Patent GB-1096891-A (GB)
Title: Improvements relating to remote supervisory and/or control systems
Inventor: NEW WILLIAM ERNEST
IPC: H04M11/04
Filed: 1963-10-30
Abstract: 1,096,891. Remote supervisory and control system. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. Oct. 27, 1964 [Out. 30, 1963], No. 42832/63. Heading H4K. A remote supervisory and/or control system comprises a control station and one or more out stations in which a communication link may be established, e.g. over the public telephone network, between the control station and the out station in response to an operation at the control station. Timing devices are provided at both the control station and the out station and the communication link is held so long as holding signals, generated by the timing device at the control station, are received at the out station within periods determined by the timing device at the out station. Fig. 2 shows a preferred arrangement of a control station in which an operator by means of switch 26 may connect a normal telephone 25 to a telephone line 24 so that he may dial the number of the required out station and be connected therewith over the normal exchange system. After dialling, the operator, via switch 26, disconnects his telephone instrument 25 and connects the supervisory and control equipment over line transformer 20. The supervisory and control equipment comprises: (a) a loud-speaker 22 and amplifier 21 over which the operator may hear messages from the out station; (b) three oscillators 17, 18 and 19 of different frequencies which may be energized to produce pulses of three respective frequencies to effect the control of equipment at the out station, the pulse length being determined by unit 16 and which of the oscillators is energized being determined by which of keys 12, 13 and 14 is depressed; and (c) a " hold " pulse generator 15 which causes pulses of oscillator 19 to be transmitted to the line for a quarter of a second once every three seconds, to be utilized at the out station to maintain the connection over the telephone system so long as the control station is connected to the line. Fig. 3 shows an out station in which ringing current received over the telephone line is detected in ringing detector 28b and starts the sequence controller 30. After a predetermined period, e.g. 12 seconds, an answering condition is placed on the line at unit 28a and switch unit 32 selects from a record store 33 a recording to be played back over the line announcing the out station number. After the station number has been announced twice the sequence controller 30 causes switch 32a to change over and replay to the line that one of a number of stored recordings selected by the switches 32b and 32c. After the end of this message the sequence controller operates switch 31 and connects incoming signals over the line transformer 29 to the filter and detector circuits 34 so that V.F. code signals from the control station may be detected and, via gate 40 and decoder 39, be entered into store 41 to be used to effect appropriate control operations at the out station. A further message, e.g. indicating the result of the control operation, may then be sent to line followed by a further control interval, the sequence repeating for as long as the connection is held. During the control phase of operation the " hold " pulses are detected by detector 37 and used to maintain the connection. A voice immunity circuit 38 is provided to prevent speech signals being incorrectly interpreted as control signals. Fig. 4 shows a portion of the sequence control circuit concerned with the reception and processing of the " hold " signal. Cam 42, which operates switches 43 and 43a is rotated by the record reproducing mechanism which makes one revolution during each control phase of the operation, i.e. switch 31, Fig. 3, in its lower position, and one revolution during each reproduce phase of the operation, i.e. switch 31 in the position shown in Fig. 3. During the control phase " hold " pulses from detector 37 are fed via switch 43 to store 45 during the first half of the cycle and store 44 during the second half. Store 45 is reset at the end of the control phase and ensures that, if a hold pulse is received during the first half of the control cycle the connection is held until the end of the control cycle, and store 44 is reset at the end of the reproduce cycle and ensures that if a hold pulse is received during the second half of the control cycle the connection is held until the end of the reproduce cycle. In addition switch 43a is closed during the first half cycle of each cycle to by-pass the gates 46 and 47 controlled by the stores 44 and 45 so that the connection is always held over the first half of each cycle. Release of the " hold " circuit 49, i.e. due to no hold pulses having been received from detector 37 during the previous control cycle and switch 43a being in its open condition, cause the sequence controller to be reset and the line circuit to be released at unit 28a, Fig. 3, to make the equipment ready to receive a further call from the exchange.