WO2011073764A2

WO2011073764A2 - Distributed combi sensors

Info

Publication number: WO2011073764A2
Application number: PCT/IB2010/003236
Authority: WO
Inventors: Koyilothu Sarinkumar Anakkat; Ruknudeen Fazludeen
Original assignee: Honeywell International Inc.
Priority date: 2009-12-18
Filing date: 2010-12-14
Publication date: 2011-06-23
Also published as: WO2011073764A3

Abstract

The embodiments are related to a sensor, a sensing system, and a sensing method, which may be used for sensing multiple measurands (e.g., gases or temperature variations), hi an embodiment, the sensor may include a fiber Bragg grating and a coating material coated, either on n cladding or on a partially removed cladding of the fiber Bragg grating An interaction between a particular measurand (e.g., a gas such as CO2) and the coating material (e.g., poly allyl amine) may cause a change in the refractive index of the fiber Bragg grating. The sensor may detect the particular measurand based on the change in the refractive index of the fiber Bragg grating.

Description

DISTRIBUTED COMBI SENSORS

TECHNICAL FIELD

[0001 ] Various embodiments described herein relate generally to a sensor, and more particularly to distributed combi sensors for multiple measurand sensing.

BACKGROUND

(0002] Fire sensors play a major role to save li ves and properties during a fire outbreak. A simple fire mainly includes white and black particles, heat, and gases (such as CO and C02). A disadvantage existing in many present day fire sensors is a slow response. The slow response may be a result of the need of contact with sufficient heat or smoke in a sensing chamber. It may take time for such heat or smoke to accumulate in the sensing chamber. Additionally, many present day fire sensors are discrete and thus may be difficult to detect fires beyond a particular range. Also distributed multiple gas detection with no electrical power across sensing elements is of great demand in mining industry for detecting gases like CH4, C02 etc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Some embodiments are illustrated by way of examples, and not by way of limitation, in the figures of the accompanying drawings in which:

[0004] Figure 1 is a diagram illustrating a sensor to detect a particular measurand according to an example embodiment;

[0005] Figure 2 is a diagram illustrating a detection system to detect multiple measurands according to an example embodiment; and

[0006] Figure 3 is a flow diagram illustrating a method to detect multiple measurands by using a plurality of distributed combi. sensors according to an example embodiment.

DETAILED DESCRIPTION [0007] In the following detailed description of embodiments of the subject matter, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration some embodiments in which the subject matter may be practiced,

[0008] The term "combi sensor" in the description refers to the presence of multiple sensors distributed along an optical fiber for the detection of multiple measurands (e.g., gases). The term ''FBG" in the description denotes a "Fiber Bragg Grating". The term "TDR" in the description denotes a "Time Domain Reflectometer". The term "OTDR" in the description denotes an "Optical Time Domain Reflectometer".

[0009] In some embodiments, a sensor including a Fiber Bragg Grating (FBG). which is coated, either on a cladding or on a partially removed cladding of FBG, with a coating material and coupled to an optical fiber, may be used to sense a particular measurand (e.g., a gas or a temperature variation). In one embodiment, the coating material may be a polymer material. When a particular measurand (e.g., a gas CO2) interacts with the coating material (e.g., poly allyl amine), the effective refractive index of the FBG will change. The change in the effective refractive index of the FBG can be probed by using a broadband light, which is centered on a particular wavelength and propagated in the optical fiber. Since the interaction between the coating material and a particular measurand may cause the changes in the effective refractive index of the FBG, the particular measurand can be detected by detecting the changes in the effective refractive index of the FBG.

[0010] In some embodiments, a system including a plurality of combi sensors and a time domain reflectometer, in combination with dispersive elements, coupled to the optical fiber may be used to sense multiple measurands (e.g., multiple gases or a temperature variation) based on the detection of the changes in the effective refractive index of the FBGs.

[0011] In some embodiments, a method may be used to detect multiple measurands. The method may include, for example, attaching a plurality of FBGs (each FBG being coated with a coating material either on the cladding or. on the partially removed cladding) to an optical fiber; detecting a change of the effective refractive index of each FBG by using a time domain reflectometer (TDR), in combination with dispersive elements, and a broadband light pulse propagated in the optical fiber; and determining a measurand (e.g., a gas or a temperature variation) based on the change of the effective refractive index of each FBG caused by an interaction between the measurand (e.g., a gas CO2) and the coating material (e.g.. Poly A llyl Amine (PAA)). The method may also _. locate the measurand based on the detection of the change of the effective refractive index of each fiber Bragg grating with the help of OTDR using the time of flight information of the reflected light.

[0012] Figure 1 is a diagram illustrating a sensor 100 according to an example embodiment. The sensor 100 may include a FBG 10 and a coating material 20 coated either on the cladding or on the partially removed cladding of the FBG 10: The coating material 20 interacts with a particular measurand and thus causes a change in the effective refractive index of the FBG 10. Therefore, the particular measurand can be detected by the detection of the change in the effective refractive index of the FBG 10.

