JP2005172713A - Flow velocity sensor, flow direction determination method, and flow velocity determination method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flow velocity sensor capable of measuring a flow velocity in a river or the like accurately with a simple constitution without providing a complicated constitution such as a mechanical driving part or a strain generation part. <P>SOLUTION: In this flow velocity sensor, heating plates 2 are stuck on both surfaces of a heater 3 provided with a heater electrode 5, and an FBG 4 connected to a sensor cable 1 is fixed on the heating plate 2 with an epoxy resin, and the heater 3, the heating plate 2 and the FBG 4 are molded integrally with a waterproof material by a waterproof mold 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a flow velocity sensor, a flow direction determination method, and a flow velocity determination method that detect a flow direction and a flow velocity of a river or the like using an FBG (fiber Bragg grating).

  When a typhoon or heavy rain floods, the river water level crosses the embankment, resulting in river inundation, or scouring the riverbed or riverbed, resulting in destruction of the embankment or bridge. Therefore, it is important to constantly monitor the river flow velocity in order to predict river flooding and scouring phenomena.

Examples of the prior art using an optical fiber as a means for measuring the flow velocity include the following.
(1) A method in which a cup-type rotor is rotated by a fluid flow, a strain is applied to an optical fiber type strain sensor for each rotation, and a flow velocity is obtained from the number of rotations of the cup-type rotor (see Patent Document 1).
(2) A method of converting the water pressure received by the pressure receiving plate into strain of the optical fiber and detecting the strain with an optical fiber strain measuring instrument (see Patent Documents 2 and 3).
JP 2001-194378 A JP 2002-202163 A JP 2000-162226 A

  However, in the method described in Patent Document 1, there is a problem that an accurate measurement cannot be performed when there is an obstacle in the water because there is a mechanical drive unit that rotates the cup-type rotor. Further, in the method described in Patent Document 2, it is necessary to provide a pressure receiving plate and a strain generating portion, and in the method described in Patent Document 3, it is necessary to provide a tension applying mechanism. However, there was a disadvantage that the size was increased.

  Accordingly, an object of the present invention is to provide a flow rate sensor capable of accurately measuring a flow rate of a river or the like with a simple configuration without providing a complicated configuration such as a mechanical drive unit or a strain generation unit, and the flow rate sensor. It is an object to provide a flow direction determination method and a flow velocity determination method using the above.

  In order to achieve the above object, the flow rate sensor of the present invention is characterized in that measurement plates are provided on both sides of the heating means, and optical fiber Bragg gratings are respectively fixed to the measurement plates.

  It is desirable that the heating means, the measurement plate, and the optical fiber Bragg grating are integrally molded with a water resistant material.

  In addition, the flow direction determination method of the present invention measures the temperature of the measurement plates provided on both surfaces of the heating means with an optical fiber Bragg grating, compares the temperature of both measurement plates, and determines the lower temperature and the flow direction. It is characterized by determining.

  The heating means can be turned on and off periodically to repeat heating and natural cooling, and the temperature rising gradients during heating of the two measuring plates can be compared to determine the flow direction of the lower temperature gradient as the upstream side. .

  Furthermore, in the flow rate determination method of the present invention, the temperature of the measurement plates provided on both sides of the heating means is measured with an optical fiber Bragg grating to calculate the equilibrium temperature difference between the two measurement plates, and the previously determined fluid The collision speed of the fluid is detected based on the relationship between the collision speed and the equilibrium temperature difference between the collision surface and the back surface of the fluid.

  Periodically turning on and off the power supply of the heating means to repeat heating and natural cooling, measuring the temperature rise gradient during heating of the two measurement plates, and the relationship between the fluid collision speed and the temperature rise gradient determined in advance The collision speed of the fluid can also be detected based on the above.

  Since the flow rate sensor of the present invention has a simple configuration provided with a heating means, a measurement plate, and an optical fiber Bragg grating, the sensor itself can be miniaturized. In addition, since a drive unit or the like for applying a strain is not required unlike a conventional strain sensor, measurement cannot be performed by an obstacle in water.

  In addition, since the flow direction determination method of the present invention compares the temperature of both measurement plates measured by the optical fiber Bragg grating and determines the flow direction of the lower one as the upstream side, accurate flow direction determination can be performed by a simple method. It becomes possible.

  Furthermore, the flow velocity determination method of the present invention is based on the relationship between the equilibrium velocity difference between the fluid collision velocity and the fluid collision surface and the back surface, which is obtained in advance as the equilibrium temperature difference between the two measurement plates measured by the optical fiber Bragg grating. Since the collision speed of the fluid is detected by collating, it is possible to accurately determine the flow velocity despite the simple method.

  Embodiments of a flow rate sensor of the present invention will be described below with reference to the drawings.

  1 (a) and 1 (b) show an embodiment of a flow rate sensor of the present invention.

  In this flow rate sensor, the heating plate 2 is attached to both sides of the heater 3 provided with the heater electrode 5, the FBG 4 connected to the sensor cable 1 is fixed on the heating plate 2 with an epoxy resin, and the heater 3, The heating plate 2 and FBG 4 are integrally molded with a water-resistant material by a water-resistant mold 6.

  The heating plate 2 is a thin plate made of a material having a high thermal conductivity such as a metal or a polymer plastic material. The FBG 4 fixed on the heating plate 2 is used to measure the temperature on the heating plate 2. The reflection wavelength of the FBG 4 changes depending on the temperature, and the amount of change is about 10 to 60 pm per 1 ° C., which changes depending on the material of the heating plate 2 to which the FBG 4 is attached. Therefore, by measuring the relationship between the reflection wavelength of the FBG 4 and the temperature when the production of the flow velocity sensor is completed, the temperature can be measured. A method for detecting the flow direction and the flow velocity from the temperature on the heating plate 2 on both sides measured by the FBG 4 will be described below.

