Abstract:
A fluid sensor system capable of sensing a fluid level or a volume of fluid held by a reservoir, such as a container or a tank. In one embodiment, the system may include a magnetic element in a flotation device that suspends the magnetic element in the fluid held by the reservoir, so that the magnetic element randomly floats in proximity to a top of the fluid surface. Two or more magnetic field sensors or magnetometers are associated with the reservoir in at least two different locations, spaced apart from one another. The system further includes a processor coupled to the sensors. The magnetic field sensors may sense the strength of the magnetic field around the magnetic element to generate signals that are sent to the processor. The processor may then determine the location of the magnetic element within the reservoir based on the signals. The determined location can be correlated to a volume of fluid within the tank which is output to another device and/or a user.

Description:
TECHNICAL FIELD 
       [0001]    The present application relates to a fluid level sensor, and more particularly to a field-based fluid level sensor system. 
       BACKGROUND 
       [0002]    Fluid level sensors are used in a variety of applications that involve detecting a level of fluid within a container. One application of growing significance is in the field of fuel senders for fuel tanks in vehicles. In a conventional arrangement, a fuel sender, more generally known as a type of fluid level sensor, can be disposed within a fuel tank, and may include a float that is mechanically coupled to a main body of the sender unit and that rises and falls along with the fuel level in the container. The float may be rotatably coupled to the main body via a float arm whose angular position corresponds to the float position and therefore the fluid level in the container. Conventionally, an electrical or actively powered sensor is placed within the container as part of the fuel sender and along with the float to sense the angular position of the float arm. Examples of such active sensors include rheostat sensors and inductive-based sensors. Such a sensor is conventionally powered via wiring or an electrical connection, or both, by a power supply external to the container. As a result, installation and use of the fuel sender involves providing power to components (e.g., the electronic sensor) within the container. Further, installation and use of the fuel sender also involves disposing mechanical as well as electrical components within the container, thereby increasing the complexity of installation and any potential repair efforts. 
         [0003]    Incorporation of electrical components and providing power thereto into a container can present several design considerations. Conventionally, if the fluid being stored in the container is corrosive or generally reactive, the fuel sender is constructed such that the electrical components and associated electrical conductors are sealed from the fluid by non-reactive materials. Such a construction, including use of such non-reactive materials, can increase the cost and complexity of the fuel sender. 
         [0004]    Another design consideration with respect to use of electrical components within a fluid container includes limiting or constraining the voltage or current, or both, supplied to the electrical components. In this way, the power supply may be limited to substantially avoid ignition of potentially flammable vapor within the container. Component selection of the fuel sender is often driven by these considerations. 
       SUMMARY OF THE DESCRIPTION 
       [0005]    The current embodiments provide a fluid sensor system capable of sensing a fluid level or a volume of fluid held by a reservoir, such as a container or a tank. 
         [0006]    In one embodiment, the system may include a magnetic element having a flotation device that suspends the magnetic element in the fluid held by the reservoir, so that the magnetic element randomly floats in proximity to a top of the fluid surface. Two or more magnetic field sensors, optionally magnetometers, are associated with the reservoir in at least two different locations, spaced apart from one another. The system further includes a processor coupled to the sensors. The magnetic field sensors may sense the strength of the magnetic field around the magnetic element to generate signals that are sent to the processor. The processor may then determine the location of the magnetic element within the reservoir based on the signals. The determined location can be correlated to a volume of fluid within the tank which is output to another device and/or a user. 
         [0007]    In another embodiment, the processor may triangulate the location or position of the magnetic element within the reservoir based on one or more signals sensed by one or more magnetic field sensors. The magnetic field strength in proximity to each of the one or more magnetic field sensors may vary based on the distance between each respective magnetic field sensor and the magnetic element. The processor may be coupled to memory that stores instructions relating to a functional relationship between the magnetic field strength sensed by the one or more magnetic field sensors and fluid level or volume of fluid held by the reservoir. The functional relationship may account for variations in movement of the flotation device on or adjacent a surface of the fluid so that such movement does not affect a determined fluid level based on the sensed magnetic field strengths. As an example, the processor may be determine the location of the flotation device by calculating angles, based on output from the one or more magnetic field sensors, relative to known locations of the one or more magnetic field sensors. The calculated angles may be relative to a fixed baseline defined by the known locations of the one or more magnetic field sensors. As another example, in an embodiment having three magnetic field sensors disposed at fixed positions, the processor may triangulate the position of the magnetic element as a function of variances in the sensed strength of the magnetic field emanating from the magnetic element. 
