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Control Cabinet
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A block diagram of the indoor control cabinet installation is given in the drawing above. It encorporates a programmable logic controller which is connected to a standard INTERBUS branch terminal, a eight-channel digital output terminal and a eight-channel digital input terminal via a local bus. The INTERBUS branch terminal is connected to a fiber-optic converter which provides the long-distance connection to the outdoor section of the system via one glass fiber pair.
The program executed by the PLC is hardly worth to mention. It just queries the states of outdoor input terminals and commands respective indoor output terminals into the same state and vice versa. The same functionality can also be obtained by use of a so-called field multiplexer but this one can not do anything else. So in order to also be able to provide some more sophistcated processing if necessary (e.g. recognition of travel direction) a simple PLC solution was preferred.
The digital input and output channels are all based on dry contacts. That means that every input channel can be controlled by simply connecting a switch; there is no extra power supply required. The output channels are potential-free relay contacts.
The power supply unit is made up from a lightning resp. surge protection, a 24 VDC power adapter and an uninterruptible power supply which can buffer power for at least three minutes.
All components are mounted on 35 mm DIN rail. The drawing below gives the mechanical dimensions of the scheduled parts.
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