Technical Field
[0001]
The present invention relates to a multipass cell, a gas analyzer including
the multipass cell, and a method for manufacturing a mirror for the multipass cell.
Background Art
[0002]
Some gas analyzers using light absorption as disclosed in Patent
Literature 1 use what is called a multipass cell which has a pair of mirrors
10 arranged oppositely to each other in a cell main body, into which sample gas is
introduced, to cause multireflection of light between the mirrors.
[0003]
The use of the multipass cell as described above increases a light path
length, thus permitting an increase in a distance of interaction between the light
15 and the sample gas and permitting an improvement in sensitivity.
[0004]
However, the multipass cell disclosed in Patent Literature 1 is of a type
called a Herriot cell, which uses, as the pair of mirrors, spherical mirrors with
reflecting surfaces of a circular shape in a plan view, so that a height and a width
20 of the cell main body needs to be larger than those of the spherical mirrors, and
there is limitation on a reduction in a volume of an inner space of the cell main
body.
[0005]
Consequently, there is also limitation on an improvement in a
25 replacement speed of the sample gas introduced into the inner space, raising a
3
problem of failure in obtaining a response speed required for analysis, for
example, upon measurement of exhaust gas or the like whose discharge amount of
each component fluctuates in accordance with a behavior of an internal
combustion engine.
5
Citation List
Patent Literature
[0006]
Patent Literature 1: Japanese Unexamined Patent Application Publication
10 No. 2010-243270.
Summary of Invention
Technical Problem
[0007]
15 Thus, the present invention has been made to solve the problem described
above, and it is a main object of the present invention to provide a multipass cell
permitting a reduction in a volume of an inner space into which sample gas in
introduced.
20 Solution to Problem
[0008]
Specifically, a multipass cell according to one aspect of the present
invention includes: a cell main body with an inner space into which sample gas is
introduced; and a pair of mirrors including a first mirror and a second mirror
25 provided oppositely to each other in the inner space, wherein light incident from
4
an incidence window of the cell main body is subjected to multireflection between
the pair of mirrors and is emitted from an emission window of the cell main body,
wherein: the pair of mirrors are configured such that light spots formed on a
reflecting surface of each of the mirrors are scattered in an elongated region of a
predetermined width through the light multireflection; and each of the mirrors 5 s is
formed into an elongated shape along a longitudinal direction of the elongated
region.
[0009]
With the multipass cell configured as described above, the pair of mirrors
10 are configured such that the light spots formed on the reflecting surface are
scattered in the elongated region of the predetermined width and are formed into
elongated shapes along the longitudinal direction of the elongated region, thus
permitting more drastic downsizing of the pair of mirrors than that in a
conventional case.
15 Consequently, a required volume of the inner space of the cell main body
can be made very small, consequently making it possible to improve a
replacement speed of the sample gas introduced into the inner space, which
permits a dramatic improvement in a response speed of analysis.
[0010]
20 To achieve the downsizing of the mirrors while increasing a light path
length through the multireflection, a length of each of the mirrors along the
longitudinal direction of the elongated region is preferably twice or more and
more preferably three times or more as long as a length of each of the mirrors
along a width direction orthogonal to the longitudinal direction.
25 [0011]
5
As the multipass cell, there is a type called an astigmatic Heriot cell
which is different from the Heriot cell described in Background Art. This type
uses, as the pair of mirrors, toroidal mirrors having mutually orthogonal two axes
with different curvature radiuses instead of using the spherical mirrors, and by
focusing the light spots on a region where the reflecting surface is located, 5 d, use
efficiency of the mirrors is improved, consequently achieving the downsizing of
the mirrors.
However, to fabricate the toroidal mirrors with high accuracy, an
advanced processing technology is required, resulting in a more remarkable
10 increase in manufacturing costs of the toroidal mirrors as compared to those of the
spherical mirrors.
[0012]
Thus, to achieve downsizing of the volume of the inner space without
leading to the remarkable increase in the manufacturing costs, it is preferable that
15 each of the mirrors be configured such that the light spots are scattered in the
elongated region by use of the spherical mirror.
[0013]
Examples listed as embodiments for scattering the light spots on the
elongated region of the predetermined width include an embodiment such that the
20 light spots are scattered on a straight line, a parabola, or an ellipse in the elongated
region.
[0014]
When a length of the cell main body along a longitudinal direction of the
mirror is longer than a length of the cell main body along a width direction of the
25 mirror, the cell main body is of a flat shape, which can provide a smaller volume
6
of the inner space than that of a conventional cell main body.
[0015]
To use the multipass cell, positions of the mirrors need to be adjusted
such that light incident from an incidence window of the cell main body is
subjected to multireflection between the pair of mirrors and is emitted from a5 n
emission window of the cell main body. Examples listed as methods for
adjusting the aforementioned positions include a method for pushing and pulling a
plurality of sections of the mirror by using a plurality of adjustment screws to
thereby adjust orientation of the mirrors while varying a lifting direction and a
10 heading direction of the mirrors.
However, the method for the adjustment described above adjusts the
orientation of the mirrors by repeating operation of pushing and pulling the
plurality of adjustment screws, thus requiring great labor for the adjustment and
also resulting in an increase in the number of components as a result of providing
15 the plurality of adjustment screws, which leads to a cost increase accordingly.
[0016]
Thus, it is preferable that the cell main body have at least two cell
elements forming the cell main body, that the first mirror be fixed at one of the at
least two cell elements and the second mirror be fixed at another one of the at
20 least two cell elements, and that a slide mechanism of sliding, with respect to the
one of the cell elements, the another one of the cell elements be provided between
the at least two cell elements.
[0017]
With the multipass cell configured as described above, the mirrors are
25 respectively fixed at the at least two cell elements forming the cell main body and
7
the slide mechanism of sliding, with respect to the one of the cell elements, the
another one of the cell elements is provided between these cell elements, and thus
the position adjustment of the mirrors can be performed by sliding the another one
of the cell elements by the slide mechanism.
Consequently, it is possible to simply adjust the positions of the mirror5 s
with a small number of components without using, for example, the adjustment
screws for varying the lifting direction and the heading direction of the mirrors.
[0018]
To more simplify the positioning of the mirrors, it is preferable that each
10 of the mirrors be positioned in a direction orthogonal to a predetermined reference
plane with respect to the reference plane, and that the slide mechanism slide, with
respect to the one of the cell elements, the another one of the cell elements along
an in-plane direction parallel to the reference plane.
With such configuration, the position adjustment of the mirrors in the
15 direction orthogonal to the reference plane can no longer be required, making it
possible to complete the position adjustment of the mirrors by sliding the cell
element along the in-plane direction parallel to the reference plane.
[0019]
To configure the slide mechanism with a small number of components
20 without placing another member between the at least two cell elements, it is
preferable that the slide mechanism have: a first slide surface formed at the one of
the cell elements; and a second slide surface formed at the another one of the cell
elements and making surface contact with the first slide surface, and change
positions of the pair of mirrors in the in-plane direction.
