| In grain production, storage, processing and distribution process, moisture content is the guarantee grain quality, measurement of the quality and net content index technical means of the indispensable. Grain moisture content measurement is a complex and difficult task, has experienced a from simple to complex, from static dynamic, from manual to automatic process, produce to different kinds of grain moisture content the measure methods and systems. In agricultural production each domain got certain applications, but because each measuring the limitations of each method, it is difficult to get extensive and mature applications.Time-domain transmission technology (TDT) is based on electromagnetic wave signal in a medium, because the spread of dielectric properties of medium the spread of electromagnetic wave diversity and speed changing and measuring. This technology has currently in soil humidity measurement can be widely used, its sensor structure forms are probe sensor. Probe sensor is one of the basic form of electromagnetic wave transmission lines, because the structure characteristics of the sensor for soil, sand, such as the moisture content of micro granular media measurement has obvious distinguish ability, but its grain, etc, the moisture content of the food products measuring distinguishing ability declined obviously, and cause grain particles are irregular, and probe larger and larger, so the gap between such as cereals food on the electromagnetic wave propagation speed less effect. In order to improve the resolution of grain moisture content TDT and sensitivity, this paper studies and designed a new sensor -- with time domain transmission axis sensor with axis, the electromagnetic transmission lines is another kind of form, as a kind of waveguide devices, coaxial cables can electromagnetic energies will be limited in its inner cavity, electromagnetic wave transmission speed with axis within the medium by the influence of the dielectric constants. If filling in the same axis between two conductors and the grain as the carrier of the electromagnetic wave propagation, the different moisture content of grain can change the electromagnetic wave propagation speed.This paper first studied the dielectric properties, according to grain moisture from the grain, determine the existence form the equivalent dielectric constant and grain moisture content relationship. Secondly on electromagnetic waves propagation wave is studied, the spread of exploring with grain equivalent dielectric constant, then determines the relationship between the parameters characteristics with axis sensor. Then designed for TDT grain moisture content measurement circuit system, analyzes the characteristics and a function module design, and key points of data collection system design. Finally, on the basis of the experimental data of grain moisture content TDT measurement model, and verifies the accuracy of model. |