         [0008]    In yet another embodiment, the system may include a flotation device joined with a magnetic element and that floats in proximity to a surface of the fluid held by a fluid reservoir. One or more magnetic field sensors may be disposed on or in proximity to a wall of the fluid reservoir, and may provide sensor output indicative of a magnetic field strength. The magnetic field strength may vary as a function of the position of the magnetic element with respect to the one or more magnetic field sensors. As an example, the one or more magnetic field sensors may include a plurality of magnetic field sensors disposed at different positions, and the magnetic field strength sensed by each on the magnetic field sensors may be different depending on the relative distance from the magnetic element. 
         [0009]    In still another embodiment, movement of the flotation device may be substantially constrained to a single axis of travel by a flotation guide, such a rod or tube. 
         [0010]    In even another embodiment, movement of the filtration device may be substantially random about the surface of the fluid held by the fluid reservoir. 
         [0011]    In a further embodiment, the one or more magnetic field sensors may be disposed at various locations, including internally or externally, or a combination thereof, with respect to the fluid reservoir. As an example, the one or more magnetic field sensors may be disposed outside the fluid reservoir and the flotation device may be disposed inside the fluid reservoir, thereby avoiding placing electric circuitry of the sensor system within the fluid reservoir. Further, the magnetic field sensors may be disposed on a wall of the fluid reservoir or adjacent thereto. 
         [0012]    In yet a further embodiment, the flotation device including the magnetic element may be constructed such that the flotation device self-orients while floating. For instance, the flotation device may be weighted such that, in floating in proximity to a surface of the fluid, the flotation device rights itself to substantially maintain a particular orientation with respect to a surface of the Earth or the gravitational acceleration vector of the Earth. As another example, the flotation device may be constructed to include a greater amount of buoyant composition distributed away from a center of mass of the flotation device so that the flotation device orients itself with respect to the surface of the fluid. 
         [0013]    In still another embodiment, a method of determining a fluid level of fluid held by a fluid reservoir includes floating a magnetic element in proximity to the surface of the fluid. In one embodiment, the magnetic element may randomly float with respect to the surface. In another embodiment, the magnetic element may be constrained to movement along a single axis of travel. 
         [0014]    The method according to this embodiment may include sensing first and second magnetic field strengths from respective first and second magnetic field sensors that are disposed at different positions. The first and second magnetic field strengths may respectively vary or change based on a relative position between the magnetic element and the first and second magnetic field sensors. Based on the sensed first and second magnetic field strengths, a position of the magnetic element may be determined and correlated to a fluid level of the fluid held by the fluid reservoir. Optionally, the fluid level of the fluid may be determined directly from the sensed first and second magnetic field strengths. 
         [0015]    In even a further embodiment, a fluid level sensor system may determine a fluid level of fluid held by a reservoir based on information relating to sensed magnetic field strength from one or more locations. The sensed magnetic field strength may be different at each location and may vary based on a relative position or distance between each location and a magnetic element. The magnetic element may be coupled to a flotation device that floats the magnetic element in proximity to a surface of the fluid. With this configuration, the fluid level sensor system according to one embodiment may determine a fluid level without disposing circuitry or other electrical components into the fluid reservoir or in contact with the fluid. Further, in one embodiment, installation and operation of the fluid level sensor system can be simpler than conventional systems in that the flotation device can be dropped into the reservoir and can randomly float toward areas not readily accessible for measurement by conventional systems. For instance, the fluid level sensor system according to one embodiment can be configured to sense fluid level within differently shaped reservoirs, including reservoirs having narrow passages or volumes that conventional float arm-based fuel senders do not operate within. These and other advantages and features of the invention will be more fully understood and appreciated by reference to the description of the current embodiment and the drawings. 
         [0016]    Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited to the details of operation or to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention may be implemented in various other embodiments and of being practiced or being carried out in alternative ways not expressly disclosed herein. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. Further, enumeration may be used in the description of various embodiments. Unless otherwise expressly stated, the use of enumeration should not be construed as limiting the invention to any specific order or number of components. Nor should the use of enumeration be construed as excluding from the scope of the invention any additional steps or components that might be combined with or into the enumerated steps or components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  shows a field-based fluid level sensor system according to a first embodiment associated with a fluid container. 
           [0018]      FIG. 2  depicts a representative view of the fluid level sensor system according to the first embodiment. 
           [0019]      FIG. 3  shows a representative graph of the functional relationship between magnetic field strength and a level of fluid in the fluid container according to the first embodiment. 
           [0020]      FIG. 4  shows a field-based fluid level sensor system according to a second embodiment arranged conjunction with the fluid container. 
           [0021]      FIG. 5  shows a representative graph of the functional relationship between magnetic field strength and a level of fluid in the container according to the second embodiment. 
           [0022]      FIG. 6  shows a magnetic float according to the first embodiment. 
           [0023]      FIG. 7  shows a magnetic flow according to a third embodiment. 
           [0024]      FIG. 8  shows a magnetic flow according to a fourth embodiment. 
