Abstract:
A spool system for the deployment of a fluid level sensor with a flexible element. The system may be used with a variety of different sensors that may be deployed into a fluid containment tank from the spool. The sensor deployment system may be installed on closed or open tanks and is operable with tanks of various construction materials. The system is operable with tanks containing a wide range of fluids (water, oil, etc.) although it finds preferred application with remotely located oil field storage tanks The system includes a flexible sensor line positioned on a spool within a sealed enclosure. The spool may be rotated manually through the use of an external hand crank, or may be operated automatically. The spool enclosure is in open communication through a top collar of the tank (for closed tanks) for deployment of the flexible sensor. For tanks that are pressurized the spool enclosure serves to maintain the tank pressure. For open tanks the system may be mounted on a bracket on the side wall of the tank. Adjacent the spool enclosure is a sealed electronics enclosure in signal communication with the flexible sensor on the spool through slip ring contacts and signal wire conductors. The electronics of the system may preferably include a power input connector and RF (or other electromagnetic wave) transmitters, receivers, and antennas.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under Title 35 United States Code §119(e) of U.S. Provisional Patent Application Ser. No. 61/839,289, filed: Jun. 25, 2013, the full disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to sensor systems and methods for measuring the level of a liquid within a tank. The present invention relates more specifically to a spooled sensor system, easily deployed within tanks of varying sizes, and operable to remotely monitor the level of liquid in the tank. 
         [0004]    2. Description of the Related Art 
         [0005]    Many efforts have been made in the past to provide systems and methods for monitoring the level of liquids within tanks. Many such systems are implemented within the petroleum industry and are used in association with oil field tanks and the like located at well sites, typically in remote areas. One of the most important considerations in the oil and gas industry is the process of monitoring well production. Because wells are often located in remote areas, it is difficult to monitor production as it is pumped into tanks from the wells and thereafter pumped out of tanks into pipe lines or, more frequently, transport tanker trucks. It can be time consuming and inefficient to manually monitor liquid levels within the field tanks, especially with the frequency that is often required with modern production schedules. Automated tank level monitoring systems have therefore been developed. 
         [0006]    While there are many automated tank level monitoring systems currently in use, most suffer from the limitation that they must be specifically manufactured for the particular tank on which they are installed. Because oil field tanks come in a wide range of shapes, sizes, and configurations, it is difficult to make one, or even a few, standard sized tank level monitoring systems. This is especially true with regard to the structure and size of the sensor element disposed within the tank. It would be desirable, therefore, to have a tank level sensor system that could be easily installed on any of a wide range of tank configurations without the need for significant customization in the manufacturing process or in the installation process. It would be desirable if the size (length) and configuration of the sensor system could be standardized at manufacture and any necessary adjustments to the size could be easily made with a “plug and play” installation. 
         [0007]    Some efforts have been made to introduce flexible sensor systems into the industry whereby a long sensor structure may be introduced into a tank without the need for initially structuring rigid columns, tubes, pipes, and other vertical frameworks, typically used in conjunction with tank level monitoring systems. Even such flexible sensor systems, however, must be adapted (primarily by customizing their length) for a particular installation and often require significant time and labor to install, test, and/or calibrate before being operable. 
         [0008]    It would be desirable to have a flexible sensor system that could be easily installed on any of a large number of different sized tanks with different tank configurations and without the need for a rigid sensor column or standpipe. 
       SUMMARY OF THE INVENTION 
       [0009]    In fulfillment of the above and other objectives, the present invention provides a spool or reel system for the deployment of a flexible fluid level sensor. The present invention provides a system for use with a number of different types of flexible fluid level sensors, each of which may be deployed into a fluid containment tank from the spool or reel. The sensor deployment system may be installed on closed or open tanks and is operable with steel tanks, fiberglass tanks, and tanks made of polymer materials. The system is operable with tanks containing a wide range of fluids (water, oil, etc.) although it finds its preferred application with remotely located oil field storage tanks. The system includes a flexible sensor positioned on a spool within a spark proof or explosion proof enclosure. The spool may be rotated manually through the use of an external hand crank, or in alternate embodiments may be operated automatically. The spool enclosure is in open communication with and through the tank collar of the tank (for closed tanks) for deployment of the flexible sensor. For tanks that are pressurized the spool enclosure serves to maintain the tank pressure. For open tanks the system may be mounted on a bracket on the side wall of the tank. Adjacent the spool enclosure is a separate and fully sealed electronics enclosure in signal communication with the flexible sensor on the spool through slip ring contacts and signal wire conductors. The electronics of the system may preferably include a power input connector and RF (or other electromagnetic wave) transmitters, receivers, and antennas. 
