Technical Field
[0001]
The present invention relates to an analysis device and the like used in
applications such as gas component analysis.
5 Background Art
[0002]
Conventionally, as disclosed in Patent Literature 1, there has been an analysis
method for quantifying the concentration of a gas to be measured, by modulating an
injection current of a semiconductor laser and sweeping its oscillation wavelength, and
10 obtaining an absorption spectrum of the measurement-target gas (tunable diode laser
absorption spectroscopy (TDLAS)).
Citation List
Patent Literature
[0003]
15 Patent Literature 1: JP 2016-90521 A
Summary of Invention
Technical Problem
[0004]
However, in the absorption spectroscopy that uses a laser, such as the TDLAS,
20 the form of the absorption spectrum may change not only because of the effect of an
interference component having a light absorption spectrum overlapping with that of the
target component (interference effect), but also because of a change in the concentration
of a coexisting component coexisting at a high concentration (about several % to several
tens %) (coexistent effect). Specifically, the width of the light absorption spectrum
25 broadens, and the absorption peak drops (broadening). As a result, a concentration
3
measurement of the target component may suffer from an error. When the concentration
of the target component itself is high, the target component itself becomes a coexisting
component, and the coexistent effect occurs due to a concentration change in the target
component itself (self-broadening). In other words, a coexisting component can be said
5 to be a component that gives a broadening effect to the component itself or to another
component. In addition, in the absorption spectroscopy that uses a laser, such as the
TDLAS, the concentration of the target component also suffers from a measurement
error due to a wavelength shift in the light emitted from the laser, the wavelength shift
being caused by a change in factors such as the ambient temperature. In other words, in
10 any one of these cases, the light absorption spectrum of the target component may
change, and the resultant concentration measurement of the target component may
suffer from an error.
[0005]
The present invention has been made in consideration of the problem
15 described above, and a main object of the present invention is, in an analysis device that
uses light absorption, to correct a change in a light absorption spectrum caused by a
coexistent effect of a coexisting component or by a wavelength shift, and to make an
accurate measurement of the concentration of the target component.
[0006]
20 As illustrated in FIG. 10(A), it has been known that, a light absorption
spectrum broadened due to the effect of a coexisting component has a wider spectrum
and a lower absorption peak depending on the concentration of the coexisting
component, but the total area of the light absorption spectrum remains almost
unchanged. When there is a pressure fluctuation, by contrast, although the light
25 absorption spectrum broadens, the height of the absorption peak remains almost
4
unchanged, as illustrated in FIG. 10(B).
[0007]
Therefore, focusing on the difference and the similarity between a change
resulting from a coexistent effect and that resulting from the pressure fluctuation, in the
5 light absorption spectrum, the inventors of the present application newly introduced a
broadening factor FB, which represents a rate of a change in the light absorption
spectrum of the target component, caused by the coexisting component included in a
sample. The inventors then have found out that, denoting an absorbance signal under a
certain pressure P as A (t, P), an absorbance signal A’ (t, P) resultant of broadening by
10 the broadening factor FB, which is caused by the coexistent effect, can be approximated
using the following equation.
[0008]
[Equation 1]
15 [0009]
In other words, a change in the spectrum caused by a coexistent effect is
almost the same as that resulting from changes in the pressure multiplied by a factor of
FB and in the absorbance multiplied by a factor of 1/FB. The basic concept of the present
invention is to use this relation to convert the broadening resultant of a coexistent effect
20 into a change in the pressure, and to make a correction for the coexistent effect
simultaneously with that for pressure.
[0010]
In addition, because the light absorption spectrum also changes due to a
wavelength shift in the light source caused by a change in the ambient temperature or
25 the like, it is also necessary to detect and to correct this change.
5
Solution to Problem
[0011]
In other words, an analysis device according to the present invention is an
analysis device that analyzes a target component included in a sample, the analysis
5 device including: a light source that irradiates the sample with reference light; a
photodetector that detects an intensity of sample light that is the reference light having
transmitted through the sample; a parameter determining unit that determines a
parameter representing a change in a light absorption spectrum of the target component
or a change in a light absorption spectrum of an interference component, the change
10 being caused by a coexisting component included in the sample or by a wavelength shift
of the reference light; and a concentration calculating unit that calculates a corrected
concentration of the target component, from an intensity-related signal related to the
intensity of the sample light, by using the parameter representing the change in the light
absorption spectrum.
