Infra-red gas analysers

Claim 1

AN INFRA-RED GAS ANALYSER COMPRISING A SOURCE OF RADIATION, MEANS DIRECTING SAID RADIATION INTO A SAMPLE BEAM PATH AND A REFERENCE BEAM PATH, A CELL CONTAINING A SAMPLE GAS UNDER TEST LOCATED IN SAID SAMPLE PATH, A DETECTOR COMPRISING MEANS DEFINING A CHAMBER, A DIAPHRAGM DIVIDING SAID CHAMBER INTO TWO SEPARATE COMPARTMENTS, A FIXED ELECTRODE LOCATED ADJACENT SAID DIAPHRAGM ONE COMPARTMENT RECEIVING RADIATION FROM THE SAMPLE PATH AND THE OTHER COMPARTMENT RECEIVING RADIATION FROM THE REFERENCE PATH, A FIRST GAS LOCATED IN BOTH COMPARTMENTS, SAID FIRST GAS BEING IDENTICAL WITH A GAS WHOSE PRESENCE IN THE SAMPLE GAS IS TO BE MEASURED, AN ADDITIONAL GAS LOCATED IN BOTH SAID COMPARTMENTS, SAID ADDITIONAL GAS LOCATED IN BOTH SAID COMPARTMENTS, SAID ADDITIONAL GAS HAVING A REGION OF ABSORPTION DIFFERENT FROM THAT OF ANY OF THE GASES PRESENT IN THE SAMPLE GAS, A BALANCING SHUTTER IN ONE BEAM PATH, FILTER MEANS INSERTABLE IN AT LEAST THE SAMPLE PATH DURING CHECKING PERIODS ONLY, SAID FILTER MEANS BEING ARRANGED TO ABSORB ALL THE WAVELENGTHS CAPABLE OF BEING ABSORBED BY GAS TO BE DETERMINED IN THE SAMPLE BUT TO TRANSMIT THE WAVELENGTHS CAPABLE OF BEING ABSORBED BY SAID ADDITIONAL GAS IN THE DETECTOR, AND A ROTATING-SHUTTER INTERRUPTING BOTH BEAM PATHS INTERMITTENTLY BETWEEN THE SOURCE AND THE DETECTOR.