Laser Gas Analyzer

Abstract

To provide a laser gas analyzer with which it is possible to easily adjust the beam diameter of a laser beam in a light reception unit and adjust the incident angle of a laser beam to the light reception unit.SOLUTION: A laser gas analyzer 100 according to one embodiment of the present disclosure measures the concentration or the presence of a measurement object gas existing in a measurement object space. The laser gas analyzer 100 comprises: a wavelength-variable laser element 112 that emits laser light of a wavelength range including the light absorption wavelength of an absorption line spectrum of the measurement object gas; a movement mechanism 117 that cyclically moves the laser element 112 in a direction for changing the optical axis direction of the laser element 112; a light reception element 122 that receives the laser light having passed through the measurement object space; and a received light signal processing unit 121 that executes processing, including received light signal averaging processing, on the received light signal outputted from the light reception element 122, thereby determining the concentration or the presence / absence of the measurement object gas.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to laser-based gas analyzers. [Background technology]

[0002] Each gas molecule has a unique light absorption wavelength and an absorption line spectrum that indicates the absorption intensity. Laser light is light with a narrow spectral line width at a specific wavelength. A laser gas analyzer causes a target gas to absorb laser light having a light absorption wavelength that is absorbed by the target gas, which is a gas molecule, and detects the presence or absence of the target gas based on the amount of laser light absorbed at the light absorption wavelength. In addition, a laser gas analyzer can also detect the concentration of a target gas by utilizing the fact that the amount of laser light absorbed at the light absorption wavelength is proportional to the concentration of the target gas.

[0003] A conventional technology for a laser gas analyzer that performs such gas analysis is disclosed in, for example, Patent Document 1. As shown in Fig. 1 of Patent Document 1, the technology of Patent Document 1 includes a tunable laser element 12 capable of scanning the wavelength over the spectral line width of the absorption line spectrum of the target gas, a light receiving element 22 that detects the intensity of the laser light passing through gases generated by various processes at DC and multiples of the modulation frequency of the laser light, a received light signal processing unit 21 including a lock-in amplifier and a microprocessor, a modulated light generating unit 11, and a communication line 30 that connects the modulated light generating unit 11 and the received light signal processing unit 21.

[0004] The laser gas analyzer of Patent Document 1 performs detection by wavelength modulation spectroscopy. That is, a tunable laser element 12 emits a laser beam whose wavelength is swept by a driving current and modulated at a specific frequency, and the laser beam is detected by a light receiving element 22. In the light receiving signal processing unit 21, a lock-in amplifier performs lock-in detection of the detection signal of the light receiving element 22 at a multiple of the modulation frequency of the laser beam, and a microprocessor calculates the gas concentration based on the amplitude of the lock-in detection waveform obtained by the lock-in detection. This type of laser gas analyzer is suitable for measuring trace gases because the signal-to-noise ratio is improved by the lock-in detection.

[0005] When the composition of multiple gases present in the measurement space is fixed, the amplitude of the lock-in detection waveform obtained by the absorption of the measurement gas is a function of the wavelength modulation amplitude, and has a maximum value. Therefore, when calibrating the standard gas, the signal-to-noise ratio can be maximized by adjusting the wavelength modulation amplitude so that the amplitude of the lock-in detection waveform becomes a maximum. Then, the microprocessor can calculate the gas concentration based on the correspondence relationship (e.g., proportionality) between the gas concentration of the measurement gas and the amplitude of the lock-in detection waveform.

[0006] Incidentally, since a laser gas analyzer measures the laser light emitted from the light-emitting part by receiving it with the light-receiving part, it is important to align the optical axes of the light-emitting part and the light-receiving part. Therefore, as shown in Fig. 8 of Patent Document 2, for example, it is common to adjust the angle of the light-receiving part or the light-emitting part by deforming the bellows part of the pipe to which the light-receiving part or the light-emitting part is attached with an adjustment bolt, so that the laser light emitted from the light-emitting part can be received by the light-receiving part. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-106742 A [Patent Document 2] Patent No. 6191345 Summary of the Invention [Problem to be solved by the invention]

[0008] However, after the installation of the laser gas analyzer is completed, the installation site of the laser gas analyzer may be slightly deformed due to thermal expansion caused by the process that produces the gas to be measured, vibration of the location where the laser gas analyzer is installed, etc. In laser gas analyzers, the measurement optical path length is often set over a wide range, such as 0.5 m to 10 m, so even a slight deformation of the installation site may affect the light reception at the light receiving unit. In this case, after the installation work is completed, the worker generally readjusts the angle of the light receiving unit or the light emitting unit when the process is stable. However, since the angle adjustment at this stage is an adjustment that is optimal for the process conditions, if the process conditions change, the angle must be adjusted again.

[0009] A possible method for avoiding angle adjustments due to process effects after installation work is to slightly expand the beam diameter of the laser light in advance so that the light receiving element can receive the laser light even if there is a slight deviation in the installation angle of the light emitting unit or the light receiving unit. A possible method for adjusting the beam diameter of the laser light is, for example, changing the distance between the tunable laser element 12 and the collimating lens 13 with screws, spacers, etc. in Figure 1 of Patent Document 1. However, expanding the beam diameter of the laser light has the effect of reducing the signal level of the light received by the light receiving element, etc. Therefore, even when adjusting the beam diameter of the laser light, it is preferable to adjust it according to the conditions of the installation site so that the beam diameter does not expand more than necessary. Furthermore, if it becomes necessary to adjust the angle of incidence of the laser light on the light-receiving unit when adjusting the beam diameter, the mounting angle of the light-emitting unit or the light-receiving unit must be readjusted, making the adjustment process complicated.

