Patent GB-816972-A (GB)
Title: Automatic changeover means for carrier circuits
IPC: B61L7/08
Filed: 1957-06-20
Abstract: 816,972. Electric selective signalling systems. WESTINGHOUSE AIR BRAKE CO. June 20, 1957 [June 25, 1956], No. 19473/57. Class 40 (1). A remote control and indication system transmitting data by a plurality of frequency channels, each channel comprising a transmitter and receiver for the associated frequency has means for replacing a faulty frequency channel by a spare frequency channel, a spare frequency channel being provided for both directions of data transmission. As described, the invention is applied to a known type of control and indication system comprising a central control office, Figs. 1a-1c, 1d (lower part) and a controlled field station, Figs. 1d (upper part), 1e, 1f, which control is effected on four frequencies A, A1, B, B1 transmitted over two transmission lines and indication at the office on four frequencies C, D, E, F transmitted over the same transmission lines. A spare control channel 1S and indication channel 2S is provided. In the at-rest condition of the apparatus, the four indication and both spare carrier transmitters are energized so that relays LC, LD, LE, LF at the office are energized. A code check relay CK, Fig. 1b, is held energized over a circuit including its contact a and contacts a of the relays LC-LF so that it is de-energized during a code transmission period, and re-energized by the final code step. Failure of indication carrier channel.-If the indication carrier channel C fails, then the relay LC is de-energized to release the relay CK. The office transmitter relay OT is then energized, is held over its contact a, and initiates a thrice repeated coding action. In the first step of the first code, the latch relay CHC, Fig. 1a, corresponding to the faulty channel C is operated to its reverse position over a circuit established by the alternately operating relays OY, OZ when the relay OY operates to its reverse position and the relay OZ to its normal position, and the relay 01, the first of a counting chain 01, 02, 03 which energize and release once each in each code. The first code then completes, relay OX releasing on the final step to complete a circuit for energizing the appropriate office change-over relay CHCP, Fig. 1b, which holds and disconnects the relay LC from the receiver C when contact b changes over, contacts c and d preparing circuits for connecting the relay LC to the spare receiver 2S. The second code is initiated by the release of the relay CK and energization of the relay OT. A control code character is transmitted to the station in the first code step to prepare circuits for substituting the spare transmitter. The receipt of this character causes the relay FCHC, Fig. 1e, to be energized over a circuit including contacts of the relay F1, the counting chain relays at the station being stepped by the onperiods of control carrier currents of frequency A or A1. The relay FCHC holds and by its change-over contact c interrupts the energizing circuit for the transmitter 2S thereby deenergizing the relay L2S at the office. The repeater relay L2SP releases shortly afterwards to complete the circuits for connecting the relay LC to the receiver 2S and for connecting the relay L2S to the receiver C. The release of the relay L2S causes a control character to be transmitted to the station to energize the corresponding relay L2SK thereby energizing its repeater relay L2SKP which holds and completes the substitution action by replacing the transmitter C by the transmitter 2S. Closure of contact c of the relay L2SKP completes a circuit to energize the transmitter C so that carrier current of frequency C will be transmitted to the office when the defective channel is repaired. A third code now follows on the first step of which the office relay CHC is returned to normal to close its contacts b, c, thereby completing indication registry circuits. Audible and visual indications of the failure of a channel may be provided by circuits not described. Resetting.-When notified that the defective channel has been repaired, the operator presses the reset button CHRSPB, Fig. 1d, to energize a relay RS which de-energizes a slow-torelease relay RSP. This causes relays ONOR, OSB, FNOR, FSB to momentarily release, the opening of contacts b of relays FNOR, FSB interrupting the holding circuit for the relay FCHC which releases to open the circuit for the relay L2SKP which also releases returning the station to its initial condition. The opening of contacts c of the relays ONOR, OSB releases the relay CHCP, Fig. 1b. The relay L2SP is re-energized and holds since the relay L2S is energized, the office thus being returned to its normal condition. Failure of control carrier channel.-Suppose that the system is at rest in a non-coding condition. The control carrier transmitters other than the spare transmitter are normally off, so failure is not detected until a code is initiated. The control carrier transmitters A, A1, B, B1 are energized over the contacts of the relay OT, the reception by the station of a correct control signal being indicated by the release at the office of the line indication relays LC-LF. The control line relays LA, LA1, LB, LB1 at the station energize to energize the station transmitter relay FT which in turn energizes the line repeater relay LP. The indication carrier currents are thus removed from the line circuit so that the relays LC-LF release. In the case of failure of the control channel A1, however, the relays FT and LP are not energized, and when the three control carrier currents are received at the station a circuit is closed to energize the change-over relay FCH thereby completing a circuit for the change-over relay FCHA1 corresponding to the defective channel which holds until manually reset. The office relay TP, Fig. lb, is energized and initiates a hunting action which continues until the spare transmitter 1S is substituted for the transmitter of the defective channel. Failure of transmission line.-The normal transmission lines 1, 2 are kept energized by a battery 13 and failure in a line causes the office relay ONOR and transmitter relay FNOR to release thereby de-energizing the slow-release relays OLCH, FLCH to change over transmission to the stand-by transmission lines 1, 2.