Measuring and testing – Fluid flow direction – With velocity determination
Reexamination Certificate
2000-09-01
2003-01-07
Oen, William (Department: 2855)
Measuring and testing
Fluid flow direction
With velocity determination
Reexamination Certificate
active
06502459
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to the measurement of properties of an incoming air stream, and more particularly, to the measurement of velocity and incident angle of an incoming air stream.
The measurement of the velocity and incident angle of an incoming air stream has many applications, including flight control applications, industrial process stream applications, combustion control, weather monitoring applications, etc. For flight control applications, the precise orientation or attitude of an aircraft relative to an incoming air stream, as well as the air velocity, are important components of the total “air data” information package used by modem flight control systems.
In most cases, air speed is detected by sensing the difference between head and static pressure, often using Pitot tubes. This approach operates well at speeds above about 60 knots if a very accurate differential pressure sensor or two absolute pressure sensors are used, at considerable expense. Additional sensors are typically needed to detect the orientation or attitude of an aircraft.
One way to detect the attitude of an aircraft is to use vane transducers, which include several mechanically rotating vanes that find an orientation that results in a balanced pressure or air speed on either of side of the vanes. By detecting the resulting orientation of the vanes, the attitude of the aircraft can be determined. A limitation of such a sensor system is that the mechanical rotating vanes often reduce the reliability and response time of the sensor. In addition, most vane transducers have a relatively large radar cross-section, which is undesirable in many applications, such as military applications.
SUMMARY OF THE INVENTION
The present invention overcomes many of the disadvantages of the prior art by providing a rugged microsensor assembly that can measure both velocity and angular direction of an incoming air stream. The microsensor assembly preferably includes at least two flow sensors, each orientated to measure a different velocity component of the incoming air stream. The velocity components are related by the geometry between the sensors. The angular direction and velocity of the incoming air stream can be determined by examining the measured velocity components. Such a microsensor can provide a fast response time and a relatively small radar cross-section It is contemplated that the microsensor of the present invention may be used in a wide variety of applications, including for example, flight control applications, industrial applications, weather monitoring applications, etc.
In one illustrative embodiment of the present invention, the sensor assembly includes a first sensor and a second sensor. The first sensor measures the velocity component of the incoming air stream that extends along a first sensor axis. The second sensor measures the velocity component of the incoming air stream that extends along a second sensor axis, wherein the first sensor axis is rotated from the second sensor axis to intersect the second sensor axis at an intersection point.
From the outputs of the first and second sensors, the angular direction and velocity of the incoming air stream can be determined. During operation, if the angular direction of the air stream deviates in one direction, the velocity components of the incoming air stream that extend along the first sensor axis increase, and the velocity components of the incoming air stream that extend along the second sensor axis decrease. Likewise, if the angular direction of the air stream deviates in the other direction, the velocity components of the incoming air stream that extend along the first sensor axis decrease, and the velocity components of the incoming air stream that extend along the second sensor axis increase. By examining the velocity components measured by the first and second sensors, and using the relative geometry between the sensors, the angular direction of the air stream can be determined.
Preferably, both the first sensor and the second sensor are thin-film microanemometers such as available microbridge flow type sensors, each having at least one elongated heater element and at least one elongated sensor element, both in thermal communication with the incoming air stream. The elongated heater and sensor elements preferably extend perpendicular to the associated sensor axis. For example, the elongated heater and sensor elements of the first microbridge flow sensor preferably extend perpendicular to the first sensor axis, and the elongated heater and sensor elements of the second microbridge flow sensor preferably extend perpendicular to the second sensor axis.
The heater elements of the first and second microbridge flow sensors are then energized by either a common or separate heater energizers. The heater energizers preferably cause an elevated temperature condition in each of the elongated heater elements, which in turn, cause an elevated temperature condition in adjacent upstream and downstream sensor elements, and in the air stream. The temperature distribution near the thin-film bridge is transmitted symmetrical about the heater element when no air flow is present, and is disturbed when air flow is present. The amount of disturbance is related to the velocity of the air-stream along the corresponding sensor axis.
The sensor elements of the first and second microbridge flow sensors preferably have a resistance that changes with temperature. Accordingly, the sensor elements of the first microbridge flow sensor can be used to sense the temperature distribution provided by the heater element of the first microbridge flow sensor. Likewise, the sensor elements of the second microbridge flow sensor can be used to sense the temperature distribution provided by the heater element of the second microbridge flow sensor.
More specifically, and in one illustrative embodiment, one sensor element is positioned upstream from the heater element, and the other is positioned downstream. The heater element is then heated a predetermined amount above the ambient temperature of air-stream. When there is a positive air-stream, the upstream sensor element is cooled, and heat conduction from the heater element to the downstream sensor element is promoted. As a result, the temperature of the downstream sensor element is increased, and a difference in temperature between the sensor elements appears. This temperature difference can be related to the velocity component of the air-stream along the corresponding sensor axis.
Alternatively, and in another illustrative embodiment, the heater energizer provides a transient elevated temperature condition in each of the elongated heater elements, which in turn, causes a transient elevated temperature condition in the air stream. Each sensor element, which preferably has a resistance that changes with temperature, can be used to sense when the transient elevated temperature condition in the air stream arrives at the corresponding sensor element. The time lag between the transient elevated temperature condition in the heater element and the resulting transient elevated temperature condition in the sensor elements can be related to the velocity component of the air-stream along the corresponding sensor axis.
In this embodiment, each microbridge flow sensor may have a corresponding time lag detector for determining the time lag values. One time lag value may correspond to the time lag, or delay, between the transient elevated temperature condition in the heater element and the resulting transient elevated temperature condition in a first (e.g., upstream) sensor element. Another time lag value may correspond to the time lag between the transient elevated temperature condition in the heater element and the resulting transient elevated temperature condition in a second (e.g., downstream) sensor element.
The velocity component of the incoming air stream that extends along the first sensor axis can be determined using the two time lag values of the first microbridge flow sensor. Likewise, the ve
Bonne Ulrich
Kubisiak David
Satren Ernie A.
Weeres Steve R.
Crompton Seager & Tufte
Honeywell International , Inc.
Oen William
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