Abstract:
A liquid level measuring apparatus for measuring the level of a liquid in a bladder with flexible walls in which liquid in a container raises and lowers a plurality of floats, each float containing a magnetic element oriented in a vertical position. The floats are positioned within an inner guide tube. Pins of non-magnetic material restrict the vertical movement of the floats to sections of the inner guide tube with one float per section. The inner guide tube is placed inside the bladder. After placement of the inner guide tube, an outer sleeve is slid over the inner guide tube from the outside of the bladder with the bladder wall between the inner guide tube and outer sleeve. The outer sleeve contains magnetic reed switches that can be activated by the magnetic elements in the inner guide tube. Means of orientating the inner guide tube inside the bladder and assuring that the outer collar is at the correct position on inner guide tube such that the magnetic reed switches are activated by their associated float magnetic when the float magnetic is at the bottom of its section in the inner guide tube are provided. An electronic output device monitors the state of the magnetic reed switches to indicate the liquid level.

Description:
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       OTHER PUBLICATIONS  
       [0002]    The CamelBak Products, LLC web site http://www.camelbak.com; U.S. Pat. 7,063,243 B2 (Forsman, June 2006) assigned to CamelBak Products, LLC, Petaluma, Calif. (US) and Coto Technology Technical &amp; Applications Information [Switches] p 142. 
       RELATED APPLICATIONS 
       [0003]    This application is a continuation of U.S. provisional patent application 61/108,933, entitled “Liquid Level Measuring Apparatus” which was filed on Oct. 28, 2008 with claims  1 - 9  of this application the same as claims  1 - 9  of the referenced provisional application. 
     
    
     FIELD OF THE INVENTION 
       [0004]    This invention relates to a liquid level measuring apparatus, in particular liquid level measuring apparatus of the type having a vertical guide tube having a plurality of permanent magnets encapsulated in buoyant capsules, a plurality of magnetic reed switches enclosed in a sleeve partially surrounding the tube and a means to indicate approximate liquid levels in a non-rigid plastic bladder. 
       BACKGROUND OF THE INVENTION 
       [0005]    The measurement of the level of a liquid in a container by use of one or a plurality of reed switches that are activated by one or a plurality of permanent magnets is well known as disclosed in U.S. Patents. The following U.S. patents are representative of such disclosures:
   U.S. Pat. No. 3,419,695   U.S. Pat. No. 3,678,750   U.S. Pat. No. 3,826,139   U.S. Pat. No. 4,056,979   U.S. Pat. No. 4,064,755   
 
         [0011]    These devices typically use a toroidal shaped permanent magnet that is enclosed within a buoyant capsule that floats on the surface of the liquid. The reed switches are held in a cylindrical tube. The capsule is place over the tube such that the tube is within and perpendicular to the capsule hole such that the two are co-axially aligned with each other. Sufficient clearance between the tube and the capsule allows the capsule to move up and down the tube with changes in the level of the liquid. When the capsule reaches the level of a reed switch, the switch is activated, providing a means for indicating the level of the liquid, such as closing an electrical circuit, 
         [0012]    The precession of the level measurement can be increased by increasing the number of reed switches. Thus, apparatus such as described in U.S. Pat. Nos. 5,374,846 and 6,571,626 B1 may incorporate as many as 1040 sensors. 
         [0013]    Other devices, similar to the above referenced, may use other magnetic sensing elements rather than reed switches. The use of Hall Effect devices is described in U.S. Pat. Nos. 6,481,278 B1 and 6,563,306 B2. 
