Patent GB-790768-A (GB)
Title: Control circuit for pulse generator
IPC: H04N5/06
Filed: 1954-06-11
Abstract: 790,768. Pulse generating circuits. STANDARD TELEPHONES & CABLES, Ltd. June 11, 1954 [June 17, 1953], No. 17292/54. Class 40 (6). In a system for supplying a reliable source of pulses such as described in Specification 702,692 a control circuit is provided which disconnects one or other of the two pulse sources when that source develops a fault. Half of the basic pulse generator is shown, Fig. 2, the left-hand half being exactly similar to that shown. The oscillator OSC produces pulses Pa22, Fig. 3, the corresponding oscillator in the left-hand section producing a pulse Pa 12. The output of the oscillator is fed through an amplifier to a phasesplitting circuit PHS1 providing an output Pa22 and its inverted form. The latter is fed over synchronizing lead L21 to the corresponding oscillator to maintain synchronism. The trailing edge of the negative-going pulse from PHS1 is applied to a mono-stable multi-vibrator MMV1 triggering it to produce a pulse Pa23 which is fed through phase-splitting circuit PHS2, giving an output Pa23 and an inverted form at terminal P9. The pulse Pa23 is fed through pulse-shaping network PSH to provide the triggering pulse Pa24 which causes a second mono-stable multi.-vibrator MMV2 to operate, generating the pulse Pb23 which is integrated to provide pulse Pb24. This pulse is applied with the differentiated pulsePb25 derived by circuit DIF from the negative-going version of pulse Pa23 appearing at P9. Amplifier AMP2 is biased so that neither of the input pulses is effective by itself but when the peaks of the pulses Pb24, Pb25 coincide an output pulse is generated which is effective to trigger the longtime constant circuit MMV3. This circuit is reset by a pulse derived from the point P4 in the left-hand generator giving a pulse which is a negative-going version of Pa12. An output pulse Pb26 is generated at point P12 which may be fed through a cathode follower CFL. The pulse Pb16 from the left-hand generator is applied over lead L13 to a gate G2 to which the inhibiting pulse Pb26 is also fed. As long as synchronism exists between the pulses Pb16, Pb26 there is no output from the gate G2 but when a pulse exists on line L13 and no inhibiting pulse Pb26 is effective, an output from the gate occurs to operate the device A2 which removes the power supply from line L2 and operates relay Br2 to disconnect the terminals Pa22, Pa23 and Pa24, the relay locking over contact br1 and reset key K. The gate may be a gas tube connected as described in Specification 702,692. If pulse Pb26 fails or shortens causing the positive-going edge to lag as may occur if pulse Pa22 lengthens, then the comparator operates. If the pulse Pa22 shortens, thereby bringing forward the positive-going edge of pulse Pb26, then the wrong device A would operate. This may be overcome by arranging that the pulse Pa24 is derived from the leading edge of pulse Pa22, so that only when the pulse Pa22 is the correct length will the pulses Pb24, Pb25 coincide to provide a correct output pulse Pb26. It is stated that if a pulse generator of the type employed in Specification 746,622 is employed the output pulse Pa22 is unlikely to decrease and will either lengthen or fail completely. A pair of generators may feed a pair of distributers in turn feeding power amplifiers, Fig. 4 (not shown), with cross-connections so that failure may occur in more than one of the stages without the system ceasing to provide the required pulse trains.