Method and apparatus for eliminating and compensating thermal transients in gas analyzer

A gas analyzer comprising:

• a measuring volume for through flow of a sample gas mixture, at least one gas component of which is to be analyzed for determining its concentration in said mixture, and having first and second transparent ends;
• a radiation source for providing a beam of electromagnetic radiation having a wavelength range, said beam directed to pass said measuring volume through said first and second transparent ends thereof;
• a heat sink for said radiation source;
• at least one thermal detector having an active radiation detecting sensor element with at least one support structure and receiving the radiation exiting said measuring volume, said thermal detector having a reference sensor element within the same support structure and protected from said radiation, said thermal detector generating an output signal indicative of a property of said at least one gas component of said mixture in the measuring volume;
• a thermal mass:
• formed of a material having high thermal conductance;
• having a cavity with a bottom step and a rim, and a first length therebetween;
• and
• extending towards the radiation source;
• in said at least one support structure:
• a frontal edge and a base plate lip, and a second length therebetween;
• a radial gap between the thermal mass and the support structure;
• and
• press means urging said support structure in said cavity;
• whereupon, depending on the predetermined difference between said first length and said second length, a more efficient thermal contact is either between said frontal edge and said bottom step, or between said base plate lip and said rim.

A method for determining a concentration of at least one gas component in a sample gas mixture by providing a radiation source that directs a beam of electromagnetic radiation having a wavelength range to pass a measuring volume, through which said sample gas mixture is delivered, and by detecting intensity of a rest radiation exiting said measuring volume and said at least one optical bandpass filter, the method comprising the steps of:

• transferring generated heat from said radiation source to a heat sink;
• allowing said rest radiation to hit an active radiation detecting sensor element in a thermal detector and protecting a reference sensor element of the same thermal detector from said rest radiation;
• said thermal detector having a support structure carrying said detecting and reference sensor elements, and generating an output signal indicative of a property of said at least one gas component of said mixture in the measuring volume;
• evening out temperature differences around said thermal detector by allowing heat to be conducted in a thermal mass having high thermal conductance and dimensions to surround said thermal detector and extending towards said radiation source;
• thermally isolating said thermal mass, said measuring volume, and said radiation source from ambience by at least one thermal barrier;
• conducting said generated heat from said heat sink along at least thermally conductive outer surface layers;
• arranging one or several contacts between said support structure of the thermal detector and said thermal mass such that mean heat flow times between said one or several contacts and said reference sensor element along a convection route and a conduction route are at least approaching each other.