Rf energy conveyor oven
AssigneeComdel, Inc.
InventorSteven Thomas Ottaway
Life of this patent
Estimating the term…
Abstract
RF energy provided by electrodes positioned between a product is used to heat a product that exhibits a variable impedance during the heating process. As the product's impedance changes during the heating process, RF heating system impedance can be maintained constant by adjusting the distance between the electrodes, adjusting the impedance of a variable impedance device connected between the RF power source and an electrode, or a combination of electrode distance adjustment and impedance adjustment of the variable impedance device. The system is particularly applicable to the heating or pasteurization of bulk food products with multiple heating zones.
Claims16
An oven for heating a product, the oven comprising:
- a conveyor apparatus to convey the product through the oven;
- one or more first electrodes;
- one or more second electrodes, the one or more second electrodes disposed relative to the one or more first electrodes to form a heating path between the one or more first electrodes and the one or more second electrodes through which the product is conveyed on the conveyor apparatus;
- one or more variable impedance devices, each of the one or more variable impedance devices having an adjustable impedance, and an input and an output, the output of an each one of the one or more variable impedance devices exclusively connected to at least one of the one or more first electrodes;
- and
- one or more power sources, each of the one or more power sources having an RF power output, the RF power output of each one of the one or more power sources exclusively connected between the input of at least one of the one or more variable impedance devices and at least one of the one or more second electrodes, the RF power output of each of the one or more power sources supplying RF power with a potential difference between the one or more first electrodes and the one or more second electrodes to radiate a RF energy between the one or more first electrodes and the one or more second electrodes, the RF energy to heat the product as the product is conveyed through the heating path;
- whereby heating of the product is controlled by varying the adjustable impedance of each of the one or more adjustable impedance devices in an each circuit formed by one of the one or more power sources, one of the one or more variable impedance devices, one or more first electrodes and one or more second electrodes, as the product is conveyed through the heating path.
The oven of claim 12 wherein the adjustable impedance of each of the one or more variable impedance devices for the each one of the plurality of heating zones and the length of the adjustable length electrode feeder is varied as the product is conveyed between the one or more first and second electrodes in the each one of the plurality of heating zones to maintain a substantially constant impedance of the each circuit.
The oven of claim 12 further comprising a controller, the controller varying the adjustable impedance of each of the one or more adjustable impedance devices and varying the length of the adjustable length electrode feeder apparatus, responsive to one or more operating parameters of the oven.
The oven of claim 12 further comprising an air moisture content sensor exposed to an RF voltage for sensing moisture of the air entering or leaving the heating path, the sensor comprising:
- a tuned circuit comprising an air-spaced coaxial capacitor connected in parallel with a shunt inductance;
- a frequency source operating at the natural resonant frequency of the tuned circuit to resonant the tuned circuit;
- and
- a rectifier means connected across the tuned circuit to produce a rectified dc output voltage proportional to the RF voltage and calibrated to the moisture content of the air;
- whereby as moisture of the air varies the dielectric constant of the air-spaced capacitor changes to produce a change in the rectified dc output voltage.
The oven of claim 12 wherein the one or more first electrodes are offset from the one or more second electrodes whereby the radiated RF energy produces a skewed energy distribution relative to the direction of travel of the product in the heating path.
A method of heating a product in an oven comprising the steps of:
- conveying the product through a heating path in one or more heating zones of the oven;
- subjecting the product to an RF energy as the product is conveyed through the heating path, the RF energy produced by an RF power source and radiated between one or more first electrodes and one or more second electrodes disposed on opposing sides of the product as the product is conveyed through the heating path;
- and
- adjusting the impedance of a circuit formed by the RF power source and the one or more first and second electrodes by a variable impedance means inserted in the circuit as the product is conveyed through the heating path.
Dependencies are inferred from the claim text.