Resistive Heater Calibration via Resistance-Temperature Correlation
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Solution Overview
Problem
Multizone pedestal heaters with two-wire resistive heating elements face inaccuracies in temperature calculation due to manufacturing variations, material batch variations, age of the heater, number of cycles, and other factors, leading to inconsistent heater performance.
Innovation Solution
A method involving powering a heater to a first temperature setpoint, concurrently obtaining resistance and reference temperature measurements as the heater cools passively, and generating a resistance-temperature calibration table to correlate these measurements, thereby addressing the inaccuracies in temperature calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If predefined resistance-temperature data tables are used for temperature calculation, then the control system can determine temperature based on resistance measurements, but manufacturing variations and material batch variations cause inaccuracies in calculated temperatures
Solution Approach 1:
The patent applies parameter changes by transitioning from fixed predefined resistance-temperature data tables to dynamically generated calibration curves. Each heater element undergoes individual calibration that captures its specific resistance-temperature relationship, accounting for manufacturing variations and material batch differences. This customizes the temperature calculation parameters for each heater rather than using universal standardized data.
Solution Approach 2:
The patent implements feedback through an iterative calibration process where actual temperature measurements from reference sensors are compared with calculated temperatures from resistance measurements. The calibration curve is adjusted based on this feedback to minimize the difference between measured and calculated temperatures, improving accuracy for each specific heater element.
2Measurement precision
If individual calibration is performed for each heater element, then temperature measurement accuracy is improved, but the calibration process becomes more complex and time-consuming
Solution Approach 1:
The patent applies self-service by designing a calibration system where the heater element itself serves as the test subject during its own calibration process. The calibration procedure uses the heater's inherent resistive properties and integrates temperature sensing directly into the calibration routine, eliminating the need for separate external calibration equipment and simplifying the overall process.
Solution Approach 2:
The patent implements universality by creating a standardized calibration methodology and software routine that can be applied to all heater elements regardless of their specific variations. The same calibration procedure and data processing algorithm work universally across different heater batches, making the complex calibration process manageable through automation and standardization.
3Reliability
If heater performance variations due to age and usage cycles are accounted for, then long-term temperature accuracy is improved, but requiring frequent recalibration increases maintenance time
Solution Approach 1:
The patent applies preliminary action by performing comprehensive calibration at multiple predetermined temperature points during the initial setup and at scheduled intervals. This advance calibration captures the heater's behavior across its full operating range, creating a robust calibration curve that remains accurate through extended use. The system also monitors resistance changes over time to predict when recalibration may be needed, allowing proactive scheduling rather than reactive maintenance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method generates accurate resistance-temperature calibration data, improving the precision of temperature determination in multizone heaters by accounting for individual heater variations.
Implementation Method 1
the heater comprises a resistive heating element having a varying temperature coefficient of resistance
Implementation Method 2
the resistive material defines a temperature coefficient of resistance (TCR), and the temperature of the resistive heating elements can be determined based on the TCR and measured resistance of the heating element
Data Source
Figure 1A
Figure 1B
Figure 2A~2B
AI summary
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.