| In order to develop a yield measurement system on combine harvester and promote the development of precision agriculture, "Research Center for Precision Agriculture of China Agricultural University" has been working on the research of "the development of grain yield monitoring and mapping system on combine harvester" since 2001. The aim is to measuring grain yield, location of fields, area etc. dynamically during harvesting. Then scientific decision-making on farming management can be made. The task comprises grain moisture real time measurement for correcting yield data.The thesis reviewed many methods to measure grain moisture. Through synthetical compare and analysis, the author decided to realize grain moisture real time measurement by means of capacitance method. A suit of machinery equipments and control system to realize continuous measurement has been developed. According the results of signal test of imported sensor and the requirement of monitor designed by task team, the sensor signal process circuit was designed. The measuring theory of capacitor sensor and the factors that affecting measuring result have been explored and analyzed. The circuit has been designed in three methods. After comparing and analysis, the method of using CAV424 as a key component to design the sensor has been chosen..Through lots of simulative tests and field tests, the conclusion can be made that the technique of imported sensor can measure grain moisture in the range of 8%~34% with an error of 0~l percentage. The sensor designed by author can measure grain moisture in the range of 10%~25% with an error of 0~2 percentage. Finishing one time of grain renewing in sampling channel needs about 28 seconds. Consecutive experiments has been done for 4 days (June 11th -June 14th) and all the system ran well. Generally speaking, measuring grain moisture real time can be realized and the technique has good extending prospect.
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