Fibre-optic thermal detector

FIELD: physics.

SUBSTANCE: thermal detector has an illuminating and a receiving light guide, the first ends of which are connected to a light source and a photodetector, and second ends to a guided Y fibre-optic splitter, the common input/output of which is fitted with a heat-sensitive element, having a mirror surface and made in form of an opaque blind made from material with shape memory effect, attached by one end to the butt-end of a measuring light guide. The blind is given reversible shape memory at flexure. In the initial state, below the direct martensitic transformation temperature, the free end of the blind is tightly pressed by the mirror side to the butt-end of the measuring light guide, thereby completely covering the aperture of the light guide. In a state higher than the inverse martensitic transformation temperature, the free end of the blind deviates by an acute angle from the plane of the butt-end of the measuring light guide.

EFFECT: faster operation owing to reduction of the size and weight of the heat-sensitive element, simplification, reduced loss when transmitting reflected light flux to the receiving light guide and high sensitivity owing to significant change in intensity for small temperature changes.

5 dwg

 

The invention relates to measuring technique and can be used in systems temperature/heat control as a thermal relay, alarms systems fire alarm companies, residential areas, railway and road transport; thermostats in temperature of different objects, including biological; sensors overheating of liquid and vapor in the radiator water cooling, oil-shirts transformers cooling, heat exchangers, steam boilers; thermal sensors for process control in other areas of technology. The device can be used for remote temperature measurement, especially in conditions of high level radio frequency and electromagnetic interference.

Known fiber optic temperature sensors containing illuminating and receiving fibers and heat-sensitive element on the basis of Bragg gratings (CN patent No. 101253392 (A), G01D 5/353; G01D 5/38; G01K 11/32; G01L 9/00, 27.08.2008; US patent No. 2006146909 (A1), G01J 5/00, 06.07.2006; US patent No. 2001022804 (A1), G01K 5/52; G01K 11/32; G01K 5/00; G01K 11/00, 20.09.2001) and based on resonant systems (US patent No. 2003118075 (A1), G01K 11/32, G01K 11/00, 26.06.2003; patent RU No. 2161783 C2, G01K 11/32, 30.12.1998; RU patent No. 2110049 C1, G01K 11/32, G02B 6/00, 23.08.1996; RU patent No. 2082119 C1, G01K 11/32, 20.05.1994; US patent No. 6141098, G01B 009/02, 31.10.2000), which is registered with the phase modulation of the SV is the generated by changes of the ambient temperature. Known fiber optic sensor (patent US 5641955, G01D 5/26, G01D 5/353, G01K 5/48, G01K 5/00, H01J 005/16, 24.06.1997)containing temperature-sensitive elements of the alloy with shape memory effect, which when heated remember given them the shape and exert mechanical pressure on the optical fiber, which is measured using the interferometer. However, such sensors are structurally complex, for temperature measurement requires expensive specialized equipment.

Fiber-optic sensors, the principle of which is based on amplitude modulation of light propagating in the fiber, are more simple and cheap.

For example, the known fiber-optic temperature sensors (US patent No. 5419636, G01K 5/00, G01K 5/52, 30.05.1995; JP patent No. 2009052964 (A), G01K 11/12, G01K 11/00, 12.03.2009), in which the section of the fibre is removed from the shell is covered with a material with a different coefficient of thermal expansion. The change of the ambient temperature leads to microengine on the sensitive area of the fiber and, as a consequence, the intensity of light passing through this area.

Known fiber optic sensor (patent CA No. 2671146 (A1), G01K 5/00, G01K 5/48, G01K 15/00, 26.06.2008), which contains at least one light-emitting optical fiber and one in the fiber, receiving light, and located between the tensile object that overlaps the emitted light when the temperature of the object.

The disadvantage of these sensors is their large thermal inertia, limiting the performance of the device.

