Patent Publication Number: US-2004050158-A1

Title: Liquid level sensing gauge assembly and method of installation

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] This invention relates to an improved gauge assembly for monitoring the level of fluid in a storage tank or like container, and to an improved, convenient method for installing such a gauge assembly.  
       [0003] 2. Description of the Related Technology  
       [0004] A great variety of devices have been used to determine and provide indications of the liquid level in storage tanks and other such vessels. However, monitoring the level of storage tanks which contain petroleum products or other volatile liquids presents special requirements that have not been fully satisfied by the technology that is in common use today.  
       [0005] Petroleum products such as oil and gasoline contain viscous components that tend to coat any surface to which they are exposed. This effectively precludes the use of visual sight gauges for fluid level monitoring. The volatile nature of such fluids also makes their monitoring with electronic level sensing equipment more dangerous and otherwise problematic.  
       [0006] Float level gauges have been used in the past to monitor the level of petroleum-based products. Such a gauge is disclosed in U.S. Pat. No. 3,482,447 to Bennett. This device includes an analog gauge that is synchronized with an internal drum. Wrapped about the drum is a gauge line that is connected to a float element. The drum is biased in a first rotary direction by an elongated coil-type spring, which keeps the gauge line in tension. As the float element rises or falls in response to the level of the liquid within a storage tank, the analog display reflects the resultant rotation of the drum. Another mechanically based flow level gauge, disclosed in U.S. Pat. No. 5,144,836 to Webb advantageously is designed so as to keep installation time to a minimum while working on tanks that are already in operation, and to be quickly and easily calibrated to reflect the liquid level within a tank after it is installed. These gauges utilize an analog clocklike display having a first indicating hand that is calibrated to indicate inches and a second indicating hand that is calibrated to indicate feet. The gauge disclosed in the Webb patent has enjoyed significant commercial success because of these advantages and the reliable mechanical design. However, with the growing use of electronic and particularly digital electronic technology, there is a need to be able to electronically monitor fluid level within such storage tanks. Specifically, it is clear that there exists a need in the prior art for a liquid level gauge which is convenient to install, which can be quickly calibrated to reflect the level of liquid within a storage tank to which it is mounted, which is mechanically simple and inexpensive to manufacture, which protects the environment against escape of vapors from the storage tank and that is furthermore compatible for use in conjunction with electronic control system.  
       SUMMARY OF THE INVENTION  
       [0007] Accordingly, it is an object of the invention to provide a system and method for a liquid level gauge which is convenient to install, which can be quickly calibrated to reflect the level of liquid within a storage tank to which it is mounted, which is mechanically simple and inexpensive to manufacture, which protects the environment against escape of vapors from the storage tank and that is furthermore compatible for use in conjunction with an electronic control system.  
       [0008] In order to achieve the above and other objects of the invention, a gauge assembly for measuring the amount of a liquid in a storage tank or like container includes, according to a first aspect of the invention, an outer housing, a float member, a filament connected to the float member, a spool member rotatably mounted within the outer housing, the spool member being constructed and arranged to pay out the filament, analog indicator structure on the outer housing for displaying a value which corresponds to the rotary position of the spool member; and electronic detection structure for detecting a position of the analog indicator structure, whereby the gauge assembly is further compatible with an electronic monitoring system.  
       [0009] According to a second aspect of the invention, a system for monitoring the amount of a liquid in a storage tank or like container includes a storage tank; a float member mounted for movement within the storage tank, an analog display, mechanical linkage structure for controlling the analog display in response to a position of the float member, electronic detection structure, mechanically connected to the mechanical linkage structure, for detecting a position of the analog indicator structure; and monitoring structure for monitoring information received from the electronic detection structure.  
       [0010] According to a third aspect of the invention, a method for monitoring the amount of a liquid in a storage tank or like container includes steps of mounting a mechanical level gauge to a storage tank; calibrating the level gauge mechanically while simultaneously calibrating electronic detection structure that is mechanically connected to the mechanical level gauge; using the level gauge to monitor the amount of a liquid in the storage tank; and using the electronic detection structure to monitor the amount of a liquid within the storage tank.  
       [0011] A kit for monitoring the amount of liquid in a storage tank according to a fifth aspect of the invention includes a mechanical gauge having a mechanical display that is indicative of the fill level of the storage tank; an electronic sensor that is mechanically connected to the mechanical gauge; and a computer interface device for coupling the electronic sensor to a personal computer.  
       [0012] These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013]FIG. 1 is a perspective view of a gauge assembly constructed according to a preferred embodiment of the invention shown in its mounted position upon a storage tank;  
     [0014]FIG. 2 is a partially fragmented cross-sectional view through the gauge assembly depicted in FIG. 1 and the storage tank;  
     [0015]FIG. 3 is another cross-sectional view of the gauge assembly that is depicted in FIGS. 1 and 2;  
     [0016]FIG. 4 is a diagrammatical view depicting a portion of the gear train in the gauge that is constructed according to FIGS.  1 - 3 ; and  
     [0017]FIG. 5 is a schematic depiction of another portion of the preferred embodiment of the invention; and. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
     [0018] Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to FIG. 1, a gauge assembly  10  for a storage tank  12  of the type that is adapted to be filled with a liquid product  14 , such as a petroleum product, monitors a fill level  16  by utilizing a float member  18  that is constructed and arranged to float on an upper surface of the liquid product  14 . As may be seen in FIG. 1, gauge assembly  10  includes a filament  22  having a distal end  20  that is connected to float member  18 , preferably by a clip mechanism  80 , as may be seen in FIG. 3.  
