Patent Description:
Liquid level sensing devices are used to monitor a level of liquid in a container, such as an engine oil tank. One example of a liquid level sensing device is a resistive-type sensor with multiple reed switches and varying resistance values for each reed switch.

In some aircraft, the liquid level sensing device indicates when the oil level in the aircraft engine has reached a level that requires oil to be added in the tank prior to running the engine. The liquid level sensing device may also be used to determine dispatchability of the aircraft. The correctness of the liquid level sensing device is therefore important and in some cases, critical, and improvements are needed.

<CIT> discloses a prior art method according to the preamble of claim <NUM>.

In accordance with a broad aspect, there is provided a method for detecting a fault of a fluid level sensing device associated with an aircraft engine, the fluid level sensing device arranged to measure a variance in a fluid level. The method comprises triggering a timer, while the timer is running, receiving a measurement indicative of the fluid level from the fluid level sensing device, resetting the timer when at least one timer-reset condition has been met, and outputting a fault signal when the timer reaches a timer threshold before the at least one timer-reset condition is met; wherein the at least one timer-reset condition comprises any one of the fluid level reaching a low fluid threshold and the fluid level decreasing by a predetermined amount.

In an embodiment according to any of the previous embodiments, the low fluid level threshold corresponds to a level of fluid consumable by the aircraft over a given time period, and the timer threshold is set to be less than the given time period.

In an embodiment according to any of the previous embodiments, the at least one timer-reset condition comprises receiving a manual request to reset the timer.

In an embodiment according to any of the previous embodiments, the method further comprises pausing the timer when the engine is shut down and resuming the timer when the engine restarts.

In an embodiment according to any of the previous embodiments, the timer-reset condition comprises detecting an increase in the fluid level between engine shutdown and engine restart.

In an embodiment according to any of the previous embodiments, the fluid sensing device comprises a plurality of switches.

In an embodiment according to any of the previous embodiments, the method further comprises determining a lowest active switch from the plurality of switches from the measurement indicative of the fluid level, and wherein the at least one timer-reset condition comprises a new lowest active switch being detected.

In an embodiment according to any of the previous embodiments, the plurality of switches are reed switches and wherein the fluid level sensing device comprises a floating device configured to move vertically with the fluid level to activate and deactivate the reed switches.

In an embodiment according to any of the previous embodiments, the timer threshold varies as a function of the measurement indicative of the fluid level.

In accordance with another broad aspect, there is provided a system for detecting a fault of a fluid level sensing device associated with an aircraft engine, the fluid level sensing device arranged to measure a variance in a fluid level. The system comprises at least one processing unit and at least one non-transitory computer-readable memory having stored thereon program instructions. The program instructions are executable by the at least one processing unit for triggering a timer, while the timer is running, receiving a measurement indicative of the fluid level from the fluid level sensing device, resetting the timer when at least one timer-reset condition has been met, and outputting a fault signal when the timer reaches a timer threshold before the at least one timer-reset condition is met; wherein the at least one timer-reset condition comprises any one of the fluid level reaching a low fluid threshold and the fluid level decreasing by a predetermined amount.

In an embodiment according to any of the previous embodiments, the program instructions are further executable for pausing the timer when the engine is shut down and resuming the timer when the engine restarts.

In an embodiment according to any of the previous embodiments, the timer-reset condition comprises detecting an increase in the fluid level between engine shutdown and engine restart. In an embodiment according to any of the previous embodiments, the fluid sensing device comprises a plurality of switches.

In an embodiment according to any of the previous embodiments, the program instructions are further executable for determining a lowest active switch from the plurality of switches from the measurement indicative of the fluid level, and wherein the at least one timer-reset condition comprises a new lowest active switch being detected.

Any of the above features may be used together, in any combination.

There is described herein a method and system for fault detection of a fluid level sensing device associated with an engine, such as an aircraft engine or an engine used in an industrial setting. In some embodiments, the fluid level sensing device is an oil sensing system. Although an oil sensing system will be used throughout the disclosure as an example, other types of fluids, such as fuel and water, are also applicable.

The engine may be a gas turbine engine, such as a turbofan engine, a turboshaft engine, a turboprop engine, and the like. <FIG> illustrates an example gas turbine engine <NUM> of a type provided for use in subsonic flight, generally comprising in serial flow communication, a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. High pressure rotor(s) <NUM> of the turbine section <NUM> are drivingly engaged to high pressure rotor(s) <NUM> of the compressor section <NUM> through a high pressure shaft <NUM>. Low pressure rotor(s) <NUM> of the turbine section <NUM> are drivingly engaged to the fan rotor <NUM> and to other low pressure rotor(s) (not shown) of the compressor section <NUM> through a low pressure shaft <NUM> extending within the high pressure shaft <NUM> and rotating independently therefrom.

