PASSIVE AND ACTIVE CALIBRATION METHODS FOR A RESISTIVE HEATER
A method of calibrating a heater includes powering the heater to a first temperature setpoint. The heater includes a resistive heating element that has a varying temperature coefficient of resistance. The method further includes concurrently obtaining a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater cools from a first temperature setpoint to a second temperature setpoint that is lower than the first temperature setpoint, and generating a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.
1 . A method of calibrating a heater, the method comprising:
powering a heater in an isothermal environment to a first temperature setpoint, wherein the heater comprises a resistive heating element having a temperature coefficient of resistance;
concurrently obtaining a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from a first temperature setpoint to a second temperature setpoint; and
generating a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.
2 . The method of claim 1 further comprising turning-off power to the heater when the heater is at the first temperature setpoint to passively cool the heater.
3 . The method of claim 1 , wherein the reference member is an exterior surface of the heater.
4 . The method of claim 3 , wherein the plurality of reference temperature measurements of the surface of the heater are obtained with an infrared camera.
5 . The method of claim 1 , wherein the plurality of reference temperature measurements are obtained with a thermocouple wafer and the reference member is the thermocouple wafer.
6 . The method of claim 1 , wherein to obtain a resistance measurement from among the plurality of resistance measurements, the method further comprises measuring at least one of an electric current and a voltage concurrently with the plurality of reference temperatures, and determining the resistance measurement based on the measured at least one electric current and the voltage.
7 . A method of calibrating a heater, the method comprising:
powering the heater in a designated environment to a first temperature setpoint, wherein the heater comprises a resistive heating element having a varying temperature coefficient of resistance;
concurrently obtaining a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from a first temperature setpoint to a second temperature setpoint that is lower than the first temperature setpoint; and
generating a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.
8 . The method of claim 7 , wherein the designated environment is an isothermal environment.
9 . The method of claim 7 , wherein the designated environment is an operating environment in which the heater is operable to heat a workpiece.
10 . The method of claim 7 further comprising turning-off power to the heater when the heater is at the first temperature setpoint to passively cool the heater.
11 . The method of claim 7 , wherein the reference member is an exterior surface of the heater.
12 . The method of claim 11 , wherein the plurality of reference temperature measurements of the exterior surface of the heater are obtained with an infrared camera.
13 . The method of claim 7 , wherein the plurality of reference temperature measurements are obtained with a thermocouple wafer and the reference member is the thermocouple wafer.
14 . The method of claim 7 , wherein to obtain a resistance measurement from among the plurality of resistance measurements, the method further comprises measuring at least one of an electric current and a voltage concurrently with the plurality of reference temperatures, and determining the resistance measurement based on the measured at least one electric current and the voltage.
15 . A control system for controlling a heater having a resistive heating element, the control system comprising:
a power converter configured to provide an output voltage that is adjustable to the heater;
a controller configured to determine the output voltage to be applied to the heater, the controller comprises:
a memory configured to store a plurality of control programs for controlling the heater, wherein the plurality of control programs includes a calibration process; and
a processor configured to execute the plurality of control programs, wherein with the heater is in a designated environment, the calibration process includes instructions to:
turn-on power to the heater to heat the heater to a first temperature setpoint;
concurrently obtain a plurality of resistance measurements of the resistive heating element and a plurality of reference temperature measurements of a reference member as the heater passively cools from the first temperature setpoint to a second temperature setpoint; and
generate a resistance-temperature calibration table that correlates the plurality of resistance measurements with the plurality of reference temperature measurements.
16 . The control system of claim 15 , wherein the calibration process further includes instructions to turn-off power to the heater when the heater is at the first temperature setpoint to passively cool the heater.
17 . The control system of claim 15 , wherein the reference member is an exterior surface of the heater.
18 . The control system of claim 15 , wherein the second temperature setpoint is lower than the first temperature setpoint.
19 . The control system of claim 15 , wherein the designated environment is an isothermal environment.
20 . The control system of claim 15 , wherein to obtain a resistance measurement from among the plurality of resistance measurements, the calibration process further includes instructions to measure at least one of an electric current and a voltage concurrently with the plurality of reference temperature measurements, and determine the resistance measurement based on the at least one electric current and the voltage.