| 摘要 |
PURPOSE:To reduce the installation cost by measuring light transmitted through a gap and detecting variation in optical transmission loss due to the gap. CONSTITUTION:Optical fibers 1 and 2 are provided having end surfaces 1a and 2a opposite each other across the gap and both optical fibers 1 and 2 are fixed by optical fiber fixing members 3 and 4. Then, when an abutting part 12 abuts on a door which is open, a force operates as shown by an arrow A and the member 3 is pressed through a nut 10 to move toward the other member 4. This movement presses an outside pipe 7 and a coil spring 9 in compressing directions and the gap between the end surfaces 1a and 2a becomes small, so that the optical transmission loss DELTAP also decreased accordingly. For the purpose, light transmitted from one optical fiber to the other is measured to find the optical transmission loss due to the gap, whose width is calculated to decide an on-off state, i.e. whether the door is open or closed from whether or not the width is larger than a set value. Thus, the installation cost is reducible. |
