Method and circuit arrangement for determining the entry and/or exit of

Abstract

A method and a circuit arrangement for determining the entry and/or exit of a vehicle into or out of a predetermined monitoring zone, which is defined by at least one inductive measuring loop whose change in inductance, which occurs as a result of the entry of a vehicle into the monitoring zone or the exit of a vehicle out of the monitoring zone, is used to control the oscillation frequency of an oscillator circuit is disclosed. In this method a measuring signal which corresponds to the oscillation frequency of the oscillator circuit and a reference signal which corresponds to a reference oscillation frequency are subtracted from one another. The difference signal thus formed is processed in an analysis device for display purposes. In order to achieve a relatively high degree of measuring accuracy, while employing circuit components which possess a relatively low operating frequency, it is provided that the measuring signal which corresponds to the oscillation frequency of the oscillator circuit is obtained and that on the occurrence of a first measuring pulse in a measuring pulse sequence derived from the oscillation signal of the oscillator circuit and with a reduced pulse rate, at the beginning of a measuring interval determined by a preselectable number of measuring pulses, a bistable trigger element is set to emit a specific output signal. On the occurrence of the output signal, which, for the duration of the selected measuring interval, counting pulses are counted with a pulse rate which is high in comparison to the pulse rate of the measuring pulses in a counting pulse counter whose counter signal, which is emitted at the end of the selected measuring interval, is made available as the measuring signal which corresponds to the oscillation frequency of the oscillator circuit.