Laser gas analyzer and purge gas supply method

Abstract

A laser gas analyzer 100 includes a purge gas inlet 221 that supplies purge gas to a first region 22, a light emitter 11 that emits a measurement light toward a second region 23, a first reflector 18 that reflects the measurement light in the first region, a second reflector 28 that reflects the measurement light in the second region, a light receiver 13 that receives first reflected light and second reflected light, and a controller 15 that calculates and outputs, as a measurement result, concentration of a component to be measured in the second region, based on intensity of the measurement light and the second reflected light. The controller controls opening and closing of a solenoid valve of the purge gas inlet based on the concentration of the component to be measured in the first region, calculated based on intensity of the measurement light and the first reflected light.

Description

LASER GAS ANALYZER AND PURGE GAS SUPPLY METHODCROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority to and the benefit of Japanese Patent Application No. 2023-33164 filed March 3, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a laser gas analyzer and a purge gas supply method.Background

[0003] Conventionally, gas measurement devices for measuring the concentration of a gas component to be measured in purge gas are known (see, for example, Patent Literature (PTL) 1).

[0004] PTL 1: CN 101393115 BSummary

[0005] (Technical Problem) The device described in PTL 1 keeps purge gas flowing. Reduction of purge gas usage is sought.

[0006] In view of the above, it would be helpful to provide a laser gas analyzer and a purge gas supply method that are able to reduce the amount of purge gas used. (Solution to Problem)

[0007] (1) A laser gas analyzer according to at least one embodiment includes a housing, a purge gas inlet, a light emitter, a first reflector, a second reflector, a light receiver, and a controller. The housing includes a wall that defines a first region where purge gas is supplied, and a window that allows light to be transmitted between the first region and a second region containing a component to be measured. The purge gas inlet includes a solenoid valve operable to supply the purge gas to the first region. The light emitter is disposed in the first region and is operable to emit measurement light toward the second region. The first reflector is disposed in the first region and reflects a portion of the measurement light that has traveled only in the first region as first reflected light. The second reflector is disposed in the second region and reflects a portion of the measurement light that has traveled to the second region as second reflected light toward the first region. The light receiver is disposed in the first region and receives the first reflected light and the second reflected light. The controller calculates concentration of the component to be measured in the second region based on intensity of the measurement light and intensity of the second reflected light and outputs the concentration as a measurement result. The controller calculates concentration of the component to be measured in the first region based on the intensity of the measurement light and intensity of the first reflected light. The controller controls opening and closing of the solenoid valve of the purge gas inlet based on the concentration of the component to be measured in the first region.

[0008] According to the present embodiment of the laser gas analyzer, a purge gas supply period is limited by controlling supply of the purge gas based on the concentration of the component to be measured in the first region. That is, the purge gas does not have to be constantly supplied. By limiting the purge gas supply period, the amount of purge gas used is reduced.

[0009] (2) The laser gas analyzer described under (1) above, wherein the concentration of the component to be measured in the purge gas is less than a first threshold value. The controller opens the solenoid valve of the purge gas inlet when the concentration of the component to be measured in the first region is the first threshold value or more. The controller closes the solenoid valve of the purge gas inlet when the concentration of the component to be measured in the first region is less than the first threshold value.

[0010] The laser gas analyzer according to the present embodiment is able to control the concentration of the component to be measured in the first region to be less than the first threshold value while limiting the purge gas supply period. As a result, both a reduction in the amount of purge gas used and maintenance of measurement accuracy of the concentration of the component to be measured in the second region are realized.

[0011] (3) The laser gas analyzer described under (1) above, wherein the solenoid valve of the purge gas inlet includes a three-way solenoid valve operable to switch between instrument air and defined concentration oxygen gas as the purge gas to supply the first region. The controller controls the three-way solenoid valve to supply the instrument air to the first region when concentration of oxygen gas in the first region is in a defined range including the defined concentration. The controller controls the three-way solenoid valve to supply the defined concentration oxygen gas to the first region when the concentration of the oxygen gas in the first region is outside the defined range.

[0012] The laser gas analyzer according to the present embodiment generally supplies the instrument air to the first region as the purge gas, and supplies the defined concentration oxygen gas as the purge gas when the oxygen concentration in the first region falls outside the defined range. That is, the laser gas analyzer determines whether to supply the defined concentration oxygen gas as the purge gas to the first region based on the measurement result of the oxygen concentration in the first region. When the oxygen concentration in the first region is in the defined range, the supply of the oxygen gas as the purge gas is stopped, thereby reducing the amount of the oxygen gas used. The reduced use of the oxygen gas reduces cost burden or environmental impact. Further, the use of the instrument air instead of a high purity gas such as nitrogen gas as the purge gas also reduces the cost burden or environmental impact.

[0013] (4) The laser gas analyzer described under any one of (1) to (3) above, wherein the light emitter includes a first light emitter and a second light emitter. The light receiver includes a first light receiver and a second light receiver. The first light emitter is operable to emit a first measurement light toward the first reflector. The first light receiver receives the first measurement light reflected by the first reflector as the first reflected light. The second light emitter is operable to emit a second measurement light toward the second reflector. The second light receiver receives the second measurement light reflected by the second reflector as the second reflected light.

[0014] The laser gas analyzer according to the present embodiment is able to measure the concentration of the component to be measured in the second region and the concentration of the component to be measured in the first region in parallel by including two sets of combinations of light emitter and light receiver, and is able to maintain measurement accuracy while measuring the concentration of the component to be measured in the second region.