15 [0012]
Because such a configuration calculates a corrected concentration of the target
component, being corrected using a parameter representing a change in the light
absorption spectrum of the target component or of the interference component, the
change resulting from a coexisting component included in the sample or a wavelength
20 shift of the reference light, it is possible to correct a change in the light absorption
spectrum caused by the coexistent effect of a coexisting component or that caused by a
wavelength shift, and to measure the concentration of the target component highly
accurately.
[0013]
25 Examples of the parameter representing the change in the light absorption
6
spectrum include a broadening factor and a wavelength shift amount of the reference
light, the broadening factor representing a rate of the change in the light absorption
spectrum of the target component or the change in the light absorption spectrum of the
interference component, the change being caused by the coexisting component included
5 in the sample.
[0014]
With this, the concentration calculating unit calculates a corrected
concentration of the target component, by correcting the coexistent effect of the
coexisting component or the wavelength shift of the reference light, using the intensity10 related signal related to the intensity of the sample light, and the broadening factor or
the wavelength shift amount described above.
[0015]
The parameter determining unit may determine the broadening factor by
fitting reference data to sample data, the reference data being data related to light
15 absorption signals of the target component and of the interference component the
broadening factor of which or a pressure of which is known, and the sample data being
data related to a light absorption signal obtained from the intensity of the sample light.
The fitting herein means comparing and matching the sample data with the reference
data. Note that, before using in the comparison and the matching, the reference data is
20 converted using the pressure value of the sample and the relationship of the equation
mentioned above (Equation 1). An example of a specific method of the comparison and
matching include a non-linear least squares method involving an iterative calculation
using the steepest descent, the Gauss-Newton method, or the Levenberg-Marquardt
algorithm, for example.
25 [0016]
7
The parameter determining unit may also determine the broadening factor by
using relationship data indicating a relationship between concentrations of the
coexisting component and the broadening factor, and a measured concentration of the
coexisting component.
5 [0017]
The parameter determining unit may determine a wavelength shift amount by
fitting reference data to sample data, the reference data being data related to light
absorption signals of the target component and of the interference component for which
a wavelength shift amount is known, and the sample data being data related to a light
10 absorption signal obtained from the intensity of the sample light.
[0018]
The parameter determining unit may also determine the wavelength shift
amount of the reference light by using relationship data indicating a relationship
between ambient temperatures and wavelength shift amounts, and a measured ambient
15 temperature.
[0019]
Preferably, the analysis device further includes a correlation value calculating
unit that calculates a correlation value between the intensity-related signal related to the
intensity of the sample light and a predetermined feature signal. The concentration
20 calculating unit calculates a corrected concentration of the target component, the
corrected concentration being corrected for the coexistent effect of the coexisting
component or for the wavelength shift of the reference light, using the correlation value
and the parameter representing the change in the light absorption spectrum of the target
component or the change in the light absorption spectrum of the interference
25 component.
8
With this configuration, the correlation value between the intensity-related
signal related to the intensity of the sample light and the feature signal is calculated, and
the concentration of the target component is calculated using the calculated correlation
value. Therefore, it is possible to get a grasp of the feature of the absorption signal using
5 a much smaller number of variables, without converting the absorption signal into the
absorption spectrum, and is also possible to measure the concentration of the target
component by a simple calculation, without performing a complicated spectrum
calculation process. For example, general spectral fitting requires several-hundred data
points, but in the present invention, the concentration can be calculated at an accuracy
10 equivalent thereto by using several to several tens of correlation values at most. As a
result, a processing load can be reduced dramatically, and a high-performance
processing unit will be no longer necessary. Furthermore, the cost and the size of the
analysis device can be reduced.
