| 摘要 |
<p>The device comprises a sight glass (3) embedded in the door (1), a semitransparent mirror (5) inclined behind the sight glass (3) and of which the semitransparent surface (6) is adjacent to the sight glass (3) and an optical receiver (7) arranged in the reflecting axis of the mirror (5). The device is used in the building industry.</p> |
