METHOD AND DEVICE FOR THE MEASUREMENT OF THE CONCENTRATION OF GAS IN A GASEOUS MIXTURE

摘要

Light is transmitted via an optical fibre to a measuring cell containing the gas to be examined and is allowed to pass through the measuring cell, and the emergent light is transmitted via an optical fibre to a measuring device and compared in the latter with a reference light. It is known to utilise the absorption of light at an absorption wavelength characteristic of methane gas for this purpose. The object is now to determine the gas concentration using another principle. This is essentially achieved in that the change in the optical density of the gas mixture in a measuring cell is determined from a comparison with the beat frequency of the light occurring in connection with the Zeeman effect. For this purpose, a laser resonator has a magnetic field passing through it axially and consequently emits two polarised light beams of slightly different frequency which superimpose to produce a beat whose frequency is measured by means of photodiodes. The two frequencies are separated from each other, one is passed through the measuring cell and the other through a reference cell, both are again superimposed, the frequency of the measured beat is determined and the latter is compared with the frequency of the reference beat at the output of the laser.