| 摘要 |
PROBLEM TO BE SOLVED: To achieve a cost reduction or the miniaturization and weight reduction and an enhancement of measuring accuracy, by dispensing with the supply of a reference signal necessary for extracting a higher harmonic component in the gas concentration measuring instrument that uses a TDLAS measuring method. SOLUTION: The measuring signal obtained in PD 4 is digitized, and the measuring signal itself is multiplied by a second multiplier 63. Since a modulation frequency component is contained in the measurement signal, a secondary higher harmonic component is produced by the second multiplier 63 and extracted through BPF 64 to be set as the reference signal. If the measurement signal and the reference signal are multiplied by a first multiplier 62, the secondary higher harmonic component contained in the measuring signal is converted into a DC component by frequency conversion; and as a result, an AC components which are unnecessary in LPF 65 are removed. Scanning frequency is preset to about nine times, without lowering the cut-off frequency of the LPF 65 too much so as to eliminate the effect exerted on an absorption peak waveform that accompanies wavelength scanning. COPYRIGHT: (C)2010,JPO&INPIT
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