Patent Description:
The electromagnetic environment includes energy which is the same type of energy (i.e., electrical energy) that is used by electrical and electronic equipment to process and transfer information. As such, this environment may represent a hindrance to the proper operation of systems that depend on such equipment causing latent faults within the systems of an aircraft.

Unfortunately, at present, a large cost in designing and building a commercial aircraft is providing redundant systems to deal with situations where a fault occurs when there is an undiscovered latent fault in the same system. In general, aircraft certification requires addressing latent faults and one specific latent fault that needs to be considered is possibly abraded wires in the fuel tank of an aircraft. More specifically, abraded insulation on wires in the fuel tank of the aircraft in combination with a lightning strike, static charge during fueling, or charge from another abraded wire could cause an electrical arc through the abraded location.

Known approaches to address this issue have included aircraft manufactures installing numerous extra wire mounting brackets to maintain separation between wires, and to mandate more frequent inspections inside the fuel tank of an aircraft. Some of the problems associated with these approaches includes, for example, the substantial added cost of installation and inspection of adding extra brackets that are placed in the aircraft to keep wires away from each other and from any other conductive materials. The extra weight of such brackets can add to the total weight of the aircraft. Moreover, the added costs, difficulty, and resulting downtime of inspecting these wires in the field which may include emptying the fuel tanks and sending people and/or inspection equipment physically into the fuel tanks to visually inspect the wires. As a result, the aircraft must be removed from service for the inspection, the labor cost of performing the inspection may be high, and the burden of safety and proper ergonomic techniques used during the physical inspection may be substantial.

As such, there is a need for a system and method that addresses these problems and detects the abraded insulation cheaply and reliably enough to, among other benefits, eliminate the need for the extra brackets and most of the physical inspections of the wires within the fuel tank of the aircraft.

<CIT> discloses a diagnostic method which permits the on-line and nondestructive diagnosis of the insulation degradation in a portion of the wiring in aircraft comprising: a) measuring the current flow at location of the aircraft wiring utilizing an optical current sensor with a bandwidth of de to <NUM>; b) determining the current flow within a high frequency bandwidth; and c) analysing the results of the current flow differential determination and initiate the following: i) detect and locate the point of cable failure; ii) initiate an alarm annunciation; and iii) initiate an on-board sectionalized fire suppression system.

<CIT> discloses, in accordance with its abstract, a system that finds breaches in solid insulation, as well as detecting insufficient air gaps between conductors. The system detects breaks in solid insulation by applying high voltages. The system for testing conductors is composed of a high voltage breakdown tester, a means of connecting the tester to conductors, and an added gas that is used to displace air in the proximity of the conductors.

Aspects of the invention are disclosed in the independent claims. Optional features of aspects are defined in the dependent claims.

An abraded wire detection system ("AWDS") for detecting an abrasion on a wire in a fuel tank according to a first aspect is disclosed. The AWDS includes an electrode on the fuel tank, a power source, and a current sensor in electrical series with the power source, wire, and the electrode. The current sensor includes circuitry that detects a current from the wire to the electrode. Additionally disclosed is an aircraft having a fuel tank, a wire within the fuel tank, and the AWDS.

In an example of operation, the AWDS operates as part of a method for detecting the abrasion on the wire. Specifically, the method includes filling the fuel tank with electrically conductive fuel that submerges the wire and applying a voltage signal on the wire with a power source. Furthermore, the method also includes receiving a current on the electrode in electrical series with a fuel tank wall and determining if an abrasion is present on the wire from the received current. In this example, the received current corresponds to the voltage signal.

Other devices, apparatus, systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description.

The invention may be better understood by referring to the following figures. In the figures, like reference numerals designate corresponding parts throughout the different views.

Disclosed is an abraded wire detection system ("AWDS") for detecting an abrasion on an insulated wire in a fuel tank. The AWDS includes an electrode on the fuel tank, a power source, and a current sensor in electrical series with the power source, insulated wire, and the electrode. The current sensor includes circuitry that detects a current from the wire to the electrode. Additionally disclosed is an aircraft having a fuel tank, an insulated wire within the fuel tank, and the AWDS.

