Dynamic Heating Temperature Control for Thermal Flow Sensor Aging
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Solution Overview
Problem
Conventional thermal-type air flow sensors face issues with aging deterioration of the heating resistor, leading to changes in resistance value and sensitivity characteristics, especially under severe environmental conditions, requiring complex correction circuits and resulting in measurement errors.
Innovation Solution
A thermal type flow measuring apparatus with a heating resistor on a thin substrate and a bridge circuit, where temperature-sensitive resistors are placed near the heating resistor, allowing the heating temperature to be adjusted based on air flow, maintaining low temperatures during idling and increasing as air flow rises, reducing soiling and aging-related errors without complicating the circuit or sensor structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the heating temperature of the heating resistor is lowered to prevent aging deterioration, then the reliability is improved, but the sensitivity of the sensor is decreased
Solution Approach 1:
The heating temperature is made dynamic rather than fixed. The bridge circuit automatically adjusts the heating temperature based on real-time air flow conditions, allowing the system to operate at lower temperatures during idle conditions (improving reliability) and higher temperatures during high air flow conditions (maintaining sensitivity).
Solution Approach 2:
The operating temperature parameter of the heating resistor is changed dynamically according to air flow conditions. The system transitions from a static temperature operation to a variable temperature operation, optimizing both reliability and sensitivity at different operating points.
2Measurement precision
If the heating temperature is increased to maintain sensitivity, then the measurement precision is improved, but the soiling of the heating resistor increases
Solution Approach 1:
The heating temperature is dynamically adjusted based on air flow conditions. During high air flow conditions, the temperature can be increased to maintain sensitivity, while during idle conditions, the temperature is lowered to prevent soiling and thermal migration of particles.
Solution Approach 2:
The patent utilizes the natural cooling effect of air flow over the heating resistor. The air flow that would otherwise cause soiling actually serves to cool the resistor and prevent particle accumulation when the heating temperature is reduced, converting a potential harmful effect into a beneficial one.
3Measurement precision
If a correction circuit is added to compensate for aging deterioration, then the measurement precision is improved, but the device complexity is increased
Solution Approach 1:
The bridge circuit performs self-compensation for aging effects. By incorporating temperature-sensitive resistors that respond to the same thermal environment as the heating resistor, the circuit automatically compensates for resistance value changes due to aging, eliminating the need for external correction circuits.
Solution Approach 2:
The compensation function is merged into the existing bridge circuit structure. The temperature-sensitive resistors are integrated within the same circuit assembly as the heating resistor, combining the heating and compensation functions in a single unified circuit rather than adding separate correction circuitry.
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 configuration enhances sensitivity in high air flow areas, prevents aging deterioration, and reduces measurement errors due to soiling and thermal migration, while maintaining low heating temperatures to prevent particle collection, effectively addressing the challenges faced by conventional sensors.
Implementation Method 1
a heating resistor provided in a thin part of a substrate and a bridge circuit for driving the heating resistor to have a preset heating temperature
Implementation Method 2
a part or whole of at least one of the temperature sensitive resistors is placed in the thin part and near the heating resistor so that the temperature sensitive resistor is influenced by a heat of the heating resistor
Data Source
AI summary
A thermal type flow measuring apparatus includes a heating resistor provided in a thin part of a substrate and a bridge circuit for driving the heating resistor to have a preset heating temperature, wherein resistor elements on sides forming the bridge circuit are temperature sensitive resistors, a part or whole of at least one of the temperature sensitive resistors is placed in the thin part and near the heating resistor so that the temperature sensitive resistor is influenced by a heat of the heating resistor, and the preset heating temperature is increased as the flow of fluid is increased. This configuration introduces flow dependency into the heating temperature of the heating resistor.