Method of monitoring engine performance parameters of a gas turbine engine

A method of monitoring engine performance parameters of a gas turbine engine during its operation. The method includes sensing the performance parameters and generating analog sensor outputs, producing digital data by conditioning the analog sensor outputs with at least one hub unit that is mounted sufficiently close to the engine to be subjected to a first temperature in excess of 125° C., receiving the digital data from the hub unit with a collector unit subjected to a second temperature of less than the first temperature, receiving the digital data from the collector unit with a distributor computer unit subjected to a third temperature of less than the second temperature, and processing the digital data with the distributor computer unit to assess the engine performance parameters of the engine. The conditioning step is performed with a control circuit board and at least one signal conditioning circuit board within the hub unit.

BACKGROUND OF THE INVENTION

The present invention generally relates to electronic equipment, and more particularly to a method of monitoring an apparatus operating in a high temperature environment, such as a gas turbine engine.

Aircraft gas turbine engines undergo testing during their development, as well as during production and subsequent servicing. Numerous engine performance parameters are typically monitored to assess the performance of an engine, including various temperatures, pressures, flow rates, forces, rotational speeds, etc. As nonlimiting examples, it is typically desirable to monitor engine inlet, compressor and exhaust gas temperatures, pressures within the fan, compressor and turbine sections, fuel and airflow rates, compressor and fan rotor speeds, blade tip clearances, mechanical stresses and part vibrations. Development and flight test aircraft engines may be required to have thousands of sensors to monitor the various parameters of interest.

Engine testing is typically conducted on a stationary test stand that is often located outdoors. A nonlimiting example of such a test stand100is schematically represented inFIG. 1. The stand100is represented as including a vertical support column102mounted to a foundation104in the ground, and a head (thrust) frame106mounted on the column102from which an aircraft engine108is mounted for testing. The head frame106includes an adapter110to which the engine108is attached with a pylon112that is appropriately configured for the particular engine108.

During engine testing, the engine108and its immediate surroundings can reach very high temperatures. For example, temperatures may approach or exceed 260° C. surrounding the engine core beneath the engine cowling (nacelle)114, as well as on the head frame106and its adapter110. While sensors used to monitor the engine108have been developed to withstand these temperatures, the electronics used to process the sensor data have been limited to much lower temperatures. For example, typical commercial electronic components are often limited to about 85° C., and even military standard components are typically rated to not higher than 125° C. As such, each sensor typically requires a separate continuous wire or tube to carry its output signal to a remote data acquisition system, which is often located within an enclosed facility equipped with a controlled environment. The facility may be a considerable distance from the engine test stand, for example, 50 meters to in excess of 300 meters. Routing, managing and maintaining the numerous (potentially thousands) of data wires and tubes requires a considerable effort. Consequently, the ability to reduce the length and number of wires and tubes would be helpful and beneficial.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a method of monitoring engine performance parameters of a gas turbine engine operating on a stationary test stand, or during on-wing flight test, or during normal aircraft operation.

According to a first aspect of the invention, the method includes mounting sensors on the engine to sense the engine performance parameters and generate analog sensor outputs, producing digital data by conditioning the analog sensor outputs with at least one hub unit that is mounted sufficiently close to the engine and the test stand so as to be subjected to a first temperature in excess of 125° C., receiving the digital data from the hub unit with a collector unit mounted sufficiently close to the engine and the test stand so as to be subjected to a second temperature of less than the first temperature, receiving the digital data from the collector unit with a distributor computer unit located sufficiently remote from the test stand so as to be subjected to a third temperature of less than the second temperature, and processing the digital data with the distributor computer unit to assess the engine performance parameters of the engine. The conditioning step is performed with a control circuit board and at least one signal conditioning circuit board within the hub unit. The control circuit board and the signal conditioning circuit board comprise electrical circuit components that define an analog signal processing path and have accuracy and precision characteristics that drift in response to component aging and to changes in the first temperature to which the hub unit is subjected. The collector unit comprises an enclosure containing a system voltage reference device and means for maintaining the system voltage reference device at a regulated temperature. The system voltage reference device is operated to produce a reference voltage. A continuous calibration scheme is performed by periodically applying the reference voltage and a zero voltage to the signal conditioning circuit board to determine and remove errors in the analog signal processing path resulting from the drifts of the electrical circuit components of the control circuit board and the signal conditioning circuit board.