Although a gas turbine engine <NUM> is illustrated, the system and method for fault detection may apply to any other suitable engine. In particular, the method and system for fault detection may apply to any type of engine (as well as any application and/or industry) which uses a container of fluid that is emptied and replenished regularly and for which it is desirable to know the level of fluid as well as the health of a fluid level sensing device used to monitor the level of fluid. For example, diesel engines, typical car engines (internal combustion engine), or the like, may apply.

Referring to <FIG>, there is illustrated a fault detection system <NUM>, which is illustratively part of an Electronic Engine Controller (EEC) <NUM>. The EEC <NUM> may be part of a Full Authority Digital Engine Control (FADEC), which is used to control the operation and performance of the engine <NUM>. The fault detection system <NUM> is connected to a fluid level sensing device <NUM>, which may be used to monitor any level of fluid (e.g. water, oil, or the like) in any suitable vessel or container <NUM> that defines a volume of the fluid. In one embodiment, the fluid level sensing device <NUM> monitors a level of oil in an oil tank of the engine <NUM>.

Referring to <FIG> in addition to <FIG>, in one embodiment, the fluid level sensing device <NUM> is a resistive-type sensor, such as a reed switch level sensor. The fluid level sensing device <NUM> comprises a stem <NUM> that extends along an axis A and is configured to be positioned in a fluid contained in the fluid container <NUM> (e.g. in the oil contained in the engine's oil tank). An elongated electrical circuit is enclosed in the stem <NUM>. The electrical circuit comprises a resistor line <NUM> with a number (N) of resistors <NUM><NUM>, <NUM><NUM>,. , <NUM>N, which are vertically aligned along the axis A and serially connected by wires <NUM>. The electrical circuit also comprises a wire <NUM> that connects to the resistors <NUM><NUM>, <NUM><NUM>,. , <NUM>N through magnetic switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N (e.g. reed switches). The magnetic switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N are illustratively each actuatable between an open and a closed position (or state) and are nominally open. One end of each switch <NUM><NUM>, <NUM><NUM>,. , <NUM>N is connected to a resistor <NUM><NUM>, <NUM><NUM>,. , <NUM>N and another end of each switch <NUM><NUM>, <NUM><NUM>,. , <NUM>N is connected to a common node (e.g. terminal <NUM> of wire <NUM>). It should be understood that, although the fluid level sensing device <NUM> is illustrated in <FIG> as comprising N = <NUM> resistors and N = <NUM> switches, any other suitable number of resistors and switches may apply depending on the characteristics of the engine <NUM>.

A floating device <NUM> (e.g. a ring float) encircles the stem <NUM> and is configured to move vertically (i.e. rise or lower) along the axis A with the fluid level in the fluid container <NUM>. In particular, as the fluid container <NUM> (e.g. the oil tank) is replenished (e.g. upon engine shutdown) and the level of fluid in the fluid container <NUM> (e.g. the level of oil in the engine's oil tank) increases, the floating device <NUM> moves up along the axis A (in the direction of arrow B). As the fluid container <NUM> is drained (e.g. upon engine operation) and the level of fluid in the fluid container <NUM> decreases, the floating device <NUM> moves down along the axis A (in the direction of arrow C).

The floating device <NUM> carries a magnetic element, such as one or more permanent magnets. When the floating device <NUM> moves adjacent to a given one of the switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N, the given switch <NUM><NUM>, <NUM><NUM>,. , or <NUM>N is activated (i.e. closes) under the magnetic force generated by the magnetic element, thereby completing the circuit between a terminal <NUM> of the resistor line <NUM> and terminal <NUM> and providing a path for electrical current to travel through the applicable resistors <NUM><NUM>, <NUM><NUM>,. When the floating device <NUM> moves away from the given switch <NUM><NUM>, <NUM><NUM>,. , or <NUM>N, the switch <NUM><NUM>, <NUM><NUM>,. , or <NUM>N is deactivated (i.e. opens). On a nominally operating fluid level sensing device <NUM>, only one switch <NUM><NUM>, <NUM><NUM>,. , or <NUM>N is activated at any given time. Thus, as the floating device <NUM> is moved upwardly and downwardly, different ones of the switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N are closed by the proximity of the magnetic element, thereby providing a complete circuit through a different number of resistors <NUM><NUM>, <NUM><NUM>,. , <NUM>N to provide a voltage value. Although the terminals <NUM>, <NUM> are shown to be at a bottom end of the device <NUM>, they may be provided at a top end.

