Development Of Thermal Gas Mass Flowmeter

The flowmeter is a device for measuring fux,and utilizes heat transfer theories andhydromechanics theories that is to say exchange for quantity of heat between flowing liquidand heater.Applying advanced method of semiconductor and integrate circuit technology,theadvantage of the thermal mass flow sensor is diminutive volume and easy standardization forproduction.Thermal mass flow sensor has unique constant temperature principium asmathematical model for measuring medium mass flow without compensation of temperatureand pressure.The flowmeter applies intelligent and pocket design,and adopts AVRmicro-controller ATmega8 of ATMEL Corp. as MCU,which integrates 8-channel 10-bit15kSPS ADC ,three PWM channel,Advanced RISC Architecture,23 Programmable DigitalI/O Lines,Watchdog Timer,abundant On-Board Memory and On-Chip JTAG debug and soon.Measuring precision of ADC has achieved±0.1％,temperature coefficient 0.2％,T=±10℃,better linearity.The display system is constructed by 4-bit LED, which havesabundant function menus. Software of MCU is updated by ISP serial-port device which isconnected to a computer, the software is developed with C in IAR EmbeddedWorkbench. Computer can finish the parameter and the table setting of dataacquisition. Check table and linear interpolation method is used to compute mass fluxvalue. The flowmeter can be calibrated by pressing SET button before the system working. Inaddition the system can real-time inspect the real-time flux, accumulative total flux and sensorinput voltage. The accumulative total flux can be saved in a I~2C ferroelectric random accessmemory. In this paper, author expatiates the layouting of function, building the physical andmathematics model for thermal gas mass flow sensor, software and hardware designing todebugging,developing sample of instrument.