Thermal Conductivity Gas Sensor with Heating Unit
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Solution Overview
Problem
Concentration measurement accuracy is compromised when gases with significantly different thermal conductivity rates are mixed, as the relationship between thermal conductivity and concentration becomes non-linear, especially at lower temperatures, making it difficult to accurately determine the concentration of a target gas in a mixture.
Innovation Solution
A concentration measurement device that uses a heating unit to heat the gas mixture, allowing the concentration of the target gas to be uniquely determined based on thermal conductivity, by applying a second voltage higher than the initial voltage used for flow rate measurement, ensuring a one-to-one correlation between electromotive force and concentration, even in mixtures with gases having vastly different thermal conductivity rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If thermal conductivity measurement is used to determine gas concentration in a mixture, then concentration measurement can be achieved, but measurement accuracy deteriorates when gases have significantly different thermal conductivity rates of change with temperature
Solution Approach 1:
The patent applies parameter changes by heating the gas mixture to a specific temperature range (e.g., 50°C to 150°C) where the thermal conductivity characteristics of different gases result in a monotonic relationship between thermal conductivity and concentration. This temperature control transforms the measurement conditions to ensure accurate concentration determination even when gases have different thermal conductivity rates of change.
Solution Approach 2:
The patent implements preliminary action by pre-heating the gas mixture before concentration measurement to establish optimal measurement conditions. The heating unit raises the gas temperature in advance to a range where the thermal conductivity-concentration relationship is well-defined and monotonic, ensuring accurate measurements from the start of the measurement process.
2Measurement precision
If a heating unit is used to heat the gas mixture for accurate concentration measurement, then measurement accuracy improves, but device complexity and energy consumption increase
Solution Approach 1:
The heating unit serves multiple functions: it heats the gas mixture to optimize thermal conductivity measurement conditions, and it also prevents condensation of the gas mixture. This multi-functionality reduces the need for separate heating devices, thereby minimizing the increase in device complexity while maintaining measurement accuracy.
Solution Approach 2:
The patent merges the heating function with the measurement system by integrating the heating unit directly into the sensor assembly. This consolidation combines the heating function with the thermal conductivity measurement function, reducing the number of separate components and simplifying the overall device structure.
3Device complexity
If thermal conductivity measurement is performed without heating control, then device complexity is reduced, but measurement accuracy deteriorates due to non-monotonic relationship between thermal conductivity and concentration
Solution Approach 1:
The patent changes the temperature parameter of the gas mixture to a controlled range where the thermal conductivity-concentration relationship becomes monotonic. By maintaining the gas temperature within this optimized range through the heating unit, the system achieves accurate concentration measurements without requiring complex additional measurement systems.
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 enhances the accuracy of concentration measurement by maintaining a one-to-one correlation between thermoelectric output and concentration, effectively reducing errors in mixed gas environments where thermal conductivity rates differ substantially.
Implementation Method 1
a sensor (2, 22, 23, 24) configured to measure a concentration of a measurement target gas (oxygen, argon, hydrogen) in a mixture of gases on the basis of thermal conductivity of the measurement target gas
Implementation Method 2
The flow sensor includes, for example, a sensor having a heater on a thin film (a membrane) and thermopiles arranged so as to sandwich the heater. When a heat distribution generated by the heater heating the thin film is disturbed by a flow of fluid, the disturbance is measured as a difference in thermoelectric power generated in the thermopile.
Implementation Method 3
a heating unit configured to heat the mixture of gases so that a concentration of the measurement target gas can be uniquely determined with respect to the thermal conductivity
Data Source
AI summary
It is possible to reduce a decrease in accuracy of measuring the concentration of a measurement target gas even in a case where, in a mixture of gases, there is a gas greatly different from another gas in a rate of change in thermal conductivity with respect to temperature. The concentration measurement device includes a sensor configured to measure the concentration of a measurement target gas in a mixture of gases on the basis of thermal conductivity of the measurement target gas, the mixture of gases including two or more components, and a heating unit configured to heat the mixture of gases so that the concentration of the measurement target gas can be uniquely determined with respect to the thermal conductivity.