Fluorescent gas analyzer

A gas analyzer comprising an analytical portion comprising a source of radiation selected to cause a selected gas to fluoresce, a cell for containing a sample and to premit irradiation of the sample with said radiation, first reference detector means, means to divert a predetermined portion of the source radiation to said reference detector means;

• second detection means to produce pulses proportional to the fluorescence emitted by the sample while it is being irradiated, means to accumulate a value proportional to the radiation detected by said first detector and means to compare said value to a preset value and to produce a control signal when said values are equal and to determine the amount of time required for said first detector value to equal said preset value, photon accumulator means, means to direct the pulses detected by said second detector to said photon accumulator means while said source is on, dark current accumulator means, means to direct the pulses detected by said second detector to said dark current acccumulator means while said source is off, means to substract the value on said dark current accumulator means generated during a source-off cycle from the value on said photon accumulator means generated during a source-on cycle, and output means to output the difference value produced.

A gas analyzer comprising a source of selected radiant energy, means to turn the source on and off for selected periods of time, means to irradiate a gas sample with a predetermined amount of said radiation to cause the gas of interest in said sample to fluoresce, means to determine the elapsed time required for said source to output said predetermined amount of radiation, means to generate a digital value proportional to the re-emitted fluorescence from the gas of interest, means to generate a digital value proportional to the dark current within said analyzer while said source is off, and means to subtract said value proportional to the dark current from the value of the detected fluorescent light.

A method of determining the content of a first gas in a gas sample, comprising the steps of selecting a radiant energy to cause the first gas only to fluoresce, actuating a source of said selected energy, exposing said sample to a predetermined amount of said selected energy from said source, detecting the fluorescence re-emitted by said irradiated sample, generating a value proportional to the accumulated detected fluorescence, diverting a predetermined portion of the radiation from said source, detecting said diverted source radiation, generating a value proportional to the accumulated detected diverted source radiation, comparing the value of said accumulated diverted radiation to a predetermined value corresponding to said predetermined amount of energy to thereby measure said predetermined amount of energy used to expose said sample;

• determining a value for the dark current correction by accumulating dark current pulses for a length of time substantially equal to the time said source was activated to produce said predetermined amount of energy;
• subtracting the value of said accumulated dark current pulses from the value of said accumulated fluorescence, and outputting the value obtained by said subtraction step.