Railway signal system

A railway signal system for monitoring a railroad track to produce a system output signal upon detecting a train on the monitored track, comprising:

• transmitter means for generating an electrical signal;
• coupling means for coupling such electrical signal to the track for transmission therein as a track signal;
• receiver means coupled to the track for receiving such track signal, said receiver means including detecting means responsive to a change in such track signal caused by such a train for detecting the same, and said detecting means including an amplifier means for developing a control signal having at least a DC signal component the voltage of which is proportionally representative of the voltage of such track signal, and said detecting means being responsive to such control signal for effecting production of such system output signal;
• and automatic gain control means for increasing the gain of said amplifier means when the voltage of such DC signal component drops below a predetermined level as such a train approaches the system tie points to the track, whereby upon occurrence of a train leaving the track island defined between the system tie points to the track the magnitude of such control signal rapidly increases and said detecting means also rapidly ceases to effect production of such system output signal.

A railway signal system for monitoring a railroad track to produce a system output signal upon detecting a train on the monitored track, comprising:

• transmitter means for generating an electric signal;
• coupling means for coupling such electric signal to the track for transmission therein as a track signal;
• receiver means coupled to the track for receiving such track signal, said receiver means including detecting means responsive to a change in such track signal caused by such a train for detecting the same and thereupon to effect production of such system output signal;
• and time delay lock-out means for maintaining production of such system output signal for a predetermined duration in response to the occurrence of said detecting means effecting production of such system output signal.

A railway signal system for monitoring a railroad track to produce a system output signal upon detecting a train on the monitored track, comprising:

• transmitter means for generating an electric signal;
• coupling means for coupling such electric signal to the track for transmission therein as a track signal;
• receiver means coupled to the track for receiving such track signal, said receiver means including detecting means responsive to a change in such track signal caused by such a train for detecting the same and thereupon to effect production of such system output signal, said detecting means including means for developing a control signal having an average substantially DC voltage component proportionally representative of the voltage of such track signal;
• broken rail detector means coupled to said detecting means for effecting production of such system output signal upon occurrence of a rapid increase in the voltage of such control signal caused by the occurrence of a broken rail in the monitored track;
• and disable circuit means coupled to said broken rail detector means for preventing the latter from effecting production of such system output signal when said detecting means has already effected production of such system output signal.

A railway signal system for monitoring a railroad track to produce a system output signal upon detecting a train on the monitored track, comprising:

• transmitter means for generating an electric signal;
• coupling means for coupling such electric signal to the track for transmission therein as a track signal;
• receiver means coupled to the track for receiving such track signal, said receiver means including detecting means for detecting such a train, said detecting means being responsive to a change in such track signal to produce a first signal when no train is detected and a second signal when such a train is detected for effecting production of such system output signal, said detecting means including means for developing a control signal having an average substantially DC voltage level proportionally representative of the voltage of such track signal;
• low signal detector means coupled to said detecting means for producing an AC output signal when the voltage level of such control signal is above a predetermined voltage and a DC output signal when such voltage level is below such predetermined voltage;
• output circuit means coupled to said detecting means for producing such system output signal when the latter has detected such a train and produced such second signal;
• and AC coupling means for AC coupling said low signal detector means to said output circuit means to supply a power input signal thereto, whereby a DC output signal from said low signal detector means will effect removal of such power input signal causing said output circuit means to produce such system output signal.

A railway signal system for monitoring a railroad track to produce a system output signal upon detecting a train on the monitored track, comprising:

• transmitter means for generating an electric signal;
• coupling means for coupling such electric signal to the track for transmission therein as a track signal;
• receiver means coupled to said track for receiving such track signal, said receiver means including a train detecting portion and a signal monitoring portion;
• said train detecting portion including train detecting means responsive to a change in such track signal caused by a train on the monitored track for effecting production of such system output signal, said train detecting means producing an AC output signal when no train is detected and a DC output signal when a train is detected;
• said signal monitoring portion including monitor means responsive to the voltage and current parameters of such track signal for effecting production of such system output signal when at least one of such parameters is outside a predetermined range of desirable levels, said signal monitoring portion producing an AC output signal when such parameters are at satisfactory levels and a DC output signal when at least one of such parameters is at an undesirable level;
• output circuit means for producing such system output signal, said output circuit means including first and second stages, each having an input for receiving a respective input signal to effect operation of the same, whereby upon termination of an input signal to at least one of said stages said output circuit means produces such system output signal;
• and first means for AC coupling said train detecting portion to said input of said first stage to supply an input signal thereto when said train detecting portion produces an AC output signal, and second means for AC coupling said signal monitoring portion to said input of said second stage to supply an input signal thereto when said signal monitoring portion produces an AC output signal.