Abstract:
A contaminant detector disposed within a base fluid for detecting the presence of a contaminating fluid includes a conductive core, a conductive sensor probe extending from the core in non-conductive relation, and a circuit board within the core. The circuit board is electrically connected to the sensor probe and electrically insulated from the core. Electrical power applied to the core creates a closed field loop for measuring the localized capacitance of the base fluid. When sufficient contaminating fluid exists in the base fluid to change the localized capacitance, an alarm is sounded to indicate the presence of the contaminating fluid.

Description:
BACKGROUND OF THE INVENTION 
   For almost all combustion engine vehicles such as automobiles, aircraft and boats, small amounts of water contained in the liquid fuel will downgrade the performance of the combustion engine. Excessive amounts of water in the liquid fuel could cause a failure of combustion and result in a catastrophic failure at the cost of equipment and/or human life. 
   Water can be easily introduced into liquid fuel tanks through either natural means, such as condensation, or through human error. The fuel system industry has paid special attention to preventing water from entering vehicle fuel tanks and fueling systems. Many fueling systems are designed to incorporate filters/treaters/processors that remove water and/or particles during the tank filling process. Water can accumulate in the storage tanks from condensation and ambient temperature changes. Additional onboard filtering systems are needed to insure that all the water has been removed from the fuel prior to the fuel being sent to the engine to be burned. While it is the function of the fuel filtration system to effectively remove water, it is also known that these filtration elements can degrade from excessive water and/or other contaminants in the fuel itself. 
   A number of existing water detection devices are currently used in the fuel system filtration industry. Many of these existing designs take advantage of the higher density of water compared to the most common petroleum base liquid fuel. Other designs use the electrical conductivity of water to complete an electrical circuit to indicate the presence of water. As water is filtered out of the fuel, it accumulates at the lowest point in the fueling tank, normally in the bottom of the filter vessel. It is at this location that the water detection device is installed. Prior detection devices can normally be categorized as either a mechanical or electrical devices. 
   The most common type of mechanical detection device includes a buoy. The buoy is weighted such that it will not float in pure fuel. Therefore, the buoy will stay in the down position when the tank is filled with pure fuel. When sufficient contaminant water has accumulated, the buoy floats and triggers an alarm and/or shutdown. A disadvantage of the mechanical design is that it has a number of moving parts that can easily become jammed by contaminants commonly found in the water that accumulates in the harsh environment at the bottom of a fuel tank or filter vessel. 
   The most common type of electrical water detector utilizes the electrical conductivity of water versus the non-conductive fuel as the means to detect the existence of accumulated water. This is an effective means to detect water in a relatively clean environment. However, petroleum fuel when mixed with water provides a hospitable environment for bacterial micro-growth. This bacteria can form an electrically insulated film over the water detector isolating the sensing electrodes from the water rendering the detector useless. 
   Another drawback with the existing water detector designs is that the fueling industry normally demands that the detector be periodically certification tested to insure its proper function. For most prior art water detectors, water is introduced into the fuel system in order to perform a realistic function test. This practice contradicts the requirement to remove water from the fuel system. The industry is reluctant to perform this action but quite often forced to accept it due to the lack of a better choice. 
   Accordingly, there is a need for a contaminant detection device with few moving parts that can become jammed by contaminants, and that is not susceptible to failure from bacterial growth on the sensing electrodes. Moreover, a contaminant detection device is needed which eliminates the undesirable practice of having to introduce water into the fueling system for a realistic function test. Such a new contaminant detection device must provide an effective means of alerting the fueling system operator when excessive amounts of contaminant are accumulated in the fuel/water separator vessel. With an additional control subsystem, this detection device can also disable the fueling system to prevent the malfunctioning filter element from passing water downstream. The present invention fulfills these needs and provides other related advantages. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a contaminant detector disposed within a base fluid for detecting the presence of a contaminating fluid. The contaminant detector comprises a conductive housing, a conductive core slidingly disposed within the housing, a conductive sensor probe extending from the core in non-conductive relation, means for charging the sensor probe and providing an opposite electrical charge to the core and housing to create a closed field loop through the base fluid, means for measuring the localized capacitance of the base fluid in proximity to the sensor probe in the housing, and means for producing an alarm signal in response to a change in the measured localized capacitance to indicate the presence of the contaminating fluid in the base fluid above a pre-set threshold. 
   The housing extends from the proximate end of the core to beyond the distal end of the core and is configured such that the sensor probe extends beyond the distal end of the housing in non-conductive relation. A sliding seal between the proximate end of the core and the housing prevents fluid from leaking through. 
   A sensor cap is mounted over that portion of the sensor probe that extends beyond the housing and a spring biases the sensor probe away from the housing. The spring in conjunction with the sensor cap maintains the sensor probe a fixed distance from the housing. An insulating washer between the sensor cap and the housing maintains the sensor probe in electrical isolation from the housing. Two or more openings in the housing adjacent to the sensor probe permit the passage of fluid into the housing to reach the sensor probe. 
