Patent Description:
Overheat detection is especially important in an environment, such as an aircraft environment, that cannot practically be evacuated. Overheat detection may facilitate the mitigation of system failures. Overheat detection is typically performed along bleed air ducts and in compartments containing bleed air ducts. Bleed air refers to pressurized air that is bled from the compressor section of the engine or auxiliary power unit. The bleed air may be used for pressurization, air conditioning, wing and engine deicing, water system pressurization and other functions. A leak in the bleed air system can lead to loss of system function, overheat, or fire. In some cases, other areas containing heat generating equipment, such as the auxiliary power generation equipment, may also be monitored for overheat. <CIT> discloses overheat detection using a fibre Bragg grating array by time-of-flight. <CIT> relates to an optical fiber grating sensing and temperature self-compensation-based hoop loosening self-monitoring device and method. <CIT> discloses a fibre-grating-based vibration fault monitoring method of a pipeline system.

The present invention provides a detection system for use in an aircraft, as claimed in claim <NUM>.

In addition to one or more of the features described herein, the system also includes one or more photodetectors to detect an amplitude of the reflected signals at different wavelengths.

In addition to one or more of the features described herein, the system also includes a circulator to direct the light from the light source into the optical fiber and to direct the reflected signals to the one or more photodetectors.

In addition to one or more of the features described herein, the light source generates the light as pulses, with each pulse having one of the two or more wavelengths.

In addition to one or more of the features described herein, the system also includes a second optical fiber arranged in parallel with the optical fiber along the structure and affixed with the clamps.

In addition to one or more of the features described herein, the second optical fiber includes the two or more sets of FBGs.

In addition to one or more of the features described herein, the processing circuitry identifies the overheat condition using the optical fiber and to identify the vibration using the second optical fiber.

In addition to one or more of the features described herein, each of the two or more FBGs of the optical fiber has a different grating pitch than others of the two or more FBGs and generates the reflected signals with a different reflected wavelength than the others of the two or more FBGs.

In addition to one or more of the features described herein, the overheat condition and the vibration cause a shift in the reflected wavelength of the reflected signals produced by affected ones of the two or more FBGs, the shift being periodic over a predefined duration when based on the vibration and the shift being non-periodic over the predefined duration when based on the overheat condition.

In addition to one or more of the features described herein, the processing circuitry identifies a portion of the optical fiber that experiences the overheat condition or the vibration and one or more of the clamps that are affected based on identifying which of the two or more FBGs are the affected ones of the two or more FBGs.

The present invention also provides a method of assembling a detection system in an aircraft as claimed in claim <NUM>.

In addition to one or more of the features described herein, the method also includes arranging one or more photodetectors to detect an amplitude of the reflected signals at different wavelengths.

In addition to one or more of the features described herein, the method also includes arranging a circulator to direct the light from the light source into the optical fiber and to direct the reflected signals to the one or more photodetectors.

In addition to one or more of the features described herein, the arranging the light source includes configuring the light source to generate the light as pulses, with each pulse having one of the two or more wavelengths.

In addition to one or more of the features described herein, the method also includes arranging a second optical fiber in parallel with the optical fiber along the structure and affixed with the clamps.

In addition to one or more of the features described herein, the configuring the processing circuitry includes the processing circuitry identifying the overheat condition using the optical fiber and identifying the vibration using the second optical fiber.

In addition to one or more of the features described herein, the arranging the optical fiber includes each of the two or more FBGs of the optical fiber having a different grating pitch than others of the two or more FBGs and generating the reflected signals with a different reflected wavelength than the others of the two or more FBGs.

In addition to one or more of the features described herein, the configuring the processing circuitry to identify the overheat condition and monitor the vibration includes identifying that the overheat condition and the vibration cause a shift in the reflected wavelength of the reflected signals produced by affected ones of the two or more FBGs, the shift being periodic over a predefined duration when based on the vibration and the shift being non-periodic over the predefined duration when based on the overheat condition.

In addition to one or more of the features described herein, the configuring the processing circuitry includes the processing circuitry identifying a portion of the optical fiber that experiences the overheat condition or the vibration and one or more of the clamps that are affected based on identifying which of the two or more FBGs are the affected ones of the two or more FBGs.

