Abstract:
To provide a concentration measuring method with which the concentration of a predetermined chemical component can be accurately, quickly, and nondestructively measured down to a concentration range of an extremely small amount with a simple means, and to provide a concentration measuring method with which the concentration of a chemical component in an object to be measured can be accurately and quickly measured down to a concentration range of a nano-order extremely small amount in real time, the method having universality, i.e., the ability to be embodied in various forms and modes. Light having a first wavelength and light having a second wavelength, which have different light absorptances with respect to an object to be measured, are each radiated onto the object to be measured using a time-sharing method; the light having the first wavelength and the light having the second wavelength, optically passing through the object to be measured as a result of the irradiation with the light having the first and second wavelengths, are received with a common light receiving sensor; a differential signal between a signal related to the light having the first wavelength and a signal related to the light having the second wavelength to be output from the light receiving sensor according to the received light is formed; and the concentration of a chemical component in the object to be measured is derived on the basis of the differential signal.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a concentration measuring method related to a concentration of a predetermined chemical component in a liquid or a gas, a sugar content in a fruit or a vegetable, a sake meter value (sweetness/dryness) of Japanese sake, or the like. 
         [0003]    2. Description of the Background Art 
         [0004]    In the manufacture of a semiconductor, mixed gases are often supplied from the same line inside a treatment chamber of a semiconductor manufacturing device. The supply of such a mixed gas requires that a mixture ratio of component gases be kept constant during the treatment process period, and instantaneously changed as intended. To this end, a flow rate control device, such as a flow control system component (FCSC), for example, that comprises a gas flow rate measurement mechanism and a gas flow rate adjustment mechanism is arranged in the gas supply line. In this FCSC, the degree to which the flow rate per unit time (hereinafter also referred to as “unit flow rate”) of each component gas that constitutes the mixed gas can be accurately measured is important. 
         [0005]    Today, in a semiconductor manufacturing process in which there are many opportunities to implement a treatment process such as film formation or etching at an atomic- to nano-order level, the unit flow rate of each component gas in a mixed gas immediately prior to introduction to a treatment chamber needs to be measured accurately and instantaneously down to a range of a small amount. 
         [0006]    In such a conventional flow rate control device that satisfies the requirement described above, generally the flow rate of each single component gas prior to mixture is measured and the target mixture ratio of the mixed gas is calculated from the measured flow rate values. 
         [0007]    Nevertheless, the mixture ratio of the mixed gas at the moment of introduction into the treatment chamber (hereinafter also referred to as “actual mixture ratio”) is not always guaranteed to be the same as the mixture ratio calculated from the measured flow rate values (hereinafter also referred to as “measured mixture ratio”) during process execution. Thus, conventionally a feedback mechanism is provided that measures the flow rate of each single component gas either continually or at a predetermined interval, and adjusts each of the flow rates so that, when the flow rate of any single component gases fluctuates, the mixture ratio becomes the original predetermined mixture ratio based on the new value (Patent Document 1, for example). 
         [0008]    On the other hand, examples of a gas concentration measuring system include a system that uses a partial pressure measurement sensor that measures the partial pressure of a material gas by a non-dispersive infrared absorption method, and calculates the concentration of the material gas on the basis of the partial pressure measurement value of this sensor by a mathematical operation (Patent Document 2, for example). 
         [0009]    Further, in metal-organic compound chemical vapor deposition (MOCVD; chemical vapor deposition that uses a metal-organic compound) as well, formation of a uniform film requires control of the supplied concentration of the metal-organic compound so that the supplied concentration of the metal-organic compound is constant during the film formation process period, or so that the supplied concentration fluctuates in accordance with the component distribution of the metal-organic compound to ensure formation of a film with a preferred component distribution. Generally, the metal-organic compound is mixed into a carrier gas via bubbling or the like, and supplied to the treatment chamber. The used metal-organic compound is not limited to a single compound, and a plurality of compounds may be used as well. Examples of the method used to supply the raw material gases of a plurality of types of metal-organic compounds in accordance with design values include a method for using infrared gas analysis means (Patent Document 3, for example). 
         [0010]    Furthermore, in the field of fruit and vegetable production and shipping as well, measurement of the concentration of a component such as a sweetness component of the fruit or vegetable is important in determining the sales price of the fruit or vegetable to be shipped. That is, the sweetness of a fruit or vegetable such as an apple, pear, peach, persimmon, strawberry, or watermelon significantly affects the sales price of the product, and thus knowing whether or not the sweetness is ideal for harvest for shipping is a matter of keen interest to the fruit and vegetable producer. One method for ascertaining the sweetness of a fruit or vegetable is to measure the sugar content in the fruit or vegetable in a non-contact manner using infrared light (Patent Document 4, for example). 
         [0011]    Further, medically related, the ability to instantaneously measure blood components in the bloodstream, for example, such as the red blood cell count, white blood cell count, platelet count, reticulocyte count, and hemoglobin level in a living body in a non-contact (non-destructive, non-invasive) manner without drawing blood would not only alleviate the burden of the patient but also mentally and physically alleviate the labor burden of doctors, nurses, and medical technicians. Thus, the ability to easily and instantaneously take such measurements in a living body in a non-contact, non-invasive manner has been desired. For example, recently the number of diabetes patients in younger demographics is on the rise, increasing the demand for test methods that allow tests to be conducted easily, quickly, and with high accuracy. Furthermore, not only are there many patients under doctor care, but there are many latent patients (potential patients) as well, and the number of cases in which, for example, such a patient experiences a sudden drop in blood sugar level while driving, fully or partially loses consciousness, and causes an accident is increasing daily. While the concentration of glucose (blood sugar level, blood sugar) in the blood is normally continually adjusted within a certain range by the activity of various hormones (insulin, glucagon, cortisol, and the like), when this adjustment mechanism fails for any of a variety of reasons, the amount of sugar in the blood increases abnormally, resulting in diabetes. Diabetes is a disease that refers to a condition in which the blood sugar level (concentration of glucose in the blood) is abnormally high, and is diagnosed when the blood sugar level or hemoglobin Alec value exceeds a certain standard. Diabetes may cause symptoms attributable to the high blood sugar itself and also, over time, glycation in which glucose, having a high concentration in the blood, binds with protein in the vascular endothelium due to the high reactivity of the aldehyde group, resulting in the gradual destruction of microvessels in the body, causing serious disorders (microangiopathies including diabetic neuropathy, diabetic retinopathy, and diabetic nephropathy) in various organs in the body, including the eyes and kidneys (complications). Thus, appropriate blood sugar management is important in the treatment of diabetes, including continual strict blood sugar control, medical diet and therapeutic exercise review, insulin dose adjustment and review, verification/prediction of low blood sugar by medical treatment, alleviation of low blood sugar anxiety, and avoidance of severe hyperglycemia. 
         [0012]    Measurement of blood sugar level in medical institutions such as hospitals is generally performed by a so-called invasive method for drawing blood from a finger, arm, or the like of the living body. Further, diabetes patients are tested for blood sugar level during treatment under the care of a physician in the hospital. On the other hand, in many cases the blood sugar level needs to be measured daily, and thus a patient must often perform blood sugar level measurements on his or her own using a self-monitoring of blood glucose (SMBG) device in a hospital bed or at home. While measurement has become rather simple, blood still must be drawn either by the patient or with the help of another. Blood is drawn by puncturing a finger or an arm. This puncturing is associated with pain and a puncture wound, placing physical and mental stress on the patient. While recently the use of a painless needle may be considered, association with a puncture wound cannot be avoided, and health safeguards for preventing infection caused by open wounds and the like are required. Recently, as a solution to this problem, non-invasive methods are proposed (Patent Documents 5 and 6, for example). 
         [0013]    On the other hand, in Japan, both the blood sugar level and the hemoglobin A1c value must be measured to assess diabetes. Examples of methods for measuring both the blood sugar level and the hemoglobin A1c value include the method set forth in Patent Document 7. 
         [0014]    Furthermore, a method that allows measurement of a sake meter value (hereinafter “SMV”), acidity, and amino acidity in the manufacturing process of Japanese sake, with high accuracy, promptness, and a simple configuration, has been in demand. Japanese sake is a liquor delicate in flavor and aroma. Japanese sake is gauged in terms of sweetness/dryness by its SMV, and in terms of full-bodied/light flavor by its acidity. The SMV refers to the amount of sugar and acid dissolved in the sake, and is a unit that expresses the specific gravity of the refined sake. The SMV is measured by bringing the temperature of the sake to be measured to 15° C., and then floating a hydrometer called an SMV meter in the sake. Japanese sake having the same weight as distilled water at 4° C. is given an SMV of “0.” Any lighter sake is indicated by a positive (+) value, and any heavier sake is indicated by a negative (−) value. In Japanese sake, what determines sweetness is glucose concentration. 
