JP6201551B2 - Gas analyzer - Google Patents

Description

  The present invention relates to a gas analyzer that measures specific gas amount information in a gas by using laser absorption spectroscopy. The present invention relates to a gas analyzer that measures a water vapor amount (specific gas amount information) in a flow path of a fuel cell.

  One method for measuring the amount of water vapor in a gas is absorption spectroscopy using the fact that water molecules absorb only light in a specific wavelength region (eg, 1.3 μm band). Since this absorption spectroscopy can be measured without contact with the sample gas to be measured, the amount of water vapor in the sample gas can be measured without disturbing the field of the sample gas.

Among such absorption spectroscopy methods, in particular, “wavelength tunable semiconductor laser absorption spectroscopy” using a wavelength tunable semiconductor laser as a light source can be realized with a simple apparatus configuration.
For example, in a gas analyzer utilizing “wavelength tunable semiconductor laser absorption spectroscopy”, an incident optical window and an emission optical window formed in a pipe with respect to a pipe (gas cell) in which a sample gas flows in a predetermined direction It is common to add a wavelength tunable semiconductor laser and a light detection sensor (light receiving part) provided to face each other so that an optical path (optical path length L) is formed across the pipe via ( For example, see Patent Document 1).

According to such a gas analyzer, the laser light of a predetermined wavelength irradiated from the wavelength tunable semiconductor laser is obstructed by the light shielding action of water molecules present in the sample gas while passing through the pipe. Then, using the fact that the amount of light incident on the photodetection sensor decreases corresponding to the concentration of water molecules in the sample gas, the light enters the photodetection sensor with respect to the amount of laser light emitted from the wavelength tunable semiconductor laser. The concentration of water molecules is calculated by measuring the amount of laser light. FIG. 6 is a graph showing an example of an absorption spectrum obtained by the gas analyzer. The vertical axis is the received light intensity I, and the horizontal axis is the frequency ν. Note that I ₀ (ν) is the received light intensity I when the water molecule is not absorbed at the frequency ν, and is derived by creating an approximate expression based on the received light intensity I of the non-absorbing wavelength. .

  Here, an example of arithmetic processing using the absorption spectrum shown in FIG. 6 will be described. From Lambert-Beer's law, the following formula (1) holds.

Here, I ₀ (ν) is the light intensity when the water molecule is not absorbed at the frequency ν, I (ν) is the transmitted light intensity at the frequency ν, c (mol / cm ³ ) is the number density of the water molecules, L (cm) is the length of the optical path passing through the sample gas, and S (T) (cm ⁻¹ / (mol / cm ⁻² )) is a function of the gas temperature T at a predetermined absorption line intensity.

Here, FIG. 7 is a graph in which the vertical axis is ln (I ₀ (ν ₀ ) / I (ν ₀ )) and the horizontal axis is the frequency ν. Therefore, the value on the left side of Equation (1) can be obtained by determining the area of the graph shown in FIG. As an example of a method for obtaining the area of the graph of FIG. 7, taking the rectangle approximation as an example, the left side of Equation (1) can be transformed as shown in Equation (2) below.

Note that ν _max is the upper frequency limit of the absorption band (absorption peak), ν _min is the lower frequency limit of the absorption band, and n is the number of measurement points per waveform.

  On the other hand, the following equation (3) holds for S (T) on the right side of equation (1).

S ₀ is the line intensity in the standard state, Q (T) is a partition function, B (T) is a Boltzmann factor, and SE (T) is a correction formula for stimulated emission.
Furthermore, Q (T), B (T), and SE (T) on the right side of Expression (3) can be expressed as the following Expressions (4), (5), and (6), respectively.

Note that S ₀ , constants a to d, and E ₁ can be obtained from the HITRAN database or the like. Therefore, if the gas temperature value T and the light intensity changes I (ν), I ₀ (ν) can be obtained, the number density c of water molecules can be calculated.

The relationship between the number density c of water molecules and the partial pressure value P _{H2O of} water can be expressed as the following formula (7).

Here, k is a Boltzmann constant. Thereby, the partial pressure value P _H2O (water vapor amount information) of water can be calculated.

