| 摘要 |
1416747 Road signs M AMANN 24 May 1973 [25 May 1972] 24883/73 Heading E1G [Also in Divisions G1 and G5] A sign includes a transparent element e.g. 34 or 134 movable between a light reflective or light emitting member 52 or 152 and an opening 20, 22 in a housing 12, and measuring means which detects the degree of dirt accumulation on the transparent element and, when it exceeds a set limit, actuates a drive means to move the element to replace the dirty section with a clean section. At set intervals, the drive moves either the transparent element or a separate test element on a small amount to a photoelectric measuring device consisting of a light emitting diode and photosensitive resistance 46 which comprises the measuring means. If the element is clean, the drive is switched off but, if it is dirty, the element is driven on sufficiently to replace the dirty section with a clean one. The said intervals may be dependent upon the ambient temperature. The drive may be controlled by a photometer so as to operate only after dark. The element may be a continuous belt passing through a cleansing bath 160 and past brushes 164-168 or may be a rigid, rotatable cylinder coated with P.T.F.E. |