[0015] (5) The laser gas analyzer described under any one of (1) to (3) above, wherein the first reflector is a beam splitter disposed on an optical path where the measurement light travels from the light emitter to the second reflector. The light receiver includes a first light receiver and a second light receiver. The first light receiver receives the measurement light reflected by the beam splitter as the first reflected light. The second light receiver receives the measurement light transmitted through the beam splitter and reflected by the second reflector as the second reflected light.

[0016] The laser gas analyzer according to the present embodiment reduces the number of light emitters by one, by including a beam splitter as the first reflector.

[0017] (6) The laser gas analyzer described under any one of (1) to (3) above, wherein the first reflector is movable to positions on or off an optical path where the measurement light travels from the light emitter to the second reflector. The light receiver receives the measurement light reflected by the first reflector as the first reflected light when the first reflector is positioned on the optical path. The light receiver receives the measurement light reflected by the second reflector as the second reflected light when the first reflector is positioned off the optical path.

[0018] The laser gas analyzer according to the present embodiment reduces the number of light emitters and light receivers by one each, by including a reflector that is moveable on and off the optical path of the measurement light as the first reflector.

[0019] (7) A purge gas supply method according to at least one embodiment is performed by a laser gas analyzer. The laser gas analyzer includes a housing, a purge gas inlet, a light emitter, a first reflector, a second reflector, a light receiver, and a controller. The housing includes a wall that defines a first region where purge gas is supplied, and a window that allows light to be transmitted between the first region and a second region containing a component to be measured. The purge gas inlet includes a solenoid valve operable to supply the purge gas to the first region. The light emitter is disposed in the first region and is operable to emit measurement light toward the second region. The first reflector is disposed in the first region and reflects a portion of the measurement light that has traveled only in the first region as first reflected light. The second reflector is disposed in the second region and reflects a portion of the measurement light that has traveled to the second region as second reflected light toward the first region. The light receiver is disposed in the first region and receives the first reflected light and the second reflected light. The controller calculates concentration of the component to be measured in the second region based on intensity of the measurement light and intensity of the second reflected light and outputs the concentration as a measurement result. The purge gas supply method includes the controller calculating concentration of the component to be measured in the first region based on absorbance calculated using the intensity of the measurement light and intensity of the first reflected light. The purge gas supply method includes the controller controlling opening and closing of the solenoid valve of the purge gas inlet based on the concentration of the component to be measured in the first region. (Advantageous Effect)

[0020] According to the laser gas analyzer and the purge gas supply method of the present disclosure, the amount of the purge gas used is reduced.

[0021] In the accompanying drawings: FIG. 1 is a schematic diagram illustrating an example structure of a laser gas analyzer according to a comparative example; FIG. 2 is a schematic diagram illustrating an example structure of a laser gas analyzer according to an embodiment of the present disclosure; FIG. 3 is a diagram illustrating an example of functional blocks of a laser gas analyzer; FIG. 4 is a diagram illustrating an example of an absorption spectrum when a component to be measured is oxygen; FIG. 5 is a flowchart illustrating an example of control procedures for a solenoid valve that controls oxygen concentration in a first region; FIG. 6 is a flowchart illustrating an example of control procedures for a three-way solenoid valve that controls oxygen concentration in a first region; FIG. 7 is a schematic diagram illustrating an example structure in which a first reflector is a beam splitter; and FIG. 8 is a schematic diagram illustrating an example structure in which a first reflector is movable.DETAILED DESCRIPTION

[0022] (Comparative example) As illustrated in FIG. 1, a laser gas analyzer 900 according to a comparative example includes a first region 922 and a second region 923. The first region 922 is a region outside a pipe 930 where a gas to be measured is flowing. The second region 923 is a region inside the pipe 930 where the gas to be measured is flowing.

[0023] The laser gas analyzer 900 according to the comparative example includes an end 914, a flange 929, and a housing 921. The laser gas analyzer 900 is attached to the pipe 930 by the flange 929. The first region 922 is a region between the end 914 and the flange 929.

[0024] The second region 923 is a region bounded by the housing 921 and the flange 929. The housing 921 has openings through which the gas to be measured may pass in and out of the second region 923.

[0025] The laser gas analyzer 900 according to the comparative example includes a light emitter 911 and a light receiver 913 disposed in the first region 922 and a reflector 928 disposed in the second region 923. Further, the laser gas analyzer 900 includes a controller 915 that controls the light emitter 911 and the light receiver 913.

[0026] The light emitter 911 emits a measurement light 911a toward the reflector 928. The reflector 928 reflects the measurement light 911a toward the light receiver 913. The light receiver 913 receives the measurement light 911a reflected by the reflector 928. The measurement light 911a passes through both the first region 922 and the second region 923.

[0027] The controller 915 controls the measurement light 911a emission by the light emitter 911. The controller 915 also obtains received light intensity of the measurement light 911a at the light receiver 913. The controller 915 calculates concentration of a component to be measured in the second region 923 based on intensity of the measurement light 911a emitted by the light emitter 911 and the received light intensity of the measurement light 911a at the light receiver 913.

[0028] The laser gas analyzer 900 according to the comparative example is configured to supply purge gas to the first region 922 and fill the first region 922 with the purge gas by flowing the purge gas into the first region 922. When the component to be measured is oxygen, nitrogen is used as the purge gas. Components of the purge gas are known. The atmosphere in the first region 922 is stabilized when the first region 922 is filled with the purge gas. For example, when the component to be measured is oxygen, pure nitrogen is supplied as the purge gas so that the measurement light 911a passing through the first region 922 is not absorbed by the oxygen, thereby enhancing the measurement accuracy of oxygen concentration in the second region 923. Accordingly, the laser gas analyzer 900 according to the comparative example constantly supplies the purge gas so that the first region 922 is always filled with the purge gas.