According to a second aspect of the invention, in addition to certain aspects recited above, the method may further include multiplexing a plurality of the analog sensor outputs generated by the sensors to produce an individual multiplexed analog output, scaling the analog sensor outputs of the individual multiplexed analog output with at least one amplifier with adjustable gain to produce an individual conditioned multiplexed analog output from which the corresponding digital data are produced, and controlling the amplifier and the adjustable gain thereof with the control circuit board.

A technical effect of the invention is that, by tiering the system to include hub and collector units that are capable of operating at much higher temperatures than the distributor unit, digital data processing can be performed by the distributor unit located remote from the gas turbine engine using more temperature-sensitive hardware of the type conventionally used to process digital data. On the other hand, the hub and collector units and their electronic hardware, and particularly the control and signal conditioning circuit boards of the hub unit, are specially adapted for high temperature operation, preferably without the use of active cooling. Furthermore, the continuous calibration scheme removes errors that would otherwise exist in the analog signal processing path as a result of the accuracy and precision characteristics of the electrical circuit components of the control circuit board and the signal conditioning circuit board tending to drift due to component aging and the high temperature environment of the hub unit. In accordance with the second aspect of the invention, the multiplexing capability can reduce the number of wires or cables necessary to transmit data to the distributor unit, which may be located a considerable distance from the engine being monitored.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2is a block diagram representing various units of a monitoring system10adapted for monitoring performance parameters of a gas turbine engine while the engine is mounted and operating on a stationary test stand, for example, the test stand100represented inFIG. 1. The system10can also be used to monitor an engine during on-wing flight tests, as well as during normal aircraft operation. While the monitoring system10is particularly well suited for monitoring a gas turbine engine, and for convenience will be described in reference to the engine108and its stand100represented inFIG. 1, the use of the system10is not limited to such applications. Instead, the system10is more broadly applicable to a wide variety of situations in which there is a desire or need to monitor performance parameters of an apparatus operating in an environment subjected to elevated temperatures.

As represented inFIG. 2, the system10is generally identified as having units12,14,16and18that are located in four environments34,36,38and40with respect to the gas turbine engine108. The first unit12comprises an array of sensors20appropriately located in and around the engine108to monitor performance parameters of the engine108for the purpose of assessing the performance of the engine. Any number of sensors20may be employed by the system10, and the sensors20may be of various types, for example, to monitor temperatures, pressures, flow rates, forces, rotational speeds, etc., of the engine108, as was previously discussed in reference toFIG. 1. Certain types of sensors20are typically employed in large numbers during the monitoring of engine operation, including thermocouples, resistance temperature detectors (RTDs), and pressure transducers. Because the sensors20are located to directly detect the parameters of interest, the unit (array)12of sensors20is indicated inFIG. 2as being located in a “high temperature engine environment”34, where maximum temperatures exceeding 200° C. are often encountered by the system10and may reach as high as 260° C. or more. Suitable sensors20for use in the system10are commercially available and commonly used for monitoring gas turbine engine parameters, and therefore will not be discussed in any detail here. The particular output signals generated by the sensors20will depend on the type of sensors20used, though in most cases the signals will be analog signals that must be digitized in order for their data to be used by computer processing equipment to assess the performance of the engine.

The remaining primary units14,16and18of the system10are identified inFIG. 2as located in environments36,38and40where lower temperatures are likely to occur. A first of these units will be referred to as a hub unit14, with which the sensors20directly communicate through any suitable wires, tubes, or other appropriate connectors commonly employed with the particular type of sensors20used. The hub unit14represented inFIG. 2will typically be one of a number of hub units14that may be used in the system10, depending on the number of sensors20and the number of sensors20each hub unit14can manage. Similar to the environment34for the sensors20, the environment36for the hub unit14is identified as a “high temperature engine environment”34, in that the hub units14are adapted to be located in close proximity to the engine108, for example, within about three meters of the engine108, such as the engine core environment beneath the engine cowling114. In addition to locations directly on the engine108and beneath its cowling114, other locations may include adjacent locations on the head frame106or adapter110of the stand100, where very high temperatures are still likely to be encountered by the system10. For example, temperatures beneath the cowling114and adjacent locations on the head frame106or adapter110often exceed 125° C., and can reach much higher temperatures, for example, higher than 200° C. and potentially as high as 260° C. or more. Consequently, electronic components of the hub units14must be capable of withstanding significantly higher temperatures than is possible with conventional electronic components and even military standard components.