[0020]
15 Preferably, the analysis device according to the present invention is an
analysis device that analyzes a target component in a sample including one or more
interference components interference effects of which are to be removed, wherein the
correlation value calculating unit calculates a plurality of correlation values using a
number of feature signals equal to or more than a sum of a number of types of the target
20 component and a number of types of the interference component, and the concentration
calculating unit calculates the concentration of the target component using the plurality
of correlation values and the parameter representing the change in the light absorption
spectrum of the target component or the change in the light absorption spectrum of each
one of the one or more interference components.
25 [0021]
9
Preferably, the analysis device according to the present invention further
includes a storage unit that stores a sole correlation value that is a correlation value
between a per unit concentration of the target component and a per unit concentration of
each of the plurality of interference components, the sole correlation value being
5 obtained from the intensity-related signal when only the corresponding interference
component exists with the target component, and from the plurality of feature signals,
wherein the concentration calculating unit calculates the concentration of the target
component using a plurality of correlation values obtained by the correlation value
calculating unit, the plurality of sole correlation values, and the parameter representing
10 the change in the light absorption spectrum of the target component or the changes in
the interference components.
[0022]
Specifically, it is preferable for the concentration calculating unit to correct
the plurality of sole correlation values by using the parameter representing the change in
15 the light absorption spectrum of the target component or the change in the light
absorption spectrum of the interference component, and to calculate the concentration of
the target component by using the plurality of corrected sole correlation values and the
plurality of correlation values obtained by the correlation value calculating unit.
With this configuration, it is possible to determine the concentration of the
20 target component by removing the interference effect and the coexistent effect of the
coexisting component or the effect of the wavelength shift of the reference light, using a
simple and reliable operation of solving simultaneous equations including several to
several tens of elements at most.
[0023]
25 More specifically, it is preferable that the concentration calculating unit
10
calculates the concentration of the target component by solving simultaneous equations
including the plurality of correlation values obtained by the correlation value calculating
unit, the plurality of corrected sole correlation values, and the concentrations of the
target component and each of the interference components.
5 [0024]
For the purpose of correcting the sole correlation values, it is preferable to
obtain the sole correlation values corresponding to each of the components under a
plurality of known pressures or with a plurality of known wavelength shifts of the
reference light, and to store the sole correlation values in advance in the storage unit. In
10 this manner, a sole correlation value can be corrected using the broadening factor or the
wavelength shift amount determined by the parameter determining unit. Note that the
sole correlation values stored in advance in the storage unit may be obtained with
known broadening factors, instead of known pressures, but it is not easy to create a
condition where a broadening factor is known. Therefore, it is preferable to use sole
15 correlation values obtained under known pressures.
[0025]
In addition, preferably, when there is a fluctuation in the sample pressure
during a measurement, the sample pressure is monitored using a pressure sensor or the
like, and the sole correlation value is corrected using the pressure value. In this manner,
20 it becomes possible to correct the coexistent effect of the coexisting component and the
effect of the pressure fluctuation at the same time.
[0026]
At this time, the concentration calculating unit may correct the sole
correlation value using the sole correlation values of each of the components, the sole
25 correlation values being obtained for each of a plurality of known pressures of the
11
sample, the plurality of correlation values obtained by the correlation value calculating
unit, the pressure value inside the cell, and a relationship represented by following
equation (Equation 2).
[0027]
5 [Equation 2]
[0028]
Where p denotes the pressure of the sample measured by the pressure sensor,
FB denotes the broadening factor determined by the broadening factor determining unit,
10 sij denotes a sole correlation value corresponding to each of the pressures stored in the
storage unit, and s'ij denotes a corrected sole correlation value. The above equation
(Equation 2) indicates that the corrected sole correlation value s'ij is obtained by, for a
sole correlation value sij(p) with a sample pressure p at time of a sample measurement,
by multiplying 1/FB to the sole correlation value resultant of multiplying the pressure by
15 FB.
When the interference component is also affected by the broadening caused
by the coexisting component, it is also possible to determine a separate broadening
factor for the interference component, and to correct the sole correlation value of the
interference component. In this manner, the measurement accuracy can be further
20 improved.
