CLAIM OF PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 11/737,986, filed Apr. 20, 2007, the entire disclosure of which is incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to detecting pressure variations, including pressure spikes, in fuel dispensers to reduce and/or eliminate fuel measurement inaccuracies that result from such pressure variations. 
     BACKGROUND OF THE INVENTION 
     In a typical fueling transaction, a customer drives a vehicle up to a fuel dispenser in a fueling environment. The customer arranges for payment, either by paying at the pump, paying the cashier with cash, using a credit card or debit card, or some combination of these methods. The nozzle is inserted into the fill neck of the vehicle, and fuel is dispensed into the fuel tank of the vehicle. A display on the fuel dispenser indicates the amount of fuel that has been dispensed during the fueling transaction. The customer relies on the fuel dispenser to measure the amount of fuel dispensed accurately and charge the customer accordingly. 
     Operating internally within the fuel dispenser are valves that open and close the fuel flow path and a meter that measures the amount of fuel dispensed. The purpose of the meter is to accurately measure the amount of fuel delivered to the customer&#39;s vehicle so that the customer may be billed accordingly and fuel inventory updated. For pre-pay transactions, the fuel dispenser also relies on the meter to measure the fuel dispensed so as to control the termination of fuel dispensing. 
     Fuel dispenser meters may be positive displacement or inferential meters. Positive displacement meters measure the actual displacement of the fuel, while inferential meters determine fuel flow indirectly using a device responsive to fuel flow. In other words, inferential meters do not measure the actual volumetric displacement of the fuel. Inferential meters have some advantages over positive displacement meters. Chief among these advantages is that inferential meters may be provided in smaller packages than positive displacement meters. With either positive displacement or inferential meters, the meter generates a meter signal that is responsive to the amount of fuel flowing in the fuel flow path. The meter communicates the meter signal to a control system in the fuel dispenser. 
     One example of an inferential meter is described in U.S. Pat. No. 5,689,071, entitled “WIDE RANGE, HIGH ACCURACY FLOW METER.” The &#39;071 patent describes a turbine flow meter that measures the flow rate of a fluid by analyzing rotations of turbine rotors located inside the fuel flow path of the meter. As fluid enters the inlet port of the turbine flow meter in the &#39;071 patent, the fluid passes across two turbine rotors, which causes the turbine rotors to rotate. The rotational velocity of the turbine rotors is sensed by pick-off coils. The pick-off coils are excited by an alternating current signal that produces a magnetic field. As the turbine rotors rotate, the vanes on the turbine rotors pass through the magnetic field generated by the pick-off coils, thereby superimposing a pulse on the carrier waveform of the pick-off coils. The superimposed pulses occur at a frequency (pulses per second) proportional to the turbine rotors&#39; rotational velocity and hence proportional to the measured rate of flow. The pulses are sent to a control system as meter signals in the form of pulser signals. The control system receives the meter signals from the meter and converts the meter signals into the fuel flow rate and the volume of fuel dispensed. 
     A problem may occur with accurately measuring fuel flow when a customer is fueling his or her automobile at a retail fuel dispenser. If a non-steady state condition occurs, for example, by the costumer closing and opening the fuel nozzle in a rapid fashion, known as a “nozzle snap,” inaccuracy in fuel measured by the meter is introduced. The nozzle snap creates a pressure shock wave that causes a flow disturbance at the meter resulting in a false flow indication. If a flow switch is employed to detect when flow stops, the pressure shock wave causes the flow switch to bounce. The control system that receives the meter signals from the meter registers fuel flow without taking into account the flow disturbance. The cumulative effect of the nozzle snaps and the flow switch bouncing, if present, results in meter measurement inaccuracies. Meter measurement inaccuracies may cause the fuel dispenser displays to register false fuel flow rate and fuel volume dispensed, and may cause the accuracy to be outside of allowable limits. 
     Therefore, a need exists for a fuel dispenser to accurately measure fuel flow with a meter even during a nozzle snap or other non-steady state condition. 
     SUMMARY OF THE INVENTION 
     The present invention is a system and method for enhancing the accuracy of fuel flow measurement by detecting and compensating for pressure variations, such as pressure spikes or shock waves, created by a nozzle snap or other non-steady state condition. The pressure variations may cause flow disturbances, including, for example, unsteady flow or transient flow, which in turn may introduce meter measurement inaccuracies. Pressure variations can be “seen” locally at a fuel dispenser as a result of nozzle snaps, or remotely as a result of a remote nozzle snap occurring at another fuel dispenser. 
     In one embodiment, a metered fuel line pressure sensor is positioned downstream from a meter in a metered fuel line of a fuel dispenser. The metered fuel line pressure sensor is connected to a control system in the fuel dispenser and sends a metered fuel line pressure signal to the control system. If the pressure in the metered fuel line incurs a variation or surge, such as a pressure spike, the metered fuel line pressure sensor senses the pressure variation and sends a metered fuel line pressure signal reflecting the pressure variation to the control system. The control system receives and recognizes the metered fuel line pressure signal as a pressure variation in the metered fuel line. The control system determines that the pressure variation was caused by a nozzle snap based on rapid increase and decrease of pressure or other criteria compensates for the pressure variation by disregarding the meter signals and not converting the meter signals from the meter for a predetermined amount of time to allow the pressure in the metered fuel line to return to a pressure indicative of normal steady state fuel flow. Once the predetermined time has expired, the control system resumes converting the meter signals. 
