EP0830575A1

EP0830575A1 - Liquid level gauge assembly including potentiometer with conductive polymeric element

Info

Publication number: EP0830575A1
Application number: EP95933033A
Authority: EP
Inventors: Herbert G. Ross, Jr.; Carl A. Taylor
Original assignee: Rochester Gauges LLC
Current assignee: Rochester Gauges LLC
Priority date: 1995-06-07
Filing date: 1995-09-01
Publication date: 1998-03-25
Also published as: AU3583895A; WO1996041136A1; EP0830575A4

Abstract

A liquid level gauge assembly utilizing one or more polymeric resistive elements is provided which measures the liquid level in a tank using a three-terminal voltage divider network or a two-terminal voltage or current network. The resistive elements being in slidable contact with a conductor mounted on a float such that the voltage across, or current through the resistive elements vary with the position of the conductor along the resistive elements. An elongate member (406) having external longitudinal grooves (414, 416, 418, 420) formed therein extends into the fluid in the tank. The polymeric resistive elements are in the form of electrically conductive strips (422, 424) and are positioned within grooves (416, 420) in the elongate member. The float (426) is provided with an opening for receiving the elongate member and electrical contacts (428, 430) supported thereon for making sliding contact with the conductive strips. The contacts of the float are electrically connected together to form the float conductor. Guide projections (426A, 426B) are provided on the float for engaging grooves (414, 418) of the elongate member.

Description

LIQUID LEVEL GAUGE ASSEMBLY INCLUDING POTENTIOMETER WITH CONDUCTIVE POLYMERIC ELEMENT

TECHNICAL FIELD OF THE INVENTION

This invention relates to gauges, and in particular, a gauge with a potentiometer as a liquid level sender. In particular, the invention is directed to a gauge particularly useful for measuring liquid level of fluids which can support corrosion.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of pending U.S. Application Serial No. 08/157,906 filed November 24,

BACKGROUND OF THE INVENTION

Gauges are well known in many different configurations for providing an indication of the fluid level in a vessel. Such gauges include float mechanisms having the float arm on a pivot which is in contact with a resistive element positioned close to the pivot. The point of contact along the resistance element changes as the float moves in response to changes in the liquid level. Since the resistive element of such gauges is contained within the tank, it is subject to electrochemical corrosion. One approach to minimize the electrochemical corrosion problem with such gauges is to provide a series of current pulses through the resistance element rather than a constant current, such as shown in U.S. Patent No. 4,782,699.

The corrosion problem can be prevented by isolating the resistance element of the gauge from the tank and contents. In these gauges, a magnet is mounted at the pivot of the float arm and moves as the float moves in response to changes in liquid level. A second magnet is placed in proximity of the magnet on the float and is magnetically coupled with the magnet on the float. This second magnet is attached to a pointer assembly. Thus, movement of the float causes movement in the magnet attached to the float pivot, and as a result of the magnetic coupling, the magnet attached to the dial indicator moves the indicator in response to changes in fluid level. In other embodiments, the second magnet is attached to a wiper element which makes contact with a resistive strip. In this way, the resistive strip is maintained outside the vessel and out of contact with the fluid, such as shown in U.S. Patent No. 4,911,011. However, such configurations have certain drawbacks, which include that typically the resistive strip and dial mechanism is small. Thus, precision can suffer. Also, in rough handling environments such as vehicles, etc. , vibration may cause the dial assembly to move in relation to the float assembly, thus momentarily throwing off calibration.

Other assemblies include gauge assemblies using a resistive element with a float mechanism in direct sliding contact with the resistive element. Such assemblies are shown in U.S. Patent Nos. 4,513,617 and 4,724,705. Metal resistive elements placed in contact with the fluid to be measured are highly subject to corrosion which can either significantly decrease performance or destroy performance. This is because most fluids, including gasoline, contain electrolytes, water vapor or small amounts of water. Also, gases such as methane and propane usually contain water vapor. As a result, there are galvanic and electrolytic reactions leading to corrosion of metals. The corrosion problems will become more pronounced as there is greater consumption of alternative fuels in response to environmental regulations. Thus, there will be a need for a gauge which is resistant to corrosion for use with gasoline blends such as (a) gasohol, a mixture of 10% ethanol with gasoline, (b) methanol and t-butyl alcohol mixtures with gasoline, (c) ethanol, methyl isobutyl ketone and other alcohols with gasoline,

(d) methanol and other alcohols blended with gasoline,

(e) methyl t-butyl ether blended with gasoline, (f) other ethers blended with gasoline, and (g) oxygenated compounds blended with gasoline. Also, other fuel additives can contribute to corrosion, such as detergents, dispersants, brocides, dyes and deicers. The corrosion potential limits the application of gauges where the metal resistive element is immersed in the fluid. Such units also have the drawback that the resistive wire winding presents a rough surface, creating uneven friction loads and the possibility of lost contact with the float. Further, such resistive wires are usually an iron-nickel alloy highly susceptible to electrochemical corrosion and are very thin. The present invention is a voltage divider gauge assembly immersible in fluids.

Thus, there has been a need to provide a gauge which overcomes the disadvantages of prior assemblies. The gauge of the present invention has improved accuracy over gauges employing a magnetic coupling. The gauge assembly of the present invention also has the advantage that the resistive element can be placed in fluids which have been shown to be conducive to corrosion. The gauge also has the advantage of providing a relatively long resistive area which allows for greater resolution and precision. In addition, the device has the additional advantages of reduced cost by simplified design, greater linearity of response and flexibility. Another advantage of the present gauge is that the length of the float guide and resistive elements and the resistive element cross-section can be easily varied to fit different sizes of tanks without requiring change in electrical components to provide read-out of the fluid level.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to an apparatus to be used in conjunction with a voltage source and voltage indicator for measuring the fluid level in a tank or vessel. The apparatus has an elongate electrically resistive polymeric member extending into the fluid with one end connected to a first terminal of the voltage source and the second end connected to a second terminal of the voltage source. A second elongate member is provided, also extending into the fluid, one end of which is connected to one terminal of the high impedance voltage indicator. The other terminal of the voltage indicator is connected to one of the terminals of the voltage source. A float is provided which carries an electric conductor that maintains sliding contact with the first resistive member and the second member. Thus, the voltage provided to the voltage indicator is a function of the position of said float, and thereby the fluid level in the tank. The second elongate member may be either electrically conductive or may be a second electrically resistive polymeric member. In the preferred embodiment, the second elongate member is an electrically resistive polymeric member. In a preferred embodiment of one aspect, the overall resistance along the length of the two members is above about 3000 ohms.

In another aspect, the present invention relates to an apparatus to be used in conjunction with a voltage or current source and a voltage or current indicator. The apparatus has an elongate electrically resistive polymeric member extending into the fluid with one end connected to a first terminal of a voltage source or a current source. A second elongate member is provided, also extending into the fluid, one end of which is connected to a second terminal of a voltage indicator or a current indicator. A float is provided which carries an electric conductor that maintains sliding contact with the first resistive member and the second member. Thus, the voltage or current provided to the voltage indicator or current indicator is a function of the position of said float, and thereby the fluid level in the tank. The second elongate member may be either electrically conductive or may be a second electrically resistive polymeric member. In the preferred embodiment, the second elongate member is an electrically resistive polymeric member. In a preferred embodiment of one aspect, the overall resistance along the length of the two members is about 300 ohms.