         [0010]    Each type of flexible sensor system will typically include a tension weight that is first deployed through the tank collar to direct the flexible sensor in a generally vertical line to the bottom of the tank (more specifically, to just off the bottom of the tank). Some sensor embodiments utilize one or more floats surrounding the flexible sensor with magnets that trigger elements within the flexible sensor to detect the level of oil or water on the vertical sensor column. Other spooled flexible sensor systems anticipated by the structures of the present invention may operate utilizing terminal end sensors or long wire or tube wave guide sensor methodologies. The common characteristic of each of the sensor systems described in the present invention is the manner in which the flexible sensor may be deployed from the spool to any specific length required by the particular tank installation and may be immediately operable at that length by way of the electronics, programming, and connections to the flexible sensor as structured. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1A  is a partial schematic perspective view of a first implementation of the sensor system of the present invention utilized in conjunction with a sensor line made up of magnetically sensitive sensor elements. 
           [0012]      FIG. 1B  is a detailed cross-section view of a typical flexible printed circuit board (PCB) sensor device with discrete magnetically sensitive sensor elements. 
           [0013]      FIG. 1C  is a top plan view of an alternate configuration of the sensor shown in  FIG. 1A  with a series of rigid printed circuit board (PCB) elements connected through flexible conductors, again utilizing discrete magnetically sensitive sensor elements. 
           [0014]      FIG. 2A  is a partial schematic perspective view of a second implementation of the sensor system of the present invention, utilized in conjunction with a differential pressure sensor system. 
           [0015]      FIG. 2B  is a detailed cross-sectional view of a typical sensor line structure for the system shown in  FIG. 2A . 
           [0016]      FIG. 3A  is a partial schematic perspective view of a third implementation of the sensor system of the present invention, utilized in conjunction with a guided wave radar sensor system. 
           [0017]      FIG. 3B  is a detailed cross-sectional view of a typical sensor line structure for the system shown in  FIG. 3A . 
           [0018]      FIG. 4A  is a partial schematic perspective view of a fourth implementation of the sensor system of the present invention, utilized in conjunction with a magnetostrictive wire (wave guide) sensor system using time domain reflectometry (TDR). 
           [0019]      FIG. 4B  is a detailed cross-sectional view of a typical sensor line structure for the system shown in  FIG. 4A . 
           [0020]      FIG. 5A  is a partial schematic perspective view of a fifth implementation of the sensor system of the present invention, utilized in conjunction with a wave form tube (wave guide) sensor system using time domain reflectometry (TDR) with mechanical or electromagnetic waves. 
           [0021]      FIG. 5B  is a detailed cross-sectional view of a typical sensor line structure for the system shown in  FIG. 5A . 
           [0022]      FIG. 6A  is a partial schematic perspective view of a sixth implementation of the sensor system of the present invention, utilized in conjunction with a capacitance sensor system. 
           [0023]      FIG. 6B  is a detailed cross-sectional view of a typical sensor line structure for the system, shown in  FIG. 6A . 
           [0024]      FIG. 7  is a partially schematic perspective view of an example of one type of power system, operable in remote locations, for use in conjunction with the systems of the present invention. 
           [0025]      FIG. 8  is a perspective view of an installation of the system of the present invention on a typical oil field tank structure. 
           [0026]      FIG. 9A  is an elevational side view of the spool enclosure and electronics enclosure components of the system of the present invention. 
           [0027]      FIG. 9B  is a partial cross-sectional end view of the spool enclosure component of the system of the present invention. 
           [0028]      FIGS. 10A &amp; 10B  are detailed front and side views of the embodiment of the present invention shown generally in  FIG. 1C . 
           [0029]      FIG. 11  is an electronic schematic block diagram showing the functional operation of the daisy chain arrangement of the sensor elements of the system of the present invention shown generally in  FIG. 1C . 
           [0030]      FIG. 12  is a schematic diagram showing an overview of a length of flexible sensor strip extending into a tank with the floating magnets positioned adjacent the sensor strip. 
