Abstract:
Disclosed are method and apparatus for measuring density, that can simultaneously measure gaseous substance density and solid particulate material density and further can simultaneously measure the densities of a plurality of materials such as black smoke, white smoke, and water vapor in the solid particulate material in a simple and reliable manner. The method for measuring density comprises applying a laser beam having an absorption wavelength inherent in a gaseous material contained in an object to be measured, to the object to detect a light transmittance and a light absorption amount and detecting the density of gaseous materials in the object and the density of solid particulate materials in the object. The relationship between the density of a plurality of kinds of solid particulate materials including black smoke and white smoke and a laser beam attenuation level in each absorption wavelength is preset. Laser beams having a plurality of respective absorption wavelengths are applied to the gaseous substance to be measured. The attenuation levels of the applied laser beams having the plurality of absorption wavelengths are measured. The measured attenuation levels are compared with the attenuation levels calculated based on the present relationship to calculate the densities of the plurality of kinds of solid particulate materials.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a measuring method and device for measuring density as to a gaseous substance and a particulate matter in a gas which is a gas generated in a closed vessel such as a boiler, a refuse incinerator, and a combustion chamber of combustion engine, a gas that is emitted outward from the closed vessel or the emitted gas that is prone to stay around a gas flow stagnation area. 
         [0003]    2. Background of the Invention 
         [0004]    The methods by use of laser technologies for measuring the density of the gaseous substances and particulate matters in the gas have been conventionally developed whereby the gas is generated in a closed vessel such as a combustion chamber for a boiler, a refuse incinerator, a combustion engine and so on. The gas density measuring technologies by use of laser make use of the property of each kind of gaseous substances; namely, a gaseous substance has the property of absorbing a laser having a component of a wavelength peculiar to the gaseous substance. In other words, the density of a specific gaseous substance is identified by applying a laser including the specific wavelength equivalent to the absorption wavelength peculiar to the gaseous substance toward the measurement object gas containing the gaseous substance, as well as, by performing the spectrum analysis regarding the laser that passes through the measurement object gas. 
         [0005]    It is, hereby, noted that the term “laser” in this specification mainly relates to the lasers that emit a broad spectrum of light, or emit different wavelengths of light simultaneously. 
         [0006]    On the other hand, as for the measurement of the density of a particulate matter suspending in the measurement object gas, a method has been conventionally made use of, whereby a predetermined amount of the gas containing the particulate matter is taken as a sample for analysis; the sampled amount of the gas is passed through a filter paper (e.g. a filter paper placed in a cylinder strainer); the difference between the weight of the paper filter after the sampled amount of the gas is passed through the filter paper and the weight of the paper filter before the sampled amount of the gas is passed through the filter paper is estimated so that the particulate matter in the predetermined amount of the sampled gas. 
         [0007]    As an example method described above, the patent reference 1 (JP1998-185814) discloses a method for measuring density as to a gaseous substance and a particulate matter by use of the laser technology; namely, the patent reference 1 discloses a density measuring device for simultaneously measuring the densities as to a gaseous substance and a particulate matter, by applying the laser corresponding to the special absorption wavelength peculiar to the gaseous substance, toward the measurement object gas (the gas and the particulate matter therein). In the technology of the patent reference 1, as shown in  FIG. 9 , the base attenuation Ap regarding the base laser transmittance (transmissivity) corresponds to the attenuation due to the particulate matter; the peak attenuation (absorption) Ag of a sharp valley shape corresponds to the attenuation due to the gaseous substance; thus, the density of the particulate matter can be computed by use of the measured value Ap, while the density of the gaseous substance can be computed by use of the measured value Ag. 
         [0008]    Further, the patent reference 2 (JP Patent 3185310) discloses a smoke detector for detecting the smoke emitted from a traveling car (or vehicle); according to the disclosed technology, the to-be-detected smoke may be black smoke, white smoke, water vapor or mixture of white smoke and water vapor; a part of the light (laser) outputted from the laser emitting means is scattered or reflected in the measurement object gas containing the particulate matters; a part of the light is received by a plurality of laser receiving means; according to the light reception conditions of the laser receiving means, the state (such as density information) of the smoke (black smoke, white smoke, water vapor or mixture of white smoke and water vapor) can be estimated. 
         [0009]    As described above, the patent reference 1 discloses a density-measuring device that simultaneously measures both densities regarding the gaseous substance and the particulate matter; however, the density regarding the particulate matter is estimated as one overall value; the technology according to the patent reference 1 dose not make a distinction among particulate matters in black smoke, white smoke and water vapor; the technology does not reach a level where the density regarding the particulate matter in each smoke can be separately measured. Hereby, it is noted that black smoke, white smoke and water vapor (steam white smoke) mean black smoke containing black solid particulates, white smoke containing liquid particulates and water vapor containing water particulates, respectively. 
