Abstract:
A volumetric flow meter that includes a defined volume and sensors that detect when liquid begins to fill the defined volume and when that volume is full. A circuit or equivalent logic is preferably provided to generate a signal representative of flow rate based on the size of the defined volume and time required to fill that volume. The flow meter is constructed of economical and durable components. A method of flow metering is also disclosed.

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 60/046,844, filed May 5, 1997, and having the same title and inventor as above. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to flow measuring and metering devices and more specifically to a volumetric flow measuring and metering devices. 
     BACKGROUND OF THE INVENTION 
     There are many types of known flow metering and measuring devices and they include the following. Mass flow meters utilize temperature sensors that are placed upstream and downstream of a heating coil. The mass flow rate is inversely proportional to the temperature difference between the sensors. These flow meters are designed primarily for metering gas flow. 
     Turbine flow meters utilize a flowtube that contains a small propeller, or turbine, mounted co-axially. The angular speed of the tube is equivalent to flow rate. These flow meters produce an electrical output proportional to turbine speed. 
     In positive displacement flow meters, fluid enters the flow sensor chamber forcing a piston to move. Piston motion is proportional to flow rate and the flow meter produces an output signal based on the frequency of piston motion. 
     In vortex transmitter flow meters, flow passes baffles inside a transmitter, causing vortices to form. The frequency of the vortices is directly proportional to flow rate. Vortices cause pressure fluctuations which are sensed, amplified, and converted to an output signal. 
     Doppler flow meters utilize an ultrasonic beam that is transmitted at an angle into a fluid to be metered. Impurities in the fluid reflect the beam at a slightly different frequency to a receiving sensor. The Doppler shift value is proportional to flow velocity. 
     In magnetic flow meters, movement of a conductive fluid through a magnetic field generates a signal proportional to velocity. This technique utilizes the Faraday principle. 
     In differential pressure flow meters, a pressure difference is measured across an orifice. Flow is proportional to this pressure difference. 
     Though these flow meters have had a beneficial impact on flow metering, they are disadvantageous for one or more of the following reasons. They present an undesirable high back pressure to the sensed fluid. They are sensitive to particulates in the fluid or they require high particulate concentration for the fluid to be measured. Air bubbles can effect the accuracy of flow rate determination or can block flow. Many of these sensors measure flow indirectly by measuring the velocity and hence may provide undesirably inaccurate flow rates. The cost of some of the sensors used in these systems is undesirably high. 
     A need thus exists for a flow measuring and metering devices that has low susceptibility or sensitivity to particulate levels, does not produce back pressure and is accurate and inexpensive to produce and use, amongst other features. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a flow measuring and metering devices that has low susceptibility to substances or air bubbles in a flow being metered. 
     It is also an object of the present invention to provide a flow measuring and metering devices that does not produce a back pressure. 
     It is another object of the present invention to provide a flow measuring and metering devices that utilizes gravitational forces in metering flow rate. 
     It is another object of the present invention to provide a flow measuring and metering devices that is accurate in performance and economical to produce and operate. 
     These and related objects of the present invention are achieved by use of the volumetric flow measuring apparatus described herein. 
     The attainment of the foregoing and related advantages and features of the invention should be more readily apparent to those skilled in the art, after review of the following more detailed description of the invention taken together with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a volumetric flow measuring devices in accordance with the present invention. 
     FIG. 2 is a partial cross-sectional view of the volumetric flow measuring device of FIG. 1 in accordance with the present invention. 
     FIG. 3 is a block diagram of an embodiment of an electronic circuit for use in the flow measuring device of FIG. 1 in accordance with the present invention. 
     FIG. 4 is a block diagram of another embodiment of an electronic circuit for use in the flow measuring device of FIG. 1 in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a perspective view of a volumetric flow measuring device  10  in accordance with the present invention is shown. Measuring device  10  preferably includes a cylindrical tube  12  to which is attached an end cap  14 . An inlet adapter  16  is provided in a wall of tube  12 . A housing  40  for an electronic control circuit is mounted to tube  12 . Cable  44  supplies power to the electronic circuit and provides a path for the flow rate output signal. As will be described in more detail below liquid flows into inlet adapter  16  and fills a volume therebelow. Sensors are provided in this volume to determine the amount of time required for filling. When full, a plug in end cap  14  is withdrawn to permit liquid in the tube to flow out. The volume and rate of filling determine flow rate. Tube  12  and end cap  14  are preferably made of PVC and housing  40  is preferably a NEMA No. 4 enclosure. 
     Referring to FIG. 2, a partial cross-sectional view of measuring device  10  of FIG. 1 in accordance with the present invention is shown. Tube  12  houses a solenoid  20  from which extends a shaft  22 . Plug  26  is affixed to the distal end of this shaft and moves in the direction indicated by Arrow A. Energizing solenoid  20  moves plug  26  from the opening. A coil spring  27  biases plug  26  towards a closed position and functions to close the opening when the solenoid is not energized. A support member  24  is fixedly connected to tube  12 , for example by a screw, or other suitable fastening means. Support member  24  provides a first hole through which shaft  22  passes and a second hole through which sensor wires  30  pass. Support member  24  may alternatively be fashioned such that an individual hole for each sensor wire is provided. Solenoid  20  is steadfastly connected to support member  24 , again by screws or other suitable fastening means. 
     Wire  30  includes sensor wires  31 - 33  which connect to the electronic circuit  42  and descend into tube  12 . Wire  31  is the start count wire and extends downward to a defined start count level. Wire  32  is the stop count wire and extends downward to a defined stop count level. Wire  33  is positioned adjacent wires  31 , 32  and serves as a signal return therefor when a sufficient volume of water is present in the flow meter to support conduction. Accordingly, when water or another suitable liquid fills tube  12  to the level of start wire  31 , a start count signal is propagated along wire  31  to the electronic circuit. When the water reaches the level of stop wire  32 , a stop count signal is propagated along wire  32  to the electronic circuit. 
     Housing  40  is preferably mounted to tube  12  with PVC cement. Holes  13 , 41  are preferably sealed with silicon seal and hole  43  is sealed with a NEMA compression fitting (not shown) which is well known. 
     Wires  31 - 33  are preferably made of NiCr or like material because of its high level of resistance to corrosion. Holes  13  and  41  are respectively formed in tube  12  and housing  40  for the passage of wires  31 - 33  and solenoid activation wire  21  from tube  12  to electronic circuit  42 . A clock circuit  45  within electronic circuit  42  calculates the time to fill the volume between sensor wires  31 , 32 . Electronic circuit  42  also includes electronic flow rate calculting circuitry. Hole  43  is also provided in housing  40  for passage of wire  44 . 
     Referring to FIG. 3, a block diagram of an embodiment of electronic circuit  42  in accordance with the present invention is shown. Wire  31  feeds into input amplifier  51  and wire  32  feeds into input amplifier  52 . Wire  33  provides a reference to these amplifiers and this amplifier arrangement effectively provides a threshold for determining whether liquid is present or not. The outputs of amplifiers  51 , 52  are input to an microprocessor such as the Model 16C52 of Microchip Corporation. A crystal oscillator  54  is also coupled to processor  56 . The processor is programmed to calculate flow rate (FR) using the following equation: 
     
