Self normalizing radiant energy monitor and apparatus for gain

Abstract

Method and apparatus for measuring the quantity of sample materials which provides stable measurements for extended periods of time. A source beam containing measuring radiation and reference radiation is directed through a sample material. The measuring radiation consists of spectral energy that interacts substantially with the sample material. The reference radiation consists of spectral energy with substantially different interaction properties with the sample material. Radiation is directed along separate analyzing and normalizing information channels wherein the radiation has substantially different sample interaction. Analyzing and normalizing detectors provide responses to radiation in respective analyzing information channel or normalizing information channel. A measuring mode is established by inserting a first filter into the source beam to allow substantially only measuring radiation to propagate to the detectors, creating measuring responses. A normalizing mode is established by inserting a second filter into the source beam to allow substantially only reference radiation to propagate to the detectors, creating normalizing responses. The detector responses are used collectively with appropriate signal processing means to obtain a measurement of sample quantity which is substantially independent from variations in measuring radiation intensity, variations in reference radiation intensity, changes in optical collection efficiencies for both detectors, and changes in gain from the response signals from both detectors.