JP2003254798A - Sensor sensitivity of dynamic range setting method using fbg - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the sensor sensitivity or the dynamic range easily settable according to a performance requirement in a sensor comprising an FBG (optical fiber Bragg diffraction grating) 14 provided on a tensile face of a bending member 10, wherein the amount of deflection thereof changes by the amount of a physical quantity. <P>SOLUTION: Optical fibers 16 located at the both sides of the FBG 14 are fixed to the bending member 10 by fixing blocks 20. The sensor sensitivity or a dynamic range is controlled by a height of the fixing block 20. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for setting a sensitivity or a dynamic range of a physical quantity sensor using an FBG (optical fiber Bragg diffraction grating). 2. Description of the Related Art When light is incident on one end of an optical fiber provided with an FBG in a longitudinal direction, the FBG reflects only light of a specific wavelength. When stretching strain is applied to the FBG, the wavelength of the reflected light shifts to the longer side. Therefore, the pressure can be detected by attaching the FBG to a member (for example, a diaphragm) whose deflection amount changes due to a pressure change and measuring the wavelength shift amount of the reflected light (Japanese Patent Application Laid-Open No. 2001-83031). The temperature can be detected by attaching the FBG to a member (for example, a bimetal) whose amount of deflection changes due to a temperature change and measuring the amount of wavelength shift of the reflected light. A conventional sensor using an FBG has been configured by fixing the entire length of the FBG to the bending surface side of a bending member, the bending amount of which changes with a change in a physical amount, with an adhesive. [0004] In a sensor using a conventional FBG, since the flexible member and the FBG expand and contract integrally, the sensitivity or dynamic range of the sensor is limited to that of the flexible member. It depends on the characteristics. Therefore, when manufacturing the sensor, in order to set the sensitivity or the dynamic range as the sensor to the required sensitivity or the dynamic range, it is necessary to select a flexure member or an FBG that matches the sensitivity or the dynamic range. In view of the above problems, an object of the present invention is to provide a sensitivity of a sensor using an FBG that can change a sensitivity or a dynamic range as a sensor even when the same flexible member and FBG are used. Another object is to provide a method for setting a dynamic range. Means for Solving the Problems In order to achieve this object, the present invention relates to a sensor in which an FBG is attached to a bending surface of a bending member whose bending amount changes due to a change in a physical amount. The optical fiber portions on both sides of the FBG are fixed to the bending member via a fixing block, and the sensitivity or dynamic range of the sensor is set according to the height of the fixing block. In the present invention, it is preferable that the interval for fixing the optical fiber portions on both sides of the FBG (the interval between the inner end faces of the fixed block) is set to the length of the FBG + about 1 to 10 mm on one side. Further, it is preferable that the height of the fixed block is set to a height that does not make contact with the FBG when the bending member is bent. Hereinafter, embodiments of the present invention will be described.
This will be described in detail with reference to the drawings. In FIG. 1, reference numeral 10 denotes a flexible member (for example, a metal plate) whose periphery is fixed and supported on the inner wall of the pressure vessel 12. When pressure is applied to one surface of the flexure member 10, flexure corresponding thereto occurs. The FBG 14 is attached to the flexible member 10 at the center of the surface opposite to the surface to be pressurized (the surface on the tensile side of the deflection). The protective coating 18 is removed from the FBG 14 and the optical fibers 16 on both sides near the FBG 14 so that the optical fibers 16 on both sides of the FBG 14 are fixed blocks.
