Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Content or effect of a constituent of a liquid mixture
Reexamination Certificate
2001-11-08
2004-05-11
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Content or effect of a constituent of a liquid mixture
C073S061490, C073S579000, C073S643000
Reexamination Certificate
active
06732575
ABSTRACT:
TECHNICAL FIELD
This invention relates to fluid parameter measurement in pipes and more particularly to measuring speed of sound and parameters related thereto of fluids in pipes using acoustic pressures for use in industrial sensing applications.
BACKGROUND ART
An industrial process sensor is typically a transducer that responds to a measurand with a sensing element and converts the variable to a standardized transmission signal, e.g., an electrical or optical signal, that is a function of the measurand. Industrial process sensors utilize transducers that include flow measurements of an industrial process such as that derived from slurries, liquids, vapors and gasses in refinery, chemical, paper, pulp, petroleum, gas, pharmaceutical, food, mining, minerals and other fluid processing plants. Industrial process sensors are often placed in or near the process fluids, or in field applications. Often, these field applications are subject to harsh and varying environmental conditions that provide challenges for designers of such sensors. Flow measurement is one of the largest segments of the industrial sensing and instrumentation market. Industries in which flow measurement is prevalent includes petroleum, chemical, pulp, paper, food, and mining and minerals.
Typical electronic, or other, transducers of the prior art often cannot be placed in industrial process environments due to sensitivity to electromagnetic interference, radiation, heat, corrosion, fire, explosion, or other environmental factors. It is for these reasons that fiber optic based sensors are being incorporated into industrial process control environments in increasing number.
Further, it is known that the speed of sound a
mix
of fluids in pipes may be used to determine various parameters of the fluid, such as is described in U.S. Pat. No. 4,080,837, entitled “Sonic Measurement of Flow Rate and Water Content of Oil-Water Streams”, to Alexander et al., U.S. Pat. No. 5,115,670, entitled “Measurement of Fluid Properties of Two-Phase Fluids Using an Ultrasonic Meter”, to Shen, and U.S. Pat. No. 4,114,439, entitled “Apparatus for Ultrasonically Measuring Physical Parameters of Flowing Media”, to Fick. Such techniques have a pair of acoustic transmitters/receivers (transceivers) that generate a sound signal and measure the time it takes for the sound signal to travel between the transceivers. This is also known as a “sing-around” or “transit time” method. However, such techniques require precise control of the acoustic source and are costly and/or complex to implement in electronics.
Also, these techniques use ultrasonic acoustic signals as the sound signal measured, which are high frequency, short wavelength signals (i.e., wavelengths that are short compared to the diameter of the pipe). Typical ultrasonic devices operate near 200 k Hz, which corresponds to a wavelength of about 0.3 inches in water. In general, to allow for signal propagation through the fluid in an unimpeded and thus interpretable manner, the fluid should be homogeneous down to length scales of several times smaller than the acoustic signal wavelength. Thus, the criteria for homogeneity of the fluid becomes increasingly stricter with shorter wavelength signals. Consequently, inhomogeneities in the fluid, such as bubbles, gas, dirt, sand, slugs, stratification, globules of liquid, and the like, will reflect or scatter the transmitted ultrasonic signal. Such reflection and scattering inhibit the ability of the instrument to determine the propagation velocity. For this reason, the application of ultrasonic flowmeters have been limited primarily to well-mixed flows.
SUMMARY OF THE INVENTION
Objects of the present invention include provision of a system for measuring the speed of sound of fluids in pipes in industrial fluid processes.
According to the present invention, an apparatus for industrial sensing applications for measuring at least one parameter of a mixture of at least one fluid in a pipe, comprising a spatial array of at least two pressure sensors, disposed at different axial locations along the pipe, and each measuring an acoustic pressure within the pipe at a corresponding axial location, each of said sensors providing an acoustic pressure signal indicative of the acoustic pressure within the pipe at said axial location of a corresponding one of said sensors; and a signal processor, responsive to said pressure signals, which provides a signal indicative of a speed of sound of the mixture in the pipe.
According further to the present invention, the signal processor comprises logic that calculates a speed at which sound propagates along the spatial array.
According further to the present invention, the signal processor comprises logic that calculates a frequency domain representation of (or frequency based signal for) each of the acoustic pressures signals. According still further to the present invention, the signal processor comprises logic that calculates a ratio of two of the frequency signals. In still further accord to the present invention, the sensors comprise at least three sensors.
According still further to the present invention, the pressure sensors are fiber optic Bragg grating-based pressure sensors. Still further accord to the present invention, at least one of the pressure sensors measures a circumferential-averaged pressure at a given axial location of the sensor. Further according to the present invention, at least one of the pressure sensors measures pressure at more than one point around a circumference of the pipe at a given axial location of the sensor.
The present invention provides a significant improvement over the prior art by providing a measurement of the speed of sound a
mix
of a mixture of one or more fluids within a pipe (where a fluid is defined as a liquid or a gas) by using an axial array of acoustic (or ac, dynamic, unsteady, or time varying) pressure measurements along the pipe. An explicit acoustic noise source is not required, as the background acoustic noises within the pipe (or fluid therein) will likely provide sufficient excitation to enable characterization of the speed of sound of the mixture by merely passive acoustic listening.
The invention works with acoustic signals having lower frequencies (and thus longer wavelengths) than those used for ultrasonic meters, such as below about 20 k Hz (depending on pipe diameter). As such, the invention is more tolerant to the introduction of gas, sand, slugs, or other inhomogeneities in the flow.
The invention will work with arbitrary sensor spacing and arbitrary flow Mach numbers Mx; however, if the sensors are equally spaced and the axial velocity of the flow is small and therefore negligible compared to the speed of sound in the mixture (i.e., Mach number of the mixture Mx is small compared to one), the speed of sound a
mix
may be determined as an explicit function of the frequency domain representation (frequency based signal) for the acoustic pressure signals at a given evaluation frequency &ohgr;.
Since the speed of sound is an intrinsic property of mixtures, the present invention can be used to measure any parameter (or characteristic) of any mixture of one or more fluids in a pipe in which such parameter is related to the speed of sound of the mixture a
mix
, e.g., fluid fraction, temperature, salinity, sand particles, slugs, pipe properties, etc. or any other parameter of the mixture that is related to the speed of sound of the mixture. For example, the present invention may be used to measure fluid volume fractions (or composition or cut or content) of a mixture of any number of fluids in which the speed of sound of the mixture a
mix
is related to (or is substantially determined by), the volume fractions of two constituents of the mixture, e.g., oil/water, oil/gas, water/gas. Also, the present invention can be used to measure the speed of sound of any mixture and can then be used in combination with other known quantities to derive phase content of mixtures with multiple (more than two) constituents.
The present invention allows the speed of sound t
Gysling Daniel L.
Kersey Alan D.
Paduano James D.
CiDRA Corporation
Larkin Daniel S.
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