         [0015]    In contrast to SMV which gauges sweetness/dryness, acidity (level of light/full-bodied flavor) gauges richness and depth. A Japanese sake with a higher acidity has a more full-bodied flavor, while a Japanese sake with a lower acidity has a lighter flavor. Given the same SMV, a Japanese sake with a high acidity is spicier while a sake with a low acidity is sweeter. Conversely, a Japanese sake with low acidity tends to lack a smooth, clean finish, and have a shallow flavor. This acidity, however, affects not only richness, but the actual sweet/spicy flavor as well. In general, a higher acidity tends to result in a spicier taste. Conversely, a low acidity results in a sweeter taste, even if the sugar content is not high. Acidity is measured by the number of titration millimeters of a 1/10 normal sodium hydroxide solution that is required to neutralize 10 milliliters of the refined sake. If this value is high, expressions such as “plain” are used. If this value is low, expressions such as “rich” are used. Further, with Japanese sake, amino acidity (tastiness) is also important. Amino acids are elements that bring savoriness, and high amino acidity results in an increase in savory elements, and thus a rich sake flavor. However, savoriness does not necessarily increase as the amino acidity is increased, resulting in an off-flavor when too high. 
         [0016]    As described above, in the manufacture of Japanese sake, the management of SMV, acidity, and amino acidity significantly affects the business value (hereinafter also referred to as “sales value”) of the manufactured sake. The SMV, acidity, and amino acidity sensitively fluctuate according to humidity, temperature, and sanitary aspects, and thus humidity, temperature, and sanitary aspects are strictly controlled in the manufacture of Japanese sake and SMV, acidity, and amino acidity are frequently measured in the manufacturing process. 
       PATENT DOCUMENTS 
       [0000]    
       
         Patent Document 1: Japanese Laid-Open Patent Application No. 2012-138407 
         Patent Document 2: Japanese Laid-Open Patent Application No. 2010-109304 
         Patent Document 3: Japanese Laid-Open Patent Application No. 2006-324532 
         Patent Document 4: Japanese Laid-Open Patent Application No. 2003-114191 
         Patent Document 5: Japanese Laid-Open Patent Application No. 2008-256398 
         Patent Document 6: Japanese Laid-Open Patent Application No. 2006-141712 
         Patent Document 7: Japanese Laid-Open Patent Application No. 2012-137500 
       
     
       SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
       [0024]    In the concentration measuring method or concentration adjustment method set forth in each of the patent documents described above, problems such as the following exist. 
         [0025]    In Patent Document 1, the flow rate is measured on an upstream side of the treatment chamber and merely fed back, and thus the problem of whether or not the measured mixture ratio and actual mixture ratio are identical remains unresolved. Furthermore, while the length of the supply line from the mixing position to the position of introduction into the treatment chamber needs to be adequately set to ensure that the mixed state of the gases is uniform, doing so makes it all the more difficult to regard the measured mixture ratio and actual mixture ratio as identical. To ensure that the measured mixture ratio and the actual mixture ratio are identical, one may consider positioning the mixing position and the introduction position as close to each other as possible, but doing so results in the problem that it is difficult to guarantee a uniform mixture. Attempting to resolve such problems in addition to the problems described above results in an increasingly complex mechanism, and requires rather advanced control technology. Additionally, according to the configuration of Patent Document 1, measurement is performed by flow rate measurement, and thus gases cannot be specified. 
         [0026]    In the case of Patent Document 2, measurement is performed by partial pressure measurement and thus the method is unsuitable for such high accuracy measurement as addressed here. Furthermore, the measurement error undeniably increases when the partial pressure measurement is performed in a range of an extremely small order. 
         [0027]    The method disclosed in Patent Document 3 is configured to individually adjust any one of first infrared gas analysis means for measuring the concentration of each raw material gas in a mixed gas supplied from a gas mixing chamber to a reaction chamber, second infrared gas analysis means for measuring a concentration of each raw material gas in a discharged gas discharged from the reaction chamber, the flow rate control means for calculating an amount of consumption of each raw material gas inside the reaction chamber based on the measurement results of the first and second infrared gas analysis means and setting the difference between the calculated value and a predetermined design value as a control amount, a gas supply source temperature control unit, and a substrate temperature control unit. Thus, the raw material gases consumed not by film formation but by an inner wall surface of the reaction chamber and the like are not taken into consideration, making it difficult to form a thin film having a uniform film thickness and uniform components. Moreover, a specific example of the infrared gas analysis means is not illustrated in Patent Document 3. As a result, while formation of a thin film having uniform components and a uniform film thickness at the nano-order level requires strict control of the supplied concentration of the metal-organic compound in order to supply the metal-organic compound to the treatment chamber at a predetermined concentration for a certain period of time, demanding high accuracy in concentration measurement, this demand is not simply satisfied. 
         [0028]    The method set forth in Patent Document 4 irradiates two monochromatic lights having different wavelengths onto a fruit or a vegetable, determines each coefficient of an identification formula from values of light transmittances Ta, Tb of a plurality of actual measurement examples in relation to each monochromatic light and values of a sugar content C of actual measurements of the examples, and uses the data of each determined coefficient as well as the measured light transmittances of the two monochromatic lights to find the sugar content using the identification formula. This method, therefore, merely finds the average sugar content of the fruit or vegetable subjected to sugar content measurement. Thus, in the case of a fruit or a vegetable having a high sugar content near the peel or core, it may be difficult to avoid inclusion of a fruit or a vegetable that has an inadequate sugar content depending on the section consumed and thus decreases product price in a shipment. 
         [0029]    In the methods of Patent Documents 5 and 6, measurement errors attributable to patient nervousness and perspiration in the affected measurement region or a rise in body temperature cannot be avoided. Measurement methods of a blood sugar measuring device include enzyme electrode methods and enzyme colorimetric (colorimetric determination) methods. Enzyme electrode methods include glucose oxidase (GOD) methods and glucose dehydrogenase (GDH) methods. Enzyme colorimetric (colorimetric determination) methods include hexokinase (HX) methods and glucose oxidase/peroxidase (GOD/POD) methods. However, while errors are not evident in the measurement value of each device, when a hematocrit (a test for checking the percentage of red blood cells in a given sample of blood) value is between 20% and approximately 60%, the problem arises that the methods indicate a high value for blood having a hematocrit value below 20%, such as in patients with severe anemia or dialysis patients, and conversely a low value for hypervolemic blood having a hematocrit value above 55%, such as in newborns and in women prior to menstruation. Thus, the methods are inappropriate for patients with severe anemia and dialysis patients. Furthermore, GOD methods are problematic in that the measured blood sugar level decreases to the extent that the partial pressure of the dissolved oxygen in the blood is high. Thus, GOD methods are not appropriate for patients that use oxygen for breathing control. In addition, a normal measurement value may not be obtained for reasons attributable to verification of blood drawing and blood dotting procedures, how the test paper is attached, how the measurement device is used, and the like. 
         [0030]    The method set forth in Patent Document 7 takes measurements using the same measurement principle of detecting coloring from hemoglobin, coloring from saccharized hemoglobin, and coloring from glucose by reflecting light having different wavelengths. While offering the advantages of simplifying and reducing the size of the device, the method requires a reagent and coloring work for three types of coloring, i.e., hemoglobin, saccharized hemoglobin, and glucose, and also comes with the burden of drawing blood. 
         [0031]    Further, while humidity, temperature, and sanitary aspects are strictly controlled in the manufacture of Japanese sake, and SMV, acidity, and amino acidity are frequently measured in the manufacturing process, a method for measuring SMV, acidity, and amino acidity quickly and accurately down to a concentration range of an extremely small amount in a non-destructive manner using simple means has not yet been provided. 
         [0032]    As understood from the above description, a concentration measuring method that allows quick and accurate measurement of a concentration of a predetermined chemical component down to a concentration range of an extremely small amount in a non-destructive manner using simple means has not yet been provided. 
         [0033]    Further, a concentration measuring method that allows measurement of the concentrations of a plurality of chemical components in an object to be measured with high accuracy in real time using the same measurement system and the same conditions, regardless if the component is a gas, a liquid, or a solid, has not yet been provided. 
         [0034]    Furthermore, a concentration measuring method that allows quick and accurate measurement of the concentration of a chemical component in an object to be measured down to a concentration range of an extremely small amount in the nano order in real time, the method having universality, i.e., the ability to be embodied in various forms and modes, has not yet been provided. 
         [0035]    Furthermore, a concentration measuring method that allows quick and accurate measurement of the concentrations of a plurality of chemical components in an object to be measured in real time using a simple configuration has not yet been provided. 
         [0036]    The present invention was achieved as a result of close research on the points described above. 
         [0037]    It is therefore an object of the present invention to provide a concentration measuring method that allows quick and accurate measurement of a concentration of a chemical component in real time, using a simple configuration. 
         [0038]    Another object of the present invention is to provide a concentration measuring method that allows quick and accurate measurement of a concentration of a chemical component in an object to be measured, down to a concentration range of an extremely small amount in the nano order in real time using a simple configuration, regardless if the component is a gas, a liquid, or a solid, the method having universality, i.e., the ability to be embodied in various forms and modes. 
