Gas monitoring in the process industry using diode laser spectroscopy

Gas monitors for industrial applications must have high reliability and require little maintenance. Monitors for in-situ measurements using tuneable diode laser absorption spectroscopy in the near infrared, can meet these requirements. A brief description of monitors using high-frequency wavelength modulation spectroscopy with second-harmonic detection is presented. Some problems related to industrial applications are discussed, in particular line broadening effects, and frequency drift of diode lasers. Typical applications for monitoring of O-2, CO, NH3, HCl and HF are described together with measurements from several installations. The monitors show continuous measurements with fast response and good sensitivity, all of which is difficult to obtain with conventional techniques such as wet chemical analysis.