25 [0020]
8
It is preferable that the slide mechanism has a guide surface making
contact with the another one of the cell elements and regulating a slide direction
of the another one of the cell elements.
With such configuration, it is possible to complete the position
adjustment of the mirrors by sliding the cell element in a slide direction regulate5 d
by the guide surface, resulting in more simplified positioning of the mirrors.
[0021]
Moreover, a gas analyzer according to another aspect of the present
invention includes: the multipass cell described above; a light source emitting
10 light to the incidence window; a light detector detecting the light emitted from the
emission window; and an information processor analyzing the sample gas based
on a light intensity signal detected by the light detector.
With such a gas analyzer, the same effects as those of the multipass cell
described above can be provided.
15 [0022]
Further, a method for manufacturing a mirror for a multipass cell
according to still another aspect of the present invention refers to a method for
manufacturing a pair of mirrors including a first mirror and a second mirror being
provided oppositely to each other in an inner space of a cell main body into which
20 sample gas is introduced and configuring a multipass cell with the cell main body,
wherein a pair of prototype mirrors including a first prototype mirror and a second
prototype mirror serving as prototypes of the pair of mirrors are cut into elongated
shapes, and the shapes of the pair of prototype mirrors are changed such that light
spots formed on reflecting surfaces of the pair of mirrors are scattered in an
25 elongated region of a predetermined width through light multireflection.
9
[0023]
With the mirror of an elongated shape manufactured by such a method,
more drastic downsizing than that in a conventional case can be achieved.
Consequently, a required volume of the inner space of the cell main body can be
made very small, consequently making it possible to improve a replacement spee5 d
of the sample gas introduced into the inner space and permitting a dramatic
improvement in a response speed of analysis.
Advantageous Effects of Invention
10 [0024]
According to the present invention configured as described above, the
volume of the inner space into which the sample gas is introduced can be made
small, making it possible to improve the replacement speed of the sample gas and
permitting the improvement in the response speed of the analysis.
15
Brief Description of Drawings
[0025]
FIG. 1 is an overall schematic diagram of a gas analyzer according to one
embodiment of the present invention;
20 FIG. 2 is a cross-sectional view illustrating a configuration of a multipass
cell of the same embodiment;
FIG. 3 is a plan view illustrating a configuration of each mirror of the
same embodiment;
FIG. 4 is a perspective view illustrating a configuration of a pair of
25 mirrors of the same embodiment;
10
FIG. 5 is a cross-sectional view illustrating configuration of the multipass
cell of the same embodiment;
FIG. 6 is a plan view illustrating the configuration of the multipass cell of
the same embodiment;
FIG. 7 is a cross-sectional view illustrating a configuration of a multipa5 ss
cell of a modified embodiment;
FIG. 8 is a cross-sectional view illustrating the configuration of the
multipass cell of the modified embodiment;
FIGS. 9(a) and 9(b) are diagrams illustrating light spots formed on a
10 reflecting surface of a mirror of the modified embodiment;
FIG. 10 is a functional block diagram of an information processor
according to the modified embodiment;
FIG. 11 is a schematic diagram illustrating a method for modulating a
laser oscillation wavelength according to the modified embodiment;
15 FIG. 12 is a diagram illustrating one example of a modulation signal, an
output signal of a light detector, and measurement results according to the
modified embodiment; and
Fig. 13 is a schematic diagram illustrating main parts of an analyzer of
the modified embodiment.
20
Description of Embodiments
[0026]
Hereinafter, one embodiment of a gas analyzer according to the present
invention will be described with reference to the drawings.
25 [0027]
11
A gas analyzer 100 of the present embodiment analyzes, for example,
sample gas, such as exhaust gas exhausted from an internal combustion engine, by
using an Infrared spectroscopy such as NDIR, and more specifically includes, as
illustrated in FIG. 1: a semiconductor laser 10 serving as a light source; a
multipass cell 20 into which the sample gas is introduced and also which ca5 uses
multireflection of light from the semiconductor laser 10; a light detector 30 which
detects the light emitted from the multipass cell 20; and an information processor
40 which analyzes a component contained in the sample gas based on a light
intensity signal detected by the light detector 30.
10 The gas analyzer 100 according to the present invention has the multipass
cell 20 which is discriminative, and each of sections other than the multipass cell
20 will be first described.
[0028]
The semiconductor laser 10 is a quantum cascade laser (QCL) as one
15 kind of the semiconductor laser 10 here, and oscillates mid-infrared (4 μm to 10
μm) laser light. This semiconductor laser 10 is capable of modulating
(changing) an oscillation wavelength by a provided current (or voltage). Note
that as long as the oscillation wavelength is variable, a laser of a different type
may be used, and for example, a temperature may be changed to change the
20 oscillation wavelength.
[0029]
The light detector 30 uses a heat type such as a relatively low-cost
Thermopile here, but a different type, for example, a quantum photoelectric
device such as highly responsive HgCdTe, InGaAs, InAsSb, or PbSe may be used.
25 [0030]
12
The information processor 40 includes: an analog electric circuit which
includes a buffer, an amplifier, etc.; a digital electric circuit which includes a CPU,
a memory, etc.; an AD converter and a DA converter which serve as a relay
between the analog and digital electric circuits; and so on. As a result of
cooperation of the CPU and surrounding devices thereof in accordance with 5 a
predetermined program stored in a predetermined region of the memory, the
information processor 40 demonstrates functions of receiving an output signal
from the light detector 30 and performing calculation processing on a value of the
output signal to calculate concentration of a measurement target component.
10 [0031]
Next, the multipass cell 20 as a characteristic of the gas analyzer 100
according to the present invention will be described in detail.
[0032]
As illustrated in FIG. 2, the multipass cell 20 includes: a cell main body 1
15 with an inner space S into which sample gas is introduced; and a pair of mirrors 2
which are provided oppositely to each other in the cell main body 1. The
multipass cell 20 is configured such that light incident from an incidence window
W1 of the cell main body 1 is subjected to multireflection between the pair of
mirrors 2 and emitted from an emission window W2 of the cell main body 1.
20 Note that the incidence window W1 and the emission window W2 are formed of a
transparent material such as quartz, calcium fluoride, or barium fluoride which is
hardly subjected to light absorption in an absorption wavelength band of the
measurement target component (for example, CO or CO2 here) contained in the
sample gas.
