Patent Publication Number: US-9417635-B2

Title: Method and apparatus for capacitive sensing the top level of a material in a vessel

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/645,137, filed Dec. 22, 2009, which claims the benefit of U.S. Provisional Patent Application No. 61/140,511, the disclosures of which are expressly incorporated by reference herein. 
    
    
     FIELD 
     The present invention relates to a method and apparatus for sensing a top level of a material in a vessel, and in particular to a method and apparatus for capacitive sensing the top level of a material in a vessel. 
     BACKGROUND 
     In the field of material transfer from one point to another, it is often desired to assess the level of material in a vessel in order to determine when to initiate a control event. These control events could include turning on a fluid transfer pump, opening valves or drains, or adding a material to the container. For liquids, as a reservoir of fluid becomes too high, some means is often used to transfer the fluid from the high reservoir to another location such as either another reservoir or to discharge the fluid into the environment. 
     A number of techniques have been utilized in the past to accomplish this goal. Each of these prior techniques has its disadvantages. For some technologies, a sensor must be in direct contact with the material to be sensed and may suffer from corrosion, chemical reaction or physical wear of the sensor, resulting in premature failure. For other technologies, the complexity and cost of implementation may be barriers to a cost-effective product. 
     In previous fluid systems a mechanical float has often been used whereby the float would actuate a lever arm and an electric switch, or other form of electrical contact. The float, being of a lower density than the fluid, would ride with the top surface of the fluid as it rises and falls. A mechanical linkage between the float and the switch may suffer from mechanical wear. Additionally the float must be made from a substance that is not attacked by the fluid. In some applications where the fluid is not homogeneous, such as sewage applications, the float may become tangled or blocked by materials dispersed in the fluid. 
     In systems using an optical emitter and receiver to ‘see’ the material, the sensor may be sensitive to variations in the clarity of the material. Over time, if algae slime is allowed to grow in the fluid reservoir, the algae may block the transmission of the beam of light and give false indications. If powder residue from a loose solid material is allowed to build up on an optical sensor, the emitter and/or receiver can become partially blocked and also cause false indications. Likewise, with infrared emitters and receivers, the surface of the sensors must be cleaned occasionally to have accurate transmission. 
     Ultrasonic technology has been used to reflect back from the surface of a material and sense the distance from the sensor to the surface of the material. These sensors require relatively expensive circuitry and microprocessor control to determine the distance based on the time it takes for an ultrasonic pulse to be emitted, hit the surface of the material, and bounce back to the source. If the surface of the material is agitated (particularly in fluids), reflections of the wave can bounce off at angles and then off the walls of the reservoir introducing error in the received waveform. It is quite common for a reservoir or basin to have the inflow of fluid at a high enough rate to cause waves and agitation of the surface of the fluid. 
     Conductive probes of stainless steel or similar metal are also commonly used. These metal probes are set at a specific vertical level, and when they contact a conductive material such as impure water, the water forms a conductive path between the probes and activates some other part of a circuit. These metal probes may suffer from corrosive or chemical attack by the fluid being sensed. These metal probes can also acquire a build up of contaminants on the surface that adversely affects the measurement. Some fluids may either vary in their conductivity or are not conductive at all and cannot be sensed accurately. 
     Other systems rely on sensing the pressure in a compartment or under a flexible diaphragm that is in contact with the fluid to be sensed. The amount of pressure sensed gives an indication of the height of the fluid above the contact point. These systems are highly sensitive to environmental temperature since the temperature also drastically affects the pressure in the compartment with the sensor. The flexible diaphragm can also be chemically attacked by the fluid or simply become aged and crack from continuous mechanical flexing. 
     SUMMARY 
     In an exemplary embodiment of the present disclosure, a method for sensing the top level of a material in a vessel is provided. In another exemplary embodiment of the present disclosure, an apparatus for sensing the top level of a material in a vessel is provided. In yet another exemplary embodiment of the present disclosure, a method for sensing changes in the top level of a material in a vessel is provided. In still another exemplary embodiment of the present disclosure, an apparatus for sensing changes in the top level of a material in a vessel is provided. 
     In an exemplary embodiment of the present disclosure, a method of controlling a level of a material in a vessel is provided. The method comprising the steps of: placing at least two capacitive sensors proximate to the material in the vessel, a first capacitive sensor arranged to monitor a first range of levels in the vessel and a second capacitive sensor arranged to monitor at least a first level in the vessel, the first level being a part of the first range of levels; monitoring an output of the first capacitive sensor; monitoring an output of the second capacitive sensor; and determining a current level of the material in the vessel based on the output of the first capacitive sensor and the output of the second capacitive sensor. The output of the second capacitive sensor being used to improve an accuracy of the determined current level. In one example, the first level is at an endpoint of the first range of levels. In another example, the first level is between a first endpoint and a second endpoint of the first range of levels. In yet another example, the method further comprises the step automatically adjusting an amount of material in the vessel based on the current level when the current level corresponds to a control event. In a variation thereof, the amount of material in the vessel is reduced when the current level corresponds to the control event. In a further variation thereof, a controller determines if the current level corresponds to the control event and in response thereto activates a material control device to reduce the amount of material in the vessel. In yet another variation thereof, the amount of material in the vessel is increased when the current level corresponds to the control event. In a further variation thereof, a controller determines if the current level corresponds to the control event and in response thereto activates a material control device to increase the amount of material in the vessel. In another example, the material is flowable material. In still another example, the material is fluid. In yet still another example, a controller determines if the current level corresponds to an alarm event and in response thereto provides an indication to an alarm device. In still a further example thereof, the controller includes an analog circuit and the step of monitoring an output of the first capacitive sensor includes the step of integrating a voltage associated with the first capacitive sensor over time. In yet still a further example, the controller includes an analog circuit and the step of monitoring an output of the second capacitive sensor includes the steps of integrating a voltage associated with the second capacitive sensor over time; comparing the integrated voltage to a threshold voltage. In a further example, the controller based on whether the integrated voltage crosses the threshold voltage determines a correction for a monitored voltage associated with the first capacitive sensor. In yet a further example, the first range of levels is a variable range. In a variation thereof, the method further comprises the step of setting an endpoint of the first range of levels based on at least one user input. In still a further example, the method further comprises the steps of powering up a power circuit when the current level approaches a level corresponding to a control event; and automatically adjusting an amount of material in the vessel based on the current level when the current level reaches the level corresponding to the control event. In yet still a further example, the method further comprises the steps of automatically adjusting an amount of material in the vessel with a material control device based on the current level when the current level has moved in a first direction and corresponds to a control event; determining if the current level continues to move in the first direction while the material control device is active; and if the current level continues to move in the first direction provide an indication to an alarm device. 
     In another exemplary embodiment of the present disclosure, a method of controlling a level of a material in a vessel is provided. The method comprising the step of placing at least three capacitive sensors proximate to the material in the vessel. A first capacitive sensor arranged to monitor a first range of levels in the vessel. A second capacitive sensor arranged to monitor at least a first level in the vessel. The first level being a part of the first range of levels. A third capacitive sensor arranged to monitor at least a second level in the vessel. The second level being a part of the first range of levels. The method further comprising the steps of monitoring an output of the first capacitive sensor; determining a level of the material based on the output of the first capacitive sensor; monitoring an output of the second capacitive sensor when the determined level is proximate to the first level in the vessel; monitoring an output of the third capacitive sensor when the determined level is proximate to the second level in the vessel; and determining a current level of the material in the vessel based on the output of the first capacitive sensor and at least one of the output of the second capacitive sensor when the determined level is proximate to the first level in the vessel and the output of the third capacitive sensor when the determined level is proximate to the second level in the vessel. The output of the second capacitive sensor and the output of the third capacitive sensor being used to improve an accuracy of the determined current level. In one example, the method further comprises the step automatically adjusting an amount of material in the vessel based on the current level when the current level corresponds to a control event. 
