Thermal Gas Mass Flowmeter

Thermal Gas Mass Flowmeter (Thermal Mass Flowmeter), which based on the principle of convection heat transfer gas flow measurement, originated in the late 60s. Measurement tools and compensation methods have been greatly improved With the development of microelectronics technology. TMF have characteristics such as being measured with small flow, stability and high reliability, minimal pressure loss, high measure range, easy installation, good reproducibility, and reasonable cost. TMF is widely used in gas flow measurement in the semiconductor industry, such as measurement of air, natural gas, coal gas, vehicle exhaust, oxygen and paralysis agent in medical cause, heating and ventilation, it also usually used to measure the flow of mixed gas.This project has designed a TMF with automatic temperature compensation. After extensive research and analysis has being made on domestic and foreign academic literature and productions of research, the design plan has been carried out, which maximize accuracy and reliability based on reasonable cost.This topic makes detailed description and classification of TMF in the early stage of design, and the design plan is divided into constant current and temperature measurements based on the measurement circuit. Decision has been made by establishing the physical model and analysis of simulation data and curves, and a new type of temperature compensation circuit design is advanced. Multi-point distribution is used to improve the reliability of measurement.MSP430 MCU is used as the core of hardware design, and the design is divided into sampling module, computing module and communication module. The sampling module is connected to measurement part, which changes measured flow into voltage signal and adjust it into input signal; The computing module compute the flow rate and accumulated flow, which are displayed on the LCD; The communication module is mainly responsible for the communication between TMF and PC. Software design include AD converter, volume computing, analog signal output, LCD display and so on, which also adopt modular design to facilitate system maintenance and upgrades. An experimental platform has been designed to test the sensitivity, accuracy and reliability of automatic temperature compensation of TMF. Data were analyzed and curve fitted. The results showed that this subject has achieve the overall performance goals of the plan.