Optics: measuring and testing – Of light reflection
Reexamination Certificate
1998-08-14
2001-10-16
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Of light reflection
Reexamination Certificate
active
06304328
ABSTRACT:
Pursuant to 37C.F.R. 1.96 (c) this patent includes an appendix which will not be printed but is available on one microfiche (16 frames).
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to temperature and concentration measurement, and more particularly relates to non-contact temperature and concentration measurement on liquid surfaces using reflectance techniques.
2. Brief Description of the Prior Art
It is desirable to measure temperature at a liquid surface for a number of applications. For multi-component liquids, it is also desirable to measure concentration. Although the surface temperature and concentration are important parameters, it has proven difficult to measure them with conventional techniques.
Some prior measurement techniques rely on direct-contact; i.e., a sensor or probe must come in contact with the liquid to be measured. Such measurement techniques, however, have the drawbacks of the potential for contamination; the inconvenience of introducing a probe into the liquid to be measured; and the invasive nature of the measurement which may influence the process being measured.
Accordingly, there has been interest in non-contact measurement techniques. One well-known prior method is use of a commercial infrared thermometer. Such thermometers exhibit poor accuracy for measurement of temperature of surfaces where the emissivity is not close to unity, for example, liquids and highly reflective metals.
In an effort to overcome the problems associated with infrared surface temperature measurement, efforts have been made to develop laser-based techniques. Such techniques have been disclosed in the following publications: T. Q. Qiu et al., “Novel Technique for Noncontact and Microscale Temperature Measurements,”
Experimental Heat Transfer
, v.6, 231-41 (1993); A. S. Lee et al., “Temperature Measurement by Thermoreflectance at Near Grazing Angles,”
Proceedings of the
1996
A.S.M.E. International Mechanical Engineering Congress and Exposition
, v.59, 77-82 (Atlanta, Ga., Nov. 17-22, 1996); and A. S. Lee and P. M. Norris, “A New Optical Method for Measuring Surface Temperature and Large Incident Probe Angles,”
Rev. Sci. Instrum.
, v.68, 1307-11 (1997). However, these prior techniques have focused almost exclusively on temperature measurement of surfaces of solid-state materials; relatively little attention has been paid to liquids.
Optical techniques for measuring concentration in liquids have been known previously. One paper discloses an optical probe which relies on changes in the index of refraction to measure liquid concentration. T. L. Bergman, “Miniature Fiber-Optic Refractometer for Measurement of Salinity in Double-Diffusive Thermohaline Systems,”
Rev. Sci. Instrum.
, v.56, 291-96 (1985). However, the techniques set forth in this paper still require immersion of a probe in the liquid. Measurement of salt concentration based on the image distortion of a fine wire as it passes through a variable-concentration liquid has also been disclosed. T. L. Bergman, “Measurement of Salinity Distributions in Salt-Stratified, Double-Diffusive Systems by Optical Deflectometry,”
Rev. Sci. Instrum.
, v.57, 2538-42 (1986). This technique measures concentration in the bulk liquid as an integrated effect of concentration variation along the light path. Again, however, immersion of a sensor, in this case, the fine wire, was required with the attendant disadvantages.
In view of the foregoing deficiencies with current techniques for measurement of temperature and concentration at a liquid surface, it would be desirable to develop an apparatus and method for non-contact temperature and concentration measurement on liquid surfaces. In addition to affording a non-invasive measurement technique, it would be desirable if the apparatus and method permitted remote monitoring and location of test and analysis equipment, imperviousness to harsh and corrosive environments, and very high spatial precision. Yet further, it would also be desirable if the apparatus and method were capable of fast response times and high reliability and repeatability.
SUMMARY OF THE INVENTION
The present invention, which addresses the shortcomings of the current systems, provides an apparatus for non-contact measurement of either the temperature or, for multi-component systems, the concentration at a surface of a liquid specimen. The apparatus includes a light source which produces a measurement light beam, and a detector. A container for the liquid specimen can optionally be provided. The measurement light beam has a measurement light beam intensity, and impinges on the surface of the liquid specimen and reflects back as a reflected light beam with a reflected light beam intensity. The reflected light beam intensity is related to both the reflectivity, R, of the liquid surface and to the measurement light beam intensity. The detector receives the reflected light beam and determines either the temperature or the concentration of the liquid specimen based on the reflected light beam intensity.
The light source can be a coherent light source. For temperature measurement, the liquid is preferably either a single component liquid or a multi-component liquid with a substantially constant concentration. Conversely, for concentration measurement, the liquid is a multi-component liquid which is preferably maintained in a substantially isothermal condition.
For temperature measurement, a temperature change of the liquid is determined from the equation:
&Dgr;
R
{tilde over (=)}(
dR/dn
)(∂
n/∂T
)&Dgr;
T
where:
&Dgr;R is a change in the reflectivity of the liquid from a reference state as determined from the reflected light beam intensity and the measurement light beam intensity,
n is the index of refraction of the liquid,
dR/dn is the first derivative of the reflectivity with respect to n,
T is the temperature of the liquid,
∂n/∂T is the first derivative of n with respect to the temperature,
&Dgr;T is a change in the temperature of the liquid from a known initial value,
R=((n−1)/(n+1))
2,
and
dR/dn=4(n−1)/(n+1)
3
.
Similarly, for concentration measurement, a change in concentration of the liquid is determined using the formula:
&Dgr;
R
{tilde over (=)}(
dR/dn
)(∂
n/∂C
)&Dgr;
C
where:
&Dgr;R is a change in the reflectivity of the liquid from a reference state as determined from the reflected light beam intensity and the measurement light beam intensity,
n is the index of refraction of the liquid,
dR/dn is the first derivative of the reflectivity with respect to n,
C is the concentration of the liquid system expressed on a volume or mass basis,
∂n/∂C is the first partial derivative of n with respect to the concentration (expressed consistently with C),
&Dgr;C is a change in the concentration of the liquid from a known initial value,
R=((n−1)/(n+1))
2,
and
dR/dn=4(n−1)/(n+1)
3
.
A beam splitter can be provided to split off a reference beam in order to account for fluctuations in intensity of the light source. Intensity of the reflected and reference beams can be determined using photodetectors such as photodiodes, suitable transresistance amplifiers, and digital voltmeters. If desired, output from the voltmeters can be input to a computer which performs required calculations.
A method, according to the present invention, for non-contact measurement of one of temperature and concentration at a surface of a liquid specimen includes the steps of causing a measurement light beam to impinge on the surface of the liquid and to reflect back as a reflected light beam; detecting the reflected light beam; and dete
BakerBotts L.L.P.
Font Frank G.
Ratliff Reginald A.
Research Foundation of State University of New York, The Office
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