     In another exemplary embodiment of the present disclosure, an apparatus for controlling a level of a material in a vessel is provided. The apparatus comprising a first capacitive sensor arranged to monitor a first range of levels in the vessel; a second capacitive sensor arranged to monitor at least a first level in the vessel, the first level being a part of the first range of levels; a controller operatively coupled to the first capacitive sensor and the second capacitive sensor; and a material control device operatively coupled to the controller. The material control device having a first configuration wherein a fluid conduit external to the vessel is not in fluid communication with an interior of the vessel and a second configuration wherein the fluid conduit external to the vessel is in fluid communication with the interior of the vessel, the controller changing the configuration of the material control device based on an output of the first capacitive sensor and an output of the second capacitive sensor, the output of the second capacitive sensor being used to improve an accuracy of the determined current level. In one example, the material control device removes material from the interior of the vessel in the second configuration. In a variation thereof, the material control device is a pump. In another variation thereof, the material control device is a valve. In another example, the material control device adds material to the interior of the vessel in the second configuration. In a variation thereof, the material control device is a pump. In another variation thereof, the material control device is a valve. In another example, the apparatus further comprises a non-capacitive sensor arranged to monitor at least a second level in the vessel. The second level being a part of the first range of levels. In a variation thereof, the non-capacitive sensor is selected from the group of a mechanical float; a heat sensor; a conductive probe, and a pressure sensor. In a further variation thereof, the second level is spaced apart from the first level. In another variation thereof, the second level is equal to the first level. 
     Additional features and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of illustrative embodiments exemplifying the best mode of carrying out the invention as presently perceived. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The above-mentioned and other features of the invention, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  illustrates a sensor module including a coplanar plate capacitive sensor positioned in a vessel containing a material; 
         FIG. 2  illustrates a top view of the sensor module of  FIG. 1 ; 
         FIG. 3  illustrates the sensor module of  FIG. 1  having a build-up of contaminant; 
         FIG. 4  illustrates a top view of the sensor module of  FIG. 3 ; 
         FIG. 5  illustrates a sensor module having a plurality of sensors positioned proximate to a material in a vessel, a controller coupled to the sensor module, and a fluid control device coupled to the controller; 
         FIG. 6  illustrates an exemplary arrangement of the sensor module of  FIG. 5 ; 
         FIG. 7  illustrates exemplary outputs for each of the sensors of the sensor module of  FIG. 5 ; 
         FIG. 8  illustrates an exemplary output for a first sensor of the sensor module of  FIG. 5 ; 
         FIG. 9  illustrates an exemplary output for a second sensor of the sensor module of  FIG. 5 ; 
         FIG. 10  illustrates an exemplary processing sequence of the controller associated with the sensor module; 
         FIG. 11  illustrates another exemplary processing sequence of the controller associated with the sensor module; 
         FIG. 12  illustrates another exemplary sensor module having a plurality of sensors positioned proximate to a material in a vessel, a controller coupled to the sensor module, and a fluid control device coupled to the controller; 
         FIG. 13  illustrates yet another exemplary sensor module having a plurality of sensors positioned proximate to a material in a vessel, a controller coupled to the sensor module, and a fluid control device coupled to the controller; 
         FIG. 14  illustrates an exemplary controller associated with the sensor module of any of the Figures; 
         FIG. 15  illustrates an exemplary controller associated with the sensor module of any of the Figures; 
         FIG. 16  illustrates a sump system including a sensor module; 
         FIG. 17  illustrates a wastewater system including a sensor module; 
         FIG. 18  illustrates a condensate system including a sensor module associated with an air conditioning system; 
         FIG. 19  illustrates a condensate system including a sensor module associated with a gas furnace system; 
         FIG. 20  illustrates an air humidifier system including a sensor module; 
         FIG. 21  illustrates a fuel dispensing system including a sensor module; 
         FIG. 22  illustrates an exemplary controller associated with the sensor module of any of the Figures; and 
         FIG. 23  illustrates an exemplary controller associated with the sensor module of any of the Figures. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to  FIG. 1 , a control system  100  is shown. Control system  100  includes a sensor module  102  which monitors a top level  104  of a material  106  in a vessel  108 . Exemplary materials include flowable products, such as liquids, gels, granular material, liquids with suspended solids, and other materials which may flow through a conduit. Exemplary liquids include water based liquids and fuel products. As described throughout this disclosure, material  106  is a fluid, such as water. However, the systems described herein may be used with any type of flowable product. 
     Control system  100  further includes a controller  110  which is operatively coupled to sensor module  102 . In the illustrated embodiment, controller  110  is operatively coupled to sensor module  102  through wires  112 . In one embodiment, controller  110  is operatively coupled to sensor module  102  through a wireless connection. Control system  100  monitors sensor module  102  and based thereon operates a fluid control device  120 . Fluid control device  120  is shown as being operatively coupled to controller  110  through wires  124 . In one embodiment, fluid control device  120  is operatively coupled to controller  110  through a wireless connection. 
     Fluid control device  120 , as illustrated, controls the movement of material  106  from vessel  108 . In one embodiment, fluid control device  120  is a valve which has a first configuration wherein an interior  114  of vessel  108  is in fluid communication with a fluid conduit  122  which is in fluid communication with the valve and a second configuration wherein the interior  114  of vessel  108  is not in fluid communication with fluid conduit  122 . In one embodiment, fluid control device  120  is a pump which pumps material  106  from interior  114  of vessel  108  through fluid conduit  122  to another location. In one embodiment, fluid control device  120  controls the movement of material  106  from a fluid supply  101  to the interior  114  of vessel  108 . 
     Fluid supply  101  may be any system that provides fluid to vessel  108 . Exemplary fluid supplies  101  include groundwater, condensate from an air conditioning system, condensate from a gas furnace, rainwater runoff, a municipal water supply, and any other system which provides fluid. 
     Sensor module  102  is shown including a covering  130  which separates at least one sensor  132  from material  106 . Covering  130  keeps material  106  from contacting sensor  132 . Exemplary coverings  130  include plastic and other suitable non-conductive materials for creating a barrier between material  106  and sensor  132 . In one embodiment, sensor  132  is separated from material  106  by placing sensor  132  on an exterior  116  of vessel  108 . In this situation, covering  130  is the wall  118  of vessel  108 . 
     Referring to  FIG. 2 , sensor  132  includes two spaced apart elements  134  and  136 . Elements  134  and  136  are electrodes which form a capacitive sensor with material  106  serving as part of the dielectric of the capacitive sensor when material  106  is at a height in vessel  108  that material  106  is adjacent to at least a portion of element  134  and element  136 . Sensing a material by measuring the capacitance of a sensor which has its electric field coupled with the material so that the material becomes a dielectric is known. Embodiments have been used that can sense the presence of a material versus the presence of air due to the relatively large difference in their dielectric constants (also referred to as relative permittivity). Air has a typical dielectric constant of 1.0, whereas a material such as water has a typical dielectric constant of about 79. 
     Many devices utilizing this capacitive effect have improved upon those of the past. These devices work well for sensing a material initially and may work well for many years in controlled environments. However, in some environments the sensor can begin to build up a coating of residue or contaminant or in the case of fluids such as water they can start to grow slime algae on the surface. Over time the base capacitance of the sensor changes since this added material changes the dielectric of the sensor. Normally this would add to the effective capacitance of the sensor when the material needing to be sensed is not present. When the material to be sensed is present the measured capacitance could have a positive or negative error depending upon the relative dielectric constant of the contaminant on the sensor versus the dielectric constant of the material to be measured. The sensitivity of discerning the material is also affected since the material is now farther from the sensor&#39;s electrodes. 
     A basic capacitor passes an alternating current (sine wave) from one electrode to the other electrode based on the equation:
 
