DESIGN AND TESTING OF AN INSTRUMENTTO MEASURE EQUILIBRIUM MOISTURE CONTENT OF GRAIN

ABSTRACT. Two instruments to measure the equilibrium moisture content (EMC) of grain were designed and tested under different grain conditions to determine their measurement time and suitability for quick spot measurements. An initial prototype was developed and tested and used to refine a second prototype. Both used a relatively inexpensive digital relative humidity and temperature sensor. Objectives were to determine factors affecting measurement performance and methods to minimize the effect of the factors which degraded performance. Specifically, the time response of the sensor was considered a major obstacle in obtaining quick measurements. Results showed that airflow over the sensor (0.60 m3/h) was required to reduce measurement times to an acceptable level. Modeling of the initial measured data with an exponential equation helped to predict when the sensor readings were in equilibrium with the grain environment, and reduce measurement time, but significant error can occur between predicted EMC and actual EMC values. Error correction methods were developed that reduced the error significantly but the methods are potentially sensitive to changes in the operating parameters of the instrument