the electric heating element in an apparatus for sterilely cutting and welding together a pair of thermoplastic tubes incorporates within the heating element a fusible signal means connected in parallel electrical circuit with the resistor of the heating element for indicating previous use of the heating element . the fusible signal means is capable when intact of providing a signal to a microprocessor controlling operation of the apparatus indicative of previous nonuse of the heating element and is automatically destructed upon energization of the heating element resistor during the first use of the heating element so as to be incapable of providing such nonuse signal upon a subsequent energization . if the nonuse signal is not generated , e . g ., the heating element has been previously used , the microprocessor is programmed to reject the heating element , thereby eliminating risks resulting from reusing the heating element .