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Distributed and spatially averaged fiber optic temperature sensors and method using same

  • US 5,499,313 A
  • Filed: 09/13/1994
  • Issued: 03/12/1996
  • Est. Priority Date: 08/06/1982
  • Status: Expired due to Fees
First Claim
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1. A method for sensing temperature changes at a plurality of locations, comprising the steps of:

  • (a) providing a light-transmitting optical fiber system along a path including said locations, said optical fiber system having a first end and a second end and a sensing element at each of said locations, each sensing element being so characterized that, when exposed to the temperature changes to be sensed and transmitting interrogating light of suitable wavelength or wavelengths λ

    v and an intensity Po, it converts a fraction α

    Po of the intensity of said interrogating light into a light separable from the interrogating light, at least part of the intensity of which is emitted from the sensing element at wavelengths λ

    f different from λ

    v, where α

    is a temperature-dependent fraction smaller than unity, the value of which increases with increasing temperature within a temperature range, the intensity of said light of wavelengths λ

    f being substantially proportional to the value of α

    ;

    (b) injecting said interrogating light of intensity Po and wavelength or wavelengths λ

    v into the optical fiber system at said first end thereof, thereby converting at each sensing element a fraction α

    Po of the intensity of said injected interrogating light into a light separable from the interrogating light, at least part of the intensity of which is emitted from each sensing element at wavelengths λ

    f different from λ

    v, the value of α

    varying as a known function of temperature, said emitted light having an intensity varying with the value of α

    ;

    (c) selectively directing a fraction of the intensity of said emitted light of wavelengths λ

    f received by said photodetector means;

    (d) sensing the variations of the intensity of said emitted light of wavelengths λ

    f received by said photodetector means; and

    (e) thereby sensing the temperature changes of the sensing elements from the variations of the intensity of said light of wavelengths λ

    f received by said photodetector means.

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