Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2001-07-27
2003-08-12
Le, N. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S500000, C439S188000
Reexamination Certificate
active
06605948
ABSTRACT:
TECHNICAL FIELD
This invention relates to programming plugs used to customize the control systems of modern gas turbine engines, and particularly to a test system for testing the wiring configuration of the programming plug.
BACKGROUND OF THE INVENTION
Modern gas turbine engines, such as those used to power commercial aircraft, operate under the direction of a full authority digital electronic control system (FADEC). The FADEC includes numerous control schedules. These control schedules include power setting schedules that govern steady state engine power, and other schedules that control engine transient response and regulate a number of variable geometry features, such as the pitch angle of variable pitch stator vanes. In operation, the FADEC receives command signals, feedback signals and environmental signals. An example of a command signal is a signal representing the throttle position set by the aircraft pilot. Examples of feedback signals include signals representing engine parameters (e.g. rotational speeds, internal pressures, and internal temperatures). Examples of environmental signals include signals indicating environmental conditions (e.g. ambient pressures and temperatures). The FADEC processes these signals, as prescribed by the various control schedules, to produce a series of electrical output signals. The output signals drive fuel valves and various actuators to regulate engine thrust and ensure peak engine performance and operability.
Engine manufacturers frequently offer distinct “families” of engines, each of which comprises several closely related engine “models”. Each engine model, when equipped with its FADEC, satisfies the requirements of a particular aircraft or of a mission profile specified by the aircraft owner. For example, the assignee of the present application offers several models of its PW-4000 engine family, among them the PW-4156, which produces 56,000 pounds of thrust for the Airbus Industries A-300 aircraft; the PW-4152, which produces 52,000 pounds of thrust, also for the Airbus Industries A-300 aircraft; and the PW-4158, which produces 58,000 pounds of thrust for the Airbus Industries A-310 aircraft.
Because the engine models within a given engine family are closely related, it is common practice to equip those engine models with inter-operable, interchangeable FADEC units. Such FADEC units include omnibus control schedules that are applicable to all engine models subsumed by the engine family, as well as a comprehensive collection of model-specific control schedules. In addition, the FADEC may include a collection of “EPR modifiers”, which are described below. Such an inter-operable FADEC is interchangeable amongst the engine models and can be readily customized for each model.
The above-mentioned EPR modifier is employed by the FADEC's power or thrust setting control loop. Ideally, the power setting loop would control engine thrust directly. However, the thrust produced by an engine installed on aircraft cannot be easily and accurately measured, and so cannot serve as a feedback parameter for the power setting loop. Accordingly, the engine manufacturer selects a surrogate parameter representative of thrust to serve as the power setting parameter. One parameter known to be useful as a power setting feedback parameter is engine pressure ratio (EPR) which is the ratio of stagnation pressure at the engine exhaust nozzle discharge plane to stagnation pressure at the engine's air intake duct. The relationship between thrust and EPR varies slightly between individual engines, even individual engines of the same model. In order to account for these differences without introducing excessive complexity into the control system power setting schedules, it is common practice to apply a bias to the EPR feedback signal. This EPR bias is referred to as an “EPR modifier”. A collection of selectable, predefined EPR modifiers is stored in the memory of a typical inter-operable FADEC. In practice, each individual engine is tested to determine how much its relationship between thrust and EPR deviates from a pre-established norm. The magnitude of the deviation defines the EPR bias that must be applied to the EPR feedback signal. The predefined EPR modifier whose magnitude best approximates the desired EPR bias may then be selected as described below.
A FADEC is customized for a specific engine model and individual engine by an electrically energized engine programming plug (EPP) also referred to as a data plug. An EPP includes an array of pins, each receivable by an externally accessible socket in the FADEC. Several of the pins are electrically grounded to form a common ground terminal. The remaining pins are data input pins that, taken collectively, encode a bit string. The bit string tailors the FADEC to a particular engine model, and to a particular individual engine, by establishing which model-specific control schedules and which EPR modifier the FADEC will obey. The bit represented by each pin depends on whether or not that pin is connected to the ground terminal. Data pins connected to the ground terminal represent the binary digit “0”, whereas data pins not connected to the ground terminal represent the binary digit “1”. The ground connections are usually effected by jumper wires.
The jumper wire connections are made by a technician who consults an EPP wiring instruction document for the engine model and EPR modifier of interest. The wiring instructions identify which pins to connect to the ground terminal and which to leave ungrounded. When installed in a FADEC, the properly wired EPP constrains the FADEC to obey the model-specific schedules and EPR modifier appropriate for the engine model and individual engine of interest. Once correctly wired, the EPP corresponds to an engine manufacturer's part number. For example, an EPP wired for the PW-4156 engine model would bear a different part number than if it were wired for the PW-4152 engine model. Each EPP also has a numerical EPP class designation, independent of the part number, depending on which of the several EPR modifiers the EPP is wired to select.
Clearly, it is important to ensure that the EPP is correctly wired. Otherwise the data pins may represent an invalid or incorrect bit string. Conventional practice is for the technician to verify the state of each data pin (grounded or ungrounded) by checking for electrical continuity between each pin on the EPP. The technician carries out the checks with a digital ohmmeter that indicates a small resistance (approximately zero Ohms) for grounded data pins and a large resistance, perhaps 1 mega-Ohm, for ungrounded pins. The technician records the measured resistance readings and compares them to correct values on an instruction sheet. This is a painstaking, labor intensive process. In the event that incorrect wiring were detected, the technician would have to correct the wiring error and then repeat the continuity checks, or at least check those pins affected by the wiring error.
What is needed is an apparatus and method for quickly and reliably testing for correct wiring of an engine programming plug.
SUMMARY OF THE INVENTION
It is, therefore, an object of the invention to provide an apparatus and method for quickly and conveniently testing for correct wiring of an engine programming plug.
According to the invention, a tester for validating the wiring configuration of an engine programming data plug includes a computer governed circuit for automatically acquiring data from the plug and a computer commanded display system for reporting the condition of the plug. In one particular embodiment, the tester circuitry includes an array of multiplexers responsive to an incrementable selection signal for concurrently acquiring one data bit from a prescribed data pin in each of several groups of data pins. The computer operates under the authority of an executable computer program that assesses the condition of the programming plug relative to a set of predefined standards.
The principal advantage of the invention is its ability to quickly va
Baran Kenneth C.
Kerveros James
Le N.
United Technologies Corporation
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