Solid state non-dispersive IR analyzer using electrical current-modulated microsources
AssigneeCriticare Systems, Inc.
InventorsN. C. Joseph Lai, Edward J. Zuperku, Roy A. Henning
Life of this patent
Estimating the term…
Abstract
A non-dispersive infrared gas analyzer of the type typically used to measure concentrations of gases in medical and industrial applications has no moving parts and employs two or more miniature infrared sources ("microsources") which are electrical current-modulated to produce modulated infrared radiation for synchronous detection. The microsources are operated at different frequencies. The frequency-multiplexed detector signal is demodulated and ratioed to yield an output which is correlated to the gas concentration in the sampler chamber.
Claims23
An optical system for measuring levels of a selected gas, comprising:
- a sample chamber which defines a measuring axis;
- first and second broad band IR sources, each comprising a pair of conductors and a radiating film disposed across the conductors such that current passing between the conductors heats the radiating film;
- a first band-pass filter positioned to filter IR radiation generated by the first IR source to form a measuring beam in which radiation outside of a first IR band aligned with a selected absorption peak of the selected gas is attenuated;
- a second band-pass filter positioned to filter IR radiation generated by the second IR source to form a reference beam in which radiation outside of a second IR band, different from the first IR band, is attenuated;
- a beam splitter positioned to combine the measuring beam and the reference beam and to direct the resulting combined beam through the sample chamber along the measuring axis;
- a detector responsive to the combined beam after it has passed through the sample chamber;
- means for supplying modulated current to the first and second IR sources such that the radiating elements each radiate IR energy in a distinctive time pattern;
- means, responsive to the detector, for generating a first signal indicative of the amplitude of the measuring beam incident on the detector and a second signal indicative of the amplitude of the reference beam incident on the detector;
- and
- means for combining the first and second signals to determine a measure of the level of the selected gas in the sample chamber.
An optical system for measuring levels of a selected gas, comprising:
- a sample chamber which defines a measuring axis;
- a first optical source operative to generate a measuring beam directed along the measuring axis through the sample chamber, said measuring beam comprising radiation at a wavelength corresponding to a selected absorption peak of the selected gas;
- a detector responsive to the measuring beam after it has passed through the sample cell to produce a detector signal;
- means for supplying a time modulated current to the first optical source such that the measuring beam is substantially sinusoidal at frequency f.sub.1 ;
- means for combining an f.sub.1 frequency component of the detector signal with an additional signal matched in frequency to the f.sub.1 frequency component of the detector signal to form a resulting signal having a periodic component at 2.multidot.f.sub.1 and a low frequency component, wherein the low frequency component varies in amplitude in accordance with the amplitude of the f.sub.1 frequency component of the detector signal;
- and
- means for measuring the amplitude of the low frequency component of the resulting signal to determine the amplitude of the f.sub.1 frequency component of the detector signal.
Dependencies are inferred from the claim text.