         [0014]    While these patents address many of the requirements of measuring the liquid level in a container, they do not address the particular requirements addressed by the present apparatus. Many sports and recreation enthusiasts such as bicyclists, hikers and joggers are concerned with dehydration. This is indicated by the number of backpacks that are available that contain a plastic bag or bladder or reservoir meant to contain a drink liquid referred to as hydration systems. As suggested by the name, the backpack is carried on the individual&#39;s back with straps that go over the shoulders. The backpack may be large enough to contain items other than the bladder such as those a hiker may carry or only large enough to carry the bladder. A flexible plastic tube goes from the bladder over the individual&#39;s shoulder with a mouth piece or nozzle at the other end. Thus the individual can drink from the bladder without removing it from the backpack. One advantage these hydration systems offer over say water bottles is that they provide hands free access to the hydration liquid and do not cause the user to loss concentration or vision while drinking. However, a disadvantage to these hydration systems is that with the liquid container being carried on the back, the individual user typically is not able to monitor the amount or level of liquid in the bladder. Once the bladder is filled with liquid, they are seal usually with a screw on cap to prevent the liquid from spilling outside or otherwise being squeezed out. In addition, since the bladders are reused multiple times and are not considered disposable, they must be easily washed. Also, a liquid level measuring device must not require making modifications to the bladder such as making holes in the bladder for lead wires. 
         [0015]    Other technologies such as commercially available charge-transfer sensor integrated circuits are used for measuring liquid levels in a container. These devices work by monitoring the change of capacitance between electrodes placed on the outside of non-conductive containers. Typically, one or more active electrically conductive electrodes such as aluminum or copper foil are attached to one side of the container and a ground or common electrically conductive electrode on the opposite side. While such a system would work for our application, it has disadvantages. With the bladder filled with an aqueous solution, the dielectric constant of the material between an active electrode and the common electrode is high (78 for water) while the distance between them is relatively large. As liquid leaves the bladder the dielectric constant drops to approximately 2-3 (for plastics). Also, the distance between the electrodes also decreases. Referring to the equation used to calculate the capacitance of a parallel plate capacitor, Eq. 1, we see that a decrease in dielectric constant results in a decrease in capacitance while a decrease in distance between the parallel plates increases the capacitance. Thus, the changes have opposite effects on the capacitance. If the changes were the same (for example, if κ decreased buy a factor 30 and d decreased by a factor of 30) there would be no net change in capacitance. Such technologies are more suited for fixed wall containers. 
         [0000]        C=κε   0A/d    Eq. 1 
         [0016]    Where C is the capacitance in farads, κ is the dielectric constant of the material between the parallel plates, ε 0  is the permittivity constant, A the area of the plates, and d the distance between the plates. 
         [0017]    Another disadvantage of this method is that it requires the electrode to be solidly attached to the bladder and be able to withstand washing coming off or the foil cracking and loosing electrical conductivity. In general, this technology is better suited for rigid containers where the only change occurs in the permittivity of media between electrodes and the distance between electrodes remains constant. 
       SUMMARY OF THE INVENTION 
       [0018]    The present apparatus meets these needs. The tube with magnetic floats is easily placed inside the bladder through the filler hole and is likewise easily removed for washing and cleaning. Furthermore, no leads or electrical wiring must go from the inside of the bladder to the outside. Nor is there any electrical circuitry inside the bladder. No modification of the bladder is required. Finally, the apparatus, not requiring a multitude of components nor costly components, is of low cost to manufacture. 
         [0019]    The liquid level measuring device according to the description herein comprises a plurality of magnet float capsules and an equal number of magnetic reed switches. The magnet float capsules are contained in a semi-rigid plastic tube that fits vertically within the plastic non-rigid bladder containing the fluid. Both ends of the tube are open so that the lumen of the tube is contiguous with the inside of the bladder so that the liquid level in the tube is equal to the liquid level in the bladder. The tube is separated into sections using plastic pins with each section containing a magnet float. The pins restrict the movement of the magnet floats to their respective sections while allowing the free flow of the liquid into and out of the tube. The length of the pins with the exception of one of the end pins is equal to the outer diameter of the tube so that the ends of the pins are flush with the outer wall of the tube. 
