| 摘要 |
<p>A light source is mounted on a pillar and includes an optical fibre, which is contained in a tubular support within the housing, and rearwardly projects outside the housing. The light source also includes a mirror which is displaceable by a motor such as to orient the beam either towards an opening, aimed at a spaced photodetector, or towards a reference photodiode to establish a reference for comparison with the light detected at the photodetector. The photodetector also includes a mirror assembly, rotatable by a stepper motor to be either in a measuring position, in which case it diverts the received beam towards a central photodiode surrounded by four servo-controlling photodiodes, or a reference position. Each of the five photodiodes produces an output to an amplifier, which supplies a signal representative of the received light signal intensity. The meter may be used to determine visibility at an airport.</p> |