           [0031]      FIGS. 13A-13C  are data plots showing the sensor readings for the example sensor and floating magnet arrangement shown in  FIG. 12 .  FIG. 13A  plots the raw data from the sensors,  FIG. 13B  provides a curve fitting analysis of the raw data, and  FIG. 13C  provides the reduction of the curve fitting analysis to a measured level value for each of the two floating magnets. 
           [0032]      FIG. 14  is an open side view of a further alternate embodiment of the spool enclosure assembly of the present invention shown mounted and secured with a coupling to the liquid tank. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    Reference is made to  FIGS. 1A-1C  for a description of a first implementation of the system of the present invention in conjunction with a flexible sensor element comprising magnetically sensitive sensor elements, such as Hall Effect sensors or reed switches. Sensor system  10  generally includes spark proof or explosion proof enclosure  12  connected to and open through aperture  15  to tank collar  14 . This spool side of the enclosure is in flow communication with, and where applicable, maintains a seal with the tank environment. Where the installation is on an open tank the spool enclosure is positioned on a bracket on the side wall (or a frame structure) of the tank and is, of course, open to the atmosphere through the lower port aperture  15 . The electronics of the system are contained within a separate enclosure  16  positioned next to the spool enclosure  12 . Signal connections between the two enclosures are described in more detail below. 
         [0034]    Within spool enclosure  12  is positioned spool  18 , operable by external hand crank  20  in the preferred embodiment. Those skilled in the art will recognize that operation of spool  18  may be accomplished by other means apart from the manual operation of hand crank  20 . As reduced power consumption is one of the goals of the present invention, the preferred embodiment utilizes an easily deployed system that involves turning of hand crank  20  which rotates spool  18  on axle  22 . Ratcheting latch  24  allows the spool to be fixed in a rotated position after deployment of the flexible sensor element, depending on the specific application at hand. 
         [0035]    A quantity of flexible sensor  26  is reeled onto spool  18  in the manner shown. Preference is to have a single coil stack of sensor element on the spool. The end of flexible sensor  28  may be drawn out from spool  18  in the deployment process. With the sensor system shown in  FIG. 1A  (i.e., utilizing discrete magnetically sensitive sensor elements), a number of floats are positioned around flexible sensor element end  28  in a manner that allows the floats to move up and down the vertically oriented length of sensor element and thereby function as the fluid level measuring device. In the preferred embodiment, these floats include water float  30  with incorporated location magnet  36  having a specific gravity in the range of 0.94-0.99. As water float  30  moves up and down sensor element  28 , magnet  36  triggers components within the sensor in a manner that is detectable by the electronics of the system outside of the tank. Above water float  30  is oil float  32  which incorporates location magnet  38  and should have a specific gravity of 0.60 or less. In addition, tank collar  14  incorporates location magnet  40  as a manner of referencing the deployment and position of the sensor system within the tank. 
         [0036]    The electronics enclosure  16  includes a printed circuit board (PCB) with sensor control, event logic electronics, satellite modem electronics, mesh radio electronics, and the necessary power and signal connections. Printed circuit board  42  receives power from a short-pin safe power in connector  44 . Outside communication with the system of the present invention is accomplished through a number of communications protocols by way of antenna radome  46 . 
         [0037]      FIGS. 1B &amp; 1C  provide additional detail on two different types of flexible sensor systems utilizing magnetically sensitive sensor elements in conjunction with the embodiment shown in  FIG. 1A .  FIG. 1B  is a cross-sectional view of a first type of flexible sensor  28   a  that comprises a flexible printed circuit board  48  positioned with a plurality of magnetically sensitive sensor elements  50 . This combination of sensor devices and flexible PCB is shown surrounded by a flexible sleeve  52 . 
         [0038]      FIG. 1C  shows an alternate embodiment  28   b  of the sensor system shown in  FIG. 1A  wherein the flexible PCB is replaced by multiple rigid PCB sections  54 , each with a discrete magnetically sensitive sensor element  56  interconnected with flexible conductor paths  58  (either discrete wires or small lengths of flexible circuit elements). This combination is again surrounded by a flexible sleeve  60 . In place of a flexible sleeve shown and described, each of the embodiments shown in  FIGS. 1A-1C  may alternately be structured with coated or encapsulated components. 
