JP2024125074A - Laser gas analyzer and purge gas supply method - Google Patents

Abstract

A laser gas analyzer and a purge gas supply method are provided that are capable of reducing the amount of purge gas used.
[Solution] A laser gas analyzer 100 includes a purge gas supply unit 221 that supplies a purge gas to a first region 22, a light emitter 11 that emits measurement light toward a second region 23 containing a component to be measured, a first reflector 18 that reflects the measurement light at the first region 22, a second reflector 28 that reflects the measurement light at the second region 23, a light receiver 13 that receives the first reflected light and the second reflected light, and a control unit 15 that calculates the concentration of the component to be measured in the second region 23 based on the intensity of the measurement light and the intensity of the second reflected light, and outputs the result as a measurement result. The control unit 15 calculates the concentration of the component to be measured in the first region 22 based on the intensity of the measurement light and the intensity of the first reflected light, and controls the opening and closing of a solenoid valve of the purge gas supply unit 221 based on the concentration of the component to be measured in the first region 22.
[Selected figure] Figure 2

Description

This disclosure relates to a laser gas analyzer and a purge gas supply method.

Conventionally, gas measurement devices that measure the concentration of a gas component to be measured in a purge gas are known (see, for example, Patent Document 1).

Chinese Patent Publication No. 101393115

The device described in Patent Document 1 continues to flow purge gas. There is a need to reduce the amount of purge gas used.

The present disclosure has been made in consideration of the above points, and aims to provide a laser gas analyzer and a purge gas supply method that can reduce the amount of purge gas used.

(1) A laser gas analyzer according to some embodiments includes a housing, a purge gas supply unit, a light emitter, a first reflector, a second reflector, a light receiver, and a controller. The housing has a wall defining a first region to which purge gas is supplied, and a window that transmits light between the first region and a second region containing the component to be measured. The purge gas supply unit has an electromagnetic valve that supplies the purge gas to the first region. The light emitter is disposed in the first region and emits measurement light toward the second region. The first reflector is disposed in the first region and reflects the light of the measurement light that has traveled only through the first region as a first reflected light. The second reflector is disposed in the second region and reflects the light of the measurement light that has traveled to the second region as a 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 control unit calculates the concentration of the measurement target component in the first region based on the intensity of the measurement light and the intensity of the first reflected light, and outputs the result as a measurement result. The control unit calculates the concentration of the measurement target component in the second region based on the intensity of the measurement light and the intensity of the second reflected light. The control unit controls the opening and closing of the solenoid valve of the purge gas supply unit based on the concentration of the measurement target component in the first region.

According to the laser gas analyzer of this embodiment, the supply of purge gas is controlled based on the concentration of the component to be measured in the first region, thereby limiting the supply period of the purge gas. In other words, the purge gas does not have to be supplied all the time. By limiting the supply period of the purge gas, the amount of purge gas used is reduced.

(2) In the laser gas analyzer described in (1) above, the concentration of the measurement target component contained in the purge gas may be less than a first threshold. The control unit may open the solenoid valve of the purge gas supply unit when the concentration of the measurement target component in the first region is equal to or greater than the first threshold. The control unit may close the solenoid valve of the purge gas supply unit when the concentration of the measurement target component in the first region is less than the first threshold.

The laser gas analyzer according to this embodiment can control the concentration of the component to be measured in the first region to be less than the first threshold while limiting the supply period of the purge gas. As a result, it is possible to both reduce the amount of purge gas used and maintain the measurement accuracy of the concentration of the component to be measured in the second region.

(3) In the laser gas analyzer described in (1) above, the solenoid valve of the purge gas supply unit may include a three-way solenoid valve that switches between instrument air and oxygen gas of a predetermined concentration as the purge gas and supplies the purge gas to the first region. The control unit may control the three-way solenoid valve to supply the instrument air to the first region when the concentration of oxygen gas in the first region is within a predetermined range including the predetermined concentration. The control unit may control the three-way solenoid valve to supply oxygen gas of the predetermined concentration to the first region when the concentration of oxygen gas in the first region is outside the predetermined range.

The laser gas analyzer according to this embodiment supplies instrument air as a purge gas to the first region in principle, and supplies a predetermined concentration of oxygen gas as a purge gas when the oxygen concentration in the first region falls outside a predetermined range. In other words, the laser gas analyzer determines whether to supply a predetermined concentration of oxygen gas as a 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 within the predetermined range, the supply of oxygen gas as a purge gas is stopped, thereby reducing the amount of oxygen gas used. The reduction in the amount of oxygen gas used reduces the cost burden or the environmental load. In addition, the use of instrument air as a purge gas instead of a high purity gas such as nitrogen gas also reduces the cost burden or the environmental load.

(4) In the laser gas analyzer described in any one of (1) to (3) above, the light emitting unit may have a first light emitting unit and a second light emitting unit. The light receiving unit may have a first light receiving unit and a second light receiving unit. The first light emitting unit may emit a first measurement light toward the first reflecting unit. The first light receiving unit may receive the first measurement light reflected by the first reflecting unit as the first reflected light. The second light emitting unit may emit a second measurement light toward the second reflecting unit. The second light receiving unit may receive the second measurement light reflected by the second reflecting unit as the second reflected light.

