HIGHLY ACCURATE CO2 GAS SENSOR USING A MODULATION-TYPE PYROELECTRIC INFRARED DETECTOR

We have developed a highly accurate CO2 gas sensor which utilizes a pyroelectric infrared (IR) detector containing a solid state chopper and an optical filter. We have improved the noise of the IR detector and the dependence of the sensitivity on the optical filter characteristics. The noise of the IR detector is suppressed by optimization of the gate resistance value and by development of a new structure for IR sensing to compensate for extraneous noise. The magnitude of the noise is improved about one-half compared with the magnitude in the conventional detector. The sensitivity to CO2 has been raised by investigating the optimum conditions of the optical filter. The accuracy of the CO2 gas sensor using the new IR detector is +/-0.03% at a 5% CO2 gas concentration and +/-0.12% at a 20% concentration.