In an example of operation, the AWDS operates as part of a method for detecting the abrasion on the insulated wire. Specifically, the method includes filling the fuel tank with electrically conductive fuel that submerges the insulated wire and applying a voltage signal on the insulated wire with a power source. Furthermore, the method also includes receiving a current on the electrode in electrical series with a fuel tank wall and determining if an abrasion is present on the insulated wire from the received current. In this example, the received current corresponds to the voltage signal.

More specifically, in <FIG>, a system block diagram of an example of an implementation of an aircraft <NUM> having a fuel tank <NUM> and the AWDS <NUM> is shown in accordance with the present disclosure. The AWDS <NUM> is in electrically connected with the fuel tank <NUM> via an electrical connection path <NUM>, where the electrical connection path <NUM> may include one or more wires or other type of conductors. In this example, both the fuel tank <NUM> and the AWDS <NUM> are shown as being part of a wing <NUM> of the aircraft <NUM>; however, it is appreciated by those of ordinary skill in the art, that the fuel tank <NUM> and AWDS <NUM> may be part of either wing <NUM> or <NUM>, both wings <NUM> and <NUM>, and part of the fuselage <NUM> of the aircraft <NUM>.

Turning to <FIG>, a system block diagram of an example of an implementation of the AWDS <NUM> (shown in <FIG>) is shown in accordance with the present disclosure. In this example, the AWDS <NUM> includes a power source <NUM>, a current sensor <NUM>, and at least switches <NUM> and <NUM>. The power source <NUM> is in electrical series with an electrode <NUM> and ground <NUM> via signal path <NUM> and the current sensor <NUM> via signal path <NUM>, respectively. The electrode <NUM> is in electrical series with a fuel tank wall <NUM>. In this example, the fuel tank <NUM> is assumed to have conductive walls (i.e., fuel tank wall <NUM>) that may be constructed from a metal or another conductive material. An insulated wire <NUM> is shown going through a cavity <NUM> (i.e., the inside) of the fuel tank <NUM>. The insulated wire <NUM> includes at least one inner wire <NUM> encased in a wire insulation <NUM>. In this example, the insulated wire <NUM> is shown to have an abrasion <NUM> within the cavity <NUM> of the fuel tank <NUM>. The abrasion <NUM> has worn away part of the wire insulation <NUM> exposing part of the inner wire <NUM> to the cavity <NUM> of the fuel tank <NUM>. The inner wire <NUM> is in electrical series with the first switch <NUM> and second switch <NUM>; furthermore, the inner wire <NUM> is also in electrical series with the current sensor <NUM> via signal path <NUM>. The insulated wire <NUM> is shown to be in electrical series (via the first switch <NUM> and second switch <NUM>, respectively) with other electrical/electronic parts of the aircraft <NUM> that for simplicity of illustration are shown as a first load <NUM> and second load <NUM>. In another example, it will be appreciated by those of ordinary skill in the art that the insulated wire <NUM> may enter the fuel tank <NUM> at only one point and connect to load <NUM> at some location inside tank <NUM> within cavity <NUM>, for example, if the load <NUM> is a dielectric-coated electrode in a fuel quantity indication system. In such a case, the load <NUM> may have effectively infinite resistance, so switch <NUM> may be omitted. As such, in this example, the AWDS <NUM> includes at least one switch <NUM>.

In this example, the fuel tank wall <NUM> is assumed to be conductive but it is appreciated that the fuel tank wall <NUM> may be also constructed out of non-conductive composite materials (i.e., the fuel tank <NUM> is non-conductive). In the case of a non-conductive fuel tank <NUM>, the inner surface of the fuel tank <NUM> may include some conductive material (not shown) to allow for electrical conductivity with the electrode <NUM>. As an example, the conductive materials may be conductive bands (such as, for example, metal bands) that run along the inside of the cavity <NUM> along in the inner surface of the fuel tank wall <NUM> similar to "tiger stripes. " These bands may then be in electrical series with the electrode <NUM>. These bands would also help dissipate any electric change accumulation in an electrically conductive fuel <NUM>.

It is appreciated by those of ordinary skill in the art that the electrode <NUM> may be a part of the fuel tank wall <NUM> in the case of a conductive fuel tank <NUM> or part of the conductive materials in a non-conductive fuel tank <NUM>.

It is appreciated by those of ordinary skill in the art that while only one insulated wire <NUM> is shown in this example for the purpose of ease of illustration, the fuel tank <NUM> have a plurality of insulated wires (not shown) running through the cavity <NUM> of the fuel tank <NUM>. As such, it is appreciated that the AWDS <NUM> may be in electrical series with every individual insulated wire running through the cavity <NUM> or there may be a plurality of AWDS (not shown) in electrical series with the plurality of insulated wires.