 I   C   =VωC= 2 VπfC  
 
     wherein I C =current through the capacitor, V=Voltage across the electrodes, ω=angular frequency, π≈Pi≈3.14159, f=frequency of the alternating current, and C=capacitance. 
     Accordingly the amount of alternating current that can be passed through the capacitor for a given frequency is directly proportional to the capacitance. Capacitance is defined mathematically as C=Q/V where C is capacitance in Farads; Q is the amount of charge in Coulombs; and V is the voltage potential across the plates in Volts. 
     For two parallel plates in a vacuum, C=∈ 0 (A/d), where ∈ 0 =permittivity constant of free space (8.85×10 −12  F/m); A=total plate area; and d=distance between the plates. 
     Since the capacitance is inversely proportional to the distance between the plates, through the dielectric, this distance is critical to the sensitivity of a capacitance sensor. It is much easier to sense an object close to the plates than far away from the plates. Therefore any build up of material on the surface of the sensor inhibits the measurement of material  106  and changes the value measured. 
     Returning to  FIG. 2 , a sensor  132  is formed based on the fringing field  140  between element  134  and element  136 . In one embodiment, element  134  and element  136  are coplanar plates. The distance, ‘d’, is now the distance from the surface of elements  134  and  136  to the dielectric material to be sensed, namely the thickness of covering  130 . 
     Referring to  FIGS. 3 and 4 , a contaminant  142  is shown building up on the surface of covering  130 . As contaminant  142  builds up, it adds to the dimension, ‘d’, as illustrated in  FIG. 4 . This buildup of contaminant  142  changes the output of sensor module  102  for a given level  104  of material  106 . One solution to this problem is to require regular cleaning of the surface of covering  130 . However, the present disclosure provides methods for calibrating out changes to the capacitance of sensor  132  due to contaminant over time as explained in conjunction with the exemplary sensor module  200  shown in  FIG. 5 . 
     Referring to  FIG. 5 , sensor module  200  includes a first capacitive sensor  202 , a second capacitive sensor  204 , a third capacitive sensor  206 , and a fourth capacitive sensor  208 . Each of capacitive sensors  202 - 208  monitors a given region of interior  114  of vessel  108 . Referring to  FIG. 6 , an exemplary configuration of sensor module  200  is shown. Capacitive sensor  202  is comprised of a first element or electrode  210  and a second element or electrode  212  which are generally equidistant. Capacitive sensor  204  is comprised of a first element or electrode  214  and second element or electrode  212  which are generally equidistant. Capacitive sensor  206  is comprised of a first element or electrode  216  and second element or electrode  212  which are generally equidistant. Capacitive sensor  208  is comprised of a first element or electrode  218  and second element or electrode  212  which are generally equidistant. In the illustrated embodiment, each of sensors  202 - 208  share a common element, namely second element  212 . In one embodiment, sensors  202 - 208  do not share a common element. 
     Further, although four sensors are illustrated more or less sensors may be included. In one embodiment, sensor module  200  includes at least two sensors which have overlapping monitoring regions. As indicated in  FIGS. 5 and 6 , capacitive sensor  202  generally monitors top level  104  of material  106  when top level  104  is between level  230  (L 1 ) and level  240  (L 6 ), capacitive sensor  204  monitors top level  104  of material  106  when top level  104  is between level  230  (L 1 ) and level  232  (L 2 ), capacitive sensor  206  monitors top level  104  of material  106  when top level  104  is between level  238  (L 5 ) and level  240  (L 6 ), and capacitive sensor  208  monitors top level  104  of material  106  when top level  104  is between level  234  (L 3 ) and level  236  (L 4 ). 
     Referring to  FIG. 7 , an ideal output curve  250  for capacitive sensor  202  as a function of top level  104  of material  106  is shown. As shown, ideal output curve  250  is generally constant, as represented by segment  252 , as material  106  approaches level  230 . Between level  230  and level  240 , ideal output curve  250  changes in a generally linear fashion with changes in top level  104  of material  106 , as represented by segment  254 . Above level  240 , ideal output curve  250  again is a generally constant output, as represented by segment  256 . In a similar fashion, an ideal output curve  258  for capacitive sensor  204  as a function of top level  104  of material  106  is shown. As shown, ideal output curve  258  is generally constant, as represented by segment  260 , as material  106  approaches level  230 . Between level  230  and level  232 , ideal output curve  258  changes in a generally linear fashion with changes in top level  104  of material  106 , as represented by segment  262 . Above level  232 , ideal output curve  258  again is a generally constant output, as represented by segment  264 . Further, an ideal output curve  266  for capacitive sensor  208  as a function of top level  104  of material  106  is shown. As shown, ideal output curve  266  is generally constant, as represented by segment  268 , as material  106  approaches level  234 . Between level  234  and level  236 , ideal output curve  266  changes in a generally linear fashion with changes in top level  104  of material  106 , as represented by segment  270 . Above level  236 , ideal output curve  266  again is a generally constant output, as represented by segment  272 . Lastly, an ideal output curve  274  for capacitive sensor  206  as a function of top level  104  of material  106  is shown. As shown, ideal output curve  274  is generally constant, as represented by segment  276 , as material  106  approaches level  238 . Between level  238  and level  240 , ideal output curve  274  changes in a generally linear fashion with changes in top level  104  of material  106 , as represented by segment  278 . Above level  240 , ideal output curve  274  again is a generally constant output, as represented by segment  280 . 
     Although capacitive sensor  202  may alone serve as a capacitive sensor to monitor top level  104  of material  106  between level  230  and level  240 , the additional sensors  204 - 208  may be selectively energized and have their output measured by controller  110 . As shown in  FIG. 7 , for a sensor that is substantially horizontal, such as capacitive sensor  204 , the output from this sensor is more a step response as compared to the output of a sensor that is substantially vertical, such as capacitive sensor  202 . 
     In one embodiment, the output or characteristic monitored for each of sensors  202 - 208  is a voltage. In one embodiment, the output or characteristic monitored for each of sensors  202 - 208  is a current. In one embodiment, the output or characteristic monitored for each of sensors  202 - 208  is a frequency of the oscillator. 
     Referring to  FIG. 8 , another representation of ideal output curve  250  for capacitive sensor  202  is shown.  FIG. 8  illustrates the difference between a generally ideal curve  250  for capacitive sensor  202  and a curve  250 ′ corresponding to contaminant  142  build up on covering  130 . As shown in  FIG. 8 , the output of capacitive sensor  202  is changed due to the presence of the contaminant buildup  142 . Referring to  FIG. 9 , another representation of ideal output curve  258  for capacitive sensor  204  is shown.  FIG. 9  illustrates the difference between a generally ideal curve  258  for capacitive sensor  204  and a curve  258 ′ corresponding to contaminant  142  build up on covering  130 . As shown in  FIG. 9 , the output of capacitive sensor  204  is also changed due to the presence of the contaminant buildup  142 . The effect of contaminant  142  on the output of a sensor is dependent on many factors such as geometry of the sensor, sensing area, distance between the sensor active area and the sensed fluid, type of fluid, type of residues, and other factors. In one embodiment, the error shift on a substantially horizontal sensor (such as capacitive sensor  204 ) might be up to about 0.2 inches for water and the error shift on a substantially vertical sensor (such as capacitive sensor  202 ) might be more like about 1.5 inches for water. 
     Due to the relatively quick transition from segment  260  to segment  264  for capacitive sensor  204  the primarily horizontally arranged sensors, may be used to improve the signal to noise ratio of sensor module  200  and to make sensor module  200  far less sensitive to the build-up of contaminant  142  over time. A transition in output of sensor  204  may be used as a more accurate guide for the top level  104  of material  106  then capacitive sensor  202  alone. In this manner, capacitive sensor  204 , capacitive sensor  206 , and capacitive sensor  208  provide generally discrete or digital steps and capacitive sensor  202  provides a continuous analog feedback. The transitions of capacitive sensor  204  (as well as capacitive sensor  206  and capacitive sensor  208 ) may be used to calibrate capacitive sensor  202  so that capacitive sensor  202  may be used as a variable or analog output to show the top level  104  of material  106  over a large range of heights (from level  230  to level  240 ). 
     In one embodiment, the output of sensor  204  (as well as sensors  206  and  208 ) is monitored and classified as one of three separate states. The three states for capacitive sensor  204  are shown in  FIG. 9 . Controller  110  associates any voltage level at or above V B  as the top level  104  of material  106  being at or below level  230  (state: HIGH), any voltage level above V A  and below V B  as the top level  104  of material  106  being between level  230  and level  232  (state: TRANSITION), and any voltage level less than V A  as the top level  104  of material  106  being at or above level  232  (state: LOW). In one embodiment, the output of sensor  204  (as well as sensors  206  and  208 ) is monitored and classified as one of two separate states, LOW and HIGH. With reference to  FIG. 9 , the TRANSITION state is removed and controller  110  associates any voltage level at or above V C  as the top level  104  of material  106  being at or below level  230  (state: HIGH), any voltage level at or less than V C  as the top level  104  of material  106  being at or above level  232  (state: LOW). By monitoring when capacitive sensor  204  changes states controller  110  may recalibrate capacitive sensor  202 . As such, a LOW state indicates the presence of material  106  and a HIGH state indicates the absence of material  106 . 
     This is illustrated with reference to  FIG. 8 . As shown in  FIG. 8 , at a top level  104  of material  106  equal to level  232  capacitive sensor  202  should provide an output of 290. However, due to a buildup of contaminant  142  on covering  130 , capacitive sensor  202  provides an output of 292 which on the ideal curve  250  would correspond to a top level  104  of material  106  equal to a level of 233. As such, if controller  110  was relying on ideal curve  250  it would record an error Δh in top level  104  of material  106  if capacitive sensor  202  was used alone. This error would falsely provide a positive offset in the height meaning the controller  110  would consider the material  106  to be higher than it actually is. But, controller  110  may look at the output of capacitive sensor  204 , which has a LOW state when the top level  104  of material  106  is at level  232 . By identifying when capacitive sensor  204  transitions from the TRANSITION state to the LOW state (in the case of three states) or from (HIGH to LOW in the case of two states), controller  110  is able to include an offset (ΔH) to the value determined from the actual output of sensor  202  to better approximate the top level  104  of material  106 . The sign of the offset (ΔH) being determined based on the measured level of material  106  with sensor  202 .
 
