| 摘要 |
An electronic system which emulates the operation of a polar relay for applying coded pulses to railway tracks has separate signaling circuits having signaling devices responsive to a separate inputs which provide operating power to the circuits. The circuits are interlocked by connecting the inputs to the signaling devices in inverse relationship. One input excludes the other. The signaling devices may be light emitting isolators with switching transistors which control the application of current pulses through the rails of the track while isolating the track battery which supplies the current for these pulses from the local battery which provides the inputs to the signaling circuits. The signaling circuits establish current paths through the light emitting signaling devices at predetermined times after the inputs are applied to emulate the pickup and drop away time of the polar relay. The switching circuits use complementary symmetry power transistors which provide fail safe operation in the signaling system in the event of a short-circuit failure mode throughout. Dual sets of bridge circuits and transient absorbers protect against voltage surges from the track such as may be due to lightning. Operating windings for local circuit relays are connected in series with the power transistors and operate only in response to actual signaling conditions. The signaling circuits and the switching circuits are arranged so that operating current for a circuit which functions to produce track current pulses of one polarity is available only if the circuit which would provide track current pulses of the opposite polarity is inoperative so as to guard against unsafe signaling conditions. |