         [0010]    Further, in the technology according to the patent reference 2, the particulate matter in each smoke such as black smoke, white smoke, or water vapor is measured only independently; the densities regarding the particulate matter and the specific gaseous substance such as NH 3  (ammonia) or NOx (nitrogen oxide) in emission gases cannot be simultaneously measured. 
       DISCLOSURE OF THE INVENTION 
       [0011]    In view of the above-described background, the present invention aims at providing a density-measuring device that can simultaneously measure both densities regarding a plurality of gaseous substances and a plurality of particulate matters whereby the device can easily and surely measure the densities regarding the particulate matters such as black smoke, white smoke and water vapor; further, the present invention aims at providing a density-measuring method in response to the device. 
         [0012]    In order to overcome the problems in the conventional technologies, the first invention of the present application is a density measuring method for detecting densities of gaseous substance and particulate matter in a measurement object gas containing the gaseous substance and the particulate matter on a basis of transmittance and attenuation of a laser measured by irradiating the laser including a wavelength equivalent to an absorption wavelength peculiar to the gaseous substance through the measurement object gas; the method comprising steps of: 
         [0013]    establishing a relation between laser attenuation and a density of each particulate matter such as black smoke or white smoke in response to each absorption wavelength peculiar to each gaseous substance in advance; 
         [0014]    irradiating laser having at least one wavelength equivalent to each gaseous substance to be measured; and
       determining the density of each particulate matter by measuring the laser attenuation in response to the wavelength of the laser, and comparing the measured attenuation with the attenuation computed by use of the relation established in advance.       
 
         [0016]    The second invention of the present application is density measuring device for detecting densities of gaseous substance and particulate matter in a measurement object gas containing the gaseous substance and the particulate matter on a basis of transmittance and attenuation of a laser measured by irradiating the laser including a wavelength equivalent to an absorption wavelength peculiar to the gaseous substance through the measurement object gas; the device comprising: 
         [0017]    at least one laser emitting means that irradiates the laser including at least one wavelength equivalent to the absorption wavelength peculiar to each gaseous substance to be measured; 
         [0018]    at least one laser receiving means that receives the laser irradiated by the laser emitting means; 
         [0019]    a laser attenuation coefficient map in which a relation between laser attenuation and a density of each particulate matter such as black smoke or white smoke in response to each absorption wavelength peculiar to each gaseous substance is established in advance; 
         [0020]    at least one laser attenuation computing means that computes the attenuation of the laser having passed through the measurement object gas on the basis of the laser received by the laser receiving means; and a particulate matter density computation means that computes the density regarding each particulate matter by comparing the attenuation computed by the laser attenuation computing means with the attenuation computed by use of an attenuation coefficient of the laser attenuation coefficient map. 
         [0021]    According to the first and second inventions, lasers including wavelengths equivalent to absorption wavelengths peculiar to the gaseous substances are irradiated through the measurement object gas; a laser attenuation coefficient map in which the relation between the attenuation and the density of each particulate matter such as black smoke or white smoke is predeterminately established in response to each absorption wavelength peculiar to each gaseous substance; the attenuation in response to the wavelength of the laser is measured; and, the measured attenuation is compared with the attenuation that is computed by use of the established relation between the attenuation and the density of each particulate matter such as black smoke or white smoke, so that the density of each particulate matter is determined. Thus, the densities regarding particulate matters such as black smoke, white smoke and so on in the density-measurement object gas can be detected at the same time. 
         [0022]    More concretely, for instance, the laser including wavelength λ 1  is assumed to be the laser for detecting the density of CO (carbon monoxide) included in the measurement object gas; further, for instance, the laser including wavelength λ 2  is assumed to be the laser for detecting the density of ammonia NH 3  (ammonia) included in the measurement object gas; thereby, an attenuation coefficient “a” for black smoke with respect to the laser of the wavelength λ 1  and an attenuation coefficient “b” for white smoke with respect to the laser of the wavelength λ 1  are predetermined; further, an attenuation coefficient “c” for black smoke with respect to the laser of the wavelength λ 2  and an attenuation coefficient “d” for white smoke with respect to the laser of the wavelength λ 2  are predetermined. Incidentally, these attenuation coefficients are established as shown in  FIGS. 4 and 5  that give explanation about a map (a registered relationship graph between laser attenuation and smoke density) of laser attenuation regarding black smoke and white smoke, respectively. 
         [0023]    Further, the laser attenuation A λ1  regarding the laser of the wavelength λ 1  and the laser attenuation A λ2  regarding the laser of the wavelength λ 2  can be expressed in the following equations (1) and (2), with respect to the black smoke density N b  and the white smoke density N w . In other word, the attenuations A λ1  and A λ2  can be primary expressions regarding the densities N b  and N w . 
