Abstract: There is disclosed a gas sensor comprising an electromagnetic radiation source, a detector which is sensitive to radiation from the source and a waveguide which comprises at least a part of an optical path from the source to the detector through a gas sample, the waveguide comprising a first waveguide portion which extends from the radiation source and a reflector which is arranged to change the direction of and laterally displace radiation conducted from the source through the first waveguide portion into a second waveguide portion which is separate to the first waveguide portion and which conducts received radiation towards the detector. The gas sensor can be formed as a layered structure. A convoluted passage allows gas access to the optical path.

Abstract: In a catalytic sensor, a bead is located within a can having an aperture in its front surface. The bead is surrounded by thermally insulating material such as glass fiber and a filter material is arranged between the bead and the aperture in the can. This acts to remove H2S or other inhibiting gases before they reach the bead and impair its performance. The thermally insulating material allows the filter material to be included whilst still permitting the bead to be operated at a high temperature.

Abstract: A gas monitor includes an infra-red source enclosed within a housing having inner surfaces which are reflective. Radiation emitted from the source reflects off ellipsoidal surfaces and intermediate planar surfaces to be focussed at a sensor, being reflected five times. Radiation is absorbed by gas within the housing and a comparison of the source intensity and detected intensity gives a measure of the gas concentration. Use of ellipsoidal reflective surfaces directs emitted radiation along a plurality of routes having substantially the same path length, hence giving an accurate measure of the gas concentration with a compact device. In another embodiment, off axis parabolas are used to direct the radiation through the gas.