pressure control unit that is connected to the measuring air chamber by an air path, closing an air inlet solenoid valve, opening an air outlet solenoid valve, and closing the air outlet solenoid valve when the pressure of the measuring air chamber reaches a pressure threshold before sampling.

[0126] It should be noted that, in the present invention, the pressure threshold before injection and the pressure threshold before cleaning may be the same or different, the pressure threshold after injection and the pressure threshold after cleaning may be the same or different, and the pressure threshold before injection corresponding to the end of different sample exhaust steps may be the same or different.

[0127] The samples to be tested include breath samples and ambient air samples, and the cleaning gas is processed air or sample gas to be tested.

[0128] As described above, the present embodiment does not directly obtain the CO concentration by converting the CO test level, but obtains the CO concentration by using the measured CO2 level, and then obtains the CO correction level, and then obtains the CO level of the exhaled breath and the ambient air according to the CO test level and the obtained CO correction level. The CO level is calibrated, so based on the calibrated CO level, the obtained CO concentration is more accurate, and the influence of the high concentration of CO2 in the exhaled breath on the measurement of the trace CO concentration is effectively eliminated, and the difficulty of removing CO2 before measuring the trace CO in the exhaled breath by using the infrared spectroscopy method is overcome.

[0129] Embodiment 2

[0130] The system for measuring trace CO concentration in alveolar gas of this embodiment includes a CO measuring chamber, a CO2 measuring chamber, a sample injection unit, a cleaning unit, and a main control unit for executing the measuring method described in the first embodiment.

[0131] refer to Figure 2 More specifically, the CO measuring chamber includes: an infrared chamber body 10, an infrared generator and an infrared detector 17 arranged on the outer wall of the infrared chamber body 10, an optical system arranged in the infrared chamber body 10, an air pressure control unit connected to the infrared chamber body 10 by an air path, a pressure sensor connected to the infrared chamber body 10 by an air path, etc.

[0132] The infrared light emitted by the infrared generator is detected by the infrared detector 17 after passing through the optical system. An air inlet 21 is provided at the top of the infrared air chamber body 10, and an air outlet 22 is provided at the bottom of the infrared air chamber body 10. The air inlet 21 includes an air inlet solenoid valve, and the air outlet 22 includes an air outlet solenoid valve. The air pressure control unit includes an air pump or an air cylinder or other pressure control processing equipment or devices that can pressurize or depressurize the measuring air chamber.

[0133] The main control unit can set the vacuum processing mode, set the number of injections, set the pressure threshold before cleaning, set the pressure threshold after cleaning, set the pressure threshold before injection, set the pressure threshold after injection, control the opening and closing of the solenoid valve and the analysis and processing of the measurement signal, and execute the measurement method described in Example 1.

[0134] It should be noted that the measuring gas chamber is actually divided into a CO measuring gas chamber and a CO2 measuring gas chamber, and this embodiment only introduces the CO measuring gas chamber.

[0135] Wherein, a constant temperature module is arranged in the infrared detector.

[0136] The optical system includes a narrowband filter 16 that meets specific parameter requirements. Theoretically, the narrowband filter 16 can be set at any position on the optical path between the infrared light source 13 and the infrared detector 17. In this embodiment, the narrowband filter 16 is set at a position close to the infrared detector 17. The infrared detector 17 is arranged opposite to the narrowband filter 16 and detects the light passing through the narrowband filter 16. Specifically, the specific technical parameter requirements of the narrowband filter 16 are: the central wavelength of the permeable infrared light is 4.705μm±0.095μm, the infrared light transmittance at the central wavelength is greater than or equal to 30%, and the half-height width is not greater than 0.25um.

[0137] Specifically, the infrared generator is arranged on the top of the infrared air chamber body 10 and light penetration is achieved between the infrared generator and the infrared air chamber body 10 through a transparent glass 15 , and the infrared detector 17 is arranged at the bottom of the infrared air chamber body 10 .

