is the number of vibrations occurring in the time unit of one second. The formu- la symbol is ‘f’ and the unit of measure Hertz (Hz). The mains frequency in Europe is 50 Hz, while some power supply networks overseas operate at a fre- quency of 60 Hz. Frequencies above 60 Hz are referred to as medium frequencies. Normal operating frequencies for induction furnaces are:
70 Hz, 95 Hz, 150 Hz, 250 Hz, 500 Hz, 750 Hz, 1,000 Hz, 2,000 Hz and more rarely higher frequencies such as 3 kHz, 4 kHz, 5 kHz and 10 kHz for very small fur- naces and inductive heating for forging or hardening.