The voltage value(s) measured between the terminal <NUM> of the resistor line <NUM> and the wire <NUM> (e.g. the terminal <NUM> thereof) can be obtained at the EEC <NUM> (e.g. via suitable signal lines, not shown) and used to detect the fluid level (e.g. by converting the voltage value(s) into information related to the position of the floating device <NUM>). In one embodiment, the EEC <NUM> is connected to the fuel level sensing device <NUM> at both terminals <NUM> and <NUM> and provides a voltage (having a given value) at terminal <NUM>. When the floating device <NUM> causes a given switch (e.g. the switch <NUM><NUM>, as illustrated in <FIG>) to close, electrical current in turn flows from terminal <NUM> and passes through the electrical circuit completed by activation of the given switch (e.g. passes through resistors <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM>) before travelling across the given switch towards terminal <NUM>. The EEC <NUM> thus receives, from the fluid level sensing device <NUM>, a sensor reading comprising voltage measurements and determines the liquid level accordingly. As the fluid level varies, the EEC <NUM> can detect step changes in voltage resulting from successive actuation (i.e. selective activation and deactivation) of the switches <NUM><NUM>, <NUM><NUM>,. In one embodiment, the lowest voltage is measured at the EEC <NUM> when the fluid container <NUM> is full and the highest voltage is measured at the EEC <NUM> when the fluid container <NUM> is empty. Based on knowledge of the voltage provided by the EEC <NUM> at terminal <NUM>, of the voltage received by the EEC <NUM> at terminal <NUM>, and of the difference between the provided and the received voltages, the EEC <NUM> can determine the resistance that is present in the electrical circuit. Once the resistance is obtained, the EEC <NUM> is then able to identify the actuated switch and the level of fluid accordingly.

In the example illustrated in <FIG>, each resistor <NUM><NUM>, <NUM><NUM>,. , <NUM>N has a resistance of <NUM> Ohms. When the floating device <NUM> is positioned adjacent switch <NUM><NUM>, the switch <NUM><NUM> activates (i.e. closes), as shown in <FIG>, and the resulting voltage read by the EEC <NUM> would correspond to a resistance of about <NUM> Ohms. When the fluid level decreases, resulting in the floating device <NUM> falling to a position adjacent the switch <NUM><NUM>, the voltage read by the EEC <NUM> would correspond to a resistance of about <NUM> Ohms. As the floating device <NUM> further lowers (i.e. as the fluid container <NUM> empties), the floating device <NUM> successively passes nearby the switches <NUM><NUM> and <NUM><NUM>, resulting in voltage measurements which correspond to resistances of about <NUM> Ohms and about <NUM> Ohms. Similarly, if the fluid container <NUM> is empty and is then filled, the EEC <NUM> successively measures voltage values corresponding to resistance values of about <NUM> Ohms, <NUM> Ohms, <NUM> Ohms, <NUM> Ohms, and <NUM> Ohms as the switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N are successively closed (and opened) as the floating device <NUM> rises. As used herein, the term about (a given resistance value) should be understood to mean substantially equal to (the given resistance value), within a predetermined tolerance.

Thus, for a normally operating fluid level sensing device <NUM>, the switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N are successively activated and deactivated with the changing fluid level. The sensor reading obtained from the fluid level sensing device <NUM> can then be used by the fault detection system <NUM> of <FIG> to diagnose a fault or failure of the fluid level sensing device <NUM>.