The laser gas analyzer according to this embodiment has two combinations of light-emitting and light-receiving parts, so that 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 can be measured in parallel, and the measurement accuracy can be maintained while measuring the concentration of the component to be measured in the second region.

(5) In the laser gas analyzer described in any one of (1) to (3) above, the first reflecting section may be a beam splitter located on an optical path along which the measurement light travels from the light emitting section to the second reflecting section. The light receiving section may have a first light receiving section and a second light receiving section. The first light receiving section may receive the measurement light reflected by the beam splitter as the first reflected light. The second light receiving section may receive the measurement light that passes through the beam splitter and is reflected by the second reflecting section as the second reflected light.

The laser gas analyzer of this embodiment can eliminate one of the light-emitting parts by providing a beam splitter as the first reflecting part.

(6) In the laser gas analyzer described in any one of (1) to (3) above, the first reflecting section may be configured to be movable between a position off the optical path along which the measurement light travels from the light emitting section to the second reflecting section, and a position on the optical path. When the first reflecting section is located on the optical path, the light receiving section may receive the measurement light reflected by the first reflecting section as the first reflected light. When the first reflecting section is off the optical path, the light receiving section may receive the measurement light reflected by the second reflecting section as the second reflected light.

The laser gas analyzer according to this embodiment can reduce the number of light-emitting elements and light-receiving elements by one by providing a movable reflecting element on the optical path of the measurement light as the first reflecting element.

(7) A purge gas supply method according to some embodiments is performed by a laser gas analyzer. The laser gas analyzer includes a housing, a purge gas supply unit, a light emitter, a first reflector, a second reflector, a light receiver, and a control unit. The housing has a wall that defines a first region to which purge gas is supplied, and a window that transmits light between a second region containing a component to be measured and the first region. The purge gas supply unit has an electromagnetic valve that supplies the purge gas to the first region. The light emitter is disposed in the first region and emits measurement light toward the second region. The first reflector is disposed in the first region and reflects the light of the measurement light that has traveled only through the first region as a first reflected light. The second reflector is disposed in the second region and reflects the light of the measurement light that has traveled to the second region as a 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 control unit calculates the concentration of the measurement target component in the second region based on the intensity of the measurement light and the intensity of the second reflected light, and outputs the result as a measurement result. The purge gas supplying method includes a step in which the control unit calculates the concentration of the measurement target component in the first region based on the absorbance calculated using the intensity of the measurement light and the intensity of the first reflected light. The purge gas supplying method includes a step in which the control unit controls the opening and closing of an electromagnetic valve of the purge gas supplying unit based on the concentration of the measurement target component in the first region.

The laser gas analyzer and purge gas supply method disclosed herein reduce the amount of purge gas used.

FIG. 2 is a schematic diagram showing a configuration example of a laser gas analyzer according to a comparative example. FIG. 1 is a schematic diagram illustrating a configuration example of a laser gas analyzer according to an embodiment of the present disclosure. FIG. 2 is a diagram showing an example of a functional block of a laser gas analyzer. FIG. 2 is a diagram showing an example of an absorption spectrum when the component to be measured is oxygen. 5 is a flowchart showing an example of a control procedure of a solenoid valve that controls the oxygen concentration in a first region. 5 is a flowchart showing an example of a control procedure of a three-way solenoid valve that controls the oxygen concentration in a first region. 10 is a schematic diagram showing a configuration example in which a first reflecting portion is a beam splitter; FIG. 11 is a schematic diagram showing a configuration example in which a first reflecting section is movable. FIG.

Comparative Example
1, the laser gas analyzer 900 according to the comparative example includes a first region 922 and a second region 923. The first region 922 is a region outside a pipe 930 through which a gas to be measured flows. The second region 923 is a region inside the pipe 930 through which the gas to be measured flows.

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 a pipe 930 by the flange 929. The first region 922 is the region between the end 914 and the flange 929.

The second region 923 is an area surrounded by the housing 921 and the flange 929. The housing 921 has an opening through which the gas to be measured can pass so that the gas to be measured can enter and exit the second region 923.

The laser gas analyzer 900 according to the comparative example includes a light emitting section 911 and a light receiving section 913 located in a first region 922, and a reflecting section 928 located in a second region 923. The laser gas analyzer 900 also includes a control section 915 that controls the light emitting section 911 and the light receiving section 913.

The light emitting unit 911 emits the measurement light 911a toward the reflecting unit 928. The reflecting unit 928 reflects the measurement light 911a and causes it to travel toward the light receiving unit 913. The light receiving unit 913 receives the measurement light 911a reflected by the reflecting unit 928. The measurement light 911a passes through both the first region 922 and the second region 923.

The control unit 915 controls the measurement light 911a emitted by the light-emitting unit 911. The control unit 915 also acquires the received light intensity of the measurement light 911a at the light-receiving unit 913. The control unit 915 calculates the concentration of the measurement target component in the second region 923 based on the intensity of the measurement light 911a emitted by the light-emitting unit 911 and the received light intensity of the measurement light 911a at the light-receiving unit 913.

