Patent ID: 12253493

DESCRIPTION OF EMBODIMENTS

Each embodiment of the present invention will be described with reference to the drawings. Similar elements are designated with similar numerical references throughout a plurality of drawings. The terms used herein to refer to geometric shapes such as a cylindrical shape and a column shape may also refer to modified versions of the original geometric shapes modified to emphasize the function and aesthetic appearance of members.

FIG.1illustrates a gas concentration measurement apparatus1according to a first embodiment of the present invention. The gas concentration measurement apparatus1includes a gas sensor10and a body12. The gas sensor10includes a sensor enclosure14containing an ultrasonic transducer. The sensor enclosure14has a hollow cylindrical shape, that is, a column shape with a closed top. The sensor enclosure14includes, on its peripheral wall, ventilation holes16through which mixture gas such as air is allowed to flow into the sensor enclosure14. Under the control of the body12, ultrasound is transmitted from the ultrasonic transducer to the interior of the sensor enclosure14, and the ultrasound reflected within the sensor enclosure14is received by the ultrasonic transducer. The body12determines, based on the time when the ultrasonic transducer transmits ultrasound and the time when the ultrasonic transducer receives the ultrasound, a propagation time corresponding to a round-trip propagation time of ultrasound within the sensor enclosure14, and determines, based on the propagation time, the concentration of target gas.

FIG.2is a perspective view of the gas sensor10. The sensor enclosure14includes a front enclosure18and a rear enclosure20. The front enclosure18has an arch shaped upper part, corresponding to three-quarters of a front face of the sensor enclosure14. A rear face of the front enclosure18and a front face of the rear enclosure20are engaged with each other to form the sensor enclosure14. The front enclosure18and the rear enclosure20include a plurality of ventilation holes16for communication between the inside and the outside of the sensor enclosure14. Each ventilation hole16extends along the axis of the cylindrical shape of the sensor enclosure14. Thus, each ventilation hole16has a vertical length that is longer than a lateral length (width).

FIG.3Ais a front view of the gas sensor10, andFIG.3Bis a cross section (a cross section perpendicular to the axial direction) taken along AA line inFIG.3A. As illustrated inFIG.3A, the gas sensor10includes, on its front face, seven ventilation holes16arranged in three rows: two ventilation holes16arranged laterally in an upper row; three ventilation holes16arranged laterally in a middle row; and two ventilation holes16arranged laterally in a lower row. The ventilation hole16on the left in the upper row is disposed above a space between the ventilation hole16on the left in the middle row and the ventilation hole16at the center in the middle row, and the ventilation hole16on the right in the upper row is disposed above a space between the ventilation hole16on the right in the middle row and the ventilation hole16at the center in the middle row. The ventilation hole16on the left in the lower row is disposed below a space between the ventilation hole16on the left in the middle row and the ventilation hole16at the center in the middle row, and the ventilation hole16on the right in the lower row is disposed below a space between the ventilation hole16on the right in the middle row and the ventilation hole16at the center in the middle row.

FIG.4is a rear view of the gas sensor10. The gas sensor10includes, on its rear face, eight ventilation holes16arranged in three rows: three ventilation holes16arranged laterally in an upper row; two ventilation holes16laterally arranged in a middle row; and three ventilation holes16laterally arranged in a lower row. The ventilation hole16on the left in the middle row is disposed below a space between the ventilation hole16on the left in the upper row and the ventilation hole16at the center in the upper row, that is, above a space between the ventilation hole16on the left in the lower row and the ventilation hole16at the center in the lower row. The ventilation hole16on the right in the middle row is disposed below a space between the ventilation hole16on the right in the upper row and the ventilation hole16at the center in the upper row. that is, above a space between the ventilation hole16on the right in the lower row and the ventilation hole16at the center in the lower row. The ventilation holes16on the left and right and at the center in the upper row are disposed above the ventilation holes16on the left and right and at the center in the lower row, respectively, via a region where the ventilation holes16in the middle row are arranged.

