PURPOSE: To solve a problem with a change in a resistance temperature characteristic caused by delay of heat transfer from current supply time and heat hysteresis of a PTC heating element as well as to provide a safe water bed which can endure long-term use by using the PTC heating element as a heating element, detecting a heating temperature of the heating element when it is heated by current supply, and carrying out current supply control on the heating element in a heating system used in the water bed.
CONSTITUTION: A detecting electrode wire 11 adjacent to a pair of electrode wires 9 covered with a temperature sensing resin layer 12 is covered with a resistance 13 composed of an electrically conductive composition and is formed integrally and a highly quick heatable safe water bed composed of a heater unit of a PTC heating element having a polyester film 14 to cover the whole of the resistance 13 and a controller to carry out temperature detection and current supply control, can be provided. The electrically conductive composition being prepared by mixing and dispersing, in a high density polyethylene, microscopic electrically conductive particles obtained by dispersing carbon black in a high density polyethylene and dividing and cross-linking the compound resin.
YAMAZAKI TADATAKA
YANAGIDA NAOKO
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