         [0039]    In general, the operation of the systems shown in  FIG. 1A  involves positioning and placement of the enclosures onto the tank collar with the end of the spooled flexible sensor line directed through the tank collar into the tank. Once fixed to the tank collar with a sealed connection, the user rotates the external handle which turns the spool of sensor line and deploys the end of the sensor element into the tank according to the length required by the specific tank size and configuration. A locking latch system described above then fixes the spool at the desired deployment length for operation of the sensor system. 
         [0040]    Reference is next made to  FIGS. 2A &amp; 2B  for a description of a second embodiment of the system of the present invention implemented in conjunction with a differential pressure sensor type tank level measurement device. Most of the components of this system are the same or similar to those shown in  FIG. 1A  and for system  70  include, explosion proof enclosure  72  as the spool enclosure attached to tank collar  74  as shown. Sensor passage into the tank is provided by way of opening  75  in tank collar  74 . Electronics are once again configured separately in the electronics enclosure  76 . Spool  78  retains a quantity of sensor element line  86  and may be turned by external handle  80  which rotates spool axle  82 . With this type of pressure based sensor system, vent  83  must be positioned within spool  78  at the terminal end of sensor element line  86 . 
         [0041]    Deployed sensor element line  88  terminates in a differential pressure sensor  90  that incorporates a diaphragm capable of measuring, by way of its displacement, the difference in pressure associated with the quantity (depth) of fluid above the sensor. Electronic components, including circuit board  94 , power in connector  98 , and communications antenna  96  are each similar to those described above in conjunction with  FIG. 1A . The tank collar in each of the preferred embodiments of the present invention will preferably incorporate defouling brushes to help prevent degradation of the sensor line as it is deployed. In the system shown in  FIG. 2A , a spacer  92  provided at the base of the sensor helps to prevent clogs from forming in the differential pressure sensor component  90 .  FIG. 2B  is a cross-sectional view of sensor element line  88  showing vent tube  100  and wire leads  102  that provide power and signal communication to and from differential pressure sensor  90 . 
         [0042]    Reference is next made to  FIGS. 3A &amp; 3B  which provide a third implementation of the spooled sensor system of the present invention in conjunction with a guided wave radar sensor platform and method. System  110  again includes spark proof or explosion proof enclosure  112  positioned on tank collar  114  in flow communication with the tank by way of aperture opening  115 . Electronics are positioned within separate electronics enclosure  116 . Spool  118  is again rotated by external handle  120  connected to spool axle  122 . Locking latch  124  provides a manner of fixing the spool after deployment. 
         [0043]    A quantity of reeled sensor element line  126  is positioned on spool  118 . Sensor line  128  is deployed from spool  118  with the tank end incorporating tension weight  130 . In this type of sensor system, tank collar  114  incorporates not only defouling brushes, but a grounding wall and radar launch point  132 . Necessary electrical connections (not shown) are made between the radar launch point and the electronics of the system. The overall control components are once again included within electronics enclosure  116  which includes circuit board  134 , receives power in through connector  138 , and transmits and receives signals through antenna  136 . 
         [0044]      FIG. 3B  shows in cross-sectional detail that sensor line  128  in this embodiment may be a simple length of stranded steel cable  140  that acts as a wave guide for a radio frequency (RF) pulse directed down and reflected back through the cable  140 . 
         [0045]    Reference is next made to  FIGS. 4A &amp; 4B  for a description of a further alternate embodiment of the system and method of the present invention utilizing a magnetostrictive wire based sensor system. This embodiment is structured and is operable in a manner very similar to the embodiment shown in  FIG. 1A  which, once again, relies on the use of magnets contained within floats to identify the levels of various liquids within the tank. System  150  is configured with explosion proof enclosure  152 , again attached to tank collar  154 , that provides open communication there through into the tank by way of aperture  155 . Electronics enclosure  156  is positioned next to spool enclosure  152 . 
         [0046]    Reel  158  contains a length of sensor line  166  which again is deployed into the tank as sensor line end  168 , weighted with tension weight  174  as shown. Water float  170  contains location magnet  176  and oil float  172  contains location magnet  178 . Again, the preferred embodiment also incorporates a location magnet  180  positioned in tank collar  154 . The electronics of the system once again are incorporated onto circuit board  182  positioned within electronics enclosure  156 . Power in connector  184  connects an external power source and antenna  186  allows for two-way communication with the remote office tank level monitoring system.  FIG. 4B  is a detailed cross-sectional view of a typical magnetostrictive wire sensor system that incorporates a central element  190  comprising a magnetostrictive alloy surrounded by a non-interactive shield or conduit structure  188 . 
