Structural monitoring system using fiber optics

• US 4,812,645 A
• Filed: 03/27/1987
• Issued: 03/14/1989
• Est. Priority Date: 08/24/1981
• Status: Expired due to Fees

• Current Assignee: G2 Systems
• Original Assignee: G2 Systems
• Inventors: Griffiths, Richard W.
• Primary Examiner(s): Westin, Edward P.
• Application Number:
  US07/032,042
• Time in Patent Office: 718 Days
• Field of Search: 250/227, 250/231 R, 250/231 P, 73/705, 73/800, 350/96.15, 350/96.16, 350/96.23, 350/96.29, 356/73.1, 356/32
• US Class Current: 250/227.14
• CPC Class Codes: G01B 11/18 using photoelastic elements
• CPC Class Codes: G01L 1/243 using means for applying force perpendicular to the fibre axis
• CPC Class Codes: G01L 1/245 using microbending
• CPC Class Codes: G01M 11/086 Details about the embedment of the optical fiber within the DUT
• CPC Class Codes: G01P 13/00 Indicating or recording presence, absence, or direction, of movement electric switches H01H; counting moving objects G06M7/00

Abstract

An optical fiber is securely and continuously engaged by a structure such as a pipeline, offshore platform, bridge, building, dam or even a natural object or fluid medium. A light signal is passed into one end of the optical fiber. Any physical movement of the structure, or sectional movements along the optical fiber path, such as deflection, bending, displacement (changes in linear uniformity) or fracture of the structure caused, for example, by stress, strain, pressure, temperature, etc., will necessarily affect the optical fiber. As a consequence, detectable changes will occur in the "electro-optic signature" (for measurements made at the input end of the optical fiber) or in the light signal transmission (for measurements made at the opposite end of the optical fiber). Such measurements made at the input end include reflections resulting from Rayleigh back-scattering and can periodically or continuously be made to determine the magnitude and location of the aforementioned physical movements of the structure. In addition, by utilizing additional optical fibers, the direction and rate, i.e., dynamics, of such physical movements can be determined. The optical fiber itself can be used as a communication link for the transmission of data and voice.

Claims

1. A method of determining the pressure acting upon a structure at any point along a continuum of points located between spaced points on the structure, said method including the steps of:

coupling at least one optical fiber continuously to said structure to extend from at least one of the spaced points to the other and thereby engage all points along the structure between said spaced points so that physical movement of the structure resulting from pressure acting upon the structure between said spaced points will result in physical movement of the optical fiber;

passing a first light signal into said optical fiber; and

detecting reflection changes in said first light signal resulting from said physical movement to thereby provide an indication that a pressure-caused physical movement has taken place and an indication of the location and magnitude of said movement.

2. An apparatus for monitoring pressure acting upon a structure between spaced points on the structure including, in combination:

at least one optical fiber;

means for coupling said optical fiber continuously to said structure to extend from at least one of the spaced points to the other and thereby engage all points along the structure between said spaced points so that physical movement resulting from pressure acting upon the structure between said spaced points will result in physical movement of the optical fiber;

means for passing a first light signal into said optical fiber;

means for detecting and indicating reflection changes in said first light signal as a consequence of said physical movement; and

means responsive to said detected reflection changes for indicating the location and magnitude of said physical movement.

3. A method of monitoring a physical movement occurring at any point between spaced points on a structure, including the steps of:

coupling with coupling means at least one optical fiber continuously to said structure to extend from at least one of the spaced points to the other and thereby engage all points along the structure between said points so that physical movement of the structure between said spaced points will result in physical movement of the optical fiber;

passing a first light signal into said optical fiber; and

detecting attenuations in said first light signal resulting from said physical movement to thereby provide an indication that a physical movement has taken place.

4. An apparatus for monitoring a physical movement between spaced points on a structure including, in combination:

at least one optical fiber;

means for coupling said optical fiber continuously to said structure to extend from at least one of the spaced points to the other and thereby engage all points between said spaced points so that physical movement of the structure at a location between said spaced points will result in physical movement of the optical fiber at a location corresponding with the location of movement of the structure;

means for passing a first light signal into said optical fiber; and

means for detecting and indicating attentuations in said first light signal to thereby detect that a physical movement has taken place.