Electrical resistance heating element with signal means to indicate first use

In an electrical heating element for welding first and second thermoplastic tubes together transversely of the axis of each tube, said heating element consisting essentially of, as an outer layer, a folded sheet of metal having a thermal conductivity of at least about 173 watts/m.degree.K. at a 0.10 mm thickness and a tensile yield strength of at least about 34.times.10.sup.4 kPa at 0.10 mm thickness, an electrical resistor comprising an etched stainless steel foil disposed inside the fold of said folded sheet of metal;

• and a layer of dielectric adhesive, stable to about 260.degree. C., between inner surfaces of said folded sheet of metal and surfaces of said resistor, thereby bonding the resulting structure together, the improvement comprising an etched fusible signal strip of stainless steel connected in parallel electrical circuit with the resistor, said fusible signal strip being disposed within the fold of said folded sheet of metal so as to be incorporated within the heating element, said fusible signal means being capable when intact of providing a signal indicative of previous nonuse of said heating element and being automatically self-destructable upon energization of said heating element resistor during first use of the heating element so as to be incapable of providing the signal indicative of previous nonuse upon a subsequent energization of said heating element resistor, said fusible signal strip being made during etching of the resistor.

In an apparatus for forming a sterile connection between two thermoplastic tubes, which apparatus comprises a cutting means, a pair of mounting blocks adapted to receive and hold the two tubes, means to provide movement between said blocks and said cutting means to a position such that the cutting means is between said blocks and traversing where the blocks are adapted to receive tubes, means adapted to realign said blocks to a position where two different tube ends are aligned with and facing each other, means to separate said blocks and cutting means while urging said blocks together;

• and a microprocessor to control the means to provide movement between blocks and cutting means;
• the improvement comprising the cutting means having an electrical resistance heating element with a fusible signal means incorporated therein to indicate first use of the element, said fusible signal means being connected in parallel electrical circuit with the resistor of said heating element, said fusible signal means being capable when intact of providing a signal to the microprocessor indicative of previous nonuse of said heating element and being automatically self-destructable upon energization of said heating element resistor during first use of the heating element so as to be incapable of providing the signal indicative of previous nonuse upon a subsequent energization of said heating element resistor.