Patent GB-753928-A (GB)
Title: Improvements relating to coded carrier remote control systems
IPC: B61L7/08
Filed: 1954-05-28
Abstract: 753.928. Electric selective signalling. WESTINGHOUSE AIR BRAKE CO. May 28, 1954 [May 29, 1953], No. 15853/54. 'Class 40 (1) In a remote control system wherein a coded "control" current of one carrier frequency f1 is sent from an office to effect a selective control operation at one of a plurality of line stations, and a change of state of a device at a station is indicated at the office by transmitting coded "indication" current of a second carrier frequency f2 common to all stations, the office retransmits a received indication code at the carrier frequency f1 to check step-by-step and co-ordinate the sending of indication codes from different stations, a retransmitted code rendering all stations except a selected one ineffective to transmit. Preferably a pilot carrier of frequency f2 is applied continuously to the transmitting line or other medium for controlling the indication transmitter at each station so that all station transmitters generate at the same frequency and in phase, as disclosed in Specification 737.617. When the pilot carrier is not used, further circuitry is necessary at each station for co-ordination of the transmission of control and indication codes; the pilot carrier may, however, be used with this additional circuitry. Fig. 2 shows the apparatus of any one station, and Fig. 1 shows the office equipment of which only one control panel OCP, that associated with the station of Fig. 2, is shown. Transmitting a control code. On the selected station control panel OCP, Fig. 1, a lever ARL corresponding to the desired control (only one lever ARL is shown) is moved to its other position and the start button SB depressed to energize a start relay OST. Relay OST locks and energizes a master relay OM which also locks and, in known manner, e.g. as described in Specification 589,750, actuates a transmitting relay OT, by way of a coding unit OCU, in accordance with a predetermined time code, the first portion of which identifies the selected station and the second portion the selected apparatus to be controlled at that station. An oscillator VT1 of the control transmitter CT normally transmits unmdoulated carrier at frequency f1 to the line 1LW-2LW by way of amplifier VT2, transformer T1 and filter F1. and is keyed by the transmitting relay OT to code the carrier correspondingly. At all stations the control code carrier f1 is filtered at F4, Fig. 2a, and by way of a control receiver CR e.g. as described in Specification 737,617, actuates a code follower relay FC. A coding unit SCU similar to that at the office interprets the control code received by the follower relay FC and, in known manner, at the selected Station only, selectively energizes one of a group of control relays of which only the selected one, HS is shown. This relay effects the desired control of the selected device AR, e.g. a railway side 'signal, or switch operating mechanism, which is assumed to have only two operative positions. Control of indication carrier by pilot carrier. The pilot carrier frequency f2 is continuously fed by an oscillator VT3, Fig. 1, to line over a filter F2, and at each station, is passed selectively by a filter F5 via a receiver PR to a frequency converter stage BA, which selects e.g. the second harmonic of f2 as indication carrier frequency f3 this frequency passing via amplifiers LTS ,PAM, and a filter F6 to line only when the stages BA, LTS are keyed. Transmitting an indication code. Movement of any device AR. Fig. 2, shifts a contact 30 correspondingly to de-energize a start relay FST which energizes a master relay FM. This relay actuates a transmitting relay FT via a coding unit SCU, in a manner similar to that of the office transmitting relay OT, in accordance with a time code indicative of the station and the particular device AR in question. The transmitting relay FT keys the stages BA, LTS of the station transmitter thereby connecting the coded carrier f3 to line. When a pilot carrier is not used the transmitting relay OT keys a transmitter IT, Fig. 2a operating at frequency f3 but otherwise similar to the office transmitter. At the office the coded indication carrier f3 is filtered at F3 and fed through an indication receiver IR, e.g. as described in Specification 737,617 to actuate a code following relay OC. The code received by the follower relay OC is repeated by a relay OR to the coding unit OCU which interprets the code and, in accordance therewith, actuates selectively the indicator relay WK and lights the indicator lamp NL corresponding to the actuated device AR, Fig. 2. Re-transmitting an indication code. Provided the master relay OM at the office is released, i.e. no control signal is being sent, the code following relay OC keys the transmitter CT to retransmit the indication code to line at frequency f1, so that each indication code step is repeated back at the control signal frequency f1 substantially simultaneously with its reception at the office. At all stations the code following relay FC responds to the retransmitted code. At all stations other than the transmitting station the FC relays pass the retransmitted code to their coding units SCU thereby preventing these stations from transmitting. At the transmitting station the code following relay FC should operate in step with the code transmitting relay FT and this is checked by relays CD1, CD1P. Relay CD1 picks up if the correct stepping is not maintained and stops further transmission of the indication code. Code co-ordination and preference arrangements. If a control and one or more indication signals are initiated at the same time the first pulse of the control code which is made long, holds the code following relay FC at each transmitting station for a longer period than the station transmitting relay FT, since the first step of all indication codes is made short. The relatively long operation of FC functions, in known manner, to release a relay IL in the code unit SCU and operates a code disagreement relay CD which de-energizes the master relay FM to change the unit SCU from transmitting to receiving and causes the indication code to be stored. The control signal is thus given preference. If two or more indication signals are initiated simultaneously, the resulting interference causes the check relay CDI to operate at each of the stations concerned to suppress transmission. The slow release relay CDIP at each of these stations then energizes the code follower relay FC and its right hand winding to advance the associated coding unit SCU and thereby operate FT which de-energizes FC. Relays FC. FT then interact to advance the associated code unit SCU relay chain until the relay S at one of the stations in question nicks up on its selected code step. Preference is thus given to the station whose S relay is first to pick up i.e. the station having the lowest station number. The operated S relay connects indication carrier f3 to line to actuate relay OC at the office which removes control carrier f1 from the line until release of relays LBP, S in the unit SCU, to lock the office and the interfering stations against transmitting. At each of the non-preferred interference stations, relay CD1 is released and a relay SS picks up and locks to hold the station in receiving condition and store its indication. After the SS relays of these "lockedout" stations have been operated, the preferred station proceeds to send its indication code. The SS relays at the non-preferred stations are held until the preferred station has completed its indication signal, when each such station may initiate the sending of the stored code. Should there be more than one station concerned, preference is again determined as indicated above. During the preference or separation determining operation described above, the office or another station may initiate a code signal and send it without waiting provided that the S relay at the preferred one of the interfering stations has not operated. To prevent loss of a control code sent to a station in the process of separation, an office look-out relay SCP is provided and is operated to reset the office coding unit if the S relay in the selected sation coding unit does not pick-up on the same step as the S relay in the office coding unit. It also assures that transmission of a control code cannot be completed by the office coding unit unless it is being received by the selected station. The checking relays CD1, CD1P may be dispensed with when a pilot carrier is used.