[0013] In some embodiments, the particular measurand may be a gas (e.g., CO, CO2 or CH4) or a temperature variation. In an embodiment, the coating material 20 may be a polymer material. For example, a gas CO2 sensitive material such as PAA or a composite of PAA with carbon nanotubes may be used as. a coating material to detect the existence of a gas CO2. Similarly, gas CO or CH4 sensitive materials may be used as coating materials to respectively detect the existence of a gas CO or CH4. For example, CO gas can be detected by coating poly aniline in combination with zeolite as mentioned in the reference Materials Science & Engineering B, 117 (2005) 276 and CH4 gas can be detected by coating Palladium (Pd) in combination with carbon nanotubes as per the references Sensors & Actuators B, 139 (2009) 453 arid the references there in. In an embodiment, a pyroelecirie material (e.g., BaTiO3 or PbTiO3) may be used as a coating material to detect the existence of a temperature variation or bare FBG without any coating can also be used to detect temperature variation. [0014] Figure 2 is a diagram illustrating a detection system 200 to detect multi measurands (e.g., gases or a temperature variation) according to an example embodiment. The detection system 200 may include an optical fiber 30, a plurality of combi sensors 100 attached (or spliced) to the optical fiber 30, and a time domain reflectometer (TDR) 40 coupled to the optical fiber 30.

[0015] In some embodiments, each sensor 100 may include a FBG 1 0 and a coating material 20 coated either on the cladding or partially removed cladding of the FBG 10. Each coating material is.adapted to interact with a particular measurand (e.g., a gas or a temperature variation). As shown in Figure 2, the plurality of combi sensors (e.g.. 100A, 1 00B and 100C) are respectively coated with different coating materials to detect multiple measurands (e.g., a temperature variation, a CO gas and a CO2 gas or the combination can be CH4 gas, CO gas and C02 gas) respectively. The interaction between a coating material 20 of a sensor 100 and a particular measurand may cause a change in the effective refractive index of the FBG 10 of the sensor 100.

[0016] In some embodiments, the TDR 40, in combination with dispersive elements, may be used to detect a change in the effective refractive index of the FBG 10 of each sensor 100 (e.g., 1 OOC) so as to identify and locate the existence of a measurand (e.g., gas C02). In an embodiment, the TDR 40 may be an Optical Time Domain Reflectometer (OTDR). The TDR 40 may, for example, include a light emitting diode 42 to emit a broadband light into an end of the optical fiber 30, a light detector 44 to collect a reflected broadband light from the same end of the optical fiber 30, and a control circuit 46 to control the operation ofthe TDR 40.

[0017] In some embodiments, the index change of the FBG 10 of each sensor 100 can be probed by the TDR 40 with a broadband light, which is centered on a wavelength and propagated in the optical fiber 30. In an embodiment, the TDR 40 may identify the existence of a measurand (e.g., a gas C02) by identifying the effective refractive index change of the FBG 10 of the sensor 100 (e.g., 100C). In an embodiment, the concentration of a gas measurand (e.g., C02) can be determined by measuring the shift in the Bragg wavelength with the TDR 40. The relationship between the Bragg wavelength and the effective index of a FBG 10 of a sensor 100 can be represented by the following equation:

Bragg Wavelength = 2 * Effective Index * Grating Period

[0018] TDR is an electronic instrument used to characterize and locate incidents (or faults) in an optical fiber. A TDR may transmit a short rise time pulse along the optical fiber. If the optical fiber is of uniform impedance and properly terminated, the entire transmitted pulse will be absorbed in the far-end termination and no signal will be reflected toward the TDR. Any impedance discontinuities will cause some of the incident signal to be sent back towards the source. Increases in the impedance create a reflection that reinforces the original pulse whilst decreases in the impedance create a reflection that opposes the original pulse. Because of this sensitivity to impedance variations, a TDR may verify optical fiber impedance characteristics, splice and connector locations and associated losses, and estimate optical fiber lengths.

[0019] The TDR 40 (as shown in Figure 2), in combination with dispersive elements, may identify and locate the effective index changes of the FBGs 10 of the sensors 100, which are coupled to the optical fiber 30. The TDR 40 thus can identify and locate a particular measurand (e.g., a gas C02) from a combi sensor system, which responds to and interacts with a coating material 20 (e.g., PAA) coated of a FBG 10 of a sensor 100 (e.g., sensor 1 00C).

[0020] Figure 3 is a flow diagram illustrating a method 300 of detecting multiple gases by using a plurality of distributed combi sensors including FBGs 100 as shown in Figure 2 according to an example embodiment.

[0021] In 302, a plurality of sensors 1 00. are attached to an optical fiber 30. Each sensor 100 includes a FBG 10 and a coating material 20 either on the cladding or on the partially removed cladding of the FBG 10. The plurality of sensors 100 can be distributed on- the walls, roofs, and floors for example without disturbing the any of the existing setups. [0022] In an embodiment, only the combi sensors 100 of the detection system 300 are exposed to the outside atmosphere, with proper protection from dust and humidity, while other parts such as the optical fiber 30 may be shielded. In an embodiment, the combi sensors 100 may be attached to the optical fiber 30 through splicing. This arrangement helps to do a point by point- repairing without disturbing the overall system 200. Maintenance and replacement of the sensors 100 can be carried out easily.

