| 摘要 |
The invention relates to a method of detecting the presence of a gas or a liquid in a conduit by sensing the reflective properties of a flat surface which is being obliquely illuminated by semi-monochromatic light on the said surface which is an inner wall of the conduit, said surface being optically reflective when a gas is present in the conduit, and transmissive when a liquid which has an index of refraction significantly higher than that of the gas is present in the conduit as well as to an apparatus therefor. |
