Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Reexamination Certificate
2002-09-20
2003-08-19
Gutierrez, Diego (Department: 2859)
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
C374S121000, C374S131000, C250S483100, C250S484300, C436S136000, C422S082050, C422S082130, C422S083000
Reexamination Certificate
active
06607300
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and devices for the measurement of temperatures and air and oxygen pressures with a single paint, optical fiber or other probe, and more particularly to said methods and devices using photoluminescent probes.
BACKGROUND
The measurement of oxygen pressure using photoluminescent dyes has been known for decades. The 1971 U.S. Pat. No. 3,612,866 to Stevens describes a method for determining oxygen concentrations from the quenching of the photoluminescence of the hydrocarbon pyrene embedded in oxygen-permeable plastics. Bacon and Demas used polymer-immobilized ruthenium complexes with for the same purpose [
Anal. Chem
. 59, 2780-85 (1987)]. U.S. Pat. No. 4,810,655 to Khalil and Gouterman provide a historical background referencing work done up to about 1986, including but not limited to the use of these and other photoluminescent materials, notably platinum porphyrins, at the tip of optical fibers for measuring oxygen pressure in blood. U.S. Pat. No. 5,965,642 to Gouterman and Carlson update that account to about 1997 and also describe the use of oxygen-sensitive photoluminescent dyes as paints used for mapping air pressure distributions on aerodynamic surfaces in wind tunnel studies. All of the above references use photoluminescent indicators so characterized that, when excited by a pulse of light of microsecond or sub-microsecond duration and wavelength or wavelengths within their lowest energy electronic absorption band, they emit a luminescence light with a decay time &tgr;
ox
which decreases in a known manner with increasing oxygen pressure. The decrease &tgr;
ox
parallels the quenching effect of the oxygen pressure. If &tgr; is the luminescence decay time in the absence of oxygen and
t
ox
is the decay time in the presence of oxygen, then &tgr;/&tgr;
ox
=I
0
/I
ox
, where I
0
is the luminescence intensity in the absence of oxygen and I
ox
is the lower luminescence intensity in the presence of oxygen.
There is a need, in a plurality of fields, to measure simultaneously or quasi-simultaneously (within one or a few seconds) both the temperature of an object or environment and a second parameter, physical or chemical. In most cases the main objective is to measure said second parameter, but its measurement is substantially affected by temperature. In clinical practice it is often necessary to measure both the oxygen pressure and the temperature of blood or a tissue with a fiber optic technique. A preferred method for measuring oxygen pressure is the use of an oxygen-sensitive photoluminescent dye. The dimensional constrains may require that the same probe be a temperature probe as well.
Demas et al. disclosed that the same ruthenium complexes used for measuring oxygen pressure can be used as temperature indicators [
Proc. SPIE
, 1796, 71-75 (1992)], but in order to use the complexes as temperature probes it was necessary to exclude oxygen from them. His work did not teach or anticipate a way to measure temperature while the probe luminescence was being simultaneously quenched by oxygen.
U.S. Pat. No. 6,303,386 to Klimant et al. describes a system for measuring both oxygen pressure and temperature using a probe having two sensing layers. One layer has an immobilized oxygen-sensing porphyrin. The other layer has an immobilized ruthenium complex for measuring temperature. Only the oxygen-sensing layer was permeable to oxygen. The arrangement required two light sources and associated optical filters, and two photodetectors and associated electronics.
The measurement of air pressure distributions on three dimensional aerodynamic test surfaces is one of the many applications of pressure-sensitive paints, and the preferred paint technology is still, to this date, based on the oxygen quenching of photoluminescence. One limitation of this technique is that the pressure readings are affected by temperature changes. If temperature gradients are relatively large over the test surface the prior art requires a temperature-sensitive paint in addition to the pressure-sensitive paint. In some applications where two or multiple parts of the body under study are subject to identical fields, for instance rotor blades in turbomachinery, one can separate the pressure-sensitive paint from the temperature-sensitive paint and perform independent measurements on the two paints, which requires two different sensor systems. In parts of the surface under study where both temperature and pressure readings are required on the same point, the two paints must be applied, one on top of the other. This, in addition to requiring two sensor systems, may introduce serious compatibility problems between the two paints, as one paint may interfere with the measurements performed on the other.
Prior art temperature sensing techniques for moving objects like rotor blades use a luminescent paint applied to the object and having a temperature-dependent luminescence decay time &tgr;
T
, which decreases in a known manner with increasing temperature as the luminescence quantum efficiency of the paint decreases. In order to get accurate data, the use of two sensing layers as in the prior art is subject to stringent requirements for the temperature sensing layer, as listed by Allison et al. “A Survey of Thermally Sensitive Phosphors for Pressure Sensitive Paint Applications”, ISA Paper 472, May 2000. They are, inter alia:
1) Very uniform coatings;
2) The luminescence decay time &tgr;
T
must be shorter than 10 microseconds;
3) The luminescence should be excitable with a blue emitting diode (LED);
4) The luminescence spectrum should be different from that of the pressure sensing layer;
5) The luminescence of the phosphor should not excite the pressure sensing layer to luminesce.
These requirements could be relaxed, or even eliminated, if one could measure temperature and air pressure accurately and independently of each other, but with the same indicator. That would also greatly minimize the sources of error and greatly reduce the complexity of the measuring system.
There is a need, therefore, for a simple measuring system wherein the same oxygen-sensitive photoluminescent material used as a pressure probe can be used as a temperature probe. It is also desirable that the added temperature measurement on the pressure probe do not substantially increase the complexity of the pressure measuring system or require a different dedicated temperature measurement system.
One prior art system for measuring temperature, suitable for use with fiber optic techniques and referred to herein as the Thermally Activated Direct Absorption (TADA) system, is based on the direct measurement of a temperature-dependent optical absorption, using photoluminescent probes as the absorption indicators. The system is described in U.S. Pat. No. 5,499,313 to Kleinerman, which incorporates teachings from previous patents to Kleinerman. The system is suitable for measuring temperatures at any chosen point or at a multiplicity of points along which a long optical fiber probe is deployed, but it loses accuracy in temperature ranges within which the luminescence efficiency of the probe is substantially degraded. Furthermore, nothing in that patent or any other prior art teaches how to measure temperature and another physical or chemical variable with a photoluminescent indicator which is being simultaneously affected by both variables, or how to measure surface temperature distributions with a single indicator dispersed in a non-homogeneous coating.
OBJECTIVES OF THE INVENTION
It is the main object of the present invention to provide simple and inexpensive optical methods and instrumentation for measuring the temperature of objects or environments in the presence of other, simultaneously acting physical or chemical variables.
It is another object of the present invention to improve the TADA system so it can be used in temperature ranges within which the luminescence efficiency of the probe is substantially degraded.
It is a specific object of the present invention to pro
Gutierrez Diego
Verbitsky Gail
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