Optical Measurement of Water Vapor Concentration and Gas Pressure

A technique is proposed to realize simultaneous measurement of water vapor concentration and total gas pressure. The technique is based on distributed feedback laser diode wavelength scanning, and it is in conjunction with Levenberg-Marquardt algorithm (LMA). Water vapor concentration at a pressure of 5.7 atm has been measured with a differential value between the peak value and the base line, which is derived from the fitting absorption spectrum after LMA processing; and measuring accuracy
${<}{\rm 20}~{\rm ppm}$
has been achieved. Simultaneously, gas pressure inside the gas cell can be obtained by calculating full width at half maximum after application of this fitting algorithm, and an accuracy better than 5% has been achieved in a range of 1.02–7.48 atm.