A Wireless Transmission-based Thermal Gas Flow Meter Design

With the continuous acceleration of industrial process,in order to effectively carry out production and control,the demand for data measurement is getting higher and higher.The flow rate of fluid is one of the important parameters of measurement and control.The traditional constant temperature difference thermal flowmeter is limited by the measurement circuit itself,and the maximum heating current is limited,so the measurement range is limited.The traditional constant power thermal flowmeter has heat exchange between two probes at low flow rate,which affects the measurement accuracy.In this paper,a thermal mass flowmeter combining the constant temperature difference method and the constant power method is proposed,which can be well compatible with the small flow measurement at low flow rate and the large flow measurement at high flow rate.At the same time,wireless transmission is used for data transmission.Firstly,by comparing the advantages and disadvantages of constant temperature difference method and constant power method,a measurement method combining constant temperature difference method and constant power method is proposed.The relationship between flow rate,temperature difference and power is derived by Kim ' s formula.The feasibility of the measurement method is proved by matlab simulation.In this paper,fuzzy PID control algorithm is used to complete the constant control of temperature difference and power.Firstly,the advantages and disadvantages of common bit control algorithm,PID control algorithm,fuzzy control algorithm and fuzzy PID control algorithm are compared,and the superiority of fuzzy PID control algorithm is verified by simulation.By comparing the common wireless communication technologies,Zig Bee is selected for wireless networking,and the network topology of the thermal flowmeter is proposed.In this paper,STM32F407 is selected as the main control MCU,and AD7606 chip is used to collect the voltage value of the signal processing circuit.The digital potentiometer X9111 is used to realize the voltage control of the bridge circuit.CC2630 and ATK-M750 modules are used for wireless data transmission.The software part mainly includes the flow meter main program design,control algorithm program design,acquisition program design and data communication program design.In this paper,the calibration and test are carried out by the sonic nozzle calibration device.The experimental data show that the measurement accuracy of the flowmeter can reach ± 1.5 %in the measurement range of 0 – 1600 kg / h,which verifies the feasibility of the measurement method.