in temperature and pressure so as to deflect diaphragm 9 of diaphragm capacitor 10 as indicated the infrared energe beam is periodically interrupted by rotating shutter 7 so as to produce alternating pressure variations which are converted into an alternating electrical signal at a resistor 11 which is connected to diaphragm capacitor 10 and a power supply flow the alternating signal is amplified and rectified by a signal processing stage 13 which produces an output signal corresponding to the water vapor content of measurement gas 3 and which is indicated by measuring instrument 14 in similar manner this embodiment of the invention may be incorporated into a known two beam gas analyzer having a reference path such as that described hereinabove with respect to fig2 fig4 shows a gas analyzer having a non selective receiver and subtractive filtering the infrared energy produced by infrared source 1 is directed by reflector 2 so as to propagate through measuring cell 4 and through two cells 15 and 15 39 which are disposed in parallel a measurement gas 3 is circulated through measurement cell 4 cell 15 may contain a gas with sulfur hexafluoride while cell 15 39 contains other gas components of the measurement gas 3 or a non absorbing gas the radiation energy which propagates through cells 15 and 15 39 contacts non selective radiation receivers in the form of temperature responsive resistors 16 and 16 39 which are connected in a difference circuit with a power supply 17 the current flowing through resistors 16 and 18 correspond to the water vapor content of measurement gas 3 resistor 18 39 may be advantageously adjusted to preselect the null point.