Patent Pro is an interactive software program that comes on CD ROM and is designed to assist in the drafting of patent applications. It was primarily designed by two patent attorneys with more than 20 years of experience between them. The software is sold through "Kernel Creations, Ltd.", and can be purchased for about $330.00 from their Web Page at http://www.4patpro.com/, or by calling them direct at 1-888-472-8776.

The program is targeted toward someone with minimal skills in drafting patent applications. The purpose of its design is to give an inventor that is unskilled in drafting patents an easy, thorough way to draft and file a utility application, therefore reducing legal fees. It is not designed to teach a person how to prosecute an application.

This paper attempts to provide a critical evaluation of the Patent Pro software. It will discuss the advantages and disadvantages of the use of the program by either a beginning inventor, or an experienced patent attorney. It will also include an appendix containing a comparison of a patent application drafted with and without the use of the PatentPro software.

The Patent Pro manual is short and simple. Its only 37 pages long, and easy to read. This is in keeping with the designers philosophy of simplicity. The designers felt that it was important to keep the manual simple because its target market of beginners would not want to wade through voluminous texts to learn how to write a patent. The designers rely on the structured format of the program itself, and the many sample patents to do the teaching.

The manual does a good job in explaining how the program works, and gets you started quickly, with a minimum of amount of problems. It explains each section of the program clearly, and shows you how to use the program to create a patent through the use of an example for a better mouse trap. The manual also has a chapter in how to file a patent application.

When PatentPro is first booted up it will display the "PatentPro Table of Contents" page. This allows the user easy entry into the five sections of the program by clicking on their respective icons. These sections are: 1) Starting, 2) Is It Patentable, 3) Forms, 4) Reference Library, and 5) Patent Pro. Each section will be discussed in detail below.

The "Starting" icon is the button to click on if your not sure where to begin. This section is divided into three subsections: 1) Introduction to PatentPro, 2) Frequently Asked Questions, and 3) Other Forms of Protection.

The "Introduction" subsection give a basic overview of the software and the philosophy behind it.

The "Frequently Asked Questions" subsection provides answers to questions relating to: the patent application; dealing with the Patent and Trademark Office; after filing the patent application; after the patent issues; and developing and marketing your invention.

Finally the "Other Forms of Protection" subsection provides a brief discussion of alternative forms of Intellectual Property protection. These include copyrights, trademarks, trade secrets, design patents, plant patents, the constitutional basis for the patent laws, and a fairly in depth summary of provisional applications.

The "Is It Patentable" section is divided into four subsections: 1) What can be patented, 2) Must be useful, new and non - obvious, 3) Avoiding pitfalls, and 4) Patent searching. This section is designed to allow the user to explore if the invention is suitable for a patent.

The "What can be patented" subsection explains the 35 USC 101 statutory definition of what is patentable, i.e. inventions or discoveries that are new, useful, and non - obvious. It also lists the various categories that an invention must fall into, such as a machine or a process. Finally it provides a list of items that are not patentable in order to give the reader a better notion of what is patentable.

The "Avoiding Pitfalls" subsection describes some of the ways a printed publication can become a bar against patentability. It also explains that in the United States it is the inventor that must file the application and no one else. This subsection also provides suggestions on how to establish an invention date before you file.

The "Patent Searching" subsection lists various publications that can potentially be used to perform a novelty search on the patent. Some of these publications, such as the Manual of Patent Examining Procedure would be extremely difficult to use without the proper training. However, one of the more useful features of this subsection is its discussion of the Patent and Trademark Depository Libraries (PTDLs). The subsection provides a comprehensive list of the names and telephone numbers of all the PTDLs in the United States.

The "Forms" section is divided into four subsections: 1) Filing with patent office,

2) Non - disclosure agreements, 3) Print patent assignment form, 4) Edit an existing form. This section details many of the forms that are involved in filing, prosecuting, and / or transferring ownership of the patent application or patent.

The "Filing with the patent office" subsection provides the following forms: 1) Transmittal form to Patent Office, 2) Declaration of Inventors, 3) Small Entity form, 4) Recordation of assignment, 5) Information disclosure statement, and 6) Information disclosure citation in an application.

