GB1149060A - Improvements relating to thermally sensitive magnetic devices - Google Patents

Abstract

1,149,060. Temperature alarms. E. H. TAYLOR. 18 Dec., 1967 [16 Dec., 1966], No. 56516/66. Heading G4N. [Also in Division H1] A temperature sensitive alarm comprises a thermally sensitive magnetic device including a permanent magnet mounted in a surrounding housing, the housing or part thereof being formed of a material having a Curie temperature below the temperature at which the magnetic properties of the permanent magnet are affected, the device being arranged to actuate a warning device by induction of an electric current in the warning device at temperatures either above or below the Curie temperature. The arrangement of the permanent magnet and the housing is such that either below or above the Curie temperature of the material a locally intense magnetic field is produced by the device. A cylindrical permanent magnet 1 is mounted in a pot 2 of " Curie material " and surrounded by an aluminium spacer 3. This device acts as a normal pot magnet until the Curie temperature is passed whereupon the magnetic circuit through 2 is broken and the annular magnetic field no longer exists. In another embodiment (Fig. 2, not shown) a polepiece (4) of " Curie material " is provided on the magnet 1 to give a device working in the same way. Another series of devices is disclosed which work in the opposite way, i.e. they have no effective magnetic field at room temperature but exhibit a magnetic field once the Curie temperature is passed. In one embodiment (Fig. 3, not shown) the device is identical in shape with that shown in Fig. 1, but the spacer 3 is made of the " Curie material ". In other embodiments (Figs. 4 to 8, not shown) combinations of aluminium spacers, polepieces and " Curie material " keepers are employed to give pot magnets and shallow-pot magnets, some having bolted keepers. The pot magnets may be used to form temperature sensitive electric switches or fluid valves, whilst auxiliary heating coils may be used to heat the magnets. The " Curie materials " may be nickel/iron, copper/nickel, pure nickel, "Nilo" (RTM) or Ferroxcube Mn-Zn ferrite whilst the permanent magnet may be Alcomax III (RTM).