| 摘要 |
<p>700,149. Unattended repeaters. STANDARD TELEPHONES & CABLES, Ltd. Feb. 4, 1952, No. 2887/52. Class 40 (4). In a communication system having a number of unattended stations spaced along a route, a defective station is located over a circuit common to all the unattended stations by measuring the resistance of the circuit between the defective station, which terminates the circuit on the occurrence of a fault, and a second predetermined unattended station which is nearer to the attended station than the defective. station and can terminate the circuit in response to a signal from the attended station. This arrangement overcomes difficulties in station identification which arise when the resistance between stations is less than the resistance variation due to temperature of the total line. When the common line 6, Fig. 1 is earthed by a relay 19 at a defective station a fault alarm (not shown) at the attended station is operated by a relay 33 and the attendant operates key 29 to disconnect the alarm and couple the bridge measuring circuit. The first measurement indicates the location of the fault relative to the predetermined unattended station or " dividing " station, and switch arm 24 is set to the position corresponding to the section indicated. Line 6 is earthed at the appropriate " dividing station " by a key 36 at the attended station which operates relay 11 or 16 in accordance with the direction of the current through conductors 7, 8, and with resistance 23 at zero the. bridge is balanced by adjusting resistor 26. When key 36 is released the value of resistor 23 necessary to rebalance the bridge indicates which station past the " dividing station " is defective. The number of " dividing stations " should be large enough to keep the resistance variation between two of them less than the resistance between two ordinary unattended stations. Additional wires, e.g. interstice wires in a coaxial cable, may be used for terminating additional dividing stations or a different method of selectivity actuating the relays may be employed. In an alternative arrangement (Fig. 2, not shown) a pair of wires is used for the common circuit to avoid errors due to earth currents.</p> |
