Method of and device for contactless temperature measurement of an object independently of radiation emissivity

A device for determining spectral emissivity of an object with high accuracy, comprising:

• a spectrometer having an inlet for receiving visible or infrared filtered radiation from a measured object;
• a modulator provided with at least two filters for consecutively passing the radiation in discrete visible and/or infrared wavelength ranges;
• a detector arranged opposite the modulator for converting the filtered radiation into a corresponding electrical signal;
• an analog/digital converter for converting said electrical signal into a digital signal, connected to the detector;
• a timing logic circuit connected between the modulator and the analog/digital converter to clock the digital signal at the output of the converter in synchronism with the modulator;
• a microprocessor connected to the output of the analog/digital converter programmed for iterative computation and having its output connected to a display unit;
• a closed measuring housing having black inner walls and an output window communicating with the inlet of the spectrometer, emissivity of the inner wall of the measuring housing being unity;
• a sample holder arranged at one end of the measuring housing, the measured object having the form of a sample supported in the sample holder;
• a heating and/or cooling device arranged in the sample holder to heat and/or cool the sample;
• a controllable deviating mirror rotatably supported in the measuring housing opposite the window and being tiltable between a first and a second position for reflecting in the first position thereof the radiation from the sample into the window and, in the second position thereof, reflecting the radiation from an opposite inner wall portion of the measuring housing into the window, the deviating mirror being adjusted for similarly reflecting radiation in either position thereof such that iteration of values received by the detector, the emissivity of the object is then computed in said microprocessor and displayed on said display unit.

A method of simultaneous, contactless measurement of the temperature of an object, values of its spectral emissivity and the ambient temperature, comprising the steps of:

• (a) detecting values of spectral radiance or spectral radiant intensity L.sub.M, .lambda.i in a plurality of visible or infrared wavelength ranges;
• (b) placing the measured values in a set of at least three equations as follows:
• L.sub.M, .lambda.1 =.epsilon..L.sub.T.sbsb.obj,.lambda.1 +(1-.epsilon.). L.sub.T.sbsb.Umg, .lambda..sub.1
• L.sub.M, .lambda.2 =.epsilon.. L.sub.T.sbsb.obj, .lambda.2 +(1-.epsilon.). L.sub.T.sbsb.Umg, .lambda.2
• L.sub.M, .lambda.3 =.epsilon.. L.sub.T.sbsb.obj, .lambda.3 +(1-.epsilon.). L.sub.T.sbsb.umg, .lambda.3
• where the measured values L.sub.M, .lambda..sbsb.1 are expressed as the sum of the radiance L.sub.T.sbsb.obj, .lambda.i, according to Planck's radiation law, of a black body of temperature T.sub.obj of the object, multiplied by the object and the radiance L.sub.T.sbsb.Umg, .lambda.i, according to Planck's of a black body of temperature T.sub.Umg of the environment of the object, multiplied by the reflectivity .rho. of the object expressed in the object's emissivity .epsilon. as 1-.epsilon.;
• and
• (c) solving iteratively this set of equations to obtain the true values of the temperature T.sub.obj, the emissivity .epsilon. of the object and the temperature T.sub.Umg of the environment of the object.