AC Moisture Sensing in Clothes Dryers to Prevent Electrode Aging
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Solution Overview
Problem
Existing clothes drying appliances using DC voltage sensors for moisture content measurement face issues such as electrolysis, spatial polarization effects, and high computational effort, leading to reduced electrode lifespan and inaccurate moisture estimation.
Innovation Solution
The method employs an AC voltage signal with frequencies between 200 Hz and 2000 Hz, specifically 400 Hz, to reduce electrolysis and polarization effects, and uses peak detection and logarithmic filtering to enhance accuracy, allowing for improved moisture content estimation with reduced computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a DC voltage signal is applied to the electrodes for moisture content measurement, then the measurement can be performed, but electrolysis occurs that deteriorates the electrode material and accelerates aging
Solution Approach 1:
The patent changes the voltage signal parameter from DC to AC with frequencies between 200 Hz and 2000 Hz. This parameter change eliminates electrolysis while maintaining moisture content measurement capability, as the alternating current direction prevents the electrochemical reactions that occur with DC voltage.
Solution Approach 2:
The patent applies periodic AC voltage signals instead of continuous DC voltage. The periodic reversal of current direction prevents ion accumulation and electrolysis at the electrodes, extending their operational lifespan while enabling continuous moisture monitoring.
2Measurement precision
If a DC voltage signal is applied to the electrodes, then the measurement can be performed, but spatial polarization effects occur that reduce measurement accuracy
Solution Approach 1:
The patent changes the voltage signal from DC to AC, which eliminates spatial polarization effects. The alternating current prevents charge accumulation in the clothes material, ensuring consistent and reliable moisture content measurements throughout the drying process.
3Productivity
If conventional moisture content estimation methods are used, then the drying cycle can be controlled, but the computational effort is rather high
Solution Approach 1:
The patent changes the measurement signal from DC to AC, which simplifies the computational requirements. The AC signal enables the use of envelope detection and peak detection methods that are computationally less intensive than conventional DC-based moisture estimation algorithms.
4Measurement precision
If the electrodes are regularly covered by clothes during tumbling, then moisture content can be monitored, but the constant contact and disengagement causes measurement variability
Solution Approach 1:
The patent uses periodic AC voltage signals that synchronize with the tumbling motion. By detecting peak values at specific phases of the AC cycle when clothes contact the electrodes, the system obtains consistent measurements despite the periodic contact and disengagement during drum rotation.
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 increases the accuracy of moisture content estimation by up to 40% while extending electrode lifespan and simplifying computations, providing more consistent and precise drying results.
Implementation Method 1
the electrodes are subject to clothes electrolysis that deteriorates the electrode material and accelerates aging of the electrodes
Implementation Method 2
the current sensor exhibits adverse spatial polarization effects
Implementation Method 3
the current measurement is also a measurement of the clothes' electrical conductance
Data Source
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AI summary
The method is used for operating a clothes drying appliance (1) to dry clothes (6), wherein a moisture content of the clothes (6) is determined by measuring a current running through the clothes (6) and wherein an AC voltage signal is applied to the clothes (6), (S3). The appliance (1) is adapted to perform such method. The appliance (1) may comprise at least an AC voltage generator (3) generating an AC voltage, at least one electrode (5) being connected to output ports of the AC voltage generator (3), the at least one electrode (5) being coverable by the clothes (6); and a control circuit (2) functionally connected to the at least one electrode (5) for determining a conductance representative of a moisture content of the clothes (6) from a measured AC current between the electrodes (5).