     In another embodiment of the present invention, a metered fuel line pressure sensor is positioned downstream from a meter in a metered fuel line of a fuel dispenser. An inlet manifold pressure sensor is positioned in an inlet manifold of the fuel dispenser. The metered fuel line pressure sensor and the inlet manifold pressure sensor are connected to a control system of the fuel dispenser and send a metered fuel line pressure signal and an inlet manifold pressure signal, respectively, to the control system. If the pressure in the metered fuel line incurs a variation or surge, the metered fuel line pressure sensor sends a metered fuel line pressure signal to the control system reflecting the pressure variation in the metered fuel line. Similarly, if the pressure in the inlet manifold spikes, the inlet manifold pressure sensor sends an inlet manifold pressure signal to the control system reflecting the pressure variation in the inlet manifold. 
     The control system receives and recognizes the metered fuel line pressure signal as a pressure variation, such as a pressure spike, in the metered fuel line and receives and recognizes the inlet manifold pressure signal as a pressure variation in the inlet manifold. Because pressure spikes occurred in both the metered fuel line and the inlet manifold, the control system determines that the pressure variations were caused by a remote nozzle snap. A remote nozzle snap is a nozzle snap that occurs at some point in the fueling environment other than at the fuel dispenser. For example, a nozzle snap may be occurring at a different fuel dispenser in the fueling environment. The control system compensates for the pressure variations by disregarding the meter signals and not converting the meter signals from the meter for a predetermined amount of time to allow the pressure in the metered fuel line and the inlet manifold to return to a pressure indicative of normal steady state fuel flow. Once the predetermined time has expired, the control system resumes converting the meter signals. 
     In yet another embodiment of the present invention, a metered fuel line pressure sensor is positioned downstream from a meter in a metered fuel line of a fuel dispenser. A fuel supply line pressure sensor is positioned upstream from the meter in the fuel supply line of the fuel dispenser. The metered fuel line pressure sensor and the fuel supply line pressure sensor send a metered fuel line pressure signal and a fuel supply line pressure signal, respectively, to a control system of the fuel dispenser. If the metered fuel line pressure signal is less than the fuel supply line pressure signal, the control system determines that fuel is flowing in the proper direction through the meter and converts the meter signals from the meter. If the metered fuel line pressure signal is equal to or greater than the fuel supply line pressure signal, the control system determines that the fuel is not flowing or is flowing in a reverse direction and stops converting the meter signals from the meter. The control system resumes converting the meter signals from the meter when the metered line pressure signal becomes less than the fuel supply line pressure signal indicating normal steady state fuel flow. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  is a schematic diagram of a fueling environment of a retail service station in the prior art; 
         FIG. 2  illustrates a partial front view of a fuel dispenser in the prior art; 
         FIG. 3  illustrates a schematic diagram of a turbine flow meter of the prior art that may be used as the meter in one embodiment of the present invention; 
         FIG. 4  illustrates a schematic diagram of the fuel flow path and fuel flow components of a fuel dispenser in accordance with one embodiment of the present invention; 
         FIG. 5  illustrates a schematic diagram of a fuel dispenser control system, a meter and other fuel flow components in accordance with one embodiment of the present invention; 
         FIGS. 6A and 6B  illustrate a flowchart diagram of the operation of a control system of a fuel dispenser to compensate the fuel flow rate and fuel volume dispensed based on received pressure signals in accordance with one embodiment of the present invention; 
         FIG. 7  illustrates a graphic plot of pressure in the inlet manifold, fuel supply line and metered fuel line of a fuel dispenser in response to nozzle actions including a nozzle snap; 
         FIG. 8  illustrates a flowchart diagram of the operation of a control system of a fuel dispenser to compensate the fuel flow rate and fuel volume dispensed based on a nozzle snap; 
         FIG. 9  illustrates a graphic plot of pressure in the inlet manifold, fuel supply line and metered fuel line of a fuel dispenser in response to nozzle actions including a remote nozzle snap; 
         FIG. 10  illustrates a flowchart diagram of the operation of a control system of a fuel dispenser to compensate the fuel flow rate and fuel volume dispensed based on a local and a remote nozzle snap; and 
         FIG. 11  illustrates a flowchart diagram of the operation of a control system of a fuel dispenser to determine the proper flow of fuel through a meter by comparing a metered fuel line pressure with a fuel supply line pressure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     The present invention is a system and method for enhancing the accuracy of fuel flow measurement by detecting and compensating for pressure variations, such as pressure spikes or shock waves, created by a nozzle snap or other non-steady state condition. The pressure variations may cause flow disturbances, which in turn may introduce meter measurement inaccuracies. Pressure variations can be “seen” locally at a fuel dispenser as a result of nozzle snaps, or remotely as a result of a remote nozzle snap occurring at another fuel dispenser. For certain types of meters used in fuel dispensers, the meter may continue to send to the control system meter signals indicating fuel flow even though flow disturbances are introduced in the fuel flow path interrupting the fuel flow and/or causing the fuel to flow in the reverse direction. The flow disturbances may be due to pressure waves or pulses created by a non-steady state condition. The non-steady state condition may be caused by a nozzle snap. The flow disturbances result in meter inaccuracies. In addition, a flow switch may be incorporated in the fuel flow path to detect when fuel flow stops. The pressure waves or pulses will cause the flow switch to bounce, sending false flow signals to the control system. The cumulative effect of the meter measurement inaccuracies and the flow switch bouncing causes the fuel dispenser displays to register false fuel flow rate and fuel volume dispensed. This effect is described in U.S. Pat. No. 6,935,191, entitled “FUEL DISPENSER FUEL FLOW METER DEVICE, SYSTEM AND METHOD,” which is hereby incorporated by reference in its entirety. 
