Patent Description:
Measurement systems can be used to observe various parameters to control machine operation and monitor system health. Some locations within a machine can be difficult to measure due to moving parts, internal operating environment, or machine configuration. Further, complex electronics used for sensing may not be suitable for higher temperature environments, such as proximate to fuel combustion locations. Environmental factors can also impact the accuracy of some measurement systems due to thermal expansion, vibration, strain, and other such factors which can vary during machine operation.

<CIT> discloses an apparatus having a transmitter/receiver arranged to transmit a signal through a waveguide, and to receive reflections from a reference member and external members. <CIT> discloses a device having a waveguide into which electromagnetic waves are transmitted, a first portion of the electromagnetic waves being reflected by a sealing element in the waveguide and a second portion being transmitted through said sealing element.

Viewed from one aspect there is provided a system of a machine according to claim <NUM>.

According to a first embodiment, a system of a machine includes a waveguide system and a radio frequency transceiver/detector coupled to the waveguide system and configured to emit a calibration signal in the waveguide system to establish a reference baseline between the radio frequency transceiver/detector and a calibration plane associated with an aperture of the waveguide system, emit a measurement signal in the waveguide system to transmit a radio frequency signal from the radio frequency transceiver/detector out of the aperture of the waveguide system, and detect a reflection of the measurement signal at the radio frequency transceiver/detector based on an interaction between the measurement signal and a component of the machine. A measurement result of the reflection of the measurement signal can be adjusted with respect to a reflection of the calibration signal. The waveguide system includes a ceramic window proximate to the aperture of the waveguide system, and a power-controlled switch proximate to the ceramic window. The power-controlled switch is configured to reflect the calibration signal and allow the measurement signal through the ceramic window based on a power difference between the calibration signal and the measurement signal.

Viewed from a second aspect there is provided a system for a gas turbine engine according to claim <NUM>.

In one embodiment, a system for a gas turbine engine includes network of a plurality of nodes distributed throughout the gas turbine engine, a controller of the gas turbine engine, and a radio frequency sensing system coupled to the network of nodes. Each of the nodes can be associated with at least one sensor and/or actuator of the gas turbine engine and operable to communicate through one or more radio frequencies. The controller can be operable to communicate with the network of nodes through the one or more radio frequencies. The radio frequency sensing system can include a waveguide system and a radio frequency transceiver/detector coupled to the waveguide system and configured to emit a calibration signal in the waveguide system to establish a reference baseline between the radio frequency transceiver/detector and a calibration plane associated with an aperture of the waveguide system, emit a measurement signal in the waveguide system to transmit a radio frequency signal from the radio frequency transceiver/detector out of the aperture of the waveguide system, and detect a reflection of the measurement signal at the radio frequency transceiver/detector based on an interaction between the measurement signal and a component of the gas turbine engine. A measurement result of the reflection of the measurement signal can be adjusted with respect to a reflection of the calibration signal. The waveguide system includes a ceramic window proximate to the aperture of the waveguide system, and a power-controlled switch proximate to the ceramic window. The power-controlled switch is configured to reflect the calibration signal and allow the measurement signal through the ceramic window based on a power difference between the calibration signal and the measurement signal.

Optionally, the component monitored by the radio frequency sensing system is a rotating component of the gas turbine engine.

Viewed from a third aspect there is provided a method of self-referencing radio frequency sensing in a machine according to claim <NUM>.

In an embodiment, a method of self-referencing radio frequency sensing in a machine includes emitting a calibration signal in a waveguide system to establish a reference baseline between a radio frequency transceiver/detector and a calibration plane associated with an aperture of the waveguide system in the machine. A measurement signal is emitted in the waveguide system to transmit a radio frequency signal from the radio frequency transceiver/detector out of the aperture of the waveguide system. The calibration signal is reflected by a power-controlled switch. The measurement signal is allowed to pass through a ceramic window proximate to the power-controlled switch based on a power difference between the calibration signal and the measurement signal. A reflection of the measurement signal is detected at the radio frequency transceiver/detector based on an interaction between the measurement signal and a component of the machine. A calibrated measurement result associated with the component of the machine is determined based on adjusting a measurement result of the reflection of the measurement signal with respect to a reflection of the calibration signal that is detected.

