Gas concentration measuring device based on single mode and single optical fiber

Abstract

The invention relates to a gas concentration measuring device based on a single mode and a single optical fiber, which comprises a laser transmitter, an optical fiber collimator, a detector, an optical circulator and a multi-reflection measuring cell, the optical circulator comprises three circulators and three corresponding ports, one end of the circulator I is connected with a port I through a single optical fiber, and the other end of the circulator II is connected with a port II through a single optical fiber. Two optical fibers are separated from the other end of the circulator I and are respectively connected with a circulator II and a circulator III, the circulator II and the circulator III are respectively connected with a port II and a port III, the port I is connected with an optical fiber collimator, the port II is connected with a laser transmitter, the port III is connected with a detector, and the optical fiber collimator is connected to a light ray inlet of a multi-reflection measuring cell. According to the invention, a long optical path can be realized through the small-size measuring cell, the optical path is easy to adjust and control, the mirror surface utilization rate is high, installation and adjustment are easy, and the measuring precision is high.

Description

Technical Field

[0001] The invention relates to a gas concentration measuring device, in particular to a gas concentration measuring device based on a single mode and a single optical fiber, and belongs to the technical field of environmental detection. Background Art

[0002] Laser absorption spectroscopy technology has the advantages of high sensitivity, high resolution, non-contact and real-time performance. It is widely used in the field of gas concentration measurement. Its principle is to identify molecules and determine the concentration of absorbing substances by measuring the absorption spectrum of molecules on a given optical path.

[0003] The traditional optical method for measuring gas concentration is the one-way direct absorption method. This method can only achieve the purpose of gas detection by setting a longer optical path. However, in practical applications, it is usually limited by the installation space and the size of the instrument and equipment, and it is impossible to set a longer optical path. In order to solve this problem, the prior art uses multiple reflection technology to achieve a longer optical path in a smaller volume space. Currently, the commonly used multi-path absorption measurement cell structures include the White cell and the Herriott cell. The White cell is usually composed of three concave reflectors. After the light source enters the measurement cell from the emission hole, it is reflected multiple times by the three reflectors and then emitted from the exit hole. Even light with a large divergence angle can be reflected, but because it is a multi-reflector structure, the optical path adjustment process is more complicated to operate and the mirror utilization rate is relatively low; the Herriott cell is usually composed of two concave reflectors. The light source is generally a laser with high collimation. The laser enters from a small hole on a reflector and exits from another small hole after reflecting a certain number of times. The position and angle of the incident light are changed by adjusting the collimator adjustment frame to observe the reflected light spots on the two concave reflectors, and the number of reflections and the optical path length are calculated based on the reflected light spots. The structure is simple and the optical path is easier to adjust and control. However, it often requires high collimation of the light source and the angle of the incident light to be set in advance to prevent the incident light from overlapping with the outgoing light. Therefore, the optical path design and the collimation of the laser are relatively strict. The spatial volume of the White Pool and the Herriott Pool is relatively large. When detecting some special gases, the gas response time is very long due to the large gas adsorption characteristics. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a gas concentration measuring device based on a single mode and a single optical fiber, which can realize a long optical path through a small volume measuring cell, and the optical path is easy to adjust and control, the mirror utilization rate is high, the installation and adjustment are easy, the measurement accuracy is high, and the gas response time is short.

[0005] A gas concentration measuring device based on a single mode and a single optical fiber comprises a laser transmitter, an optical fiber collimator, a detector, an optical circulator, and a multiple reflection measuring cell, wherein the optical circulator comprises three circulators and corresponding three ports, one end of the circulator I is connected to the port I through a single optical fiber, two optical fibers are separated from the other end of the circulator I and are respectively connected to the circulator II and the circulator III, the circulator II and the circulator III are respectively connected to the port II and the port III, the port I is connected to the optical fiber collimator, the port II is connected to the laser transmitter, the port III is connected to the detector, and the optical fiber collimator is connected to the light entrance of the multiple reflection measuring cell.

[0006] Furthermore, a reflector I and a reflector II are respectively installed on the inner walls at both ends of the multiple reflection measurement cell. Reflector I is a plane reflector and is arranged at one end of the light entrance. Reflector II is a concave reflector and is arranged at the other end opposite to the light entrance. The mirror size of reflector I is smaller than the mirror size of reflector II.

