Photoacoustic gas detection for fire warning

A detector for measuring the gas concentration of carbon dioxide based on an infrared photoacoustic principle is presented. Many molecules and particles in the atmosphere cause extinction of an incident beam of infrared radiation due to absorption and scattering processes. The absorption occurs at wavelengths which are very specific for each molecule. In the miniaturized gas detector presented the ambient gas enters a small cell (approx. 1 cm(3)) via a diffusion membrane. The gas is irradiated with pulsed infrared light at the specific absorption wavelength for carbon dioxide. The absorption of the radiation energy by the gas molecules causes slight variations of the pressure inside the measuring cell which can be detected with a commercial microphone. The amplified and subsequently linearized microphone signal is proportional to the gas concentration present. The applicability of the photoacoustic principle for the detection of combustion gases is discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.