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Methods and apparatus for compensating a radiation sensor for temperature variations of the sensor. In one example, the radiation sensor is a thermal sensor having at least one property that varies as a function of temperature. The thermal sensor outputs signals based on thermal radiation of interes

Methods and apparatus for compensating a radiation sensor for temperature variations of the sensor. In one example, the radiation sensor is a thermal sensor having at least one property that varies as a function of temperature. The thermal sensor outputs signals based on thermal radiation of interest from a particular radiating body in its view. These signals may contain significant undesirable components due in part to changes in temperature of the sensor itself. Methods and apparatus of the invention compensate the sensor for temperature variations of the sensor that are not due to the radiation of interest, so as to significantly reduce undesirable components in the instantaneous signals output by the sensor. In one example, this is accomplished without thermally stabilizing the sensor itself (i.e., dynamic temperature compensation). In another example, the sensor is thermally stabilized selectively at various predetermined temperatures as a function of the ambient temperature in the proximity of the sensor.

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Methods and apparatus for compensating a radiation sensor for temperature variations of the sensor. In one example, the radiation sensor is a thermal sensor having at least one property that varies as a function of temperature. The thermal sensor outputs signals based on thermal radiation of interes

Methods and apparatus for compensating a radiation sensor for temperature variations of the sensor. In one example, the radiation sensor is a thermal sensor having at least one property that varies as a function of temperature. The thermal sensor outputs signals based on thermal radiation of interest from a particular radiating body in its view. These signals may contain significant undesirable components due in part to changes in temperature of the sensor itself. Methods and apparatus of the invention compensate the sensor for temperature variations of the sensor that are not due to the radiation of interest, so as to significantly reduce undesirable components in the instantaneous signals output by the sensor. In one example, this is accomplished without thermally stabilizing the sensor itself (i.e., dynamic temperature compensation). In another example, the sensor is thermally stabilized selectively at various predetermined temperatures as a function of the ambient temperature in the proximity of the sensor. age level is not more than about 10% of the second voltage level.9. The method of claim 6, wherein the modifying step comprises determining whether to increase or decrease the frequency of the RF signal, wherein the determination is a function of, at the least, the sensed power applied to the circuit and the sensed reflected power.10. In a radio frequency (RF) heating system for heating a material that is capable of being heated when exposed to an RF field, wherein the RF heating system comprises a circuit having a radiator for producing an RF Field and a resonant frequency that changes while the material is being heated, a method for heating the material, comprising the steps of: providing to the circuit a signal having a frequency, thereby causing the radiator to produce the RF field; and tracking the resonant frequency of the circuit, at least during a portion of a period during which the material is being heated by the RF heating system, so that the frequency of the signal follows the resonant frequency of the circuit, wherein the tracking step comprises the steps of: (a) measuring the amount of power applied to the circuit and/or the amount of power reflected from the circuit;(b) determining whether the resonant frequency is increasing or decreasing, wherein the determination is a function of, at the least, the measured amount of power applied to the circuit or the measured amount of power reflected from the circuit and a previously measured amount of forward power to the circuit or reflected power from the circuit;(c) increasing the frequency of the signal if in step (b) it was determined that the resonant frequency is increasing; and(d) decreasing the frequency of the signal if in step (b) it was determined that the resonant frequency is decreasing.11. The method of claim 10, wherein the tracking step comprises the step of measuring both the amount of power applied to the circuit and the amount of power reflected from the circuit.12. The method of claim 11, wherein the determination as to whether the resonant frequency is increasing or decreasing is a function of, at the least, the measured amount of power applied to the circuit and the measured amount of power reflected from the circuit.13. The method of claim 11, wherein the tracking step further comprises the step of determining a ratio of the amount of power applied to the circuit to the amount of power reflected from the circuit, and wherein the determination as to whether the resonant frequency of the circuit is increasing or decreasing is based, at least in part, on the ratio.14. The method of claim 11, wherein the tracking step further comprises the step of determining a ratio of the amount of power reflected from the circuit to the amount of power applied to the circuit, and wherein the determination as to whether the resonant frequency of the circuit is increasing or decreasing is based, at least in part, on the ratio.15. A method of using an RF heating system to heat a material, wherein the RF heating system comprises a circuit having a resonant frequency, comprising the steps of: (a) determining an estimate of the resonant frequency of the circuit and applying an RF signal to the circuit, wherein the frequency of the RF signal is substantially equal to the estimated resonant frequency of the circuit; (b) measuring