The Flow Field Characters Research And Uncertainty Evaluation Of PVTt Gas Flow Standard Device

Characterized by its high accuracy,simple.structure,stable performance,and so on,pVTt gas flow standard device gradually applied to the verification of critical flow venturi nozzle and some other gas flow meters,and it is the important part of the flow quantity traceability system in our country.Therefore,based on the pVTt gas flow standard device research project in the Zhejiang Institute of Metrology,we carry out the control system and temperature field characters research of the pVTt gas flow standard device.Firstly,the working principle and structure of pVTt gas standard device are summarized,including the mass flow calculation model and the mathematical model of the discharge coefficient of the nozzle,then sort out several common humidity correction method,comparison of four main methods are made.Secondly,the temperature field characteristics of 0.5 m3 collection tank are studied based on the simulation results.Thirdly,the hardware of the system is improved,and the software is adjusted correspondingly on the basis of the original system.With PLC millisecond timer interrupt and output functions of number,the internal clock of the PLC is used as the time reference of the flow device,functions such as timing,signal sampling and component control of the device are realized finally.The verification system of the upper computer adopts the LabVIEW programming language,and the man-machine interface is friendly.Then,the air tightness test,the system time difference test,and nozzle verification experiment are carried out according to the verification regulations.The repeatability of the five collection tanks are all less than 0.03%,which meets the design requirements of the device,and experimental studies have been carried out based on the current temperature measurement program,then to make a comparative study on the temperature field distribution in the collection tank under different stability conditions and different collection time.Finally uncertainty evaluation of the pVTt standard device is accomplished based on the experimental data,which is better than 0.05%(k=2).