         [0047]    Reference is next made to  FIGS. 5A &amp; 5B  for a further alternate embodiment of the system of the present invention implemented in conjunction with a wave guide tube type sensor system operable in conjunction with the transmission (and reflection) of a wave form through air or a material, measuring distance by known time domain reflectometry (TDR) techniques. System  200  again provides spool enclosure  202  attached to tank collar  204  providing opening  205  into the tank. Spool  208  maintains a quantity of wave guide tube  216  and may be deployed by rotation of handle  210  turning spool axle  212  as described above. Locking latch  214  fixes the spool in position after deployment. 
         [0048]    The tank end of wave guide tube  218  is again deployed using tension weight  224 . Water float  220  incorporates magnet  226  and is magnetically coupled to float marker  225  positioned on the inside of wave guide tube  218 . In a similar manner, oil float  222  incorporates magnet  228  magnetically coupled to float marker  227 . Tank collar  204  likewise incorporates location magnet  230  magnetically coupled to marker  229 . Implementation of the wave guide tube sensor system of the present invention comprises operation of transducer  213  at the spooled end of sensor tube  216  which directs a wave form pulse down the sensor wave guide to encounter each of the markers  225 ,  227  &amp;  229 . The reflected waves are then detected and measured and the level of each marker identified as well as a reflection from to lower end of the wave guide (typically positioned just above the floor of the tank). 
         [0049]      FIG. 5B  provides a detailed view of a typical cross-section of sensor tube  218  comprising a length of flexible tubing that carries the wave forms down the wave guide sensor tube and the reflected wave forms up from the internal markers that are magnetically coupled to the float magnets and the tank collar magnet. In  FIG. 5B  marker  225  is shown positioned within the sensor tube surrounded by tubing wall  238 . 
         [0050]    Reference is next made to  FIGS. 6A &amp; 6B  for a further alternate implementation of the sensor system of the present invention in conjunction with a capacitance sensor based operation. System  240  again comprises spool enclosure  242  positioned next to electronic enclosure  246 . Spool enclosure  242  is connected to tank collar  244  and provides opening  245  into the tank. Spool  248  is again configured with a reeled length of sensor line  256  and is operable by means of external handle  250  which turns spool axle  252  and rotates spool  248 . Locking latch  254  fixes spool  248  into place after deployment. 
         [0051]    Capacitance sensor line  258  terminates in the tank with tension weight  260 . Operation of the system, seen best with the cross-sectional view of  FIG. 6B , comprises a measurement of changes in the capacitance across a dielectric material  272  between two conductors  268  &amp;  270 . The presence of a liquid outside and surrounding the dielectric  272  changes the capacitance in a manner that is measurable from the end of the sensor line. Once again, the electronics that serve to measure these changes are positioned on circuit board  262  within electronics enclosure  246 . Power input  264  and communications antenna  266  are structured in a manner similar to the systems described above. 
         [0052]    Reference is next made to  FIG. 7  which provides one example of a suitable source of power for operation of the sensor system, typically at a remote location in an oil field. Power system  280  primarily comprises solar panel  284  generally positioned at an approximate 45° angle and optimally oriented based on the geographic location of the system&#39;s deployment. The typical suitable solar panel would provide 10-20 watts of power that charges a 12 volt battery system  288  operable in the range of 3-20 Amp hours. Electronic circuit board  290  provides the necessary charging circuitry, monitors battery health and battery strength, and likewise incorporates a short pin safety input/output connector  292 . This input/output connector provides not only connection for power to the system, but also may include signal communication to relay power system health data to the communications circuitry of the sensor system. In addition, power and signal data connector  294  is provided to connect power system  280  to additional or auxiliary power systems. Where power is available at the site of the tank (typically in the form of 110 VAC or 220 VAC) an AC to DC convertor with a voltage regulator (not shown) may be used in place of the solar panel/rechargeable battery system shown. 
