MEMS Mass Flow Sensor for Utility Gas Metering
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Solution Overview
Problem
Mechanical gas meters in the medium pressure range face issues with dynamic range limitations, vulnerability to floating particles, and the need for costly flow computers to compensate for pressure and temperature variations, leading to accuracy and maintenance challenges.
Innovation Solution
A utility meter incorporating a microfabricated silicon mass flow sensor with a Venturi structure and flow conditioners, utilizing MEMS thermal mass flow sensors and an electronic control board for enhanced dynamic range and stability, eliminating the need for separate temperature and pressure compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If mechanical meters (turbine or rotary) are used for medium pressure gas measurement, then they have long service life and reliability, but they suffer from limited dynamic range and vulnerability to floating particles
Solution Approach 1:
The patent replaces mechanical measurement systems (turbine or rotary meters) with a non-mechanical thermal mass flow sensor system. The thermal mass flow sensor uses heating elements and temperature sensing to measure gas flow through thermal conduction and convection principles, eliminating moving parts while achieving both high reliability and extended dynamic range capability.
Solution Approach 2:
The patent changes the measurement parameter from mechanical displacement or rotation to thermal properties (temperature difference, heat transfer coefficient). By measuring the temperature difference between heated and reference zones, the system achieves a much wider dynamic range while maintaining reliability through solid-state sensing.
2Ease of operation
If rotary meters are used for gas measurement, then they provide basic flow measurement, but they are vulnerable to damage from floating particles and require heavy maintenance
Solution Approach 1:
The patent eliminates mechanical components (rotors, gears, seals) that are susceptible to particle damage by using a thermal mass flow sensor with no moving parts. The sensing elements are solid-state heating coils and temperature sensors that are inherently resistant to contamination from floating particles in the gas stream.
Solution Approach 2:
The thermal mass flow sensor provides maintenance-free operation by using self-heating elements that continuously operate without mechanical wear. The system automatically compensates for environmental conditions and requires no manual intervention, calibration, or replacement due to particle exposure.
3Measurement precision
If mechanical meters with flow computers are used for temperature and pressure compensation, then volumetric changes are compensated, but the system becomes extremely expensive and adds metrology errors
Solution Approach 1:
The patent replaces the mechanical volumetric metering system with a thermal mass flow sensor that directly measures mass flow rate. Since mass flow is independent of temperature and pressure conditions, the complex flow computer hardware and software for volumetric compensation becomes unnecessary, dramatically reducing system cost and eliminating associated metrology errors.
Solution Approach 2:
The patent changes the fundamental measurement approach from volumetric flow (which requires T&P compensation) to mass flow measurement. The thermal mass flow sensor inherently measures mass flow by detecting heat transfer proportional to the mass of gas flowing through the sensor, making external compensation systems obsolete.
4Adaptability or versatility
If thermal mass flow sensors are used for gas measurement, then they provide mass flow measurement with extended dynamic range, but they require flow conditioning to achieve stability at medium pressure
Solution Approach 1:
The patent introduces flow conditioning elements (flow straighteners, honeycomb structures, or diffusers) as intermediary components upstream of the thermal mass flow sensor. These conditioners stabilize the flow profile and reduce turbulence before the gas enters the sensing zone, enabling accurate measurements across an extended dynamic range without requiring complex sensor designs.
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 stable and accurate flow measurement with a large dynamic range, reduced maintenance needs, and cost-effectiveness, while maintaining performance comparable to mechanical meters.
Implementation Method 1
A Wheatstone bridge circuit consisting of the heater and reference resistor is designed to achieve constant temperature control of heater resistor.
Implementation Method 2
One of the resistors is built as a reference resistor to monitor the ambient temperature while another one of the resistors is functioned as a heater.
Implementation Method 3
The silicon MEMS flow sensor is based on the principles of anemometry and calorimetry, and sometimes they are also called as silicon MEMS thermal mass flow sensor.
Implementation Method 4
The flow channel is designed using a standard Venturi structure where the sensor probe assembly is positioned at the center of the smallest inner diameter along the Venturi structure to improve flow stability.
Data Source
AI summary
This invention is related to an apparatus which incorporates a microfabricated silicon mass flow sensor to measure city gas flow rate in a medium pressure range for utility industry which is dominated by conventional mechanical meters such as turbine and rotary meters. The microfabricated mass flow sensor is so called micro-electro-mechanical systems (a.k.a. MEMS) device. Due to the small feature size of micro scale for MEMS mass flow sensor, the invented apparatus includes many advantages such as low power consumption, compact package, high reliability and extended dynamic measurement range. This apparatus is also provided with a stable flow conditioning to achieve a desired dynamic range capability. Furthermore, because of the high accuracy characteristic, the apparatus in this invention could be applied for custody transfer or tariff in utility industry as well.