Abstract:
A method and apparatus for measuring the mass of liquid within collapsible, bulk fabric storage containers is provided wherein a number of pressure pads arranged in a grid pattern supports the container and undergo deflection creating an increase in the pressure of fluid within their interior which may be measured and correlated to the mass of the liquid within the container.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 12/608,292 filed Oct. 29, 2009. U.S. application Ser. No. 12/608,292 is expressly incorporated herein by reference in its entirety to form part of the present disclosure. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a method and apparatus for measuring the liquid quantity in bulk containers, and, more particularly, to one or more deflection members arranged in a grid pattern which supports the bulk container and produces a pressure measurement that may be correlated to the mass of liquid within the container. 
       BACKGROUND OF THE INVENTION 
       [0003]    On the battlefield, the armed forces rely heavily on collapsible fabric storage containers for temporary storage of fuel and water. These bulk containers range in size from 3000 gallons to 210,000 gallons, and because they are made of fabric such containers assume different size and shape depending on the amount of liquid in their interior. Bulk fabric tanks of this type pose several technical difficulties in accounting for the volume of fuel and water used by the armed forces, due to problems in accurately measuring volume in a container of variable size and shape. 
         [0004]    The current method for tracking the volume of fuel or water in bulk fabric storage containers is to measure the liquid as the container is filled or emptied using flow meters. One limitation of flow meters is that they are relatively inaccurate. It has been found that volume measurements taken on the contents of existing bulk fabric storage containers by flow meters may vary as much as 6% to 10%, plus or minus, compared to actual volume. This assumes that the flow meters are reset on a daily basis. If the flow meters are not reset, the accuracy is even worse due to cumulative error. 
         [0005]    Another issue with bulk fabric storage containers is that even if current measurement techniques were capable of accurately determining volume levels during filling and/or emptying, the walls of such containers are semi-permeable and liquid can be lost through the walls via diffusion. Losses also occur through the venting system of the container. Consequently, volume measurements depending on flow meters are subject to further inaccuracies as liquid is pumped in or out of the container during use. 
       SUMMARY OF THE INVENTION 
       [0006]    This invention is directed to a method and apparatus for measuring the mass of liquid within collapsible, bulk fabric storage containers wherein a deflection member arranged in a grid pattern undergoes deflection in response to the application of a load creating an increase in the pressure of fluid within its interior which is measured and correlated to the mass of the load. 
         [0007]    In one presently preferred embodiment of this invention, the deflection member comprises at least one flexible line arranged in a grid pattern on which a container is positioned. The flexible line(s) has a hollow interior filled with a fluid, e.g. liquid or gas. The cross sectional area of the flexible line(s) decreases under the application of a load, e.g. as a container thereon is filled with liquid, and this results in an increase in the pressure of the fluid within the line(s). A pressure measurement device, such as a digital pressure gauge, is coupled to the line(s) and produces a measurement of the fluid pressure therein that may be correlated to the mass of the liquid within the container. A temperature sensor may also be coupled to the line(s) of the grid pattern to account for the effects of temperature change of the fluid in the line(s) on the pressure measurement. 
         [0008]    The cross sectional area of the line(s) varies with the mass of the liquid within the container, and the pressure of the fluid within the line(s) changes accordingly. Because the container rests upon the grid pattern formed by the flexible line(s), changes in the size and shape of the container as it is filled and emptied do not affect the accuracy of the pressure measurements taken by the pressure measurement device. 
         [0009]    The at least one flexible line noted above may comprise a single flexible line oriented in a zig-zag or other grid pattern having a dimension to accommodate the size of the container, or, alternatively, a number of flexible lines may be arranged in a grid pattern and connected to one another or to one or more common lines which are coupled to one or more pressure measurement devices and a temperature sensor. The flexible line(s) may be secured in a grid pattern on a mat for ease of deployment and transport, or merely connected to one another and placed directly on a surface beneath a container. The flexible lines may be commercially available fabric-covered, flexible fire hoses, typically having a core formed of resilient elastomeric material surrounded by a fiber jacket made of polyester or similar materials. 