25 [0033]
13
The multipass cell 20 of the present embodiment is of a type called a
Herriot cell, and uses spherical mirrors as the pair of mirrors 2. The mirrors 2
are arranged such that light axes LA and LB thereof overlap each other. The
multipass cell 20 is designed such that light which has passed through a light
passage hole h formed at one of the mirrors 2 is subjected to multireflecti5 on
between reflecting surfaces 21 of the respective mirrors 2 so as to provide a
predetermined number of paths and/or a predetermined light path length and the
light passes through the light passage hole h again. Note that the light passage
hole h here is formed so as to gradually widen from the reflecting surface 21
10 towards a rear surface thereof, but a shape of the light passage hole h may be
changed as appropriate. Hereinafter, to make discrimination between the pair
of mirrors 2, the mirror 2 formed with the light passage hole h is referred to as a
first mirror 2A and the mirror 2 arranged oppositely to the first mirror 2A is
referred to as a second mirror 2B. Note that arrangement and the number of
15 light passage holes h may be changed as appropriate. For example, the light
passage hole h may be formed not only at the first mirror 2A but also at the
second mirror 2B or may be formed at only the second mirror 2B. Moreover,
for example, as long as light is introduced into or out of a section between the
mirrors 2A and 2B from surroundings of the first mirror 2A and the second
20 mirror 2B, the light passage hole h may not be formed at both of the first mirror
2A and the second mirror 2B.
[0034]
Thus, as illustrated in FIG. 3, the mirror 2 of the present embodiment is
configured such that light spots P formed on the reflecting surface 21 of each
25 mirror 2 are scattered in an elongated region Z of a predetermined width through
14
light multireflection. Note that FIG. 3 illustrates the second mirror 2B
representing the pair of mirrors 2, but the first mirror 2A also has the same
configuration as that of the second mirror 2B excluding a point that the first
mirror 2A is formed with the light passage hole h.
[5 0035]
More specifically, as illustrated in FIG. 3, the elongated region Z is a
region with, for example, a width of approximately several millimeters which is
sandwiched between a pair of mutually parallel virtual lines X in a plan view of
the reflecting surface 21 of the mirror 2, and the elongated region Z is a band-like
10 region here. The virtual lines X regulate a region where the light spots P are to
be scattered on the reflecting surface 21. The pair of virtual lines X in the
present embodiment sandwich a center line M which passes through a center O of
the mirror 2 and are also mutually parallel straight lines which are provided at
equal distances from the center line M. The virtual lines X in FIG. 3 are
15 illustrated on more inner sides than an outer edge of the mirror 2 for the sake of
description, but the outer edge of the mirror 2 and the virtual lines X actually
coincide, in other words, the entire reflecting surface 21 is set as the elongated
region Z. However, the virtual lines X may be set on the even more inner sides
than the outer edge of the mirror 2, in other words, the elongated region Z may be
20 set on part of the reflecting surface 21. Note that the pair of virtual lines X do
not necessarily have to be parallel to each other and are not limited to the straight
lines but may be, for example, curved lines or wavy lines.
[0036]
The pair of mirrors 2 are designed such that the light spots P are scattered
25 on a line such as, for example, a straight line, a parabola, or an ellipse (including
15
part of an ellipse) in the elongated region Z described above. More specifically,
for the pair of mirrors 2, various parameters such as a mirror diameter, an
inter-mirror distance, a diameter of the light passage hole h, and curvature radius
of the reflecting surface 21 are appropriately set, and the mirror 2 is configured
such that the light spots P are scattered on the center line M passing through th5 e
center O of the mirror 2.
Note that the light spots P do not necessarily have to be scattered on a
single line and may be scattered on, for example, a plurality of straight lines, a
plurality of parabolas, or a plurality of ellipses.
10 [0037]
Next, listed as one example of a detailed method for manufacturing the
mirrors 2 is a method for cutting prototype mirrors (for example, flat mirrors) as
prototypes of the pair of mirrors 2 into elongated shapes and adjusting curvature
of the reflecting surface of each prototype mirror such that the light spots P
15 formed on the reflecting surfaces 21 of the pair of mirrors 2 are scattered in the
elongated region Z described above through the light multireflection.
[0038]
Each of the mirrors 2 as described above is of an elongated shape such
that a longitudinal direction of the mirror 2 is parallel to a longitudinal direction of
20 the elongated region Z. More specifically, a length La of the mirror 2 along the
longitudinal direction of the elongated region Z is at least twice or more, more
preferably, three times or more, and approximately six times in the present
embodiment as long as a length Lb of the mirror 2 along a width direction
orthogonal to the longitudinal direction of the elongated region Z.
25 [0039]
16
As illustrated in FIG. 4, each mirror 2 is provided with a plurality of
through holes 2h which are formed so as to penetrate through each mirror 2 in the
aforementioned width direction. Each mirror 2 is screwed into the cell main
body 1 with these through holes 2h in between. Note that the through holes 2h
may be formed on rear surfaces of the reflecting surfaces 5 s 21.
[0040]
Subsequently, the cell main body 1 will be described.
[0041]
As illustrated in FIGS. 2, 5, and 6, the cell main body 1 is a housing of,
10 for example, a substantially rectangular solid shape which stores the
aforementioned pair of mirrors 2 in the inner space S, and the pair of mirrors 2 are
arranged oppositely to each other along the longitudinal direction. In the present
embodiment, each of the pair of mirrors 2 is of an elongated shape with a small
thickness, and thus a flat shape with a small thickness is used as the cell main
15 body 1. Consequently, an inner shape of the cell main body 1 is also flat, which
can therefore provide the inner space S with small capacity, more specifically, a
volume of the inner space S here is, for example, approximately several tens of
milliliters. Note that the flat shape here may be changed to a rectangular solid
shape or an elliptical shape in a plan view as appropriate.
20 Hereinafter, for the sake of description, a longitudinal direction of the cell
main body 1 is referred to as a front-back direction, and a direction orthogonal to
the longitudinal direction of the cell main body 1 is referred to as a horizontal
direction, as illustrated in FIGS. 2 and 6, and a direction orthogonal to the
front-back direction and the horizontal direction, that is, a thickness direction of
25 the cell main body is referred to as a vertical direction, as illustrated in FIG. 5.
17
[0042]
As illustrated in FIGS. 2 and 5, the cell main body 1 is formed with: an
introduction path L1 which communicates with the inner space S and also which
is provided for introducing sample gas from the outside; and a lead-out path L2
which communicates with the inner space S and also which is provided 5 d for
leading out the sample gas to the outside.
[0043]
One side wall (hereinafter referred to as a front wall 1a) of the cell main
body 1 is provided with the aforementioned incidence window W1 and emission
10 window W2 as illustrated in FIG. 5, and one light transmitting plate 3 provided at
the front wall 1a is also used as both the incidence window W1 and the emission
window W2 in the present embodiment. One light transmitting plate 3 can be used
as both the incidence window W1 and the emission window W2 as described
above, because the light passage hole h formed on one mirror 2 is used as the
15 entrance and the exit of light. This configuration makes it possible to reduce the
number of manufacturing parts and reduce the manufacturing cost.
Note that the incidence window W1 and the emission window W2 may
be provided at mutually different side walls or may be formed by mutually
different light transmitting plates 3.
20 [0044]
The light transmitting plate 3 of the present embodiment is fitted in a
recess formed at the front wall 1a with an elastic member such as a packing in
between, and a pressing member 4 is further provided on a more outer side of the
light transmitting plate 3 with an elastic member such as a packing in between.