         [0020]    The magnetic reed switches are contained in a sleeve approximately the same length of the tube with inner diameter somewhat larger than the outside diameter of the tube. A slit in the sleeve somewhat wider than the thickness of the bladder when it is empty of liquid runs its entire length. The tube is placed against the wall of the bladder such that the wall of the bladder substantially encloses the tube longitudinally. The sleeve is positioned on the outside of the bladder along the tube such that the sleeve and the tube align co-axially with each other with the wall of the bladder separating the two effectively clamping the tube in place. This is accomplished by sliding the sleeve along the tube until the reed switches are at the same level as the magnet floats when the magnet floats are at the bottom of their respective section. To ensure that the magnet reed switches align with the magnet floats, a stop on one end of the tube is included so the sleeve can be slide up to said stop but not past it. This stop could be accomplished by making the outer diameter of the tube at one end larger than the inner diameter of the sleeve. A preferred way which will be made obvious is to increase the length of the pin used to restrict the movement of a magnet float at one end of the tube such that one end of the pin protrudes slightly from outer wall of the tube with the other end of the pin remaining flush with the outer wall of the tube. The slit at one end of the sleeve is made wider to accommodate the protruding end of the pin. This method ensures both the proper alignment of the magnet floats with the magnetic reed switches and the radial orientation of the tube. 
         [0021]    Once the sleeve is positioned in such a manner, the bladder can be filled with liquid and the filling orifice closed. With the bladder filled with liquid, the magnet floats are at the topmost travel in their respective sections as set by the plastic pin and are sufficiently distanced from the associated magnetic reed switch as to not affect the state of the magnetic reed switch. As the level of the liquid in the bladder drops, first the top most magnet float drops until it reaches the lower most travel of its section determined by the position of the plastic pin. At this point, the magnet in the float is juxtaposed with its respective magnetic reed switch, activating the switch. As the level of the liquid in the bladder continues to drop, the next highest magnet float drops until it too reaches the bottom most travel of its section, activating its associated magnetic reed switch. This continues until the lowest magnet float reaches the bottom most travel of its section, activating its magnetic reed switch. The state of the magnetic reed switches is monitored by an electronic circuit. Such a circuit, for example, would light a LED associated with the lowest activated magnetic reed switch and an audio alarm would sound when the lowest magnetic reed switch closes. 
         [0022]    As the level of the liquid in the bladder drops, the bladder above the liquid level collapses. At some point, collapsed bladder closes off the top of the tube. At this point, the level of the liquid in the tube will no longer fall even when the level of the liquid in the bladder falls. In effect, a vacuum in the top of the tube is formed. To prevent this from occurring, vent holes are made at specific distances along the tube. These holes must face into the bladder volume to be effective. If, for example, they were oriented against the wall of the bladder, they would be blocked off and would not act as a vent. Having these holes aligned with the protruding pin, when the apparatus is assembled as described above, the vent holes are automatically oriented toward the bladder volume. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a front view of an embodiment of the present invention mounted on a liquid containing bladder; 
           [0024]      FIG. 2  is a cross section view in the horizontal top plane showing the relation between the inner guide tube, flexible bladder wall, and outer sleeve of  FIG. 1 ; 
           [0025]      FIG. 3  is a cross section view in the vertical or frontal plane showing the relation of the major components particularly that of the magnetic reed switches and magnet floats and the inner guide tube and outer sleeve of  FIG. 1 ; 
           [0026]      FIG. 4  is a view of the outer guide sleeve of  FIG. 1 ; 
           [0027]      FIG. 5  is a cross section view in the vertical or front plane of the inner guide tube showing the magnet floats and pins of  FIG. 1 ; 
           [0028]      FIG. 6  is a cross section view in the vertical or frontal plane of the outer sleeve showing the imbedded magnetic reed switches of  FIG. 1 ; 
           [0029]      FIG. 7  shows an implementation of the output device. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Referring to the drawings, and in particular  FIG. 1 , the reference numeral  10  generally indicates the liquid level measuring apparatus of the present invention consisting of inner guide tube  40 , outer sleeve  60  and level indicator output device  80  attached to a flexible plastic bag  20 , herein after referred to as bladder consisting of two layers, a front layer  202  and a back layer  204  of thin flexible plastic material such as a polyurethane with said layers  202  and  204  sealed together along their entire outer edges by some method such as RF welding to form outer seam  206 . Filler hole  208  is used to add liquid to bladder  20  and, after filling, is sealed with a screw-on cap and drink tube  210  at the bottom of bladder  20  allows the user to suck the liquid from bladder  20  partially filled with liquid  214 . The level of the liquid in bladder  20  is indicated by  212 . Such bladder  20  is typically carried in a backpack used by hikers and bikers. The liquid level measuring apparatus  10  is attached to bladder  20  along one edge of bladder  20  with inner guide tube  40  inside bladder  20  and outer sleeve  60  outside of bladder  20 .  FIG. 2  shows this arrangement of bladder  20 , inner guide tube  40  and outer sleeve  60  with bladder  20  front layer  202  and back layer  204  and seam  206  longitudinally around inner guide tube  40  with outside sleeve  60  around the outside in a cross sectional view. 
