Portable water detector for fuel tanks
BACKGROUND AND SUMMARY 
     The invention provides a portable device for detecting water or other foreign fluids in fuel tanks, particularly water in diesel fuel. 
     The invention provides a simple tethered tubular cartridge lowered into the fuel tank and having a pair of probe electrodes sensing a lower resistance current path through water present in the diesel fuel, and associated alarm circuitry. A top cap covers and seals the top end of the cartridge and secures an insulated electrical lead extending therethrough, and is configured for easy retrieval. A bottom cap covers and seals the bottom end of the cartridge and mounts and locates the probe electrodes, and includes a projection element preventing electrical shorting of the probe electrodes through a wall of the fuel tank. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the invention in use. 
     FIG. 2 is a side elevation view partially cut away of the tubular cartridge of the portable water detector in accordance with the invention. 
     FIG. 3 is a bottom view of the bottom cap of FIG. 2. 
     FIG. 4 is a bottom view of the top cap of FIG. 2. 
     FIG. 5 is a circuit diagram of the detection circuitry in accordance with the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a portable water detector generally designated at 2. A tubular cartridge 4 has a pair of probe electrodes 6 and 8. An insulated electrical lead 10 serves as a tether line connected to cartridge 4 for lowering the cartridge into a fuel tank 12, and for upwardly withdrawing and retrieving the cartridge from the fuel tank. Tether line 10 includes a pair of electrically conductive wires 14 and 16, FIG. 2, connected to respective probe electrodes 6 and 8. A portable hand-held box 18, FIGS. 1 and 5, is at the opposite end of tether line 10 from cartridge 4 and contains sensing circuitry connected to the wires in the tether line for sensing reduced electrical resistance between probe electrodes 6 and 8, for example the lower resistive path through water as compared with diesel fuel. Box 18 includes an audio and/or visual alarm 20 to provide an indication of water in the fuel, and a user operated manual ON/OFF switch 22. 
     Referring to FIGS. 2-4, cartridge 4 is an elongated hollow brass tube or cylinder. A top cap 24, of molded PVC, covers the top end of tubular cartridge 4 and is secured and sealed thereto by epoxy. Insulated electrical lead 10 extends through a central aperture 26 in cap 24 and is secured thereto by epoxy along the interface of drilled hole 26 and by epoxy shown at 28 along the underside of cap 24. Lead 10 includes electrically conductive copper wires 14 and 16 extending downwardly within cartridge 4 to the bottom thereof. A bottom cap 30, of molded PVC, covers the bottom end of tubular cartridge 4 and is secured and sealed thereto by epoxy. Electrodes 6 and 8 extend downwardly through drilled holes 32 and 34 in bottom cap 30 and have lower tips 6a and 8a for immersion and contact with the fuel in fuel tank 12 when cartridge 4 is lowered into the tank. When there is water in the tank, such water provides a lower electrical resistance path between electrodes 6 and 8 than through diesel fuel. Sensing circuitry, to be described, is provided for sensing the differential electrical resistance. Bottom cap 30 includes an integrally molded extension or projection finger 36 extending downwardly from the bottom side of cap 30 and having a lower tip 36a slightly extended beyond and lower than the lowermost extent of electrode tips 6a and 8a, as shown at dimension 37, to prevent short-circuiting electrical engagement of the electrode tips with a wall of the fuel tank. Such short-circuiting electrical path through a fuel tank wall between the probe electrode tips would give a false indication. 
     Bottom cap 30 includes a first disc-like portion 38 external to tubular cartridge 4 and having a diameter substantially the same as the outer diameter of cartridge 4 and sealed by epoxy to the bottom end of the cartridge along a horizontal annular surface 40. Bottom cap 30 includes a second disc-like portion 42 on top of first disc-like portion 38 and within tubular cartridge 4 and having a diameter substantially the same as the inner diameter of cartridge 4 and sealed by epoxy to the cartridge along the vertical cylindrical inner wall surface 44 of the cartridge. Probe electrodes 6 and 8 extend through each of the first and second disc-like portions throuch the noted drilled holes 32 and 34. The probe electrodes are brass and are connected to copper wires 14 and 16 by soldering at 46 and 48. Probe electrodes 6 and 8 are sealed and secured to bottom cap 30 by epoxy at 50 on the top side of the cap. Electrodes 6 and 8 may also be retained by friction fit in respective holes 32 and 34 and/or staking of same. The combined vertical thickness of disc-like portions 38 and 42 provides sufficient stock to retain probe electrodes 6 and 8 and to locate such electrodes to prevent engagement with cartridge 4 and to provide proper external spacing and extension of the electrodes. 