In this example, the power source <NUM> may be a direct current ("DC"), such as, for example, a battery, or alternating current ("AC") power supply. The current sensor <NUM> is, or includes, a module, device, component, or circuit configured to measure current such as, for example, an ammeter (commonly known as an "amp meter"). The current sensor <NUM> may be a digital or analog device. As an example, the current sensor <NUM> may include a threshold detector that detects if a current between the insulated wire <NUM> and the electrode <NUM> is above a predetermined current level. In general, the current sensor <NUM> measures the current leaking from the power source <NUM> to insulated wire <NUM>, through the electrically conductive fuel <NUM>, and the fuel tank wall <NUM> to the electrode <NUM>. When the current exceeds a predetermined threshold, the insulated wire <NUM> is identified as abraded.

It is appreciated by those of ordinary skill in the art that circuits, components, modules, and/or devices of, or associated with, the AWDS <NUM> are described as being in electrical series with each other. In this document, in electrical series represents connecting the circuits, components, modules, and/or devices of, or associated with, the AWDS <NUM> along a single electrical signal path such that the same current flows through all of the circuits, components, modules, and/or devices of, or associated with, the AWDS <NUM>. In this example, the closed circuit of AWDS <NUM> (the signal path from ground <NUM> through the signal path <NUM>, power source <NUM>, signal path <NUM>, current sensor <NUM>, signal paths <NUM> and <NUM>, insulated wire <NUM>, abrasion <NUM>, signal path <NUM> through the fuel <NUM>, fuel tank wall <NUM>, electrode <NUM>, and signal path <NUM> back to ground <NUM>) is a series circuit where the current <NUM> is passing through every point in the series circuit and has a constant magnitude value.

In an example of operation, the AWDS <NUM> operates as part of a method for detecting the abrasion <NUM> on the insulated wire <NUM>. Specifically, the method includes filling the cavity <NUM> of the fuel tank <NUM> with the electrically conductive fuel <NUM> that submerges the insulated wire <NUM>, applying a voltage signal <NUM> on the insulated wire <NUM> with the power source <NUM>, and receiving a current <NUM> on the electrode <NUM> that is passed to the current sensor <NUM>. The current sensor <NUM> measures the amount of current <NUM> that passes from the inner wire <NUM> at the abrasion <NUM> to the electrode <NUM> that is in electrical series with the fuel tank wall <NUM>. This current <NUM> is caused by the exposure of the inner wire <NUM> to the electrically conductive fuel <NUM> that is in electrical series with the inner surface <NUM> via physical contact within the cavity <NUM>. As a result, the inner wire <NUM> is in electrical series with the electrode <NUM> via a signal path <NUM> though the electrically conductive fuel <NUM>.

In general, before applying the voltage signal <NUM>, the aircraft <NUM> should be parked so that no acceleration forces (i.e., g-forces) or electrically conductive fuel <NUM> sloshing exposes the abrasion <NUM> to air or changes the capacitance of the insulated wire <NUM> during the measurement of current <NUM>.

In this example, the power source <NUM> is configured to produce the voltage signal <NUM> that has a predetermined voltage value that is generally small and no greater than the operating voltage of the highest voltage insulated wire in cavity <NUM> of the fuel tank <NUM>. As an example, the voltage signal <NUM> may be, for example, <NUM> volts or less, which generally produces an electric arc discharge in air of no more than approximately <NUM> microjoules of energy.

The electrically conductive fuel <NUM> is typically an antistatic fuel that is a fuel mixture of aircraft fuel with a conductivity improving additive. The conductivity improving additive is generally known as anti-static additives or static dissipater additives that increase the electrical conductivity of the aircraft fuel, such as, for example jet fuel. For example, jet fuel is a petroleum mixture of a large number of different hydrocarbons and typically has low conductivity in the order of approximately one (<NUM>) conductivity unit ("CU") to about <NUM> CU, where <NUM> CU is equal to <NUM> pico Siemens/meter (<NUM> pS/M) that equal <NUM> × <NUM>-<NUM> ohm-<NUM> meter-<NUM>. For comparison purpose, deionized water has a conductivity of about <NUM> million CU. An example of the anti-static additive utilized in the electrically conductive fuel <NUM> may be STADIS® <NUM> produced by Innospec of Englewood, Colorado. As a result, the electrically conductive fuel <NUM> reduces the chances of igniting the electrically conductive fuel <NUM> because its improved electrical conductive helps in dissipating any static charges that are accumulated either as a result of a lighting strike, static charge during fueling, or from the electrically conductive fuel <NUM> moving through pipes, hoses, values, or filters in the fuel system of the aircraft <NUM>.