The laser gas analyzer 900 according to the comparative example is configured to supply a purge gas to the first region 922, and fills 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. The components of the purge gas are known. When the first region 922 is filled with the purge gas, the atmosphere of the first region 922 is stabilized. For example, when the component to be measured is oxygen, pure nitrogen is supplied as the purge gas, so that the measurement light 911a that passes through the first region 922 is not absorbed by oxygen, and the measurement accuracy of the oxygen concentration in the second region 923 is improved. Therefore, 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.

However, the constant supply of purge gas increases the amount of purge gas used. There is a need to reduce the amount of purge gas used. The laser gas analyzer 100 according to this embodiment can reduce the amount of purge gas used. An embodiment of the present disclosure will be described below with reference to the drawings.

(Laser-based gas analyzer 100 according to an embodiment of the present disclosure)
2, the laser gas analyzer 100 according to this embodiment includes a first region 22 and a second region 23. The first region 22 is a region outside the piping 30 through which the gas to be measured flows. The second region 23 is a region inside the piping 30 through which the gas to be measured flows.

The first region 22 is a section that analyzes the components to be measured by emitting measurement light to the gas to be measured and receiving reflected light, as described below. The first region 22 is controlled so that it does not contain the components to be measured contained in the gas to be measured, and is also called the non-measurement section. The second region 23 is a section that passes the measurement light and reflected light through the gas to be measured, causing light absorption in the absorption spectrum corresponding to the gas to be measured. The second region 23 is also called the measurement section, as it is filled with the gas to be measured.

In this embodiment, the measurement target gas is a gas containing a measurement target component such as oxygen (O ₂ ), carbon monoxide (CO), or carbon dioxide (CO ₂ ). The measurement target gas may contain one or more measurement target components. The pipe 30 extends in the vertical direction in FIG. 2 . The measurement target gas flows along the extension direction of the pipe 30.

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 a pipe 30 by the flange 29. The flange 29 has a window configured to allow the second measurement light 11a described below to pass from the first region 22 to the second region 23, and to allow the second reflected light 13a to pass from the second region 23 to the first region 22. The first region 22 is an area surrounded 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 combination of the wall 12 and the window of the flange 29 is also referred to as a housing.

As shown in FIG. 3, the laser gas analyzer 100 includes a purge gas supply unit 221 that supplies purge gas to the first region 22 and a purge gas exhaust unit 222 that exhausts the purge gas from the first region 22. The wall 12 or end 14 (see FIG. 2) that defines the first region 22 includes a pipe (not shown) that supplies purge gas as the purge gas supply unit 221. The purge gas supply unit 221 includes an electromagnetic valve that opens when supplying purge gas to the first region 22. The wall 12 or end 14 that defines the first region 22 also includes a pipe (not shown) that exhausts the purge gas as the purge gas exhaust unit 222. The purge gas exhaust unit 222 includes a check valve that allows gas to flow only in the direction of exhausting the gas from the first region 22 to the outside of the first region 22.

The first region 22 is filled with purge gas by flowing the purge gas from the purge gas supply section 221 to the purge gas exhaust section 222. The first region 22 is configured so that the purge gas can be sealed within the first region 22 by closing the solenoid valve of the purge gas supply section 221 when the first region 22 is filled with purge gas. In other words, the first region 22 is configured to have high airtightness when the solenoid valve of the purge gas supply section 221 is closed.

As the purge gas, a gas that does not contain the target component in the measurement gas or a gas in which the concentration of the target component is less than a predetermined concentration is supplied. The predetermined concentration may be a concentration that is sufficiently low so as not to affect the absorption spectrum of the target component in the second region 23. When the target component is oxygen (O ₂ ), for example, nitrogen (N ₂ ) may be used as the purge gas.

The second region 23 is an area surrounded 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 an opening through which the gas to be measured can pass so that the gas to be measured can enter and exit the second region 23.

As shown in Figures 2 and 3, 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 located in a first region 22. The first light emitter 16 and the second light emitter 11 are also collectively referred to as the light emitter. The first light receiver 17 and the second light receiver 13 are also collectively referred to as the light receiver. The laser gas analyzer 100 includes a first reflector 18 located in the first region 22, and a second reflector 28 located in the second region 23. The laser gas analyzer 100 includes a control unit 15 that controls the light emitter and the light receiver.

The first light emitter 16 is configured to emit the first measurement light 16a toward the first reflector 18. The first reflector 18 is configured to reflect the first measurement light 16a and cause it to travel toward the first light receiver 17 as the 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 only through the first region 22.

The second light emitter 11 is configured to emit the second measurement light 11a toward the second reflector 28. The second reflector 28 is configured to reflect the second measurement light 11a and cause it to travel toward the second light receiver 13 as the 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. The optical path through which the second measurement light 11a and the second reflected light 13a pass is along a direction (left-right direction in FIG. 2) that is approximately perpendicular to the direction in which the piping 30 extends.

The first light emitter 16 has a laser that emits laser light as the first measurement light 16a, and a laser driving circuit that supplies current to the laser. The second light emitter 11 has a laser that emits laser light as the second measurement light 11a, and a laser driving circuit that supplies current to the laser. The laser may be configured to include a tunable semiconductor laser that can sweep (scan) the wavelength in a range including the absorption wavelength of the gas to be measured. The laser driving circuit may be configured to include a transistor or a laser driving IC (Integrated Circuit) that can supply a driving current to the laser based on a control signal from the control unit 15.