     The present invention is directed to compensating the fuel volume measurement of fuel dispensed by a fuel dispenser based on pressure variations, such as pressure spikes, detected in the fuel flow path of the fuel dispenser. Pressure sensors detect pressure in the fuel flow path of a fuel dispenser and communicate pressure signals reflecting the pressure sensed to a control system of the fuel dispenser. Based on the pressure signals, the control system determines whether there is a non-steady state condition in the fuel flow path, such as one caused by a nozzle snap. If the control system determines that there was such a non-steady state condition, the control system stops converting meter signals from the meter into fuel flow rate and fuel volume dispensed signals for a predetermined period of time to allow the pressure in the fuel flow path to return to a level indicative of normal, steady state fuel flow. Alternatively, the control system may mathematically adjust the conversion calculation to compensate for the non-steady state period. After expiration of the predetermined period of time, the control system resumes converting the meter signals in a normal manner. 
     This patent application references pressure variations as including pressure spikes, pressure surges, and/or pressure shock waves. Each of these terms are used interchangeably to express a pressure variation indicative of flow disturbances, for example, unsteady flow or transient flow. Each of one term versus another is not meant to limit the invention or its application beyond pressure variations in any manner. 
     In the main embodiment of the present invention, a turbine flow meter is described as the meter of the fuel dispenser. The turbine flow meter may be one as described in U.S. Pat. No. 5,689,071, entitled “WIDE RANGE, HIGH ACCURACY FLOW METER,” which is hereby incorporated by reference in its entirety. Note, however, that the present invention can be practiced with any type of meter including a positive displacement meter. Before discussing the particular aspects of the present invention, a brief description of a fueling environment is provided. 
       FIG. 1  illustrates a conventional exemplary fueling environment  10 . Such a fueling environment  10  may comprise a central building  12 , a plurality of fueling islands  14 , and a car wash  16 , for example. The central building  12  need not be centrally located within the fueling environment  10 , but rather is the focus of the fueling environment  10  and may house a controller  18 , which may be a site controller (SC)  18 , which in an exemplary embodiment may be the G-SITE® sold by Gilbarco Inc. of Greensboro, N.C. The site controller  18  may include a memory  20  and may control the authorization of fueling transactions and other conventional activities as is well understood. 
     Further, the site controller  18  may have an off-site communication link  22  allowing communication with a remote host processing system  24  for content provision, reporting purposes, or the like, as needed or desired. The off site communication link  22  may be routed through the Public Switched Telephone Network (PSTN), the Internet, both, or the like, as needed or desired. 
     The car wash  16  may have a point of sale (not shown) associated therewith that communicates via an on-site communication link  25  with the site controller  18  for inventory and/or sales purposes. The on-site communication link  25  may be a Local Area Network (LAN), pump communication loop, other communication channel or line, or the like. The car wash  16  alternatively may be an optional stand alone unit and need not be present in a given fueling environment. 
     The fueling islands  14  may have one or more pumps or fuel dispensers  26  positioned thereon. The fuel dispensers  26  may be, for example, the ECLIPSE® or ENCORE® fuel dispenser sold by Gilbarco Inc. of Greensboro, N.C. The fuel dispensers  26  are in electronic communication with the site controller  18  via the on-site communication link  25 . 
     The fueling environment  10  also has one or more underground storage tanks (UST)  30 A,  30 B adapted to hold fuel  32 A,  32 B therein. One underground storage tank  30 A, for example, may store high octane fuel  32 A, while the other underground storage tank  30 B may store low octane fuel  32 B. The underground storage tanks  30 A,  30 B may be double-walled tanks. Further, each underground storage tank  30 A,  30 B may include a liquid level sensor or other sensor (not shown) positioned therein. The sensors may report to a tank monitor (TM)  34 A,  34 B associated therewith. The tank monitor  34  may communicate with the fuel dispensers  26  via the on-site communication link  25 , either through the site controller  18  or directly, as needed or desired, to determine amounts of fuel  32  dispensed, and compare fuel  32  dispensed to current levels of fuel  32  within the underground storage tanks  30  to determine if the underground storage tanks  30  are leaking. Although not shown in  FIG. 1 , the tank monitor  34  may also be positioned in the central building  12 , and may be located near the site controller  18 . 
     Fuel  32  flows from the underground storage tanks  30  to the fuel dispensers  26  via an underground fuel delivery system comprising main fuel line, piping or conduit  38 A,  38 B and branch fuel line, piping or conduit  40 A,  40 B. The branch fuel line  40  allows fuel  32  to flow from the main fuel line  38 , through other flow components (shown on  FIG. 4 ) to a meter  28  located in each fuel dispenser  26 . An exemplary underground fuel delivery system is illustrated in U.S. Pat. No. 6,435,204, entitled “FUEL DISPENSING SYSTEM,” which is hereby incorporated by reference in its entirety. 
