| 摘要 |
Frequency-modulated signals are used with a view to improved safeguarding of correct assignment of electrical signals for all-clear signalling and occupied signalling of a track circuit on the one hand and of an evaluation device on the other, specifically for each track circuit with a code which is typical for said circuit. A digital circuit with a period duration measuring device, in which the track voltage supplies the time base, serves to evaluate these frequency-modulated track voltages with a low modulation index. The pulses of a quartz generator (G) are counted by a multi-stage binary counter (BZ). The outputs of this binary counter (BZ) are connected to the inputs of a storage and converter circuit (SU). The latter is programmed in such a way that two address areas are specified while taking into account predetermined tolerances of the upper and lower frequency value of the track voltage, by means of which address areas a first or second identification is output only in the case of upper or lower counter results of the binary counter (BZ) lying in the tolerance range. The identifications are finally fed to a decoder element (DD) which only outputs an all-clear report for the respective track section in the case of frequency-modulated telegrams which are assigned to the respective track section. <IMAGE>
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