[0138] Specifically, the infrared generator includes: a closed shell, a modulation wheel drive motor 12 arranged outside the closed shell, and an infrared light source 13, a gas filter modulation wheel 11 including a nitrogen cavity and a CO cavity, and an optical coupler 14 for sensing the modulation frequency, which are arranged inside the closed shell; the drive motor 12 is connected to the modulation wheel 11 to drive the modulation wheel 11 to rotate.

[0139] The nitrogen chamber of the gas filter modulation wheel 11 is filled with high-purity nitrogen, and the CO chamber is filled with carbon monoxide with a concentration higher than 30% (the rest of the gas is nitrogen). In this embodiment, the gas in the CO chamber is 100% carbon monoxide.

[0140] Specifically, the optical system further includes an incident light reflector 31, an outgoing light reflector 32, a first concave mirror 41, a second concave mirror 42, and a third concave mirror 43. The incident light reflector 31 is arranged directly below the light-transmitting glass 15, the outgoing light reflector 32 is arranged directly above the narrow-band filter 16, the first concave mirror 41 is arranged on the first side wall of the infrared air chamber body 10, the second concave mirror 42 and the third concave mirror 43 are arranged on the second side wall of the infrared air chamber body 10 and are arranged side by side up and down, the center height of the first concave mirror 41 is consistent with the height of the midline of the second concave mirror 42 and the third concave mirror 43, the first side wall and the second side wall are two side walls of the infrared air chamber body 10 that face each other, as shown in FIG. Figure 2 The infrared light enters the infrared air chamber body 10 through the transparent glass 15, and then is reflected several times by the incident light reflector 31, the second concave mirror 42, the first concave mirror 41, the third concave mirror 43, and the outgoing light reflector 35, and then filtered by the narrow-band filter 4 and received by the infrared sensor 5.

[0141] The working principle of measuring the CO test level in this embodiment is: during the test, when the infrared light passes through the nitrogen cavity of the modulation wheel 11, the segment light of the infrared light that can be absorbed by CO will not be absorbed by the nitrogen in the nitrogen cavity. At this time, the infrared light passing through the nitrogen cavity is used as the test light; at the same time, when the infrared light passes through the CO cavity of the modulation wheel 11, the segment light of the infrared light that can be absorbed by CO will be absorbed by the CO in the CO cavity. At this time, the mid-infrared light passing through the CO cavity is used as the reference light. After passing through the modulation wheel 11, the light is incident into the infrared gas chamber body 10 through the light-transmitting glass 15, reaches the incident light reflector 31, and then reflects to the second concave mirror 42, continues to reflect to reach the first concave mirror 41, and then continues to reflect to the third concave mirror 43, and then continues to reflect to the outgoing light reflector 32, and then is filtered by the narrow-band filter 16 and received by the infrared sensor 17, and a voltage value related to the CO concentration in the gas pool is obtained. This CO test level acquisition scheme is different from the existing CO test level acquisition scheme, and it further solves the defect that the CO2 in the exhaled breath must be removed before testing in the existing scheme.

[0142] The CO2 level test is an existing technology and will not be described in detail here. After the CO2 level and the CO test level are obtained through testing, the method of the first embodiment can be used to obtain the trace CO concentration in the alveolar gas.

[0143] In summary, the measurement method and system for eliminating the interference of CO2 in a gas sample on the measurement of CO concentration of the present invention have the following beneficial effects: the present invention does not directly obtain the CO concentration by converting the CO test level, but obtains the CO2 concentration by using the measured CO2 level, and then obtains the CO correction level, and then obtains the CO level of the exhaled breath and the ambient background gas according to the CO test level and the obtained CO correction level. The CO level is calibrated, so based on the calibrated CO level, the obtained CO concentration is more accurate, and the influence of the high concentration of CO2 in the exhaled breath on the measurement of the trace CO concentration is effectively eliminated, and the difficulty of removing CO2 before measuring the trace CO in the exhaled breath by using the infrared spectroscopy method is overcome, and the problem of having to remove CO2 when measuring CO containing a higher concentration of CO2 by the infrared spectroscopy method is perfectly solved.