     The tank monitor  34  may communicate with the site controller  18  and further may have an off-site communication link  36  for leak detection reporting, inventory reporting, or the like. Much like the off-site communication link  22 , the off-site communication link  36  may be through the PSTN, the Internet, both, other communication line, or the like. If the off-site communication link  22  is present, the off-site communication link  36  need not be present and vice versa, although both links may be present if needed or desired. As used herein, the tank monitor  34  and the site controller  18  are site communicators to the extent that they allow off-site communication and report site data to a remote location. 
     For further information on how elements of a fueling environment  10  may interact, reference is made to U.S. Pat. No. 5,956,259, entitled “INTELLIGENT FUELING,” which is hereby incorporated by reference in its entirety. Information about fuel dispensers may be found in commonly owned U.S. Pat. No. 5,734,851, entitled “MULTIMEDIA VIDEO/GRAPHICS IN FUEL DISPENSERS” and U.S. Pat. No. 6,052,629, entitled “INTERNET CAPABLE BROWSER DISPENSER ARCHITECTURE,” which are hereby incorporated by reference in their entireties. An exemplary tank monitor  34  is the TLS-350R manufactured and sold by Veeder-Root Company of Simsbury, Conn. 
     The front of a fuel dispenser  26  of the prior art is illustrated in  FIG. 2 . The fuel dispenser  26  includes a housing  42  and may have an advertising display  48  proximate the top of the housing  42  and a video display  50  at eye level. The video display  50  may be the Infoscreen® manufactured and sold by Gilbarco Inc. The video display  50  may be associated with auxiliary information displays relating to an ongoing fueling transaction that includes the number of gallons of fuel dispensed displayed on a volume display  52 , and the price of such fuel dispensed on a price display  54 . The displays  48 ,  50 ,  52  and  54  may include the capability of displaying streaming video and further may include liquid crystal displays (LCDs) as needed or desired. The branch fuel line  40  enters the fuel dispenser  26  through the bottom of the fuel dispenser  26 . The meter  28  and other flow components (not shown) are mounted within the housing  42  of the fuel dispenser  26 . The fuel  32  is eventually delivered into a fuel tank of a vehicle (not illustrated) via a hose  44  and a nozzle  46 . 
     In most fuel dispensers  26 , a submersible turbine pump (STP) (not illustrated) associated with the UST is used to pump fuel to the fuel dispenser  26 . Some fuel dispensers  26  may be self-contained, meaning fuel is drawn to the fuel dispenser  26  by a pump controlled by a motor (neither shown) positioned within the housing  42 . The meter  28  and other fuel flow components of the fuel dispenser  26  are located in a different compartment from the electronic components and separated by a vapor barrier (not shown) as is well understood and as is described in U.S. Pat. No. 5,717,564, entitled “FUEL PUMP WIRING,” which is hereby incorporated by reference in its entirety. Accordingly, the fuel flow path extends from the underground storage tanks  30  to the nozzle  46  where it is dispensed into the fuel tank of a vehicle. 
       FIG. 3  illustrates one particular type of meter  28  in the prior art that may be used in the present invention. This meter  28  is a turbine flow meter  28 . An example of a turbine flow meter  28  is described in U.S. Pat. No. 5,689,071 entitled “WIDE RANGE HIGH ACCURACY FLOW METER” previously referenced in the background of the invention above. The turbine flow meter  28  is comprised of a meter housing  55  that is typically constructed out of a high permeable material such as monel, a nickel-copper alloy, stainless steel, or 300-series non-magnetic stainless steel, for example. The meter housing  55  forms a cylindrical hollow shape that forms an inlet and outlet for fuel  32  to flow through the turbine flow meter  28 . A shaft  56  is placed internal to the meter housing  55  to support one or more turbine rotors  58 ,  60 . In the present example, two turbine rotors are illustrated; a first turbine rotor  58 , and a second turbine rotor  60 , but only one turbine rotor  58  may be used as well. 
     The turbine rotors  58 ,  60  rotate in an axis perpendicular to the axis of the shaft  56 . The turbine rotors  58 ,  60  contain one or more vanes  62 , also known as blades. As fuel  32  passes through the inlet of the turbine flow meter  28  and across the vanes  62  of the turbine rotors  58 ,  60 , the turbine rotors  58 ,  60  and the vanes  62  rotate at a velocity proportional to the rate of flow of the fuel  32  flowing through the turbine flow meter  28 . The proportion of the rotational velocity of the first turbine rotor  58  to the second turbine rotor  60  is determined by counting the vanes  62  passing by the pickoff coils  64 ,  65 . The rotational velocity of the turbine rotors  58 ,  60  can be used to determine the flow rate of fuel  32  passing through the turbine flow meter  28 , as is described in the aforementioned U.S. Pat. No. 5,689,071. 
     In the present example, there are two pickoff coils—a first pickoff coil  64  placed proximate to the first turbine rotor  58 , and a second pickoff coil  65  placed proximate to the second turbine rotor  60 . It is noted that the turbine flow meter  28  can be provided with only one turbine rotor  58  to detect flow rate as well. Also, the meter housing  55  may be comprised of two different permeable materials such as described in U.S. Pat. No. 6,854,342 entitled “INCREASED SENSITIVITY FOR TURBINE FLOW METER,” which is incorporated herein by reference in its entirety. 
     The pickoff coils  64 ,  65  generate a magnetic signal that penetrates through the permeable meter housing  55  to reach the vanes  62 . As the turbine rotors  58 ,  60  rotate, the vanes  62  superimpose a meter signal  66  in the form of a pulser signal on the magnetic signal generated by the pickoff coils  64 ,  65 . The meter signal  66  is analyzed by a control system  68  to determine the velocity of the vanes  62  that in turn can be used to calculate the flow rate and/or volume of fuel  32  flowing through the turbine flow meter  28 . 
