Patent GB-390028-A (GB)
Title: Improvements in and relating to devices for indicating or signalling rises in temperature
IPC: H01B7/32
Filed: 1932-06-21
Abstract: 390,028. Cables; detecting, indicating, and locating faults. WEISET, M., 67, Hohenzollernkorso, Tempelhof, Berlin. June 21, 1932, No. 17510. Convention date, June 22, 1931. [Classes 36 and 37.] Relates to alarm devices of the kind in which the temperature sensitive element is a continuous line comprising two electric conductors one of which is readliy fusible ; and consists in separating the two conductors by non-continuous insulating material so that the fusible conductor, when fused, can make contact with the other conductor through the gaps in the insulation. As shown in Fig. I, a fusible wire 1 is insulated from a non-fusible conductor 5 by insulating tape or cord 3 wound in spaced spirals. The conductor 5 may be in the form of a tube or a braiding of iron or copper tape or wire. In a modification, Fig. II, both conductors 1, 2 are in the form of wire provided with spirally-wound insulation 3. The wires are both enclosed in insulation 4, 12. More than one non-fusible wire 2 may be provided, in which case the wire 1, when fused, will act to bridge the conductors 2. In use, the conductors 1, 5 or 1, 2 may be connected in a circuit including a source of current and a signalling device. In case of overheating, the fusible conductor will melt and short-circuit the conductors. Such short-circuit may be indicated by an insulation tester arranged between the conductors. The position of the short-circuit may be determined by connecting the conductors through any suitable resistancemeasuring instrument. To facilitate this, the cross sections of the conductors should be in the inverse ratio of their electrical conductivities. The line may be used for detecting the incipient breakdown of the insulation of power cables. In Fig. III, the line 7 is arranged between the cores of a multiple-core cable. In case of insulation breakdown, the heavy dielectric losses result in local heating at the weakened point. This fuses the conductor 1 of the line 7, causing the operation of any signalling device artanged in circuit with it. The average working temperature of the cable can be determined by measuring the resistances of the conductors of the line. The line may be constructed as shown in Fig. IV. The conductor 5, which is in the form of spiral ribbon, is surrounded by seamless insulation 10, and about this a third conductor 11 of spiral ribbon is wound. The fusible conductor 1 may be reinforced by a non-fusible wire 9. The insulation 10 is preferably a cellulose derivative, to avoid the possibility of the conductor 1 fusing during manufacture, as might occur during vulcanization of rubber insulation. The conductor 11 is covered by insulation 12, which may be waterproofed, and may contain substances which will evolve a fire-extinguishing gas when heated. In use, the conductor 11 may be connected in circuit with signal devices which will give an alarm should it be broken. The Specification as open to inspection under Sect. 91 describes also an alarm circuit, Fig. VI (Cancelled), utilizing the line carried around the area to be protected, wherein the conductors 1, 5 are connected in parallel with a battery B, an ammeter 13 being arranged in each conductor. A short-circuit between the conductors will be indicated by a change in the currents passing through the ammeters. The ammeter scales may be calibrated to give a direct reading of the position of the short-circuit. In a modification, the ammeters are replaced by voltmeters and resistances arranged in parallel ; or they may be replaced by relays controlling signal circuits. A further alarm system, Fig. VIII (Cancelled), employs the line shown in Fig. IV. The conductors 1, 5 are connected through a resistance 19, and through a relay 29 and ammeter 28 to a battery B<1>. If the conductor 1 or 5 is broken, the relay armature 21 will close an alarm circuit at 22. In case of a short-circuit, the increased current in the relay causes a second signal circuit to be closed at 24. The conductors 5, 11 are similarly connected through a battery B<2> and two relays 30, 31. In case of a break in either conductor, the relav 30 closes an alarm circuit at 26. In case of a short-circuit, the relay 31 closes a second alarm circuit at 27. In another circuit, Fig. V (Cancelled) (not shown), employing a line as shown in Fig. IV, separate signal circuits are actuated by a short-circuit between conductors 1 and 5 or 5 and 11. When a short-circuit is signalled, its position is found by switching in a Wheatstone bridge. If the supply. battery of the system is run down, a relay actuates a further signal. Further switches are provided whereby the Wheatstone bridge can be employed for determining the continuity of each conductor. Hand switches for testing purposes also are provided. Another form of line, Fig. IX (Cancelled), comprises a fusible conductor 1, discontinuous insulation 3, continuous insulation 4, and the conductors 5, 11. In this arrangement, fusion of the conductor 1 causes a definite break in it, without short-circuit to the conductor 5. The position of the break can be found by measuring the capacity of the conductor 1 against that of the conductor 5. This subject-matter does not appear in the Specification as accepted.