[0144] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for eliminating the interference of CO2 in a gas sample on the measurement of CO concentration, characterized in that: The method comprises the following steps: Step 1: According to the measured CO2 level of the gas sample, the CO2 concentration of the gas sample is obtained by using a pre-established first standard curve of CO2 level and CO2 concentration; Step 2: According to the CO2 concentration of the gas sample, the CO correction level of the gas sample is obtained by using a pre-established second standard curve of CO correction level and CO2 concentration; Step 3: Add the CO test level of the gas sample measured to the CO correction level of the gas sample obtained in step 2 to obtain the CO level of the gas sample; Step 4: according to the obtained CO level of the gas sample, the CO concentration of the gas sample is obtained by using a pre-established third standard curve of CO level and CO concentration; The first standard curve is obtained by the following experimental method: inserting a high concentration of CO2 standard gas into the air inlet of the measurement system, cleaning the air chamber, and measuring the actual CO2 level value P before and after the air intake. 1-CO2 and P 2-CO2 , P 2-CO2 Subtract P 1-CO2 Get the net value of CO2 level after deducting the background P (2-1)-CO2 As the CO2 level of the CO2 standard gas with a higher concentration; insert the CO2 standard gas with a lower concentration into the air inlet of the measurement system, clean the air chamber, and measure the CO2 level before and after the air intake to obtain the actual value P 3-CO2 and P 4-CO2 , P 4-CO2 Subtract P 3-CO2 Get the net value of CO2 level after deducting the background P (4-3)-CO2 As the CO2 level of the CO2 standard gas with a lower concentration; according to P (2-1)-CO2 , P (4-3)-CO2 and the CO2 concentration of the CO2 standard gas corresponding to each of them, and fitting to obtain the first standard curve; The second standard curve is obtained by the following experimental method: inserting a mixed standard gas of CO2 and CO with a high CO2 concentration into the air inlet of the measurement system, cleaning the air chamber, and measuring the actual value P of the CO test level before and after the air intake. 5-CO and P 6-CO , P 6-CO Subtract P 5-CO Get the CO test level net value P (6-5)-CO The CO test level of the standard gas of the CO2 and CO mixed standard gas with a higher CO2 concentration; insert the CO2 and CO mixed standard gas with a lower CO2 concentration into the air inlet of the measurement system, clean the air chamber, and measure the CO level before and after the air intake to obtain the actual value P 7-CO and P 8-CO , P 8-CO Subtract P 7-CO Get the CO test level net value P (8-7)-CO The CO test level of the standard gas of the CO2 and CO mixed standard gas with a lower CO2 concentration; according to the known CO concentration values ​​of the two mixed standard gases with higher and lower CO2 concentrations, the third standard curve is checked to obtain the CO level theoretical value P of the mixed standard gas with a higher CO2 concentration (6-5)’-CO The theoretical value of CO level P of the mixed standard gas with a lower CO2 concentration (8-7)’-CO ; P (6-5)’-CO Subtract P (6-5)-CO Get the CO correction level P of the mixed standard gas with a higher CO2 concentration 校1-CO , P (8-7) ’ -CO Subtract P (8-7)-CO Get the CO correction level P of the mixed standard gas with lower CO2 concentration 校2-CO According to P 校1-CO and P 校2-CO and their corresponding CO2 concentrations, and fitted to obtain the second standard curve; The third standard curve is obtained by the following experimental method: inserting a high concentration of CO standard gas into the air inlet of the measurement system, cleaning the air chamber, and measuring the actual CO level value P before and after the air intake. 1-CO and P 2-CO , P 2-CO Subtract P 1-CO Get the net value of CO level after deducting the background value P (2-1)-CO As the CO level of the CO standard gas with a higher concentration; insert the CO standard gas with a lower concentration into the air inlet of the measurement system, clean the gas chamber, and measure the CO level before and after the air intake to obtain the actual value P 3-CO and P 4-CO , P 4-CO Subtract P 3-CO Get the net value of CO level after deducting the background value P (4-3)-CO The CO level of the CO standard gas with a lower concentration; according to the CO level P (2-1)-CO and CO level P (4-3)-CO and the CO concentration of their respective corresponding CO standard gases, and the third standard curve is obtained by fitting.