As previously noted, an overheat detection system in an aircraft detects overheat conditions, for example, along bleed air ducts in various locations of aircraft such as the left and right engine strut, left and right wings and body, and main wheel well. A prior approach to overheat detection involves eutectic salt packed into an Inconel tube with a center nickel wire conductor. When an overheat condition occurs, impedance of the eutectic salt drops, causing current flow between the outer sheath and center nickel conductor that is sensed as a signal of the overheat condition. Another prior approach involves using an optical fiber with fiber Bragg gratings (FBGs) for overheat detection. In both cases, the Inconel tube or optical fiber may be run along an aircraft structure with clamps affixing the tube or fiber to the structure at different positions. These clamps hold the linear overheat sensors in place, ensuring proper positioning of the sensor as well as providing structure and strength to the sensor assembly. However, if one or more of the clamps is loose or broken, the result may be long unsupported sections of the tube or fiber that are vulnerable to vibration. The vibration can lead to failure of the overheat detection system. If a clamp fails, there may be insufficient support for the sensor holding structure. This lack of support could result in the structure experiencing higher than expected vibration and possibly sensor damage or loss of the intended functionality of overheat detection. Clamp damage may be caused during maintenance or because of aging and fatigue, for example.

Embodiments of the systems and methods detailed herein relate to overheat detection with clamp health monitoring. Two optical fibers secured by the same clamps may be used such that one performs overheat detection and the other performs vibration monitoring. Alternately, one optical fiber may be used to perform both overheat detection and vibration monitoring. Monitoring for loss of clamping capability may provide an alert to the possibility of eventual loss of the overheat sensor and may allow preventative maintenance to ensure continued proper operation of the overheat system. Optical fibers typically refer to a core, cladding, and coating. The optical fibers according to one or more embodiments may be within a protective tubing. Thus, for example, two optical fibers may refer to one tubing that includes the two sets of cores, cladding, and coating or two sets of cores, cladding, and coating in two separate tubes.

<FIG> illustrates aspects of an exemplary aircraft <NUM> that includes a detection system <NUM> that performs overheat detection and clamp health monitoring according to one or more embodiments. Part of a structure <NUM> (e.g., bleed air duct, fuselage) is shown. An optical fiber <NUM> is shown affixed to the structure <NUM> by clamps <NUM> that are spaced along the structure <NUM>. As discussed with reference to <FIG>, two optical fibers <NUM> may be part of the detection system <NUM> according to alternate embodiments. As discussed with reference to <FIG>, light is injected into the one or more optical fibers <NUM> and reflected light is detected to monitor overheat and the condition of the clamps <NUM>. As shown in <FIG>, FBGs <NUM> are inscribed in the one or more optical fibers <NUM> to facilitate the monitoring.

<FIG> illustrates aspects of a detection system <NUM> that performs overheat detection and clamp health monitoring according to one or more embodiments. According to the exemplary embodiment shown in <FIG>, one optical fiber 210a is used for overheat detection, and the other optical fiber 210b is used to monitor the state of the clamps <NUM>. A long unsupported portion <NUM> of the optical fibers <NUM> is indicated. This area may have resulted from a clamp <NUM> breaking or falling off, for example, and the optical fiber <NUM> in this portion <NUM> may be more susceptible to vibration. The FBGs <NUM> inscribed at different parts of the optical fibers <NUM> are shown in <FIG> and the grating period of each set of FBGs <NUM> is different. The optical fibers 210a, 210b may be identical in the FBGs <NUM> that they include but could also have different variations in the grating period of the FBGs <NUM> according to alternate embodiments. In both the separate optical fiber <NUM> embodiment shown in <FIG> and the single optical fiber <NUM> shown in <FIG>, the one or more optical fibers <NUM> may be single mode or multi-mode.

<FIG> details aspects of a detection system <NUM> that performs overheat detection and clamp health monitoring according to one or more embodiments. An optical fiber <NUM> is shown affixed to a structure <NUM> by clamps <NUM>. FBGs <NUM> are shown inscribed in the optical fiber <NUM>. Four sets of FBGs <NUM> are shown in <FIG>. Each set of FBGs <NUM> has a different grating period p. A light source <NUM> produces light L. The light L may be produced in pulses with each pulse having a different wavelength λ, for example. A circulator <NUM> directs the light L from the light source <NUM> into the optical fiber <NUM>. Each set of FBGs <NUM> reflects only the light of a particular wavelength λpi that corresponds with its grating period pi, where i is an index for each set of FBGs <NUM>. Because each set of FBGs <NUM> has a different grating period pi, each set of FBGs <NUM> reflects light of a different wavelength λpi.

When the optical fiber <NUM> is subjected to an overheat condition or vibration, a set of FBGs <NUM> that is affected (i.e., is also subjected to a temperature change or vibration) will reflect a wavelength λpi' that is shifted from the wavelength λpi corresponding to its initial grating period pi. This is because a temperature change or vibration will change the initial grating period pi of the set of FBGs <NUM>. By arranging an optical fiber <NUM>, as shown, with different initial grating periods pi that reflect different wavelengths λpi, a shift in one or more of those wavelengths λpi may be used to identify the affected area of the optical fiber <NUM>.