In another aspect, the present invention relates to an apparatus to be used in conjunction with a voltage source and voltage indicator for measuring the fluid level in a tank or vessel. The apparatus has a support member extending into the tank with a float arm pivotally attached to the support member. An elongate electrically resistive polymeric member is attached to the support member and has one end connected to a first terminal of the voltage source and the second end connected to a second terminal of the voltage source. A second elongate member is provided, also attached to the support member, one end of which is connected to one terminal of the voltage indicator. The other terminal of the voltage indicator is connected to one of the terminals of the voltage source. Attached to the float arm is a contact assembly that maintains sliding contact with the first resistive member and the second member. Thus, the voltage provided to the voltage indicator is a function of the position of said float arm, and thereby the fluid level in the tank. The second elongate member may be either electrically conductive or may be a second electrically resistive polymeric member. In the preferred embodiment, the second elongate member is an electrically resistive polymeric member. In a preferred embodiment of one aspect, the overall resistance along the length of the two members is above about 3000 ohms. In yet another aspect, the present invention relates to an apparatus to be used in conjunction with a voltage or current source and a voltage or current indicator. The apparatus has a support member extending into the tank with a float arm pivotally attached to the support member. An elongate electrically resistive polymeric member is attached to the support member and has one end connected to a first terminal of a voltage source or a current source and the other end connected to a terminal of a voltage indicator or a current indicator. Attached to the float arm is a contact assembly that maintains sliding contact with the resistive member. Thus, the voltage or current provided to the voltage indicator or current indicator is a function of the position of said float arm, and thereby the fluid level in the tank. In a preferred embodiment of one aspect, the overall resistance along the length of the member is about 300 ohms.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like reference numerals refer to like parts.

Figure 1 is a cross-sectional view of one embodiment of the apparatus connected to voltage source and voltage indicator,

Figure 2 is a cross-sectional view of a tank with a nonuniform cross-section, together with a nonuniform resistance element,

Figure 2A is a cross-sectional view of the nonuniform resistance element along line 2A-2A,

Figure 3 is a cross-sectional view of the second embodiment of the present invention,

Figure 3A is a schematic of an alternate circuit, Figure 3B is a schematic of an alternate circuit, Figure 4A is a cross-section of an alternate embodiment of the float assembly along line 4A-4A, Figure 4B is a partial side view of the alternate embodiment of the float assembly.

Figure 5A is another cross-sectional view of an alternate float assembly along line 5A-5A of Figure 5B, Figure 5B is a partial side view, Figure 6A is a cross-sectional view of yet another embodiment of the float assembly and elongate members along line 6A-6A of Figure 6B,

Figure 6B is a partial side view of another float assembly, Figure 7A is a cross-sectional view of a multiple float embodiment of a float assembly along line 7A-7A of Figure 7C, Figure 7B is a cross-sectional view of a multiple- float embodiment of a float assembly along line 7B-7B of Figure 7C,

Figure 7C is a partial side view of a multiple-float embodiment of another float assembly.

Figure 8A is a cross-sectional view of a float assembly which includes a fill tube.

Figure 8B is a cross-sectional view taken along lines 8B shown in Figure 8A, Figure 9A is a sectional elevation view of a gauge assembly in accordance with the present invention wherein a central structure has planar polymeric resisted elements on opposite sides of a central insulator,

Figure 9B is a cross-sectional view taken along lines 9B shown in Figure 9A,

Figure 11 is a side view in partial cross section of one embodiment of the gauge assembly of the present invention,

Figure 11A is a cross-sectional view of Figure 11 along line 11A,

Figure 12 is an electrical schematic of the gauge assembly of Figure 11 contacted to an appropriate receiver circuit,

Figure 13 is a side view of another embodiment of the gauge assembly of the present invention,

Figure 14 is a cross-sectional view of a portion of Figure 13,

Figure 16 is a longitudinal cross-sectional view of an alternative embodiment of the pivot assembly, Figure 16A is a frontal view of the alternative embodiment of Figure 16,

Figure 17 is a side view in partial cross section of another embodiment of the gauge assembly of the present invention, and Figure 17A is a cross-sectional view of Figure 17 along line 17A.

DETAILED DESCRIPTION

Vertical float gauge assembly

In one embodiment, a single resistive polymeric element is used, and in the second embodiment, two resistive polymeric elements are used. In the preferred embodiment, two resistive polymeric elements are used. A first embodiment of the invention employing one resistive polymeric element is shown in Figure 1. In Figure 1, gauge assembly 10 has a base 12 defining a plurality of apertures 14a, 14b and 14c, providing for communication of electrical leads 16, 18 and 20. The leads 16, 18 and 20 are connected to respective terminals 22, 24 and 26, which are mounted on and insulated from base 12. Base 12 also has passing therethrough bolt passageways 28 for purposes of mounting the gauge assembly 10 to a tank wall 32, shown in phantom. Alternatively, base 12 can be provided with threaded surface 30 for mounting to tank wall 32. It will be appreciated that the base 12 may be provided either with threaded surface 30 for engaging the tank wall 32 or may be provided with bolt passageways 28 for connection to tank wall 32. A gasket 34, shown in phantom, can be provided for making a fluid- tight seal between the base 12 and tank wall 32. Other methods and devices can be employed for mounting the base to the tank, such as a cam lock connection or a bayonet connection. Extending from the base 12 into the tank is elongate electrically resistive polymeric member 36 and an elongate electrically conductive member 38. The first end 40 of elongate electrically resistive polymeric member 36 is attached to base 12 and the second end 42 of elongate electrically resistive polymeric member 36 is dimensioned so that it will extend into the tank. Preferably, the second end of elongate electrically resistive polymeric member 36 is attached to bottom bushing 44. A first end 46 of elongate electrically conductive member 38 is attached to base 12 and has a second end 48 extending into the tank, which is also preferably connected to bottom bushing 44. Bottom bushing 44 defines a passageway 50 through which electrical lead 18 may pass. A float 52 is provided to float near the surface 53 of the liquid 54 and support float conductive member 56 mounted on float 52 in slidable contact with elongate electrically resistive polymeric member 36 and elongate electrically conductive member 38. As used herein float means any device which is buoyant in the liquid. The float may be of such buoyancy that it floats very near the surface, or may be of such buoyancy where the top of the float rests on the surface of the liquid, or may be of intermediate buoyancy where a portion of the float is above the surface of the liquid and a portion extends below the liquid. Selection of proper buoyancy can be advantageous of some applications. For example, where the fluid to be measured is of high lubricity and relatively low corrosion, it may be beneficial to position the float and the float conductive member such that the float conductive member is immersed in the fluid and is lubricated by it to facilitate sliding of the float. On the other hand, where the fluid does not have advantageous lubricating properties or has high corrosive potential, the float conductive member may be mounted on a float such that it makes sliding contact above the surface of the fluid to further minimize corrosion potential. Float 52 may be of any desired configuration which maintains slidable contact of float conductive member 56 with elongate elements 36, 38. In the embodiment of Figure 1, float 52 is slidably disposed over elongate electrically resistive polymeric member 36 and elongate electrically conductive member 38. Float 52 is buoyed on surface 53 of the liquid 54 contained in the tank. Float 52 is slidable along elongate electrically resistive polymeric member 36 and elongate electrically conductive member 38 in response to changes in the level of liquid surface 53. Mounted on float 52 is float conductive member 56 which slidingly contacts elongate electrically resistive polymeric member 36 and elongate electrically conductive member 38. Preferably, float conductive member 56 is provided with a plurality of contacts 59 for providing electrical contact with elongate electrically resistive polymeric member 36 and a plurality of contacts 60 for providing electrical connection to elongate electrically conductive member 38. Preferably, contacts 59, 60 are resilient such that they maintain contact with elongate electrically resistive polymeric member 36 and elongate electrically conductive member 38 while still permitting float 52 to slide along elongate members 36, 38 and to maintain sliding electric contact with those members as the float 52 moves in response to changes in the level of liquid surface 53. The contacts 59 and 60 are preferably made of graphite which has been impregnated with silver.

