Circuit for the inductive heating of a metal
An inductive welding device includes a circuit for the inductive heating of a metal that is embedded in a non-magnetic bed. A transformer induces eddy currents in the metal as a function of an exciter current and an exciter voltage and forms a load impedance together with the metal to be heated. Temperature monitoring is provided for the metal to be heated. The load impedance is operated in the region of the resonant frequency of the load impedance. The exciter current and exciter voltage and their phase shift relative to each other are measured and logged when the metal is heated. A temperature progression which is proportional to the phase shift is calculated from the exciter current, exciter voltage, and phase shift.
1. An induction welding device comprising:
a non-magnetic bed,
a metal embedded in the non-magnetic bed,
a circuit for inductive heating of the metal and for monitoring a temperature of the metal, the circuit comprising a transformer and the metal,
wherein the transformer induces eddy currents in the metal as a function of an exciter current and an exciter voltage,
wherein the transformer and the metal together form a load impedance,
wherein the load impedance has a resonant frequency,
wherein the exciter current, the exciter voltage, and a phase shift of the exciter current and the exciter voltage relative to each other are measured and logged when the metal is heated,
wherein a temperature progression of the metal is calculated from the exciter current, the exciter voltage, and the phase shift, and
wherein the temperature progression is proportional to the phase shift.
2. The induction welding device according to claim 1 , wherein the exciter voltage is applied to the load impedance,
wherein an exciter frequency of the exciter voltage is changed for calibration such that the phase shift and a load impedance change are produced,
wherein the metal comprises a PTC thermistor or an NTC thermistor, and
wherein a change in resistance of the PTC thermistor or the NTC thermistor is calculated from the exciter current, the exciter voltage, and the phase shift using a mathematical model of the load impedance.
3. The induction welding device according to claim 2 , wherein the load impedance change is logged.
4. The induction welding device according to claim 1 , further comprising a memory,
wherein the metal comprises a PTC thermistor or an NTC thermistor,
wherein a resistance of the PTC thermistor or of the NTC thermistor is always calculated during operation,
wherein the resistance remains constant in a region and subsequently rises,
wherein the temperature progression is calculated from a progression of the resistance, and
wherein the temperature progression is calibrated to a melting temperature inherent to a material of the non-magnetic bed before the temperature progression is stored in the memory.
5. The induction welding device according to claim 1 , wherein the non-magnetic bed is a plastic bed.