MEMS Mass Flow Meter Thermal Measurement Accuracy
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Solution Overview
Problem
Conventional rotameters offer low accuracy for volumetric flow measurement, lack temperature and pressure compensation, and are not capable of digital data output, making them unsuitable for modern applications that require precise and remote communication, especially in high-speed flow conditions.
Innovation Solution
The development of MEMS mass flow meters using silicon micromachined technology with serpentine-shape thermistors and a Wheatstone bridge circuit for calorimetric flow measurement, enabling low-power, cost-effective, and accurate mass flow measurement for various gases, including those previously limited to dry and clean gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional rotameters are used for flow measurement, then cost is low and ease of manufacture is good, but measurement precision is poor and temperature-pressure compensation is not available
Solution Approach 1:
The patent replaces the mechanical float-based rotameter system with a MEMS-based thermal mass flow meter that uses heated thermistors and electrical circuits to measure flow. This substitution enables precise digital measurements with temperature and pressure compensation while maintaining cost-effectiveness through semiconductor manufacturing processes.
Solution Approach 2:
The invention changes the measurement parameter from simple volumetric displacement (rotameter) to thermal conductivity-based mass flow measurement. By heating thermistors and measuring heat transfer to the flowing gas, the system achieves accurate mass flow measurement with temperature and pressure compensation capabilities.
2Measurement precision
If MEMS mass flow sensors are used, then measurement precision and data communication capability are improved, but power consumption increases
Solution Approach 1:
The patent implements periodic heating cycles of the thermistors rather than continuous heating. The control circuit activates heating elements in alternating sequences, measuring thermal responses during each cycle. This periodic operation reduces average power consumption while maintaining measurement accuracy through repeated sampling.
Solution Approach 2:
The system dynamically adjusts heating power and measurement frequency based on flow conditions. During high flow rates, shorter measurement cycles are used, while low flow conditions trigger longer measurement intervals. This dynamic adaptation optimizes power consumption across varying operational requirements.
3Adaptability or versatility
If conventional flow meters are used, then simplicity is maintained, but adaptability to different gases and digital communication is limited
Solution Approach 1:
The patent designs a universal MEMS thermal mass flow meter that can measure multiple gas types through software-based gas conversion factors. The device includes a library of conversion factors for different gases, allowing a single hardware platform to serve multiple applications without physical reconfiguration, thereby achieving versatility without proportional increases in hardware complexity.
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 MEMS mass flow meters provide significant improvements in accuracy, data communication, and installation ease while maintaining a low cost, offering ±(1.5% reading+0.25% full scale) accuracy and extended battery life, with the ability to measure different gases using a gas conversion factor, and low pressure loss, making them suitable for industrial applications.
Implementation Method 1
The heater thermistor is elevated to a constant temperature higher than the ambient temperature
Implementation Method 2
silicon micromachined mass flow sensors based on the principles of anemometry and calorimetry
Implementation Method 3
The sensing elements of the flow sensors mainly comprise four serpentine-shape thermistors which are made of same thin film materials with high temperature coefficient of resistance (TCR)
Data Source
AI summary
With increasing demands on data communication and remote control in current industrial processes or gas measurement applications, development of new technologies would be necessary. The current invention presents a MEMS mass flow meter that are cost compatible with conventional variable area flow meters while providing all digital data process including accumulated flow rate measurements, user programmable flow rate alarm and flow data storage. These in-line meters provide packages in pipe diameter from 4 mm up to 100 mm. It is powered with battery and can be used as a stand-alone hand-held option. The meter is also equipped with the industrial standard RS485 Modbus communication interface for easy network and remote management.