<p>Dual beam gas sensor has an infra-red source (12), a cell (16) filled with gas to be analyzed and a second cell (18) filled with reference gas. A detector (20) on the opposite side of the cells detects radiation transmitted through them. A diaphragm wheel (14) allows alternate transmission of radiation through the analysis cell and the reference cell with at least two dark phases. An independent claim is included for a method for determination of gas components using the sensor.</p>
