| 摘要 |
Induction heating apparatus, typically for metal melting, with multiple zone temperature control has an induction coil (10) divided into individual sections (10a, b,c) associated with respective zones and powered in parallel under regulation from control means (20) as shown in figure 1. To give precise and efficient automatic regulation of the zone temperatures the power supply is provided by a resonant invertor (14) as a medium frequency pulsed output and at an instantaneously selected level which is the sum of the power requirements of all the zones at any instant, and the average power applied in each zone is controlled by pulse width modulation with switching to high power for a proportion, determined by demand in that zone, of each of successive standard time periods.
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