Here, FIG. 4 is a schematic configuration diagram showing an example of a gas analyzer using wavelength tunable semiconductor laser absorption spectroscopy, and FIG. 5 is a block diagram of the gas analyzer shown in FIG. One direction horizontal to the ground is defined as an X direction, a direction horizontal to the ground and perpendicular to the X direction is defined as a Y direction, and a direction perpendicular to the X direction and the Y direction is defined as a Z direction.
The gas analyzer 101 includes a light source unit 110, a light receiving unit 120, a pressure sensor 31 that measures the pressure value _Ptotal , a gas temperature sensor 32 that measures the gas temperature value T, and a laser control unit that controls the light source unit 110. 50 and a control unit 160 composed of a microcomputer and a PC.

Such a gas analyzer 101 is used to measure the partial pressure value P _H2O of moisture in the sample gas flowing in the sample flow path 70 connected to each of the supply and exhaust lines to the fuel cell system. . The sample flow path 70 extends in the Z direction, and on the side wall of the sample flow path 70, there are an incident optical window 71, and an output optical window 72 facing the incident optical window 71 with a distance L in the X direction. Is formed. The sample gas flows in the Z direction in the sample flow path 70.

For the light source unit 110, for example, a distributed feedback (DFB) semiconductor laser diode for optical communication is used. The laser diode can adjust the oscillation wavelength of the laser within a predetermined wavelength range (phase velocity constant A / ν _end to phase velocity constant A / ν _start ) in the near infrared region. It is controlled by a control signal from. The light source unit may be a laser having any structure in the infrared or other wavelength region as long as it is a wavelength tunable semiconductor laser, and a quantum cascade laser or the like may be used although it is relatively expensive. .
The laser diode is arranged so that laser light is incident in the X direction from the incident optical window 71 into the sample flow path 70, and the laser light is irradiated to the sample gas.

The light receiving unit 120 only needs to be able to convert light intensity into an electrical signal, and for example, a photodiode is used. The photodiode is arranged so as to receive the laser light emitted in the X direction from the emission optical window 72 to the outside of the sample flow path 70, and the intensity I (ν) of the laser light that has passed through the sample gas is determined. Receive light. As a result, a spectral waveform including the intensity I (ν) of the laser beam in the central wavelength portion of the absorption spectrum of water molecules and the intensity I (ν) of the laser light in the non-absorption wavelength portion on both sides of the central wavelength portion is photophotographed. By obtaining with a diode, the control unit 160 calculates I ₀ (ν) and I (ν).

The pressure sensor 31 is installed in the sample flow path 70, and measures a pressure value _Ptotal that is the total pressure of the sample gas at predetermined time intervals. The gas temperature sensor 32 is also installed in the sample flow path 70, and measures the gas temperature value T, which is the temperature of the sample gas, at predetermined time intervals.

The laser control unit 50 includes a laser current control unit 51 that controls the laser current and a laser temperature adjustment unit 52 that controls the laser temperature.
The control unit 160 includes a CPU 161, a memory 162, a display unit 63, and an input device 64. Further, the function processed by the CPU 161 will be described in the form of a block. The CPU 161 includes a calculation unit 161a that calculates a partial pressure value _PH2O in the sample gas.

Then, the laser beam intensity I (ν), pressure value P _total , and gas temperature value T are converted into digital values by the A / D conversion units 1, 2, and 3, respectively, and the calculation unit 161a calculates I ₀ from the digital values. (Ν) and I (ν) are calculated and applied to equation (1) to obtain a number density c, and the obtained number density c is applied to equation (7) to obtain a partial pressure value P _H2O. .
Note that the calculation unit 161a may calculate the amount (concentration) of water vapor in the sample gas using the partial pressure value _PH2O and the pressure value _Ptotal .

JP 2010-237075 A

By the way, an absorption spectrum as shown in FIG. 6 is obtained by the gas analyzer 101 as described above. When the pressure value P _{total of the} sample gas flowing in the sample flow path 70 is high, the sample gas When the concentration of is high, even if the oscillation wavelength of the laser diode is adjusted to the maximum, the absorption in the absorption spectrum (when ν _start becomes larger than ν _min or ν _end becomes smaller than ν _max ). The range from the peak frequency upper limit ν _max to the frequency lower limit ν _min cannot be covered. As a result, I ₀ (ν) cannot be calculated accurately, or the area of the graph as shown in FIG. 7 cannot be obtained accurately. There was a thing.

