Thermal Conductivity Sensor Bridge Circuit for Gas Composition Correction
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Solution Overview
Problem
Conventional thermal based MEMS flow sensors struggle to accurately measure gas flow when the gas composition varies or is unknown, as they rely on specific gas identities for precise mass flow determination.
Innovation Solution
A cost-effective, small, and low-power thermal conductivity and diffusivity sensor is integrated into or used concurrently with conventional mass flow sensors, utilizing a bridge circuit with temperature-stable tail resistors to determine thermal properties of fluids, allowing for correction of mass flow measurements by measuring power dissipation and rate of temperature rise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional thermal based MEMS flow sensors are used to measure gas flow, then the measurement is simple and direct, but the accuracy deteriorates when gas composition varies or is unknown
Solution Approach 1:
The patent measures thermal conductivity and thermal diffusivity parameters of the gas to characterize its composition. By detecting these thermal parameters through the bridge circuit and temperature-stable resistors, the system adapts to different gas compositions and corrects mass flow measurements accordingly, resolving the accuracy issue when gas composition varies.
2Measurement precision
If thermal conductivity and diffusivity sensor is integrated with mass flow sensor, then the measurement accuracy for unknown gas compositions is improved, but the device complexity increases
Solution Approach 1:
The patent combines thermal conductivity/diffusivity sensing elements with the mass flow sensor into a single integrated device. The bridge circuit incorporates both the mass flow sensing elements and the thermal property sensing elements, allowing simultaneous measurement of mass flow and thermal properties to correct for gas composition variations.
Solution Approach 2:
The bridge circuit is designed to perform multiple functions: measuring mass flow rate and simultaneously determining thermal conductivity and thermal diffusivity. This multi-functionality allows a single device to handle both flow measurement and gas composition characterization, improving accuracy without requiring separate independent systems.
3Measurement precision
If temperature-stable resistors are used in the bridge circuit to determine thermal properties, then the thermal property measurement accuracy is improved, but the manufacturing cost increases
Solution Approach 1:
The patent uses temperature-stable resistors with specific resistance temperature coefficients to compensate for thermal effects in the bridge circuit. By selecting resistors with appropriate thermal characteristics, the system achieves accurate thermal conductivity and diffusivity measurements while maintaining manufacturing feasibility through standard resistor selection and circuit design.
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
Enables accurate correction of mass flow values for unknown gas compositions by determining thermal conductivity and diffusivity, enhancing the precision of gas flow measurement across various industrial applications.
Implementation Method 1
a heating element configured to be substantially in direct thermal coupling with the fluid flowing through the flow channel
Implementation Method 2
an upstream resistive element having a first resistance that changes with temperature; a downstream resistive element having a second resistance that changes with temperature
Data Source
AI summary
Embodiments relate generally to a sensor for sensing a thermal property of a fluid and may comprise an upstream resistive element having a first resistance that changes with temperature; a downstream resistive element having a second resistance that changes with temperature, wherein the downstream resistive element is situated downstream of the upstream resistive element in the flow direction of the fluid; and at least one tail resistor configured to determine one or more thermal properties of the fluid, wherein the upstream resistive element and the downstream resistive element are operatively connected in a bridge circuit, wherein the at least one tail resistor is stable with temperature, and wherein the at least one tail resistor is electrically coupled to at least one of the upstream resistive element or the downstream resistive element.