Method and apparatus for measuring gas, including standardisation.

摘要

Apparatus for measuring a gas comprises a tube (16) along which a beam (22) of radiation proceeds from a source (20) to a detector (24). The tube (16), which might be disposed transverse a chimney stack, has lower and upper apertures (26a, 26b), through which the gas can enter the tube and leave it. Each aperture can be opened and closed either by a rotatable apertured inner tube (18) or by respective doors (18a, 18b) or sets of doors (118a to 119b). The apparatus permits standardisation of measurement according to Beer's law either at a single frequency or using two frequencies of radiation.