         [0031]    A more detailed sketch of the present apparatus is depicted in  FIG. 3 . The liquid level measuring apparatus includes an inner guide tube  40  made of a non-magnetic material such as polypropylene that contains a plurality of magnet floats, in this case and for a clearer understanding two floats  422  and  424  are described, each float containing a permanent magnet and outer sleeve  60  also made of a non-magnetic material such as but not limited to polypropylene or ABS containing an equal number of magnetic reed switches as there are magnet floats, in this case two magnetic reed switches  622  and  624 . It is understood that more float/switch combinations can be used for measurement of more liquid levels with the constraint that the magnetic floats must move sufficiently away from the reed switches such that the reed switches will be deactivated. Inner guide tube  40  is placed inside bladder  20  in a vertical orientation. Outer sleeve  60  has a longitudinal slit  602  in  FIG. 4  running its full length somewhat wider than the thickness of bladder  20  when empty that is slightly wider than the thickness of bladder  20  front layer  202  and back layer  204 . Liquid level measuring apparatus  10  is set up or installed on bladder  20  by first placing inner guide tube  40  inside bladder  20  through filler hole  208  while bladder  20  is empty. Inner guide tube  40  is then held against bladder  20  wall such that bladder  20  wall substantially encircles inner guide tube  40  preferably where front layer  202  and back layer  204  are sealed together at seam  206 . From the outside, outside sleeve  60  is slid onto bladder  20  and inner guide tube  40 , with bladder  20  layers  202  and  204  in slit  602  of sleeve  60 . Electrical conductors  640  in  FIG. 7  connect magnetic reed switches  622  and  624  to electronic circuitry that monitors the state of magnetic reed switches  622  and  624  and indicates the level of liquid in bladder by activating output components such as LEDs, a LCD, and/or audio buzzers. 
         [0032]      FIG. 5  shows inner guide tube  40  in more detail. Inner guide tube  40  contains magnet floats  422  and  424  that can freely move longitudinally up and down within inner guide tube  40  and pins  442 ,  444  and  446  that restrict the up-down movement of magnet floats  422  and  424 . Magnet floats  422  and  424  contain permanent magnets  432  and  434  that are located at the bottom of the floats. The remaining volume of the magnet floats  422  and  424  is filled with atmospheric air that give the floats sufficient buoyancy so the top of the float is slightly above or at the level of the liquid  212 . Pins  442 ,  444  and  446  separate inner guide tube  40  into two sections  482  and  484 , each section containing a magnet float. The diameter of pins  442 ,  444  and  446  is sufficiently small to allow the free flow of liquid into and out of inner guide tube  40  but sufficiently large to restrict the movement of magnet floats  422  and  424 . With the exception of top pin  446 , the length of the pins is equal to the outer diameter of inner guide tube  40 . In this embodiment, the topmost pin, pin  446 , is somewhat longer than the other pins so that it protrudes from inner guide tube  40  into the body of bladder  20  and is in line with vent holes  462  and  464 . The protruding end of this pin is used to align inner guide tube so vent holes  462  and  464  are oriented into bladder  20  rather than against layer  202  or  204 . Of course, lengthening bottom pin  442  and making the length of top pin  464  equal to the outer diameter of inner guide tube  40  would be equally effective. Both ends of inner guide tube  40  are open to allow the liquid in the bag to also fill inner guide tube  40 . As liquid level  212  in bladder  20  drops from full, top float  424  drops until it reaches pin  444  and stops. At this