Further, instead of calculating I ₀ (ν) from the absorption spectrum as shown in FIG. 6, the intensity of the reference light I ₀ (ν) is received by dividing the laser light into divided measurement light and reference light. When the double beam method is used, I ₀ (ν) can be accurately calculated by the double beam method, but if the range from the frequency upper limit ν _max to the frequency lower limit ν _min of the absorption peak cannot be covered. The area of the graph of FIG. 7 could not be obtained accurately.
Further, instead of obtaining the area of the graph by the double beam method, it is also possible to obtain the maximum intensity value of I (ν) and calculate the partial pressure value P _{H2O of} moisture from the maximum intensity value of I (ν). However, in this calculation method, the absorption peak changes under the influence of a plurality of parameters such as the pressure value P _total , the gas temperature value T, and the gas concentration, so that there is a problem that accuracy is lowered.

Even when the oscillation wavelength of a laser diode using a wavelength tunable semiconductor laser cannot cover the range from the upper frequency limit ν _max to the lower frequency limit ν _min , the moisture partial pressure value P _H2O can be accurately determined. The method that can be obtained was examined. First, in order to accurately calculate I ₀ (ν), the double beam method was used. Next, it is known that the absorption peak in the absorption spectrum is a curve that can be expressed by several mathematical formulas depending on the range of the pressure value _Ptotal of the sample gas. Therefore, ln (I ₀ (ν) / I (ν)) is expressed by the following equation (8) using the absorption waveform profile function Φ (ν).

In other words, the absorption waveform profile function Φ (ν) is a function that becomes 1 when integrated over the entire frequency ν. When the pressure value P _total of the sample gas is equal to or higher than the atmospheric pressure (101.3 kPa), it is known that the Lorentz-type absorption waveform profile function Φ (ν) is obtained. It holds. FIG. 3 is a graph in which the vertical axis is ln (I ₀ (ν ₀ ) / I (ν ₀ )) and the horizontal axis is the frequency ν, and ln (I ₀ (ν) / I (ν)) If the frequency ν at which is the maximum value is ν ₀ , the relationship of the following formula (10) is established between the frequency ν ₁ and the frequency ν ₂ .

Here, at the frequency ν ₀ , the equation (8) becomes the following equation (11).

Therefore, if ln (I ₀ (ν ₀ ) / I (ν ₀ )), frequency ν _1, and frequency ν _{2 are} known, the number density c of water molecules can be calculated using equations (9) and (11). The water partial pressure value P _H2O can be calculated.

On the other hand, when the pressure value P _total of the sample gas is less than atmospheric pressure (133 Pa), it is known to take a Gaussian absorption waveform profile function Φ (ν), and the following equation (12) holds.

Therefore, if ln (I ₀ (ν ₀ ) / I (ν ₀ )), frequency ν ₁ and frequency ν _{2 are} known, the number density c of water molecules can be calculated using equations (11) and (12). The water partial pressure value P _H2O can be calculated.
Therefore, the present applicant has found a method for obtaining the partial pressure value P _{H2O of} moisture using ln (I ₀ (ν ₀ ) / I (ν ₀ )), frequency ν ₁ and frequency ν ₂ . As a result, when the area from the upper frequency limit ν _max to the lower frequency limit ν _min of the absorption peak in the absorption spectrum cannot be covered, the method for obtaining the area of the graph of FIG. In the present invention, since ln (I ₀ (ν ₀ ) / I (ν ₀ )), frequency ν ₁ and frequency ν ₂ are used, the partial pressure value P _{H2O of} water can be accurately calculated. Further, even when the base portion of the absorption peak overlaps with another absorption peak, it is possible to suppress the influence of the other absorption peak.

By the way, in the method as described above, it is important to obtain the frequency ν ₀ , the frequency ν _1, and the frequency ν ₂ in ln (I ₀ (ν) / I (ν)). However, when electrical noise or laser-specific optical interference noise occurs, the graph of ln (I ₀ (ν) / I (ν)) is as shown in FIG. As shown in FIG. 8, when some noise is mixed in the vicinity of the center wavelength of absorption, the maximum value of ln (I ₀ (ν) / I (ν)) is detected largely erroneously due to noise, and further absorbs the frequency ν. Will be regarded as the center wavelength of. In addition, fluctuations due to optical interference are also observed, which greatly affects the calculation error of the half width. Furthermore, since the optical interference noise appears as a standing wave with respect to the frequency ν, and becomes a noise that cannot be removed by the temporal averaging process, in ln (I ₀ (ν) / I (ν)) It is difficult to obtain the frequency ν ₀ , the frequency ν _1, and the frequency ν ₂ .

