Abstract:
A method and system for monitoring a level of liquid fuel in a tank having a known capacity, wherein the tank fluidly communicates with a fuel supply line through which the fuel is delivered in gaseous form. The method comprises measuring a flow rate of gaseous fuel flowing through the supply line, calculating an expended fuel volume based on the measured flow rate, and determining a remaining liquid fuel level in the tank based on the expended fuel volume and tank capacity. A delivery of liquid fuel to the tank is prompted in response to the remaining liquid fuel level.

Description:
FIELD OF THE DISCLOSURE  
         [0001]    This disclosure generally relates to fuel delivery systems and, more particularly, to systems for monitoring a remaining fuel level in a fuel supply tank.  
         BACKGROUND OF THE DISCLOSURE  
         [0002]    In certain fuel delivery systems, such as a propane gas system, the consumers are supplied propane gas from a tank of liquefied propane. The tank is typically isolated from any established fuel pipelines, and therefore must be periodically refilled. A float level sensor is used in the propane tank to monitor the liquefied propane level. In such systems, the user periodically views the tank level sensor and then requests delivery of replacement propane as required. While such fuel level sensors which are mounted in the tank can provide a reliable indication of the liquefied propane level remaining in the tank, they are difficult to maintain and time-consuming to repair when needed in view of their placement within the tank itself.  
           [0003]    It is therefore desired to provide a propane tank level monitoring system which can not only sense and display the level liquefied propane in the tank, but which can also provide a signal to a central location to use the information to track gas usage rate and to schedule delivery of replacement fuel as needed. In particular, it is desired to provide an in-line gas flow rate sensor for sensing the gas flow rate from which the level of the propane remaining in the tank can be derived. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the several figures and in which:  
         [0005]    [0005]FIG. 1 is a schematic diagram of a propane gas tank distribution system incorporating an in-line flow rate sensor according to the present invention;  
         [0006]    [0006]FIG. 2 is a schematic diagram illustrating an in-line flow rate sensor according to the present invention including an in-line flow tube;  
         [0007]    [0007]FIG. 3 is a cross sectional view illustrating a gas flow rate sensor in accordance with the present invention;  
         [0008]    [0008]FIG. 4 is a schematic diagram of an alternative gas fuel distribution system; and  
         [0009]    [0009]FIG. 5 is a flow chart illustrating steps for measuring gas fuel flow rate and scheduling delivery of additional gas fuel to the tank. 
     
    
     DETAILED DESCRIPTION  
       [0010]    [0010]FIG. 1 illustrates a propane gas distribution system  10  which includes a tank  12  containing a supply of propane gas. A pressure regulator  14  regulates the gas pressure in a supply conduit  16  which is coupled to an in-line flow rate sensor  18 . The gas flow output of the flow rate sensor  18  is coupled on an outlet conduit  20  to users  21  of the propane gas. The gas flow rate sensor  18  includes a communication link to provide a signal on output line  22  representing the gas flow rate which signal is coupled to a report station  24 . The report station  24  uses the gas flow rate information to determine the level of propane remaining within the propane tank  12  and can then schedule delivery of replacement gas to the tank  12  as needed.  
         [0011]    [0011]FIG. 2 schematically illustrates the in-line gas flow rate sensor  18  in accordance with the present invention which includes a flow tube  26  and an auxiliary housing  28  mounted on the flow tube  26 . A movable magnet  30  is mounted within the flow tube  26  and acted upon by the gas flow from conduit  16  to provide a changing flux density in response to the changing gas flow rate. A magnetic sensor  32 , such as a Hall effect sensor, is mounted in the auxiliary housing  28  and closely adjacent the magnet  30  so as to detect the changing flux density corresponding to the changing gas flow rate. A pressure sensor  34  is mounted in the flow tube to detect the pressure of the gas inlet from inlet conduit  16 . A temperature sensor  36  is mounted in the auxiliary housing  28  to detect the gas temperature. The respective outputs of the magnetic sensor  32 , pressure sensor  34  and temperature sensor  36  are coupled to a communications link  37  for supplying the corresponding information on output line  22  to the report station  24 . With this information the gas flow rate can be obtained using a well known algorithm, such as the Universal Gas Sizing Equation, and the level of gas remaining in the tank  12  also can be readily obtained.  
