Using multispectral imaging to measure temperature profiles and emissivity of large thermionic dispenser cathodes

The authors measured temperature, temperature uniformity, and emissivity of two large thermionic tungsten cathodes. This was necessary because their operating life is strongly affected by nonuniformities in temperature. The cathodes were self-heated 6.5 and 8-in. disks operating in a vacuum at about 1l00 °C. We measured the temperature of the cathodes by a combination of multispectral imaging using a conventional CCD camera and spot pyrometry using three spot pyrometers. We took images at the blue end of the spectrum (0.4 μm) to determine temperature accurate to 3% K. Spot pyrometers at the red end of the spectrum (to 1.8 μm) yielded emissivity with an uncertainty of 15%. We emphasized using data in the blue to determine the temperature and data in the red to determine emissivity. Our analysis displays data so that assumptions in determining temperature and emissivity are transparent. Because we obtained a linear relationship between camera counts and integrated exitance of a blackbody, we concluded that the camera was calibrated correctly.