Known fiber optic temperature sensor (patent RU №2256890 C1, G01K 11/32, 03.03.2004), which contains illuminating and receiving fibers, the first ends of which are connected, respectively, to the light source and the photodetector, and the second - to capsule, which due to reflections from intracapsular mirror is the transmission of the light flux from the illumination optical fiber to the receiving fiber. Connecting the illuminating and receiving fibers to a capsule made through directional Y-shaped fiber optic splitter, General I / o, which is fixed in the capsule opposite the intracapsular mirror, which is made at the end of the rod attached to its opposite end at the bottom of the capsule with a clearance relative to the inner side of the capsule. The capsule and the rod are made of dielectric materials which differ in their coefficients of thermal linear expansion.

The principle of the sensor prototype based on the commit changes optical communication between the light and the receiving light guides Newcastle "end light fiber intracapsular mirror - the face of the receiving light guide". This relationship changes when the temperature changes as a result of different thermal expansion capsules, and acting inside capsules I / o Y-shaped fiber optic splitter, leading to changes in the intensity of the output light flow.

This invention is the closest analogue to the proposed device, i.e. the prototype.

The drawback of the prototype is restricted, in particular, the accurate measurement of the temperature at relatively high speeds change of the ambient temperature, because, first, you need a considerable amount of time for heating/cooling of the capsule and rod of dielectric material, a second, different rate of heating/cooling, which leads to errors in the temperature measurement.

In addition, the device is a prototype require complicated alignment and harmonization intracapsular mirror and common I / o fiber optic splitter.

The task of the invention is to increase the performance of the sensor by reducing the size and mass of the sensitive element and the simplification of the device.

In addition, the implementation of the device is achieved technical result consists in reducing poterba transmission of the reflected light flux into the receiving fiber and increasing the sensitivity of the sensor due to significant changes in the intensity returned to the receiving optical fiber, the light flux with small changes temperature.

This task is solved by the creation of a fiber optic sensor that contains illuminating and receiving fibers, the first ends of which are connected, respectively, to the light source and the photodetector, and the second is directed to the Y-shaped fiber-optic splitter, General I / o, which is provided with a thermosensitive element having a mirror surface due to the reflection from which the transmission of the light flux from the illumination optical fiber for receiving the optical fiber, while the sensing element is designed as a miniature thin opaque curtains from a material with shape memory effect, with one end attached to the end of the measuring light guide connected to a common input the output of the splitter, and curtain set reversible shape memory bending in such a way that in the initial state (below the temperature of the direct martensitic transformation in the material of the blinds) the free end of the roller blind his side mirror tightly against the end face of the measuring light guide completely overlapping svetonapravlyayuschim aperture of the fiber and in the condition above the temperature of the reverse martensitic transformation in the material of the blinds is rejected at an acute angle from the plane of the end face of the measuring light guide.

The invention is illustrated by the schematic, h is tegami, showing:

Figure 1 - fiber-optic sensor.

Figure 2 - the sensing element from a material with APP.

Fiber-optic temperature sensor (the temperature sensor) contains (1) lighting 1 and output 2 optical fibers, the first ends of which are connected, respectively, to the light source 3 and a sensor 4, and the second is directed to the Y-shaped fiber-optic splitter 5, the total I / o of the coupler 5 is connected with one end of the measuring light guide 6, at the other end of which is the sensing element 7, having a mirror surface facing the end face of the light guide 6, due to the reflection from which the transmission of the light flux from the illumination optical fiber 1 to the receiving light guide 2. The optical fiber 6 may be of considerable length for remote temperature measurement.

The sensing element 7 is designed as a miniature thin opaque curtains from a material with shape memory effect (APF), for example, from an alloy of Ti50Ni25Cu25(at.%), manufactured by the method of fast quenching from the melt in the form of a tape with a thickness of 10-50 μm and a width of 1-10 mm Shutter 7 one end fixed on the end face of the light guide 6, for example heat-resistant (up to 1000°C) adhesive TC-1000, and its other end free (figure 2). The shutter 7 can be mounted as direct the military in the plane of the end face of the optical fiber 6 (figa, b)and on the lateral surface (FIGU, g).

