Abstract:
Methods, systems, and computer program products for using a reference meter to provide automated calibration for a fuel dispenser are disclosed. According to one method, first historical metering data associated with a fuel flow meter and second historical metering data associated with a reference meter are maintained within a memory. The first historical metering data is compared with the second historical metering data. It is determined whether a difference exists between the first historical metering data and the second historical metering data that can be corrected by calibration of the fuel flow meter. In response to determining that a difference exists between the first historical metering data and the second historical metering data that can be corrected by calibration of the fuel flow meter, an automated calibration of the fuel flow meter is performed.

Description:
CLAIM OF PRIORITY 
       [0001]    This application is a divisional application of and claims priority to U.S. patent application Ser. No. 11/757,019, filed Jun. 1, 2007, the entire disclosure of which is hereby incorporated by reference for all purposes as if set forth verbatim herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system and method for automated calibration of a fuel flow meter in a fuel dispenser using a reference meter. 
       BACKGROUND OF THE INVENTION 
       [0003]    Fuel dispensers dispense petroleum and alternative fuel products at retail service stations and fueling environments and convenience store operations around the world. Regulations require that fuel dispensers accurately dispense fuel within strict volumetric tolerances. In this regard, fuel dispensers employ fuel flow meters that measure the amount of fuel delivered to a customer&#39;s vehicle and charged to the customer. In addition to regulatory requirements governing the accuracy of fuel flow meters, inaccurate fuel dispensing transactions can generate significant losses for retail fuel dispenser operators in the form of lost profits and increased costs associated with dispensed fuel products. 
         [0004]    One type of fuel flow meter that is commonly used within a fuel dispenser to measure fuel delivered to a vehicle is a positive displacement meter (PDM). PDMs measure fuel delivered by measuring the amount of displaced fuel within a known-volume container within the meter. PDMs are also used in a variety of other fluid dispensing environments. PDMs are reasonably priced and, when calibrated properly, are capable of accurately metering fuel transactions across a broad range of fuel flows that occur within a retail fueling environment. 
         [0005]    However, PDMs may include dynamic seals which experience wear and leak over time. Additionally, the displacement volume increases within the cylinder bore of a PDM over time due to wear and sediment buildup. These factors result in a change in accuracy for a PDM over time. This change in accuracy is known as “drift” and results in inaccurate meter readings for the PDM. For example, as a cylinder in a PDM wears over time, the displacement within the cylinder of the PDM increases. The increased displacement results in a larger volume within the cylinder and this larger volume results in more fuel being dispensed for a given fuel dispenser transaction than is measured by the PDM. The unmeasured fuel translates into lost profits and increased costs during fuel dispensing transactions. Further, as a meter drift increases prior to calibration, the rate at which profits are lost also increases. 
         [0006]    In order to prevent or reduce the effect of meter drift, PDMs must be periodically calibrated to adjust for the drift that results from the bearing wear, dynamic seal wear, sediment buildup, and cylinder wear within the PDMs. Calibration must be performed frequently enough to maintain the accuracy of the fuel flow meter within regulated limits. 
         [0007]    Calibration may be performed for a PDM by changing an electronic calibration factor associated with the PDM that defines the volumetric value of a pulse train generated by a rotary encoder attached to a rotating shaft within the PDM representative of the displacement volume. This pulse train is received by an electronic control system within the fuel dispenser electronics and is converted into a volumetric value representing the volume dispensed by the PDM. Periodic calibration provides a periodic adjustment of the electronic calibration factor for the given PDM. 
         [0008]    This required periodic calibration is performed within conventional fuel dispensing systems manually, which adds an additional maintenance expense to each conventional fuel dispenser produced. This additional maintenance expense is incurred throughout the life of the dispenser. These maintenance fees associated with periodic calibration can be significant over time. Accordingly, calibration schedules are typically selected in order to balance the lost profits that result from drift with the expense of calibrating a fuel dispenser. Additionally, conventional fuel dispenser operators pay the maintenance fees and have become accustomed to considering them as a cost of doing business. 
         [0009]      FIG. 1  illustrates an exemplary characteristic curve for a typical PDM. The horizontal axis represents a flow rate in gallons per minute (GPM), and the vertical axis represents percent error in the metered fuel transaction. The data represented by the characteristic curve correlates the percent error with various flow rates within the PDM. As such, the characteristic curve quantifies the percent error for a given PDM over the flow rate range of operation for the PDM. The percent error may then be used to adjust metered quantities for the PDM based upon the flow rate measured throughout a fuel dispenser transaction. 
         [0010]    The electronic calibration factor for any given volume of fuel flow may be obtained from the characteristic curve. As can be seen from  FIG. 1 , the characteristic curve represented within the flow range illustrated is relatively flat. A term known as “spread” characterizes the variance of a meter error percentage across flow rates for a meter. The spread for a given meter may be relatively flat or may be dynamic over an operating range for the given meter. The characteristic represented within  FIG. 1  may be considered a “flat spread” for purposes of the description herein. PDMs generally have a flat spread. 