[0029] However, the constant supply of the purge gas increases the amount of the purge gas used. A reduction in the amount of the purge gas used is sought. A laser gas analyzer 100 according to the present embodiment is able to reduce the amount of the purge gas used. Embodiments of the present disclosure are described below with reference to the drawings.

[0030] (Laser gas analyzer 100 according to embodiment of present disclosure) As illustrated in FIG. 2, the laser gas analyzer 100 according to the present embodiment includes a first region 22 and a second region 23. The first region 22 is a region outside a pipe 30 where a gas to be measured is flowing. The second region 23 is a region inside the pipe 30 where the gas to be measured is flowing.

[0031] The first region 22 is a section where a component to be measured is analyzed by emitting a measurement light with respect to a gas to be measured and receiving the reflected light, as described below. The first region 22 is controlled to not, in principle, contain the component to be measured in the gas to be measured, and is also referred to as a non-measurement section. The second region 23 is a section where the measurement light and reflected light pass through the gas to be measured to cause light absorption in an absorption spectrum corresponding to the gas to be measured. The second region 23 is filled with the gas to be measured and is also referred to as a measurement section.

[0032] According to the present embodiment, the gas to be measured is assumed to be a gas containing a component to be measured such as oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), or the like. The gas to be measured may contain one or more components to be measured. The pipe 30 extends in the vertical direction in FIG. 2. The gas to be measured flows along the direction in which the pipe 30 extends.

[0033] The laser gas analyzer 100 includes a wall 12, an end 14, a flange 29, and a housing 21. The laser gas analyzer 100 is attached to the pipe 30 by the flange 29. The flange 29 includes a window configured to allow a second measurement light 11a, described below, to be transmitted from the first region 22 to the second region 23 and a second reflected light 13a to be transmitted from the second region 23 to the first region 22. The first region 22 is a region bounded by the wall 12, the end 14, and the flange 29. In other words, the first region 22 is defined by the wall 12, the end 14, and the flange 29. The structure of the wall 12 and the window in the flange 29 is also referred to as a housing.

[0034] As illustrated in FIG. 3, the laser gas analyzer 100 includes a purge gas inlet 221 that supplies a purge gas to the first region 22 and a purge gas outlet 222 that discharges the purge gas from the first region 22. The wall 12 or the end 14 that define the first region 22 (see FIG. 2) includes piping, not illustrated, that supplies the purge gas as the purge gas inlet 221. The purge gas inlet 221 includes a solenoid valve that opens when supplying the purge gas to the first region 22. The wall 12 or the end 14 that define the first region 22 includes piping, not illustrated, that discharges the purge gas as the purge gas outlet 222. The purge gas outlet 222 includes a check valve that allows gas to flow only in the direction of discharge from the first region 22 to outside the first region 22.

[0035] The first region 22 is filled with the purge gas by flowing the purge gas from the purge gas inlet 221 to the purge gas outlet 222. The first region 22 is configured so that the purge gas may be contained within the first region 22 by closing the solenoid valve of the purge gas inlet 221 while the first region 22 is filled with the purge gas. That is, the first region 22 is configured to be highly airtight when the solenoid valve of the purge gas inlet 221 is closed.

[0036] A gas that does not contain the component to be measured in the gas to be measured or a gas with a concentration of the component to be measured less than a defined concentration is supplied as the purge gas. The defined concentration is sufficiently low to not affect the absorption spectrum of the component to be measured in the second region 23. When the component to be measured is oxygen (O2), then nitrogen (N2), for example, may be used as the purge gas.

[0037] The second region 23 is a region bounded by the housing 21 and the flange 29. In other words, the second region 23 is defined by the housing 21 and the flange 29. The housing 21 has openings through which the gas to be measured may pass in and out of the second region 23.

[0038] The laser gas analyzer 100 includes a first light emitter 16, a second light emitter 11, a first light receiver 17, and a second light receiver 13 disposed in the first region 22, as illustrated in FIG. 2 and FIG. 3. The first light emitter 16 and the second light emitter 11 may also be collectively referred to as a light emitter. The first light receiver 17 and the second light receiver 13 may also be collectively referred to as a light receiver. The laser gas analyzer 100 includes a first reflector 18 disposed in the first region 22 and a second reflector 28 disposed in the second region 23. The laser gas analyzer 100 includes a controller 15 that controls the light emitter and the light receiver.

[0039] The first light emitter 16 is configured to emit first measurement light 16a toward the first reflector 18. The first reflector 18 is configured to reflect the first measurement light 16a toward the first light receiver 17 as first reflected light 17a. The first light receiver 17 receives the first reflected light 17a that is the first measurement light 16a emitted from the first light emitter 16 and reflected by the first reflector 18. The first measurement light 16a and the first reflected light 17a pass through only the first region 22.

[0040] The second light emitter 11 is configured to emit second measurement light 11a toward the second reflector 28. The second reflector 28 is configured to reflect the second measurement light 11a toward the second light receiver 13 as second reflected light 13a. The second light receiver 13 receives the second reflected light 13a that is the second measurement light 11a emitted from the second light emitter 11 and reflected by the second reflector 28. The second measurement light 11a and the second reflected light 13a pass through both the first region 22 and the second region 23. An optical path along which the second measurement light 11a and the second reflected light 13a pass is along a direction (left to right in FIG. 2) that is approximately perpendicular to the direction in which the pipe 30 extends.