In contrast, the environments38and40for the remaining two units16and18of the system10, referred to as a collector unit16and a distributor unit18, are identified as a “near-engine environment”38and a “low temperature environment”40. The former is designated as such because the collector unit16is adapted to be located in proximity to the engine108but not as close to the engine core as the hub units14. For example, the collector unit16may be located within the engine fan case environment or on the stand100, such as on the head (thrust) frame106, at distances of about three to ten meters from the core of the engine108. At these locations, temperatures will usually exceed 55° C., but are significantly less than 260° C. and typically less than 125° C. Consequently, electronic components of the collector unit16must typically be capable of withstanding high temperatures, though not as high as the hub units14. In some situations, military standard components rated up to 125° C. may be used, and possibly conventional electronic components rated up to 85° C.

On the other hand, the low temperature environment40of the distributor unit18permits the use of conventional electronic components rated at no more than 85° C. The environment40is designated as “low temperature” in that the distributor unit18can be and preferably is located in a controlled-temperature environment, for example, an enclosed facility that is near the test stand100and is stabilized with air-conditioning to maintain a temperature of less than 55° C. For on-wing engine operation, the environment40may be within the aircraft. The distributor unit18preferably has the most processing power of the system10, and therefore will typically comprise one or more computer servers, personal computers, and/or other processing equipment adapted for data processing, collectively represented by a distributor computer42inFIG. 2. In addition to a real-time calibration functionality discussed below, the distributor computer42may also provide the capability of engineering unit conversion, system configuration, and database functionality. Suitable equipment for the distributor computer42are likely to be relatively sensitive to temperature, and therefore benefit from being housed at roughly room temperature. The low temperature environment40is typically remotely located from the engine test stand100, for example, in excess of fifty meters.

FIG. 2schematically represents the hub unit14as comprising a processor control board22and one or more analog signal conditioning boards24. These boards22and24are preferably enclosed in a housing44, schematically represented inFIG. 2as completely surrounding and enclosing the boards22and24. The processor control board22and analog signal conditioning boards24operate together to convert the analog output signals of the sensors20to digital data that can be processed by the distributor unit18. According to certain preferred aspects of the invention, the processor control board22and analog signal conditioning boards24also combine to perform additional processes to ensure the integrity of the analog output signals received from the sensors20prior to their analog-digital conversion. As will be explained in more detail below, one such additional process is to provide a continuous calibration feature that detects any drift in the accuracy and precision characteristics of the electronic components of the analog signal conditioning boards24and the processor control board22that can result from component aging and variations in temperature, such as the extreme temperature changes to which the hub unit14is subjected. The calibration feature produces calibration data that can be used by the distributor computer42to perform real-time corrections of the digital data acquired from the hub unit14via the collector unit16, and more particularly a collector computer26of the unit16. Another preferred process is to multiplex the analog output signals of multiple sensors20into multiplexed analog outputs, thereby reducing the number of connections required to transmit the digital data to the collector unit16over, for example, a serial data connector such as an RS-485 serial communications cable. Still another preferred process is to interleave the multiplexed analog outputs of one group (bank) of sensors20with the multiplexed analog outputs of other banks of sensors20, so that the individual analog output signals of the multiplexed analog outputs more quickly “settle” between the sets of outputs. These and other aspects of the hub unit14will be discussed in further detail below.