The first light receiving unit 17 receives the first reflected light 17a that passes only through the first region 22 and is optically absorbed by the purge gas. The second light receiving unit 13 receives the second reflected light 13a that passes through both the first region 22 and the second region 23 and is optically absorbed by both the purge gas and the gas to be measured. The light receiving unit may include, for example, a light receiving element such as a photodiode or a phototransistor, a voltage conversion circuit that converts the light detection current from the light receiving element into a voltage, and an amplifier. The light receiving unit detects the received reflected light with the light receiving element and outputs the received light intensity to the control unit 15. The light receiving element is not limited to a photodiode or a phototransistor and may include various other elements.

The control unit 15 controls the first light-emitting unit 16 and the second light-emitting unit 11 to control the emission intensity of the first measurement light 16a and the second measurement light 11a. The control unit 15 may control the emission wavelength or intensity of the laser light emitted by the light-emitting unit, or the pulse width or duty ratio when the light-emitting unit emits the laser light in pulses.

The control unit 15 acquires output signals corresponding to the received light intensity from the first light receiving unit 17 and the second light receiving unit 13, and processes the output signals. The control unit 15 may calculate the absorption spectrum in the first region 22 or the second region 23 based on the output signals. The control unit 15 may calculate the components contained in the purge gas or their concentrations based on the absorption spectrum in the first region 22. The control unit 15 may calculate the components contained in the measurement target gas or their concentrations based on the absorption spectrum in the second region 23.

The control unit 15 may be configured to include a processor such as a CPU (Central Processing Unit) or a dedicated circuit such as an FPGA (Field Programmable Gate Array). The control unit 15 may be configured to execute programs that realize various functions of the laser gas analyzer 100. The control unit 15 may include a memory unit. The memory unit may store various information used in the operation of the control unit 15, or programs for realizing the functions of the control unit 15. The memory unit may function as a work memory for the control unit 15. The memory unit may be configured, for example, as a semiconductor memory. The memory unit may be configured separately from the control unit 15.

The laser gas analyzer 100 may further include an interface. The interface may include, for example, a communication interface for communicating with an external device by wire or wirelessly. The interface may include a display device. The display device may include various displays such as a liquid crystal display. The interface may include an audio output device such as a speaker. The interface may include an input device for accepting input from a user. The input device may include, for example, a keyboard or physical keys, or may include a touch panel or touch sensor, or a pointing device such as a mouse.

(Example of operation of measuring the concentration of a measurement target component by the laser gas analyzer 100)
The laser gas analyzer 100 of this embodiment is an analyzer based on the TDLAS (Tunable Diode Laser Absorption Spectroscopy) method. In TDLAS, a semiconductor laser beam with a line width much narrower than the gas absorption line width is transmitted through the gas to be measured, and the wavelength is swept (scanned) by modulating the driving current at high speed, and the amount of transmitted light is measured to measure one independent absorption spectrum. Specifically, in the laser gas analyzer 100, the control unit 15 changes the wavelength of the measurement light within a predetermined range by continuously changing the magnitude of the driving current that drives the laser of the light emitting unit. When the measurement light passes through the gas to be measured, components of the wavelength corresponding to the gas to be measured are absorbed. For example, many gas molecules such as carbon monoxide (CO), carbon dioxide (CO ₂ ), hydrocarbons (C _n H _m ), ammonia (NH ₃ ), or oxygen (O ₂ ) have light absorption spectra due to the transition of molecular vibration and rotational energy in the wavelength range from infrared to near infrared. The absorption spectrum is specific to the component molecule. According to the Lambert-Beer law, absorbance is proportional to the component concentration and the optical path length, so the concentration of the target component can be calculated by measuring the absorption spectrum intensity.

The absorption spectrum of a gas to be measured is determined based on the type and concentration of the component to be measured contained in the gas to be measured. For example, the absorption spectrum when the component to be measured is oxygen (O ₂ ) is shown 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 λ _O2 is locally reduced compared to the light intensity at other nearby wavelengths. The light intensity not absorbed by the component to be measured is represented as I _n . The light intensity absorbed by the component to be measured is represented as I _a .

When the component to be measured is oxygen (O ₂ ), the control unit 15 sweeps the wavelength of the measurement light in a predetermined wavelength range including the wavelength λ _O2 . The range in which the wavelength is swept may be determined so that the light intensity graph becomes a flat graph independent of the wavelength on the short wavelength side and the long wavelength side of the wavelength λ _O2 as shown in FIG. 4. When the component to be measured is O ₂ , the scan range of the measurement light may be set to, for example, 0.1 nm to 0.2 nm. The line width of the measurement light may be set to, for example, 0.0002 nm.

When the wavelength of the measurement light is swept by changing the drive current supplied to the laser, the light intensity on the short wavelength side and the light intensity on the long wavelength side detected by the light receiving unit are different. The control unit 15 performs a baseline flattening process so that the light intensity on the short wavelength side and the light intensity on the long wavelength side are the same.

When the component to be measured is oxygen (O ₂ ), the absorbance Ab at the wavelength λ _O2 is expressed by the following formula (1).

