| 摘要 |
The invention relates to a device for monitoring the presence of vehicles within specific traffic areas by means of at least one induction loop, the change in inductance of which is detected via an oscillator and passed onto an evaluation circuit, the pulses generated from the oscillations of the oscillator being converted into a timing signal which is proportional to the oscillator frequency and is digitally measured by means of a constant base frequency and the change in which signal, resulting from the inductance change, is determined in the evaluation circuit and is further processed as a control signal when a programmable threshold value is exceeded. In order also to be able to monitor relatively large traffic areas, namely relatively long rail sections, the induction loop is laid in the region of a rail line in such a way that the partial lengths of the induction loop which run parallel to the rails are arranged directly at the rail base and the rail line is constructed, by means of two short circuit connectors arranged at a distance from one another, to form a short circuit loop separated from the induction loop. At least one further switchable short circuit connector can be arranged between the short circuit connectors.
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