Patent ID: 7251032

Claim:
An optical monitoring system for determining at least one constituent of a specimen, said apparatus comprising: an optical switch receiving a light beam with an absorption spectrum from the specimen and having a plurality of outputs; a first filter in optical communication with a first one of said plurality of outputs of said optical switch, said first filter having a first filter output, said first filter being a molecular filter representing a first constituent and having a first filter transmittance; a first photodetector in optical communication with said first filter output, said first photodetector responsive to said light beam when switched to said first filter and having a first photodetector output indicating a first filter intensity of said light beam, a second filter in optical communication with a second one of said plurality of outputs of said optical switch, said second filter having a second filter output, said second filter being a neutral density filter having a second filter transmittance equal to said first filter transmittance; a second photodetector in optical communication with said second filter output, said second photodetector responsive to said light beam when switched to said second filter and having a second photodetector output indicating a reference intensity of said light beam; and a power sensor in communication with said first photodetector output and said second photodetector output, said power sensor responsive to an intensity of said light beam whereby said first filter intensity is compared to said reference intensity to determine if the specimen contains said constituent.