| 摘要 |
The invention is concerned with a method and apparatus for real time analysis of gas mixtures, e g determination of air quality, including at least one resonator ( 1, 11 ), means for gas transportation to and from the resonator ( 1, 11 ), e g by diffusion or transit flow via openings ( 5 ) means for activation ( 2 ) and detection ( 3 ) of an acoustic signal within the resonator ( 1, 11 ), at least one means ( 7 ) for measurement of the temperature within the resonator ( 1, 11 ), and at least one means ( 4 ) for the determination of both the resonance frequency and the quality factor of the resonator ( 1,11 ) in real time. These entities are related to the average molecular mass and viscosity or thermal conductivity, respectively, of the gas mixture. The resonator ( 1, 11 may include a compliant element, e g a constricted volume ( 6 ) and an inertial element, e g ist opening ( 5 ) or may support standing acoustic waves, in which the sound wavelength is related to a physical dimension of the resonator ( 1, 11 ). The determination of resonance frequency and quality factor is preferably based on phase detection within a phase locked loop and is thereby independent of magnitude. In addition to self oscillations at a frequency determined by the resonance frequency, a repetitive frequency modulation is being generated by which a quantity representing the quality factor of the resonator ( 1, 11 ) is being generated in real time. Furthermore, means ( 7 ) for compensation of temperature or pressure dependence of the resonance frequency or quality factor are included. By an arithmetic-logical unit, e g a microprocessor ( 9, 17 ), measured values related to air quality, e g carbon dioxide concentration, relative humidity and temperature are being made available. |
