Gas spectrometer construction having an improved alignment feature

For an across-the-stack gas analyzing spectrometer of the type including a gas detector assembly on one side of the stack, and a radiation source assembly on the opposite side of the stack, with a stack opening associated with each assembly to permit the transmission of radiation therebetween, and having:

• air window assembly means connecting at least one of said radiation source and detector assemblies to said stack and including a hollow central core part through which clean air from an external source is passed into said stack to prevent flow of contaminated gas from aid stack toward said source or detector assembly, the improvement comprising:
• air window tube means, of substantially smaller diameter than said stack opening, so as to provide an annular space therebetween, extending into said stack opening from said air widow assembly means;
• said air window tube means includes opening means therein to direct air into said annular space between said tube and stack opening to reduce contaminant build-up in said annular space;
• and
• spherical joint means between said air window assembly means and said stack to accommodate aligning said radiation source assembly with said detector assembly across said stack.