LEVEL=MEASURED LEVEL−Δ H  
 
     When the sensor module  200  is first installed, the sensors  202 - 208  should respond generally in accordance with their respective ideal curves. Over time, as contaminant  142  builds up a shift will begin to creep into the measured values resulting in an offset being necessary. Over time the value of the offset increases as the thickness of contaminant  142  increases. When a voltage is being monitored the increase in the thickness of contaminant  142  results in a lower monitored voltage and thus a positive error in height (uncorrected measured level is higher than actual level). As such, over time the value of the offset at a given level generally increases. In one embodiment, the system may adjust for offsets until the corrections start to overlap the location of other sensors. For example, the offset from sensor  208  may result in the material height being lower than or at the location of sensor  204 , but based on the output of sensor  204  it is known that the material is at or above sensor  204 . In one embodiment, the system may continue to operate as long as the system is able to detect the state changes at sensor  204  and sensor  206  and as long as the corrected height is within the active range of sensor  202 . 
     In one embodiment, the output of sensors  204 ,  206 , and  208  have a hysteresis which results in different threshold values depending on which direction the output signal is moving (signal descending or signal ascending). For the examples provided herein, hysteresis is not accounted for. 
     Referring to  FIG. 10 , a first exemplary processing sequence  300  for controller  110  is shown. In one embodiment, processing sequence  300  is software stored in a memory  111  accessible by controller  110 . Processing sequence  300  sets an initial offset value (ΔH) equal to zero, as represented by block  302 . In one embodiment, the initial offset value (ΔH) is set equal to a value stored in memory  111 , such as the last determined offset value. Controller  110  then measures the output of sensor  202 , as represented by block  304 . Controller  110  based on the measured output of sensor  202  determines a level of material  106  in vessel  108  based on the measured output of capacitive sensor  202  and the value of the height error (ΔH), as represented by block  306 . In one embodiment, controller  110  has a lookup table with output values for capacitive sensor  202  which correspond to levels of material  106  based on curve  250 . In one example, controller  110  takes the computed level from the lookup table based on the measured output from capacitive sensor  202  and adds the height error thereto to determine the level for material  106  in vessel  108 . 
     Controller  110  compares the determined level to various control events stored in memory  111 , as represented by block  308 . An exemplary control event is powering on the pump when fluid control device  120  is a pump. Another exemplary control event is shutting off the pump when fluid control device  120  is a pump. For these two examples, controller  110  provides a control signal to fluid control device  120 , as represented by block  310 . If the determined level does not correspond to a control event, controller  110  compares the determined level to various alarm events stored in memory  111 , as represented by block  312 . An exemplary alarm event is the sounding of an audio alarm when top level  104  of material  106  exceeds a threshold level. For this example, controller  110  provides a control signal to an alarm device  113 . Exemplary alarm devices include audio alarm devices, such as speakers, horns, and other suitable audio devices; visual alarm devices, such as lights, displays, and other suitable visual devices; and tactile alarm devices, such as vibration devices and other suitable tactile devices. 
     If the determined level does not correspond to an alarm event, in one embodiment controller  110  cycles through the remaining sensors  204 ,  206 , and  208  to determine if an updated height error (ΔH) is needed, as generally represented by portion  316  of processing sequence  300 . Controller  110  cycles through each of the remaining sensors  204 ,  206 , and  208  to see if any has an output which corresponds to a change of state. Controller compares the current state to the last state stored in memory  111 . 
     As shown in  FIGS. 14 and 15  and explained herein, circuitry is provided which provides a measured output of a sensor as a digital indication of the state of the sensor based on the output of an operational amplifier  448 . In one embodiment, controller  110  simply monitors a voltage or other output associated with the sensor and compares that measured value to a threshold value to decide the state of the sensor. 
     Returning to  FIG. 10 , the first sensor is capacitive sensor  204 , as represented by block  318 . Controller  110  measures the output from capacitive sensor  204 , as represented by block  320 , and determines the state of sensor  204 , as represented by block  322 . If the state of sensor  204  has not changed, controller  110  checks the next sensor until all sensors have been checked, as represented by blocks  324  and  326 , or until a sensor output corresponds to a change in state, as represented by block  322 . 
     If the measured output for a given sensor corresponds to a threshold value, controller  110  determines an updated height error (ΔH), as represented by block  328 . This updated height error (ΔH) is used by controller  110  to calibrate the next measurement of capacitive sensor  202 , as represented by blocks  304  and  306 . 
     Referring to  FIG. 11 , in one embodiment, if the determined level for capacitive sensor  202  does not correspond to an alarm event, controller  110  based on the determined level from sensor  202  checks less than all of the remaining sensors  204 - 208  to determine if an updated height error (ΔH) is needed, as generally represented by portion  336  of processing sequence  330 . 
     Controller  110  based on historical determined levels of material  106  may determine the direction (rising or falling) of level  104 . Controller then determines if the last determined level is approaching a state change of any of the remaining sensors  204 - 208 , as represented by block  338 . In one embodiment, approaching a state change means that the last determined level is within 0.2 inches of when the respective sensor of the remaining sensors  204 - 208  changes state. If not, controller  110  returns to block  304 . If so, controller  110  selects the sensor, as represented by block  340 , and measures the output of the selected sensor, as represented by block  342 . Controller  110  checks to see if the measured output corresponds to a state change, as represented by block  344 . If not, controller  110  returns to block  304 . If so, controller  110  determines an updated height error (ΔH), as represented by block  328 . This updated height error (ΔH) is used by controller  110  to calibrate the next measurement of capacitive sensor  202 , as represented by blocks  304  and  306 . 
     Referring to Tables I-IV below, a representation of the data stored in memory  111  is shown. Table I represents the data stored in relation to sensor  202 . The data includes the sensor ID, the current measured output value; the current height error value (ΔN); the current determined level based which is the sum of the current measured output value and the current height error (ΔN); and historical level data. The historical level data provides an indication of the current direction of level  104  and may be used to determine flow rate (assuming the data is time stamped) and other parameters. With historical data related to capacitive sensor  202 , controller  110  may track patterns of top level  104  of material  106  as a function of time of day. One exemplary pattern would be fluid filling patterns. Another exemplary pattern would be fluid draining patterns. 
                                     TABLE I                   MEA-       DETER-           SEN-   SURED       MINED   HISTORICAL LEVEL       SOR   OUTPUT   (ΔH)   LEVEL   DATA                  202   {VALUE}   {VALUE}   {VALUE}   {VALUE};                       {VALUE}; {VALUE}; . . .                    
Table II represents the data stored in relation to sensors  204 - 208 . The data includes the sensor ID, the last state of the sensor, and the reference voltage (VC in the case of a two state system). Controller  110  based on the last state value can determine if a current determined state represents a change in state.
 
