Nulling device for detection of trace gases by NDIR absorption

摘要

A nondispersive gas analyzing apparatus is described having a first chamber for containing a first gas, the density of which is determined. A source of radiant energy is provided for passing radiant energy through the first chamber. Modulation means are provided for modulating the radiant energy passing through the first chamber by modulating the volume of the chamber at the acoustic resonance frequency of the first gas and the chamber. Signal generating means, including a second chamber for containing a gas which is heated by radiant energy emerging from the first chamber and a microphonic means responsive to the resulting pressurization in the second chamber, is provided for generating a signal, having a frequency and amplitude corresponding to the modulation of the radiant energy in the first chamber.