Flow measurement system
First Claim
1. A system for measuring the flow rate of a liquid comprising:
- a primary element comprising a constriction in a closed conduit, said constriction having a modular limit and being configured so asto cause at least one of the following to fill prior to said modular limit being reached;
said closed conduit, andsaid constriction,said constriction producing pressures in said liquid,a source of compressed gas,means for releasing a plurality of bubbles of said gas exposed to said pressures,a plurality of bubbler circuits connected to said means for releasing a plurality of bubbles,means for controlling bubble release rate,at least one means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and a reference side, and said means for sensing producing a plurality of signals when excited, said plurality of signals being characterized by an offset or zero and a gain,means for simultaneously applying a single pressure to the pressure side and the reference side of said means for sensing differential pressure to produce a zero pressure signal,means for resetting the zero of said means for sensing differential pressure by reference to at least said zero pressure signal,means for generating a known pressure differential,wherein said means for generating a known pressure differential is selected from the group consisting of;
means for generating a known head and a known head loss,means for sensing pressures at a plurality of known elevations or depths in a liquid,means for sensing pressures at known elevations or depths in liquids of known density,means for generating a known gauge pressure that is referenced to atmospheric pressure, andmeans for generating a gas pressure that is regulated above atmospheric pressure,means for simultaneously imposing said known pressure differential across each said means for sensing differential pressure to produce a known pressure signal,means for resetting the gain of said means for sensing differential pressure by reference to at least said known pressure signal, andmeans for determining said flow rate by reference to said plurality of signals.
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Abstract
A portable flow measurement system comprising a primary flow metering element and a secondary flow metering element is disclosed that will find application in metering irrigation water use, urban and rural storm water runoff, infiltration/inflow and wastewater flow rates. The primary element comprises a constriction in a closed conduit that produces pressures in the liquid flowing through it that are related to the rate of flow of the liquid. The constriction is preferably configured to cause essentially simultaneous filling of the constriction and the conduit upstream from it upon increasing flow rate and/or filling of the constriction and/or the upstream pipe before the modular limit is reached. The secondary element comprises a system for transmitting and sensing the pressures produced by the primary element, computing flow rates using the sensed pressure as a basis and storing the pressure data and/or the flow rate data. The pressure transmitting and sensing subassembly comprises a plurality of bubbler circuits, a plurality of mechanisms for controlling bubble release rate, at least one and preferable two differential pressure sensors, mechanisms for simultaneously applying the same pressure to the pressure side and the reference side of each differential pressure sensor and mechanisms for simultaneously applying a known differential pressure across each differential pressure sensor.
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Citations
27 Claims
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1. A system for measuring the flow rate of a liquid comprising:
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a primary element comprising a constriction in a closed conduit, said constriction having a modular limit and being configured so as to cause at least one of the following to fill prior to said modular limit being reached; said closed conduit, and said constriction, said constriction producing pressures in said liquid, a source of compressed gas, means for releasing a plurality of bubbles of said gas exposed to said pressures, a plurality of bubbler circuits connected to said means for releasing a plurality of bubbles, means for controlling bubble release rate, at least one means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and a reference side, and said means for sensing producing a plurality of signals when excited, said plurality of signals being characterized by an offset or zero and a gain, means for simultaneously applying a single pressure to the pressure side and the reference side of said means for sensing differential pressure to produce a zero pressure signal, means for resetting the zero of said means for sensing differential pressure by reference to at least said zero pressure signal, means for generating a known pressure differential, wherein said means for generating a known pressure differential is selected from the group consisting of; means for generating a known head and a known head loss, means for sensing pressures at a plurality of known elevations or depths in a liquid, means for sensing pressures at known elevations or depths in liquids of known density, means for generating a known gauge pressure that is referenced to atmospheric pressure, and means for generating a gas pressure that is regulated above atmospheric pressure, means for simultaneously imposing said known pressure differential across each said means for sensing differential pressure to produce a known pressure signal, means for resetting the gain of said means for sensing differential pressure by reference to at least said known pressure signal, and means for determining said flow rate by reference to said plurality of signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for measuring the flow rate of a liquid comprising:
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a primary element comprising a constriction in a closed conduit, said constriction having a modular limit and being configured so as to accomplish both of the following;