It is appreciated by those of ordinary skill in the art that in this example the bottom of the power source <NUM> and electrode <NUM> are set to a ground plane that is electrically connected with ground <NUM>. As such, the voltage signal <NUM> produced by the power source <NUM> is a voltage potential that has a magnitude that is referenced to the ground plane, which is set to zero voltage by the ground <NUM>. Therefore, in this example, the current sensor <NUM> measures the amount of current <NUM> pulled from the power source <NUM> when an abrasion <NUM> is present (within the electrically conductive fuel <NUM>) that causes a circuit path to be closed around the power source where the combination of the insulated wire <NUM>, open portion of the inner wire <NUM> at the abrasion, electrically conductive fuel <NUM>, fuel tank wall <NUM>, and electrode <NUM> act as an impedance load on the power source <NUM>. This assumes that the current sensor <NUM> has very low impedance, which is usually the case.

If the current <NUM> is above a predetermined value, the current sensor <NUM>, or an alert device <NUM> in signal communication with the current sensor <NUM> via signal path <NUM>, may transmit an alert signal <NUM> that a fault exists on the insulated wire <NUM>. As an example, the current sensor <NUM>, or alert device <NUM>, may include an analog gauge that may be visually inspected or a digital system that measures the output of the current sensor <NUM> and produces the alert signal <NUM>. In this example, the fault indicates that the abrasion <NUM> is present on the insulated wire <NUM> because the amount of current <NUM> that is sensed by the current sensor <NUM> is above the predetermined value. The alert signal <NUM> may be an analog or digital signal. As an example, the predetermined value may be chosen to trigger the alert signal <NUM> when abrasion <NUM> includes a hole about one millimeter in diameter through the wire insulation <NUM> that is about one millimeter thick. The United States Department of Defense standard STAN <NUM>-<NUM> requires military jets to use enough anti-static additives to yield fuel with conductivity in the range <NUM> to <NUM> pS/m (<NUM> to <NUM> × <NUM>-<NUM> Siemens/meter). At the lower end of that conductivity range, with the applied voltage signal <NUM> equal to approximately <NUM> volts, the current <NUM> through the abrasion is about <NUM> × <NUM>-<NUM> amps, so (in this example) the predetermined value is chosen to be approximately <NUM> × <NUM>-<NUM> amps. This value is within measurement range of commercially available single-chip instrumentation amplifiers like the Intersil ISL28633.

In this example, the cavity <NUM> of the fuel tank <NUM> is filled with enough electrically conductive fuel <NUM> to submerge the insulated wire <NUM> because the insulated wire <NUM> is located below a fuel level <NUM> of the electrically conductive fuel <NUM>.

It is appreciated by those of ordinary skill in the art that the first switch <NUM> and second switch <NUM> are utilized to isolate the insulated wire <NUM> from the rest of the aircraft (i.e., the first load <NUM> and second load <NUM>) so as to limit circuit path of the AWDS <NUM> to a current path that includes power source <NUM>, current sensor <NUM>, insulated wire <NUM>, abrasion <NUM>, electrically conductive fuel <NUM>, fuel tank wall <NUM>, and electrode <NUM> back to the power source <NUM>. The first switch <NUM> and second switch <NUM> may be manual or digital switches. Once the AWDS <NUM> has completed its test method, the first switch <NUM> and second switch <NUM> are set to a closed position so that the insulated wire <NUM> may continue to electrically connect the first load <NUM> to the second load <NUM> for normal aircraft <NUM> operations.

