Communications – electrical: acoustic wave systems and devices – Echo systems – Speed determination
Reexamination Certificate
2002-08-20
2004-01-13
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
Speed determination
Reexamination Certificate
active
06678208
ABSTRACT:
BACKGROUND OF THE INVENTION
Speed sensors used in aquatic applications such as those used to determine the speed of a vessel moving through water have become more accurate at the cost of increased complexity. In the past, paddle-wheel type speed sensors were used but are now outdated due to the fact that they are vulnerable to damage by debris in the water and often impart an undesirable drag on the boat, thus, impeding forward motion. More advanced speed sensors include sophisticated electronics coupled to ultrasonic transducer pairs spaced on a motion axis of a vessel to monitor a forward speed.
According to suggested ultrasonic speed detection methods, two spaced transducers are used to monitor regions beneath the bottom-side of a vessel. Ultrasonic signals from each transducer are emitted towards randomly located reflective particles from such objects as air bubbles present in the water, while corresponding reflected signals are sampled by each respective transducer. Since the monitoring transducers are located along an axis in line with the forward motion of the vessel, each transducer monitors a substantially similar set of reflective surfaces when the vessel is moving forward. In other words, a first sensor detects reflections from a set of random particles in a fluid, while a second sensor detects reflections off a substantially similar set of the random particles at a later time based on the forward motion. Accordingly, a time difference associated with the two substantially matching but time-shifted signals can then be used in conjunction with transducer separation to determine vessel speed.
There are drawbacks associated with the aforementioned side-by-side ultrasonic transducer speed sensor. For example, significant signal processing power must typically be employed to accurately determine vessel speed since two entire sets of sampled data corresponding to the location of the vessel at a given instant in time must be analyzed to accurately determine the time difference between the two sampled reflection signals. This is a heavy price to pay for accurately determining speed of a vessel.
SUMMARY OF THE INVENTION
The present invention provides several novel improvements for reducing the complexity of processing and comparing signals. Generally, the signal processing improvements disclosed herein reduce the complexity of determining a time difference between two similar but time-shifted signals, including the processing platform upon which a corresponding algorithm runs. In one application, a simplified set of data samples are processed to derive vessel speed, without unduly compromising accuracy of the speed sensor.
More particularly, one aspect of the present invention is directed towards a system and method to determine a time difference between two similar but time-shifted signals. In an illustrative embodiment, first and second signals are sampled to generate a discrete mathematical function whose discrete sample points define overlapping ranges. For example, the discrete mathematical function itself can be a function defined by multiple discrete sample points. Typically, at least one of the multiple overlapping ranges defined by sample points can be used to interpolate a point on the mathematical function indicating a time difference between the first and second signals. Consequently, the mathematical function characterizing a time relationship between the first and second signals can be used to determine speed or other measurable quantities.
In one embodiment, the discrete mathematical function is a difference function correlating echo signals from multiple monitored regions. The echo signals can be reflections from particles, inconsistencies or structures disposed in a fluid. Each of the first and second signals can be sampled to incrementally generate a mathematical function at discrete sample points. Also, each of the first and second signals can be compared to a respective threshold signal to generate a discrete mathematical function that is in turn used to determine a time difference between the first and second signals.
A mathematical function such as a difference function can be generated at discrete sample points based on signal sampling in a first time interval. The difference function can then be analyzed in a range defined by a first pair of sample points of the difference function to interpolate a time difference between the echo signals for sample data taken in the first interval.
The mathematical function can be updated based on new samplings or signal sampling in a second time interval. For example, the difference function can be updated by continuous, periodic or intermittent sampling of the first and second signals. Consequently, the updated difference function can be analyzed to determine a time difference between signals at a particular snapshot in time.
A time difference between two echo signals can be interpolated in a particular range between sample points of the difference function. If interpolation can not be used in a given range to determine a time difference between signals, another pair of sample points of the difference function whose range at least partly overlaps with a previous pair of sample points can be used to determine a time difference between multiple signals. This technique of utilizing overlapping ranges for successive calculations can be used to more accurately determine a time difference between signals, especially if the time difference between signals is changing.
For example, consider that a change in vessel speed causes the difference function to change. As the difference function changes, a new overlapping range can be used to determine a time difference between signals. Thus, the use of multiple sample points to define overlapping ranges can result in more accurate readings and smoother transitions in displayed speed when presented to a pilot or user.
As mentioned, characteristics of the first and second signals can change over time as a result of a changing relative speed of monitored particles with respect to corresponding sensors. This results in a change in the difference function and reporting of vessel speed.
Other more specific aspects of the present invention can be employed to identify, for example, the relative speed or throughput of a fluid through a conduit such as a pipe. In this instance, a sensor device can be disposed to monitor a flow in which first and second signals are generated from guided fluid or reflective particles in the guided fluid passing through monitored regions.
A generated discrete mathematical function can include a unique point such as a zero-crossing that reflects a time difference between the first and second signals. The zero-crossing can be an imaginary or real point on the difference function that intersects with a particular reference such as an axis. More specifically, the zero-crossing can be a point at which the discrete mathematical function intercepts a reference. A specific position of the zero-crossing of the difference function can be calculated using mathematical techniques such as interpolation. For example, an imaginary line or curve can be drawn between the sample points of the difference function to determine at what point the function intersects a time axis or other relevant reference. The intersection can indicate an offset of time at which a near-perfect correlation exists between the first and second signals.
In one application, a magnitude of the first signal is proportional to an intensity of reflections in a first monitored region and a magnitude of the second signal is proportional to an intensity of reflection in a second monitored region. Consequently, speed such as vessel speed or fluid speed can be determined based on a motion of reflective structures or surfaces such as bubbles or particles that pass through both the first and second regions, but at different times. As the relative speed of reflective structures such as bubbles or particles increases through a monitored region, there will be a smaller offset in time between the two signals. Conver
Boucher Stephen G.
Sifferman Andrew M.
Tancrell Roger H.
Airmar Technology Corporation
Hamilton Brook Smith & Reynolds P.C.
Pihulic Daniel T.
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