According to the Lambert-Beer law, the absorbance Ab of the measurement target gas is proportional to the component concentration of the measurement target gas and the optical path length of the measurement light and the reflected light exposed to the measurement target gas. The control unit 15 acquires the light intensity I _n before entering the measurement target gas based on the control information of the light emitting unit, acquires the light intensity I _a after passing through the measurement target gas based on the output signal of the light receiving unit, and calculates the absorbance Ab by applying the light intensity I _n and the light intensity I _a to the above-mentioned formula (1). The control unit 15 can calculate the component concentration of the measurement target gas based on the calculated absorbance Ab and the optical path length of the measurement light and the reflected light passing through the measurement target gas. For example, in FIG. 2, when the second measurement light 11a is reflected by the second reflecting unit 28 in a direction of approximately 180 degrees, the optical path length of the second measurement light 11a and the second reflected light 13a passing through the measurement target gas is twice the length from the pipe 30 to the second reflecting unit 28. As a method for converting the absorption spectrum into the concentration of the component to be measured, various methods such as the peak height method, the spectrum area method, or the 2f method may be used.

In this embodiment, the control unit 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 of 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 _λO2 . The control unit 15 calculates the concentration of the component to be measured in the second region 23 based on the absorbance of the wavelength corresponding to the component to be measured and the optical path length, and outputs the result as the measurement result of the component to be measured.

(Example of operation for controlling the concentration of the measurement target component in the first region 22 to be less than the 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 _λO2 based on the intensity of the second measurement light 11a at the time of emission and the intensity of the second reflected light 13a received by the second light receiving unit 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 changes under the influence of the oxygen contained in the atmosphere filling the first region 22.

The laser gas analyzer 100 controls the concentration of the components to be measured contained in the atmosphere filling the first region 22 by supplying a purge gas to the first region 22.

As described above, the first region 22 is configured to have high airtightness when the solenoid valves of the purge gas supply section 221 and the purge gas discharge section 222 are closed. However, external gas may enter the first region 22 due to leakage from any of the wall section 12, the end section 14, or the flange 29 that defines the first region 22, or from the joints between these. When oxygen enters the first region 22 as an external gas, the oxygen concentration in the first region 22 increases.

When the laser gas analyzer 100 analyzes a gas to be measured using oxygen as the component to be measured, the influence of oxygen contained in the atmosphere filling the first region 22 causes an error in the measurement result of the oxygen concentration contained in the gas to be measured in the second region 23. In order to prevent an error in the measurement result of the oxygen concentration contained in the gas to be measured in the second region 23, it is necessary to reduce the oxygen concentration in the first region 22. Specifically, when the oxygen concentration in the first region 22 becomes high, oxygen can be expelled from the first region 22 by supplying a purge gas, such as nitrogen gas, to the first region 22 while discharging it, thereby reducing the oxygen concentration.

As described for the laser gas analyzer 900 in the comparative example, by continuing to flow purge gas into the first region 22, the oxygen concentration in the first region 22 is maintained at the oxygen concentration of the purge gas. However, as described for the comparative example, losses occur due to the continued flow of purge gas.

Therefore, in the laser gas analyzer 100 according to this embodiment, in order to reduce losses caused by flowing purge gas, the control unit 15 measures the oxygen concentration in the first region 22, and when the oxygen concentration in the first region 22 becomes equal to or greater than a first threshold, supplies purge gas to the first region 22 so that the oxygen concentration in the first region 22 becomes less than the first threshold. The first threshold may be determined according to the accuracy required for measuring the oxygen concentration in the second region 23. The first threshold may be set to, for example, 0.5%, but is not limited to this.

Specifically, the control unit 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 of 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 _λO2 . The control unit 15 calculates the concentration of the component to be measured in the first region 22 based on the absorbance of the wavelength corresponding to the component to be measured and the optical path length.

When the component to be measured is oxygen, the control unit 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 equal to or greater than the first threshold, the control unit 15 opens the solenoid valve of the purge gas supply unit 221 and flows the purge gas into the first region 22 in order to reduce the oxygen concentration in the first region 22 to less than the first threshold. 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. In other words, there is no need to flow the purge gas into the first region 22. Therefore, when the oxygen concentration in the first region 22 is less than the first threshold, the control unit 15 closes the solenoid valve of the purge gas supply unit 221.

<Flowchart example>
The control unit 15 of the laser gas analyzer 100 may execute a purge gas supplying method including an example of a procedure of a flowchart illustrated in Fig. 5. The purge gas supplying method may be realized as a purge gas supplying program executed by a processor constituting the control unit 15. The purge gas supplying program may be stored in a non-transitory computer-readable medium.

The control unit 15 measures the oxygen concentration in the non-measurement area (step S1). The non-measurement area corresponds to the first region 22 as described above. The oxygen concentration corresponds to the component to be measured. The control unit 15 determines whether the oxygen concentration in the non-measurement area is less than a first threshold value (step S2).

