A Method for Eliminating Beam Steering Error for the Modulated Absorption-Emission Thermometry Technique

Abstract : Modulated absorption-emission thermometry (MAET) is a non-intrusive, radiometric technique for measuring line-of-sight average temperature in high-temperature gases. The technique uses alternating measurements of emission and transmission to obtain the emissivity and the radiative intensity of the gas over a spectral band. The temperature is then calculated from the Planck function. The technique does not involve the measurement of spectral features such as line widths or strengths and therefore is suitable for high-pressure environments where spectral lines are broadened and merged. It is also suitable for environments where broadband emitters such as soot are present. Radiometric measurements in general can be made with very high accuracy. The international temperature scale (ITS-90) is realized and disseminated using radiometers and radiance sources for temperatures in the range of 973 K to 4473 K. Radiometry is a primary standard because the governing physical equation (Planck function) does not contain any temperature dependent parameters. Radiometers, or pyrometers, can be purchased off-the-shelf for temperatures from 973 K to 2973 K with accuracies in the range of 2 to 3 K. The technology for creating radiometers is mature, widely available and cost effective. Radiometers for test stand environments can be made that are rugged, compact and require no maintenance. Data acquisition rates in the MHz range and higher are possible using readily available Si, InGaAs and InSb diodes.