Use of a multiwavelength pyrometer in several elevated temperature aerospace applications

A multiwavelength pyrometer was developed for applications unique to aerosp ace environments. It was shown to be a useful and versatile technique for m easuring temperature, even when the emissivity is unknown. It has also been used to measure the surface temperatures of ceramic zircornia thermal barr ier coatings and alumina. The close agreement between pyrometer and thin fi lm thermocouple temperatures provided an independent check. Other applicati ons of the multiwavelength pyrometer are simultaneous surface and bulk temp erature measurements of a transparent material, and combustion gas temperat ure measurement using a special probe interfaced to the multiwavelength pyr ometer via an optical fiber. The multiwavelength pyrometer determined tempe rature by transforming the radiation spectrum in a broad wavelength region to produce a straight line (in a certain spectral region), whose intercept in the vertical axis gives the temperature. Implicit in a two-color pyromet er is the assumption of wavelength independent emissivity. Though the two d ata points of a two-color pyrometer similarly processed would result immedi ately in a similar straight line to give the unknown temperature, the two-c olor pyrometer lacks the greater data redundancy of the multiwavelength pyr ometer, which enables it to do so with improved accuracy. It also confirms that emissivity is indeed wavelength independent, as evidenced by a multitu de of the data lying on a simple straight line. The multiwavelength pyromet er was also used to study the optical transmission properties of a nanostru ctured material from which a quadratic exponential functional frequency dep endence of its spectral transmission was determined. Finally, by operating the multiwavelength pyrometer in a very wide field of view mode, the surfac e temperature distribution of a large hot surface was obtained through meas urement of just a single radiation spectrum.