Patent Publication Number: US-10788415-B2

Title: Analysis device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Application No. 2017-200633, filed Oct. 16, 2017, the disclosure of which is incorporated in its entirety by reference herein. 
     FIELD OF THE ART 
     This invention relates to an analysis device using a multiple-reflection cell. 
     BACKGROUND ART 
     Conventionally, an analysis device that analyzes a measuring objective component contained in a sample uses a multiple-reflection cell such as a white cell or a Heriot cell. By using the multiple-reflection cell, it is possible to elongate an optical path length without increasing the cell in size. As this result, it is possible to enlarge a detection signal such as the measuring objective component having a low concentration, resulting in improvement of measurement accuracy. 
     As shown in the patent document conceived is the Heriot cell using an astigmatic mirror whose cell body of the multiple-reflection cell is provided with a pair of mirrors for a long optical path and a pair of mirrors for a short optical path. With this arrangement, a dynamic range is enlarged by realizing the long optical path and the short optical path for a single multiple-reflection cell. 
     However, this arrangement requires a pair of the mirrors for the long optical path and a pair of the mirrors for the short optical path so that not only the structure of the multiple-reflection cell is complicated but also an inner volume of the multiple-reflection cell increases. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent document 1: WO 2011/114096 
       
    
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     The present claimed invention intends to solve all of the problems and a main object of this invention is to simplify a structure of the multiple-reflection cell and to make it possible to measure both a measuring objective component having a high concentration and a measuring objective component having a low concentration. 
     Means to Solve the Problems 
     More specifically, an analysis device in accordance with this invention is an analysis device that irradiates a light to a multiple-reflection cell into which a sample is introduced, detects the light exiting from the multiple-reflection cell and analyzes a measurement objective component contained in the sample, and is characterized by comprising a first light irradiation part that allows a first light to enter the multiple-reflection cell, and a second light irradiation part that allows a second light whose incident optical path is different from that of the first light to enter the multiple-reflection cell, and the multiple-reflection cell has a pair of reflecting mirrors that reflect the first light and the second light. 
     In accordance with this invention, since the analysis device has a pair of the reflecting mirrors that reflect the first light and the second light each having mutually different incident optical paths, it is possible to make the number of reflections of the first light by a pair of the reflecting mirrors and the number of reflections of the second light by a pair of the reflecting mirrors different from each other. Accordingly, it is possible to simplify the structure of the multiple-reflection cell and to measure both the measuring objective component having a high concentration and the measuring objective component having a low concentration. In addition, since the structure of the multiple-reflection cell can be simplified, it is possible to make the internal volume of the multiple-reflection cell small and to make a substitution rate of the sample gas fast, thereby improving responsiveness. Furthermore, since the analysis device has the first light irradiation part and the second light irradiation part, it is possible to allow the first light and the second light to enter the multiple-reflection cell simultaneously. With this arrangement, it is possible to measure both the measuring objective component having a high concentration and the measuring objective component having a low concentration simultaneously. In addition, it is also possible to measure a plurality of measuring objective components simultaneously by making a wavelength bandwidth of the first light and a wavelength bandwidth of the second light different from each other. 
     In order to simplify the structure of the analysis device by arranging the optical system such as the light irradiation part and the photoelectric detector on one side of the multiple-reflection cell, it is preferable that the multiple-reflection cell has an arrangement wherein the first light and the second light enter from one of a pair of the reflecting mirrors and the first light and the second light exit from the same reflecting mirror. 
     With this arrangement, it is preferable that an inlet and an outlet of the first light and an inlet and an outlet of the second light are formed on at least one of a pair of the reflecting mirrors. In accordance with this arrangement, there is no need of providing the cell body housing a pair of the reflecting mirrors with the inlet and the outlet in the outside of the reflecting mirrors in a front view of the reflecting mirror, it is possible to downsize the multiple-reflection cell. 
     In this case, in order to prevent the other light from unexpectedly going out from the inlet or the outlet of one light, it is preferable that a position where each of the inlet and the outlet of the first light is formed is different from a reflecting position of the second light by a pair of the reflecting mirrors, and a position where each of the inlet and the outlet of the second light is formed is different from a reflecting position of the first light by a pair of the reflecting mirrors. 
     It is preferable that the inlet and the outlet of the first light and the inlet and the outlet of the second light are formed on only one of a pair of the reflecting mirrors. In accordance with this arrangement, it is possible to simplify the structure of the other reflecting mirror. In addition, in case that the multiple-reflection cell has a cell body that houses a pair of the reflecting mirrors and that has an introducing port from which the sample is introduced and a discharging port from which the sample is discharged, the cell body may have the optical window member to input or output the first light and the second light only on one side of the cell body, it is possible to simplify the structure of the cell body. 
     In order to further simplify the structure of the cell body, it is preferable that the cell body has one optical window member from which the first light and the second light enter and exit. 
     In order to widen the measurement range from a low concentration to a high concentration, it is preferable that the first light is reflected at multiple times by a pair of the reflecting mirrors and outputted, and the second light is reflected at a number of multiple times smaller than that of the first light by a pair of the reflecting mirrors, or reflected at once by one of a pair of the reflecting mirrors and outputted. 
     Effect of the Invention 
     In accordance with the above-mentioned invention, it is possible to measure both the measuring objective component having a high concentration and the measuring objective component having a low concentration, while simplifying the structure of the multiple-reflection cell. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an overall view of an analysis device in accordance with one embodiment of this invention. 
         FIG. 2  is a cross-sectional view showing a configuration of a multiple-reflection cell of this embodiment. 
         FIG. 3  is a front view showing a positional relationship among a reflecting position, an inlet and an outlet on one of the reflecting mirrors in this embodiment. 
         FIG. 4  is a function block diagram of an information processing unit in this embodiment. 
         FIG. 5  is a pattern view showing a modulation method of a laser oscillation wavelength in this embodiment. 
         FIG. 6  is a view showing a driving electric current (voltage) and a modulation signal in this embodiment. 
         FIG. 7  is a front view showing a positional relationship among a reflecting position, an inlet and an outlet on one of the reflecting mirrors in accordance with a modified embodiment. 
         FIG. 8  is a pattern view showing a principal part of an analysis device of a modified embodiment. 
     
