| 摘要 |
Track circuits, in conjunction with an evaluation circuit for two voltages, one of which varies as a function of the clear and occupied state of the respective track section (GS), serve to monitor tracks in railway safety systems. Synchronously controlled switching devices (G1, G2) are provided which draw the alternating voltage of a transmitting device (T1) and the comparison alternating voltage (T2) with predetermined period duration from the alternating voltage sources (T34, T35, T36 and T37, T38, T39, respectively) in such a way that the two voltages remain in a constant relationship with one another with respect to their phase angle. However in comparison with the phase angle of another alternating voltage, the phase angle varies with the predetermined period duration. Using electronic load relays (G11, G12, G13 and G21, G22, G23, respectively) and voltage detectors (U1 to U6), a satisfactory, correctly sequenced switching of the load relays (G11, G12, G13 and G21, G22, G23, respectively) is ensured. <IMAGE>
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