[0007] Furthermore, the incident angle of the laser beam is 0°, and after 8 reflections by the reflector I and the reflector II, the laser beam returns to the fiber collimator along the original path, and is emitted from the port III to the detector under the action of the optical circulator.

[0008] Furthermore, the multiple reflection measuring cell is made of smooth quartz.

[0009] Furthermore, the volume of the multiple reflection measurement cell is less than 15 cm 3 , the area of ​​the reflector is less than 1cm 2 .

[0010] The single-mode, single-fiber gas concentration measuring device provided by the present invention has the following advantages:

[0011] 1) Using an optical circulator to separate the incident light and the outgoing light, a longer optical path can be achieved in a multi-reflection measurement cell with a very small volume;

[0012] 2) The multiple reflection measurement cell is compact and can be used in conjunction with an optical circulator. It uses only two reflectors to achieve a fixed number of reflection light paths, and can calculate the optical path length without frequently adjusting the angle and position of the incident light.

[0013] 3) The multiple reflection measurement cell is made of quartz material with a smooth inner wall surface, which can reduce gas adsorption, reduce ventilation time, have high space utilization, and save gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of the structure of a gas concentration measurement device based on a single mode and a single optical fiber provided by the present invention;

[0015] Figure 2for Figure 1 Schematic diagram of the structure of the multiple reflection measurement cell;

[0016] Figure 3 This is a schematic diagram of the optical path principle of multiple reflections in a multiple reflection measurement cell;

[0017] In the figure: 1. laser transmitter; 2. optical fiber collimator; 3. detector; 4. optical circulator; 4.1. circulator I; 4.2. port I; 4.3. circulator II; 4.4. circulator III; 4.5. port II; 4.6. port III; 5. multiple reflection measurement cell; 5.1. light inlet; 5.2. reflector I; 5.3. reflector II; 5.4. air inlet; 5.5. air outlet. DETAILED DESCRIPTION

[0018] In order to explain the present invention more clearly, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0019] like Figure 1 and Figure 2 As shown, a gas concentration measuring device based on a single mode and a single optical fiber comprises a laser transmitter 1, a fiber collimator 2, a detector 3, an optical circulator 4 and a multiple reflection measuring cell 5. The optical circulator 4 comprises three circulators and corresponding three ports. One end of the circulator I4.1 is connected to the port I4.2 through a single optical fiber. Two optical fibers are separated from the other end of the circulator I4.1 and are respectively connected to the circulator II4.3 and the circulator III4.4. The circulator II4.3 and the circulator III4.4 are respectively connected to the port II4.5 and the port III4.6. The port I4.2 is connected to the fiber collimator 2, the port II4.5 is connected to the laser transmitter 1, the port III4.6 is connected to the detector 3, and the fiber collimator 2 is connected to the light inlet 5.1 of the multiple reflection measuring cell 5.

[0020] The laser transmitter 1 is used to output a laser beam of a specific wavelength, the fiber collimator 2 is used to convert the transmission light in the optical fiber into collimated light, the optical circulator 4 is used to separate the incident light and the outgoing light, the detector 3 is used to capture the outgoing light signal, and the multiple reflection measurement cell 5 is used to achieve a longer optical path in a very small volume space through multiple reflection technology.

[0021] Specifically, the light emitted by the laser transmitter 1 passes through the optical circulator 4 and the optical fiber collimator 2 in turn, enters the multiple reflection measuring cell 5, and returns from the light inlet 5.1 again after multiple reflections in the measuring cell. The circulator is an irreversible device. The light can be transmitted from port II4.5 to port I4.2 with low loss, but when the light enters port II4.5 from port I4.2, a large loss will be generated. Similarly, the light can be transmitted from port I4.2 to port III4.6 with low loss, but when the light enters port I4.2 from port III4.6, a large loss will be generated. Therefore, under the action of the optical circulator, the incident light and the outgoing light can be separated, and the light is captured by the detector when it returns, and the gas concentration is analyzed by the gas analyzer after photoelectric conversion.

[0022] like Figure 2 As shown, a reflector I5.2 and a reflector II5.3 are respectively installed on the inner walls at both ends of the multiple reflection measurement cell 5. The reflector I5.2 is a plane reflector and is arranged at one end of the light entrance 5.1. The reflector II5.3 is a concave reflector and is arranged at the other end opposite to the light entrance 5.1. The mirror size of the reflector I5.2 is smaller than the mirror size of the reflector II5.3, so that the laser entering through the light entrance 5.1 can be directly projected onto the reflector II5.3.

