Mass Flow Meter Pressure Correction for Gas Accuracy
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Solution Overview
Problem
Thermal mass flow meters experience reduced measurement accuracy due to errors in flow rate measurements caused by changes in gas supply pressure and variations depending on the type of sample gas.
Innovation Solution
A mass flow meter that corrects the measured flow rate using both the primary side pressure and a coefficient specific to the sample gas, employing a flow rate calculating section, pressure measuring section, and flow rate correcting section to improve accuracy through expressions like Qoffset=Qraw×{1−(Pbase−Pin)×α, where Pin is the primary side pressure, Pbase is the reference pressure, and α is the gas coefficient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thermal mass flow meter is used to measure sample gas flow rate, then the flow rate can be detected by measuring temperature difference, but the measurement accuracy drops when the gas supply pressure changes
Solution Approach 1:
The invention introduces pressure as an additional measurement parameter and uses it to correct the flow rate measurement. By measuring both temperature difference (for flow rate) and pressure (for correction), the system compensates for pressure-induced measurement errors through calculated correction values based on the relationship between pressure changes and measurement errors
Solution Approach 2:
The invention implements a feedback mechanism where the measured pressure value is used to calculate a correction value, which is then applied to the raw flow rate measurement. This closed-loop approach continuously adjusts the measurement based on actual pressure conditions, eliminating the need for manual calibration under different pressure conditions
2Adaptability or versatility
If a thermal mass flow meter measures different kinds of sample gases, then the flow rate can be detected, but the measurement error varies depending on the sample gas type
Solution Approach 1:
The invention accounts for gas type variations by incorporating gas-specific parameters into the correction calculation. Different gases have different thermal properties that affect the temperature difference measurement, and the system compensates for this by adjusting the correction value based on the identified sample gas type
Solution Approach 2:
The invention segments the measurement system into gas-type-specific correction profiles. By categorizing gases into different types with characteristic thermal properties, the system applies tailored correction values for each gas category, improving accuracy across multiple gas types without requiring separate calibration for each individual gas
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 significantly reduces measurement errors resulting from pressure changes and accounts for the specific properties of different gases, thereby enhancing the measurement accuracy of the flow rate.
Implementation Method 1
a flow rate sensor (10) comprising a sensor section (41, 411, 412) having a thermosensitive resistive element (41a, 41b) arranged in a flow channel (2, 3, 3A) where a sample gas (G) flows
Implementation Method 2
the temperature at the downstream side sensor section becomes higher than the temperature at the upstream side sensor because the sample gas heated by the upstream side sensor flows into the downstream side sensor section
Implementation Method 3
a pressure measuring section (43) that measures a primary side pressure (Pin) in the flow channel (2)
Implementation Method 4
a flow rate correcting section (44) that corrects a measured flow rate (Qraw) obtained by the flow rate calculating section (42) by the use of the primary side pressure (Pin) obtained by the pressure measuring section (43) and a gas coefficient (α) determined by the sample gas (G)
Data Source
AI summary
In order to improve a measurement accuracy of a mass flow meter, the mass flow meter comprises a flow rate calculating section that obtains an output signal from a sensor section having a thermosensitive resistive element arranged in a flow channel where a sample gas flows and that calculates a flow rate of the sample gas, a pressure measuring section that measures a primary side pressure in the flow channel, and a flow rate correcting section that corrects the measured flow rate obtained by the flow rate calculating section by the use of the primary side pressure obtained by the pressure measuring section and a gas coefficient determined by an isobaric specific heat of the sample gas.