Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-06-09
2002-08-06
Allen, Stephone (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S577000, C250S902000, C073S293000, C340S618000, C356S133000
Reexamination Certificate
active
06429447
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an optical device for detecting a fluid level in a container.
2. Description of Prior Art
Fluid level sensors, particularly for application to gasoline tanks, are susceptible to contamination from immersion in fluid, interference from splashing fluid adversely effecting output accuracy, malfunction resulting from an abundance of moving parts and other potential malfunctions and/or erroneous readings.
Fluid level sensors for use in fuel tanks, such as in automobiles, typically rely upon a float arm connected with respect to a laser-etched card resulting in a variable resistance provided to an output sensor depending upon the relative position of the float arm in the fuel. This float arm method is widely used and accepted although it relies upon moving parts and a precision-etched sensor that is difficult to accurately manufacture.
Other prior art methods of fluid level detection attempted for use in connection with fuel tanks include an electrode used to measure fluid level based upon variation in capacitance around the electrode; a sensitive measuring diaphragm for measuring pressure created by the weight of the fluid; an ultrasonic transmitter for generating sound pressure waves reflected from the fluid surface; a microwave transmitter and receiver relying upon a dampened energy signal based upon variation of fluid level; a weight suspended from a measurable cable length repeatedly lowered into the fluid to determine the fluid level; and a series of simple circuits formed by the fluid level and a sensing probe provided with a low AC voltage. The above devices and methods for determining fluid level in a fuel tank all rely upon moving parts, expensive electronics or devices that are not adaptable to wide variations of fuel tank sizes and configurations.
SUMMARY OF THE INVENTION
The present invention relates to an optical device wherein a brightness displayed in a top surface of the optical device is inversely proportional to the percent of the device submerged in liquid. The higher the liquid level, the darker the optical device appears.
The optical device operates by light reflection. When an angled surface within a specific range of angles is under liquid, it does not reflect light, it refracts light. The optical device according to this invention relies upon the principles of total internal reflection. An optical device, such as a light pipe, having an angled surface between approximately 40° and 60° relative to normal will permit all light to internally reflect. In a typical light pipe having an index of refraction of 1.5, if the index of refraction of the material on the other side of the angled surface is lower than 1.5, such as the index of refraction of most gases including air, there will be total internal reflection. As the index of refraction of the material on the other side of the angled surface approaches 1.5, such as many liquids including water and gasoline, light will pass through the angled surface and be refracted. Therefore, if the optical device according to this invention is immersed in liquid, such as gasoline, light will not be reflected from one angled surface to another, but instead absorbed into the liquid.
By increasing the number of surfaces submerged, the amount of light reflected decreases. By increasing the total number of reflecting surfaces, the resolution of the device can be increased. The overall length can be varied for specific depth tanks. By varying these two parameters, the device can be configured in an optimal manner for each type of level sensing application.
The brightness of the optical device can be viewed by eye, or can be sensed electronically for a more accurate reading. By coloring the reflective surfaces, the device can be viewed as a change in color, instead of a change in intensity. The optical device can be coupled to a fiber optic and viewed remotely either by visual inspection or electronic conversion.
It is one object of this invention to provide an optical device for measuring fluid level that does not rely upon moving parts or complex electronics.
It is another object of this invention to provide an optical device for measuring fluid level that provides an instantaneous output of current fluid level.
It is another object of this invention to provide an optical device for measuring fluid level that provides accurate, incremental fluid level readings without appreciable interference from splash.
It is still another object of this invention to provide a device for use in connection with a variety of fuel tank sizes and configurations.
It is another object of this invention to provide a device for measuring fluid level that is capable of displaying the fluid level directly or into an electronic receiver.
It is yet another object of this invention to provide a device for measuring fluid level in fuel tanks that is durable and inexpensive.
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Lindsay Ryan
Nowak David R.
Allen Stephone
Illinois Tool Works Inc.
Pauley Petersen Kinne & Erickson
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