Differential-Pressure Flow Control for Zero-Drift Accuracy
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Solution Overview
Problem
Flow rate control devices in semiconductor and chemical manufacturing face accuracy issues due to zero-point drift in pressure sensors, particularly when downstream pressure is high, leading to significant measurement errors.
Innovation Solution
A flow rate control device incorporating a control valve, an upstream pressure sensor, a differential pressure sensor, and an arithmetic control circuit that performs proportional or differential pressure control based on the outputs from these sensors to minimize the impact of zero-point drift, using a differential pressure sensor with a strain sensor to directly measure pressure differences and an arithmetic control circuit to adjust the control valve accordingly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a pressure sensor is used to measure upstream pressure for flow rate control, then flow rate control can be performed under critical expansion condition, but measurement accuracy deteriorates due to zero-point drift especially at high downstream pressures
Solution Approach 1:
The invention changes the measurement parameter from absolute upstream pressure to differential pressure (upstream pressure minus downstream pressure). By measuring the pressure difference across the restriction part rather than the absolute upstream pressure, the system maintains flow rate control capability while significantly reducing the impact of zero-point drift errors, especially when downstream pressure is high.
2Adaptability or versatility
If downstream pressure is increased to perform flow rate control in certain operating conditions, then control range is extended, but measurement error increases due to zero-point drift
Solution Approach 1:
The invention measures differential pressure instead of absolute pressure, which transforms the measurement parameter to be less sensitive to zero-point drift. This allows the system to operate accurately across a wider range of downstream pressures, including high downstream pressure conditions where conventional absolute pressure measurement would suffer from large errors due to zero-point drift.
3Device complexity
If only upstream pressure sensor is used for control, then device complexity is reduced, but control accuracy deteriorates under non-critical expansion condition
Solution Approach 1:
The invention combines the functions of upstream pressure measurement and downstream pressure measurement into a single differential pressure sensor. This merging approach maintains device simplicity while enabling accurate flow rate determination under both critical and non-critical expansion conditions by directly measuring the pressure difference across the restriction part.
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 a flow rate control device with improved accuracy and reduced error over a wide control range, especially at high downstream pressures, by effectively mitigating the effects of zero-point drift in pressure sensors.
Implementation Method 1
a differential pressure sensor for measuring the differential pressure between the upstream side and the downstream side of the restriction part
Data Source
AI summary
The flow rate control device 10 includes a control valve 11, a restriction part 12 provided downstream of the control valve 11, an upstream pressure sensor 13 for measuring a pressure P1 between the control valve 11 and the restriction part 12, a differential pressure sensor 20 for measuring a differential pressure ΔP between the upstream and the downstream of the restriction part 12, and an arithmetic control circuit 16 connected to the control valve 11, the upstream pressure sensor 13, and the differential pressure sensor 20.