Photo-acoustic gas sensor for monitoring air-conditioned room

摘要

A photoacoustic gas sensor for detecting the presence of e.g. CO2, CO, NO, etc. in a room has a measurement chamber (1) having an air filter (2) giving access to the atmosphere of the room (V). A controller (9) generates LF pulses (i1) for energising a piezo-electric loudspeaker (7) with response registered by a suitable low-cost microphone (5) whose output signal (S) is selectively amplified (6) and stored as a system response reference by the microprocessor (13) and memory (14). The controller (9) also pulses (i2) a light-source (4) which irradiates the chamber (1) via an optical bandpass filter (3) to promote excitation of e.g. CO2 molecules and give rise to a photo-acoustic response corrected against the stored reference for ageing and/or temperature and signalled (K) at the terminal (15).