The collector hub16is schematically represented inFIG. 2as comprising the collector computer26, a power supply28, and a temperature-controlled environment30that contains a system voltage reference device32, as will be explained in more detail below. The primary function of the power supply28is to supply power to the electronic components of the system10, including the sensors20(as may be required) and the electronic components housed in the hub unit14. A preferred power supply28is a dual topology design with a switching regulator front end and linear regulator back end. The power supply28may be configured to generate multiple independently-regulated voltages for each hub unit14to increase system fault tolerance and decrease noise coupling. The collector computer26receives the digital data from the hub unit14, as well as any additional hub units14contained in the system10, prior to forwarding the digital data to the distributor computer42of the distributor unit18. The collector computer26is preferably configured to have a logging capability for synchronizing the flow of the digital data to the distributor computer42, for example, utilizing inter-range instrumentation group (IRIG) time codes or a Network Time Protocol (NTP). More particularly, the collector computer26preferably operates as an intelligent switch for the incoming digital data from multiple hub units14by accurately time stamping multiple streams of digital data coming from the hub units14, packing the data into frames, and then transmitting the data to the distributor computer42, for example, over a fiber-based Ethernet connection. Suitable components for time stamping multiple data streams and packing data into frames are well known in the art, and therefore will not be discussed in any detail here. The use of a fiber optic cable for the data connection between the collector computer26and the distributor computer42is preferred for the purpose of reducing the susceptibility of the transmission to lightening, which is desirable since the transmission cable will typically be exposed to an outdoor environment as a result of being routed between the test stand100and the remote facility housing the distributor unit18. The collector computer26, power supply28and controlled environment30may all be enclosed within a suitable protective housing (not shown) that protects these components from direct exposure to the elements.

Notably, because of multiplexing at the level of the hub units14and synchronization at the level of the collector unit16, the digital data can be supplied to the distributor unit18over a single Ethernet connection, which is in stark contrast to the typical thousands of cables and tubes previously required to transmit sensor output to a remote data acquisition system of the prior art.

FIG. 3is a block diagram representing the processor control board22, some of its components, and its connection to the analog signal conditioning boards24and the collector unit16. The processor control board22is represented as being equipped with a microprocessor46adapted to run from a program stored in ROM (read-only memory)48, such as an EEPROM (electrically-erasable programmable read only memory), and uses RAM (random access memory)50to store the digital data generated from the sensors20, as well as any variables used in calculations performed by the control board22. The microprocessor46preferably performs a gain setting function associated with the signal conditioning boards24(discussed below), controls/selects which individual or blocks of signal channels of the sensors20are read, the timing of the data acquisition, error sensing, analog-to-digital conversion, execution of any built-in test (BIT) modes, sensor adaptation (based on the types of sensors20), and the collection, formatting and transfer of the digital data to the collector computer26. As indicated inFIG. 3, the input/output (I/O) functions of the board22are preferably directed in the form of memory mapped I/O operations. As also seen inFIG. 3, the processor control board22also transmits zero and full-scale control outputs to the analog signal conditioning boards24, as well as directly communicates with the collector computer26. As will be discussed in reference to the conditioning boards24andFIG. 4, the zero and full-scale control outputs transmitted by the control board22are part of a continuous calibration scheme that periodically applies a zero voltage and reference voltage to detect and compensate for any drift in the accuracy and precision characteristics of the electronic components of the conditioning boards24resulting from variations in temperature and component aging.

As previously noted, the hub unit14is intended to operate at temperatures greater than 125° C., and preferably as high as at least 200° C. In preferred embodiments, the microprocessor46, ROM48, RAM48and passive components mounted to the control board22are capable of operating at temperatures above 200° C. To achieve this capability, the microprocessor46, ROM48and RAM48are preferably implemented with silicon-on-insulator (SOI) substrates and processing technology. As known in the art, SOI substrates typically comprise a thin epitaxial layer on an insulator. The substrate is typically formed by oxidizing one or both bonding surfaces of a pair of semiconductor (e.g., silicon) wafers prior to bonding the wafers. Most typically, a single silicon dioxide layer is grown on an epitaxial layer formed on a silicon wafer. After bonding the wafers, all but the insulator and epitaxial layer (and optionally the silicon layer of the second wafer) are etched away, such that the silicon dioxide layer forms an insulator that electrically isolates the epitaxial layer. A commercial example of a solid-state microprocessor implemented on an SOI substrate using SOI processing technology is the HT83C51 microprocessor commercially available from Honeywell. Commercial examples of RAM components implemented on SOI substrates include the HT6256 256 Kbit SRAM component available from Honeywell, and commercial examples of ROM components implemented on SOI substrates include ROM components from Twilight Technology Inc.