[0041] The first light emitter 16 includes a laser that emits a laser beam as the first measurement light 16a and laser drive circuitry that supplies electric current to the laser. The second light emitter 11 includes a laser that emits a laser beam as the second measurement light 11a and laser drive circuitry that supplies electric current to the laser. The laser may include, for example, a wavelength-variable semiconductor laser able to sweep (scan) wavelengths in a range that includes the absorption wavelength of the gas to be measured. The laser drive circuitry may include a transistor, a laser drive integrated circuit (IC), or the like that is able to supply drive current to the laser based on a control signal from the controller 15.

[0042] The first light receiver 17 receives the first reflected light 17a that passes through only the first region 22 and is subject to light absorption by the purge gas. The second receiver 13 receives the second reflected light 13a that passes through both the first region 22 and the second region 23 and is subject to light absorption by both the purge gas and the gas to be measured. The light receiver may include, for example, a light receiving element such as a photodiode, phototransistor, or the like, voltage conversion circuitry that converts a light detection current from a light receiving element to voltage, and an amplifier. The light receiver detects the reflected light received by the light receiving element and outputs received light intensity to the controller 15. The light receiving element is not limited to a photodiode or phototransistor, and may include a variety of other elements.

[0043] The controller 15 controls the first light emitter 16 and the second light emitter 11 to control emission intensity of the first measurement light 16a and the second measurement light 11a. The controller 15 may control emission wavelength or intensity of the laser light emitted by the light emitter, pulse width or duty ratio when the light emitter emits laser light in pulses, and the like.

[0044] The controller 15 obtains output signals corresponding to the received light intensity from the first light receiver 17 and the second light receiver 13, and processes the output signals. The controller 15 may calculate the absorption spectrum in the first region 22 or the second region 23 based on the output signals. The controller 15 may calculate the component or the concentration of the component in the purge gas based on the absorption spectrum in the first region 22. The controller 15 may calculate the component or the concentration of the component in the gas to be measured based on the absorption spectrum in the second region 23.

[0045] The controller 15 may include a processor such as a central processing unit (CPU) or dedicated circuitry such as a field programmable gate array (FPGA), for example. The controller 15 may be configured to execute a program that realizes various functions of the laser gas analyzer 100. The controller 15 may include a storage. The storage may store information used in the operation of the controller 15, a program to realize a function of the controller 15, and the like. The storage may function as working memory of the controller 15. The storage may be configured as a semiconductor memory, for example. The storage may be configured as a separate unit from the controller 15.

[0046] The laser gas analyzer 100 may further include an interface. Example interfaces include communication interfaces that communicate with external devices by wired or wireless means. The interface may include a display device. Example display devices include various displays such as liquid crystal displays, for example. The interface may include an audio output device such as a speaker. The interface may include an input device that accepts input from a user. Example input devices include keyboards or physical keys, touch panels or touch sensors, and pointing devices such as mice.

[0047] (Example of operation of laser gas analyzer 100 to measure concentration of component to be measured) The laser gas analyzer 100 according to the present embodiment is an analyzer based on the tunable diode laser absorption spectroscopy (TDLAS) method. In TDLAS, a semiconductor laser beam with a much narrower linewidth than the gas absorption linewidth is transmitted through the gas to be measured, the wavelength is swept (scanned) by high-speed modulation of the driving current, and transmitted light intensity is measured to obtain one independent absorption spectrum. Specifically, in the laser gas analyzer 100, the controller 15 varies the wavelength of the measurement light in a defined range by continuously varying the magnitude of the drive current that drives the laser in the light emitter. As the measurement light passes through the gas to be measured, the component at the wavelength corresponding to the gas to be measured is absorbed. For example, many gas molecules such as carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (CnHm), ammonia (NH3), oxygen (O2), and the like have light absorption spectra in the infrared to near-infrared wavelength range due to molecular vibration and rotational energy transitions. Absorption spectra are specific to component molecules. According to the Beer-Lambert law, absorbance is proportional to component concentration and optical path length. Therefore, the concentration of a target component is calculated by measuring the absorption spectrum intensity.

[0048] The absorption spectrum of the gas to be measured is determined based on the species and concentration of the component to be measured in the gas to be measured. For example, the absorption spectrum when the component to be measured is oxygen (O2) is illustrated in FIG. 4. In FIG. 4, the horizontal axis represents wavelength. The vertical axis represents light intensity. In the absorption spectrum of FIG. 4, the light intensity at wavelength lO2is locally reduced compared to the light intensity at other nearby wavelengths. The light intensity that is not absorbed by the component to be measured is represented by In. The light intensity absorbed by the component to be measured is represented by Ia.

[0049] When the component to be measured is oxygen (O2), the controller 15 causes the wavelength of the measurement light to sweep over a defined wavelength range including the wavelength lO2. The range of wavelength sweep may be determined so that the graph of light intensity is wavelength-independent and flat on the short and long wavelength sides of lO2, as illustrated in FIG. 4. The scan range of the measurement light may be set to 0.1 nm to 0.2 nm, for example, when the component to be measured is O2. Further, the linewidth of the measurement light may be set to 0.0002 nm, for example.

[0050] When the wavelength of the measurement light is swept by varying the drive current supplied to the laser, the light intensity on the short wavelength side detected at the light receiver is different from the light intensity on the long wavelength side. The controller 15 performs a baseline flattening process so that the light intensity on the short wavelength side is the same as the light intensity on the long wavelength side.