     Top cap 24 has a first disc-like portion 52 external to tubular cartridge 4 and having a diameter substantially the same as the outer diameter of the cartridge and sealed by epoxy to the top end of the cartridge along a horizontal annular surface 54. Top cap 24 has a second disc-like portion 56 within cartridge 4 of a diameter substantially the same as the inner diameter of the cartridge and sealed by epoxy to the cartridge along the vertical cylindrical inner wall surface 58 of the cartridge. Top cap 24 has an upper portion 60 on top of disc-like portion 52. The upper portion has an outer frustoconical surface 62 whose taper minimizes interference with tank protrusions during upward withdrawal and retrieval of the cartridge from the tank. Insulated electrical lead 10 extends through central hole 26 drilled vertically through portions 60, 52 and 56, and is secured by epoxy as noted above, to seal and secure lead 10 to top cap 24 and for use as a tether for lowering the cartridge into the tank and for retrieving the cartridge from the tank. It is preferred that the tether stress not be transmitted to solder connections 46 and 48. 
     FIG. 5 shows the sensing circuitry in box 18. Probe electrodes 6 and 8 are connected by electrical wires 14 and 16 through lead 10 to the circuitry in box 18, which is preferably spaced a convenient working distance from cartridge 4 by an appropriate length of lead 10. A battery 64 has positive and negative terminals 66 and 68 connected to a battery connector 70. The above noted user operated manual ON/OFF switch 22 and a diode 72 are connected in series with the battery. Alarm 20 is a piezoelectric transducer sound source connected in series with switch 22 and the battery. A first transistor 74 has a pair of main terminals 76 and 78 connected in series with switch 22, piezoelectric transducer 20 and battery 64. Transistor 74 has a control terminal 80 for controlling current conduction between main terminals 76 and 78. A second transistor 82 has a pair of main terminals 84 and 86 connected in series through switch 22 between positive battery terminal 66 and control terminal 80. Transistor 82 has a control terminal 88 connected through resistors 90 and 92 to wire 14 and probe electrode 6 and controls current conduction between main terminals 84 and 86. The other probe electrode 8 is connected by wire 16 to the negative battery terminal 68. A decrease in electrical resistance between probe electrodes 6 and 8 through water in the tank biases control terminal 88 from the negative terminal of the battery and hence biases transistor 82 into conduction to conduct current from the battery to control terminal 80 to bias transistor 74 into conduction to conduct current through piezoelectric transducer 20 and sound an alarm as an indication of water in the tank. 
     As seen in FIG. 5, ON/OFF switch 22 is connected in series with diode 72 between positive battery terminal 66 and piezoelectric transducer 20. Transistor 82 is a bipolar PNP transistor having its collector 84 connected to a node 94 between ON/OFF switch 22 and piezoelectric transducer 20. Transistor 82 has its base 88 connected to probe electrode 6 via wire 14. Transistor 82 has its emitter 86 connected through resistor 96 to control terminal 80 of transistor 74 and also connected through resistor 98 to negative battery terminal 68. Transistor 74 is a bipolar NPN transistor having its emitter 76 connected to piezoelectric transducer 20. Transistor 74 has its base 80 connected to emitter 86 of transistor 82. Transistor 74 has its collector 78 connected to negative battery terminal 68. 
     In operation, the user lowers tubular cartridge 4 into diesel fuel tank 12, and closes switch 22. If the resistance between probe electrodes 6 and 8 drops sufficiently, the collector-base junction of transistor 82 becomes sufficiently forward biased to drive transistor 82 into conduction. Conduction of transistor 82 conducts current from positive battery terminal 66 through closed switch 22 through diode 72 through the collector and emitter of transistor 82 through resistor 96 to the base 80 of transistor 74, driving the latter into conduction. Conduction of transistor 74 conducts current from the battery positive terminal 66 through closed switch 22 through diode 72 through piezoelectric transducer 20 through the emitter and collector of transistor 74 and returned to the negative battery terminal 68, thus activating the alarm from piezoelectric transducer sound source 20. 
     It is recognized that various equivalents, alternatives and modifications are possible within the scope of the appended claims.