Using a special method of thermomechanical processing of the shutter 7 is set reversible shape memory bending in such a way that in the initial state (below the temperature of the direct martensitic transformation Mtomaterial blinds 7) the free end of the shutter 7 of the mirror-side pressed against the end face of the light guide 6, completely covering svetonapravlyayuschim aperture of the fiber and in the condition above the temperature of the reverse martensitic transformation Andtothe material of the blinds is rejected at an acute angle from the plane of the end face of the light guide 6. The angle is calculated or selected experimentally depending on the size of the cross-section of the fiber 6 and svetonapravlyayuschie part, for example the diameter of the fiber and its core, and the size of the shutter 7 and its mounting so that the luminous flux reflected from the mirror surface of the shutter 7 and trapped in the light guide 6, was close to zero.

The shutter 7, for example, 500×300×10 μm made of a tape or film of the alloy with APP one of the known methods: mechanical cutting (cutting), laser cutting, photolithography.

Method of making a reversible shape memory of the shutter 7 can be implemented, for example, as follows. Cut strips of rapidly quenched amorphous alloy TiNiCu of ibeatza around a cylindrical mandrel, locked into position and annealed in a furnace for the crystallization of the alloy, for example, at 500°C for 3-30 minutes. The diameter of the mandrel and the mode of crystallization annealing are chosen so that after cooling and release of the shutter 7 it is capable of reversible angular displacement of 90 degrees at cyclic temperature change in the range of martensitic transformation.

Another way to make a reversible shape memory consists in the following. On the surface of the pre-stretched (to a value of relative deformation not exceeding the maximum martensitic shear) tape or film with APF is applied (for example, by electroplating or vacuum deposition) metal (such as Nickel or platinum) layer. Heating tape this layer will prevent the recovery by APT the original length of ribbon that will lead to Flexural deformation of composite materials.

Mirror surface roller blind is provided, for example, by manufacturing it from rapidly quenched amorphous alloy on the basis of TiNiCu with crystallization by annealing in a vacuum furnace or a thin metal layer, such as aluminum or silver, a vacuum deposition method.

As the light source 3 can be applied laser module DMPO-14 cable multimode volconn the m output terminated with an optical connector type FC/PC, and as of the photodetector 4 - receiving module DFD MM, which includes InGaAs PIN photodiode and an optical connector type FC/PC.

The optical fibers 1 and 2 can be a multimode optical fiber "quartz/quartz" type MM ⌀50/125 µm optical connector type FC/PC, a splitter 5 - standard fiber optic coupler 1×2 (50×50%) type MM ⌀50/125 μm. When the optical fibers 1 and 2, the coupler 5 and one end of the optical fiber 6 is equipped with an optical connector type FC/PC, the second end of the optical fiber 6 has a polished end face or embedded in the ceramic plate, for example, with a diameter of 1 mm.

For operation of the sensor in the special conditions of the sensing element 7 may be provided with a protective thin metal cap, for example, with a diameter of 1.2 mm and a length of 2 mm of copper. The protective cap is attached tightly, for example, using a heat-resistant adhesive, at the end of the light guide 6, preventing external mechanical impact on the curtain. At the same time, it effectively transfers heat from the environment to the blind, enabling a sensor in the gas and solid and in liquid medium.

The inventive fiber optic sensor works as follows.

