Model-Based Temperature Control for Calibration Volume Stability
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Solution Overview
Problem
Current temperature calibrators face challenges in achieving high precision and stability, especially at high temperatures, due to large inertia in the controlled system and the need for complex parameter adjustments in PID controllers, leading to temperature stability issues of ±30 mK, which is worse than the desired ±5 mK for high-precision calibrations.
Innovation Solution
A model-based control method is employed to regulate the temperature of the calibration volume, using a dynamic model that includes control and manipulated variables, disturbances, and process variables, implemented on an electronic data processing unit, which calculates future temperature values and adjusts heating and cooling elements to achieve optimal temperature stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PID controllers are used to control the temperature of the calibration volume, then the temperature can be regulated, but the temperature stability is poor (±30 mK) and complex parameter adjustment is required
Solution Approach 1:
The patent changes the control parameters from traditional PID parameters (Kp, Ki, Kd) to model-based parameters (thermal conductivity, heat capacity, geometric dimensions) that can be determined through simple measurement procedures. This transformation simplifies the control setup while improving temperature stability from ±30 mK to ±3 mK by using a thermal model that directly relates measurable physical parameters to optimal control behavior.
2Stability of the object's composition
If the heat conduction part is designed with high heat capacity to ensure thermal stability, then temperature uniformity improves, but the system inertia increases causing slow response to environmental changes
Solution Approach 1:
The patent applies dynamic control by using a thermal model that explicitly accounts for the system's thermal inertia and time constants. Instead of treating the high heat capacity as a limitation, the model-based controller uses the known thermal properties to predict future temperature states and proactively adjust heating power, achieving both temperature uniformity and fast response to environmental changes.
Solution Approach 2:
The thermal model allows the controller to perform preliminary calculations of the required heating power based on predicted future conditions. By calculating optimal control actions in advance using the known thermal properties, the system can respond quickly to environmental changes while maintaining temperature uniformity, avoiding the lag associated with reactive control.
3Temperature
If target temperatures above 500°C are controlled using conventional methods, then high temperature calibration is achieved, but temperature stability deteriorates to ±30 mK
Solution Approach 1:
The patent replaces conventional mechanical PID control with a model-based control system that uses thermal physics equations to determine optimal heating power. This substitution enables stable temperature control above 500°C by using a thermal model that accurately predicts heat distribution and losses at high temperatures, achieving ±3 mK stability where conventional methods only achieve ±30 mK.
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
This approach achieves temperature stability of about ±3 mK for target temperatures above 500°C, significantly improving upon previous methods and allowing for highly accurate calibration up to 700°C while avoiding overshoots.
Implementation Method 1
heat sources and/or heat sinks which are in thermal contact with the calibration volume through one or more heat conducting parts
Implementation Method 2
heat sinks, such as Peltier elements operated as cooling elements
Data Source
AI summary
The invention relates to a method for regulating the temperature of the calibration volume of an apparatus for comparative calibration of temperature sensors to a target temperature, wherein said calibration device comprises heat sources and/or heat sinks, which are in thermal contact via a heat conducting part or a plurality of heat conducting parts with the calibration volume, wherein in at least one process step the real thermal state is calculated, wherein the Kalman filter is fed the measurement values of a temperature sensor located in the calibration device, and in at least one more process step the future thermal state is calculated using a thermal model of the dynamics of states.