Technical Field
[0001]
The present invention relates to a gas analysis apparatus and a gas analysis method capable of
correcting the effects of gas, such as a coexistent effect and an interference effect.
5
Background Art
[0002]
As a gas analysis apparatus adapted to measure the concentration of a measurement target
component contained in sample gas such as an exhaust gas of an internal combustion engine, there is
10 one using an infrared absorption method.
[0003]
It is known that when measuring the concentration of a measurement target component (e.g.,
carbon monoxide (CO)) using the infrared absorption method, another gas component (e.g., carbon
dioxide (CO2)) coexistent with the measurement target component in sample gas exerts a coexistent
15 effect.
[0004]
The coexistent effect is considered to occur due to the fact (broadening phenomenon) that
wavenumbers are shifted by the intermolecular interaction of the coexistent component to thereby
broaden the linewidth of the infrared absorption spectrum of the measurement target component
20 broadens, and consequently the infrared spectrum changes into a broad shape.
[0005]
In the past, as a gas analysis apparatus capable of removing the coexistent effect, there has
been a gas analysis apparatus disclosed in Patent Literature 1. This gas analysis apparatus determines a
sensitivity adjustment coefficient using the average concentration of a coexistent component in an actual
25 sample for calibration.
[0006]
However, since the gas analysis apparatus determines a sensitivity adjustment coefficient using
the average concentration of a coexistent component in an actual sample for calibration, when
measuring gas having different coexistent component concentration from that at the time of the
2
calibration, an error due to the coexistent effect occurs. Further, in the case of measurement during
which coexistent component concentration changes every moment as well, the coexistent effect of a
coexistent component cannot be exactly eliminated.
5 Citation List
Patent Literature
[0007]
Patent Literature 1: Japanese Unexamined Patent Publication JP-A 2000-356589
Summary of Invention
Technical Problem
[0008]
Therefore, the present invention is made in order to solve the above-described problems, and a
main object thereof is to, even when the concentration of a second gas component as a coexistent
component varies, accurately correct the effect of the second gas component on a first gas component in
real time.
Solution to Problem
[0009]
20 That is, a gas analysis apparatus according to the present invention includes: a first gas analysis
part adapted to measure the concentration of a first gas component contained in sample gas; a second
gas analysis part adapted to measure the concentration of a second gas component contained in the
sample gas; a correction coefficient storage part adapted to store a correction coefficient for correcting
the effect of the second gas component on the first gas component; and a concentration correction part
25 adapted to correct the first gas component concentration obtained by the first gas analysis part on the
basis of the correction coefficient, second gas component concentration of calibration gas used for
calibrating the first gas analysis part, and the second gas component concentration obtained by the
second gas analysis part.
[0010]
3
Also, a gas analysis method according to the present invention is a gas analysis method using a
first gas analysis part adapted to measure the concentration of a first gas component contained in sample
gas and a second gas analysis part adapted to measure the concentration of a second gas component
contained in the sample gas, and the gas analysis method corrects the first gas component concentration
5 obtained by the first gas analysis part on the basis of a correction coefficient for correcting the effect of
the second gas component on the first gas component, second gas component concentration of
calibration gas used for calibrating the first gas analysis part, and the second gas component
concentration obtained by the second gas analysis part.
[0011]
10 Such gas analysis apparatus and method correct the first gas component concentration
obtained by the first gas analysis part on the basis of the correction coefficient, the second gas
component concentration of the calibration gas used for calibrating the first gas analysis part, and the
second gas component concentration obtained by the second gas analysis part, and can therefore
accurately correct the effect of the second gas component on the first gas component in real time even
15 when the concentration of the second gas component as a coexistent component varies. In addition,
even when using mixed gas containing at least the first gas component and the second gas component as
the calibration gas for the first gas analysis part, the effect of the second gas component on the first gas
component can be accurately corrected in real time.
[0012]
20 As a specific embodiment of the correction in the gas analysis apparatus, it is conceivable that
the concentration correction part corrects the first gas component concentration on the basis of the
correction coefficient and the difference between the second gas component concentration of the
calibration gas and the second gas component concentration obtained by the second gas analysis part.
[0013]
25 As a specific embodiment of the correction in the gas analysis apparatus, it is preferable that
the gas analysis apparatus further includes a correction coefficient changing part adapted to change the
correction coefficient on the basis of the second gas component concentration of the calibration gas used
for calibrating the first gas analysis part, and the concentration correction part corrects the first gas
component concentration obtained by the first gas analysis part with use of a correction coefficient after
4
the change by the correction coefficient changing part and the second gas component concentration
obtained by the second gas analysis part.