If the oxygen concentration in the non-measurement part is not less than the first threshold (step S2: NO), that is, if the oxygen concentration in the non-measurement part is equal to or greater than the first threshold, the control part 15 opens the solenoid valve of the purge gas supply part 221 to supply purge gas to the non-measurement part to lower the oxygen concentration in the non-measurement part (step S3). After opening the solenoid valve of the purge gas supply part 221, the control part 15 returns to the measurement procedure of step S1. The control part 15 repeats the procedures from steps S1 to S3 until the oxygen concentration in the non-measurement part becomes less than the first threshold.

When the oxygen concentration in the non-measurement part is less than the first threshold value (step S2: YES), the control unit 15 closes the solenoid valve of the purge gas supply unit 221 (step S4) since there is no need to supply purge gas to the non-measurement part. After executing the procedure of step S4, the control unit 15 ends execution of the procedure of the flowchart in FIG. 5. After executing the procedure of step S4, the control unit 15 may return to the measurement procedure of step S1.

<Summary>
As described above, the laser gas analyzer 100 according to this embodiment controls the concentration of the target component in the first region 22, which is a non-measurement region, to be less than the first threshold value in order to maintain the measurement accuracy of the concentration of the target component in the second region 23, which is a measurement region. The laser gas analyzer 100 measures the concentration of the target component in the first region 22, and when the concentration of the target component becomes equal to or greater than the first threshold value, supplies a purge gas to the first region 22 to reduce the concentration of the target component. In other words, the laser gas analyzer 100 determines whether to supply a purge gas to the first region 22 based on the measurement result of the concentration of the target component in the first region 22, and controls the opening and closing of the solenoid valve of the purge gas supply unit 221. When the concentration of the target component in the first region 22 is less than the first threshold value, the supply of the purge gas is stopped, thereby reducing the amount of purge gas used.

The laser gas analyzer according to this embodiment can control the concentration of the target component in the first region to be less than the first threshold while limiting the supply period of the purge gas. As a result, it is possible to both reduce the amount of purge gas used and maintain the measurement accuracy of the concentration of the target component in the second region.

The laser gas analyzer 100 can measure the concentration of the target component in the first region 22 using the first light emitter 16 and the first light receiver 17, while measuring the concentration of the target component in the second region 23 using the second light emitter 11 and the second light receiver 13. By providing two combinations of light emitters and light receivers, the laser gas analyzer 100 can measure the concentration of the target component in the second region 23 and the concentration of the target component in the first region 22 in parallel, and can maintain the measurement accuracy while measuring the concentration of the target component in the second region 23.

The purge gas is not limited to nitrogen gas, but may be any other gas in which the concentration of the component to be measured is less than the first threshold value.

(Example of operation when purging with instrument air)
As described above, the purge gas is used to reduce the influence of absorption by the components to be measured in the first region 22, which is a non-measurement region, and to increase the measurement accuracy of the concentration of the components to be measured in the second region 23. The purge gas may also be used for another purpose, such as to stabilize the atmosphere in the first region 22, which is a non-measurement region, thereby protecting elements such as a light-emitting unit or a light-receiving unit arranged in the first region 22 from the surrounding environment. In this case, the laser gas analyzer 100 may control the concentration of the components to be measured in the first region 22, which is a non-measurement region, within a predetermined range.

In this embodiment, the component to be measured is oxygen. In addition, in this embodiment, either instrument air or oxygen gas whose concentration has been adjusted to a predetermined concentration is supplied to the first region 22 as the purge gas. Oxygen gas whose concentration has been adjusted to a predetermined concentration is also called oxygen gas of a predetermined concentration. The purge gas supply unit 221 includes a three-way solenoid valve so that either instrument air or oxygen gas of a predetermined concentration can be switched to supply to the first region 22. The predetermined concentration is a concentration included in a predetermined range that is a target for controlling the concentration of the component to be measured in the first region 22. The predetermined range of oxygen concentration is set to 20% to 22%. The predetermined concentration is set to 21%. The predetermined range or the predetermined concentration of oxygen concentration is not limited to the above example and may be set to other values. The oxygen concentration included in the instrument air is not controlled within the predetermined range. In addition, the oxygen concentration included in the measurement target gas flowing into the second region 23 is not controlled within the predetermined range.

The control unit 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. When the oxygen concentration in the first region 22 is within a predetermined range, the control unit 15 controls the three-way solenoid valve of the purge gas supply unit 221 to continue supplying instrument air to the first region 22. On the other hand, when the oxygen concentration in the first region 22 is outside the predetermined range, the control unit 15 controls the three-way solenoid valve of the purge gas supply unit 221 to supply a predetermined concentration of oxygen gas to the first region 22 in order to control the oxygen concentration in the first region 22 to be within the predetermined range.

<Flowchart example>
The control unit 15 of the laser gas analyzer 100 may execute a purge gas supply method including an example of the procedure of the flowchart illustrated in FIG.

The control unit 15 measures the oxygen concentration in the non-measurement area (step S11). The non-measurement area corresponds to the first region 22 as described above. The oxygen concentration corresponds to the component to be measured. The control unit 15 determines whether the oxygen concentration in the non-measurement area is within a predetermined range (step S12).

If the oxygen concentration in the non-measurement section is within the predetermined range (step S12: YES), the control section 15 controls the three-way solenoid valve of the purge gas supply section 221 to flow instrument air as purge gas to the non-measurement section (step S13). After executing the procedure of step S13, the control section 15 returns to the measurement procedure of step S11.

