Data processing: measuring – calibrating – or testing – Measurement system – Speed
Reexamination Certificate
2001-03-21
2003-10-14
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Speed
C702S147000, C702S142000, C702S010000, C702S095000, C702S060000, C702S010000
Reexamination Certificate
active
06633828
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to turbine engines and, more particularly, to a method and system used in electrical control sensors for shaft speed signal frequency change rate tests.
Compressor and load shaft speeds are the primary control parameters of gas turbine engines. Accurate speed measurement is essential for proper engine control. In modern engines with electronic control systems, shaft speeds are typically measured using passive variable reluctance magnetic speed sensors, which sense passing of gear teeth or similar objects. The sensors output an electrical signal to the gas turbine electronic control unit (ECU), with signal frequency proportional to the shaft speed (i.e., passing speed of the gear teeth). The ECU measures the speed by measuring the frequency of the speed pickup signal. The ECU typically conducts reasonableness tests to insure the accuracy of the signal before using it. These may include sensor impedance tests (to check whether the electrical characteristics of the sensor appear normal), and signal frequency range and change rate tests (to check whether the resulting signal characteristics appear normal, within the expected range and not changing at an unreasonable rate).
The conventional signal frequency change rate tests used to detect intermittent or “in-range” failures are unreliable because they either often detect failures that do not truly exist (false alarms) or, in order to avoid generation of false alarms, they miss real failure events. There are four typical failure modes that need to be addressed by signal frequency change rate type tests. First failure mode includes intermittent electrical sensor failures that cause a noisy signal. The other three failure modes include “in-range” failures. Second failure mode includes internal sensor failures which can cause “multiple crossings” or cases where higher than normal speeds are read occasionally. Third failure mode includes damaged gear teeth, shaft runout or excessive speed pickup installation gaps, and can cause “missed teeth” and resultant speed measurement errors. Some conventional controllers even have added sophisticated hardware circuits to detect “missing teeth”. On turbofans, the fourth failure mode is a catastrophic engine failure event called a “blade out”, which causes the controller to perceive speed incorrectly and fuel the engine up.
As can be seen, there is a need for a method and system for implementing signal frequency change rate tests, useable for detection of four intermittent or “in-range” failure modes discussed above, which is more reliable and less complex.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a system useable in electrical control sensors for shaft speed signal frequency change rate tests, detects intermittent or “in-range” failures. It has means for measuring frequency of a shaft speed signal; means for estimating a short-term variance of the measured signal using the equation: Var[x]=E[x
2
]−E
2
E
2
[x], where E[x
2
] is an estimated average of the squared measured signal over a short time interval, and E
2
[x] is a squared estimated average of the measured signal over a short time interval; means for comparing the estimated short term variance with a predefined variance limit for a predefined amount of time; and means for deeming the measured signal invalid, if the estimated variance exceeds the predefined variance limit for the predefined amount of time.
In another aspect of the present invention, a system useable in electrical control sensors for shaft speed signal frequency change rate tests, detecting intermittent or “in-range” failures, has means for measuring frequency of a shaft speed signal; means for calculating a rate of change (time derivative) of the measured signal; means for estimating a short-term variance of the measured signal rate of change using the equation: Var[x]=E[x
2
]−E
2
[x], where E[x
2
] is an estimated average of the measured signal squared rate of change over a short time interval, and E
2
[x] is a squared estimated average of the measured signal rate of change over a short time interval; means for comparing the estimated short term variance with a predefined variance limit for a predefined amount of time; and means for deeming the measured signal invalid, if the estimated variance exceeds the predefined variance limit for the predefined amount of time.
In a further aspect of the present invention, a method useable in electrical control sensors for shaft speed signal frequency change rate tests, detecting intermittent or “in-range” failures, has the steps: (a) measuring frequency of a shaft speed signal; (b) estimating a short-term variance of the measured signal using the equation: Var[x]=E[x
2
]−E
2
[x], where E[x
2
] is an estimated average of the squared measured signal over a short time interval, and E
2
[x] is a squared estimated average of the measured signal over a short time interval; (c) comparing the estimated short term variance with a predefined variance limit for a predefined amount of time; and (d) if the estimated variance exceeds the predefined variance limit for the predefined amount of time, deeming the measured signal invalid.
In yet another aspect of the present invention a method useable in electrical control sensors for shaft speed signal frequency change rate tests, detecting intermittent or “in-range” failures, has the steps: (a) measuring frequency of a shaft speed signal; (b) calculating a rate of change (time derivative) of the measured signal; (c) estimating a short-term variance of the measured signal rate of change using the equation: Var[x]=E[x
2
]−E
2
[x], where E[x
2
] is an estimated average of the measured signal squared rate of change over a predefined short term, and E
2
[x] is a squared estimated average of the measured signal rate of change over the predefined short term; (d) comparing the estimated variance with a predefined variance limit for a predefined amount of time; and (e) if the estimated variance exceeds the predefined variance limit for the predetermined amount of time, deeming the measured signal invalid.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.
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Faymon Dave
Rushinsky John
Xiong Yufei
Cherry Stephen
Honeywell International , Inc.
Robert Desmond, Esq.
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