Patent GB-1399589-A (GB)
Title: Track circuit signal repeaters and track circuit arrangements
IPC: B61L23/16
Filed: 1973-11-20
Abstract: 1399589 Track circuit WESTINGHOUSE AIR BRAKE CO 20 Nov 1973 [21 Nov 1972] 53702/73 Heading B7N In a long track circuit on a track for both way traffic the circuit is normally fed at one end with D.C. pulses and repeater stations are provided at locations intermediate the circuit ends to receive and retransmit the pulse signal. The circuit has insulated joints J at its ends but not at the intermediate locations. The circuit is normally fed with D.C. pulses from location 4 which is repeatedly controlled by a series of counting relays 4CRA, 4CRB and 4CRC, switched by a coding relay 4CT, such that in each switching sequence the location applies a D.C. pulse to the track, then applies a short circuit across the track and then connects a track relay LTR across the track. The polarity of the D.C. pulse is such that polar relay-3TR at location 3 is picked up also picking up its repeater relay 3TP. Via front contacts of these relays capacitor 3C1 is charged and when the track relay releases this is discharged through a further repeater relay 3TPP picking this up. During the release delay period of relay 3TP a D.C. pulse is applied to the track circuit of such a polarity as to operate track relays at the adjacent locations 2 and 4 but at location 4 a short circuit is connected across the track at this time so the pulse is only effective at location 2. After relay 3TP has fallen away at location 3 and until the second slow to release repeater 3TPP also releases a short circuit is connected across the rails. Location 2 is similar to location 3 and supplies a D.C. pulse to the track which is polarized to actuate the track relays at its adjacent locations, however as location 3 has a short circuit across the track at this time the pulse is only effective at location 1 where track relay RTR responds and when released at the end of the pulse picks up its repeater relay RTP which has a sufficient release delay to remain up between pulses. Contacts b of the relay RTP control signal RG and indicate the unoccupied state of the track circuit. Assume a train has to move right to left through the circuit a relay LAS is released from a remote control point whereby relay LTR at location 4 is dircetly connected across the rails and the D.C. pulse signal is cut off thus preventing the repeating action at locations 3 and 2 so that no pulse is received at location 1. When this occurs relay RTR fails to pick up and its repeater RTP drops away so that via back contacts a of these relays a counting chain of relays ICRA, ICRB, ICRC and ICRD is energized and controlled by the code relay ICT to generate a D.C. pulse sequence similar to that normally occurring at location 4. The signal now passes through the track circuit in the opposite direction and after repetition in locations 2 and 3 actuates track relay LTR at location 4 and thus alternates picking up its repeater LTP which remains up until the train enters the circuit. Release of this relay and relay RTP at location 1 signals the circuit as occupied. As the train passes location 4 the drop away of relays LTR and LTP re-energizes the counting chain which with relay contact LAS now picked up applies D.C. pulses to the line behind the train. As the train moves through the circuit these pulses from location 4 are repeated by locations 3 and 2 and because of the fewer number of counter relays at location 4 than at location 1 a pulse from location 4 repeated from locations 3 and 2 occurs during the period at location 1 when the track realy RTR is connected to the track, pick up of the relay and subsequent pick up of its repeater RTN cuts off the supply to the counting relays at location 1 and its revert to a receiving location.