| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent distortion of a peak waveform due to absorption of a target component by suppressing high-frequency noise appearing in an output of digital phase-sensitive detection when switching a wavelength of sawtooth wavelength sweep, in a gas concentration measurement instrument using a TDLAS measurement method. <P>SOLUTION: While a modulation current at a prescribed frequency for component detection and a driving current having a sawtooth waveform for wavelength sweep are superposed one over the other and are injected to a first LD 1, a driving current having a reverse sawtooth waveform, which is synchronized with the sawtooth waveform and has an opposite wavelength increase/decrease direction is injected to a second LD 5. Laser beams emitted from LDs 1 and 5 are dimmed (adjusted with respect to light quantity) by ND filters 3 and 7 and are mixed by a half mirror 4 and are radiated to a measurement cell 9. Light absorbed by the target component in a gas to be measured, at a specific wavelength is detected by an optical detector 10. Since the change in light quantity due to wavelength sweep in laser beams of two systems is canceled, a step at the time of wavelength switching is relaxed in an output of the optical detector 10, and as a result, the occurrence of high-frequency noise in phase-sensitive detection is reduced. <P>COPYRIGHT: (C)2012,JPO&INPIT |
