Detection unit of adjustable four-range absorption cell

Abstract

The invention belongs to the technical field of detection instruments. The invention provides a detection unit capable of adjusting the optical path of an absorption cell. The detection unit comprises a light source, a detector, the absorption cell, a to-be-detected substance inlet, a substrate substance inlet, a first discharged substance outlet, a first two-way valve, a second discharged substance outlet, a third discharged substance outlet, a third two-way valve, a fourth discharged substance outlet, a fourth two-way valve, a three-way valve and a substrate substance pipe, a light source and a detector are arranged at two ends of the absorption cell; the to-be-detected substance inlet and the substrate substance outlet are respectively arranged at two ends of the absorption cell; the first discharged substance outlet is formed between the to-be-detected substance inlet and the substrate substance outlet; the first discharged substance outlet is provided with a two-way valve; a three-way valve is arranged at the substrate material inlet. The detection unit has the advantages of being simple in structure, good in repeatability, high in reliability, low in cost, free and rapid in multi-optical-path switching and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of detection instruments, and in particular to the technical field of automatically adjusting the thickness of an effective absorption layer of an absorption cell to achieve detection of a wide concentration range of a substance to be detected. Background Art

[0002] Existing detection instruments usually use fixed-length absorption cells, that is, the thickness of the absorption layer cannot be adjusted after the equipment is manufactured. This will result in the instrument being unable to simultaneously take into account the measurement needs of the same substance to be tested under high and low concentration conditions, or the simultaneous measurement of multiple mixed substances to be tested with large absorbance differences.

[0003] In response to this problem, some absorption cell solutions capable of adjusting the optical path (absorption thickness) are disclosed in the prior art, which can be roughly divided into three categories: the first category is a device with a motion mechanism, which realizes optical path adjustment by controlling the relative position change of the cavity mirror and the cavity, such as patent CN103163641B discloses a device for realizing multi-optical path changes by rotating an angle mirror; patent CN111982817B discloses a device for realizing optical path adjustment by rotating a cavity; the second category is a device without a motion mechanism, which realizes optical path adjustment by increasing the number of light sources and detectors or adopting crystal optical technology, by reusing some gas cells or using electro-induced or polarization principles to change the propagation direction of the optical path, such as patent CN108732130B discloses a method for increasing the optical path by using a polarization device; the third category is to connect multiple gas cells in series, and realize optical path adjustment by manual or automatic gas path or optical path switching, such as patent CN111077083A discloses a multi-gas cell detection structure, and selects the gas cell by switching the reversing valve to realize optical path adjustment. The first type has a motion mechanism. The vibration and wear caused by the adjustment process and the slight difference in the posture of the optical element in each adjustment will lead to deviations in the optical detection results. At the same time, this type of motion mechanism has problems with service life and switching speed, which makes it difficult to meet the fast and frequent switching requirements of many industrial sites. Although the second type does not have a motion mechanism, the various optical components added are costly and complex in structure, and the debugging difficulty is relatively large; more importantly, the measurement accuracy is related to the stability of the light source intensity and the detector response. The consistency between the multi-channel light source and the detector and its consistency with the changing trend of the external environment will directly affect the performance of the instrument. Therefore, this type of solution not only adds hardware components, but also adds a lot of testing, calibration and control work. The third type of solution is simpler in structure than the first two. There is no motion mechanism and no complex optical path structure. However, the use of multiple gas pools increases the difficulty of assembly and debugging, and also doubles the number of windows on the detection path. The increase in the number of windows will greatly reduce the transmittance of the detection light, especially when the substance to be tested is polluting or corrosive, its impact on the optical path will increase exponentially. In addition, the optical path length adjustment ratio that can be achieved by this method is determined after the structure is fixed, and it cannot be flexibly adjusted in actual application. Summary of the invention

[0004] In view of this, the present invention provides a detection unit of an adjustable four-range absorption cell, comprising: a light source, a detector, an absorption cell, an inlet for a substance to be measured, an inlet for a substrate substance, a first outlet for discharged substance, a first two-way valve, a second outlet for discharged substance, a third outlet for discharged substance, a third two-way valve, a fourth outlet for discharged substance, a fourth two-way valve, a three-way valve, and a substrate substance tube; the absorption cell is an absorption cell without a reentrant light path; the light source and the detector are arranged near the absorption cell, and the detector is arranged at the place where the detection light emits from the absorption cell so as to detect the emitted detection light most efficiently; the inlet for the substance to be measured and the outlet for the substrate substance are respectively arranged at both ends of the absorption cell and leave no dead volume as much as possible; the first outlet for discharged substance is arranged between the inlet for the substance to be measured and the outlet for the substrate substance; the first outlet for discharged substance is provided with a first two-way valve; the inlet for the substrate substance is provided with a three-way valve, and the inlet for the substrate substance is connected to the first interface of the three-way valve; the second interface of the three-way valve is connected to the substrate substance tube; the third interface of the three-way valve is connected to the second outlet for discharged substance.