A technical effect of the apparatus, systems and methods is achieved by a radio frequency sensing system to monitor one or more components of a machine as described herein.

The following descriptions are by way of example only and should not be considered limiting in any way.

Various embodiments of the present disclosure are related to electromagnetic communication through and to components of a machine as part of a sensing and control system. <FIG> schematically illustrates a gas turbine engine <NUM> as one example of a machine as further described herein. The gas turbine engine <NUM> is depicted as a two-spool turbofan that generally incorporates a fan section <NUM>, a compressor section <NUM>, a combustor section <NUM> and a turbine section <NUM>. The fan section <NUM> drives air along a bypass flow path B in a bypass duct to provide a majority of the thrust, while the compressor section <NUM> drives air along a core flow path C for compression and communication into the combustor section <NUM> then expansion through the turbine section <NUM>. Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures or any other machine that requires sensors to operate with similar environmental challenges or constraints. Additionally, the concepts described herein may be applied to any machine or system comprised of control and / or health monitoring systems. Examples can include various moderate to high temperature environments, such as glass and metal forming systems, petroleum-oil-and-gas (POG) systems, ground-based turbine for energy generation, nuclear power systems, and transportation systems.

With continued reference to <FIG>, the exemplary engine <NUM> generally includes a low speed spool <NUM> and a high speed spool <NUM> mounted for rotation about an engine central longitudinal axis A relative to an engine static structure <NUM> via several bearing systems <NUM>.

A combustor <NUM> is arranged in exemplary gas turbine engine <NUM> between the high pressure compressor <NUM> and the high pressure turbine <NUM>.

In direct drive configurations, the gear system <NUM> can be omitted.

A significant amount of thrust can be provided by the bypass flow B due to the high bypass ratio. The example low pressure turbine <NUM> can provide the driving power to rotate the fan section <NUM> and therefore the relationship between the number of turbine rotors <NUM> in the low pressure turbine <NUM> and the number of blades in the fan section <NUM> can establish increased power transfer efficiency.

The disclosed example gas turbine engine <NUM> includes a control and health monitoring system <NUM> (generally referred to as system <NUM>) utilized to monitor component performance and function. The system <NUM> includes a network <NUM>, which is an example of a guided electromagnetic transmission network. The network <NUM> includes a controller <NUM> operable to communicate with nodes 68a, 68b through electromagnetic signals. The controller <NUM> may include various support interfaces and processing resources, such as input/output interfaces, processing systems, memory systems, communication interfaces, power management systems, and the like. The nodes 68a, 68b can be distributed throughout the gas turbine engine <NUM> or other such machine. Node 68a is an example of an actuator node that can drive one or more actuators/effectors of the gas turbine engine <NUM>. Node 68b is an example of a sensor node that can interface with one or more sensors of the gas turbine engine <NUM>. Nodes 68a, 68b can include processing support circuitry to transmit/receive electromagnetic signals between sensors or actuators and the controller <NUM>. A coupler <NUM> can be configured as a splitter between a waveguide <NUM> coupled to the controller <NUM> and waveguides <NUM> and <NUM> configured to establish wireless communication with nodes 68a and 68b respectively. The coupler <NUM> can be a simple splitter or may include a repeater function to condition electromagnetic signals sent between the controller <NUM> and nodes 68a, 68b. In the example of <FIG>, a radio frequency-based repeater <NUM> is interposed between the coupler <NUM> and node 68b, where waveguide <NUM> is a first waveguide coupled to the coupler <NUM> and radio frequency-based repeater <NUM>, and waveguide <NUM> is a second waveguide coupled to the radio frequency-based repeater <NUM> and node 68b. Collectively, waveguides <NUM>, <NUM>, <NUM>, <NUM> are configured to transmit radio frequencies (e.g., electromagnetic signals) between the controller <NUM> and one or more of the nodes 68a, 68b. The transmission media within waveguides <NUM>-<NUM> may include dielectric or gaseous material. In embodiments, the waveguides <NUM>-<NUM> can be hollow metal tubes. The waveguides <NUM>-<NUM> may be rigid or may include flexible material. The disclosed system <NUM> may be utilized to control and/or monitor any component function or characteristic of a turbomachine, aircraft component operation, and/or other machines.

