Calibration of nondispersive infrared photometer

Claim 1

In a calibration device provided for selective inclusion in radiation paths for purposes of calibrating a nondispersive infrared photometer which includes an infrared radiation source, possibly with modulation, a pair of chambers associated with measuring and reference paths, one of the chambers being a measuring chamber, a second one of the chambers being a reference chamber, said chambers being defined by a longitudinally divided tube and being symmetrically configured with respect to a longitudinal dividing and partitioning plane, the photometer, further including receiver, detector and filter structure, the calibration device comprising: a carrier made of good heat conductive material and being provided with a first pair of calibration chambers and a second pair of calibration chambers so that in dependence upon the position of the carrier the first pair of calibration chambers or the second pair of calibration chambers is in optical alignment with the detector and with said measuring and reference chambers; said carrier being movable in a direction that is in an interface plane defining respective partitioning of the pairs of calibration chambers and of the partitioning plane of the tube; all calibration chambers being of similar cross section; the first pair of these calibration chambers in the carrier including a gas filling that is the same in both calibration chambers while as to the second pair, one of the calibration chambers of the second pair contains the same kind of reference gas as contained in said reference chamber while the other calibration chamber is filled with a calibration gas; and window means associated with said calibration chamber pairs such that the number of optically effective boundary surfaces of the windows are the same regardless whether the first or the second pair are placed into alignment with said measuring and reference chambers.