[0010] An object of the present disclosure is to provide a laser gas analyzer that can easily adjust the beam diameter of laser light at the light receiving unit and the angle of incidence of laser light to the light receiving unit. [Means for solving the problem]

[0011] A laser gas analyzer according to one embodiment of the present disclosure is a laser gas analyzer that measures the concentration or presence or absence of a target gas present in a measurement space, and includes a tunable laser element that emits laser light in a wavelength band that includes the optical absorption wavelength of the absorption line spectrum of the target gas, a moving mechanism that periodically moves the laser element in a direction that changes the optical axis direction of the laser element, a light receiving element that receives the laser light that has passed through the measurement space, and a light receiving signal processing unit that performs processing on the light receiving signal output from the light receiving element, including averaging processing of the light receiving signal, to determine the concentration or presence or absence of the target gas. Effect of the Invention

[0012] According to one aspect of the present disclosure, it is possible to easily adjust the beam diameter of the laser light at the light receiving section and the angle of incidence of the laser light to the light receiving section. [Brief description of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating an example of an overall configuration of a laser gas analyzer according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a perspective view showing an example of the configuration of a moving mechanism. [Diagram 3] 11A and 11B are diagrams illustrating an example of a relationship between the operation of each feed screw of the moving mechanism and the movement of a support member. [Figure 4] FIG. 13 is a diagram showing the difference in optical paths between a first technique and a second technique. [Diagram 5] 6 is a diagram showing the relationship between the displacement length of the laser element in the optical axis direction and the amount of change in the optical path length in the first technique. FIG. [Figure 6] 13 is a diagram showing the relationship between the displacement angle of a laser element in the optical axis direction and the amount of change in optical path length in the second technique. FIG. [Figure 7] 10A and 10B are diagrams illustrating the effect of reducing interference noise by averaging a received light signal. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, a preferred embodiment of the present disclosure will be described with reference to the drawings. In the drawings, the dimensions and scale of each part may differ from the actual ones, and some parts may be shown diagrammatically to facilitate understanding. In addition, unless otherwise specified in the following description to the effect that the present disclosure is limited, the scope of the present disclosure is not limited to the embodiments described in the following description. The scope of the present disclosure includes the equivalent scope of the embodiments.

[0015] 1. Embodiment FIG. 1 is a diagram showing a schematic diagram of an example of the overall configuration of a laser gas analyzer 100 according to the present embodiment. The laser gas analyzer 100 is an apparatus that uses a laser beam to detect the concentration of a target gas contained in gas flowing between a first wall 150a and a second wall 150b facing each other, or the presence or absence of the target gas. The first wall 150a and the second wall 150b correspond to the wall portions included in the cross section of a tubular flue through which gas passes. The flue is a flow path for gas generated in an industrial or chemical process. The distance between the first wall 150a and the second wall 150b is not limited, but is in the range of, for example, 0.5 m to 10 m. In addition, in the present disclosure, an industrial process or a chemical process is simply referred to as a "process".

[0016] 1, the laser gas analyzer 100 includes a light-emitting unit 110 attached to the outside of a first wall 150a, a light-receiving unit 120 attached to the outside of a second wall 150b, and a communication line 140 used for transmitting electrical signals between the light-emitting unit 110 and the light-receiving unit 120. Note that a communication unit such as a wireless or optical communication unit may be used instead of the communication line 140.

[0017] The light emitting unit 110 is a unit that emits detection light 130, which is a laser beam, and the detection light 130 is projected into the measurement target space between the first wall 150a and the second wall 150b. In the measurement target space, a part of the detection light 130 is absorbed by the measurement target gas, and the remaining detection light 130 that is not absorbed, i.e., the transmitted light, is incident on the light receiving unit 120. The light receiving unit 120 is a unit that receives the detection light 130 that has transmitted through the measurement target space and detects the amount of the received light. The light receiving unit 120 of this embodiment also has a function of determining the concentration of the measurement target gas or the presence or absence of the measurement target gas based on the amount of the received detection light 130.

[0018] Next, the mounting structure of the light emitting unit 110 and the light receiving unit 120 will be described in detail.

[0019] The light emitting section 110 includes a light emitting section container 115 and a first adjustable flange member 152a for attaching the light emitting section container 115 to the first wall 150a. The light-emitting part container 115 is a box having an opening at an emission port 115a for emitting the detection light 130. The shape of the light-emitting part container 115 is not limited, but in this embodiment, it is a substantially rectangular parallelepiped shape. In addition, the main material and manufacturing method of the light-emitting part container 115 are not limited, but the light-emitting part container 115 in this embodiment is an aluminum die-cast product with an explosion-proof structure.

[0020] The first adjustment flange member 152a has a cylindrical portion 152a1 and a flange portion 152a2 provided at the tip of the cylindrical portion 152a1, and is mainly made of, for example, an aluminum alloy. The base end of the cylindrical portion 152a1 is firmly fixed to the light emitting portion container 115 by welding or the like so as to surround the light outlet 115a, and the detection light 130 propagates inside the cylindrical portion 152a1. On the other hand, an opening 150a1 for introducing the detection light 130 emitted from the light emitting unit 110 into the first wall 150a is provided, and a first flange 151a is fixed to the opening 150a1 by welding or the like. A flange portion 152a2 of the first adjustment flange member 152a is joined to this first flange 151a.