         [0011]    As described above, the displacement within the cylinder of a PDM increases over time due to wear within the cylinder and is known as drift. This increase will typically result in a constant and positive change over the entire range of operation for the PDM, thereby maintaining the relatively flat spread for the PDM over time. Accordingly, periodic adjustments to the characteristic curve are required in order to correct the PDM output. As a result, a calibration operation typically adjusts the characteristic curve for the PDM upward to account for drift within the PDM. 
         [0012]    Several factors can affect the fluid that flows through a PDM. These factors include pressure pulsations, flow fluctuations, rapid temperature swings in the metered fluid, rapid viscosity and density changes within the metered fluid, the presence of events that disturb the flow profile of the fluid such as water hammer effects associated with multiple nozzle snaps by a customer, and other related factors. A properly calibrated PDM can typically meter fuel under these conditions. However, a PDM may not be able to detect issues that would require stoppage of the fuel dispenser. For example, a proportional valve problem may not be detectable by use of a PDM. 
         [0013]    Accordingly, there exists a need to provide automated calibration of a fuel flow meter in a fuel dispenser to automatically adjust for meter drift that may occur from time to time. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention places a reference meter in the flow path of a fuel flow meter within a fuel dispenser to automatically calibrate the fuel flow meter. The fuel flow meter is used to accurately measure fuel flow delivered to a vehicle and charged to a customer. However, the fuel flow meter may be subject to meter drift requiring periodic calibration. The reference meter is a meter that does not typically experience meter drift and, if experienced, would be less than a typical fuel flow meter. As the fuel flow meter drifts, a control system associated with the fuel dispenser detects the drift by comparing fuel flow measurements taken from the fuel flow meter and the reference meter when fueling conditions are in a stable state, meaning the reference meter measurements are highly accurate. The control system uses the reference meter measurements either in real-time or at a later time to calibrate the fuel flow meter in an automated fashion by adjusting a calibration factor associated with the fuel flow meter. The calibration factor may be an electronic factor that is stored in the fuel flow meter or in an electronic control system that converts measurements from the fuel flow meter to volume. 
         [0015]    By use of the present invention, calibration may be performed more often than in conventional systems and may be performed automatically without manual intervention. Accordingly, lost profits and maintenance expenses may be reduced. 
         [0016]    In one exemplary embodiment, a reference meter is placed in the fuel flow path where fuel flow converges from three fuel flow meters that independently meter three different grades of fuel within a fuel dispenser. As a selected grade of fuel is dispensed, fuel flows through the fuel flow meter associated with the selected grade of fuel and flows through the reference meter in route to the dispenser hose and the customer&#39;s vehicle. A control system detects periods of stable fuel flow and takes measurements from the reference meter and the fuel flow meter. The measurements may be saved to memory to form historical metering data for the meters. The control system may compare either the real-time measurements or the historical metering data for the reference meter and the fuel flow meter to determine whether a difference exists that indicates drift has occurred in the fuel flow meter. Upon determining that drift in the fuel flow meter associated with the selected grade has occurred, the control system uses the measurements taken from the reference meter to automatically calibrate the fuel flow meter. 
         [0017]    In another exemplary embodiment, a reference meter is placed in the fuel flow path where fuel flow converges from two fuel flow meters that independently meter two different pure grades of fuel within a blending fuel dispenser. Blending fuel dispensers dispense both high-octane fuel and low-octane fuel during blending transactions and dispense pure high- or low-octane fuel during the respective pure fuel transactions. In this exemplary embodiment, blended transactions may be ignored for calibration purposes. Transactions that involve pure grades of fuel provide metering data that can be used for calibration purposes because fuel that flows through the respective fuel flow meter also flows through the reference meter without being diluted by the other pure blend. Automated calibration of the fuel flow meters can be performed based upon measurements taken during pure fuel dispenser transactions as described above and in more detail below. The present invention is not limited to positive displacement meter types. 
         [0018]    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 
         [0019]    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. 
           [0020]      FIG. 1  illustrates an exemplary characteristic curve of a positive displacement fuel flow meter according to an embodiment of the present invention; 
           [0021]      FIG. 2  illustrates an exemplary fuel dispenser capable of automated calibration of a fuel flow meter using a reference meter according to an embodiment of the present invention; 
           [0022]      FIG. 3  is a block diagram illustrating more detail of a control system for a fuel dispenser capable of automated calibration of a fuel flow meter according to the embodiment of the present invention illustrated in  FIG. 2 ; 
           [0023]      FIG. 4  is a flow chart illustrating an exemplary process for a fuel dispenser transaction providing for the storage of fuel flow measurement information that may be used during an automated calibration operation of the fuel flow meter according to the present invention; 
           [0024]      FIG. 5  is a flow chart illustrating an exemplary process for automated calibration of a fuel flow meter based on stored fuel flow measurements according to an embodiment of the present invention; and 
           [0025]      FIG. 6  illustrates an exemplary blending fuel dispenser capable of automated calibration of a fuel flow meter using a reference meter according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]    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. 
