Development Of Thermal Gas Mass Flowmeter For Small Flow

The thermal gas mass flowmeter(TMF)has a wide application prospect in the field of small flow measurement for its simple structure,small pressure loss and good reliability,but it also faces problems such as poor temperature compensation effect,therefore,research work on TMF was carried out.This paper introduced the principle and method of thermal gas mass flow measurement,and presented a dual-speed probe type thermal gas mass flow measurement scheme in view of insufficient temperature compensation capability of constant current measurement method.Using two platinum thermal resistance PT20 as the measuring components,and the flow measurement formula was deduced.By controlling the current of the PT20,the gas flow rate was calculated from the output voltage of the PT20,theoretically eliminating the influence of temperature on the flow measurement result.A flow measurement system was designed.(1)This paper developed flow sensor probes,studied the temperature characteristics of the probes.(2)This paper designsed the application control circuit with STM32F103 single chip as the core,developed the measurement control software and upper computer software interface of the flowmeter,and fitted the equation of characteristic curve function by least squares method.(3)This paper designed a constant temperature differential TMF according to the constant temperature difference measurement method.The designed flowmeter prototypes were tested on standard device for gas flow rate of sonic nozzle and the experimental results were compared and analyzed.Results show that the temperature compensation effect of the dual-speed probe type TMF is better than that of the constant temperature differential TMF.The designed flowmeters have good repeatability under different temperature environments,and can measure the small flow.