     Flow disturbances created by pressure shock waves or pulses may cause unsteady flow or transient flow resulting in the fuel flow rate varying faster or slower than the rotation of the turbine rotors  58 ,  60 . Due to the variation of the fuel flow rate, the fuel flow rate may not match the steady state calibration conditions of the meter. In this instance, the turbine rotors  58 ,  60  continue to rotate and vanes  62  continue to superimpose a signal on the pick-off coils  64 ,  65 , thereby generating the meter signals  66  as if the steady state condition exists. These meter signals  66  are communicated to the control system  68 . The control system  68  will use the meter signals  66  to determine the flow rate and/or volume of fuel  32  erroneously since fuel  32  was not flowing through the turbine flow meter  28  in the steady state condition. Accordingly, the control system  68  must have a means to determine an unsteady flow or transient flow of fuel  32  at the turbine flow meter  28  during a time independent of the meter signal  66  or flow switch signal, if a flow switch (not shown on  FIG. 3 ) is present. 
       FIG. 4  illustrates a schematic diagram of the fuel flow path and fuel flow components of a fuel dispenser  26  in accordance with an embodiment of the present invention. Although not specifically shown in  FIG. 4 , it is understood that the flow components shown are internal to or extend from the fuel dispenser  26 . Also, a dual set of several of the components are shown (A, B) to indicate separate fuel flow paths for high octane fuel  32 A and low octane fuel  32 B. It should be understood that the flow components for both octane level fuels are the same, and, accordingly, discussion of such flow components will apply to both and will not differentiate between octane level fuels. 
     The fuel  32  may travel from the UST  30  (not illustrated) to the fuel dispenser  26  via the main fuel line  38  (not illustrated) and branch fuel line  40 . The main fuel line  38  and branch fuel line  40  may be double-walled pipe. The branch fuel line  40  may pass into the housing  42  (not illustrated) of the fuel dispenser  26  first through a shear valve  70 . The shear valve  70  is designed to cut off fuel flowing through the branch fuel line  40  if the fuel dispenser  26  is impacted, as is commonly known in the industry. One illustration of a shear valve  70  is disclosed in U.S. Pat. No. 6,575,206, entitled “FLOW DISPENSER HAVING AN INTERNAL CATASTROPHIC PROTECTION SYSTEM,” which is hereby incorporated by reference in its entirety. 
     The fuel  32  may flow from the shear valve  70  through an inlet manifold  72  to a flow control valve  74 . The control system  68  (not illustrated) directs the flow control valve  74  to open and close when fuel dispensing is desired or not desired. The flow control valve  74  may be a proportional solenoid controlled valve, such as described in U.S. Pat. No. 5,954,080, entitled “GATED PROPORTIONAL FLOW CONTROL VALVE WITH LOW FLOW CONTROL,” for example, which is incorporated herein by reference in its entirety. If the control system  68  directs the flow control valve  74  to open to allow fuel  32  to be dispensed, the fuel  32  enters the flow control valve  74  and exits into a fuel supply line  76 . The fuel supply line  76  connects the flow control valve  74  with the meter  28 . 
     Fuel  32  flows through the fuel supply line  76  to and through the meter  28 . The volumetric flow rate of the fuel  32  is measured by the meter  28  as discussed with respect to  FIG. 3  above. After fuel  32  flows through the meter  28 , fuel passes through a check valve  78 . Alternatively, instead of a check valve  78 , the fuel  32  may enter a flow switch  78 . After the fuel  32  flows through the check valve/flow switch  78 , it flows through a metered fuel line  80  to an outlet manifold  82 . The high octane fuel  32 A and low octane fuel  32 B may be blended in the outlet manifold  82  to produce different octane level fuels  32 . The fuel  32  exits the outlet manifold  82  to be delivered to the hose  44  and nozzle  46  for eventual delivery into the fuel tank of a vehicle (not illustrated). 
     In  FIG. 4 , pressure sensors  84 ,  86 ,  88  are shown which may be positioned in different locations of the fuel flow path in accordance with different embodiments of the present invention. An inlet manifold pressure sensor  84  may be positioned in the inlet manifold  72 . A fuel supply line pressure sensor  86  may be positioned in the fuel supply line  76 . A metered fuel line pressure sensor  88  may be positioned in the metered fuel line  80 . The inlet manifold pressure sensor  84 , the fuel supply line pressure sensor  86  and the metered fuel line pressure sensor  88  sense the pressure in the respective locations of the fuel flow path in which each is positioned. 
       FIG. 5  illustrates a block diagram of the present invention and of the components that are illustrated in  FIG. 4 . The control system  68  may be a microcontroller, a microprocessor, or other electronics with associated memory and software programs running thereon as is well understood. The control system  68  directs the flow control valve  74 , via a valve communication line  90 , to open and close when fuel dispensing is desired or not desired. If the control system  68  directs the flow control valve  74  to open to allow fuel to flow to be dispensed, the fuel enters the flow control valve  74  from the inlet manifold  72  and exits into the fuel supply line  76  and to the meter  28 . 