         [0027]    The present invention places a reference meter in the flow path of a fuel flow meter within a fuel dispenser to automatically calibrate the fuel flow meter. The fuel flow meter is used to accurately measure fuel flow delivered to a vehicle and charged to a customer. However, the fuel flow meter may be subject to meter drift requiring periodic calibration. The reference meter is a meter that does not typically experience meter drift and, if experienced, would be less than a typical fuel flow meter. As the fuel flow meter drifts, a control system associated with the fuel dispenser detects the drift by comparing fuel flow measurements taken from the fuel flow meter and the reference meter when fueling conditions are in a stable state, meaning the reference meter measurements are highly accurate. The control system uses the reference meter measurements either in real-time or at a later time to calibrate the fuel flow meter in an automated fashion by adjusting a calibration factor associated with the fuel flow meter. The calibration factor may be an electronic factor that is stored in the fuel flow meter or in an electronic control system that converts measurements from the fuel flow meter to volume. 
         [0028]    Before discussing the particular aspects of how the reference meter obtains fuel flow measurements to perform automated calibration of the fuel flow meter, the basic components of an exemplary fuel dispenser and its control system employing fuel flow meters and a reference meter are first described with respect to  FIGS. 2 and 3  herein. 
         [0029]      FIG. 2  illustrates an exemplary embodiment of a fuel dispenser  10  capable of automated calibration of a positive displacement meter (PDM) according to an embodiment of the invention described herein. The fuel dispenser  10  includes a housing  12  with two sides  14 . The fuel dispenser  10  has a base  16  and a top  18 , with a canopy  20  supported by two side panels  22 . 
         [0030]    The fuel dispenser  10  is subdivided into multiple compartments. A hydraulic area  24  may be used to enclose hydraulic components and an electronic area  26  may be used to enclose electronic components. A vapor barrier (not shown) may be used to separate hydraulic area  24  from electronic area  26 . 
         [0031]    Several components used to control fuel flow may be housed within hydraulic area  24 . Fuel from the underground storage tanks (USTs-not shown) is pumped through a piping network into inlet or fuel dispensing pipes. An inlet pipe  28  provides a piping network from a low-octane UST (UST L ), an inlet pipe  30  provides a piping network from a medium-octane UST (UST M ), and an inlet pipe  32  provides a piping network from a high-octane UST (UST H ). 
         [0032]    A flow control valve  34  controls fuel flow from the UST L , while a flow control valve  36  and a flow control valve  38 , control fuel flow from the UST M  and the UST H , respectively. Fuel may begin to flow from the respective UST when any of the flow control valves  34 ,  36 , or  38  is opened. The flow control valves  34 ,  36 , or  38  are controlled by a control system  76 , as will be described in more detail below. 
         [0033]    When the flow control valve  34  is opened by control system  76 , fuel begins to travel through a PDM M L    40 , which is responsive to flow rate or volume. A pulser  42  may be employed to generate a signal in response to fuel movement through meter M L    40 . Similarly, when either the flow control valve  36  or  38  is opened by control system  76 , fuel begins to travel through either a PDM M M    44  or a PDM M H    48 , respectively. Meter M M    44  has a pulser  46  and meter M H    48  has a pulser  50 , each of which may also be employed to generate a signal in response to fuel movement through the respective meter  40 ,  44 ,  48 . 
         [0034]    Fuel flow from the PDMs  40 ,  44 ,  48  typically converges within a manifold  52 . The manifold  52  routes fuel flow through a reference meter (RM)  54  with an associated pulser  56 . As described above, RM  54  does not typically experience meter drift. Accordingly, measurements taken from RM  54  may be used by control system  76  to automatically calibrate the PDMs  40 ,  44 ,  48 . Because the RM  54  is known to be highly accurate, a comparison of the fuel flow measurements between the RM  54  and the PDMs  40 ,  44 ,  48  will indicate whether the PDMs  40 ,  44 ,  48  have drifted. In such a case, the fuel flow measurement from the RM  54  is taken to be the correct fuel flow measurement and is used to automatically calibrate the PDMs  40 ,  44 ,  48 . More information on the process of collecting fuel flow measurement data and automatically calibrating fuel flow meters, such as the PDMs  40 ,  44 ,  48  using the RM  54  will be described in more detail below, starting with  FIG. 4 . 
         [0035]    The RM  54  may be a higher-cost PDM, an inferential meter, or any type of meter that is capable of accurately measuring fuel flow and is either less prone or not prone to meter drift. For example, the inferential meter may be a single turbine or dual turbine rotor inferential meter like that described in U.S. Pat. No. 5,689,071, incorporated herein by reference in its entirety. In either case, the RM  54  may be used to provide calibrated measurement results and may not be susceptible to drift and other conditions associated with typical PDMs as described above. The RM  54  may provide calibration capabilities to the fuel dispenser  10  by performing data gathering associated with fuel flow through the PDMs  40 ,  44 ,  48  to provide data reference measurements. Details specific to use of an inferential meter as a reference meter and of the remaining elements of  FIG. 2  will be described after the following high-level description of fuel flow measurement within a fuel dispenser, such as fuel dispenser  10 . However, more description of the fuel dispenser  10  and its control system are further described below with respect to  FIGS. 2 and 3 . 
         [0036]    The fuel to be delivered may flow from RM  54  via an outlet pipe  58  during a fuel dispensing transaction. A data line  64  provides a signaling path from pulser  42  to the control system  76 . Data line  64  may provide signals to the control system  76  indicative of the flow rate or volume of fuel being dispensed within meter M L    40 . A data line  66  likewise provides a signaling path from pulser  46  to control system  76 . Similarly, a data line  68  and a data line  70  provide signaling paths from pulsers  50  and  56 , respectively, to control system  76 . 
