Patent GB-391428-A (GB)
Title: A process and apparatus for detecting abrupt variations in temperature
IPC: G08B17/00
Filed: 1931-07-23
Abstract: 391,428. Thermo-electric batteries. SOC. DETECTIF, 36, Rue Rochechouart, Paris. July 23, 1931, No. 21074. Convention date, Aug. 7, 1930. Void [Published under Sect. 91 of the Acts]. [Class 53.] In means for detecting abrupt variations of temperature of the kind in which groups of thermoelectric couples 1, 2, Fig. 1, are arranged in. opposition so that the resultant E.M.F. due to slow heating is zero, the thermopile comprises metal bars 17, Fig. 3, set in an insulating-bar 15. Alternate bars 17 have secured to their ends nickel-silver dics 201, 20<2> and iron discs 21<1>, 21<2>, the adjacent discs of different metal being welded together to form hot junctions 23<1>, 23<2>, as shown. The junctions 23<1> are screened by a bar 24 of heat-insulating material. The tliermopoile is in circuit with a galvanometer 9 the needle 11 of which is arranged to close a contact in an alarm circuit 12. The closing of the circuit may serve to start a fire-pump or a water sprinkler, or to close a fireproof door. In a modification, Fig. 7, the couples 1, 2 are arranged in the body of an insulating disc 61, the hot junctions of the couples lying in recesses 60 cut in the surfaces of the disc, and being covered. by metal plates 62 which serve to protect the junctions and accelerate their heating. In another modification, Fig. 9, applicable to the notification of overheating in heaps or piles of material, the couples, mounted as described with reference to Fig. 7, are arranged in insulating sleeves 67<1>. These are bult up with cylindrical metal sections 661, 662 to form a tower, which is embedded in the pile of material. The hot junctions on the outer surface of the tower heat more quickly than those on the inner surface. A top section 70 houses the galvanometer 9, alarm circuit, and alarm bell 13. Iu another modification, Fig. 11 (not shown), the thermopile is arranged as a portable unit connected by a length of flexible cable to a pin plug. Since the E.M.F. produced by the thermopile is very small, means preferably are provided for amplifying the movement of the galvanometer needle 11. As shown in Fig. 12, the needle 11 carries at its end a soft iron block 28. The initial movement of the needle brings this block within the field of an electromagnet 30, which accelerates the movement of the needle up to a point where it engages a control spring 35. This opens the electromagnet circuit at 37, allowing the needle 11 to return, and causing the armature 38 of a relay 32 to fall to close a secondary alarm circuit. At the same time, the spring 35 closes another secondary work circuit at 36. The electro-magnet is adjustable in position. In a modification, Fig. 13 (not shown), the needle 11 is arranged to tilt a mercury switch, and a permanent magnet with an adjustable core is used. Fig. 14 shows means for giving a warning of a break in the thermopile circuit. The thermopile 1, 2 and galvanometer 9 are in circuit with a control rheostat 96, and a potentiometer 95 establishes a difference of potential 101 in the circuit. The rheostat is adjusted to cause a weak current to flow in the circuit, just sufficient to hold the needle 11 in the position shown. In case of abrupt heating, the needle 11 is moved as described with reference to Fig. 12. In case of a break in the thermopile circuit, the weak current fails, and the needle falls back and bridges contacts 102, 103 in the circuit of a derangement alarm 97. In a modified arrangement for use of the small deflections of the galvanometer needle caused by the thermopile, the needle 11<1> carries a disc 39 adapted, in the operative position of the needle, to obscure an aperture 41 in a dial 40, and so out off a beam of infrared rays normally projected upon a photoelectric cell 44 by a source 43. The cell is. in circuit with a relay the armature of which is adapted to close the alarm circuit.