On-line moisture content measurement of wheat

A method has been developed which allows continuous measurement of the moisture content of a stream of hard winter wheat to an accuracy acceptable for normal grain drying operations. A test rig was designed and constructed to allow measurements to be made, on-line, of grain flowing through a sensing device. All sets of experiments were conducted at room temperature (19-24 degrees C), where the relative humidity varied from 50% to 65%. The dielectric properties were measured using wheat samples with bulk densities ranging from 625 to 891 kg/m(3). A series of simultaneous measurements of capacitance and conductance at 0.5 MHz on varieties Slejpner, Mercia, and Hereward, varying in moisture content from 11.5-21.5%, w.b., revealed that the function [(epsilon'-1)/epsilon ''] was practically independent of mass flow rate in the range from 2.0-14.4 kg s(-1) m(-2) Non-linear regression models were used to correlate moisture content with. the function [(epsilon'-1)/epsilon '']. The individual calibration equations developed for each variety could estimate moisture content with standard errors of calibration of 0.5 percentage point (Slejpner), and 0.4 percentage point (Mercia and Hereward). The maximum error of moisture estimation was 1.3 percentage points, and occurred for a sample of variety Slejpner at 21.8% moisture content. The maximum error never exceeded 0.7 percentage point for varieties Mercia and Hereward. The limitation of moisture contents to the range from 11.5 to 16.3% led to a linear relation between moisture content and the function [(epsilon'-1)/epsilon ''], reducing the standard errors of calibration to the surprisingly low value of 0.1 percentage point moisture. (C) 1996 Silsoe Research Institute