       
    
    
     DESCRIPTION 
       [0025]    A fluid level sensor system in accordance with one or more embodiments of the present disclosure is shown in  FIG. 1 , and generally designated  100 . As set forth below, the fluid level sensor system  100  may include a flotation device  102  adapted to float within a container  10 . The flotation device  102  is configured such that it is buoyant relative to a fluid  12  held by the container  10 , thereby rising and falling with a surface of the fluid  12  being held by the container  10 . In other words, the position of the flotation device  102  may be indicative of a fluid level of the fluid  12  being held by the container  10 . The fluid level sensor system  100  may be configured to detect one or more positional parameters of the flotation device  102  relative to one or more magnetometer sensors  110 ,  112 , and to determine a fluid level of the fluid  12  based on the one or more positional parameters. The positional parameters in one embodiment may include a precise spatial location of a magnetic element coupled to the flotation device  102 . 
         [0026]    The container  10  may be any type of tank or reservoir for holding fluid  12 , including for example a fuel tank. Further, the container  10  may be sealed in some applications, and unsealed or open in other applications. 
         [0027]    For purposes of disclosure, the fluid  12  within the container  10  is described at portions herein as being fuel within a fuel tank, but it should be understood that the present disclosure is not so limited and that any type of fluid may be held by the container  10  and that the fluid level sensor system  100  may be adapted to determine a fluid level of any fluid held by the container  10 . Example applications include but are not limited to septic tanks, food processing tanks, farm ponds, sewer or water treatment plants, oil refineries, oil tank, cargo containers, ship holds, grill propane tanks, rural propane tanks, clinical tanks, chemical tanks, any liquid storage tank, ballasts for watercraft. Additional example applications include fat sacks (for boats), or any other type of dynamic tank or reservoir that can change in size or shape, or both. Further example applications include aviation fuel tanks at any location on the air craft, toilet bowl reservoirs, windshield fluid tanks, hot water tanks, water holding tanks (e.g., roof tops, natural rain water), coffee makers, portable restroom reservoirs, hazardous tanks, liquefied natural gas (LNG) tanks, liquid nitrogen storage, hydrogen storage, and urea storage. 
         [0028]    The container  10  may be formed of any type of material, including nonmagnetic material or magnetic material, or a combination thereof. In principal, the material used for the container  10  may depend on the type of fluid  12  to be held by the container  10 . For example, if the fluid  12  is a fuel that reacts to several types of materials, a non-reactive material with respect to the fluid  12  may be used for the container  10 . In one embodiment, the container  10  may be formed primarily of nonmagnetic, plastic material such as polyethylene. The container  10  may be a substantially rigid such that the container substantially maintains its shape regardless of the amount of fluid being held. Alternatively, the container  10  may be soft such that the container  10  can expand or change shape, or both. For instance, the soft structure of the container  10  may enable expansion thereof such that an internal volume of the container  10  can increase to accommodate additional fluid. 
         [0029]    The fluid level sensor system  100  according to one embodiment may be a fuel sender for use in conjunction with a vehicle. In this context, the fluid level sensor system  100  may provide a fuel sender output, such as an analog voltage output or a variable resistance output, that is indicative of a fluid level of the fluid  12  held by the container  10 . This fuel sender output may be fed or provided to components of the vehicle, such as a fuel gauge. 
         [0030]    For example, the fuel sender output of the fluid level sensor system  100  may have a resistance in a range of 240-30 ohms, where 240 ohms corresponds to an empty container and 30 ohms corresponds to a full container. The fuel gauge may be configured to indicate the fluid level based on the resistance of the fuel sender output. As fuel is consumed from the fuel tank by the vehicle engine, there is a decrease in height of the fluid  12  and the flotation device  102  relative to a bottom of the fuel tank. The fluid level sensor system  100  may be configured to determine a height of the flotation device  102  based on magnetic sensor output from the one or more magnetometers  110 ,  112 , to determine a fluid level based on the determined height, and to vary the fuel sender output to correspond to the determined fluid level. In this example, as the fuel is consumed by the vehicle engine, the resistance of the fuel sender output increases. It should be understood that the fluid level sensor system  100  may provide any type of output indicative of a fluid level of fluid  12  held by the container  10 , and that the present disclosure is not limited to any particular feature or aspect of the described example. 
         [0031]    The flotation device  102  in the illustrated embodiment of  FIG. 1  may include a magnetic element, such as a permanent magnet or magnetic material, such as ferromagnetic or paramagnetic material. One example of a magnetic material is iron, but any type of magnetic material may be used. In the illustrated embodiment, the magnetic element  108 , itself, may not be buoyant relative to the fluid  12 —however, the flotation device  102  may include a buoyant composition  109  that can overcome the weight of the magnetic element  108  such that the flotation device  102 , including the magnetic element  108  and the buoyant composition  109 , may be buoyant relative to the fluid  12 . 
