Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Patent
1992-07-30
1994-10-11
Cuchlinski, Jr., William A.
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
374117, G01K 730
Patent
active
053541308
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for measuring the temperature of an electrically conductive material as defined in the introductory part of the claim annexed. The invention also relates to an apparatus for implementing the method. The method and apparatus allow the temperature of a hot, solid or molten conductive material to be measured without a contact between the measuring sensor and the object under measurement.
High temperatures of several hundreds or thousands of degrees (.degree. C.) are mainly measured using a pyrometer or a thermoelement. The former is based on the measurement of the thermal radiation emitted by the object, the latter on the thermoelectric effect.
The radiation pyrometer is a device for contactless temperature measurement. It is capable of measuring the temperature from a fairly long distance from the object. A drawback with the radiation pyrometer (e.g. in measurements in the metallurgic industry) is the fact that the emissivity of the radiating object depends, in addition to its temperature, also on the radiating material. Therefore, e.g. in the measurement of the temperature of a metal surface, an oxidic recrement layer on the surface or a layer of slag on the surface of molten metal may cause significant errors that are difficult to compensate. Similarly, smoke, dust, water vapour etc. cause errors.
The thermoelement is commonly used especially for measuring the temperature of molten metals. This device is used for direct measurement, i.e. the thermoelement is sunk into the object under measurement. The problem is the aggressivity of the circumstances. The sensors used for the measurements are generally of a disposable design and the measurements therefore relate to specific points in the objects. For continuous measurements, it is necessary to use protective tubes, and these retard the transmission of heat, increasing the measuring time lag of the element.
For practical reasons, the thermoelement is difficult to use for measuring the temperature of moving hot objects, e.g. casting or rolling blooms. Therefore, thermoelements attached to the object surface have only been used for research purposes.
It is known that the noise in a thermally balanced electric circuit is directly proportional to the temperature. A general formulation of this law is given in the dissipation theorem, which, when applied to an electric resistance, yields the so-called Nyquist theorem. A device for measuring noise temperature based on this theorem has been constructed. Using this device, the temperature can be realized by using the Bolzmann constant. This principle has been employed for accurate measurements of both low and very high temperatures. In these measurements, the noise is measured from a resistor thermally anchored on the object under measurement. However, the use of this method and device for temperature measurements on hot and particularly moving objects is prevented by the fact that the connecting leads, contacts and the resistor itself are destroyed in high temperatures.
The object of the present invention is to produce a new and improved method and apparatus for measuring the temperature of electrically conductive materials, allowing contactless measurement of the temperature of a body or an object. As for the features characteristic of the invention, reference is made to claim annexed regarding the method, and to claim annexed regarding the apparatus.
The method of the invention is based on the measurement of thermal noise using a resonant circuit without contact with the material under measurement, especially a hot object. In this method, the fluctuation of the magnetic field generated by the random motion of the charge carriers in a metal or other conductive material is measured from a distance from the surface of the material.
The method and apparatus of the invention have the following advantages. The measurement can be performed without contact with the object under measurement. Insulating materials, e.g. air, dust, water vapour and other impurities, will not disturb t
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Holappa Lauri
Seppa Heikki
Bennett G. Bradley
Cuchlinski Jr. William A.
Valtion teknillinen tutkimuskeskus
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