sentences:  Due to its flexibility and potential frequency range, the valve oscillator based induction heater was until recent years widely used throughout industry.Readily available in powers from 1 kW to 1 MW and in a frequency range from 100 kHz to many MHz, this type of unit found widespread use in thousands of applications including soldering and brazing, induction hardening, tube welding and induction shrink fitting.The unit consists of three basic elements