Reconstruction of the Temperature Profile Along an Optical Fiber Thermometer

Mapping Intimacies ◽

10.1115/imece2001/htd-24309 ◽

2001 ◽

Author(s):

Matthew R. Jones

Keyword(s):

Genetic Algorithm ◽

Optical Fiber ◽

Temperature Profile ◽

Inverse Method ◽

Elevated Temperatures ◽

Radiative Flux ◽

Metallic Coating ◽

Inversion Method ◽

Spectral Measurements ◽

Alternative Approach

Abstract A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Temperature readings are obtained by measuring the spectral radiative flux at the end of the fiber at two wavelengths. The ratio of these measurements is used to infer the temperature at the sensing tip. However, readings from blackbody optical fiber thermometers are corrupted by self-emission when extended portions of the probe are exposed to elevated temperatures. This paper describes an alternative approach for using blackbody optical fiber thermometers that avoids the problems due to self-emission. In the alternative approach, an inverse method incorporating spectral measurements is used to reconstruct the temperature profile along the fiber. A genetic algorithm is used as the basis for the inversion method.

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A Hybrid-Inverse Method for Predicting the Temperature Profile Along a Blackbody Optical Fiber Thermometer

Heat Transfer, Volume 7 ◽

10.1115/imece2002-39551 ◽

2002 ◽

Cited By ~ 1

Author(s):

David G. Barker ◽

Matthew R. Jones

Keyword(s):

Genetic Algorithm ◽

Optical Fiber ◽

Temperature Profile ◽

Inverse Method ◽

Elevated Temperatures ◽

Search Space ◽

Computational Time ◽

Inversion Algorithm ◽

Gradient Based ◽

Spectral Intensities

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Temperature readings are obtained by measuring the spectral intensity at the end of the fiber at two wavelengths. The ratio of these measurements is used to infer the temperature at the sensing tip. However, readings from blackbody optical fiber thermometers are corrupted by self-emission when extended portions of the fiber are exposed to elevated temperatures. The error due to self-emission by the fiber may be eliminated using spectral remote sensing. In this method, the radiation exiting the fiber is measured in portions of the visible and infrared spectrum, and the measured spectral intensities are used to reconstruct the temperature profile along the fiber. One method of reconstructing the temperature profile along the fiber is to use a genetic algorithm. Genetic algorithms are, however, computationally expensive. This paper describes a method for decreasing the computational time by implementing a hybrid inversion algorithm. This hybrid algorithm first uses a genetic algorithm to narrow the search space. A gradient-based method is then used to complete the inversion process. Results from the genetic algorithm alone, the gradient-based method alone and the hybrid method are presented.

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Two Fiber Optical Fiber Thermometry

10.1115/imece2000-1421 ◽

2000 ◽

Author(s):

Matthew R. Jones ◽

Jeffery T. Farmer ◽

Shawn P. Breeding

Keyword(s):

Optical Fiber ◽

Elevated Temperatures ◽

Systematic Errors ◽

Radiative Flux ◽

Metallic Coating ◽

Temperature Measurements ◽

Single Fiber ◽

Random Errors ◽

Fiber Optical

Abstract An optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity, and the emission from this cavity is approximately equal to the emission from a blackbody. Temperature readings are obtained by measuring the spectral radiative flux at the end of the fiber at two wavelengths. The ratio of these measurements is used to infer the temperature at the sensing tip. However, readings from optical fiber thermometers are corrupted by emission from the fiber when extended portions of the probe are exposed to elevated temperatures. This paper describes several ways in which the reading from a second fiber can be used to correct the corrupted temperature measurements. It is shown that two of the correction methods result in significant reductions in the systematic errors. However, these methods are sensitive to random errors, so it is preferable to use a single fiber OFT if the uncertainties in the measurements are large.

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Temperature Measurements Using a High-Temperature Blackbody Optical Fiber Thermometer

Journal of Heat Transfer ◽

10.1115/1.1571085 ◽

2003 ◽

Vol 125 (3) ◽

pp. 471-477 ◽

Cited By ~ 9

Author(s):

David G. Barker ◽

Matthew R. Jones

Keyword(s):

High Temperature ◽

Optical Fiber ◽

Temperature Profile ◽

Elevated Temperatures ◽

Short Length ◽

Experimental Results ◽

Temperature Measurements ◽

Spectral Measurements ◽

Temperature Environment ◽

High Temperature Environment

A blackbody optical fiber thermometer consists of an optical fiber whose sensing tip is given a metallic coating. The sensing tip of the fiber forms an isothermal cavity and the emission from this cavity is approximately equal to the emission from a blackbody. When a short length of the fiber is exposed to a high temperature environment, the temperature at the sensing tip can be inferred using the standard two-color approach. If, however, more than a short length of the fiber is exposed to elevated temperatures, emission by the fiber will result in erroneous temperature measurements. This paper presents experimental results that show it is possible to use additional spectral measurements to eliminate errors due to emission by the fiber and measure the tip temperature. In addition, the technique described in this paper can be used to obtain an estimate of the temperature profile along the fiber.

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Genetic Algorithm for the Reconstruction of Bragg Grating Sensor Strain Distribution

Aerospace ◽

10.1115/imece2003-42669 ◽

2003 ◽

Cited By ~ 1

Author(s):

Apninder Gill ◽

Kara Peters ◽

Michel Studer

Keyword(s):

Genetic Algorithm ◽

Optical Fiber ◽

Strain Distribution ◽

Axial Strain ◽

Simulated Data ◽

Strain Sensors ◽

Bragg Grating ◽

Inversion Method ◽

Period Distribution ◽

Bragg Grating Sensor

Optical fiber Bragg gratings are unique among embedded strain sensors due to their potential to measure strain distributions with a spatial resolution of a few nanometers over gage lengths of a few centimeters. This article presents a genetic algorithm for the interrogation of optical fiber Bragg grating strain sensors. The method calculates the period distribution along the Bragg grating which can then be directly related to the axial strain distribution. The period distribution is determined from the output intensity spectrum of the grating via a T-matrix approach. The genetic algorithm inversion method presented requires only intensity information and reconstructs non-linear and discontinuous distributions well, including regions with significant gradients. The method is demonstrated through example reconstructions of Bragg grating sensor simulated data. The development of this algorithm will permit the use of Bragg grating sensors for damage identification in regions close to localized damages where strong strain non-linearities occur.

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