The non - disclosure agreement subsection provides a standardized non - disclosure agreement form to be filled in by the "Owner" and "Recipient" of an "Idea" to be evaluated. The Recipient is described as a corporation in this agreement and must be changed to fit different circumstances.

The "Print patent assignment " subsection provides a form for transferring rights in a patent or patent application that may be printed.

The "Reference Library" section is divided into four subsections: 1) Hall of Fame patents, 2) Statutes, 3) Rules of Practice, and 4) Manual of Patent Examining Procedures.

The "Hall of Fame patents" subsection contains more than a hundred patents of famous inventions in nine different categories: 1) communications, 2) pharmaceuticals, 3) agriculture, 4) electrical components and circuitry, 5) chemical, 6) transportation, 7) electrical systems, 8) medical devices, and 9) photography. It includes such famous patents as Alexander Graham Bell’s telephone, Shockley’s transistor, and Sikorsky’s helicopter. This section is used to provide examples of successful patent applications. Additionally, 45 of these patents are utilized as examples in the Patent Pro section of this program to help guide an inventor through the drafting of his or her claims.

The "Statute" subsection is a listing of the statutes in title 35 of the United States Code. The "Rules of Practice" subsection is a listing of 37 Code of Federal Regulation. Finally the "Manual of Patent Examination Procedure" is a listing of the entire MPEP. One disadvantage is that the 1997 changes to the MPEP have not been incorporated into this program.

"Patent Pro" is the section that is used to create a patent. It is divided into two subsections: 1) Introductory remarks, and 2) Draft patent application.

The "Introductory remarks" subsection provides an overview of the philosophy behind the PatentPro software program. One can print this section out by connecting directly to a printer. However this subsection cannot be directly saved to a disk in the current version.

The "Draft patent application" subsection is the heart of the PatentPro software program. Virtually all of the work in drafting a patent application will be done here.

The "Draft patent application" subsection is divided into twelve sections corresponding to the 12 sections of a patent application. These sections can only be accessed in the order listed below as you build the application, and are the:

1. Name of the Inventors and Title of the Invention,
2. References to Related Applications (often unnecessary),
3. Drawings,
4. Lists (to analyze the invention and describe the elements of the claims),
5. Claims,
6. Abstract of the Disclosure,
7. Background of the Invention,
8. Objects of the Invention,
9. Brief Description of the Drawings,
10. Summary of the Invention,
11. Field of the Invention, and
12. Detailed Description of the Invention.

As explained in the introductory remarks, each of these 12 sections provide three screens. The first screen introduces the purpose behind the section, the second provides a drafting screen to draft the section, and the third screen gives a final check list before proceeding to the next section. In the drafting portion, you can return back to the introductory screen, see examples of issued patents, refer to the related legal materials or access commonly used patent phrases. In some sections, a rough draft is generated for you to revise. From any section, you can also look at a previous section to review what you have done.

Because PatentPro builds an application from the first section up, the later sections depend on earlier sections. So you cannot jump ahead. The user can only step forward from one section to the next. However, if you need to modify an earlier section, you can jump backwards, then step forward again.

This was done to assure that a person with minimal patent drafting skills would create an application appropriate for the Patent Office. However, this approach necessarily imposes some limitations on the more skilled agent or attorney. This is a "claims first" approach to drafting the application, and many agents or attorneys have a preference for drafting the specification first or would like to have the flexibility to apply either

approach. Additionally, more complicated applications are often created through several iterations between the drafter and the inventor, requiring changes that would be more easily accomplished with a word processor rather than within the limitations imposed by the structure of this program.

When jumping backward, you can access your prior draft of the section by clicking the Safe icon. You can copy and paste or highlight, drag and drop all or a portion of the contents of the prior draft from the safe mode into the current draft.

As you complete each section, PatentPro provides an updated chart of your progress. After you complete all the sections, PatentPro automatically generates an application ready for filing with the Patent Office.

At any time during the drafting of an application the user can save the work. However the current version only saves it to the hard drive. In order to save to disk before an application is completed, the user must first cut and paste each section separately to a word processor. Alternatively, after an application is complete, the entire application can be cut and pasted at one time.