[0021] The light receiving section 120 includes a light receiving section container 125 and a second adjustment flange member 152b for mounting the light receiving section container 125 to the second wall 150b. The light-receiving unit container 125 is a box having an opening at an inlet 125a for introducing the transmitted light of the detection light 130 into the inside. The shape of the light-receiving unit container 125 is not limited, but in this embodiment, it is a substantially rectangular parallelepiped shape. In addition, the main material and manufacturing method of the light-receiving unit container 125 are not limited, but the light-receiving unit container 125 in this embodiment is an aluminum die-cast product with an explosion-proof structure.

[0022] The second adjustment flange member 152b has a cylindrical portion 152b1 and a flange portion 152b2 provided at the tip of the cylindrical portion 152b1, and is mainly made of, for example, an aluminum alloy. The base end of the cylindrical portion 152b1 is firmly fixed to the light-receiving portion container 125 by welding or the like so as to surround the introduction port 125a, and the detection light 130 transmitted through the measurement target space is introduced into the light-receiving portion container 125 by propagating inside the cylindrical portion 152b1. On the other hand, the second wall 150b is provided with an opening 150b1 for guiding the detection light 130 transmitted through the measurement target space to the outside, and the second flange 151b is fixed to the opening 150b1 by welding or the like. The flange portion 152b2 of the second adjustment flange member 152b is joined to this second flange 151b.

[0023] In this embodiment, the first adjustment flange member 152a also serves as a means for varying the mounting angle of the light emitting unit 110 relative to the first wall 150a, i.e., the angle at which the detection light 130 emitted from the light emitting unit 110 is incident on the first wall 150a. Specifically, the first adjustment flange member 152a includes a mounting angle variable mechanism for varying the direction of the central axis of the cylindrical portion 152a1 of the first adjustment flange member 152a relative to the first flange 151a, thereby varying the mounting angle of the light emitting unit 110. The mounting angle variable mechanism of this embodiment includes a metal bellows member 152a4 that connects the flange portion 152a2 and the first flange 151a, and a plurality of adjustment bolts 152a3 that connect the flange portion 152a2 and the first flange 151a, and the direction of the central axis of the first adjustment flange member 152a relative to the first flange 151a is varied depending on the amount of displacement of each adjustment bolt 152a3.

[0024] Similarly, in this embodiment, the second adjustment flange member 152b also serves as a means for varying the mounting angle of the light receiving unit 120 relative to the second wall 150b, i.e., the angle of the detection light 130 incident on the light receiving unit 120 from the second wall 150b. Specifically, the second adjustment flange member 152b includes a mounting angle variable mechanism for varying the direction of the central axis of the cylindrical portion 152b1 of the second adjustment flange member 152b relative to the second flange 151b, thereby varying the mounting angle of the light receiving unit 120. The mounting angle variable mechanism of this embodiment includes a metal bellows member 152b4 that connects the flange portion 152b2 and the second flange 151b, and a plurality of adjustment bolts 152b3 that connect the flange portion 152b2 and the second flange 151b, and the direction of the central axis of the second adjustment flange member 152b relative to the second flange 151b is varied by the amount of displacement of each adjustment bolt 152b3.

[0025] The mounting angle varying mechanisms provided in the first adjustment flange member 152a and the second adjustment flange member 152b are not limited to the form described in this embodiment.

[0026] Next, the internal configurations of the light-emitting unit 110 and the light-receiving unit 120 will be described in detail.

[0027] The light emitting section 110 includes a laser element 112 , a collimator lens 113 , a modulated light generating section 111 , a drive current control section 116 , a moving mechanism 117 , and a moving mechanism driving section 118 , and these are housed in a light emitting section container 115 .

[0028] The laser element 112 is an example of a wavelength-tunable laser light source that emits laser light used for the detection light 130. For example, a DFB laser diode (Distributed Feedback Laser Diode), a VCSEL (Vertical Cavity Surface Emitting Laser), a DBR laser diode (Distributed Bragg Reflector Laser Diode), or the like is used as the laser element 112.

[0029] The collimating lens 113 is an example of an optical element that converts the detection light 130 emitted by the laser element 112 into parallel light, and is mainly made of a material that has high transmittance at the wavelength of the detection light 130. The detection light 130 is converted into approximately parallel light by the collimating lens 113, and is propagated to the light receiving unit 120 while suppressing loss due to diffusion. In the light emitting unit 110 of this embodiment, the collimating lens 113 is fitted into the exit port 115a of the light emitting unit container 115, thereby blocking the exit port 115a. Note that a parabolic mirror may be used instead of the collimating lens 113.

[0030] The modulated light generating unit 111 is a functional unit that sweeps the wavelength of the laser element 112 within a wavelength range including the absorption wavelength of the target gas, and outputs a signal for modulating the wavelength of the laser element 112, in order to analyze the concentration or presence or absence of the target gas by tunable laser spectroscopy and wavelength-modulated light spectroscopy. Specifically, the modulated light generating unit 111 of this embodiment includes a sweep signal generating circuit, a modulation signal generating circuit, and a drive signal generating circuit. The sweep signal generating circuit is an electric circuit that outputs a wavelength sweep drive signal that sweeps the wavelength of the laser element 112 within a wavelength range including the absorption wavelength of the gas to be measured in order to scan the absorption wavelength of the gas to be measured. The modulation signal generating circuit is an electric circuit that outputs a sinusoidal high-frequency modulation signal in order to detect the gas absorption waveform. This high-frequency modulation signal is used to modulate the wavelength of the laser element 112. The drive signal generating circuit is an electric circuit that outputs a laser element drive signal in which a high-frequency modulation signal is superimposed on a wavelength sweep drive signal.