         [0039]    Yet another object of the present invention is to provide a concentration measuring method that allows quick and accurate measurement of a concentration of a chemical component in a non-destructive, non-contact manner, down to a range of an extremely small amount using a simple configuration. 
         [0040]    Yet another object of the present invention is to provide a concentration measuring method that allows measurement of a concentration of a chemical component, down to a range of an extremely small amount with measurement errors based on environmental fluctuations and characteristic fluctuations in system components, such as electrical circuits or electronic elements, eliminated at least to the extent substantially possible. 
         [0041]    Yet another object of the present invention is to provide a concentration measuring method that allows measurement of a blood sugar level in a non-invasive manner using a simple configuration and method in a state that is at least substantially free of measurement errors attributable to patient nervousness and perspiration in the affected measurement region or a rise in body temperature (errors based on the physiological state of a specimen or an object to be measured; hereinafter also referred to as “physiological errors”). 
         [0042]    Yet another object of the present invention is to provide a concentration measuring method that allows quick and accurate measurement of concentrations of a plurality of chemical components in an object to be measured in real time, using a simple configuration. 
         [0043]    Yet another object of the present invention is to provide a concentration measuring method that allows simple and easy measurement of both a blood sugar level and a hemoglobin A1c value using the same configuration and method. 
       Means for Solving the Problems 
       [0044]    A first aspect of the present invention is a concentration measuring method for optically measuring a concentration of a predetermined chemical component in an object to be measured, the method comprising the steps of irradiating light having a first wavelength that has an absorbability with respect to the chemical component, and light having a second wavelength that has no or substantially no absorbability with respect to the chemical component or an absorbability that is relatively lower than that of the light having the first wavelength, from a single light-emitting means toward the object to be measured using a time-sharing method, receiving the light produced by the irradiation from the object to be measured by a single light-receiving means, inputting a first light-receiving signal based on the light having the first wavelength and a second light-receiving signal based on the light having the second wavelength, each produced by the received light, into a differential circuit, comparing a measured value based on an output signal output from the differential circuit in accordance with the input with data stored in advance in storage means, and deriving the concentration of the predetermined chemical component accordingly. 
         [0045]    A second aspect of the present invention is a concentration measuring method comprising the steps of irradiating light having a first wavelength and light having a second wavelength, each having a different light absorptivity with respect to an object to be measured, onto the object to be measured using a time-sharing method, receiving the light of each wavelength that optically passes through the object to be measured as a result of the irradiation of the light of each wavelength using a common light-receiving sensor, forming a differential signal between a signal related to the light having the first wavelength and a signal related to the light having the second wavelength output from the light-receiving sensor in accordance with the received light, and deriving a concentration of a chemical component in the object to be measured on the basis of the differential signal. 
         [0046]    A third aspect of the present invention is a concentration measuring method comprising the steps of irradiating a first light and a second light, each having a different light absorptivity with respect to an object to be measured, onto the object to be measured using a time-sharing method, receiving each light that optically passes through the object to be measured by irradiation of each light onto the object to be measured using a common light-receiving sensor, forming a differential signal on the basis of a signal related to the first light and a signal related to the second light output from the light-receiving sensor in accordance with the received light, and deriving a concentration of a predetermined chemical component in the object to be measured on the basis of the differential signal. 
       Effect of the Invention 
       [0047]    According to the present invention, it is possible to measure a concentration of a predetermined chemical component quickly and accurately in a non-destructive manner down to a concentration range of an extremely small amount using simple means. 
         [0048]    Further, it is possible to measure with high accuracy the concentrations of a plurality of chemical components in an object to be measured in real time using the same measurement system and the same conditions, regardless if the component is a gas, a liquid, or a solid. 
         [0049]    Furthermore, it is possible to provide a concentration measuring method that allows quick and accurate measurement of a concentration of a chemical component in an object to be measured, down to a concentration range of an extremely small amount in the nano order in real time, the method having universality, i.e., the ability to be embodied in various forms and modes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]      FIG. 1  is a timing chart for explaining the principles of a concentration measuring method of the present invention. 
           [0051]      FIG. 2  is a block diagram for explaining a configuration of a preferred embodiment of an optical concentration measuring system that embodies the concentration measuring method of the present invention. 
           [0052]      FIG. 3  is a flowchart for explaining a preferred embodiment of the concentration measuring method of the present invention. 
           [0053]      FIG. 4  is a timing chart for explaining a signal output timing of the example in  FIG. 3 . 
           [0054]      FIG. 5  is a flowchart for finding an analytical curve. 
           [0055]      FIG. 6  is a graph of a relationship between a gas concentration GC and “−log(1−ΔT).” 
           [0056]      FIG. 7  is an explanatory schematic configuration view for explaining a main component of a preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. 
           [0057]      FIG. 8  is an explanatory schematic configuration view for explaining main components of another preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. 
           [0058]      FIG. 9  is an explanatory schematic configuration view for explaining main components of yet another preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. 
           [0059]      FIG. 10  is an explanatory schematic configuration view for explaining a main component of yet another preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. 
           [0060]      FIG. 11  is an explanatory schematic configuration view for explaining a preferred example of a differential signal forming portion adopted in the present invention. 
           [0061]      FIG. 12  is an explanatory schematic configuration view for explaining another preferred example of the differential signal forming portion adopted in the present invention. 
           [0062]      FIG. 13  is an explanatory schematic configuration view for explaining yet another preferred example of the differential signal forming portion adopted in the present invention. 
           [0063]      FIG. 14  is an explanatory schematic configuration view for explaining yet another preferred example of the differential signal forming portion adopted in the present invention. 
           [0064]      FIG. 15  is a graph showing a relationship between an absorbance value measured with respect to a gas concentration and a value equivalent to three times a standard deviation of a noise superimposed on the measured signal. 
           [0065]      FIG. 16  is an outline external view illustrating an embodiment of a case in which the present invention is applied to a mobile terminal device. 
           [0066]      FIG. 17  is a block diagram of an internal configuration of an embodiment in a case in which the present invention is applied to a mobile terminal device. 
           [0067]      FIG. 18  is an explanatory schematic configuration view for explaining yet another preferred example of the differential signal forming portion adopted in the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0068]      FIG. 1  is a timing chart for explaining the principles of a concentration measuring method of the present invention. In the present invention, a concentration measuring device for embodying the concentration measuring method of the present invention is activated, and a signal of an absolute value of a background light in a space where the device is placed is read as a difference between outputs S 20  and S 10  (absolute value output X). 
         [0069]    Next, light from a light source  1  that emits light (Lλ 1 ) having a first wavelength is received by a light-receiving sensor, and a differential output signal (GΔ 1 ) of a difference between outputs S 30  and S 40  is read (output as a sum of the background light and the light of the light source  1 ). Next, light from a light source  2  that emits a light (Lλ 2 ) having a second wavelength is received by the same light-receiving sensor, and a differential output signal (GΔ 2 ) of a difference between outputs S 50  and S 60  is read (output as a sum of the background light and the light of the light source  2 ). 
         [0070]    Measurement data can be calibrated using the absolute value output X, even if a change occurs in an amount of light of the light source, an absorbance of an object to be measured as a result of a temperature change, or the like. 
         [0071]    With the light-receiving signals from the light sources  1 ,  2  output as differential output signals, noise of a circuit system can be removed, making it possible to achieve detection with high accuracy, even if the concentration is weak. 
         [0072]    In  FIG. 1 , “↑” indicates the output timing of the light-receiving sensor. While in principle the output timing “↑” includes a rise start point (t 1 ) and a fall start point (t 2 ) of the output of the light-receiving sensor, the output timing “↑” in  FIG. 1  is the timing between the rise start point (t 1 ) and the fall start point (t 2 ). This is because, when one measurement ends, an electronic circuit is partially reset for the next measurement. That is, a measurement period and a reset period may overlap due to a time lag in the circuit and thus, to reliably avoid effects therefrom, the output timing “↑” is the timing between the rise start time (t 1 ) and the fall start time (t 2 ). 
         [0073]      FIG. 2  is a block diagram of a configuration example of an optical concentration measuring system  100  serving as a preferred embodiment that embodies the concentration measuring method of the present invention. 
         [0074]    The optical concentration measuring system  100  comprises a light source portion  101 , a light-focusing optical portion  102 , a light-receiving sensor portion  106 , a differential signal forming portion  108 , a signal storage/processing portion  110 , a display unit  112 , a control unit  113 , and an operation portion  114 . 
         [0075]    The optical concentration measuring system  100  illustrated in  FIG. 2  comprises an optical gas concentration measuring sub-system  100 - 1  and a control/operation sub-system  100 - 2 . 
         [0076]    The optical gas concentration measuring sub-system  100 - 1  comprises an optical gas concentration measuring device  100 - 3 . 