     The flow rate of the fuel is measured by the meter  28 , and the meter  28  communicates the flow rate of the fuel to the control system  68  via a meter signal  66 . In this manner, the control system  68  uses the meter signal  66  to determine the volume of fuel flowing through the fuel dispenser and being delivered to a vehicle. The control system  68  updates the total volume in gallons dispensed on the volume display  52  via the volume display communication line  94 , and the price of the volume of fuel dispensed on the price display  54  via price display communication line  96 . 
     A flow switch  78 , if present, indicates to the control system  68  when fuel is flowing through the meter  28  by a signal  92  in the event the turbine rotors  58 ,  60  continue to rotate after fueling has stopped. Alternatively, the flow switch  78  may not be present and the fuel dispenser  26  may include just a check valve  78 . Fuel exits the flow switch/check valve  78  to the metered fuel line  80  and flows to the outlet manifold  82  (not shown) and then to the hose  44  and nozzle  46 .  FIG. 5  illustrates that the pickoff coils  64 ,  65  generate the meter signal  66  to the control system  68 . The pickoff coils  64 ,  65  may be incorporated into the meter  28 , or may be external to the meter  28 . 
     Although the control system  68  controls the opening and closing of flow control valve  74  to allow fuel to flow or not flow, the control system  68  cannot guarantee that fuel is flowing through the fuel dispenser  26  just because the control system  68  has directed the flow control valve  74  to be open. If there is a nozzle snap, the rapid closing and opening of the nozzle, or other non-steady state condition in the fueling environment  10 , a pressure shock wave is created that causes flow disturbances at the meter  28  resulting in a false flow indication. If a flow switch  78  is present, the pressure shock wave causes the flow switch  78  to bounce also providing an erroneous flow indication to the control system  68 . A reverse flow of the fuel  32  may also occur. Even in view of the flow disturbances caused by the pressure shock wave, the control system  68  may continue to receive the meter signals  66  from the pick-off coils  64 ,  65  of the meter  28  and may continue to register fuel flow as if the steady state condition exists thereby not taking into account the flow disturbances. 
     Pressure sensors incorporated into the flow path detect pressure shock waves that cause the flow disturbances. The pressure shock waves manifest in the form of pressure spikes. The pressure sensors are connected to the control system  68  and detect the pressure in the fuel flow path. The pressure sensors send pressure signals to the control system  68  including pressure signals that reflect the pressure spike. In  FIG. 5 , three pressure sensors are shown. The inlet manifold pressure sensor  84  is located and detects pressure in the inlet manifold  72 . The fuel supply line pressure sensor  86  is located and detects pressure in the fuel supply line  76 . The metered fuel line pressure sensor  88  is located and detects pressure in the metered fuel line  80 . The inlet manifold pressure sensor  84  communicates an inlet manifold pressure signal  98  to the control system  68 . The fuel supply line pressure sensor  86  communicates a fuel supply line pressure signal  100  to the control system  68 . The metered fuel line pressure sensor  88  communicates a metered fuel line pressure signal  102  to the control system  68 . The control system  68  may compensate the fuel flow rate and the volume dispensed in response to the pressure signals  98 ,  100  and  102 . 
       FIGS. 6A and 6B  illustrate a flow chart that describes the operation of the present invention where the control system  68  uses the pressure signals  98 ,  100  and  102  from the pressure sensors  84 ,  86  and  88  to compensate for the nozzle snap and accurately determine the volume of fuel flowing through the meter  28 . The process starts (block  200 ), and the customer initiates a fueling transaction at a fuel dispenser  28  (block  202 ). In some embodiments, the inlet manifold pressure sensor  84  is present and detects the pressure in the inlet manifold  72  (block  204 ) and communicates the inlet manifold pressure signal  98  to the control system  68  (block  206 ). The control system  68  sends a message to the flow control valve  74  to open (block  208 ). The flow control valve  74  opens and fuel flows through the flow control valve  74  (block  210 ). 
     In some embodiments of the present invention, the fuel supply line pressure sensor  86  is present and detects the pressure in the fuel supply line  76  as the fuel flows from the flow control valve  74  (block  212 ). The fuel supply line pressure sensor  86  communicates the fuel supply line pressure signal  100  to the control system  68  (block  214 ). Fuel  32  flows through the fuel supply line  76  to and through the meter  28  (block  216 ). As the fuel  32  is flowing through the meter  28 , the fuel  32  rotates the turbine rotors  58 ,  60  thereby generating meter signals  66 . The meter signals  66  are communicated to the control system  68  (block  218 ). Fuel  32  flows from the meter  28  through the flow switch/check valve  78  and the metered fuel line  80  (block  220 ). If a flow switch  78  is present, the flow switch  78  detects the flow of fuel  32  and sends the signal  92  to the control system  68  (block  222 ). It is not necessary that a flow switch  78  be included as the pressure sensors  84 ,  86 ,  88  can provide sufficient indication to the control system  68  of flow of fuel  32 . The metered fuel line pressure sensor  88  detects pressure in the metered fuel line  80  (block  224 ) and communicates the metered fuel line pressure signal  102  to the control system  68  (block  226 ). 
     The control system  68  converts the meter signals  66  into fuel flow rate and fuel volume. The control system  68  compensates the fuel flow rate and fuel volume based on the metered fuel line pressure signal  102  and, in some embodiments, the fuel supply line pressure signal  100  and the inlet manifold pressure signal  98  (block  228 ). The control system  68  then displays the fuel volume dispensed on the volume display  52  and the price for the fuel  32  dispensed on the price display  54  (block  230 ). 
