Alternating current track circuits

Alternating current track circuits for several adjoining track sections of a stretch of railway track, each of the track circuits comprising an alternating current code transmitter and an alternating current code receiver connected to track rails at opposite ends of an associated section for detecting track occupancy, for communicating signal control rate codes through the track rails and for detecting broken down insulating rail joints which may be used to define boundaries of the several track sections, wherein improvements in the track circuit for each track section comprise;

• a. circuit means including an alternating current line circuit extending along the stretch of railway track for normally communicating alternating current from the line circuit at a selected modulated rate code through rails of the associated track sections, current in any two adjoining track sections being of opposite instantaneous polarity for broken down joint protection, and
• b. the circuit means comprising means responsive to the rate coded alternating current communicated through the track rails for governing energization of a track relay comprising,
• 1. phase sensing means including comparator means for comparing the rate code modulated alternating current communicated through the track rails with a steady reference source connected to the line circuit and for generating an output rate code pattern comparable to modulations in the track rails only provided that the alternating current in the track rails is substantially 180.degree. out-of-phase with the reference source of the associated track circuit, and 2. means including a flip-flop circuit and a low pass filter for energizing the track relay only in response to the direct current rate code pattern output of the phase sensing means.