[0005] In a specific embodiment of the present invention, the positions of the light source and the detector can be interchanged.

[0006] In a specific embodiment of the present invention, the first outlet for discharging substances is arranged at a distance of one quarter of the physical length of the absorption cell from the inlet for the substance to be detected.

[0007] In a specific embodiment of the present invention, the flow direction of the substance to be detected in the absorption cell is consistent with or opposite to the propagation direction of the detection light.

[0008] In a specific embodiment of the present invention, the third outlet for discharging substances is arranged at a distance from the inlet of the substance to be detected which is half the physical length of the absorption cell.

[0009] In a specific embodiment of the present invention, the fourth outlet for discharging substances is arranged at a distance of three quarters of the physical length of the absorption cell from the inlet for the substance to be detected.

[0010] In a specific embodiment of the present invention, the detection unit of the adjustable four-range absorption cell further includes: a control module, and the control module is respectively connected to the two-way valve, the three-way valve and the detector through lines or signals.

[0011] The present invention also provides a method for measuring the concentration of a substance to be measured by the detection unit of the adjustable four-range absorption cell, comprising the following steps: determining a measurement method of a low sensitivity range, a first medium sensitivity range, a second medium sensitivity range or a high sensitivity range according to the concentration of the substance to be measured;

[0012] The low-sensitivity range measurement method comprises the following steps: the first two-way valve is opened, the third and fourth two-way valves are closed, and the first interface and the second interface of the three-way valve are connected; the substance to be measured enters the absorption cell from the substance to be measured inlet, and the substrate substance enters the absorption cell after passing through the second interface and the first interface of the three-way valve; the substance to be measured and the substrate substance are both discharged from the first discharge material outlet; the detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured;

[0013] The measurement method of the first sensitivity range comprises the following steps: the third two-way valve is opened, the first and fourth two-way valves are closed, and the first interface and the second interface of the three-way valve are connected; the substance to be measured enters the absorption cell from the substance to be measured inlet, and the substrate substance enters the absorption cell after passing through the second interface and the first interface of the three-way valve; the substance to be measured and the substrate substance are both discharged from the third discharge material outlet; the detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured;

[0014] The measurement method of the second sensitivity range comprises the following steps: the fourth two-way valve is opened, the first and third two-way valves are closed, and the first interface and the second interface of the three-way valve are connected; the substance to be measured enters the absorption cell from the substance to be measured inlet, and the substrate substance enters the absorption cell after passing through the second interface and the first interface of the three-way valve; the substance to be measured and the substrate substance are both discharged from the fourth discharge material outlet; the detector detects the light signal intensity signal in the absorption cell and calculates the concentration of the substance to be measured;

[0015] The high-sensitivity range measurement method comprises the following steps: all two-way valves are closed, and the first interface and the third interface of the three-way valve are connected; the substance to be measured enters the absorption cell from the substance to be measured inlet, and enters from the substrate material inlet and then passes through the first interface, the third interface, and the second discharge material outlet of the three-way valve before being discharged from the absorption cell; the detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured.

[0016] The detection unit provided by the present invention has the advantages of simple structure, good repeatability, high reliability, low cost, free and rapid switching of multiple optical paths, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural diagram of the detection unit of the adjustable four-range absorption cell.

[0018] Among them, 1 is the light source, 2 is the detector, 3 is the absorption cell, 4 is the inlet of the substance to be tested, 5 is the inlet of the substrate substance, 6 is the three-way valve, 7 is the first discharge material outlet, 8 is the first two-way valve, 9 is the second discharge material outlet, 10 is the substrate material tube, 11 is the third discharge material outlet, 12 is the third two-way valve, 13 is the fourth discharge material outlet, and 14 is the fourth two-way valve. DETAILED DESCRIPTION

[0019] Lambert-Beer law: also known as Beer's law, Beer's law, Beer-Lambert law, Bouguer-Lambert-Beer law, is the basic law of light absorption, applicable to all electromagnetic radiation and all light-absorbing substances, including gases, solids, liquids, molecules, atoms and ions. Lambert-Beer law means that the amount of light absorbed is proportional to the number of molecules that produce light absorption in the light path. The physical meaning is that when a beam of parallel monochromatic light passes vertically through a uniform non-scattering light-absorbing substance, its absorbance A is proportional to the concentration c of the light-absorbing substance and the thickness b of the absorption layer, and is inversely correlated with the transmittance T.

