Transient Mass Flow Controller Response Measurement
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Solution Overview
Problem
Current methods for measuring the transient response of mass flow controllers (MFCs) are inadequate due to low time resolution, pressure perturbations, and inaccuracies, which are critical in the semiconductor industry where processes are short and require precise flow control.
Innovation Solution
A gas flow controller with a piezoelectric control valve and pressure transducers is positioned between an upstream gas source and a downstream MFC, maintaining constant pressure to accurately measure transient responses by adjusting the valve to counteract pressure changes, ensuring no perturbation and high accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional flow measurement techniques (rate of rise or pressure drop methods) are used to measure MFC transient response, then flow rate can be determined, but measurement time becomes very long (up to a minute) and pressure perturbations occur that influence the MFC response
Solution Approach 1:
A capillary tube with known flow characteristics is introduced as an intermediary element between the MFC and the measurement system. The pressure drop across this capillary tube is measured to infer the flow rate through the MFC, providing a fast response that captures the transient behavior without the long measurement times of conventional methods.
Solution Approach 2:
The patent replaces the conventional mechanical measurement systems (large volume chambers for rate of rise measurements) with a pressure-sensitive polymer film that responds rapidly to pressure changes. This substitution enables fast transient measurements by using the mechanical deformation of the polymer film in response to pressure differential, which can be detected optically or electrically.
2Measurement precision
If rate of rise measurement is used to determine flow rate by measuring pressure rise in a known volume, then flow can be calculated using gas relations, but the measurement takes very long time especially for lower flow rates
Solution Approach 1:
The capillary tube serves as an intermediary that converts the flow rate into a measurable pressure drop signal rapidly. Instead of measuring pressure rise in a large volume over time, the pressure drop across the narrow capillary provides an immediate signal proportional to the instantaneous flow rate, enabling fast measurements even at low flow rates.
Solution Approach 2:
The patent changes the measurement parameter from integrated pressure rise over time to instantaneous pressure drop across a restriction. This parameter change allows the system to capture transient flow behavior in real-time rather than requiring long integration periods, significantly improving measurement speed while maintaining accuracy.
3Reliability
If pressure transducer is placed between thermal sensor and control valve to account for pressure effects, then pressure insensitive MFC performance is improved, but additional complexity is added to the device
Solution Approach 1:
The pressure measurement function is extracted from the MFC itself and placed in the external measurement system. The MFC only needs to provide the capillary tube, while the pressure transducer and measurement electronics are separate, allowing the MFC design to remain simple while still achieving pressure compensation capability.
Solution Approach 2:
The capillary tube serves multiple functions: it acts as a flow restriction that creates a measurable pressure drop, serves as a reference element for differential pressure measurement, and provides a means to infer flow rate without requiring direct flow measurement through the MFC. This multi-functionality reduces the need for additional components.
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 provides fast and accurate transient response measurements with tens of milliseconds time resolution and 1% accuracy, maintaining constant upstream and downstream pressures, thus isolating the true MFC response.
Implementation Method 1
A gas flow controller with a piezoelectric control valve and pressure transducers is positioned between an upstream gas source and a downstream MFC, maintaining constant pressure to accurately measure transient responses by adjusting the valve to counteract pressure changes
Implementation Method 2
A gas flow controller with a piezoelectric control valve and pressure transducers is positioned between an upstream gas source and a downstream MFC
Implementation Method 3
The elements are heated by applying an electric current. As the gas flows through the tube, it picks up heat from the first element and transfers it to the second element. The resulting temperature differential between the two elements is a measure of the mass flow rate of the gas.
Data Source
AI summary
An apparatus to measure the transient response of a mass flow controller (MFC). The size of a variable orifice, upstream of the MFC, is controlled such that the pressure between the orifice and the MFC is held constant during the entire time that the MFC is going through its transient response. The known relationship between the size of the orifice and the flow through it allows a determination of the transient response of the MFC.