[0031] The drive current control unit 116 includes an electric circuit that converts the laser element drive signal output by the laser drive signal generating circuit into a current, thereby supplying a drive current corresponding to the laser element drive signal to the laser element 112. By supplying the drive current to the laser element 112, the laser element 112 emits, as the detection light 130, a laser light having a wavelength and intensity corresponding to the laser drive signal, i.e., a laser light whose wavelength is swept within a wavelength range including the absorption wavelength of the gas to be measured and whose wavelength is modulated.

[0032] The modulated light generating unit 111 may have a temperature control function for controlling the temperature of the laser element 112 in order to control the wavelength of the laser element 112. Specific elements for realizing the temperature control function include, for example, a temperature sensor for detecting the temperature of the laser element 112, a temperature control element for controlling the temperature of the laser element 112, and a control circuit for controlling the temperature control element based on the temperature detected by the temperature sensor. For example, a thermistor may be used as the temperature sensor, and for example, a Peltier element may be used as the temperature control element.

[0033] The moving mechanism 117 and the moving mechanism driver 118 are for moving the laser element 112 in a plurality of predetermined directions in the internal space of the light emitting part container 115. These will be described in detail later.

[0034] The light receiving section 120 includes a light receiving element 122 , a condenser lens 123 , and a received light signal processing section 121 , which are housed in a light receiving section container 125 . The light receiving element 122 is an element that receives the detection light 130 introduced into the light receiving section 120 and outputs a light receiving signal according to the amount of received light, and includes, for example, a photodiode. The light receiving element 122 has sensitivity to the entire wavelength sweep range for the detection light 130. The condenser lens 123 is an example of an optical element that condenses the detection light 130 incident on the light receiving unit 120 onto the light receiving surface of the light receiving element 122 installed inside the light receiving unit 120. In the light receiving unit 120 of this embodiment, the condenser lens 123 is fitted into the inlet 125a of the light receiving unit container 125, thereby blocking the inlet 125a. Note that instead of the condenser lens 123, a parabolic mirror, a doublet lens, a diffractive lens, or the like may be used.

[0035] The received light signal processing unit 121 is a functional unit that determines the gas concentration or the presence or absence of a gas to be measured based on a received light signal output by the light receiving element 122. Specifically, the received light signal processing unit 121 includes a lock-in amplifier and a processor. The lock-in amplifier is an example of a synchronous detection circuit that performs lock-in detection of the received signal of detection light 130, which is modulated laser light, at a multiple of the modulation frequency of the detection light 130. When detection light 130 that has passed through the measurement target space is absorbed by the measurement target gas, an absorption waveform of the measurement target gas appears in the lock-in detection waveform obtained by lock-in detection. The processor is an arithmetic circuit that determines the concentration of the target gas based on the amplitude of the lock-in detection waveform. In detail, a signal synchronized with the wavelength sweep drive signal in the modulated light generating unit 111 is input to the arithmetic unit through the above-mentioned communication line 140, and the processor identifies a section corresponding to one wavelength sweep in the lock-in detection waveform based on the signal synchronized with the wavelength sweep drive signal, and determines the concentration of the target gas based on the amplitude of the absorption waveform of the target gas that appears in the section.

[0036] The received light signal processing unit 121 may include a low-pass filter for removing noise from the received light signal and amplifying the signal.

[0037] The installation work for installing the laser gas analyzer 100 in the flue will be described below. First, an operator installs the light-emitting unit 110 and the light-receiving unit 120 on the first wall 150a and the second wall 150b, respectively. As described above, the laser gas analyzer 100 of this embodiment can be used even in an atmosphere where flammable gas or dust may be present, since the light-emitting unit container 115 of the light-emitting unit 110 and the light-receiving unit container 125 of the light-receiving unit 120 are both explosion-proof containers.

[0038] Next, the worker adjusts the mounting angle of at least one of the light-emitting unit 110 and the light-receiving unit 120 using the first adjustment flange member 152a and the second adjustment flange member 152b, so that the detection light 130 emitted from the light-emitting unit 110 enters the light-receiving unit 120 and is received by the light-receiving element 122 of the light-receiving unit 120. In this case, the worker adjusts the mounting angle of at least one of the light-emitting unit 110 and the light-receiving unit 120 so that the maximum amount of light is received by the light-receiving unit 120.

[0039] After or during the installation work, the worker performs work to expand the beam diameter of the detection light 130 in advance so that the amount of light received by the light receiving element 122 is secured even if the installation angles of the light emitting unit 110 and the light receiving unit 120 are slightly shifted due to thermal expansion caused by the process or vibration of the first wall 150a and the second wall 150b. However, the light-emitting unit 110 of this embodiment is equipped with an explosion-proof light-emitting unit container 115 in which the laser element 112, the collimator lens 113, etc. are housed, so that it is difficult for workers at the installation site to access the inside of the light-emitting unit container 115 and adjust the beam diameter.

