circuit The output circuit has the job of matching the output of the inverter to that required by the coil. This can in it simplest form be a capacitor or in some cases will feature a combination of capacitors and transformers. Control system The control section monitors all the parameters in the load circuit, the inverter and supplies switching pulses at the appropriate time to supply energy to the output circuit. Early systems featured discrete electronics with variable potentiometers to adjust switching times, current limits, voltage limits and frequency trips. However, with the advent of microcontroller technology, the majority of advanced systems now feature digital control. The voltage-fed inverter The voltage-fed inverter features a filter capacitor on the input to the inverter and a series resonant output circuits. The voltage-fed system is extremely popular and can be used with either SCRs up to frequencies of 10 kHz, IGBTs to 100 kHz and MOSFETs up to 3 MHz. A voltage-fed inverter with a series connection to a parallel load is also known as a third order system. Basically this is similar to solid state, but in this system the series connected internal capacitor and inductor are connected to a parallel output tank circuit. The principal advantage of this type of system is the robustness of the inverter due to the internal circuit effectively isolating the output circuit making the switching components less susceptible to damage due to coil flash-overs or mismatching. The current-fed inverter The current-fed inverter is different from the voltage-fed system in that it utilizes a variable DC input followed by a large inductor at the input to the inverter bridge. The power circuit features a parallel resonant circuit and can have operating frequencies typically from 1 kHz to 1 MHz. As with the voltage-fed system, SCRs are typically used up to 10 kHz with IGBTs and MOSFETs being used at the higher frequencies. Suitable materials Suitable materials are those with high permeability (100-500) which are heated below the Curie temperature of that material. See also Induction forging Induction shrink fitting Induction hardening Induction heating Drum heater References Notes Bibliography . External links Sheffield University undertakes fundamental and applied research on enabling induction heater technologies - University of Sheffield Induction soldering using induction heater technology example from TWI Animation showing heating rates derived from FEA of mains frequency Induction Drum Heater - LMK Thermosafe Ltd Comprehensive tutorial on the