point, magnet float  424  is aligned with magnetic reed switch  624  and activates the switch. As liquid level  212  continues to drop, float  422  begins to drop until it reaches pin  442  and stops. At this point, magnet float is aligned with magnetic reed switch  622  and activates the switch. Now both magnetic reed switches  622  and  624  are activated. Vent holes  462  and  464  are to insure that a partial vacuum does not form in inner guide tube  40  as liquid level  212  drops. When liquid level  212  drops, the empty portion of bladder  20  causes front layer  202  and back layer  204  to close on each other as depicted in  FIG. 1  and at some level effectively closing the top of inner guide tube  40 . As the liquid level in bladder continues to fall, a partial vacuum above the liquid in the tube could forms and the liquid in inner guide tube  40  would no longer drop. Two vent holes  462  and  464  in inner guide tube  40  are made to allow venting of inner guide tube  40  and thus preventing a partial vacuum from forming above the liquid in inner guide tube  40  allowing the level of liquid in inner guide tube  40  to maintain the same level as liquid level  212  in bladder  20 . All component parts of inner guide tube  40  are made of a non-magnetic material such as polypropylene that meets FDA requirements for Title 21, Chapter 1, Part 177 for use as basic components of repeated food contact surfaces. 
         [0033]    Outer sleeve  60  as depicted in  FIG. 4  and in more detail in  FIG. 6  is approximately equal in length to inner guide tube  40 . The inner diameter of outer sleeve  60  is approximately equal to the outer diameter of inner guide tube  40  and the thickness of bladder  20  when emptied of liquid with sufficient clearance to allow outer sleeve  60  to be slid around inner guide tube  40  with inner guide tube  40  on the inside of bladder  20  and outer sleeve  60  on the outside of bladder  20  thus bladder layers  202  and  204  and seam  206  are between outer sleeve  60  and inner guide tube  40 . Slit  602  runs the full length of sleeve but broadens at  604  and  606  and at one end  608  of outer sleeve  60 . The width of slit  602  is slightly greater than the width of bladder  20  when empty to allow for clearance of bladder  20  layers  202  and  204  when sleeve  60  is attached to bladder  20 . Magnetic reed switches  622  and  624  are located on the opposite side of slit  602 . Magnetic reed switches  622  and  624  are molded into outer sleeve  60  with electrical conductors  640  exiting outer sleeve  60  at the top. Electrical conductors  640  are electrically attached to magnetic reed switches  622  and  624  such that the state of magnetic reed switches  622  and  624  can be determined by monitoring the voltage across the individual switches. Thus, using pull up resistors attached to a voltage source such as one or more batteries in output device  80  and connected to lead of each of magnetic reed switches  622  and  624  with the second lead of each magnetic reed switch  622  and  624  connected to common, when a switch is in the open state, the voltage at the lead of the switch will be equal to the supply voltage. When the switch is in the closed state, the voltage on the active lead will be pulled down to zero volts or common. The sleeve was molded using a polyurethane material, 7.125 inches long with inner diameter of 0.45 inches and outer diameter of 0.70 inches. Slit  602  had width of 0.08 inches and broadened regions  604  and  606  were 0.30 inches and broadened end  608  was 0.20 inches. The inner diameter of sleeve resulted in a snug fit of sleeve over inner guide tube and bladder ( FIG. 2 ) but yet easy to slide sleeve into position. Another embodiment which may be preferable in certain applications and particularly applicable to longer models is to increase the width of broadened region  606  such that the sleeve could slightly flex. 