Here, since ln (I ₀ (ν) / I (ν)) is represented by the absorption waveform profile function Φ (ν), it is a quadratic function of the frequency ν. Therefore, an approximate expression [ln (I ₀ (ν) / I (ν))] is created from the measured discrete number n of ln (I ₀ (ν) / I (ν)) using the least square method. Decided to do. Actually, in order to apply a general second-order polynomial approximation process, the reciprocal of ln (I ₀ (ν) / I (ν)) is expressed by the following equation (13) using the least square method. Decided to represent.
[Ln (I (ν) / I ₀ (ν))] = aν ² + bν + c (13)
However, a, b, and c are constants.

And if the reciprocal number of Formula (13) is calculated | required, it will become like following Formula (14).
[Ln (I ₀ (ν) / I (ν))] = 1 / − (aν ² + bν + c) (14)
However, a, b, and c are constants.

Here, FIG. 9 is a graph of [ln (I ₀ (ν) / I (ν))]. When the frequency ν at which [ln (I ₀ (ν) / I (ν))] is maximum is ν _0new , the relationship of the following formula (15) is established between the frequency _ν1new and the frequency _ν2new .

Thus, an approximate expression that could reduce the influence of such electrical noise _{[ln (I 0 (ν)} / I (ν))] and the frequency _{[nu 0new} frequency _{[nu 1 NEW} and frequency _{[nu 2NEW} in is determined, as a result The specific gas amount information in the measurement target gas can be accurately measured.

That is, the gas analyzer of the present invention irradiates the measurement target gas in the gas cell with the light source unit that irradiates the measurement target gas in the gas cell with the measurement light from the wavelength tunable semiconductor laser including the absorption wavelength absorbed by the specific gas. A split measurement light splitting unit into a split measurement light splitting into a reference light that is not irradiated onto the measurement target gas, a split measurement light receiving unit that receives the intensity of the split measurement light that has passed through the measurement target gas, and the reference light Information on the specific gas in the measurement target gas is calculated based on the reference light receiving unit that receives the intensity of the light, the intensity change I (ν) of the divided measurement light, and the intensity change I ₀ (ν) of the reference light A gas analyzer including a calculation unit, wherein the calculation unit is based on an intensity change I (ν) of the divided measurement light and an intensity change I ₀ (ν) of the reference light, and ln (I ₀ (ν) / I (ν)) and ln using the least squares method _{I 0 (ν) / I (} ν)) approximation formula from _{[ln (I 0 (ν)} / I (ν))] After you create _{a, [ln (I 0 (ν} ) / I (ν))] is When the maximum frequency ν is ν _0new , a frequency ν _1new and a frequency ν _{2new satisfying the following equation} are obtained, and ln (I ₀ (ν _0new ) / I (ν _0new )) and the frequency ν The specific gas amount information in the measurement target gas is calculated based on 1 _new and frequency ν 2 _new .

As described above, according to the gas analyzer of the present invention, regardless of the wavelength control range of the light source unit (laser), when the pressure of the measurement target gas is high or the concentration of the measurement target gas is high. Even at a certain time, the specific gas amount information in the measurement target gas can be measured. At this time, since the approximate expression [ln (I ₀ (ν) / I (ν))] is created, the influence of electrical noise or the like can be reduced, and the appropriate frequency ν _0new , frequency ν _1new, and frequency ν can be reduced. _{Since 2new} is _{calculated |} required, the specific gas amount information in measurement object gas can be measured correctly.

(Means and effects for solving other problems)
In the above invention, the computing unit, the frequency _{[nu 1 NEW} frequency _{[nu 2NEW} and the split measurement light intensity variation I ([nu) including a frequency _{[nu 1 NEW} and frequency _[nu reference light intensity variation I containing a _{2NEW Based on 0} (ν), ln (I ₀ (ν) / I (ν)) may be created.

In the above invention, [ln (I ₀ (ν) / I (ν))] may be represented by the following formula.
[Ln (I ₀ (ν) / I (ν))] = 1 / − (aν ² + bν + c) (1 4 )
However, a, b, and c are constants.