         [0032]    An example of such a flotation device  102  is shown in a sectional view in the illustrated embodiment of  FIG. 6 . The flotation device  102  in the illustrated embodiment includes a magnetic element  108  and buoyant composition  109  that is arranged to hold the magnetic element  108 . The buoyant composition  109  may encapsulate the magnetic element  108  as shown in the illustrated embodiment—but it should be understood that encapsulation is not a necessity. For example, rather than being encapsulated within the buoyant composition  109 , the magnetic element  108  may be disposed on the buoyant composition  109 . The buoyant composition  109  may include one or more voids to which a surface thereof may be joined with the magnetic element  108 . Adhesive or a mechanical interlock, or any type of joining or fastening mechanism may be used to join the magnetic element  108  and the buoyant composition  109 . 
         [0033]    Optionally, the magnetic element  108  may not be joined with the buoyant composition  109 —instead, the magnetic element  108  may be held within or constrained by the buoyant composition  109 . For instance, the magnetic element  108  may be constrained within a void of the buoyant composition  109  such that the magnetic element  108  can freely move within the void. For example, the buoyant composition  109  may include a sealed, plastic shell that is filled with an inert gas and contains the magnetic element  108 . In this way, the magnetic element  108  can freely move within the plastic shell, but because the density of the magnetic element  108  is greater than the inert gas, the magnetic element  108  may orient itself within the plastic shell such that the magnetic element  108  accelerates or lies along the gravitational acceleration vector of the Earth. 
         [0034]    In the illustrated embodiment, the magnetic element  108  may be disposed off center relative to a central axis  132  of the flotation device  102  so that the weight or density distribution of the flotation device  102  is asymmetrical. In this way, the flotation device  102  may be self-orienting. As can be seen in the illustrated embodiment of  FIG. 6 , the magnetic element  108  includes North and South poles (N-S). Because the flotation device  102  is configured to self-orient on the surface of the fluid  12 , the magnetic element  108  may be disposed such that the N-S poles are aligned normal or perpendicular to a surface of the fluid  12 . 
         [0035]    In the illustrated embodiment, the buoyant composition  109  may be a non-reactive composition that does not react to the fluid  12  held by the container  10 , and may be less dense than the fluid  12  such that the flotation device  102  floats in proximity to a surface of the fluid  12 . The buoyant composition  109  may be comprised of a plurality of compositions that together achieve buoyancy of the flotation device  102  relative to the fluid  12 . As an example, the buoyant composition  109  may include plastic having one or more voids that are filled with another composition, such as a gas. Examples of gases that may facilitate buoyancy include air, nitrogen, or inert gas. 
         [0036]    The flotation device  102  may be sized and configured so that it can be easily installed within the container  10 . In one embodiment, the flotation device  102  may be “dropped” or otherwise disposed in the container  10  through an opening of the container  10  (e.g., the fill opening) during manufacture. In an alternative embodiment, the flotation device  102  may be larger than a fill opening of the container  10 , but may be disposed within the container  10  at manufacture by placing the flotation device  102  in the container  10  during formation of the container  10  and prior to one or more openings of the container  10  being too small or sealed to prevent placement of the flotation device  102 . With this configuration, it may not be possible to remove the flotation device  102  from the container  10  without disassembling the container  10 . In one embodiment, during manufacture of the container  10 , the flotation device  102  may be installed within the container  10  and adhered to an inner wall of the container  10  using a fluid dissolvable adhesive. This way, the adhesive may prevent the flotation device  102  from freely moving within the container  10  during shipment and prior to the container  10  being filled with the fluid  12 . 
         [0037]    The fluid level sensor system  100  may include one or more magnetic field sensors  110 ,  112 , such as magnetometer sensors as mentioned herein. In the illustrated embodiment of  FIG. 1 , the one or more magnetic field sensors include a first magnetic field sensor  110  and a second magnetic field sensor  112 . The one or more magnetic field sensors  110 ,  112  may be any type of magnetic field sensor capable of sensing a magnetic field strength (e.g., a Gauss value) along one or more axes or varying an output based on strength of the magnetic field. In the illustrated embodiment, the one or more magnetic field sensors  110 ,  112  may be 3-axis magnetometers configured to sense a magnetic field strength along 3-orthogonal axes (X, Y, and Z), and may utilize a magneto resistive type sensor formed as an integrated circuit. The type of magnetic field sensor  110 ,  112  is not limited to a magnetic resistive type sensor. Any type of magnetic field sensor may be utilized, including, for example, a magnetic inductive sensor. The one or more magnetic field sensors  110 ,  112  may be disposed on or in proximity to a container wall of the container  10 . Further, the one or more magnetic field sensors  110 ,  112  may be positioned inside the container  10  or outside the container  10 , or a combination thereof. 