Prior control & diagnostic system architectures utilized in various applications include a centralized system architecture in which the processing functions reside in an electronic control module. Actuator and sensor communications were accomplished through analog wiring for power, command, position feedback, sensor excitation and sensor signals. Cables and connections include shielding to minimize effects caused by electromagnetic interference (EMI). The use of analog wiring and the required connections can limit application and capability of such systems due to the ability to locate wires, connectors and electronics in harsh environments that experience extremes in temperature, pressure, and/or vibration. Exemplary embodiments can use radio frequencies broadcast through waveguides <NUM>-<NUM> in a wireless architecture to provide both electromagnetic communication signals and power to the individual elements of the network <NUM>.

The use of electromagnetic radiation in the form of radio waves (MHz to GHz) to communicate and power the sensors and actuators using a traditionally complex wired system provides substantial architectural simplification, especially as it pertains to size, weight, and power (SWaP). Embodiments provide extension of a network where reduced SNR may compromise network performance by trading off data rates for an expansion of the number of nodes and distribution lines; thereby providing more nodes / sensors, with greater interconnectivity.

Referring to <FIG>, a guided electromagnetic transmission network <NUM> is depicted as an example expansion of the network <NUM> of <FIG>. The guided electromagnetic transmission network <NUM> can include the controller <NUM> coupled to coupler <NUM> through waveguide <NUM>. The coupler <NUM> is further coupled to coupler 67a through waveguide <NUM> and to coupler 67b through waveguide <NUM>. Coupler 67a is further coupled to three nodes 68a through waveguides 173a, 173b, 173c in parallel. Each of the nodes 68a can interface or be combined with multiple actuators <NUM>. Coupler 67b is also coupled to a radio frequency sensing system <NUM> through waveguide 174a and to node 68b through waveguides 174b. The radio frequency sensing system <NUM> can be a direct radio frequency interface where signals emitted from the controller <NUM> can be used to measure one or more components of a machine. Node 68b can interface or be combined with multiple sensors <NUM>. Although depicted in <FIG> as an extension of waveguide 174a, the radio frequency sensing system <NUM> can have an associated interface node similar to node 68b to manage signal generation separately from other communications within the guided electromagnetic transmission network <NUM>. Further, the coupler 67b may include electronics to support calibration and measurement through the radio frequency sensing system <NUM>. The radio frequency sensing system <NUM> may use radio frequency emissions in the microwave spectrum to measure component characteristics, such as turbine blades in the turbine section <NUM> of the gas turbine engine <NUM> of <FIG>. For instance, a turbine blade passing in proximity to a measurement position of the radio frequency sensing system <NUM> may be detected as a change in reflected signals with a scattering of an emitted measurement signal. Compressor blades, fan blades, and other such moving components may also or alternatively be monitored by the radio frequency sensing system <NUM>. Further, the radio frequency sensing system <NUM> may be used to detect components within a machine core or in accessory components, such as in components coupled to or in close proximity to the machine. Radio frequencies selected for use by the radio frequency sensing system <NUM> can be tuned for a desired application and can range, for example, between MHz and GHz frequency bands, although lower or higher frequencies may be supported.