For example, a portion 205x of the optical fiber <NUM> is indicated and includes a set of FBGs 310x. If the set of FBGs 310x initially provides reflections R of light with a wavelength λpx that subsequently shifts to a wavelength λpx', then an overheat condition or vibration in the portion 205x of the optical fiber <NUM> may be detected based on the shift. If vibration is detected, the clamps <NUM> on either side of the portion 205x may be checked. Alternately, a vibration indication by one of the sets of FBGs <NUM> on either side of the FBGs 310x may help to identify which clamp <NUM> in particular may be damaged. That is, if the FBGs to the right of the FBGs 310x also indicate vibration, then the clamp <NUM> between the FBGs 310x and the FBGs <NUM> to their right may be isolated for inspection, repair, or replacement. In an alternate embodiment, the FBGs <NUM> may be disposed at the clamps <NUM> rather than between them. More specifically in the exemplary embodiment with a separate optical fiber <NUM> used for vibration detection and, thus, clamp health monitoring, the FBGs <NUM> of the clamp health monitoring optical fiber <NUM> may be disposed at the clamps <NUM>. In this case, any change in strain of a clamp <NUM> (e.g., loosening of the clamp <NUM>) may be detected based on reflections R from the corresponding FBG <NUM>.

The reflections R are directed by the circulator <NUM> to one or more photodetectors <NUM>. That is, the photodetector <NUM> shown in <FIG> may be an array of photodetectors that each detect a different wavelength or wavelength range. The amplitude detected by the one or more photodetectors <NUM> may then be provided to processing circuitry <NUM>. The processing circuitry <NUM> may include one or more memory devices and processors. The processing circuitry <NUM> may identify the portion <NUM> of the optical fiber <NUM> (and thus identify proximate clamps <NUM>) affected by overheat or vibration and provide an alert, for example. An overheat condition may be distinguished from vibration based on a rate of change of the reflected wavelength from a given set of FBGs <NUM> and periodicity of the change within a duration d, as further discussed with reference to <FIG>.

<FIG> shows exemplary reflections R1 and R2 resulting from an overheat condition and from vibration. Each of the reflections R1 and R2 may correspond to a different FBG <NUM>, and each of the graphs may correspond to a different optical fiber <NUM> according to the exemplary embodiment shown in <FIG>. As <FIG> indicates, over a duration d, an overheat condition may be distinguished from vibration based on the reflections R1 and R2. As shown, over the duration d, a temperature increase results in an increase in wavelength shift Δλ over time. In that same duration d, an increase in vibration results in a periodic wavelength shift Δλ. Because some vibration is generally present in an aircraft <NUM>, a baseline vibration may be subtracted from the vibration result to determine if additional vibration resulting from an issue with one or more clamps <NUM> is present. The baseline vibration may be a calibrated value based on a type of aircraft <NUM>, for example. That is, vibration may result in a high rate of change of the shifted wavelength λpi' that is periodic, while a temperature increase (i.e., overheat condition) may result in a relatively low rate of change of the shifted wavelength λpi' that is also periodic.

As noted with reference to <FIG>, when a second optical fiber <NUM> is present, one optical fiber <NUM> may be used to monitor vibration while the other is used to perform overheat detection. When two separate optical fibers <NUM> are used, they may be in the same or in different protective tubes, a previously noted. The frequency of light L injected into the optical fiber <NUM> that is used for overheat detection may be selected to minimize the effect of vibration. Similarly, the frequency of light L injected into the optical fiber <NUM> that is used for overheat detection may be tuned to clearly demonstrate the vibration effects.

Claim 1:
A detection system (<NUM>) for use in an aircraft (<NUM>) comprising:
a first optical fiber (<NUM>, 210a) arrangeable along a structure (<NUM>) of the aircraft and affixable to the structure with clamps (<NUM>) that are spaced apart along the structure;
wherein the first optical fiber includes two or more fiber Bragg gratings (FBGs);
a light source (<NUM>) configured to generate light (L) with two or more wavelengths for injection into the optical fiber; and the system characterised by comprising
processing circuitry (<NUM>) configured to identify an overheat condition and monitor vibration experienced by the first optical fiber based on reflected signals (R) generated by the two or more FBGs (<NUM>), wherein, when the first optical fiber is affixed to the structure with clamps, the processor is furthermore configured to indicate integrity of the clamps by monitoring the vibration.