    
    
     BEST MODES OF EMBODYING THE INVENTION 
     An analysis device  100  in accordance with one embodiment of this invention will be explained with reference to drawings. 
     The analysis device  100  of this embodiment is a concentration measurement device that measures a concentration of a measuring objective component (for example, CO, CO 2 , N 2 O, NO, NO 2 , H 2 O, SO 2 , CH 4 , NH 3  or the like in this embodiment) contained in a sample gas such as an exhaust gas from, for example, an internal combustion engine, and as concretely shown in  FIG. 1 , comprises a light irradiation part  10 , a multiple-reflection cell  20  into which the sample gas is introduced and where a light from the light irradiation part  10  is reflected at multiple times, a photoelectric detecting part  30  that detects the light exiting from the multiple-reflection cell  20  and an information processing unit  40  that analyzes the measuring objective component contained in the sample gas based on a light intensity signal detected by the photoelectric detecting part  30 . 
     The light irradiation part  10  comprises a first light irradiation part  10 A that allows a first light L 1  to enter the multiple-reflection cell  20  and a second light irradiation part  10 B that allows a second light L 2  whose incident optical path is different from that of the first light L 1  to enter the multiple-reflection cell  20 . That the incident optical path is different includes that the optical paths are separated each other even though an incident angle to the multiple-reflection cell  20  is the same in addition to that an incident angle to the multiple-reflection cell  20  is different. 
     In this embodiment both the first light irradiation part  10 A and the second light irradiation part  10 B have a common semiconductor laser  11  as a light source. Concretely, both the first light irradiation part  10 A and the second light irradiation part  10 B comprise a common semiconductor laser  11  and a common beam splitter  12  that divides the laser light irradiated from the semiconductor laser  11  into two. One laser light divided by the beam splitter  12  becomes the first light L 1  and the divided other laser light becomes the second light L 2 . The second light irradiation part  10 B is further provided with an optical element  13  that introduces the other light into the multiple-reflection cell  20 . As mentioned, since the common semiconductor laser  11  is used, the first light irradiation part  10 A and the second light irradiation part  10 B allow the first light L 1  and second light L 2  to enter the multiple-reflection cell  20  simultaneously. 
     The first light irradiation part  10 A and the second light irradiation part  10 B may have a semiconductor laser respectively without commonizing the semiconductor laser. In this case, no beam splitter  12  is required. In addition, if one laser light divided by the beam splitter  12  directly enters the multiple-reflection cell  20 , an optical element such as a mirror is not required for the first light irradiation part  10 . Otherwise, similar to the second light irradiation part  10 B, the first light irradiation part  10 A may have an optical element such as a mirror that introduces the other light into the multiple-reflection cell  20 . 
     The semiconductor laser  11  is a QCL (Quantum Cascade Laser), and oscillates a laser beam of middle infrared (4 μm˜10 μm). The semiconductor laser  11  can modulate (change) an oscillation wavelength by a given electric current (or a voltage). As far as the oscillation wavelength is variable, a laser of other type may be used, and a temperature may be changed in order to change the oscillation wavelength. 
     The multiple-reflection cell  20  is, as shown in  FIG. 2 , of a type of, so called, a Heriot cell. The multiple-reflection cell  20  comprises a cell body having an internal space (S) into which the sample gas is introduced and a pair of reflecting mirrors  22 ,  23  arranged to face each other inside of the cell body  21 . 
     The cell body  21  is provided with an introducing port P 1  through which the sample gas is introduced into the internal space (S) and a discharging port P 2  through which the sample gas is discharged from the internal space (S). In addition, an incident window W 1  for allowing the light L 1 , L 2  from the first light irradiation part  10 A and the second light irradiation part  10 B to enter, and an exit window W 2  for allowing the laser light reflected by a pair of the reflecting mirrors  22 ,  23  to exit to the outside are formed on the cell body  21 . 
     The incident window W 1  and the exit window W 2  are composed of a single optical window member  211 . The optical window member  211  is made of a transparent material such as quartz, calcium fluoride, barium fluoride wherein almost no absorption in an absorption wavelength band of the measuring objective component contained in the sample gas. 
     A pair of the reflecting mirrors  22 ,  23  are arranged to face each other in the internal space (S) of the cell body  21 , and reflect the first light L 1  and the second light L 2 . The reflecting mirrors  22 ,  23  in this embodiment use an aspherical mirror such as a toroidal mirror wherein a radius of curvature of two axes that are orthogonal with each other differs each other, however, a spherical surface mirror may be used. In this case, if the toroidal mirror is used, it is possible to improve an efficiency of utilization of the mirror by focusing the light spot in an area where the reflecting surface locates, resulting in downsizing the mirror. In addition, a pair of the reflecting mirrors  22 ,  23  have the same shape of the mirror surface, however, the reflecting mirrors  22 ,  23  have a different shape of the mirror surface. 