The substrate on which the electronic components of the processor control board22are mounted is also preferably capable of withstanding temperatures of at least 260° C. A preferred high-temperature substrate material is commercially available from Rogers Corporation under the name RO4003C, which is a glass-reinforced hydrocarbon/ceramic laminate. Furthermore, the components are preferably attached with high melting point solders, a notable but nonlimiting example of which is 92.5Pb-5Sn-2.5Ag, which has a melting range of about 287 to about 296° C. To reduce thermal stresses resulting from thermal expansion and contraction of the board, the microprocessor46, ROM48, RAM50and other components on the board22are preferably through-hole components having one or more metal leads (sticks) that are inserted into through-holes (typically plated through-holes) in the substrate and then soldered to the substrate. Other approaches to reducing thermal stresses include the use of high-temperature, thermally-conductive potting materials to minimize thermal gradients, increase thermal time constants and damp vibrations, and limiting the number of metallized vias that are susceptible to breaking due to board delamination and expansion/contraction. Notably, the metal leads of the through-hole components are believed to promote the structural integrity of the vias in which they are placed.

With the above-noted high temperature capabilities, the control board22can be contained within the hub unit housing44, preferably without the need for an active cooling system dedicated to maintaining the temperature of the board22below 125° C. as would be required by conventional electronics. The term “active cooling” is used herein to mean cooling systems that are specifically designed to transfer heat from the board22and out of the hub unit housing44by conduction, convection, and/or radiation.

FIG. 4is a block diagram representing two analog signal conditioning boards24and their connection to the processor control board22ofFIG. 3. The analog signal conditioning boards24are combined with the processor control board22within the housing44of the hub unit14, and as such are also required to operate at high temperatures in the harsh environment of the engine108. The high temperature operation of the hub unit14and its conditioning boards24enables the sensors20, including thermocouples, RTDs, and pressure transducers, to be terminated directly on the engine108and their outputs conditioned prior to the A/D (analog-to-digital) conversion performed by the processor control board22. Furthermore, the hardware of the conditioning boards24preferably incorporates the previously-noted continuous calibration, multiplexing and interleaving features.

As note above, the continuous calibration scheme performed on the conditioning boards24produces calibration data that can be used by the distributor computer42to perform real-time corrections of the digital data acquired from the hub unit14. The continuous calibration scheme preferably compensates for all passive and active components on the conditioning boards24and processor control board22that may significantly affect signal accuracy. The need for a continuous calibration feature arises because, at the system level, discrete components are not currently available that do not exhibit drift over the foreseeable operating range of the hub unit14, for example, about −55° C. to above 200° C. In preferred embodiments of the invention, the continuous calibration scheme provides for zero and full-scale data to be continuously collected, while any drifting of the acquired data over time and temperature is automatically compensated.

The continuous calibration feature relies in part on the system voltage reference device32, represented inFIG. 2as located in the controlled environment30of the collector unit16remote from the hub unit14. Though a location with the collector unit16is believed to be preferred, it is foreseeable that other locations could be found suitable for system voltage reference device32. The controlled environment30is schematically represented in greater detail inFIG. 5as comprising the voltage reference device32enclosed within a housing52, which further contains a heating element54, copper plate56and thermal RTV potting material58that achieve uniform heating of the voltage reference device32. The temperature of the reference device32can be regulated to any suitable level, for example, about 55° C. to about 125° C. The reference device32generates highly-precise zero and full-scale reference voltages, which are then transmitted over dedicated differential links to the conditioning boards24.

Temperature-induced drifting in the accuracy and precision of the electrical circuit components of the conditioning boards24are captured and recorded along with the analog output signals of the sensors20during A/D conversion. During each cycle in which analog output signals are read from the sensors20, the processor control board22causes the highly-precise zero volt and reference voltage signals of the reference device32to be transmitted through all analog signal processing paths (channels) defined by the electronic components of each conditioning board24. The zero volt and reference voltage signals are then used to correct the digitalized sensor data, in that any change in the output voltage from the previous calibration reading is attributed to board-level component drift and transmitted as calibration data to the distributor computer42, which digitally corrects the digitalized sensor data before further use of the data. In practice, the zero and full-scale reference signals may be applied several times per second. Accuracies over time, temperature and distance on the order of having an accuracy on the order of about +/−20 ppm (parts per million) and less have been achieved in the analog signal processing path with the continuous calibration feature described above.