Elongate electrically resistive polymeric member 36 is attached to base 12 and electrically insulated from base 12. On first end 40 of elongate electrically resistive polymeric member 36 is clamp 61, which is electrically insulated from base 12 and connected to electrical lead 16 which is connected to terminal 22. The second end 42 of elongate electrically resistive polymeric member 36 is connected to clamp 58, which is electrically insulated from bottom bushing 44 and connected to lead 18.

Elongate electrically conductive member 38 is attached to base 12 and electrically insulated from base 12. Alternatively, base 12 can be constructed from an insulated material and itself serve as the insulator. On first end 46 of elongate electrically conductive member 38 is clamp 57, which is electrically insulated from base 12 and bottom bushing 44 and connected to electrical lead 20. Preferably, bushing 44 is electrically insulated from both elongate members 36 and 38. If desired, bottom bushing 44 can be made from a non-conductive material, such as non- conductive plastic.

In use, gauge assembly 10 is connected to a voltage source 62 and a voltage indicator 72. Voltage source 62 has a first terminal 63 connected via electrical lead 64 with terminal 22. Terminal 22 is in turn connected with electrical lead 16, which is connected to elongate electrically resistive polymeric element 36 via clamp 61. The second terminal 65 of voltage source 62 is connected via electrical lead 68 and is connected to terminal 24, which is in turn connected to electrical lead 18, which is connected electrically via clamp 58 to the second end 42 of elongate electrically resistive polymeric member 36. Electrical lead 70 is connected to first terminal 71 of voltage indicator 72 and also connected to terminal 26, which is in turn connected to electrical lead 20, which is connected electrically via clamp 57 to the first end 46 of elongate electrically conductive member 38. The second terminal 73 of the voltage indicator 72 is connected to one of the terminals of the voltage source 62, as shown here, second terminal 65. Sliding contacts 59 and 60 of float conductive member 56 complete the electrical circuit, forming a potentiometer. Thus, a voltage divider is provided and the output is a variable percentage of the voltage drop across the entire elongate electrically resistive polymeric member 36. The output voltage is measured between the first end 40 of elongate electrically resistive polymeric member 36 and the sliding contact 59. Thus, when the voltage drop across the element 36 varies due to changes to input voltage or other factors, the output voltage remains the same relative percentage of the total voltage, thereby ensuring accurate measurement of the level of liquid surface 53 even though voltage inputs vary. In the preferred embodiment of the gauge assembly 10, the voltage source 62 is a 12 or 24 volt DC power supply.

The length of elongate electrically resistive polymeric member 36 and elongate electrically conductive member 38 can easily be varied to accommodate different tank depths. Preferably, the gauge assembly 10 is of such a length that the bottom bushing 44 will stand off from the lower tank wall 74, shown in phantom. The gauge assembly 10 can be dimensioned in reference to the depth of the tank. In Figure 1, the depth of the tank is indicated generally as D. Preferably, the gauge assembly 10 is dimensioned such that the upward travel of float 52 is limited such that it will not reach the upper tank wall 32 by a desired distance represented as T in the drawing. The downward travel of the float 52 is preferably limited such that it will not contact the lower tank wall 74 by a distance represented by B. Typically, B is 10% to 20% of D. The purpose of the stand-off is to prevent the float from striking the bottom of the tank to prevent damage to the float and/or tank. The distance T provides an expansion area to allow changes in liquid volume due to changes in temperature. An important feature of the present invention is that the length of elongate electrically resistive polymeric member 36 can be varied to accommodate different tank depths while not requiring changes in the power or output processing equipment. This is an important manufacturing feature allowing use of the same base, float, and bottom bushing for a number of gauges designed for different types of tanks, requiring only changes in the length of elongate electrically resistive polymeric member(s) 36 and the elongate electrically conductive member 38.

Base 12 can be constructed of any material having suitable mechanical properties, such as aluminum, steel or plastic. Bottom bushing 44 can likewise be constructed of any suitable material such as aluminum, steel or plastic. Float 52 is made of any suitable material which is buoyant in the liquid intended to be measured, and preferably is nonconductive, such as cork or acetal copolymer. Float conductive member 56 is preferably a very corrosive- resistant conductive material. Particular useful are a resistive polymer such as used for the resistive elements, a polymer coated metal, gold, palladium, platinum, nickel, silver, and alloys thereof. Elongate electrically conductive member 38 is preferably constructed of a material which is very corrosive-resistant or which has a corrosion-resistant coating applied to its outer surfaces. Elongate electrically conductive member 38 can be a conductive polymer or made of the same metals utilized for float conductive member 56; however, the cost of such metals may make their use less desirable. A suitable material would be a conductive material, such as copper coated with a corrosion resistant conductive material such as palladium, platinum, nickel, gold, or alloys thereof. Elongate electrically resistive polymeric member 36 is constructed from a conductive polymeric material. This material is noncorrosive and will provide long life. Further, the material can be molded or machined to provide a smooth surface to allow good sliding contact with float conductor contacts 59, 60. Suitable conductive polymeric materials include thermoplastic polyester or other thermoplastics containing carbon fibers or carbon particles. In the preferred embodiment, elongate electrically resistive polymeric member 36 is a thermoplastic polyester containing carbon fibers. Such a material is available from DuPont under the trade name Rynite® CR509 RE5222BK570, which has the properties set forth below. This material is preferred for the three- wire device such as illustrated in Figures 1 and 3 because of its high resistance.

Processing Conditions: Melt Temperature - 285-315°C (545-605°F)

