Abstract:
The concentration of a liquid in a liquid supply tube, which is supplied with the liquid, is stably measured from the outside of the liquid supply tube. A liquid component concentration meter is provided with a liquid supply tube ( 14, 16 ) adapted to be supplied with a liquid; a light transmission unit ( 15 ) provided midway through the liquid supply tube ( 14, 16 ); a light emission unit ( 9, 22 ) for irradiating measurement light to the light transmission unit ( 15 ); a light reception unit ( 10, 23 ) for receiving measurement light passed through the light transmission unit ( 15 ); a support member ( 31 ) adapted to movably support the light emission unit ( 9, 22 ) and the light reception unit ( 10, 23 ) in such a way that a measurement position ( 32 ) is moved along the light transmission unit ( 15 ), wherein the measurement position ( 32 ) is a position at which light is irradiated to the light transmission unit ( 15 ) and, also, is a position at which the light passed through the light transmission unit ( 15 ) is received by the light reception unit ( 23 ); a measurement-position moving mechanism ( 2 ) for moving the support member ( 31 ) in such a way that the measurement position ( 32 ) is moved within a predetermined area in the light transmission unit ( 15 ); and a data processing unit adapted to acquire data of intensities of light received by the light reception unit ( 10, 23 ) at a plurality of measurement positions ( 32 ) and to calculate the concentration of the liquid flowing through the liquid supply tube ( 14, 16 ), based on the plural intensities of received light.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to liquid component concentration meters and, more particularly, relates to liquid component concentration meters including a light emission unit for irradiating light to a light transmission unit provided in a liquid supply tube, which is supplied with a liquid, a light reception unit for receiving light passed through the light transmission unit, and a data processing unit for calculating the concentration of the liquid based on the intensity of the light received by the light reception unit. 
         [0003]    2. Description of the Related Art 
         [0004]    As techniques for measuring the concentration of liquid in a tube, which is supplied with the liquid, there have been known liquid component concentration meters for optically measuring the concentration of liquid (refer to Patent Documents 1 and 2, for example). These liquid component concentration meters are generally inserted in tubes at their light transmission units made of glass, which are called “cells”. This is because, if measurements are performed directly on the liquids in the tubes, this will induce the problem of variations of the shapes of the tubes. Further, the tubes themselves may constitute the light transmission units, in some cases. 
         [0005]    Patent Document 1: Japanese Unexamined Patent Application, Publication No. 11-14538 
         [0006]    Patent Document 2: Publication of Japanese Patent No. 3290982 
         [0007]    In cases of measuring the concentration of a liquid within a cell or a tube by irradiating and receiving light to and from the cell or the tube, with a liquid component concentration meter, there are the followings. 
         [0008]    1) Measurement errors due to contaminations of the cell or the tube. 
         [0009]    2) Measurement errors due to air bubbles adhered to the inside of the cell or the tube. 
         [0010]    3) Measurement errors due to variations of the shape of the tube. 
         [0011]    Regarding the liquid component concentration meter disclosed in Patent Document 1, in order to avoid the problem of adhesion of air bubbles to the inside of the cell, cells with complicated shapes are suggested. 
       SUMMARY OF THE INVENTION 
       [0012]    However, any of the aspects of the liquid component concentration meter disclosed in Patent Document 1 can not provide complete effects and can not avoid measurement errors due to adhesion of air bubbles. Further, provision of a spherical-shaped member or a resistance unit in the cell will induce contaminations from the material thereof or an increase of the pipe resistance, which violates improvement of the pipe quality. 
         [0013]    Therefore, the present invention aims at providing a liquid component concentration meter capable of stably measuring the concentration of a liquid in a liquid supply tube, which is supplied with the liquid, from the outside of the liquid supply tube. 
         [0014]    A liquid component concentration meter according to the present invention includes a liquid supply tube adapted to be supplied with a liquid; a light transmission unit provided midway through the liquid supply tube; a light emission unit for irradiating measurement light to the light transmission unit; a light reception unit for receiving measurement light passed through the light transmission unit; a support member adapted to movably support the light emission unit and the light reception unit in such a way that a measurement position is moved along the light transmission unit, wherein the measurement position is a position at which light is irradiated to the light transmission unit and, also, is a position at which the light passed through the light transmission unit is received by the light reception unit; a measurement-position moving mechanism for moving the support member in such a way that the measurement position is moved within a predetermined area in the light transmission unit; and a data processing unit adapted to acquire data of intensities of light received by the light reception unit at a plurality of the measurement positions and to calculate the concentration of the liquid flowing through the liquid supply tube, based on the plural data of light intensities. 
         [0015]    In the liquid component concentration meter according to the present invention, there may be a case where the support member includes a contact unit adapted to move while contacting with a surface of the light transmission unit. 
         [0016]    A liquid component concentration meter according to another aspect of the present invention includes a liquid supply tube adapted to be supplied with a liquid; a light transmission unit provided midway through the liquid supply tube; a light emission unit for irradiating measurement light to the light transmission unit; a light reception unit for receiving measurement light passed through the light transmission unit; a support member adapted to movably support the light emission unit and the light reception unit in such a way that a measurement position is moved along the light transmission unit, wherein the measurement position is a position at which light is irradiated to the light transmission unit and, also, is a position at which the light passed through the light transmission unit is received by the light reception unit; a measurement-position moving mechanism for moving the support member in such a way that the measurement position is moved within a predetermined area in the light transmission unit; and a data processing unit adapted to acquire data of intensity of light received by the light reception unit and to calculate the concentration of the liquid flowing through the liquid supply tube, based on the data of the light intensity, wherein the support member includes a contact unit adapted to move while contacting with a surface of the light transmission unit. 
         [0017]    In the liquid component concentration meter according to the present invention according to the aspect where the support member includes the contact unit, in cases where the light transmission unit is of a tube type, the contact unit may be constituted by a cylinder unit adapted to surround a periphery of the light transmission unit and to move in parallel with a tube axis of the light transmission unit. 
         [0018]    Further, the contact unit may be made of a fluorine-based resin. 
         [0019]    In the liquid component concentration meter according to the present invention, the data processing unit may be adapted to acquire data of intensities of light received intermittently by the light reception unit while the measurement-position moving mechanism moves the measurement position. 
         [0020]    Further, in the liquid component concentration meter according to the present invention, the measurement-position moving mechanism may be adapted to move the measurement position in a direction along an axis perpendicular to the light irradiation axis for the light transmission unit. 
         [0021]    Further, in cases where the light transmission unit is of a tube type, the measurement-position moving mechanism may be either adapted to move the measurement position in a direction along a tube axis of the light transmission unit or adapted to move the measurement position in such a direction as to rotate it about the tube axis of the light transmission unit. 
         [0022]    Further, in the liquid component concentration meter according to the present invention, the data processing unit may be adapted to eliminate data of abnormal light intensities which exceed a predetermined certain range, from the data of light intensities at a plurality of the measurement positions. 
         [0023]    In this case, such abnormal light intensity data may include light intensity data different from normal light intensity data by 1% or more. Light intensity data different from normal light intensity data by 1% or more is apparently considered to be measurement errors caused by contaminations, adhesion of air bubbles and the like. Further, in cases where the liquid concentration to be determined is stable and, also, the light transmission unit has a stabilized shape, it is also possible to set a more strict condition than the aforementioned condition of 1% or more. For example, light intensity data different from normal light intensity data by 0.1% or more can be determined to be abnormal light intensity data. The condition for measurement can be determined by measuring a variance value or a standard deviation through statistics about variations of series of past determined data, and then, multiplying it by a coefficient. 
         [0024]    Further, the data processing unit may be adapted to average the light intensity data at a plurality of measurement positions or liquid concentration data determined through calculation based on the light intensity data. 
         [0025]    Further, in the liquid component concentration meter according to the present invention, the measurement-position moving mechanism may be constituted by a pneumatic actuator. However, the measurement-position moving mechanism is not limited to a pneumatic actuator and can be formed by other mechanical structures. Other examples of the measurement-position moving mechanism include a slider incorporating a stepper motor. 
         [0026]    As an example of a pneumatic actuator, the measurement-position moving mechanism may include a space for housing a unit or entirety of the support member and, further, include two air-driving pipes connected to the space with the support member sandwiched therebetween, and the measurement-position moving mechanism may be adapted to repeatedly perform an operation for supplying air into the space through one of the air-driving pipes while ejecting air from the space through the other one of the air-driving pipes and an operation opposite to the former operation for moving a unit or entirety of the support member within the space for moving the measurement position. 
         [0027]    Further, in the liquid component concentration meter according to the present invention, the light emission unit may include a light-emission-side optical fiber having one end face provided near the light transmission unit, the light reception unit may include a light-reception-side optical fiber having one end face provided at the light transmission unit, and the measurement-position moving mechanism may be adapted to move the one end face of the light-emission-side optical fiber and the one end face of the light-reception-side optical fiber with respect to the light transmission unit for moving the measurement position. 
         [0028]    Further, in the liquid component concentration meter according to the present invention, the light transmission unit may be of a tube type, and the light irradiation axis for the light transmission unit may intersect with the tube axis of the light transmission unit. 
         [0029]    A liquid component concentration meter according to the present invention includes a liquid supply tube adapted to be supplied with a liquid; a light transmission unit provided midway through the liquid supply tube; a light emission unit for irradiating measurement light to the light transmission unit; a light reception unit for receiving measurement light passed through the light transmission unit; a support member adapted to movably support the light emission unit and the light reception unit in such a way that a measurement position is moved along the light transmission unit, wherein the measurement position is a position at which light is irradiated to the light transmission unit and, also, is a position at which the light passed through the light transmission unit is received by the light reception unit; a measurement-position moving mechanism for moving the support member in such a way that the measurement position is moved within a predetermined area in the light transmission unit; and a data processing unit adapted to acquire data of intensities of light received by the light reception unit at a plurality of the measurement positions and to calculate the concentration of the liquid flowing through the liquid supply tube, based on the plural data of light intensities. 
         [0030]    With the liquid component concentration meter according to the present invention, it is possible to move the measurement position within a predetermined range in the light transmission unit, which enables measurement based on light intensity data at a measurement position where no contamination and no air bubble is adhered, thereby enabling stable measurement of the liquid concentration. 
         [0031]    Further, since the data processing unit is adapted to acquire data of intensities of light received by the light reception unit at a plurality of measurement positions, it is possible to identify abnormal data caused by adhesion of contaminations and air bubbles, based on the measurement positions and based on the intensities of light received by the light reception unit, even when contaminations and air bubbles are adhered to a unit of the light transmission unit. Further, by eliminating such abnormal data, it is possible to perform stable liquid-concentration measurement which involves less errors. 
         [0032]    In another aspect of the liquid component concentration meter according to the present invention, the support member includes the contact unit adapted to move while contacting with the surface of the light transmission unit. According to this aspect, the contact unit moves while contacting with the surface of the light transmission unit, which enables making the surface of the transmission unit clean. For example, in cases where the light transmission unit is made of a porous material, a unit of the constituents of the liquid supplied through the light transmission unit may seep onto the surface of the light transmission unit. In such cases, when there is the contact unit adapted to move while contacting with the surface of the light transmission unit, it is possible to remove, from the measurement position, the liquid constituents seeped onto the surface of the light transmission unit. Further, by employing a contact unit made of a fluorine-based resin as the contact unit, it is possible to improve the slidability of the contact unit with respect to the light transmission unit. 
         [0033]    With the liquid component concentration meter according to the present invention, the data processing unit can be adapted to acquire data of intensities of light received intermittently by the light reception unit while the measurement-position moving mechanism moves the measurement position. This enables acquiring light intensity data at plural measurement positions, without stopping the measurement-position moving mechanism and the support member at each measurement position. 
         [0034]    Further, with the liquid component concentration meter according to the present invention, the data processing unit can be adapted to eliminate abnormal light intensity data, from the data of light intensities at a plurality of the measurement positions. This enables stable measurement. 
         [0035]    Further, the data processing unit can be adapted to average light intensity data at plural measurement positions or the liquid concentration data determined through calculation based on light intensity data. This enables measurement stabilized by averaging, in comparison with conventional single-position measurements. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a view schematically illustrating an example. 
           [0037]      FIG. 2  is a plan view of a measurement unit according to the same example. 
           [0038]      FIG. 3  is a side view of the measurement unit according to the same example. 
           [0039]      FIG. 4  is a cross-sectional view for explaining operations of the measurement unit according to the same example. 
           [0040]      FIG. 5  is a cross-sectional view for explaining operations of the measurement unit according to the same example. 
           [0041]      FIG. 6  is a view illustrating an example of results of measurements according to the same example, wherein the vertical axis represents the absorbance, and the horizontal axis represents measurement positions. 
           [0042]      FIG. 7  is a view illustrating another example of results of measurements according to the same example, wherein the vertical axis represents the absorbance, and the horizontal axis represents measurement positions. 
           [0043]      FIG. 8  is a plan view of a measurement unit according to another example. 
           [0044]      FIG. 9  is a front view illustrating the measurement unit according to the same example. 
           [0045]      FIG. 10  is a front view illustrating the measurement unit according to the same example. 
           [0046]      FIG. 11  is a cross-sectional view illustrating the measurement unit according to the same example. 
           [0047]      FIG. 12  is a cross-sectional view illustrating the measurement unit according to the same example. 
           [0048]      FIG. 13  is a view schematically illustrating yet another example. 
           [0049]      FIG. 14  is a plan view of the measurement unit according to the same example. 
           [0050]      FIG. 15  is a side view of the measurement unit according to the same example. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0051]      FIG. 1  is a view schematically illustrating an example.  FIG. 2  and  FIG. 3  are views illustrating a measurement unit according to the present example.  FIG. 2  is a plan view of the measurement unit.  FIG. 3  is a side view of the measurement unit.  FIG. 4  and  FIG. 5  are cross-sectional views for explaining operations of the measurement unit according to the present example. 
         [0052]    As illustrated in  FIG. 1 , the liquid component concentration meter is generally constituted by a spectroscope unit  1 , the measurement unit  2 , and a data processing unit  3 . 
         [0053]    First, the structure of the spectroscope unit  1  will be described in detail. 
         [0054]    The spectroscope unit  1  is provided with a tungsten lamp  4  as a light source, a convex lens  5 , a rotational disk  7  including eight interference filters  6 , a convex lens  8 , a convex lens  11  and a photodetector  12 . Light emitted from the tungsten lamp  4  is condensed by the convex lens  5 , and then, passes through the interference filters  6 . In this case, the interference filters  6  held on the rotational disk  7  disperse the light into light with predetermined wavelengths within the range of 190 to 2600 nm. 
         [0055]    The light which has been dispersed by the interference filters  6  is condensed by the convex lens  8  and is irradiated to an incidence end face  9   a  of a light-emission-side optical fiber  9 . The light-emission-side optical fiber  9  is connected to the measurement unit  2 . 
         [0056]    With reference to  FIGS. 2 to 5 , the measurement unit will be described. In the measurement unit  2 , reference characters  14 ,  15  and  16  designate optically-transparent tubes through which a to-be-measured liquid is flowed. The tubes  14 ,  15  and  16  are made of a resin, such as PTFE (Poly Tetra Fluoro Ethylene) or PFA (tetra fluoro ethylene-PerFluoro Alkylvinyl ether copolymer). The to-be-measured liquid is flowed with a pump and the like into, for example, the tubes  14 ,  15  and  16 , in the order of the tubes  14 ,  15  and  16 . In the present example, the tube  15  constitutes a light transmission unit of the liquid component concentration meter according to the present invention. Further, the measurement unit  2  constitutes a measurement-position moving mechanism in the liquid component concentration meter according to the present invention. 
         [0057]    The light-emission-side optical fiber  9  is connected, at its emission end face  9   b , to a cylinder unit  31  made of for example a PTFE resin. The cylinder unit  31  has a substantially-circular-cylindrical shape which covers the periphery of the tube  15 . The cylinder unit  31  contacts, at its inner wall surface, with the tube  15 . 
         [0058]    A ball lens  22  is installed in the cylinder unit  31  and is adapted to condense the light from the emission end face  9   b  and to direct it to a measurement position  32  in the tube  15 . The light passed through the tube  15  is irradiated to a ball lens  23  installed in the cylinder unit  31  to be condensed thereby, and then, is condensed to an incidence end face  10   a  of a light-reception-side optical fiber  10 . The light-reception-side optical fiber  10  is also installed in the cylinder unit  31 . The light-emission-side optical fiber  9  and the ball lens  22  constitute a light emission unit of the liquid component concentration meter according to the present invention. The cylinder unit  31  constitutes a support member in the liquid component concentration meter according to the present invention. 
         [0059]    The cylinder unit  31  is slidably housed in a space provided in a cylinder guide unit  33 . Pipes  29  and  30  for air-driving are connected to the cylinder guide unit  33 . The air-driving pipe  29  is connected to a space  34  between the cylinder unit  31  and a wall surface  25  in the space. The air-driving pipe  30  is connected to a space  36  between the cylinder unit  31  and a wall surface  28  in the space. 
         [0060]    As illustrated in  FIG. 1 , an emission end face  10   b  of the light-reception-side optical fiber  10  is installed in the spectroscope unit  1 . The light incident to the incidence end face  10   a  of the light-reception-side optical fiber  10  enters the convex lens  11  from the emission end face  10   b  of the light-reception-side optical fiber  10 , thus is condensed thereby, and then, enters the photodetector  12 . The photodetector  12  converts the incident light into a photocurrent corresponding to the intensity of the incident light. 
         [0061]    The rotational disk  7  holds the eight interference filters  6  at even angular intervals in the circumferential direction and is driven, by a driving motor  13 , to rotate at a predetermined rotation speed, such as 1200 rpm (Revolutions Per Minute). The respective interference filters  6  have different predetermined transmission wavelengths corresponding to the to-be-measured object, within the range of 190 to 2600 nm. In this case, if the rotational disk  7  rotates, this causes the respective interference filters  6  to be successively inserted into the optical axis of the convex lenses  5  and  8 . Further, the light emitted from the tungsten lamp  4  is dispersed by the interference filters  7 , and then, is irradiated to the tube  15  containing the liquid, through the light-emission-side optical fiber  9  and the ball lens  22 . The light passed through the tube  15  passes through the ball lens  23  to be condensed thereby, then enters the light-reception-side optical fiber  10 , then passes through the convex lens  11  to be condensed thereby, and then, enters the photodetector  12 . Thus, the photodetector  12  outputs electrical signals corresponding to the absorbances for the light with the respective wavelengths. 
         [0062]    With reference to  FIG. 4  and  FIG. 5 , operations of the measurement unit  2  will be described. 
         [0063]    If the pipe  29  is supplied with air while the pipe  30  is opened to air, as illustrated in  FIG. 4 , air is introduced into the space  34  between the cylinder unit  31  and the cylinder guide unit  33 , which moves the cylinder unit  31 , thereby causing the cylinder unit  31  to impinge on the wall surface  28  of the cylinder guide unit  33  to be stopped thereby. In this state, if the pipe  30  is supplied with air while the pipe  29  is opened to air, as illustrated in  FIG. 5 , air is introduced into the space  36  between the cylinder unit  31  and the cylinder guide unit  33 , which moves the cylinder unit  31  in the opposite direction, thereby causing the cylinder unit  31  to impinge on the wall surface  25  of the cylinder guide unit  33  to be stopped thereby. Since the light-emission-side and the light-reception-side optical fibers  9  and  10  and the ball lenses  22  and  23  are installed in the cylinder unit  31 , the measurement position  32  in the tube  15  moves along with the movement of the cylinder unit  31 . In this case, the tube  15  and the cylinder unit  31  are rubbed against each other, which provides an effect of sweeping away contaminations and adhered objects on the surface of the tube  15  for keeping the light-transmission surface of the tube  15  clean. In order to further facilitate this effect, it is also possible to mount a sponge-type or rubber-type member to a unit of the cylinder  31  which comes into contact with the tube  15 . 
         [0064]    As the cylinder unit  31  moves, determined data for the respective wavelengths is acquired. In cases of making settings in such a way as to move the cylinder unit  31  from the wall surface  25  to the wall surface  28  in about 0.5 second, the interference filter disk  7  performs ten rotations within this time period, thereby enabling acquisition of about 10 light intensities for each wavelength, out of the eight wavelengths per a single rotation. 
         [0065]      FIG. 6  illustrates the data, wherein the vertical axis represents the absorbance for light with the respective wavelength, and the horizontal axis represents measurement positions. In this example, the data is acquired at 11 measurement positions. 
         [0066]    If the shape of the tube  15  were constant, namely the optical path length were constant at the respective measurement positions, the same absorbance data would be acquired at the 11 measurement positions. However, in actuality, the shape of the tube  15  is varied and, thus, the optical path length is also varied. In the case of this example, as the cylinder unit  31  moves from the wall surface  25  to the wall surface  28 , the tube  15  is slightly distorted and is significantly varied particularly at the measurement positions  9 ,  10  and  11 . In such cases, in order to stably acquire data, it is possible to calculate the averaged values over the measurement positions  1  to  11  for alleviating the influence of distortions of the tube  15  as much as possible or it is also possible to eliminate the measurement positions  9 ,  10  and  11  having significant distortions and, further, to average the remaining data for acquiring stable data. 
         [0067]    Further, data as in  FIG. 7  may be acquired. This is caused by increases of the absorbance in cases where air bubbles are adhered to some measurement positions in the tube  15  since these air bubbles intercept light at these measurement positions. As the cylinder unit  31  moves and, also, the interference filter disk  7  rotates, if some of the eight wavelengths accidentally pass through the measurement positions where air bubbles exist, this induces abnormal increases of the absorbance. In this example, the higher absorbance at the measurement positions  4 ,  5 ,  6 ,  7  and  8  are due to the influence of air bubbles. From this graph, it is possible to identify abnormal data indicating abnormally-high absorbance, which enables performing averaging processing with the abnormal data eliminated, thereby enabling more stable measurements. 
         [0068]    In this example, the measurement positions are moved by using the tube  15  itself as a cylinder shaft, but it is also possible to move the measurement positions using a general-purpose air cylinder. 
         [0069]    Further, while in this example, a method for moving the cylinder unit  31  in parallel with the axis of the tube  15  has been exemplified, it is also possible to employ rotational movements as illustrated in  FIGS. 8 to 12 . 
         [0070]      FIGS. 8 to 12  are views illustrating a measurement unit according to another example.  FIG. 8  is a plan view of the measurement unit,  FIG. 9  is a front view of the measurement unit,  FIG. 10  is a side view of the measurement unit, and  FIG. 11  and  FIG. 12  are cross-sectional views illustrating the measurement unit at a side surface thereof. 
         [0071]    The measurement unit according to this example includes a cylinder unit  53 , instead of the cylinder unit  31 , and, further includes a cylinder guide unit  54 , instead of the cylinder guide unit  33 , in comparison with the measurement unit according to the example described with reference to  FIGS. 1 to 4 . 
         [0072]    In the cylinder unit  53 , light-emission-side and light-reception-side optical fibers  9  and  10 , and ball lenses  22  and  23  are provided. The cylinder unit  53  has a substantially-circular-cylindrical shape which covers the periphery of a tube  15 . The inner wall surface of the cylinder unit  53  contacts with the tube  15 . The cylinder unit  53  is provided with a protruding unit on its outer wall surface. 
         [0073]    The cylinder unit  53  is rotatably housed in a space provided in the cylinder guide unit  54 . Pipes  29  and  30  for air-driving are connected to the cylinder guide unit  54 . The air-driving pipes  29  and  30  are connected to the space for housing the protruding unit of the cylinder unit  53  in such a way that they sandwich, therebetween, the protruding unit of the cylinder unit  53 . 
         [0074]    In the case of this example, if the pipe  29  is supplied with air while the pipe  30  is opened to air, air is introduced into the space  51  between the cylinder unit  53  and the cylinder guide unit  54 , which rotates the cylinder unit  53 , and then, stops it as in  FIG. 11 . In this state, if the pipe  30  is supplied with air while the pipe  29  is opened to air, this rotates the cylinder unit  53  in the opposite direction, and then, stops it as in  FIG. 12 . Since the light-emission-side and the light-reception-side optical fibers  9  and  10  and the ball lenses  22  and  23  are installed in the cylinder unit  53 , the measurement position  32  in the tube  15  are moved along with the rotation of the cylinder unit  53 . 
         [0075]      FIG. 13  is a view schematically illustrating another example.  FIG. 14  and  FIG. 15  are views illustrating a measurement unit according to the present example.  FIG. 14  is a plan view of the measurement unit.  FIG. 15  is a side view of the measurement unit. The present example is different from the example illustrated in  FIG. 1 , only in the unit of the measurement unit  200 , but the other units are the same as those of the example illustrated in  FIG. 1 . 
         [0076]    The measurement unit  200  includes a moving mechanism for moving the measurement position and, therefore, is capable of independently moving the measurement position in the directions of the X axis and the Y axis illustrated in  FIG. 15 . A reference character  231  designates a slider which incorporates a stepper motor for moving the measurement position along the X axis, and a reference character  232  designates a slider which incorporates a stepper motor for moving the measurement position along the Y axis. A reference character  201  designates a glass cell (a light transmission unit), and a reference character  202  designates a metal frame for fixing the glass cell  201 . Reference characters  203  and  204  designate joints for coupling the glass cell  201  to the tubes  14  and  16 , respectively. The joints  203  and  204  are pressed against the glass cell  201  in the upward and downward directions in the paper plane, thereby attaining sealing between the glass cell  201  and the joints  203  and  204 . 
         [0077]    A moving-mechanism member  207  having an angular-U shape is installed in such a way that it sandwiches the glass cell  201  and the metal frame  202 . An emission end face  9   b  of the light-emission-side optical fiber  9 , an incidence end face  10   a  of the light-reception-side optical fiber  10 , and lenses  523  and  525  associated therewith are mounted to the moving-mechanism member  207 . The moving-mechanism member  207  is arbitrarily moved along the X and Y axes through sliders  231  and  232 , thereby enabling changing the position of irradiation to the glass cell  201 . The emission end face  9   b  of the light-emission-side optical fiber  9  is connected to an emission-side unit  522  of the moving-mechanism member  207 . The convex lens  523  is installed at the emission-side unit  522  and is adapted to condense the light from the emission end face  9   b  and to direct it to the glass cell  201 . The light passed therethrough is irradiated to the convex lens  525  installed at a light-reception-side unit  526  of the moving-mechanism member  207 , thus is condensed thereby, and then, is condensed to the incidence end face  10   a  of the light-reception-side optical fiber  10 . 
         [0078]    The light-reception-side optical fiber  10  returns to a spectroscope unit  1 , as illustrated in  FIG. 13 . The spectroscope unit  1  performs the same operations as those of the example 1. The measurement unit  200 , which includes the sliders  231  and  232  and the moving-mechanism member  207  for moving the measurement position, acquires determined data for respective wavelengths, along with the movement of the measurement position. For example, the glass cell  201  has a shape with a width of 12.5 mm, a height of 39.3 mm and a thickness of 3.8 mm, and further, has a liquid-containing width (which is referred to as “a cell length” hereinafter) of 1.6 mm. To-be-measured liquids are, for example, mixed liquids composed of ammonia and hydrogen peroxide, which are liquids significantly prone to generate air bubbles. When air bubbles are adhered to the inside of the glass cell  201 , these air bubbles intercept light at the units to which the air bubbles are adhered, thereby increasing the absorbance. At units where no air bubbles exist, since the cell length is constant, and further, there is no abrupt variation in the liquid concentration, the Lambert-Beer law holds as the relationship among the attenuation of transmitted light, the liquid concentration and the light transmission length, and when the light transmission length (the cell length) is constant, there is a proportional relationship between the transmission intensity and the liquid concentration (which corresponds to the Molar concentration of the medium as follows), which enables measurement of the concentration of the liquid through measurements of the transmitted light intensity. 
         [0079]    The Lambert-Beer law: 
         [0000]      Absorbance=−log 10( I 1/ I 0)= a*b*c  
 
         [0080]    I0: The intensity of light incident to the medium 
         [0081]    I1: The intensity of transmitted light from the medium 
         [0082]    a: The molar extinction coefficient of the medium 
         [0083]    b: The light transmission length of the medium 
         [0084]    c: The molar concentration of the medium 
         [0085]    According to the aforementioned relational expression, even if the measurement position is moved in an X-Y-axis plane, constant absorbance is obtained provided that a, b and c are constant. However, if light enters a unit to which air bubbles are adhered, the air bubbles intercept the light at this unit, which significantly increases the absorbance. This makes it possible to identify the influence of air bubbles by making comparisons between data obtained before and after the movement of the measurement position in the X-Y-axis plane. This also applies to basically data obtained according to the aforementioned example. By performing averaging processing after eliminating abnormal data indicating abnormally-high absorbances, it is possible to perform stable measurements which are not influenced by air bubbles. For example, Patent Document 2 describes, in detail, a method for measuring an ammonia concentration and a hydrogen peroxide concentration from acquired stable absorbances. 
         [0086]    Although examples of the present invention have been previously described, the materials, shapes, placement and the like are merely illustrative, and the present invention is not intended to be restricted by these examples, and various changes can be made within the scope of the present invention which is defined by the claims. 
       DESCRIPTION OF THE REFERENCE NUMERALS 
       [0000]    
       
         
           
               1  Spectroscope unit 
               2 ,  200  Measurement unit (Measurement-position moving mechanism) 
               3  Data processing unit 
               9  Light-emission-side optical fiber 
               10  Light-reception-side optical fiber 
               14 ,  16  Tube (Liquid supply tube) 
               15  Tube (Light transmission unit) 
               31 ,  53  Cylinder unit 
               32  Measurement position