Surface Heater Capacitance Sensing for Isolated Temperature Measurement
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Solution Overview
Problem
Existing surface heating technologies for household appliances face challenges in accurately measuring temperature without additional sensors, particularly due to high-voltage requirements and leakage current limitations, which complicate the measurement technology and increase costs.
Innovation Solution
A panel heater with a heating conductor applied to an electrically insulating layer of temperature-dependent permittivity, featuring measuring electrodes isolated from the heating conductor, allows for capacitance measurement using a capacitance measuring device connected to these electrodes, eliminating the need for the heating conductor as a capacitor pole and ensuring safety and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the heating conductor is used as one pole of the capacitance sensor, then temperature measurement is enabled without additional sensors, but high-voltage requirements and leakage current limitations arise
Solution Approach 1:
The capacitance sensor is divided into two separate poles: the heating conductor remains dedicated to heating functions, while a separate measuring electrode is introduced for capacitance measurement. This segmentation eliminates the conflict between heating and measurement functions, allowing temperature measurement without exposing measurement circuitry to high-voltage risks.
Solution Approach 2:
A separate measuring electrode acts as an intermediary element that enables capacitance measurement without directly connecting the measurement circuit to the high-voltage heating conductor. The insulating layer serves as the dielectric medium between the measuring electrode and heating conductor, isolating the measurement side from high-voltage risks while still enabling temperature-dependent capacitance measurement.
2Measurement precision
If additional temperature sensors are used, then temperature measurement accuracy is improved, but device complexity and costs increase
Solution Approach 1:
The heating conductor serves dual purposes: it functions as both the heating element and one pole of the capacitance sensor. The insulating layer simultaneously provides electrical insulation and acts as the dielectric for temperature measurement. This multi-functionality eliminates the need for separate temperature sensors while maintaining measurement capability.
Solution Approach 2:
The heating system itself provides the components needed for temperature measurement without requiring external sensing elements. The heating conductor and insulating layer collectively form the capacitance sensor, allowing the system to self-monitor its temperature state through capacitance changes caused by temperature-dependent permittivity variations in the insulating layer.
3Object-affected harmful factors
If the substrate is isolated from ground, then leakage current requirements are circumvented, but touch protection measures are required
Solution Approach 1:
The insulating layer serves as an intermediary that provides both electrical insulation for high-voltage isolation and a grounded substrate for safety. The substrate can be connected to ground for touch protection while the measuring electrode, positioned on the insulating layer side, remains isolated from ground, thereby satisfying both safety requirements and measurement needs.
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 enables precise temperature determination without the need for additional sensors, avoiding high-voltage and leakage current concerns, and simplifies the measurement process, reducing costs and enhancing safety.
Implementation Method 1
an electrically insulating insulation layer with a temperature-dependent changeable permittivity
Implementation Method 2
determine the capacitance between a heating conductor and an electrically conductive substrate, which are separated from one another by an electrically insulating insulation layer
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A surface heater (11) for a household appliance (H1) comprises at least one strip-shaped heat conductor (104) that is applied to an electrically insulating insulation layer (103; 12), the permittivity of which changes according to the temperature. At least one measuring electrode (4, 5) that is electrically insulated in relation to the at least one heat conductor (104) is applied to the same side of the insulation layer (103) as the heat conductor (104). A household appliance (H1), in particular an appliance for cooking food, especially a cooking appliance, comprises at least one system consisting of at least one surface heater (11) and at least one temperature measuring device (K, A).