       FIG. 7  illustrates a graphic plot  103  of pressure in pounds per square inch (PSI)  104  over time in seconds  106  of the inlet manifold pressure signal  98 , the fuel supply line pressure signal  100  and the metered fuel line pressure signal  102  of the fuel dispenser  26  in response to nozzle  46  actions at the fuel dispenser  26 . The graphic plot  103  illustrates the nozzle  46  as open  108  until just after  10  seconds when the customer at the fuel dispenser  26  performs a nozzle snap  110 , also referred to as a local nozzle snap, and illustrates the nozzle  46  as closed at a time just prior to 30 seconds when the customer completes the fueling. 
     The graphic plot  103  of  FIG. 7  illustrates the inlet manifold pressure signal  98  as relatively constant reflecting the pressure within the fueling environment  10  from the underground storage tanks  30 . The fuel supply line pressure signal  100  and the metered fuel line pressure signal  102  reach a level  114  indicating that the fuel  32  is flowing normally through the fuel dispenser  26  and the fueling transaction is proceeding. The differential between the inlet manifold pressure signal  98  of approximately 30 PSI and the metered fuel line pressure signal  102  of approximately 25 PSI indicates that fuel  32  is flowing normally from the inlet manifold  72  through the meter  28 . 
     At the time of the nozzle snap  110 , a pressure spike  116  occurs. The metered fuel line pressure signal  102  rapidly increases to approximately 65 PSI or 2.5 times the normal fuel flow pressure of 25 PSI  116   a  and rapidly decreases to approximately 12 PSI or 0.5 times the normal fuel flow pressure of 25 PSI  116   b . The rapid increase and decrease in the metered fuel line pressure signal  102  indicates the flow disturbance in the metered fuel line as a result of the nozzle snap  110 . 
     As shown in  FIG. 7 , the metered fuel line pressure signal  102  begins to settle back to a normal level  116   b  and reaches that level in approximately 1.0 second from the initiation of the nozzle snap  110 . The fuel supply line pressure signal  100  also settles into a normal level  118 . 
     When the nozzle  46  is closed  112 , another pressure spike occurs  120 . The metered fuel line pressure signal  102  rapidly increases to approximately 65 PSI  120   a  but quickly settles back to 30 PSI  120   b , or the same pressure as the inlet manifold pressure signal  98 . Because there is no differential between the inlet manifold pressure signal  98  and the metered fuel line pressure signal  102 , there is no flow of fuel  32 , which is indicative of the nozzle  46  being closed  112 . 
       FIG. 8  illustrates a flowchart diagram of the operation of the control system  68  of the fuel dispenser  26  to compensate the fuel flow rate and fuel volume dispensed based on a local nozzle snap at the fuel dispenser  26 . The process starts when the pressure in the metered fuel line  80  spikes (block  300 ). The metered fuel line pressure sensor  88  detects the pressure spike in the metered fuel line  80  (block  302 ) and communicates a metered fuel line pressure signal  102  responsive to the pressure spike to the control system  68  (block  304 ). 
     The control system  68  determines that a nozzle snap occurred at the fuel dispenser  26  based on the metered fuel line pressure signal  102  (block  306 ). The pressure spike due to the nozzle snap creates the flow disturbance at the meter  28  (block  308 ). The control system compensates for the flow disturbance at the meter  26  by factoring out meter signals  66  occurring at the time of the pressure spike and for a predetermined time thereafter (block  310 ). The control system  68  may factor out the meter signals  66  by simply disregarding the meter signals  66  for that predetermined time and therefore not converting the disregarded meter signals  66  into fuel volume dispensed. Once the predetermined period of time has expired, the control system  68  may resume converting the meter signals  66  into fuel volume dispensed. Alternatively, the control system  68  may apply a mathematical factor to the conversion process to take the flow disturbance into account. 
       FIG. 9  illustrates another graphic plot  124  of pressure in pounds per square inch (PSI)  104  over time in seconds  106  of the inlet manifold pressure signal  98 , the fuel supply line pressure signal  100  and the metered fuel line pressure signal  102  of the fuel dispenser  26 . In  FIG. 9 , as in  FIG. 7 , the inlet manifold pressure signal  98  is at approximately 30 PSI, and the fuel supply line pressure signal  100  and metered fuel line pressure signal  102  reach a level indicating normal fuel flow at approximately 25 PSI  114 . Also, as in  FIG. 7 , the metered fuel line pressure signal  102  shows a rapid increase  120  at the time of nozzle close  112 . 
     However, unlike the graphic plot  103  in  FIG. 7 ,  FIG. 9  shows both the inlet manifold pressure signal  98  and the metered fuel line pressure signal  102  indicating a pressure spike  126 . The inlet manifold pressure signal  98  rapidly increases to approximately 66 PSI  126   a  while the metered fuel line pressure signal  102  rapidly increases to approximately 50 PSI  126   b . Both the inlet manifold pressure signal  98  and the metered fuel line pressure signal  102  return to normal fuel flow pressure level in approximately 0.25 seconds  126   c . The pressure spike  126  happens without any activity occurring at the nozzle  46 . Accordingly, the pressure spike  126  was caused by a pressure disturbance due to a non-steady state condition occurring at some point in the fueling environment  10  other than by the action of the customer at the fuel dispenser  26 . The pressure spike  126  was caused by a nozzle snap at another fuel dispenser, also referred to as a remote nozzle snap. 
