Optical-Fiber Sensors: Temperature and Pressure Sensors
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Optical-Fiber
Sensors: Temperature and Pressure Sensors K.T.V. Grattan and T. Sun
Abstract This article gives a brief review of advances in optical-fiber temperature and pressure sensors. Developments over the last two decades have seen enhancements in utility and performance, as more advanced techniques are applied. Applications to industrial problems are highlighted. Keywords: optical-fiber sensors, pressure measurement, temperature measurement.
Introduction Temperature and pressure are two of the most important parameters that are routinely measured in industry today worldwide, and for each there are a wide variety of sensors on the market. These have been reviewed elsewhere in some detail.1 Among the different techniques and technologies, optical-fiber methods are playing an increasingly important part. The positive features of the use of opticalfiber sensors for such measurements have been discussed elsewhere,2 but in summary they show specific advantages, particularly for niche markets, such as those in which the risk of explosion is high, where lightweight sensors and cables are needed, or where there is a significant level of interference from external rf sources. Furthermore, the increasing availability of high-quality, low-cost components that have “spun off” from the telecommunications industries, combined with the falling price of fiber and the availability of more sophisticated signal-processing systems, makes these measurement systems increasingly attractive to the sensor designer. The measurement of temperature is the subject of a detailed and scholarly work by Nicholas and White,3 who describe a range of methods and deal with the issues of calibration and traceability, which remain key aspects for the effective use of opticalfiber temperature sensors. In that text,
MRS BULLETIN/MAY 2002
surprisingly, optical-fiber methods do not feature at all, and radiation pyrometry is the only optical method presented. However, the lessons for thermometer use are universal and apply equally to the burgeoning range of optical-fiber sensors. The same characteristics often apply to pressure sensors; however, a number of important techniques (for both measurands) have been discussed by several authors in a recent survey of instrumentation and measurement by Dyer.4 In this brief review of the application of optical techniques for sensing temperature and pressure, a range of methods that has been discussed in the literature and implemented in industrial applications is considered. Reference to key published papers will provide further details for the interested reader. The two key measurands are first considered separately, yet where overlap in methods or measurement aspects occurs, as it inevitably does in indirect measurement systems, this is indicated where appropriate.
Optical-Fiber Temperature Measurement Several reviews of temperature measurement in general,5 and optical-fiber measurement in particular,6 have been produced, emphasizing various instrumental aspects of the subject. Early fiber-optic sensors
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