Self-regulating Heating Element Using Opposing Metal Oxides
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Solution Overview
Problem
Conventional electrical heating elements lack self-regulating properties, leading to overheating and potential catastrophic failures, and existing self-regulating materials like doped barium titanate have limitations such as unpredictable resistance changes and manufacturing issues resulting in non-uniform characteristics and operational failures.
Innovation Solution
A self-regulating electrical resistance heating element is created using a non-conductive substrate with alternating layers of metal oxides, one with a positive temperature coefficient and the other with a negative temperature coefficient, ensuring a constant resistance until a predetermined temperature is reached, where the resistance increases significantly, preventing overheating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If doped barium titanate is used for self-regulating heating elements, then self-regulating capability is achieved, but resistance becomes unpredictable and non-uniform across temperature range
Solution Approach 1:
The heating element is segmented into multiple discrete heating zones, each with its own temperature sensor and independent control circuitry. This segmentation allows each zone to be controlled independently, compensating for material non-uniformities and ensuring predictable resistance characteristics across the entire element.
Solution Approach 2:
The invention changes the control parameter from relying solely on material resistance characteristics to actively controlling voltage and current parameters. By using pulse-width modulation (PWM) and proportional-integral-derivative (PID) control algorithms, the system maintains predictable resistance behavior despite variations in material properties.
2Ease of manufacture
If conventional heating elements are used, then manufacturing is simple, but elements overheat and fail without self-regulation
Solution Approach 1:
The heating element incorporates temperature sensors and control circuitry that enable it to automatically monitor and regulate its own temperature. The system self-adjusts power consumption based on real-time temperature feedback, eliminating the need for external thermal protection devices while maintaining manufacturing simplicity.
Solution Approach 2:
Temperature sensors continuously monitor the heating element's temperature and feed this information back to the control circuitry. The controller adjusts power delivery in real-time based on this feedback, ensuring the element operates within safe temperature limits while maintaining simple manufacturing processes.
3Reliability
If temperature sensitive bimetallic control devices are added, then overheating protection is achieved, but device complexity increases
Solution Approach 1:
The invention replaces mechanical bimetallic control devices with electronic temperature sensing and control circuitry. Digital temperature sensors and microcontroller-based control systems provide overheating protection through software algorithms, eliminating complex mechanical components while maintaining or improving reliability.
Solution Approach 2:
The control mechanism transitions from mechanical deflection-based control to electrical parameter-based control. The system monitors temperature as an electrical parameter and adjusts power delivery accordingly, simplifying the overall device architecture while enhancing protection capabilities.
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 solution provides a safer and more efficient heating element with consistent performance across a temperature range, preventing overheating and ensuring reliable operation in large-area applications like washing machines and underfloor heating.
Implementation Method 1
a first metal oxide (14) having a positive or negative temperature coefficient of resistance below a predetermined operating temperature
Implementation Method 2
a second metal oxide (16) having a temperature coefficient of resistance opposite to that of said first metal oxide
Implementation Method 3
A self-regulating electrical resistance heating element
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
The present invention relates to a self-regulating electrical resistance heating element, to an appliance containing same, and to processes for their manufacture. The self regulating electrical resistance heating element comprises · a non-electrically conductive substrate (12); · a first metal oxide (14) having a positive or negative temperature coefficient of resistance below a predetermined operating temperature deposited on said substrate; · a second metal oxide (16) having a temperature coefficient of resistance opposite to that of said first metal oxide deposited on said substrate adjacent said first metal oxide; and · first and second electrical contacts (18; 20) disposed such that a current can pass between the contacts through the first and second metal oxides. By placing the respective metal oxides, in e.g. discreet lines, tracks or areas, adjacent one another, with a contact there between or with a sufficient overlap to ensure a good electrical contact it is possible to provide self-regulating electrical resistance heating elements for applications where a large area (compared to 20 e.g. a kettle element) is needed, such as might be the case in a washing machine, dishwasher or tumble dryer.