       
           FR =((52+adj)/ t )−1  (1) 
       
     
     where  52 +adj is a constant selected during calibration and t is the time between start and stop signals propagated on wires  31 , 32 . The calculated flow rate is output in a digital format to a digital to analog converter (DAC)  62  such as a Maxon MAX503. The analog representation of FR is output from DAC  62  to an output amplifier  64  which is provided with a stability feedback loop. From there the output signal may be propagated to a display, to scientific instrumentation used in connection with the flow meter, or to another destination. The  52 +adj value is determined by adjusting the value of the processor calibration inputs such that a correct flow rate reading is output by circuit  42  for a known flow rate. The flow is essentially determined by measuring the time required to fill a defined volume. 
     Processor  56  also controls the activation of solenoid  20 . In response to the stop signal, processor  56  enables a switch  58 . When switch  58  is enabled, power is provided to solenoid  20  over line  21 , causing the solenoid to retract shaft  22  and move plug  26  away from end cap  14 . Switch  58  is energized an amount of time sufficient for the liquid accumulation in tube  12  to move through the force of gravity out the bottom end of tube  12 . Flow meter  10  is designed to work with minimum and maximum flow rates. Minimum rates are discretionary and are determined by how long an operator is willing to wait for tube  12  to fill. The fill period can be programmed into processor  56  using known programming techniques. The maximum flow rate is determined by the volume and evacuation rate of tube  12 . The incoming flow rate cannot exceed the evacuation rate for proper operation. 
     Referring to FIG. 4, a block diagram of another embodiment of electronic circuit  42  in accordance with the present invention is shown. Wires  31 , 32  feed into input amplifier  71 , 72  and wire  33  provides a reference. When the start count signal (wire  31 ) is active, an oscillator  77  output signal is gated through NAND gate  75  to count registers  81 , 82 . The stop count signal is passed through inverter  76  to NAND  75  and disables the start count signal. The stop count signal is also propagated through a monostable multivibrator  85  to switch  87 . When the switch is enabled, power is supplied to solenoid  20  causing shaft  22  to retract and plug  26  to be lifted. 
     The output of count registers  81 , 82  is latched by latches  83 , 84  and converted to analog by digital to analog converter (DAC)  91 . The output of DAC  94  is provided to a divide module  93  which provides the reciprocal of the input, thus providing time, t, in the denominator of Eq&#39;n (1). The numerator value of  52 +adj is provided through R2R-ladder  95  and amplifier  94 . The minus 1 value is added through output amplifier  96 . A stability loop  97  is preferably provided internal or external to amplifier  96 . 
     While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as fall within the scope of the invention and the limits of the appended claims.