Mass Flow Controller Signal Correction for Parasitic Flow
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Solution Overview
Problem
Existing mass flow controllers face challenges in accurately measuring and controlling fluid flow during rapid pressure changes, leading to parasitic flow issues and prolonged engagement of feed forward control, which affects the accuracy and responsiveness of flow control.
Innovation Solution
A method and system that accelerates the flow sensor signal to match the bandwidth of the estimated parasitic flow signal, allowing for quicker switching between closed loop and feed forward control, and generating a corrected flow signal for improved accuracy and responsiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the flow sensor signal is filtered with a low time constant filter to reduce noise, then the noise level is reduced, but the response time increases and the bandwidth decreases
Solution Approach 1:
The patent applies dynamic filtering where the filter time constant is not fixed but varies based on operating conditions. The filter adapts its characteristics in real-time to maintain optimal balance between noise reduction and response speed, allowing the system to achieve low noise levels during stable operation while maintaining fast response during transient conditions.
Solution Approach 2:
The patent changes the filter parameter (time constant) dynamically based on the operating state of the mass flow controller. By adjusting the filter parameter according to whether the system is in steady-state or transient-state, the patent achieves both low noise and fast response at different operational phases.
2Measurement precision
If the estimated parasitic flow signal is filtered to match the bandwidth of the measured flow signal, then the correction accuracy is improved, but the control response during rapid pressure changes is delayed
Solution Approach 1:
The patent applies preliminary action by using the unfiltered, high-bandwidth estimated parasitic flow signal to predict and compensate for parasitic flow effects before they significantly impact the measurement. This allows the system to prepare correction signals in advance during transient conditions, reducing the overall recovery time while maintaining accuracy through subsequent filtering of the final corrected signal.
Solution Approach 2:
The patent implements dynamic correction where the filtering and correction process adapts to the current operating state. During rapid pressure changes, the system uses minimal filtering to maintain fast response, while during steady-state operation, more aggressive filtering is applied to maximize correction accuracy.
3Measurement precision
If feed forward control is used during rapid pressure changes, then the immediate flow control accuracy is improved, but the engagement time is prolonged affecting overall productivity
Solution Approach 1:
The patent uses preliminary action by implementing feed forward control that anticipates parasitic flow effects based on pressure changes. The system proactively applies correction signals before the thermal flow sensor can accurately detect the parasitic flow, thereby maintaining control accuracy during the critical transient period and reducing the time needed to return to normal closed-loop operation.
Solution Approach 2:
The patent combines feed forward control with feedback mechanisms to determine when to transition between control modes. By continuously monitoring the agreement between the estimated parasitic flow signal and the actual flow sensor signal, the system can dynamically switch from feed forward control to normal closed-loop control, optimizing both accuracy and productivity.
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 enables faster and more accurate control of fluid flow by reducing recovery time from pressure changes and improving the validity of flow measurements, ensuring precise delivery of fluid flow rates.
Implementation Method 1
by measuring the flowrate of the fluid (e.g., gas or liquid) through the sensor tube 120, a thermal flow sensor 123 can provide a flow sensor signal 150 that is indicative of the flowrate of the fluid flowing through the main path 115
Implementation Method 2
a pressure measurement signal 155 is obtained (Block 502) from a pressure sensor 178
Data Source
AI summary
Mass flow controllers and methods for correcting flow inconsistencies associated with parasitic flow of a fluid in mass flow controllers are disclosed. A method includes obtaining a pressure measurement signal of the fluid generated by a pressure sensor and receiving a flow sensor signal of the fluid generated by a flow sensor. An estimated parasitic flow signal is generated using the pressure measurement signal, and the flow sensor signal is accelerated to produce an accelerated flow sensor signal with a bandwidth that is comparable to that of the estimated parasitic flow signal. A corrected flow signal is generated using the accelerated flow sensor signal and the estimated parasitic flow signal to control the mass flow controller.