Measuring and testing – Volume or rate of flow – Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
2000-04-04
2001-09-25
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Mass flow by imparting angular or transverse momentum to the...
Reexamination Certificate
active
06293158
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus for using a Coriolis mass flowmeter with a serial, dual loop, flow tube for measuring the flow rate of a fluid through a pipeline. More particularly, the invention relates to the element used to connect the loops of the flow tube. Still more particularly, the invention relates to an anchor which connects a flow tube to a flow tube housing.
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. Nos. 4,491,025 issued to J. E. Smith, et al. of Jan. 1, 1985 and 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 force to oscillate the flow tube. When there is no flow 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. Pickoff 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 pickoff sensor signals is proportional to the mass flow rate of the material flowing through the flow tube or flow tubes.
Material flow though a flow tube creates only a slight phase difference on the order of several degrees between the inlet and outlet ends of an oscillating flow tube. When expressed in terms of a time difference measurement, the phase difference induced by material flow is on the order of tens of microseconds down to nanoseconds. Typically, a commercial flow rate measurement should have an error of less the 1%. Therefore, a Coriolis flowmeter must be uniquely designed to accurately measure these slight phase differences.
It is known to use a single loop, serial path flow tube to measure the rate of fluid flowing through a pipeline. However, the single loop, serial flow tube design has a disadvantage in that it is inherently unbalanced. A single loop, serial flow Coriolis flowmeter has a single curved tube or loop extending in cantilever fashion from a solid mount. Dual loop Coriolis flowmeters are balanced. A dual loop Coriolis flowmeter has two parallel, curved tubes or loops extending from a solid mount. The parallel flow tubes are driven to oscillate in opposition to one another with the vibrating force of one flow tube canceling out the vibration force of the other flow tube. The result is that in a properly constructed dual loop Coriolis flowmeter there are no flowmeter induced vibrations at the points of attachment between the flowmeter and the pipeline. This is called a “balanced” flowmeter. The absence of vibrations allows dual looped Coriolis flowmeter to be attached free standing to a pipeline. A single loop, serial path Coriolis flowmeter must be secured firmly to a support against which the flow tube can vibrate. The use of a support renders the use of a single loop, serial flow tube design impractical in most industrial applications because the serial flow tube requires that the pipeline be near an object that could be used as a support. Therefore, the dual loop flowmeter designs are desirable.
It is a particular problem to measure minimal flow rates of materials flowing through a pipeline. A mass flow rate through a pipeline of less than or substantially equal to 4 lbs. per minute is considered minimal for commercial applications. A Coriolis mass flowmeter measuring such small flow rates must be formed of relatively small components including tubes and manifolds. These relatively small components present a variety of challenges in the manufacturing process including but not limited to difficult welding processes.
One solution for measuring minimal flow rates has been to use a single loop, serial flow tube Coriolis effect mass flowmeter. Single loop, serial flow tube Coriolis flowmeters have certain advantages. The flow tube has a larger diameter which reduces pressure drop across the flowmeter. No manifold is necessary to split the flow into two tubes. The larger flow tube is easier to draw and weld. There are also other advantages. The problem is that single loop, serial flow tube flowmeters cannot be mounted free standing into the pipeline since they are not balanced flowmeters.
Dual loop, parallel flow tube flowmeters can be mounted freestanding into the pipeline. However, the small size necessary for measuring minimal flow rates creates design and manufacture problems for use of the dual loop, parallel flow tube design. These problems limit the industrial applications of dual loop, dual tube Coriolis flowmeters for measuring minimal flow rates.
A particular problem with dual loop, parallel flow tube design is that a manifold must be used to direct the flow entering the inlet end of the flowmeter in order to divide the flow so that it enters the two flow tubes. It is difficult to produce a manifold, by casting or otherwise, in the small dimensions necessary to measure a minimal flow rate. Also, the manifold increases pressure drop across the flowmeter. Further, the flow tubes must be welded or brazed onto the manifold it is difficult too weld very thin walled tubing. The welds and joints do not provide the smooth surface needed for sanitary applications of the flowmeter. Sanitary applications demand a continuous, smooth flow tube surface that does not promote adhesion of material to the walls of the flow tube. Further, the additional welds there are necessary reduce the manufacturing yield. Therefore, the use of a manifold is not desired in flowmeters designed for measuring minimal flow rates.
The smaller diameters of the dual flow tubes make the tubes more prone to plugging. The smaller diameter is needed to assure a sufficient flow rate through the i flow tubes. Material is more likely to plug the flow path through these flow tubes because smaller particles in the material can obstruct the smaller flow path. These obstructions can cause inaccurate readings of the flow rate and breakage of the flow tube. Therefore, the dual flow tube design does not offer a satisfactory solution for measuring minimal flow rates.
A further problem is that sometimes a Coriolis flowmeter is used to measure flow through a pipeline where the flowing material is pressurized. If a flow tube cracks, the pressured material will rapidly spray from the highly pressurized flow tube to the outside surroundings which have a lower pressure than the flow tube. The pressurized material spraying from the flow tube can damage the pipeline or surrounding structures.
Solution
The above and other problems are solved by the apparatus of the present invention that comprises a dual loop, serial path flow tube. Each of the loops is oriented in a plane parallel to the plane containing the other loop. The flow tube is enclosed in a housing to which the flow tube is connected through an anchor. The housing can be configured to contain the leakage of pressurized materials from a break in the flow tube. These advantages allow the present invention to be used to measure the flow rates, including minimal flow rates, of material flowing through the pipeline.
In the present invention, the dual loops in the serial flow tube are connected
Lister Ernest Dale
Normen David Frederick
Ollila Curtis John
Chrisman Bynum & Johnson, P.C.
Fuller Benjamin R.
Micro Motion Inc.
Thompson Jewel V.
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