Vorrichtung zur Bestimmung des Gießzeitpunktes geschmolzenen Metalls

摘要

A metal material is placed in a crucible 4. An inverter 16 outputs a voltage amplitude-modulated with a low frequency signal. The output voltage is used to RF induction heat the crucible. A photodiode 30 receives light emitted by the metal material in the crucible and develops a received-light-representative signal. A high-pass filter 34 extracts, from the received-light-representative signal, a frequency component having a frequency above the frequency of the low frequency signal. A comparator 40 develops an output signal when the output signal of the high-pass filter exceeds a reference signal provided from a peak sample-and-hold circuit 42 to which the output signal of the high-pass filter is applied as an input thereto.