   An insulator seal cartridge between the core and the sensor probe maintains the electrical isolation therebetween. In addition, an insulator also maintains the electrical isolation of the sensor probe from the core. In a preferred embodiment the base fluid comprises a fuel and the contaminating fluid comprises water. 
   The contaminant detector may be used in a process for detecting the presence of a contaminating fluid in a base fluid comprising the steps of:
         Positioning a contaminant detector having a conductive core, a sensor probe extending from the core in non-conductive relation and a circuit board electrically coupled to the sensor probe, in a tank containing the base fluid;   Applying electrical power to the circuit board;   Creating an electrical charge in the sensor probe and an opposite electrical charge in the core to create a closed field loop through the base fluid;   Measuring the localized capacitance of the base fluid in proximity to the sensor probe and the core; and   Producing an alarm signal in response to a change in the measured localized capacitance to indicate the presence of the contaminating fluid in the base fluid above a preset threshold.       

   The contaminant detector may also include a conductive housing in which the core is slidingly disposed and the sensor probe is disposed in non-conductive relation. With the housing, the creating step includes the step of creating the opposite electrical charge in the housing and the measuring step includes the step of measuring the capacitance of the base fluid through the housing. 
   A contaminant detector may be mounted vertically in a bottom wall of the tank or horizontally in a side wall of the tank. In a preferred embodiment the base fluid comprises a fuel and the contaminating fluid comprises water. The circuit board is preferably enclosed within the core and electrical power is provided from a source external to the tank. 
   Testing of the contaminant detector can be achieved by biasing the sensor probe a set distance away from the housing. The sensor probe is then pushed to within a predetermined distance of the housing against the biasing. An alarm signal is produced in response to the measured localized capacitance. The pushing of the sensor probe changes the localized capacitance between the sensor probe and the housing such that it approaches the localized capacitance when the sensor probe is biased a set distance away from the housing and an amount of the contaminating fluid in the base fluid is above the preset threshold. 
   Other features and advantages of the present invention will become apparent from the following more detailed description, taken in connection with the accompanying drawings, which illustrate, by way of example, the principles of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate the invention. In such drawings: 
       FIG. 1  is a cross-sectional view of the conductive core of a contaminant detector embodying the invention; 
       FIG. 2  is a cross-sectional view similar to  FIG. 1 , illustrating the conductive core slidably disposed in a housing; 
       FIG. 3  is a fragmented cross-sectional view of the contaminant detector of  FIG. 2  mounted in the bottom of a fuel tank; 
       FIG. 4  is a fragmented cross-sectional view similar to  FIG. 3 , illustrating the contaminant detector mounted in a sidewall of the fuel tank; and 
       FIG. 5  is a fragmented cross-sectional view similar to  FIG. 3 , showing the contaminant detector mounted in the bottom wall of a fuel tank while in a testing mode. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention is directed to a contaminant detector  10  for detecting the presence of a contaminating fluid in a base fluid. The following detailed description will describe the detector  10  in terms of a fueling system water detection device that detects the presence of water accumulated in the bottom of a fuel tank. However, the principles of the invention are applicable to systems for the detection of contaminants other than water in the presence of base fluids other than fuel. 
   As shown in  FIGS. 1 and 2 , the contaminant detector  10  consists primarily of a conductive core  12  in a conductive housing  14 . The detector  10  includes a sliding seal  16  adjacent a proximate end of the detector  10  and the housing  14  includes one or more openings  18  adjacent the distal end of the detector  10 . 
   The conductive core  12  has a sensor probe  22  that extends from the core  12  in non-conductive relation, and a circuit board  24  electrically coupled to the sensor probe  22 . The core  12  is configured such that it fits snugly inside the housing  14  of the detector  10 . The sensor probe  22  is positioned at the distal end of the core  12  such that at least a portion of the sensor probe  22  is external to the core  12 . An insulator seal cartridge  28  is positioned around the junction between the core  12  and the sensor probe  22 . Seals  30  and  32  create a fluid seal which prevents the passage of any fluid to the inside of the core  12 . 
   The circuit board  24  is positioned inside the core  12  and electrically connected to the sensor probe  22 . The circuit board  24  is also electrically connected to a connector assembly  26  by wires  34  or other means commonly known in the art. The connector assembly  26  is positioned at the proximate end of the core  12  and retained in place by fasteners  36 . An insulator  38  is positioned inside the core  12  to electrically insulate the sensor probe  22  and circuit board  24  from the core  12 . The insulator seal cartridge  28  also assists in this electrical insulation. The insulator  38  and insulator seal cartridge  28  are made from dielectric material. 
