GB1462461A - Device simulating the function of an electrothermal device - Google Patents

Abstract

1462461 Temperature indicators ROBERT PARKER RESEARCH Inc 9 April 1974 15717/74 Heading G1D The temperature of an electrothermal device 26 may be qualitatively or substantially quantitatively indicated by means of a device which simulates the function of the electrothermal device and comprises a layer of at least one liquid crystal composition 14 which is in heat exchanging relationship with a resistance heater 20 or 34 and an at least partially transparent insulating overlay over said layer having a heat capacity, size and geometry to relate to the cooling of the device 26. As described, the heater 20 or 34 has a thermal response which is proportional to the current or voltage applied to the appliance, and the lower or both transition temperature(s) of the liquid crystal composition(s) is preferably in the range of temperature developed by the heater 20 or 34. The overlay constitutes the major portion of a heat sink which is in heat exchanging relationship with the environment and provides a cooling response of the device which is proportional to the cooling response of the device 26. The variation in response of the liquid crystal composition to the heater 20 or 34 may be provided by employing a plurality of compositions having different temperature transition ranges whch experience together the same temperature Fig. 5, (not shown). Alternatively, as shown in Fig. 2 a single composition is employed which experiences a temperature gradient. Thus a bar 44, 46 is initially formed centrally at the transition temperature, splitting into two and moving outwards as outer regions reach the transition temperature and inner areas exceed the transition range. In a modification, a temperature gradient activates the liquid crystal to show the word "warm" at a region close to the heater, the word "hot" being activated at a region further from the heater Figs. 3 and 4 (not shown). The liquid crystal transition temperatures lie in the range 100-200‹F, and the crystals may be microencapsulated and be cholesteryl esters. The insulation overlay is plastics or polymeric sheet e.g. of a polymethacrylate, polycarbonate, polyvinylchloride, or polypropylene. The heater may be a resistance heater sheet,.film, foil of, for example, carbon impregnated paper or metal foil. Where a temperature gradient is required, a resistance wire may be employed, the heater generating a temperature below 400‹F.