         [0012]    The details of the schematic view FIG. 2 of the flow rate sensor  18  are shown in the cross sectional view of FIG. 3. As shown in the cross-sectional view of FIG. 3, the flow tube  26  includes an inlet tube  38  and an outlet tube  40  which are threadably joined together by an orifice guide  42 . The inlet tube  38 , the outlet tube  40 , and the orifice guide  42  are all formed of a non-magnetic metal such as brass or aluminum. A flow plate  44  is formed of a plastic material and includes a series of flow holes  46  to evenly distribute the inlet gas flow from inlet conduit  16 . A tapered plug  48  is mounted to the flow plate  44  by a threaded screw  49 .  
         [0013]    A movable orifice member  50  includes a central opening  51  surrounding the tapered plug  48  with an upstream opening  51   a  being smaller than a downstream opening  51   b  so that the central opening  51  is outwardly diverging. As shown in FIG. 3 there is an increasing space between the tapered plug  48  and the central opening  51  in the downstream flow direction.  
         [0014]    A magnet member  52  is mounted to the orifice member  50  with a flexible diaphragm  54  having its inner perimeter inserted therebetween, and with the outer perimeter of the diaphragm mounted between the outlet tube  40  and the orifice guide  42 . The magnet member  52  is slidably mounted within a cavity  56  provided in the outlet tube  40 , so that with changing gas flow rates, the plug holder  50  and attached magnet member  52  slidably move within the cavity  56 . A spring  58  is captured between the outlet tube  40  and the orifice member  50  and has sufficient resiliency to move the upstream opening  51   a  of the orifice member  50  to one end of the plug  48  as shown in FIG. 3 when there is no gas flow. As the gas flow rate is increased, the orifice member  50  and associated magnet member  52  is moved away from the closed position and eventually to a position with respect to the plug  48  representing a maximum gas flow rate position.  
         [0015]    The tapered plug  48  and the outwardly diverging central aperture are shaped so that there is a direct linear relationship provided between the change in the flow orifice (i.e., the space between the tapered plug  48  and the central opening  51 ) and the flow rate change. In other words, with the flow orifice closed as shown in FIG. 3, and going to a fully opened flow orifice position which represents the maximum gas flow rate position, the shape of plug  48  and the shape of the central opening  51  provides a linear relationship between the change in the magnetic flux density created by the movement of magnet  52  and the output from the magnetic sensor  32 . Thus, plug  48  and central opening  51  may be termed an “equal percent plug” which provides an equal percent flow orifice, i.e., with each uniform increment of orifice member  50  there is provided a constant percent of flow change through the flow orifice. Thus, a linear relationship exists between the magnetic flux density and the output of the magnetic sensor  32  in response to a changing flow rate through the flow orifice.  
         [0016]    In a constructed prototype embodiment of the invention the central aperture was formed outwardly diverging at an angle of about 10 degrees, and the tapered plug was formed inwardly converging at an angle of about 6 degrees.  
         [0017]    A mounting port  60  in the inlet tube  38  enables mounting of the pressure sensor  34 . Utilizing the output of the magnetic sensor  32 , as well as the information from the pressure sensor  34  and the temperature sensor  36  enables the gas flow rate to be determined using an algorithm well known in the industry. Once the gas flow rate has been determined, the amount of gas remaining within propane tank  12  can readily be determined, and delivery of any replacement fuel can be scheduled as required.  
         [0018]    With reference to FIG. 4, an alternative fuel supply system  100  is shown having a tank  102  for holding fuel, such as liquefied propane. The tank  102  may be positioned at a remote location or may otherwise be isolated from access to an established fuel pipeline. Consequently, the tank  102  must be periodically refilled with fuel from a distribution center. The tank  102  includes an outlet  104  connected to a supply line  106  for delivering gas fuel to one or more users  108 , and a pressure regulator  110  regulates the gas pressure in the supply line  106 .  
         [0019]    A flow rate sensor, such as flow measurement module  112 , is provided for sensing gas fuel flow and generating an output providing fuel flow information. In the illustrated embodiment, the regulator  110  and flow measurement module  112  are integrated to provide an intelligent pressure regulator, as disclosed in commonly owned U.S. Pat. Nos. 6,178,997 and 6,539,315, the disclosures of which are incorporated herein by reference. In the alternative, the regulator  110  and flow rate sensor may be provided as separate components. The flow measurement module  112  includes a processor  113 , a memory  115 , and a communication link  114  for providing a signal on an output line  116 .  