   The core  12  and housing  14  are both conductive. However, the present invention does not require electrical current to pass through the core  12 , the housing  14  or the base fluid. The core  12  and the housing  14  possess a relatively low capacitance with each other, which assists in generating a closed field loop as described below 
   A spring  40  is positioned inside the housing  14  between the distal end of the housing and the distal end of the core  12 . At least a portion of the sensor probe  22  extends beyond the distal end of the housing  14 . A sensor cap  42  is affixed to that portion of the sensor probe  22  that extends beyond the distal end of the housing  14 . An insulator washer  44  is positioned between the sensor cap  42  and the housing  14  to maintain the electrical insulation of the sensor probe from the housing  14  and core  12 . The spring  40  in combination with the sensor cap  42  biases the sensor probe  22  a fixed distance away from the housing  14 . As will be described below this fixed distance biasing is necessary for the operation of the contaminant detector  10 . 
   As shown in  FIGS. 3 and 4 , the contaminant detector  10  may be mounted in the bottom wall or sidewall of a fuel tank  46 . When the detection device assembly  10  is mounted in a fuel tank  46  the openings  18  in the distal end of the housing  14  allow liquid fuel or liquid water to reach the sensor probe  22 . The seals  30  and  32  in the insulator seal cartridge  28  prevent fuel or water from entering the inside of the core  12  and interfering with the electronic parts therein. The sliding seal  16  in the housing prevents any external leakage between the housing  14  and the core  12 . 
   In operation, electrical power is supplied to the circuit board  24  through the connector assembly  26 . The electronic circuit board  24  creates an electrical charge to the sensor probe  22  and an opposite electrical charge to the core  12  and housing  14 . The sensor probe  22  on the one hand and the core  12  and housing  14  on the other hand serve the function of sensing electrodes. These sensing electrodes with opposite charges actively project a “closed field loop” through the liquid fuel in their proximity. Using the “closed field loop”, the circuit board  24  measures the capacitance through the liquid in the proximity of the sensing electrodes. In the presence of pure fuel, the capacitance measured by the circuit board  24  is a known value. When water accumulates in the fuel tank and the water level reaches a close proximity to both the sensor probe  22  and the core  12 /housing  14 , the circuit board  24  measures changes in the localized capacitance. When the capacitance changes by a predetermined magnitude, indicating the presence of too much water, the circuit board  24  produces an output alarm signal through the connector assembly  26  to an external alarm system (not shown). 
   It is not necessary that the contaminant water actually contact the sensor probe  22  or core  12 /housing  14 . Because the capacitance is measured using the closed field loop, the alarm output signal can be generated as the water level merely approaches the sensor probe  22  or core  12 /housing  14 . It is this feature that allows the circuit board  24  to detect the presence of water even if the sensing electrodes are covered with a film of bacterial micro growth, contaminants, corrosion, etc. The water detection function of the present invention is performed solely through electronic means without any mechanical moving parts. 
   In a testing mode of the present invention, the contaminant detector  10  is designed to incorporate a test feature which simulates the presence of water in proximity to the sensing electrodes without the actual introduction of water. As described in the operation mode, the circuit board  24  measures any variation of the localized capacitance in order to determine the presence of water in proximity to the sensing electrodes. The variation of localized capacitance can be simulated by varying the distance between the sensor probe  22  and the housing  14 . As illustrated in  FIG. 5 , the core  12  can be pushed toward the housing  14  against the biasing of the spring  40 . As the sensor probe  22  approaches the housing  14  to within a predetermined distance, the localized capacitance between the sensor probe  22  and housing  14  approach the capacitance measured in the operation mode of the detector  10  in the presence of water. In this testing mode, an output signal will be sent to the external alarm system by the circuit board  24 , simulating the detection of excessive accumulated water in the fuel tank  46 . Therefore, testing of the detection device assembly can be achieved without the introduction of water into the fuel tank  46 . 
   The function of the housing  14  in the present invention is to facilitate testing of the contaminant detector  10  without the introduction of water into the fuel tank  46 . In situations where the testing requirements are not applicable, the core  12  can be used independently as the contaminant detector  10  without the inclusion of the housing  14 . In this case, the sensor core  12  may be mounted directly into the fuel tank  46 . 
   As mentioned above, the contaminant detector  10  of the present invention may be applied to the detection of the presence of any undesirable fluid in another. For the technology to be applicable, the subject fluids must possess the following physical and electrical properties:
         The fluids must not be soluble in one another;   The fluids must be of different densities such that they will separate from one another in gravity; and   The fluids must have different dielectric properties.       

   The placement of the contaminant detector  10  in the tank  46  may have to be changed depending upon the relative densities of the subject fluids. If the base fluid is more dense than the contaminant fluid then the contaminant fluid will float on top of the base fluid. In this case the contaminant detector  10  will need to be positioned such that it is near the area of the tank  46  in which the contaminant fluid will settle. 
   Although various embodiments of the present invention have been described in detail for purposes of illustration, various modifications may be made without departing from the scope and spirit of the invention.