Research On Ice Thickness And Liquid Level Measurement Method Based On Terahertz Technology

Liquid level is one of the important indicators of industrial production,and the measurement methods are widely used in food,chemical,medical industry and other fields.Currently,the liquid level measurement method can be generally divided into contact measurement and non-contact measurement.Although the contact liquid level measurement method is relatively mature,it has some adverse effects such as pollution,corrosion and leakage,etc.Therefore,the non-contact liquid level measurement method is the future development direction of liquid level measurement technology.The continuous adhesion and accumulation of ice will cause economic losses and even lead to safety accidents,affecting people's production and life.The development of an efficient and fast ice detection method can effectively reduce the potential safety hazards and economic losses caused by ice formation.Terahertz time-domain spectroscopy technology is based on the special properties of terahertz,such as low photon energy,strong penetration,transient,broadband and coherence,etc.,and has broad application prospects in the field of non-destructive testing.In this paper,a reflection terahertz time-domain spectroscopy system is constructed to realize the measurement of liquid level and ice thickness.The main work of this paper is as follows:(1)According to the requirements of liquid level and ice thickness measurement,by the generation and detection principle of terahertz,a reflective terahertz time-domain spectroscopy system is constructed,and the debugging and optimization of the system are completed.(2)Through the transmission of terahertz in multi-layer media,a liquid level measurement model is established and the model is verified.The results show that the measurement model is in good agreement with the experimental results.In addition,the error analysis of the measurement results is carried out,the absolute error of the measurement results is less than 40?m,and the influence of condensation on the inner surface of the PE film on the measurement is evaluated.The results of the repeatability experiment show that the system has good repeatability,and the standard deviation is 0.012 ps,condensation on the inner surface of the PE film will cause a measurement error of 18?m.(3)Ice thickness in five different depth molds is measured by two time-of-flight methods.The liquid level of five kinds of molds when a fixed volume of water is filled is measured with the flight time based on the reference point,and the theoretical thickness of the ice layer after the water is frozen is obtained by the liquid level.The calculation method of ice thickness based on the flight time of adjacent reflection peaks has a lower error than the calculation based on the reference point,and the average absolute error is less than 60?m.The ice layer thickness error calculated by the flight time of the reference point is higher than that flight time of adjacent reflection peaks,and the average absolute error is less than 80 ?m.