25 The pressing member 4 is of a flat plate-like shape which has, at a center part
18
thereof, a light passage hole 4a through which light passes, and the pressing
member 4 is screwed into the front wall 1a to thereby press and fix the light
transmitting plate 3.
Note that to reduce noise (fringe noise) generated through light
interference as a result of multireflection on an inside of the light transmitt5 ing
plate 3, a surface of the light transmitting plate 3 on a side facing the inner space S
is tilted with respect to a travel direction of the light from the semiconductor laser
10.
[0045]
10 The cell main body 1 of the present embodiment is divided into two cell
elements (hereafter referred to as a first cell element 11 and a second cell element
12) as illustrated in FIGS. 5 and 6. One (the first mirror 2A here) of the pair of
mirrors 2 is fixed at the first cell element 11 while the other (the second mirror 2B
here) of the pair of mirrors 2 is fixed at the second cell element 12.
15 [0046]
More specifically, the first cell element 11 and the second cell element 12
are combined to thereby form the cell main body 1, in other words, the first cell
element 11 and the second cell element 12 are one element and the other element
obtained by dividing the cell main body 1 into two, forming, for example, a shape
20 obtained by dividing a rectangular solid into two.
[0047]
The first cell element 11 forms at least part of a bottom wall 1b of the cell
main body 1, and the first mirror 2A is screwed into the bottom wall 1b with a seal
member SM in between. The first cell element 11 of the present embodiment
25 forms the bottom wall 1b and full circumference of side walls (that is, the front
19
wall 1a, a left wall 1c, a right wall 1d, and a rear wall 1e) of the cell main body 1.
[0048]
The second cell element 12 forms at least part of an upper wall 1f of the
cell main body 1, and the second mirror 2B is screwed into a portion forming the
upper wall 1f with a seal member SM in between. The second cell element 12 o5 f
the present embodiment forms almost the entire upper wall 1f of the cell main
body 1.
[0049]
As described above, since the first mirror 2A is fixed at the first cell
10 element 11 and the second mirror 2B is fixed at the second cell element 12,
combination of the first cell element 11 and the second cell element 12 positions
in a vertical direction the first mirror 2A and the second mirror 2B. That is, the
combination of the first cell element 11 and the second cell element 12 positions
each of the mirrors 2A and 2B with respect to a reference plane B parallel to the
15 light axes LA and LB of the mirrors 2A and 2B.
For example, in a case where a surface of the first cell element 11 on
which the first mirror 2A is attached, that is, an inward surface of the bottom wall
1b is defined as the reference plane B, the first mirror 2A and the second mirror
2B are positioned in a direction orthogonal to the reference plane B. Note that
20 the reference plane B may be a plane parallel to the light axes LA and LB, and
thus may be an outward surface of the bottom wall 1b, may be a surface of the
second cell element 12 on which the second mirror 2B is attached, that is, an
inward surface of the upper wall 1f, or may be a surface on which the cell main
body 1 is loaded. Moreover, in a case where a first slide surface 51 and a second
25 slide surface 52 to be described later on are parallel to each of the mirrors 2A and
20
2B, each of the first slide surface 51 and second slide surface 52 may be provided
as the reference plane B.
[0050]
In a state in which the first mirror 2A and second mirror 2B are
positioned along the vertical direction, the light axes LA and LB of the respecti5 ve
first mirror 2A and second mirror 2B are at predetermined heights along the
vertical direction from the reference plane B, more specifically, the light axes LA
and LB are at the same heights from the reference plane B.
[0051]
10 Thus, as illustrated in FIGS. 5 and 6, the cell main body 1 of the present
embodiment includes a slide mechanism 5 which is provided between the first cell
element 11 and the second cell element 12 and which slides one of the cell
elements 11 and 12 with respect to the other of the cell elements 11 and 12.
[0052]
15 The slide mechanism 5 causes slide movement of the first cell element 11
or the second cell element 12 along an in-plane direction parallel to the reference
plane B, and the slide mechanism 5 causes slide movement of the second cell
element 12 in the front-back direction and the horizontal direction in the present
embodiment as illustrated in FIG. 6.
20 [0053]
More specifically, the slide mechanism 5 has: the first slide surface 51
which is formed at the second cell element 12; and the second slide surface 52
with which this first slide surface 51 makes surface contact, and further has
push-in members 53 which push in the second cell element 12 along a slide
25 direction here.
21
[0054]
In the present embodiment, the second cell element 12 is configured to
make slide movement while making surface contact with the first cell element 11,
the first slide surface 51 is a surface of the second cell element 12 opposing the
first cell element 11, and the second slide surface 52 is a surface of the first ce5 ll
element 11 opposing the second cell element 12. The first slide surface 51 and
second slide surface 52 are both planes.
[0055]
More specifically, a step part which is slightly larger than the upper wall
10 1f is formed on upper surfaces of the side walls of the cell main body 1, that is,
the respective upper surfaces of the front wall 1a, the left wall 1c, the right wall 1d,
and the rear wall 1e, and the upper wall 1f is loaded on the step parts.
Consequently, as illustrated in FIG. 6, the upper wall 1f included in the second cell
element 12 is arranged between the front wall 1a, the left wall 1c, the right wall 1d,
15 and the rear wall 1e with a gap G in between, and the gap G permits the slide
movement of the second cell element 12 in the front-back direction and the
horizontal direction. Note that FIG. 6 illustrates a state in which the upper wall
1f included in the second cell element 12 is pushed in towards the left wall 1c, i.e.,
a state in which there is no gap G between the upper wall 1f and the left wall 1c.
20 [0056]
The push-in members 53 are provided so as to move forward and
backward with respect to the second cell element 12, more specifically, are bolts
or the like which penetrate through the side walls and also which, for example,
can be pushed and pulled by a driver.
25 In the present embodiment, the push-in members 53 are provided at a
22
plurality of parts of the side walls. More specifically, the push-in members 53
are provided at at least one of the front wall 1a and the rear wall 1e and are also
provided at at least one of the left wall 1c and the right wall 1d. The push-in
members 53 here are provided at the three side walls, i.e., the front wall 1a, the
rear wall 1e, and the right wall 1d but are not provided at the left wall 5 1c.
[0057]
Moreover, the push-in members 53 are provided at the plurality of parts
of at least one of the front wall 1a, the left wall 1c, the right wall 1d, and the rear
wall 1e. The push-in members 53 here are provided at two parts of each of the
10 front wall 1a and the right wall 1d while the push-in member 53 is provided at one
part of the rear wall 1e. As described above, providing the plurality of push-in
members 53 at the same side wall permits the slide mechanism 5 of the present
embodiment to not only cause the slide movement of the second cell element 12
in the front-back direction and the horizontal direction but also slide the second
15 cell element 12 while rotating the second cell element 12 around an axis along the
vertical direction. Note that positions of the push-in members 53 and the number
of push-in members 53 may be changed as appropriate.
