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Overview
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The sensor system shown in the drawing above is based on a layout originally suggested by Aeroplan, Zürich. It assumes a pair of sensors located close to each other at a stop bar and a third sensor some 200 meters away. It must be noted that this is only an example; modifications are always possible.
Since each sensor is in fact an array there is a bundle of optical feeder cables emerging from each one which are guided to a shielded box installed beside the taxiway which contains the signal processing equipment. Each such box can service several sensors; the number of boxes used and their location is detemined by the endeavour to keep the sensor feeders short. It is assumed that a sensor system consists of sensors with not more than ca 200 meters of distance between them. Over such relatively small distances (<= 300 m) signals can be transmitted using PCS (Plastic Clad Silica or HCS, Hard Clad Silica) fibers with simple interfaces. Box 1 and Box 2 are connected this way. The distance to some indoor control cabinet which contains the interface to the host system, however, must be assumed to be much larger. Thus, Box 1 is connected to the control cabinet with a glass fiber cable which is suitable for large distances (<= 4200 m) but requires special interfaces. Only one such longdistance connection is required per sensor system.
By implementing an industrial field bus on this communication hardware arbitrary data can be exchanged between the control cabinet and the field boxes. In the current case these data are chosen for maximum simplicity. There is a trigger signal and an error signal transmitted from every sensor to the control cabinet and a reset signal for every sensor in reverse direction. Interfacing only comprises sensing the state of a dry contact at the transmitter and transferring this state to another dry contact at the receiver. Except from processing of the optical sensor raw signals all these tasks are accomplished with standard industrial components.
The control cabinet as well as the field boxes accept a 100...240 VAC supply. They have a maximum power consumption of 120W, but it is unlikely that this value will ever be reached. |
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