Drying Conditions: 250°F for 2-4 hours, Dewpoint less than 0°F (See RYNITE® Drying Guide) Material must be dried to less than 0.02% moisture before processing. Another aspect of the conductive polymeric material is that they provide useful resistance values in quite large cross-sections, thus providing sufficient mechanical strength to serve as a float guide without need for additional structures. This is in contrast to thin wire iron/nickel alloy resistive elements, which would not provide such structural integrity over useful resistance values, are fragile, and also are easily corroded. For example, a Rynite® CR509 RE5222BK570 rod one-eighth inch square in cross-section with a volume resistivity of 15 ohms-cm (15 ohms per centimeter of length for a cross- section 1 centimeter square) was found useful. Useful polymeric resistive materials would have volume resistivity in the range of about 0.03 to about 164 ohms-cm. for a cross-sectional area one centimeter square. In the embodiment shown in Figure 1, elongate electrically resistive polymeric member 36 is of uniform cross-section, and thus provides a linear resistance measurement. Thus, if the tank is of uniform cross-section, it will provide an accurate read-out of the fluid contained in the tank. Alternatively, when the tank is of nonuniform cross- section, the resistivity of elongate electrically resistive polymeric member 36 can be controlled by shaping elongate electrically resistive polymeric member 36 such that the resistance profile of elongate electrically resistive polymeric member 36 is non-uniform and corresponds to the volume profile of the tank. This may be done in one of two ways: by the nonuniform loading of carbon fibers in the thermoplastic resistive element to vary the resistance along the member as desired, or by varying the cross-sectional area of elongate electrically resistive polymeric member 36 of uniform volume resistivity. For example, elongate electrically resistive polymeric member 36 with uniform volume resistivity can be profiled to provide a resistance reflective of the actual volume at various heights in the nonuniform vessel by varying the cross-sectional area of elongate electrically resistive polymeric member 36. The resistive polymers useful in the invention can be a wide range of resistance. The resistive polymers are selected such that the resistance of the member or members over their entire length is within a value useful for the circuitry selected for use with the gauge assembly. Figure 2 shows a cross-section of a tank 80 having a varying cross-section. Polymeric resistive element 82 is a material having uniform volume resistivity. A first side 84 of the material may remain flat to provide good sliding contact with float contact indicated by arrow 86 (float and remaining gauge components deleted for clarification) . The second side 85 of polymeric resistive element 82 can be mated to a nonconductive support member 96. Polymeric resistive element 82 can be generally of rectangular shape with varying cross-section with the cross-section increasing at form point 88 to point 90 to reflect decrease in volume from point 92 to point 94 in the tank. Then, a uniform cross-section of polymeric resistive element 82 is maintained from point 90 to point 93. The polymeric resistive element 82 may be used alone or may be mated with a nonconductive support member 96 shaped to mate with polymeric resistive element 82 such that the uniform cross-section is possible to provide mechanical strength. Thus, the total resistance from the top of polymeric resistive element 82 to contact point 86 is representative of the actual volume contained within the vessel. As the cross-sectional area is reduced, the resistance per length will increase. The polymeric material may be molded or milled in a shape such that first side 84 is smooth and presented for maintaining good sliding contact with the float conductor contacts (not shown in Figure 2) , and the second side 85 milled so as to vary the resistance as desired. Figure 2A is a cross- section of the resistive element 82 and nonconductive support member 96. The polymeric resistive element 82 can be fashioned to a particular need, such as obtaining sufficient structural strength of the polymeric resistive element 82 by varying the loading of carbon fiber to the polymeric resistive element 82. Thus, a wide range of cross-sections is possible to provide desired resistance per linear length of contact.

In Figure 1, members 36 and 38 and in Figure 3 members 128 and 130 can both be a polymer with a volume resistivity in the range of from about 0.03 to about 164 ohms-cm. The volume resistivity of each member may be the same or different, provided the overall resistance of the two members is within a range useful with the selected electronics.

The float conductor preferably has two or more resilient contacts at each end to ensure good contact with the elongate members. In a preferred embodiment, the gauge assembly 10 utilizes two elongate electrically resistive polymeric members 36 and does not employ the elongate electrically conductive member 38. Figure 3 shows a gauge assembly 100. The gauge is provided with a base 102 having threaded surface 104 for engaging the walls of the tank. The base on its bottom side 106 has a channel 108 which receives baffle shield 110. Baffle shield 110 has a number of openings 112 to permit flow of liquid to the interior of the baffle shield 110. The top end 113 of baffle shield 110 mates with channel 108 and the bottom end 114 of baffle shield 110 mates with channel 116 in bottom bushing 118. Bottom bushing 118 can also be provided with holes 120 to permit flow of fluid around the bottom bushing 118. This structure, the baffle shield 110 and bottom bushing 118, serves to dampen any wave effect on the surface of the liquid to be measured caused by movement of the tank. Attached to the bottom side 106 of base 102 are two float guides 122 which extend through passageways in the bottom bushing 118, and nuts 126 hold the bottom bushing 118 against the baffle shield 110 to provide a rigid structure. It will be appreciated that the baffle shield 110 and the float guides 122 may be secured to the base 102 and bottom bushing 118 in a number of manners. Also extending from the bottom side 106 of base 102 are first elongate resistive polymeric element 128 and second elongate electrically resistive polymeric element 130. The bottom ends of first and second elongate resistive polymeric elements 128, 130 are respectively held in position by receptacles 132, 134 in the bottom bushing 118. A conductor 138 mounted on a float 136 makes sliding electrical contact with first elongate resistive polymeric element 128 and second elongate resistive polymeric element 130. As discussed previously, the conductor mounted on the float may be made of resistive polymer material or a suitable metal. Preferably, this sliding electrical contact is provided by one or more resilient contacts 140 and 142. On top of base 102 is first, second and third terminals 144, 146 and 148. First terminal 144 is connected to insulated conductor 150, which is electrically connected to first elongate resistive polymeric element 128 at its bottom. Second terminal 146 is connected by conductor 152 to the top of first elongate resistive polymeric member 128. Third terminal 148 is connected to conductor 154, which is electrically connected to the top of second elongate resistive polymeric member 130. The bottom of second elongate resistive polymeric member 130 is electrically insulated from the bottom bushing 118. Thus, the portions of first elongate resistive polymeric member 128 and second elongate resistive polymeric member 130 above float conductor 138 represent two resistive polymeric strips connected to provide an electrical path. Thus, as the float conductor 138 slides along elongate resistive polymeric members 128 and 130, the change in resistance allows the change in voltage to be measured to provide a reading of fluid level in the tank. Any suitable circuit may be used. Figure 3 shows a power source 145 connected to the first side of voltage indicator 147 and to terminal 146. Terminal 148 is also connected to the first side of voltage indicator 147. The second side of voltage indicator 147 is connected to terminal 144. Due to the high impedance of the sender, the terminals on the base should be sealed externally against moisture and contamination by seals 159. The voltage indicator is of a high-impedance type. The contacts 140 and 142 can be the same as the contacts 59 and 60 described in reference to Figure 1.

It is possible also to delete lead 150 and terminal 144. Then the circuit shown in Figure 3A could be used where current indicator 160 would be connected to the top end of the first resistive element 162 and the second resistive element 164, which are connected by float conductor 166. This then results in what is commonly referred to as the two-wire device in contrast to what is commonly referred to as the three-wire device shown in Figures 1 and 3. The two-wire device can be used as either a voltage indicator or a current indicator, depending on how it is connected to external components. As the circuit is illustrated in Figure 3A, the device would result in indicating current. The gauge may also be wired with two wires such that it creates a voltage indicator, as shown in Figure 3B. As shown in Figure 3B, voltage source 161 is connected to element 164 with sliding float conductor 166 connecting the element 164 with element 162. The other lead of the voltage source 161 is connected to element 162 with resistor 163 interposed. In this configuration voltage indicator 167 allows for reading of the voltage. In this two-wire configuration shown in Figures 3A and 3B, it is preferable to use a higher conductivity polymeric element with a resistance which does not exceed about 300 ohms-cm. Further, it is preferred when the two-wire configuration is utilized as shown in Figures 3A and 3B that preferably both elongate members 162 and 164 are constructed of a conductive polymeric material, such as SC500 MCS sold by DuPont, and have the following characteristics.