  When this sensor is placed in a fluid and the heater 3 is energized and heated, the amount of heat generated by the heater 3 and the amount of heat taken away by the fluid are equilibrated at a temperature. Since the cooling effect by the fluid is high on the surface where the fluid collides, the equilibrium temperature is lower than that on the back surface. Since the temperature of both surfaces of the heating plate 2 is constantly measured by the FBG 4, the flow direction can be determined by comparing the equilibrium temperatures of both surfaces of the heating plate 2, and the surface with the lower temperature is the upstream side.

  The equilibrium temperature of the surface on which the fluid collides changes depending on the temperature of the fluid and the collision speed of the fluid. The amount of heat taken away by the fluid changes depending on the velocity of the collision of the fluid, so that the velocity of the collision of the fluid affects. If the back surface equilibrium temperature is determined only by the influence of the temperature of the surrounding fluid, the difference in the equilibrium temperature between the fluid impinging surface and the back surface is related to the flow velocity. Therefore, if the relationship between the collision speed of the fluid and the equilibrium temperature difference between the collision surface and the back surface of the fluid is obtained while the heater 3 is energized and heated, the flow velocity can be measured from the relationship.

  Thus, in order to measure the flow direction and flow velocity using the heat transfer on the surface to which the FBG 4 is attached, the conditions on both sides to which the FBG 4 is attached (the thickness of the water-resistant mold 6 and the thickness of the heating plate 2, It is necessary to make the area of the heating plate 2 equal). Further, if the sensor surface is uneven, the fluid flow changes, so the sensor surface needs to be as flat as possible.

  In addition, even when the power source of the heater 3 is periodically turned on and off and heating and natural cooling are repeated, the cooling effect by the fluid is high on the surface where the fluid collides, and therefore the temperature rise gradient is smaller than that on the back surface. This makes it possible to determine the flow direction. Also, the flow velocity can be detected by preliminarily determining the relationship between the fluid collision velocity and the temperature rise gradient during heating.

  As described above, since the flow velocity sensor of the present embodiment has a simple configuration in which the heater 3, the heating plate 2, and the FBG 4 are provided, the sensor itself can be reduced in size. Further, since the flow velocity is obtained from the equilibrium temperature difference between the fluid collision side and the back surface side, a conventional drive unit or the like is not required, and therefore, measurement cannot be performed due to an obstacle in the water.

FIG. 2 shows an application example of the flow rate sensor of the present embodiment.
Since the flow velocity sensor 10 of this embodiment measures the flow direction and flow velocity from the change in the reflection wavelength of the FBG, a light source (not shown), the FBG reflection wavelength measuring device 8 and the arithmetic device 9 are connected to one end of the sensor cable 1. By making the sensor cable 1 longer, the light source, the reflected wavelength measuring device 8 and the arithmetic unit 9 can be placed at a remote place, and the monitoring facility 7 can remotely monitor the flow direction and flow velocity. Moreover, since the flow rate sensor 10 is connected on one sensor cable 1 by connecting the flow rate sensor 10 in series, a plurality of sensors can be monitored, and the difference in flow rate depending on the location can be monitored. become.

  When the flow velocity sensor 10 of the present embodiment is installed in the river 12, it is fixed to the quay of the river 12, or a pillar is set up on the river 12 and fixed to the side surface. Since the flow rate sensor 10 of the present embodiment has a simple configuration, the size can be reduced as compared with the conventional flow rate sensor. For this reason, many conventional flow velocity sensors are submerged in the bottom of the river, but the flow velocity sensor 10 can be easily installed at an arbitrary depth.

  In addition, although the flow velocity sensor 10 of this embodiment needs to be installed perpendicular to the flow for accurate measurement of the flow velocity, since it is small and easy to install, it is necessary to install a plurality of sensors at different installation angles. Enables more accurate measurement.

It is an example of the flow velocity sensor of this embodiment, (a) is a perspective view, (b) is bb sectional drawing of (a). It is the schematic which shows the actual application example of the flow velocity sensor of this embodiment.

Explanation of symbols

1 Sensor cable (optical fiber)
2 Heating plate (measuring plate)
3 Heater (heating means)
4 FBG
5 Heater electrode 6 Water resistant mold 7 Monitoring facility 8 FBG reflection wavelength measuring instrument 9 Arithmetic device 10 Flow rate sensor

Claims (6)

  A flow rate sensor characterized in that measuring plates are provided on both sides of the heating means, and optical fiber Bragg gratings are fixed to the measuring plates, respectively.   The flow rate sensor according to claim 1, wherein the heating means, the measurement plate, and the optical fiber Bragg grating are integrally molded with a water-resistant material.   A flow direction determination method characterized in that the temperature of the measurement plates provided on both sides of the heating means is measured by an optical fiber Bragg grating, and the temperature of both measurement plates is compared to determine the flow direction of the lower temperature from the upstream side. .   Periodically turning on and off the power supply of the heating means to repeat heating and natural cooling, comparing the temperature rise gradients during heating of the two measurement plates, and determining the flow direction of the lower temperature gradient as the upstream side The flow direction determination method according to claim 3.   The temperature of the measurement plates provided on both sides of the heating means is measured with an optical fiber Bragg grating to calculate the equilibrium temperature difference between the two measurement plates. A method for determining a flow velocity, comprising detecting a collision speed of a fluid based on a relationship with an equilibrium temperature difference. Periodically turning on and off the power supply of the heating means to repeat heating and natural cooling, measuring the temperature rise gradient during heating of the two measurement plates, and the relationship between the fluid collision speed and the temperature rise gradient determined in advance 6. The flow velocity determination method according to claim 5, wherein the collision speed of the fluid is detected based on the above.

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