Referring back toFIG.3B, the positional relationship between the ventilation holes16disposed on the front enclosure18and the ventilation holes16disposed on the rear enclosure20will be described. Each ventilation hole16extends in the front-rear direction through the peripheral wall of the sensor enclosure14.FIG.3Bshows, with dashed and double-dotted lines, through lines22extending through the ventilation holes16and perpendicular to the axial section of the sensor enclosure14, which is a plane parallel to the front and rear faces. The through line22is a straight line extending in the same direction as the through direction of the ventilation hole16. The through lines22extending from the respective ventilation holes16pass through different locations. Therefore, the ventilation holes16disposed on the front enclosure18and the ventilation holes16disposed on the rear enclosure20do not exist on the same through lines22.

FIG.5illustrates a front view of the gas sensor10with the front enclosure18being removed. The gas sensor10includes an ultrasonic transducer30in a region below a region where the ventilation holes16are disposed in the rear enclosure20. The rear enclosure20includes, at its upper end, a top board40having a board face perpendicular to the axial direction of the sensor enclosure14. The front enclosure18is fitted to the rear enclosure20from the front, to thereby form the sensor enclosure14.

The sensor enclosure14formed from the front enclosure18and the rear enclosure20includes a cylindrical body42, as a cylindrical member, having an upper end closed with the top board40. The ultrasonic transducer30is disposed toward the lower end of the cylindrical body42, and an ultrasound propagation path along which ultrasound propagates is formed between the ultrasonic transducer30and the top board40. The sensor enclosure14further includes a plurality of ventilation holes16on the peripheral wall of the cylindrical body42.

The ratio of the area of openings of all the ventilation holes16with respect to the area of the peripheral face of the sensor enclosure14may be 6% or greater and 20% or less, and preferably 8% or greater and 15% or less. A belt-shaped ventilation region surrounding the peripheral face of the sensor enclosure14, where the ventilation holes16are disposed, may have an area which is 25% of the area of the peripheral face of the sensor enclosure14. The number of ventilation holes16in the ventilation region may be, for example, one or more and six or less per 1 cm2, and preferably two or more and five or less per 1 cm2.

Assuming thatFIG.5is an axial cross section of the gas sensor10, operation of the gas sensor10will be described. The ventilation holes16disposed in the sensor enclosure14ventilate the internal space of the sensor enclosure14serving as a concentration measurement space. Specifically, the air outside the sensor enclosure14flows through the ventilation holes16disposed in the sensor enclosure14into the sensor enclosure14. The air inside the sensor enclosure14flows through the ventilation holes16disposed in the sensor enclosure14out of the sensor enclosure14. To facilitate ventilation of the air, a user may move the gas concentration measurement apparatus1(seeFIG.1) in the air.

The ultrasonic transducer30transmits ultrasound based on a transmitting signal output from a controller included in the body12illustrated inFIG.1. The ultrasound transmitted from the ultrasonic transducer30propagates along the ultrasound propagation path formed by the cylindrical body42and is reflected by a lower face (an ultrasonic wave reflecting surface44intersecting the axial direction of the cylindrical body42) of the top board40. The ultrasound reflected by the ultrasonic wave reflecting surface44propagates along the ultrasound propagation path toward the ultrasonic transducer30, and is then received by the ultrasonic transducer30. The ultrasonic transducer30converts the reflected ultrasound to a received signal and outputs the received signal to the controller. The controller determines, based on a time when the controller outputs the transmitting signal and a time when the ultrasonic transducer30outputs the received signal, a round-trip propagation time which the ultrasound takes to propagate between the ultrasonic transducer30and the ultrasonic wave reflecting surface44. The controller further determines a propagation velocity of the ultrasound along the ultrasound propagation path based on the distance between the ultrasonic transducer30and the ultrasonic wave reflecting surface44and the round-trip propagation time, and then further determines the concentration of target gas to be measured based on the propagation velocity.

