Method and apparatus for detecting a component gas in a sample

An apparatus for detecting a component gas in a sample comprising:

• a sample chamber for containing a sample gas including the component gas to be detected;
• source means for directing infrared radiation through the sample chamber in a preselected spectral band;
• detector means responsive to radiation incident thereon in the preselected spectral band passing through the sample chamber from the source means for producing a detector output;
• signal processing means responsive to said detector output for indicating the relative concentration of the component gas to be detected, said signal processing means including
• a circuit having first, second and third inputs and adapted to producing a difference output that is the sum of a signal applied to said third input and the difference between a signal provided to said first input and a signal provided to said second input;
• first means for applying said detector output to said first output and a zero-value signal to said second input with substantially nonabsorbent gas filling the sample chamber to produce an offset value on said difference output;
• second means for applying said detector output to said first input and said offset value to said second input with a sample gas including a component gas to be detected filling said sample chamber thereby producing a difference output that indicates the relative concentration of said component gas;
• third means for applying said detector output to said first input and said offset value to said second input with a substantially nonabsorbent gas filling the sample chamber to produce a trim value on said difference output;
• and
• wherein said second means includes means for applying said trim value to said third input.

An apparatus for detecting at least one component gas in a sample comprising:

• a sample chamber for containing a sample gas including the component gas to be detected;
• source means for directing infrared radiation through the sample chamber in a preselected spectral band;
• detector means responsive to radiation incident thereon in the preselected spectral band passing through the sample chamber from the source means for producing a detector output;
• multiplexing means for applying a plurality of filters during distinct time intervals between said source means and said detector means to time-multiplex said detector output, one of said filters having radiation transmitting characteristics that will provide an indication of the concentration of the component gas to be detected;
• and
• a correction circuit adapted to applying at least one correction factor to said detector output to provide a corrected output, said correction circuit being synchronized with said multiplexing means in order to apply a particular said correction factor to said detector output for said component gas to be detected during the interval of time that said one of said filters is between said source means and said detector means.

A method for detecting at least one component gas in a sample including the steps of:

• providing a sample chamber for containing a sample gas including the component gas to be detected;
• directing infrared radiation through the sample chamber in a preselected spectral band;
• detecting radiation in the preselected spectral band passing through the sample chamber and producing a detector signal;
• imposing a plurality of filters during distinct time intervals in the path of radiation to time-multiplex said detector signal, one of said filters having radiation transmitting characteristics that will provide an indication of the concentration of the component gas to be detected;
• and
• applying a correction signal to said detector signal in synchronism with said imposing to apply a correction factor to said detector output for said component gas to be detected during the interval of time that said one of said filters is in said path of radiation and thereby providing a corrected detector value.