[0040] The laser gas analyzer 100 of this embodiment includes the above-mentioned moving mechanism 117, moving mechanism drive unit 118, and operation device 160 so that an operator can perform the relevant work without accessing the inside of the light emitting unit 110. Furthermore, these configurations are also used for adjusting the optical axis of the laser element 112 and adjusting the optical path length between the laser element 112 and the light receiving element 122 in addition to adjusting the beam diameter. This configuration will be described in detail below.

[0041] The moving mechanism 117 is a mechanism arranged at a predetermined position inside the light-emitting part container 115, and is a mechanism capable of moving the laser element 112 in a plurality of directions by adjusting at least two degrees of freedom of the six degrees of freedom of the laser element 112. The six degrees of freedom refer to the degrees of freedom of free movement of the laser element 112 regarded as a rigid body in the internal space of the light-emitting part container 115, and correspond to translational movement in each of the X-axis, Y-axis, and Z-axis directions in an orthogonal three-dimensional space, and rotational movement in the directions of rotations Rx, Ry, and Rz around the X-axis, Y-axis, and Z-axis, respectively. That is, the moving mechanism 117 of this embodiment enables the laser element 112 to be translated in each of the X-axis, Y-axis, and Z-axis directions, and to be rotated in each of the directions of rotations Rx, Ry, and Rz, inside the light-emitting part container 115.

[0042] FIG. 2 is a perspective view showing an example of the configuration of the moving mechanism 117. As shown in FIG. The movement mechanism 117 of this embodiment uses a kinematic mount, which is a form of an optical mount that supports the laser element 112. A kinematic mount is a mount that allows one or more degrees of freedom to be adjusted with high precision while constraining six degrees of freedom of the laser element 112. The movement mechanism 117 of this embodiment uses a kinematic mount that allows each of the six degrees of freedom to be adjusted.

[0043] 2, the movement mechanism 117 includes a plate-shaped support member 150 having a first main surface 150S1 that supports the laser element 112, three feed screws ST, SB, and SC whose tips abut against a second main surface 150S2 of the support member 150, and a connecting member 152 that connects the three feed screws. By manipulating each of the three feed screws ST, SB, and SC, each of the six degrees of freedom of the support member 150 that holds the laser element 112 is adjusted. In the following description, a plane parallel to the first main surface 150S1 of the support member 150 is defined as an XY plane, and a normal direction of the XY plane is defined as a Z axis. The laser element 112 is held by the support member 150 in a position in which its optical axis coincides with the Z axis.

[0044] FIG. 3 is a diagram showing an example of the relationship between the operation of each of the feed screws ST, SB, and SC of the movement mechanism 117 and the movement of the support member 150. As shown in FIG.

[0045] As shown in operation form 1, the three feed screws ST, SB, and SC are all pushed or pulled out of the connecting member 152 by the same amount, whereby the support member 150 moves translationally in the Z-axis direction, i.e., in the optical axis direction of the laser element 112. Also, as shown in operation form 2, by an operation in which one feed screw SB of the three feed screws ST, SB, and SC is pushed into or pulled out from the connecting member 152, the support member 150 rotates in the direction of rotation Rx around the X-axis. Also, as shown in operation form 3, by pushing or pulling one of the three feed screws ST, SB, and SC into or out of the connecting member 152, the support member 150 rotates in the direction of rotation Ry around the Y-axis.

[0046] Although not shown in the figure, in the moving mechanism 117 of this embodiment, the three feed screws ST, SB, and SC are each appropriately pushed in or pulled out, so that the support member 150 moves translationally in the X-axis direction and the Y-axis direction, and also rotates in the direction of rotation Rz around the Z-axis.

[0047] The movement mechanism drive unit 118 is a functional unit that drives each of the feed screws ST, SB, and SC of the movement mechanism 117, and includes actuators that drive each of the feed screws ST, SB, and SC. Note that the movement mechanism 117 may include devices that enable linear displacement, such as piezo actuators, instead of each of the feed screws ST, SB, and SC.

[0048] The operation device 160 is a device connected to the movement mechanism driving unit 118 so as to be able to send and receive signals via the communication line 140, and is provided outside the light-emitting unit 110 and the light-receiving unit 120. The operation device 160 also accepts user operations by a user such as an operator, and inputs instruction signals for instructing the driving of each of the feed screws ST, SB, and SC to the movement mechanism driving unit 118 based on the user operation. For example, an input device such as a keyboard, an output device such as a display device, and a computer system including a computer are used as the operation device 160. In this embodiment, the operation device 160 has a function of outputting various information related to the control of the light-emitting unit 110 and the light-receiving unit 120 and setting values ​​to an output device. The operation device 160 also has a function of acquiring user settings for the setting values ​​from an input device and setting the user settings. These functions allow the user to check the various information and setting values ​​and set them appropriately.

[0049] According to the laser gas analyzer 100 of this embodiment, an operator can operate the operating device 160 to drive the moving mechanism 117, thereby moving the laser element 112 arranged inside the light-emitting unit container 115 in a plurality of directions without accessing the inside of the light-emitting unit 110. By moving the laser element 112, the beam diameter of the detection light 130 emitted by the light-emitting unit 110, the optical axis of the detection light 130, and the optical path length between the laser element 112 and the light-receiving element 122 are adjusted according to the moving direction. These adjustments are described in more detail below.