         [0038]    A variety of factors may affect the sensed magnetic field strength, including the strength of the Earth&#39;s magnetic field at a particular latitude and longitude, deviations in the Earth&#39;s magnetic field potentially due to proximity to a ferromagnetic or magnetic material, and a position of the flotation device  102  relative to the magnetometer. The one or more magnetic field sensors  110 ,  112  may provide one or more outputs indicative of the magnetic field strength along the one or more axes. As an example, the one or more magnetic field sensors  110 ,  112  may provide a digital communication interface, such as an  12 C interface, through which a separate controller or sensor circuitry  120  can obtain digital information relating to a magnetic field strength along the one or more axes. As another example, the one or more magnetic field sensors  110 ,  112  may provide one or more analog outputs whose output voltage range corresponds to a range of magnetic field strength. The one or more analog outputs can be sensed and converted via an analog-to-digital converter to a digital value representative of the magnetic field strength. 
         [0039]    The fluid level sensor system  100  as described herein may include sensor circuitry  120  operably coupled to the one or more magnetic field sensors  110 ,  112  to obtain sensor information relating to a magnetic field strength along one or more axes. The sensor circuitry  120  may include a controller or microprocessor and memory with instructions to direct the microprocessor to calculate a fluid level based on the sensor information obtained from the one or more magnetometer sensors  110 ,  112 . 
         [0040]    In one embodiment, because the flotation device  102  includes a magnetic material  109 , a strength of the magnetic field sensed by the one or more magnetic field sensors  110 ,  112  may change as the flotation device  102  moves relative to the one or more magnetic field sensors  110 ,  112 . In other words, a magnetic field strength along one or more axes sensed by the first magnetic field sensor  110  may depend on a position of the flotation device  102  relative to the first magnetic field sensor  110 . Likewise, a magnetic field strength along one or more axes sensed by the second magnetic field sensor  112  may depend on a position of the flotation device  102  relative to the second magnetic field sensor  112 . The sensor circuitry  120  may obtain sensed information from the first and second magnetic field sensors  110 ,  112  that relates to magnetic field strength sensed by the respective magnetic field sensor, and determine a fluid level of the fluid  12  held by the container  10  based on the sensed information. 
         [0041]    In the illustrated embodiment, a plurality of magnetic field sensors  110 ,  112  may be disposed on or in proximity to the container  10  at different positions. For instance, the first magnetic field sensor  110  may be disposed near a full level, and the second magnetic field sensor  112  may be disposed near an empty level of the container  10 . Because the flotation device  102  can float within the container  10  and rises and falls with a fluid level of the fluid  12 , and because the plurality of magnetic field sensors  110 ,  112  are disposed of different positions, a magnetic field strength sensed by one magnetic field sensor may be different from a magnetic field strength sensed by another magnetic field sensor. The sensor circuitry  120  may analyze these different sensed magnetic field strengths to determine a position of the flotation device  102  with respect to the plurality of magnetometer sensors  110 ,  112 . In one embodiment, the sensor circuitry  120  may utilize triangulation techniques based on the relative strength of the sensed magnetic fields to determine the position of the flotation device  102 . 
         [0042]    The sensor circuitry  120  in one embodiment may include a controller or a microprocessor and memory that stores instructions to determine a fluid level of the fluid  12  held by the container  10  based on sensed magnetic field strength information. In one embodiment, as described above, the sensed magnetic field strength information may be obtained from a plurality of magnetic field sensors, each disposed at different positions, such that the relative sensed magnetic strength measured by the plurality of magnetic field sensors is indicative of a position of the flotation device  102  within the container  10 . 
         [0043]    In the illustrated embodiment of  FIGS. 2 and 3 , functional relationships among magnetic field strength, position of a magnetic field sensor, and position of the flotation device  102  are shown in relation to a fluid level of fluid  12  held by the container  10 . For purposes of disclosure, in the illustrated embodiment, the flotation device  102  includes a permanent magnet  108  that emanates a magnetic field B and is oriented with its N-S poles aligned with the gravitational acceleration vector of the Earth, which is depicted as the Z-axis in  FIG. 2 . The level of the fluid  12  held by the container  10  also corresponds to a position along the Z-axis in  FIG. 2 . While floating on the surface of the fluid  12 , the flotation device  102  can move freely in along the X and Y axes depicted in  FIG. 2 , and can rise and fall with the level of the fluid  12  along the Z-axis. It should be understood that the X, Y, and Z axes could be oriented differently, but have been chosen as shown in  FIG. 2  to facilitate discussion. 
         [0044]    The magnetic field B emanating from the flotation device  102  may vary in strength as a function of distance. More specifically, the strength of the magnetic field B may be approximately 1/r 3 , where r is a distance from the flotation device  102 . It should be understood there are several other factors that can affect magnetic field strength at a measurement point or location relative to the flotation device  102 , including, for example, orientation of the magnetic element  108  (or its principal N-S vector) relative to a point of measurement that can affect a measured strength of the magnetic field B. The physical dimensions of the magnetic element  108  may also affect the measured strength of the magnetic field B at a measurement location or point. These factors among others can affect a measured strength of a magnetic field at a point or location relative to the magnetic element  108  of the flotation device  102 . However, for purposes of disclosure, the strength of the magnetic field can be approximated as 1/r 3 . 
