Measuring and testing – Liquid level or depth gauge – Float
Reexamination Certificate
1997-05-28
2001-04-10
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Float
C073S305000, C073S308000, C073S317000
Reexamination Certificate
active
06212950
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to variable resistors and in particular to a ceramic resistor card for use in a transducer for converting a physical position into an electrical signal with interlaced glass fingers for longer wear from wiper contacts.
2. Description of the Related Art
Variable resistors are known for sensing parameters in a variety of applications. For example, the fuel level in an automobile tank is typically measured using a variable resistor having a sweep arm mechanically or electrically coupled to a float located in a fuel tank. The sweep arm position is determined by the level of fuel in the tank and the voltage value sensed across the variable resistor depends on the position of the sweep arm.
The variable resistor typically comprises a resistor card with metalized areas and thick film resistive ink. The thick film ink is deposited in precise areas to interconnect respective metalized areas. There is a wiper blade assembly having contact fingers thereon connected to the sweep arm. As the float raises and lowers according to the fluid level, the wiper contact fingers move along the resistor card in an arcuate path and make corresponding contact with the metalized areas. This results in a voltage change that generates a signal representative of the amount of fuel contained in the tank.
One problem with this type of system is that over the life of a vehicle it must go through thousands of cycles in a harsh environment. The card is often exposed to both fuel and dry conditions as the fluid level is decreased. In addition, the assembly is exposed to severe vibration resulting from the vehicle movement. The result is that wear occurs as the wiper contact fingers go back and forth over the metalizations and the electrical resistance of the metalization portions may increase and cause accuracy problems with the fuel reading. Additionally, the metalized portions may wear to the point that an open circuit results along some given or several metalization locations.
Specifically, there are problems when conductors lines are broken up into finger-like projections or short conductor lines with spaces therebetween. When a wiper blade assembly is rubbed over the spaced apart conductor lines, the edge of each conductor line begins to be worn down from repetitive impact. Additionally, the wiper blade assembly contact fingers are equally worn down faster because of the repetitive impact with the edges of the conductor lines. Further wear is encouraged by the contact fingers bouncing up and down as they travel approximately perpendicular across the orientation of the conductor line sets.
3. Related Art
Examples of patents related to the present invention are as follows, and each patent is herein incorporated by reference for the supporting teachings:
U.S. Pat. No. 3,613,042, is a variable resistance element with spaced rows of parallel tabs.
U.S. Pat. No. 4,032,881 is a resistance element with improved linearity and method of making the same.
U.S. Pat. No. 4,318,075 is a thick film potentiometer having a wiper track with conductor lines deposited in a parallel fashion.
U.S. Pat. No. 4,500,866 is a nonlinear potentiometer including an arcuate resistor pad connected to a plurality of parallel resistor pads by means of a plurality of conductor lines.
U.S. Pat. No. 4,931,764 is a low wear resistance card for use in a liquid fuel sender card.
U.S. Pat. No. 5,051,719 is a thick-film non-step resistor with accurate resistance characteristics.
U.S. Pat. No. 5,169,465 is a thick-film circuit element on a ceramic substrate.
The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicants' acknowledged duty of candor in disclosing information that may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, applicant's claimed invention.
SUMMARY OF THE INVENTION
It is a feature of the invention to provide a fuel level indicator system. The system uses a resistor card having an arc-shaped resistive path with a first set of spaced apart conductor lines and an arc-shaped resistive ink material overlying the first set of conductor lines. The first conductor lines are formed at an angle with respect to a radial line drawn from the center of the resistive path arc. There is also a first set of glass bars interlaced between the first set of each spaced apart conductor lines. The resistor card also has an arc-shaped continuously solid conductor base and a second set of spaced apart conductor lines extending from the conductor base at an angle with respect to a radial line drawn from the center of the arc-shaped conductor base. There is also second set of glass bars interlaced between the second set of each spaced apart conductor lines.
An additional feature of the invention is to provide a device that includes a wiper assembly having two sets of spaced apart wiper contacts or fingers. One of the fingers in each set engages a first conductor line and a second finger contacts a second adjacent conductor line. The wiper assembly is constructed and arranged to provide rotational movement along both the arc-shaped conductive and resistive path.
A further feature of the invention is to provide a device that has a float and a lever extending from the float connected to the wiper assembly to produce rotational movement of the wiper assembly as the float moves.
The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Further, the abstract is neither intended to define the invention of the application, which is measured by the claims, neither is it intended to be limiting as to the scope of the invention in any way.
REFERENCES:
patent: 3613042 (1971-10-01), Leerkamp et al.
patent: 4032881 (1977-06-01), Singleton
patent: 4318075 (1982-03-01), Pudelko et al.
patent: 4500866 (1985-02-01), Romann et al.
patent: 4931764 (1990-06-01), Gaston
patent: 5051719 (1991-09-01), Gaston et al.
patent: 5169465 (1992-12-01), Riley
patent: 5746088 (1998-05-01), Sawert
Cooper Deborah K.
Cooper Richard O.
Borgman Mark W.
Bourgeois Mark P.
CTS Corporation
Loo Dennis
Williams Hezron
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