[0020] Substance to be tested: refers to the target substance to be tested that needs to be measured in the substance entering the detection and analysis unit. Its form includes but is not limited to gas, liquid and multi-form mixture, and its material composition includes but is not limited to single substance and mixed substance.

[0021] Base material: refers to background material that has no response within the detector measurement range or does not interfere with the detection of the substance to be measured. Its form includes but is not limited to gas, liquid and multi-form mixture, and its material composition includes but is not limited to single substance and mixed substance.

[0022] Absorption cell: refers to the part in the detection and analysis unit used to carry substances and perform detection and analysis. Both ends are usually provided with light-transmitting components such as windows and lenses to allow the detection light to pass through. In order to achieve wide-range detection, the absorption cell in this patent specifically refers to an absorption cell whose structure can satisfy that the flow path of the substance to be detected is consistent with or opposite to the propagation path of the detection light; that is, the absorption cell can be an extension of a straight-through cell or a multiple-return cell.

[0023] Optical path: In this patent, the optical path represents the propagation distance of the detection light emitted by the light source in the absorption cell. For a straight-through absorption cell, the optical path is basically equivalent to the physical length L inside the absorption cell; for a return absorption cell, if the number of returns is n, the optical path is approximately equal to (n+1)*L.

[0024] Effective optical path: It represents the distance that the detection light emitted by the light source interacts with the substance to be tested when propagating in the absorption cell. This distance is related to the effective outlet position of the discharged substance in the absorption cell.

[0025] Range: The concentration range of the substance to be tested that can be measured based on the current effective optical path. By switching different outlets for discharging substances, the effective optical path of the absorption cell can be changed, thereby achieving the range switching of the detection unit.

[0026] Example

[0027] The present invention proposes a simpler detection unit for adjusting the optical path of the absorption cell. The absorption cell in the unit has no moving parts, does not require a complex optical structure, has a unique light source and detector, and a unique absorption cell. It is easy to assemble, simple to debug, and has low maintenance difficulty. At the same time, the absorption cell can be set with a variety of optical path adjustment ratios, and the ratios can be arbitrarily selected. In conjunction with the signal monitoring and valve control functions in the detection and analysis unit, it can achieve adaptive wide-range detection and analysis of the concentration of the substance to be tested.

[0028] The detection unit provided by the present invention can automatically adjust the thickness of the effective absorption layer of the absorption pool to achieve a wide concentration range of the substance to be detected. The detection unit is configured to set passages for the substance to be detected at different positions of the absorption pool, and control the flow direction of the substance to be detected and the proportion of the substance to be detected and the substrate in the absorption pool through valves to adjust the thickness of the absorption layer. Furthermore, without changing the detection and analysis unit, especially the structure of the absorption pool, the detection and analysis of the substance to be detected in a wide concentration range can be achieved.

[0029] The present invention provides a detection unit with adjustable optical path of an absorption cell, comprising a light source, a detector, an absorption cell, an inlet for a substance to be detected, an inlet for a substrate substance, a three-way valve, a first outlet for discharging substance, a first two-way valve, a second outlet for discharging substance, a substrate substance tube, a third outlet for discharging substance, a third two-way valve, a fourth outlet for discharging substance, and a fourth two-way valve.

[0030] The absorption cell is an absorption cell without a reversing light path. The propagation direction of the detection light in the absorption cell without a reversing light path is not changed at all.

[0031] The light source and the detector are arranged near the absorption pool, and the detector is arranged where the detection light is emitted from the absorption pool; the positions of the light source and the detector can be interchanged. The absorption pool is provided with a test substance inlet, a first discharge substance outlet, a third discharge substance inlet, a fourth discharge substance outlet and a substrate substance inlet from left to right.

[0032] The inlet for the substance to be tested and the outlet for the substrate substance are respectively arranged at the two ends of the absorption cell and no dead volume is left as much as possible, so as to fully utilize the length of the absorption cell and achieve the maximum optical path.