[0051] When the component to be measured is oxygen (O2), the absorbance Ab at the wavelength lO2is expressed by the following Formula (1).

[0052]

[0053] According to the Beer-Lambert law, the absorbance Ab of the gas to be measured is proportional to the component concentration of the gas to be measured and the optical path length of the measurement light and the reflected light exposed to the gas to be measured. The controller 15 obtains the light intensity Inbefore entering the gas to be measured based on the control information of the light emitter, and the light intensity Iaafter passing through the gas to be measured based on the output signal of the light receiver, and applies the light intensity Inand the light intensity Iato the above Formula (1) to calculate the absorbance Ab. The controller 15 is able to calculate the component concentration of the gas to be measured based on the calculated absorbance Ab and the optical path length of the measurement light and the reflected light passing through the gas to be measured. For example, in FIG. 2, when the second measurement light 11a is reflected in the direction of approximately 180 degrees at the second reflector 28, the optical path length of the second measurement light 11a and the second reflected light 13a passing through the gas to be measured is twice the length of the distance from the pipe 30 to the second reflector 28. Various methods may be used to convert the absorption spectrum to the concentration of the component to be measured, such as a peak height method, a spectral area method, a 2f method, and the like.

[0054] According to the present embodiment, the controller 15 of the laser gas analyzer 100 controls the second light emitter 11 to emit the second measurement light 11a, obtains the received light intensity when the second reflected light 13a reflected by the second reflector 28 is received by the second light receiver 13, and calculates the absorbance at the wavelength corresponding to the component to be measured. For example, when the component to be measured is oxygen, the wavelength corresponding to the component to be measured is lO2. The controller 15 calculates the concentration of the component to be measured in the second region 23 based on the absorbance at the wavelength corresponding to the component to be measured and the optical path length, and outputs as a measurement result of the component to be measured.

[0055] (Example of operation to control concentration of component to be measured in first region 22 to be less than first threshold value) As described above, when the component to be measured is oxygen (O2), the laser gas analyzer 100 calculates the absorbance Ab at the wavelength lO2based on the intensity of the second measurement light 11a at emission and the intensity of the second reflected light 13a received at the second light receiver 13. Here, the second measurement light 11a and the second reflected light 13a also pass through the first region 22. When the atmosphere filling the first region 22 contains oxygen, the absorbance Ab is affected by the oxygen in the atmosphere filling the first region 22.

[0056] The laser gas analyzer 100 controls the concentration of the component to be measured in the atmosphere filling the first region 22 by supplying the purge gas to the first region 22.

[0057] As described above, the first region 22 is configured to be highly airtight when the solenoid valves of the purge gas inlet 221 and the purge gas outlet 222 are closed. However, external gas may enter the first region 22 due to a leak from any of the wall 12, the end 14, or the flange 29 that define the first region 22, or from joins between these. When oxygen enters the first region 22 as an external gas, the oxygen concentration in the first region 22 increases.

[0058] When the laser gas analyzer 100 analyzes the gas to be measured with oxygen as the component to be measured, the effect of the oxygen contained in the atmosphere filling the first region 22 causes an error in the measurement result of the oxygen concentration in the gas to be measured in the second region 23. In order to avoid an error in the measurement result of the oxygen concentration in the gas to be measured in the second region 23, a reduction in the oxygen concentration in the first region 22 is sought. Specifically, when the oxygen concentration in the first region 22 becomes high, oxygen may be expelled from the first region 22 to reduce the oxygen concentration by supplying and discharging nitrogen gas, for example, as the purge gas in the first region 22.

[0059] As mentioned regarding the laser gas analyzer 900 according to the comparative example, by keeping the purge gas flowing in the first region 22, the oxygen concentration in the first region 22 is maintained at the oxygen concentration of the purge gas. However, as mentioned regarding the comparative example, a loss is incurred by the continuous flow of the purge gas.

[0060] Therefore, in order to reduce the loss caused by the flow of the purge gas, in the laser gas analyzer 100 according to the present embodiment, the controller 15 measures the oxygen concentration in the first region 22, and when the oxygen concentration in the first region 22 reaches a first threshold value or more, the controller 15 supplies the purge gas to the first region 22 so that the oxygen concentration in the first region 22 becomes less than the first threshold value. The first threshold is defined according to the accuracy required to measure the oxygen concentration in the second region 23. The first threshold may be set to 0.5 %, for example, but is not limited to this example.

[0061] Specifically, the controller 15 of the laser gas analyzer 100 controls the first light emitter 16 to emit the first measurement light 16a, obtains the received light intensity when the first reflected light 17a reflected by the first reflector 18 is received by the first light receiver 17, and calculates the absorbance at the wavelength corresponding to the component to be measured. For example, when the component to be measured is oxygen, the wavelength corresponding to the component to be measured is lO2. The controller 15 calculates the concentration of the component to be measured in the first region 22 based on the absorbance at the wavelength corresponding to the component to be measured and the optical path length.

[0062] When the component to be measured is oxygen, the controller 15 measures the oxygen concentration as the concentration of the component to be measured in the first region 22. When the oxygen concentration in the first region 22 is the first threshold value or more, the controller 15 opens the solenoid valve of the purge gas inlet 221 and flows the purge gas into the first region 22 to reduce the oxygen concentration in the first region 22 to less than the first threshold value. On the other hand, when the oxygen concentration in the first region 22 is less than the first threshold, there is no need to reduce the oxygen concentration. That is, there is no need to flow the purge gas into the first region 22. Therefore, the controller 15 closes the solenoid valve of the purge gas inlet 221 when the oxygen concentration in the first region 22 is less than the first threshold value.