         [0000]        A   λ1   =aN   b   +bN   w   (1)
 
         [0000]        A   λ2   =bN   b   +dN   w   (2)
 
         [0024]    Thus, the black smoke density N b  and the white smoke density N w  can be obtained by solving the simultaneous equations (1) and (2) with respect to the unknowns N b  and N w . In addition, either of the laser attenuation λ λ1  regarding the laser of the wavelength λ 1  and the laser attenuation A λ2  regarding the laser of the wavelength λ 2  is computed on the basis of the laser intensity signal in response to the intensity of each laser that is received at each laser receiving means. 
         [0025]    Thus, according to the first and second inventions, by irradiating the lasers through the density-measurement object gas, the densities regarding particulate matters in the density-measurement object gas can be simply and surely computed at the same time, on the basis of the laser attenuation corresponding to each laser of its own wavelength. 
         [0026]    An preferable embodiment according to the first invention is the density measuring method further comprising steps of: 
         [0027]    irradiating the laser not only through the measurement object gas but also through a reference cell in which a reference gas made from the gaseous substance is encapsulated; and 
         [0028]    identifying the attenuation as a measured attenuation on the basis of an intensity signal corresponding to the intensity of the laser having passed through the reference cell and a transmittance intensity signal corresponding to the transmittance intensity of the laser having passed through the measurement object gas 
         [0029]    An preferable embodiment according to the second invention is a density measuring device, 
         [0030]    wherein the laser is irradiated not only through the measurement object gas but also through a reference cell in which a reference gas made from the gaseous substance is encapsulated, and 
         [0031]    the attenuation of the laser including at least one wavelength equivalent to the absorption wavelength peculiar to each gaseous substance to be measured is computed on the basis of an intensity signal corresponding to the intensity of the laser having passed through the reference cell and a transmittance intensity signal corresponding to the transmittance intensity of the laser having passed through the measurement object gas. 
         [0032]    According to the configuration of each invention as described above, each laser attenuation in response to each laser absorption wavelength is computed on the basis of the intensity signal corresponding to the intensity of the laser having passed through the reference gas and the intensity signal corresponding to the transmittance intensity of the laser having passed through the measurement object gas; therefore, the density measurement can be prevented from being influenced by the fluctuations as to each laser intensity on the laser emitting side. 
         [0033]    Another preferable embodiment according to the first invention is a density measuring method further comprising steps of: 
         [0034]    irradiating the laser not only through the measurement object gas but also through a reference cell in which a reference gas made from the gaseous substance is encapsulated; and 
         [0035]    locking the wavelength of the laser irradiated through the measurement object gas to an absorption wavelength of the reference gas encapsulated in the reference cell on the basis of an electrical signal of the laser having passed through the corresponding reference cell. 
         [0036]    Another preferable embodiment according to the second invention is a density measuring device, 
         [0037]    wherein the laser emitted by the laser emitting means is irradiated not only through the measurement object gas but also through a reference cell in which a reference gas made from the gaseous substance is encapsulated; and 
         [0038]    the wavelength of the laser irradiated through the measurement object gas is locked to an absorption wavelength of the reference gas encapsulated in the reference cell on the basis of an electrical signal of the laser having passed through the corresponding reference cell. 
         [0039]    According to the configuration of each invention as described above, by irradiating the laser including the wavelength equivalent to the absorption wavelength peculiar to each gaseous substance, through a reference cell encapsulated with a reference gas made from the gaseous substance, as well as by locking the wavelength of the laser irradiated through the measurement object gas to the absorption wavelength of the reference gas, the laser emitted from the laser emitting means can include wavelength components of less deviation (around the absorption wavelength); thus, the measurement accuracy deterioration due to the wavelength deviation can be constrained. 
         [0040]    Another preferable embodiment according to the first invention is a density measuring method, 
         [0041]    wherein the method is further provided with a wavelength modulation means and a wavelength demodulation means, the method comprising steps of: 
         [0042]    irradiating a plurality of lasers including at least one wavelength equivalent to the absorption wavelength peculiar to each gaseous substance to be measured; and 
         [0043]    measuring the density of each gaseous substance in the measurement object gas based on absorption of the gaseous substance as to each absorption wavelength. 
         [0044]    Another preferable embodiment according to the second invention is a density measuring device comprising a wavelength modulation means and a wavelength demodulation means, wherein a plurality of lasers including at least one wavelength equivalent to the absorption wavelength peculiar to each gaseous substance to be measured are irradiated by the laser emitting means, and the density of each gaseous substance in the measurement object gas is measured based on absorption of the gaseous substance as to each absorption wavelength 
         [0045]    According to the configuration of each invention as described above, the densities as to a plurality of gaseous substances can be measured at the same time; more concretely, the densities as to a plurality of particulate matters such as black smoke, white smoke, water vapor can be measured at the same time, while the densities as to a plurality of gaseous substances can be measured. Thus, the efficiency as to the exhaust gas analysis can be enhanced. 
