Measuring and testing – Volume or rate of flow – By measuring thrust or drag forces
Reexamination Certificate
1999-12-29
2002-04-09
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring thrust or drag forces
C073S861750, C073S001160
Reexamination Certificate
active
06367336
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a flow meter and more particularly to a process gravity free fall flow meter for measuring the flow rate and accumulated weight of solid powdered, particulate or granulated materials or other solids of like nature such as seeds, grains and pellets passing through a measuring chamber.
The current state of the art in the area of the continuous measurement of flow rates and accumulated weights of solid particulate materials is limited primarily to four systems: Coriolis force flow meters, impact flow meters, flow meters based on electronic load cells, and turbine flow meters.
Of the four major classes of flow meters suitable for solid particulate materials, each can be found to have its limitations, the major examples of which can be related to the physical phenomena and forces involved in the principles of their functioning and in the complexity of mechanisms necessary for adequately controlling and compensating for the related problems and deficiencies.
As is well known to those practiced in the art, a Coriolis flow meter is a mass flow meter that measures the mass flow rate of material flowing in a flow tube supported at both ends by oscillating the flow tube and detecting a Coriolis force acting on the flow tube, said measured force being theoretically proportional to the mass flow rate of the material. The Coriolis force is detected as a difference of phases produced at symmetrical positions between the supporting points and the center portion of,the flow tube when the flow tube is driven alternately at its center portion in a direction perpendicular to the supporting axis.
In operation, the flow tube is electromechanically vibrated out-of-phase with respect to a balance tube which is provided to reduce the vibrations that would be associated with a single unbalanced flow tube. These vibrations impart a Coriolis acceleration to material flowing through the flow tube. The reaction force to this Coriolis acceleration results in a slight distortion of the vibration mode shape of the flow tube. This distortion is measured by sensors connected to, or associated with, the flow tube. The sensors may be either of the velocity or displacement type. The material flow rate is proportional to the time or phase delay between the signals generated by two such sensors positioned along the length of the straight flow tube. A single sensor may also be used. Output signals of the sensors are applied to electronic apparatus which derives the desired information, such as mass flow rate, for the material in the flow tube.
Among the problems encountered in the application of the Coriolis force for the accurate measurement of the flow rate of a material are those related to correcting errors caused by a differences in or changes in the density of the flowing material, differences in the temperature deformation of the materials comprising the flow tube, and differences in temperature in the flow tube and the resonant member. Other difficulties related to the practical functioning of Coriolis force flow meters will be apparent to those practiced in the art. The measures required to circumvent and overcome the various limitations of the Coriolis force-based systems tend to greatly increase the complexity, and therefore the cost, of such systems.
The impact flow meter is widely employed in industry due to its potential robustness and ease of insertion into flow systems. The systems are based on the measurement of one component (usually horizontal) of the force of impact imparted by the flowing material as it falls on an impact plate positioned in the general line of flow of the material of interest. The impact of the flowing material on the impact plate produces a minimal movement or distortion in the position of the plate. A sensor, force transducer or other mechanism transfers the limited movement or distortion of the impact plate to the appropriate sensing device and related electronic circuitry which then converts that signal to an instantaneous mass flow rate based on suitable calibration data.
While the theory of the impact mechanism is clear, in practice, there are several problems that can significantly affect the accuracy of the force measurement and, therefore, the calculated flow rate. Simple physics shows that the force imparted to the impact plate by falling material will be a direct function of the relative angle of impact on the plate. Any change in that impact angle produced by an improper installation of the device in the flow path or subsequent movement after installation will introduce significant errors in the calculation of the final flow rate. In addition, because the movement of the impact plate is very limited, the mechanism employed to sense and transmit the resultant impact force to the corresponding electronic circuits must by necessity be very sensitive. That sensitivity necessitates the use of measures to protect the sensing mechanism and/or correct for changes in the response of said device, all of which imply the need for more complexity and cost in the construction and operation of such devices.
In a typical configuration for such units, bulk material is allowed to fall from a defined height upon a deflector plate which has been arranged at an angle to the vertical, with the flexural moment generated in the process being determined within the flexible joint of the deflector plate. The deflector plate arrangements have certain defects which result in relatively severe inaccuracies in measurement in the case of one and the same bulk material and which make problematical use of the same unit for a variety of materials, such as in dosing processes. Because in most such units moments are measured, it is not only the impact force which is generated via changes in pulsing which is decisive, but also the specific location where the bulk material impacts the deflector plate. In this instance, considerable variations are possible, depending upon the nature of the material involved. Furthermore, the type of momentum transmission involved is essential—the degree of force transmitted is greater in the case of elastic impact than with inelastic impact. The specific impact rate, which must be taken into consideration, also varies with the type of bulk material involved and the condition of the bulk material at a given moment. The units described generally provide satisfactory results with respect to the bulk material to be weighed only through extensive calibration and generally require frequent control of such calibration.
Devices based on electronic load cells are also common in industry due to their theoretical precision and adaptability to transport belts and related systems as well as direct static weighing. Electronic load cells devices, however, are found to be extremely sensitive to physical abuse, requiring frequent calibration and control to maintain accuracy and precision. In addition, they are relatively delicate and easily broken by misuse. Their accuracy is also dependent on their proper installation so that any dislocation or movement in their location can produce significant errors in the final result.
Turbine flow meter devices have found great application in the measurement of fluid flows, especially in pressurized gas flow measurements and in simple pumped liquids such as is found in gasoline pumps. In such applications, however, the fluid flow is generally relatively constant and there exists a natural resistance in the flow field that prevents any “free wheeling” of the measuring turbine when the force of the flowing material changes. In free flowing systems such as those contemplated by the present invention, turbine flow meters are rare and those in existence must incorporate some braking mechanism to prevent “free wheeling” of the turbine, since free fall systems will not have the natural braking mechanism present in a pumped fluid system. Such braking mechanisms routinely involve some mechanical and/or electromagnetic phenomenon that requires continual or periodic monitoring of the applied braking f
Martina Guillermo Alfredo
Martina Hugo Gabriel
Myers, Jr. Drewfus Young
Bachman & LaPointe P.C.
Patel Harshad
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