[0063] <Example flowchart> The controller 15 of the laser gas analyzer 100 may execute the purge gas supply method including an example flowchart procedure illustrated in FIG. 5. The purge gas supply method may be realized as a purge gas supply program to be executed by a processor of the controller 15. The purge gas supply program may be stored on a non-transitory computer-readable storage medium.

[0064] The controller 15 measures the oxygen concentration in the non-measurement section (step S1). The non-measurement section corresponds to the first region 22 as described above. The oxygen concentration corresponds to the component to be measured. The controller 15 determines whether the oxygen concentration in the non-measurement section is less than the first threshold value (step S2).

[0065] When the oxygen concentration in the non-measurement section is not less than the first threshold value (step S2: NO), that is, when the oxygen concentration in the non-measurement section is the first threshold value or more, the controller 15 opens the solenoid valve of the purge gas inlet 221 (step S3) to supply the purge gas to the non-measurement section to lower the oxygen concentration in the non-measurement section. After the controller 15 opens the solenoid valve of the purge gas inlet 221, processing returns to the measurement procedure of step S1. The controller 15 repeats steps S1 to S3 until the oxygen concentration in the non-measurement section is less than the first threshold value.

[0066] When the oxygen concentration in the non-measurement section is less than the first threshold (step S2: YES), the controller 15 closes the solenoid valve of the purge gas inlet 221 (step S4) because there is no need to supply the purge gas to the non-measurement section. After execution of the procedure in step S4, the controller 15 ends execution of the procedures of the flowchart of FIG. 5. The controller 15 may return to the measurement procedure of step S1 after executing the procedure of step S4.

[0067] <Review> As described above, the laser gas analyzer 100 according to the present embodiment controls the concentration of the component to be measured in the first region 22 that is the non-measurement section to be less than the first threshold value in order to maintain the measurement accuracy of the concentration of the component to be measured in the second region 23 that is the measurement section. The laser gas analyzer 100 measures the concentration of the component to be measured in the first region 22 and supplies the purge gas to the first region 22 to reduce the concentration of the component to be measured when the concentration of the component to be measured reaches the first threshold value or more. That is, the laser gas analyzer 100 determines whether to supply the purge gas to the first region 22, and controls the opening and closing of the solenoid valve in the purge gas inlet 221, based on a measurement result of the concentration of the component to be measured in the first region 22. The purge gas supply is stopped when the concentration of the component to be measured in the first region 22 is less than the first threshold value, thereby reducing the amount of the purge gas used.

[0068] Further, the laser gas analyzer according to the present embodiment is able to control the concentration of the component to be measured in the first region to be less than the first threshold value while limiting the purge gas supply period. As a result, both a reduction in the amount of purge gas used and maintenance of measurement accuracy of the concentration of the component to be measured in the second region are realized.

[0069] The laser gas analyzer 100 is able to measure the concentration of the component to be measured in the first region 22 using the first light emitter 16 and the first light receiver 17, while measuring the concentration of the component to be measured in the second region 23 using the second light emitter 11 and the second light receiver 13. The laser gas analyzer 100 is able to measure the concentration of the component to be measured in the second region 23 and the concentration of the component to be measured in the first region 22 in parallel by including two sets of combinations of light emitter and light receiver, and is able to maintain measurement accuracy while measuring the concentration of the component to be measured in the second region 23.

[0070] The purge gas is not limited to nitrogen gas, and may be various other gases as long as the concentration of the component to be measured is less than the first threshold value.

[0071] (Example of operation when purging with instrument air) As described above, the purge gas is used to reduce the effect of absorption by the component to be measured in the first region 22 that is the non-measurement section, and to improve the measurement accuracy of the concentration of the component to be measured in the second region 23. The purge gas may be used for other purposes, such as to protect elements such as the light emitter or the light receiver disposed in the first region 22 from the ambient environment by stabilizing the atmosphere in the first region 22 that is the non-measurement section. In such a case, the laser gas analyzer 100 may control the concentration of the component to be measured within a defined range in the first region 22 that is the non-measurement section.

[0072] According to the present example, the component to be measured is oxygen. Further, according to the present example, as the purge gas, either instrument air or oxygen gas having a concentration adjusted to a defined concentration is supplied to the first region 22. Oxygen gas having a concentration adjusted to a defined concentration may also be referred to as defined concentration oxygen gas. The purge gas inlet 221 includes a three-way solenoid valve that may be switched to either instrument air or defined concentration oxygen gas to supply the first region 22. The defined concentration is a concentration included in the defined range that is a target for controlling concentration of the component to be measured in the first region 22. The defined range of oxygen concentration is set to be 20 % to 22 %. The defined concentration is set to be 21 %. The defined range of oxygen concentration or the defined concentration are not limited to the examples described above and may be set to other values. The oxygen concentration in the instrument air is not controlled to be in the defined range. Further, the oxygen concentration in the gas to be measured flowing in the second region 23 is not controlled to be within the defined range.

[0073] The controller 15 of the laser gas analyzer 100 measures the oxygen concentration as the concentration of the component to be measured in the first region 22. The controller 15 controls the three-way solenoid valve of the purge gas inlet 221 to continue supplying the instrument air to the first region 22 when the oxygen concentration in the first region 22 is within the defined range. When the oxygen concentration in the first region 22 is outside the defined range, the controller 15 controls the three-way solenoid valve of the purge gas inlet 221 to supply defined concentration oxygen gas to the first region 22 in order to control the oxygen concentration in the first region 22 to be within the defined range.

