Abstract:
An apparatus and method for measuring fluid flow comprising an inferential flow meter having a housing defining a fluid flow path. A pulser is operative to produce an output signal indicative of flow rate through the meter. The apparatus further includes a controller in electronic communication with the pulser so as to receive the output signal. Based on the output signal, the controller is operative to determine fluid flow in a plurality of dynamic time sub-windows corresponding to respective periods of substantially consistent instantaneous flow.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to flow meters for use in fuel dispensing environments. More particularly, the invention relates to an inferential flow meter adapted to have enhanced accuracy when pulsations occur in the flow. 
         [0002]    Inferential flow meters, e.g., a turbine flow meter, may be used in a variety of applications in fuel dispensing environments. For example, turbine flow meters are often used to meter fuel being dispensed, measure the vapor being returned to the underground storage tank in a stage two vapor recovery fuel dispenser, or measure the vapor or air released to atmosphere from the ullage area of an underground storage tank when a pressure relief valve in a vent stack is opened to relieve pressure. 
         [0003]    Turbine flow meters generally comprise a housing having inlet and outlet ports at respective ends thereof. A shaft is located inside the housing along the housing&#39;s longitudinal axis. One or more turbine rotors mounted on the shaft rotate when fluid (liquid or gas) flows through the housing via the inlet and outlet ports. A detector is typically mounted to the housing to detect rotation of one or both of the rotors. For example, the detector may be a hall effect device or pickup coil that determines rotation based on changes in a magnetic field. The detector is associated with a “pulser” that produces a series of pulses at a rate which is related to the flow rate of fluid through the meter. As such, the flow rate of the fluid flowing through the housing can be determined. 
         [0004]    Various events—such as the operation of submersible turbine pump (STP) motors, the operation of valves in the fuel flow path, or nozzle snaps—can cause substantial flow pulsations. Nozzle snaps, for example, occur when the nozzle is suddenly closed by the customer, or by a valve within the nozzle that automatically closes when the customer&#39;s fuel tank is full. These flow pulsations create transients that flow back and forth quickly through the entire hydraulic system for a few seconds. As the pulsations travel through the meter, the instantaneous speed of the turbine rotor(s) varies momentarily in response to the fluid perturbation. 
         [0005]    Meters known in the art calculate fluid flow rates based on counting the number of pulses during a programmable time window. The number of pulses is divided by the time window to derive pulses per unit of time. Calculating an average in this manner filters out instantaneous speed variations. As a result, errors in viscosity calculation and flow rate can occur. 
         [0006]    Various turbine meters of the prior art are shown and described in U.S. Pat. Nos. 7,028,561, 6,854,342, 6,692,535 and 5,689,071. Each of these patents is incorporated herein by reference in its entirety. 
         [0007]    Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
       SUMMARY OF THE INVENTION 
       [0008]    According to one aspect, the present invention provides an apparatus for measuring fluid flow comprising an inferential flow meter having a housing defining a fluid flow path. A pulser is operative to produce an output signal indicative of flow rate through the meter. The apparatus further includes a controller in electronic communication with the pulser so as to receive the output signal. Based on the output signal, the controller is operative to determine fluid flow in a plurality of dynamic time sub-windows corresponding to respective periods of substantially consistent instantaneous flow. 
         [0009]    In many exemplary embodiments, the output signal of the pulser comprises a pulse train in which pulse frequency varies with instantaneous flow. The dynamic time sub-windows may thus be ascertained by comparing duration between adjacent pulses. For example, the controller may be operative to include a series of adjacent pulses in one of the dynamic time sub-windows if respective durations therebetween are within a threshold of each other. Preferably, the controller may calculate a total delivered volume within a longer time period by determining and summing together partial delivered volume during respective dynamic time sub-windows making up the longer time period. 
         [0010]    Another aspect of the present invention provides an apparatus for measuring fluid flow comprising a turbine flow meter having a rotor. A pulser is operative to produce a pulse train in which pulse rate varies with instantaneous flow through the turbine flow meter. A controller operative to determine a total volume of fluid passing through the turbine flow meter during a time period is also provided. 
         [0011]    The controller is configured to perform the steps of: (a) determining a first partial volume based on a first pulse rate during a first time sub-window; (b) determining a second partial volume based on a second pulse rate during a second time sub-window; and (c) adding the first partial volume and the second partial volume. Preferably, the first and second time sub-windows may be dynamically determined corresponding to respective periods in which the first and second pulse rates remain substantially consistent. For example, substantial consistency may be determined by ascertaining whether the first and second pulse rates remain consistent within a predetermined threshold during the first and second time sub-windows, respectively. Pulse rates within each of the time sub-windows may be averaged during determination of the first and second partial volumes to filter out spurious variations. 