Additionally deleting a program is cumbersome on this version as well. It requires that the user open the program files of the hard drive, then the kernal file and then the PatentPro file. At that point the user must identify the file to be deleted which will be labeled "pat1", "pat2", etc.

By clicking on "Create a new patent application" the Name section is entered. The purpose screen, the first of three, explains the duty of candor and the importance of naming only the correct inventors. The drafting screen of this section prompts the user for the names and number of inventors. The check screen asks the user to verify the accuracy.

The first screen of the Title section explains the four classes of invention as 1) machine, 2) article of manufacture, 3) composition of matter, and 4) process. The drafting screen asks the user to select a description from standard terminology such as Process/Method,

Machine/Apparatus, etc. Once this is done a standard title is generated that has the terminology selected plus an area to fill in to complete the title. Finally the checklist screen asks you to again verify the data entered and gives the user a chance to correct it.

At this point the user is shown a bar graph that tells him where he is in the application drafting process. Since all of the sections that follow will have the standard three screens (purpose, draft and check) , the remaining comments will concentrate on the drafting screens only.

This section prompts the user to reference any divisional, continuation, or continuation in part application that may have been drafted earlier. This section is quite often left blank by a first time inventor.

The drawings section cannot draft an application for you. It only provides guidelines for drafting the drawings. It explains that sketches are acceptable for obtaining a filing date, and recommends sketching the drawings while drafting the application. It also say to:

• consider hiring a person skilled in preparing patent drawings,
• show the commercial embodiment and an alternate embodiment of the invention,
• use a logical numbering method,
• don’t use a reference number that is the same as a figure number,
• use clear pointers, and
• create your own drawings before submitting your application.

This section is the most critical step in the application process. The lists generated in this section are the foundation for all the claims, and every section that follows. It is in this section that the inventor must list all the elements that make up all the claims of the application.

The designers of this program, who are also experienced patent attorneys, have developed four major questions that they always ask when analyzing any person’s invention. From

these questions, four sets of lists can be generated: 1) Qualities and Benefits, 2) Primary Elements, 3) Secondary Elements, and 4) Substitute Elements.

The "Qualities and Benefits" lists comes from asking the inventor to "sell" the invention by describing the features and advantages the invention has over the existing technology. The "Primary Elements" list comes from asking the inventor to list only the essential elements that make his invention work and differentiate it from the earlier technology.

The "secondary elements" list is generated from asking the inventor to think of all the features and advantages that make his invention marketable, salable, and commercially practical. Finally the "substitute elements" list comes from asking the inventor to list all the alternate way to implement each primary element.

The primary elements list will be used to construct the first independent claim. The secondary and substitute lists will be used for dependent claims. The qualities and features will be used to construct the summary of the invention.

After the lists are generated the claims section automatically generates a rough cut of the first independent claim from the primary elements list and numbers it A1. The word processor can be used to edit the claim as the drafter sees fit. Other independent claims generated will be labeled B1, C1, and so forth. One disadvantage of the current version of the program is that there is only one set of primary elements, and therefore only one independent claim can be generated from the program. In order to generate alternative independent claims the user must regenerate the original and edit it, or use the program as a word processor to type in new independent claim language.

Once the first claim is generated, the user can click on the "Add-A-Claim" button to use the elements listed in the secondary and substitute lists to generate dependent claims. The computer will prompt the user to select which independent claim to depend off of, and which transition language to use as well. PatentPro will then insert the claim in its proper position. By using the "Show Lists" button a split screen will be displayed for easy drag and drop insertion of the selected element into the new claim.

The program does not currently check for such things as antecedent basis problems, grammar, inferential claiming, or that the listed elements properly tie together to define a structure. For these problems the program relies heavily on the 45 patents shown in the

"Patent Examples" section to teach the beginner how to write the claims. Additionally the program also provides a technical terms section, and a section of sample phrases to assist the drafter.

Once the claims are finished, the program will automatically generate the rough cut of an abstract from the first independent claim and its related dependent claims. Again, the word processor can always be used to edit the abstract.

