Patent GB-276746-A (GB)
Title: Improvements in or relating to electric signalling systems
IPC: H02J13/00
Filed: 1926-06-03
Abstract: 276,746. Automatic Telephone Manufacturing Co., Ltd., and Remington, C. June 3, 1926. Tell-tale apparatus.-In a system for supervising at a central station the condition of apparatus at a plurality of substations connected to a common pair of line wires, means are provided whereby when the lines are busy signalling from other stations is prevented. Fig. 1 shows the apparatus at a substation and Fig. 2 the apparatus at the central station. The substations are connected across the line wires A, B leading to the central office and are associated with a wire C which does not return to the central station and is used exclusively for providing a '' lock out " circuit for any station which tests the lines during signal transmission. The condition of each unit, such as the circuit breaker CB, is indicated by a pair of signal lamps GL2, RL2. The units and lamps are respectively associated with synchronously driven step-bystep switches RLS, RLSA which are rotated each time a unit changes its position. Testing the line wire to ascertain whether free or busy. When a circuit breaker, e.g. CB, changes its condition, a relay A is energized over the wiper 1 of switch RLS and the momentarily closed contacts 11, 12 associated with the circuit breaker. If another substation is signalling over the lines A, B, the relay A at the testing station completes a circuit over the line A, contact 15, relay SA1 normal contact and wiper 3 of switch MS and line C, since at the signalling station battery is connected between the lines A, C. The relay SA1 is thereby energized to open the contacts 16, 51 and prevent the transmission of impulses from the testing station. If the line is free, the relay SA1 remains de-energized and the following operations take place. The relay A energizes the relay B which closes the circuit of a slow-acting relay SA2 over the contact 16. The relay SA2 operates the magnet OM over the contacts 21, 51, 22 to step forward the switch MS and simultaneously energizes a relay SA3. After an interval the relay SA3 opens the circuit of the relay SA2 and de-energizes the stepping magnet OM. Relay SA3 is thereby de-energized to again energize the relay SA2. These relays are thus operated alternately to generate impulses for stepping the switch MS. The switch MS is operated until its wiper 1 engages the marked contact 24 to close a circuit for the relays D, C which respectively prepare the circuits over the lines A, B and transfer the impulsing circuit from the magnet OM to the stepping magnet M2 of the switch RLS. When the wiper 1 of the switch MS engages the contact 24, the wiper 3 connects negative battery to the line C and the relay D connects positive battery to the line A so that if another station tests the lines after the initiation of the supervisory signal the relay A at that station completes a circuit for the relav SA1 to prevent the transmission of signals. The switches MS at the various stations may have similar or different marking. Different marking ensures the transmission of supervisory signals in sequence in the event that circuit breakers at two or more stations change their positions simultaneously. In modifications the guarding circuit over the lines A, C may be completed immediately relay A or relay B energizes or immediately the switch MS steps off normal. Supervisory signalling. After the operation of the relays C, D by the switch MS the switch RLS is stepped forward under the control of relays SA2, SA3. Relay SA3 simultaneously operates contact 23 to transmit impulses over the lines AB and intermittently energize a relay M which operates the stepping magnet MA of the switch RLSA. The circuit breakers are associated with the first, third, fifth &c. contacts in the bank of wiper 4 of switch RIS and in the " closed " positions of the circuit breakers these contacts are marked over contacts such as 12, 36. Two impulses are transmitted over the line wires A,B for each circuit breaker and when a breaker is in its' " out ' position these impulses are of the sames polarity and energize a polarized relay PR2 which closes a circuit over the wiper 2 and the even contacts of switch RLSA for a relay FO, GO, or LHO as the stepping operation progresses. When, however, the wiper 4 engages marked contacts, such as 35, the polarity of the second impulses of the pairs corresponding to the " closed " circuit breakers is reversed bv a relay E and a polarized relay PRI energizes relays such as FI, GI or HI over the wiper 1. The relays FI, GI, &c. correspond to the. " in " positions and the relays TO, GO &c., to the open positions of the circuit breakers and the arrangement is such that each relay FO, GO &c. is first operated to control the locking circuit of its associated relay which is energized or left deenergized according to the position of the corresponding breaker. When after the complete transmission of signals the wiper 2 of the switch RLS reaches the contact 39 the relav C is deenergized and a circuit is completed for the release magnet RM of the switch MS which restores to normal. The wiper 3 of the switch RLS energizes the magnet M2 over the contact 40 and the switch RLS is automatically stepped to normal under the control of its automatically operated interrupter springs 41. If another circuit breaker changes its position during the transmission of signals, the relay A is again energized and locked up over the contacts of wiper 1 and the relay is energized to prevent release of the switch MS. A second operation of the switch RLS is thus initiated to indicate the new condition. The first impulse of a signal train operates an alarm CBA at the central station which is operated until nullified by a manually operated key 79. In a modified method of transmitting impulses over the line wires A, B, instead of reversing the polarity on both lines when a marked contact 35 is reached the potential on the line B relative to the line A may be reversed. Specifications 252,230. 252,231, 258,012, 258,178 and 258.179 are referred to.