         [0046]    According to the present invention, a measuring method and a device for measuring the density as to a plurality of gaseous substances and particulate matters in a measurement gas can be realized; thereby, the measurement gas including the gaseous substances and the particulate matters is generated in a closed vessel such as a combustion chamber for a boiler, a refuse incinerator, a combustion engine and so on, the gas being emitted outward from the closed vessel; the densities as to the gaseous substances and the densities as to the particulate matters can be measured at the same time; in addition, the densities as to a plurality of particulate matters such as black smoke, white smoke and water vapor are surely measured in a simple way at the same time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0047]      FIG. 1  shows a whole configuration as to the density-measuring device which is applied to a diesel engine for performing an exhaust gas analysis according to the present invention. 
           [0048]      FIG. 2  shows a whole configuration as to the density-measuring device according to a first embodiment of the present invention. 
           [0049]      FIG. 3  is an explanatory drawing illustrating a wavelength-locking signal. 
           [0050]      FIG. 4  is an explanatory drawing illustrating a map of laser attenuation regarding black smoke. 
           [0051]      FIG. 5  is an explanatory drawing illustrating a map of laser attenuation coefficient regarding white smoke. 
           [0052]      FIG. 6  is an explanatory drawing illustrating a comparison between a measured result by use of the method according to conventional technologies and a measured result by use of the method according to the present invention; 
           [0053]      FIG. 7  shows a whole configuration as to the density-measuring device according to a second embodiment of the present invention; 
           [0054]      FIG. 8  is an explanatory drawing illustrating a density measurement signal regarding a gaseous substance; 
           [0055]      FIG. 9  is an explanatory drawing of the technical features according to the conventional technology. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0056]    Hereafter, the present invention will be described in detail with reference to the embodiments shown in the figures. However, the dimensions, materials, shape, the relative placement and so on of a component described in these embodiments shall not be construed as limiting the scope of the invention thereto, unless especially specific mention is made. 
       First Embodiment 
       [0057]      FIG. 1  shows a density-measuring device  3  applied to an exhaust gas analysis of a diesel engine  5 , according to a first embodiment of the present invention. 
         [0058]    An exhaust gas passage  7  of the diesel engine  5  is provided with a measuring sensor unit  9  in which a plurality of lasers (two lasers in this example) are irradiated so that the lasers irradiated across the exhaust gas passage  7 . The measuring sensor unit  9  is provided with collimators (optical lens)  11   a  and  11   b  to a laser emitting side and collimators (optical lens)  13   a  and  13   b  to a laser receiving side. 
         [0059]    The density-measuring device  3  includes a first laser emitting means  15   a  and a second laser emitting means  15   b . Lasers emitted from these means  15   a  and  15   b  are carried to the measuring sensor unit  9  through optical fibers  17 . The lasers applied in the measuring sensor unit  9  pass through the exhaust gas, and reach a first laser receiving means  19   a  and a second laser receiving means  19   b . At these means  19   a  and  19   b , the lasers are converted into electronic signals that are inputted into an analyzing device  23  for analyzing the density of the gaseous substance and the particulate matter. Further, the density-measuring device  3  is provided with a wavelength modulation means  25  and a demodulation means  27 , and the analyzing device  23  is provided with a laser attenuation coefficient map  29 , an attenuation computing means  31 , a particulate matter density computation means  33  and a gaseous substance density computation means  35 . 
         [0060]    AS shown in  FIG. 2 , the first laser emitting means  15   a  as well as the second laser emitting means  15   b  configure the laser emitting source; the first laser emitting means  15   a  emits lasers including wavelength λ 1  while the second laser emitting means  15   b  emits lasers including wavelength λ 2 . The laser emitting means  15   a  has a semiconductor laser diode LD 1  and a first drive circuit therefor, while the second laser emitting means  15   b  has a semiconductor laser diode LD 2  and a second drive circuit therefor; the semiconductor laser diode LD 1  is connected to the first drive circuit that forms a LD-driver for driving the laser diode LD 1 , while the semiconductor laser diode LD 2  is connected to the second drive circuit that forms a LD-driver for driving the laser diode LD 2 ; the LD-driver controls the drive current passing the semiconductor diodes LD 1  and LD 2 . 
