Measuring and testing – Liquid level or depth gauge – Thermal type
Reexamination Certificate
1998-06-04
2001-05-01
Williams, Hezron (Department: 2856)
Measuring and testing
Liquid level or depth gauge
Thermal type
C073S30400R, C340S612000
Reexamination Certificate
active
06223595
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to non-floating fluid level sensors, and more particularly to electrical systems for sensing and controlling fluid supplied to containers, for example washing machine basins.
Electrically resistive fluid level sensors are known generally for measuring conductive and partially conductive fluid levels, and provide many advantages over floating mechanical sensors, including the substantial elimination of corrosion susceptible parts, reduced cost, and improved accuracy and reliability.
Known electrically resistive fluid level sensors include generally a pair of isolated resistive elements disposed vertically in a container so that the resistance thereof varies in some proportion to the fluid level therein. The resistive elements are usually carbon or polymeric base materials, whereby the conductive or partially conductive fluid in the container provides a relatively low resistance, or short circuit, path between the resistive elements thereby varying the effective electrical length, and thus varying the electrical resistance thereof, depending on the fluid level.
U.S. Pat. No. 5,083,460, issued Jan. 28, 1992, for example, discloses a pair of level detection resistors and one or more temperature compensating resistors disposed vertically in a tank as discussed generally above. One of the level detection or temperature compensating resistors is electrically coupled to a negative input of an amplifier circuit, and the other of the level detection or temperature compensating resistors is electrically coupled in a negative feedback loop of the amplifier between the output and the negative input. An alternating input signal generator is applied to one of the level detection resistors or the temperature compensating resistors, and generates a continuously variable amplified output signal proportional to the fluid level in the tank. The slope of the output signal increases or decreases depending upon whether the level sensing resistors are connected in the feedback loop of the amplifier or to the negative input thereof, and thermal effects on the slope of the output signal are cancelled. The amplifier and alternating input signal generator however substantially increase the overall cost of the level sensor.
The present invention is drawn toward advancements in the art of fluid level sensors, and more particularly to resistive fluid level sensors and systems.
It is an object of the present invention to provide novel resistive fluid level sensors and systems that are economical, and that overcome problems in the art.
It is also an object of the present invention to provide novel electrically resistive fluid level sensors and systems useable for sensing the level of conductive and partially conductive fluids in a container, for example washing machine basins, and for closing a supply of fluid thereto when the fluid level therein reaches a specified level.
It is another object of the present invention to provide novel electrically resistive fluid level sensors and systems that accurately sense and control fluid levels in containers, and that are not susceptible to environmental thermal variations.
It is a more particular object of the invention to provide novel electrically resistive fluid level sensors and systems comprising generally first and second elongated fluid level resistive element portions disposed substantially vertically in the container and electrically connectable by fluid in the container, and an input signal source, which is preferably a DC voltage source, electrically coupled to a first end portion of the first elongated fluid level resistive element portion, whereby an output signal across the first and second elongated fluid level resistive element portions is proportional to a fluid level in the container.
It is another more particular object of the invention to provide novel electrically resistive fluid level sensors and systems further comprising electrically insulated first and second elongated temperature resistive element portions disposed substantially vertically in the container and connected in series between the input signal source and the first and second elongated fluid level resistive element portions to substantially cancel any thermal effects on fluid level sensing and control.
It is another more particular object of the invention to provide novel electrically resistive fluid level sensors and systems further comprising the first and second elongated fluid level resistive element portions electrically coupled to a signal input of a comparator circuit, and a reference signal applied to a reference input of the comparator circuit, whereby an output signal of the comparator circuit closes the supply fluid to the container when the fluid therein reaches a specified level, which is selectable by adjusting the reference signal input to the comparator circuit.
These and other objects, aspects, features and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced generally by corresponding numerals and indicators.
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Dumbovic Steve
Francke Richard C.
Breh Donald J.
Croll Mark W.
Illinois Tool Works Inc
O'Brien John P.
Williams Hezron
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