Although the example of <FIG> depicts connections to actuators <NUM> and sensors <NUM> isolated to different branches, it will be understood that actuators <NUM>, sensors <NUM>, and radio frequency sensing systems <NUM> can be interspersed with each other and need not be isolated on dedicated branches of the guided electromagnetic transmission network <NUM>. Couplers <NUM>, 67a, 67b can be splitters and/or can incorporate instances of the radio frequency-based repeater <NUM> of <FIG>. Further, one or more instances of the radio frequency-based repeater <NUM> can be installed at any of the waveguides <NUM>, <NUM>, <NUM>, 173a-c, and/or 174a-b depending on the signal requirements of the guided electromagnetic transmission network <NUM>.

Nodes 68a, 68b and the radio frequency sensing system <NUM> can be associated with particular engine components, actuators or any other machine part from which information and communication is performed for monitoring and/or control purposes. The nodes 68a, 68b and the radio frequency sensing system <NUM> may contain a single or multiple electronic circuits or sensors configured to communicate over the guided electromagnetic transmission network <NUM>.

The controller <NUM> can send and receive power and data to and from the nodes 68a, 68b. The controller <NUM> may be located on equipment near other system components or located remotely as desired to meet application requirements.

A transmission path (TP) between the controller <NUM> and nodes 68a, 68b can be used to send and receive data routed through the controller <NUM> from a control module or other components. The TP may utilize electrical wire, optic fiber, waveguide or any other electromagnetic communication including radio frequency/microwave electromagnetic energy, visible or non-visible light. The interface between the controller <NUM> and nodes 68a, 68b can transmit power and signals.

The example nodes 68a, 68b may include radio-frequency identification devices along with processing, memory and/or the interfaces to connect to conventional sensors or actuators, such as solenoids or electro-hydraulic servo valves. The waveguides <NUM>, <NUM>, <NUM>, 173a-c, and/or 174a-b can be shielded paths that support electromagnetic communication, including, for instance, radio frequency, microwaves, magnetic or optic waveguide transmission. Shielding can be provided such that electromagnetic energy or light interference <NUM> with electromagnetic signals <NUM> (shown schematically as arrows) are mitigated in the guided electromagnetic transmission network <NUM>. Moreover, the shielding provides that the electromagnetic signals <NUM> are less likely to propagate into the environment outside the guided electromagnetic transmission network <NUM> and provide unauthorized access to information. In some embodiments, electromagnetic radiation can be in the range <NUM>-<NUM>. Electromagnetic radiation can be more tightly arranged around specific carrier frequencies, such as <NUM>-<NUM>, <NUM>, <NUM>, or <NUM>-<NUM> as examples in the microwave spectrum. A carrier frequency can transmit electric power, as well as communicate information, to multiple nodes 68a, 68b using various modulation and signaling techniques.

The nodes 68a with actuators <NUM> may include control devices, such as a solenoid, switch or other physical actuation devices. Radio frequency identification, electromagnetic or optical devices implemented as the nodes 68b with sensors <NUM> can provide information indicative of a physical parameter, such as pressure, temperature, speed, proximity, vibration, identification, and/or other parameters used for identifying, monitoring or controlling component operation. Signals from the radio frequency sensing system <NUM> may be used to detect various aspects, such as a distance, rotational speed, acceleration, vibration, component damage, and other such component parameters. Signals communicated in the guided electromagnetic transmission network <NUM> may employ techniques such as checksums, hash algorithms, error control algorithms and/or encryption to mitigate cyber security threats and interference.

In some embodiments, shielding in the guided electromagnetic transmission network <NUM> can be provided such that power and communication signals are shielded from outside interference, which may be caused by environmental electromagnetic or optic interference. Moreover, the shielding limits intentional interference <NUM> with communication at each component. Intentional interference <NUM> may take the form of unauthorized data capture, data insertion, general disruption and/or any other action that degrades system communication. Environmental sources of interference <NUM> may originate from noise generated from proximate electrical systems in other components or machinery along with electrostatic and magnetic fields, and/or any broadcast signals from transmitters or receivers. Additionally, environmental phenomena, such as cosmic radio frequency radiation, lightning or other atmospheric effects, could interfere with local electromagnetic communications.

