Mass Flow Controller Nonlinearity Compensation for Accurate Gas Flow
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Solution Overview
Problem
Mass flow controllers (MFCs) face inaccuracies in controlling gas flow due to nonlinear relationships between flow signals and actual flow rates, particularly at higher flow rates, caused by thermal mass flow sensors, which are not adequately addressed by current methods of nonlinearity adjustment.
Innovation Solution
A method and apparatus that determine a total nonlinearity characteristic function based on multiple sources of nonlinearity, including thermal and bypass nonlinearity, allowing for independent adjustments and updates to improve the accuracy of the flow signal correction, enabling more precise control of gas flow through the MFC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single total nonlinearity characteristic function is used for correction, then the device complexity is reduced, but the measurement precision deteriorates because it cannot account for different sources of nonlinearity independently
Solution Approach 1:
The total nonlinearity characteristic function is segmented into multiple independent component functions, each representing a specific source of nonlinearity (thermal nonlinearity, bypass nonlinearity, sensor nonlinearity). This segmentation allows each component to be adjusted independently based on its specific characteristics, improving measurement precision while maintaining manageable system complexity through modular architecture.
2Adaptability or versatility
If nonlinearity adjustment is made dynamically during flow rate transitions, then the adaptability improves, but the measurement precision deteriorates due to bypass nonlinearity effects at higher flow rates
Solution Approach 1:
The nonlinearity correction is segmented into separate component functions for thermal nonlinearity and bypass nonlinearity. This allows the thermal nonlinearity component to be adjusted dynamically during flow transitions while the bypass nonlinearity component remains fixed, preventing the introduction of additional errors at high flow rates while maintaining adaptability where needed.
Solution Approach 2:
Different adjustment strategies are applied to different nonlinearity components based on their local characteristics. The thermal nonlinearity component, which varies with operating conditions, is made dynamically adjustable. The bypass nonlinearity component, which causes errors at high flow rates, is kept fixed to avoid introducing additional inaccuracies. This localized quality approach optimizes precision for each specific nonlinearity source.
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 leads to more accurate control of gas flow by compensating for individual sources of nonlinearity, reducing errors and ensuring the flow signal accurately reflects the actual flow rate, even under varying operating conditions.
Implementation Method 1
An important part of an MFC is a thermal mass flow sensor that measures the mass flow rate of the gas flowing through the device
Data Source
AI summary
Mass flow controllers and methods for controlling mass flow controllers are disclosed. A method includes providing a gas through a thermal mass flow sensor of the mass flow controller and processing a sensor signal from the thermal mass flow sensor to produce a flow signal. A total nonlinearity characteristic function is determined based on nonlinearity effects on the flow signal and includes a first and second nonlinearity component function based on a first and second source of nonlinearity respectively. The total nonlinearity characteristic function is calibrated, and the first nonlinearity component function is adjusted responsive to changes in the first source of nonlinearity, after which the total nonlinearity characteristic function is updated. The flow signal is corrected to produce a corrected flow signal using the total nonlinearity characteristic function. A valve of the mass flow controller is controlled using the corrected flow signal and a setpoint signal.