[0050] [Beam diameter adjustment] The beam diameter of the detection light 130 emitted from the light emitting unit 110 is adjusted by moving the laser element 112 by the moving mechanism 117 so as to vary the distance between the laser element 112 and the collimator lens 113. The distance is a distance along the optical axis of the laser element 112, and in this embodiment, the optical axis of the laser element 112 coincides with the Z-axis. Therefore, the beam diameter of the detection light 130 is adjusted by the moving mechanism 117 translating the laser element 112 in the Z-axis direction by the operation of the operation form 1 in FIG. 3. In this case, the closer the light emitting surface of the laser element 112 is to the collimator lens 113 than the back focus of the collimator lens 113, the wider the beam diameter becomes, and conversely, the farther the light emitting surface of the laser element 112 is from the collimator lens 113 than the back focus of the collimator lens 113, the narrower the beam diameter becomes.

[0051] By adjusting the beam diameter after or during the installation work of the laser gas analyzer 100, the worker can preset the beam diameter of the detection light 130 so that the amount of light received by the light receiving element 122 is ensured even if the installation angles of the light emitting unit 110 and the light receiving unit 120 are slightly shifted due to thermal expansion caused by the process or vibration of the first wall 150a and the second wall 150b.

[0052] [Optical axis adjustment] The optical axis of the detection light 130 emitted from the light emitting unit 110, i.e., the emission angle, is adjusted by rotating the laser element 112 by the movement mechanism 117 around another axis perpendicular to the optical axis. In this embodiment, the other axes perpendicular to the optical axis are the X-axis and the Y-axis. Therefore, by performing at least one of the operation forms 2 and 3 in FIG. 3, the movement mechanism 117 rotates the laser element 112 in at least one of the directions of rotation Rx around the X-axis and rotation Ry around the Y-axis, thereby adjusting the optical axis of the detection light 130. However, in the moving mechanism 117 of this embodiment, when the optical axis adjustment is performed in the operation form 2 or the operation form 3, the position of the optical axis direction of the laser element 112 is shifted from the position before the adjustment. Therefore, after the optical axis adjustment is performed, it is preferable to eliminate the shift by pushing or pulling out the two feed screws fixed in the operation form 2 and the operation form 3 by the same amount.

[0053] After or during the installation work of the laser gas analyzer 100, the worker can fine-tune the emission angle of the detection light 130 from the light-emitting unit 110 and the incidence angle of the detection light 130 to the light-receiving unit 120 by adjusting the optical axis of the laser element 112 in addition to adjusting the installation angle using the first adjustment flange member 152a and the second adjustment flange member 152b.

[0054] [Optical path length adjustment] The optical path length between the laser element 112 and the light receiving element 122 is adjusted by the movement mechanism 117 by translating the laser element 112 in the optical axis direction or by moving the laser element 112 in a direction in which the optical axis direction changes. In this embodiment, the translational movement of the laser element 112 in the optical axis direction is performed by the operation of operation form 1 in FIG. 3. In this embodiment, the directions in which the optical axis direction is changed are the direction of rotation Rx and the direction of rotation Ry. The movement of the laser element 112 in the direction of rotation Rx and the direction of rotation Ry is performed by the operation of operation form 2 and operation form 3 in FIG. 3.

[0055] In this embodiment, the change in the optical path length between the laser element 112 and the light receiving element 122 is used to solve the problem of optical interference in the laser gas analyzer 100. In more detail, it is generally known that in a laser gas analyzer, when the detection light emitted from the laser element is reflected multiple times by various optical elements such as a collimating lens and reaches the light receiving element, the detection light that reaches directly and the detection light that reaches after being reflected multiple times interfere with each other and reinforce or cancel each other out, resulting in an interference signal being superimposed on the light receiving signal of the light receiving element as interference noise (see, for example, JP 2019-117147 A).

[0056] In contrast, by changing the optical path length between the laser element 112 and the light receiving element 122, the reflection position of the interference light in optical elements such as the collimator lens 113 and the condenser lens 123 changes, causing a phase shift. Therefore, by periodically and repeatedly changing the optical path length within a small range and averaging a plurality of light receiving signals obtained during one period, the effect of optical interference can be reduced. In this case, the "trace amount" is on the same order as the wavelength of the laser light, for example, a value from one-fewth to several times the wavelength. However, when the optical path length is changed by translational movement of the laser element 112 in the optical axis direction, the beam diameter of the laser light also changes due to the change in the distance between the laser element 112 and the collimator lens 113. Therefore, it is preferable that the "trace amount" is set to a range in which the amount of light received by the light receiving element 122 does not change significantly. The period during which the optical path length changes is arbitrary, but is desirably sufficiently longer than the sweep period of the wavelength of the laser light. For example, the period during which the optical path length changes is about 300 to 800 times the sweep period of the wavelength of the laser light. When the sweep period of the wavelength of the laser light is 0.15 ms, a period during which the optical path length changes is appropriately 45 ms to 120 ms.

[0057] In this embodiment, while gas analysis is being performed in the laser gas analyzer 100, the operating device 160 controls the moving mechanism drive unit 118 to drive the moving mechanism 117, thereby periodically moving the laser element 112 over a small range (i.e., by vibrating it with a small amplitude), thereby repeatedly and periodically changing the optical path length over a small range, making it possible to perform analysis with reduced interference noise.