                             TABLE II                   LAST   REFERENCE       SENSOR   STATE   VOLTAGE (V C )                  204   HIGH   {VALUE}       206   LOW   {VALUE}       208   LOW   {VALUE}                    
Table III represents the data stored in relation to control events for control system  100 . The data includes a control event ID, the level corresponding to the control event; and the action to be taken by controller  110 .
 
                                     TABLE III                       CONTROL EVENT   LEVEL   ACTION                          1   L 2     TURN PUMP OFF           2   L 5     TURN PUMP ON           3   L 3     {VALUE}                        
Table IV represents the data stored in relation to alarm events for control system  100 . The data includes an alarm event ID, the level corresponding to the alarm event; and the type of alarm. As shown in Table IV, the type of alarm may be dependent on more than the level  104 . Based on the alarm event, controller  110  may provide an alarm signal to the appropriate alarm device.
 
     
       
         
           
               
               
               
             
               
                 TABLE IV 
               
               
                   
               
               
                 ALARM EVENT 
                 LEVEL 
                 ALARM TYPE 
               
               
                   
               
             
            
               
                 1 
                 L 6   
                 IF PUMP ON; LEVEL RISING TOO FAST 
               
               
                 2 
                 L 6   
                 IF PUMP OFF; PUMP MALFUNCTION 
               
               
                 3 
                 L 1   
                 {VALUE} 
               
               
                   
               
            
           
         
       
     