         [0037]    As fuel is dispensed from the fuel dispenser  10 , the control system  76  receives signaling from pulsers associated with the meters described above that are involved with the dispensing transaction. In response to receipt of signaling from the pulsers  42 ,  46 ,  50 , the control system  76  may provide transaction-level and calibration control functionality within the fuel dispenser  10 . The control system  76  collects meter flow measurements, performs calibration operations associated with PDMs M L    40 , M M    44 , and M H    48 , and performs calculations such as cost associated with a fuel dispensing transaction. 
         [0038]    Additionally, the control system  76  may provide external communication capabilities for the fuel dispenser  10  via an interface  78  to a remote terminal  80 . The remote terminal  80  may be used to collect information from multiple fuel dispensers, such as fuel dispenser  10 . The remote terminal  80  may also be used for status information reporting associated with calibration activities and meter problems. 
         [0039]    As a dispensing transaction progresses, fuel is then delivered from the outlet pipe  58  to a hose  82  and through a nozzle  84  into the customer&#39;s vehicle (not shown). The fuel dispenser  10  includes a nozzle boot  86 , which may be used to hold and retain the nozzle  84  when not in use. The nozzle boot  86  may include a mechanical or electronic switch (not shown) to indicate when the nozzle  84  has been removed for a fuel dispensing request and when the nozzle  84  has been replaced, signifying the end of a fueling transaction. A control line  88  provides a signaling path from the electronic switch to the control system  76 . The control system  76  uses signaling received via the control line  88  in order to make a determination as to when a fueling transaction has been initiated or completed. 
         [0040]    The fuel dispenser  10  also includes a user interface  90  to allow a user/customer to interact with and control a dispenser transaction at the fuel dispenser  10 . The user interface  90  includes a variety of input and output devices and also includes a transaction price total display  92  that may be used to present the customer with the price to be charged to the customer for fuel. The user interface  90  also includes a transaction gallon total display  94  that may be used to present the customer with the measurement of fuel dispensed in units of gallons or liters as a volume of fuel dispensed from the fuel dispenser  10 . 
         [0041]    The fuel dispenser  10  illustrated in  FIG. 2  is a multi-product dispenser that is capable of dispensing different grades of fuel. The price-per-unit (PPU) for each grade of fuel is displayed on displays  96 . Octane selection buttons  98  are provided for the customer to select which grade of fuel is to be dispensed before dispensing is initiated. 
         [0042]    The user interface  90  may also include a large display screen  100  that may be used to provide instructions, prompts, and/or advertising or other information to the customer. Customer selections may be made in response to prompts on the display screen  100  by use of soft keys  102  or keys on a keypad  104 . The soft keys  102  may be designed to align proximate prompts for the customer to indicate his or her desired choice in response to a question or request. The fuel dispenser  10  may also include a card reader  106  that is adapted to receive a magnetic stripe card, such as a credit or debit card, for payment of fuel dispensed. The fuel dispenser  10  may further include other payment or transactional type devices to receive payment information for transaction processing associated with fueling transactions such as a pre-paid dispenser transaction, including a bill acceptor  108 , an optical reader  110 , a smart card reader  112 , and a biometric reader  114 . The fuel dispenser  10  includes a receipt printer  116  so that a receipt with a recording of the dispensing transaction carried out at the fuel dispenser  10  may be generated and presented to the customer. 
         [0043]    As previously described, the control system  76  may be used to collect metering measurements from the pulsers  42 ,  46 ,  50  associated with the meters  40 ,  44 ,  48  within fuel dispenser  10  and for communication purposes with the remote terminal  80  via use of the interface  78 . The control system  76  also controls the user interface  90  during fuel dispensing transactions. 
         [0044]    It should be noted that multiple reference meters may be used within the fuel dispenser  10  without departing from the scope of the subject matter described herein. Accordingly, a reference meter may be placed at a location associated with each PDM  40 ,  44 ,  48 . However, because only one grade of fuel is dispensed during any transaction within a non-blended dispenser, a single reference meter may provide the most cost-effective calibration capabilities for the fuel dispenser  10 . 
         [0045]    For the case of a blended fuel dispenser, as with non-blended dispensers, either multiple or single reference meters may be used. However, in the case of a single reference meter, statistical sampling of calibration-related data may be performed when a pure product (e.g., low-octane or high-octane) is dispensed rather than during blended transactions. 
         [0046]      FIG. 3  illustrates the control system  76  in more detail for purposes of describing portions of the control system  76  associated with the control of components within the fuel dispenser  10  during a fueling transaction and during an automated calibration of a PDM within the fuel dispenser  10  according to an embodiment of the subject matter described herein. 
         [0047]    The transaction price total display  92  and the transaction gallon total display  94  are illustrated within  FIG. 4  for purposes of illustrating exemplary connectivity with components within the user interface  90  (not shown in  FIG. 4 ). For purposes of illustration, other components within the user interface  90  are not illustrated within  FIG. 4 . Likewise, the interface  78  is illustrated with a reference to the remote terminal  80  in order to provide exemplary connectivity for signaling purposes at the interface  78 . 