[0014]
It is preferable that the correction coefficient indicates the relationship between second gas
5 component concentration and the relative error of first gas component concentration at the second gas
component concentration, and the correction coefficient changing part changes the correction coefficient
on the basis of the difference between second gas component concentration at which the relative error of
the first gas component concentration is zero under the condition of the correction coefficient and the
second gas component concentration of the calibration gas used for calibrating the first gas analysis part.
10 [0015]
As a specific changing method to be employed by the correction coefficient changing part, it is
conceivable that the correction coefficient changing part shifts the correction coefficient so as to make
second gas component concentration at which the relative error of the first gas component concentration
is zero equal to the second gas component concentration of the calibration gas.
15 [0016]
It is preferable that the first gas analysis part and the second gas analysis part include a detector
using an NDIR method. In particular, when the first gas analysis part and the second gas analysis part
are configured to include one NDIR detector having a single cell, the length of the cell is specified. As
a result, a usable wavelength is limited and it is likely to exert effects such as a coexistent effect. In the
20 case of such a configuration, the effect of the present invention is notably produced.
[0017]
When measurement target components in the sample gas are carbon monoxide (CO) and
carbon dioxide (CO2), the coexistent effect of the carbon dioxide (CO2) on the carbon monoxide (CO)
causes a measurement error. In this case, the first gas component is the carbon oxide (CO) and the
25 second gas component is the carbon dioxide (CO2).
Advantageous Effects of Invention
[0018]
According to the present invention configured as described above, even when the
5
concentration of the second gas component as a coexistent component varies every moment, the effect
of the second gas component on the first gas component can be corrected in real time.
Brief Description of Drawings
5 [0019]
FIG. 1 is a schematic diagram illustrating the configuration of a gas analysis apparatus
according to the present invention;
FIG. 2 is a functional configuration diagram of a calculation device in the same embodiment;
FIG. 3 is a diagram illustrating relational expressions representing correction coefficients
10 before and after change in the same embodiment; and
FIG. 4 is a diagram illustrating the relative errors of CO concentration before and after
correction in the same embodiment.
Description of Embodiments
15 [0020]
In the following, one embodiment of a gas analysis apparatus according to the present
invention will be described with reference to the drawings.
[0021]

20 A gas analysis apparatus 100 of the present embodiment is one adapted to analyze multiple gas
components contained in exhaust gas discharged from an exhaust gas source such as an engine. In the
present embodiment, the gas analysis apparatus 100 is one that, using a non-dispersive infrared
absorption method (NDIR method), simultaneously measures the multicomponent gas containing
carbon monoxide (CO) as a first gas component and carbon dioxide (CO2) as a second gas component
25 both contained in engine exhaust gas. The gas analysis apparatus 100 does not have to be one adapted
to simultaneously measure the multicomponent gas but may be one using an optical absorption method
other than the NDIR method, such as an FTIR method.
[0022]
Note that CO2 as the second gas component exerts a coexistent effect on CO as the first gas
6
component in the NDIR method. That is, the infrared absorption spectrum of CO as the first gas
component broadens because wavenumbers are shifted by the intermolecular interaction of CO2.
[0023]
Specifically, as illustrated in FIG. 1, the gas analysis apparatus 100 includes: a first gas analysis
5 part 2 adapted to continuously measure the concentration of CO contained in the engine exhaust gas; a
second gas analysis part 3 adapted to continuously measure the concentration of CO2 contained in the
engine exhaust gas; and a calculation device 4 adapted to acquire outputs from the respective analysis
parts 2 and 3 and calculate the concentrations of CO and CO2 contained in the engine exhaust gas.
[0024]
10 The first gas analysis part 2 and the second gas analysis part 3 are ones including NDIR
detectors, and configured using a single shared cell. Specifically, the analysis parts 2 and 3 include: the
measurement cell 10 into/from which the engine exhaust gas is introduced/led out; an infrared ray
irradiation part 11 adapted to irradiate the measurement cell 10 with infrared light, such as an infrared
light source; and the infrared detectors 12 adapted to detect infrared rays having passed through the
15 measurement cell 10.
[0025]
The infrared detectors 12 in the present embodiment are pyroelectric infrared detectors, and
include a detector 12a for CO measurement and a detector 12b for CO2 measurement. In addition, the
infrared detectors 12 also include a detector 12c for hydrocarbon (HC) measurement and a detector 12d
20 for a comparison signal. Between the respective detectors 12a to 12d and the measurement cell 10,
optical filters 13a to 13d are provided, and the respective optical filters 13a to 13d have different
transmission characteristics, and correspond to absorption wavelengths of CO, CO2, and HC, and a
reference wavelength at which any of them does not cause absorption. Note that as the infrared
detectors 12, in addition to the pyroelectric infrared detectors, pneumatic cell infrared detectors, detectors
25 using lead selenide, thermopile detectors, or the like can be used.
