Abstract:
A wiper for use in a system for monitoring fluid level in a fluid storage container. The wiper has a body portion, a first lengthwise end, a second lengthwise end, a first side, a second side opposite the first side, a width and a pair of resilient contact members electrically connected to one another. Each contact member extends from a corresponding side of the body portion. The wiper also has a guide portion attached to the first lengthwise end. The guide portion has a width larger than the width of the body portion. The wiper includes a recess formed in each side of the body portion for receiving a corresponding resilient contact member thereby allowing the resilient contact members to be compressed so as to be substantially flush with the body portion. In one embodiment, the recesses extend through the guide portion. In one embodiment. the wiper includes an electrically conductive member that has a portion thereof that is embedded in the body portion. The electrically conductive member has a first portion and a second portion extending from the first and second sides of the body portion, respectively. Each portion of the electrically conductive member defines a corresponding one of the resilient contact members.

Description:
This application claims the benefit of the filing date of commonly owned and U.S. Provisional Application Ser. No. 60/056,326 filed Aug. 12, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field Of The Invention 
     The present invention generally relates to a system for monitoring the level of fluids. 
     2. Problem To Be Solved 
     In many industrial, commercial and residential settings, it is often necessary to monitor the level of fluids, such as water, fuel or oil, which is stored in tanks or other fluid holding apparatuses. Conventional fluid monitoring systems typically utilize a device that is located on the fluid storage tank which provides a visual readout of the fluid level. Such conventional systems typically use a float-type gauge that includes a pivoted or swinging arm carrying a float at its outer end. A vertically oriented rod having a top end and a bottom end is pivotally attached to the swinging arm. As the float rises and falls with the fluid level, the vertically oriented rod also rises and falls. An indicator device comprising a transparent tube or container having indicia thereon is located above the tank. The top end of the vertically oriented rod is movably disposed within the plastic tube. A scale comprising indicia is formed on the plastic tube to enable visual monitoring of the indicator. The scale may be configured to provide units of measure in fractions of the capacity of the tank or containing apparatus or in gallons, liters, etc. Such a conventional system is disclosed in U.S. Pat. No. 2,446,844. 
     A significant disadvantage of the conventional system described above is that the monitoring of the fluid level must take place at the fluid tank. This creates a significant inconvenience when the fluid storage tank or container is at a remote location. 
     Another disadvantage of the conventional system described above is that when a plurality of fluid storage tanks are present, determining the fluid level in all the tanks can be a time consuming process. 
     The disadvantages described above also apply to residential settings. For example, in most homes, heating fuel tanks are typically located in the basement. Use of the conventional fluid monitoring system described above requires that the home owner descend into the basement to visually monitor the fuel level in the tank. Descending into the basement may be very difficult for the elderly and may even be impossible for the handicapped. 
     Bearing in mind the problems and deficiencies of the conventional fluid level monitoring systems, it is an object of the present invention to provide a new and improved system for monitoring the level of fluid in a fluid storage tank or container. 
     It is another object of the present invention to provide a new and improved system for monitoring the level of fluid in a fluid storage tank or container that provides information concerning fluid level to a location remote from the fluid storage tank or container. 
     It is a further object of the present invention a new and improved system for monitoring the level of fluid in a fluid storage tank or container that can be manufactured inexpensively. 
     It is yet a further object of the present invention to provide a new and improved system for monitoring the level of fluid in a fluid storage tank or container that measures the fluid level in the fluid storage tank or container with a high degree of accuracy. 
     It is another object of the present invention to a new and improved system for monitoring the level of fluid in a fluid storage tank or container that can inexpensively be integrated with existing fluid storage tanks or containers. 
     Other objects and advantages of the present invention will be apparent to one of ordinary skill in the art in light of the ensuing description of the present invention. 
     SUMMARY OF THE INVENTION 
     The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which is directed to, in a first aspect, to a system for monitoring fluid level in a fluid storage container wherein the container has a device that has a movable portion for contacting fluid in the fluid storage container and moving in response to the changes in the level of fluids in the container, the system comprises a signal sending unit and a display device. The signal sending unit is responsive to the movement of the moveable portion of the device and produces variations in the magnitude of an electrical signal wherein a particular magnitude of the electrical signal corresponds to a particular level of fluid in the fluid storage container. The display device is responsive to the magnitude of the electrical signal for displaying the level of fluid in the fluid storage container. 
     In a related aspect, the present invention is directed to a system for monitoring fluid level in a fluid storage container comprising: 
     (a) a device having a movable portion for contacting fluid in the fluid storage container and moving in response to changes in the level of the fluid in the container; 
     (b) a signal sending unit responsive to the movement of the movable portion, the signal sending unit producing variations in the magnitude of an electrical signal wherein a particular magnitude of the electrical signal corresponds to a particular level of fluid in the fluid storage container; and 
     (c) a display device responsive to the electrical signal for displaying the level of fluid in the fluid storage container. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the invention are believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a block diagram of one embodiment of the fluid level monitoring system of the present invention. 
     FIG. 1A is an elevational view, in cross-section, of a sending unit depicted in the block diagram of FIG.  1 . 
     FIG. 2 is a view taken along line  2 — 2  of FIG.  1 A. 
