Isotope gas measuring apparatus

An isotope gas measuring apparatus for measuring concentrations of different components in a sample gas, comprising:

• first and second sample cells through which said sample gas passes;
• a control cell filled with a gas having no absorbance at a wavelength of infrared light to be measured;
• a light source for irradiating infrared light to the first and second sample cells and said control cell;
• an optical coupler connected to the first and second sample cells and the control cell for coupling lights from the first and second sample cells and the control cell;
• a first interference filter disposed between the first sample cell and the optical coupler for allowing one particular wavelength of the light source for measuring one of the components to pass therethrough;
• a second interference filter disposed between the second sample cell and the optical coupler for allowing another particular wavelength of the light source for measuring another of the components to pass therethrough;
• and
• an optical detector connected to the optical coupler for sequentially detecting lights from the optical coupler.