If the oxygen concentration in the non-measurement section is not within the predetermined range (step S12: NO), that is, if the oxygen concentration in the non-measurement section is outside the predetermined range, the control section 15 controls the three-way solenoid valve of the purge gas supply section 221 to flow oxygen gas of the predetermined concentration as purge gas to the non-measurement section (step S14). After executing the procedure of step S14, the control section 15 returns to the measurement procedure of step S11.

The control unit 15 can control the oxygen concentration in the first region 22, which is the non-measurement region, to within a predetermined range by repeating the steps in the flowchart of FIG. 6.

<Summary>
As described above, the laser gas analyzer 100 according to this embodiment normally supplies instrument air as a purge gas to the first region 22, and when the oxygen concentration in the first region 22 falls outside a predetermined range, switches to oxygen gas of a predetermined concentration as the purge gas. That is, the laser gas analyzer 100 determines whether to switch to oxygen gas of a predetermined concentration as the purge gas to be supplied to the first region 22 based on the measurement result of the oxygen concentration in the first region 22. When the oxygen concentration in the first region 22 is within the predetermined range, the supply of oxygen gas is stopped, thereby reducing the amount of oxygen gas used. The reduction in the amount of oxygen gas used reduces the cost burden or the environmental load. In addition, the use of instrument air as a purge gas instead of a high-purity gas such as nitrogen gas also reduces the cost burden or the environmental load.

(Other configuration examples regarding the light emitting section, the light receiving section, and the reflecting section)
In the 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. The first reflector 18 reflects the first measurement light 16a. The second reflector 28 reflects the second measurement light 11a. Other configuration examples regarding the light emitter, the light receiver, and the reflector will be described below.

As shown in FIG. 7, the laser gas analyzer 100 may include a beam splitter 185 as the first reflecting section 18. The beam splitter 185 is disposed on the optical path of the second measuring light 11a. The beam splitter 185 reflects a portion of the second measuring light 11a and causes it to proceed to the first light receiving section 17 as the first reflected light 17a. The beam splitter 185 transmits a portion of the remaining light of the second measuring light 11a that is not reflected, and causes it to proceed to the second region 23 and the second reflecting section 28.

The control unit 15 of the laser gas analyzer 100 may use the product of the transmittance of the second measurement light 11a by the beam splitter 185 and the intensity of the second measurement light 11a as the light intensity I _n before entering the measurement gas in the second region 23, and use the received light intensity of the second reflected light 13a received by the second light receiving unit 13 as the light intensity I _a after passing through the measurement gas in the second region 23, to calculate the absorbance of the measurement component in the second region 23. The control unit 15 may use the product of the reflectance of the second measurement light 11a by the beam splitter 185 and the intensity of the second measurement light 11a as the light intensity I _n before entering the measurement gas in the first region 22, and may use the received light intensity of the first reflected light 17a received by the first light receiving unit 17 as the light intensity I _a after passing through the measurement gas in the first region 22, to calculate the absorbance of the measurement component in the first region 22.

The laser gas analyzer 100 illustrated in FIG. 7 does not need to include the first light-emitting unit 16 by including a beam splitter 185 as the first reflecting unit 18. In other words, one of the light-emitting units is eliminated.

As shown in FIG. 8, the laser gas analyzer 100 may include a movable reflector as the first reflector 18. The movable reflector is configured to be movable to either a position off the optical path of the second measurement light 11a or a position on the optical path. The movable reflector is represented as reflector 181 when it is off the optical path of the second measurement light 11a, and as reflector 182 when it is on the optical path of the second measurement light 11a.

When the movable reflector is out of the optical path of the second measurement light 11a (in the state of the reflector 181), the laser gas analyzer 100 can receive the second reflected light 13a, which is the second measurement light 11a reflected by the second reflector 28, at the second light receiving unit 13. In this case, the control unit 15 of the laser gas analyzer 100 can calculate the absorbance of the measurement target component in the second region 23 based on the intensity of the second measurement light 11a and the received intensity of the second reflected light 13a at the second light receiving unit 13.

On the other hand, when the movable reflector is positioned on the optical path of the second measurement light 11a (the state of the reflector 182), the laser gas analyzer 100 can receive the reflected light 13b, which is the measurement light 11b reflected by the reflector 182, at the second light receiving unit 13. The measurement light 11b does not pass through the second region 23, so it corresponds to the first measurement light 16a. Also, the reflected light 13b does not pass through the second region 23, so it corresponds to the first reflected light 17a. Therefore, the control unit 15 of the laser gas analyzer 100 can calculate the absorbance of the measurement target component in the first region 22 based on the intensity of the measurement light 11b corresponding to the first measurement light 16a and the received intensity at the second light receiving unit 13 of the reflected light 13b corresponding to the first reflected light 17a.

The laser gas analyzer 100 illustrated in FIG. 8 can measure the absorbance of the measurement target component in the second region 23 and the absorbance of the measurement target component in the first region 22 by dividing the measurement period. The laser gas analyzer 100 illustrated in FIG. 8 does not need to have the first light emitter 16 and the first light receiver 17 by providing a movable reflector as the first reflector 18. In other words, one light emitter and one light receiver are eliminated.