         [0010]    In an alternative embodiment of this invention, the deflection member comprises a number of discrete pressure pads arranged in a grid pattern and connected to one another by substantially inflexible hoses or other conduits. Each pressure pad, and the non-flexible hoses connecting them, is filled with a fluid. The cross sectional area of the pressure pads decreases under the application of a load which results in an overall increase in pressure within the grid pattern, as sensed by a pressure measurement device connected thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is schematic, elevational view of a grid pattern of flexible lines according to one embodiment of this invention supporting a collapsible, bulk fabric storage container; 
           [0013]      FIG. 2  is a cross sectional view of a flexible line, in an unloaded condition, having a first cross sectional area; 
           [0014]      FIG. 3  is a cross sectional view similar to  FIG. 2 , except with the flexible line under load and having a second cross sectional area; 
           [0015]      FIG. 4  is a perspective view of one embodiment of a single flexible line arranged in a grid pattern and secured to a mat wherein one end of the line is connected to a digital pressure gauge; 
           [0016]      FIG. 5  is a perspective view of an alternative embodiment of a grid pattern comprising a number of flexible lines; 
           [0017]      FIG. 6  is a perspective view of another embodiment of a grid pattern comprising a number of flexible lines; 
           [0018]      FIG. 7  is a perspective view of a first group of flexible lines connected to a first common line coupled to a digital pressure gauge, and a second group of flexible lines connected to a second common line coupled to another digital pressure gauge; 
           [0019]      FIG. 8  is a perspective view of an alternative embodiment of this invention in which a number of pressure pads arranged in a grid pattern are connected to one another by substantially inflexible hoses or other conduits; 
           [0020]      FIG. 9  is a cross sectional view of a pressure pad depicted in  FIG. 8 , in an unloaded condition, having a first cross sectional area; and 
           [0021]      FIG. 10  is a cross sectional view similar to  FIG. 9 , except with the pressure pad under load and having a second cross sectional area. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Referring initially to  FIG. 1-7 , one embodiment of a measuring apparatus  10  according to this invention is illustrated. As schematically depicted in  FIG. 1 , the apparatus  10  may support a collapsible, bulk fabric storage container  14  of the type currently utilized by the armed forces for storing fuel, water and other liquids. The container  14  includes an inlet  16  for filling it with liquid, and one or more outlets  18  for emptying the liquid. As noted above, the container  14  may be formed of a fabric material which assumes an irregular shape and size depending upon the amount of liquid within its interior. 
         [0023]    The apparatus  10  may be configured in a variety of grid patterns, each of which comprises a deflection member in the form of one or more flexible lines  20 . In the presently preferred embodiment, and as best viewed in  FIGS. 2 and 3 , each flexible line  20  may have the construction of a fire hose or similar conduit with a core or inner layer  22  defining a hollow interior  24  and an outer layer  26  encircling the inner layer  22 . The inner layer  22  may be formed of an elastomeric material, such as thermoplastic polyurethane elastomer, or any other suitable material that is resistant to puncture and tearing and is capable of undergoing deflection in response to the application of a load but then returning to its original shape. The outer layer  26  may be formed of any suitable abrasion and puncture resistant material, such as polyester. The hollow interior  24  of the flexible line  20  is filled with a fluid, e.g. an incompressible liquid or a compressible gas such as air. 
         [0024]    Various types of commercially available fire hoses are suitable for use as a flexible line  20  in the apparatus  10  of this invention. Fire hoses intended to transport water from a pumper to the hose nozzle may have a nominal inside diameter of 38 mm to 76 mm and operate at pressures up to about 2,760 kPa. Supply and relay hoses are typically larger in diameter, e.g. from 89 mm to 127 mm nominal inside diameter, and operate at pressures up to about 2,070 kPa. is Forestry hoses are smaller, in the range of 25 mm to 38 mm nominal inside diameter, and operate at pressures up to about 3,105 kPa. It is contemplated that the flexible lines  20  may also be constructed of the material used to fabricate the bulk container  14 . 
         [0025]    As noted above, the apparatus  10  may be configured in a number of grid patterns. Referring to  FIG. 4 , a single flexible line  20  is arranged in a zig-zag grid pattern  28  and affixed to a mat  29  to maintain its shape. The mat  29  may be formed of a flexible material so that the apparatus  10  as depicted in  FIG. 4  may be rolled up for ease of transport. One end of the flexible line  20  in grid pattern  28  is closed and the other is coupled to a pressure measurement device  30 . One suitable pressure measurement device  30  may be a digital pressure gauge. Additionally, a temperature sensor  31  may be connected to the flexible line  20 . Both the pressure measurement device  30  and the temperature sensor  31  may be connected to a display  32 , described more fully below in connection with a discussion of the operation of apparatus  10 . 