         [0048]    Fuel flows from UST L , UST M , and UST H  are illustrated within  FIG. 4  by the use of dashed lines and arrows entering the flow control valves  34 ,  36 , and  38 , respectively. Dashed lines further represent fuel flow from the flow control valves  34 ,  36 ,  38  through the PDMs M L    40 , M M    44 , and M H    48  of the fuel dispenser  10 . As can be seen from  FIG. 3 , as fuel flows through any of the PDMs  40 ,  44 ,  48  within the fuel dispenser  10 , the flow continues through the RM  54  and then to the hose  82 , ultimately to be deposited in the customer&#39;s vehicle. 
         [0049]      FIG. 3  includes three control lines not illustrated in  FIG. 2 . A control line  118  provides a signaling path from the control system  76  to the flow control valve  34 . The control line  118  may be used by the control system  76  to control the opening and closing of the flow control valve  34 . Accordingly, when a fueling transaction is initiated by a customer that includes fuel from the UST L , the control system  76  opens the flow control valve  34  to allow fuel to flow from the UST L  through PDM M L    40  and RM  54  toward the hose  82 . As fuel begins to flow, pulsers  42  and  56  will begin to generate signals indicative of fuel flow within the respective meters. This signaling may be provided to the control system  76  via data lines  64  and  70 , respectively. The control system  76  may then perform transactional activities, such as updating the transaction price total display  92  and the transaction gallon total display  94 . Further, when stable fuel flow is detected within RM  54 , the control system  76  may also perform calibration-related activities, as will be described in more detail below. 
         [0050]    Similar to the description above for the control line  118 , a control line  120  and a control line  122  provide signaling paths for control of flow control valves  36  and  38 , respectively. The description of activities associated with the control system  76  in relation to control line  118  applies to control line  120  and control line  122 . For example, when a fueling transaction is initiated by a customer that includes fuel from the UST M , the control system  76  opens the flow control valve  36  by use of signaling on the control line  120  to allow fuel to flow from UST M  through the PDM M M    44  and RM  54  toward the hose  82 . Pulsers  46  and  56  may be used to capture fuel flow measurements within the PDM M M    44  and RM  54 , respectively. Likewise, when a dispenser transaction is initiated by a customer that includes fuel from the UST H , the control system  76  opens the flow control valve  38  by use of signaling on the control line  122  to allow fuel to flow from the UST H  through the PDM M H    48  and RM  54  toward the hose  82 . Pulsers  50  and  56  may be used to capture fuel flow measurements within the PDM M H    48  and RM  54 , respectively. 
         [0051]    In addition to information related to fuel flow, such as flow rate and volume, temperature, viscosity, and other information may also be tracked within the fuel dispenser  10 . A memory  124  may be used by the control system  76  to store collected data for purposes of detecting drift, problems within the PDMs  40 ,  44 ,  48 , and in order to determine or predict when a PDM has gone or will go out of calibration tolerances. The memory  124  may be any volatile or non-volatile storage medium, or may be a combination of the two. The memory  124  may further include disk-based, optical, or any other storage medium suitable for a given application and may be used to store the fuel flow measurement information captured and described in relation to  FIG. 4  below. 
         [0052]    Turning to  FIG. 4 , an exemplary process for a fuel dispenser transaction capable of storing fuel flow measurement information for use during an automated calibration operation within a fuel dispenser is illustrated. Before the RM  54  can be used to calibrate the PDMs  40 ,  44 ,  48  in an automated fashion, measurements of the RM  54  must be obtained by the control system  76  and compared to the fuel flow measurements of the PDMs  40 ,  44 ,  48 . Note that the processes described below are performed by the control system  76  in an exemplary embodiment of the present invention, but may be performed by any control system. 
         [0053]    As illustrated in  FIG. 4 , the process starts (step  400 ), and the control system  76  may wait for a dispenser transaction to be initiated by a customer (decision  402 ). When a dispenser transaction is initiated, the control system  76  begins measurement operations. Next, the control system  76  samples measurement data for a positive displacement meter associated with the selected fuel grade (step  404 ). For example, the control system  76  may sample data associated with meter M L    40 . The control system  76  samples data associated with a reference meter, such as the RM  54  (step  406 ). The price and gallons associated with the current metered volume may be based upon the sampled measurement data for the PDM associated with the selected fuel grade (step  408 ). 
         [0054]    Next, a determination is made as to whether the flow rate is within range and stable (decision  410 ). This determination may be made by using fuel flow metering information derived from signaling provided by a reference meter, such as the RM  54 . As will be described in more detail below, costs may be decreased for an implementation of the automated calibration capabilities described herein by selecting an inferential meter for use in a flow range smaller than the entire range of operation for the fuel dispenser  10 . Accordingly, there may be a desired range within which to collect data for calibration purposes. As such, a determination is made as to when the flow range is within the desired range and stable for the chosen reference meter. 
         [0055]    Several factors can affect fluid flow stability. These factors include, for example, a presence of numerous nozzle snaps, water hammer effects, and other fluid dynamic activity within the fuel dispenser  10 . An inferential reference meter may be used to detect these conditions and may accordingly be used to determine when the fuel flow is stable. 