As part of the calibration scheme, the conditioning boards24also provide for multiplexing of multiple signal channels from the sensors20, enabling each conditioning board24to condition multiple sensor signals through a fewer number of circuit paths, for example, two as represented inFIG. 4. Signals from multiple sensors20are represented inFIG. 4as passing through multiplexors60to generate multiplexed analog outputs, thereby reducing the number of connections required to transmit the digital data to the collector unit16over a serial data connector. Within each circuit path, the multiplexed analog outputs are conditioned with an instrumentation operational amplifier62. Each amplifier62is represented inFIG. 4as incorporating active gain changes64controlled by the processor control board22, which enables each conditioning board24to be used to scale many different sensor types with different voltage outputs to a set output voltage prior to A/D conversion.

As further evidenced fromFIG. 4, switches68can be used to interleave the multiplexed analog outputs of one bank (group) of sensors20along one circuit path on the board24with the multiplexed analog outputs of another bank of sensors20on another circuit path of the same board24to increase system throughput. As one series of multiplexed analog outputs from one bank of sensors20is output to the A/D converter of the processor control board22, sensor outputs on other banks of sensors20are at various stages of settling. Once the series of multiplexed analog outputs from the first bank of sensors20has been read by the A/D converter, the next bank can be chosen while signals of the first bank begin to settle on a different sensor20. This feature allows a higher system level throughput to be implemented with slower, but higher-temperature capable circuit components of the processor control board22and conditioning boards24.

The conditioning board24depicted inFIG. 4is further represented as incorporating dynamic, dual-time constant filtering66on the amplifier outputs of each operational amplifier62and controlled by the processor control board22. This feature further enables rapid settling when switching between the circuit paths over which the multiplexed analog outputs are transmitted, while still providing a high level of low pass filtering to reduce electrical noise of a sensor output signal present in the engine test environment. Dynamic filtering can be achieved by, for example, removing a resistor from an RC circuit, allowing a rapid output change from one channel voltage to another, then switching the resistor back into the circuit to minimize sensor noise and ripple, improving the analog data quality presented to the A/D converter (ADC).

Notably, each conditioning board24is preferably able to accommodate both positive and negative input voltages, for example, in the event that the sensors20include thermocouples and pressure transducers that can output negative voltages. Additionally, because the conditioning boards24are located in the high temperature environment of the hub unit14, “cold junction” compensation conventionally performed on thermocouples board can be “hot junction” compensation since thermocouples among the sensors20may be at a lower temperature than the thermocouple wire-to-reference junction measured by the conditioning board24. For this reason, the instrumentation operational amplifiers62are preferably capable of differential voltages and scales these ± voltages to a positive-only voltage range necessary for A/D conversion.

As with the processor control board22, at least some of the circuit components of the analog signal conditioning boards24are preferably implemented with SOI technology to allow operation of the boards24at temperatures of at least 200° C., enabling the entire hub unit14to operate at such elevated temperatures. As a result, the hub unit14and its control and conditioning boards22and24overcome prior limitations of data acquisition systems that have necessitated that each individual sensor output must be transmitted by wire or tube to a remote location a considerable distance from an engine under test. Such restrictions have resulted in long wires and tubes routed from engines to the data acquisition systems, incurring additional expense, introducing additional sources of error, and necessitating a considerable amount of man-hours to install and debug. In contrast, the hub unit14can be placed directly on the head frame106, its adapter110, or even directly on the engine108, for example, under the cowling114, resulting in a relatively short distance (for example, less than three meters) between the sensors20and their terminations on the hub unit14.

While the invention has been described in terms of a preferred embodiment, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configuration of the units12,14,16and18and the components could differ from that shown, and materials and processes other than those noted could be used. Therefore, the scope of the invention is to be limited only by the following claims.