         [0053]    Power system  280  is structured on and within enclosure frame  282  which is preferably fixed with magnetic feet  286  so as to be attached and secured to the top of the typical steel oil field tank in a position adjacent to the sensor system of the present invention. Tanks constructed of non-magnetic materials would require steel plates or the like be adhered to the top of the tank before the power system  280  is installed. Preferably, the overall enclosure frame  282  of power system  280  is itself an explosion proof enclosure as it comprises electrical power generating components in close proximity to petroleum storage tanks. 
         [0054]    Reference is next made to  FIG. 8  which provides an overview of an installation of a typical system of the present invention on an oil field tank. Tank structure  300  in this case is provided with a clean out line  302  as well as supply line  303 , typically from an operational production well. Load line  304  may be utilized to draw product (the “sale” point) from the tank either by a pipe line or more commonly by tanker truck transport. Ladder  306  is shown as typically positioned on tank  300  allowing user access to the various components positioned on domed top platform  310  of tank  300 . Such installations typically include a thief hatch  308  as well as other vent components normally associated with such tank structures. 
         [0055]    In the example installation shown in  FIG. 8 , the tank collar is positioned on the tank through domed top platform and has been fixed with sensor system  312 . Power system  314  is connected to sensor system  312  by way of electrical and signal line connection  316 . Antenna  318  is now positioned for appropriate RF (or other EM wave) signal (terrestrial and/or satellite) communication. 
         [0056]    Reference is next made to  FIGS. 9A &amp; 9B  for a more detailed description of the housing associated with the spooled flexible sensor system  320 . As indicated above, the spooled flexible sensor housing  330  should be spark proof or explosion proof and should be sized to contain the maximum length of the sensor line  346  required by the full range of tanks to which it might be installed. The housing  330  should have a seal rating of IP  67 . The housing will, as described above, incorporate a handle  352  that extends externally to the housing  330  for raising and lowering the flexible sensor line  346 . The handle  352  may be locked in place with an indexed, spring loaded, latching mechanism, again as described above. On the exterior of the housing  330  where the axle attaches to the handle  352  is an IP  67  rated stainless steel bearing  354 . Within the housing, the axle is attached to an internal pillow block bearing  348 . Between the pillow block bearing  348  and the exterior wall of the housing  320  is an electrical contact slip ring  350  for communicating power to the sensor line and/or signal data from the sensor line. 
         [0057]    The output of the slip ring  350  connects to an IP  67  rated electrical connector  340  that allows connection to the sensor line from outside of the sealed spool housing  330 . In the typical installation these electrical and signal connections would be conveyed directly into the electronics enclosure  332  without the need for external cabling or conductors. The axle may preferably be hollow in order to allow the flexible sensor spool end to be attached to the input of the slip ring  350 . The spool housing  330  is completely sealed except for one opening on the lower panel that allows the sensor line  346  to pass through into the tank  324  through the tank collar  322 . This opening will typically be a stainless steel tube that is fit with an IP  67  rated stainless steel seal bearing  328 . The bearing may be fitted into the appropriate sized tank adaptor  326 . Once the tank adaptor  326  is screwed into the tank  324  and properly tightened, the system is completely sealed so as to allow no gases or other materials to escape. The purpose of the stainless steel bearing  328  and tank adaptor  326  is to allow rotational positioning of the sensor housing to fit the needs of installation. Once the housing is in place, another indexed spring loaded latch (not shown) will lock the complete housing so that it can not spin freely. 
         [0058]      FIG. 9A  is a partially schematic side view of the spooled sensor system showing an alternate arrangement of the spool enclosure  330  and the electronics enclosure  332  of the system  320 . The various bearings and seals described above are disclosed.  FIG. 9B  is a partial cross-sectional view of the spool system shown in  FIG. 9A  within the enclosures  330  and  332 , disclosing the manner in which the axle of the spool  338  conducts whatever power or signal line requirements there are with the sensor line  346  through the appropriate slip ring  350  and bearings  354  &amp;  348  to the electronics enclosure  332 . The components within electronics enclosure  332  include, as described above, circuit board  344 , power in connector  334 , and communications antenna  336 . 
