Stability coriolis mass flow meter

Details Stability coriolis mass flow meter Stability coriolis mass flow meter

1992-01-16

1994-04-12

Goldstein, Herbert

Measuring and testing

Volume or rate of flow

Mass flow by imparting angular or transverse momentum to the...

G01F 184

Patent

active

053015576

DESCRIPTION:

BRIEF SUMMARY
In the art of measuring mass flow rates of flowing substances it is known that flowing a fluid through an oscillating flow conduit induces Coriolis forces which tend to twist the conduit in a direction essentially transverse to the direction of fluid flow and also to the axis about which oscillation occurs. It is also known that the magnitude of such Coriolis forces is related to both the mass flow rate of the fluid passing through the conduit and the angular velocity at which the conduit is oscillated.
One of the major technical problems historically associated with efforts to design and make Coriolis mass flow rate instruments was the necessity either to measure accurately or control precisely the angular velocity of an oscillated flow conduit so that the mass flow rate of the fluid flowing through the flow conduits could be calculated using measurements of effects caused by Coriolis forces. Even if the angular velocity of a flow conduit could be accurately determined or controlled, precise measurement of the magnitude of effects caused by Coriolis forces raised another severe technical problem. This problem arose in part because the magnitude of generated Coriolis forces is very small in comparison to other forces such as inertia and damping, therefore resulting Coriolis force-induced effects are minute. Further, because of the small magnitude of the Coriolis forces, effects resulting from external sources such as vibrations induced, for example, by neighboring machinery or pressure surges in fluid lines, may cause erroneous determinations of mass flow rates. Such error sources as discontinuities in the flow tubes, unstable mounting of the tubes, use of tubes lacking mechanically reproducible bending behavior, etc., often completely masked the effects caused by generated Coriolis forces, greatly diminishing the practical use of a mass flow meter.
A mechanical structure and measurement technique which, among other advantages: (a) avoided the need to measure or control the magnitude of the angular velocity of a Coriolis mass flow rate instrument's oscillating flow conduit; (b) concurrently provided requisite sensitivity and accuracy for the measurement of effects caused by Coriolis forces; and (c) minimized susceptibility to many of the errors experienced in earlier experimental mass flow meters, is taught in U.S. Pat. Nos. Re 31,450, entitled "Method and Structure for Flow Measurement" and issued Nov. 29, 1983; 4,422,338 entitled "Method and Apparatus for Mass Flow Measurement" and issued Dec. 27, 1983; and 4,491,025 entitled "Parallel Path Coriolis Mass Flow Rate Meter" and issued Jan. 1, 1985. The mechanical arrangements disclosed in these patents incorporate curved continuous flow conduits that are free of pressure sensitive joints or sections, such as bellows, rubber connectors or other pressure deformable portions. These flow conduits are solidly mounted at their inlet and outlet ends, with their curved portions cantilevered from the support. For example, in flow meters made according-to any of the aforementioned patents, the flow conduits are welded or brazed to the support, so that they are oscillated in spring-like fashion about axes which are located essentially contiguous with the solid mounting points of the-flow conduits or, as disclosed in U.S. Pat. No. 4,491,025, essentially at the locations of solidly attached brace bar devices designed to clamp two or more conduits rigidly at points located forward of the mounting points.
By so fashioning the flow conduits, a mechanical situation arises whereby, under flow conditions, the forces opposing generated Coriolis forces in the oscillating flow conduits are essentially linear spring forces. The Coriolis forces, opposed by essentially linear spring forces, deflect or twist the oscillating flow conduits containing flowing fluid about axes located between and essentially equidistant from the portions of those flow conduits in which the Coriolis forces manifest themselves. T-he magnitude of the deflections is a function of the magnitude of the genera

REFERENCES:
patent: 4823613 (1989-04-01), Cage et al.

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