Thermal Mass Flow Meter Droplet Adhesion Protection
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Solution Overview
Problem
Thermal mass flowmeters face challenges in achieving high accuracy and reliability in gas flowrate measurement due to droplet adhesion, which can lead to thermal deterioration and breakage, and existing solutions struggle to balance measurement precision with droplet adhesion detection and control response.
Innovation Solution
A thermal mass flowmeter with an output impedance adjustment mechanism and current limit mechanism is implemented to control the calorific value of the heating element, preventing overheating and thermal deterioration by adjusting the output impedance and limiting current flow when droplets adhere, thereby ensuring accurate measurement and preventing breakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the heating element operates at high temperature to improve measurement accuracy, then measurement precision is improved, but the sensor portion becomes vulnerable to thermal deterioration and breakage when droplets adhere
Solution Approach 1:
The control circuit performs preliminary detection of droplet adhesion by monitoring resistance changes before the heating element reaches high temperatures. When droplet adhesion is detected, the circuit preemptively limits the heating power or shuts down the heating element, preventing thermal deterioration before it occurs. This preliminary action resolves the contradiction by enabling high-accuracy measurement during normal operation while protecting the sensor when contaminants are present.
2Measurement precision
If the heating element temperature is increased to enhance measurement accuracy, then measurement precision is improved, but the risk of breakage due to droplet adhesion increases
Solution Approach 1:
The control circuit continuously monitors the resistance of the heating element and uses this feedback to detect droplet adhesion. When the resistance change indicates droplet presence, the system immediately adjusts the heating power accordingly. This feedback mechanism allows the heating element to operate at optimal temperatures for accurate measurement while automatically preventing conditions that would lead to breakage, thus resolving the strength-precision contradiction.
3Reliability
If droplet adhesion detection and control mechanisms are added to prevent thermal deterioration, then reliability is improved, but device complexity increases
Solution Approach 1:
The control circuit performs multiple functions using the same hardware components: it measures the heating element's resistance for droplet detection, controls the heating power to prevent thermal deterioration, and maintains accurate flowrate measurement. By making the control circuit multi-functional, the system achieves improved reliability without proportionally increasing device complexity, as the same circuitry serves multiple protective and measurement purposes simultaneously.
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 solution enables higher accuracy in gas flowrate measurement while preventing thermal deterioration and breakage caused by droplet adhesion, ensuring the reliability of the thermal mass flowmeter.
Implementation Method 1
a sensor element portion (10) having a heating element (11) generating heat by conduction
Implementation Method 2
heat is emitted to the air through the resistive film
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
In order to provide a thermal mass flowmeter which makes higher accuracy of gas flowrate measurement possible while reliability in the thermal mass flowmeter is ensured (while deterioration or breakage caused by droplet adhesion is prevented), the thermal mass flowmeter according to the present invention has a heating element for generating heat by conduction, a temperature detection bridge circuit for detecting a temperature of the heating element, and a sensor element driving circuit portion connected to the heating element and the temperature detection bridge circuit and executing conduction control to the heating element, in which the sensor element driving circuit portion has an output mechanism and an output impedance adjustment mechanism and the output impedance adjustment mechanism is disposed between the output mechanism and the heating element and its output impedance is higher than an electric resistance value of the heating element and less than 1 MΩ.