曝光一定时单相机辐射测温范围的影响因素分析

Analysis of the Influencing Factors of Radiation Temperature Measurement Range of a Single Camera at a Certain Exposure

针对单相机单波长测温和比色测温过程中测温范围较窄的问题,以单波长测温过程为基础,推导了相机传感器动态范围和工作波长对单相机测温范围影响的理论公式,并对波段选取过程中的影响因素进行了分析。理论分析结果表明:相机动态范围和波长的选取限制了一次曝光时测温范围的最大跨度值,在相机传感器唯一确定时,相机动态范围一定,根据波段选取原则选定工作波段,选定估计温度范围下限之后,由公式即可确定待测温度上限,再根据实际测温范围调整波段和估计测温下限;配合调节曝光及光圈,充分利用相机传感器的全动态范围,可实现单相机辐射测温法中宽温度范围的测量。此外,通过涡流加热实验和熔池温度场测量实验对上述影响因素进行验证,选取更优波长和更优曝光时间,可提高单次测温跨度至少40%,为单相机测温技术的具体实施提供技术参考。

As a common means of non-contact temperature measurement technology,radiation temperature measurement is often limited by the performance of the detector,and the temperature measurement range is narrow,which can not meet the measurement needs of wide temperature range distribution.The analysis of radiation temperature measuring range and influencing factors of a single camera has certain application value in practical engineering applications.As the error of temperature measurement is an important issue to be considered in the process of temperature measurement,this paper briefly introduces the principle of monochrome temperature measurement and two-color temperature measurement and analyzes the influence mechanism of temperature measurement error in detail.The accurate measurement of emissivity is the key factor affecting the error of temperature measurement in the monochromatic method.The accuracy of the colorimetric method is higher than that of the monochromatic method,which can meet the need of temperature measurement accuracy in actual working conditions.Aiming at the problem that the temperature range of the single camera is narrow in the process of single wavelength temperature measurement,the process of object radiation energy conversion into camera and imaging is introduced in detail from the process of single wavelength temperature measurement,and the theoretical formula of the influence of camera sensor dynamic range and working wavelength on the temperature range of the single camera is derived.Combined with the formula,then the influence mechanism of exposure time on the temperature range of radiation thermometry was analyzed,and the influencing factors in the process of band selection are analyzed.The reference principle of band selection is given to select the band where the object radiation is stronger than diffuse reflection and ambient light as far as possible.In colorimetric thermometry,the selection of two working bands should be close to meet the premise that the emissivity of the two bands is approximately equal.The central band and bandwidth of the filter should be selected according to the actual conditions of the test,in order to ensure a high temperature measurement accuracy and a wide range of temperature measurements.The theoretical analysis results show that the selection of camera dynamic range and wavelength limits the maximum span of temperature measurement range during one exposure.When the camera sensor is uniquely determined,the dynamic range of the camera is certain,and the working band is selected according to the band selection principle.After the lower limit of the estimated temperature range is selected,the upper limit of the temperature to be measured can be determined by the formula.Then the band and the lower limit of the estimated temperature are adjusted according to the actual temperature measurement range.By adjusting the exposure and aperture,and making full use of the full dynamic range of the camera sensor,the measurement of the wide temperature range in the radiometric thermometry method of a single camera can be realized.According to the formula,combined with the induction eddy current heating device,the relevant experiments are carried out,and the measurement of a wide temperature range in the single camera radiometric method is realized.Combined with the on-line measurement of the molten pool temperature field,the spectral response function of the camera and the characteristics of the optical components were considered comprehensively,and the relevant verification of the formula was carried out.In addition,for the distribution range of different temperatures,the influence of working wavelength and exposure time on the temperature range is similar,which verifies the results of the theoretical analysis.The selection of better wavelength and better exposure time can improve the single temperature measurement span by at least 40%,which provides important technical reference for the specific implementation of single camera temperature measurement technology.