[0058] As described above, there are two methods for varying the optical path length: the first method for translating the laser element 112 in the optical axis direction, and the second method for changing the optical axis direction of the laser element 112. The difference in the effect of reducing interference noise between the first method and the second method will be described in detail below.

[0059] 4 is a diagram showing the difference in the optical path between the first method and the second method. In the figure, the fixed form shows the case where the laser element 112 is fixed at a predetermined reference position. The straight line Ks shows the optical axis in a state where it coincides with the Z axis. According to the first technique, the laser element 112 periodically translates in the optical axis direction with a small displacement length α (i.e., the laser element 112 vibrates in the optical axis direction with a displacement length α), so that the optical path length changes in a certain section A between the laser element 112 and the collimator lens 113. Therefore, the influence of the interference light occurring in section A is reduced by averaging the received light signal. However, since the optical path length does not change in section B between the collimator lens 113 and the focusing lens 123, and in section C between the focusing lens 123 and the light receiving element 122, the influence of the interference light occurring in sections B and C is not reduced.

[0060] According to the second technique, the laser element 112 rotates in the direction of rotation Rx or Ry, so that the direction of the optical axis changes periodically by a small displacement angle θ around the straight line Ks (i.e., the laser element 112 vibrates around the straight line Ks (Z-axis) within the range of the displacement angle θ). As a result, the incidence angle and the emission angle of the detection light 130 change on the optical surfaces of the collimator lens 113 and the condenser lens 123, respectively, and therefore the optical path length changes in all of the sections A, B, and C. Therefore, according to the second technique, unlike the first technique, the averaging process of the received light signal can reduce the influence of the interference light occurring in all of the sections A, B, and C.

[0061] Fig. 5 is a diagram showing the relationship between the displacement length α of the laser element 112 in the optical axis direction and the change amount D of the optical path length in the first method. Fig. 6 is a diagram showing the relationship between the displacement angle θ of the laser element 112 in the optical axis direction and the change amount D of the optical path length in the second method. The displacement angle θ in the optical axis direction is the angle of the optical axis with respect to the Z-axis direction. Furthermore, the change amount D of the optical path length is the difference between the longest optical path length Kmax and the shortest optical path length Kmin between the laser element 112 and the light receiving element 122. The longest optical path length Kmax and the shortest optical path length Kmin are shown in Fig. 4. As shown in Fig. 5, in the first method, even if the displacement length α of the laser element 112 in the optical axis direction increases, the change amount D of the optical path length is almost constant. In contrast, as shown in Fig. 6, in the second method, the change amount D of the optical path length increases as the displacement angle θ in the optical axis direction increases. Therefore, it can be seen that the second method enables the optical path length to be changed more by varying the displacement angle θ of the optical path length, and is expected to be more effective than the first method in reducing the effects of interference light by averaging the received signal.

[0062] FIG. 7 is a diagram illustrating the effect of reducing interference noise by averaging the received light signal. The detection examples shown in FIG. 7 each show a lock-in detection waveform obtained by the received light signal processing unit 121 performing lock-in detection of the received light signal in a state in which the target gas is not present in the target space, in other words, in a state in which the absorption of the detection light 130 in the target space is negligible. Specifically, Example A is an example of a lock-in detection waveform obtained by the received light signal processing unit 121 in a state in which the laser element 112 is fixed at a predetermined reference position. Example A shows overlapping lock-in detection waveforms B1, B2, B3, and B4 obtained by the received light signal processing unit 121 each time the displacement angle θ in the optical axis direction changes to four different angles by the second method. Example C shows a waveform after averaging the four lock-in detection waveforms B1, B2, B3, and B4 in Detection Example 2. As shown in Example B, the optical path length changes every time the angle of the optical axis direction of the laser element 112 changes, and therefore the phase of the interference noise changes. Therefore, as shown in Example C, by averaging the lock-in detection waveforms B1, B2, B3, and B4 over a fixed time period, a lock-in detection waveform with significantly reduced interference noise can be obtained.

[0063] As described above, by using the second method as a method for varying the optical path length, the optical path length can be changed in each section between all optical elements such as the collimator lens 113 and the condenser lens 123, and the influence of the interference light in each section can be reduced, compared to the first method. In addition, since the change amount D of the optical path length between the laser element 112 and the light receiving element 122 becomes larger, a greater effect in reducing the influence of the interference light can be expected.

[0064] As described above, the laser gas analyzer 100 of this embodiment includes a light emitting unit 110 having a wavelength-variable laser element 112 that emits laser light (detection light 130) in a wavelength band including the optical absorption wavelength of the absorption line spectrum of the gas to be measured, a modulated light generating unit 111 that sweeps the wavelength of the laser light emitted by the laser element 112 in the wavelength band and outputs a laser element drive signal for modulating the wavelength of the laser light, and a drive current control unit 116 that supplies a drive current corresponding to the laser element drive signal to the laser element 112. The laser gas analyzer 100 also includes a light receiving unit 120 having a light receiving element 122 that receives the laser light transmitted through the space to be measured, and a light receiving signal processing unit 121 that determines the concentration or presence or absence of the gas to be measured based on the light receiving signal output from the light receiving element 122. Furthermore, the light emitting section 110 includes a moving mechanism 117 that enables the laser element 112 to be moved in the optical axis direction and the laser element 112 to be moved in a direction that changes the optical axis direction.