[0058]
Further, the slide mechanism 5 of the present embodiment has a guide
20 surface 54 which makes contact with the second cell element 12 and also which
regulates a slide direction of the second cell element 12. The guide surface 54 is
a surface which extends along the slide direction of the second cell element 12,
and here extends in the front-back direction to regulate the slide movement in the
horizontal direction. More specifically, the guide surface 54 is a surface which
25 regulates the push-in of the second cell element 12 by the push-in members 53
23
while making contact with the second cell element 12, and is a portion of the side
wall (the left wall 1c here) of the cell main body 1 opposing the side wall of the
second cell element 12. As described above, the guide surface 54 of the present
embodiment is provided at the first cell element 11, but the guide surface 54 may
be provided at a different member while the different member is put between 5 n the
first cell element 11 and the second cell element 12.
[0059]
With the multipass cell 20 configured as described above, the pair of
mirrors 2 are configured such that the light spots P on the reflecting surface 21 are
10 scattered in the elongated region Z of the predetermined width, and are formed
into the elongated shapes along the longitudinal direction of the elongated region
Z, thus permitting more drastic downsizing of the pair of mirrors 2 than that in a
conventional case.
Consequently, a required volume of the inner space S of the cell main
15 body 1 can be made very small, consequently making it possible to improve a
replacement speed of the sample gas introduced into the inner space S, which
permits a dramatic improvement in a response speed of analysis.
[0060]
More specifically, the length La of the mirror 2 along the longitudinal
20 direction of the elongated region Z is twice or more (approximately 6 times in the
present embodiment) as long as the length Lb of the mirror 2 along the width
direction orthogonal to the longitudinal direction of the elongated region Z.
Then a length of the cell main body 1 along the longitudinal direction of the
mirror 2 is longer than a length of the cell main body 1 along a width direction of
25 the mirror 2, forming the cell main body 1 into a flat shape.
24
Consequently, downsizing of the mirrors 2 can be achieved while
providing a long light path through multireflection, making it possible to make the
volume of the inner space S much smaller than that of a conventional cell main
body 1.
[5 0061]
To achieve the downsizing of the mirrors 2 in the multipass cell 20, a
possible mode is such that the reflecting surfaces 21 are provided as toroidal
surfaces. However, to fabricate toroidal mirrors with high accuracy, an advanced
processing technology is required, resulting in high manufacturing costs.
10 On the contrary, the multipass cell 20 of the present embodiment is a
Heriot cell which uses the spherical mirrors as the pair of mirrors 2, thus
permitting a reduction in the manufacturing costs while achieving the downsizing
of the volume of the inner space S.
[0062]
15 Moreover, since the toroidal mirror has two axes with mutually different
curvature radiuses, for example, a position and orientation of each mirror needs to
be severely determined upon assembly of the multipass cell in order to achieve
light multireflection between the pair of mirrors.
On the contrary, the number of curvature radiuses of the spherical mirrors
20 used as the pair of mirrors 2 is fixed as one in the present embodiment, thus
providing more favorable assembly characteristics than that in a case where
toroidal mirrors are used.
[0063]
Further, the first mirror 2A is fixed at the first cell element 11, the second
25 mirror 2B is fixed at the second cell element 12, and the slide mechanism 5 is
25
provided between the first cell element 11 and the second cell element 12, thus
permitting easy position adjustment of each mirror 2 only through sliding of the
first cell element 11 or the second cell element 12 by the slide mechanism 5.
[0064]
In addition, the pair of mirrors 2 are positioned with respect to 5 the
reference plane B in the direction orthogonal to this reference plane B and the
slide mechanism 5 slides one of the cell elements with respect to the other of the
cell elements in the in-plane direction parallel to the reference plane B, and thus
can make the position adjustment of the mirrors 2 in the direction orthogonal to
10 the reference plane B unnecessary. That is, the sliding of the first cell element 11
or the second cell element 12 along the in-plane direction parallel to the reference
plane B makes it possible to complete the position adjustment of each mirror 2,
resulting in more simplified positioning of the mirrors 2.
[0065]
15 Furthermore, the slide mechanism 5 has the second slide surface 52
which is formed at the first cell element 11 and the first slide surface 51 which is
formed at the second cell element 12, thus permitting formation of the slide
mechanism 5 with a small number of components without placing a different
member between the two cell elements.
20 [0066]
Moreover, since the slide mechanism 5 has the guide surface 54 which
makes contact with the second cell element 12 and also which regulates the slide
direction of the second cell element 12, the siding of the second cell element 12 in
the slide direction regulated by the guide surface 54 makes it possible to complete
25 the position adjustment of the pair of mirrors 2, permitting simplification of the
26
positioning of the pair of mirrors 2.
[0067]
Moreover, the first cell element 11 and the second cell element 12 are
obtained by dividing the cell main body 1 of a substantially rectangular solid
shape into two, thus permitting formation of the multipass cell 20 with a minim5 um
possible number of components.
[0068]
Further, since the second cell element 12 forms part of the upper wall 1f
of the cell main body 1, removal of the second cell element 12 from the first cell
10 element 11 permits, for example, simple cleaning of an inside of the cell main
body 1, which can improve maintainability of the cell main body 1. In particular,
upon analysis of exhaust gas as in the present embodiment, contamination of the
inside of the cell main body 1 can easily be cleaned. Moreover, the combination
of the first cell element 11 and the second cell element 12 permits alignment of
15 the light axes of the pair of mirrors 2 after maintenance such as cleaning, which
can therefore improve the maintainability and the assembly characteristics at once.
[0069]
Note that the present invention is not limited to the embodiments
described above.
20 [0070]
For example, the second cell element 12 forms the upper wall 1f of the
cell main body 1 in the embodiment above, but as long as the first cell element 11
forms at least part of the cell main body 1 and the first mirror 2A is fixed, and as
long as the second cell element 12 forms at least part of the cell main body 1 and
25 the second mirror 2B is fixed, shapes of the first cell element 11 and the second
27
cell element 12 can be changed to various kinds.
More specifically, the second cell element 12 may form part the upper
wall 1f of the cell main body 1 as illustrated in FIG. 7, or the first cell element 11
may form at least the bottom wall 1b and the rear wall 1e and the second cell
element 12 may form at least the upper wall 1f and the front wall 1a as illustra5 ted
in FIG. 8.
[0071]
Moreover, the slide mechanism 5 of the embodiment above causes the
slide movement of the second cell element in the front-back direction and the
10 horizontal direction, but the slide mechanism 5 may cause the slide movement in
only one of the front-back direction and the horizontal direction or may cause the
slide movement in the vertical direction (the thickness direction of the cell main
body 1). Further, the slide mechanism 5 may cause slide movement of the first
cell element with respect to the second cell element.