It should be understood that, although the fluid level sensing device <NUM> is described and illustrated herein as a resistive-type sensor comprising multiple reed switches <NUM><NUM>, <NUM><NUM>,. , or <NUM>N (with varying resistance values for each reed switch) and a floating device <NUM>, any suitable (e.g. non-resistive) fluid level sensing device may apply. For example, each resistor <NUM><NUM>, <NUM><NUM>,. , <NUM>N may be replaced by a battery supplying a given voltage (e.g. <NUM> volts) and the terminal <NUM> may be disconnected from the EEC <NUM>. As the floating device <NUM> moves upwardly and downwardly, different ones of the switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N are closed by the proximity of the magnetic element, thereby providing a complete circuit through a different number of batteries to provide a voltage value. For example, when the floating device <NUM> rises and causes switch <NUM><NUM> to close, this in turn closes the electrical circuit and a voltage of <NUM> volts (provided by the battery replacing resistor <NUM><NUM>) is then detected by the EEC <NUM> at terminal <NUM>. When the floating device <NUM> lowers and causes switch <NUM><NUM> to close, switch <NUM><NUM> returns to its open state and the batteries replacing resistors <NUM><NUM> and <NUM><NUM> are then connected in series, thus causing a voltage of <NUM> volts (<NUM> volts + <NUM> volts) to be detected at terminal <NUM>. In another example, the fluid level sensing device may be a capacitive fluid level sensor, whereby a parallel plate capacitor is immersed in the fluid container <NUM>. As the fluid level changes, the amount of dielectric material between the plates changes, which causes the capacitance to change as well. A second pair of capacitive plates in the fluid container <NUM> may be used as a reference. Other embodiments may apply.

In some embodiments, the fluid level sensing device <NUM> provides a digital measurement indicative of the fluid level in the fluid container <NUM>. In other embodiments, the fluid level sensing device <NUM> provides an analog measurement indicative of the fluid level in the fluid container <NUM>. In some embodiments, an analog to digital conversion is performed on the measurement.

In some embodiments, each switch <NUM><NUM>, <NUM><NUM>,. , <NUM>N corresponds to a fluid level when it gets activated. Each switch can be translated into a volume of fluid remaining in the fluid container <NUM>, that translation being a function of sensor granularity and a design of the fluid container <NUM>. The volume of fluid remaining can itself be translated into a time of operation left, as a function of fluid consumption rate.

Referring to <FIG>, there is illustrated a graph <NUM> showing at <NUM> an example progression of the actual fluid level in the fluid container <NUM> as it is consumed during engine operation over time. Overlaid on the actual fluid level <NUM> is the sensor reading at <NUM> as received from the fluid level sensing device <NUM>, as the floating device <NUM> successively activates switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N during normal operation of the fluid level sensing device <NUM>. The plurality of switches <NUM><NUM>, <NUM><NUM>,. , <NUM>N are illustratively represented as <NUM> to <NUM> along the vertical axis of the graph <NUM>, with switch <NUM><NUM> represented by <NUM>, <NUM><NUM> represented by <NUM>, etc. In the example, the sensor reading <NUM> is a discretized function of the fluid level and therefore shown as a step function. When the fluid level sensing device <NUM> is operating properly, the sensor reading <NUM> generally follows the actual fluid level <NUM>.

Various factors can affect the actual fluid level <NUM>, such as but not limited to gulping, fluid consumption, fluid temperature variations, and aircraft attitudes. Gulping refers to the fluid entering and exiting certain cavities of the engine as a function of engine geometry. Aircraft attitudes may affect the center of gravity of the fluid container <NUM>, thus temporarily changing the reading of the fluid level sensing device <NUM> during certain aircraft maneuvers.

If the floating device <NUM> is obstructed from descending due to an obstacle, the actual fluid level <NUM> may diverge from the sensor reading <NUM>, as illustrated in <FIG>. As shown, the floating device <NUM> is obstructed at about <NUM>% of the fluid level, which is reached a little before three hours of engine operation. At this point, the sensor reading <NUM> remains constant despite the actual fluid level <NUM> continuing to decrease.

In accordance with some embodiments, the fault detection system <NUM> is configured to detect the divergence of the sensor reading <NUM> (or the position of the floating device <NUM>) with the actual fluid level <NUM> in the fluid container <NUM>. More generally, the fault detection system <NUM> is configured to detect a fault of the fluid level sensing device <NUM> associated with an aircraft engine, such as engine <NUM>. In addition to an obstruction to the floating device <NUM>, the fault detection system <NUM> may also detect any fault resulting in an inaccurate sensor reading, such as but not limited to a broken open switch, a damaged switch, a demagnetized floating device <NUM>, and the like.

A timer is used to ensure that the sensor reading <NUM> continues to decrease over time, as per the normal operation of the fluid level sensing device <NUM>. The timer is triggered at time T = <NUM>, for example when the engine is first turned on or when the fluid container <NUM> is filled to a given level. The initial starting of the timer may be manual or automated as a function of one or more timer-starting conditions. While the timer is running, the sensor reading is monitored. If the timer reaches a timer threshold before a timer-reset condition is met, a fault signal is output indicative of an issue. The timer is reset every time a timer-reset condition is met.