[0033] The first discharge material outlet, the third discharge material outlet and the fourth discharge material outlet are respectively arranged between the inlet of the substance to be measured and the outlet of the substrate material, so as to divide the optical path of the absorption cell into four different ranges; the first range is the distance between the first discharge material outlet and the inlet of the substance to be measured; the second range is the distance between the inlet of the substance to be measured and the third discharge material outlet; the third range is the distance between the inlet of the substance to be measured and the fourth discharge material outlet; the fourth range is the distance between the inlet of the substance to be measured and the inlet of the substrate material. The first discharge material outlet is provided with a first two-way valve to realize the conduction and closing of the pipeline; the third discharge material outlet is provided with a third two-way valve to realize the conduction and closing of the pipeline; the fourth discharge material outlet is provided with a fourth two-way valve to realize the conduction and closing of the pipeline.

[0034] The first outlet for discharged substances may be arranged between the inlet for the substance to be detected and the third outlet for discharged substances, preferably at a distance of one quarter of the physical length of the absorption cell from the inlet for the substance to be detected.

[0035] The third outlet for discharging substances may be arranged at a distance from the inlet for the substance to be detected that is two quarters of the physical length of the absorption cell.

[0036] The fourth outlet for discharging substances may be arranged at a distance from the inlet for the substance to be detected that is three quarters of the physical length of the absorption cell.

[0037] The substrate material inlet is provided with a three-way valve, the substrate material inlet is connected to the first interface of the three-way valve; the second interface of the three-way valve is connected to the substrate material pipe; the third interface of the three-way valve is connected to the second discharge material outlet.

[0038] The first two-way valve, the third two-way valve and the fourth two-way valve can be two-way valves that can be controlled to open or close by a circuit.

[0039] The three-way valve can be a three-way valve that can be controlled to open or close by a circuit.

[0040] The detection unit of the adjustable four-range absorption cell also includes a control module, which is respectively connected to the first two-way valve, the third two-way valve, the fourth two-way valve and the three-way valve through lines or signals; the control module is connected to the detector through lines or signals.

[0041] The absorption cell is an absorption cell in which the flow direction of the substance to be tested is consistent with or opposite to the propagation direction of the detection light; it can also be a gas cell with one or more return light paths built with optical elements with return functions such as reflectors and dove prisms.

[0042] Furthermore, by monitoring the detector signal, automatic control of valves and passages is achieved through a program, thereby realizing adaptive wide-range detection and analysis of the concentration of the substance to be measured.

[0043] The present invention proposes a detection unit of an adjustable four-range absorption cell, the structure of which is as follows: Figure 1 As shown. The detection light emitted by the light source passes through the absorption cell, interacts with the substance to be measured in the absorption cell, and then enters the detector. The detector can analyze the type and concentration of the substance to be measured by comparing the changes in the light signal when there is no substance to be measured and when there is a substance to be measured in the absorption cell. The control module analyzes the detector signal intensity in real time, and adaptively controls the first two-way valve, the third two-way valve, the fourth two-way valve and the three-way valve according to the instrument measurement requirements, adjusts the ratio of the substance to be measured and the substrate substance in the absorption cell, and changes the maximum absorption layer thickness to achieve the switching of the first range, the second range, the third range and the fourth range, thereby achieving the change of the measurement concentration range.

[0044] The method for measuring the concentration of a substance to be tested comprises the following steps:

[0045] A measurement method for determining a low sensitivity range, a first medium sensitivity range, a second medium sensitivity range or a high sensitivity range according to the concentration of the substance to be measured;

[0046] The low-sensitivity range measurement method comprises the following steps:

[0047] The first two-way valve is opened, the third two-way valve and the fourth two-way valve are closed, and the first interface and the second interface of the three-way valve are connected.

[0048] The substance to be tested enters the absorption cell from the substance to be tested inlet, and the substrate enters the absorption cell after passing through the second interface and the first interface of the three-way valve;

[0049] The substance to be tested and the substrate substance are both discharged from the first discharge outlet;

[0050] The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured.

[0051] The method for measuring the first sensitivity range comprises the following steps:

[0052] The first two-way valve and the fourth two-way valve are closed, the third two-way valve is opened, and the first interface and the second interface of the three-way valve are connected.

[0053] The substance to be tested enters the absorption cell from the substance to be tested inlet, and the substrate enters the absorption cell after passing through the second interface and the first interface of the three-way valve;

[0054] The substance to be tested and the substrate substance are both discharged from the third substance discharge outlet;

[0055] The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured.

