Gas concentration measurement device

A gas concentration measurement device including a laser light source for emitting laser light with a variable wavelength, a laser controller for driving the laser light source so as to modulate the wavelength of the laser light with a frequency f and to let a center point of the modulation range sweep a predetermined wavelength range repeatedly at a frequency lower than the frequency f, a measurement cell into which a gas to be analyzed will be introduced, and a photodetector for detecting the laser light that has passed through the measurement cell, where a concentration of a specific component in the gas to be analyzed is determined based on a harmonic component contained in a signal produced by the photodetector, the gas concentration measurement device comprising:

• an A/D converter for converting an output signal from the photodetector into a digital signal;
• a signal processor for generating a reference signal having a frequency nf (where n is a predetermined integer greater than one), and for multiplying the digital signal converted by the A/D converter and the reference signal;
• a first digital filter for reducing selectively signal component of frequency mf (where m is an integer greater than zero) from the product of the multiplication by the signal processor;
• and
• a second digital filter as a low-pass filter for extracting a direct-current component from the output signal of the first digital filter.