         [0012]    According to another aspect, the present invention provides a method of determining flow of a fluid through an inferential flow meter. One step of the method involves detecting a pulse train having a plurality of pulses occurring at a pulse rate indicative of fluid flow rate through the inferential flow meter. Pulse rates of the plurality of pulses are determined. Another step of the method involves grouping adjacent pulses having substantially consistent pulse rates into a plurality of time sub-windows. Respective partial volumes for each of the time sub-windows are also determined. The respective partial volumes are added to determine a total delivered volume. 
         [0013]    A further aspect of the present invention provides a fuel dispenser comprising a fluid flow conduit for delivering fuel from a storage tank. A hose having a proximal end and a distal end is also provided. The proximal end of the hose is in fluid communication with the fluid flow conduit. A nozzle is connected to the distal end of the hose. An inferential flow meter is located in line with the fluid flow conduit. A pulser associated with the inferential flow meter produces an output signal indicative of flow rate through the inferential flow meter. 
         [0014]    The fuel dispenser further comprises a controller in electronic communication with the pulser so as to receive the output signal. Based on the output signal, the controller is operative to determine fluid flow in a plurality of dynamic time sub-windows corresponding to respective periods of substantially consistent instantaneous flow. 
         [0015]    Other objects, features and aspects of the present invention are provided by various combinations and subcombinations of the disclosed elements, as well as methods of practicing same, which are discussed in greater detail below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
           [0017]      FIG. 1  is a schematic diagram of a fuel dispenser for fueling vehicles that may utilize one or more turbine flow meter constructed in accordance with the present invention; 
           [0018]      FIG. 2  is a diagrammatic perspective view of a turbine flow meter constructed in accordance with an embodiment of the present invention; 
           [0019]      FIG. 3  is an illustration of a flow pattern of a turbine flow meter constructed in accordance with the embodiment of  FIG. 2 ; 
           [0020]      FIG. 4  is a graph illustrating a pulse train output by a turbine flow meter during the presence of flow pulsations and the corresponding fluid flow rate; 
           [0021]      FIG. 5  is a graph illustrating dynamic time windows that may be utilized to measure accurately the time-varying flow rate illustrated in  FIG. 4 ; and 
           [0022]      FIG. 6  is a flowchart illustrating a process for determining flow volume in accordance with the present invention. 
       
    
    
       [0023]    Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
         [0025]      FIG. 1  illustrates a pair of turbine flow meters  10 A and  10 B utilized in a fuel dispenser  40 . As is well-known, a fuel dispenser such as fuel dispenser  40  is used to dispense and measure the amount of fuel being delivered to a vehicle (not shown). Accurate meters are required to measure fuel dispensing to comply with Weights &amp; Measures regulatory requirements. 
         [0026]    Fuel dispenser  40  may be a blending type fuel dispenser wherein a low-octane fuel  41  stored in a low-octane underground storage tank (UST)  42  and a high-octane fuel  43  stored in a high-octane underground storage tank (UST)  44  are blended together by fuel dispenser  40  to deliver either a low-octane fuel  41 , high-octane fuel  43 , or a mixture of both to a vehicle. Low-octane fuel  41  is supplied to fuel dispenser  40  through a low-octane fuel supply conduit  46 . Likewise, high-octane fuel  43  is delivered to fuel dispenser  40  through a high-octane fuel supply conduit  48 . Both low-octane fuel  41  and high-octane fuel  43  pass through fuel dispenser  40  in their own independent flow paths. Each fuel  41 ,  43  encounters a valve  50 ,  52  that controls whether the fuel is allowed to enter into fuel dispenser  40 , and if so at what flow rate. 
         [0027]    As either low-octane fuel  41 , high-octane fuel  43 , or both pass through their respective turbine meters  10 A,  10 B, the fuels come together in the blend manifold  54  to be delivered through a hose  56  and nozzle  58  into the vehicle. Valves  50 ,  52  may be proportionally controlled and may be under the control of a controller  60  in fuel dispenser  40  via control lines  62 ,  64 . U.S. Pat. No. 4,876,653 entitled “Programmable Multiple Blender,” incorporated herein by reference in its entirety, describes a system for blending low and high octane fuels. 
