Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
1999-04-30
2001-10-16
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
C073S861270, C073S861356
Reexamination Certificate
active
06301973
ABSTRACT:
ORIGIN OF THE INVENTION
The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of 1958, Public Law 85-568 (72 Stat. 435; 42 U.S.C. 2457).
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and methods for non-intrusive measurements of internal pressure and/or other measurements and, more specifically, to hoop-mode and bending-mode resonance vibration of a tubular section for determining internal pressure and/or other measurements such as those produced by Coriolis mass flow meters.
2. Description of Prior Art
Traditional measurements of gas pressure in a plumbing system typically require penetration through a vessel wall to provide a coupling or pressure port from the enclosed gas to the transducer's sensing surface. The pressure port is connected to a fluid-coupled sensor such as a pressure responsive diaphragm. In some systems, it is desirable to provide a non-intrusive pressure sensor whereby it is meant that no sensor surface other than a section of containment conduit such as steel pipe is in contact with the fluid so that it is not necessary to penetrate an existing wall to contact a diaphragm. Moreover, a non-intrusive sensor as disclosed herein preferably permits fluid to flow therethrough in an unrestricted manner through a section of pipe and can be retrofitted to the plumbing of a system by addition of the section of pipe. As far as could be determined, non-intrusive pressure sensors are not available from commercial vendors.
While a non-intrusive pressure measurement system may be useful for various applications, a particular application of interest is that of monitoring the health of propulsion system components such as the Helium Pressurization Components of the Space Shuttle's Orbital Maneuvering System and Reaction Control System. Thus, there is also a desire to measure pressures of specific gases and therefore for determining whether different gases may cause a difference in the response of a vibrational pressure measuring device irrespective of gas pressure.
Coriolis flow measurement devices are commercially available for measuring liquid flow and, more recently, gas flow. The physical operating principle in such meters is based on a Coriolis acceleration. In some cases, these devices are also used to measure gas density and temperature. The presently available Coriolis flow measurement devices fall into two general categories according to the vibrational mode used in the sensing pipes, i.e., hoop-mode and bending-mode implementations. There are many bending-mode implementation variations with respect to the shape of the bend and the location of the sensors some of which variations are discussed in some of the following listed patents. The operation of Coriolis type flow measurement is based on a Coriolis acceleration of the fluid mass within a pipe section and results in a measurable deflection. The deflection is directly proportional to mass flow through the tube. While rotational motion may be used to implement a Coriolis type flow meter, vibration may also be used to produce the same Coriolis force. The bending mode implementation for a Coriolis flow meter utilizes a vibration mode for which a curved segment of pipe is cantilevered about the axis of an adjacent straight section. Sensors on each of the two legs of the vibrated U-hoop or bent pipe sense the difference in phase of the two legs resulting from the twist caused by the constrained fluid segment. This relative phase difference is the physical operating principle of the bending-mode Coriolis mass flow meter. The hoop-mode implementation for a Coriolis flow meter utilizes a vibration mode for which a narrow cross-section of a straight section of pipe is vibrationally squeezed such as by a driving element that may be a piezoelectric element or other driver element. The pinching vibration causes a slight deflection velocity that is detected by another sensor which for certain modes of vibration may be located at the diametrically opposite side from the driver element. Physical parameters sensed in the commercial Coriolis-type meters include the phase shift between axially displaced sensors, the frequency or period of the vibrated pipe segment, and the pipe temperature. Numerous implementations have demonstrated that the mass flow rate for these meters is proportional to the phase shift between appropriately located sensors on the vibrated pipe carrying the process fluid. The frequency of the vibrating pipe segment, usually driven at resonance or slightly off resonance, is typically measured to calculate the density of the gas and to compensate the density dependence of the flow measurement. The temperature of the pipe is typically measured to provide temperature compensation for the elastic coefficient of the tube, but that temperature is also often taken to be a satisfactory approximation for the temperature of the fluid. This latter approximation is typically close for most fluids but becomes increasingly poorer with decreasing fluid density.
N. M. Keita discloses a theoretical and measured pressure effect on meter characteristics of frequency and mass flow sensitivity for constant fluid density in “Behavior of Straight Pipe Coriolis Mass Flowmeters in the Metering of Gas: Theoretical Predictions with Experimental Verification” from
Flow Measurement and Instrumentation,
Vol. 5, No. 4 (1994): pp. 289-294. However, Keita states that the pressure effect (on mass flow sensitivity error) is due to stress stiffening of the mechanical oscillator, is strongly dependent on design, and is not easy to compute. Possibly for this reason Keita's goal is to provide corrections for mass flow rate measurement rather than determine pressure directly.
U.S. Pat. No. 4,600,855, issued Jul. 15, 1986, to J. S. Strachan, discloses an apparatus for measuring pressure within a conduit whose resonant frequency varies with the pressure of the fluid within the tube. As shown, the device requires insertion into the pressure media to be measured, i.e., blood artery pressure, and is therefore an intrusive type of pressure sensor rather than a non-intrusive sensor. The device is not intended to be used with gas or with flowing fluid. The axial length of the sensors limits sensitivity of the device and, due to multiple modes of vibration, would probably not be operable when used when fluid flows therethrough. The disclosed range of measurable pressures is not adequate for certain operations. Excitation means are not disclosed. Other types of measurements are not disclosed. Bending mode and, effectively, hoop-mode operation are not disclosed.
U.S. Pat. No. 5,585,567, issued Dec. 17, 1996, to P. Van Manen discloses an apparatus for exciting at least the fundamental radial circumferential mode of vibration and the first harmonic thereof in a gas bottle. Both frequencies are used for determining the pressure of the bottle. The device is apparently not intended to be particularly accurate as the inventor states that the need is to quickly determine whether a gas bottle is pressurized or not where the bottles are often stacked closely together.
U.S. Pat. No. 3,021,711, issued Feb. 20, 1962, to G. Arvidson, discloses an intrusive-type pressure sensor, with the pressure coupled to a sensing device within a housing rather than a pipe section through which fluid can freely flow. The invention is characterized by the provision of a hollow body capable of being set in vibration by feeding energy thereto. The respective pressure or difference pressure is supplied to the device through one or two openings within a housing to allow a pressure or difference pressure between two fluids to be measured.
U.S. Pat. No. 3,257,850, issued Jun. 28, 1966, to R. R. Kooiman, discloses an intrusive type of sensor which in the tubular form thereof uses a flexible diaphragm for detecting pressure vibration.
U.S. Pat. No. 4,098,133, issued Jul. 4, 1978, to Frische et al., discl
Barr Hardie R.
Patel Harshad
The United States of America as represented by the Administrator
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