         [0026]    The embodiment of apparatus  10  shown in  FIG. 7  employs a grid pattern  34  comprising a number of first flexible lines  20 ′ each connected to a first common line  36 , and a number of second flexible lines  20 ″ each connected to a second common line  38 . One end of the common line  36  is closed and the other end is connected to a pressure measurement device  30 ′. Similarly, one end of the common line  38  is closed and the other end is connected to a pressure measurement device  30 ″. Each of the pressure measurement devices  30 ′ and  30 ″  38  is connected to a display  32 , which also connects to a temperature sensor (not shown) as in  FIG. 4 . 
         [0027]    The embodiment of this invention illustrated in  FIG. 5  depicts an alternative grid pattern  40 , and  FIG. 6  shows still another grid pattern  42  which also appears in  FIG. 1 . The grid patterns  40 ,  42  of these embodiments each comprise a number of flexible lines  20  arranged in parallel columns ( FIG. 5 ), or intersecting columns and rows ( FIG. 6 ). The hollow interiors  24  of some or all of the flexible lines  20  in such grid patterns  40 ,  42  may communicate with one another and connect to one or more pressure measurement devices  30  and a temperature sensor  31  (not shown in  FIGS. 5 and 6 ). 
         [0028]    The operation of the measuring apparatus  10  illustrated in  FIGS. 1-7  of this invention is predicated on the concept that changes in the cross sectional area of the flexible line(s)  20  in response to the application of a load create changes in the pressure of the fluid within the hollow interior  24  thereof which may be sensed by the pressure measurement devices  30 ,  30 ′ and  30 ″. As schematically depicted in  FIG. 2 , a flexible line  20  having a generally circular shape when unloaded may assume a generally oval shape under the application of a load represented by arrow  44  in  FIG. 3 . The cross sectional area of the circular-shaped flexible line  20  in  FIG. 2  is greater than that of the oval-shaped flexible line  20  in  FIG. 3 , although both have the same perimeter dimension. As the cross sectional area of flexible line  20  decreases, the pressure of the fluid within its hollow interior  24  increases. This increase in pressure is conceptually based on the ideal gas law, PV=nRT, where P is the absolute pressure of the gas, V is the volume of the gas, n is the amount of substance in the gas, R is the gas constant and T is the absolute temperature. According to the ideal gas law, if temperature T is held constant, a decrease in volume results in an increase in pressure. As a practical matter, temperature of the fluid within the flexible line(s)  20  varies according to the weather conditions in which the container  14  is located. Consequently, a temperature sensor  31  is provided with each of the grid patterns  28 ,  34 ,  40  and  42  described above to compensate for the pressure change of the fluid within the flexible line(s)  20  due to changes in temperature. 
         [0029]    It is contemplated that a number of different means may be employed to correlate the fluid pressure within the hollow interior  24  of flexible lines  20  with the mass of liquid within the container  14 . One method of correlating fluid pressure to liquid mass may be to calibrate a particular grid pattern  28 ,  34 ,  40  or  42  at different temperatures within a range of average temperature for the area in which the apparatus  10  may be used. The calibration procedure may proceed as follows. Assuming a container  14  to be used with the apparatus  10  has a known mass when empty and a known mass when full of a particular liquid, e.g. fuel, water etc., readings from the pressure measurement device(s)  30 ,  30 ′ or  30 ″ coupled to the flexible tube(s)  20  of such grid patterns  28 ,  34 ,  40  or  42  may be obtained from the application of weights thereto equal to the mass of the container  14  when it is empty, equal to the mass of the container  14  when it is full of liquid, and, equal to the mass of the container  14  at each of a desired number of increments in between empty and full. In this manner, each reading obtained from the pressure measurement device  30  may be calibrated to a known mass applied to the flexible line(s)  20  in a particular grid pattern  28 ,  34 ,  40  or  42 , at a known temperature. 
