Evanescent wave liquid level sensor with density compensation
AssigneeHughes Aircraft Company
InventorsDavid B. Chang, Victor Vali, Keith V. Pearson, Albert F. Lawrence
Life of this patent
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Abstract
An evanescent wave liquid level sensor for measuring the density-compensated level of a liquid in a container. The sensor employs an eccentric core optical fiber fully immersed in the liquid to be measured. Light is injected into one end of the fiber. Some of the light will be lost due to evanescent wave losses. Changes in the ratio of the intensity of the input light and the reflected light are due solely to changes in the density of the liquid. Changes in the liquid density can then be used to compensate a liquid level measurement. Since the liquid temperature is related to its density, the sensor can also be used to measure changes in the liquid temperature.
Claims20
A liquid level sensor for measuring the level of liquid within a container and with compensation for liquid density changes, comprising:
- a level sensor optical fiber disposed within said container and extending through the range of liquid surface positions to be measured by the system, wherein said level sensor fiber is characterized by an inner fiber core and an outer fiber cladding, the cladding thickness appropriate to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- a first density sensor optical fiber positioned to be completely immersed in said liquid, said density sensor fiber characterized by an inner fiber core and an outer fiber cladding, the cladding thickness appropriate to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- means for injecting light into said level sensor fiber and for injecting light into said density sensor fiber;
- means for determining the loss of light traversing said level sensor fiber at least once to provide an indication of the nominal liquid level;
- means for determining the loss of light traversing said density sensor fiber;
- and
- processing means responsive to said respective loss determining means for compensating said nominal liquid level by any changes in the liquid density to provide a compensated liquid level value.
A liquid level sensor for measuring the level of liquid within a container and with compensation for liquid density, comprising:
- a level sensor optical fiber disposed within said container and extending through the range of liquid surface positions to be measured by the system, wherein said level sensor fiber is characterized by an inner fiber core and an outer fiber cladding, the thickness of fiber cladding on the fiber portion which extends through said range of positions being selected to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- a density sensor optical fiber completely immersed in said liquid, said density sensor fiber characterized by an inner fiber core and an outer fiber cladding, the thickness of fiber cladding being selected to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- means for injecting light into said level sensor fiber and for injecting light into said density sensor fiber;
- means for determining a first ratio of input light intensity to the intensity of light which has passed through said level sensor fiber;
- means for determining a second ratio of input light intensity to the intensity of light which has passed through said density sensor fiber;
- and
- processing means responsive to said first ratio and said second ratio for providing a level signal indicative of the liquid level in said container, said processing means comprising means for compensating the level indicated by the value of said first ratio by the value of said second ratio to compensate said level indication with changes in the density of the liquid.
A method for measuring the level of liquid within a container, comprising a sequence of the following steps:
- disposing a level sensor optical fiber within said container and extending through the range of liquid surface positions to be measured by the system, wherein said fiber is characterized by an inner fiber core and an outer fiber cladding, the thickness of fiber cladding on the fiber portion which extends through said range of positions being selected to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- completely immersing a density sensor optical fiber in said liquid within said container, said density sensor fiber characterized by an inner fiber core and an outer fiber cladding, the thickness of fiber cladding being selected to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- injecting light into said level sensor fiber and into said density sensor fiber;
- determining the loss of light which has passed through said level sensor fiber at least once;
- determining the loss of light which has passed through said density sensor fiber at least once;
- and
- processing said respective light losses to provide a signal indicative of the liquid level in the container and which is compensated for changes in the density of the liquid level.
A system for measuring characteristics of a parameter of a liquid in a container, comprising:
- a plurality of optical fibers dispersed within said liquid and disposed so that each fiber is fully immersed within said liquid, each said fiber characterized by an inner fiber core and an outer fiber cladding, the cladding thickness appropriate to provide significant evanescent wave loss when the cladding is immersed in the liquid;
- means for injecting light into said plurality of optical fibers;
- means for determining the loss of light traversing each said fiber at least once;
- and
- processing means responsive to said respective light losses to determine one or more characteristics of said parameter at dispersed locations throughout said liquid.
The system of clam 15 wherein said parameter is the liquid temperature, and said characteristic comprises changes in said temperature over time.
Dependencies are inferred from the claim text.