Differential Thermal Gas Sensor Structures for Disturbance Compensation
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Solution Overview
Problem
Thermal sensor devices face challenges in accurately determining the concentration of a target gas due to cross-sensitivities to disturbance gases, temperature, and pressure changes, which affect the accuracy of measurements.
Innovation Solution
A thermal sensor device with first and second measurement structures having different heat dissipation capabilities, utilizing a weighted difference of temperature signals from these structures to reduce sensitivity to disturbance gas concentration changes, and optionally incorporating a heater bridge with temperature sensors to minimize heater drifts and pressure sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single thermal sensor is used to measure target gas concentration, then the measurement is simple and low-cost, but the accuracy is compromised due to cross-sensitivity to disturbance gases
Solution Approach 1:
The single thermal sensor is segmented into two measurement structures with different heat dissipation capabilities (different thermal conductances to the substrate). This segmentation allows the system to distinguish between target gas and disturbance gas effects by comparing responses from the two structures, thereby improving measurement accuracy without adding multiple independent sensors
Solution Approach 2:
The two measurement structures are designed with different local thermal properties (different thermal conductances to substrate). This local quality difference creates distinct responses to the same gas composition, enabling the system to mathematically separate and compensate for disturbance gas effects while maintaining a relatively simple overall device structure
2Measurement precision
If additional sensors (humidity sensor, temperature sensor, pressure sensor) are added to compensate for cross-sensitivities, then the measurement accuracy is improved, but the device complexity and cost increase
Solution Approach 1:
The two measurement structures serve multiple functions simultaneously: they both detect thermal changes caused by target gas concentration variations, and they also provide differential information for compensating disturbance gas effects. This multi-functionality eliminates the need for separate humidity, temperature, and pressure sensors, reducing device complexity while maintaining accuracy
Solution Approach 2:
The measurement structures serve themselves by providing the necessary differential information for compensation. The system uses its own internal response variations (caused by different thermal conductances) to automatically compensate for disturbance gases, eliminating the need for external compensation sensors and reducing overall device complexity
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 device achieves reduced sensitivity to disturbance gas and pressure changes, enhancing the accuracy of target gas concentration measurements by compensating for these interferences in the output signal.
Implementation Method 1
Heat transfer between the heater and the temperature sensors is influenced by heat transfer through the fluid
Implementation Method 2
the heater is provided with heating power, and the steady-state response and/or transient response of the temperature sensors to the heating power is measured
Implementation Method 3
the first and second measurement structures have different heat dissipation capabilities, i.e., when heat is transferred to these measurement structures through the gas sample, these measurement structures dissipate the heat to the environment with different efficiencies
Data Source
AI summary
A thermal sensor device serves for determining a concentration of a target gas in a gas sample that further comprises a disturbance gas. The thermal sensor device comprises first and second measurement structures (1, 2) comprising first and second temperature sensors (TS1, TS2) and a heater element (31) operable to cause heat transfer to the measurement structures through the gas sample. Processing circuitry provides heating power (P_3) to the heater element and derives an output signal (S) based on a response of the temperature sensors to the heating power, the output signal being indicative of a concentration of the target gas in the gas sample. The first and second measurement structures have different heat dissipation capabilities, and the processing circuitry derives the output signal from a weighted difference of temperature signals from the first and second temperature sensors. Thereby, a cross-sensitivity of the output signal to a concentration change of the disturbance gas may be reduced or eliminated.