Microwave Water Content Detection Device Based On Double Detection

Grain is one of the raw materials of grain products,according to the variety of grain,its internal moisture content is different.Excessive moisture not only wastes the transportation cost of grain,but also is damaged by mildew and harmful insects during storage,causing grain fever,mildew and deterioration.The amount of moisture directly determines the processing mode and storage form of grain products,which is of great significance to the production process of grain industry.Microwave method is widely used for nondestructive measurement of moisture content in grain samples among various methods currently applied in grain samples.According to the difference in the structure of the detection device,the microwave method can be divided into three categories: space wave method,resonant cavity method and transmission line method.In the category of space wave method,the microwave transmission method and microwave reflection method are divided into two categories according to the different microwave signals received.Because the reflection method is not restricted by the detection of the sample thickness and a single horn antenna can realize the microwave signal sending and receiving,easy to install and change the position,so the reflection method is chosen to detect the moisture content of grain.However,in the experiment of measuring the moisture content of grain samples by microwave reflection method,it was found that there was a principle error in measuring the moisture content of grain samples with large grains,that is,the bulk density had a great influence on the detection accuracy.The bulk density causes a principle error to the detection accuracy of the device for water content detection by the single transmitting and receiving microwave reflectivity method through the effect of microwave on the roughness of the surface of corn and the number of corn particles per unit volume,which leads to the unsatisfactory repeatability and linearity of data.Therefore,a microwave moisture content detection device based on double detection is designed on the basis of single transmitting and single receiving of traditional microwave reflection signal.Double received two road detection unit probe by a quarter wavelength,when small changes in water samples and the location of the horn antenna,the double detection unit's two presents voltage value opposite change tendency,this trend can effectively solve the packing density of the sample surface roughness affects the accuracy of testing data of moisture content.The function relation between the output voltage value of the two-channel detection unit and the water content can also solve the error influence caused by the small increase or decrease of the particle number in the same volume by establishing a mathematical model according to the characteristics of the opposite variation trend of the two voltage signals.Finally,the principle error caused by the bulk density of grain samples on the results of moisture content detection device was solved from two aspects.This paper introduces in detail the microwave sensor detection principle and structure design,hardware design,software design,double detection unit moisture content detection experimental data processing and analysis.The double detection unit in the device can well offset the impact of the bulk density on the moisture content detection accuracy,so that the device can realize the online real-time nondestructive detection of the moisture content of large grain samples.