Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2007
Publication Date: 9/1/2008
Citation: Armstrong, P.R., Weiting, M. 2008. Design and Testing of an Instrument to Measure Equilibrium Moisture Content of Grain. Applied Engineering in Agriculture. 24(5):617-624. Interpretive Summary: An instrument probe was developed to measure the equilibrium moisture content (EMC) of grain using a relative humidity (RH) and temperature (T) sensor. The probe was designed for insertion into the top of grain bulks. Advantages of this method of moisture measurement are that the sensor is inexpensive and is interchangeable. Disadvantages are that moisture measurements rely on the accuracy of ERH and T predictions of moisture and the response time of the sensors are slow to equilibrate to the grain environment. Instrument response time was substantially improved by forcing airflow over the sensor and using prediction models to determine the equilibrium value of the sensor. Measurements time was reduced to approximately five minutes or less.
Technical 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 their suitability for quick spot measurements. An initial prototype was tested and information was used to refine a second prototype. Both used an inexpensive digital relative humidity and temperature sensor. Result show that airflow over the sensor (0.60 m3/hr) is required to reduce measurement time to an acceptable level. Modeling a small time window of the initial EMC data with an exponential equation helped to predict when the sensor readings are in equilibrium with the grain environment but significant error results between predicted EMC and actual EMC values. A correction method was developed that significantly reduced the EMC prediction error by correlating the time rate of change of EMC, at a specific time, with the EMC prediction error. This correction method, though, may be sensitive to changes in the operating parameters of the instrument.