         [0059]    Reference is next made to  FIGS. 10A &amp; 10B  for additional detail regarding the sensor embodiment shown generally in  FIG. 1C . In this embodiment, the flexible printed circuit board is replaced by multiple rigid printed circuit board (PCB) sections  504  each with a discrete magnetically sensitive sensor element  506 . These rigid PCB sections  504  are interconnected with flexible conductor paths  508 , again either as discrete wires or short lengths of printed conductive pathways. The detail shown in  FIG. 10A  discloses the configuration of the rigid PCB sections  504 , as well as the placement of the sensor elements  506  and the conductor paths or wires interconnecting the various rigid PCB sections  504 . 
         [0060]    In the preferred embodiment, the sensor elements  506  are approximately 0.5″ in height (distance D 2 ) spaced 0.5″ apart (distance D 3 ) so as to provide 1″ intervals (distance D 1 ) between each of the sensor elements, according to their placement on the rigid PCB sections  504  and the placement of the rigid PCB sections  504  on the flexible conductor component  502 . As shown in the embodiment in  FIG. 10A , connections between the discrete rigid PCB sections  504  can be made utilizing as few as nine connections on each PCB section. As shown, a ground path  512  and a power path  510  are present across each of the sections as is a home conductor path  514 . Daisy chain connections are made between each rigid PCB section  504  that provide clock  516 , data  518 , and CE (carrier envelope) signal  520 . The above described geometry and arrangement for the sensor chain allows for curved flexibility in at least one direction suitable for coiling the sensor on a spool as is essential to the structure and operation of the present invention. 
         [0061]      FIG. 10B  is a side view of a portion of the sensor line and shows the manner in which the individual rigid PCB sections  504   a - 504   c  may be attached at a single point (along the row of electrical conductor connections) in a manner that allows the sensor string to maintain its overall flexibility while reducing the cost of manufacturing the sensor string as a whole. Individual rigid PCB sections  504  may be manufactured and placed on the less expensive flexible conductor  502  in a manner that greatly reduces the cost of manufacture and still retains the accuracy required with precise spacing of the sensor elements. 
         [0062]    Reference is next made to  FIG. 11  which provides an electronic schematic block diagram showing the various components associated with the sensor elements placed on the rigid PCB sections shown generally in  FIG. 10A .  FIG. 11  provides the components associated with a representative section of the flexible sensor string that is repeated indefinitely between the master microcontroller unit and a terminator microcontroller unit. In the example or section of sensor string shown in  FIG. 11 , three microcontroller units (MCU) are positioned in a chain between a master serving as the top end of the chain and a terminator serving as the tail end of the chain. Each individual microcontroller unit (MCU) serves as slave to the unit above it and as master to the unit below it. Each MCU is connected to its own temperature sensor and magnetic sensor (a Hall Effect sensor in the embodiment described). 
         [0063]    The daisy chain operation proceeds as follows. Power is applied and the master unit  530  asserts WAKE signal line  550  to MCU1  532 . MCU1  532  takes a reading from the Hall Effect sensor  538  and the temperature sensor  540 . The master microcontroller  530  reads four bytes of data  554  from MCU1  532  and determines if checksums match. If so, the master  530  stores this value as SENSOR 1 data. 
         [0064]    In turn, MCU1  532  asserts a WAKE signal line  550  to MCU2  534 . MCU2  534  takes a reading from its Hall Effect sensor  542  and temperature sensor  544 . MCU1  532  reads four bytes of data  554  from MCU2  534 . If checksums match, MCU1  532  stores this value. MCU1  532  now stores four bytes of data from MCU2  534  and on the next read from MCU1  532  by the master  530 , will not read the Hall Effect sensor  538  or the temperature sensor  540 , but instead MCU1  532  will send the value from MCU2  534 . 
         [0065]    This process is repeated between MCU2  534  and MCU3  536 . MCU2  534  asserts a WAKE signal line  550  to MCU3  536 . MCU3  536  takes a reading from its Hall Effect sensor  546  and temperature sensor  548 . MCU2  534  reads four bytes of data  554  from MCU3  536  and, if checksums match, MCU2  534  stores this value. MCU2  534  now stores four bytes of data  554  from MCU3  536  and on the next read from MCU1  532  will not read its Hall Effect sensor  542  or its temperature sensor  544 , but instead MCU2  534  will send the value from MCU3  536 . 
         [0066]    The values therefore walk up the chain on subsequent reads by the master microcontroller unit  530 . The last module in the chain, referred to as the terminator MCU  537 , sends a pre-defined value instead of readings from a Hall Effect sensor or temperature sensor. When the master controller  430  sees this value, it recognizes that the end of the chain has been reached. 
