Temperature control method using imperfections (imperfection) of impedance matching as control variables

摘要

A radio frequency heating current to heat the load of a heater (15) whose impedance varies substantially with temperature. The change in impedance of the load (15) changes the degree of mismatch between the power transmission system (10, 11, 12) and the load (15) resulting in a change in the voltage which is reflected back to the power transmission system (10, 11, 12) by the load (15). The reflected voltage is sensed (13) and its magnitude is compared to the voltage of a reference source (22). The difference between the reference source and the reflected voltage is used to turn off the power to the load when the reflected voltage (Vr) exceeds the reference voltage (AVr). The load temperature then drops and the power to the load is restored after a selected predetermined time. A directional coupler (13) may be employed to isolate the reflected voltage. The isolated reflected voltage (KVr) is compared with a reference voltage, to produce a difference signal. The power supply is turned on and off depending on the magnitude of the difference signal, thereby producing a pulsating current that holds the load temperature constant.