Then, in the above invention, the operation unit may be displayed by storing a, b, and c in _{[ln (I 0 (ν)} / I (ν))].
According to the gas analyzer of the present invention, the absorption spectrum waveform information at the time of measurement can be converted as an extremely small number called a polynomial approximation coefficient. Therefore, the information is stored as additional information together with the calculation result (specific gas amount information). If this is done, the light absorption state at the time of measurement can be easily confirmed, which is useful for determining abnormality of the apparatus.

  Furthermore, in the above-described invention, the calculation unit substitutes the Lorentz-type absorption waveform profile function Φ (ν) or the Gauss-type absorption waveform profile function Φ (ν) into the following formula, thereby The specific gas amount information may be calculated.

The schematic block diagram which shows an example of the gas analyzer which is one Embodiment of this invention. The block diagram of the gas analyzer shown in FIG. A graph in which the vertical axis is ln (I ₀ (ν ₀ ) / I (ν ₀ )) and the horizontal axis is frequency ν. The schematic block diagram which shows an example of the gas analyzer using a wavelength-tunable semiconductor laser absorption spectroscopy. The block diagram of the gas analyzer shown in FIG. The graph which shows an example of the absorption spectrum obtained with the gas analyzer. A graph in which the vertical axis is ln (I ₀ (ν ₀ ) / I (ν ₀ )) and the horizontal axis is frequency ν. ln (I ₀ (ν) / I (ν)) graph. Graph of [ln (I ₀ (ν) / I (ν))].

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments described below, and it goes without saying that various aspects are included without departing from the spirit of the present invention.

FIG. 1 is a schematic configuration diagram showing an example of a gas analyzer according to an embodiment of the present invention, and FIG. 2 is a block diagram of the gas analyzer shown in FIG. One direction horizontal to the ground is defined as an X direction, a direction horizontal to the ground and perpendicular to the X direction is defined as a Y direction, and a direction perpendicular to the X direction and the Y direction is defined as a Z direction. The same reference numerals are assigned to the same components as those of the conventional gas analyzer 101 described above.
The gas analyzer 1 measures the light source unit 10, the measurement light dividing unit 15 that divides the divided measurement light and the reference light, the divided measurement light receiving unit 20, the reference light receiving unit 21, and the pressure value _Ptotal . A pressure sensor 31, a gas temperature sensor 32 that measures a gas temperature value T, a laser control unit 50 that controls the light source unit 10, and a control unit 60 that includes a microcomputer or a PC are provided.

The light source unit 10 is, for example, a distributed feedback system (DFB) semiconductor laser diode for optical communication. The laser diode can adjust the oscillation wavelength of the laser within a predetermined wavelength range (phase velocity constant A / ν _end to phase velocity constant A / ν _start ) in the near infrared region. It is controlled by a control signal from. The light source unit 10 only _needs to be able to irradiate laser light (measurement light) including a wavelength of (A / ν _2new ) or more and (A / ν _1new ) or less that is absorbed by water molecules (specific gas). From the point of measuring the range from _ν1new to the frequency _ν2new with high resolution, m is close to 2 (A / _ν2new ′) or more (A / _ν1new ′) in relation to the following equation (16). It is preferable to irradiate the laser beam.

The measurement light splitting unit 15 is, for example, a half mirror that splits the laser light in two directions, and transmits the part of the laser light emitted from the laser diode and irradiates the sample gas with the split measurement light and the laser light. The remaining light is reflected and divided into reference light that is not irradiated onto the sample gas. Thereby, even when the oscillation wavelength of the laser diode cannot cover the range from the frequency upper limit ν _max to the frequency lower limit ν _min of the absorption peak, I ₀ (ν) can be obtained accurately.

The split measurement light receiving unit 20 may be anything as long as it can convert light intensity into an electrical signal, and for example, a photodiode is used. The photodiode is arranged so as to receive laser light (divided measurement light) emitted in the X direction from the emission optical window 72 to the outside of the sample flow path 70, and has an intensity I (ν that has passed through the sample gas. ) Is received at the number of measurement points (measurement ch) n.
The reference light receiving unit 21 only needs to be capable of converting light intensity into an electrical signal, and for example, a photodiode is used. The photodiode is arranged so as to receive the laser beam (reference beam) reflected in the Z direction by the measurement beam splitting unit 15 and has a laser beam (reference) having an intensity I ₀ (ν) that does not pass through the sample gas. Light) is received at the number of measurement points (measurement ch) n. That is, the intensity change I ₀ (ν) of the measurement light when the water molecule is not absorbed is acquired.