The above describes an embodiment of the present disclosure with reference to the drawings, but the specific configuration is not limited to this embodiment, and various modifications are also included within the scope that does not deviate from the spirit of this disclosure.

100 Laser gas analyzer 11 Second light emitting unit (11a, 11b: measurement light)
12 Wall part 13 Second light receiving part (13a, 13b: reflected light)
14 End 15 Control unit 16 First light emitting unit (16a: measurement light)
17 First light receiving section (17a: reflected light)
18 First reflecting unit (181, 182: movable reflecting unit)
185 Beam splitter 21 Housing 22 First region (221: purge gas supply section, 222: purge gas exhaust section)
23 Second region 28 Second reflecting portion 29 Flange 30 Pipe

Claims (7)

A housing having a wall portion defining a first region to which a purge gas is supplied, and a window that transmits light between a second region containing a component to be measured and the first region;
a purge gas supply unit having an electromagnetic valve for supplying the purge gas to the first region;
a light emitting unit disposed in the first region and configured to emit measurement light toward the second region;
a first reflecting portion disposed in the first region and configured to reflect, as a first reflected light, light of the measurement light that has traveled only through the first region;
a second reflecting portion disposed in the second region and configured to reflect the light of the measurement light traveling to the second region toward the first region as a second reflected light;
a light receiving section disposed in the first region and configured to receive the first reflected light and the second reflected light;
a control unit that calculates a concentration of the measurement target component in the second area based on the intensity of the measurement light and the intensity of the second reflected light, and outputs the calculated concentration as a measurement result;
The control unit is
calculating a concentration of the measurement target component in the first region based on the intensity of the measurement light and the intensity of the first reflected light;
controlling opening and closing of the solenoid valve of the purge gas supply unit based on the concentration of the measurement target component in the first region;
Laser gas analyzer. The concentration of the measurement target component contained in the purge gas is less than a first threshold value,
The control unit is
opening an electromagnetic valve of the purge gas supply unit when the concentration of the measurement target component in the first region is equal to or greater than the first threshold value;
closing the solenoid valve of the purge gas supply unit when the concentration of the measurement target component in the first region is less than the first threshold value;
2. The laser gas analyzer according to claim 1. the solenoid valve of the purge gas supply unit includes a three-way solenoid valve that switches between instrument air and oxygen gas having a predetermined concentration as the purge gas and supplies the purge gas to the first region,
The control unit is
When the concentration of oxygen gas in the first region is within a predetermined range including the predetermined concentration, the three-way solenoid valve is controlled to supply the instrument air to the first region;
When the concentration of oxygen gas in the first region is outside the predetermined range, the three-way solenoid valve is controlled so as to supply oxygen gas of the predetermined concentration to the first region.
2. The laser gas analyzer according to claim 1. The light emitting unit has a first light emitting unit and a second light emitting unit,
the light receiving unit includes a first light receiving unit and a second light receiving unit,
The first light emitting unit emits a first measurement light toward the first reflecting unit,
the first light receiving unit receives the first measurement light reflected by the first reflecting unit as the first reflected light;
The second light emitting unit emits a second measurement light toward the second reflecting unit,
The second light receiving unit receives the second measurement light reflected by the second reflecting unit as the second reflected light.
4. A laser gas analyzer according to claim 1. the first reflecting unit is a beam splitter located on an optical path along which the measurement light travels from the light emitting unit to the second reflecting unit,
the light receiving unit includes a first light receiving unit and a second light receiving unit,
The first light receiving unit receives the measurement light reflected by the beam splitter as the first reflected light,
The second light receiving unit receives, as the second reflected light, the measurement light that passes through the beam splitter and is reflected by the second reflecting unit.
4. A laser gas analyzer according to claim 1. The first reflecting unit is configured to be movable between a position outside an optical path along which the measurement light travels from the light emitting unit to the second reflecting unit and a position on the optical path,
The light receiving unit is
When the first reflecting portion is located on the optical path, the measurement light reflected by the first reflecting portion is received as the first reflected light;
When the first reflecting unit is out of the optical path, the measurement light reflected by the second reflecting unit is received as the second reflected light.
4. A laser gas analyzer according to claim 1. A housing having a wall portion defining a first region to which a purge gas is supplied, and a window that transmits light between a second region containing a component to be measured and the first region;
a purge gas supply unit having an electromagnetic valve for supplying the purge gas to the first region;
a light emitting unit disposed in the first region and configured to emit measurement light toward the second region;
a first reflecting portion disposed in the first region and configured to reflect, as a first reflected light, light of the measurement light that has traveled only through the first region;
a second reflecting portion disposed in the second region and configured to reflect the light of the measurement light traveling to the second region toward the first region as a second reflected light;
a light receiving section disposed in the first region and configured to receive the first reflected light and the second reflected light;
a control unit that calculates a concentration of the measurement target component in the second region based on an intensity of the measurement light and an intensity of the second reflected light, and outputs the calculated concentration as a measurement result,
a step of the control unit calculating a concentration of the measurement target component in the first region based on an intensity of the measurement light and an intensity of the first reflected light;
and a step in which the control unit controls opening and closing of an electromagnetic valve of the purge gas supply unit based on a concentration of the component to be measured in the first region.

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