         [0056]    When a determination has been made that the flow rate is within range and stable, the control system  76  stores the fuel flow measurement information that may be used for calibration purposes at block  412 . The fuel flow measurement information that may be stored for both meters includes, for example, information such as flow rate, volume, temperature, and viscosity of the fuel. As will be described in more detail below, the fuel flow measurement information may be stored for multiple samples to provide statistical capabilities within a calibration operation. 
         [0057]    Additionally, when the fuel flow measurement information for multiple flow rate ranges is being stored, the fuel flow measurement information may be marked relative to the current flow rate range for the sampled information. Further, if multiple flow rate ranges are to be monitored, the control system  76  may make a determination as to which of the multiple flow rate ranges the metered fluid is currently in and may store fuel flow measurement information associated with that flow range. 
         [0058]    Upon storage of the fuel flow measurement information (step  412 ), or when the flow rate is not within range and stable (decision  410 ), the control system  76  determines whether the dispenser transaction is complete (decision  414 ). When a determination is made that the dispenser transaction is not complete, the control system  76  may return to capture new fuel flow measurement data (step  404 ). When a determination is made that the dispenser transaction is complete, the control system  76  may return to await a new dispenser transaction (step  402 ). 
         [0059]    Once the control system  76  has collected fuel flow measurement information from the meters  40 ,  44 ,  48 , the control system  76  can perform the automated calibration of the PDMs  40 ,  44 ,  48 . The calibration may be performed in real-time as the fuel flow measurement information is gathered, or may be performed later in time after fuel flow measurement information is gathered and stored as described in the process in  FIG. 4  above. 
         [0060]      FIG. 5  illustrates an exemplary process for automated calibration of the PDMs  40 ,  44 ,  48  within the fuel dispenser  10  after fuel flow measurement information is gathered and stored. Again, the process is performed by either the control system  76  or other control system. The process described in  FIG. 5  may be performed in conjunction with the process of  FIG. 4  or may be a separate process. The process starts (step  500 ), and the control system  76  process may wait for a calibration operation to be initiated (step  502 ). A calibration operation may be initiated in a variety of ways. For example, a calibration operation may be initiated in a scheduled fashion. Scheduling of calibration operations may be performed at the fuel dispenser  10  in response to scheduled events that are initiated by use of configuration parameters designating calibration scheduling that may be set at installation time or at a later time. Configuration parameters may be set via the remote terminal  80  and the remote terminal  80  may also request calibration operations to be performed at the fuel dispenser  10 . The remote terminal  80  may also query (not shown) the fuel dispenser  10  in order to retrieve historical metering data from the fuel dispenser  10  associated with the RM  54  and any or all of the PDMs  40 ,  44 ,  48 . Accordingly, in addition to an initiation by the fuel dispenser  10 , the remote terminal  80  may initiate a calibration operation by triggering a scheduling event at the fuel dispenser  10 . Further, the remote terminal  80  may monitor, query, and request calibration for multiple fuel dispensers, such as the fuel dispenser  10 , at a single retail site or may monitor, query, and request calibration for multiple fuel dispensers at multiple sites without departure from the scope of the subject matter described herein. 
         [0061]    Scheduled calibration times may be selected such that the times selected for calibration operations are less likely to result in a calibration operation during a fueling transaction. A calibration operation may also occur either periodically or in response to a detection of drift or some other change in the stored data for the meters that suggests that a calibration operation may be beneficial. Additionally, a calibration operation may be initiated via a request received at the interface  78  from the remote terminal  80 , either initiated by an external process or a network operator. 
         [0062]    As a further example, the process of  FIG. 5  could be initiated in response to the storage of the flow rate, volume, temperature, and viscosity for both meters within  FIG. 4  at step  412 . In such a case, a status flag or other indicator could be queried to determine whether a calibration operation should be performed based upon any of the indicia described above (decision  502 ) and, when a calibration operation is not to be initiated, the process of  FIG. 4  may continue uninterrupted to determine whether the fueling transaction has completed (decision  414 ). 
         [0063]    When a determination has been made that a calibration operation is to be performed (decision  502 ), the process retrieves historical metering data in the form of data samples that have been stored for the RM  54  and for the PDM  40 ,  44 ,  48  to be calibrated (step  504 ). The process compares the historical metering data for the meters at block  506 . This comparison may include data samples taken since the last calibration or may include data samples taken prior to the last calibration. Further, the comparison may include comparison of data samples taken across the entirety of the stored data. 
         [0064]    This comparison may further take the form of any statistical tool available for performing analysis on a data set in order to either determine historical trends in the data analyzed or to predict future trends. For example, variance or standard deviation calculations, time averages, and linear regressions may be performed in order to determine changes in the data stored. Additionally, predictive algorithms, like Kalman filters and various other statistical predictive tools for example, may be used to predict, when drift in the PDMs  40 ,  44 ,  48  will be beyond calibration tolerances. By use of a statistical predictive tool, a determination may be made of when the PDMs  40 ,  44 ,  48  should be replaced and a report may be generated indicating that the fuel flow meter should be scheduled for replacement. Alternatively, a repair report indicating that the PDM  40 ,  44 ,  48  needs to be serviced may be issued in order to allow maintenance or replacement of an aging PDM prior to a terminal condition within the PDM  40 ,  44 ,  48 . Reports may be issued from control system  76  to a system operator associated with the remote terminal  80  via the interface  78 . 
