Thermal Mass Flow Sensor Correction for Setpoint Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Mass flow controllers using thermal flow sensors face inaccuracies due to non-linear sensitivity changes with flow rate, leading to delayed actual flow reaching setpoints and measurement discrepancies.
Innovation Solution
A method and apparatus that gradually apply non-linearity corrections to the flow signal from thermal mass flow sensors, using a nonlinearity compensator to adjust the measured flow signal based on predicted sensor sensitivity values, ensuring accurate flow control by accounting for transient thermal processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-linearity correction is applied to the flow sensor signal, then measurement precision is improved, but the system complexity increases due to additional correction mechanisms
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the non-linearity correction based on the instantaneous flow rate. The correction factor is varied as a function of flow rate, transforming the fixed correction approach into a dynamic one that adapts to changing flow conditions, thereby improving measurement precision across the entire operating range.
Solution Approach 2:
The patent replaces complex mechanical correction mechanisms with an electronic/software-based correction system. Instead of using additional physical sensors or mechanical adjustment devices, the non-linearity correction is implemented through signal processing algorithms that calculate and apply correction factors electronically, reducing device complexity while maintaining measurement precision.
2Productivity
If traditional nonlinearity adjustment is used, then device complexity is kept low, but productivity decreases due to slow response time in reaching setpoint
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing non-linearity correction factors for various flow rates during a calibration phase. These pre-computed correction factors are then quickly retrieved and applied during operation, eliminating the need for complex real-time calculations and enabling rapid response to setpoint changes, thus improving productivity without increasing operational complexity.
Solution Approach 2:
The patent implements a feedback mechanism where the measured flow rate is continuously monitored, the appropriate non-linearity correction factor is selected based on the current flow level, and the corrected flow signal is used to drive the control valve. This closed-loop feedback system ensures rapid convergence to the setpoint by continuously adjusting the control signal based on the difference between desired and actual flow rates.
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 improves the accuracy of mass flow control by stabilizing the flow signal sensitivity over time, reducing measurement errors and ensuring the actual flow rate aligns with the setpoint more effectively.
Implementation Method 1
thermal mass flow sensor that measures the mass flow rate of the gas flowing through the device
Implementation Method 2
thermal mass flow sensor 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 flow sensor signal from the thermal mass flow sensor of the mass flow controller to produce a measured flow signal. The measured flow signal is corrected to produce a corrected flow signal by gradually changing non-linearity correction to the measured flow signal when a flow rate of the gas changes. A valve of the mass flow controller is controlled using the corrected flow signal and a setpoint signal.