Asymmetrical Inflow Circuit Package for Thermal Flow Meter Accuracy
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Solution Overview
Problem
Conventional thermal flow meters face challenges in achieving high measurement accuracy due to difficulties in evenly dividing air flow through the air flow sensing portion, leading to inconsistencies in flow rate measurement.
Innovation Solution
The thermal flow meter design includes a bypass passage with asymmetrical inclined and arc cross-sectional inflow-end surfaces to evenly divide the measurement target gas, allowing for precise flow path division and improved heat transfer for accurate flow rate measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional thermal flow meter uses a sealing resin covering the sensor chip with a flush end surface, then the structure is simple and easy to manufacture, but the air flow cannot be evenly divided leading to low measurement accuracy
Solution Approach 1:
The patent applies asymmetry by designing the inflow-side end surface of the circuit package with different shapes for the measurement surface side and backside surface side. Specifically, the measurement surface side has an inclined surface while the backside surface side has a different inclined surface, creating an asymmetrical structure that evenly divides the air flow into two equal paths. This asymmetrical design resolves the contradiction by improving measurement accuracy through balanced flow division while maintaining a relatively simple integrated package structure.
Solution Approach 2:
The patent applies local quality by creating different surface geometries at specific locations of the circuit package. The inflow-side end surface features localized inclined surfaces on the measurement surface side and backside surface side, while other portions of the package maintain conventional structures. This localized modification allows the air flow to be evenly divided at the critical measurement region without unnecessarily complicating the entire device structure.
2Measurement precision
If the inflow-side end surface of the circuit package is asymmetrical, then the air flow is evenly divided improving measurement accuracy, but the manufacturing complexity increases
Solution Approach 1:
The asymmetrical inflow-side end surface design directly addresses the measurement accuracy issue by creating balanced flow paths. The measurement surface side and backside surface side have different inclined surfaces that work together to evenly split the air flow. This asymmetrical geometry is designed to be manufacturable using conventional molding techniques, balancing the need for precise flow division with practical manufacturing capabilities.
Solution Approach 2:
The patent incorporates curved or arc-shaped cross-sectional surfaces in the inflow-side end surface design. These curved surfaces help to smoothly guide and divide the air flow without creating turbulence or dead zones. The curvature provides gradual flow transitions that are easier to manufacture with high precision compared to sharp angular features, thus improving both measurement accuracy and manufacturability.
3Measurement precision
If the air flow sensing portion is not evenly divided, then the device structure remains simple, but flow velocity variations cause measurement inconsistencies
Solution Approach 1:
The asymmetrical inflow-side end surface creates a symmetrical flow division effect by balancing the flow paths on either side of the measurement surface. The different inclined surfaces on the measurement surface side and backside surface side work together to ensure equal flow distribution, eliminating velocity variations that would cause measurement inconsistencies.
Solution Approach 2:
The bypass passage is configured to divide the air flow into two separate flow paths that pass on opposite sides of the measurement surface. This segmentation of the flow path, combined with the asymmetrical inlet geometry, ensures that the heat generator receives consistent thermal conditions from evenly divided air streams, improving measurement consistency.
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 the measurement accuracy of gas flow rates by minimizing the impact of flow velocity variations and temperature differences, resulting in a more reliable and precise thermal flow meter.
Implementation Method 1
an air flow sensing portion for measuring a flow rate of the measurement target gas by performing heat transfer with the measurement target gas flowing through the bypass passage
Data Source
AI summary
A thermal flowmeter circuit package having a side of a measurement surface 430 of the circuit package and a flow path 387 at a side of the backside of measurement surface 431 of a rear surface of the measurement surface 430, and an inflow-side end surface of the circuit package for dividing the measurement target gas 30 has different shapes at the side of the measurement surface and at the side of the backside of measurement surface. The inflow-side end surface of the circuit package for dividing the measurement target gas 30 is formed with a reference line 700 dividing the measurement target gas 30, and an end surface 701a at the side of the measurement surface with respect to the reference line and an end surface 701b at the side of the backside of measurement surface with respect to the reference line are formed to be asymmetrical.