Temperature sensing induction heating tool
An induction heating tool that holds voltage or current supplied to the induction tank circuit constant and tracks changes in the other of voltage or current during each induction heating cycle. The disclosed induction heating tool exploits the fact that the resistance an attachment plate increases along with the temperature of the attachment plate. During an induction heating cycle, the attachment plate is magnetically coupled to a work coil and the resistance of the attachment plate is reflected to the circuit. Changes in the resistance of the attachment plate alter the pattern of energy delivery from the work coil to the attachment plate in a predictable way. Calculations accurately predict the temperature of the attachment plate over a wide variety of ambient conditions, including the presence of moisture at the membrane/attachment plate interface. The disclosed induction heating tool produces consistent results without calibration for ambient conditions.
1 . A method of securing a membrane to a structure, said method comprising:
securing an attachment plate to the structure, said attachment plate comprising conductive metal and having a top surface facing away from the structure, said top surface of the attachment plate coated with a heat activated adhesive;
placing the membrane over the attachment plate so that the attachment plate is covered by the membrane and the attachment plate is between the membrane and the structure with the top surface of the attachment plate facing a bottom surface of the membrane;
providing a power supply connected to a tank circuit, said power supply having a pre-determined constant output voltage or pre-determined constant output current;
connecting the tank circuit to an induction coil;
positioning the induction coil adjacent a top surface of a portion of the membrane extending over the attachment plate;
activating said power supply to energize said tank circuit, which resonates at a resonant frequency to generate an oscillating magnetic field emanating from the induction coil, said oscillating magnetic field inducing eddy currents in the conductive metal of the attachment plate magnetically coupled to the induction coil to heat the attachment plate;
providing a control circuit connected to measure the output voltage or output current of the power supply that is not held constant;
calculating the electrical resistance of the attachment plate using measured changes in the output voltage or output current that is not held constant; and
deactivating said power supply in response to a calculated change in electrical resistance of the attachment plate that correlates to a pre-determined target temperature for the attachment plate.
2 . The method of securing the membrane to the structure of claim 1 , wherein the power supply maintains a constant output voltage and the control circuit measures changes in the output current of the power supply.
3 . The method of securing the membrane to the structure of claim 2 , wherein said step of calculating includes using changes in the current drawn from the power supply to calculate the electrical resistance of the attachment plate.
4 . The method of securing the membrane to the structure of claim 1 , wherein the control circuit maintains the pre-determined target temperature of the attachment plate for a pre-determined period of time before deactivating the power supply.
5 . The method of securing the membrane to the structure of claim 4 , wherein the control circuit increases said pre-determined period of time in response to an input corresponding to an ambient temperature below a pre-determined temperature or an input corresponding to the presence of moisture on the attachment plate.
6 . The method of securing the membrane to the structure of claim 1 , wherein said control circuit employs a look up table to correlate said electrical resistance to a temperature of said attachment plate.
7 . A method of securing a membrane to a structure, said method comprising:
securing an attachment plate to the structure, said attachment plate comprising conductive metal and having a top surface facing away from the structure, said top surface of the attachment plate coated with a heat activated adhesive;
placing the membrane over the attachment plate so that the attachment plate is covered by the membrane and the attachment plate is between the membrane and the structure with the top surface of the attachment plate facing a bottom surface of the membrane;
magnetically coupling the attachment plate to an induction heating circuit by:
positioning an induction coil adjacent a top surface of a portion of the membrane extending over the attachment plate;
energizing the induction coil with a high frequency alternating current to generate an oscillating magnetic field emanating from the induction coil, said oscillating magnetic field inducing eddy currents in the conductive metal of the attachment plate to heat the attachment plate;
wherein the attachment plate is magnetically coupled to the induction heating circuit by the oscillating magnetic field;
said induction heating circuit comprising a power supply constructed to generate said high frequency alternating current from a source of electrical power, and a control circuit connected to measure changes in power consumed by the power supply, said method comprising:
measuring changes in the power consumed by the power supply while the attachment plate is magnetically coupled to the induction heating circuit;
calculating an electrical resistance of the attachment plate using measured changes in the power consumed by the power supply; and
deactivating said power supply in response to a calculated change in electrical resistance of the attachment plate that correlates to a pre-determined target temperature for the attachment plate.
8 . The method of securing the membrane to the structure of claim 7 , wherein said control circuit employs a look up table to correlate said electrical resistance to a temperature of said attachment plate.
9 . The method of securing the membrane to the structure of claim 7 , wherein an increase in temperature of the attachment plate causes an increase in resistance of the attachment plate and an increase in power consumed by the power supply.
10 . The method of securing the membrane to the structure of claim 7 , wherein the control circuit maintains the pre-determined target temperature of the attachment plate for a pre-determined period of time before deactivating the power supply.
11 . The method of securing the membrane to the structure of claim 10 , wherein the control circuit increases said pre-determined period of time in response to an input corresponding to an ambient temperature below a pre-determined temperature or an input corresponding to the presence of moisture on the attachment plate.