         [0020]    A report station  118 , which may be positioned remote from the flow measurement module  112  such as at a fuel distribution center, is communicatively coupled to the communication link  114  via the output line  116 . The report station  118  may include a controller  120  having a memory  122 . The report station  118  receives the fuel flow information and schedules delivery of replacement gas to the tank  102  as needed.  
         [0021]    In operation, the propane is stored in the tank  102  as a liquid. The tank may require pressurization to maintain the propane in the liquid state. As the regulator  110  opens, propane exits the tank in gaseous form to travel through the supply line  106 . As the propane gas passes through the supply line  106 , the flow sensor measures process variables that may be used to calculate gas flow rate. Downstream of the regulator  110  and flow sensor, the gas fuel flows through the supply line  106  to the end user  108 .  
         [0022]    [0022]FIG. 5 is a flow chart of a method for monitoring the level of fuel in the tank and scheduling delivery of additional fuel to the tank that may be executed by the fuel distribution system  100 . At block  150 , a tank capacity is stored in memory. Where the flow rate sensor includes a processor and memory, such as with the flow measurement module  112 , the tank capacity may be stored in either the flow measurement module memory  115  or the report station controller memory  122 , or both.  
         [0023]    At block  152 , the rate of gas fuel flow through the supply line  106  is measured. As noted above, the flow rate may be obtained using any known method or device. Where the flow measurement module  112  is used, the flow rate is inferred using a standard flow equation and measured process parameters such as upstream and downstream fluid pressure and throttling element position. Alternatively, the report station controller  120  may be programmed with the flow equation, and the flow measurement module  112  may simply forward the measured parameters to the controller  120 . Based on the measured flow rate, an expended volume of fuel is calculated at block  154 . Again, the expended volume may be calculated by the flow measurement module  112  or by the report station controller  120 .  
         [0024]    At block  156 , the remaining fuel level in the tank is determined. The remaining fuel level may be calculated by subtracting the expended fuel volume from the stored tank capacity. To calculate the remaining fuel level, the expended fuel volume may first be converted from a gas volume to a liquid volume to determine the remaining liquid volume of propane in the tank  102 . Alternatively, the liquid volume capacity may be converted to a gas volume capacity, and the expended fuel volume may be subtracted from the gas volume capacity of the tank  102 .  
         [0025]    Based on the remaining fuel level, a low fuel alarm may be generated at block  158 . The low fuel alarm may be generated when the remaining fuel level corresponds to a user-entered low level limit. Once again, the steps described in block  156  and  158  may be performed by either the report station  118  or the flow sensor. Finally, the report station  118  may schedule a delivery of additional fuel to the tank at block  160 . The new delivery may be scheduled in response to the low fuel alarm, and will typically be prompted by the report station controller  120 .  
         [0026]    It will be appreciated that various devices may be employed as the flow rate sensor, each of which may generate different fuel flow information. The flow rate sensor may simply detect upstream fluid pressure, downstream fluid pressure, and regulator throttling element position. These measured variables may then be forwarded to the report station  118 , which may be programmed to calculate flow rate based on the variables. Alternatively, the flow sensor may sense the process variables and calculate the fuel flow rate, which is then forwarded to the report station  118 . In response, the report station  118  may calculate a total volume of expended gas fuel and a remaining fuel level in the tank. Still further, where the flow rate sensor includes a microprocessor, such as with the flow measurement module  112 , it may execute each of the calculations noted above and forward only the low fuel level alarm to the report station  118 . Alternatively, the flow rate sensor may calculate fuel flow and the expended fuel volume and forward the expended fuel volume to the report station  118 . The report station may include a memory having the tank volume capacity and low fuel level stored thereon, and therefore may calculate the remaining tank volume and generate a low fuel alarm as appropriate.  
         [0027]    In addition to generating flow rate information for determining the remaining fuel level in the tank, the flow sensor may forward additional information to the report station  118  for other diagnostic purposes. For example, the flow sensor may include a memory for storing high and low pressure limits, logic based alarm conditions, or other process control parameters that may indicate faulty system equipment or abnormal operating conditions, such as those disclosed in commonly owned U.S. Pat. No. 6,441,744, which is incorporated herein by reference. The flow measurement module  112  may generate alarms based on these parameters and forward the alarms to the report station  118 , which may respond by scheduling a maintenance visit for the gas fuel system.  
         [0028]    The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications will be obvious to those skilled in the art.