         [0045]    In the illustrated embodiment of  FIGS. 2 and 3 , the flotation device  102  is depicted at a Z-axis position corresponding to a fluid level between full (or 100% full) and half-full (or 50% full). The magnetic field sensors  110 ,  112  are disposed respectively near the full and empty positions. As a result, as can be seen, a distance r 2  between the first magnetic field sensor  110  and the flotation device  102  is smaller than a distance r 2  between the second magnetic field  112  and the flotation device  102 . The measured magnetic field strength B 1  in proximity to the first magnetic field sensor  110  is therefore likely to be greater than the measured magnetic field strength B 2  in proximity to the second magnetic field sensor  112 . Based on the measured magnetic field strengths B 1 , B 2 , the sensor circuitry  120  may calculate a fluid level of the fluid  12  corresponding to the Z-axis position of the flotation device  102 . More particularly, the sensor circuitry  120  may determine the fluid level as a function of the measured magnetic field strengths B 1 , B 2  according to some function F. In one embodiment, the first magnetic field sensor  110  may be positioned at or near the full Z-axis position, and the second magnetic field sensor  112  may be positioned at or near the empty Z-axis position. The sensor circuitry  120  may determine fluid level based on the difference between a) the sensed magnetic field strength of the first magnetic field sensor  110  and b) the sensed magnetic field strength of the second magnetic field sensor  112 . The functional relationship between fluid level or Z-axis position and the sensed magnetic field strengths may be linear and calculated, for example, based on the difference in sensed magnetic field strength between the “empty” sensor and the “full” sensor. The Z-axis difference may be factored out because the distance to three points are determined or known: 1) the determined distance between the magnet and the empty sensor, 2) the determined distance between the magnet and the full sensor and 3) the known distance between the empty sensor and the full sensor. 
         [0046]    In the illustrated embodiment, because the flotation device  102  is allowed to float along the surface of the fluid  12 , the flotation device  102  may move freely in an X-Y plane or along the X-axis and the Y-axis. This free movement may cause variations in the magnetic field strength measured by the first and second magnetometers  110 ,  112 . In other words, as the flotation device  12  floats freely in a direction toward or closer to the first magnetic field sensor  110 , the measured magnetic field strength B 1  may increase. And, likewise, as the flotation device  102  floats freely in a direction farther from the first magnetic field sensor  110 , the measured magnetic field strength B 1  may decrease. The same can be said for the measured magnetic field strength B 2  sensed by the second magnetic field sensor  112 . 
         [0047]    Although the flotation device  102  may move freely along the X and Y axes, the Z-axis position of the flotation device  102  may be substantially stable or constant (assuming no changes in actual fluid level and no changes in orientation of the container  10  relative to the gravitational acceleration vector of the Earth. In other words, the position of the flotation device  12  corresponding to a fluid level may be substantially constant in a stable environment. As mentioned herein, movement of the flotation device  12  in an X-Y plane or along the X and Y axes may correspond to a change in the respective distances r 1 , r 2  between the first and second magnetometer sensors  110 ,  112  and the flotation device  12 . However, in the illustrated embodiment, there is a functional relationship between the distances r 1 , r 2  and the Z-axis position or a fluid level such that the sensor circuitry  120  can determine a fluid level or Z-axis position based on an indication of the distances r 1 , r 2 . 
         [0048]    The respective distances r 1 , r 2  between the one or more magnetometer sensors  110 ,  112  and the flotation device  102  may not be directly measurable, but in the illustrated embodiment, information relating to these distances may be determined based on the measured magnetic field strengths B 1 , B 2 . Based on the measured magnetic field strengths B 1 , B 2  obtained from the one or more magnetic field sensors  110 ,  112 , the sensor circuitry  120  may determine the fluid level or Z-axis position of the flotation device  102  in the container  10 . The functional relationship between the measured magnetic field strength B 1 , B 2  may yield information relating to the distances r 1 , r 2  and therefore the Z-axis position of flotation device  102 . 
         [0049]    In the illustrated embodiment of  FIG. 3 , a functional relationship between the magnetic field strength B 1 , B 2  and fluid level or Z-axis position is shown. For purposes of disclosure, the functional relationship is depicted as being generally linear; however, it should be understood that the functional relationship may not be linear. For instance, the functional relationship may be parabolic or exponential. It should also be understood that the functional aspects used to determine the Z-axis position of the flotation device  102  may be based on additional parameters, including measured parameters or predetermined parameters or a combination thereof. In embodiments in which there are more than two measured magnetic field strengths obtained from more than two magnetometer sensors, the functional relationship may be represented by a corresponding number of dimensions. 