The control unit 60 includes a CPU 61, a memory 62, a display unit 63, and an input device 64. Further, the function processed by the CPU 61 will be described as a block. An arithmetic expression 61a that creates an approximate expression [ln (I ₀ (ν) / I (ν))] and calculates a partial pressure value P _H2O in the sample gas. Have Further, the memory 62 stores a Lorentz-type absorption waveform profile function Φ (ν), a Gauss-type absorption waveform profile function Φ (ν) and the like in advance, and an approximate expression [ln ( I ₀ (ν) / I (ν))], and approximate expression coefficient storage area 62b for storing a, b, and c.

The calculation unit 61a includes an approximate expression creating unit that creates an approximate expression [ln (I ₀ (ν) / I (ν))]. The approximate expression creation unit converts the intensity change I (ν) of the divided measurement light with respect to the wavelength and the intensity change I ₀ (ν) of the reference light with respect to the wavelength by the A / D conversion units 1 and 4, respectively. from the _{value, ln (I 0 (ν)} / I (ν)) by _{creating, ln (I 0 (ν)} / I (ν)) by using the least square method from the approximate formula [ln _{(I 0} (ν ) / I (ν))].

Specifically, the laser control unit 50 sequentially emits laser light from the laser diode of the light source unit 10 from the wavelength of A / ν _{end to} the wavelength of A / ν _start at n points. The intensity change I (ν) of the divided measurement light received by the measurement light receiving unit 20 and the intensity change I ₀ (ν) of the reference light received by the reference light receiving unit 21 are sequentially acquired at n points. . In this case, be set by the input device 64 so as to irradiate the laser light become closer _(A / ν 2new ') or _(A / ν 1new') wavelengths below m to 2 in relation to formula (16) preferable.

Then, approximate expression creation unit calculates the _{ln (I 0 (ν) /} I (ν)) at each point n, _{ln (I 0 (ν) /} I (ν)) reciprocal ln of (I (ν) An approximate quadratic polynomial represented by equation (13) is created from / I ₀ (ν)) using the least square method. For example, a = 0.0063, b = −3.1867, and c = 407.6069 are calculated. Further, an approximate expression [ln (I ₀ (ν) / I (ν))] represented by the equation (14) is created. Then, a = 0.0063, b = −3.1867, and c = 407.6069 are stored in the approximate expression coefficient storage area 62b.

The calculation unit 61a converts the pressure value _Ptotal and the gas temperature value T into digital values by the A / D conversion units 2 and 3, respectively, and [ln (I ₀ (ν) / I (ν))] is the maximum value. the frequency [nu made when the _{[nu 0new,} obtains a frequency _{[nu 1 NEW} and frequency _{[nu 2NEW} the relationship of equation (15) holds, a _{[ln (I 0 (ν 0new} ) / I (ν 0new))] frequency Based on ν _1new , frequency ν _2new, and digital values, the measurement performed when the pressure value P _total of the sample gas is higher than the atmospheric pressure (101.3 kPa) is applied to Equation (9) and Equation (11). The number density c is obtained, and the partial pressure value PH _{2 O} is obtained by applying the number density c to the equation (7). Further, in the measurement performed when the pressure value P _total of the sample gas is less than the atmospheric pressure (133 Pa), the number density c is obtained by applying the equation (11) and the equation (12) to the number density c. ) To obtain the partial pressure value PH _{2 O.}

Specifically, the frequency ν of n at which the approximate expression [ln (I ₀ (ν) / I (ν))] is maximum is ν _0new . Next, the arithmetic unit 61a, based on the equation (15) obtains a frequency _{[nu 1 NEW} and frequency _{[nu 2NEW.} Then, the calculation unit 61a uses the gas temperature value T measured by the gas temperature sensor 32 for the measurement performed when the pressure value _Ptotal is equal to or higher than the atmospheric pressure (101.3 kPa). ) To obtain the number density c, and the number density c to the formula (7) to obtain the partial pressure value P _H2O . At this time, a = 0.0063, b = −3.1867, and c = 407.6069 stored in the approximate expression coefficient storage area 62b as additional information may be displayed. On the other hand, in the measurement performed with the pressure value P _total being less than atmospheric pressure (133 Pa), the number density by applying the gas temperature value T measured by the gas temperature sensor 32 to the equations (11) and (12). c is obtained, and the number density c is applied to the equation (7) to obtain the partial pressure value PH _{2 O.} At this time, a = 0.0063, b = −3.1867, and c = 407.6069 stored in the approximate expression coefficient storage area 62b as additional information may be displayed.

