The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 03, 1999
Filed:
Dec. 31, 1996
R Andrew Wood, Bloomington, MN (US);
Thomas M Rezachek, Cottage Grove, MN (US);
Rudy R Hegel, Richfield, MN (US);
Honeywell Inc., Minneapolis, MN (US);
Abstract
A photoacoustic gas sensing system includes either separate lasers or an arrangement of emitters and filters, to provide infrared energy within at least two distinguishable frequency bandwidths, modulated at two or more associated and different modulating frequencies. The modulated energy signals illuminate a gas cell containing a mixture of gases that experience temperature and pressure fluctuations responsive to the radiant energy. An amplified microphone signal, produced responsive to the pressure fluctuations, is detected at the different modulation frequencies to provide two or more detector signals in digital form. These signals are processed in combination with predetermined constants derived by calibrating the system, to generate two or more concentration values corresponding to the individual gases involved. The system can utilize a photoacoustic cell with walls formed entirely of a polymer that is both gas-permeable and transparent to the infrared radiation. If desired, a temperature sensor and a pressure sensor near the cell provide respective signals based on ambient temperature and ambient pressure. These ambient condition signals are used to provide concentration measurements corrected for changes in ambient temperature and pressure, including pressure differences due to differences in elevation. Temperature and light sensors can be included to reduce temperature-dependent and time-dependent variations in sensor calibration.