15 [0072]
The cell main body 1 may be divided into three or more cell elements or
may be formed of a single cell element, and the shape of the cell main body 1 is
not limited to that in the embodiment above. Further, the cell main body 1 may
not include the slide mechanism 5.
20 [0073]
The method for manufacturing the pair of mirrors 2 is not limited to that
in the embodiment above, and for example, a pair of prototype mirrors as the pair
of mirrors 2 are first manufactured. This prototype mirror is a spherical mirror
with a reflecting surface of a circular shape in a plan view.
25 For each prototype mirror, various parameters such as a mirror diameter,
28
an inter-mirror distance, a diameter of a light passage hole, and a curvature radius
of a reflecting surface are appropriately set so that light spots formed on the
reflecting surface of each prototype mirror are scattered in the elongated region
described above through light multireflection between the mirrors.
Then cutting and removing a portion of each prototype mirror other 5 than
the elongated region results in manufacture of the pair of mirrors into elongated
shapes along the elongated region. Note that as long as the elongated region Z is
left, the whole of each prototype mirror other than the elongated region does not
necessarily have to be removed.
10 [0074]
Moreover, the embodiment has been described above, referring to the
case where the longitudinal direction of the mirror 2 and the longitudinal direction
of the elongated region Z are parallel to each other, but, for example, the
longitudinal direction of the elongated region Z may be tilted with respect to the
15 longitudinal direction of the mirror 2 as illustrated in FIG. 9A.
Further, the light spots P do not have to be scattered on a straight line,
and, for example, may be scattered on an ellipse as illustrated in FIG. 9B.
[0075]
The slide mechanism 5 is configured in the embodiment above such that
20 the first cell element 11 and the second cell element 12 make surface contact with
each other, but the slide mechanism 5 may be configured such that a different
member is provided between the first cell element 11 and the second cell element
12 and sliding is achieved through surface contact of the different member with
the first cell element 11 and the second cell element 12. Note that the number of
25 different members is not limited to one and a plurality of different members may
29
be provided.
[0076]
Moreover, the sample gas (sample) may be not only exhaust gas but also
the air or a liquid or a solid as a sample. In this sense, the present invention is
applicable not only to gas as a measurement target component but also to a 5 liquid
or a solid. Moreover, the measurement target can be used not only for
absorbance of the light transmitted through but also for calculation of absorbance
caused by the reflection.
[0077]
10 The embodiment has been described above, referring to the case where
the multipass cell 20 is a Heriot cell, but the multipass cell 20 may be a white cell.
[0078]
The pair of mirrors 2 are spherical mirrors in the embodiment above, but
toroidal mirrors may be used as the pair of mirrors 2.
15 [0079]
The embodiment has been described above, referring to the case where
the light source is a quantum cascade laser (QCL) as one type of a semiconductor
laser, but the light source may be a semiconductor laser other than the quantum
cascade laser. Moreover, the light source does not necessarily have to be a
20 semiconductor laser and may be, for example, a lamp using a filament or may be
an LED light source. Further, the light source is not limited to the one which
emits mid-infrared light but may be the one which emits near infrared light or far
infrared light or may be the one which emits ultraviolet light.
[0080]
25 The embodiment has been described above on the assumption that the
30
gas analyzer 100 adopts the NDIR method, but the gas analyzer according to the
present invention may adopt, for example, an FTIR method or an NDUV method.
[0081]
Further, the following description may be provided for analysis
pr5 inciples.
[0082]
First, before describing the analysis principles, the functions of the
information processor 40 will be described.
As illustrated in FIG. 10, the information processor 40 exerts the
10 functions as a light source control section 41 which controls output of the light
source 10 and a signal processing section 42 which receives the output signal
from the light detector 30 and performs the calculation processing on the value of
the output signal to calculate concentration of the measurement target component.
[0083]
15 The light source control section 41 outputs a current (or voltage) control
signal to thereby control a current source (or a voltage source) of the
semiconductor laser 10, thereby changing a drive current (or a drive voltage)
thereof with a predetermined frequency and in turn modulating the oscillation
wavelength of laser light outputted from the semiconductor laser 10 with the
20 predetermined frequency.
[0084]
In the present embodiment, the light source control section 41 changes
the drive current to a sinusoidal form and modulates the oscillation frequency to a
sinusoidal form (see a modulation signal of FIG. 12). Moreover, as illustrated in
25 FIG. 11, the oscillation wavelength of the laser light described above is adapted to
31
be modulated where a peak of a light absorption spectrum of the measurement
target component is defined as the center.
[0085]
The signal processing section 42 includes: a first calculation section 421,
a frequency component extraction section 422, a second calculation section 5 on 423,
etc.
The first calculation section 421 calculates a logarithm (hereinafter
referred to as an intensity ratio logarithm) of a ratio between a light intensity of
laser light (hereinafter referred to as measurement target light) which is
10 transmitted through the multipass cell 20 while the sample gas is sealed and light
absorption is caused by the measurement target component therein and a light
intensity of laser light (hereinafter referred to as reference light) which is
transmitted through the multipass cell 20 in a state in which light absorption is
substantially zero.
15 [0086]
More specifically, the former and latter light intensities are each
measured by the light detector 30 and measurement result data obtained through
the measurement is stored into a predetermined region of the memory, and the
first calculation section 421 calculates the aforementioned intensity ratio
20 logarithm with reference to the measurement result data.
[0087]
Thus, the former measurement (hereinafter referred to as sample
measurement) is performed, needless to say, for each sample gas. The latter
measurement (hereinafter referred to as reference measurement) may be
25 performed either before or after the sample measurement, or may be performed,
32
for example, only once at appropriate timing and results of the measurement may
be stored into the memory and used commonly with the sample measurement.
[0088]
Note that in the present embodiment, to provide the state in which the
light absorption is substantially zero, zero gas, for example, N2 gas with whic5 h
light absorption becomes substantially zero in a wavelength band where light
absorption of the measurement target component is observed is sealed in the
multipass cell 20, but different gas may be used or an inside of the multipass cell
20 may be vacuumed.
10 [0089]
The frequency component extraction section 422 performs lock-in
detection of the intensity ratio logarithm (hereinafter referred to as absorbance
signal), which has been calculated by the first calculation section 421, with a
reference signal having a frequency n-times (where n is an integer of 1 or more) as
15 large as the modulation frequency described above and extracts a frequency
component included in the reference signal from the aforementioned intensity
ratio logarithm. Note that the lock-in detection may be performed through
digital calculation or calculation made by an analog circuit. Moreover, the
extraction of the frequency component may be performed through not only the
20 lock-in detection but also through a method such as, for example, Fourier series
expansion.
[0090]
The second calculation section 423 calculate the concentration of the
measurement target component based on results of the detection performed by the
25 frequency component extraction section 422.
33
[0091]
Next, one example of operation of this gas analyzer 100 will be described
in combination with detailed description of the various sections described above.
