A novel multi-band plenoptic pyrometer for high-temperature applications

Abstract

A snapshot, multi-band imaging pyrometer was developed for two-dimensional, high-temperature measurements. The multi-band pyrometer is composed of a plenoptic camera and a continuous wavelength filter (450 nm–850 nm), located at the aperture plane of the primary imaging lens. A microlens array forms micro-images of the color filter with a resulting spectral resolution of approximately 25 nm per pixel. A wavelength calibration method was developed to use eight narrow-band light-emitting diodes at discrete wavelengths with sub-pixel wavelength location determined using a weighted intensity centroid algorithm. Temperature calibration was conducted using a graphite block as a gray-body radiator placed in a box furnace with controlled temperatures of 600 ∘C–1100 ∘C. Temperature is estimated at each microlens location using the spectral pyrometry method, which reduces the dependency of the measurement on a priori knowledge of material emissivity. Simulated data with Gaussian noise demonstrates reduced uncertainty at higher temperatures and larger bit-depths. Experimental measurements with a heated graphite block demonstrated accuracy within the uncertainty bounds of a reference thermocouple (±0.75%). In addition, validation experiments were conducted in the more dynamic environments of a strand burner and a solidifying copper pool, which contain high-temperature, moving particles and phase dependent emissivity, respectively. The addition of alumina particles to solid fuel produced an expected increase of over 400 ∘C that was measured by both a multi-band imaging pyrometer and a thermocouple. The pyrometer demonstrated the ability to measure temperatures for liquid and solid phases of copper simultaneously with temperature accuracy better than 5%, despite larger differences in material emissivity.