         [0030]    For purposes of illustration, an empty container  14  placed on a flexible line  20  within a grid pattern  28 ,  34 ,  40  or  42  may result in no deflection or reduction in cross sectional area of such line  20 , as shown in  FIG. 2 , but when filled the container  14  may cause the flexible line  20  to reduce in cross sectional area as depicted in  FIG. 3 . As the container  14  is emptied from a filled condition, the cross sectional area of the flexible line  20  increases from that shown in  FIG. 3  to that illustrated in  FIG. 2 . The pressure of the fluid within the hollow interior  24  of the flexible tube  20 , in turn, corresponds to its cross sectional area between the unloaded and fully loaded extremes depicted in  FIGS. 2 and 3 . The different pressure readings provided by the pressure measurement devices  30 ,  30 ′ and  30 ″ may be correlated to the values obtained during the calibration process described above to provide an accurate indication of the mass of the liquid in the container  14  at any point between empty and full for a given temperature. The pressure measurement device  30  and the temperature sensor  31  may be connected to a display  32  having a processor or other memory device. The display  32  may compare the reading or signal received from the pressure measurement device  30  and the reading or signal from the temperature sensor  31 , to the data obtained from the calibration procedure described above and provide a digital display of the mass of the liquid within the container  14  corresponding to the sensed pressure at a sensed temperature. 
         [0031]    Alternatively, it is contemplated that an algorithm may be employed to directly convert readings from the pressure measurement devices  30 ,  30 ′ and  30 ″ to a digital display of the mass of liquid within a container  14 , accounting for the temperature of the fluid within the line(s)  20  in the area the container  14  is located as sensed by the temperature sensor  31 . The algorithm may be contained within a processor associated with the display  32 . 
         [0032]    Referring now to  FIGS. 8-10 , an alternative embodiment of a measuring apparatus  50  according to this invention is illustrated. The apparatus  50  comprises a number of discrete pressure pads  52  arranged in a grid pattern  54  and connected by lines  56  which are substantially inflexible under the application of a load applied by the container  14  when completely filled. The pressure pads  52  are preferably generally disc-shaped, although other shapes may be utilized, with a core or inner layer  58  defining a hollow interior  60  and an outer layer  62  encircling the inner layer  58 . The hollow interior  60  of pressure pads  52  and lines  56  are filled within a fluid such as a liquid or air. Such layers  58  and  62  may be formed of the same materials as the flexible line(s)  20  described above in connection with a discussion of  FIGS. 1-7 . 
         [0033]    The pressure pads  52  behave in essentially the same fashion as flexible line(s)  20  under the application of a load. A pressure pad  52  having the cross-sectional shape depicted in  FIG. 9  when unloaded may assume the shape illustrated in  FIG. 10  under the application of a load represented by arrow  64  in  FIG. 10 . The cross sectional area of the pressure pad  52  in  FIG. 9  is greater than that of the pressure pad  52  in  FIG. 10 , although both have the same perimeter dimension. As the cross sectional area of pressure pad  52  decreases, the pressure of the fluid within its hollow interior  60  increases. The pressure within the grid pattern  54  may be sensed by a pressure measurement device  30 , and the temperature of the fluid within the pressure pads  52  and lines  56  may be determined by a temperature sensor  31 . Both the pressure measurement device  30  and the temperature sensor  31  are preferably coupled to a display  32 . Further, the measuring apparatus  50  is calibrated, and operates in the same fashion, as the measuring apparatus  10  described above. 
         [0034]    Among the advantages of the measuring apparatus  10  and the measuring apparatus  50  of this invention is that they are capable of providing accurate readings of the mass of liquid within a container  14  that is flexible and varies in size and dimension as it transitions between an empty and filled state. So long as the overall dimension of the grid patterns  28 ,  34 ,  40 ,  42  and  54  are at least equal to the dimension of the container  14  when full, a decrease in the size of the container  14  does not affect the pressure measurements needed to obtain an indication of the mass of liquid within the container  14 , as described above. The container  14  may even extend in between adjacent flexible lines  20  within a grid pattern  28 ,  34 ,  40  or  42 , or between pressure pads  52  within the grid pattern  54 , and touch the surface beneath, without impairing the accuracy of pressure readings. Further, the measuring apparatus  10  and the measuring apparatus  50  are light weight, portable and relatively inexpensive to manufacture or repair. 
         [0035]    While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. 
         [0036]    For example, while only the grid pattern  28  depicted in  FIG. 4  is illustrated with a mat  29  connected to a flexible line  20  it is contemplated that any or all of the other grid patterns  34 ,  40 ,  42  and  54  could employ a mat  29 . Further, the grid patterns  28 ,  34 ,  40 ,  42  and  54  are depicted for purposes of illustration only and other arrangements of one or more flexible lines  20 , or pressure pads  52 , in different grid patterns are considered within the scope of this invention. 
         [0037]    Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.