[0056] The second sensitivity range measurement method comprises the following steps:

[0057] The first two-way valve and the third two-way valve are closed, the fourth two-way valve is opened, and the first interface and the second interface of the three-way valve are connected.

[0058] The substance to be tested enters the absorption cell from the substance to be tested inlet, and the substrate enters the absorption cell after passing through the second interface and the first interface of the three-way valve;

[0059] The substance to be tested and the substrate substance are both discharged from the fourth substance discharge outlet;

[0060] The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured.

[0061] The high-sensitivity range measurement method comprises the following steps:

[0062] The first two-way valve, the third two-way valve and the fourth two-way valve are closed, and the first interface and the third interface of the three-way valve are connected.

[0063] The substance to be tested enters the absorption pool from the substance to be tested inlet, and enters from the substrate inlet, passes through the first interface, the third interface, and the second discharge outlet of the three-way valve, and then is discharged from the absorption pool;

[0064] The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured.

[0065] For example, when the concentration of the substance to be tested is low and the sensitivity of the instrument needs to be improved, the control module can be used to connect the a and b ports of valve F1, close the c port, and close the three valves F2 at the same time, so that the detection and analysis unit is at the maximum optical path. In this way, the substance to be tested enters the absorption cell and is discharged from the device through the b port of valve F1. The substance to be tested fills the entire absorption cell. At this time, the thickness of the absorption layer is the largest and the sensitivity of the device is the highest. When the concentration of the substance to be tested is high and the absorption saturation causes the inability to measure normally, the control module can be used to connect the a and c ports of valve F1, close the b port, and open the first, second or third valve F2 at the same time, so that the detection and analysis unit is at the minimum optical path, the first medium optical path or the second medium optical path. In this way, the substance to be tested enters the absorption cell and is discharged from the analysis and detection unit through the first valve F2, the second valve F2 or the third valve F2. At the same time, the substrate substance enters the absorption cell through the port a of the valve F1 and is also discharged from the analysis and detection unit through the same valve F2. At this time, the substance to be tested and the substrate substance respectively fill the left half and the right half of the absorption cell bounded by the first valve F2, the second valve F2 or the third valve F2. Since the substrate substance has no effect on the substance to be tested, the thickness of the absorption layer is the left part of the first valve F2, the second valve F2 or the third valve F2. Therefore, the concentration of the substance that can be measured by the analysis and detection unit is increased, and the increase ratio is positively correlated to the ratio of the total volume of the absorption cell to the volume on the left side of the first valve F2, the second valve F2 or the third valve F2.

[0066] An adaptive wide-range detection and analysis unit proposed in the present invention can adjust the optical path by opening and closing valves at different positions on the absorption pool, thereby realizing wide-range measurement of the substance to be tested. At the same time, under the action of the control module, automatic adjustment of the detection range is realized, thereby fully meeting the rapid and accurate measurement of the substance to be tested under conditions of a wide range of concentration changes.

[0067] The present invention has the following characteristics: the optical-mechanical structure of the detection and analysis unit has no moving parts, good repeatability and strong reliability; the detection and analysis unit has a simple structure, no complex or expensive optical parts, and uses the same set of light sources and detectors for different optical path measurements, which is low in cost and good in stability. There is no need to consider the calibration problems caused by changing the light source or detector during the optical path switching process; the detection and analysis unit uses a single absorption cell, and no additional windows or optical elements are added to the detection path, so the detection flux is large and the anti-pollution ability is strong. At the same time, the minimum optical path or the medium optical path length can be adjusted by reserving the position of the valve, and the integration of more optical path lengths can be achieved by further increasing the number of exhaust ports and valves, and free and fast switching of multiple optical paths can be achieved under the action of the control module.

[0068] The detection and analysis unit proposed in the present invention can measure the forms of the substances to be tested, including but not limited to gas, liquid and multi-form mixtures, and its components include but are not limited to single substances and mixed substances (which can be used for wide range measurements of single substances and for simultaneous measurements of mixed substances with different absorption coefficients), and the injection methods include but are not limited to positive pressure injection and negative pressure injection.