In the initial state at a temperature below Mtothe free end of the shutter 7 is pressed against the end face of the optical fiber 6 (IgA, in), while the optical radiation from the light source 3 through the light guide 1, the coupler 5 and the light guide 6, falls on the mirror surface of the shutter 7 (figure 1). The light reflected from the surface of the shutter 7, is introduced back into the light guide 6, and a portion of the radiation passing through the optical fiber 2, fall on the photodetector 4, the output of which luminous flux is converted into an electrical signal. The increase in the temperature of the environment in which the sensor leads to the fact that the material of the shutter 7 starts to happen structural phase transformation of the martensitic type, accompanied by a change in the shape of the shutter 7 by implementing APP. In accordance with a pre-specified form roller 7 starts to bend, increasing the deflection angle from the plane of the optical fiber 6 with increasing temperature, while part of the light reflected from the mirror surface roller blind 7 enters the light guide 6 and the photodetector 4. The result is a decrease in the intensity of the signal at the output of the photodetector 4, reaching its minimum value after reaching the temperature of the reverse martensitic transformation Andtothe material of the shutter 7, when the shutter 7 is in the final state (figb, g). When cooled to a temperature of Mtothe shutter 7 is returned to its original state due to the implementation of reversible APP, snuggling zerkal the th surface to the end face of the light guide 6, and the intensity of the output signal at the photodetector 4 again increases to its maximum value.

Tight pressing of the shutter 7 of the mirror surface to the end face of the measuring light guide 6 provides the maximum return of the reflected light flux back into the light guide 6, thereby increasing the sensitivity of the device by increasing the ratio of signal to noise. When this deviation blinds 7 at a small angle from the plane of the end face of the light guide 7 (under small temperature changes) leads to a significant change in the intensity of the returned light guide 6 of the light flux and, accordingly, the intensity of the output signal at the photodetector 4, for example, when using multimode optical fiber type MM ⌀50/125 μm as a measuring fiber deflection roller blind 7 from the plane of the end face of the light guide 6 even on the corner of 1-5 degrees can lead to a decrease in the intensity of the returned light guide 6 of the light flux by 60-90%. Thus, it can significantly improve the sensitivity of the sensor.

The device can be used for temperature measurement, and as a threshold of the temperature sensor. In the first case, for the manufacture of blinds 7 preferably is selected hysteresis-free material with APF, possessing a wide temperature range of martensitic transformed who I am, and in the second case - mainly material with APP with the most narrow range of martensitic transformation.

Operating temperature range of the sensor is determined by the critical temperature martensitic phase transformations in the material with APP and can vary in a wide interval (for example, from -150 to +400°C) due to changes in the composition of the alloy.

The inventive fiber optic sensor provides increased performance of the sensor in comparison with analogues due to significantly reduce the size and mass of the sensitive element, and also allows to considerably simplify the device.

In addition, the inventive device provides a reduction of losses at the input reflected from the shutter of the light flux in the measuring optical fiber in comparison with the known devices, thereby increasing the sensitivity of the device.

In addition, the claimed invention improves the sensitivity of the sensor due to significant changes in the intensity returned to the measuring optical fiber, the light flux at small angles of deflection of the roller blind from the plane of the end face of the measuring light guide, i.e. at small temperature changes.

When this sensor is optically passive and has a high resistance to electromagnetic noise.

Fiber optic thermogut the IR, contains illuminating and receiving fibers, the first ends of which are connected respectively to the light source and the photodetector, and the second is directed to the Y-shaped fiber-optic splitter, General I / o, which is provided with a thermosensitive element having a mirror surface due to the reflection from which the transmission of the light flux from the illuminating light guide for receiving light guide, characterized in that the sensing element made in the form of opaque curtains from a material with shape memory effect, with one end attached to the end of the measuring optical fiber connected to the common input-output coupler, with the shutter set reversible shape memory bending in such a way that in the initial state, is lower than the temperature of the direct martensitic transformation in the material of the blinds, the free end of the roller blind his side mirror tightly against the end face of the measuring light guide completely overlapping svetonapravlyayuschim aperture of the fiber and in the condition above the temperature of the reverse martensitic transformation in the material of the blinds is rejected at an acute angle from the plane of the end face of the measuring optical fiber.



 

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