BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to the measurement of the quantity of liquid in a container, vessel, barrel, drum, or the like. More particularly this invention relates to an improved liquid level measurement device having a float drive mechanism that includes a magnetic coupler arranged to activate an indicator pointer to indicate the liquid level in a container or the like.  
       DESCRIPTION OF PRIOR ART  
       [0002]     There are many instances in which it is essential or desirable to be able to measure the level of liquid in a container, barrel, or the like, and in that manner determine the volume or quantity of liquid in the container. For example, numerous companies, business, shops, institutions and other organizations either transporting, storing or dispersing of liquid products, find it convenient to introduce chemicals, lubricants and fuels directly from shipping containers, i.e., drums, barrels, into their processes. This saves time and expense of having additional large bulk storage tanks and equipment to transfer the contents of the bulk storage tanks to the smaller containers. Drums are used throughout the world to transport, store, distribute, and dispense a variety of liquid products. For example, manufacturing firms use individual drums or an entire rack or rows of racks in their manufacturing processes. Material handling dealers and suppliers of chemical products package and distribute their liquid products in drums. In addition, farms, construction sites, schools, machine shops, printing firms, military, government, and numerous other organizations find the use of containers a useful way of handing their liquid products requirements.  
         [0003]     A frequently used device for measuring the liquid contents of drums and or containers is a liquid level detector. There are a number of devices in the market place that serve this purpose. One of these devices is the standard sight gauge consisting of a metal pipe with a glass window to view of the level of liquid. The viewing glass has a gauge registered to the nearest gallon. In addition, the device is equipped with a T-connection threaded on one end to fit a standard {fraction (3/4)} inch threaded bunghole and to accommodate a faucet on the other end of the T-connection. The sight gauge devices suffer from a number of deficiencies that make them unsatisfactory for extended-life measuring purposes. For example, the device is not equipped with a pressure relief valve for drum venting purposes and must rely on a separate device to provide this capability. The glass view port is subject to fogging due to condensation and discolorization and lacks the convenience of a large dial for easy, at a glance reading. Also the external mounting design lends itself to damage through mishandling and breakage.  
         [0004]     Another device in use in the measurement of drums, small tanks and containers is a self-contained unit with a magnet-equipped float that moves with the liquid level along the unit stem, inside the storage container. A liquid level readout is obtained by simply removing the protective cap at the top of the unit and lifting the calibrated indicator (within the unit) until magnetic interlock with the float is felt. The indicator is then lowered back inside the unit for storage and is protected by the screw cap when not in use. This unit suffers from a number of deficiencies, namely it is cumbersome to use, provides readouts in inches only, does not provide at-a-glance check of drum contents, and is not applicable to stack drum racks, and is restrictive in use in confined storage spaces were the drum must be moved to an open floor space to be used. This unit is not equipped with a built in pressure relief valve capability.  
         [0005]     The wood dipstick is another method for measurement of container liquid levels but at best gives an approximate measurement of liquid levels. This approach is dependent upon the residual liquid wetline to indicate the liquid level in the container. The wet line is subjected to evaporation when exposed to air or to the elements, which distorts the accuracy of the measurement, and leads to approximate readings at best The gauge on the typical wood stick is not refined and therefore lacks accuracy and provides approximate measurements at best. The stamped painted gauge on the stick is subject to ware and fads in time. In addition, the wood construction of the stick leads to splintering and breakage over time.  
         [0006]     Another device used to measure liquid levels within containers is a drum gauge that is confined to upright mounted drums. The device consists of an indicator with a plastic housing with an attached flexible rod, the top of which is affixed with a washer used as a pointer. The indicator is screwed into the drum bunghole for mounting to the drum. The indicator is inscribed with a scale calibrated in gallons, liters and inches. As float moves up or down with changing liquid levels the indicator rod with the attached washer pointer registers against the scale. As in the instance of the sight gauge device, the plastic indicator housing containing the imprinted scale is subject to the corrosive effects of fumes venting from the container into the indicator housing. In addition, the plastic housing is subject to fogging. These two conditions contribute to reduce visibility in viewing the readout of liquid levels and shorten the useful life of the device. In addition; the device tends not to deploy easily in a full drum condition because when the float and associated rod contact the liquid the unit extends in a horizontal direction and thus contacts the side of the drum prohibiting deployment. In a full drum, tank or container, the cap must be removed and an adjustment made prior to installation of a device for measuring the liquid level.  