         [0067]    Reference is next made to  FIG. 12  which provides an overview of the sensor operation within a tank  562  in conjunction with the floating magnet elements  570  &amp;  572  proximal to the various microcontroller units  568  containing the Hall Effect sensors. The polarity of the respective magnets  570  &amp;  572  are opposite so as to provide a distinguishing signature (reflected in the data plots described below). The communications unit  560  wakes up from a sleep cycle and applies power to the daisy chain strand. Master microcontroller  564  reads values from MCU1 (and so on) by way of the method described above. This is repeated until all sensors from the daisy chain are read (i.e. the terminator MCU is identified). 
         [0068]    The data received is fit to curves and a position is determined based upon a curve fitting approach as shown in  FIGS. 13A-13C . The discrete sensor readings are plotted  580  on the graph shown in  FIG. 13A  with a curved fitting function  582  disclosed on the graph of  FIG. 13B . The curve fitting algorithm results in discrete position information  584  &amp;  586  that identifies, in this example, Magnet 1 positioned at the 4″ level with Magnet 2 positioned at the 12″ level. As discussed above, this provides accurate level measurements for two different fluids (such as water and oil) contained within the tank. 
         [0069]    In the manner of operation described above, the sensor system is capable of operating with low power requirements based upon its process of cascading power down to only that sensor being measured. In other words, the individual MCU devices are not all powered simultaneously in order for the daisy chain operation to be carried out. Power is required and drawn only by the MCU that is providing the signal information at a given point in time. 
         [0070]    Reference is finally made to  FIG. 14  for a description of a further alternate implementation of the system of the present invention in conjunction with a flexible sensor element comprising magnetically sensitive sensor elements, such as Hall Effect sensors or reed switches. Sensor system  600  generally includes spark proof or explosion proof enclosure  602  having an enclosure base  614  connected to and open through cam and groove fittings  616  &amp;  618 . This spool side of the enclosure  602 , shown open for clarity, is in flow communication with, and where applicable, maintains a seal with the tank environment. The electronics of the system in this embodiment are not shown but are understood to be contained within a separate enclosure positioned next to the spool enclosure  602 . Signal connections between the two enclosures are as described above. 
         [0071]    Within spool enclosure  602  is positioned spool  604 , operable by external hand crank  610  in this embodiment. Ratcheting latch  607  allows the spool to be fixed in a rotated position after deployment of the flexible sensor element  612 , depending on the specific application. A quantity of flexible sensor  606  is reeled onto spool  604  in the manner shown. The end of flexible sensor  612  may be drawn out from spool  604  in the deployment process. Tank collar coupling  616  &amp;  618  incorporate a location magnet as described above to provide a manner of referencing the deployment and position of the sensor system within the tank. 
         [0072]    In general, the operation of the system shown in  FIG. 14  involves positioning and placement of the enclosure onto the tank collar with the end of the spooled flexible sensor line directed through the tank collar into the tank. Once fixed to the tank collar with a sealed connection, the user rotates the external handle which turns the spool of sensor line and deploys the end of the sensor element into the tank according to the length required by the specific tank size and configuration. A locking latch system described above then fixes the spool at the desired deployment length for operation of the sensor system. 
         [0073]    Although the present invention has been described in conjunction with a number of preferred embodiments, those skilled in the art will recognize that alternate embodiments of the sensor line itself may be likewise structured onto the spooled deployment configuration defined and described herein. A number of sensor methodologies lend themselves not only to flexible sensor lines, but also to the spooling configuration of the system of the present invention. Specific details regarding the manner in which the sensor systems operate according to known techniques such as TDR measurements and other known methodologies, can be implemented in conjunction with the spooled flexible sensor structures of the present invention. 
         [0074]    Implementation of the system of the present invention finds its best application in conjunction with a unique, low power, daisy chain sensor array interrogation process. Eliminating the need to simultaneously power and interrogate a large linear array of sensors, the methods of the present invention provide a solution to the problems associated with remote monitoring of a tank positioned at some distance from utility power lines. Those skilled in the art will recognize, however, that the systems and methods described herein find beneficial applicability in environments where such utility based power is readily available. Overall, the system and method of the present invention provide as close to a “plug and play” tank level measurement device as possible, providing both versatility and accuracy, especially in remote locations.