         [0077]    The optical concentration measuring sub-system  100 - 1  comprises the light source portion  101 , the light-focusing optical portion  102 , the light-receiving sensor portion  106 , the differential signal forming portion  108 , the signal storage/processing portion  110 , and the display unit  112 . The control/operation sub-system  100 - 2  comprises the control unit  113  and the operation portion  114 . 
         [0078]    An object  104  to be measured, subject to concentration measurement of a preferred chemical component, is arranged in a predetermined position between the light-focusing optical portion  102  and the light-receiving sensor portion  106 . 
         [0079]    While the light source portion  101  illustrated in  FIG. 2  comprises two light sources including a light source  101   a  that emits the light (Lλ 1 ) having the first wavelength and a light source  101   b  that emits the light (Lλ 2 ) having the second wavelength, the present invention is not limited thereto, allowing a single light source that emits the light (Lλ 1 ) having the first wavelength and the light (Lλ 2 ) having the second wavelength. 
         [0080]    A light-emitting portion capable of irradiating light having two or more different wavelengths such as described above may comprise two or more light-emitting elements, each capable of irradiating light having one type of wavelength. Furthermore, the light-emitting portion preferably comprises at least one light-emitting element capable of irradiating light having two or more different wavelengths (multiple wavelength light-emitting element). This decreases the number of light-emitting elements arranged in the device interior, making it possible to reduce the size of the device. 
         [0081]    When two light sources are adopted, disposing the two light sources as close to each other as possible so that each light can be irradiated on substantially the same optical axis increases the accuracy of the measured value, and is thus preferred. 
         [0082]    When a single light source is adopted, the light (Lλ 1 ) and the light (Lλ 2 ) are selectively separated by means such as a wavelength selecting optical filter prior to being irradiated onto the object  104  to be measured. 
         [0083]    When the lights (Lλ 1 , Lλ 2 ) having the two wavelengths are irradiated using a single light source, the device is designed so that the light having the applicable wavelength is irradiated in accordance with an irradiation timing using an optical wavelength selecting filter such as a spectrum filter. 
         [0084]    While the light (Lλ 1 ) having the first wavelength and the light (Lλ 2 ) having the second wavelength may each be light having a single wavelength, adoption of light having multiple wavelengths, each having a bandwidth for a wavelength, is preferred, taking into consideration ease of acquisition of the light source, such as an LED, and cost. Such light preferably has a center wavelength (wavelength with a peak intensity) of λ 1  or λ 2 . 
         [0085]    In the present invention, the light (Lλ 1 ) is light having a wavelength that has an absorbability with respect to a chemical component subject to concentration measurement. In contrast, the light (Lλ 2 ) is a light having a wavelength that has no or substantially no light absorbability with respect to the chemical component, or an absorbability with respect to the chemical component that is relatively lower than that of the light (Lλ 1 ). 
         [0086]    In the present invention, a light such as the light (Lλ 2 ) is preferably adopted since measurement accuracy increases when there is no absorbability with respect to the chemical component or to the extent the absorbability differs from that of the light (Lλ 1 ). 
         [0087]    When the concentrations of a plurality of chemical components are measured using the same object to be measured, the light (Lλ 1 ) is prepared in a quantity equivalent to the number of chemical components to be measured. That is, given N as the number of chemical components, the light (Lλ 1 ) is prepared in a quantity of n (Lλ 1   n , where n is a positive integer). Among the lights (Lλ 1   n , where n is a positive integer), the light selected as applicable is the light having a wavelength or a wavelength range that exhibits an absorbability with respect to the one chemical component only and no or substantially no absorbability with respect to any other chemical component. For example, when glucose and hemoglobin are measured using the same object to be measured, light (Lλ 11 ) that exhibits absorbability with respect to glucose but not with respect to hemoglobin, and light (Lλ 12 ) that does not exhibit absorbability with respect to glucose but does with respect to hemoglobin are selected. 
         [0088]    For the light (Lλ 2 ), light that exhibits no or substantially no absorbability with respect to either chemical component is selected. 
         [0089]    As the light source of the light source portion, needless to say, a light source that emits light according to these conditions is selected and used. 
         [0090]    The light (Lλ 1 ) and the light (Lλ 2 ) are irradiated onto the object  104  to be measured in accordance with a time-sharing method. 
         [0091]    The light (Lλ 1 ) and the light (Lλ 2 ) are preferably irradiated onto the same optical axis or substantially the same optical axis when irradiated onto the object  104  to be measured. That is, even when a chemical component subject to concentration measurement has a spotted distribution or an uneven distribution spatially or temporally in the object  104  to be measured, when the positions in which the light (Lλ 1 ) and the light (Lλ 2 ) pass through the object  104  to be measured are the same or substantially the same, the measurement period is, at the same time, extremely short, resulting in the advantage of achieving a highly accurate measurement minimally affected by measurement errors. 
         [0092]    An irradiated light  103  formed by the light (Lλ 1 ) or the light (Lλ 2 ) is irradiated onto the object  104  to be measured and, as a result, a transmitted light  105  exits from the exact opposite side of the object  104  to be measured. 
         [0093]    The transmitted light  105  enters a light-receiving surface of a light-receiving sensor located in the light-receiving sensor portion  106 . 
         [0094]    The light-receiving sensor portion  106  outputs an electric signal  107  in response to the received light. 
         [0095]    The signal  107  is either a signal  107   a  based on the light (Lλ 1 ) or a signal  107   b  based on the light (Lλ 2 ). 
         [0096]    The signal  107   a  and the signal  107   b  are input to the differential signal forming portion  108  either sequentially based on a set time difference or simultaneously. 
         [0097]    When input based on a set time difference, the signal input first may, depending on the case, be held for a predetermined period in a predetermined circuit inside the differential signal forming portion  108  in accordance with a timing for forming the differential signal. 
         [0098]    A differential output signal  109  output from the differential signal forming portion  108  in accordance with the input of the signal  107  is transferred to the signal storage/processing portion  110  and stored/processed so as to output an output signal  111 . 
         [0099]    The output signal  111  is transferred to the display unit  112 . The display unit  112  that received the output signal  111  displays a concentration display of the measured chemical component on a display screen of the display unit  112  as a value corresponding to the output signal  111 . 
         [0100]    The above series of processes is controlled by the control unit  113  in accordance with instructions from the operation portion  114 . 
         [0101]    The light-receiving sensor constituting the light-receiving sensor portion  106  may be a single element such as a photodiode, or a line sensor or area sensor in which a predetermined number of light-receiving pixels is one-dimensionally or two-dimensionally disposed, respectively. 
         [0102]    When the chemical component to be measured is not uniform in the object  104  to be measured, a measurement error resulting from positional dependency may decrease the measurement accuracy, and thus adoption of a line sensor or an area sensor is preferred. In particular, adoption of an area sensor that has a light-receiving surface having a size that covers an exiting surface from which the transmitted light  105  exits, orthogonal to the optical axis of the object  104  to be measured, can significantly increase measurement accuracy, and is thus preferred. 
         [0103]    While the light (Lλ 1 ) and the light (Lλ 2 ) have each been described using a light having a single wavelength, the wavelength is not necessarily limited thereto in the present invention, and the wavelength may have a bandwidth (wavelength range). That is, in the present invention, a luminous flux having a predetermined wavelength range may be used. 
         [0104]    Next, an example of actual concentration measurement using the system  100  of  FIG. 2  will be described on the basis of  FIGS. 3 and 4 .  FIG. 3  is a flowchart for explaining a preferred embodiment of the concentration measuring method of the present invention. 
         [0105]    When a button switch of the operation portion  114 , or the like, for starting measurement is pressed, concentration measurement is started (step  201 ). 
         [0106]    In step  202 , the existence or absence of the specimen  104  serving as the object to be measured, including if the specimen  104  is appropriately placed in a predetermined position, is determined. When it is determined that the specimen  104  has been appropriately placed, the first light (Lλ 1 ) and the second light (Lλ 2 ) necessary and appropriate for measuring the concentration of a chemical component to be measured in the specimen  104  are selected in step  202 . 
         [0107]    Selection of the first light (Lλ 1 ) and the second light (Lλ 2 ) is made by setting the light source  101   a  for the first light (Lλ 1 ) and the light source  101   b  for the second light (Lλ 2 ) in predetermined positions in the optical concentration measuring system  100 , or dispersing the light using a spectroscope. 
         [0108]    When selection is based on the establishment of a light source, selection of the first light (Lλ 1 ) and the second light (Lλ 2 ) can be made in advance from an absorption spectrum of the chemical component to be measured in the specimen  104 , allowing step  203  to be performed before step  201 . 
         [0109]    Next, in step  204 , acquisition of an analytical curve for deriving the concentration value of the chemical component to be measured based on measurement data is started. 
