Mode selection apparatus for multiple tube coriolis type mass flow meters
First Claim
1. A dual tube Coriolis mass flow sensor structure comprising:
- a pair of tubular members which are spaced apart and extend generally in parallel, and which have corresponding longitudinal extremities joined together to provide parallel flow paths for flowing material;
drive means for applying oscillatory drive forces to both of said tubular members to cause portions between the extremities of said tubular members to oscillate relative to each other in a first mode of oscillation due to said drive forces, and to oscillate relative to each other in a second mode of oscillation due to Coriolis forces induced by the mass of material flowing through said tubular members;
motion detecting means disposed to detect Coriolis force induced motion of said tubular members as said material flows therethrough; and
mode selection means including at least one elongated memberhaving distal ends rigidly affixed to respective ends of said tubular members so that said elongated member extends generally transverse to the longitudinal axes of said tubular members, andhaving low stiffness about at least one axis passing through the intersection of said elongated member and the longitudinal axis of one of said tubular members, such that, for at least one of said modes of oscillation, said mode selection means does not provide a node said stiffness being selected to modify the vibrational stiffness of and shift the natural frequency of said sensor structure in one of said modes of oscillation relative to the natural frequency of said structure in the other of said modes of oscillation.
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Abstract
An improvement to a mass flow rate sensor which includes the provision of at least one mode selection plate at each of the inlet and outlet ends of the sensor. The plates are provided in addition to other tube end termination means and are configured to have predetermined stiffness characteristics (area moments of inertia) in the X, Y and Z axes. In one preferred embodiment, the mode selection plates are configured in a generally squashed H-shaped configuration in which the tube ends pass through the centers of the vertical legs of the H and the cross member of the H spans the space between the two tubes. In other embodiments, the plates are variously configured to alter the stiffness characteristics along the various axes of the mode selection plate.
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Citations
9 Claims
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1. A dual tube Coriolis mass flow sensor structure comprising:
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a pair of tubular members which are spaced apart and extend generally in parallel, and which have corresponding longitudinal extremities joined together to provide parallel flow paths for flowing material; drive means for applying oscillatory drive forces to both of said tubular members to cause portions between the extremities of said tubular members to oscillate relative to each other in a first mode of oscillation due to said drive forces, and to oscillate relative to each other in a second mode of oscillation due to Coriolis forces induced by the mass of material flowing through said tubular members; motion detecting means disposed to detect Coriolis force induced motion of said tubular members as said material flows therethrough; and mode selection means including at least one elongated member having distal ends rigidly affixed to respective ends of said tubular members so that said elongated member extends generally transverse to the longitudinal axes of said tubular members, and having low stiffness about at least one axis passing through the intersection of said elongated member and the longitudinal axis of one of said tubular members, such that, for at least one of said modes of oscillation, said mode selection means does not provide a node said stiffness being selected to modify the vibrational stiffness of and shift the natural frequency of said sensor structure in one of said modes of oscillation relative to the natural frequency of said structure in the other of said modes of oscillation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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Specification