It should be appreciated that while the system <NUM> is explained by way of example with regard to a gas turbine engine <NUM>, other machines and machine designs can be modified to incorporate built-in shielding for monitored or controlled component in a guided electromagnetic transmission network. For example, the system <NUM> can be incorporated in a variety of harsh environment machines, such as manufacturing and processing equipment, a vehicle system, an environmental control system, and all the like. As a further example, the system <NUM> can be incorporated in an aerospace system, such as an aircraft, rotorcraft, spacecraft, satellite, or the like. The disclosed system <NUM> includes the network <NUM>, <NUM> that provides consistent communication with electromagnetic devices, such as the example nodes 68a, 68b, and removes variables encountered with electromagnetic communications such as distance between transmitters and receiving devices, physical geometry in the field of transmission, control over transmission media such as air or fluids, control over air or fluid contamination through the use of filtering or isolation and knowledge of temperature and pressure.

The system <NUM> provides for a reduction in cable and interconnecting systems to reduce cost and increases reliability by reducing the number of physical interconnections. Reductions in cable and connecting systems further provides for a reduction in weight and additional redundancy. Moreover, additional sensors can be added without the need for additional wiring and physical connections to the controller <NUM>, which may provide for increased system accuracy and response. Embodiments can provide a "plug-n-play" approach to add a new node, potentially without a requalification of the entire system but only the new component; thereby greatly reducing qualification burdens.

<FIG> is a schematic view of a radio frequency sensing system <NUM>, which is described for explanatory purposes. In the example of <FIG>, the radio frequency sensing system <NUM> includes a waveguide system <NUM> and a radio frequency transceiver/detector <NUM> coupled to the waveguide system <NUM> and configured to emit a calibration signal in the waveguide system <NUM> to establish a reference baseline between the radio frequency transceiver/detector <NUM> and a calibration plane <NUM> associated with an aperture <NUM> of the waveguide system <NUM>, emit a measurement signal in the waveguide system <NUM> to transmit a radio frequency signal from the radio frequency transceiver/detector <NUM> out of the aperture <NUM> of the waveguide system <NUM>, and detect a reflection of the measurement signal at the radio frequency transceiver/detector <NUM> based on an interaction between the measurement signal and a component of a machine (e.g., gas turbine engine <NUM> of <FIG>). The measurement can be detected based on a scattering with respect to a component, such as a blade or other rotating component <NUM>. A measurement result of the reflection of the measurement signal is adjusted with respect to a reflection of the calibration signal. The waveguide system <NUM> can include a calibration channel <NUM> with a reflective load <NUM> configured to reflect the calibration signal emitted from the radio frequency transceiver/detector <NUM>. The waveguide system <NUM> can also include a measurement channel <NUM> configured to emit the measurement signal out of the aperture <NUM> and receive the reflection of the measurement signal. The waveguide system <NUM> can further include a coupler <NUM> configured to subtract the reflection of the calibration signal from the reflection of the measurement signal. The coupler <NUM> can be a hybrid coupler that continuously subtracts the calibration signal from measurement signal as part of an analog process and may reduce the burden on the radio frequency transceiver/detector <NUM> by eliminating digital computation. The calibration can correct for environmental changes, such as temperature increase (thermal expansion), vibration, strain, and the like in the waveguide system <NUM>.

