Thermal Conductivity Sensor Common Mode Noise Rejection
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Solution Overview
Problem
Existing sensors for determining thermal conductivity of fluids face sensitivity limitations due to ambient temperature fluctuations and convective or flow effects, which are difficult to mitigate without compromising time response.
Innovation Solution
A sensor design where both measurement and reference sections are held within the same environment, allowing for common mode rejection of background noise, with a diffusive element to minimize flow effects and thermal breaks to reduce thermal leaks, enabling precise measurement of thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a sealed reference element is used in a stable medium to negate temperature changes, then temperature stability is improved, but it cannot compensate for flow or convective effects and requires precise matching
Solution Approach 1:
The patent merges the reference element and measurement element into a single integrated sensor structure where both elements are positioned in close proximity within the same housing. This allows both elements to experience the same flow and convective conditions while the reference element remains thermally isolated, enabling simultaneous compensation of temperature, flow, and convective effects without requiring separate matched components
Solution Approach 2:
The patent introduces a thermal isolation structure (insulating material) as an intermediary between the reference element and the fluid flow path. This intermediary blocks thermal conduction from the fluid to the reference element while allowing the reference element to still experience pressure and flow conditions, enabling selective compensation
2Object-affected harmful factors
If convective effects are minimized through purely diffusion driven systems, then convective interference is reduced, but time response becomes poor
Solution Approach 1:
The patent applies different flow conditions to different regions: the measurement element is positioned in the main flow path to experience forced convection for fast response, while the reference element is positioned in a region with minimized flow effects through thermal isolation, allowing each element to operate under optimal local conditions
3Temperature
If ambient temperature fluctuations are measured, then temperature compensation can be applied, but sensitivity to actual thermal conductivity changes is reduced
Solution Approach 1:
The patent segments the sensor into distinct measurement and reference portions with different thermal coupling characteristics. The measurement element is thermally coupled to detect fluid thermal conductivity changes, while the reference element is thermally isolated to detect only ambient temperature changes, allowing separate processing of these signals to achieve both compensation and sensitivity
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 design enhances sensor performance by rejecting noise and allowing for fast and accurate determination of thermal conductivity, even in dynamic fluid compositions, with improved sensitivity and quick response to fluid changes.
Implementation Method 1
The basic time independent equation for thermal conductivity between two surfaces of area A, separated by a medium of thermal conductivity K
Implementation Method 2
K can also be measured in the time domain where the thermal gradient is changing with time
Implementation Method 3
Efforts to minimise convective effects through designs to have purely diffusion driven systems
Data Source
Figure 1~2
Figure 3
AI summary
The present invention provides a sensor for determining the thermal conductivity of a fluid. The sensor comprises a sensing module located within a housing having inlet and outlet ports for a fluid under test. The sensing module comprising a reference base surface and a sensing element spaced therefrom and having measure and reference sections. There are also provided electrical power monitoring means for monitoring the power through the measure and reference sections in order to generate a signal indicating the power difference due to thermal conductivity through the fluid.