         [0061]    Further, toward the first drive circuit of the first laser emitting means  15   a , a first modulation signal f 1  is applied from a first wavelength-modulating means  37 , and a first wavelength locking signal w 1  is applied from a first demodulating means  41 . Toward the second drive circuit of the second laser emitting means  15   b , a second modulation signal f 2  is applied from a second wavelength-modulating means  39 , and a second wavelength locking signal w 2  is applied from a second demodulating means  43 . 
         [0062]    The above-described modulation signals f 1  and f 2  are applied to the corresponding laser emitting means so as to perform frequency modulation regarding lasers; the modulation signal f 1  is also applied to the first demodulating means  41  in order to establish a synchronizing signal that can be used for intensifying the modulation signal f 1 ; similarly, the modulation signal f 2  is also applied to the second demodulating means  43  in order to establish a synchronizing signal that can be used for intensifying the modulation signal f 2 . 
         [0063]    The lasers that are received by the measuring sensor unit  9  are carried to the first laser receiving means  19   a  and the second laser receiving means  19   b . The lasers that are carried to the first laser receiving means  19   a  and the second laser receiving means  19   b  are converted into electrical signals (that are called intensity signals herein) in response to the strength of lasers; namely, the first laser receiving means  19   a  and the second laser receiving means  19   b  output the intensity signals. The first laser receiving means  19   a  comprises a photodiode PD 1 , while the second laser receiving means  19   b  comprises a photodiode PD 2 ; the photodiodes PD 1  and PD 2  convert the received lasers into electrical signals. Further, each of the laser receiving means  19   a  and  19   b  comprises a preamp (preamplifier) that amplifies the converted electrical signals. The intensity signals outputted at the first laser receiving means  19   a  or the second laser receiving means  19   b  are decomposed into DC (direct-current) components and AC (alternating-current) harmonic components, by use of DC component detecting means (not shown) and AC component detecting means (not shown); the decomposed DC component corresponds to the attenuation Ap (the base attenuation Ap in  FIG. 9 ) regarding the laser transmittance; the attenuation Ap is attributable to the particulate matter and the density thereof; the signal regarding the DC component is inputted into the analyzing device  23  as a transmittance intensity signal I 1  (for the first laser receiving means  19   a ) or I 2  (for the second laser receiving means  19   a ). 
         [0064]    Meanwhile, the laser emitted from the first laser emitting means  15   a  are demultiplexed by a demultiplexer and carried into a first reference cell  45  in which a reference gas under a certain level of pressure is encapsulated; thereby, the properties of the encapsulated gas are to be already known. The laser carried into the first reference cell  45  passes through the encapsulated gas and are received by a third laser receiving means  47 , in which the intensity of the laser is converted into electrical signals, and then the electrical signals are converted by the third laser receiving means  47  to be inputted into the first demodulating means  41 . Further, into the first demodulating means  41 , the first modulation signal f 1  is inputted from the first wavelength-modulating means  37 , and synchronizing signals that synchronizes to the first modulation signal f 1  are produced out of the electrical signals converted by the third laser receiving means  47 , at the first demodulating means  41 ; and, the absorption wavelength of the laser that is absorbed in the encapsulated gas in the reference cell is accurately detected. The detected absorption wavelength is peculiar to the kind of the encapsulated gas. Further, the first wavelength locking signal w 1  is transmitted from the first demodulating means  41  toward the drive circuit in the first laser emitting means  15   a , so that the laser diode LD 1  in the first laser emitting means  15   a  oscillates the laser of the absorption wavelength. 
         [0065]    Likewise, the explanation analogous to the above can be given as to the laser that is emitted from the second laser emitting means  15   b  and is carried into a second reference cell  49  shown in  FIG. 2 . The laser carried into the second reference cell  49  passes through the encapsulated gas and are received by a fourth laser receiving means  51 , in which the intensity of the laser is converted into electrical signals. The electrical signals converted by the fourth laser receiving means  51  are inputted into the second demodulating means  43 . Further, into the second demodulating means  43 , the second modulation signal f 2  is inputted from the second wavelength-modulating means  39 , and synchronizing signals that synchronizes to the second modulation signal f 2  are produced out of the electrical signals converted by the fourth laser receiving means  51 , at the second demodulating means  43 . Further, the second wavelength locking signal w 2  is transmitted from the second demodulating means  43  toward the drive circuit in the second laser emitting means  15   b , so that the laser diode LD 2  in the second laser emitting means  15   b  oscillates the laser beams of the absorption wavelength. 
         [0066]    Incidentally, in the first reference cell  45 , carbon monoxide (CO), for instance, as a reference gas to be measured is encapsulated; and, in the second reference cell  49 , ammonia (NH 3 ), for instance, as a reference gas to be measured is encapsulated. The accurate wavelength λ 1  is detected by use of the first reference cell  45 , while the accurate wavelength λ 2  is detected by use of the second reference cell  49 ; and, the wavelength locking signals w 1  and w 2  are outputted.  FIG. 3  shows a concrete example as to the wavelength-locking signal with respect to the laser wavelength; the modulation is performed within a wavelength control range as shown, in  FIG. 3 . 