Drying Conditions: 250°F for 2-4 hours, Dewpoint less than 0°F. The baffle shield 110 may be made from aluminum, plastic or other material having suitable strength. The float guides 122 are preferably made from a material which is noncorrosive and which provides sufficient tensile strength, such as aluminum, stainless steel and some plastics. Preferably, float guides 122 are attached to the base 102 and bottom bushing 118 with threaded connections and nuts 126. As will be apparent, this embodiment also allows the easy variation of length of the gauge to accommodate various sizes and depths of tanks. Another feature of the present invention is that in certain applications, much of the device may be constructed from molded plastics. For example, the base 102 can be made from molded plastic with lead conductors 150, 152 and 154 molded directly into the base 102, as well as molding into the base 102 the top ends of the first and second elongate resistive members 128 and 130. The float may have any number of designs and it is not necessary that the float encircle either of the elongate resistive polymeric elements, as long as the float is positioned in a fashion to permit the flexible contacts of the float conductor to maintain sliding electrical contact between the elongate electrically resistive polymeric member 36 and elongate conductor member 38 in the first embodiment or the two elongate electrically resistive polymeric members 128, 130 in the second embodiment. For example, Figures 4A, 4B, 5A, 5B, 6A and 6B show alternate embodiments of the float assembly. Other portions of the gauge have been deleted for purposes of clarification.

Figure 4A is a cross-sectional view of one such embodiment of a float assembly taken along line 4A-4A of Figure 4B, which is a partial side view. In Figure 4A, float 170 is slidably disposed over member 172. Member 172 serves as both a float guide and as part of the electric circuitry. It can serve either as the elongate electrically resistive polymeric element or the elongate conductive element. Float 170 has a protrusion 174 which is dimensioned to be slidably received by channel 176 on guide member 178. In the bottom of the channel 176 is a strip 180. Strip 180 may be an elongate electrically resistive polymeric element. Strip 180 may be an elongate conductive member if member 172 is a resistive polymeric material. Float 170 carries float conductor 182, having resilient contacts 184 and 186 for making slidable electric contact between member 172 and strip 180. Like items are shown by like numbers in Figure 4B. Thus, in the embodiment where the elongate conductive member is utilized, either member 172 or strip 180 could be the elongate conductive member and the other member would be the elongate resistive element. In the embodiment employing two resistive elements in series, both member 172 and strip 180 would be elongate electrically resistive polymeric elements.

Figure 5A is a cross-sectional view of another embodiment of the float and elongate member taken along line 5A-5A of Figure 5B. Figure 5B is a partial side view. Shown in Figure 5A is float 200, which is slidably disposed around two float guides 202 and carries conductor 204. In proximity to the float are two support elements 206 to receive elongate structures 208 in channel 210. Slidable contact of conductor 204 with both elongate structures 208 is provided by resilient contacts 212 of conductor 204. In this embodiment, the elongate structures 208 may both be elongate electrically resistive polymeric elements or one of them may be an elongate conductive element and the other an elongate resistive polymeric element. Figures 6A and 6B show yet another variation of a float assembly. Figure 6A is a cross-sectional view of Figure 6B on line 6A-6A. Shown in Figure 6A is float 250 defining a desired shape which has a passageway therethrough to permit sliding engagement with float guide 252. Preferably, float 250 is provided with alignment projections 254 for mating with alignment channels 256 in float guide 252. Float guide 252 defines a passageway 258 through which conductor 260 passes. Float guide 252 also defines first and second elongate channels 262 and 264, respectively. Disposed within elongate channels 262 and 264 are first elongate electrically resistive polymeric member 268 and a second elongate member 270. In the preferred embodiment, second elongate member 270 is an elongate resistive polymeric element, but in an alternate embodiment can be an elongate conductive element. Float 250 carries float conductor 272, which connects first elongate electrically resistive polymeric member 268 and second elongate member 270 by slidable contact through flexible contacts 274 and 276. Corresponding numbers are used in Figure 6B for like items. At the bottom of float guide 252 is a bottom bushing 280. Conductor 260 protrudes from the bottom of bottom bushing 280 and is connected to the lower end of first elongate electrically resistive polymeric member 268. Thus, in this embodiment, the float guide 252 not only serves to guide the float 250, but also supports the first elongate electrically resistive polymeric member 268 and second elongate member 270, as well as the bottom bushing 280, and permits passage of the conductor 260 through its center. Preferably, the float guide 252 is made from a nonconductive material such as molded plastic. This embodiment has the advantage that first elongate electrically resistive polymeric member 268 can be placed in the channel 262 and the element may be of different resistivity values. Thus, the same construction can be utilized but yet allow varying the resistive value per unit length of the guide by substituting resistive polymeric members having differing volume resistivities. Elongate member 270 can be either an elongate resistive element or an elongate conductive element. In the event an elongate conductive element is selected, it can be relatively thin and small because it will be supported by the float guide 252. Thus, use of noncorrosive expensive metals such as gold, platinum, etc. , for the elongate conductive element becomes more economically feasible. The elongate element 270 may also be copper or other conductor. Elongate member 270, the float 250 and the first elongate electrically resistive polymeric member 268 are electrically insulated from one another except at contacts with float conductor 272. As described above, the float conductor may also be in the form of a resistive polymeric member. Those skilled in the art will appreciate that more than one float and pair of elongated members can be provided in the same gauge assembly. A separate electrical circuit can be made from each such set of a float and associated pair of elongated members. Thus, two or more separate electrical circuits can be provided in a single gauge assembly. In this way, one gauge assembly can be used to separately measure the levels of immiscible liquids of different densities contained in the same tank, for example water and gasoline. One float would have a density allowing it to float on the less dense liquid and a second float would have a density such that it would sink in the less dense liquid but would float on the more dense liquid. Figures 7A, 7B and 7C show an embodiment of a float assembly utilizing multiple floats to measure immiscible liquid levels. Figure 7A is a cross-sectional view of Figure 7C on line 7A-7A. Shown in Figure 7A is upper float 300 defining a desired shape which has a passageway 302 therethrough to permit sliding engagement with float guide 304. Preferably, upper float 300 is provided with alignment projections 306 for mating with alignment channels 308 in float guide 304. In some embodiments, upper float 300 may also define ballast pockets 309 which may be left empty or filled with correspondingly-sized ballast plugs 311 of different materials so as to allow adjustment of the overall density of upper float 300. Float guide 304 defines a passageway 310 through which a first conductor 312 and a second conductor 314 pass.

Float guide 304 also defines first, second, third, and fourth elongate channels 316, 318, 320 and 322, respectively. Disposed within elongate channels 316 and 318 are first elongate electrically resistive polymeric member 324 and second elongate member 328, respectively. Similarly disposed within elongate channels 320 and 322 are third elongate electrically resistive polymeric member 326 and fourth elongate member 330, respectively. In the preferred embodiment, second and fourth elongate members 328 and 330 are elongate resistive polymeric elements, but in an alternative embodiment can be elongate conductive elements. Upper float 300 carries first float conductor 332, which connects first elongate polymeric resistive member 324 and second elongate member 328 by slidable contact through flexible contacts 334 and 336.

Corresponding numbers are used in Figure 7B for like items. Figure 7B is a cross-sectional view of Figure 7C on line 7B-7B. Shown in Figure 7B is lower float 338 defining a desired shape which has a passageway 340 therethrough to permit sliding engagement with float guide 304. Preferably, lower float 338 is provided with alignment projections 342 for mating with alignment channels 308 in float guide 304 and with ballast pockets 343 for receiving ballast plugs 345 for adjusting the overall density of lower float 338. Lower float 338 carries second float conductor 344, which connects third elongate polymeric resistive member 326 and fourth elongate member 330 by slidable contact through flexible contacts 346 and 348.

