Pressure-Based Mass Flow Ratio Control With Linearized Sensing
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Solution Overview
Problem
Pressure-based flow ratio control systems face challenges with nonlinear relationships between pressure sensor signals and flow rates, requiring knowledge of gas properties, and low differential pressure measurements can be inaccurate due to the error band of absolute pressure sensors.
Innovation Solution
Incorporating a laminar flow element as a pressure drop element to create a linear response between secondary flow rates and pressure signals, and using a differential pressure sensing element to improve accuracy, especially in low pressure drop conditions, by replacing one absolute pressure sensor with a differential pressure sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure-based flow sensors are used to avoid thermal flow sensor drift, then reliability is improved, but the relationship between pressure sensor signal and flow rate becomes highly nonlinear requiring knowledge of gas properties
Solution Approach 1:
The patent transforms the measurement parameter from direct pressure measurement to differential pressure measurement across a flow restrictor. This parameter change linearizes the relationship between the sensor signal and flow rate, eliminating the need for complex gas property knowledge while maintaining the reliability advantages of pressure-based sensing.
2Device complexity
If a common pressure sensor is shared at the inlet of the FRC, then device complexity is reduced, but measurement precision deteriorates due to inability to capture local pressure variations
Solution Approach 1:
The patent introduces a flow restrictor as an intermediary element between the common pressure sensor and the secondary flow lines. This intermediary creates a measurable pressure differential that captures local flow conditions, enabling accurate flow rate measurement while still using a single shared pressure sensor.
3Manufacturing precision
If laminar flow element is used to create linear response, then the relationship between flow rate and pressure signal is improved, but differential pressure across the element becomes very low falling within error band of absolute pressure sensors
Solution Approach 1:
The patent uses a flow restrictor as an intermediary that creates a measurable pressure differential. By positioning the pressure sensor to measure across this restrictor rather than using absolute pressure sensors, the system captures the pressure drop directly, achieving both linear flow response and measurable differential pressure signals.
4Measurement precision
If differential pressure sensing element is used to replace one absolute pressure sensor, then measurement precision is improved for low pressure drop conditions, but device complexity increases
Solution Approach 1:
The flow restrictor acts as a mediator that enables the use of a differential pressure sensor to directly measure the pressure drop across it. This configuration provides accurate low differential pressure measurement while simplifying the overall sensor architecture compared to using multiple absolute pressure sensors with complex differential calculations.
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 precise control of secondary flow rates without prior knowledge of gas properties and enhances measurement accuracy, particularly in low pressure drop scenarios, providing a more stable and accurate flow ratio control.
Implementation Method 1
a laminar flow element may be chosen
Implementation Method 2
a differential pressure sensing element in communication with the pressures upstream and downstream of the pressure drop element
Data Source
AI summary
A system and method for dividing a single mass flow into secondary flows of desired ratios to total flow. Each secondary flow line includes a pressure drop element, an absolute pressure sensor and a differential pressure sensor. The nonlinear relationship between flow and pressures can be transformed into a function of the absolute and differential pressures that has a linear relationship with the flow.