     FIG. 3 is an elevational view, partially in cross-section, of a wiper shown in FIG.  1 A. 
     FIG. 4 is a View taken along line  4 — 4  of FIG.  3 . 
     FIG. 5 is a block diagram of a power supply and fluid level gauge depicted the block diagram of FIG.  1 . 
     FIG. 6 is a front, elevational view of an analog gauge used in one embodiment of the gauge depicted in the block diagram of FIG.  5 . 
     FIG. 7 is a rear, elevational view of the analog gauge shown in FIG.  6 . 
     FIG. 8 is an elevational view, in cross-section, of an alternate embodiment of a sending unit. 
     FIG. 9 is a side, elevational view of a wiper shown in FIG.  8  and illustrates the attachment of a conductive contact. 
     FIG. 10 is a front, elevational view of the wiper shown in FIG.  9 . 
     FIG. 11 is a view taken along line  11 — 11  in FIG.  10 . 
     FIG. 12 is a view similar to that of FIG.  9  and illustrates how a user may depress the sides of the conductive contact member. 
     FIG. 13 is a front, elevational view of a contact member shown in FIG.  8 . 
     FIG. 14 is a block diagram of an alternate embodiment of the fluid monitoring system of the present invention. 
     FIG. 15 is a block diagram of an alternate embodiment of the fluid monitoring system of the present invention. 
     FIGS. 15A-C illustrates, partially in block diagram and partially in schematic form, an alternate embodiment of the fluid monitoring system of the present invention. 
     FIG. 16 is a block diagram of an alternate embodiment of the fluid monitoring system present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In describing the preferred embodiments of the present invention, reference will be made herein to FIGS. 1-15C of the drawings in which like numerals refer to like features of the invention. 
     Referring to FIGS. 1,  1 A and  3 , fluid level monitoring system  10  of the present invention includes signal sending unit  11 . Sending unit  11  generally comprises transparent lens  12  and a wiper assembly operative within lens  12 . The wiper assembly includes wiper  14  and is discussed in detail below. In a preferred embodiment, lens  12  is substantially cylindrical in shape. However, lens  12  may be configured in other shapes as well. In a preferred embodiment, lens  12  is fabricated from Lexan™. However, other suitable materials can also be used. 
     Referring to FIGS. 1 and 2, system  10  of the present invention further comprises lens adapter  16 . In the case of retrofitting an existing fluid level measurement device, lens adapter  16  is fluidly connected to the existing opening to which the conventional visual indicator lens was attached. In a preferred embodiment, lens adapter  16  is threadedly attached to the existing opening via threads  18 . Lens  12  is attached to lens adapter  16  by lens retaining plate  20  and retaining screws  22 . As shown in FIG. 1A, lens seal  24  is positioned between lens  12  and lens adapter  16 . In a preferred embodiment, lens seal  24  is substantially washer-shaped. Other types of shapes may be used as well. Retaining screws  22  are disposed through openings in retaining plate  20  and threadedly engaged with corresponding threaded inlets formed in lens adapter  16 . Seal  17  is intermediate lens adapter  16  and the existing fluid storage device and provides a fluid-tight connection between lens adapter  16  and the fluid storage device. In a preferred embodiment, seal  17  is an O-ring. 
     Referring again to FIGS. 1,  1 A and  3 , the wiper assembly comprises wiper  14 , reference conductor (or commutator)  26 , resistive conductor  28 , and wiper brushes  30 ,  32  that are attached to wiper  14 . Reference conductor  26  and resistive conductor  28  are positioned within the interior of lens  12 . In a preferred embodiment, reference conductor  26  and resistive conductor  28  are spaced about 180° apart. In one embodiment, reference conductor  26  has a width of about 0.25 inch and a thickness of about 0.06 inch. In a preferred embodiment, reference conductor  26  comprises a silver-plated brass strip. However, it is to be understood that reference conductor  26  may be fabricated from other suitable materials with different dimensions. Reference conductor  26  and reference conductor  28  are secured against movement by slot or detent  34  formed in the upper portion  36  of lens  12 . Reference and resistive conductors  26  and  28  are further secured against movement by screws  3 A and  4 A which are disposed through standoffs  42  and  44 , respectively, and threadedly engage lens  12 . 
     Referring to FIG. 1A, in a preferred embodiment, resistive conductor  28  is comprised of a wire-wound rheostat having a core comprised of a strip of nylon or Garrolite having a width of about ¼ inch and a thickness of about {fraction (1/16)} inch. Preferably, the winding is comprised of #34 gauge nickel, chromium wire with 250 equidistant turns spaced across the length of the rheostat. In an alternate embodiment, resistive conductor  28  may be realized by a strip of nylon or garrote that is coated with a semi-conductive material, e.g. Cermet. The rheostat, having the configuration described above, provides variable resistances between about 0 to 200 ohms. 
