Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1995-11-15
1997-11-04
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
25022718, 385 12, 356 32, 374131, G01K 1100, G01L 124, G01B 1116
Patent
active
056842970
ABSTRACT:
The present invention relates to a method of detecting and/or measuring changes in a physical magnitude by means of a distributed sensor, changes being detected and/or measured at a plurality of "measurement" points along said sensor, said sensor comprising an optical fiber having an optical core for guiding the majority of light waves, said optical core including a plurality of diffraction gratings distributed along said optical fiber, each situated at one of said measurement points, said diffraction gratings all having substantially the same central reflection wavelength in the absence of strain, the method comprising the following steps: injecting a "detection" light signal into an "inlet" end of said optical fiber, the wavelength of the light signal being close to said central reflection wavelength; determining the power of one of the reflected signals, referred to as the "detected reflected power", as a function of time; comparing said detected reflected power as a function of time with the power reflected as a function of time by the sensor in the absence of any change in said physical magnitude, referred to as the "idle" reflected power; and detecting change in said physical magnitude whenever said detected reflected power differs from said idle reflected power.
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A. D. Kersey et al, "Multi-element Bragg-grating Based Fibre-Laser Strain Sensor", Electronics Letters, vol. 29, No. 11, May 27, 1993, pp. 964-966.
Alcatel Cable
Lee John R.
Westin Edward P.
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