Patent ID: 6885453

Claim:
A gas permeable probe for use in an optical analyzer for an exhaust gas stream flowing through a duct or chimney, the probe comprising: an elongate hollow structure having first and second ends and a side wall, with an optical cavity defined between said first and second ends within said side wall, a filter forming part of said elongate hollow structure, a mounting structure at said first end adapted for mounting said elongate hollow structure within said duct or chimney including a tube disposed within the mounting structure having first and second opposite ends, an optical window at said first end permitting a light beam originating from an optical analyzer to enter into said optical cavity to travel from said first end to said second end, said mounting structure comprising a first mounting flange at said first end of said elongate hollow structure, said first mounting flange containing said optical window, the probe further comprising a mating flange secured to said second opposite end of said tube and sealingly connected to said first mounting flange, a ring-shaped connecting member between said first mounting flange and said mating flange and a ring heater disposed around said connecting member, said mating flange being connected to said connecting member and said first mounting flange being connected to said connecting member, respective seals between said mating flange and said ring heater, between said ring heater and said connecting member, between said connecting member and said first mounting flange and between said first mounting flange and said optical window, and a retroreflector provided at said second end for returning said light beam to said first end of said hollow structure, wherein said first opposite end of the tube is located remote from said first end of said elongate hollow structure and is closed by a first window adapted to transmit said light beam from an optical analyzer into the tube and said second end of said tube is closed by said optical window adapted to transmit said beam of light from said tube into said optical cavity and said returned light beam from said optical cavity into said tube, said tube thereby defining a closed cavity, said closed cavity being one of an evacuated cavity and a cavity containing a neutral gas.