         [0065]    Next, a determination is made based upon the chosen statistical tool and historical period over which the comparison was performed as to whether a variation has been detected across the stored data (decision  508 ). When a variation is not detected, the process may return to decision  502  to await a new calibration request. When a variation is detected, the process may make a determination as to whether the variation constitutes drift (decision  510 ). 
         [0066]    When a determination has been made that the variation is not drift, the control system  76  makes a determination as to whether the variation is beyond a threshold variation suitable for continued operation within the fuel dispenser  10  (step  512 ). When a determination has been made that the variation is not beyond a suitable threshold variation and that the variation is a variation other than drift, the process may log the variation by storing a log entry including the resulting statistical analysis (step  514 ). This stored log entry may then become a factor used in future comparisons (step  506 ). In this way, the historical data set used to determine the extent of variations over time may be augmented and enhanced with each log entry. Upon entry of the variation log, the process may return to decision point  502  in order to await a new calibration request. 
         [0067]    When a determination has been made that the variation is beyond a suitable threshold variation, the process shuts the PDM  40 ,  44 ,  48  down and issues a report indicating that a variation that is beyond the suitable threshold has occurred (step  516 ). As with other reporting and interface situations described above, the control system  76  may use the interface  78  to communicate with the remote terminal  80  in order to issue such a report. The control system  76  may further set a flag or create another indication, for example within the memory  124 , to indicate that the affected PDM  40 ,  44 ,  48  may not be used for dispensing fuel until a repair operation has been performed. Upon performance of the repair operation, the flag may be cleared and the fuel grade may then again be dispensed by the fuel dispenser  10 . When the shutdown operation and the report and flag generation are completed, the process may return to decision  502  to await another calibration request. It should be noted that no fuel will be dispensed from a meter that is shutdown. Accordingly, the control system  76  may use the previously created flag in order to avoid calibration requests for a meter that has been shutdown. Any requests that may be generated by an external process, such as a process operating at the remote terminal  80 , may be responded to with an indication that the PDM  40 ,  44 ,  48  is not currently operational. 
         [0068]    When a determination is made at decision point  510  that the variation detected at decision  508  is drift, the process initiates calibration of the PDM  40 ,  44 ,  48 . The process makes a determination as to whether there is an on-going dispenser transaction in progress (decision  518 ). When there is an on-going dispenser transaction in progress, the process may wait until the transaction is completed. When the transaction is completed, the process calibrates the PDM  40 ,  44 ,  48  by adjusting the calibration values for the PDM  40 ,  44 ,  48  (step  520 ). Adjusting these calibration values may include changing an electronic calibration factor associated with the PDM  40 ,  44 ,  48  that defines the volumetric value of a pulse train generated by a rotary encoder attached to a rotating shaft within the PDM  40 ,  44 ,  48 . As with other data, the calibration values for the PDMs  40 ,  44 ,  48  associated with the fuel dispenser  10  may be stored within the memory  124 . Upon calibration of the PDM  40 ,  44 ,  48 , the process may return to decision  502  to await another calibration request. 
         [0069]    The above-described invention may also be used in conjunction with other type of dispensers, such as blending fuel dispensers for example.  FIG. 6  illustrates an exemplary blending fuel dispenser capable of automated calibration of a PDM according to an embodiment of the present invention. A blended dispenser typically has all of the capabilities of a non-blended dispenser. Accordingly, the fuel dispenser  10  is redrawn within  FIG. 6  to illustrate a blended dispenser embodiment. As can be seen by comparison of  FIG. 2  with  FIG. 6 , there is no reference to an underground storage tank for medium-grade fuel. Additionally, certain components of the fuel dispenser  10  are not present within  FIG. 6 . The inlet pipe  30 , the flow control valve  36 , the PDM M M    44 , and the pulser  46  are not present within the blended dispenser embodiment of the fuel dispenser  10  illustrated in  FIG. 6 . As described above, a blended embodiment of a fuel dispenser, such as the fuel dispenser  10 , may perform according to the description herein and may use either multiple meters or may use a single reference as illustrated. However, in the case of a single reference meter, statistical sampling of calibration-related data may be performed when a pure product (e.g., low-octane or high-octane) is dispensed rather than during blended transactions. Accordingly, the control system  76  may determine when a pure product is being dispensed and the process of  FIG. 4  may be modified to operate when a pure product is being dispensed. 
