Dryer Moisture Sensing Circuit With Line Noise Filtering
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Solution Overview
Problem
Existing moisture sensing circuits in clothes dryers face inaccuracies due to noise related to the line operating frequency, which affects the accuracy of moisture content detection.
Innovation Solution
A moisture sensing circuit with a pair of spaced-apart electrode sensors and an active filter that suppresses noise related to the operating line frequency, using a first low pass filter and a voltage follower amplifier to provide a filtered voltage signal, and an over voltage suppressor amplifier to protect the microprocessor controller from high voltage spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If electrode sensors are used to detect moisture content in clothes, then moisture detection capability is provided, but the detected signal contains noise related to line operating frequency that reduces measurement accuracy
Solution Approach 1:
The patent extracts and removes the harmful power line frequency noise component from the moisture sensing signal while preserving the useful moisture-related signal variations. This is achieved through filtering techniques that separate the desired signal from the noise, directly addressing the contradiction by taking out the harmful interference.
Solution Approach 2:
The patent introduces intermediary filtering circuits and signal processing components between the electrode sensors and the microprocessor controller. These intermediaries process the raw sensor signal to eliminate power line noise before the signal is used for moisture determination, thereby resolving the contradiction through intermediate signal conditioning.
2Device complexity
If the moisture sensing circuit directly processes the raw voltage signal from sensors, then simple circuit design is maintained, but signal accuracy deteriorates due to unfiltered power line noise
Solution Approach 1:
The patent introduces intermediary filtering circuits and signal processing components between the electrode sensors and the microprocessor controller. These intermediaries process the raw sensor signal to eliminate power line noise before the signal is used for moisture determination, thereby resolving the contradiction through intermediate signal conditioning.
Solution Approach 2:
The patent replaces direct electrical connection with electronic filtering mechanisms. Instead of using complex hardware modifications to the sensors themselves, the solution substitutes signal processing electronics that can selectively remove noise frequencies while preserving the moisture signal.
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 solution improves the accuracy of moisture-related signals by filtering out power line noise, ensuring more reliable moisture detection during the drying process.
Implementation Method 1
a pair of spaced apart electrode sensors for sensing the electrical resistance of the clothes when the clothes contact the electrodes
Implementation Method 2
A first low pass filter is provided in the circuit... The active filter suppresses noise related to operating line frequency
Data Source
AI summary
A moisture sensing circuit for a clothes dryer in which clothes tumble during drying has a pair of spaced apart electrode sensors for sensing the electrical resistance of the clothes when the clothes contact the electrodes. The circuit has an active filter for suppressing noise related to the operating line frequency of the clothes dryer to provide a filtered voltage signal representative of voltage drop across the electrode sensors with the line frequency noise suppressed.