| 摘要 |
<p>The water detecting apparatus (2) has a source (10) of infra-red radiation which is reflected off the inner surface (12) of a pipe wall (14) onto a mirror (16) directing the infra-red signal along a path (18) to an infra-red detector (22) connected by an electrical signal path (24) to an electronic control (26). The path (18) is interrupted by a rotating chopper (28) having windows occupied by two optical filters (34 and 36). The filter (34) only passes an infra-red signal of wavelength 1900 nm. (nanometres) which is absorbed by water, whilst the filter (36) only passes an infra-red signal of wavelength 2200 nm. another wavelength absorbed by water but not to the same extent as the 1900 nm. wavelength. The 2200 nm. wavelength serves as a reference signal. When the strength of the infra-red signal passed by filter (34) decreases in relation to the strength of the infra-red reference signal passed by filter (36), this is due to water on the surface (12) absorbing the 1900 nm. wavelength more than the 2200 nm., and the control (26) causes indicator (6) to indicate the presence of the water.</p> |