         [0050]    The Z-axis position of the flotation device  102 , in the illustrated embodiment of  FIG. 3 , may functionally correspond to the ratio between (a) the magnetic field strength B 1  measured by the first magnetic field sensor  110  and (b) the magnetic field strength B 2  measured by the second magnetic field sensor  112 . For instance, at the Z-axis position corresponding to Z_Actual, the ratio between the magnetic field strengths B 1 , B 2  may follow a linear relationship despite changes in strength due to position changes along the X axis and the Y axis, or both. As the flotation device  102  moves farther away from both the first and second magnetometer sensors  110 ,  112 , the measured magnetic field strengths B 1 , B 2  may decrease in a corresponding manner—however, as shown in  FIG. 3 , the ratio between the measured magnetic field strengths B 1 , B 2  and the Z-axis position may follow a linear relationship along the line labeled Z_Actual. As a result, the sensor circuitry  120  may obtain the measured magnetic field strength B 1 , B 2  from the first and second magnetic field sensors  110 ,  112 , and calculate the Z-axis position or fluid level as a function of the measured magnetic field strengths B 1 , B 2 . If the Z-axis position changes, similar functional relationships based on the measured magnetic field strengths B 1 , B 2  may be implemented to determine the Z-axis position change, including, for example, those shown and labeled as Z 100% , Z 50%  and Z 0%  in  FIG. 3 . 
         [0051]    In some applications, the container  10  may be in motion and may not remain static. Vehicle applications, such as cars or watersports, are examples of such non-static applications. As a result, the fluid  12  held by the container  10  may be in motion, and the float  12  may also be in motion. This type of motion may be considered unrelated to the actual fluid level of the fluid  12  held by the container  10 , but may affect or cause variations in the sensed magnetic field strength of the one or more magnetic field sensors  110 ,  112 . Filtering of the sensed magnetic field strength may be implemented to substantially remove or prevent sensor variations unrelated to changes in the fluid level from affecting the determined fluid level of the fluid level sensor system  100 . Kulman filtering is one example of a filter technique that may be in conjunction with preventing unrelated motion from affecting the calculated fluid level. 
         [0052]    A fluid level sensor system in accordance with one embodiment of the present disclosure is shown in  FIG. 4 , and generally designated  200 . The fluid level sensor system  200  may be similar to the fluid level sensor system  100  described herein, but with several exceptions. For example, the fluid level sensor system  200  may include a flotation device  202 , a magnetic field sensor  210 , and sensor circuitry  220  similar in some respects to the flotation device  102 , the one or more magnetic field sensors  110 ,  112 , and the sensor circuitry  120  described in connection with the fluid level sensor system  100 . In the illustrated embodiment, the fluid level sensor system  200  may be configured such that the flotation device  202  is constrained by a flotation guide  204  to travel substantially along a single axis. A position of the flotation device  202  along this single axis may correspond to a fluid level of the fluid  12  held by the container  10 . 
         [0053]    The single axis of travel in the illustrated embodiment of  FIG. 4  may be aligned with a longitudinal axis of the flotation guide  204 , along which the flotation device  202  may travel. In the illustrated embodiment, the flotation guide  204  may be in the form of a rod or tube disposed through an aperture of the flotation device  202 . This rod configuration of the flotation guide  202  may enable the flotation device  202  to freely move along the longitudinal axis of the flotation guide  202 , or to freely rise and fall with the fluid level of the fluid  12  held by the container  10 . In one embodiment, the flotation guide  202  may be coupled to a container cap that enables insertion of the flotation guide  202  through an aperture into the container  10  and configured to seal the aperture to prevent the fluid  12  from exiting through the aperture. 
         [0054]    Because the flotation device  202  may be constrained to movement in substantially a single axis, the functional relationship utilized by the sensor circuitry  220  may be configured to determine a fluid level based on a sensed magnetic strength from a single magnetic field sensor—although it should be understood the present disclosure, including the fluid level sensor system  200 , is not limited to use of a single magnetic field sensor. In other words, in the illustrated embodiment of  FIG. 5 , a plurality of magnetometer sensors may be disposed at different positions, similar to the fluid level sensor system  100 . The fluid level sensor system  200  may obtain and analyze the sensed magnetic field strengths from the plurality of magnetic field sensors to determine a fluid level. 