[0092]
First, as described above, the light source control section 41 controls 5 ontrols the
semiconductor laser 10 and modulates a wavelength of the laser light with the
aforementioned modulation frequency where the peak of the absorption spectrum
of the measurement target component is defined as the center.
[0093]
10 Next, when the zero gas has been sealed into the multipass cell 20
automatically or by an operator, the first calculation section 421 which has
detected this phenomenon performs the reference measurement.
More specifically, the output signal from the light detector 30 is received
while the zero gas is sealed in the multipass cell 20 and a value of the output
15 signal is stored into a measurement result data storage section. The value of the
output signal of the light detector 30 in the reference measurement, that is, an
intensity of the reference light is expressed in a time series graph as illustrated in
FIG. 12A. That is, only a change in light output by modulation of the drive
current (voltage) of the laser is expressed in the output signal of the light detector
20 30.
[0094]
Thus, when the sample gas has been sealed into the multipass cell 20
automatically or by the operator, the first calculation section 421 performs the
sample measurement. More specifically, the output signal from the light detector
25 30 is received while the sample gas is sealed in the multipass cell 20, and the
34
value of the output signal is stored into a predetermined region of the memory.
The value of the output signal of the light detector 30 in the sample measurement,
that is, the intensity of the measurement target light is expressed in a time series
graph as illustrated in FIG. 12B. It is found that a peak caused by absorption
appears for each half cycle of modulati5 on.
[0095]
Next, the first calculation section 421 synchronizes each measurement
data with a modulation cycle and calculates an intensity ratio logarithm of the
light intensity of the measurement target light and the light intensity of the
10 reference light. More specifically, calculation equal to an expression
(Expression 1) below is performed:
[Expression 1]
where Dm(t) denotes the intensity of the measurement target light;
15 Dz(t) denotes the intensity of the reference light; and
A(t) denotes the intensity ratio logarithm (absorbance signal).
The absorbance signal is expressed in a graph with time plotted at a
horizontal axis as illustrated in FIG. 12C.
[0096]
20 Note that as a way of obtaining the intensity ratio logarithm, the ratio
between the intensity of the measurement target light and the intensity of the
reference light may first be calculated and then the logarithm thereof may be
obtained, or a logarithm of the measurement target light and a logarithm of the
intensity of the reference light may each be obtained and they may be subtracted.
35
[0097]
Next, the frequency component extraction section 422 performs lock-in
detection of the aforementioned intensity ratio logarithm with a reference signal
having a frequency twice as large as the modulation frequency, that is, extracts the
frequency component twice as large as the modulation frequency, and stores da5 ta
thereof (hereinafter referred to as lock-in data) into a predetermined region of the
memory. Note that the lock-in data may be obtained by subtracting what is
obtained by subjecting each of the logarithm of the measurement target light and
the logarithm of the intensity of the reference light to the lock-in detection.
10 [0098]
A value of the lock-in data becomes a value proportional to the
concentration of the measurement target component, and based on the value of the
lock-in data, the second calculation section 423 calculates a concentration
indication value indicating the concentration of the measurement target
15 component.
[0099]
Thus, with such configuration, even upon fluctuation in laser light
intensity due to some factor, given offset is only added to the aforementioned
intensity ratio logarithm, causing no change in the waveform. Therefore, a value
20 of each frequency component calculated by performing lock-in detection of the
intensity ratio logarithm does not change and the concentration indication value
does not change, which can therefore expect highly accurate measurement.
[0100]
A reason for this will be described as follow.
25 Fourier series expansion of the absorbance signal A(t) is typically
36
expressed by an expression (Expression 2) below.
Note that an in (Expression 2) denotes a value proportional to the
concentration of the measurement target component, and the second calculation
section 423 calculates the concentration indication value indicating the
concentration of the measurement target component based on the value an5 .
[Expression 2]
where fm denotes a modulation frequency; and
n denotes a multiple with respect to the modulation frequency.
10 [0101]
On the other hand, A(t) is also expressed in the expression (Expression 1)
described above.
[0102]
Next, the absorbance signal A’(t) in a case where the laser light intensity
15 fluctuates by α times due to some reason during the measurement is expressed as
in an expression (Expression 3) below.
[Expression 3]
[0103]
20 As is clear from the expression (Expression 3), the absorbance signal
A’(t) is obtained by only adding -ln(α) as a fixed value to the absorbance signal
A(t) when the laser light intensity does not fluctuate, thus proving that the value an
of each frequency component does not change even upon a change in the laser
37
light intensity.
[0104]
Therefore, there is no influence on the concentration indication value
determined based on the value of the frequency component twice as large as the
modulation frequency5 .
The above is the example of operation of the gas analyzer 100 in a case
where an interference component other than the measurement target component is
not included in the sample gas.
[0105]
10 Next, an example of operation of the gas analyzer 100 in a case where
one or a plurality of interference components (for example, H2O) having light
absorption in a peak light absorption wavelength of the measurement target
component are included in the sample gas will be described.
[0106]
15 First, principles will be described.
Shapes of light absorption spectra of the measurement target component
and the interference component are different, and thus waveforms of the
absorbance signals in a case where these components are independently present
are different and ratios of the respective frequency components are different
20 (linear independence). Using this, relationship between the value of each
frequency component of the measured absorbance signal and each frequency
component of the absorbance signals of the previously obtained measurement
target component and interference component is used to solve simultaneous
expressions, whereby concentration of the measurement target component for
25 which an influence of interference has been corrected can be provided.
38
[0107]
Where Am(t) and Ai(t) respectively denote absorbance signals per unit
concentration in a case where the measurement target component and the
interference component are each independently present and anm and ani denote the
frequency components of the respective absorbance signals, expressi5 ons
(Expressions 4 and 5) below are formed.
[Expression 4]
[Expression 5]
10
[0108]
The absorbance signal value A(t) in a case where concentration of the
measurement target component and the interference component are present as Cm
and C1 is expressed by an expression (Expression 6) below by linearity of each
15 absorbance.
[Expression 6]
[0109]
Where a1 and a2 respectively denote frequency components of fm and 2fm
39
in A(t), simultaneous expressions (Expression 7) below are formed based on the
expression (Expression 6) described above.
[Expression 7]
[5 0110]
Each of frequency components anm and ani (where n is a natural number,
and n=1,2 here) in a case where the measurement target component and the
interference component are each independently present can previously be obtained
through flow of each span gas, and thus concentration Cm of the measurement
10 target gas from which the influence of interference is removed can be determined
through simple and reliable calculation of solving the simultaneous expressions
(Expression 7) described above.
[0111]
The gas analyzer 100 operates based on the aforementioned principles.