[0074] <Example flowchart> The controller 15 of the laser gas analyzer 100 may execute the purge gas supply method including the example flowchart procedure illustrated in FIG. 6.

[0075] The controller 15 measures the oxygen concentration in the non-measurement section (step S11). The non-measurement section corresponds to the first region 22 as described above. The oxygen concentration corresponds to the component to be measured. The controller 15 determines whether the oxygen concentration in the non-measurement section area is in the defined range (step S12).

[0076] When the oxygen concentration in the non-measurement section is in the defined range (step S12: YES), the controller 15 controls the three-way solenoid valve of the purge gas inlet 221 to flow the instrument air as the purge gas to the non-measurement section (step S13). The controller 15 returns to the measurement procedure of step S11 after executing the procedure of step S13.

[0077] When the oxygen concentration in the non-measurement section is not in the defined range (step S12: NO), that is, when the oxygen concentration in the non-measurement section is outside the defined range, the controller 15 controls the three-way solenoid valve of the purge gas inlet 221 to flow the defined concentration oxygen gas as the purge gas to the non-measurement section (step S14). The controller 15 returns to the measurement procedure of step S11 after executing the procedure of step S14.

[0078] The controller 15 is able to control the oxygen concentration in the first region 22 that is the non-measurement section to be in the defined range by repeating the flowchart procedures of FIG. 6.

[0079] <Review> As described above, the laser gas analyzer 100 according to the present embodiment supplies the instrument air to the first region 22 as the purge gas during normal operation, while switching to supplying the defined concentration oxygen gas as the purge gas when the oxygen concentration in the first region 22 falls outside the defined range. That is, the laser gas analyzer 100 determines whether to switch to supplying the defined concentration oxygen gas as the purge gas to the first region 22 based on a measurement result of the oxygen concentration in the first region 22. When the oxygen concentration in the first region 22 is in the defined range, the supply of the oxygen gas is stopped, thereby reducing the amount of the oxygen gas used. The reduced use of the oxygen gas reduces cost burden or environmental impact. Further, the use of the instrument air instead of a high purity gas such as nitrogen gas as the purge gas also reduces the cost burden or environmental impact.

[0080] (Other examples for light emitter, light receiver, and reflector) According to an embodiment described above, the laser gas analyzer 100 includes the first light emitter 16 and the second light emitter 11 as the light emitter, and the first light receiver 17 and the second light receiver 13 as the light receiver. Further, the first reflector 18 reflects the first measurement light 16a. The second reflector 28 reflects the second measurement light 11a. Other examples of configurations for the light emitter, the light receiver, and the reflector are described below.

[0081] As illustrated in FIG. 7, the laser gas analyzer 100 may include a beam splitter 185 as the first reflector 18. The beam splitter 185 is disposed on the optical path of the second measurement light 11a. The beam splitter 185 reflects some of the second measurement light 11a that proceeds to the first receiver 17a as the first reflected light 17a. The beam splitter 185 transmits some of the remaining light of the second measurement light 11a that is not reflected and proceeds to the second region 23 and the second reflector 28.

[0082] In order to calculate the absorbance of the component to be measured in the second region 23, the controller 15 of the laser gas analyzer 100 may use the product of the transmission ratio of the second measurement light 11a by the beam splitter 185 and the intensity of the second measurement light 11a as the light intensity Inbefore entering the gas to be measured in the second region 23, and the received light intensity of the second reflected light 13a received by the second light receiver 13 as the light intensity Iaafter passing through the gas to be measured in the second region 23. In order to calculate the absorbance of the component to be measured in the first region 22, the controller 15 may use the product of the reflection ratio of the second measurement light 11a by the beam splitter 185 and the intensity of the second measurement light 11a as the light intensity Inbefore entering the gas to be measured in the first region 22, and the received light intensity of the first reflected light 17a received by the first light receiver 17 as the light intensity Iaafter passing through the gas to be measured in the first region 22.

[0083] The laser gas analyzer 100 illustrated in FIG. 7 does not need to include the first light emitter 16, due to including the beam splitter 185 as the first reflector 18. That is, the number of light emitters is reduced by one.

[0084] As illustrated in FIG. 8, the laser gas analyzer 100 may include a mobile reflector as the first reflector 18. The mobile reflector is configured to be movable to positions on or off the optical path of the second measurement light 11a. The mobile reflector is represented as a reflector 181 when positioned off the optical path of the second measurement light 11a and a reflector 182 when positioned on the optical path of the second measurement light 11a.

[0085] In the state where the mobile reflector is off the optical path of the second measurement light 11a (state of the reflector 181), the second measurement light 11a is reflected by the second reflector 28 and the laser gas analyzer 100 is able to receive the second reflected light 13a at the second light receiver 13. In this case, the controller 15 of the laser gas analyzer 100 is able to calculate the absorbance of the component to be measured in the second region 23 based on the intensity of the second measurement light 11a and the intensity of the second reflected light 13a received at the second light receiver 13.

[0086] On the other hand, in the state where the mobile reflector is on the optical path of the second measurement light 11a (state of the reflector 182), the measurement light 11b is reflected by the reflector 182 and the laser gas analyzer 100 is able to receive the reflected light 13b at the second light receiver 13. The measurement light 11b does not pass through the second region 23 and corresponds to the first measurement light 16a. Further, the reflected light 13b does not pass through the second region 23 and is therefore equivalent to the first reflected light 17a. Accordingly, the controller 15 of the laser gas analyzer 100 is able to calculate the absorbance at the component to be measured in the first region 22 based on the intensity of the measurement light 11b corresponding to the first measurement light 16a and the intensity of the reflected light 13b corresponding to the first reflected light 17a at the second light receiver 13.