In the preferred embodiment, both upper and lower floats are initially constructed as "generic" floats with empty ballast pockets and identical structure, thus simplifying manufacturing. Such "generic" floats are then transformed as needed into upper floats 300 or lower floats 338 through the insertion of ballast plugs 311 or 345 appropriate for the liquid to be measured. The floats are then oriented on float guide 304 such that a different pair of elongate members are contacted by each float conductor. Alternatively, upper and lower floats may be constructed with unique structures depending upon their intended application.

Corresponding numbers are used in Figure 7C for like items. Figure 7C shows upper float 300, which has an overall density such that it floats on surface 350 of less dense liquid 352, and lower float 338, which has an overall density such that it sinks in less dense liquid 352 but floats on surface 354 of more dense liquid 356. At the bottom of float guide 304 is bottom bushing 358. First conductor 312 protrudes from the bottom of bottom bushing 358 and is connected to the lower end of the first elongate electrically resistive polymeric member 324, thus completing a first electrical sub-circuit along with flexible contact 334, first float conductor 332, flexible contact 336, and second elongate member 328. Similarly, second conductor 314 protrudes from the bottom of bottom bushing 358 and is connected to the lower end of third elongate electrically resistive polymeric member 326, thus completing a second electrical sub-circuit along with flexible contact 346, second float conductor 344, flexible contact 348, and fourth elongate member 330. When connected to suitable monitoring circuitry, the first sub- circuit can be used to monitor the level 350 of the less dense liquid 352 and the second sub-circuit can be used to monitor the level 354 of the more dense liquid 356.

Those skilled in the art will appreciate how the concept of multiple-float float assemblies utilizing elongate electrically resistive polymeric members as described above can be extended to encompass float assemblies suited for measuring three or more independent fluid levels.

Other embodiments and cooperating structures between the float and the resistive elements will be apparent to those skilled in the art.

Referring to Figures 8A and 8B, there is shown a gauge assembly 400 which includes a base 402 which mounts to an opening in a tank (not shown) . The base 402 includes a cylindrical opening 404 which receives an elongate, cylindrical, nonconductive body 406. The body 406 has a cylindrical interior passageway opening 408. A fill tube 410 extends through the base 402 and through the opening 408 to a bottom bushing 412. The fill tube 410 has a bottom opening 410A which is open to the interior of a tank (not shown) for transferring fluid to and from the tank. The bushing 412 is connected to the lower end of the cylindrical body 406 and has the fill tube 410 passing therethrough. The bushing 412 is a nonconductive member made of a material such as plastic. The cylindrical body 406 has external longitudinal grooves 414, 416, 418 and 420. An elongate, polymeric conductive strip 422 is located in groove 420, and a similar polymeric strip 424 is located in groove 416. A float 426 has an interior opening for receiving the cylindrical body 406. The float 426 has interior standouts 426A and 426B which respectively engage the grooves 414 and 418 to maintain alignment of the float 426 about the body 406. Float 426 includes contacts 428 and 430 which are similar to the contacts 59 and 60 described above. The contacts 428 and 430 are interconnected by conductor 432. The contacts 428 and 430 slidably engage the polymeric strips 422 and 424, respectively. The gauge assembly 400 has a three-wire configuration, such as described above for gauge 10 shown in Figure 1. The three sensor wires are 434, 436 and 438. These are wrapped about the neck of the fill tube 410 for stress relief. Wire 434 extends down the interior opening 408 and through the bushing 412 for connection to the lower end of polymeric strip 422. ire 436 is connected to the top end of polymeric strip 422. The wire 438 is connected to the top end of polymeric strip 424. The measurement technique is the same as that shown in Figure 1 utilizing the voltage source 62 and the voltage indicator 72.

The polymeric elements 422 and 424 have preferable dimensions consisting of a width in the range of 0.150- 0.500 inch and a thickness in the range of 0.030-0.100 inch. The length is dependent upon the size of the tank in which the gauge is installed. The composition of the polymeric strips 422 and 424 is preferably 0-30% fiberglass, 20-60% carbon particles and 30-60% a polyester resin, such as PET. The specific polymeric material PET is polyethylene terephthalate. The polymeric elements are preferably a moldable composite sheet (MCS) . These are produced preferably by compression molding rather than ejection molding. Injection molding can use plasticizers which can react with some store fluids such as gasoline causing the piece to become tacky.

Referring now to Figures 9A and 9B, there is shown a gauge assembly 450 which includes a base 452 that is fitted to an opening in a tank (not shown) . The base 452 is fitted with terminals 454, 456 and 458, each of which has a corresponding wire that is used in a three-wire sensing arrangement, such as shown in Figure 1. The terminals 454, 456 and 458 are connected respectively to wires 460, 462 and 464. The base 452 has an annular opening 466 and a center rectangular opening 468. A cylindrical body 470 is fitted into the annular opening 466. The body 470 is provided with holes 470A to permit fluid to float the interior of the body. A bushing 472 is connected to the lower end of the cylindrical body 470. The bushing 472 has holes 472A for permitting fluid to flow into the interior of the body 470.

A multi-layer structure 474 extends within the interior of the cylindrical body 470 and is secured to the rectangular opening 478 at one end and to the bushing 472 at the opposite end. The structure 474 has a rectangular configuration with conductive polymeric strips 476 and 478 on the outsides and a nonconductive layer 480 on the interior. The polymeric strips 476 and 478 have the same size, configuration and composition as the polymeric strips 422 and 424 described above in reference to Figures 8A and 8B. The nonconductive layer 480 has a thickness of approximately 0.040-0.050 inches. It comprises the same material as the polymeric members 476 and 478 but without the carbon particles. The multi-layer structure 474 is preferably formed by compression molding such that the structure 474 is a single rigid element. A float 482 is positioned within the cylindrical body 470 and includes vertical grooves 482A and 482B. The cylindrical body 470 is provided with opposing vertical linear standout tracks 484 and 486 which respectively engage the grooves 482A and 482B. The float 482 includes contacts 488 and 490, which are similar to the contacts 59 and 60 described above in reference to Figure 1. The contacts 488 and 490 are connected via a line 492. The contacts 488 and 490 respectively have a sliding engagement with the exposed service of the polymeric strips 476 and 478. This contact is maintained as the float 482 arises and lowers depending upon the level of fluid in the tank.

The wire 460 is connected to the top end of the polymeric element 476. The wire 462 extends down the edge of the multi-layer structure 474 and passes through the bushing 472 and connects to the bottom end of the polymeric strip 476. The wire 464 is connected to the upper end of the polymeric strip 478.

