Time resolution enhancement of a fiber-optic two-color pyrometer

摘要

A fiber-optic two-color pyrometer has been developed at the Institute of Heat Transfer and Air Conditioning at RWTH Aachen to measure temperatures at surfaces with low emissivities with a high time and space resolution. A fused silica fiber is used to transmit the radiation to the pyrometer from measuring positions with limited optical access. The two-color principle allows accurate measurements of absolute temperatures of surfaces with unknown emissivities if the assumption of a gray body behavior at the measurement wavelengths is valid. The minimum temperature which can be measured with the pyrometer is limited due to the small radiation energy at low temperatures given by Planck's law, the emissivity of the body and the size of measurement area. At present temperatures of low emissivity metallic surfaces with sizes of 0.4 mm can be measured down to 250 deg C. A new application to measure temperatures during high speed turning required a time resolution above the maximum of 2 mu s. To enhance the time resolution of the pyrometer the electronics was modified and a 30 MHz data acquisition board has been applied to the system. With this configuration a nanosecond time resolution is possible but the minimum measurable temperature increases. Different aspects for the limitation of the time resolution will be discussed. A new set-up with a nanosecond spark-flashlight will be described for the test of the transient response of the pyrometer and some test measurements will be presented.