| The pVTt gas flow standard device that measures mass flow indirectly isa kind of primary standard, mainly used to calibrate the critical flow nozzle, also canbe used to calibrate other gas flowmeter. The pVTt gas flow standard has manycharacteristics such as high accuracy, simple structure, steady performance and soon, it is an important part of flow magnitude tracing system in our country.At present, the pVTt gas flow standard established in China is not many, withflow range and efficiency needed to be promoted urgently, and the study oftemperature characteristics in collection tank is few. Therefore, based on the pVTtgas flow standard device research project in the Zhejiang Institute of Metrology, wecarry out the control system and temperature field characteristics research of thepVTt gas flow standard device.First, based on the work principle and performance requirements of the pVTtgas flow standard device, the measurement and control system is designed. Based onPLC, we develop the lower computer system to record time, process signals offlowmeter, conduct actuator and so on. And based on the graphical programmingsoftware LabVIEW, we develop the PC control system to realize man-machineinterface management, process monitoring, database inquiry, report printing and soon.Secondly, in order to improve the accuracy of temperature measurement,temperature field characteristics are achieved based on the flow field simulation ofthe collection tank, and on that basis we carry out the research on thermometerarrangement. For the26m3and the0.5m3collection tank, using equal-volumedivided scheme and evenly layout scheme to arrange the measurement points, thenanalysis the results and compare their influence on the accuracy of temperaturemeasurement. The results show that there is only a small difference between their measurement results, but the accuracy of the equal-volume divided scheme is better,its maximum difference between the arithmetic mean value and the averagetemperature of gas is no more than0.003K.Finally, we build a pVTt experimental device to test the its performance andcalibrate critical flow nozzle. The repeatability of the0.05m3collection tank is0.056%, and the repeatability of the0.01m3collection tank is0.075%, then theinfluence factor of the repeatability is analyzed. |
