A process gas analyzer and method for analyzing a process gas carried in a plant section, wherein light from a light source is passed through the process gas and detected via a detector, evaluated in an evaluation unit to produce an analysis result with respect to the absorption in the process gas, where chambers or purging pipes, present between the light source and the plant section and also between the detector and the plant section, are flushed with a purge gas to analyze the process gas, and where the volume flow rate of the purge gas is periodically modulated and the effect of the purge gas on the analysis result is determined based on changes in the detected absorption caused by the modulation and removed from the analysis result to enable a high degree of compensation for measurement errors caused by the purging.