As described above, according to the gas analyzer 1 of the present invention, regardless of the wavelength control range of the laser diode, the sample gas pressure value _Ptotal is high or the sample gas concentration is high. Sometimes, the partial pressure value P _H2O (specific gas amount information) in the sample gas can be measured. At this time, since the approximate expression [ln (I ₀ (ν) / I (ν))] is created, the influence of electrical noise or the like can be reduced, and the appropriate frequency ν _0new , frequency ν _1new, and frequency ν can be reduced. _{Since 2new} is obtained, the partial pressure value _PH2O in the sample gas can be accurately measured. Further, the partial pressure value P _H2O can be obtained with a load considerably smaller than the calculation for obtaining the area of the graph.

<Other embodiments>
In the gas analyzer 1 described above, the pressure sensor 31 is provided. However, when the pressure value _Ptotal is known or when a change that affects the measurement is not assumed, the equations (9) and (9) are used. In (11) and (12), the pressure value _Ptotal is not necessary, and the pressure sensor 31 that causes an increase in size may not be provided, and the gas temperature value T may be known. If no change that would affect the measurement is assumed, the gas temperature sensor 32 may not be provided.

  The present invention can be used in a gas analyzer or the like that measures information on the amount of water vapor in a gas using laser absorption spectroscopy.

DESCRIPTION OF SYMBOLS 1 Gas analyzer 10 Light source part 15 Measurement light division part 20 Division | segmentation measurement light light-receiving part 21 Reference light light-receiving part 61a Calculation part 70 Sample flow path (gas cell)
71 Optical window for entrance 72 Optical window for exit

Claims (5)

A light source unit that irradiates measurement light in a gas cell with measurement light from a wavelength tunable semiconductor laser including an absorption wavelength absorbed by the specific gas;
A measurement light dividing unit that divides the measurement light into the measurement target gas in the gas cell and the reference light that does not irradiate the measurement target gas;
A divided measurement light receiving unit that receives the intensity of the divided measurement light that has passed through the measurement target gas;
A reference light receiving unit for receiving the intensity of the reference light;
A gas analyzer comprising: an arithmetic unit that calculates specific gas amount information in the measurement target gas based on an intensity change I (ν) of the divided measurement light and an intensity change I ₀ (ν) of the reference light. ,
The calculation unit creates ln (I ₀ (ν) / I (ν)) based on the intensity change I (ν) of the divided measurement light and the intensity change I ₀ (ν) of the reference light, and the minimum two An approximate expression [ln (I ₀ (ν) / I (ν))] is created from ln (I ₀ (ν) / I (ν)) using multiplication, and then [ln (I ₀ (ν) / I When the frequency ν at which (ν))] becomes the maximum value is ν _0new , a frequency ν _1new and a frequency ν _{2new satisfying} the relationship of the following expression are obtained, and [ln (I ₀ (ν _0new ) / I ( ν _0new ))], frequency ν _1new, and frequency ν _2new , the specific gas amount information in the measurement target gas is calculated.
The arithmetic unit, based on the frequency _{[nu 1 NEW} and frequency _[nu division measurement light intensity variation I containing a _2NEW ([nu), the frequency _{[nu 1 NEW} frequency _{[nu 2NEW} and intensity of the reference light changes _{I 0} containing a ([nu) The gas analyzer according to claim 1, wherein ln (I ₀ (ν) / I (ν)) is created. The gas analyzer according to claim 1 or 2, wherein [ln (I ₀ (ν) / I (ν))] is represented by the following formula.
[Ln (I ₀ (ν) / I (ν))] = 1 / − (aν ² + bν + c) (1 4 )
However, a, b, and c are constants. 4. The gas analyzer according to claim 3, wherein the calculation unit stores and displays a, b, and c in [ln (I ₀ (ν) / I (ν))]. The computing unit calculates specific gas amount information in the measurement target gas by substituting the Lorentz-type absorption waveform profile function Φ (ν) or the Gauss-type absorption waveform profile function Φ (ν) into the following equation. The gas analyzer according to any one of claims 1 to 4, wherein: