Patent Number: 
Section: claims

1. A measuring device comprising:a housing comprising two surfaces facing away from each other, the housing being provided with a flow path structure, a first cavity, and a second cavity, whereinthe flow path structure has two openings on the two surfaces respectively and comprises a first side surface and a second side surface facing each other,the first cavity comprises one end opening on the first side surface,the second cavity faces the first cavity across a center axis of the flow path structure and comprises one end opening on the second side surface;a first cell disposed in the first cavity, made from a transparent material, and having a substantially cylindrical shape, both end surfaces of the first cell being flat surfaces;a second cell disposed in the second cavity, made from a transparent material, and having a substantially cylindrical shape, both end surfaces of the second cell being flat surfaces;a light emitting section configured to irradiate a hydraulic oil flowing in the flow path structure with light via the first cell in a direction substantially orthogonal to the center axis; anda light receiving section disposed facing the light irradiating section across the first cell, the flow path structure, and the second cell;the first cavity and the second cavity having centers substantially coinciding with an optical axis being a center of light emitted from the light irradiating section,wherein:the flow path structure comprises both ends shaped into a round cavity;the flow path structure has such a tapered shape that a shape in a plane substantially orthogonal to the center axis changes from the round cavity to a long cavity having two sides substantially orthogonal to the optical axis; andthe tapered shape is formed such that a taper angle is approximately 60 degrees with respect to the center axis. 2. The measuring device according to claim 1, wherein:the first side surface and the second side surface are flat surfaces;an end surface of the first cell disposed in the first cavity and the first side surface are substantially in the same plane; andan end surface of the second cell disposed in the second cavity and the second side surface are substantially in the same plane. 3. The measuring device according to claim 2, wherein a distance between the first side surface and the second side surface is smaller than a length of the first side surface and the second side surface in the direction substantially orthogonal to the center axis. 4. The measuring device according to claim 2,wherein:the first cell comprises a first main portion having a substantially cylindrical shape and a first flange portion formed at an end of the first main portion and having a substantially circular plate shape with a diameter greater than a diameter of the first main portion;a first sealing member is disposed between the first cavity and the first main portion;a first pressing member is disposed within the housing;the first pressing member presses the first cell; andend surfaces, on the first main portion side, of the first flange portion is pressed against the housing, andwherein:the second cell comprises a second main portion having a substantially cylindrical shape and a second flange portion formed at an end of the second main portion and having a substantially circular plate shape with a diameter greater than a diameter of the second main portion;a second sealing member is disposed between the second cavity and the second main portion;a second pressing member is disposed within the housing;the second pressing member presses the second cell; andend surfaces, on the second main portion side, of the second flange portion is pressed against the housing. 5. The measuring device according to claim 1, wherein a distance between the first side surface and the second side surface is smaller than a length of the first side surface and the second side surface in the direction substantially orthogonal to the center axis. 6. The measuring device according to claim 1,wherein:the first cell comprises a first main portion having a substantially cylindrical shape and a first flange portion formed at an end of the first main portion and having a substantially circular plate shape with a diameter greater than a diameter of the first main portion;a first sealing member is disposed between the first cavity and the first main portion;a first pressing member is disposed within the housing;the first pressing member presses the first cell; andend surfaces, on the first main portion side, of the first flange portion is pressed against the housing, andwherein:the second cell comprises a second main portion having a substantially cylindrical shape and a second flange portion formed at an end of the second main portion and having a substantially circular plate shape with a diameter greater than a diameter of the second main portion;a second sealing member is disposed between the second cavity and the second main portion;a second pressing member is disposed within the housing;the second pressing member presses the second cell; andend surfaces, on the second main portion side, of the second flange portion is pressed against the housing. 7. A measuring device comprising:a housing comprising two surfaces facing away from each other, the housing being provided with a flow path structure, a first cavity, and a second cavity,the flow path structure has two openings on the two surfaces respectively and comprises a first side surface and a second side surface facing each other,the first cavity comprises one end opening on the first side surface,the second cavity faces the first cavity across a center axis of the flow path structure and comprises one end opening on the second side surface;a first cell disposed in the first cavity, made from a transparent material, and having a substantially cylindrical shape, both end surfaces of the first cell being flat surfaces;a second cell disposed in the second cavity, made from a transparent material, and having a substantially cylindrical shape, both end surfaces of the second cell being flat surfaces;a light emitting section configured to irradiate a hydraulic oil flowing in the flow path structure with light via the first cell in a direction substantially orthogonal to the center axis; anda light receiving section disposed facing the light irradiating section across the first cell, the flow path structure, and the second cell;the first cavity and the second cavity having centers substantially coinciding with an optical axis being a center of light emitted from the light irradiating section,wherein a distance between the first side surface and the second side surface is smaller than a length of the first side surface and the second side surface in the direction substantially orthogonal to the center axis. 8. A measuring device comprising:a housing comprising two surfaces facing away from each other, the housing being provided with a flow path structure, a first cavity, and a second cavity,the flow path structure has two openings on the two surfaces respectively and comprises a first side surface and a second side surface facing each other,the first cavity comprises one end opening on the first side surface,the second cavity faces the first cavity across a center axis of the flow path structure and comprises one end opening on the second side surface;a first cell disposed in the first cavity, made from a transparent material, and having a substantially cylindrical shape, both end surfaces of the first cell being flat surfaces;a second cell disposed in the second cavity, made from a transparent material, and having a substantially cylindrical shape, both end surfaces of the second cell being flat surfaces;a light emitting section configured to irradiate a hydraulic oil flowing in the flow path structure with light via the first cell in a direction substantially orthogonal to the center axis; anda light receiving section disposed facing the light irradiating section across the first cell, the flow path structure, and the second cell;the first cavity and the second cavity having centers substantially coinciding with an optical axis being a center of light emitted from the light irradiating section,wherein:the first cell comprises a first main portion having a substantially cylindrical shape and a first flange portion formed at an end of the first main portion and having a substantially circular plate shape with a diameter greater than a diameter of the first main portion;a first sealing member is disposed between the first cavity and the first main portion;a first pressing member is disposed within the housing;the first pressing member presses the first cell; andend surfaces, on the first main portion side, of the first flange portion is pressed against the housing, andwherein:the second cell comprises a second main portion having a substantially cylindrical shape and a second flange portion formed at an end of the second main portion and having a substantially circular plate shape with a diameter greater than a diameter of the second main portion;a second sealing member is disposed between the second cavity and the second main portion;a second pressing member is disposed within the housing;the second pressing member presses the second cell; andend surfaces, on the second main portion side, of the second flange portion is pressed against the housing.