     In one embodiment, control system  100  also includes at least one user input  115  (see  FIG. 5 ). With sensor module  200  monitoring top level  104  of material  106  over a large range with a passive sensor, various dynamic setpoints for either control events or alarm events may be established. These dynamic setpoints may be set through user input  115 . An exemplary user input  115  is a knob which changes a value of a variable resistive element. Another exemplary user input  115  is one or more buttons, dials, or other inputs which provide a digital setpoint value to controller  110 . In the case of multiple setpoints, a lookup table of setpoints may be stored in memory  111 , such as shown in Tables III and IV for control events and alarm events, respectively. 
     This arrangement permits an operator to turn a knob and be able to adjust the pump on or off level as needed for a given application. For example, if control system  100  was designed for a maximum distance from pump on to pump off of twelve inches, this range may be adjusted down for applications where space is constrained and a twelve inch differential would cause overflowing of the vessel while still maximizing the range to minimize the number of power cycles to the pump and prolong life of a pump. 
     In one embodiment, controller  110  monitors the top level  104  of material  106  while in a power save or sleep mode and then wakes-up the power circuit for pump or fluid control device  120  when the top level  104  nears a setpoint that requires action by the pump or fluid control device  120 . This results in reduced power consumption. This system may be used with a portable power supply or a conventional plug-in power supply to save on energy consumption. 
     In some applications, such as rainwater evacuation, the flow rate of fluid from fluid supply  101  into vessel  108  may exceed the flow rate of fluid leaving vessel  108  through fluid control device  120 . As such, the fluid level  104  in vessel  108  continues to rise, even though fluid control device  120  has been activated. This continued rise may be monitored and used as an alarm event to notify someone prior to overflowing. This is indicated as alarm event  1  in Table IV. 
     In another case the top level  104  of material  106  may be lowering, but at a slower rate which will result in fluid control device  120  staying on longer than it is rated for. This would be an alarm event to notify someone that the fluid control device  120  is in danger of overheating and shutting down. 
     In another case, the evacuation rate is tracked and used to identify a clogged fluid conduit  122  or otherwise faulty fluid control device  120 . In this case, an alarm event is triggered to notify someone of the potential clog or maintenance problem. 
     In one embodiment, controller  110  is programmed to keep top level  104  at a constant level. In one embodiment, controller  110 , is programmed to reduce the top level  104  of material  106  in vessel  108  if the top level  104  reaches an upper threshold. In one example, controller  110  reduces the top level  104  until a lower threshold is reached. In one embodiment, controller  110 , is programmed to raise the top level  104  of material  106  in vessel  108  if the top level  104  is at a lower threshold. In one example, controller  110  raises the top level  104  until an upper threshold is reached by controlling a fluid control device  120  associated with fluid supply  101 . 
     Referring to  FIG. 12 , in one embodiment sensor module  200  includes multiple vertical sensors  202  and  350 . This increases the overall range of sensor module  200 . In the illustrated embodiment, capacitive sensor  202  and capacitive sensor  350  overlap at least a portion of their monitoring regions. In one embodiment, capacitive sensor  202  and capacitive sensor  350  do not overlap. Two additional horizontal sensors  352  and  354  are also included. 
     Referring to  FIG. 13 , in one embodiment, control system  100  includes additional types of sensors in addition to sensors  200 - 208  or in place of at least one of sensors  204 - 208 . In one example, a heat sensor  360 , such as a heater element with an embedded thermistor may be placed at a level that a transition is to be monitored. When no material  106  is present at that level, a given amount of current would produce a particular temperature at the thermistor. When material  106  is present at that level, the temperature of heat sensor  360  steps to a totally different value. Certain types of material will cause the temperature to increase while other types of materials will cause the temperature to decrease. 
     In one embodiment, the heat sensor  360  would only need to be used occasionally. It would be turned on when controller  110  determines that the material  106  is approaching the level of the sensor. This would prolong the life of heat sensor  360 . Heat sensor  360  may be used to calibrate capacitive sensor  202 . In one embodiment, the heating element and thermistor are potted or encapsulated to a metal plate such as stainless steel so that the metal is in direct contact with the material  106  to be measured but the electronics are protected from the material  106 . 
     In another example, a pair of conductive probes  362  are placed at a level of material  106  to be monitored. When no material  106  is present at the level to be monitored, a conductive path is not present between the conductive probes. When material  106  is present at the level to be monitored, the material  106  provides a conductive path between the probes. 
     In one embodiment, the conductive probes  362  would only need to be used occasionally. They may be energized when controller  110  determines that the material  106  is approaching the level being monitored by conductive probes  362 . Conductive probes  362  may be used to calibrate capacitive sensor  202 . 
     In yet another example, a mechanical float  364 , is placed at a level of material  106  to be monitored. When no material  106  is present at the level to be monitored, a float member of mechanical float is in a lower position which results in an associated electrical circuit being in either an open or closed state. As the level of material  106  rises the position of the float member also rises. When material  106  is present at the level to be monitored, the material  106  raises the float member to position wherein the associated electrical circuit is in the other of an open or closed state. Mechanical float  364  may be used to calibrate capacitive sensor  202 . 
     Referring to  FIG. 14 , an exemplary embodiment of controller  110  is shown. Controller  110  includes a microprocessor  400  having an associated memory  111  and an analog-to-digital converter  402 . An exemplary microprocessor is Model No. ATTINY 13-20PU available from Atmel Corporation. Another exemplary microprocessor is Model No. PIC12F629T-I/SN available from Microchip Technology. Another exemplary microprocessor is Model No. MC9S08QG4CPAE available from Freescale Semiconductor. Controller  110  also includes a circuit  404 . Circuit  404  includes a pulse generator circuit  406  which produces a generally square wave output at node  408 . Pulse generator circuit  406  includes a NAND gate  410  having a constant voltage supply  412  as a first input and an oscillator  414  as a second input. Oscillator  414  includes resistor  416  and capacitor  418 . Diode  420  serves to separate node  408  from oscillator  414  when the output of NAND gate  410  goes low. 
     In one embodiment, pulse generator circuit  406  generates a square wave pulse with a frequency in the range of about 20 kHz to about 300 kHz. In one embodiment, pulse generator circuit  406  generates a square wave pulse with a frequency up to about 30 kHz. In one embodiment, pulse generator circuit  406  generates a square wave pulse with a frequency of about 30 kHz. In one embodiment, pulse generator circuit  406  generates a square wave pulse with a frequency of about 26 kHz. In one embodiment, pulse generator circuit  406  generates a square wave pulse with a frequency in the range of about 20 kHz to about 30 kHz. 
     A sensor selection circuit  421  is also shown. Each of sensors  202 - 208  have a first element or electrode coupled to the emitter of a respective transistor  422 - 428  and a second element or electrode coupled to ground. The collector of each of transistors  422 - 428  are coupled to a capacitor  430  which is in turn coupled to node  408 . A respective sensor  202 - 208  may be placed in series with capacitor  430  by turning on the respective transistor  422 - 428 . The respective transistor is turned on by applying a small current through the respective one of control inputs  432 - 438 . Each of control inputs  432 - 438  are coupled to microprocessor  400 . As such, microprocessor  400  may selectively control which individual sensor or combination of sensors are in series with capacitor  430  via control inputs  432 - 438 . 
     The voltage at node  408  is integrated over time with an integrator circuit  440 . Integrator circuit  440  includes resistor  442  and capacitor  444 . The output of integrator circuit  440  is provided at node  446  which is coupled to a non-inverting input of an operational amplifier  448 . The inverting input of operational amplifier  448  is coupled to a node  456  of a voltage divider circuit  450 . Voltage divider  450  includes resistor  452  and resistor  454 . 
     In operation, an output  460  of operational amplifier  448  is low until the voltage at node  446  exceeds the constant input voltage provided by voltage divider circuit  450  at node  456 . At that point, the output  460  of operational amplifier  448  goes high. Output  460  works well to detect when the output of a given sensor has crossed a threshold value, such as one of voltage V A , V B , and V C  in  FIG. 9 . As such, output  460  provides an input for microprocessor  400  to determine when one of sensors  204 - 208  changes states. 
     As each of sensors  204 - 208  may have different setpoints or multiple setpoints (such as V A  and V B ), in one embodiment, one or both of resistor  452  and resistor  454  are replaced with a plurality of resistors in parallel which are selectively placed in the circuit  450  as resistor  452  through transistor switches, in the same manner as described in relation to sensors  202 - 208 . This provides a mechanism whereby microprocessor  400  is able to select the appropriate threshold voltage based on the state change to be monitored. For example, with reference to  FIG. 9 , a first R 4  may be used to establish the threshold voltage at node  456  to be V A  and a second R 4  may be used to establish the threshold voltage at node  456  to be V B . In a similar fashion, in one embodiment, the charging resistor  455  may be replaced with a plurality of resistors in parallel which are selectively placed in the circuit by microprocessor  400  as resistor  455  through transistor switches, in the same manner as described in relation to sensors  202 - 208 . This provides a mechanism for changing the charging time for the sensors  202 - 208 . 
     With regard to capacitive sensor  202 , microprocessor  400  is not interested in a threshold setpoint, rather just the output of capacitive sensor  202 . As such, microprocessor  400  also has a connection to node  446  to monitor the output voltage when transistor  422  is turned on. In one embodiment, shown in  FIG. 23 , the output of sensor  202  may be adjusted based on one of the horizontal sensors, sensor  204  shown, with an analog circuit  470  instead of controller  400 . Operational amplifier  472  in circuit  470  functions to calibrate the vertical sensor  202  by subtracting out the voltage from the lowest horizontal sensor  204 . In the case of circuit  470 , the capacitance of sensor  204  should closely match the capacitance of the corresponding portion of sensor  202 . 
     In one embodiment, the values of the components shown in  FIG. 14  are the values provided in Table V below. 
                                     TABLE V                       Identifier   Description   Value                                                            R6   Charging Resistor   110K   ohm           C2   Inline Capacitor   1   nF           R1   NAND gate Oscillator control   75K   ohm           C1   NAND gate Oscillator control   560   pF           R2   Integrator   10K   ohm           C3   Integrator   0.22   uF           R3   Pull up Resistor   33K   ohm           C4       0.22   uF           R4   Voltage Divider   10K   ohm           R5   Voltage Divider   10K   ohm                        
In one embodiment, the capacitance of sensors  202 - 208  are in the range of 8 pF to 300 pF.
 