the forward power to the circuit; (c) measuring the reflected power from the circuit; (d) determining a ratio of the reflected power to the forward power; (e) decreasing the frequency of the RF signal applied to the circuit after performing steps (b) and (c); (f) after performing step (e) then performing the steps of: (g) measuring the forward to the circuit; (h) measuring the reflected power from the circuit; and (i) determining the ratio of the reflected power to the forward power; (j) comparing the ratio determined in step (i) to the ratio determined in step (d); (k) increasing the frequency of the RF signal if, base d on the comparison, it is determined that the ratio determined in step (i) is greater than the ratio determined in step (d); and (l) decreasing the frequency of the RF signal if, based on the comparison, it is determined that the ratio determined in step (i) is less than the ratio determined in step (d). 16. A method of using an RF heating system to heat a material, wherein the RF heating system comprises a circuit having a resonant frequency, comprising the steps of: (a) determining an estimate of the resonant frequency of the circuit and applying an RF signal to the circuit, wherein the frequency of the RF signal is substantially equal to the estimated resonant frequency of the circuit; (b) measuring the forward power to the circuit; (c) measuring the reflected power from the circuit; (d) determining a ratio of the forward power to the reflected power; (e) decreasing the frequency of the RF signal applied to the circuit by an offset amount after performing steps (b) and (c); (f) after performing step (e) then performing the steps of: (g) measuring the forward to the circuit; (h) measuring the reflected power from the circuit; and (i) determining the ratio of the forward power to the reflected power; (j) comparing the ratio determined in step (i) to the ratio determined in step (d); (k) increasing the frequency of the RF signal if, based on the comparison, it is determined that the ratio determined in step (i) is less than the ratio determined in step (d); and (l) decreasing the frequency of the RF signal if, based on the comparison, it is determined that the ratio determined in step (i) is greater than the ratio determined in step (d). 17. In an RF heating system for heating a material, wherein the RF heating system comprises a circuit having a radiator for heating the material and a resonant frequency that changes while the material is being heated, a method for efficiently heating the material, comprising the steps of: placing the material close enough to the radiator so that an electromagnetic field produced by the radiator will heat the material; providing a signal to the circuit, the signal having a frequency; measuring the power applied to the circuit; measuring the power reflected from the circuit; and tracking the changes in the resonant frequency of the circuit while the material is being heated by either increasing or decreasing the frequency of the signal by a offset amount so that the frequency of the signal follows the resonant frequency of the circuit, wherein the decision as to whether to increase or decrease the frequency of the signal is based, at least in part, on measurements of both the forward and reflected power. 18. An RF heating system for heating a material, comprising: a circuit, wherein the circuit has a resonant frequency that changes while the material is being heated; a signal generator that generates a signal having a frequency; an amplifier coupled between the circuit and the signal generator that amplifies the signal, wherein the amplified signal is provided to the circuit; a forward power sensor that senses the forward power to the circuit; a reflected power sensor that senses the reflected power from the circuit; and a processor coupled to the forward power sensor, the reflected power sensor, and the signal generator, wherein the processor controls the signal generator so that the frequency of the signal generated by the signal generator tracks the resonant frequency of the circuit while the material is being heated, and wherein the processor uses the sensed forward and reflected power in controlling the signal generator. 19. The heating system of claim 18, wherein the circuit includes a radiator for producing an electromagnetic field when the amplified signal is provided to the circuit, where the field is used to heat the material.20. The heating system of claim 19, wherein the radiator comprises an induction coil.21. A metho d for tracking the resonant frequency of a circuit comprising the steps of: (1) generating a signal having a frequency (F); (2) providing the signal to the circuit; (3) setting a direction flag to either a first value or a second value; (4) measuring the power applied to the circuit or the power reflected from the circuit; (5) if the direction flag is set to the first value, then decrease the frequency of the signal provided to the circuit to a new frequency (Fnew), where Fnew equals F minus an offset amount; (6) if the direction flag is set to the second value, then increase the frequency of the signal provided to the circuit to a new frequency (Fnew), where Fnew equals F plus an offset amount; (7) measuring the power applied to the circuit or the power reflected from the circuit; (8) determining which of F and Fnew appears closer to the resonant frequency of the circuit, wherein the determination is based at least in part on the applied or reflected power as measured in steps (4) and (7); (9) if F appears closer to the resonant frequency of the circuit and the direction flag is set to the first value, then set the direction flag to the second value and increase the frequency of the signal provided to the circuit; (10) if F appears closer to the resonant frequency of the circuit and the direction flag is set to the second value, then set the direction flag to the first value and decrease the frequency of the signal provided to the circuit. 22. 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