[0029]
A program for an analysis device according to the present invention is a
program applied to an analysis device including a light source that irradiates a sample
with reference light, and a photodetector that detects sample light having transmitted
12
through the sample, the program causing the analysis device to implement functions as:
a parameter determining unit that determines a parameter representing a change in a
light absorption spectrum of a target component or a change in a light absorption
spectrum of an interference component, the change being caused by a coexisting
5 component included in the sample or by a wavelength shift of the reference light; and a
concentration calculating unit that calculates a corrected concentration of the target
component, from an intensity-related signal related to an intensity of the sample light,
by using the parameter representing the change in the light absorption spectrum.
[0030]
10 Furthermore, an analysis method according to the present invention is an
analysis method for analyzing a target component included in a sample by using a light
source that irradiates the sample with reference light, and a photodetector that detects
sample light having transmitted through the sample, the analysis method including:
determining a parameter representing a change in a light absorption spectrum of the
15 target component or a change in a light absorption spectrum of an interference
component, the change being caused by a coexisting component included in the sample
or by a wavelength shift of the reference light; and calculating a corrected concentration
of the target component, from an intensity-related signal related to an intensity of the
sample light, by using the parameter representing the change in the light absorption
20 spectrum.

WE CLAIM:
1. An analysis device that analyzes a target component included in a sample, the
analysis device comprising:
a light source that irradiates the sample with reference light;
5 a photodetector that detects an intensity of sample light that is the reference
light having transmitted through the sample;
a parameter determining unit that determines a parameter representing a
change in a light absorption spectrum of the target component or a change in a light
absorption spectrum of an interference component, the change being caused by a
10 coexisting component included in the sample or by a wavelength shift of the reference
light; and
a concentration calculating unit that calculates a corrected concentration of the
target component, from an intensity-related signal related to the intensity of the sample
light, by using the parameter representing the change in the light absorption spectrum.
15 2. The analysis device as claimed in claim 1, wherein the parameter representing
the change in the light absorption spectrum is a broadening factor or a wavelength shift
amount of the reference light, the broadening factor representing a rate of the change in
the light absorption spectrum of the target component or the change in the light
absorption spectrum of the interference component, the change being caused by the
20 coexisting component included in the sample.
3. The analysis device as claimed in claim 2, wherein the concentration
calculating unit calculates a corrected concentration of the target component, by
correcting the coexistent effect of the coexisting component or the wavelength shift of
the reference light, using the intensity-related signal related to the intensity of the
25 sample light, and the broadening factor or the wavelength shift amount.
47
4. The analysis device as claimed in claim 2 or 3, wherein the parameter
determining unit determines the broadening factor by fitting reference data to sample
data, the reference data being data related to light absorption signals of the target
component and of the interference component the broadening factor of which or a
5 pressure of which is known, and the sample data being data related to a light absorption
signal obtained from the intensity of the sample light.
5. The analysis device as claimed in claim 2 or 3, wherein the parameter
determining unit determines the broadening factor by using relationship data indicating
a relationship between concentrations of the coexisting component and the broadening
10 factor, and a measured concentration of the coexisting component.
6. The analysis device as claimed in claim 2 or 3, wherein the parameter
determining unit determines a wavelength shift amount by fitting reference data to
sample data, the reference data being data related to light absorption signals of the target
component and of the interference component for which a wavelength shift amount is
15 known, and the sample data being data related to a light absorption signal obtained from
the intensity of the sample light.
7. The analysis device as claimed in claim 2 or 3, wherein the parameter
determining unit determines the wavelength shift amount of the reference light by using
relationship data indicating a relationship between ambient temperatures and
20 wavelength shift amounts, and a measured ambient temperature.
8. The analysis device as claimed in any one of claims 1 to 7, further comprising
a correlation value calculating unit that calculates a correlation value between the
intensity-related signal related to the intensity of the sample light and a predetermined
feature signal, wherein
25 the concentration calculating unit calculates a corrected concentration of the
48
target component, the corrected concentration being corrected for the coexistent effect
of the coexisting component or for the wavelength shift of the reference light, using the
correlation value and the parameter representing the change in the light absorption
spectrum of the target component or the change in the light absorption spectrum of the
5 interference component.