       SUMMARY OF THE INVENTION  
       [0007]     An object of the invention is to provide an improved liquid level measuring device for use in the side and end reading modes.  
         [0008]     Another object of the invention is to provide improved performance, reliability, accuracy and diversity within competitive price structures and conventional manufacturing processes.  
         [0009]     The liquid level measurement device according to the invention includes an indicator having a 360° rotational movement for mounting on a container providing a pendulous self-aligning visual reading related to the level of the liquid in the container. The rotational feature of the indicator accommodates the movement of the indicator rather than requiring changing the position of the container to view liquid level measurements. The liquid level measurement device has a frame section that is threadedly mounted in the container&#39;s bunghole. The indicator is then snapped-on or threaded on the housing and frame section completing the installation. The frame has a buoyant float adapted for floating on the surface of the liquid in the container.  
         [0010]     In a preferred embodiment the liquid level measurement device has a 270° fractional turn helix as a driver for an attached magnetic coupling, which together with a matching magnetic coupling contained in the indicator comprises a magnetic coupler. The magnetic coupler provides the capability of using a sealed environment to convey the level of liquid in a container by the use of magnetics, which eliminates the requirements for the conventional shaft, and bearing combination, which prevents a sealed environment.  
         [0011]     The fractional turn helical driver is connected to a flexible coupling that is in turn connected to a rod arranged to rotate a first portion of the magnetic coupler. The magnetic coupler then transfers this rotation to the indicator dial. The flexible coupling provides the capability of using the invention to measure liquid depth in both horizontally and vertically oriented containers.  
         [0012]     The frame section has two guide bars that engage the float and prevent the float from having a rotational motion instead of the desired linear motion as the float moves in an upward or downward direction on the fractional turn helix. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is shows an embodiment of the present invention mounted for use on a horizontally oriented container;  
         [0014]      FIG. 2  shows the embodiment of  FIG. 1  used with a horizontally oriented container that has been deformed;  
         [0015]      FIG. 3  shows the invention being used with a horizontally mounted container using the mid-container bunghole.  
         [0016]      FIG. 4  shows the invention being used with a container resting on a surface that is not level;  
         [0017]      FIG. 5  is a partial cross sectional view showing structural features of the invention being used with a horizontal container  
         [0018]      FIG. 6  is an end view of a conventional container used to hold liquids;  
         [0019]      FIG. 7  is an end view of an indicator dial that may be used with the present invention;  
         [0020]      FIG. 8  is a perspective view of a float and guide and guide bar arrangement that may be included in the present invention;  
         [0021]      FIG. 9  is a cross sectional view showing a float and a pair of guide rods that may be used with the embodiment of the invention shown in  FIG. 4 ;  
         [0022]      FIG. 10  is a bottom plan view showing guide rods and an base plate that may be included in the present invention;  
         [0023]      FIG. 11  is a side elevation view showing a base plate and bottom end portions of the guide rods of  FIG. 9 ;  
         [0024]      FIG. 12  is a perspective view showing a magnetic coupler that may be included in the present invention; and  
         [0025]      FIG. 13  illustrates structural features of a venting system including the “snap-fit” capability of the indicator that may be included in the embodiment of the invention shown in  FIG. 5 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     Turning now to the drawings and particularly to  FIG. 1 , a container  20  is depicted for illustrative purposes as being located on a level surface  22  and partially filled with a liquid  24 . A liquid level measurement device  26  according to the invention is mounted to the container  20 . It is a primary purpose of the liquid level measurement device  26  to measure the depth of the liquid  24  from which (knowing the tank geometry) the volume of liquid  24  in the container  20  can be determined.  
         [0027]     Referring to  FIGS. 1 and 6 , the container  20  typically has openings  28  and  30  provided in a lid  32  for adding or dispensing liquids. The openings  28  and  30  typically are threaded and have diameters of 0.75 inch and 2 inches respectively. As shown in  FIG. 5 , the liquid level measurement device  26  has a threaded coupling  34  that may be used to mount the liquid level measurement device  26  in the opening  30 .  