     The winding of the rheostat can determine resistance per lineal length of conductor and behavior of the output gauge. The winding of the rheostat may be modified to compensate for the inaccuracies in monitoring fluid level resulting from the geometry of the fluid tank and the circular motion of the fluid gauge arm (referred to as the “trigonometric function”). In other words, the equidistant spacing of the winding may be altered to accommodate for non-linear fuel readings at maximum and minimum fluid levels resulting from curvature of the storage tank and to the circular movement of the float rod in the storage tank. Similarly, altering the rheostat winding also can compensate for differences in the accuracy of commercially available fluid gauges. Altering the rheostat winding, as described above, is known as “shading”. Shading the rheostat enables system  10  to be integrated with existing fluid storage tanks and yet provide highly accurate information regarding the level of fluid in the storage tank. Similarly, if a Cermet strip is used, the strip is configured to have a non-linear taper in order to accommodate the non-linear fuel readings mentioned above. Altering the spacing of the winding turns of the rheostat or creating the non-linear taper, as discussed above, provide increased accuracy in the measurement of the level of fluid in the tank. 
     Referring to FIGS. 1A and 3, float rod  46  is movably attached to wiper  14 . In one embodiment, end portion  48  of float rod  46  is disposed within bore  50  of wiper  14 . Set screw collar  52  connects end portion  48  to wiper  14  and allows float rod  46  to pivot or swivel with respect to wiper  14 . The ability of float rod  46  to pivot or swivel with respect to wiper  14  prevents movement of float rod  46 , as a result of changes in the fluid level, from applying any torque or other forces upon wiper  14  that would impede or interfere with the movement of wiper  14 . Other suitable methods of attachment may also be used that will allow for independent movement of float rod  46 . 
     As shown in FIGS. 1A and 3, wiper  14  moves in a vertical fashion as indicated by arrow  54  as a result of the vertical movement of float rod  46 . As shown in FIG. 3, conductive spring  58  is located within cavity  60  in upper portion  62  of wiper  14 . Spring  58  is interposed between brushes  30  and  32  to maintain brushes  30  and  32  in constant contact with reference conductor  26  and resistive conductor  28 . Referring to FIGS. 3 and 4, upper portion  62  of wiper  14  comprises portions  62   a  and  62   b  that extends on either side of reference or resistive conductors  26  or  28 , respectively, so as to function as a guide in maintaining wiper brushes  30  and  32  in alignment and contact with conductors  26  and  28 , respectively. Referring to FIG. 4, spring  58  is shown in phantom. 
     Referring to FIG. 1A, O-rings  64  and  66  are positioned within corresponding cavities or detents formed in lens  12  and are in a sealing relationship with standoffs  42  and  44 . Screws  38   a  and  40   a  pass through lens  12  and threadedly engage standoffs  42  and  44 . When screws  38   a  and  40   a  threadedly engage standoffs  42  and  44 , O-rings  64  and  66  are compressed into the aforementioned cavities. 
     In one embodiment, system  10  includes an additional feature for providing visual monitoring of fluid level in a fluid tank. Specifically, lens  12  may be configured to include indicia (not shown) thereon and which represents predetermined levels of fluid in the storage tank or container. As shown in FIG. 1A, indicator stripe  68  is formed on upper portion  62  of wiper  14 . Stripe  68  is horizontally oriented so as to align with the indicia on lens  12 . The level of fluid in the storage tank is indicated by the position of stripe  68  with respect to the indicia on lens  12 . Stripe  68  and the indicia on lens  12  enable a user, that is located at the storage tank, to visual monitor the level of fluid in the storage tank. It is to be understood that stripe  68  and the indicia on lens  12  provide an additional, but optional, feature of monitoring the fluid level in the storage tank and is not required by system  10  to provide information related to the level of fluid in the storage tank or container. 
     Referring to FIGS. 1 and 5, system  10  further includes remote fluid level gauge  70  and power supply  72 . Power supply  72  includes an input (not shown) for receiving an a.c. (alternating current) voltage. Preferably, the input a.c. voltage is between about 112 VAC and 118 VAC. More preferably, the a.c. input voltage is about 115 VAC. Power supply  72  includes a fused, low voltage d.c. (direct current) power supply transformer (not shown) that has input windings connected to the input a.c. voltage discussed above. Power supply  72  provides wire or electrical conductor  74  that connects reference conductor  26  to ground potential. Power module  72  provides wire or electrical conductor  76  that is connected to resistive conductor  28 . Conductors  74  and  76  are connected to screws  38   b  and  40   b,  respectively (see FIG.  1 ). Power supply  72  includes internal circuitry that connects conductors  74  and  76  to output conductors  78  and  80 , respectively. Power module  72  further includes conductor  77  that connects the chassis of power supply  72  to ground potential. Power module  72  also provides a supply voltage +Vcc on conductor  82 . In a preferred embodiment, +Vcc is between about 12 volts d.c. and 15 volts d.c. More preferably, +Vcc is about 14 volts d.c. Conductors  78 ,  80  and  82  are inputted into gauge  70 . In a preferred embodiment, power module  72  includes a “zero” trim potentiometer (not shown) for adjusting or calibrating gauge  84 . 
     Referring to FIGS. 5-7, gauge  70  can be any type of commercially available digital or analog display gauge. In one embodiment, gauge  70  is realized as an analog bezel gauge  84  shown in FIGS. 6 and 7. FIG. 7 is a rear view of gauge  84 . Gauge  70  can also be configured as the digital display  510  shown in FIG. 16 which is discussed below. 