         [0110]    The analytical curve can be acquired by reading the data of an analytical curve stored in advance in a storage portion of the optical concentration measuring system  100 , or by creating a new analytical curve as described in  FIG. 5 . 
         [0111]    Once acquisition of the analytical curve is complete, measurement of the specimen  104  is started as indicated in step  206 . 
         [0112]    When measurement is started, the first light (Lλ 1 ) and the second light (Lλ 2 ) are irradiated onto the specimen  104  for a predetermined period by time-sharing at a predetermined interval. 
         [0113]    The first light (Lλ 1 ) and the second light (Lλ 2 ) that passed through the specimen  104  are received by a light-receiving sensor set in the light-receiving sensor portion  106  (step  207 ). 
         [0114]    When the light-receiving sensor receives each transmitted light of the first light (Lλ 1 ) and the second light (Lλ 2 ) by time-sharing, an output signal of a size corresponding to the amount of received light is output each time light is received. In accordance with this output signal, “−log(1−ΔT)” is calculated (step  208 ). 
         [0115]    Next, in step  209 , whether or not “−log(1−ΔT)” is in the range of the analytical curve is determined. 
         [0116]    If “−log(1−ΔT)” is within the range of the analytical curve, the concentration of the targeted chemical component in the specimen  104  is derived on the basis of the analytical curve data (step  210 ). 
         [0117]    Next, in step  209 , whether or not “−log(1−ΔT)” is in the range of the analytical curve is determined. 
         [0118]    If “−log(1−ΔT)” is within the range of the analytical curve, the concentration of the targeted chemical component in the specimen  104  is derived on the basis of the analytical curve data (step  210 ). 
         [0119]      FIG. 4  is a timing chart for explaining a signal output timing of the example in  FIG. 3 . That is,  FIG. 4  is a timing chart showing the time responses of an output OUT 1  of the first light source  101   a , an output OUT 2  of the second light source  101   b , an output OUT 3  of the light-receiving sensor, an output OUT 4  of the differential signal, and a gas concentration GC. 
         [0120]    Here, “output of the light source” is the amount of light emitted during the period that the light is on (hereinafter “ON period”) and, when the light has high directivity, is substantially equivalent to the amount of light received by the light-receiving sensor. 
         [0121]    In the present invention, each light from the light sources  101   a ,  101   b  can be focused by the light-focusing optical portion  102  as illustrated in  FIGS. 7 to 9 , or a branch-type optical fiber  801  can be adopted as illustrated in  FIG. 10 , and thus as long as the light sources  101   a ,  101   b  are arranged by bringing an emitting surface of the light sources  101   a ,  101   b  near or in contact with an incident surface of the light-focusing optical portion  102  or an incident surface of the branch-type optical fiber  801 , it is possible to make the amount of light emitted during the ON period of each of the light sources  101   a ,  101   b  close to or substantially equivalent to the amount of light received by the light-receiving sensor. 
         [0122]    The gas concentration GC can, for example, be measured as a change in concentration of the target gas obtained by detecting an output signal (differential signal output OUT 4 ) at timings T 1  to T 4  illustrated in  FIG. 4  and deriving the value from the detected output signal value and the analytical curve acquired in advance. 
         [0123]      FIG. 4  illustrates a state of the gas concentration GC increasing in stages over time. 
         [0124]    When the output OUT 1  of the first light source and the output OUT 2  of the second light source are output on the same axis at mutually predetermined and repeated intervals at timings such as illustrated in  FIG. 4 , the gas to be measured does not exist before timing T 1 , and thus the output OUT 3  of the light-receiving sensor is output as pulses S 11 , S 21  having the same size. 
         [0125]    During the period between timings T 1  and T 2 , the period between timings T 2  and T 3 , and the period between the timings T 3  and T 4 , the pulses S 12 , S 22 , S 13 , S 23 , S 14 , S 24  are output. While the sizes of the pulses S 12 , S 13 , S 14  are the same as the size of the pulse S 11 , the sizes of the pulses S 22 , S 23 , S 24  decrease in stages in accordance with the level of light absorption of the gas to be measured. That is, because the light from the second light source is absorbed in the gas to be measured and the amount of light received by the light-receiving sensor gradually decreases in accordance with the gas concentration, the sizes of the pulses S 22 , S 23 , S 24  decrease in stages in accordance with the level of concentration of the gas to be measured. 
         [0126]      FIG. 5  explains an example of a method for acquiring an analytical curve in advance, prior to measurement of the gas concentration.  FIG. 5  is a flowchart for finding the analytical curve. 
         [0127]    To acquire the analytical curve, an analytical curve acquiring device is used. 
         [0128]    When acquisition of the analytical curve is started (step ST 1 ), whether or not an optical measuring cell has been prepared is determined in step ST 2 . 
         [0129]    Once the optical measuring cell has been prepared, the flow proceeds to step ST 3 . In step ST 3 , whether or not a predetermined carrier gas has been introduced into the cell interior in a predetermined unit amount is determined. 
         [0130]    When it is determined that the predetermined carrier gas has been introduced into the cell interior in a predetermined unit amount, the flow proceeds to step ST 4 . 
         [0131]    This step of determining whether or not the carrier gas has been introduced may be omitted, or the step may be changed to a step for determining if the cell interior has reached a predetermined degree of vacuum. This determination of whether the cell interior has reached a predetermined degree of vacuum may be omitted as well. 
         [0132]    In either case, the cell interior needs to be cleaned before proceeding to step ST 4  in order to acquire a more accurate analytical curve. 
         [0133]    In step ST 4 , a plurality of gases subject to concentration measurement is sequentially introduced into the cell, and the absorbance of the gas of each concentration is measured. 
         [0134]    Once measurement is completed, the flow proceeds to step ST 5 . 
         [0135]    In step ST 5 , the analytical curve is created on the bases of the absorbance measurement data. 
         [0136]      FIG. 6  illustrates an example of an analytical curve created in this way. 
         [0137]      FIG. 6  is a graph showing a relationship between the gas concentration GC and “−log(1−ΔT).” 
         [0138]    Once the analytical curve is created, the flow can transition to concentration measurement of the specimen. 
         [0139]    Next, a preferred embodiment according to the present invention illustrated in  FIGS. 7 to 10  will be described. In  FIGS. 7 to 10 , the same components as those in  FIG. 2  will be denoted using the same reference numerals. 
         [0140]      FIG. 7  is an explanatory schematic configuration view for explaining a main component  100   a  of a preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention.  FIG. 7  is an example of concentration measurement by transmitted light. 
         [0141]    In a main component  500 , the light source portion comprises the first light source  101   a  that emits the first light (Lλ 1 ) and the second light source  101   b  that emits the second light (Lλ 2 ). 
         [0142]    The first light (Lλ 1 ) emitted from the first light source  101   a  is focused on the optical axis by the light-focusing optical portion  102 , passed along the optical axis as an irradiated light  103   a , and irradiated onto the object  104  to be measured. The amount of the irradiated light  103   a  not absorbed in the object  104  to be measured exits the object  104  to be measured as a transmitted light  105   a.    
         [0143]    The transmitted light  105   a  enters the light-receiving surface of the light-receiving sensor portion  106 . 
         [0144]    When the transmitted light  105   a  is received by the light-receiving sensor portion  106 , the electric signal  107  photoelectrically converted in accordance with the amount of the transmitted light  105   a  is output from the light-receiving sensor portion  106 . 
         [0145]    The signal  107  output from the light-receiving sensor portion  106  is input to the differential signal forming portion  108  configured by a differential signal forming circuit. 
         [0146]    The second light (Lλ 2 ) emitted from the second light source  101   b  is passed along the optical axis as an irradiated light  103   b  and irradiated onto the object  104  to be measured in the same way as the first light (Lλ 1 ), and a transmitted light  105   b  exits the object  104  to be measured accordingly. 
         [0147]    In the case of the second light (Lλ 2 ), the light is either not absorbed in the object  104  to be measured, or absorbed with a low absorbability compared to the first light (Lλ 1 ). Thus, the amounts of the irradiated light  103   b  and the transmitted light  105   b  are either the same or substantially the same, or the difference thereof is less than the difference between the irradiated light  103   a  and the transmitted light  105   a.    
         [0148]      FIG. 8  is an explanatory schematic configuration view for explaining main components of another preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. Except for the fact that  FIG. 8  is an example of measurement by reflected light while  FIG. 7  is an example of measurement by transmitted light, the example in  FIG. 8  is the same as that in  FIG. 7 , and thus a detailed description thereof will be omitted. 
         [0149]      FIG. 9  is an explanatory schematic configuration view for explaining main components of yet another preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. 
         [0150]    Except for the fact that  FIG. 9  is an example of measurement by scattered light while  FIG. 7  is an example of measurement by transmitted light, the example in  FIG. 9  is the same as that in  FIG. 7 , and thus a detailed description thereof will be omitted. 