The program cannot write the background section. However it explains that the background section is supposed to help the reader appreciate the problem solved by the invention, provide support for the claims, and should list the deficiencies of the prior art.

The background section screen provides three tabs:

• History of Technology tab, where a brief history of the technology should be presented,
• Prior Technology tab, where the key prior technology should be described, and
• Deficiency in Prior Technology tab, where deficiencies in the prior technology should be pointed out.

The program explains that the objects, or objectives of the patent are to "sell the invention to the reader by describing features desired in the invention without detailing any means for achieving the features. Objects should provide a link between the problems identified in the Background section and the inventions defined in the claims." The program also provides a list of commonly used introductory phrases. It also suggests looking at the Patent Examples section for help in drafting this section. Finally, the computer automatically drafts a rough cut of the objects from the "Qualities and Benefits" list.

The program provides typical figure descriptions and standard descriptive phrases under the "Sample Phrases Button." When that button is clicked a figure of a telephone that best illustrates the sample phrase used is shown to the right of the phrase. Once the

proper phrase is selected the line is inserted into a figure list, and the number of the figure is left to be filled in. Again the word processor can be used to edit the phrase.

A rough cut of the summary of the invention is automatically generated by the program from the independent claims drafted earlier. The program also explains that the summary is a short description of the invention that is easily derived from the independent claims. Again the word processor can be used to edit the summary if required.

The program opens the first sentence of this section by providing the general opening phase "This invention relates generally to the field of." Thereafter, a space is left to be filled in by the drafter to finish describing the field. The program then uses the preamble of the first independent claim to close the first sentence.

The program cannot write a detailed description of the invention. It must rely on the inventors knowledge of his invention for this. The program also relies on its Sample Patents to help assist any drafter through writers block. The first screen of this section does outline a method for drafting the Detailed Description by using the following six steps:

1. Describe what is old and already known from your drawing,
2. Characterize what is new, using the wording of the broadest independent claim,
3. Describe in detail what is new, using the vocabulary that you have established in the claims,
4. Discuss the operation of the device (or the flow of the method) including all of the alternative way to make or use the invention,
5. Restate the advantages of the invention briefly and succinctly, and
6. Define any critical or important terms that you have used as broad as possible.

Plans for future revisions of the PatentPro software will include on line links to the IBM and U.S. PTO web sites. Other potential revisions to the software will be evaluated from the suggestions and feedback of PatentPro customers.

Writing a patent application can be a major task for anyone, but especially for a beginner. Recent decisions have made it clear that the courts are imposing an ever increasing burden on the drafter of the patent to clearly define the metes and bounds of the invention; Warner - Jenkins v. Hilton Davis, 117 S. Ct. 1040 (1997); Markman v. Westview Instruments, 116 S. Ct. 1384 (1996); Valmont Industries v. Reinke Manufacturing, 25 USPQ 2d 1451 (1993); Bell & Howell v. Altek Systems, 132 F. 2d 701 (1997); Sage Products, Inc. v. Devon Industries, Inc., 126 F. 3d 1420 (1997). The clear trend by the courts is to require greater emphasis that the patent claims be strictly limited to their meaning and scope as defined by the public record, by the patent itself. As a result the courts are imposing a greater legal burden on the drafters to devote the time, care, and skill to accomplish this task.

The basic concept of this program is a good one. It is to provide a mechanism to allow an inventor to draft as much of the application as possible, and therefore avoid a good deal of legal costs. The basic problem is that it is those very beginners that will be the most prone to making errors. Therefore, it is important that the final draft of an application, whether it is generated by this program or by any other means, be reviewed by a skilled attorney or agent.

Kernal Creation provides technical support that offers a free and comprehensive review of the draft patent application for the first time user. This service includes a review and comments by an experienced patent attorney. Reviews of future drafts on additional inventions can also be provided for a fee.

The PatentPro guarantee is posted on the web and reads as follows:

"PatentPro is backed by practicing patent attorneys, so using PatentPro is guaranteed. When you use PatentPro, attorney's registered to practice before the U.S. Patent and Trademark Office provide both technical and legal support—all for no additional cost. At any time while preparing your application, if you have any questions, or just want to know if you are on the right track, simply telephone, fax, or e-mail us. Our patent attorneys will review your application and offer suggestions, corrections, modifications, or whatever it takes to keep you going until you've completed your application. Patent attorneys will also review your final application and filing forms, and talk you through the steps to file with the Patent Office."

