Fibre optic sensor for the continuous measurement liquids level and other parameters
First Claim
1. An indicating device for showing the level of the interface between two fluids in a container, wherein one fluid has a higher index of refraction than the other, comprising at least two optical fibres, each having at least a portion thereof embedded in a transparent substrate material of similar refractive index to that of the fluid with a higher refractive index, one of said fibres being a source fibre optically connected to a light source, the other being doped with a fluorescent doping material and being a detector fibre optically connected to a detector, the fibres being arranged within the substance such that light emitted from said source fibre illuminates the interior of the substrate, which serves as a larger waveguide, and (a) is coupled into said detector fibre when total internal reflection occurs at the substrate/fluid interface, which is the case when air or a fluid of relatively low refractive index is present, or (b) is not coupled into said detector fibre when refraction occurs at the substrate/fluid interface, which is the case when the fluid of higher refractive index, namely the fluid whose level is to be measured, is present.
11 Assignments
0 Petitions
Accused Products
Abstract
A fibre optic sensor, particularly for ascertaining fluid levels, utilizes at least two optical fibres having at least a portion thereof embedded in a transparent substrate material of similar refractive index. One of the fibres is coupled to a light source, the other to a light detector. The source fibre illuminates the interior of the substrate so that light exiting the source fibre is coupled to the detector fibre when total internal reflection at the substrate/fluid interface occurs in the presence of a first fluid. In the presence of a second fluid of higher refractive index than the first fluid, there will be no coupling, due to the loss of light into the fluid by refraction. The mechanism for coupling light into the detector fibre is fluorescence within that fibre causing it to provide a light signal which varies with the level of the second fluid. Several different embodiments, to achieve continuous level sensing or the sensing of other parameters, are disclosed. As well, the issue of lead fibre insensitivity to changes in optical attenuation is addressed through a novel scheme which requires two light sources and two light detectors and utilizes the self attenuation of the fluorescent optical fibre to achieve a ratiometric measurement.
-
Citations
17 Claims
- 1. An indicating device for showing the level of the interface between two fluids in a container, wherein one fluid has a higher index of refraction than the other, comprising at least two optical fibres, each having at least a portion thereof embedded in a transparent substrate material of similar refractive index to that of the fluid with a higher refractive index, one of said fibres being a source fibre optically connected to a light source, the other being doped with a fluorescent doping material and being a detector fibre optically connected to a detector, the fibres being arranged within the substance such that light emitted from said source fibre illuminates the interior of the substrate, which serves as a larger waveguide, and (a) is coupled into said detector fibre when total internal reflection occurs at the substrate/fluid interface, which is the case when air or a fluid of relatively low refractive index is present, or (b) is not coupled into said detector fibre when refraction occurs at the substrate/fluid interface, which is the case when the fluid of higher refractive index, namely the fluid whose level is to be measured, is present.
Specification