         [0151]      FIG. 10  is an explanatory schematic configuration view for explaining a main component of yet another preferred embodiment of the optical concentration measuring system that embodies the concentration measuring method of the present invention. Except for the fact that  FIG. 10  adopts a branch-type optical fiber  801  for the light-focusing optical portion  102  in the example in  FIG. 7 , the example in  FIG. 10  is the same as that in  FIG. 7 , and thus a detailed description thereof will be omitted. 
         [0152]      FIG. 11  illustrates a circuit diagram for explaining a preferred example of the differential signal forming portion adopted in the present invention. 
         [0153]    A differential signal forming portion  900  comprises a (charge) integrating amplifier  902 , a sample/hold circuit  903 , and a differential amplifier  904 . 
         [0154]    When the transmitted light, reflected light, or scattered light produced upon irradiation of light having a predetermined wavelength for concentration measurement onto the object  104  to be measured subject to concentration measurement, such as a fruit or a vegetable, is received by a photodiode  901  for light reception, an electric signal P 1  corresponding to the amount of received light is output from the photodiode  901 . The electric signal P 1  is input to the integrating amplifier  902 . The integrating amplifier  902  is provided for sensitivity enhancement so as to allow measurement down to subtle changes in gas concentration of the specimen  107 . 
         [0155]    The output signal of the integrating amplifier  902  is input to the sample/hold circuit  903 . A sampled/held analog signal is input to the differential amplifier  904 . 
       Gas Concentration Measurement Example Embodying Present Invention 
       [0156]    Next, an example that embodies the present invention will be described using a gas concentration measurement example. 
         [0157]    A preferred embodiment of the concentration measuring method for measuring concentration by using a plurality of lights having different wavelengths and irradiating the plurality of lights by time-sharing will now be described. 
         [0158]    In the following, a preferred embodiment of a gas concentration measurement example that uses transmitted light for measurement will be primarily described. 
         [0159]    Cases where reflected light or scattered light is used for measurement rather than transmitted light, needless to say, also fall into the category of the present invention, and are naturally within the technical field. 
         [0160]    Further, the embodiment described below, needless to say, can be easily developed even in a case where the concentration of a solution or the sugar content of a fruit or a vegetable is measured rather than the concentration of a gas. 
         [0161]    To embody the present invention as a gas concentration measuring device, the measuring device may comprise a regular light source, a light-receiving photodiode, electronic circuit components, and the like that are easily acquirable, based on a premise of compatibility with the measurement target, and thus in the following descriptions matters obvious to persons skilled in the art will be omitted and main points will be simplified. 
         [0162]    The specimen (object to be measured) is, for example, a gas that flows through a gas pipe. 
         [0163]    The gas pipe is provided with an incident surface into which light (a measured light hλ) used for measurement enters, and an exiting surface from which light, having passed through the gas pipe, exits to the outside. 
         [0164]    The incident surface and the exiting surface are made of a material having a transmittance of “1” or substantially “1” with respect to the measured light h. 
         [0165]    Regardless of whether the gas that flows through the gas pipe is a single type or a plurality of types of mixtures, the measuring device can measure the concentration of the target gas. In the following, the case of the single type is described using trimethylgallium (TMGa), for example, as the gas serving as the specimen. 
         [0166]    Other examples of the specimen gas type include trimethylindium (TMIn) and titanium tetrachloride (TiCl4). 
         [0167]    In the gas concentration measurement of trimethylgallium (TMGa), an LED that emits light (Lλ 1 ) having a center light wavelength of 500 nm is adopted as the first light source  101   a , for example, and the light intensity thereof is 1.0 mW/cm 2 /nm. 
         [0168]    An LED that emits light (Lλ 2 ) having a center light wavelength of 230 nm is adopted as the second light source  101   b , and the light intensity thereof is 1.0 mW/cm 2 /nm. 
         [0169]    In the present invention, the light (Lλ 1 )  103   a  emitted from the first light source  101   a  and the light (Lλ 2 )  103   b  emitted from the second light source  101   b  are transmitted through the specimen  104  at separate times (by time-sharing), and enter the light-receiving sensor of the light-receiving sensor portion  106 . As the light-receiving sensor, a photodiode (S336-18BQ) manufactured by Hamamatsu Photonics K.K, for example, may be used. The received light sensitivity of the light-receiving sensor in this case is 0.26 A/W at a light wavelength of 500 nm, and 0.13 A/W at a light wavelength of 230 mm. 
         [0170]    The output signal  107  of the light-receiving sensor portion  106  is input to the differential signal forming circuit  108 , and the output signal  109  is output from the differential signal forming circuit  108  accordingly. 
         [0171]    A light source that emits light having an absorbance that changes depending on the concentration of the gas of the specimen  104 , and a light source that emits light having an absorbance that does not or substantially does not change depending on the concentration of the gas of the specimen  104  are adopted as the first light source  101   a  and the second light source  101   b , respectively. 
         [0172]    While the above gas concentration measurement example has been described using the configuration in  FIG. 7  that measures transmitted light, naturally the measurement can be applied to the configuration in  FIG. 8  that uses a reflected light and to the configuration in  FIG. 9  that uses a scattered light without having to particularly re-describe the details. 
         [0173]    Further, while an optical path of the first light source  101   a  and an optical path of the second light source  101   b  differ in the object  104  to be measured if the light-focusing optical portion  102  does not exist in the configuration illustrated in  FIG. 7 , preferably the first light source  101   a  and the second light source  101   b  are arranged as close to each other as possible so as to bring the optical paths as close to the same optical path as possible. 
         [0174]    Or, the optical paths can be made substantially identical when the branch-type optical fiber  801  is adopted as illustrated in  FIG. 10  in place of the light-focusing optical portion  102 , and thus adoption of the branch-type optical fiber  801  is preferred. 
         [0175]      FIG. 11  is a configuration diagram for explaining a configuration of a preferred example of the differential signal forming circuit. 
         [0176]    The differential signal forming circuit  900  illustrated in  FIG. 11  is provided with the (charge) integrating amplifier  902  to increase sensitivity so that subtle changes in the gas concentration of the specimen  107  can be measured. 
         [0177]    The output signal of the (charge) integrating amplifier  902  is input to the sample/hold circuit  903 . 
         [0178]    A sampled/held analog signal is input to an analog-digital converter (ADC)  1301 . 
         [0179]    An optical signal based on the first light source, an optical signal based on the second light source, and a differential signal between these two signals are output from the ADC  1301 . 
         [0180]      FIG. 4  is a timing chart showing the time responses of the output OUT 1  of the first light source  101   a , the output OUT 2  of the second light source  101   b , the output OUT 3  of the light-receiving sensor, the output OUT 4  of the differential signal, and the gas concentration GC, and this is as previously described. 
         [0181]    Here, “output of the light source” is the amount of light emitted during the ON period and, when the light has high directivity, is substantially equivalent to the amount of light received by the light-receiving sensor. 
         [0182]    In the present invention, the light from the light sources  101   a ,  101   b  can be focused by the light-focusing optical portion  102  as illustrated in  FIGS. 7 to 9 , or the branch-type optical fiber  801  can be adopted as illustrated in  FIG. 10 , and thus as long as the light sources  101   a ,  101   b  are arranged by bringing the emitting surface of the light sources  101   a ,  101   b  near or in contact with the incident surface of the light-focusing optical portion  102  or the incident surface of the branch-type optical fiber  801 , it is possible to make the amount of light emitted during the ON period of the light sources  101   a ,  101   b  close to or substantially equivalent to the amount of light received by the light-receiving sensor. 
         [0183]    In general, absorbance is given based on the following formula: 
         [0000]      [Formula 1] 
         [0000]      −log( I/I   c )=−log(1−Δ T )=α K    (1)
 
         [0184]    Here, “I 0 ” indicates the intensity of the incident light, “I” indicates the intensity of the transmitted light, and “K” indicates the gas concentration. α is a coefficient and is determined by an optical path length in the specimen  104 , a light absorption coefficient of the gas subject to concentration measurement in the specimen  104 , and the like. 
         [0185]    Further, “ΔT” indicates the absorbance difference. In this embodiment, the optical path lengths are set so that a is substantially 0 for the first light source  101   a , and 2.18×10-4/ppm for the second light source  101   b . Given “I 1 ” as the intensity of the transmitted light of the light (Lλ 1 ) emitted from the first light source  101   a  and “I 2 ” as the intensity of the transmitted light of the light (Lλ 2 ) emitted from the second light source  101   b , formula (1) can be modified to formula (2) when I 1  uses the fact that the transmittance difference with respect to the optical wavelength of the first light source, regardless of gas concentration, is substantially 0. 
         [0000]    
       
         
           
             
               
                 
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         [0186]    Here, “X” is the output value of the differential signal, and is equivalent to “I 2 −I 1 .” 
         [0187]    According to this formula, the absorbance of the specimen  104  can be measured with high accuracy using the output OUT 1  of the first light source  101   a  having an absorptivity that changes in accordance with the gas concentration, and the output OUT 2  of the second light source  101   b  having an absorptivity that does not change in accordance with the gas concentration. 
