Thermal measuring and testing – Temperature measurement – In spaced noncontact relationship to specimen
Patent
1996-09-24
1998-10-06
Gutierrez, Diego F. F.
Thermal measuring and testing
Temperature measurement
In spaced noncontact relationship to specimen
374183, 374110, 374112, 374120, G01K 116, G01K 300, G01K 314, G01K 722
Patent
active
058167064
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for determining the internal temperature of an object or body, said method comprising measuring heat flux from the surface of an object through a structure which is positioned against it and whose thermal conductivity is known.
2. Description of the Prior Art
Known solutions are implemented, for example, by thermometers measuring the temperature of a human being from the surface of the skin or by thermometers measuring the temperature of the contents of a process container from the surface of the container.
Heat flux through the surface layer of any object depends not only on the difference between the temperature of the object and the ambient temperature but also on the thermal conductivity of the object, the thermal conductivity being a characteristic of the material of which the object is made. The colour of the object has an effect on the temperature of the object: the darker the surface, the better it emits heat to the environment.
In measuring the thermal conductivity of the surface layer of living tissue, such as the human body, it has been found that thermal conductivity is clearly dependent on dermal circulation, i.e. on the coefficient of internal thermal conductivity. The basic level consists of the thermal conductivity of proteins and lipides, which is of the order of 1.8 mW/cm*K. When dermal circulation is stimulated, the water content of the tissue increases. Thus, when the circulation is at its most stimulated, the thermal conductivity of water, 6 mW/cm*K, can be added to the basic level of thermal conductivity. The range of thermal conductivity is thus from 1.8 to 7.8 mW/cm*K.
To develop a method for measuring the internal temperature of an object is a difficult task in many respects. The practical implementation requires solving of many problems, such as the effect of thermal losses, the calculation or measurement of internal temperature, calibration, etc. Determining the thermal conductivity of skin, for instance, is an extremely difficult task, and it is impossible unless calibration and approximation are performed for each measurement. Such a determination method is not suitable for rapid measurements in which the aim is to obtain relatively accurate results with a thermometer that is easy to use.
OBJECTS AND SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and apparatus for determining the internal temperature in a structure simply and rapidly, directly from the surface of any object or living tissue. To achieve this, the method of the invention is characterized by measuring the surface temperature and ambient temperature of said object or body on both sides of two structures whose thermal conductance are known, eliminating the unknown thermal conductance of said object or body from the solutions by combining the doubled solutions and determining the internal temperature of said object or body on the basis of the combined solution.
The apparatus according to the invention for determining the internal temperature is based on a heat flux sensor to be positioned against the surface of an object or body for measuring heat flux from the surface of said object through the sensor. The apparatus according to the invention is characterized in that said apparatus comprises doubled sensors each of which comprises two thermosensitive elements positioned substantially opposite to each other, and a structure which is provided between them and whose thermal conductivity is known and by which the surface temperature and ambient temperature of said object or body can be measured, and a calculation unit by which the function of the heat flux in relation to the internal temperature of the object or body can be solved on the basis of the measured temperature values, and by which the doubled solutions can be combined to determine the internal temperature of said object or body on the basis of the combined solution.
The method and apparatus according to the
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Heikkila Ilkka
Nissila Seppo
Gutierrez Diego F. F.
Polar Electro OY
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