         [0067]    Further, the intensity of the electrical signal outputted by the third laser receiving part means  47  is regarded as an incident intensity signal I 01 , while the intensity of the electrical signal outputted by the fourth laser receiving part means  51  is regarded as an incident intensity signal I 02 ; and, both the signals I 01  and I 02  are inputted into the analyzing device  23 . 
         [0068]    The density analysis performed in the analyzing device  23  is explained as follows. 
         [0069]    As shown in  FIGS. 4 and 5 , the analyzing device  23  (cf.  FIG. 1 ) is provided with a laser attenuation coefficient map  29  (a registered relationship between laser attenuation and smoke density).  FIG. 4  gives an explanation about a map of laser attenuation regarding black smoke; for instance, in order to identify the density of CO (carbon monoxide) included in a gas, an attenuation coefficient “a” regarding a laser including wavelength λ 1  as well as an attenuation coefficient “c” regarding a laser including wavelength λ 2  is established in  FIG. 4 , both the attenuation coefficients “a” and “c” being established in relation to the attenuation regarding black smoke. Further, in  FIG. 4 , each of the attenuation coefficients “a” and “c” is established as a linear function or a substantially linear function with respect to the laser attenuation. 
         [0070]    On the other hand,  FIG. 5  gives an explanation about a map of laser attenuation regarding white smoke; for instance, in order to identify the density of CO (carbon monoxide) included in a measuring object gas, an attenuation coefficient “b” regarding a laser including wavelength λ 1  as well as an attenuation coefficient “d” regarding a laser including wavelength λ 2  is established in  FIG. 5 , both the attenuation coefficients “b” and “d” being established in relation to the attenuation regarding white smoke. Further, in  FIG. 5 , each of the attenuation coefficients “b” and “d” is established as a linear function or a substantially linear function with respect to the laser attenuation. 
         [0071]    Further, the following equations (1) and (2) hold as to the laser attenuation A λ1  regarding the wavelength λ 1  as well as the laser attenuation A λ2  regarding the wavelength λ 2  under a coexistence condition of black smoke and white smoke. Here, the density of the black smoke is N b  and the density of the white smoke is N w . 
         [0000]        A   λ1   =aN   b   +bN   w   (1)
 
         [0000]        A   λ2   =bN   b   +dN   w   (2)
 
         [0072]    Thus, the black smoke density N b  and the white smoke density N w  can be obtained by solving the simultaneous equations (1) and (2) with respect to the unknowns N b  and N. 
         [0073]    The laser attenuation A λ1  regarding the wavelength λ 1  as well as the laser attenuation A λ2  regarding the wavelength λ 2  is computed by use of the attenuation computing means  31  in which A λ1  and A λ2  are computed by use of the following formula: 
         [0000]        A   λ1 =−Log( I   1   /I   01 )
 
         [0000]      and 
         [0000]        A   λ2 =−Log( I   2   /I   02 ),
 
         [0000]    where I 01  is the incident intensity signal outputted by the third laser receiving means  47 , I 02  is the incident intensity signal outputted by the third laser receiving means  51 , I 1  is the transmittance intensity signal that means the intensity of the laser received by the first laser receiving means  19   a , and I 2  is the transmittance intensity signal that means the intensity of the laser received by the second laser receiving means  19   b . It is noted that the computation as to the values A λ1  and A λ2  is performed on the basis of the electrical intensity signals outputted by a plurality of the laser receiving means that actually receive the lasers and convert the laser intensities into electrical signals. 
         [0074]    Incidentally, the computations for solving the black smoke density N b  and the white smoke density N w  by use of the equations (1) and (2) are performed by the particulate matter density computation means  33  that is provided in the analyzing device  23 . 
         [0075]    Further, as is the above-described case with the density computation as to the black smoke and white smoke, in a case where the density regarding solid particulate matter of water vapor is to be additionally identified, attenuation coefficient for each of the black smoke, white smoke and water vapor as to the wavelength λ 1 , λ 2  and λ 3  are set in advance, and the following equations (3), (4) and (5) in which the density of the water vapor (N s ) is included to the equations (1) and (2) are used: 
         [0000]        A   λ1   =aN   b   +bN   w   +eN   s   (3),
 
         [0000]        A   λ2   =cN   b   +dN   w   +fN   s   (4),
 
         [0000]      and 
         [0000]        A   λ3   =gN   b   +hN   w   +iN   s   (5),
 
         [0076]    hereby, the attenuation coefficients a, c and g relate to the black smoke; the attenuation coefficients b, d and h relate to the smoke; the attenuation coefficients e, f and i relate to the water vapor; and, 
         [0077]    Thus, the black smoke density N b , the white smoke density N w  and the water vapor density N s  can be obtained by solving the simultaneous equations (3) to (5) with respect to the unknowns N b , N 1  and N s . 