         [0188]    Thus, there is no need to measure gas concentrations to create an analytical curve for each measurement using known reference samples. 
         [0189]    A gas densitometer can measure changes in absorptivity in a stable manner, even if there are changes in the measurement system, gas temperature, or the like. 
         [0190]    Setup is performed so that an integrated charge (1) of the integrating amplifier  902  based on the first light source  101   a  and the integrating charge (2) of the integrating amplifier  902  based on the second light source  101   b  when the gas concentration is “0” are equal or substantially equal. 
         [0191]    Here, in this embodiment, an integration period (1) during output of the first light source  101   a  and an integration period (2) during output of the second light source  101   b  were adjusted so that the charges were 6.1×10−9 C. 
         [0192]    The integration period (1) and the integration period (2) of this embodiment were set to 4.0 msec and 2.0 msec, respectively. 
         [0193]      FIG. 15  shows a relationship between an absorbance value measured with respect to a gas concentration and a value equivalent to three times a standard deviation of a noise superimposed on the measured signal at this time. 
         [0194]    Further, when measurement was made using this charge, the main noise component was confirmed as photon shot noise. 
         [0195]    Based on the results, when the charge value is 6.1×10-9 C, the effect of the photon shot noise proportional to the square root of the signal charge became relatively small, making it possible to measure an absorbance difference ΔT up to 5×10-5 with 99% reliability. That is, the gas concentration could be measured to an accuracy of 0.1 ppm. 
         [0196]    Further, according to the embodiment of the present invention, output is obtained from a difference between signals based on two lights having different wavelengths, even if the temperature changes, making it possible to cancel an amount of fluctuation in a transmittance that changes according to temperature. Thus, even if there is temperature fluctuation during measurement, stable sensitivity can be achieved with high accuracy. 
         [0197]    In the present invention, a communication module for short-range communication, such as WiFi, Bluetooth (registered trademark), or Near Field Communications (NFC), or a communication module for satellite communication is incorporated in the concentration measuring device that embodies the present invention, making it possible to make the concentration measuring device function as an information terminal device on a network. For example, a patient in a hospital can measure his or her blood sugar level in the hospital bed using a non-invasive type of concentration measuring device according to the present invention when it is time for measurement or when instructed by the nurse station, and send the measurement data as is to the nurse station. This makes it possible to alleviate the labor burden of a nurse in terms of making hospital room visits for each patient and taking measurements. 
         [0198]    Furthermore, while, for example, a person at risk for diabetes, a person with a low or high blood sugar level being observed and treated at home, or the like may experience an abnormality in blood sugar level while driving a vehicle, become light-headed, no longer be able to drive or find it difficult to drive normally, and cause an accident, such a person can wear a non-invasive type concentration measuring device that comprises a communication function according to the present invention and have the device perform measurements while he or she is driving. In such a case, the device can detect an abnormality in blood sugar level, immediately send the signal indicating abnormality detection to the vehicle that the person is driving, and automatically stop the vehicle in a prompt manner or automatically guide the vehicle to a safe area such as the side of the road and stop the vehicle. Moreover, carried insulin can then be administered and recovery to normalcy achieved. 
         [0199]    Further, the data of the abnormal detection can be automatically sent along with necessary personal data of the driver to a family doctor or nearby hospital to request emergency instructions from the hospital. 
         [0200]    While  FIG. 11  illustrates a preferred example of the differential signal forming circuit in the realization of the present invention, the present invention is not limited thereto, allowing adoption of the differential signal forming circuits illustrated in  FIGS. 12 to 14  as preferred examples as well. 
         [0201]    In  FIGS. 12 to 14 , components that fulfill the same functions as those denoted with the reference numerals in  FIG. 11  are denoted using the same reference numerals as  FIG. 11 . 
         [0202]    The configuration illustrated in  FIG. 12  is the same as that in  FIG. 11  except that, in addition to a circuit for a differential signal output  905 , a circuit for a pre-differential signal output  1001  has been added. 
         [0203]    With the addition of the circuit for the pre-differential signal output  1001 , there is the advantage that, compared to the configuration illustrated in  FIG. 11 , even if fluctuation occurs in the absolute value of absorbance due to temperature change or the like, or temporal fluctuation occurs in the light output of the light source, the amount of these fluctuations can be measured and calibrated. 
         [0204]    In the configuration illustrated in  FIG. 13 , two systems for signal transmission (sample/hold circuits  903   a ,  903   b →differential amplifiers  904   a ,  904   b ) and the ADC  1301  are further provided compared to the configuration illustrated in  FIG. 12 . 
         [0205]    This configuration results in the advantage of being able to eliminate the offset of the integrating amplifier compared to that in  FIG. 12 . 
         [0206]      FIG. 14  is an example of a circuit designed in more detail than the example in  FIG. 13 . 
         [0207]    In  FIG. 14 , an integrating (accumulation) amplifier portion  1401 , which is similar to the integrating amplifier  902 , and a 1/10× amplifier portion  1402  are provided. In addition, the differential amplifier portions  904   a ,  904   b  are each provided with two instrumentation amplifiers for differential output. 
         [0208]    Such a configuration results in the advantage of being able to eliminate the offset of the differential amplifiers. 
         [0209]    Next, an embodiment of a preferred example of an electronic device comprising the concentration measuring function according to the present invention will be described. 
         [0210]      FIGS. 16 and 17  are outline configuration views illustrating an embodiment when the present invention is applied to a mobile terminal device. 
         [0211]      FIG. 16  is an outline external view, and  FIG. 17  is a block diagram of the internal configuration. 
         [0212]    A mobile terminal device  1701  illustrated in  FIGS. 16 and 17  comprises a global positioning system (GPS) positioning portion  1703 , a calculation processing portion  1704 , a storage device  1705 , and a display unit  1706 . 
         [0213]    When the device does not require GPS positioning, the GPS positioning portion  1703  is omitted. 
         [0214]    Further, the device may comprise the GPS positioning portion  1703 , and an acceleration sensor  1708  and an angular velocity sensor  1709  may be omitted. 
         [0215]    Examples of the mobile terminal device  1701  include a mobile electronic device such as a mobile telephone device having a navigation function, a personal digital assistant (PDA), a tablet, or a mobile PC, a wristwatch, and a wearable article such as a scouter, a necklace, a ring, or a bracelet having an electronic device function. 
         [0216]    Examples of the mobile terminal device  1701  further include a mobile barometer or altimeter for mountain climbing, and a stopwatch. 
         [0217]    The mobile terminal device  1701  is capable of intercommunicating with a device equipped with a transceiver function such as a transceiver base, a transceiver satellite, a NAVI system mounted to a vehicle, a handheld NAVI device, a transceiver connected to a private network system, or other mobile terminal device. 
         [0218]    Description is given in the following using the example of a transceiver satellite  1702  as an example of a device equipped with a transceiver function. 
         [0219]    The GPS positioning portion  1703  functions as a first current position calculating portion that receives a position information signal sent from the transceiver satellite  1702  and identifies a current position. 
         [0220]    The calculation processing portion  1704  receives detection signals of the vertical acceleration sensor  1708  that detects a number of steps and the angular velocity sensor  1709  that detects a direction, autonomously identifies the current position based on these, and executes navigation processing. The calculation processing portion  1704  comprises a microcomputer, a central processing unit (CPU), and the like. 
         [0221]    The storage device  1705  comprises a ROM  1705   a  that stores a processing program executed by the calculation processing portion  1704  and stores a storage table required in calculation processing, a RAM  1705   b  that stores calculation results and the like required in calculation processing, and a non-volatile memory  1705   c  that stores the current position information when navigation processing ends. 
         [0222]    The display unit  1706  displays navigation image information output from the calculation processing portion  1704 , and comprises a liquid crystal display unit, an organic EL display unit, or the like. 
         [0223]    A clock portion  1707  displays a year, month, day, and time corrected using the current time information that indicates the year, month, day, and time output from the GPS positioning portion  1703  when the GPS positioning portion  1703  is activated. 
         [0224]    The calculation processing portion  1704  receives the current position information output from the GPS positioning portion  1703 , the current time information that indicates the year, month, day, and time output from the clock portion  1707 , the acceleration information output from the acceleration sensor  1708  mounted on a hip position of the user that retains the mobile terminal device  1701 , the angular velocity information corresponding to the direction of the walking by the user and output from the angular velocity sensor  1709 , such as a gyroscope, mounted to the mobile terminal device  1701 , and concentration measurement information from a concentration measuring portion  1701  according to the present invention. 
         [0225]    The concentration measuring portion  1710  comprises the optical concentration measuring system illustrated in  FIGS. 7 to 10  or an optical concentration measuring device comprising the same functions as the system, and may be detachably mounted to the mobile terminal device  1701  main body or integrally configured with the main body. 