As illustrated inFIG.3B, in the gas sensor10of this embodiment, each ventilation hole16extends in the front-rear direction through the peripheral wall of the sensor enclosure14. The ventilation holes16disposed in the front enclosure18and the ventilation holes16disposed in the rear enclosure20do not exist on common through lines22. The flow of air flowing into the gas sensor10through the ventilation holes16disposed in the front enclosure18and attempting to flow out through the ventilation holes16disposed in the rear enclosure20is therefore blocked by a region of the rear enclosure20where the ventilation holes16are not disposed. Similarly, the flow of air flowing into the gas sensor10through the ventilation holes16disposed in the rear enclosure20and attempting to flow out through the ventilation holes16disposed in the front enclosure18is blocked by a region of the front enclosure18where the ventilation holes16are not disposed. This configuration maintains ventilation of the interior of the sensor enclosure14and simultaneously prevents rapid inflow of the air to be measured into the sensor enclosure14, thereby reducing a change in the propagation velocity and propagation direction of ultrasound within the sensor enclosure14. This prevents an error in the time in which the ultrasound makes a round-trip within the concentration measurement space, thereby reducing an error in gas concentration measurement. Further, the ventilation holes16extending along the axial direction of the cylindrical shape of the sensor enclosure14facilitate ventilation of the interior of the sensor enclosure14which is axially elongated.

The ventilation holes16need not extend perpendicularly to the axial cross section, or the through lines22need not extend from the corresponding ventilation holes16toward the same direction. In other words, the depth direction of each ventilation hole16need not be normal to the axial cross section, or the through lines22need not extend in the same direction from the ventilation holes16. For example, each ventilation hole16may extend in a direction perpendicular to the peripheral face of the sensor enclosure14.

The ventilation hole16in the rear enclosure20may be disposed at locations out of the line of sight directed from the ventilation holes16in the front enclosure18toward the rear face. Similarly, the ventilation holes16in the front enclosure18may be disposed at locations out of the line of sight directed from the ventilation holes16in the rear enclosure20toward the front face. In other words, the plurality of ventilation holes16may be disposed such that a first side of the sensor enclosure14is not visible from an opposite second side of the sensor enclosure14through the ventilation holes16viewed from the peripheral wall.

Experimental results for the gas sensor10will be described. In an experiment in which the ventilation holes16had the same shape as those illustrated inFIGS.2,3A, and3B, the aperture ratio of a single ventilation hole16was in the range from 0.68% to 0.78%, the aperture ratio of all ventilation holes16was 10.9%, and the number of ventilation holes16per 1 cm2was 1.3, a detection time was 4.5 seconds, and an exhaust time was 19 seconds. Here, the detection time refers to a time between when the gas sensor10was placed in air containing 5% of helium and when 90% of the convergence value of concentration measurements was reached. The exhaust time refers to a time starting from a state where the gas sensor10was placed in air containing 5% of helium and the concentration measurement corresponded to the convergence value to when the gas sensor10was placed in air containing no helium and the concentration measurement was 0. Further, in an experiment in which the aperture ratio of a single ventilation hole16was in the range from 0.55% to 0.62%, the aperture ratio of all ventilation holes16was 8.8%, and the number of ventilation holes16per 1 cm2was 1.3, the detection time was 7 seconds and the exhaust time was 27 seconds.

FIG.6illustrates a perspective view of a gas sensor50according to a second embodiment of the present invention.FIG.7Aillustrates a front view of the gas sensor50, andFIG.7Billustrates a cross section along a line BB inFIG.7A. The gas sensor50includes a lattice-shape rib structure54on a peripheral face of a sensor enclosure52. The rib structure54includes circumferential protrusions56surrounding the sensor enclosure52and vertical protrusions58which are linear protrusions extending vertically, and has a lattice shape. A plurality of circumferential protrusions56are formed on the peripheral face of the sensor enclosure52at predetermined intervals, and adjacent circumferential protrusions56are coupled by a plurality of vertical protrusions58arranged in the circumferential direction at predetermined intervals. The plurality of vertical protrusions58are arranged vertically in straight lines and disposed at predetermined intervals in the circumferential direction. As illustrated inFIG.7B, the vertical protrusions58protrude from the peripheral face of the sensor enclosure52in the same direction as the through direction of the ventilation holes16. The openings of the ventilation holes16are located in a region enclosed by adjacent circumferential protrusions56and adjacent vertical protrusions58. The circumferential protrusions56and the vertical protrusions58may traverse the openings of the ventilation holes16.