If the power source <NUM> is an AC power supply producing an AC voltage signal <NUM> having a predetermined high frequency, the first switch <NUM> and second switch <NUM> may be implemented as two choke coils that are configured to block the AC voltage signal <NUM>. As an example, the predetermined frequency may be selected to minimize reactive currents that could complicate measurement of the leakage current <NUM>. For example, the predetermined frequency may be chosen so that the inductive impedance (given by the product of 2π, the predetermined frequency, and the inductance per unit length of the insulated wire <NUM>) is equal and opposite to the capacitive impedance (given by the reciprocal of the product of 2π, the predetermined frequency, and capacitance per unit length of the insulated wire <NUM>). In this example, the inner wire <NUM> has a diameter of approximately one (<NUM>) millimeter and the wire insulation <NUM> has a dielectric constant that is approximately unity and the magnetic susceptibility is approximately unity. As such, the inductive impedance of the inner wire <NUM> is approximately equal and opposite to the capacitive impedance at frequencies near <NUM> megahertz. Typically, the inner wire <NUM> may have a diameter approximately equal to one millimeter or somewhat larger, and the wire insulation <NUM> may have a dielectric constant approximately equal to unity or somewhat larger, so the frequency range may be within a factor of <NUM> of <NUM> megahertz.

Utilizing this method, the AWDS <NUM> allows abraded wire faults to be classified as part of the "standard maintenance" procedure of the aircraft <NUM> instead of as a latent fault. This would allow the removal of weight and costly excess layers of protection in the fuel tank <NUM> by reducing the number of wire brackets in the cavity <NUM> of the fuel tank <NUM>. The aircraft <NUM> may then be scheduled for standard maintenance. Moreover, the AWDS <NUM> may reduce the frequency or required rigor of inspections for abrased (e.g. abraded) wires in the cavity <NUM> of the fuel tank <NUM>, which would result in the aircraft <NUM> being more often in service, reducing labor costs of the inspections, and other possible costs.

In <FIG>, a flowchart of an example of an implementation of a method <NUM> performed by the AWDS <NUM> is shown in accordance with the present invention. The method starts <NUM> and proceeds <NUM> by filling the cavity <NUM> of the fuel tank <NUM> with the electrically conductive fuel <NUM> that submerges some or all of the insulated wire <NUM> below the fuel level <NUM>. The insulated wire <NUM> is then isolated <NUM> from the rest of the aircraft <NUM> by placing the first switch <NUM> and second switch <NUM> into the open position (causing an open circuit) and the voltage signal <NUM> is applied <NUM> to the insulated wire <NUM>. The leakage current (i.e., current <NUM>), corresponding to the applied voltage signal <NUM>, is received <NUM> at the electrode <NUM> and the amount of current <NUM> is measured <NUM> by the current sensor <NUM>. The current sensor <NUM>, or the alert system <NUM>, then determines <NUM> if an abrasion <NUM> is present on the insulated wire <NUM>. This determination is based on includes determining if the received current <NUM> is above a predetermined current level. The method then ends <NUM>.

It will be understood that various aspects or details of the disclosure may be changed without departing from the scope of the invention. It is not exhaustive and does not limit the claimed inventions to the precise form disclosed. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation. Modifications and variations are possible in light of the above description or may be acquired from practicing the invention. The scope of the invention to which this European patent relates is defined by the appended claims.

The flowchart and block diagrams in the different depicted example of implementations illustrate the architecture, functionality, and operation of some possible implementations of apparatuses and methods in an illustrative example. In this regard, each block in the flowchart or block diagrams may represent a module, a segment, a function, a portion of an operation or step, some combination thereof.

In some alternative examples of implementations, the function or functions noted in the blocks may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved. Also, other blocks may be added in addition to the illustrated blocks in a flowchart or block diagram.

Claim 1:
An abraded wire detection system 'AWDS' (<NUM>) adapted for detecting an abrasion (<NUM>) on an insulated wire (<NUM>) in a fuel tank (<NUM>), the AWDS (<NUM>) comprising:
a power source (<NUM>) configured to apply a voltage signal (<NUM>) on the insulated wire (<NUM>);
an electrode (<NUM>) in electrical series with a fuel tank wall (<NUM>) of the fuel tank (<NUM>), wherein the electrode is configured for receiving a current (<NUM>) corresponding to the voltage signal (<NUM>); and
a current sensor (<NUM>) in electrical series with the power source (<NUM>), the insulated wire (<NUM>), and the electrode (<NUM>), wherein the current sensor (<NUM>) includes circuitry that is configured to detect a current (<NUM>) from the insulated wire (<NUM>) to the electrode (<NUM>).