| 摘要 |
A gas monitor includes an infra-red source 5 enclosed within a housing 2 having inner surfaces which are reflective. Radiation emitted from the source 5 reflects off ellipsoidal surfaces 7 and 8 and intermediate planar surfaces 3 and 9 to be focussed at a sensor 6, 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 7 and 8 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.
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