Abstract: An improved method and apparatus for electrically heat welding a thermoplastic fitting having an electric resistance heating element disposed therein. A controlled quantity of electric power is supplied to the heating element during the welding process to insure the making of a high quality weld. After the size of heating element and fitting are determined, a substantially constant voltage level electric power is supplied to the heating element of the fitting. When it is determined that the welding process is proceeding abnormally, the supply of electric power is terminated unless the abnormality is that the current level is too high. In that case, instead of terminating the welding process, the voltage of the electric power is reduced to that which results in current levels substantially equal to predetermined current levels for the size of heating element and fitting being welded which often results in a good weld being obtained even where the heating element is partially shorted out.

Abstract: A method and apparatus for electrically heat welding a thermoplastic fitting having an electric resistance heating element disposed therein whereby a regulated quantity of electric power is supplied to the heating element during the welding process and the making of a high quality weld is insured. In accordance with the method, electric power is supplied to the resistance heating element of the fitting. The impedance and optionally, the resistance of the heating element are measured using low voltage electric power and the size of the fitting to be welded is determined therefrom. The initial magnitude of the current flowing through the heating element is sensed and compared with predetermined current levels for the size of fitting to be welded at various temperatures whereby the total time the controlled electric power should be supplied to the heating element of the fitting for the making of a high quality weld is determined.