| 摘要 |
The invention relates to a device having an orifice covered by an optical device (3), which is to be prevented from being dirtied. For that reason the device comprises a housing (1), in which a ring-shaped socket (2) supporting the optical device is rotatably journalled by means of a bearing arranged around the periphery of the socket (2). Moreover, the socket (2) is provided with a rim of turbine blades (8) against which one or more jets of pressure air from nozzles (10, 11) in the housing (1) are directed.
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