     One reflecting mirror  22  is provided with an inlet X 1  to input the first light L 1  into a space between a pair of the reflecting mirrors  22 ,  23 , an outlet X 2  to output the first light L 1  to the outside of the space between the reflecting mirrors  22 ,  23 , an inlet X 3  to input the second light L 2  into the space between a pair of the reflecting mirrors  22 ,  23  and an outlet X 4  to output the second light L 2  to the outside of the space between the reflecting mirrors  22 ,  23 . As mentioned, since the inlet X 1  and the outlet S 2  for the first light L 1  and the inlet X 3  and the outlet X 4  for the second light L 2  are formed only on the reflecting mirror  22 , it is possible to simplify the structure of the other reflecting mirror  23 . 
     In this embodiment, the first light L 1  entering from the inlet X 1  exits from the outlet X 2  after reflecting at multiple times by reflecting surfaces of a pair of the reflecting mirrors  22 ,  23 . In addition, the second light L 2  entering from the inlet X 3  exits from the outlet X 4  after reflecting once by the reflecting surface of the other reflecting mirror  23 . In other words, the second light L 2  of this embodiment is not reflected by the reflecting mirror  22 . In addition, the entering direction and the exiting direction of the second light L 2  are so formed between a plane where the entering direction of the first light L 1  passes and a plane where the exiting direction of the first light L 1  passes. 
     A positional relationship between the reflecting spots (reflecting positions) of the first light L 1  and each of the inlets and the outlets X 1 ˜X 4  of the reflecting mirror  22  is shown in  FIG. 3 . Each of the positions where the inlet X 1  and the outlet X 2  for the first light L 1  are formed is different from a position where the second light L 2  is reflected by the reflecting mirror  23 . In addition, each of the positions where the inlet X 3  and the outlet X 4  for the second light L 2  are formed is different from a position where the first light L 1  is reflected by a pair of the reflecting mirrors  22 ,  23 . More concretely, each of the inlet X 3  and the outlet X 4  for the second light L 2  is formed on the reflecting mirror  22  at a part where there is no reflecting spot for the first light L 1 . Then, the reflecting surface of the reflecting mirror  22  is so designed that the inlet X 3  and the outlet X 4  of the second light L 2  can be formed on the part where there is no reflecting spot for the first light L 1 . 
     In addition, in this embodiment, each of the inlet X 1  and the outlet X 2  for the first light L 1  is formed by a common through bore formed on a center part of the reflecting mirror  22 . In addition, the inlet X 3  and the outlet X 4  for the second light L 2  are formed at symmetrical positions across the inlet X 1  (the outlet X 2 ) of the first light L 1 . 
     The photoelectric detecting part  30  comprises a first photoelectric detector  30 A that detects the first light L 1  exiting from the multiple-reflection cell  20  and a second photoelectric detector  30 B that detects the second light L 2  exiting from the multiple-reflection cell  20 . The first photoelectric detector  30 A and the second photoelectric detector  30 B of this embodiment use a thermal type sensor such as a thermopile that is comparatively inexpensive, however, a high responsive quantum type photoelectric element such a HgCdTe, InGaAs, InAsSb or PbSe may be used. 
     The information processing unit  40  comprises an analog electric circuit having a buffer and an amplifier, a digital electric circuit having a CPU and a memory, an AD converter and a DA converter that mediate between the analog electric circuit and the digital electric circuit. The information processing unit  40  receives an output signal from a light source control part  41  that controls an output of the semiconductor laser  2  or the photoelectric detectors  30 A,  30 B and produces a function as a signal processing part  42  that conducts an arithmetic processing on a value of the output signal and calculates a concentration of the measuring objective component by cooperatively operating the CPU and its peripheral devices according to predetermined programs stored in a predetermined area of the memory. 
     Each part will be explained. 
     The light source control part  41  controls a current source (or a voltage source) of the semiconductor laser  11  by outputting a current (or a voltage) control signal. The light source control part  41  changes a driving current (or a driving voltage) by the use of a predetermined frequency, and consequently modulates the oscillation wavelength of the laser light output from the semiconductor laser  11  by the use of the predetermined frequency. 
     In this embodiment, the light source control part  41  changes the driving current in a sine wave shape and modulates the above-mentioned oscillation frequency in the sine wave shape (refer to a modulation signal in  FIG. 6 ). In addition, as shown in  FIG. 5 , the oscillation wavelength of the laser light is moderated with a peak of an absorbance spectrum of the measuring objective component as the center. The first light irradiation part  10 A and the second light irradiation part  10 B allows the first light L 1  and the second light L 2  to enter the multiple-reflection cell  20  at once by the semiconductor laser  11  being controlled by the light source control part  41 . That the first light L 1  and the second light L 2  enter at once may include a state wherein the first light L 1  and the second light L 2  exist in the multiple-reflection cell  20  instantaneously even though the timing when the first light L 1  and the second light L 2  enter the multiple-reflection cell  20  is not completely the same. 
