Mass Flow Controller Calibration via Pressure-Flow Ratio
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Solution Overview
Problem
Existing mass flow controllers in semiconductor production face challenges in achieving high accuracy calibration due to variations in pressure, mass flow rate, and tank volume changes over time, leading to errors in flow rate control.
Innovation Solution
A mass flow controller with a calibrating valve, a tank, mass-flow-rate-sensing, and pressure-sensing mechanisms, along with a calibration control system that uses reference and calibrating data to adjust for variations, ensuring accurate mass flow rate calibration by comparing the ratio of pressure decrements to mass flow rate integrals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional mass flow controllers are used with fixed calibration, then initial calibration accuracy is achieved, but accuracy deteriorates over time due to pressure, temperature, and component variations
Solution Approach 1:
The patent implements dynamic calibration by continuously monitoring pressure and temperature variations and adjusting the mass flow rate control in real-time. The calibration is no longer fixed but adapts to changing environmental conditions and component drift, resolving the contradiction between initial accuracy and long-term stability.
Solution Approach 2:
The system incorporates feedback mechanisms where pressure sensors and temperature sensors continuously monitor system conditions, and the control unit adjusts the mass flow rate based on this feedback. This closed-loop control maintains calibration accuracy over time by compensating for drift and environmental variations.
2Measurement precision
If calibration is performed frequently to maintain accuracy, then measurement precision is improved, but productivity decreases due to operational interruptions
Solution Approach 1:
The patent enables continuous calibration during semiconductor production operations by using a control unit that can adjust mass flow rates in real-time without requiring system shutdown. The calibration process becomes continuous rather than periodic, maintaining accuracy while preventing production interruptions.
Solution Approach 2:
The system performs self-calibration automatically using embedded pressure and temperature sensors along with the control unit, eliminating the need for manual calibration interventions. This automated self-service calibration maintains precision without requiring production staff involvement or operational stoppages.
3Measurement precision
If manual calibration procedures are used, then calibration can be performed, but ease of operation deteriorates due to complex procedures and operational disruption
Solution Approach 1:
The system automatically performs calibration using the control unit, pressure sensors, and temperature sensors without requiring manual intervention. The calibration process is self-executing, simplifying operation while maintaining the necessary calibration capability for accurate measurements.
Solution Approach 2:
The patent replaces manual mechanical calibration procedures with an automated electronic control system that uses pressure and temperature sensor data to compute and apply calibration adjustments. This substitution of mechanical/manual operations with electronic automation simplifies the calibration process while preserving measurement 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
The solution provides high accuracy in mass flow rate calibration, accounting for pressure and mass flow rate variations, and allows for remote calibration without disrupting semiconductor production operations.
Implementation Method 1
When the gas flows at a mass flow rate Q through the sensor pipe 14, the gas is heated by the resistor R1 on the upstream side and flows to the resistor R4 on the downstream side, resulting in the movement of heat to generate temperature difference between the resistors R1, R4.
Implementation Method 2
A pair of series-connected resistors R1, R4 made of a material having resistivity changeable with temperature are wound around the sensor pipe 14.
Implementation Method 3
a pressure-sensing means (46) for sensing the pressure of the gas to output pressure data
Implementation Method 4
a calibration control unit (48) for calculating mass flow rate calibration by comparing a ratio, determined from the pressure data and the mass flow rate data, to a reference ratio
Data Source
AI summary
A method for calibrating a mass flow controller comprising a calibrating valve disposed on the most upstream side of a path, a mass flow rate control valve mechanism, a tank provided at the path on the upstream side of the mass flow rate control valve mechanism, a mass-flow-rate-sensing means, a pressure-sensing means, a means for controlling the mass flow rate control valve mechanism, and a mass flow rate calibration control means, the method comprising the steps of (1) permitting a fluid at a set mass flow rate to flow through the path, (2) setting the mass flow rate control valve mechanism at a degree of opening that the mass flow rate of the fluid is equal to the set mass flow rate, (3) closing the calibrating valve, (4) measuring the pressure and mass flow rate of the fluid after a fluid flow from the tank is stabilized, (5) determining a variation ratio of the pressure and mass flow rate to reference pressure and mass flow rate measured by the same procedures in an initial state, and (6) performing calibration depending on the variation ratio.