         [0078]    Incidentally, the attenuation coefficient e is an attenuation coefficient that represents the relation between the black smoke density and the laser attenuation, in relation to the laser including wavelength λ 3  that passes through the measurement object gas. The attenuation coefficient f is an attenuation coefficient that represents the relation between the white smoke density and the laser attenuation, in relation to the laser including wavelength λ 3  that passes through the measurement object. The attenuation coefficient g is an attenuation coefficient that represents the relation between the water vapor density and the laser attenuation, in relation to the laser including wavelength λ 1  that passes through the measurement object gas. The attenuation coefficient h is an attenuation coefficient that represents the relation between the water vapor density and the laser attenuation, in relation to the laser including wavelength λ 2  that passes through the measurement object gas. The attenuation coefficient i is an attenuation coefficient that represents the relation between the water vapor density and the laser attenuation, in relation to the laser including wavelength λ 3  that passes through the measurement object gas. 
         [0079]    According to the first embodiment as described above, a plurality of lasers of the absorption wavelengths λ 1  and λ 2  in relation to gaseous substances contained in the measurement object gas is irradiated through the measurement object gas, and a plurality of the laser attenuation coefficients for each of the absorption wavelengths regarding particulate matters such as black smoke and white smoke is established in advance so as to predetermine the attenuation coefficients on the basis of already known information and establish them in the laser attenuation coefficient map  29 . Further, the attenuations A λ1  and A λ2  for each of the lasers irradiated are measured, and each measured attenuation is correlated to the calculated attenuation by use of the attenuation coefficient map  29  in which the attenuation coefficients are established, so that the set of simultaneous equations with respect to the densities regarding the particulate matters such as black smoke and white smoke in the measurement object gas is solved. Thus, by solving the simultaneous equations, the densities of the particulate matters such as black smoke and white smoke can be simply and surely computed. 
         [0080]    Further, in the embodiment as described thus far, the intensity of the lasers passing through the first reference cell  45  and the second reference cell  49  in which a reference gas of the gaseous substance to be measured is encapsulated is converted into the intensity electrical signals as an incident intensity signals I 01  or I 02 . Moreover, the intensity signal of each lasers passing through the measurement object is converted into transmittance intensity signals I 1  or I 2 . Based on the incident intensity signals I 03  and I 02  as well as the transmittance intensity signals I 1  and I 2 , the density measurement by use of the lasers regarding the absorption wavelengths is performed; thus, the density measurement results can be free from the influence of the intensity fluctuations of the lasers on the oscillating side. 
         [0081]    Further, while the lasers are applied toward the measurement object gas including the particulate matters or gaseous substance, 
         [0000]    the lasers are applied toward the first reference cell  45  and the second reference cell  49  in which the reference gases are encapsulated. Based on the electrical signal corresponding to the intensity of the laser passing through the first reference cell  45  or the second reference cell  49 , the wavelength of the laser emitted by the first laser emitting means  15   a  or the second laser emitting means  15   b  is synchronized to (locked around) the absorption wavelength peculiar to the gas encapsulated in the first reference cell  45  or the second reference cell  49 . Thus, the wavelength of the laser passing through the first reference cell  45  is locked around the absorption wavelength λ 1  of the reference gas encapsulated in the first reference cell  45  and the wavelength of the laser passing through the second reference cell  49  is locked around the absorption wavelength λ 2  of the reference gas encapsulated in the second reference cell  49 ; therefore, the deviation of the wavelength of each laser emitting means  15   a  or  15   b  is restrained; accordingly, the density measurement accuracy is prevented from being deteriorated due to the wavelength deviation. 
         [0082]    In  FIG. 6 , an example result as to the black smoke density measurement according to this first embodiment is compared with the measurement result according to the conventional technology, namely a gas sampling approach. 
         [0083]    As shown in the area A of  FIG. 6 , according to the conventional technology, the delays in measuring responses by use of conventional measuring devices are recognized, and the relaxation (i.e. being not sharp) as to the response curve is observed as well. On the contrary, according to this first embodiment, it is confirmed that the density detection with improvements in the measuring responses can be realized. 
       Second Embodiment 
       [0084]    Next, the second embodiment according to the present invention is explained in consultation with  FIGS. 7 and 8 . 
         [0085]    In addition to the density measurement as to a plurality of particulate matters in the measurement object gas which is explained in the first embodiment, the second embodiment treats with the density measurement as to a plurality of gaseous substances in the measurement object gas; namely, the density measurement as to the particulate matter and the density measurement of the gaseous substance are performed. Incidentally, the same elements in the second embodiment as in the first embodiment are marked with the same symbols, and the explanation as to the same elements is omitted. 