[0026]
The calculation device 4 is a dedicated or general-purpose computer including a CPU, a
memory, an input/output interface, an AD converter, and the like, and in accordance with an analysis
program stored in the memory, calculates the CO concentration, the CO2 concentration, and HC
7
concentration.
[0027]
Specifically, the calculation device 4 is one adapted to acquire output signals (light intensity
signals) from the infrared detectors 12 constituting the first and second gas analyzers 2 and 3, and using
5 absorption spectra obtained from the light intensity signals from the respective detectors 12a to 12d,
calculate the CO concentration, CO2 concentration, and HC concentration.
[0028]
In addition, the calculation device 4 has a function of correcting the coexistent effect of the
CO2 as the second gas component on the CO as the first gas component, and in accordance with the
10 analysis program stored in the memory, as illustrated in FIG. 2, fulfills functions as a concentration
calculation part 40, a correction coefficient storage part 41, a correction coefficient changing part 42, a
concentration correction part 43, and the like.
[0029]
The concentration calculation part 40 is one adapted to calculate the CO concentration, CO2
15 concentration, and HC concentration using the absorption spectra obtained from the light intensity
signals from the respective detectors 12a to 12 d.
[0030]
The correction coefficient storage part 41 is one adapted to store a correction coefficient for
correcting the coexistent effect of the second gas component on the first gas component. Correction
20 coefficient data indicating the correction coefficient is preliminarily inputted to the correction coefficient
storage part 41 before product shipment or before product operation.
[0031]
Note that as illustrated in FIG. 3, the correction coefficient is one indicating the relationship
between CO2 concentration and the relative error of CO concentration at the CO2 concentration. The
25 saving format of the correction coefficient may be a function format indicating the relationship, or a table
format such as a lookup table.
[0032]
Also, the relative error of CO concentration at the CO2 concentration refers to a ratio of an
error to CO concentration (exact value) in the absence of the coexistent effect of CO2. The error is
8
represented by the difference between the CO concentration in the absence of the coexistent effect of
CO2 and the CO concentration in the presence of the coexistent effect of CO2.
Relative error = ([CO concentration_under coexistent effect] - [CO concentration_not under coexistent effect]) /
[CO concentration_not under coexistent effect] x 100 %
5 [0033]
The correction coefficient changing part 42 is one adapted to change the correction coefficient
on the basis of second gas component concentration of calibration gas used for calibrating the first gas
analysis part 2. Note that the infrared detectors 12 including the first gas analysis part 2 in the present
embodiment are calibrated using mixed gas of a known concentration of CO and a known concentration
10 of CO2 as the calibration gas. Also, data on the second gas component concentration of the calibration
gas used for calibrating the first gas analysis part 2 is stored in the correction coefficient storage part 41
or another data storage part.
[0034]
For example, when the correction coefficient is one indicating that the relative error of CO
15 concentration at a CO2 concentration of 0 (zero) is zero, the correction coefficient changing part 42
changes the correction coefficient in the following manner using the CO2 concentration of the calibration
gas used for calibrating the first gas analysis part 2 as a parameter.
[0035]
When mixed gas of a known concentration of CO and a known concentration (e.g., 10 %vol)
20 of CO2 is used for calibrating the first gas analysis part 2 as the calibration gas, the calibration is
performed such that the relative error becomes zero at the known CO2 concentration (10 %vol).
Accordingly, the correction coefficient changing part 42 changes the correction coefficient on the basis
of the difference between the CO2 concentration (0 %vol) at which the relative error of CO
concentration is zero under the condition of the concentration coefficient and the CO2 concentration
25 (10 %vol) of the calibration gas used for calibrating the first gas analysis part 2. That is, the correction
coefficient changing part 42 shifts and changes the correction coefficient such that at the CO2
concentration of the calibration gas used for the calibration, the relative error of the CO concentration
becomes zero (see FIG. 3). Note that the CO2 concentration (0 %vol) used for changing the correction
coefficient, at which the relative error is zero, may be the CO2 concentration (0 %vol) at which the
9
relative error is within a predetermined range. The predetermined range is one selected by a user.
