Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
1999-03-19
2001-10-30
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
active
06308580
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to Coriolis flowmeters. More particularly, this invention relates to reducing a flag dimension of a Coriolis flowmeter by vibrating the entire length of the flow tubes. Still more particularly, this invention relates to the use of two sets of brace bars where a first pair of brace bars adequately separates the frequencies of vibration and a second set of brace bars enhances zero stability in the system.
PROBLEM
It is known to use Coriolis effect mass flowmeters to measure mass flow and other information of materials flowing through a pipeline as disclosed in U.S. Pat. No. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and Pat. No. Re. 31,450 to J. E. Smith of Feb. 11, 1982. These flowmeters have one or more flow tubes of a curved configuration. Each flow tube configuration in a Coriolis mass flowmeter has a set of natural vibration modes, which may be of a simple bending torsional, or coupled type. Each flow tube is driven to oscillate at resonance in one of these natural modes. The natural vibration modes of the vibrating, material filled system are defined in part by the combined mass of the flow tubes and the material within the flow tubes. Material flows into the flowmeter from a connected pipeline on the inlet side of the flowmeter. The material is then directed through the flow tube or flow tubes and exits the flowmeter to a pipeline connected on the outlet side.
A driver applies a force to the flow tube in order to cause the flow tube to oscillate in a desired mode of vibration. Typically, the desired mode of vibration is a first out of phase bending mode. When no material is flowing through the flowmeter, all points along a flow tube oscillate with an identical phase. As the material begins to flow, Coriolis accelerations cause each point along the flow tube to have a different phase with respect to other points along the flow tube. The phase on the inlet side of the flow tube lags the driver, while the phase on the outlet side leads the driver. Sensors are placed on the flow tube to produce sinusoidal signals representative of the motion of the flow tube. The phase difference between the two sensor signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes. Electronic components connected to the sensor then use the phase difference and frequencies of the signals to a determine mass flow rate and other properties of the material.
An advantage that Coriolis flowmeters have over other mass flow measurement devices is that flowmeters typically have less than 0.1% error in the calculated mass flow rates of a material. Other conventional types of mass flow measurement devices such as orifice, turbine, and vortex flowmeters, typically have 0.5% or greater errors in flow rate measurements. Although Coriolis mass flowmeters have greater accuracy than the other types of mass flow rate devices, the Coriolis flowmeters are also more expensive to produce. Users of flowmeters often choose the less expensive types of flowmeters preferring to save cost over accuracy. Therefore, makers of Coriolis flowmeters desire a Coriolis flowmeter that is less expensive to manufacture and determines mass flow rate with an accuracy that is within 0.5% of the actual mass flow rate in order to produce a product that is competitive with other mass flow rate measurement devices.
One reason that Coriolis meters are more expensive than other devices is the need for components that reduce the number of unwanted vibrations applied to the flow tubes. One such component is a manifold which affixes the flow tubes to a pipeline. In a dual tube Coriolis flowmeter, the manifold also splits the flow of material received from a pipeline into two separate flows and directs the flows into separate flow tubes. In order to reduce the vibrations caused by outside sources, such as a pump, that are connected to the pipeline, a manifold must have a stiffness that is sufficient enough to absorb the vibrations. Most conventional manifolds are made of cast metal in order to have a sufficient mass. Furthermore, there is a spacer between the manifolds that maintains the spacing between inlet and outlet manifolds. This spacer is also made out of a metal or other stiff material in order prevent outside forces from vibrating the flow tubes. The large amount of metal used to create these castings increases the cost of the flowmeter. However, the elimination of unwanted vibrations greatly increases the accuracy of the flowmeters.
A second problem for those skilled in the Coriolis flowmeter art is that flowmeters may have a flag dimension that is too big to be used in certain applications. For purposes of this discussion, flag dimension is the length that a flow tube loop extends outward from a pipeline. There are environments where space is constrained or is at a premium. A flowmeter having a typical flag dimension will not fit in these confined areas. There is a need for a Coriolis flowmeter that has a reduced flag dimension that can be inserted into a pipeline in a confined area or where space is at a premium and still provides readings that are within the 0.5% of the actual flow rate of a material.
SOLUTION
The above and other problems are solved and an advance in the art is made by the provision of a Coriolis flowmeter having a reduced flag dimension in the present invention. The Coriolis flowmeter of the present invention does not have a conventional manifold and spacer. Therefore, the cost to produce the flowmeter of the present invention is reduced. The Coriolis flowmeter of the present invention also has a reduced flag dimension which allows the Coriolis flow meter of the present invention to be used in areas where space is at a premium and it would be impossible to use a conventional Coriolis flowmeter having a conventional flag dimension.
In order to eliminate a conventional manifold and to reduce the flag dimension of a Coriolis flowmeter, the entire length of each flow tube must vibrate to increase the sensitivity of the flowmeter. Therefore, the flowmeter must be designed in the following manner. The flowmeter has a pair of flow tubes that aligned parallel to one another.
Each flow tube is a continuous length of flow tube divided in several segments. At an inlet end and an outlet end of each flow tube, the flow tubes have in-line segments which have a longitudinal axis that is oriented in a first plane that contains the connected pipeline. A first end of the in-line segments connects the flow tubes to inlet and outlet manifolds. Bending segments in each flow tube extend outward from a second end of the in-line segments of the flow tube. Each bending segment is a curved section of tube that changes orientation of the longitudinal axis of the flow tube from the first plane to a direction that is substantially perpendicular to the first plane containing the pipeline.
A u-shaped segment extends between the two bending segments of each flow tube. The u-shaped segment has a first section that extends outward from a first bending segment with a longitudinal axis oriented in a direction that is substantially perpendicular to the first plane containing pipeline. A second, curved section of the u-shaped segment bends the flow tube to connect the first section and a third section of the u-shaped segment. A third section of the u-shaped segment has a longitudinal axis that is substantially perpendicular to the first plane and connects the curved section of the u-shaped segment to a second bending segment to complete the flow tube. In a preferred embodiment, the first section and third section of the u-shaped segment extend outward from the bending segments with a longitudinal axis that is substantially three degrees from being perpendicular with the first plane which allows the flowmeter to be self-draining when the pipeline and first plane are oriented substantially perpendicular to the ground.
Since the entire length of each flow tube must vibrate in order to reduce the flag dimension of the flowmeter, a first set and a second
Crisfield Matthew T.
Johnston Steven James
McCarthy John Richard
Chrisman Bynum & Johnson, P.C.
Micro Motion Inc.
Patel Harshad
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