In operation, the float 482 moves up and down depending upon the level of fluid in the tank while the contacts 488 and 490 maintain electrical contact with the polymeric strips 476 and 478. The polymeric strip 476 acts a voltage divider and has the available voltage source connected between the ends thereof. The voltage at a particular point is picked off by the contact 488 and transferred through the conductor 492 to the contact 490 so that the voltage is then transferred through the polymeric strip 478, line 464 and terminal 458 to a voltage indicator. The polymeric strips 476 and 478 may or may not have the same resistivity. Pivot gauge assembly

With reference to Figures 11 and 12, one embodiment of the gauge assembly of the present invention is shown. Like numbers refer to corresponding parts in different figures. Figure 11 shows gauge assembly 510 in partial cross section (the base is in cross section) mounted to tank 512 (shown in partial phantom) to respond to a range of liquid level in tank 512. Gauge assembly 510 comprises a base 514 and a float support member 532 attached to base 514. The base 514 (shown in cross section) defines a plurality of passageways 516, 518, and 520 through which electrical conductors 522, 524 and 526 may pass. The passageways can be holes through which the conductors pass or can be formed by molding the conductors into the base. The base can have threaded surface 528 for mounting to the tank. Many other means for mounting the base to the tank can be used such as screws passing through aperture 530. Other mechanisms include cam lock joints and bayonet joints.

Extending from the base 514 is float support member 532 having a first end 534 attached to base 514 and a second end 572 adapted for extending into said tank and supporting the float arm 536 and float 538. Float 538 may be a separate material from the float arm 536 such as cork. Alternatively, it may be a hollow portion of float arm 536 such as a hollow aluminum cylinder. Float arm 536 is pivotally attached to support member 532 by pivot pin 540. Float arm 536 is allowed to pivot around pin 540 from the empty position 542 to the full position shown in phantom 544. Preferably the gauge includes float arm stops 546 and 548. Float arm stops 546 and 548 are pins attached to support member 532 and extend outwardly past float arm 536 and act to limit the arc through which the float arm may travel.

Attached to float arm 536 is contact assembly 550 which provides electrical contact between first arcuate resistive member 552 and second arcuate resistive member 554. The first end of arcuate resistive member 552 is connected to voltage source 556 via electrical conductors 558, 522 and 560. The second end of the first arcuate resistive member 552 is connected to the other side of the voltage source via electrical conductors 562, 524 and 564. The first end the second arcuate resistive member 554 is connected to voltage indicator 566 via electrical conductors 568, 526 and 570. The other side of the voltage indicator 566 is connected to the second end of the first arcuate resistive member 552 via electrical conductors 564, 524 and 562.

Figure 11A shows a cross-sectional view of Figure 11 along line 11A. Support member 532 defines an aperture 533 which preferably contains a bushing 535 pressed into the aperture. The bushing 535 defines a passageway through which pin 540 passes and can rotate. Pin 540 defines a passageway 541 through which float arm 536 may pass. Preferably, float arm 536 is connected to pin 540 such that float arm 536 does not rotate with respect to pin 540. Alternatively, float arm 536 and pivot pin 540 made be made in one integral piece, or welded or soldered together. In the embodiment shown, pivot pin 540 is held in place with respect to support member 532 by bushing 535 and by nuts 537 and 539. Also mounted on support member 532 is insulating member 551. Adhered to insulating member 551 is first and second arcuate resistive members 552 and 554. It will be understood that when support member 532 is made of a nonconductive material resistive members 552 and 554 may be adhered directly to support arm 532. Insulating member 551 and resistive members 552 and

554 may be glued together, bolted together, screwed together, or attached in any suitable means. Contact assembly 550 at the end of float arm 536 has conductor element 553 attached by any suitable means so that it is electrically insulated from the float arm such as rivet

555 and insulator. Conductor element 553 may be of any suitable material and preferably a very corrosive resistant material such as a resistive/conductive polymer, gold, palladium, platinum, nickel, silver and alloys thereof. The conductor element 553 can be made of a conductive/resistive polymeric material used for the arcuate resistive member. Conductor element 553 makes sliding contact with resistive members 552 and 554. As float arm 536 and pin 540 rotate about support member 532 the point of contact between conductor element 553 and first and second resistive members 552 and 554 will change. Thus, the relative position of conductor element 553 along the arcs of resistive members 552 and 554 will vary as fluid level in the tank varies. One benefit of the present invention is that first and second resistive members 552 and 554 being made of a conductive/resistive polymeric material can be made with a smooth planar surface for sliding contacting with conductor element 553. This is in contrast to prior art wound resistive wires which present a series of ridges and valleys to the wiper arm. This was a potential source for collecting contamination, where a wiper arm and resistive member made of small gauge coil wire were not only subject to corrosion, but were also subject to mechanical abrasion in view of their size. In contrast, the present invention allows resistive members to be made with a high degree of mechanical strength. Further, the resistive members 552 and 554 are finished to provide a smooth planar surface upon which conductor element 553 may slide. To some extent the resistive/conductive polymers used to make members 552 and 554 are self lubricating, thus facilitating sliding contact. Further, because resistive members 552 and 554 can be of a shape having a high degree of mechanical strength compared to thin wire coiled resistance elements, the conductor element can be made in a heavier gauge and also have a greater contact pressure with the resistive elements of the present invention than would be the case for thin wire coiled resistive elements. Additionally, the flat surface of the resistive members can be cleaned of contamination to some degree by the wiping action of the conductor element as it moves in response to movements of the float arm. As the float rotates about pin 540 and contact assembly 550 moves in response to movement of the float, its position along resistive members 552 and 554 thereby varies the resistance of the circuit. Figure 12 illustrates a simplified circuit of the device shown in Figure 11. Many different types of configurations of float arm and contact assembly may be used with the present invention.

Figures 13 and 14 illustrate another embodiment of the gauge assembly. Base 582 has mounting holes 590 through which fasteners, for example, screws or bolts or rivets, can be placed to attach base 582 to tank 587.

With additional reference to Figure 13, second end 588 comprises a portion of float support member 584 and housing 592 mounted thereto with rivets 594. Housing 592 has hub portion 596 defining a hole 598 and opposite hole 600 in support member 584. Housing 592 has an open side 602 indicated on Figure 13.

With additional reference to Figure 14, pivotal axle 604 is rotatably mounted in second end 588 of the support member 584. Pivotal axle 604 has a first end 606 disposed through hole 598 and second end 608 disposed through hole 600. Pivotal axle 604 has a block portion 610 that has passageway 612 extending therethrough. First end 606 can then be deformed to raise a radial ridge 650 and retaining washer 651 is placed between radial ridge 650 and the hub portion 596.

Float arm 622 extends from pivot axle 604 in a direction non-parallel to the rotational axis of pivot axle 604. Preferably, float arm 622 is perpendicular to the rotational axis of pivot axle 604, but certain applications may dictate that float arm extend obliquely from the rotational axis. Float arm 622 has a proximal end 624 at pivot axle 604 and a distal end 626 with the float 630 attached thereto. Float arm 622 is pivotable about the rotational axis of pivot axle 604. Proximal end 624 is inserted into passageway 612 of block portion 610. Proximal end 624 can be retained in passageway 612 by any suitable means. In the preferred embodiment, block portion 612 is crimped around proximal end 624. A crimping device can be placed about two opposing flat surfaces 616 to crimp block portion 610 around proximal end 624. If desired, float arm and pivot axle may be made of a single piece. In an alternative embodiment shown in Figures 16 and 16A, pivot axle 604' and proximal end 624' of float arm 622* are of a one piece T-shape construction. Second end 588' of support member 584* comprises a pin 632 fixed at one end to housing 592' and at the other end to support member 584'. Pivot axle 604' is generally annular and is rotatably mounted about pin 632.

Float 630 rises and falls with the liquid level in tank 587 by swinging arcuately up and down about the rotational axis of pivot axle 604, the position of contact support 658 will change along the first and second arcuate resistive members 652 and 654. The length and configuration of float arm 622 as well as the size and type of float 630 are a matter of the parameters of a specific application, for example, size of tank, placement of gauge assembly, type of liquid, etc.