     Although described as monitoring the output of each of capacitive sensors  202 - 208  separately, in one embodiment, controller  110  may monitor each of capacitive sensors  202 - 208  at the same time in series. In one example a separate circuit  404  and pulse generator circuit  406  are provided for each of capacitive sensors  202 - 208  and controller  110  monitors the output  460  for each in series. In another example, multiple sensors of capacitive sensor  202 - 208  may be turned on with the arrangement shown in  FIG. 14 . As such, the turned on sensors are placed in parallel and a combined capacitance is measured at at least one of node  446  and output  460 . 
     In one embodiment, controller  110  includes a processing sequence to monitor one or more of capacitive sensor  202 - 208  as vessel  108  is filling or draining at a constant rate. The change of the capacitance of capacitive sensor  202 - 208  should be generally linear for levels within their monitoring ranges. As such, based on the elapsed time and a knowledge of the geometry of vessel  108 , controller  110  can determine an expected top level  104  of material  106  and compare that to a measured top level  104  to adjust out changes in the respective sensors  202 - 208 , such as drift. This also allows for both warning of a maintenance need or for activating an alarm if one or multiple sensors stop functioning, while allowing the system to operate on the remaining sensors. 
     In one embodiment, controller  110  monitors a current associated with one or more of the respective capacitive sensors  202 - 208  instead of a voltage. Referring to  FIG. 15 , a circuit  500  is coupled to microprocessor  400 . Circuit  500  includes a pulse generator circuit  406  and a sensor selection circuit  421 . Circuit  500  also includes voltage divider circuit  450  which provides a reference voltage at node  456 . The reference voltage is the non-inverting input to operational amplifier  448 . The inverting input to operational amplifier  448  is the voltage at node  506  which is between resistor  502  and resistor  504 . 
     Resistor  504  is a current sense resistor. With the arrangement shown in  FIG. 15 , when the sense resistor  504  has little to no current flowing through it, the voltage across sense resistor  504  is small and the resulting voltage at node  506  is very close to the supply voltage  412 . This is above the voltage of node  456  and hence the output of operational amplifier  448  is low. As the current through resistor  504  increases the voltage at node  506  drops. This drop, if continued, eventually falls below the reference voltage at node  456  resulting in the output from operational amplifier  448  going high. As the effective capacitance of the sensor increases due to a material covering more and more of the sensors capacitive elements more AC current can then flow through the sensor to ground. This results in a drop in the voltage at node  408  and also an increase in current that is supplied through the current sense resistor  504 . 
     In one embodiment, the values of the components shown in  FIG. 15  are the values provided in Table VI below. 
                                     TABLE VI                       Identifier   Description   Value                                                            R6   Charging Resistor   105K   ohm           C2   Inline Capacitor   1   nF           R1   NAND gate Oscillator control   75K   ohm           C1   NAND gate Oscillator control   560   pF           R7   Current Sense Resistor   3K   ohm           C3   Integrator   0.67   uF           R3   Pull up Resistor   33K   ohm           C4       0.22   uF           R4   Voltage Divider   2K   ohm           R5   Voltage Divider   200K   ohm                        
Based on the values in the above table, the reference voltage at node  456  is about 11.88 VDC (assuming constant voltage supply  412  is about 12 VDC). Since the voltage from the reference is less than the voltage from the sense resistor  504  when the current through resistor  504  is small the output  460  of operational amplifier  448  is low. When enough current (about 40 microamps) flows through the sense resistor  504 , the voltage at node  506  drops to below the 11.88V reference at node  456  and the output  460  of operational amplifier  448  goes high.
 
     In one embodiment, controller  110  monitors a frequency of the oscillator based on one or more of the respective capacitive sensors  202 - 208  instead of a voltage. As the level of material  106  rises and affects more and more of the surface area of a given sensor, the effective capacitance of that sensor changes. This change in capacitance affects the oscillation frequency of the oscillator  414 . The basic function of oscillator  414  is controlled by resistor  416  and capacitor  418  such that depending on how fast capacitor  418  charges the frequency of oscillation can go up or down. The amount of feedback current through resistor  416  is also affected by node  408  and the capacitance of the sensor or sensors which are currently part of the circuit. By counting the oscillations or pulses of oscillator  414 , controller  110  may detect a change in the capacitance of the sensor or sensors which are currently part of the circuit. Referring to  FIG. 22 , an exemplary analog circuit  458  is shown connected to controller  400 . Circuit  458  is comprised of a modified oscillator  414 ′ which includes sensor selection circuit  421  to selectively place one or more of sensors  202 - 208  in parallel with capacitor  418 . Controller  400  counts the pulses from oscillator  414 ′ to provide an indication of the effective capacitance of whichever sensors  202 - 208  that are selected with sensor selection circuit  421 . 
     Referring to  FIG. 16 , an exemplary sump system  600  is shown. Sump system  600  includes a basin  602  which is placed below ground level  606 . Basin  602  is generally surrounded by an aggregate  610  which facilitates the flow of water from the surrounding soil  612  into basin  602  through opening  608  in the wall  604  of basin  602 . Sensor module  200  is shown coupled to an interior of wall  604 . In one embodiment, sensor module  200  is coupled to an exterior of wall  604 . In one embodiment, sensor module  200  is coupled to a support (not shown). 
     Sump system  600  includes a pump  620  which displaces water from the interior of basin  602  and communicates the water to a discharge fluid conduit  624 . Fluid enters the pump  620  from a lower surface  622  of pump  620 . A check valve  626  is placed between pump  620  and discharge fluid conduit  624  to prevent backflow of water from discharge fluid conduit  624  into basin  602 . The operation of pump  620  is controlled by controller  110  through the measurements of one or more sensors of sensor module  200 . Sump system  600  assists in the removal of moisture from a crawl space area  628 . 
     Referring to  FIG. 17 , an exemplary wastewater system  650  is shown. Wastewater system  650  receives wastewater through an input fluid conduit  652  into a vessel  654 . Controller  110  monitors the level of wastewater in vessel  654  with sensor module  200  and activates a pump  656  to displace the wastewater through an output fluid conduit  658 . The wastewater enters pump  656  through a bottom  660  of pump  656 . Sensor module  200  is shown coupled to an interior of vessel  654 . In one embodiment, sensor module  200  is coupled to an exterior of vessel  654 . In one embodiment, sensor module  200  is coupled to a support (not shown). 
     Referring to  FIG. 18 , an exemplary condensate system  700  is shown. Condensate system  700  is used with an air conditioning system  702 . During the operation of air conditioning system  702 , water  705  condenses on evaporator coils  704 . Water  705  is typically cold. This water  705  is carried by a fluid conduit to a tank  706  of condensate system  700 . In the illustrated embodiment, water  705  enters tank  706  through one or more of openings  708 . Controller  110  monitors the level of water in tank  706  through sensor module  200 . Controller  110  activates a pump  710  to remove water  705  from tank  706 . Pump  710  communicates the water  705  to a fluid conduit  712  coupled to an outlet nozzle  714  of tank  706 . In one embodiment, outlet nozzle  714  includes a check valve to prevent water  705  from reentering tank  706 . 
     Referring to  FIG. 19 , condensate system  700  is shown receiving water  705  from a gas furnace system  730 . The water  705  leaving gas furnace system  730  is hot water, potentially near the boiling point. During operation of gas furnace system  730  the water  705  is produced from the chemical reaction of burning methane  732  in the presence of oxygen  734  in a combustion unit  735 . This reaction produces heat, carbon dioxide and water.
 