In the example of <FIG>, the radio frequency transceiver/detector <NUM> can emit a microwave signal stx(t). The signal can be divided into two halves, stx_target(t) and stx_ref(t) , by the coupler <NUM> as the measurement channel <NUM> and the calibration channel <NUM>. The transmitted signals reflect back from a reflective load <NUM> at the end of the calibration channel <NUM> and in the measurement channel <NUM> from the target can result in return signals in the waveguide system <NUM>. Return signals in the calibration and measurement channels <NUM>, <NUM> are named stx_ref(t) and stx_target(t), respectively. Return signals reflected through the coupler <NUM> can result in two signals that may be expressed as sum and difference of reflected signals indicated as stx_ref(t) + stx_target(t) and stx_ref(t) - stx_target(t). A receiver positioned at the radio frequency transceiver/detector <NUM> can receive the difference signal, sref(t) - starget(t). This is a calibrated signal which carries information of a signal bouncing off the target alone. The difference signal can be the signal that carries target information with respect to the waveguide aperture <NUM>. This way, each time a measurement is taken at the transceiver location, the difference signal can be a calibrated signal, and may carry information regarding the target, e.g., the effect of all system components in between radio frequency transceiver/detector <NUM> and waveguide aperture <NUM> can be subtracted.

<FIG> is a schematic view of a radio frequency sensing system <NUM>, which is described for explanatory purposes. In the example of <FIG>, the radio frequency sensing system <NUM> includes a waveguide system <NUM> and a radio frequency transceiver/detector <NUM>. The waveguide system <NUM> can include a ceramic window <NUM> proximate to an aperture <NUM> of the waveguide system <NUM>. The ceramic window <NUM> can be configured to allow radio frequencies, such as microwave frequencies, to exit the aperture <NUM> while limiting external contaminants from entering the waveguide system <NUM>. Rather than including physically separate waveguide channels for calibration and measurement as in the waveguide system <NUM> of <FIG>, the waveguide system <NUM> can include a mode selective filter <NUM> proximate to the ceramic window <NUM>. The mode selective filter <NUM> can be configured to reflect a calibration signal <NUM> emitted by the radio frequency transceiver/detector <NUM> and allow a measurement signal <NUM> emitted by the radio frequency transceiver/detector <NUM> through the ceramic window <NUM> based on a mode difference between the calibration signal <NUM> and the measurement signal <NUM>. The measurement signal <NUM> can be reflected back with respect to a component, such as a blade or other rotating component <NUM>. Since both the calibration signal <NUM> and the measurement signal <NUM> follow substantially the same path within the waveguide system <NUM>, environmental factors that impact the waveguide system <NUM> can be subtracted out by observing the difference in reflections of the calibration signal <NUM> and the measurement signal <NUM> to accurately measure a distance <NUM> between the aperture <NUM> and the component <NUM> as environmental conditions change. The radio frequency transceiver/detector <NUM> or other system component can be configured to perform the subtraction based on phase or timing using analog or digital techniques.

In the example of <FIG>, the waveguide system <NUM> may have a rectangular cross-section with the measurement signal <NUM> emitted at a dominant mode having a lowest cut-off frequency, which can be referred to as transverse electric (TE) <NUM> mode, while the calibration signal <NUM> can be emitted at a higher frequency mode, such as TE <NUM> mode. The mode selective filter <NUM> can include structures, such as conductive posts, placed across the waveguide cross section at about ¼ and ¾ positions to reflect the TE <NUM> mode and allow the TE <NUM> mode to pass.