     The signal processing part  42  comprises a first calculation part  421 , a frequency component extracting part  422  and a second calculation part  423 . 
     The first calculation part  421  calculates a logarithm of a ratio between a light intensity of the laser light (hereinafter also called as the measuring objective light) passing the multiple-reflection cell  20  in a state wherein the sample gas is enclosed in the multiple-reflection cell  20  and the light absorption due to the measuring objective component generates in the multiple-reflection cell  20  and the light intensity of the laser light passing the multiple-reflection cell  20  in a state wherein the light absorption is substantially zero. 
     More specifically explained, both of the former light intensity and the later light intensity are measured by the photoelectric detectors  30 A,  30 B, and measured result data are stored in a predetermined area of the memory, and the first calculation part  421  calculates the above-mentioned logarithm of the ratio of the light intensity by referring the measured result data. 
     The measurement of the former light intensity (hereinafter also called as the sample measurement) is, as a matter of course, conducted for each sample gas. The measurement of the later light intensity (hereinafter also called as the reference measurement) may be conducted before or after the sample measurement, or at any appropriate timing, for example, the measurement is conducted only once and the measured result is stored in the memory and the stored measured result is used commonly for each sample measurement. 
     In this embodiment, in order to make the light absorption substantially zero a zero gas whose light absorption is substantially zero in a wavelength bandwidth wherein the light absorption of the measuring objective component is observed, for example, N 2  gas is enclosed in the multiple-reflection cell  20 , however, other gas may be enclosed, or inside of the multiple-reflection cell  20  may be vacuumed. 
     The frequency component extracting part  422  conducts lock-in detection on the logarithm of the ratio of the light intensity (hereinafter also called as the absorbance signal) calculated by the first calculation part  421  by the use of the reference signal having a frequency of n (n is an integer number more than or equal to 1) times as many as the modulation frequency, and extracts the frequency component owned by the reference signal based on the logarithm of the ratio of the light intensity. The lock-in detection may be conducted not only by a digital operation but also by an arithmetic operation using an analog circuit. In addition, the extraction of the frequency component is not only the lock-in detection but also using a method of, for example, Fourier series development. 
     The second calculation part  423  calculates a concentration of the measuring objective component based on a detection result by the frequency component extracting part  422 . 
     Next, one example of an operation of the analysis device  100  will be explained together with an explanation of each component in detail. 
     First, as mentioned above, the light source control part  41  controls the semiconductor laser  11  and modulates the wavelength of the laser light with the peak of the absorbance spectrum of the measuring objective component as the center by the modulation frequency. 
     Next, when the zero gas is enclosed in the multiple-reflection cell  20  by an operator or automatically, the first calculation part  421  detects it and conducts the reference measurement. 
     Concretely, the first calculation part  421  receives the output signal from the photoelectric detectors  30 A,  30 B in a state that the zero gas is enclosed in the multiple-reflection cell  20 , and stores the value of the output signal in the measured result data storing part. The value of the output signal from the photoelectric detectors  30 A,  30 B while conducting the reference measurement, namely the reference light intensity expressed in a chronological graph is shown in  FIG. 6( a ) . More specifically, only the change of the light output modulated due to the driving electric current (voltage) of the laser light is shown in the output signal of the photoelectric detectors  30 A,  30 B. 
     Then, when the sample gas is enclosed inside of the multiple-reflection cell  20  by the operator or automatically, the first calculation part  421  conducts the sample measurement. Concretely, the first calculation part  421  receives the output signal from the photoelectric detectors  30 A,  30 B in a state that the sample gas is enclosed in the multiple-reflection cell  20 , and stores the value of the output signal in a predetermined area of the memory. The value of the output signal from the photoelectric detectors  30 A,  30 B while conducting the sample measurement, namely the measuring objective light intensity expressed in a chronological graph is shown in  FIG. 6( b ) . It becomes clear that the peak due to absorption appears for every half cycle of the modulation. 
     Next, the first calculation part  421  calculates the intensity ratio logarithm between the light intensity of the measuring objective light and the light intensity of the reference light by synchronizing each measuring data to the modulation cycle. Concretely, an operation equal to the following expression (Expression 1) is conducted. 
     