It is fixed to the flexible member 10 via 20. That is, FB
G14 is separated from the surface of the flexible member 10 and is fixedly supported by the flexible member 10 at two points on both sides. The fixing block 20 can be fixed to the flexible member 10 by means such as soldering, welding or bonding. However, it is preferable to fix the fixing block 20 by soldering or welding in order to enhance reliability. Further, the optical fiber 16 can be fixed to the fixing block 20 by means such as soldering or bonding, but it is preferable to fix the optical fiber 16 by soldering in order to enhance reliability. Optical fiber 16
Is fixed to the fixing block 20 by soldering, the surface of the optical fiber 16 is plated by electroless plating or the like and then soldered. Optical fiber 16 fixed block 20
When fixing the FBG 14, the FBG 14 is fixed with a slight tension applied so as not to cause slack. When pressure is applied to the flexure member 10 to which the FBG 14 is attached as described above, the flexure member 10 flexes, and tension is applied to the FBG 14 to extend the FBG 14. F
The extension strain of the BG 14 increases as the height of the fixed block 20 increases, even if the flexure of the flexure member 10 is the same. For example, FIGS. 2A and 2C show a sensor in which the characteristics of the flexible member 10 and the FBG 14 are the same and only the height of the fixed block 20 is different. Flexure member 10 for these two sensors
When the same pressure is applied to each of the members to generate the same amount of flexure as in (B) and (D), the stretching strain of the FBG 14 is larger than that in the case where the height of the fixing block 20 is low (B). (D) where the height of the block 20 is high is larger. F
An increase in the elongation strain (increase in the wavelength shift amount) of the BG14 means that the sensitivity of the sensor increases or the dynamic range increases. In other words, the sensitivity or dynamic range of the sensor can be set by the height of the fixed block 20. More specifically, in FIG. 1, the dimensions of the flexible member 10 are 100 mm × 100 mm × 1 mm (thickness), the material is SS400, the length of the FBG 14 is 10 mm, the interval between the fixed blocks 20 is 15 mm, When the length is 1 mm, the flexure 10
When a uniformly distributed load of 50 kPa is applied to the FBG 14, the elongation strain of the FBG 14 becomes about 0.05%. On the other hand, the height of the fixed block 20 is
At 3 mm (other conditions being the same), the elongation strain of FBG14 is about 0.15%. That is, if the height of the fixed block 20 is increased, the FBG 14
Since the wavelength shift amount becomes large, the sensitivity as a sensor can be increased accordingly, and the dynamic range can be widened. In the above-described sensor, when the distance between the fixed blocks is increased, the risk of disconnection of the optical fiber including the FBG increases, and the sensor is easily affected by vibration and the like. Therefore, it is advantageous that the interval between the fixed blocks is small, but if it is too small, the following problem occurs. That is, the fixing material (solder or adhesive) easily adheres to the FBG, and if the fixing material adheres to the FBG, irregular stress is applied to the FBG with the curing of the fixing material, which adversely affects the measurement accuracy. When solder is used as the fixing material, heat at the time of melting the solder may deteriorate the FBG. Therefore, the interval between the fixed blocks is
In the case of 10 mm, at least 12 mm or more is required, and setting to about 30 mm is sufficient. [0015] The height of the fixed block is set according to the amount of deflection of the bending member. Further, the height of the fixed block needs to be set so that the FBG does not contact the flexible member when the flexible member is bent. As described above, according to the present invention,
By fixing the FBG to the flexible member via the fixed block, the sensitivity or the dynamic range of the sensor can be set according to the required performance depending on the height of the fixed block. Therefore, sensors having various sensitivities or dynamic ranges can be easily manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an example of a method for setting the sensitivity or dynamic range of a sensor using an FBG according to the present invention, (A) is a longitudinal sectional view, and (B) is a bottom view. FIG. 2A is an explanatory view showing a sensor in which an FBG is attached to a flexible member via a fixed block having a low height,
(B) is an explanatory view showing a state in which the bending member of the sensor of (A) is bent, and (C) is an explanatory view showing a sensor in which an FBG is attached to the bending member via a fixing block higher than (A). (D) is an explanatory view showing a state in which the bending member of the sensor of (C) is bent. [Description of References] 10: Flexure member 14: FBG 16: Optical fiber 20: Fixed block

Claims (1)

Claims: 1. A sensor in which an FBG (optical fiber Bragg diffraction grating) is attached to a bending surface of a bending member of which a bending amount changes due to a change in a physical amount. A sensor sensitivity or dynamic range setting method using an FBG, wherein an optical fiber portion is fixed to the bending member via a fixing block, and the sensor sensitivity or dynamic range is set according to the height of the fixing block.