Temperature-compensated and density-independent moisture content determination in shelled maize by microwave measurements

Moisture content of shelled maize, Zea mays L., was correlated with the att enuation and phase shift of electromagnetic waves travelling through a laye r of grain. Several calibration equations are presented in the paper that a re based on measurements taken at 15.2 GHz for various grain densities, moi sture contents and temperatures. Validation of the calibration equations in dicated that moisture content can be predicted with an uncertainty less tha n +/-0.72% moisture content w.b. at the 95% confidence level. Moisture pred ictions are largely independent of bulk density variations at temperatures from 4 to 45 degrees C and moisture contents from 9 to 19% w.b. By followin g one approach described, the grain bulk density can be determined from the same measurements with an uncertainty of less than 25 kg/m(3). With anothe r approach, the grain bulk density cannot be determined, but moisture conte nt is determined independent of the material bulk density and compensated f or temperature. No differences among three maize hybrids were observed in t he measured data. (C) 1999 Silsoe Research Institute.