         [0028]     The liquid level measurement device  26  according to the invention may be advantageously employed for measuring liquids of great variety in tanks. It is considered within the sprit of this invention to make the measurement device small-sized for uses such as measuring liquid depth in drums, barrels, jumbo, rectangular shop tanks, oval shaped tanks for shop, home heating generators and numerous other applications. Therefore, for the convenience of description of the invention, it is described in connection with measuring the depth (and thus amount) of liquids stored and dispensed in such containers.  
         [0029]     The liquid level measurement device  26  includes an indicator  42 , a housing  44 , an upper frame section  45  extending from the housing  44 , a lower frame section  48  that extends into the liquid  24  and a float  50  that moves along the lower frame section  48  in response to changes in the liquid level. The lower frame section  48  is an elongated structure having an overall length such that it extends to a location near the lowermost portion  52  of the container  20 . Differing containers have varying lengths, and to conform to this requirement the frame section along with the fractional turn helix and the guide bars can be modified to conform to differing dimensions of the containers involved.  
         [0030]     The lower frame  48  includes an upper plate  56  and a baseplate  58  with a pair of guide bars  60  and  62  arranged to extend between them. The fractional turn helix  64  has a bottom projection  66  that extends into a recess  68  in the baseplate  58 . The helix has an upper end  67  that is connected to a flexible shaft  70  that is in turn connected to a rod  72  through variable length coupler  90 . The fractional turn helix  64  is suspended between the guide bars  60  and  62 . The lower ends of the guide bars  60  and  62  may be fastened to the base plate  58 . The upper ends of the guide bars  60  and  62  are connected to the upper plate  56 . The fractional turn helix  64  is suspended centrally between the guide bars  60  and  62  with the upper end of the fractional turn helix  64  extending through a passage  74  in the upper plate  56 .  
         [0031]     Referring to  FIGS. 5 and 8 , the float  50  preferably is formed as a cylinder and preferably has a central passage  76  extending therethrough. The passage  76  preferably extends through the center of the float  50  and has a rectangular cross section. A pair of circular passages  78  and  80  is formed near opposite side portions of the float  50 . The float  50  is mounted in the frame so that the guide bars  60  and  62  extend through the passages  78  and  80  and the fractional turn helix  64  extends through the passage  76 . The guide bars  60  and  62  are parallel so that the float  50  is constrained to linear movement up and down as the liquid level changes in the container. The fractional turn helix  64  can be rotated about its vertical axis. As the height of the float  50  changes, the rectangular cross section fractional turn helix  64  engages the surfaces of the rectangular central passage, which produces a torque on the fractional turn helix  64 . The liquid level measurement device  26  is calibrated so that the angular orientation of the fractional turn helix  64  as it rotates about the vertical axis indicates the liquid level in the container  20 .  
         [0032]     Referring to  FIGS. 9-11 , instead of having cylindrical passages  78  and  80 , the float  50  may include a pair of slots  82  and  84 . The slots  82  and  84  extend the full length of the cylindrical float  50  and are arranged to be diametrically opposite one another. The guide rods  60  and  62  fit inside the slots  82  and  84  so that the float  50  is constrained to vertical movement along the guide rods. The lower ends of the guide rods  60  and  62  may be connected together below the base plate  58  as shown in  FIGS. 10 and 11 .  
         [0033]     As the device  26  is inserted and secured to the container  20  by threading into the selected container hole, the liquid level measurement device  26 , as a two axis pendulous system, self aligns seeking the local vertical to adjust for any small angle in any two-plane container orientation. As the lower frame section  48  is inserted into the container  20 , the float  50  tends to seek the level of the liquid  24  contained therein.  
         [0034]     As shown in  FIGS. 5 and 12 , the rod  72  is connected to a first magnetic assembly  98  to support it in a cavity  100  in the housing  43 . A second magnetic assembly  102  is mounted in the cavity  100  by a rod  104  that is rotatably mounted in the housing  45 . As shown in  FIG. 12 , the first magnetic assembly  98  preferably comprises a pair of magnets  106  and  108  mounted in a disk  110  with opposite poles being adjacent an end  112 . The second magnetic assembly  102  preferably comprises a pair of magnets  114  and  116  mounted in a disk  118  with opposite poles being adjacent an end  120 . The magnetic assemblies  98  and  102  are arranged so that magnets of opposite polarity face one another. Because the magnetic poles of opposite polarity attract one another, they automatically align and remain in alignment as the helix  64  and the rod  72  rotate in response to changes in the liquid level.  