Claims

1. The detection unit of the adjustable four-range absorption cell is characterized by: include: Light source, detector, absorption cell, inlet for substance to be tested, inlet for substrate substance, three-way valve, first outlet for discharged substance, first two-way valve, second outlet for discharged substance, substrate substance tube, third outlet for discharged substance, third two-way valve, fourth outlet for discharged substance, fourth two-way valve; The light source and the detector are arranged near the absorption pool; the detector is arranged at the place where the detection light is emitted from the absorption pool; the absorption pool is an absorption pool without a return light path; the absorption pool is provided with a test substance inlet, a first discharge substance outlet, a third discharge substance inlet, a fourth discharge substance outlet and a substrate substance inlet from left to right; The inlet for the substance to be tested and the outlet for the substrate substance are respectively arranged at two ends of the absorption cell; The first discharge material outlet, the third discharge material inlet and the fourth discharge material outlet are respectively arranged between the test material inlet and the substrate material outlet; the first discharge material outlet is provided with a first two-way valve; the third discharge material outlet is provided with a third two-way valve; the fourth discharge material outlet is provided with a fourth two-way valve; The substrate material inlet is provided with a three-way valve, the substrate material inlet is connected to the first interface of the three-way valve; the second interface of the three-way valve is connected to the substrate material pipe; the third interface of the three-way valve is connected to the second discharge material outlet.

2. The detection unit of the adjustable four-range absorption cell according to claim 1, characterized in that: The positions of the light source and the detector can be interchanged.

3. The detection unit of the adjustable four-range absorption cell according to claim 1, characterized in that: The first discharge material outlet is arranged between the test material inlet and the third discharge material inlet.

4. The detection unit of the adjustable four-range absorption cell according to claim 3, characterized in that: The first outlet for discharging substances is arranged at a distance of one quarter of the physical length of the absorption cell from the inlet for the substance to be detected.

5. The detection unit of the adjustable four-range absorption cell according to claim 1, characterized in that: The third outlet for discharging substances is arranged at a distance of two quarters of the physical length of the absorption cell from the inlet for the substance to be tested.

6. The detection unit of the adjustable four-range absorption cell according to claim 3, characterized in that: The fourth outlet for discharging substances is arranged at a distance of three quarters of the physical length of the absorption cell from the inlet for the substance to be detected.

7. The detection unit of the adjustable four-range absorption cell according to claim 1, characterized in that: The flow direction of the substance to be detected in the absorption cell is consistent with or opposite to the propagation direction of the detection light.

8. The detection unit of the adjustable four-range absorption cell according to claim 1, characterized in that: Also includes: A control module is respectively connected with the first two-way valve, the third two-way valve, the fourth two-way valve, the three-way valve and the detector through lines or signals.

9. A method for measuring the concentration of a substance to be tested by using a detection unit of an adjustable four-range absorption cell according to any one of claims 1 to 8, The method is characterized in that it comprises the following steps: A measurement method for determining a low sensitivity range, a first medium sensitivity range, a second medium sensitivity range or a high sensitivity range according to the concentration of the substance to be measured; The low-sensitivity range measurement method comprises the following steps: The first two-way valve is opened, the third two-way valve and the fourth two-way valve are closed, and the first interface and the second interface of the three-way valve are connected; The substance to be tested enters the absorption cell from the substance to be tested inlet, and the substrate enters the absorption cell after passing through the second interface and the first interface of the three-way valve; The substance to be tested and the substrate substance are both discharged from the first discharge outlet; The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured; The method for measuring the first sensitivity range comprises the following steps: The first two-way valve and the fourth two-way valve are closed, the third two-way valve is opened, and the first interface and the second interface of the three-way valve are connected. The substance to be tested enters the absorption cell from the substance to be tested inlet, and the substrate enters the absorption cell after passing through the second interface and the first interface of the three-way valve; The substance to be tested and the substrate substance are both discharged from the third substance discharge outlet; The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured; The second sensitivity range measurement method comprises the following steps: The first two-way valve and the third two-way valve are closed, the fourth two-way valve is opened, and the first interface and the second interface of the three-way valve are connected. The substance to be tested enters the absorption cell from the substance to be tested inlet, and the substrate enters the absorption cell after passing through the second interface and the first interface of the three-way valve; The substance to be tested and the substrate substance are both discharged from the fourth substance discharge outlet; The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured; The high-sensitivity range measurement method comprises the following steps: The two-way valves are all closed, and the first and third interfaces of the three-way valve are connected; The substance to be tested enters the absorption pool from the substance to be tested inlet, and enters from the substrate inlet, passes through the first interface, the third interface, and the second discharge outlet of the three-way valve, and then is discharged from the absorption pool; The detector detects the light signal in the absorption cell and calculates the concentration of the substance to be measured.

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