The lattice-shape rib structure54disposed on the peripheral face of the sensor enclosure52provides the following advantages. Specifically, the air attempting to flow into the sensor enclosure52from diagonally upward or diagonally downward is directed by the circumferential protrusions56in a direction perpendicular to the periphery of the sensor enclosure52. This reduces the flow of air flowing into the sensor enclosure52from diagonally upward or downward through the ventilation holes16disposed in the front enclosure60and flowing out through the ventilation holes16disposed downward or upward in the rear enclosure62. This configuration similarly reduces the flow of air flowing into the sensor enclosure52diagonally upward or downward through the ventilation holes16disposed in the rear enclosure62and flowing out through the ventilation holes16disposed downward or upward in the front enclosure60. Thus, the circumferential protrusions56reduce passage of the diagonally upward or downward air with respect to the sensor enclosure52through the sensor enclosure52.

The air to flow into the sensor enclosure52from the right or left of the ventilation hole16is directed by the vertical protrusion58in a direction perpendicular to the peripheral face of the sensor enclosure52. This prevents the flow of air flowing into the ventilation holes16disposed on the front enclosure60from diagonally forward right or left and flowing out of the ventilation holes16on the left or right disposed in the rear enclosure62. This configuration similarly prevents the flow of air flowing into the ventilation holes16disposed on the rear enclosure62from diagonally rearward right or left and flowing out of the ventilation holes16on the left or right disposed in the front enclosure60. The vertical protrusions58thus reduce passage of the air in the diagonally right and left directions with respect to the front face or the rear face of the sensor enclosure52.

The rib structure54formed on the peripheral face of the sensor enclosure52prevents rapid flow of the mixture gas such as air to be measured into the sensor enclosure52to reduce a change of the propagation velocity of ultrasound within the sensor enclosure52. More specifically, the circumferential protrusions56prevent the flow of air passing through the ventilation holes16having an axial length greater than its lateral width, diagonally upward or downward. The vertical protrusions58prevent the flow of air passing through the ventilation holes16having a lateral width greater than its axial length, from diagonally forward left or rearward right, or from diagonally rearward left or forward right. This results in a reduction in an error of time during which the ultrasound propagates the concentration measurement space to thereby reduce an error in the gas concentration measurements. The rib structure54formed on the peripheral face of the sensor enclosure52further enhances the mechanical strength of the sensor enclosure52.

While in the above embodiments the sensor enclosure (14,52) has a hollow cylindrical shape, the sensor enclosure (14,52) may have a shape of a hollow polygonal cylinder or a hollow elliptical cylinder, for example. In the above embodiments, the ventilation hole16has a shape extending along the axis of the sensor enclosure (14,52), but the ventilation hole16may have a shape of a perfect circle, an ellipse, or a rectangle, for example. Further, the cylindrical body may include, on its inner peripheral face corresponding to the peripheral face, a gas-liquid separation membrane formed of a hollow fiber membrane such as PTFE, PP, PE, silicone resin, for example, attached to the inner peripheral face, to thereby prevent entrance of water droplets and dust into the gas concentration measurement space within the cylindrical body.

REFERENCE SIGNS LIST

1gas concentration measurement apparatus,10,50gas sensor,14,52sensor enclosure,16ventilation hole,18,60front enclosure,20,62rear enclosure,22through line,30ultrasonic transducer,40top board,42cylindrical body,44ultrasonic wave reflecting surface,54rib structure,56circumferential protrusion,58vertical protrusion.