Research Of Temperature Field Radiation Measurement And Its Calibration

Since Planck’s law was established in1900, radiation thermometry has always been the key research issue. Based on Planck’s law, the surface temperature of an object can be determined by the measurement of emitted radiation. Radiation measurement sensor has been developed from a single sensor to a sensor array, and it also promotes the development of radiation thermometry from the traditional measurement at a point to the field measurement. Besides of the array sensor technology, the optical imaging technology which can result in the imaging effect is necessary for temperature field radiation measurement. And the imaging effect has influences on temperature field radiation measurement and its calibration. In some sense, the radiation measurement by lens imaging can be carried out within a finite solid-angle. Can the temperature of the object with non-diffuse emission be determined by radiation measurement within the finite solid-angle? In this paper, the problems of temperature field radiation measurement and its calibration have been investigated.At first, based on the mathematical descriptions of radiation measurements with a pinhole or a lens, radiation measurements for spectrum or spectrum band have been studied and it can been seen that if the radiation energy flux is used as the input quantity of sensors, the traditional analysis method for sensors can be employed, while if the spectrum radiation intensity emitted from the measurement target is used, a constant factor will be introduced, compared with the traditional analysis method for sensors. In addition, the factor for pinhole imaging is different from that for lens imaging.Secondly, the imaging effect in temperature field radiation measurement has been studied.In this paper, the mathematical descriptions of the imaging and non-imaging radiation measurement are deduced based on the basic equations of radiation measurement and the correspondence between the infinitesimal planes of the target and the pixels of the sensor array. Because the imaging plane will not change the radiation transfer from the target to the sensor, the mathematical descriptions of the imaging effect can be obtained by comparing the two mathematical descriptions. A concrete analysis of the imaging effect based on pinhole imaging and lens imaging has been carried out. The results show that the primary cause of the imaging effect is the imaging optical axis angle while the subsidiary cause is the imaging zenith angle, and the influence of the subsidiary cause is determined by the difference between the imaging optical axis angle and the imaging zenith angle.Thirdly, multi-spectral thermometry for a non-diffuser based on radiation measurement within a finite solid-angle has been investigated. The equation for monochromatic radiation thermometry within a finite solid-angle is deduced, and it is found that if the surface temperature and spectral emissivity can be solved at the same time, the specific radiation measurement conditions for multi-spectral thermometry should be generally met that radiation measurement should be implemented within an infinitesimal solid-angle or within a finite solid-angle only for a perfect diffuser. When the directional spectral emissivity modeled by finite polynomial series is employed and proper mathematical transformation is used, a universal equation for monochromatic radiation thermometry is obtained. So the above restrictions in radiation measurement can be got rid of, but spectral emissivity may not be solved simultaneously.Meanwhile, the primary spectrum pyrometry for a non-diffuser based on radiation measurement within a finite solid-angle has been studied. Primary spectrum pyrometry should be generally carried out by radiation measurement within an infinitesimal solid-angle or within a finite solid angle in case of diffuse emission, so that the radiation thermometry equations become a closed system for temperature and other undetermined parameters. The radiation thermometry equation which can be used for temperature measurement of non-diffusive objects within a finite solid-angle has been deduced based on the linear emissivity model and a proper mathematical transformation. This equation is universal in radiation measurement, based on which equations for primary spectrum pyrometry are deduced. These equations are also universal in radiation measurement. The emissivity scaleplates under different measurement conditions are limited to the same range, but have different physical meanings.Finally, one method for getting rid of the influence of the imaging effect in temperature field radiation measurement has been proposed in this paper. The key problem in radiation thermometry is that the emissivity of an object is unknown, so multi-channel radiation thermometry including multi-spectral thermometry and multi-band thermometry has been proposed by emissivity constructing. If normalization of measurement data is used in multi-band thermometry, the influence of the imaging effect can be got rid of, and the calibration of spectral responsivity is needed in stead of the absolute radiation calibration. The mathematical descriptions of the calibration by substitution method based on reference sensor have been deduced and it can be seen that when divergent light is used to illuminate, absolute spectral responsivity calibration for the digital camera can not be conducted derectly while the relative spectral responsivity calibration can do by substitution method. Calibration experiments have been completed using the ZLX-DR calibration system based on the above analisis. In stead of normalization of measurement data, a new method has been proposed at the same time that the non-spectral parameter including the influence of the imaging effect is immigrated into the undetermined coefficients of emissivity modeled by finite series, which will not affect the solution of the true surface temperature. And by using this method the calibration of spectral responsivity is needed in stead of the absolute radiation calibration.