         [0034]    The alignment of outer sleeve  60  with inner guide tube  40  is critical as is the orientation of inner guide tube  40  in bladder  20 . First, inner guide tube  40  must be oriented in bladder  20  such that vent holes  462  and  464  are directed into bladder  20  proper rather than against either layer  202  or  204  of bladder  20 . This is accomplished increasing the length of one of the end pins  442  or  446  such that it protrudes past the outer wall of inner guide tube  40 ,  FIG. 3  showing the top pin  446  as the protruding pin, and that the protruding end of the pin be in alignment with vent holes  462  and  464  in inner guide tube  40 . With widened slit  608  on the same end of outer sleeve  60  as protruding pin  446  on inner guide tube  40 , when outer sleeve  60  is slid onto bladder  20  and inner guide tube  40 , protruding pin  446  will slide into widened end slit  608  and inner guide tube will be oriented correctly in bladder  20 . Protruding pin  446  also acts as a stop for aligning outer sleeve with inner guide tube  40 . By sliding outer sleeve  60  onto bladder  20  and inner guide tube  40  until protruding pin  446  reaches the end of widened slit  608  the magnet sections  482  and  484  will be aligned with magnetic reed switches  622  and  624  when magnet floats  422  and  424  are at the bottom of their respective sections and will be in correct proximity to activate magnetic reed switches. 
         [0035]    Floats  422  and  424  in  FIG. 5  may be constructed of any suitable non-magnetic material but when used in a liquid meant for drinking, the material must meet certain FDA requirements such as those defined in Title 21, Chapter 1, Part 177 “use as basic components of repeated food contact surfaces.” The float should be hermetically sealed. The float must be sufficiently light to maintain buoyancy such that with magnet  432  and  434  placed at the bottom of the float, the top of the float will be slightly above the level of the liquid. The float is elongated or capsule shaped with outer diameter sufficiently less than the inner diameter of inner guide tube  40  as to allow unhindered vertical movement within the float&#39;s restricted section of vertical movement and minimize surface tension between the float and the inner wall of the inner guide tube  40 . The float must also be of sufficient length so as to maintain vertical alignment within the inner guide tube. The magnets may be of bar or cylindrical shape and are fixed at one end of the float either through the molding process, use of adhesive, or mechanical fit such that the magnet field is parallel to the longitudinal axis of the float with either N pointing to the more distant end of the float or S pointing to the more distant end of the float. Alignment of magnets  432  and  434  with respect to the magnetic reed switches is of critical importance for consistency of switch operation. The preferred alignment of magnets  432  and  434  is with their N and S poles oriented parallel to the switch as shown in  FIG. 3  thus the importance of the floats maintaining vertical alignment within the inner guide tube as shown in  FIG. 5 . This orientation provides for the highest reliability and minimizes the affect of switch sensitivity. If either of the poles of the magnet were pointed directly at the magnetic reed switch an “off” zone exists when the magnet is positioned at the center of the switch and the switch would become deactivated. Although this arrangement would work by not allowing the magnet to reach the center of the switch, this could still create reliability and repeatability problems. Another problem with this orientation of the magnets is if a float would to rotate on its longitudinal axis. If this rotation were less than 180°, neither pole of the magnet would be pointing at the switch and the magnet may or may not activate the switch depending on the angle of rotation and sensitivity of the switch. Switch sensitivity (as defined by the amount of magnetic force required to activate the switch) can vary be a factor of 2 or 3 within the same switch model further complicating the issue of reliability. The worst condition is if the float rotated 90°, in which case the magnet would most likely not activate the switch. 
         [0036]    Three conductor cable  640  connects magnet reed switches  622  and  624  to output device  80 . Removable clips can be used to secure cable  640  to drink tube  210 . In some hydration systems, drink tube exits the backpack through a small hole. Taking this into consideration, an electrical connector preferably with a locking mechanism connects and disconnects cable  640  to output device is necessary. Level indicator output device,  FIG. 7  contains battery powered electronic logic circuitry such as a microcontroller for monitoring the state of magnetic reed switches  622  and  624 , battery condition circuitry and output components such as LEDs  822   a - c  indicating the liquid level height of Full, Mid, or Low, a buzzer to indicate that a change in level has occurred such as from Full to Mid or Mid to Low. The buzzer can also act as a warning when to liquid drops to the Low level, and LED  822   d  to indicate low battery voltage.