         [0035]     The magnet assemblies  98  and  102  are arranged so that they are attracted to one another such that rotation of the first magnet assembly  98  causes rotation of the second magnet assembly  102 .  
         [0036]     The employment of the magnetic coupler approach makes possible another embodiment of the present invention. As shown in  FIG. 5 , the indicator  42  is arranged to be snap-fit on the housing  44 . A spring  122  is mounted in a cavity  124  in the housing  45 . A plunger  126  is fastened to the spring  122 . The housing  44  includes a groove  127  arranged to receive the plunger when sufficient force is used to urge the indicator  42  toward the housing  44 . The snap-fit mounting arrangement allows the indicator  42  along with insert  40  and housing  45  to rotate 360° to seek the local vertical. Locating pin  130  secures indicator  42  to insert  40 . The indicator  42  can be easily removed from one container and attached to another. This embodiment of the invention permits multiple measurements of similar configured containers with a single indicator in addition to protecting the indicator from damage through miss handling and damage from material handling equipment. In the event that the container is positioned in a protective cabinet or the like, the indicator  42  can be removed for clearance purposes.  
         [0037]     When the indicator  42  is removed, from the housing  44 , the first magnetic  98  assembly remains in the position it was in while the indicator was attached if no liquid is removed from the container  20 . The angular position of the first magnetic assembly  98  is a function only of the liquid level. When the indicator  42  is reattached to the housing  44 , the second magnetic assembly returns to its previous angular position to indicate the liquid level.  
         [0038]     In addition, this use of a magnetic coupler provides a sealed environment between the contents of the container and the outer environment and eliminates the need for conventional shafts and prevents the associated leakage of fumes and liquid that can contaminate instrument components and the environment. The magnetic coupler feature also provides for the means for the snap on snap off feature of the indicator that permits the removal of the indicator from the device with out the need to remove the entire device from the container or the like. This feature also accommodates the multiple readings of numerous containers with a single indicator and hence avoiding contamination of liquid products. The sealed containment feature makes it possible to ship containers with internally mounted devices less the indicator. Another feature of the device is the use of the flexible coupling  70  to accommodate the free axial movement of the frame section  48  of the device and assure a continual alignment with the vertical.  
         [0039]     Referring to  FIGS. 5 and 13 , the invention includes a pressure relief system  144  for venting to relieve pressure caused by heating and to prevent formation of a partial vacuum when the liquid cools and when liquid is drained from the container  20 . When the indicator assembly  42  is attached to the housing  44 , an indicator guide pin  130  aligns with a guide pin receptor hole  132  in the insert  40 . As best shown in  FIG. 13 , in the automatic venting mode a plunger pin  136  compresses a spring  138  permitting ball  139  to open a vent hole  140  in the insert  40 . The venting action passes through a vent passage  142  to a pressure release assembly  144  that includes a piston  146 , a spring  148  and a cap  150 . As the venting pressure impacts the piston  146 , the spring  148  contracts to permit the piston  146  to assume an open position, which relieves the pressure in the container  20 . As shown in  FIGS. 14 and 15 , the pressure relief system  144  may be manually opened by pulling outward on the cap  150  and then turning it to lock it in an open position.  
         [0040]     Although the present invention described in connection with a preferred embodiment it is to be understood that modifications within the scope of the invention may occur to those skilled in the appertaining art.
A system for actuating an indicator in response to a depth change in a liquid that is confined to a container comprises a housing, a float constrained to vertical movement in response to changes in liquid depth in the container and an actuator arranged to move in response to vertical movement of the float. A flexible coupling is connected to the actuator and arranged to maintain the actuator in a vertical orientation in the liquid when the actuator and the housing are out of vertical alignment, and a coupler mechanism arranged to transfer movement of the actuator to the indicator.