In the embodiment of Figure 13, first resistive member 652 and second resistive member 654 are mounted to insulation material 656. Insulation material 656 is mounted to second end 588. Contact support 658 is mounted to pivot axle 604 and extends radially outward. Insulator 660 is positioned between contact support 658 and contact 662. Insulator 660 and contact 662 are mounted to contact support 658 with a non conducting rivet 664. Contact support 658 is positioned so that contact 662 is in slidable contact with first resistive member 652 and second member 654 thereby causing a conductive path between first resistive member 652 and second resistive member 654. Thus, as float arm 622 pivots, the extent of arc of the first resistive member 652 that the current flows through changes thus providing a signal proportional to the liquid level in the tank.

Figure 17 shows an alternate embodiment of what is commonly referred to as a two-wire gauge, meaning it will be compatible with external circuits designed to receive two leads from the gauge assembly. In Figure 17, gauge assembly 700 is shown with base 702 shown in cross section and a side view of support member 704. Support member 704 has a first end 706 attached to base 702 or first end 706 may be integral with base 702, and having a second end 708. Float arm 710 is pivotally attached to support member 704 by pivot pin 712. At the first end of float arm 710 is float 714 and at the second end of float arm 710 is contact assembly 716. Contact assembly 716 makes contact with arcuate polymeric resistive member 718. As float arm 710 moves from the empty position shown in Figure 17 to the full position 780 shown in phantom, contact assembly 716 moves along arcuate resistive member 718 between first end 720 of resistive member 718 and second end 722 of resistive member 718. The first end 720 of resistive member 718 is connected to electrical conductor 724. Contact assembly 716 is electrically connected to conductor 726. Base 702 defines passageways 728 and 730 through which conductors 724 and 726 pass to be attached to respective terminals 732 and 734. Figure 17A is a cross-sectional view along line 17A of Figure 17. Support member 704 defines passageway 736. Pressed into passageway 736 is bearing 738. Depending on the materials of construction, bearing 738 can be eliminated. Bearing 738 defines a passageway through which pivot pin 712 passes. Float arm 710 is attached to pivot pin 712. Preferably, it is attached such that it will not rotate with respect to pivot pin 712. The combination of float arm 710 and pivot pin 712 are rotatably attached to support member 704. Support member 704 also has attached insulating base 740. Attached to insulating base 740 is arcuate resistive member 718. If support member 704 is made with an insulating material, insulating base 740 may be eliminated.

Arcuate resistive member 718 is in sliding contact with contact assembly generally indicated as 716. Contact assembly 716 comprises contact arm 742 which makes contact with resistive member 718. Contact arm 742 is attached to float arm 710 and in turn is connected to conductive washer 746. Contact arm 742 and washer 746 may be of the same piece of material. Adjacent to conductive washer 746 is preferably conductive spring washer 748. Adjacent to conductive spring washer 748 on the side opposite conductive washer 746 is second conductive washer 750. Second conductive washer 750 is connected to electrical conductor 726. Adjacent to the second conductive washer 750 is insulating washer 752 made of an insulating material. And adjacent to insulating washer 752 is nut 754. Nut 754 and nut 756 hold pivot pin 712 in bushing 738. In the embodiment shown, pivot pin 712 is made of insulating material. However, the pivot pin may be made of a noninsulating material in which case an insulating sleeve or coating should be provided, such as Teflon® around the pivot pin so that contact between the pin and the conductive washers is not made. Alternatively, it is not necessary to electrically isolate the contact arm 742 if it is grounded. The design may easily be modified to account for the insulating properties of various components, it being understood the desire is to complete a circuit between resistive member 718 and conductor 726. Also, it is not necessary to use conductive spring washer 748. It is preferred to use the spring washer 748 to make the assembly more easily rotatable, and to assure positive contact between conductive washer 746 and conductive washer 750.

Although several embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications, and substitutions of parts and elements with departing from the spirit of the invention.

Claims

CLAIMS :What is claimed is:

1. Apparatus for use in conjunction with a voltage source and voltage indicator for measuring the level of fluid in a tank, comprising: an elongate member for extending into said fluid, said member comprising a homogeneous supporting matrix of thermoplastic resin and glass fiber, said matrix having first and second parallel, longitudinal regions, wherein said first region of said matrix is electrically conductive and said second region of said matrix is electrically non-conductive, said first region having an exposed surface, a float, and at least a first electrical contact supported by said float for making sliding contact with the exposed surface of said first region.

2. Apparatus as recited in Claim 1 including: a third longitudinal region of said matrix wherein said third region is electrically conductive and has an exposed surface and said first and third regions are on opposite sides of said second region, and a second electrical contact supported by said float for making sliding contact with the exposed surface of said third region and wherein said first and second electrical contacts are electrically connected together.

3. Apparatus as recited in Claim 2 wherein said first region is more electrically conductive than said third region.

4. Apparatus as recited in Claim 1 wherein said float has an opening for receiving said elongate member.

5. Apparatus as recited in Claim 4 wherein said opening in said float is at the center of said float and said opening receives said elongate member.

6. Apparatus as recited in Claim 1 wherein said first region of said matrix includes carbon for making said first region electrically conductive.

7. Apparatus for use in conjunction with a voltage source and voltage indicator for measuring the level of fluid in a tank, comprising: an elongate member for extending into said fluid, said member having a first longitudinal groove therein, a first elongate, electrically conductive strip positioned in said first groove, a float, and a first electrical contact supported by said float for making sliding contact with said first conductive strip.

8. Apparatus as recited in Claim 7 wherein said elongate member includes: a second longitudinal groove, a second electrically conductive strip positioned in said second groove, and said float having a second electrical contact electrically connected to said first electrical contact, said second contact for making sliding contact with said second conductive strip.

9. Apparatus as recited in Claim 7 wherein said float has an opening for receiving said elongate member.

10. Apparatus as recited in Claim 9 wherein said opening in said float is a center opening which receives said elongate member.

11. Apparatus as recited in Claim 7 wherein said elongate member has at least a second longitudinal, external groove therein and said float has a guide projection for engaging said second groove of said elongate member.

12. Apparatus as recited in Claim 11 wherein said float has an internal opening and said guide projection extends into said internal opening of said float.

13. Apparatus as recited in Claim 7 wherein said first groove is external to said elongate member.

14. Apparatus for use in conjunction with a voltage source and voltage indicator for measuring the level of fluid in a tank, comprising: an elongate member for extending into said fluid, said member having at least a first and a second longitudinal groove therein, first and second elongate, electrically conductive strips positioned respectively in said first and second grooves, a float having an opening for receiving said elongate member, and first and second electrical contacts supported by said float for making respective sliding contact with said first and second conductive strips, said first and second contacts electrically connected together.

15. Apparatus as recited in Claim 14 wherein said opening in said float is at the center of said float.

16. Apparatus as recited in Claim 14 wherein said first conductive strip is more electrically conductive than said second conductive strip.

17. Apparatus as recited in Claim 14 wherein said elongate member has at least a third longitudinal, external groove therein and said float has a guide projection for engaging said third groove of said elongate member.

18. Apparatus as recited in Claim 17 wherein the opening of said float is a center opening and said guide projection extends into said center opening of said float for engaging said third groove of said elongate member.