Robust optical measurement of water vapor in steel-making process

Based on tunable diode laser spectroscopy (TDLS), we develop a simple and efficient humidity monitoring scheme to improve reliability of measurement under randomly changing transmission condition. This measurement scheme can detect the humidity of a monitored system in either high or low scattering condition such as powder coal fired furnace in steel-making process. Distributed feed-back (DFB) diode laser is used to evaluate the relative and absolute humidity by making direct absorption measurement near 938 nm region where 2nu 1 + nu 3 water vapor transition band exists. This system gives reliable measurement results under either high or low scattering condition.