1976-02-01

A New Approach to Flowmetering-Simple Mechanical Device Allows Use of Reasonably Specified Pressure Transducer for Flow and for Total Volume Metering 760019

ABSTRACT

The measurement of average velocity or kinetic energy of moving fluid is most often for the purpose of determining the volumetric rate of fluid flow or the mass rate of fluid flow. The determination of fluid flow rate is most often for the purpose of measurement or control of total accumulated fluid volume or fluid mass. Such measurement is called flowmetering. There are many widely differing types of flowmeters available. They can be classified broadly into two groups; one which presents little or no interference or impedance to the flow stream, and one wherein the mechanism of metering significantly influences the flow stream. The low or zero impedance type are exotic and generally require a great deal of specialized knowledge of specific properties of the fluid flowing. For example, the hot wire anemometer type of flowmeter requires precise knowledge of fluid thermal properties as a function of velocity. For another example, the nuclear magnetic resonance type of obstructionless flowmeter requires precise knowledge of the number of hydrogen atoms present per unit volume or mass of fluid.

Most commonly used flowmeters partially obstruct or add impedance to the fluid stream. These also fall into two categories; one utilizing mechanisms dependent upon displacement or position change, and the other dependent upon pressure change. The first type, using such compliant mechanisms as turbine wheels, sliding capacitor plates, sliding potentiometer contacts, oscillating vanes, suffer the usual array of problems associated with precision machines with moving parts. They are delicate, expensive, and require watchmaker caliber labor to build and repair if accuracy is to be achieved. The type of flowmeter dependent upon pressure change, properly conceived, has no moving parts. In this paper, the traditional pressure transducer flowmeters are described. The pressure/flow square law problem and its relation to accuracy is described. A novel solution to the square law accuracy problem is offered. Pressure transducer accuracy is examined. A technique of improving pressure transducer accuracy in flowmetering is offered. In composite, a new flowmeter design is recommended.

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