In some embodiments, the timer-reset condition corresponds to a decrease in the fluid level as represented by the sensor reading, by a predetermined amount. For example, if the sensor reading is analog, having the fluid level decrease by a given percentage or a given volume may cause the timer to be reset. The amount or percentage used to cause the timer to be reset may be determined as a function of various factors.

In the case of a discretized sensor reading, the timer-reset condition may correspond to the reading having decreased by one or more units.

When the sensor reading is indicative of a given switch being active, the timer-reset condition may be the activation of a new switch indicative of a lower fluid level than a previous switch. For example, and with reference to <FIG>, if the timer is started when switch <NUM><NUM> is active and switch <NUM><NUM> gets activated, this may cause the timer to be reset as it is indicative of the floating device <NUM> moving downwards along the A axis. In some embodiments, two or more switch levels are required to cause the timer to be reset. For example, a jump from switch <NUM><NUM> to switch <NUM><NUM> if two switch levels are used, or a jump from switch <NUM><NUM> to switch <NUM><NUM> if three switch levels are used, may cause the timer to be reset. The number of switch levels may be selected as a function of sensor granularity and/or other factors.

In some embodiments, the timer-reset condition corresponds to the fluid level reaching a low-fluid threshold and an alert regarding low fluid is issued and/or confirmed. Referring to <FIG>, an example low-fluid level threshold is shown at <NUM>. When the sensor reading <NUM> indicates that the fluid level has reached the low-fluid level <NUM>, an alert or warning is issued, either to the cockpit or to another system of the aircraft and/or engine. This action triggers a maintenance flag for the fluid container <NUM> to be refilled. Since the aircraft will not be dispatched until the maintenance flag is addressed, and the maintenance flag will only be removed if the fluid container <NUM> is refilled, the timer may be reset.

In some embodiments, the timer-reset condition comprises a manual request to reset the timer, for example through a maintenance panel or from an input in the cockpit.

In some embodiments, the timer-reset condition comprises an engine restart combined with a higher fluid level reading than a previous fluid level reading. For example, if the fluid level at the time of engine shut down is read from the sensor reading to be at switch <NUM><NUM> and the fluid level at the time of the next engine start-up is read to be at switch <NUM><NUM>, then the timer is reset. This is to account for a refilling of the fluid container <NUM> when the engine is shut down without a manual request to restart the timer or the resetting of a maintenance flag.

In some embodiments, the fault detection system <NUM> is configured to recognize a plurality of timer-reset conditions and the timer will reset when any one of the timer-reset conditions is met.

A specific and non-limiting example is illustrated in <FIG>. In this example, the timer-reset condition corresponds to one switch level. When the engine is started at time T=<NUM>, a gulping effect causes the sensor reading to go from switch <NUM> to switch <NUM>, triggering a reset of the timer. As the engine operates, the fluid gets consumed and switch <NUM> gets activated, causing the timer to be reset again.

In some embodiments, the timer is paused when the engine is turned off and resumes when the engine starts again. The EEC <NUM> may record the last sensor reading (or last active switch) at the time of engine shutdown. The fault detection system <NUM> may compare the last sensor reading (or last active switch) to a current sensor reading (or current active switch) when the engine starts up again. The timer would only be reset upon engine restart if the current sensor reading was greater than the last sensor reading.

The timer-threshold is defined such that the fault detection system <NUM> triggers a fault signal indicating that the fluid level sensing device <NUM> may be malfunctioning. The timer-threshold may be application specific and set as a function of various parameters. In some embodiments, the timer-threshold is set to be greater than the expected time to reach a next lower level, which is a function of sensor granularity and fluid consumption rate: <MAT>.

Tf is the timer threshold and Z is the time taken to reach a next lower level of fluid. Z may be due to acceptable production variations and other environmental factors.

In some embodiments, the timer-threshold is set to a value that is less than or equal to the time it takes to consume the fluid left in the fluid container <NUM> when the low-fluid level <NUM> is reached: <MAT>.

X is the time from low fluid level to no fluid, assuming a failure free system (i.e. without any rupture of the fluid system or some other failure cause that would cause rapid loss of fluid). X may be set as a function of acceptable production variation and other environmental factors. In some embodiments, X may be set as a function of a fluid consumption rate of a given engine. For example, some engine types may consume fluid at a faster rate than other engine types. In some cases, engine wear may also cause a variance in fluid consumption rate from one engine to another. Using the time from low fluid level to no fluid to set the timer-threshold prevents a scenario where the engine would run out of fluid in-flight, should the malfunction occur shortly before the low-fluid level <NUM> is reached but the time left on the timer to reach the timer threshold is greater than the time it takes to consume the remaining fluid in the fluid container <NUM>.