15 Specifically, the gas analyzer 100 in this case stores the frequency
components a1m, a2m, a1i, and a2i of the respective absorbance signals in a case
where the measurement target component and the interference component are
each independently present by, for example, previous measurement through the
previous flow of span gas into a predetermined region of the memory. More
20 specifically, as is the case with the aforementioned example, the intensity of the
measurement target light and the intensity of the reference light are measured for
each of the measurement target component and the interference component to
calculate intensity ratio logarithms (absorbance signals) thereof, and for example,
lock-in detection is performed based on the aforementioned intensity ratio
40
logarithms to obtain the frequency components a1m, a2m, a1i, and a2i, and the
frequency components are then stored. Note that instead of the frequency
components, the absorbance signals Am(t) and Ai(t) per unit concentration may be
stored and the frequency components a1m, a2m, a1i, and a2i may be calculated based
on the expression (Expression 4) described above5 .
[0112]
Then the gas analyzer 100 specifies the measurement target component
and the interference component by, for example, inputting by an operator.
[0113]
10 Next, the first calculation section 421 calculates the intensity ratio
logarithm A(t) in accordance with the expression (Expression 1) described above.
Then the frequency component extraction section 422 performs lock-in
detection of the intensity ratio logarithm with the reference signal having the
modulation frequency fm and the frequency 2fm twice as large as the modulation
15 frequency fm to extract the frequency components a1 and a2 (lock-in data) and
store the frequency components a1 and a2 into the predetermined region of the
memory.
[0114]
Then the second calculation section 423 assigns the expression
20 (Expression 7) described above with the values a1 and a2 of the lock-in data and
the values of the frequency components a1m, a2m, a1i, and a2i stored in the memory
or calculation equal thereto is performed to calculate concentration (or
concentration indication value) Cm indicating the concentration of the
measurement target gas from which the influence of interference has been
25 removed. At this point, the concentration (or the concentration indication value)
41
Ci of each interference component may be calculated.
[0115]
Note that even in a case where two or more interference components are
present, higher-order frequency components the number of which is equal to the
number of interference components can be added and simultaneous expressi5 ons
whose number of elements is equal to the number of component types can be
solved to thereby determine concentration of the measurement target component
from which the influence of interference has been removed in the same manner.
[0116]
10 Specifically, in a case where n-types of gas are present through
combination of the measurement target component and the interference
component, where the frequency component of the kth-gas type i×fm is aik and
concentration of the k-th gas type is Ck, expressions (Expression 8) below are
formed:
15 [Expression 8]
[0117]
Solving n-element simultaneous expressions expressed by the
expressions (Expression 8) can determine the concentration of each gas of the
20 measurement target component and the interference component.
[0118]
42
Moreover, a harmonic component of which order is higher than n may be
added to create simultaneous expressions whose number of elements is larger than
the number of gas types and determine concentration of each gas by a least-square
method, thereby making it possible to achieve concentration determination with a
smaller error for measurement noise5 .
[0119]
The sample measurement and the reference measurement are performed
by the single light detector in the embodiment described above, but as illustrated
in FIG. 13, two light detectors 31 and 32 may be used with the light detector 31
10 provided for the sample measurement and the light detector 32 provided for the
reference measurement. In this case, light from the light source 2 is branched by
a half mirror 33. Moreover, a reference cell may be arranged on a light path for
the reference measurement. Note that it is possible that zero gas or reference gas
whose concentration is already known is sealed into the reference cell.
15 [0120]
The present invention is not limited to the embodiment above, and it is
needless to say that various modifications can be made within a range not
departing from spirits of the present invention.
20 Reference Signs List
[0120]
100 Gas analyzer
20 Multipass cell
1 Cell main body
25 2A,B Mirror
43
21 Reflecting surface
P Light spot
Z Elongated region
11 First cell element
12 Second cell eleme5 nt
5 Slide mechanism
51 First slide surface
52 Second slide surface
53 Push-in member
10 54 Guide surface

WE CLAIM:
1. A multipass cell comprising a cell main body with an inner space into
which sample gas is introduced and a pair of mirrors including a first mirror and a
second mirror provided oppositely to each other in the inner space, wherein light
incident from an incidence window of the cell main body is subjected 5 ted to
multireflection between the pair of mirrors and is emitted from an emission
window of the cell main body, wherein:
the pair of mirrors is configured such that light spots formed on a
reflecting surface of each of the mirrors are scattered in an elongated region of a
10 predetermined width through the light multireflection; and
each of the mirrors is formed into an elongated shape along a longitudinal
direction of the elongated region.
2. The multipass cell according to claim 1, wherein:
15 a length of each of the mirrors along the longitudinal direction of the
elongated region is twice or more as long as a length of each of the mirrors along
a width direction orthogonal to the longitudinal direction of the elongated region.
3. The multipass cell according to claim 2, wherein
20 the length of each of the mirrors along the longitudinal direction is three
times or more as long as the length of each of the mirrors along the width
direction.
4. The multipass cell according to claim 1, wherein
25 each of the mirrors is configured such that the light spots are scattered in
45
the elongated region by use of a spherical mirror.
5. The multipass cell according to claim 1, wherein
the light spots are scattered on a straight line, a parabola, or an ellipse in
the elongated reg5 ion.
6. The multipass cell according to claim 1, wherein
a length of the cell main body along a longitudinal direction of the mirror
is longer than a length of the cell main body along a width direction of the mirror.
10
7. The multipass cell according to claim 1, wherein:
the cell main body has at least two cell elements forming the cell main
body;
the first mirror is fixed at one of the at least two cell elements and the
15 second mirror is fixed at another one of the at least two cell elements; and
a slide mechanism of sliding, with respect to the one of the cell elements,
the another one of the cell elements is provided between the at least two cell
elements.
20 8. The multipass cell according to claim 7, wherein:
each of the mirrors is positioned in a direction orthogonal to a
predetermined reference plane with respect to the predetermined reference plane;
and
the slide mechanism slides, with respect to the one of the cell elements,
25 the another one of the cell elements along an in-plane direction parallel to the
46
reference plane.
9. The multipass cell according to claim 7, wherein
the slide mechanism has: a first slide surface formed at the one of the cell
elements; and a second slide surface formed at the another one of the ce5 ll
elements and making surface contact with the first slide surface.
10. The multipass cell according to claim 7, wherein
the slide mechanism has a guide surface making contact with the another
10 one of the cell elements and regulating a slide direction of the another one of the
cell elements.
11. A gas analyzer comprising:
the multipass cell according to claim 1;
15 a light source emitting light to the incidence window;
a light detector detecting the light emitted from the emission window;
and
an information processor analyzing the sample gas based on a light
intensity signal detected by the light detector.
20
12. A method for manufacturing a mirror for a multipass cell as a pair of
mirrors including a first mirror and a second mirror being provided oppositely to
each other in an inner space of a cell main body into which sample gas is
introduced and forming the multipass cell with the cell main body, wherein
25 a pair of prototype mirrors including a first prototype mirror and a second
47
prototype mirror serving as prototypes of the pair of mirrors are cut into elongated
shapes, and the shapes of the pair of prototype mirrors are changed such that light
spots formed on a reflecting surface of the pair of mirrors are scattered in an
elongated region of a predetermined width through light multireflection.