         [0028]    Controller  60  determines when a fueling operation is allowed to begin. Typically, a customer is required to push a start button  78  and to indicate which grade of fuel  41 ,  43  is desired. Controller  60  thereafter controls valves  50 ,  52  to allow low-octane fuel  41  or high-octane fuel  43  to be dispensed, depending on the type of fuel selected by the customer. 
         [0029]    After fuel  41 ,  43  passes through both valves  50 ,  52 , it flows through the associated one of turbine meters  10 A,  10 B. If only a low-octane fuel  41  or high-octane fuel  43  was selected by the customer to be dispensed, controller  60  would only open one of the valves  50 ,  52 . As fuels  41 ,  43  flow through turbine meters  10 A,  10 B, the respective pulsers will produce a corresponding pulser signal  66 ,  68  that is input into controller  60 . 
         [0030]    Controller  60  determines the quantity of flow of fuel flowing through turbine meters  10 A,  10 B for the purpose of determining the amount to charge the customer. In this regard, controller  60  uses the data from the pulser signals  66 ,  68  to generate a totals display  70 . Totals display  70  includes an amount to be charged to the customer display  72 , gallons (or liters) dispensed display  74  and the price per unit of fuel display  76 . As one skilled in the art will appreciate, controller  60  may be implemented in various combinations of hardware, firmware, or software, as necessary or appropriate. 
         [0031]    In other embodiments, a turbine meter of the present invention may be used in a vent stack of an underground storage tank at a service station. Specifically, it may be desirable to measure the amount of air flowing through a vent stack using meter  10  to determine how often and how much air is separated by a membrane and released to atmosphere for any number of diagnostic or information purposes. The membrane may either permeate hydrocarbons or permeate oxygen or air as disclosed in U.S. Pat. Nos. 5,464,466 and 5,985,002, incorporated herein by reference in their entirety. In other embodiments, meter  10  may measure the amount of vapor being returned to the underground storage tank in a stage two vapor recovery system. 
         [0032]      FIG. 2  illustrates a turbine flow meter  10  constructed in accordance with an embodiment of the present invention. Meter  10  includes a housing  12  that forms an inlet port  14  and an outlet port  16  for ingress and egress of fluid (liquid or gas), respectively. A shaft  18  or other support structure is located inside of housing  12  along a central axis A. In this embodiment, a pair of turbine rotors  20  and  21  that rotate in a plane perpendicular to axis A are located at selected axial positions on shaft  18 . For example, shaft  18  may be stationary but supports rotors  20  and  21  for rotation. Generally, a bearing set will be interposed between each of the rotors and the shaft  18  to facilitate the respective rotor&#39;s rotation. 
         [0033]    Referring now also to  FIG. 3 , rotor  20  is located slightly upstream of rotor  21 , and serves to condition the flow to rotor  21 . In particular, rotor  20  includes one or more vanes  22  (also known as blades) that cause rotation when impinged by the flowing fluid. Similarly, rotor  21  includes one or more vanes  23 . Vanes  22  and  23  are preferably spaced evenly around the periphery of the respective rotor hub. In addition, vanes  22  of rotor  20  are preferably canted oppositely from vanes  23  of rotor  21 . This orientation of vanes  22  and  23  causes the two rotors to rotate in opposite directions (shown by arrows  32  and  36 ) at a rotational speed indicative of the fluid flow rate. 
         [0034]    Because vanes  22  are canted, the straight fluid flow is converted into a generally swirling pattern with an angular trajectory based on angle  27  of vanes  22 . This angular trajectory is generally oblique to the longitudinal axis of meter  10  (shown as “A”). After passing through rotor  20 , the fluid impinges vanes  23  of rotor  21 . The angular trajectory of the flow due to rotor  20  increases the material&#39;s angle of incidence with vanes  23 . As a result, the driving force used to impart rotational movement on turbine rotor  21  also increases. This facilitates rotation of rotor  21  at lower flow rates than may otherwise be the case. 
         [0035]    As can be seen in  FIG. 2 , a detector  30  is located on housing  12  adjacent to rotor  21 . The output of detector  30  is provided to a pulser  32  which produces a serial pulse train used by the controller to determine flow rate and thus amount of fluid dispensed. Any suitable detector may be utilized, such as a magnetic detector. Examples of typical magnetic detectors that have been used in turbine flow meters are pickup coils and hall effect sensors. In either case, rotation of rotor  21  produces a characteristic signal which is used to generate the pulse train output of pulser  32 . As one skilled in the art will appreciate, housing  12  should be formed of a nonmagnetic material if a magnetic sensor is used. In contrast, rotor  21  should be formed wholly or partly of a magnetic material. While detector  30  is shown adjacent to rotor  21  in this case, embodiments are contemplated in which the detector is located adjacent to a separate encoder wheel which rotates with the rotor. 
