Self-Correcting Pressure Mass Flow Control Under High Back Pressure
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Solution Overview
Problem
Existing pressure-based mass flow controllers struggle to accurately determine the flow rate when downstream pressure exceeds half of the upstream pressure, leading to erroneous calculations and inability to detect control errors due to excessive downstream pressure.
Innovation Solution
Incorporating a second pressure sensor to measure the pressure drop across the flow restriction, either differential or absolute, in conjunction with an absolute pressure sensor downstream, and using a self-correcting mechanism involving a shutoff valve, reference volume, and proportional valve to adjust pressure and achieve the setpoint flow rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pressure-based mass flow controller is used to control fluid flow, then the flow rate can be controlled by modulating upstream pressure, but the controller cannot accurately determine the actual flow rate when downstream pressure exceeds half of the upstream pressure
Solution Approach 1:
The patent implements a feedback mechanism where the controller performs rate of decay measurements to determine actual flow rate, compares it with the setpoint flow rate, and automatically adjusts the proportional valve to correct any discrepancy. This closed-loop feedback system ensures accurate flow control even when downstream pressure varies or exceeds half of upstream pressure, resolving the measurement accuracy issue under these conditions.
Solution Approach 2:
The controller performs self-verification by conducting rate of decay measurements and automatically detecting and correcting its own control errors. The system monitors its own performance and adjusts its operation without external intervention, ensuring maintained accuracy despite varying downstream pressure conditions.
2Measurement precision
If a shutoff valve is activated to perform rate of decay measurement, then the actual flow rate can be determined accurately, but continuous fluid delivery is interrupted during the measurement process
Solution Approach 1:
The patent implements periodic rate of decay measurements rather than continuous interruption of fluid delivery. The shutoff valve is activated at periodic intervals to perform measurements, allowing the system to maintain continuous operation while periodically verifying and correcting flow accuracy. This periodic approach balances measurement needs with continuous productivity.
Solution Approach 2:
The controller performs rate of decay measurements in advance to determine actual flow rate before making adjustments. By measuring first and then adjusting the proportional valve accordingly, the system ensures accurate flow control is established proactively, maintaining continuous delivery while ensuring accuracy.
3Manufacturing precision
If the flow control algorithm is corrected based on rate of decay measurement results, then the actual flow rate can be brought closer to the setpoint, but the system complexity increases due to additional sensors and correction mechanisms
Solution Approach 1:
The patent makes the existing pressure sensors and controller perform multiple functions. The same pressure sensors used for basic flow control also perform rate of decay measurements for verification. The controller itself handles both normal operation and self-correction algorithms, eliminating the need for separate dedicated verification hardware and reducing overall system complexity.
Solution Approach 2:
The system performs self-verification and self-correction using its own existing components. The controller uses its built-in pressure sensors and processing capability to conduct rate of decay measurements, detect errors, and adjust the proportional valve accordingly. This self-service approach avoids adding external verification equipment, maintaining simplicity while achieving high precision.
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 configuration allows for accurate determination of the actual flow rate, independent of downstream pressure variations, and enables continuous fluid delivery during flow verification, ensuring precise control and correction of flow rates.
Implementation Method 1
measuring a first pressure using a first pressure sensor of the fluid or gas in the flow path downstream to a flow restrictor
Implementation Method 2
performing a rate of decay measurement in the flow path using a reference volume which is upstream to the flow restrictor
Implementation Method 3
adjust a second pressure at a second pressure sensor upstream to a flow restrictor by using a proportional valve to achieve an actual flow rate that is closer to a received setpoint flow rate
Data Source
AI summary
A self-correcting pressure-based mass flow control apparatus includes outlet pressure sensing to enable correction for non-ideal operating conditions. Further the mass flow control apparatus having a fluid pathway, a shutoff valve in the fluid pathway, a reference volume in the fluid pathway, a first pressure measuring sensor in fluid communication with the reference volume, a first temperature measuring sensor providing a temperature signal indicative of the fluid temperature within the reference volume, a proportional valve in the fluid pathway, and a second pressure measuring sensor in fluid communication with the fluid pathway.