         [0055]    In the illustrated embodiment, the sensor circuitry  220  may determine fluid level based on a functional relationship between (a) a position of the flotation device  202  that corresponds to a fluid level and (b) sensor output from the magnetic field sensor  210 . For example, the fluid level of the fluid  12  held by the container  10  may functionally correspond to a measured magnetic field strength B of a single magnetic field sensor  210 . With the magnetic field sensor  210  being positioned in proximity to a full level, and with the flotation device  202  being constrained to movement that is substantially linear or along a single axis, the stronger the measured magnetic field strength B, the closer the flotation device  202  is to the magnetic field sensor  210 . The weaker the magnetic field strength B, the farther the flotation device  202  is from the magnetic field sensor  210 . Weakening of the magnetic field strength B may be indicative of the flotation device  202  may be falling or moving away from the magnetic field sensor  210 . 
         [0056]    The flotation device  202 , as discussed herein, may be configured in a variety ways. In the illustrated embodiment, the flotation device  202  may include an aperture through which the flotation guide  204  may be disposed. The flotation device  202 , like the flotation device  102 , may include a magnetic element and a buoyant composition. 
         [0057]    An example embodiment of a flotation device similar to the flotation device  202  is shown in  FIG. 8 , and generally designated  402 . The flotation device  402  may be similar to the flotation device  202 , and includes an aperture  403 . The flotation device  402  may also include buoyant material  409  similar to the buoyant material  109  described in connection with the flotation device  102 . The aperture  403  of the flotation device  402 , when used in conjunction with a rod-type flotation guide, may allow the flotation device  402  to spin or rotate about the flotation guide. This spin or free rotation may result from sufficient clearance existing between the flotation guide and the flotation device  402  such that the flotation device  402  can freely move along a longitudinal axis of the flotation guide. In one embodiment, the flotation device may interlock with a portion of the flotation guide along the longitudinal length thereof such that free spin or rotation is substantially prevented. 
         [0058]    In the illustrated embodiment of  FIG. 8 , the flotation device  402  may include a plurality of magnetic element  404 ,  405 ,  406 ,  407  disposed about a center of the flotation device  402  in a manner that is substantially uniform. In this way, as the flotation device  402  freely spends or freely rotate about the flotation guide, a magnetic field strength emanating from the plurality of magnetic element  404 ,  405 ,  406 ,  407  may appear to be substantially the same from the perspective of the magnetometer sensor  210 . 
         [0059]    An alternative embodiment of a flotation device is shown in  FIG. 7 , and generally designated  302 . The flotation device  302  may be similar to the flotation device  102 , including a magnetic element  308  and buoyant composition  309 . The distribution of the buoyant material  309  in the flotation device  302  may aid in maintaining alignment of the flotation device  302 . For instance, in the illustrated embodiment, a principal component of the buoyant composition  309  may be distributed away from a center of the flotation device  302  (e.g., a center of mass), thereby causing first or second primary flotation surfaces  304 ,  306  to be oriented with respect to a surface of the fluid  12 . In this way, the magnet element  308  may be aligned in a particular manner relative to a surface of the fluid  12  or the Earth. As an example, in the case of the magnetic element  308  being a permanent magnet with a N-S pole, the magnetic element  308  may be positioned within the buoyant composition  309  such that the N-S pole is aligned with the surface of the fluid  12 —though the N-S pole may be up or down in this configuration. 
         [0060]    Optionally, the magnetic element may be disposed on a surface of the buoyant composition  309 , as shown in broken lines in the illustrated embodiment of  FIG. 7 , and generally designated  308 ′. The magnetic element  308 ′ may be affixed to the buoyant composition  309  during manufacture, facilitating production of the buoyant composition  309  separate from the magnetic element  308 ′. 
         [0061]    Directional terms, such as “vertical,” “horizontal,” “top,” “bottom,” “upper,” “lower,” “inner,” “inwardly,” “outer” and “outwardly,” are used to assist in describing the invention based on the orientation of the embodiments shown in the illustrations. The use of directional terms should not be interpreted to limit the invention to any specific orientation(s). 
         [0062]    The above description is that of current embodiments of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. This disclosure is presented for illustrative purposes and should not be interpreted as an exhaustive description of all embodiments of the invention or to limit the scope of the claims to the specific elements illustrated or described in connection with these embodiments. For example, and without limitation, any individual element(s) of the described invention may be replaced by alternative elements that provide substantially similar functionality or otherwise provide adequate operation. This includes, for example, presently known alternative elements, such as those that might be currently known to one skilled in the art, and alternative elements that may be developed in the future, such as those that one skilled in the art might, upon development, recognize as an alternative. Further, the disclosed embodiments include a plurality of features that are described in concert and that might cooperatively provide a collection of benefits. The present invention is not limited to only those embodiments that include all of these features or that provide all of the stated benefits, except to the extent otherwise expressly set forth in the issued claims. Any reference to claim elements in the singular, for example, using the articles “a,” “an,” “the” or “said,” is not to be construed as limiting the element to the singular. Any reference to claim elements as “at least one of X, Y and Z” is meant to include any one of X, Y or Z individually, and any combination of X, Y and Z, for example, X, Y, Z; X, Y; X, Z; and Y, Z.