       
         
           
             
               
                 
                   
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     Wherein, D m (t) is the intensity of the measuring objective light, D z (t) is the light intensity of the reference light, and A (t) is the intensity ratio logarithm (absorbance signal). A graph with the absorbance signal plotted as the horizontal axis is shown in  FIG. 6( c ) . 
     As a method for obtaining the light intensity ratio logarithm, the intensity ratio logarithm may be obtained after calculating the ratio between the measuring object light intensity and the reference light intensity, or the logarithm of the measuring objective light intensity and the logarithm of the reference light intensity may be obtained respectively and then the difference therebetween may be obtained. 
     Next, the frequency component extracting part  422  conducts lock-in detection on the light intensity ratio logarithm by the use of the reference signal having the frequency as being twice as many as the modulation frequency, more specifically, extracts the frequency component as being twice as many as the modulation frequency, and stores the data (hereinafter also called as the lock-in data) in the predetermined area of the memory. The frequency component extracting part  422  may conduct lock-in detection by the use of the reference signal having the frequency of, for example, three or more other integral multiple of modulation frequency. In addition, the lock-in data may be obtained by subtracting a logarithm of the reference light intensity on which lock-in detection is conducted from a logarithm of the measurement objective light on which lock-in detection is conducted. 
     The value of the lock-in data becomes a value proportional to the concentration of the measuring objective component, and the second calculation part  423  calculates a concentration indication value indicating the concentration of the measuring objective component based on the value of the lock-in data. 
     In accordance with this arrangement, even though the laser light intensity fluctuates due to some factors, a certain offset is just added to the above-mentioned intensity ratio logarithm and the waveform does not change. Accordingly, since the value of each frequency component calculated with the procedure of the lock-in detection does not change and the concentration indication value does not change, it is possible to expect an accurate measurement. 
     The detailed reason will be explained as follows. 
     Generally, when an absorbance signal A (t) is developed by Fourier series development, it is represented by the following expression (Expression 2). 
     Here, a n  is a value proportion to the concentration of the measuring objective component in the expression (2), and the second calculation part  423  calculates the concentration indication value indicating the concentration of the measuring objective component based on the value an. 
     
       
         
           
             
               
                 
                   
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     Wherein, f m  is a modulation frequency, and n is a multiple of the modulation frequency. 
     Meanwhile, A (t) is also expressed by the above-mentioned (Expression 1). 
     Next, in case that the laser light intensity fluctuates α times due to some elements during the measurement, the absorbance signal A′ (t) is expressed by the following expression (Expression 3). 
     
       
         
           
             
               
                 
                   
                     
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     As is clear from the expression (Expression 3), A′ (t) is a value wherein −ln (α) as being a constant value is added to the absorbance signal A (t) in case that there is no fluctuation in the laser light intensity. Accordingly, it becomes clear that the value a n  of each frequency component does not change even though the laser light intensity changes. 
     Accordingly, there is no influence on the concentration indication value determined based on the value of the frequency component as being twice as many as the modulation frequency. 
     The above is an example of the operation of the analysis device  100  in case that no interference component other than the measuring objective component is contained in the sample gas. 
     Next, an example of the operation of the analysis device  100  will be explained in case that one or more interference components (for example, H 2 O) having the light absorption in the peak light absorption wavelength of the measuring objective component are contained in the sample gas. 
     First, a principle will be explained. 
     Since the light absorption spectrum of the measuring objective component is different from that of the interference component, a waveform of each absorbance signal in case that the component exists by itself differs each other and a ratio of each frequency component differs (linearly independent). By making use of this, it is possible to obtain the concentration of the measuring objective component whose interference influence is corrected by solving simultaneous equations by the use of the relationship of each frequency component between the absorbance signal of the previously obtained measuring objective component and that of the interference component. 
     When each of the absorbance signal per unit concentration in case that each of the measuring objective component and the interference component exists by itself respectively is expressed by A m  (t), A i  (t) and each frequency component of the absorbance signal is expressed by a nm , a ni , the following expressions (Expression 4, Expression 5) are established. 
     
       
         
           
             
               
                 
                   
                     
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                                 ⁢ 
                                 
                                   nf 
                                   m 
                                 
                                 ⁢ 
                                 t 
                               
                               + 
                               
                                 ϕ 
                                 n 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
               
             
           
         
       
     
     The absorbance signal A (t) in case that the concentration of each of the measuring objective component and the interference component is C m , C i  respectively is expressed by the following expression (Expression 6) due to linearity of each absorbance. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           A 
                           ⁡ 
                           
                             ( 
                             t 
                             ) 
                           
                         
                         ⁢ 
                           
                         = 
                       
                     
                     
                       
                           
                         ⁢ 
                         
                           
                             
                               C 
                               m 
                             
                             ⁢ 
                             
                               
                                 A 
                                 m 
                               
                               ⁡ 
                               
                                 ( 
                                 t 
                                 ) 
                               
                             
                           
                           + 
                           
                             
                               C 
                               i 
                             
                             ⁢ 
                             
                               
                                 A 
                                 i 
                               
                               ⁡ 
                               
                                 ( 
                                 t 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                           
                         = 
                       
                     
                     
                       
                           
                         ⁢ 
                         
                           
                             
                               C 
                               m 
                             
                             ⁡ 
                             
                               ( 
                               
                                 
                                   a 
                                   
                                     0 
                                     ⁢ 
                                     m 
                                   
                                 
                                 + 
                                 
                                   
                                     ∑ 
                                     
                                       n 
                                       = 
                                       1 
                                     
                                     ∞ 
                                   
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   
                                     
                                       a 
                                       nm 
                                     
                                     ⁢ 
                                     
                                       cos 
                                       ⁡ 
                                       
                                         ( 
                                         
                                           
                                             2 
                                             ⁢ 
                                             π 
                                             ⁢ 
                                             
                                                 
                                             
                                             ⁢ 
                                             
                                               nf 
                                               m 
                                             
                                             ⁢ 
                                             t 
                                           
                                           + 
                                           
                                             ϕ 
                                             n 
                                           
                                         
                                         ) 
                                       
                                     
                                   
                                 
                               
                               ) 
                             
                           
                           + 
                         
                       
                     
                   
                   
                     
                         
                     
                     
                       
                           