         [0070]    Returning to the previous description regarding use of an inferential meter as a reference meter as the RM  54 , certain benefits related to inferential meters may be advantageously utilized to provide calibration capabilities for the fuel dispenser  10 . For example, inferential meters do not require calibration. Accordingly, the fuel dispenser  10  may continually provide calibration capabilities for the PDM  40 ,  44 ,  48  associated with it. Statistical determinations may be used to determine whether the accuracy of a PDM is changing over time. For example, sampling over a number of dispensing transactions may be performed to determine if drift has occurred in association with the relevant PDM  40 ,  44 ,  48 . When drift is detected, the calibration factor for the PDM  40 ,  44 ,  48  may be adjusted in accordance with the change in accuracy to correct for the drift within the PDM  40 ,  44 ,  48 . This statistical analysis may be applied during different flow rates to correct the spread of the meter or may be applied during specific flow rate windows when the PDM  40 ,  44 ,  48  is known to have a relatively flat spread. In the latter case, the RM  54  would not be required to operate over wide flow rate ranges and may accordingly result in a less costly reference meter being suitable for use. Exemplary ranges for operation of the RM  54  may include two to five (2-5) gallons per minute (GPM), four to seven (4-7) GPM, two to ten (2-10) GPM, and any other range of operation that provides an overlapping range with the PDMs  40 ,  44 ,  48  and includes typical operating flow rates for the fuel dispenser  10 . 
         [0071]    Additionally, an inferential meter may be used to sense stability of the fluid flow through it. For example, pressure pulsations, flow fluctuations, rapid temperature swings in the metered fluid, rapid viscosity and density changes within the metered fluid, the presence of events that disturb the flow profile of the fluid such as water hammer effects associated with multiple nozzle snaps by a customer, and other related factors may all be detected by use of an inferential meter. Further, by use of an inferential meter, other problems such as a proportional valve problem may be detectable. 
         [0072]    Because an inferential meter may be used to detect these characteristics within the fluid flowing through the meter, an inferential meter may also be used to determine when fuel flow through the inferential meter is stable. By sampling the flow characteristics within a reference meter, such as an inferential meter, for a period of time, fluid flow within both the reference meter and an active PDM may be determined to be stable for a time period sufficient to ensure that the flow is stable in both meters. The time required may vary depending upon the number of customers conducting fueling operations as well as the number of times that a customer snaps the nozzle during a fueling transaction. Flow rate stability may occur and be usable for calibration data acquisition in the range of milliseconds (e.g., three milliseconds) and up to time durations of more than a minute. Night-time dispenser transactions may occur when fewer customers are purchasing fuel. Accordingly, night-time transactions may result in longer stable periods for use during calibration data gathering phases. 
         [0073]    It is during these detectable stable periods that data acquisition may be performed in order to provide calibration data for the PDMs  40 ,  44 ,  48 . By concurrently capturing data from both the reference meter and the active PDM  40 ,  44 ,  48 , metering data captured from the RM  54  may be used to provide an accurate reference measurement with which to compare the metering data captured from the active PDM  40 ,  44 ,  48 . 
         [0074]    In order to provide calibration capabilities, the RM  54  may be a fully-calibrated meter from the factory or may be calibrated initially on-site during installation. When the RM  54  is a fully-calibrated meter from the factory, it may be used to perform initial calibration of the PDMs  40 ,  44 ,  48  within the fuel dispenser  10  during the first several dispensing transactions performed. Accordingly, initial savings may be achieved by eliminating the initial costly calibration expenses associated with site start-ups. As an alternative, an initial on-site calibration may be performed, as is currently done with site start-ups. In this case, factory calibration costs associated with the RM  54  could be eliminated. Either alternative provides long-term calibration cost savings because the RM  54  may be used to perform the periodic calibration of the PDMs  40 ,  44 ,  48  within the fuel dispenser  10 , as will be described in more detail below. 
         [0075]    In addition to providing calibration capabilities within the fuel dispenser  10 , the RM  54  may also provide maintenance and fraud detection. For example, if flow is registered within the RM  54  and no flow is registered within the active PDM  40 ,  44 ,  48 , an error condition could be generated. This error condition could indicate either required maintenance or fraud. Further, fraud may be more difficult to perpetrate because a perpetrator would be required to defeat two meters instead of just one. Additionally, if large differences in flow rate are detected between the RM  54  and the active PDM  40 ,  44 ,  48 , a hydraulic defect within the PDM  40 ,  44 ,  48  or fraudulent behavior such as a change in the calibration data for the PDM  40 ,  44 ,  48  may be detected. Wear within the active PDM  40 ,  44 ,  48  beyond acceptable calibration limits may also be detected by the RM  54 . In the event that a PDM has experienced wear beyond calibration limits, a notification message may be generated to indicate that the PDM needs to be replaced. As described above, once the PDM is replaced, it may be calibrated by the RM  54  without a need for manual calibration activities. 
         [0076]    As an additional consideration, retrofitting of existing fuel dispensers is possible. A reference meter may be placed within a fuel dispenser and appropriate fuel plumbing and circuitry may be changed in order to accommodate the reference meter. 
         [0077]    The subject matter described herein for using a reference meter to provide automated calibration for a fuel dispenser may be implemented in hardware, software, firmware, or any combination thereof. In one embodiment, the subject matter described herein can be implemented as a computer program product including computer-executable instructions embodied in a computer-readable medium. Exemplary computer-readable media suitable for implementing the subject matter described herein includes chip memory devices, disk memory devices, programmable logic devices, application-specific integrated circuits, and downloadable electrical signals. In addition, a computer program product that implements the subject matter described herein may be located on the single device or computing platform or may be distributed across multiple devices or computing platforms. 
         [0078]    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.