2. The method according to claim 1, characterized in that The method further comprises: The exhaled air and the ambient background gas are respectively used as the gas samples and the CO concentrations in the exhaled air and the ambient background gas are measured through the steps 1 to 4 respectively. The endogenous CO concentration in the exhaled air is obtained by subtracting the CO concentration in the ambient background gas from the CO concentration in the exhaled air.

3. The method according to claim 2, characterized in that The method further comprises: Collect the subject's exhaled breath and the ambient air of the place where the subject was before the exhaled breath was collected; Insert the collected exhaled air into the air inlet of the measurement system, and after sampling according to the set sampling method, measure the CO2 level and CO test level in the exhaled air respectively; Insert the collected ambient background gas into the air inlet of the measurement system. After sampling according to the set sampling method, measure the CO2 level and CO test level in the ambient background gas respectively.

4. The method according to claim 1, characterized in that: The method further includes: when the intercept of the fitted second standard curve is not zero, correcting the second standard curve by the following method: A mixed standard gas of CO2 and CO with different CO2 concentrations is used as the sample gas, and the known CO concentration value of the sample gas is the nominal value; The sample gases are measured in order of CO2 concentration from high to low, and the CO concentration values ​​of the sample gases are obtained by executing the steps 1 to 4 as experimental measurement values. When the difference between the experimental measurement value of a certain sample gas and the nominal value reaches a preset upper limit of the deviation allowable value, the CO2 concentration corresponding to the sample gas is used as the CO2 concentration lower limit to be found; Connect the coordinates formed by the CO2 concentration lower limit value and the CO correction level queried on the second standard curve whose intercept is not zero according to the CO2 concentration lower limit value and the coordinate origin, and use this connecting line to replace the section from the CO2 concentration lower limit value to the CO2 concentration zero of the fitted second standard curve whose intercept is not zero, so as to obtain a corrected second standard curve applicable to all CO2 concentration values.

5. The method according to claim 1, characterized in that The method further comprises: the sampling mode of the measuring system during measurement comprises: negative pressure sampling, or / and direct sampling by air pump, or / and sampling by air cylinder; The negative pressure injection specifically comprises: The measuring gas chamber is vacuumed according to a set vacuuming treatment mode, so that the pressure in the measuring gas chamber reaches a set pressure threshold before sampling, wherein: the pressure threshold before sampling is less than the atmospheric pressure, and the vacuuming treatment mode includes directly vacuuming the measuring gas chamber and cleaning the measuring gas chamber once or multiple times before vacuuming; Perform one or more injections according to the set injection times, wherein each injection is based on the internal and external pressure difference of the measuring chamber formed by vacuuming, so that the sample to be tested connected to the air inlet end of the measuring chamber automatically enters the measuring chamber.

6. A measurement system for eliminating the interference of CO2 in a gas sample on the measurement of CO concentration, characterized in that: The system comprises a CO measuring gas chamber that meets specific technical parameter requirements, a CO2 measuring gas chamber, a sampling unit, a cleaning unit, and a main control unit that performs the measurement method according to any one of claims 1 to 5; The CO measurement chamber comprises an optical path system, and the optical path system comprises a narrowband filter (16). The specific technical parameter requirements of the narrowband filter (16) are as follows: the central wavelength of the permeable infrared light is 4.705 μm±0.095 μm, the infrared light transmittance at the central wavelength is greater than or equal to 30%, and the half-height width is not greater than 0.25 μm.

7. The system according to claim 6, characterized in that The CO measurement chamber further comprises: an infrared chamber body (10), an infrared generator and an infrared detector (17) arranged on the infrared chamber body (10); the optical path system is arranged between the infrared generator and the infrared detector (17), and the infrared light emitted by the infrared generator passes through the optical path system and is detected by the infrared detector (17); A constant temperature module is provided in the infrared detector, the narrow-band filter (16) is provided at any position on the optical path between the infrared light source (13) and the infrared detector (17), and the infrared detector (17) detects light passing through the narrow-band filter (16).

Images