Measurement Of Acoustic Flight Time And Attenuation Coefficient In Grain

The tomography imaging temperature field detection technique is a new technology developed on the basis of process analysis imaging technology.The technique is used to measure the average temperature of each path by measuring the acoustic flight time on each path,and the visualization of the temperature information is realized by the appropriate reconstruction algorithm.This method has the advantages of wide temperature range,non-contact measurement and large measurement range,so that it can be used in many fields.Monitoring the temperature distribution of stored grain is one of the applications of acoustic temperature measurement.Due to the huge grain production in China,the annual loss of grain due to mildew is very serious.And food is hot bad conductor,food moldy,pests,and water abnormalities will be reflected in the temperature changes,clear and understand the hot spots in food production and place to determine whether the food is in a safe state is particularly important.Therefore,monitoring the temperature change of food is of great significance.This paper studies the measurement of sound wave time in grain.Firstly,this paper introduces the basic principle of acoustic temperature measurement and the relationship between sound velocity and temperature in food,and establishes the sound wave time measurement system.Secondly,the selecteion and comparison of the sound source signal is made.This paper introduces the generation principle of Chirp signal and m sequence,and the two signals are prepared applied in the acoustic flight time measurement system,combined with the basic mutual calculation to measure the time of sound wave in grain.It is concluded that the acoustic flight time obtained by the m sequence is superior to the Chirp signal in stability and reveals the reason.This paper also studies the effect of wavelet noise suppression on acoustic flight time measurement.The anti-jamming ability of the sound source signal is described by measuring the stability of the acoustic flight time under the two kinds of sound source signals by using the cross-correlation method combined with wavelet suppression.Experiments show that the Chirp signal is a sound source signal,it can obtain more stable time than wavelet suppression,and the acoustic time of the m sequence is stable and can be processed without wavelet denoising.It is shown that the m sequence is superior to the Chirp signal in anti-interference ability.There are many factors that affect the sound wave time measurement in the grain,and the attenuation of the acoustic amplitude is one of the main reasons.The acoustic attenuation coefficient characterizes the attenuation of the acoustic wave in the unit propagation length and can be used to measure the attenuation of the acoustic signal.In order to accurately measure the acoustic flight time in grain and accurately estimate the signal intensity of sound waves in grain at different frequencies,a sound wave attenuation coefficient measurement system based on direct method is designed and implemented in this paper.In order to verify the feasibility of the acoustic attenuation measurement method,the measurement of the acoustic attenuation coefficient is simulated and feasibility of the proposed method is verified.And the application of the system in the grain of the actual measurement,obtained the sound attenuation coefficient and the frequency of the curve,to understand the attenuation of the sound waves in food,to achieve the actual needs of the unit of sound attenuation coefficient in meters.