Calibration And The Measurement Error Analysis Of Infrared Imaging System For Temperature Measurement

Non-contact infrared temperature measurement has been widely used in industry and national defense due to its many merits such as not changing the measured temperature field, the wide temperature measurement range, and the ability to measure both distant and small objects and so on. Since the emissivity of the object is normally less than 1, those radiations reflected from background objects and radiated directly from solar can enter into the optical system inevitably, which will then cause the error on the temperature measurement and thus might bring huge economic losses to the end users. In this paper, factors that affect the precision of the temperature measurement are systematically analyzed and solutions to eliminate the errors are put forword.The thermal infrared imager was calibrated by using a standard black body light source with a plate shape in laboratory, and the relation between the average grey level of the black body's image and its temperature was derived. The influence of the object-system distance on the accuracy of temperature measurement by using IR System was analyzed. With the relation between the illuminance on the focal plane array of the IR system and the numerical aperture of the image space, the theoretical analysis of the influence of object-system distance on the accuracy of temperature measurement was carried out. The temperature difference between the measured temperature and the real temperature versus the object-system distance was characterized. A solution was proposed to reduce the measurement error and increase the temperature measurement accuracy. The influences of emissivity measurement error and background temperature error on temperature measuremet are analyzed. The results show that the higher the object's temperature, the larger the temperature measurement error. In particular, when the object's temperature is close to the background's temperature, the influence of background's temperature on temperature measurement is obviously signicant and can not be ignored. Therefore, if the object'stemperature is higher, the emissvity's effect on the temperature measurement must be considered. On the other hand, if the object's temperature is lower, the background temperature's effect on the temperature measurement must be evaluated and corrected.In order to reduce the error further, the influence of the imager itself and the temperature rise of focal plane array(FPA)on the accuracy of temperature measurement was discussed and characterized as well. The experimental results show that the measured temperature is dependent on the FPA'temperature. when the FPA' temperature is stable, the measured temperature is smaller than the real one, the relative error is within the range of 8-10%. Therefore, a proper compensation of this parts error can effectively reduce the temperature measurement error.With a three-waveband CCD sharing one optical system, a camera which can image in ultraviolet, visible and near infrared wavebands is realized. The filter transmissivity in three wavebands of ultraviolet (350-380nm), visible (380-760 nm) and near infrared (760-1000nm) has been obtained. Using integrating sphere as a uniform light source, calibration of the three-waveband camera was done. The relation between the grey level of the image and the radiance of the integrating sphere for different exposure time ranging from 0.125 ms to 8ms in three wavebands is characterized. It is shown that the grey level has a linear function with the radiance for different exposure time in all three wave bands.