CH 4 +2O 2 →CO 2 +2H 2 O
 
Sensor module  200  is well suited to handle both cold water and hot water.
 
     Referring to  FIG. 20 , an exemplary steam humidifier system  750  is shown. Steam humidifier systems may be used to provide moisture to a clean room environment. A typical steam humidifier system  750  has a supply tank, such as vessel  108 , in which water  752  is heated to just under boiling with a heater  754 . A small amount of water  752  is passed from the supply tank  108  to a fluid conduit  756  wherein it is heated with a heater  757  beyond the boiling point and added to an air stream from an air supply  758 . The steam produced is relatively pure water. Over time the supply tank  108  builds up more and more minerals that do not escape through the steam. A conductivity sensor  760  is connected to the supply tank  108  to measure the conductivity of the water  752 . As mineral content in the water  752  increases, the conductivity of the water  752  increases. Once the conductivity reaches a threshold value, controller  110  operates fluid control device  120  to purge vessel  108  down to a preset level and subsequently refill vessel  108  with fresh water up to a preset level. Controller  110  may also add fresh water as water is removed to fluid conduit  756  during normal operation of steam humidifier system  750 . In one embodiment, the passage of water from vessel  108  to fluid conduit  756  is through another fluid control device  120  under the control of controller  110 . 
     Referring to  FIG. 21 , an exemplary fuel filling system  800  is shown. In fuel filling system  800 , a pump  802  is placed in an underground storage tank  804  that holds fuel  805 . Exemplary fuels include gasoline, diesel, and other fuels. Pump  802  pumps fuel from underground storage tank  804  to a fuel dispensing unit  808  through a fluid conduit  806 . The fuel is then communicated to a fuel tank of a vehicle or other container through a nozzle  810 . As the fuel  805  is pumped to fuel dispensing unit  808  the level  812  of fuel  805  drops. Sensor module  200  may be monitored by controller  110  to determine a level of fuel  805 . In addition, fuel  805  is added to underground storage tank  804  through a delivery fluid conduit  814 . As fuel  805  is added, the level  812  is raised. Once again sensor module  200  may be monitored by controller  110  to determine the level  812  of fuel  805  as fuel  805  is being added. In one embodiment, sensor module  200  is coupled to an interior of underground storage tank  804 . In one embodiment, sensor module  200  is coupled to an exterior of underground storage tank  804 . In one embodiment, sensor module  200  is coupled to a support (not shown). 
     In one embodiment of the present disclosure, a method for determining the level of a fluid or other medium in a container is provided. The method may comprise arranging more than one electrode in an offset fashion substantially along the primary axis to be measured so as to be capacitively coupled with the medium, wherein the medium forms the dielectric of a capacitor, connecting one side of the electrodes so that they are in communication with the mutual charging circuit, connecting the opposing electrodes so that they are in communication with the electrical return circuit or analog common, the charging electrodes and the opposing electrodes forming a capacitive sensor with the medium to be measured as the dielectric, charging and discharging selectable electrodes in a controlled fashion so that the rise time and fall time are affected by the presence of the medium being sensed, passing the mutual connection of the sensor through an integrator circuit and recording the resulting voltage level as different combinations of (or single) electrodes are activated, analyzing the voltage result for different combinations of activated electrodes over time, and making decisions regarding the level of the medium based on the relative voltages for different electrode combinations. 
     The method may include evaluating the result over time to distinguish change events which can be used to calibrate the sensor. 
     The method may include using a variable charging resistor to allow for shifting the range of capacitance sensing. 
     The method may include incorporating a separate electrode at the bottom of the sensor as a control element to be covered by the medium whenever the medium is present wherein any contaminant/scale/slime/algae build up can be sensed and subtracted out of the main sensor input. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a separate heating element and temperature sensing device is placed within the sensing region of the main sensor and by sensing the change in heat dissipation a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a mechanical float is placed within the sensing region of the main sensor and by switching a switch due to the rising of the float a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a pair of conductive probes are placed within the sensing region of the main sensor and by sensing the conductance through the medium a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a pressure transducer is placed within the sensing region of the main sensor and by sensing the pressure through the medium a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     In one embodiment of the present disclosure, an apparatus for determining the level of a fluid or other medium in a container is provided. The apparatus may comprise a sensor element consisting of various electrodes at different positions forming electric field generators, an electrical pulse generator, an electrical circuit that integrates the overall voltage level at the sensor over time, means for analyzing the voltage over time, means for determining the level of the medium based on the measured voltage, and means for activating control elements to respond to the determined level of the material. 
     In one embodiment of the present disclosure, a method for determining the level of a fluid or other medium in a container is provided. The method may comprise arranging more than one electrode in an offset fashion substantially along the primary axis to be measured so as to be capacitively coupled with the medium, wherein the medium forms the dielectric of a capacitor, connecting one side of the electrodes so that they are in communication with the mutual charging circuit, connecting the opposing electrodes so that they are in communication with the electrical return circuit or analog common, the charging electrodes and the opposing electrodes forming a capacitive sensor with the medium to be measured as the dielectric, charging and discharging selectable electrodes in a controlled fashion so that the rise time and fall time are affected by the presence of the medium being sensed, passing the mutual connection of the sensor through a current monitor circuit and recording the resulting current level as different combinations of (or single) electrodes are activated, analyzing the current result for different combinations of activated electrodes over time, and making decisions regarding the level of the medium based on the relative current for different electrode combinations. 
     The method may include evaluating the result over time to distinguish change events which can be used to calibrate the sensor. 
     The method may include using a variable charging resistor to allow for shifting the range of capacitance sensing. 
     The method may include incorporating a separate electrode at the bottom of the sensor as a control element to be covered by the medium whenever the medium is present wherein any contaminant/scale/slime/algae build up can be sensed and subtracted out of the main sensor input. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a separate heating element and temperature sensing device is placed within the sensing region of the main sensor and by sensing the change in heat dissipation a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a mechanical float is placed within the sensing region of the main sensor and by switching a switch due to the rising of the float a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a pressure transducer is placed within the sensing region of the main sensor and by sensing the pressure through the medium a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     The method may include incorporating a calibration feature to adjust for changing conditions over time where a pair of conductive probes are placed within the sensing region of the main sensor and by sensing the conductance through the medium a secondary feedback as to the location of the medium is provided so as to adjust the readings from the main sensor. 
     In one embodiment of the present disclosure, an apparatus for determining the level of a fluid or other medium in a container is provided. The apparatus may comprise a sensor element consisting of various electrodes at different positions forming electric field generators, an electrical pulse generator, an electrical circuit that monitors the overall current through the sensor(s) over time, means for analyzing the current over time, means for determining the level of the medium based on the measured current, and means for activating control elements to respond to the determined level of the material. 
     Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the spirit and scope of the invention as described and defined in the following claims.