                         ⁢ 
                         
                           
                             C 
                             i 
                           
                           ⁡ 
                           
                             ( 
                             
                               
                                 a 
                                 
                                   0 
                                   ⁢ 
                                   i 
                                 
                               
                               + 
                               
                                 
                                   ∑ 
                                   
                                     n 
                                     = 
                                     1 
                                   
                                   ∞ 
                                 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 
                                   
                                     a 
                                     ni 
                                   
                                   ⁢ 
                                   
                                     cos 
                                     ⁡ 
                                     
                                       ( 
                                       
                                         
                                           2 
                                           ⁢ 
                                           π 
                                           ⁢ 
                                           
                                               
                                           
                                           ⁢ 
                                           
                                             nf 
                                             m 
                                           
                                           ⁢ 
                                           t 
                                         
                                         + 
                                         
                                           ϕ 
                                           n 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                               
                             
                             ) 
                           
                         
                       
                     
                   
                   
                     
                       
                           
                         = 
                       
                     
                     
                       
                           
                         ⁢ 
                         
                           
                             
                               a 
                               
                                 0 
                                 ⁢ 
                                 m 
                               
                             
                             ⁢ 
                             
                               C 
                               m 
                             
                           
                           + 
                           
                             
                               a 
                               
                                 0 
                                 ⁢ 
                                 i 
                               
                             
                             ⁢ 
                             
                               C 
                               i 
                             
                           
                           + 
                         
                       
                     
                   
                   
                     
                         
                     
                     
                       
                           
                         ⁢ 
                         
                           
                             ∑ 
                             
                               n 
                               = 
                               1 
                             
                             ∞ 
                           
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
                             
                               ( 
                               
                                 
                                   
                                     a 
                                     nm 
                                   
                                   ⁢ 
                                   
                                     C 
                                     m 
                                   
                                 
                                 + 
                                 
                                   
                                     a 
                                     ni 
                                   
                                   ⁢ 
                                   
                                     C 
                                     i 
                                   
                                 
                               
                               ) 
                             
                             ⁢ 
                             
                               cos 
                               ⁡ 
                               
                                 ( 
                                 
                                   
                                     2 
                                     ⁢ 
                                     π 
                                     ⁢ 
                                     
                                         
                                     
                                     ⁢ 
                                     
                                       nf 
                                       m 
                                     
                                     ⁢ 
                                     t 
                                   
                                   + 
                                   
                                     ϕ 
                                     n 
                                   
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
               
             
           
         
       
     
     Wherein, if each of the frequency component of f m  and 2f m  of A (t) is a 1 , a 2  respectively, the following simultaneous equations (Expression 7) are established due to the above mentioned (Expression 6).
 
 a   1m   C   m   +a   1i   C   i   =a   1  
 
 a   2m   C   m   =a   2i   C   i   =a   2   Expression 7
 
     If each span gas is flown in advance, since it is possible to previously obtain each frequency component a nm , a ni  (n is a natural number, and n=1, 2 in this embodiment) in case that each of the measuring objective component and the interference component exists by itself respectively, the concentration C m  of the measuring objective gas from which the interference influence is removed can be determined by a simple and secure arithmetic operation just by solving the above simultaneous equations (Expression 7). 
     The analysis device  100  runs based on the above-mentioned principle. 
     More specifically, the analysis device  100  measures in advance and stores the frequency component a 1m , a 2m , a 1i , a 2i  of each absorbance signal in case that each of the measuring objective component and the interference component exists by itself in the predetermined area of the memory by flowing the span gas in advance. More concretely, similar to the above-mentioned example, the analysis device  100  measures the measuring objective light intensity and the reference light intensity for each of the measuring objective component and the interference component, calculates these intensity ratio logarithm (absorbance signal), obtains each frequency component a 1m , a 2m , a 1i , a 2i  by means of the lock-in detection based on the intensity ratio logarithm and stores them. In addition to the above-mentioned, the analysis device  100  may calculate the frequency component a 1m , a 2m , a 1i , a 2i  by the use of the above-mentioned expression (Expression 4) by storing the absorbance signal A m  (t), A i  (t) per unit concentration. 
     The analysis device  100  specifies the measuring objective component and the interference component by the input of the operator. 
     Next, the first calculation part  421  calculates the intensity ratio logarithm A (t) according to the expression (Expression 1). 
     Then, the frequency component extracting part  422  conducts the lock-in detection on the intensity ratio logarithm by the use of the reference signal having the modulation frequency f m  and twice frequency 2f m  as many as the modulation frequency, extracts each frequency component a 1 , a 2  (lock-in data) and stores the extracted frequency component a 1 , a 2  in the predetermined area of the memory. 
     Then, the second calculation part  423  applies the values of the lock-in data a 1 , a 2  and the values of the frequency component a 1m , a 2m , a 1i , a 21 , stored in the memory to the above-mentioned expression (Expression 7), or conducts an arithmetic operation equal to this, and calculates the concentration (or the concentration indication value) C m  indicating the concentration of the measuring objective gas from which the interference influence is removed. At this time, the concentration (or the concentration indication value) C i  of each interference component may be calculated. 
     Also in case wherein two or more interference components exist, if higher order frequency components whose number corresponds to the number of the interference components are added, it is possible to determine the concentration of the measuring objective component from which the interference influence is removed by solving the simultaneous equations whose number of unknowns is the same as the number of the type of the component. 
     More specifically, generally in case n types of gasses exist in the measuring objective component and the interference component, if the frequency component of i×f m  of the k-th gas type is a ik , and the concentration of the k-th gas type is C k , the following expression (Expression 8) is established. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           a 
                           11 
                         