     When the fueling is complete and the nozzle  46  closed  112 , the metered fuel line pressure signal  102  reacts in a similar fashion as in  FIG. 7 . The metered fuel line pressure signal  102  rapidly increases but quickly settles back to the same pressure as the inlet manifold pressure signal  98 . Because there is no differential between the inlet manifold pressure signal  98  and the metered fuel line pressure signal  102 , there is no flow of fuel  32 , which is indicative of the nozzle  46  being closed. 
       FIG. 10  illustrates a flowchart diagram of the operation of the control system  68  of the fuel dispenser  26  to compensate the fuel flow rate and fuel volume dispensed based on a local nozzle snap at the fuel dispenser  26  and a remote nozzle snap at some other location in the fueling environment  10 . The process starts when the pressure in the metered fuel line  80  spikes (block  400 ). The metered fuel line pressure sensor  88  detects the pressure spike in the metered fuel line  80  (block  402 ) and communicates a metered fuel line pressure signal  102  responsive to the pressure spike to the control system  68  (block  404 ). 
     The control system  68  determines that a nozzle snap occurred somewhere in the fueling environment  10  based on the metered fuel line pressure signal  102  (block  406 ). The control system  68  investigates the status of the inlet manifold pressure sensor  84  (block  408 ). The control system  68  determines whether it received an inlet manifold pressure signal  98  indicting a pressure spike on the inlet manifold  72  (block  410 ). 
     If the control system  68  determines that it did not receive an inlet manifold pressure signal  98  indicative of a pressure spike in the inlet manifold  72 , the control system  68  determines that a local nozzle snap occurred at the fuel dispenser  26  (block  412 ), which created a flow disturbance at the meter  28  (block  414 ). The control system  68  compensates for the flow disturbance at the meter  28  due to the local nozzle snap by factoring out the meter signals  66  occurring at the time of the pressure spike and for a predetermined time thereafter (block  416 ). 
     If the control system determines that it did receive an inlet manifold pressure signal  98  indicative of a pressure spike in the inlet manifold  72 , the control system  68  determines that a remote nozzle snap occurred somewhere in the fueling environment  10  (block  418 ) which created a flow disturbance at the meter  28  (block  420 ). The control system  68  compensates for the flow disturbance at the meter  28  due to the remote nozzle snap by factoring out the meter signals  66  occurring at the time of the pressure spike and for a predetermined time thereafter (block  422 ). 
     The predetermined time for factoring out the meter signals  66  due to a local nozzle snap may not be the same as the predetermined time for factoring out the meter signals  66  due to a remote nozzle snap, and, preferably, may be different. The control system  68  may factor out the meter signals  66  by simply disregarding the meter signals  66  for that predetermined time and therefore not converting the disregarded meter signals  66  into fuel volume dispensed. Once the predetermined period of time has expired, the control system  68  may resume converting meter signals  66  into fuel volume dispensed. Alternatively, the control system may apply a mathematical factor to the conversion process to take the flow disturbance into account. The mathematical factor used to compensate for a local nozzle snap may not be the same as the mathematical factor used to compensate for a remote nozzle snap. 
       FIG. 11  illustrates a flowchart diagram of the operation of the control system  68  of the fuel dispenser  26  to determine the proper flow of fuel  32  through the meter  28  by comparing the metered fuel line pressure with the fuel supply line pressure. The process begins by control system  68  comparing the metered fuel line pressure signal  102  with the fuel supply line pressure signal  100  and the inlet manifold pressure signal  98  (block  500 ). 
     The control system  68  determines whether the metered fuel line pressure signal  102  is higher than either the fuel supply line pressure signal  100  or the inlet manifold pressure signal  98  (block  502 ). If the control system  68  determines that the metered fuel line pressure signal  102  is not higher than the fuel supply line pressure signal  100 , then fuel  32  is flowing normally through the meter  28  (block  504 ) and the control system  68  continues to convert the meter signals  66  into fuel flow rate and volume dispensed (block  506 ). 
     If the control system  68  determines that metered fuel line pressure signal  102  is higher than the fuel supply line pressure signal  100 , then fuel  32  is flowing in the reverse direction (block  508 ). The control system  68  recognizes the reverse fuel flow and does not convert any meter signals  66  into fuel flow rate and fuel volume dispensed (block  510 ). The process operates in a continuous loop with the control system  68  comparing the metered fuel line pressure signal  102  with the fuel supply line pressure signal  100  and the inlet manifold pressure signal  98  (block  500 ). 
     Although the use of pressure sensors in determining and compensating for the existence of non-steady state conditions in a fueling environment is described, one of ordinary skill in the art will understand and appreciate that pressure sensors may be used to determine fuel flow and enhance meter operation in steady state conditions also. Moreover, the pressure sensors may be used instead of a flow switch. In particular, not only can the level of pressure detected by a pressure sensor be used to determine fuel flow, but the differential in pressure from a pressure sensor located downstream from the pressure detected by a pressure sensor located upstream may be used to determine and enhance the accuracy of fuel flow rate and fuel volume dispensed. 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
A system and method for compensating a calculated or flow rate of fuel dispensed to a vehicle via a fuel flow path in response to a determination of a non-steady state condition based on data corresponding to a signal transmitted by a pressure sensor operatively coupled to the fuel flow path and configured to sense pressure therein, where the pressure sensor is adapted to transmit a signal representative of the sensed pressure.