         [0086]    The whole configuration of  FIG. 7  corresponds to that of  FIG. 2  as per the first embodiment; in addition to the first embodiment, a third demodulating means  55 , a fourth demodulating means  57  and the gaseous substance density computation means  35  (cf.  FIG. 1 ) are provided in this second embodiment. 
         [0087]    As explained in the first embodiment, the laser that is carried to the first laser receiving means  19   a  is converted into electrical signals (intensity signals) in response to the intensity of laser; namely, the first laser receiving means  19   a  outputs the intensity signals that are decomposed into DC (direct-current) components and AC (alternating-current) harmonic components (contents) by use of DC component detecting means (not shown) and AC component detecting means (not shown); the decomposed DC component corresponds to the attenuation Ap (the base attenuation Ap in  FIG. 9 ) regarding the laser transmittance; the attenuation Ap is attributable to the particulate matter and the density thereof; and, the attenuation Ap is used for computing the density as to the particulate matter. 
         [0088]    On the other hand, out of the decomposed DC components, the third demodulating means  55  extracts a signal that synchronizes with the first modulation signal f 1  outputted by the first wavelength-modulating means  37 ; the signal extracted by the third demodulating means  55  passes through a filter that removes the noises of the extracted signal described just above. Thus, the demodulating means produces a peak absorption signal in the demodulated signals. On the basis of the magnitude (size) of the peak absorption signal, the density of the gaseous substance in the measurement object gas is detected. The attenuation (absorption) Ag of the peaked shape as shown in  FIG. 9  represents the attenuation attributable to the gaseous substance; hence, the density of the gaseous substance can be computed by use of the attenuation Ag. In this specification, the attenuation Ag is described as the peak attenuation. 
         [0089]    By use of the peak (attenuation) signal A 1  (equivalent to the attenuation Ag as described above) that is obtained by the third demodulating means  55  and the transmittance intensity signal I 1  that is outputted by the first laser receiving means  19   a , the density N g1  of the gaseous substance absorbing the laser of the wavelength λ 1  is calculated by the formula N g1 =α 1 * A 1 /I 1  thereby the symbol α 1  denotes a proportional coefficient. 
         [0090]    As is the case with the density N g1  of the gaseous substance, the density N g2  of the gaseous substance absorbing the laser of the wavelength λ 2  is calculated by the formula N g2 =α 2 ·A 2 /I 2  thereby the symbol α 2  denotes a proportional coefficient. Incidentally, the calculations as to the densities N g1  and N g2  are performed by the gaseous substance density computation means  35  in the analyzing device  23 . 
         [0091]    According to the second embodiment, the densities as to two kinds of gaseous substances (CO and NH 3 ) can be measured; in other words, in addition to the density measurement as to black smoke and white smoke, the density measurement as to the two kinds of gaseous substances can be performed at the same time. Thus, the efficiency as to the exhaust gas analysis of the diesel engine  5  can be enhanced. 
         [0092]    Further, when three kinds of gaseous substances (e.g. CO, NH 3  and NO x ) are taken into consideration instead of two kinds of gaseous substances (e.g. CO, and NH 3 ), the efficiency of the density measurements as to the exhaust gas is further improved, since the density measurement as to as to a plurality of the particulate matters such as black smoke, white smoke and water vapor can be performed at the same time in parallel with the density measurement as to the gaseous substances. 
         [0093]    In addition, it is needless to say that the number regarding the gaseous substances that can be handled at the same time is limited to neither two nor three. As a matter of course, the densities as to particulate matters of more than three kinds, if required, can be measured at the same time in parallel with the density measurement as to a plurality of gaseous substances. 
         [0094]    In the above explanation about the first and second embodiments, the semiconductor laser diode is taken as an example of laser source; naturally, other laser oscillation devices that can perform wavelength modulation or amplitude modulation can be made use of. 
       INDUSTRIAL APPLICABILITY 
       [0095]    According to the present invention, a measuring method and a device for measuring the density as to a plurality of gaseous substances and particulate matters in a measurement gas is provided; thereby, the measurement gas including the gaseous substances and the particulate matters is generated in a closed vessel such as a combustion chamber for a boiler, a refuse incinerator, a combustion engine and so on, the gas being emitted outward from the closed vessel; the densities as to the gaseous substances and the densities as to the particulate matters can be measured at the same time; in addition, the densities as to a plurality of particulate matters such as black smoke, white smoke and water vapor are surely measured in a simple way at the same time. Thus, the present invention provides a useful density measuring method and a useful density-measuring device thereof.