Appendix A is a comparison of a patent drafted with the use of PatentPro and without PatentPro on the same invention disclosure. In this case the drafter is a law student that has recently passed the patent bar exam.

Appendix A shows a comparison of a patent drafted with the use of PatentPro and without PatentPro on the same invention disclosure. In this case the drafter is a law student that has recently passed the patent bar exam.

The first application (pages 12 – 22) is with the use of PatentPro.

The patent application has been left in its "rough cut" form. That is, no editing was done after the PatentPro program generated its first pass at an application from the input supplied by the student. Much of the input supplied was taken directly from the application shown on pages 23-32, which was actually drafted first.

The second application (pages 23 – 32) is without the use of PatentPro.

The drawings were not able to be displayed on these applications, but can be treated as being identical.

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Field of the Invention

The present invention relates to a device for detecting the level of liquid contained in a tank, in particular, for detecting the level of liquid contained in the tank and generating a corresponding electric signal.

Background of the Invention

Liquid level sensors are known, and in many applications are subjected to harsh environments, such as within the confines of motor vehicle fuel tanks.

A fuel level sensor that is typical of the prior art is disclosed in U.S .Pat. No. 4,702,107. This prior art fuel tank level sensor consists of a rectangular, supportive, and insulating substrate that has deposited on it (by the same method used for producing printed circuits) conductive tracks on one side and resistive tracks on the opposite side. A float with a rectangular slot surrounds the substrate and is designed to follow the level of fuel in the tank. The float contains a conductive element designed to contact the conductive and resistive tracks on the substrate, and provide electrical continuity between them. The top of the fuel sensor has interconnections designed to provide electrical continuity between the conductive and resistive tracks and a supply of electric current.

In this prior art design an electric current flows down a length of resistive track to the float, where it is shunted for return up the conductive track to provide a measurable resistive signal. The length of the resistive path that the current flows through represents a resistive value that is inversely proportional to the level of the fuel. Presently it is most economical to use deflection meters that use a resistance that is directly proportional to liquid level. Additional, and costly circuitry is required to further process the signal from the inversely proportional resistance for use with such economical deflection meters.

Resistance that is directly proportional to the fuel level can be provided if an extra wire is run to the bottom of the resistive track. In this situation the current flows through the wire and up from the bottom of the resistive track, across the float and out through the conductive track. The length of the resistive path, and thus the resistance, that the current flows through is directly proportional to the level of the float/liquid. However, there are significant problems with this design. The wire is an additional cost and manufacturing consideration. Furthermore, the wire must be submerged to the bottom of the tank where the environment is most corrosive and severe. The wire also presents a potential obstruction for the float, which must be able to freely follow the level of the fluid. The wire provides an undesirable connection which can break and detract from the reliability of the sensor.

In place of the extra wire, a separate conductive track can be deposited on the insulating substrate to carry the current to the bottom. This however encounters an additional problem with electrolysis. Water that contaminates a fuel tank settles to the bottom and does not mix with the fuel. Since the entire length of the separate exposed conductive track is at a high potential, and since water is an electrolyte, ions can migrate between the high and low potential tracks along the entire exposed lengths submerged in the water. This causes electrolysis, corrosion and/or premature failure of the sensor.

Summary of the Invention

The present invention provides a liquid level sensor with a buried conductor that is not exposed and produces a signal that is directly proportional to liquid level.

According to the invention a liquid level sensor is constructed of a vertical member which is comprised of the buried or insulated conductor that is used as the core of the vertical member. The buried conductor is encased in a protective insulating layer that is capable of withstanding the harsh environment of a fuel tank. A resistive strip is disposed on a surface of the buried conductor. A conductive interconnection electrically connects the buried conductor to the resistive strip proximate to respective bottoms thereof. A conductive strip is disposed on another surface of the insulating layer of the buried conductor. The conductive strip and resistive strip are substantially parallel to each other along the length of the vertical member. A float surrounds the vertical member, and freely follows the level of the liquid in the tank. The float contains a shunt that contacts and provides electrical continuity between the resistive strip and the conductive strip. The buried conductor and the conductive strip are configured having connections to an electric circuit that provides a current that flows down the buried conductor, through the conductive interconnection, up the resistive strip, across the shunt at the level of the float, and up through the conductive strip. The amount of resistance seen by the current is proportional to the liquid level.

