Method and apparatus for monitoring maintenance of calibration condition in respiratory gas spectrometer

A method for monitoring maintenance of a desired calibration condition of a respiratory gas spectrometer for measuring the concentration of one or more predetermined components in respiratory gas samples, comprising:

• first providing first and second calibration radiation beams on corresponding first and second optical pathways, said first optical pathway passing through a corresponding first containment area of said spectrometer, and said spectrometer being in a desired calibration condition;
• first detecting an intensity of said first and second calibration radiation beams to obtain corresponding first and second calibration condition values;
• placing the spectrometer into use to measure the concentration of one or more predetermined components of respiratory gas samples;
• second providing first and second test radiation beams on said corresponding first and second optical pathways, said first optical pathway passing through the corresponding first containment area of said spectrometer, and said spectrometer being in an in-use condition;
• second detecting an intensity of said first and second test radiation beams to obtain corresponding first and second test condition values;
• and
• using said first and second calibration condition values and said first and second test condition values to monitor an in-use condition of the gas spectrometer in relation to said desired calibration condition, said using step comprising:
• comparing said first calibration condition value and said first test condition value to determine whether a difference therebetween exceeds a first predetermined value;
• comparing said second calibration condition value and said second test condition value to determine whether a difference therebetween exceeds a second predetermined value;
• alerting a user that variation from said calibration condition exists when both of said first and second predetermined values are exceeded.

A respiratory gas spectrometer comprising:

• an infrared radiation source;
• an optical assembly for receiving infrared radiation from the source and directing said infrared radiation on first and second optical paths;
• a sample gas chamber positioned on the first optical path and positioned so that the second optical path passes outside of the sample gas chamber;
• a detector for detecting an intensity of the infrared radiation passing through the sample gas chamber on the first optical path, for detecting an intensity of the infrared radiation on the second optical path passing outside of the sample gas chamber, and for providing corresponding first and second outputs;
• a memory device for storing calibration condition information established using said first and second outputs with the gas spectrometer in a desired calibration condition;
• and
• a comparator for comparing said stored calibration condition information with in-use condition information established using the first and second outputs with the gas spectrometer in an in-use condition, wherein the in-use condition is monitored in relation to the desired calibration condition.

A method for monitoring maintenance of a desired calibration condition of a respiratory gas spectrometer for measuring the concentration of one or more predetermined components respiratory gas samples, comprising:

• first providing first and second calibration radiation beams on corresponding first and second optical pathways, said first optical pathway passing through a sample gas chamber, wherein said sample gas chamber is purged to remove gaseous components corresponding with said one or more predetermined components, said second optical pathway passing through a reference gas chamber, and said spectrometer being in a desired calibration condition;
• first detecting an intensity of said first and second calibration radiation beams to obtain corresponding first and second calibration values;
• placing the spectrometer into use to measure the concentration of one or more predetermined components of respiratory gas samples, said respiratory gas samples being contained in said sample gas chamber;
• second providing first and second test radiation beams on said corresponding first and second optical pathways, said first optical pathway passing through said sample gas chamber, wherein said sample gas chamber is purged to remove gaseous components corresponding with said one or more predetermined components, said second optical pathway passing through said reference gas chamber, and said spectrometer being in an in-use condition;
• second detecting an intensity of said first and second test radiation beams to obtain corresponding first and second test condition values;
• and
• using said first and second calibration condition values and said first and second test condition values to monitor an in-use condition of the gas spectrometer in relation to said desired calibration condition.