Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
1999-07-22
2001-10-02
Williams, Hezron (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S064530, C073S061790
Reexamination Certificate
active
06295873
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus and method to measure the transit time of an ultrasonic wave through a sample, specifically useful for identifying characteristics of interest in liquid samples.
BACKGROUND OF THE INVENTION
Certain characteristics of liquids have traditionally been measured in order to develop a composite of the overall quality of the liquid. Liquid characteristics that have been measured to develop such a composite include the following: pH, turbidity, amount of dissolved oxygen, suspended solids, and dissolved solids. Devices used for performing these measurements (specific examples being the pH meter and dissolved oxygen and turbidity probes) typically require special handling, frequent adjustment, and manual calibration.
Sensor probes for remotely monitoring impurity levels in a liquid, such as water, are typically based on pH sensors, which require special handling and periodic calibration, thus limiting their use in remote applications. Other sensors for water, such as dissolved oxygen and turbidity probes, require even more frequent calibration. Water sampling kits, such as the Hach Kit, are inexpensive; however, the need for manual intervention during tests using such equipment is high, therefore rendering the process costly and inconvenient. Also, known sensors for monitoring liquids in process control systems in manufacturing must be vigilantly maintained, adjusted, and manually calibrated by specially trained technicians. Because of the harsh environments within which some of the known sensors must be capable of operation, they are expensive to maintain, as well as to buy.
U.S. Pat. No. 5,473,934, “Ultrasonic Fluid Composition Monitor,” issued to Wesley Cobb on Dec. 12, 1995, describes a method of, and apparatus for, continuously monitoring the composition of a fluid mixture traveling through a conduit, where the fluid mixture can be a liquid/liquid or a liquid/solid. Ultrasonic propagation parameters and temperature are measured and compared to calibrated data based on analytical measurements of samples of the process fluid mixtures. Since this monitor is directed only to analyzing a flowing sample with equipment clamped to the outside of a conduit; it is not conducive to field (remote) use.
U.S. Pat. No. 5,060,507, “Method and Apparatus for Fluid Mixture Monitoring, Constituent Analysis, and Composition Control,” issued to John Urmson, et al, on Jun. 21, 1989, describes another method and apparatus for fluid mixture monitoring and controlling using an acoustic sensing technique. A fluid sample and a reference fluid in elongated chambers are pulsed by sound waves; the system senses either the resonant frequencies in the chambers or the time lapse for the sound waves to traverse the chambers and determines composition of the fluid mixture by ratiometrically comparing the time-based measurements. The complexity of the device and the nature of the interaction between the reference fluids indicate that this monitor is also not conducive to field work.
U.S. Pat. No. 4,630,482, “Method and Apparatus for Ultrasonic Measurements of a Medium,” issued to John Traina on Jun. 17, 1985, describes yet another method and apparatus for measuring the time required for an ultrasonic tone burst to traverse a medium from a transmitter to a receiver. Two transducers are required; a demodulator for high turbulence environments is preferred.
There is a need for a simple sensor system designed to speedily and easily identify chosen characteristics in liquids that avoids the problems typical of known monitors, i.e., complex equipment, elaborate electronics, complex sampling techniques, continual maintenance, frequent adjustment, and manual adjustment. There is also a need for a low-maintenance sensor system suitable for remote operation, i.e., that can be used without human operators and/or in situ. There is, still further, an ongoing need for miniaturized, easily handled sensor systems.
SUMMARY OF THE INVENTION
Accordingly, the above-identified needs are met by the present invention, which provides a sensor system that measures transit time through a sample to detect non-uniform or non-conforming constituents in a liquid sample. Differences in transit time through the actual sample, in comparison to a predetermined reference transit time through a “pure” sample, represent small changes in the velocity of sound transmitted.
The sensor system of the invention is capable of remote operation. “Remote,” as used herein, is defined as the capability of autonomous and/or in situ function, i.e., the present invention may be operated away from a testing facility and human operators, and does not need to be “plugged in” or connected to other equipment.
The inventive system comprises at least one ultrasonic transducer coupled to a precision electronic timing circuit to detect transit time and a means for comparing reference transit time data obtained in a calibration step to data obtained during testing, all in a package suitable for autonomous operation. The timing circuit captures changes in transit time over the necessarily small time intervals (nanoseconds) required. The entire system may be miniaturized. For example, it is anticipated that miniature piezoelectric ultrasonic transducers may be used to stimulate responses.
In operation, using a liquid sample as an example, a pulse of ultrasonic energy is applied to the sample in a vessel of known dimensions. The elapsed time between the applied pulse and an echo signal from the opposite end of the vessel (i.e., transit time) is precisely measured. The properties of the pure liquid and the reference transit time have been predetermined in the only calibration step required for this system and have been programmed into the apparatus. Data representing transit time through the actual sample are obtained and compared to the predetermined transit time. Differences (even very small changes) between the actual transit time and the reference transit time indicate changes in the liquid's physical characteristics, more specifically in the purity of the liquid, and those changes are communicated to the user.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 3553636 (1971-01-01), Baird
patent: 3985030 (1976-10-01), Charlton
patent: 4145917 (1979-03-01), Brazhnikov et al.
patent: 4630482 (1986-12-01), Traina
patent: 5060507 (1991-10-01), Urmson et al.
patent: 5255564 (1993-10-01), Glad et al.
patent: 5333162 (1994-07-01), Condreva
patent: 5473934 (1995-12-01), Cobb
Caress Virginia B.
Durkis James C.
Fayyaz Nashmiya
Kehl Dickson G.
The United States of America as represented by the United States
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