Patent GB-862138-A (GB)
Title: Improvements in or relating to electric remote indication systems
Inventor: BARTLETT THOMAS HENRY
IPC: H04B17/40
Filed: 1959-11-04
Abstract: 862,138. Repeating systems. STANDARD TELEPHONES & CABLES Ltd. Nov. 4, 1959, No. 37377/59. Class 40 (4). A fault circuit at a terminal station monitors a supervisory line by periodically connecting a potential across the line in series with a relay, a repeater subject to fault causing the relay to respond by connecting a short-circuit across the line, means being provided to release the relay should line capacitance produce a surge sufficient to operate the relay on connection of the potential when no fault is present. As shown in Fig. 1 a repeater station R in a carrier transmission system, in which a pilot wave accompanies the side band in each direction of transmission, operates relay 8 connecting rectifier 11 across the line if one pilot signal is too weak or too strong, or operates relay 9 to connect oppositely poled rectifier 12 across the line should the other pilot be similarly at fault, or operates relay 10 to completely short-circuit the line should power fail. At the left-hand terminal station A a switch 15 connects the line to fault indicator 14, the circuit for which is shown in Fig. 2, an oscillator 13 causing contacts 30 to make and break the contacts c1 and c2 of relay C at 15- second intervals. When C is made it connects sensitive relay DA to the supervisory line 37, 38, in series with a battery 31. When C releases it similarly connects the sensitive relay DB. Should the surge of current on to the line operate either DA or DB the relays connect a second winding by contacts in series with battery 32 to force release the relay once surge current begins to fall off. These contacts also connect up slowto-operate relays EA and EB. Should rectifier 11 be put across the line only relay DA responds, while rectifier 12 across the line causes only relay DB to respond; a complete shortcircuit causing both to respond. Under these fault conditions current through DA, or DB, or both, is stronger than the force release current so the relays hold up long enough to operate one or other or both of relays EA, EB, which lock up and operate warning lamps or alarms 16, 17. Reset keys 43 and 49 are provided. At the righthand terminal station B, a fault indicator 18, shown in detail in Fig. 3, is used and comprises the transistors 59 and 60 driving relays FA, FB. At each alternation of potential applied to the supervisory line at the terminal station A, as described above, one of the relays FA, FB will release and the other will operate. When rectifier 11 is connected across the line to indicate a fault relay FA remains released; rectifier 12 having the same effect on relay FB. So long as one of the relays FA, FB is operated a relay G cannot operate but if one or other falls back, G locks up and one lamp 20 or 21 is continuously lighted while the other flashes. For a complete short-circuit fault indication both FA and FB fall back and both lamps 20 and 21 light continuously. A reset key 66 is provided. Each terminal station has a Wheatstone bridge 22, 23, the polarity of which may be switched to select rectifier 11 or 12, use of which enables the faulty station to be identified by the impedance of the line up to the fault.