Upstream Mass Flow Verifier Dead Volume Compensation
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Solution Overview
Problem
Non-pressure insensitive mass flow controllers (MFCs) face measurement errors due to dead volume in the flow path, which cannot be compensated for by the MFC itself, leading to inaccuracies in flow verification.
Innovation Solution
An upstream mass flow verifier (MFV) with a chamber and control valves measures the rate of decay in pressure and temperature to independently verify the flow rate, accounting for dead volume errors by incorporating the dead volume into its calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an upstream mass flow verifier is used to measure flow rate, then measurement capability is provided, but dead volume in the MFC causes pressure variations that worsen measurement precision
Solution Approach 1:
The patent introduces a compliant element (such as a bellows or flexible membrane) as an intermediary component between the upstream mass flow verifier and the non-pressure-insensitive MFC. This compliant element absorbs pressure variations caused by dead volume effects, preventing them from reaching the MFC and affecting flow measurement accuracy. The intermediary isolates the measurement system from the harmful pressure fluctuations while allowing continuous operation.
Solution Approach 2:
The patent modifies the physical parameters of the flow path by introducing a compliant element with specific elasticity characteristics. This changes the pressure dynamics in the system, allowing pressure variations to be absorbed and dampened before affecting the MFC. By adjusting the compliance parameter of the intermediary element, the system can be optimized to minimize measurement errors while maintaining operational flexibility.
2Device complexity
If a non-pressure insensitive MFC is used, then device simplicity is maintained, but measurement accuracy deteriorates due to inability to compensate for dead volume errors
Solution Approach 1:
The compliant element serves as a passive intermediary that compensates for the lack of active pressure sensing and compensation in non-pressure-insensitive MFCs. Instead of adding complex pressure sensors and control algorithms to the MFC, the compliant element mechanically absorbs pressure variations, providing error compensation through its physical properties rather than electronic control.
Solution Approach 2:
The patent extracts the pressure compensation function from the MFC itself and places it in a separate compliant element in the flow path. This separation allows the MFC to remain simple and non-pressure-insensitive while the external compliant element handles the pressure variation absorption, effectively decoupling the measurement accuracy requirement from the MFC design complexity.
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 allows for accurate verification of MFC performance by compensating for dead volume errors, ensuring precise flow rate measurements even in non-pressure insensitive MFCs.
Implementation Method 1
By measuring the temperature of the fluid in the chamber, and the rate of decay of pressure from the chamber, the flow rate through the MFC can be independently measured
Implementation Method 2
By measuring the temperature of the fluid in the chamber, and the rate of decay of pressure from the chamber, the flow rate through the MFC can be independently measured
Data Source
AI summary
This disclosure relates to mass flow verification systems for and methods of measuring and verifying the mass flow through a mass flow delivery/measurement device such as a mass flow controller. A mass flow verification system comprises a preset volume, a temperature sensor, and a pressure sensor. The measured verified flow determined by the mass flow verification system can be adjusted to compensate for errors resulting from a dead volume within the mass flow measurement device.