Research On Error Analysis And Precision-promotin Method Of Thermal Mass Flowmeter

The thermal mass flowmeter is a kind of instrument which realizes flow measurement based on heat transfer principle. It is now a hot research area in mass flowmeter field since it is simple in theory and structure, low in cost, large in flow range, little in pressure loss and high in repeatability and reliability, for which it has been widely used in automotive electronics, semiconductor industry, energy and environmental protection domains. However, current error theory research in thermal mass flowmeter is scarce, as a result, many thermal mass flowmeters on the market only compensate temperature which causes large error, thus the measurement accuracy is not high. Furthermore, as the component that directly perceives the flow signal, the electric and thermal characteristics of thermal flowmeter sensors have a major impact on precision of the whole system, but the in-depth theoretical study is also very few.Facing the problem of low measurement accuracy, the following aspects are researched in this paper:1) On the basis of comprehensive study in all kinds of sensors, the widely used hot film integrated resistance, platinum film resistance and thermal resistance are chosen and the characteristic parameters of these sensors are analyzed in-depth, then the concept of response time is put forward which affects flow measurement markedly, finally relevant experiments are set up to study it;2) The source of measurement uncertainty of thermal mass flowmeter is comprehensively researched including measurement principle, data processing, component performance and so on. The impact of various measurement uncertainties on measurement accuracy of flow rate is analyzed. The main measurement uncertainties caused by gas temperature change and inserting depth deviation are researched focally, corresponding measurement uncertainty propagation coefficient are given eventually.3) The present temperature control and temperature compensation methods are analyzed in detail and the shortcomings and insufficiency of them are pointed out. On basis of this one precision promoting methods are put forward including digital closed-loop temperature control and digital temperature compensation method.4) Experimental platform is designed and constructed to conduct the calibration experiment of thermal mass flowmeter prototype, then calibration data is fitting to obtain characteristic curve under different temperature points as well as the function of characteristic curve coefficient to temperature, finally experiment is designed to verify the veracity and effectiveness of the proposed precision promoting methods.