Gas-sensing technology is an important forefront topic in the research field of sensing technology now. Gas-sensing technology, which employs laser diode (LD) and light emitted diode(LED) as light resource, has multitude advantages over traditional approaches, such as high sensitivity, multiple selection, wide dynamic range, good signal to noise ratio and quick response time. Especially optical fiber sensor is more safe and reliable for the electrical insulation between the optical fiber sensor and the signal processing circuit. With the rapid development of optical fiber communication technology, low-cost and high quality near infrared laser and light emitted diode working at room temperature become widely available. The emit wavelength from these light resource is not only consistent with the three low-decay windows of fiber optics, but also with many wide-frequency or recombination absorption spectrum of environmental and industrial gases. Therefore optical fiber gas sensor can meet on-line measurement in high-temperature, poisonous and dangerous situation where human being and traditional instruments can hardly accomplish.Carbon monoxide (CO) is used as a research example. Based on the theory and experimental approaches of optical fiber infrared absorption sensing, mathematical model and system design for optical fiber on-line gas measurement are presented. The detail contents are as following:The molecule's structure, the molecule's spectrum and infrared spectrum structure of CO are analyzed. It's the solid foundation for measurement wavelength selection and effectively eliminated cross sensitivity.According to Lambert-Beer law and related optical signal processing technology, the mechanism of gas concentration detection based on spectrum absorption using optical fiber to transmit signal is investigated.Two fundamental approaches, differential optical absorption spectra (DOAS) and wavelength modulation harmonic measurement, for gas light absorption detection are discussed. DOAS is adopted based on the existing laboratory condition. The mathematical model of DOAS is founded with the characteristic of medium light... |