     Referring to FIGS. 1 and 5, as float rod  46  moves vertically as a result of changes in the fluid level in the storage tank thereby causing movement of wiper  14 . Brushes  30  and  32  contact reference conductor  26  and resistive conductor  28 , respectively, as wiper  14  moves thereby generating a varying resistance between reference conductor  26  and screw  40 . As described above, screw  40   b  is connected to conductor  76  which is connected to conductor  80  that is inputted into gauge  70 . Since the resistance between reference conductor  26  and screw  40  varies as wiper  14  moves, the signal carried on conductors  76  and  80  is referred to as a resistive signal. Thus, as the float rod  46  moves in response to changing fluid level in the fluid tank, the resistive signal carried on conductor  80  also varies thereby causing movement of needle  92  of gauge  84 . 
     In an alternate embodiment, sending unit  11  includes opening  90  in top portion  36  of lens  12  and screw  92 , which in a preferred embodiment, is threadedly engaged with opening  90 . Opening  90  is sized for receiving calibration rod  94 . Washer  96  provides a hermetic seal between screw  92  and top portion  36  of lens  12 . In a preferred embodiment, washer  96  is an elastomeric polyethylene washer. 
     Referring to FIG. 8, there is shown alternate system  100  for monitoring the fluid level in a storage tank or other fluid holding container. System  100  generally comprises transparent lens  102  and a wiper assembly that is operative within lens  102 . In a preferred embodiment, lens  102  is substantially identical to lens  12  discussed above. However, lens  102  may be configured to have any other shape as well. Lens includes stepped portions  102   a,    102   b  which will be described below. The wiper assembly will be  20  discussed in detail below. Lens  102  further includes openings  103   a,    103   b  that received screws (not shown) for securing components of the wiper assembly. The aforementioned screws function in the same manner as screws  38   a  and  40   a  discussed above (see also FIG.  1 A). 
     Referring to FIG. 8, system  100  of the present invention further comprises lens retaining plate  104  and adapter  106 . Retaining plate  104  is substantially identical in construction to retaining plate  20  discussed above. Retaining plate  104  engages stepped portions  102   a  and  102   b.  Screws  108  are disposed through corresponding openings  110  in retaining plate  104  and are threadedly engaged with corresponding threaded inlets  112  formed in adapter  106 . As screws  108  are threadedly inserted into openings  112 , retaining plate  104  exerts a downward force upon the lens  102  so as to maintain lens  102  within bore or cavity  106   a.  O-ring seal  114  is positioned between lens  102  and adapter  106 . The downward force created by retaining plate  104  and screws  108  in conjunction with seal  114  create a sealing relationship between lens  102  and adapter  106 . In the case of retrofitting and existing fluid storage tank, adapter  106  is configured to have threads formed on portion  115  so it may be fluidly threadedly connected to the existing opening in the fluid storage tank to which the conventional visual indicator lens was attached. O-ring type seal  116  is positioned between adapter  106  and the existing fluid level measurement device. A fluid, air tight relationship is formed between adapter  106  and the fluid tank as adapter  106  is threadedly engaged with the preexisting opening in the fluid storage tank. 
     Referring again to FIGS. 8-12, the wiper assembly that is operative within lens  102  comprises wiper  118 , reference conductor  120 , resistive conductor  122 , and contact member  124  that is attached to wiper  118 . Reference conductor  120  and resistive conductor  122  are positioned within the interior of lens  102 . In a preferred embodiment, reference conductor  120  and resistive conductor  122  are spaced about 180° apart. In one embodiment, reference conductor  120  and resistive conductor  122  are fabricated in the same manner as reference conductor  26  and resistive conductor  28 , respectively, previously described above. However, it is to be understood that reference conductor  120  and resistive conductor  122  may be fabricated from other suitable materials with different dimensions. Reference conductor  120  and resistive conductor  122  are secured against movement by slots or detents  126  formed in upper portion  128  of lens  102 . Reference conductor  120  and resistive conductor  122  are further secured against movement by screws (not shown) that are disposed through screw inlets  103   a  and  103   b.  The aforementioned screws  38   a  and  40   a  threadedly engage reference and reference conductors  120  and  122 , respectively. 
     Referring to FIGS. 9-11, wiper  118  comprises body portion  130 , upper portion  132  and lower portion  133 . Wiper  118  is contoured for minimizing mechanical hysteresis in operation. Upper portion  132  is preferably rounded and includes extended portions  134   a  and  134   b  that contact reference conductor  120  as wiper  118  vertically moves within lens  102 . Extended portions  134   a  and  134   b  function as guides and provide steady and stable movement as wiper  118  vertically moves within lens  102 . Wiper  118  further includes vertically oriented recesses  136  and  138 . The purpose of recesses  136  and  138  will be discussed below. Wiper  118  further includes opening or bore  140  that extends through wiper  118 . Opening  140  is sized for receiving a set-screw collar (not shown) that movably attaches float rod  142  to wiper  118 . In a preferred embodiment, opening  140  is rectangular shaped. The set-screw collar permits float rod  142  to swivel or rotate without applying a torque to wiper  118 . Thus, any movement of float rod  142  resulting from installation or a change in fluid level in the storage tank will not impede or interfere with the movement of wiper  118 . Wiper  118  further includes longitudinal bore  143  that is sized for receiving one end of the threadedly attached calibration rod described above. In a preferred embodiment, wiper  118  is fabricated from lightweight, durable nonconductive materials such as plastic, PVC, Delrin™, etc. 
