Radiation detection of gas compositions

Claim 1

Equipment for the monitoring of gas in-situ comprising an infra-red source adapted to propagate a radiation beam through ducting or the like through which the gas to be analysed passes, a detector spaced from the infra red source responsive to radiation from the beam, a band-pass filter in the beam path to restrict beam radiation incident on the detector to a predetermined wavelength range, and a filter cell adapted to be positioned in the radiation path between the detector and the source, said cell being filled with the gas component requiring analysis, the detector and source being arranged such that the detector is responsive to beam radiation that passes in the ducting only through the gas to be analysed and to beam radiation that passes through the gas to be analysed and the cell, the detector being connected in a circuit including first means for measuring radiation passing through a first radiation path, second means for measuring radiation passing through a second radiation path, said gas to be analysed being in said first and second radiation paths, said gas component filter cell being in only said second radiation path, third means responsive to said first means and second means respectively for obtaining two levels of radiation, fourth means for determining a difference between the two levels of radiation, a fifth means for dividing the difference by either of the two levels of radiation received by the detector, an output of said circuit being a function of the amount of monitored gas present in the gas flow, including calibration means comprising a second infra red source generating radiation along a sight path, said sight path including an enclosure containing a fixed concentration of gas or no gas, said detector being selectively exposed in said sight path for equipment calibration.