Lambda Probe Sensing in Cooking Chambers for Moisture Detection
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Solution Overview
Problem
Existing cooking appliances face challenges in accurately determining properties like humidity in the cooking chamber due to temperature limitations of sensors, leading to inaccurate measurements and interference from cooling air, especially when the vapor duct is closed or the cooling fan is off.
Innovation Solution
A cooking appliance equipped with a lambda probe that operates in both conventional and decomposition modes, allowing it to measure oxygen and moisture content directly within the cooking chamber by differentiating between measurement signals, thereby reducing cross-sensitivities and enabling precise detection of cooking states and processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sensors are installed outside the cooking chamber (in vapor duct or cooling fan area), then the sensors can operate within their temperature tolerance range, but the measurement signal is falsified by cooling air and no analyzable signal is available when vapor duct is closed or cooling fan is switched off
Solution Approach 1:
A lambda probe is introduced as an intermediary sensor that can withstand high temperatures and be directly installed in the cooking chamber. The lambda probe measures oxygen concentration in the cooking atmosphere, which serves as an indirect but accurate indicator of moisture content, thereby resolving the contradiction between sensor durability and measurement accuracy.
Solution Approach 2:
The measurement approach is changed from direct humidity sensing to oxygen concentration measurement. By monitoring oxygen levels in the cooking chamber atmosphere, the system indirectly determines moisture content with high precision, while the sensor operates reliably in high-temperature environments.
2Measurement precision
If a lambda probe is used to measure oxygen content in the cooking chamber, then moisture content can be determined through oxygen displacement, but the measurement signal includes both atmospheric oxygen and oxygen from water decomposition at high temperatures
Solution Approach 1:
The lambda probe operates in alternating measurement modes: conventional mode for standard oxygen measurement and decomposition mode for water-specific oxygen measurement. By periodically switching between these modes, the system distinguishes between atmospheric oxygen and oxygen from water decomposition, enabling accurate moisture determination despite signal complexity.
Solution Approach 2:
The lambda probe's operating voltage is changed between two distinct levels: a first voltage for conventional oxygen measurement and a second, higher voltage for water decomposition measurement. This parameter change enables the probe to selectively measure different oxygen sources, simplifying the interpretation of measurement signals.
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 allows for reliable detection of cooking states, progress, and contamination, enabling precise control and regulation of cooking processes, including moisture and pyrolysis management, independent of cooling air flow, and operates effectively at high temperatures.
Implementation Method 1
Lambda probes based on an ionically conductive sensor element, typically made of zirconium dioxide (ZrO2), generally compare a galvanic potential of an electrode on the sample gas side with a galvanic potential of a reference electrode
Implementation Method 2
Lambda probes based on an ionically conductive sensor element, typically made of zirconium dioxide (ZrO2), generally compare a galvanic potential of an electrode on the sample gas side with a galvanic potential of a reference electrode
Implementation Method 3
operating the lambda probe in alternating operation between conventional operation and decomposition operation, the lambda probe in decomposition operation having a Pumping voltage is operable, which is higher than a decomposition voltage of water, so that it is decomposed onto the lambda probe impinging water into hydrogen and oxygen
Data Source
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AI summary
The cooking appliance (1) is equipped with a cooking chamber (2) and at least one sensor (8, 10, 11) for detecting at least one property of the cooking chamber (2), the at least one sensor comprising at least one lambda probe (8, 10). . The lambda probe (8, 10) can in particular protrude into the cooking chamber (2).