     Referring to FIGS. 9,  10 ,  12  and  13 , conductive contact member  124  comprises closed end  144  which is embedded within wiper  118  and sides  146  and  148  that are attached to closed end  144 . Sides  146  and  148  are resilient and have curved ends  150  and  152 , respectively, for contacting reference and resistive conductors  120  and  122 , respectively. The curvature of ends  150  and  152  facilitates smooth and steady contact with reference conductors  120  and  122  and minimizes mechanical hysteresis. In a preferred embodiment, contact  124  is fabricated from materials that exhibit superior conductivity and connectivity to display gauge  70  with a minimum of noise and spurious signals. Preferably, the materials from which contact  124  is fabricated allow for contact with reference and resistive conductors  120  and  122 , respectively, while exerting a minimum force upon conductors  120  and  122 . In a preferred embodiment, the force exerted upon conductors  120  and  122  by sides  146  and  148  of contact  124  is between about 6 and 8 grams, inclusive. More preferably, the force exerted upon conductors  120  and  122  by sides  146  and  148  of contact  124  is about 7 grams. In a preferred embodiment, contact  124  is fabricated from alloys selected from the group of palladium, platinum, silver and gold. However, it is to be understood that contact  124  may be fabricated from other alloys having similar characteristics as those mentioned above. In one embodiment, contact  124  is molded into wiper  118  during the formation of wiper  118 . In another embodiment, contact  124  is fixed within a square hole in wiper  118  with a stake pin. Preferably, the stake pin is fabricated from material that is similar to the material from which wiper  118  is fabricated. 
     Referring to FIGS. 9 and 12, during placement of wiper  118  within lens  102 , a user of sending unit  100  depresses sides  146  and  148  (as indicated by arrows  156  in FIG. 9) of contact  124  with his or her fingers  154  so that sides  146  and  148  are positioned within recesses  136  and  138 , respectively, of wiper  118 . Thus, the resiliency of sides  146  and  148  and recesses  136  and  138  facilitate placement of wiper  118  within lens  102 . 
     Referring to FIGS. 5 and 8, sending unit  100  is interconnected with power module  72  and gauge  84  in the same manner as system  10 . Conductor  76  is connected to a screw (not shown) that is disposed within inlet  103   b  via the standoff and threadedly engaged with resistive conductor  122 . Similarly, conductor  74  is connected to a screw (not shown) that is disposed within inlet  103   a  and threadedly engaged with reference conductor  120  via the standoff. Referring to FIGS. 1 and 5, float rod  142  moves vertically within lens  102  as a result of the change in fluid level in the storage tank thereby causing movement of wiper  118 . Ends  150  and  152  of contact  124  contact reference conductor  120  and resistive conductor  122 , respectively, as wiper  118  moves thereby generating a varying resistance between reference conductor  120  and the screw (not shown) that is disposed within inlet  103   b.  As described above, within power supply  72 , conductor  76  is connected to conductor  80  that is inputted into gauge  70 . Since the resistance between reference conductor  120  and the screw disposed in inlet  103   a  varies as wiper  118  moves, the signal carried on conductors  76  and  80  is referred to as a resistive signal. As the float rod  142  moves in response to changing fluid level in the fluid tank, the resistive signal carried on conductor  80  also varies thereby causing movement of needle  92  of gauge  84 . 
     Referring to FIG. 14, there is shown alternate fluid level monitoring system  200  of the present invention which provides an indication of instantaneous fluid usage. System  200  includes signal sending unit  202  that generally comprises the a lens, wiper and rheostat configuration as described above in sending units  11  and  100 . Sending unit  202  includes circuitry for converting the resistive signal (described above as being carried on conductor  76 ) into a voltage signal  204  wherein the magnitude of the voltage at any point in time is represents a particular level of fluid in the storage tank. In a preferred embodiment, the resistive signal provides resistances between about 10 and 180 ohms. This feature has been described above in the discussions pertaining to sending units  11  and  100 . In a preferred embodiment, the voltage range of signal  204  is between about 0 volts and 5 volts. Voltage signal  204  is inputted into analog-to-digital (“ADC”)  206  that converts the voltage signal to a digital signal  208 . The number of bits in signal  208  depends upon the desired accuracy. In a preferred embodiment, signal  208  is comprises of eight (8) bits. Digital signal  208  is then inputted into data cache  210  which temporarily caches signal  208 . Data cache  210  then outputs digital signal  212  which is a time-delayed version of digital signal  208 . Digital signal  212  is inputted into microprocessor  214 . Microprocessor  214  can process digital signal  212  in a time-dependent format for fuel consumption rate display. Microprocessor  214  outputs digital signal  216  for input into display  218 . Microprocessor  214  can also store the data as well as transmit the data to microprocessors or computers of other systems. Display  218  can be realized by a LED (light-emitting diode) display or a LCD (liquid crystal display) that displays the number represented by digital signal  216 . In a preferred embodiment, display  218  displays the fluid level and the fluid usage per unit of time. Digital signal  216  is also used in the derivative time-domain for instantaneous usage calculation. Thus, system  200  can be used to determine the real-time-usage of fluid. In an alternated embodiment, analog-to-digital converter  206 , cache  210  and display  218  can be realized by a single integrated circuit such as a DATEL DMS-20PC Series Display. 