<FIG> is a schematic view of a radio frequency sensing system <NUM>, which can be used to implement at least a portion of the radio frequency sensing system <NUM> of <FIG>. In the example of <FIG>, the radio frequency sensing system <NUM> includes a waveguide system <NUM> and a radio frequency transceiver/detector <NUM>. The waveguide system <NUM> can include a ceramic window <NUM> proximate to an aperture <NUM> of the waveguide system <NUM>. The ceramic window <NUM> can be configured to allow radio frequencies, such as microwave frequencies, to exit the aperture <NUM> while limiting external contaminants from entering the waveguide system <NUM>. Rather than including physically separate waveguide channels for calibration and measurement as in the waveguide system <NUM> of <FIG>, the waveguide system <NUM> can include a power-controlled switch <NUM> proximate to the ceramic window <NUM>. The power-controlled switch <NUM> can be configured to reflect a calibration signal emitted by the radio frequency transceiver/detector <NUM> and allow a measurement signal emitted by the radio frequency transceiver/detector <NUM> through the ceramic window <NUM> based on a power difference between the calibration signal and the measurement signal. The measurement signal can be reflected back with respect to a component, such as a blade or other rotating component <NUM>. Since both the calibration signal and the measurement signal follow substantially the same path within the waveguide system <NUM>, environmental factors that impact the waveguide system <NUM> can be subtracted out by observing the difference in reflections of the calibration signal and the measurement signal to accurately measure a distance <NUM> between the aperture <NUM> and the component <NUM> as environmental conditions change. The radio frequency transceiver/detector <NUM> or other system component can be configured to perform the subtraction based on phase or timing using analog or digital techniques.

In the example of <FIG>, radio frequency emissions <NUM> of the radio frequency transceiver/detector <NUM> can vary in power to distinguish the calibration signal and the measurement signal. For example, radio frequency emissions <NUM> for the measurement signal can have a lower amplitude and higher frequency than the calibration signal. The calibration signal and the measurement signal can be multiplexed to switch between emitting each of the calibration signal and the measurement signal. For example, the radio frequency transceiver/detector <NUM> can emit the measurement signal, switch to emitting the calibration signal, and switch back to emitting the measurement signal over a period of time. As one example, the power-controlled switch <NUM> can include a detector circuit <NUM> that may be formed of two diodes having opposing orientations relative to each other. The detector circuit <NUM> can also include a series connected capacitor (C) and inductor (L/<NUM>) between each diode and a corresponding rail <NUM>, <NUM>. An inductor (Liris) can also be connected to each rail <NUM>, <NUM>.

<FIG> is a schematic view of a radio frequency sensing system <NUM>, which is described for explanatory purposes. In the example of <FIG>, the radio frequency sensing system <NUM> includes a waveguide system <NUM> and a radio frequency transceiver/detector <NUM>. The waveguide system <NUM> can include a ceramic window <NUM> proximate to an aperture <NUM> of the waveguide system <NUM>. The ceramic window <NUM> can be configured to allow radio frequencies, such as microwave frequencies, to exit the aperture <NUM> while limiting external contaminants from entering the waveguide system <NUM>. The waveguide system <NUM> can include an optical source emitter and detector <NUM>. The optical source emitter and detector <NUM> may be incorporated with the radio frequency transceiver/detector <NUM>. The optical source emitter and detector <NUM> can be configured to emit a calibration signal <NUM> as an optical signal (e.g., a laser) and detect reflection of the calibration signal <NUM> off of the ceramic window <NUM>. A measurement signal <NUM> emitted by the radio frequency transceiver/detector <NUM> can be a radio frequency signal, such as a microwave signal, configured to pass through the ceramic window <NUM>. The measurement signal <NUM> can be reflected back with respect to a component, such as a blade or other rotating component <NUM>. Since both the calibration signal <NUM> and the measurement signal <NUM> follow substantially the same path within the waveguide system <NUM>, environmental factors that impact the waveguide system <NUM> can be subtracted out by observing the difference in reflections of the calibration signal <NUM> and the measurement signal <NUM> to accurately measure a distance <NUM> between the aperture <NUM> and the component <NUM> as environmental conditions change. The radio frequency transceiver/detector <NUM> or other system component can be configured to perform the subtraction based on phase or timing using analog or digital techniques.