Protective boots are provided at the top and bottom of the vertical member to enhance durability and to prevent corrosion.

Features of the invention include provision of a level sensor that is not susceptible to electrolysis. The sensor according to the invention is also more corrosion resistant. A further feature of the invention is that it is durable and highly reliable. The level sensor can be implemented as a fuel level sensor advantageously incorporated, along with a fuel pump, into an enclosed module with an open bottom designed to receive fuel. The liquid level sensor according to the invention has a minimum number of discrete parts and is inexpensive to manufacture.

Brief Description of the Drawings

Other features and benefits of the invention will be more clearly understood with reference to the specification and the accompanying drawings, of which:

Fig. 1 is a perspective, cutaway view of a fuel module that is open at its bottom, and which contains both a fuel level sensor according to the invention, and a fuel pump.

Fig. 2 is a perspective, cutaway view of the fuel level sensor of figure 1; and

Fig. 3 is a section view on line 3 – 3 in figure 2.

Detailed Description

As illustrated in Fig. 1, a liquid level sensor 20 according to the invention is implemented for sensing fuel level and is modularly constructed in a fuel module 12. The sensor is enclosed in a housing which has a bottom 14 that is open to allow fuel to enter its interior 16. The fuel module contains a fuel pump 18 and the fuel level sensor 20 as described in detail hereinafter.

The fuel level sensor 20, illustrated in greater detail in Fig. 2, is constructed of a vertical member 22 and a float assembly 38. The vertical member is comprised of a rectangular, stainless steel, buried conductor 24 with two major planar surfaces. The buried conductor is the core of the vertical member and acts as a conductor. The buried conductor is encased in a porcelain layer 28. A resistive strip 26, which in this illustrative embodiment is a thick film of CERMET, is disposed on one of the major planar surfaces of the porcelain encased buried conductor. A conductive nickel pad 30 is disposed at the bottom of the buried conductor 24 and the bottom of the resistive strip 26 and provides electrical continuity there between. A conductive strip 32, made of beryllium copper, is disposed on a second major planar surface substantially parallel to the resistive strip 26.

The top and bottom ends of the vertical member 22, including the conductive nickel pad 30, are encased in nitrile rubber boots 34 and 36 to enhance durability and prevent corrosion.

The float assembly 38 is formed of nylon, hollow plastic, or metal as known in the art. It is configured with a rectangular slot 40 dimensioned to accommodate the vertical member 22, and to permit the float to freely follow the level of the fuel. Within the slot 40 the float assembly carries a shunt 42, which includes four contacts 44, 46, 48, and 50. The contacts provide electrical continuity between the resistive strip 26 and the conductive strip 32 when the vertical member 22 is disposed in the slot 40 of the float assembly 38.

The top of the buried conductor 24 and the conductive strip 32 are adapted to connect to respective wires including an input wire 52 and an output wire 54. The input and output wires 52, 54 are in turn connected to an electric circuit. In operation, current will flow through the input wire 52 and down the buried conductor 24, across the nickel pad 30, and up the resistive strip 26. At the shunt 42 of float assembly 38, the current flows across to the conductive strip 32, and up and out through the output wire 54 connected to the conductive strip. Thus the amount of resistance seen by the current is directly proportional to the float/liquid level.

The fuel level sensor configured according to the invention is reliable, durable, and inexpensive to manufacture. Further, the possibility of corrosion and electrolysis is minimized because the high potential buried conductor is encased in a protective, insulating layer.