     Referring to FIG. 15, there is shown alternate fluid level monitoring system  300  of the present invention. System  300  includes signal sending unit  302  that generally comprises the lens and rheostat configuration as described above in sending units  11  and  100 . Sending unit  302  outputs a resistive signal  304 . (This is the signal described above as being carried on conductor  76 ). The resistance presented by signal  304  is preferably within the range of 3 and 200 ohms, inclusive, wherein the actual resistance at any point in time represents a particular fluid level in the storage tank. Signal  304  is inputted into power module  306 . Power module  306  includes a comparator circuit and an alarm activation signal circuit that is responsive to the comparator circuit. The comparator circuit compares the resistance of  304  to a predetermined threshold. In a preferred embodiment, module  306  includes at least one potentiometer for varying the predetermined fluid level alarm thresholds. In one embodiment, the input threshold is set at 50 ohms for a 10-180 ohm sending unit. In a preferred embodiment, power module  306  is configured as the combination of power supply  360  and adjustment control module  374  shown in FIGS. 15A and 15B and described below. 
     Referring to FIG. 15, when the resistance presented by signal  304  decreases below the predetermined threshold, power module  306  outputs signals  308  that indicate the actual fuel level and that such fuel level is below the predetermined thresholds. Signals  308  are inputted into alarm control circuit  310 . Alarm control circuit includes a plurality of inputs for receiving signal  312  outputted by building temperature alarm  314  and signal  316  outputted by burner lockout indicator  318 . Building temperature alarm  314  includes a thermostat and is activated when the temperature within a building (in which system  300  is being used) falls below a predetermined threshold. In one example, the threshold temperature is 40°. In one embodiment, the thermostat is positioned on or in proximity to the storage tank so as to monitor the approximate temperature of the fuel as well. In another embodiment, the thermostat is located with the gauge at a remote location. In an alternate embodiment, system  300  is configured to include a programmable thermostat that will enable personnel to program threshold temperatures. In another embodiment, system  300  includes a display, similar to display  218  (see FIG.  14 ), that is mounted in the same housing or enclosure as the thermostat that controls the burner and building temperature. Burner lockout indicator  318  is connected to the conventional “burner reset” switch typically used in most residences and commercial buildings. Burner lockout indicator  318  is activated when the reset switch is activated for any reason, e.g. burner ignition failure, no burner fuel, etc. Thus, signal  316  indicates whether the burner reset switch has been activated. 
     Referring to FIG. 15, alarm control circuit  310  outputs fault signal  320  when: (i) signals  308  indicate the level of fuel in the fuel storage tank that is below the predetermined threshold, (ii) signal  312  indicates the building temperature is below a predetermined threshold, and (iii) signal  316  indicates the burner reset switch has to be activated for the burner to continue operation. Fault signal  320  is inputted into telephone interface  322 . Fault signal  320  comprises the following information: (i) a signal or signals indicating whether the fuel level is below a predetermined thresholds, (ii) a signal indicating whether the building temperature is below a predetermined threshold, and (iii) a signal indicating whether the burner reset switch has to be activated for the burner to continue operation. Interface  322  includes a plurality of inputs for receiving exterior or incoming phone lines and in-house (or in-building) phone lines. In response to receiving signal  320 , telephone interface  322  couples signal  323  to the external or incoming phone lines for transfer to central receiver  324 . Central receiver  324  is located at a remote location and includes a computer that processes, stores and displays all the information contained in signal  323 . In one embodiment, receiver  324  also includes audio alarms to notify personnel via telephone answering machines or pagers that the fluid level or other alarm conditions described above are below the predetermined threshold. 
     Referring to FIG. 15, in an alternate embodiment, alarm control circuit  310  comprises an audio message system that outputs a specific audio message to telephone interface  322  for transmission over the phone lines. In such a configuration, central receiver  324  comprises a voice mail system for receiving and storing the audio messages. 
     Referring to FIGS. 15A-C, there is shown another embodiment of the fluid level monitoring system of the present invention. This system comprises sections  350 ,  352  and  354 . Section  350  comprises signal sending unit  356 , analog fuel gauge  358  and power supply  360 . Sending unit  356  function in the same manner as sending units  11  and  100  described above. Sending unit  356  has output  362  that carries the resistive signal that is representative of the level of fuel in the fuel storage tank. Sending units  356  and power supply  360  each have a ground node that is coupled to ground potential via conductors  363  and  372 , respectively. Analog gauge  358  functions in the same manner as gauge  70  described above (see FIGS.  1  and  5 ). Gauge  358  includes inputs  364 ,  366  and a ground node coupled to ground potential via conductor  368 . Power supply  360  has inputs coupled to an a.c. (alternating current) voltage source, e.g. 115 VAC, and d.c. voltage outputs  370  and  372 . In a preferred embodiment, the d.c. output voltage from supply  360  is between about 18 and 25 volts VDC. Output  372  is coupled to ground potential. 
