Dual Thermal Sensor Mass Flow Control at Low Pressure Difference
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Solution Overview
Problem
Mass flow controllers (MFCs) face limitations in dynamic range and measurement accuracy at low pressure differences, requiring multiple sensor types and complex calibration processes, which increases development costs and reduces product reliability.
Innovation Solution
A mass flow controller design utilizing multiple thermal flow sensor units with identical characteristics, where the output signals from these units are added to improve the signal-to-noise ratio, allowing for precise flow rate measurement even at low pressure differences without the need for multiple sensor types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the flow rate of the fluid flowing through the sensor flow path is increased, then the heat transfer from the upstream heating resistor to the downstream heating resistor improves, but the fluid cannot sufficiently receive heat or transfer heat, resulting in loss of measurement linearity
Solution Approach 1:
The invention divides the single sensor flow path into multiple parallel sensor flow paths (first sensor flow path and second sensor flow path). Each path has its own heating resistors and measures flow rate independently. The control unit combines measurements from both paths to achieve accurate measurement across a wider flow rate range, resolving the contradiction between sufficient heat transfer and measurement linearity.
2Adaptability or versatility
If the flow rate of the fluid passing through the sensor flow path is decreased, then the dynamic range increases, but the signal-to-noise ratio decreases due to white noise from the sensor winding resistance
Solution Approach 1:
The invention merges the output signals from multiple flow sensor units into a combined measurement. By adding the signals from parallel sensor paths, the useful flow rate signal is enhanced while random noise components tend to average out, improving the signal-to-noise ratio at low flow rates while maintaining extended dynamic range capability.
3Adaptability or versatility
If multiple types of flow sensors are used to cover different flow ranges, then the dynamic range and measurement accuracy improve, but the device complexity and calibration requirements increase
Solution Approach 1:
The invention uses multiple sensor flow paths with identical or substantially similar configurations, making each path universally capable of measuring the same flow rate range. This uniform design allows the system to achieve extended dynamic range through parallel operation and signal combination, while avoiding the complexity of calibrating and managing multiple different sensor types with different characteristics.
4Productivity
If the resistance of the bypass flow path is reduced to maintain overall flow rate at low pressure difference, then the maximum flow rate is maintained, but the flow rate through the sensor flow path decreases, narrowing the dynamic range
Solution Approach 1:
The invention segments the flow measurement function across multiple parallel sensor paths, allowing each path to operate independently. This enables the system to maintain adequate flow rate through sensor paths even when bypass resistance is reduced, preserving both maximum flow rate capability and dynamic range through the combined measurement capability of multiple paths.
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 approach enhances the signal-to-noise ratio, simplifies calibration, reduces manufacturing costs, and improves measurement accuracy across a wider range of flow rates, while maintaining product reliability.
Implementation Method 1
electrically heating the fluid flowing through the sensor flow path by heating resistors provided on an upstream side and a downstream side thereof
Implementation Method 2
measures a mass flow rate of the fluid from a temperature difference detected as a resistance value difference between both heating resistors
Data Source
AI summary
To provide an MFC capable of improving an S/N ratio of a sensor signal even when a pressure difference between both sides of the MFC is small and a flow rate in the sensor flow path is low. Provided is a mass flow controller including a fluid flow path that allows a fluid to pass therethrough, a plurality of flow sensor units that measure a mass flow rate of the fluid, an adjusting valve that adjusts a flow rate of the fluid passing through the fluid flow path, and a control unit that controls a degree of open of the adjusting valve. The flow sensor units are each a thermal flow sensor unit. The control unit calculates a mass flow rate from an added output signal obtained by adding the output signals of the plurality of flow sensor units, and controls the degree of open of the adjusting valve.