[0087] The laser gas analyzer 100 illustrated in FIG. 8 is able to measure the absorbance of the component to be measured in the second region 23 and the absorbance of the component to be measured in the first region 22 by dividing a measuring period. The laser gas analyzer 100 illustrated in FIG. 8 does not need to include the first light emitter 16 and the first light receiver 17, due to including the mobile reflector as the first reflector 18. That is, the numbers of light emitters and light receivers are reduced by one each.

[0088] The above description of embodiments according to the present disclosure is provided with reference to the drawings. Specific configurations are not limited to the embodiments described, and variations are included without departing from the scope of the present disclosure.

[0089] 100 laser gas analyzer 11 second light emitter (11a, 11b: measurement light) 12 wall 13 second light receiver (13a, 13b: reflected light) 14 end 15 controller 16 first light emitter (16a: measurement light) 17 first light receiver (17a: reflected light) 18 first reflector (181, 182: mobile reflector) 185 beam splitter 21 housing 22 first region (221: purge gas inlet, 222: purge gas outlet) 23 second region 28 second reflector 29 flange 30 pipe

Claims

1. A laser gas analyzer comprising: a housing including a wall that defines a first region where purge gas is supplied, and a window that allows light to be transmitted between the first region and a second region containing a component to be measured; a purge gas inlet including a solenoid valve operable to supply the purge gas to the first region; a light emitter disposed in the first region and operable to emit measurement light toward the second region; a first reflector disposed in the first region and reflecting a portion of the measurement light that has traveled only in the first region as first reflected light; a second reflector disposed in the second region and reflecting a portion of the measurement light that has traveled to the second region as second reflected light toward the first region; a light receiver disposed in the first region and receiving the first reflected light and the second reflected light; and a controller that calculates concentration of the component to be measured in the second region based on intensity of the measurement light and intensity of the second reflected light and outputs the concentration as a measurement result, wherein the controller calculates concentration of the component to be measured in the first region based on the intensity of the measurement light and intensity of the first reflected light, and controls opening and closing of the solenoid valve of the purge gas inlet based on the concentration of the component to be measured in the first region.

2. The laser gas analyzer according to claim 1, wherein the concentration of the component to be measured in the purge gas is less than a first threshold value, and the controller opens the solenoid valve of the purge gas inlet when the concentration of the component to be measured in the first region is the first threshold value or more, and closes the solenoid valve of the purge gas inlet when the concentration of the component to be measured in the first region is less than the first threshold value.

3. The laser gas analyzer according to claim 1, wherein the solenoid valve of the purge gas inlet includes a three-way solenoid valve operable to switch between instrument air and defined concentration oxygen gas as the purge gas to supply the first region, and the controller controls the three-way solenoid valve to supply the instrument air to the first region when concentration of oxygen gas in the first region is in a defined range including the defined concentration, and controls the three-way solenoid valve to supply the defined concentration oxygen gas to the first region when the concentration of the oxygen gas in the first region is outside the defined range.

4. The laser gas analyzer according to any one of claims 1 to 3, wherein the light emitter includes a first light emitter and a second light emitter, the light receiver includes a first light receiver and a second light receiver, the first light emitter is operable to emit a first measurement light toward the first reflector, the first light receiver receives the first measurement light reflected by the first reflector as the first reflected light, the second light emitter is operable to emit a second measurement light toward the second reflector, and the second light receiver receives the second measurement light reflected by the second reflector as the second reflected light.

5. The laser gas analyzer according to any one of claims 1 to 3, wherein the first reflector is a beam splitter disposed on an optical path where the measurement light travels from the light emitter to the second reflector, the light receiver includes a first light receiver and a second light receiver, the first light receiver receives the measurement light reflected by the beam splitter as the first reflected light, and the second light receiver receives the measurement light reflected by the second reflector after passing through the beam splitter as the second reflected light.

6. The laser gas analyzer according to any one of claims 1 to 3, wherein the first reflector is movable to positions on or off an optical path where the measurement light travels from the light emitter to the second reflector, and the light receiver receives the measurement light reflected by the first reflector as the first reflected light when the first reflector is positioned on the optical path, and receives the measurement light reflected by the second reflector as the second reflected light when the first reflector is positioned off the optical path.

7. A purge gas supply method performed by a laser gas analyzer comprising: a housing including a wall that defines a first region where purge gas is supplied, and a window that allows light to be transmitted between the first region and a second region containing a component to be measured; a purge gas inlet including a solenoid valve operable to supply the purge gas to the first region; a light emitter disposed in the first region and operable to emit measurement light toward the second region; a first reflector disposed in the first region and reflecting a portion of the measurement light that has traveled only in the first region as first reflected light; a second reflector disposed in the second region and reflecting a portion of the measurement light that has traveled to the second region as second reflected light toward the first region; a light receiver disposed in the first region and receiving the first reflected light and the second reflected light; and a controller that calculates concentration of the component to be measured in the second region based on intensity of the measurement light and intensity of the second reflected light and outputs the concentration as a measurement result, the purge gas supply method comprising: the controller calculating concentration of the component to be measured in the first region based on the intensity of the measurement light and intensity of the first reflected light; and the controller controlling opening and closing of the solenoid valve of the purge gas inlet based on the concentration of the component to be measured in the first region.

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