                         ⁢ 
                         
                           C 
                           1 
                         
                       
                       + 
                       
                         
                           a 
                           12 
                         
                         ⁢ 
                         
                           c 
                           2 
                         
                       
                       + 
                       
                         
                           a 
                           13 
                         
                         ⁢ 
                         
                           C 
                           3 
                         
                       
                       + 
                       … 
                       + 
                       
                         
                           a 
                           
                             1 
                             ⁢ 
                             n 
                           
                         
                         ⁢ 
                         
                           C 
                           n 
                         
                       
                     
                     = 
                     
                       a 
                       1 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       
                         
                           a 
                           21 
                         
                         ⁢ 
                         
                           C 
                           1 
                         
                       
                       + 
                       
                         
                           a 
                           22 
                         
                         ⁢ 
                         
                           c 
                           2 
                         
                       
                       + 
                       
                         
                           a 
                           23 
                         
                         ⁢ 
                         
                           C 
                           3 
                         
                       
                       + 
                       … 
                       + 
                       
                         
                           a 
                           
                             2 
                             ⁢ 
                             n 
                           
                         
                         ⁢ 
                         
                           C 
                           n 
                         
                       
                     
                     = 
                     
                       a 
                       2 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       
                         
                           a 
                           31 
                         
                         ⁢ 
                         
                           C 
                           1 
                         
                       
                       + 
                       
                         
                           a 
                           32 
                         
                         ⁢ 
                         
                           c 
                           2 
                         
                       
                       + 
                       
                         
                           a 
                           33 
                         
                         ⁢ 
                         
                           C 
                           3 
                         
                       
                       + 
                       … 
                       + 
                       
                         
                           a 
                           
                             3 
                             ⁢ 
                             n 
                           
                         
                         ⁢ 
                         
                           C 
                           n 
                         
                       
                     
                     = 
                     
                       a 
                       3 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   ⋮ 
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       
                         
                           a 
                           
                             n 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             1 
                           
                         
                         ⁢ 
                         
                           C 
                           1 
                         
                       
                       + 
                       
                         
                           a 
                           
                             n 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             2 
                           
                         
                         ⁢ 
                         
                           c 
                           2 
                         
                       
                       + 
                       
                         
                           a 
                           
                             n 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             3 
                           
                         
                         ⁢ 
                         
                           C 
                           3 
                         
                       
                       + 
                       … 
                       + 
                       
                         
                           a 
                           nn 
                         
                         ⁢ 
                         
                           C 
                           n 
                         
                       
                     
                     = 
                     
                       a 
                       n 
                     
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   8 
                 
               
             
           
         
       
     