[0023] In 304, a change in the effective refractive index of the FBG 10 of each sensor 100 is detected by a TDR 40 and a broadband light pulse propagating in the optical fiber 30. In an embodiment, an optical time domain reflectometer (OTDR), in combination with dispersive elements, is used for detecting the change in the effective refractive index of the FBG 10 of each sensor 100.

[0024] In 306, a measurand (e.g., a gas CO2) is determined by a TDR 40, in combination with dispersive elements, based on the effective refractive index change of the FBG 20 of a sensor 100 (e.g., 100C). The effective refractive index change of the FBG 10 in each sensor 100 is caused by an interaction between the measurand (e.g., a gas CO2) and the coating material 20 of the sensor 100 (e.g., 100C). For example, the detection of the effecti ve refractive index change of each fiber Bragg grating may be baaed on a shift in a center wavelength of the broadband light pulse.

[0025] In 308, a measurand (e.g., a gas CO2) is located by the TDR 40 based on the detection of the effective refractive index change of the fiber Bragg grating of the sensor 100 (e.g., 100C). For example, by using an Optical Time Domain (OTDR) 40. the detection system 200 can locale the occurrence of an incident (such as a fire) with one foot resolution.

[0026] The utilization of the FBG based approach for sensing multiple measurands (such as heat, CO, CO2 and CH4) improves the detection capacity of the sensors by coating each fiber Bragg grating with coating materials, which are specific to those gases for example. Each coating material corresponds to and interacts with a particular measurand. The detection system thus can detect other gases like NO, NO2, SO2 etc from more complex fire or from any other sources. Since no voltages are needed for the combi sensors, the combi sensors are free from electric connections.

[0027] While there has been described herein the principles of the application, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation to the scope of the application.

Accordingly, it is intended by the appended claims, to cover all, modifications of the application which fall within the scope of the application.

Claims

1. A sensor comprising:

a fiber Bragg grating (FBG); and ^' . a coating material coated either on a cladding or on a partially removed cladding of the fiber Bragg grating and adapted to interact with a measurand to cause a change in an effective refractive index of the fiber Bragg grating.

2. The sensor of claim 1 , wherein the coating material includes a polymer material.

3. The sensor of claim 1 , wherein the measurand includes a gas or a temperature variation.

4. The sensor of claim 3, wherein the gas includes CO, CO2 or CH4.

5. A system of detecting multiple measurands comprising:

an optical fiber; and

a plurality of fiber Bragg gratings attached to the optical fiber, each fiber Bragg grating being coated with a coating material either on a cladding or on a partially removed cladding of the FBG thereof, the coaling material being adapted to interact with a measurand to cause a change in an effective refractive index of the fiber Bragg grating.

6. The system of claim 5, wherein the coating material includes a polymer material.

7. The system of claim 5, further comprising:

a time domain refiectometer (TDR), in combination with dispersive elements, coupled to the optical fiber to detect the change in the effective refractive index of a fiber Bragg grating of the plurality of fiber Bragg gratings so as to identify and locate the measurand.

8. The system of claim 5, wherein the time domain reflectometer includes an optical time domain reflectometer (OTDR) in combination with dispersive elements.

9. The system of claim 5, wherein the measurand includes a gas or a temperature variation.

10. The system of claim 9, wherein the gas includes CO, CO2 or CH4.

1 1. A method of detecting multiple measurands, comprising;

attaching a plurality of fiber Bragg gratings to an optical fiber, each fiber Bragg grating being coated with a coating material either on a cladding or on a partially removed cladding of the FBG;

detecting a change in the refractive index of each fiber Bragg grating by a time domain reflectometer in combination with dispersive elements; and

determining a measurand based on the change of the effective refractive index of each fiber Bragg grating caused by an interaction between the measurand and the material.

12. The method of claim 1 1 , wherein the coating material includes a polymer material. ·

13. The method of claim 1 1 , wherein detecting the change of the effective refractive index of each fiber Bragg grating is based on a shift in a center wavelength of the broadband light pulse,

14. The method of claim 1 1 , wherein detecting the change of the effective refractive index of each fiber Bragg grating utilizes a broadband light pulse propagating in the optical fiber.

15. The method of claim 1 1 , further comprising:

locating the measurand based on the detection. of the change of the effective refractive index of each fiber Bragg grating.

16. The method of claim 1 1 , wherein the time domain reflectometer includes an optical time domain reflectometer in combination with dispersive elements.

17. The method of claim 1 1 , wherein the measurand includes a gas or a temperature variation.

1 8. The method of claim 1 1 , wherein the coating material includes poly allyl amine (PAA) or a composite of poly ally] amine with carbon nanotubes for detecting CO2.

19. The method of claim 1 1 , wherein the coating materia] includes poly aniline in combination with zeolite for detecting CO.

20. The method of claim_. 1 1 , wherein the coating material includes Palladium <Pd) in combination with carbon nanotubes for detecting CH4.