<FIG> is a flow chart illustrating a method <NUM> of self-referencing radio frequency sensing in a machine, such as the gas turbine engine <NUM> of <FIG>. The method <NUM> of <FIG> is described in reference to <FIG> and may be performed with an alternate order and include additional steps. For purposes of explanation, the method <NUM> is primarily described in reference to <FIG> but can also be implemented on the guided electromagnetic transmission network <NUM> of <FIG> and other network variations and a variety of machines. The machine may operate in or produce a mixed temperature environment including higher temperatures (e.g., > <NUM> degrees C) beyond the normal range of microelectronics, which is typically less than <NUM> degrees C. The local temperature at different sections of the machine can vary substantially, such as upstream from combustion, at a fuel combustion location, and downstream from combustion.

At block <NUM>, a calibration signal in a waveguide system <NUM>, <NUM>, <NUM>, <NUM> is emitted to establish a reference baseline between a radio frequency transceiver/detector <NUM> and a calibration plane <NUM> associated with an aperture <NUM> of the waveguide system <NUM>, <NUM>, <NUM>, <NUM> in a machine. The machine can be the gas turbine engine <NUM> of <FIG>.

At block <NUM>, a measurement signal is emitted in the waveguide system <NUM>, <NUM>, <NUM>, <NUM> to transmit a radio frequency signal from the radio frequency transceiver/detector <NUM> out of the aperture <NUM> of the waveguide system <NUM>, <NUM>, <NUM>, <NUM>.

At block <NUM>, a reflection of the measurement signal is detected at the radio frequency transceiver/detector <NUM> based on an interaction between the measurement signal and a component <NUM> of the machine.

At block <NUM>, a calibrated measurement result associated with the component <NUM> of the machine is determined based on adjusting a measurement result of the reflection of the measurement signal with respect to a reflection of the calibration signal. The reflection of the calibration signal can be subtracted from the reflection of the measurement signal by a coupler <NUM> of the waveguide system <NUM>, where the coupler <NUM> can be a <NUM>-dB hybrid coupler having ports to support a calibration channel <NUM> and a measurement channel <NUM>. In an explanatory example referring to <FIG>, a calibration signal <NUM> is reflected by a mode selective filter <NUM>, and a measurement signal <NUM> is allowed to pass through the mode selective filter <NUM> based on a mode difference between the calibration signal <NUM> and the measurement signal <NUM>. Alternatively, referring to <FIG>, in an embodiment a calibration signal can be reflected by a power-controlled switch <NUM>, and a measurement signal is allowed to pass through the power-controlled switch <NUM> based on a power difference between the calibration signal and the measurement signal. As a further example described for explanatory purposes with reference to <FIG>, calibration signal <NUM> is an optical signal configured to reflect off of ceramic window <NUM>, and the measurement signal <NUM> can be a microwave signal configured to pass through the ceramic window <NUM>.

Claim 1:
A system (<NUM>; <NUM>) of a machine, the system comprising:
a waveguide system (<NUM>); and
a radio frequency transceiver/detector (<NUM>) coupled to the waveguide system and configured to emit a calibration signal in the waveguide system to establish a reference baseline between the radio frequency transceiver/detector and a calibration plane (<NUM>) associated with an aperture (<NUM>) of the waveguide system, emit a measurement signal in the waveguide system to transmit a radio frequency signal from the radio frequency transceiver/detector out of the aperture of the waveguide system, and detect a reflection of the measurement signal at the radio frequency transceiver/detector (<NUM>) based on an interaction between the measurement signal and a component (<NUM>) of the machine, wherein a measurement result of the reflection of the measurement signal is adjusted with respect to a reflection of the calibration signal, wherein the system (<NUM>; <NUM>) is configured to detect the reflection of the calibration signal;
wherein the waveguide system (<NUM>) comprises a ceramic window (<NUM>) proximate to the aperture (<NUM>) of the waveguide system, and the waveguide system (<NUM>) comprises a power-controlled switch (<NUM>) proximate to the ceramic window (<NUM>), wherein the power-controlled switch is configured to reflect the calibration signal and allow the measurement signal through the ceramic window based on a power difference between the calibration signal and the measurement signal.