PTC CIRCUIT PROTECTIVE ELEMENT

PROBLEM TO BE SOLVED: To easily determine a failed part by providing a membrane changing color with heat generated by an abnormal current and indicating the part where the abnormal current is generated. SOLUTION: High density polyethylene is mixed with carbon black and an antioxidant by means of a Banbury mixer and extruded to produce a pellet. It is then extruded into a sheet and electrodes are formed on the opposite sides thereof by hot pressing metal foils before being cut into a PTC circuit protective element. Subsequently, the element is coated with a pigment of tetraiodine mercury copper complex salt changing color reversibly at 70 deg.C disposed into a binder, i.e., acryl resin and then dried. The element is connected electrically in series with a variable resistor at 25 deg.C and applied, at first with a voltage of 10 V. Resistance of the variable resistor is then decreased gradually to increase the current and the voltage drop across the element. When the operating temperature of the element is reached, the current decreases abruptly, and the color on the surface of the element changes from red to dark brown violet.