| 摘要 |
PROBLEM TO BE SOLVED: To enhance the measurement accuracy of a gas concentration, while restraining the circuit scale from becoming large. SOLUTION: A double-wave shifted frequency signal generating part 45 generates a (2f+▵f) reference signal, having a frequency (2f+▵f) which is shifted by a shift frequency▵f from a double-wave shifted frequency of a modulated frequency fm; a detector 46 generates a 2f component, based on the output from a bandpass filter 44, by combining the (2f+▵f) reference signal, generated in the double-wave shifted frequency signal generating part 45, with the output from the band-pass filter 44; a high band component of 1f or more is fully attenuated by a low-pass filter 47; and a▵f component is extracted in a low-pass filter 50, from a value peak-held in a peak-and-hold circuit 49 so as to be output as a 2f component detection signal. COPYRIGHT: (C)2009,JPO&INPIT
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