         [0226]    When the concentration measuring portion  1710  is detachably mounted to the main body, the concentration measuring portion  1710  can be removed from the main body at the time of measurement and, for example, brought into contact with the body of a person, allowing measurement of the sugar level in the blood, for example. 
         [0227]    The concentration measuring portion  1710  and the main body are both provided with a communication module for short-range communication, such as Wifi, Bluetooth (registered trademark), or NFC, making it possible to perform communication between the concentration measuring portion  1710  and the main body even when the concentration measuring portion  1710  is removed from the main body. 
         [0228]    According to the mobile terminal device  1710 , concentration measurement data, position information data, and specific individual data stored in the storage device  1705  can be sent to a transmission destination. For example, when an abnormality arises in the blood sugar level of a person while driving a vehicle, a signal indicating the abnormality is sent to the vehicle, causing the vehicle to automatically stop and, at the same time, the concentration measurement data, the position information data, and specific individual data is sent to a family doctor or a hospital in which the family doctor is located, making it possible to request instructions for appropriate treatment from the doctor and, in some cases, promptly dispatch an emergency vehicle. 
         [0229]    A communication portion  1711  that performs wireless communication with an external wireless communication device is connected to the calculation processing portion  1704 . 
         [0230]    The ROM  1705   a  stores a storage table of position information by region. 
         [0231]    Additionally, the ROM  1705   a  stores an autonomous positioning calculation program for performing autonomous positioning calculations, and a calculation portion selection processing program for selecting either current position information calculated by the GPS positioning portion  1703  or current position information calculated by the autonomous positioning calculation processing performed by the autonomous positioning program. 
         [0232]    The storage table of position information by region charts the names of prefectures across the country, the seat names of governments of each prefecture, and the latitude (N) and the longitude (E) of each seat of government. 
         [0233]    The calculation processing portion  1704  executes the autonomous positioning calculation processing in accordance with the autonomous positioning calculation program that performs autonomous positioning calculations. 
         [0234]    This autonomous positioning calculation processing is started when autonomous calculation processing is selected by the calculation portion selection processing and, once the previous current position identified by the GPS positioning portion  1703  is set as the initial position in the initial state, is executed as timer interrupt processing every predetermined time period (10 msec, for example) with respect to a predetermined main program. 
         [0235]    That is, first the autonomous positioning calculation processing reads an angular velocity θv detected by the angular velocity sensor  1709 , then integrates the angular velocity θv, calculates the direction θ, and transitions to the next step. 
         [0236]    In the next step, the autonomous positioning calculation processing reads a vertical acceleration G detected by the acceleration sensor  1708 , calculates a number of steps P from a change pattern of the vertical acceleration G, multiplies a pace width W set in advance by the calculated number of steps P to calculate a moved distance L, updates the current position information on the basis of the calculated direction θ and the moved distance L, displays the updated current position information on the display unit  1706  over map information, ends the timer interrupt processing, and returns to the predetermined main program. 
         [0237]    Furthermore, the calculation processing portion  1704  executes calculation portion selection processing that selects either the current position information identified by the GPS positioning portion  1703  in accordance with the calculation portion selection processing program or the current position information identified by the autonomous positioning calculation processing. 
         [0238]    According to this calculation portion selection processing, execution is started when the navigation processing is selected on the mobile terminal device  1701  after power ON. 
         [0239]    Examples of the mobile terminal device  1701  include a mobile electronic device such as a mobile telephone device having a navigation function, a personal digital assistant (PDA), a tablet, or a mobile PC, a wristwatch, and a wearable article such as a scouter, a necklace, a ring, or a bracelet having an electronic device function. 
         [0240]    While in the examples heretofore formation of the differential signal has been exemplified by formation via an electric circuit (hardware) such as a differential circuit and a differential amplification circuit, the present invention is not limited thereto, allowing formation using software of digital calculation processing. 
         [0241]    An example of a preferred embodiment will be described using  FIG. 18 . 
         [0242]    The embodiment illustrated in  FIG. 18  comprises a differential signal forming portion  1800  and a light-receiving sensor portion  1801 . 
         [0243]    The differential signal forming portion  1800  comprises an integrated circuit portion  1802 , an analog-digital converting (A/D converting) portion (ADC)  1803 , and a differential signal forming element portion  1804 . 
         [0244]    The light-receiving sensor portion  1801  is provided with a photodiode  1805  as a light-receiving sensor for measurement. The integrated circuit portion  1802  is provided with an operational amplifier  1806 , a capacitor C 1 , and a switch SW 1 . 
         [0245]    While the example of the differential signal forming portion  900  illustrated in  FIG. 11  forms the differential signal  905  using an analog signal, a differential signal  1809  in the example illustrated in  FIG. 18  is formed by performing digital calculation processing after analog-digital conversion (A/D conversion) of a signal  1807  output from the integrated circuit portion  1802 . 
         [0246]    An output terminal of the photodiode  1805  is electrically connected with an inverting input pin of the operational amplifier  1806 . 
         [0247]    The non-inverting pin of the operational amplifier  1806  is grounded. 
         [0248]    Between the integrated circuit portion  1802  and the ADC  1803 , a switch SW 2  is provided as necessary and a signal transmission path is formed. The signal transmission path can be formed by electrically connecting the area between the integrated circuit portion  1802  and the ADC  1803 . 
         [0249]    When two lights (a first light and a second light) differing in wavelength or wavelength band are sequentially irradiated by time-sharing onto an object (specimen) to be measured, the first light and the second light that pass through the object to be measured are sequentially received by the photodiode  1805  by time-sharing in accordance with the irradiation. 
         [0250]    When the photodiode  1805  receives the light, an optical charge is produced, and the optical charge is accumulated in the capacitor C 1 . A signal  1807  of a voltage of a size corresponding to this accumulated charge is output from the integrated circuit portion  1802  when the switch SW 2  is turned ON. The signal  1807  is input to the analog-digital conversion means (ADC)  1803 , converted into a digital signal, and output from the ADC  1803  as a signal  1808 . The digitized signal  1808  is input to the differential signal forming element portion  1804 . 
         [0251]    Either a signal  1808   a  corresponding to the first light or a signal  1808   b  corresponding to a second light, whichever is input first, is temporarily saved in the differential signal forming element portion  1804  interior at least until the signal to be subsequently input is input. 
         [0252]    When the signals  1808   a ,  1808   b  respectively corresponding to the first light and the second light to be measured are sequentially input to the differential signal forming element portion  1804 , differential signal formation processing is implemented in the differential signal forming element portion  1804  on the basis of these signals  1808   a ,  1808   b , and the differential signal  1809  is output from the differential signal forming element portion  1804 . 
         [0253]    As described above, the concentration measuring method of the present invention has universality, i.e., the ability to be embodied in various forms and modes. 
       DESCRIPTIONS OF REFERENCE NUMERALS 
       [0000]    
       
           100  Optical concentration measuring system 
           100 - 1  Optical concentration measuring sub-system 
           100 - 2  Control/Operation sub-system 
           100 - 3  Optical concentration measuring device 
           101  Light source portion 
           101   a ,  101   b  Light source 
           102  Light-focusing optical portion 
           103 ,  103   a ,  103   b  Irradiated light 
           104  Object to be measured 
           105 ,  105   a ,  105   b  Transmitted light 
           106  Light-receiving sensor portion 
           107 ,  107   a ,  107   b  Electric signal 
           108  Differential signal forming portion 
           109  Differential output signal 
           110  Signal storage/processing portion 
           111  Output signal 
           112  Display unit 
           113  Control unit 
           114  Operation portion 
           201  to  211  Step 
           500 ,  600 ,  700 ,  800  Optical gas concentration measuring system 
           801  Branch-type optical fiber 
           801   a ,  801   b  Branch optical path 
           802   a ,  802   b  Irradiated light 
           900 ,  1000 ,  1300 ,  1400  Differential signal forming portion (circuit configuration) 
           901  Photodiode 
           902  Integrating amplifier 
           903 ,  903   a ,  903   b  Sample/Hold circuit 
           940 ,  904   a ,  904   b  Differential amplifier 
           905  Differential signal output 
           906  Pre-differential signal output 
           1101  Differential signal forming element portion 
           1301  ADC 
           1302  Signal output 
           1401  Integrating amplifier portion 
           1402  1/10× integrating amplifier portion 
           1701  Mobile terminal device 
           1703  GPS positioning portion 
           1704  Calculation processing portion 
           1705  Storage device 
           1706  Display unit 
           1708  Acceleration sensor 
           1709  Angular velocity sensor 
           1800  Differential signal forming portion 
           1801  Light-receiving sensor portion 
           1802  Integrated circuit portion 
           1803  Digital-analog converting portion 
           1804  Differential signal forming element portion 
           1805  Photodiode 
           1806  Operational amplifier 
           1807 ,  1808  Signal 
           1809  Differential signal 
         Lλ 1  Light having a first wavelength 
         Lλ 2  Light having a second wavelength