Alternatively the buried conductor 24 can be virtually any conductive material, including steels, iron, aluminum, copper alloys, or the like. The resistive strip 26 can be other resistive materials, such as discrete resistors, a wire wound resistor, or the like. The porcelain insulating layer 28 can also be any of various insulating materials capable of withstanding the harsh environment of a fuel tank, or other applications, such as glass, ceramic, advanced composites, or the like. The conductive strip 32 could also be configured of a variety of conductive metals such as aluminum, copper, gold alloys, or the like.

Likewise the nickel pad 30 could be various conductive metals such as steels, iron, aluminum, copper alloy, or the like, while the nitrile rubber boots 34, 36 could be any of a number of elastomer or plastic or other materials that are capable of withstanding the harsh environment of a fuel tank or other applications, such as thermal plastics, neoprene, glass, ceramic, advanced composites, teflon, nylon, or the like.

Additionally, the shape of the vertical member 22 could be cylindrical or any number of symmetrical shapes, while the shape of the float assembly 38 could also be any of a number of geometrical shapes.

Furthermore, although the liquid level sensor herein was described as a fuel level sensor for use in a fuel pump module, it will be appreciated that it can be used in other applications such as fresh water and sea water level sensing in marine applications, sewage level sensing in sewage treatment applications, chemical level sensing in chemical process applications, or the like.

Although the invention has been shown and described with respect to exemplary embodiments thereof, various other changes, omissions, and additions in form and detail thereof may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A liquid level sensor comprising:

a vertical member, including

a conductor,

an insulator encasing said conductor,

a resistive element disposed on said insulator,

a conductive element electrically interconnecting said resistive element to

said conductor proximate to a bottom of said vertical member, and

an external conductor disposed on said insulator;

a float; and

a contact assembly disposed on said float, said contact assembly electrically

interconnecting said resistive element and said external conductor.

2. The liquid level sensor of claim 1 further comprising:

a first protective boot encasing a top of said vertical member; and

a second protective boot encasing said bottom of said vertical member, including

said conductive element.

3. The liquid level sensor of claim 1 wherein:

said resistive element is comprised of a cermet resistive strip.

4. The liquid level sensor of claim 1 wherein said external conductor is comprised of a conductive strip, that is substantially parallel to said resistive strip.

5. The liquid level sensor of claim 1 implemented as a fuel level sensor and further comprising a housing having an interior, said interior containing said fuel level sensor, and said housing having a bottom being open to allow fuel to enter said interior.

6 The liquid level sensor of claim 5 wherein said interior of said housing further contains a fuel pump.

7. A liquid level sensor comprising:

a vertical member, including

an insulative means for encasing said first conductive means,

resistive means for providing linear resistance to said electric current

a second conductive means for electrically interconnecting said resistive

member, and

an external conductive means for conducting said electric current disposed

a float means for following the level of a liquid; and

a shunting means for electrically interconnecting said resistive means to said

8. The liquid level sensor of claim 7 further comprising:

a first protective means for encasing said top of said vertical member, and

a second protective means for encasing said bottom of said vertical member,

including said second conductive means.

9. The liquid level sensor claim 7 implemented as a fuel level sensor and further comprising a housing having an interior, said interior containing said fuel level sensor, and having a bottom, said bottom being open to allow fuel to enter said interior.

10 The liquid level sensor of claim 9 wherein said interior of said housing further

contains a fuel pump.

Abstract

A liquid level sensor that produces a signal that is directly proportional to liquid level. The liquid level sensor is constructed of a vertical member which is comprised of a buried or insulated conductor that is used as the core of the vertical member and acts as a conductor to the bottom of a resistive strip. A conductive interconnection electrically connects the buried conductor to the resistive strip proximate to respective bottoms thereof. The buried conductor is encased in a protective insulating layer that is capable of withstanding the environment. The resistive strip and a conductive strip are disposed on the outside surface of the insulating layer, and run substantially parallel to each other along the length of the vertical member. A float surrounds the vertical member, and freely follows the level of the fuel in the tank. The float contains a shunt that contacts and provides electrical continuity between the resistive strip and the conductive strip. The buried conductor and the conductive strip are configured having connections to an electric circuit that provides a current that flows down the buried conductor, through the conductive interconnection, up the resistive strip, across the shunt at the level of the float, and up through the conductive strip. Thus the amount of resistance seen by the current is proportional to the fluid level.