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In recent years there has been a great deal of interest in the development of devices capable of measuring elevated surface temperatures. Tests conducted in high-temperature facilities depend upon accurate temperature measurements for their intelligent interpretation. Thermocouples are generally used wherever possible but in many instances another method is required. Optical pyrometry has also been used extensively in industrial and laboratory applications. The absolute accuracy is generally not as good as with thermocouples, but this is a relatively minor consideration at elevated temperatures. The study of ablation and refractory materials has inspired the investigation of a new technique of determining surface temperatures and intricate temperature profiles. Attempts have been made to install thermocouple probes in ablation materials, but this is restrictive since probes tend to alter the homogeneity of the material and cause erosion around the probes. Thermocouples embedded in the material would not effectively measure the surface temperature because of the extreme temperature gradient through an ablation material. The general requirements for a surface temperature measuring technique demanded by the ablation program could be described as follows: It was desired to measure the absolute surface temperature. Secondly, a system was needed that would be capable of determining surface temperature profiles over a large area. A survey of commercially available equipment did not reveal any device that would be entirely satisfactory without considerable modification. Preliminary studies of various methods of temperature measurement indicated that a photographic technique offered the best all-around possibilities.
Siviter, James H.
Aeronautical Research Engineer, National Aeronautics and Space Administration, Langley Field, Va.