Thermal measuring and testing – Temperature measurement – Nonelectrical – nonmagnetic – or nonmechanical temperature...
Patent
1995-02-02
1997-09-30
Gutierrez, Diego F.F.
Thermal measuring and testing
Temperature measurement
Nonelectrical, nonmagnetic, or nonmechanical temperature...
374137, 25022714, 356 44, 385 13, G01K 1132
Patent
active
056720084
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a reconfigurable multipoint temperature sensor.
DISCUSSION OF THE BACKGROUND
Fibre-optic temperature or stress sensors have been the subject of numerous studies throughout the world. The field of intrinsic temperature or stress sensors has expanded particularly by virtue of the use of an optical fibre as the sensor (use of high-birefringence or polarization-maintaining optical fibres).
Production of optical sensors distributed along a birefringent fibre has made it possible to use N elementary sensors corresponding to N segments of sensor fibre. These various segments are defined by using coupling points serving as markers (delimiting these segments).
The production of coupling points on optical fibres has been studied for a long time, and today various production techniques are used, among which are: fibre and bonding the two portions after having rotated one of the fibre portions through an arbitrary angle. The main drawbacks of this method are the introduction of losses due to the reflections off the faces of the fibres and the control of the alignment and rotation of the fibre cores (diameter of the order of 5 .mu.m); fibre of chosen length is held at its ends and the fibre is rotated at one end, the other remaining fixed. A torsional stress is thus created. Using localized heating of the fibre, a polarization coupling point is thus produced. The drawbacks of this method are the use of a locally stripped fibre, a high-voltage generator and an electric arc in order to create the coupling point or points, and the irreversibility of the method of creating the coupling points; using a holographic method. The production of coupling points using this method is nowadays mainly studied by the BERTIN Company and many studies have concerned the production of index gratings in the fibres for sensor applications. The drawback of this method resides in its complexity of implementation, the need to use an additional high-power laser to produce the index gratings, and the need to employ a process for masking the fibre.
From the document DE-A-4,011,440, a measurement device is known based on an optical fibre associated with a shape-memory material which applies a longitudinal contraction to the fibre when it adopts its memorized state. This device does not make it possible to measure various temperatures or to make measurements at several points with the same optical fibre.
SUMMARY OF THE INVENTION
The subject of the present invention is an optical-fibre multipoint temperature sensor such that it is possible to define several independent temperature sensors on this optical fibre at positions, with respect to the fibre, which can be modified as required or can be defined after installing the fibre, without damaging the fibre or cutting it, without introducing losses, without having recourse to additional equipment, and all this as simply as possible.
The sensor in accordance with the invention, of the fibre-optic type, which interacts with a light source, a device for optically reading a variation in light flux and an element made of shape-memory alloy arranged on the optical fibre, this element being designed and taught so that when it is at temperatures lying on one side of the transition temperature of the constituent material it exerts virtually no stress on the fibre, and when it is at temperatures lying on the other side of the said transition temperature it exerts on the fibre a stress which can be measured by the said read device, is characterized in that the sensor is a multipoint sensor composed of several elements made of shape-memory alloy distributed along the optical fibre and in that the read device is of the time-domain reflectometry (OTDR) type.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be better understood on reading the detailed description of two embodiments, taken by way of non-limiting examples and illustrated by the appended drawing in which:
FIG. 1 is a block diagram of a sensor device in accordance with th
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Bonniau Philippe
Chazelas Jean
Turpin Marc
"Thomson-CSF"
Gutierrez Diego F.F.
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