Measuring and testing – Volume or rate of flow – By measuring thrust or drag forces
Reexamination Certificate
2000-10-13
2001-07-03
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring thrust or drag forces
C073S861740
Reexamination Certificate
active
06253625
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to devices in fluid paths that indicate flow rate, and more particularly to target type flow meters having a target in the flow path attached to a stalk having attached strain gauges immersed in the fluid for enhanced sensitivity.
DESCRIPTION OF THE PRIOR ART
Target flow meters have distinct advantages over other types of flow meters. They operate on the principle that the amount of force generated by onrushing fluid passing a disc target whose surface is oriented perpendicular to the direction of flow is proportional to the square of the flow velocity. The drag beyond the target produces a lower pressure area than ahead of the target, producing a net force that bends the stalk. This makes for easy calibration. The target typically is mounted by a rigid stalk to a bendable balance beam to permit its deflection by the force. Strain gauges affixed to the balance beam outside the fluid measure the bending of the balance beam. They have no moving parts, only a bending part for minimal maintenance. Because of the considerable loss of energy in bending the balance beam, these flow meters are not sensitive. These flow meters have the advantage that the electrical elements and wires are all outside the fluid, eliminating sealing and leakage problems.
Nusbaum, in U.S. Pat. No. 3,098,384 teaches a twisted blade immersed in a sewage flow. The blade is periodically retracted and wiped of contaminants. A pair of waterproof strain gauges are bonded to the blade to measure how much the blade is twisted in response to the flow rate. A complex relationship between degree of twist and flow rate must be established for each installation.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a target flow meter that is more sensitive. It is another object that the flow meter be simpler and more compact in structure. The target flow meters of the invention have a target positioned in the flow path by an attached flexing stalk. The stalk has a substantially oblong cross section with the longer sides disposed transverse to the flow path. Strain gauges are applied directly to the stalk on the longer sides within the fluid chamber to sense the bending of the stalk in response to the force. The stalk may be specially constructed to concentrate the bending at the strain gauges. Wires connected to the strain gauges pass through a pressure seal to the outside. The wires and gauges may be coated to isolate them from the fluid. Direct simple mathematical relationship is maintained between the flow rate and strain gauge output in the turbulent flow range. Because the strain gauges are immersed in the same fluid as the target, there is less error associated with temperature differences between the fluid and ambient than in flow meters whose gauges are outside the fluid. A temperature sensing element may be included with the strain gauges for enhanced measurement accuracy. These and other objects, features, and advantages of the invention will become more apparent when the detailed description is studied in conjunction with the drawings in which like elements are designated by like reference characters in the various drawing figures.
REFERENCES:
patent: 2826914 (1958-03-01), Reiley
patent: 3098384 (1963-07-01), Nusbaum
patent: 3340733 (1967-09-01), Lasher
patent: 3599139 (1971-08-01), Low
patent: 4604906 (1986-08-01), Scarpa
patent: 4788869 (1988-12-01), Li
patent: 4892114 (1990-01-01), Maroney
patent: 5425278 (1995-06-01), Perkins
patent: 6003387 (1999-12-01), Larson et al.
Blum Alvin S.
Kaylor Stephen
Samuelson Duane
Yowell Gordon
Blum Alvin S.
Patel Harshad
Predator Systems Inc.
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