[0036]
For example, when under the condition of a correction coefficient before change, the relative
error of CO at a CO2 concentration of 0 %vol is 0 %, and the relative error of CO at a CO2 concentration
5 of 10 %vol is 2.65 %, under the condition of a correction coefficient after the change, the relative error of
CO at a CO2 concentration of 0 %vol is -2.65 %, and the relative error of CO at a CO2 concentration of
10 %vol is 0 %.
[0037]
The concentration correction part 43 is one adapted to, using the correction coefficient after the
10 change by the correction coefficient changing part 42 and the CO2 concentration calculated by the
concentration calculation part 40 using the light intensity signals from the second gas analysis part 3,
correct the CO concentration calculated by the concentration calculation part 40 using the light intensity
signals from the first gas analysis part 2.
[0038]
15 Specifically, the calculation device 4 corrects the CO concentration on the basis of the
functions of the correction coefficient changing part 42 and concentration correction part 43 in
accordance with the following expression.
[0039]
C(CO)_corr = C(CO) / (1 + f(C(C2)))
20 Here, f(C(CO2)) represents a function (the correction coefficient after the correction) indicating
the relative error of the CO concentration, and
f(C(CO2) = K1 x C(CO2) x C(CO2) + K2 x C(CO2) - {K1 x C(C2 span) x C(CO2_span) + K2
x C(CO2_span)}
[0040]
25 C(CO)_corr: CO concentration [%vol] at the time of actual measurement after the correction
C(CO): the CO concentration [%vol] at the time of actual measurement before the correction
C(CO2): the CO2 concentration [%vol] at the time of actual measurement
C(CO2_span): Coexistent CO2 concentration [%vol] at the time of span calibration of the CO
meter
10
K1, K2: Coefficients obtainable by experiment (in the present embodiment, coefficients when
the relationship between CO2 concentration and the relative error of CO concentration is approximated
to a quadratic curve).
[0041]
5 FIG. 4 illustrates the relative errors of CO concentration before and after correction obtained
when the span calibration of the NDIR detectors were performed using mixed gas having a CO2
concentration of 14 %vol as the calibration gas.
As can be seen from FIG. 4, it turns out that correcting the coexistent effect in accordance with
the present embodiment allows the relative error of CO concentration after the correction to fall within a
10 range of ±1 %.
[0042]

The gas analysis apparatus 100 according to the present embodiment configured as described
above corrects CO concentration obtained by the first gas analysis part 2 on the basis of a correction
15 coefficient after change by the correction coefficient changing part 42 and CO2 concentration at the time
of actual measurement obtained by the second gas analysis part 3, and can therefore accurately correct
the coexistent effect of CO2 on CO in real time even when the concentration of CO2 as a coexistent
component varies. Note that when using the infrared detectors 12, an interference effect may be
caused by the superposition between a CO2 absorption spectrum and a CO absorption spectrum;
20 however, the interference effect is small as compared with the above-described coexistence effect. In
order to more accurately measure CO concentration, the interference effect of CO2 on CO may be
further corrected in addition to the present embodiment. The interference effect can be corrected using
a similar method to that for the coexistence effect by storing a correction coefficient for interference
effect correction in the correction coefficient storage part 41.
25 [0043]

Note that the present embodiment is not limited to the above-described embodiment.
[0044]
For example, the above-described embodiment is one such that the calculation device 4
11
includes the correction coefficient changing part 42 and the correction coefficient changing part 42
changes a correction coefficient. However, without changing a correction coefficient, the concentration
correction part 43 may correct first gas component concentration using as a parameter the difference
between second gas component concentration at which the relative error of the first gas component
5 concentration is zero under the condition of the correction coefficient and second gas component
concentration of a calibration gas used for calibrating the first gas analysis part 2. That is, the
concentration correction part 43 may be adapted to correct the first gas component concentration
obtained by the first gas analysis part 2 on the basis of the unchanged correction coefficient and second
gas component concentration obtained by the second gas analysis part 3, and further correct the
10 corrected first gas component concentration on the basis of the difference between the second gas
component concentration at which the relative error of the first gas component concentration is zero
under the condition of the correction coefficient and the second gas component concentration of the
calibration gas used for calibrating the first gas analysis part 2.
