Patent GB-723373-A (GB)
Title: Two-way facsimile telegraph system
IPC: H04N1/36
Filed: 1952-07-18
Abstract: 723,373. Facsimile telegraphy. CREED & CO., Ltd. July 18, 1952 [Aug. 8, 1951], No. 18215/52. Class 40 (3). In a two-station facsimile system with combined transmitter-receiver instruments controlled by " send " and " receive " switches and each having a paper-carrying drum driven by a synchronous motor, operation of the " send " switch at one station causes its drum to rotate continuously and to send phasing impulses to the other station, at which operation of the " receive " switch closes an interrupted circuit for its drum motor so that it rotates at a slower effective speed until the two drums are brought into phase. The circuit arrangements illustrated are specially designed for use with instruments constructed as described in Specification 723,352. Normal operation. Operation of "send" switch 34 energizes relay PWR from mains A-B and energizing the transmitting amplifier circuit TP, the lamp transformer 66, and the drum and chopper-disc motors DM, CM. At the same time rectifier SR applies positive battery to lead 90. Relay ACR operates from the mains and completes a circuit from battery lead 90 over leads 94, 96, 99, 101 to line L2. This connection is interrupted once per revolution of drum 20 by relay LP connected to a commutator contact, a delay circuit DN in the circuit of relay LP preventing its operation until the drum is rotating at full speed. The circuits at the receiving station are identical with those at the transmitting station but the lines L1, L2 are cross-connected. At the receiving station, relay LR operates but does not respond to the interruptions by reason of a shunt-circuit through condenser 122. Relay LR connects up the calling buzzer and when " receive " switch 36 is operated, power relay PWR operates, the buzzer is disconnected, the receiving amplifier RP is energized, and the drum motor is driven over a circuit including contacts 112 of relay LP which circuit is interrupted once per revolution of the drum so that the motor runs effectively below synchronous speed. At each operation of relay LP the shunt-circuit through condenser 122 is opened, so that when line relay LR receives an interrupting impulse from the sending station at the same time that relay LP operates, indicating that both drums are in the same phase, the line relay releases and relay PH, no longer short-circuited, pulls up. Relay PH short-circuits relay LP to prevent further interruptions of the drum-motor circuit, energizes the feed motor FM for the longitudinal motion of the drum and the stylus motor SM for moving the stylus 24 into contact with the drum (see Specification 723,352) and connects positive battery to line L2 to operate the line relay LR at the transmitting station. Here relay PH operates at the next pulse through relay LP and starts the feed motor FM. The " send " switch is automatically released by the drum at the end of transmission (or manually by " stop " button 38 in the case of a short message) and battery is removed from line L2. At the receiving station, relay ACR operates over a switch closed during the movement of the drum and connects up a buzzer to notify the receiving subscriber. Preventing incorrect operation. If a calling subscriber presses the " receive # switch by mistake, the momentary operation of relay BR energizes relay ACR which locks up and sounds the buzzer. If a called subscriber presses the "send" switch by mistake, relay PWR completes an alternative circuit for the buzzer which thus continues to sound after the switch has been operated. If both subscribers operate their " send " switches at about the same time, slow-release relay TS at each station, which normally operates momentarily over condenser 208 when a " send " switch is operated, will lock over a front contact of the line relay LR, release relay ACR and sound the buzzer until one subscriber presses his " stop " button.