     If the simultaneous equations with n unknowns expressed by this expression (Expression 8) is solved, it is possible to determine the concentration of each gas in the measuring objective component and the interference component. 
     In addition, a higher harmonic component of a degree higher than n may be also added to create simultaneous equations with unknowns whose number is bigger than the number of the gas types and each gas concentration may be determined by the use of the least squares method. With this procedure, it is possible to determine the concentration of the component with less error due to the measurement noise. 
     In accordance with the analysis device  100  of this embodiment, since the analysis device  100  has a pair of the reflecting mirrors  22 ,  23  that reflect the first light L 1  and the second light L 2  each having mutually different incident optical paths, it is possible to make the number of reflections of the first light L 1  by a pair of the reflecting mirrors  22 ,  23  and the number of reflections of the second light L 2  different from each other. Accordingly, it is possible to simplify the structure of the multiple-reflection cell  22  and to measure both the measuring objective component having a high concentration and the measuring objective component having a low concentration. In addition, since the structure of the multiple-reflection cell  20  can be simplified, it is possible to make the internal volume of the multiple-reflection cell  20  small and to make a substitution rate of the sample gas fast, thereby improving the responsiveness. Furthermore, since the analysis device  100  has the first light irradiation part  10 A and the second light irradiation part  10 B, it is possible to allow the first light L 1  and the second light L 2  to enter the multiple-reflection cell  20  simultaneously. With this arrangement, it is possible to measure both high concentration and low concentration of a single measuring objective component simultaneously and to widen a measurement range. 
     This invention is not limited to the above-mentioned embodiment. 
     For example, the inlet X 1  and the outlet X 2  of the first light L 1  and the inlet X 3  and the outlet X 4  of the second light L 2  are formed on the reflecting mirror  22  in the above-mentioned embodiment, however, at least one of them may be formed on the other reflecting mirror  23 . 
     In addition, the second light L 2  having a short optical path reflects once in the above-mentioned embodiment, however, the number of reflections of the second light L 2  may be any as long as the number is less than that of the first light L 1 . 
     Furthermore, the inlet X 1  and the outlet X 2  of the first light L 1  are formed by a common through bore in the above-mentioned embodiment, however, they may be formed by separate through bores, or the inlet X 3  and the outlet X 4  of the second light L 2  may be formed by a common through bore. In addition, the inlet or the outlet of the first light L 1  and the second light L 2  may be formed by a common through bore, or all of them may be formed by a common through bore. 
     If each of the inlet X 1  and the outlet X 2  of the first light L 1  is formed by a separate through bore, and each of the inlet X 3  and the outlet X 4  of the second light L 2  is formed by a separate through bore, conceived is shown in  FIG. 7 . In other word, it can be conceived that an opposite direction of the inlet X 1  and the outlet X 2  and an opposite direction of the inlet X 3  and the outlet X 4  differ each other. In  FIG. 7 , these directions are formed to be orthogonal each other, however, it is not limited to this. In accordance with this arrangement wherein the inlets X 1 ,  3  and the outlets X 2 , X 4  are so formed, the entering direction and exiting direction of the second light L 2  are formed to be located between a surface passing the entering direction of the first light L 1  and a surface passing the exiting direction of the first light L 1 . 
     Furthermore, for example, the light may enter from a periphery of the reflecting mirror  22  to a space between a pair of the reflecting mirrors  22 ,  23  or exit from the space between a pair of the reflecting mirrors  22 ,  23  without providing a pair of the reflecting mirrors with an inlet and an outlet of the first light and the second light. 
     In addition, if the light source of the first light irradiation part  10 A and the light source of the second light irradiation part  10 B are separately provided so as to make a wavelength bandwidth of the first light L 1  different from a wavelength bandwidth of the second light L 2 , it is also possible to measure a plurality of measuring objective components simultaneously. 
     The first light L 1  and the second light L 2  enter the multiple-reflection cell  20  simultaneously in the above-mentioned embodiment, however, they may enter with a time difference. In accordance with this arrangement, it is possible to detect the first light L 1  and the second light L 2  by using a single photoelectric detector, thereby simplifying the structure of the analysis device  100 . In addition, the first light L 1  and the second light L 2  are made to be a pulse oscillated pulse light and to enter the multiple-reflection cell alternately. 
     In the above-mentioned embodiment explained is a case that the multiple-reflection cell  20  is a Heriot cell, however, the multiple-reflection cell  20  may be a White cell. 
     In addition to the measurement principle in the above-mentioned embodiment, the analysis device  100  may use, for example, an NDIR method, an FTIR method or an NDUV method. 
     The analysis device in accordance with the above-mentioned embodiment may analyze an exhaust gas exhausted from an exhaust pipe of an automobile on a chassis dynamometer or running on an actual road, an exhaust gas exhausted from an engine during a test by a power train test device, or exhaust gas exhausted from an engine tested by an engine dynamo. A pair of the reflecting mirrors tend to be dirty for the analysis device that analyzes the exhaust gas exhausted from the automobile. However, the analysis device in accordance with this invention has a pair of the reflecting mirrors and a pair of a purge mechanism for each reflecting mirror will do to clean the mirrors with spraying a purge gas, namely, only a pair of the purge mechanism will do, thereby simplifying the device structure. 
     Furthermore, the analysis device may have an arrangement to conduct the measurement by switching the optical path: in case that the concentration value of the measuring objective component obtained by the information processing unit is compared with a predetermined threshold value and the measuring objective component is bigger than the threshold value, a short optical path length (second light) is used for the measurement, and in case that the concentration of the measuring objective component is smaller than the threshold value, a long optical path length (first light) is used for the measurement. 
     The multiple-reflection cell is configured by housing a pair or the reflecting mirrors in the cell body in the above-mentioned embodiment, however, the multiple-reflection cell may be configured by a space sandwiched by a pair of the reflecting mirrors without housing a pair of the reflecting mirrors in the cell body (having no cell body). 
     In addition, the sample gas is not limited to the exhaust gas and may be atmosphere, liquid or solid. In this sense, not only the measuring objective component is not limited to gas, and the present claimed invention may be applied to liquid or solid. In addition, it is possible to apply this invention not to the absorbance of the light penetrating and passing the measuring object but also to calculation of the absorbance due to reflection. 
     The sample measurement and the reference measurement are conducted by the use of a single photoelectric detector in the above-mentioned embodiment, however, as shown in  FIG. 8 , two photoelectric detectors  31 ,  32  may be used and one photoelectric detector  31  may be for the sample measurement and the other photoelectric detector  32  may be for the reference measurement. In this case, the light from the light source  2  is branched by a half mirror  33 . In addition, the reference cell may be arranged on the optical path for the reference measurement. It can be conceived that zero gas or a reference gas whose concentration is known is enclosed in the reference cell. 
     The light source is not limited to the semiconductor laser, and may be any other type as long as it is a short wavelength light source having a half-value width enough to secure the measurement accuracy and it can conduct wavelength modulation. 
     The present claimed invention may be variously modified without departing from the spirit of the invention. 
     EXPLANATION OF CODES 
     
         
           100  . . . analysis device 
           10 A . . . first light irradiation part 
         L 1  . . . first light 
           10 B . . . second light irradiation part 
         L 2  . . . second light 
           20  . . . multiple-reflection cell 
           21  . . . cell body 
           22  . . . one reflecting mirror 
           23  . . . other reflecting mirror 
         X 1  . . . inlet of first light 
         X 2  . . . outlet of first light 
         X 3  . . . inlet of second light 
         X 4  . . . outlet of second light 
         P 1  . . . introducing port 
         P 2  . . . discharging port 
           211  . . . optical window member 
           30 A . . . first photoelectric detector 
           30 B . . . second photoelectric detector