GB642725A - Improvements in or relating to gas analysers - Google Patents

Abstract

<PICT:0642725/III/1> In a known system for detecting the presence of a particular gas depending on the fact that a given gas absorbs infra-red energy mainly from a characteristic portion of the spectrum, radiant energy from heaters A interrupted by a rotary shutter i is passed through similar tubes B to similar chambers C containing the gas in question and communicating with the respective halves of a third chamber divided by a diaphragm D. One only of the tubes B contains the sample to be tested. In the absence of the gas from the test sample, both tubes pass the characteristic radiation equally to chambers C and no effect is produced. If, however, the gas is present, the characteristic radiation is absorbed by the sample and the associated chamber C is heated less than the other. As a result a pulsating pressure difference is caused between the two chambers and the resulting vibration of the diaphragm D which forms a condenser with a perforated plate is detected electronically. In the present invention, the system is adapted for the detection of two or more gases by filling the chambers C with a mixture of these gases and providing filters F for the absorption of those parts of the spectrum that are characteristic of the gas or gases with which any particular test is not concerned. A single filter only may be used since the tube B used for comparison purposes contains dry CO2 free air and may be partially blanked off to keep the energy in the two paths the same. Liquid or solid filters may be used.