For example, when the first gas component concentration obtained by the first gas analysis
15 part 2 is 5 %vol and the second gas component concentration obtained by the second gas analysis part 3
is 6 %vol, the concentration correction part 43 obtains a relative error using the correction coefficient
(e.g., the correction coefficient before the change in the above-described embodiment). In this case, the
relative error is approximately +2 %. Then, the concentration correction part corrects the first gas
component concentration (5 %vol) using the relative error (approximately 2 %). Subsequently, the
20 concentration correction part 43 further corrects the corrected first gas component concentration
(approximately 4.9 %) using a change in relative error (a shift amount: -2.65 %) under the condition of
the correction coefficient shifted on the basis of the difference between the second gas component
concentration (0 %vol) at which the relative error of the first gas component concentration is zero under
the condition of the correction coefficient and the second gas component concentration (e.g., 10 %vol)
25 of the calibration gas used for calibrating the first gas analysis part 2. In this case, the further corrected
first gas component concentration is approximately 5.37 %vol.
[0045]
Also, the above-described embodiment is one adapted to analyze the engine exhaust gas, but
besides may be adapted to analyze sample gas such as environmental gas.
12
[0046]
Further, in the above-described embodiment, the first gas analysis part 2 and the second gas
analysis part 3 are configured using the single cell, but may be respectively configured as single
component meters.
5 [0047]
In addition, the above-described embodiment is one adapted to correct the coexistent effect of
CO2 on CO between the two components (CO and CO2). However, the present invention may be one
adapted to correct the coexistent effect of CO on CO2, correct the coexistent effect between other two
components (e.g., two components selected from CO2, H2O, HC, NO, SO2 or the like), or correct the
10 coexistent effect among three components or more (three components or more selected from CO, CO2,
H2O, HC, NO, SO2 or the like).
[0048]
Still in addition, the correction coefficient in the above-described embodiment indicates that at
a CO2 concentration of 0 %vol, the relative error of CO is 0 %, but may be one indicating that at another
15 CO2 concentration, the relative error of CO is 0 %.
[0049]
Yet in addition, the present invention may be one such that without obtaining a correction
coefficient after change by the correction coefficient changing part, a correction coefficient preliminarily
shifted on the basis of second gas component concentration of a calibration gas is stored in the correction
20 coefficient storage part 41, and the concentration correction part uses the changed correction coefficient
stored in the correction coefficient storage part 41.

WE CLAIM:
1. A gas analysis apparatus comprising:
a first gas analysis part adapted to measure concentration of a first gas component contained in
5 sample gas;
a second gas analysis part adapted to measure concentration of a second gas component
contained in the sample gas;
a correction coefficient storage part adapted to store a correction coefficient for correcting an
effect of the second gas component on the first gas component; and
10 a concentration correction part adapted to correct the first gas component concentration
obtained by the first gas analysis part on a basis of the correction coefficient, second gas component
concentration of calibration gas used for calibrating the first gas analysis part, and the second gas
component concentration obtained by the second gas analysis part.
15 2. The gas analysis apparatus as claimed in claim 1, wherein
the concentration correction part corrects the first gas component concentration on a basis of
the correction coefficient and a difference between the second gas component concentration of the
calibration gas and the second gas component concentration obtained by the second gas analysis part.
20 3. The gas analysis apparatus as claimed in claim 1, wherein
the correction coefficient indicates a relationship between second gas component
concentration and a relative error of first gas component concentration at the second gas component
concentration,
the gas analysis apparatus further comprising a correction coefficient changing part adapted to
25 shift and change the correction coefficient so as to make second gas component concentration at which
the relative error of the first gas component concentration is zero equal to the second gas component
concentration of the calibration gas, wherein
the concentration correction part corrects the first gas component concentration obtained by
the first gas analysis part with use of a correction coefficient after the change by the correction coefficient
15
changing part and the second gas component concentration obtained by the second gas analysis part.
4. The gas analysis apparatus as claimed in claim 1, wherein
the first gas analysis part is calibrated with use of mixed gas containing at least the first gas
5 component and the second gas component.
5. The gas analysis apparatus as claimed in claim 1, wherein
the first gas analysis part and the second gas analysis part include a detector using an NDIR
method.
10
6. The gas analysis apparatus as claimed in claim 1, wherein
one of the first gas component and the second gas component is carbon monoxide (CO), and
the other of the first gas component and the second gas component is carbon dioxide (CO2).
15 7. The gas analysis apparatus as claimed in claim 1, wherein
the sample gas is exhaust gas discharged from an internal combustion engine.
8. A gas analysis method using a first gas analysis part adapted to measure concentration of a
first gas component contained in sample gas and a second gas analysis part adapted to measure
20 concentration of a second gas component contained in the sample gas,
the gas analysis method correcting the first gas component concentration obtained by the first
gas analysis part on a basis of a correction coefficient for correcting an effect of the second gas
component on the first gas component, second gas component concentration of calibration gas used for
calibrating the first gas analysis part, and the second gas component concentration obtained by the
25 second gas analysis part.