[0065] According to this configuration, the beam diameter can be adjusted by moving the laser element 112 in the optical axis direction, and the angle of incidence of the laser light to the light receiving unit 120 can be adjusted by moving the laser element 112 in a direction that changes the optical axis direction, which can be easily performed simply by operating the moving mechanism 117.

[0066] The laser gas analyzer 100 of this embodiment includes a movement mechanism drive unit 118 including an actuator that drives the movement mechanism 117 , and an operation device 160 that instructs the movement mechanism drive unit 118 to move the laser element 112 by the movement mechanism 117 . According to this configuration, an operator can drive the moving mechanism 117 by operating the operation device 160, and can easily adjust the beam diameter and the incident angle of the laser light to the light receiving unit 120.

[0067] In the laser gas analyzer 100 of this embodiment, the light emitting section 110 includes a light emitting section container 115 having an explosion-proof structure, and the laser element 112 and the moving mechanism 117 are housed in the light emitting section container 115 . According to this configuration, an operator can easily adjust the beam diameter and the incident angle of the laser light to the light receiving unit 120 by operating the operating device 160 without opening the light emitting unit container 115.

[0068] In the laser gas analyzer 100 of this embodiment, the movement mechanism 117 includes a kinematic mount. According to this configuration, the laser element 112 can be moved with high precision.

[0069] In the laser gas analyzer 100 of this embodiment, the laser element 112 is periodically moved by a moving mechanism 117 in the optical axis direction or in at least one direction that changes the optical axis direction. According to this configuration, the influence of interference light caused by multiple reflections at optical elements such as the collimator lens 113 and the condenser lens 123 can be reduced. In particular, by periodically moving the laser element 112 in a direction that changes the optical axis direction, the influence of interference light occurring between each of the optical elements can be reduced.

[0070] 2. Variations The above-described embodiment may be modified in various ways. Examples of modifications that may be applied to the above-described embodiment are given below.

[0071] For example, in the above-described embodiment, the operating device 160 may instruct the movement mechanism driving unit 118 to drive the movement mechanism 117 based on an external control signal. According to this configuration, for example, it is possible to drive the moving mechanism 117 even from a remote location, and adjust the beam diameter and the incident angle of the laser light to the light receiving unit 120.

[0072] Furthermore, for example, in the above-described embodiment, the operating device 160 may instruct the movement mechanism driving unit 118 to drive the movement mechanism 117 based on a light receiving signal from the light receiving unit 120 or a signal output from the light receiving signal processing unit 121. According to this configuration, the moving mechanism 117 can be automatically driven in response to the light receiving state at the light receiving section 120 to adjust the beam diameter and the incident angle of the laser light to the light receiving section 120.

[0073] Also, for example, in the above-described embodiment, a mechanism that can adjust six degrees of freedom for the laser element 112 has been described as the movement mechanism 117. However, the movement mechanism 117 may be any mechanism that can adjust the degrees of freedom to move the laser element 112 in the optical axis direction and to move the laser element 112 in a direction that changes the optical axis direction. [Explanation of symbols]

[0074] 100...laser gas analyzer, 110...light emitting unit, 111...modulated light generating unit, 112...laser element, 113...collimating lens, 115...light emitting unit container, 116...driving current control unit, 117...moving mechanism, 118...moving mechanism driving unit, 120...light receiving unit, 121...light receiving signal processing unit, 122...light receiving element, 123...condensing lens, 125...light receiving unit container, 130...detection light (laser light), 152a...first adjustment flange member, 152a3...adjusting bolt, 152a4...bellows member, 152b...second adjustment flange member, 152b2...flange portion, 152b3...adjusting bolt, 152b4...bellows member, 160...operating device.

Claims

1. A laser gas analyzer that measures the concentration or presence of a target gas in a measurement space, a tunable laser element that emits laser light in a wavelength band that includes an optical absorption wavelength of the absorption line spectrum of the measurement target gas; a moving mechanism for periodically moving the laser element in a direction that changes the direction of the optical axis of the laser element; a light receiving element that receives the laser light that has passed through the measurement target space; a light receiving signal processing unit that performs processing including averaging processing on the light receiving signal output from the light receiving element to determine the concentration or presence or absence of the measurement target gas; A laser gas analyzer comprising:

2. a modulated light generating unit that sweeps the wavelength of the laser light emitted by the laser element in the wavelength band and outputs a laser element drive signal for modulating the wavelength of the laser light; a drive current control unit that supplies a drive current to the laser element in response to the laser element drive signal; The laser gas analyzer of claim 1 further comprising:

3. a movement mechanism drive unit including an actuator that drives the movement mechanism; an operation device that instructs the movement mechanism drive unit to move the laser element by the movement mechanism; The laser gas analyzer of claim 1 further comprising:

4. The moving mechanism periodically moves the laser element, so that the optical path length between the laser element and the light receiving element changes periodically at a period that is 300 to 800 times the sweep period of the laser light.

2. The laser gas analyzer of claim 1.

5. An explosion-proof light-emitting unit container that houses the laser element and the moving mechanism The laser gas analyzer of claim 1 further comprising:

6. A first adjustment flange member fixed to the light emitting portion container; a bellows member connecting the first adjustment flange member and a second adjustment flange member fixed to a wall of the measurement target space; a plurality of adjustment bolts that connect the first adjustment flange member and the second adjustment flange member; The direction of the first adjustment flange member relative to the second adjustment flange member is variable according to the amount of displacement of each of the plurality of adjustment bolts.

6. The laser gas analyzer of claim 5.

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