     Referring to FIG. 15B, section  352  comprises adjustment control module  374 . Output  370  is coupled to one end of fuse  376 . The other end of fuse  376  is coupled to an input of voltage regulator  378 . In a preferred embodiment, regulator  378  is a 15 VDC voltage regulator. The output of voltage regulator  378  is coupled to one end of potentiometer  380 . In a preferred embodiment, potentiometer  380  has a resistance range between 0 and 10 K ohms. Potentiometer  380  is adjusted to provide a predetermined fuel level threshold. The wiper of potentiometer  380  is coupled to one end of resistor R 3 . In a preferred embodiment, resistor R 3  has a resistance of about 10 K ohms. The other end of resistor R 3  is coupled to the inverting input  382  of amplifier  383 . In a preferred embodiment, amplifier  383  is an operational amplifier. More preferably, amplifier  383  is a LM 358 Dual Operational Amplifier. Amplifier  383  has a ground node  384  coupled to ground potential. Referring to FIGS. 15A and 15B, power input  366  of gauge  358  is coupled to the power supply input  386  of amplifier  383 . Signal input  364  of gauge  358  is coupled to one end of resistor R 4 . In a preferred embodiment, resistor R 4  has a resistance of about 10 K ohms. Referring to FIG. 15B, adjustable resistor  387  has one end coupled to non-inverting input  385  of amplifier  383 . Adjustable resistor  387  provides hysteresis adjustment for the fuel level threshold set by potentiometer  380 . In a preferred embodiment, adjustable resistor  387  has a resistance range of 0 ohms to 100 Kohms. The other end of adjustable resistor  387  is coupled to output  388  of amplifier  383 . Output  388  is coupled to one end of resistor R 5 . In a preferred embodiment, resistor R 5  has a resistance of about 51 ohms. The other end of resistor R 5  is coupled to the anode of light emitting diode (“LED”)  390 . The cathode of LED  390  is coupled to input  392  of relay  394 . LED  390  functions as a relay activation indicator. Relay  394  includes a coil or inductor  395  that preferably has a 12 volt and 144 mw (milliwatt) rating. One end of  395  inductor is coupled to input  392 . The other end of inductor  395  is coupled to output  396  which is coupled to ground potential. Relay  394  further includes outputs  397  and  398 . These outputs will be discussed below. Amplifier  383 , and its associated components, and relay  394  form one fuel level alarm channel. The positive feedback to the amplifier  383  “pulls in” relay  394  and introduces an electrical hysteresis. Adjustable resistor  387  provides activation/reset bandwidth. For example, the alarm is activated when the level in the fuel storage tank falls below ¼ tank and the relay is reset when the fuel level rises to a predetermined reset level, i.e. ⅜ tank. 
     Referring to FIG. 15B, adjustment control module  374  further includes a second fluid level alarm channel which will now be described. Intput  366  of gauge  358  is coupled to one end of potentiometer  400 . In a preferred embodiment, potentiometer  400  has a resistance range between 0 and 10 K ohms. Potentiometer  380  is adjusted to provide a predetermined fluid threshold. The wiper of potentiometer  400  is coupled to one end of resistor R 6 . In a preferred embodiment, resistor R 6  has a resistance of about 10 K ohms. The other end of resistor R 6  is coupled to inverting input  402  of amplifier  404 . In a preferred embodiment, amplifier  404  is an operational amplifier. More preferably, amplifier  404  is a LM 358 Dual Operational Amplifier. Amplifier  404  has a ground node  406  coupled to ground potential. Referring to FIGS. 15A and 15B, input  366  of gauge  358  is coupled to the power supply input  408  of amplifier  404 . Signal input  364  of gauge  358  is coupled to one end of resistor R 7 . In a preferred embodiment, resistor R 7  has a resistance of about 10 K ohms. The other end of resistor R 7  is coupled to non-inverting input  410  of amplifier  404 . Referring to FIG. 15B, potentiometer  412  has one end coupled to non-inverting input  410  of amplifier  404 . Potentiometer  412  provides hysteresis adjustment for the fluid level threshold set by potentiometer  400 . In a preferred embodiment, potentiometer  412  has a resistance range of 0 ohms to 100 Kohms. The other end of potentiometer  412  is coupled to output  414  of amplifier  404 . Output  414  is coupled to one end of resistor R 8 . In a preferred embodiment, resistor R 8  has a resistance of about 51 ohms. The other end of resistor R 8  is coupled to the anode of light emitting diode (“LED”)  416 . The cathode of LED  416  is coupled to input  418  of relay  420 . LED  416  functions as a relay activation indicator. Relay  420  includes a coil or inductor  422  that preferably has a 12 volt and 144 mw (milliwatt) rating. One end of  422  inductor is coupled to input  418 . The other end of inductor  422  is coupled to output  424  which is coupled to ground potential. Relay  420  further includes outputs  426  and  428 . These outputs will be discussed below. Amplifier  404 , and its associated components, and relay  420  form the second fuel level alarm channel. The positive feedback to the amplifier  404  “pulls in” relay  420 . Potentiometer  412  provides activation/reset bandwidth as discussed above for the first fuel alarm channel. 