In some embodiments, the timer-threshold is set to take into account a longest mission duration: <MAT>.

Where LM is the time of the longest mission. This would ensure that a pilot is advised prior to a critical flight that the fluid level sensing device <NUM> is not reliable.

In some embodiments, the timer-threshold is set to take into account the fluid remaining below the last activated level: <MAT>.

Where Y is the time remaining until the next level is reached. An example is illustrated in <FIG>, where a longest mission duration (LM) is <NUM> hours, a time from low fluid level to no fluid (X) is <NUM> hours, and the time remaining until the next switch is activated (Y) is <NUM> hours. The timer-threshold is therefore set to <NUM> hours. In this scenario, a fault is detected before the last mission is started.

In some embodiments, the timer-threshold is a fixed value that remains constant until it is changed by an operator. In some embodiments, the timer-threshold can vary as a function of the sensor reading. For example, the timer-threshold may be greater when the sensor reading indicates that the fluid container <NUM> is filled at greater than <NUM>% capacity and lower when the sensor reading indicates that the fluid container <NUM> is filled at less than <NUM>% capacity. In another example, the timer-threshold may vary as a function of which switch is currently active, or which switch caused a reset to the timer. A switch associated with a higher fluid level would have a higher timer-threshold than a switch associated with a lower fluid level. Other embodiments may also apply depending on the practical implementation.

<FIG> is an example embodiment of a computing device <NUM> for implementing the fault detection system <NUM> described above. The processing unit <NUM> may comprise any suitable devices configured to cause a series of steps to be performed such that instructions <NUM>, when executed by the computing device <NUM> or other programmable apparatus, may cause the functions/acts/steps specified in the method described herein to be executed. The processing unit <NUM> may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a CPU, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof.

The memory <NUM> may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

It should be noted that the computing device <NUM> may be implemented as part of a FADEC or other similar device, including an electronic engine control (EEC), engine control unit (EUC), engine electronic control system (EECS), and the like. In addition, it should be noted that the techniques described herein can be performed by a computing device <NUM> substantially in real-time.

<FIG> is a specific and non-limiting example of a method <NUM> as implemented by the computing device <NUM> for performing fault detection by the fault detection system <NUM>. The engine starts, followed by the timer starting. The EEC <NUM> saves the active switch of the fluid level sensing device <NUM> as the "lowest switch". If a switch lower than the "lowest active switch" is activated, the timer is restarted. If the low-fluid level switch is activated, the timer is restarted. If a manual reset is requested through a maintenance panel, the timer is reset. If the engine is shutdown, the timer is paused. When the engine is restarted, if the active switch is higher than the "lowest switch" (i.e. associated with a higher fluid level), the timer is reset. Otherwise, the timer resumes. If none of the timer-reset conditions are met and the timer reaches the timer-threshold, a fault signal is output and the timer is stopped.

Although illustrated as sequentially, the steps of checking for the various timer-reset conditions may be performed concurrently. In addition, the order in which the steps of checking the various timer-reset conditions may differ from that illustrated in the method <NUM> of <FIG>.

The methods and systems for detecting a fault of a fluid level sensing device as described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device <NUM>. Alternatively, the methods and systems for detecting a fault may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems for detecting a fault may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems for detecting a fault may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processing unit <NUM> of the computing device <NUM>, to operate in a specific and predefined manner to perform the functions described herein.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention defined by the appended claims.

Claim 1:
A method for detecting a fault of a fluid level sensing device (<NUM>) associated with an aircraft engine (<NUM>), the fluid level sensing device (<NUM>) arranged to measure a variance in a fluid level (<NUM>), the method comprising:
triggering a timer;
while the timer is running, receiving a measurement indicative of the fluid level (<NUM>) from the fluid level sensing device (<NUM>);
resetting the timer when at least one timer-reset condition has been met; and
outputting a fault signal when the timer reaches a timer threshold before the at least one timer-reset condition is met;
characterised in that:
the at least one timer-reset condition comprises any one of the fluid level (<NUM>) reaching a low fluid threshold and the fluid level (<NUM>) decreasing by a predetermined amount.