     [0019] Referring now to FIG. 3, it will be seen that filament  22  passes through an opening  26  that is defined in a housing  32  of gauge assembly  10 . Filament  22  is wound about a drum  24  that is mounted for rotation within the housing  32 , as is shown in both FIGS. 2 and 3. A biasing mechanism  28  is provided for biasing the drum  24  in a first rotary direction that will wind the filament  22  onto drum  24 , so that biasing mechanism  28  will tend to pull float member  18  toward housing  32 , thereby keeping filament  22  taut for purposes of accuracy. Preferably, biasing mechanism  28  includes a constant force spring  30 .  
     [0020] Looking now to FIG. 1, it will be seen that gauge assembly  10  preferably includes a clock-type face having distance indicia  36  marked therearound that is in a base-twelve numbering system to represent feet and inches, rather than hours and minutes. A small hand  38  is mounted to traverse clock face  34  to represent feet, and a large hand is also mounted to traverse clock face  34  to represent inches. Both small and large hands  38 ,  40  are mechanically connected to drum  24  via a gear train  54 , which will be described in greater detailed below.  
     [0021] As may be seen best in FIGS.  2 - 4 , gear train  54  includes a first pinion  56  that is mechanically connected to drum  24  to rotate with drum  24 . As may best be seen in FIG. 4, a second pinion  58  is positioned to be driven by first pinion  56 . A third pinion  60  that is smaller than second pinion  58  is mounted coaxially with second pinion  58  to rotate with second pinion  58 . A fourth pinion  62  is connected to rotate with small hand  38  on clock face  34 . A fifth pinion  64  is connected to rotate with large hand  40  on clock face Fourth pinion  62  is larger than fifth pinion  64 , and is engaged to be driven by third pinion  60 . Fifth pinion  64  is engaged to be driven by second pinion  58 . The different reduction ratios provided by third pinion  60  and fourth pinion  62 , and second pinion  58  and fifth pinion  64 , respectively, will ensure that large hand  40  will circumferentially traverse clock face  34  twelve times for each time that small hand  38  circumferentially traverses clock face  34 .  
     [0022] As is shown in FIG. 3, an electronic detection device  110  is mechanically coupled to gear train  54  by a mechanical coupling arrangement that includes an idler gear  106 , which is driven by fourth pinion  62 , and a pinion  108  that is driven by idler gear  106 . This mechanical coupling could be effected in any one of a plurality of different ways, all of which fall within the ambit of the invention. Electronic detection device  110  in the preferred embodiment is a rotary position dependent device, most preferably a multirotational potentiometer. Alternatively, electronic detection device  110  could be constructed as a variable capacitor, a variable inductor, or any other position dependent device having variable electronic properties.  
     [0023] As may be seen in FIG. 5, electronic detection device  110  is constructed and arranged to communicate electronically with an analog to digital converter PC card  124 , which is installed within a personal computer  116  that includes a display device  118 , such as a monitor, and an input device  120 , such as a keyboard or mouse. As may be seen in FIG. 1, a multiple conductor cable  86  contains wires that connect the electronic detection device  111  and the personal computer  116 . Gauge assembly  10  and the analog to digital computer card  124  are preferably sold together as a kit  122  to customers together with software for converting the digital output of the analog to digital card  124  into information as to the fill status of the aboveground storage tank that will be displayed by the personal computer  116 . The electrical signals within the cable  86  are preferably kept at current and voltage levels that are known in the industry as “intrinsically safe,” whereby the risk of igniting flammable liquids or vapors in kept to a minimum.  
     [0024] Personal computer  116  preferably runs the Windows operating system, and the software that is provided with the kit  122  permits an operator to enter information such as the date on which the aboveground tank has been filled and the identity of the fuel in the tank, such as, for example, diesel or gasoline. After installation of the gauge  10  into the aboveground storage tank and installation of the analog to digital card  124  and the software into the personal computer  116 , the software will initially ask an operator to enter information that is relevant to the tank that is to be monitored, such as the height and length of the tank. The software will provide an intuitive display of the fuel level within the tank, and will indicate to an operator when the fuel level is critically low or when the tank is overfilled. Fuel levels may also be displayed quantitatively, such as in liters or gallons.  
     [0025] In operation, electronic detection device  110  will be monitored by the central processing unit  116 , with the electronic value indicated by the electronic detection device  110  being detectable by the central processing unit  116  as indicative of a particular level or volume of fluid within the tank  12 . In order to calibrate this electronic monitoring system, an operator needs only to calibrate the manual system as described above, adjusts the position of the clock gauge to a known value, and enter the known value using the input device  120 . As the system is used, this electronic monitoring system can verify the accuracy of the clock gauge and can further be used for remote detection of the volume level, such as by a remote service center facility that is located several miles from the tank  12 .  
     [0026] The invention further includes a process of retrofitting existing mechanical gauges with electronic devices  110  according to the invention.  
     [0027] It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.