9. The analysis device as claimed in claim 8 that analyzes a target component in
a sample including one or more interference components interference effects of which
are to be removed, wherein
the correlation value calculating unit calculates a plurality of correlation
10 values using a number of feature signals equal to or more than a sum of a number of
types of the target component and a number of types of the interference component, and
the concentration calculating unit calculates the concentration of the target
component using the plurality of correlation values and the parameter representing the
change in the light absorption spectrum of the target component or the change in the
15 light absorption spectrum of each one of the one or more interference components.
10. The analysis device as claimed in claim 9, further comprising a storage unit
that stores a sole correlation value that is a correlation value between a per unit
concentration of the target component and a per unit concentration of each of the
plurality of interference components, the sole correlation value being obtained from the
20 intensity-related signal when only the corresponding interference component exists with
the target component, and from the plurality of feature signals, wherein
the concentration calculating unit calculates the concentration of the target
component using a plurality of correlation values obtained by the correlation value
calculating unit, a plurality of the sole correlation values, and the parameter representing
25 the change in the light absorption spectrum of the target component or the changes in
49
the interference components.
11. The analysis device as claimed in claim 10, wherein the concentration
calculating unit corrects the plurality of sole correlation values by using the parameter
representing the change in the light absorption spectrum of the target component or the
5 change in the light absorption spectrum of the interference component, and calculates
the concentration of the target component by using the plurality of corrected sole
correlation values and the plurality of correlation values obtained by the correlation
value calculating unit.
12. The analysis device as claimed in claim 11, wherein the concentration
10 calculating unit calculates the concentration of the target component by solving
simultaneous equations including the plurality of correlation values obtained by the
correlation value calculating unit, the plurality of corrected sole correlation values, and
the concentrations of the target component and each of the interference components.
13. The analysis device as claimed in any one of claims 10 to 12, further
15 comprising a pressure sensor that monitors a pressure of the sample, wherein
the concentration calculating unit corrects the sole correlation value using a
pressure value obtained by the pressure sensor.
14. The analysis device as claimed in claim 13, wherein
the concentration calculating unit corrects the sole correlation value by using
20 the sole correlation values of each of the components, the sole correlation values being
obtained for each of a plurality of known pressures of the sample, the plurality of
correlation values obtained by the correlation value calculating unit, the pressure value
inside the cell, and a relationship represented by following equation (Equation 2),
[Equation 2]
50
where, p denotes the pressure of the sample measured by the pressure sensor;
FB denotes the broadening factor determined by the broadening factor determining unit;
sij denotes a sole correlation value corresponding to each of the pressures stored in the
5 storage unit; and s'ij denotes a corrected sole correlation values, and
the equation (Equation 2) indicates that the corrected sole correlation value s'ij
is obtained, for a sole correlation value sij(p) with a sample pressure p at time of a
sample measurement, by multiplying 1/FB to the sole correlation value resultant of
multiplying the pressure by FB.
10 15. A program applied to an analysis device that includes a light source that
irradiates a sample with reference light, and a photodetector that detects sample light
having transmitted through the sample, the program causing the analysis device to
implement functions as:
a parameter determining unit that determines a parameter representing a
15 change in a light absorption spectrum of a target component or a change in a light
absorption spectrum of an interference component, the change being caused by a
coexisting component included in the sample or by a wavelength shift of the reference
light; and
a concentration calculating unit that calculates a corrected concentration of the
20 target component, from an intensity-related signal related to an intensity of the sample
light, by using the parameter representing the change in the light absorption spectrum.
16. An analysis method for analyzing a target component included in a sample by
using a light source that irradiates the sample with reference light, and a photodetector
that detects sample light having transmitted through the sample, the analysis method
51
comprising:
determining a parameter representing a change in a light absorption spectrum
of the target component or a change in a light absorption spectrum of an interference
component, the change being caused by a coexisting component included in the sample
5 or by a wavelength shift of the reference light; and
calculating a corrected concentration of the target component, from an
intensity-related signal related to an intensity of the sample light, by using the parameter
representing the change in the light absorption spectrum.