System and process for controlling dielectric ovens

Abstract

A control system for controlling the heating of a product in a dielectric oven comprises at least one dielectric heating circuit including an electromagnetic energy source, such as a triode vacuum tube, having an anode and a resonant circuit including at least one inductor and at least a pair of capacitors. Each capacitor includes two capacitor plates and one of these capacitor plates is moveable, such that each pair of capacitors forms a variable capacitor in which the product to be heated is a dielectric. The system also includes at least one ammeter for measuring actual anode current at the anode. A motor is used to increase or decrease a distance between the plates of at least one of said capacitors, thereby adjusting the electromagnetic energy delivered to the product. A processor receives ammeter measurements, whereby the distance between the pair of capacitor plates is adjusted to increase or decrease the actual anode current. The processor also receives, stores, and retrieves a requested anode current and compares the requested anode current to the actual anode current to determine whether to increase or decrease the distance between the pair of capacitor plates. Alternatively, the electromagnetic energy source may have a duty cycle adjusted by a keying circuit or an anode voltage adjusted by a voltage control device, or both. The processor may include a timer, whereby an average actual anode current is measured. The processor may receive, store, and retrieve a requested average anode current and compares this current to the actual average anode current to adjust the electromagnetic field electrically by either increasing or decreasing the duty cycle or increasing or decreasing the anode voltage of the electromagnetic energy source, or both, and thereby increase or decrease the average actual anode current.