JPH0255741B

For determining the partial pressure and concentration of a measuring gas which is in mixture with at least one additional gas according to an optical absorption technique, in which a beam of light having a predetermined intensity and alternatingly and cyclically having a first spectral distribution in which the light intensity will be reduced by passage through the measuring gas and a second spectral distribution in which the light intensity will not be reduced by passage through the measuring gas, is passed through such a mixture and its radiation intensity after passage through the mixture is measured in a radiation detector having an active element which is heated by the radiation and which produces an output representative of its degree of heating and composed of alternating measuring signal segments, resulting, respectively, from light having the first and the second spectral distribution, and adjacent signals segments are processed in order to compensate for various interference effects, the detector output is delivered to an input amplifier having a large signal to noise ratio, and signal inaccuracies due to superimposition of each signal segment portion produced by heating of the active element on a component representing the cooling behavior which the element would experience after the preceding heating period if further heating did not occur are compensated by integrating, in an integration member, successive portions of the detector output with respect to an integration base which has a fixed value relative to the detector output value corresponding to a constant active element temperature.