         [0036]      FIG. 4  shows the relationship between flow rate  100  and the frequency of pulses produced by pulser  32 . In this regard, pulser  32  produces a pulse train  102  comprised of individual pulses  104  will be output from pulser  32 . As can be seen, pulses  104  occur at a frequency related to the fluid flow rate. As indicated at  106 , the frequency of pulses  104  increases during times of high flow rate. Conversely, as indicated at  108 , the frequency of pulses  104  decreases as the flow rate decreases. 
         [0037]    During times of flow pulsations or other perturbations, the frequency of pulses  104  may fluctuate quite rapidly. If the pulse rate is averaged over a time window without regard to instantaneous speed variations, then errors can occur in determining viscosity and flow rate. In contrast, controller  60  preferably determines the volumetric of fluid flow through the meter based on the instantaneous flow rate as determined by meter  10 . In particular, preferred embodiments of the present invention calculate a series of instantaneous flow rates as dynamic sub-windows based upon rotor pulse duration. The series is then summed over a period of time to yield an improved volumetric flow calculation. Preferably, there may be some filtering within each sub-window filter out spurious variations. 
         [0038]      FIG. 5  illustrates one manner in which dynamic sub-windows can be created to determine volumetric in accordance with the present invention. Once the flow rate changes, either quickly due to a flow pulsation or slowly, the frequency of pulses  104  in pulse train  102  delivered to controller  60  by pulser  32  will also change. When controller  60  detects a frequency change in the pulse train, a new time window is created that captures all of pulses  104  at or near the new frequency. The new frequency is translated to a flow rate by controller  60  and multiplied by the amount of time the fluid was flowing at that rate. The volumetric flow at this new rate is then added to the previously calculated volumetric flow to ascertain the total flow through meter  10 . 
         [0039]    Therefore, depending on how often the fluid flow rate changes and the number of flow pulsations, the dynamic time windows can be of varying widths (durations). The process of determining the volumetric flow during a particular time window and adding that volume to the previously computed volume is repeated as long as fluid is flowing through meter  10 . For example,  FIG. 5  shows a situation in which three dynamic windows (or “sub-windows”)  110 ,  112 ,  114  are created based on the varying flow rate. As can be seen, time windows  110 ,  112  and  113  capture the first, second, and third set of similar frequency pulses, respectively. The width (i.e., time duration) of each time window is variant to more fully capture the variations in flow rate that can occur (such as due to flow pulsations) as the fuel is dispensed. 
         [0040]    In a preferred embodiment, dynamic time windows may include pulses of slightly differing frequencies. Within the particular sub-window, the pulse rates are averaged to filter out spurious variations such as may occur due to data acquisition errors. If the variation in pulse frequency from one pulse to the next exceeds a given threshold, however, controller  60  generates a new time window. 
         [0041]      FIG. 6  illustrates a preferred process that may be performed by controller  60  in accordance with the present invention. The process begins as indicated at  120 . As indicated at  122  and  124 , the process then detects successive pulses P and P+1. As indicated at  126 , the duration between P and P+1 is then compared to the duration between P and the pulse before it. If the difference exceeds a certain threshold, a decision is made (as indicated at  128 ) to begin a new sub-window (as indicated at  130 ). If not, the same sub-window is continued (as indicated at  132 ). Within each sub-window, the pulse durations are preferably averaged (as indicated as  134 ) to filter out spurious variations. 
         [0042]    Delivered volume for a specified time period can then be determined (as indicated at  136 ). Preferably, delivered volume will be calculated by determining the volume delivered during each sub-window making up the longer time period and adding them together. This can be expressed as: 
         [0000]      Delivered volume=(DT 1 *FR 1 )+(DT 2 *FR 2 )+ . . . +(DT n *FR n )       Or generally:         
         [0000]      Delivered volume=Sum(DT i *FR i )       Where:
           DT=time duration of a sub-window   FR=flow rate during a sub-window   For sub-windows i=1 to n (total sub-windows in larger window)   
                 
         [0048]    It can thus be seen that the present invention provides an apparatus and method for achieving accurate determinations of delivered volume even in the presence of flow pulsations. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. For example, controller  60  may be separated from pulser  32  as illustrated above, or may in some cases be located adjacent to or incorporated into the pulser. 
         [0049]    In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention as further described in the appended claims.