[0023] The incident angle of the laser beam is 0°, and after 8 reflections by the reflector I5.2 and the reflector II5.3, it returns to the fiber collimator 2 along the original path, and is emitted from the port III4.6 to the detector 3 under the action of the optical circulator 4. Figure 3 As shown, the multiple reflection measuring cell 5 provided by the present invention has an incident angle of 0° for the laser, that is, the light beam is incident vertically into the multiple reflection measuring cell, and the gas to be measured is introduced into the multiple reflection measuring cell 5 through the air inlet 5.4. The light beam passes through the gas to be measured and is transmitted to position ① of the reflector II5.3, and then, under the action of the reflector I5.2 and the reflector II5.3, the light beam is transmitted in sequence along the route of ①→②→③→④→③→②→① and is received by the optical fiber collimator 2. The number of reflections is fixed and the reflection route is the original return route. Therefore, there is no need to observe the reflected light spot on the reflector and calculate the number of reflections by changing the position and angle of the incident light. Under the action of the optical circulator 4, the incident light and the outgoing light overlap without affecting the measurement data. The structure is simple, easy to use, and the measurement data is accurate.

[0024] The multiple reflection measuring cell 5 is made of smooth quartz. The inner wall smoothness of the quartz measuring cell can reach 16 microns, so it can reduce the adsorption of gas. For example, when measuring hydrogen chloride gas, due to its high adsorption, it takes a long time to pass the gas to reach a measurable concentration. The use of a small-sized quartz measuring cell with a smooth inner wall and a small surface area can reduce adsorption, that is, it can reduce the ventilation time, high space utilization, and save gas.

[0025] The volume of the multiple reflection measuring cell 5 is less than 15 cm 3 , the area of ​​the reflector is less than 1 cm. For example, in this embodiment, the size of the multiple reflection measuring cell 5 is 10 mm*5 mm*257 mm (width*height*length), and a 2 m optical path can be obtained through multiple reflections, so that a small-sized measuring cell can achieve high-precision measurement. Since the incident light and the reflected light coincide, and only two reflectors are used, the size of the reflector can be small, and the width can be narrower than that of the previous multiple reflection measuring cell, so the application range is wide and the measurement accuracy is high.

[0026] Those skilled in the art should understand that, in the description of the present invention, it is necessary to understand that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0027] In the present invention, unless otherwise clearly stipulated and limited, for example, it can be a fixed connection, a detachable connection, or an integrated one; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. Unless otherwise clearly defined, for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0028] Specific embodiments are used in the present invention to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. For ordinary technicians in this field, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A gas concentration measurement device based on a single mode and single optical fiber, comprising a laser transmitter, an optical fiber collimator, a detector, and a multiple reflection measurement cell, characterized in that: It also includes an optical circulator, which includes three circulators and corresponding three ports. One end of circulator I is connected to port I through a single optical fiber, and two optical fibers are separated from the other end of circulator I and respectively connected to circulator II and circulator III. Circulator II and circulator III are respectively connected to port II and port III. Port I is connected to a fiber collimator, port II is connected to a laser transmitter, port III is connected to a detector, and the fiber collimator is connected to the light entrance of a multiple reflection measurement cell.

2. The gas concentration measurement device based on single mode and single optical fiber according to claim 1 is characterized in that: Reflector I and reflector II are respectively installed on the inner walls at both ends of the multiple reflection measurement cell. Reflector I is a plane reflector and is arranged at one end of the light entrance. Reflector II is a concave reflector and is arranged at the other end opposite to the light entrance. The mirror size of reflector I is smaller than the mirror size of reflector II.

3. The gas concentration measurement device based on single mode and single optical fiber according to claim 2, characterized in that: The incident angle of the laser beam is 0°, and after 8 reflections from the reflector I and the reflector II, it returns to the fiber collimator along the original path, and is emitted from the port III to the detector under the action of the optical circulator.

4. The gas concentration measurement device based on single mode and single optical fiber according to claim 1, characterized in that: The multiple reflection measuring cell is made of smooth quartz.

5. The gas concentration measurement device based on single mode and single optical fiber according to any one of claims 1 to 4, characterized in that: The volume of the multiple reflection measurement cell is less than 15 cm 3 , the area of ​​the reflector is less than 1cm 2 .

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