Development Of Industrial Thermal Gas Mass Flowmeter

The thermal gas mass flowmeter (TMF) with good characteristic such as simplestructure, good reliability and low cost is widely used in industrial production. In theforeseeable future, TMF will be further risen in the use ratio. The domestic literatures inresearch and development of flowmeter are less. In this thesis, two kinds of thermal gasmass flowmeters are designed and the development process is described in detail. They areconstant temperature differential type TMF and constant temperature type TMF.In the constant temperature differential type TMF, platinum resistance Pt20and Pt1000are used as measuring elements in the flow sensor. The circuit is reasonably devised sothat the temperature of Pt20is constantly100℃higher than Pt1000. The flowmeasurement circuit is excogitated according to probe characteristics. After flow systemcalibration, the mass gas flow is calculated through the output voltage of probe.In the constant temperature type TMF, the constant temperature semiconductor thermalprobe in the flow sensor is made by CMOS process craft. It is constantly kept in105℃after electrify. AD590is used as the temperature probe. And then the gas flowmeasurement circuit is excogitated according to probe characteristics. The meter is rugged,impact resistance, corrosion resistance and good stability.MCU C8051F410is both used as the master microcontroller in flow meter converterof the TMF. The functional relationship between the output voltage and real-time massflow in two flowmeters is obtained through standard flow generating system. And then thereal-time mass flow is concluded during the piecewise linear interpolation. The flowmeterand computer are directly connected by RS-485communication interface to achieve aflow meter to set and read the various parameters, in order to achieve different workingconditions to ensure meter accuracy. The flow measurement range can be set, and4~20mA is outputted in the full scale to achieve the industrial control.