     Referring to FIG. 15C, section  354  comprises power supply  434 , automatic voice/pager dialer control panel  436 , relay  438  and relay  440 . In a preferred embodiment, power supply outputs 12 volts d.c. Power supply  434  has outputs  440  and  442 . Control panel  436  includes contact strips  444 ,  446  and  452 . Contact  444  is coupled to outputs  440  and  442  of power supply  434 . Contact  446  is coupled to incoming phone lines  448  and in-house phone lines  450 . Referring to FIGS. 15B and 15C, terminals  397  and  398  of relay  394  are coupled to contact strip  452  of control panel  436 . Terminals  426  and  428  of relay  420  are also coupled to contact strip  452 . Referring to FIG. 15C, relay  438  includes terminals  454  and  456  that are coupled to contact strip  452  of control panel  436 . Similarly, relay  440  includes terminals  458  and  460  that are coupled to contact strip  452  of control panel  436 . All connections to control panel  436  on contact strip  452  are dry contacts. 
     In an alternate embodiment, systems  200  and  300  may be combined with a burner-control thermostat to achieve a system for monitoring the level of fluid in a storage tank that allows (i) display of the fluid level in the storage tank, (ii) control of the temperature of the temperature of the building housing the storage tank, (iii) the below-threshold temperature, and (iv) the instantaneous fluid usage rate to be observed at a remote location. In such a configuration, display  218  is incorporated into central receiver  324 . Systems  200  and  300  are suitable for situations wherein the usage of fluids, such as fuel, oil, gas, drinking water, etc. must be monitored for reasons related to fluid conservation. 
     Referring to FIG. 16, there is shown alternate system  500  of the present invention for remote monitoring the level of fluids in a storage tank. Although the ensuing description is in terms of specific voltages and circuitry, it is to be understood that system  500  may be configured to use other types of circuitry and voltage levels. System  500  includes power supply  501 . In a preferred embodiment, the supply voltage +Vcc is 12 volts d.c. @ 500 ma. (milli-amperes). Power supply  72  (see FIG. 5) may be used to supply the voltage +Vcc. The supply voltage +Vcc is inputted into voltage regulator  502 . In a preferred embodiment, regulator  502  is a five (5) volt regulator and outputs five (5) volt line  504 . Line  504  is coupled to one end of resistor R 1  and resistor R 2 . In a preferred embodiment, resistor R 1  has a resistance of about 48 K ohms and resistor R 2  has a resistance of about  4 K ohms. System  500  further includes a “zero trim” adjustment circuit  506 . In a preferred embodiment, circuit  506  is configured as a potentiometer that has input  507  and wiper  508 . The potentiometer of circuit  506  preferably has a resistance range between 0 ohms and 50 K ohms, inclusive. Input  507  is coupled to the other end of resistor R 1 . Wiper  508  is coupled to “INPUT LOW” of digital meter  510 . 
     Referring to FIG. 16, display  510  is preferably a digital volt meter. Display  510  receives a supply voltage from voltage regulator  502 . In a preferred embodiment, voltage regulator circuit  502  provides a regulated output voltage of 5 volts d.c. Resistors R 1  and R 2  are padding resistors that protect display  510  from over-voltage during adjustment of the potentiometers of circuits  506  and  512 . 
     Referring to FIG. 16, system  500  further includes “span” adjustment circuit  512 . In a preferred embodiment, circuit  512  is configured as a potentiometer that includes input  513  and wiper  515 . The potentiometer of circuit  512  preferably has a resistance range between 0 ohms and 46 K ohms, inclusive. The other end of resistor R 2  is coupled to input  513 . The wiper  515  is coupled to “INPUT HIGH” of digital meter  510 . 
     Referring to FIG. 16, system  500  further includes circuit  516  that produces a signal that is representative of the level of fluid in the storage tank. In preferred embodiment, circuit  516  is configured as sending units  11  or  100  described above. Thus, circuit  516  comprises a wiper, a reference conductor and resistive conductor. The reference conductor of circuit  516  is connected to wiper  517  of circuit  512 . As described in above for sending units  11  and  100 , the wiper of circuit  516  moves between the reference conductor and resistive conductor. Circuit  516  outputs a resistive signal that is coupled to wiper  515  of circuit  512 . Adjustment circuit  512  provides for adjustment of the level of the resistive signal to a predetermined level that corresponds to a given fluid or liquid storage tank capacity that is within the operational limits of the digital meter. 
     The present invention provides systems that may be used to monitor the (i) fluid or liquid level in a fluid storage device, (ii) the temperature of the building that houses the fluid storage device, and (iii) usage rate of any type of fluids, e.g. water, fuel, oil, gas, etc. and provide the monitored parameters to remote locations. The present invention: 
     a) is inexpensive to manufacture; 
     b) can be integrated into level measurement devices of existing fluid storage tanks; 
     c) uses a minimum of electrical power; 
     d) can be used to monitor the usage of water and fuels for purposes of conservation; and 
     e) provides highly accurate data regarding the level and the usage of the fluids as well as the temperature of the housing in which the fluid is stored. 
     While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.