to cause the constriction to fill with the liquid at substantially the same flow rate as the closed conduit upstream from said constriction, as the flow rate increases, andto cause at least one of the following to fill prior to said modular limit being reached; said closed conduit, and said constriction, said constriction producing pressures in said liquid, a source of compressed gas, means for releasing a plurality of bubbles of said gas exposed to said pressures, a plurality of bubbler circuits connected to said means for releasing a plurality of bubbles, means for controlling bubble release rate, at least one means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and a reference side, and said means for sensing producing a plurality of signals when excited, means for simultaneously applying a single pressure to the pressure side and the reference side of said means for sensing differential pressure to produce a zero pressure signal, means for resetting the zero of said means for sensing differential pressure by reference to at least said zero pressure signal, means for generating a known pressure differential wherein said means for generating a known pressure differential is selected from the group consisting of; means for generating a known head and a known head loss, means for sensing pressures at a plurality of known elevations or depths in a liquid, means for sensing pressures at known elevations or depths in liquids of known density, means for generating a known gauge pressure that is referenced to atmospheric pressure, means for generating a gas pressure that is regulated above atmospheric pressure, means for simultaneously imposing said known pressure differential across each said means for sensing differential pressure to produce a known pressure signal, means for resetting the gain of said means for sensing differential pressure by reference to at least said known pressure signal, and means for determining said flow rate by reference to said plurality of signals. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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18. The system of claim 9 wherein
said means for generating a known pressure comprises a double-bubbler arrangement. -
19. The system of claim 9 wherein said known pressure is variable so as to allow a high accuracy over a selected span of pressure measurement.
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20. The system of claim 9 wherein said at least one means for sensing differential pressure has a span and a linear response to a plurality of different applied pressures and said known pressure is higher than said span so as to produce a greater accuracy of pressure measurement over said span.
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21. The system of claim 9 wherein said means for recalibrating has an accuracy that is characterized by an error in pressure measurement expressed as a percent of full scale,
said error being less than an error achieved by a conventional temperature-compensated pressure transducer. -
22. The system of claim 9 wherein said system comprises an integrated pneumatic circuit comprising a plurality of elements mounted on or within a manifold, said plurality of elements comprising:
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said source of compressed gas, said plurality of bubbler circuits connected to said source of compressed gas, said means for releasing bubbles of said gas exposed to said pressures, said means for controlling bubble release rate associated with said plurality of bubbler circuits, said at least one means for sensing differential pressure connected to said plurality of bubbler circuits, said means for sensing having a pressure side and a reference side, and said means for sensing producing signals when excited, said means for simultaneously applying a first pressure to the pressure side and the reference side of said means for sensing differential pressure to produce a zero pressure signal, said means for zeroing said means for sensing differential pressure by reference to at least said zero pressure signal, said means for generating a second known pressure that is different from atmospheric pressure, said means for simultaneously imposing said known pressure to the pressure side and said first pressure to the reference side of said means for sensing differential pressure to produce a second pressure signal, and said means for recalibrating said means for sensing differential pressure by reference to at least said second pressure signal.
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23. The system of claim 9 comprising a datalogger/controller software program that causes said datalogger/controller to operate and store data.
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24. The system of claim 9 comprising a datalogger/controller that stores data and a modem to transmit said data to a computer.
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25. The system of claim 9 comprising a datalogger/controller that stores data and a packet radio station to transmit said data to a computer.
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26. An apparatus for metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to the atmosphere, comprising:
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a tubular venturi metering device arranged in the pipe, which device has an open ended bore therethrough having an axis end-to-end thereof, said bore having an entrance section adjacent a first end thereof which converges toward the second end of the bore but terminates short of the axis of the bore so that the throat is formed in the bore which opens to said second end, said device being arranged in the pipe to accept flow into said entrance from the pipe and otherwise to substantially block the pipe, the cross-sectional area of the throat relative to that of the entrance section being configured so that the entrance will fill prior to the throat on rising water level before the modular limit is reached, means for determining the head of liquid in said entrance section and in said throat.
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27. An apparatus for metering the flow of liquid which is flowing by gravity in an elongated pipe that is open to the atmosphere, comprising:
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a tubular venturi metering device arranged in the pipe, which device has an open ended bore therethrough having an axis end-to-end thereof, said bore having an entrance section adjacent a first end thereof which converges toward the second end of the bore but terminates short of the axis of the bore so that the throat is formed in the bore which opens to said second end, said device being arranged in the pipe to accept flow into said entrance from the pipe and otherwise to substantially block the pipe, the cross-sectional area of the throat relative to that of the entrance section being configured so that the throat will fill prior to the throat on rising water level before the modular limit is reached, means for determining the head of liquid in said entrance section and in said throat.
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Specification