Rui Zhang Heilongjiang Institute of Measurement and Verification P. R. China

 GB/T21305:2007  Cereals and cereal products -- Determination of moisture content -- Reference method  Method: Heating (oven) methods (130± 3) ℃.  Applies to: wheat, rice (paddy, milled), barley, millet, rye, oats, triticale, sorghum in the form of grains, milled grains, semolina or flour.  Not applicable to: maize and pulses.  Equivalent to: ISO712:1998 "Cereals and cereal products -- Determination of moisture content -- Reference method"

MC Methods Direct Heating Methods Electric oven drying Rapid weight-loss Decompression Infrared heating and drying Chemical Methods Distillation Karl-fischer Indirect Electrometric Capacitance type Resistance type Ray Infrared Microwave Neutron Acoustic

 Heating method  Based on mass loss through heating in a heating oven  (105±2) ℃ method  a standard method with a single measurement time of 2~3h  used as calibration for other methods  (130±3) ℃ electric heating method  most commonly used in lab

 Uncertainty: U=0.4%~0.6% (k=2)  Advantages: Direct method Traceable to a balance of 1mg resolution High accuracy Good reliability  Disadvantages: Long time (at least 3 hours) High demand for operator

 Others  Decompression method  Not influenced by the shape of grains  Free of special pre- treatment  Ease of operation  High reliability  Suitable for quality control  Infrared heating method  Using infrared lamps  High precision  Easy to use  Wide rang of measurement.  Time consuming (1030min).

MC Methods Direct Heating Methods Electric oven drying Rapid weight-loss Decompression Infrared heating and drying Chemical Methods Distillation Karl-fischer Indirect Electrometric Capacitance type Resistance type Ray Infrared Microwave Neutron Acoustic

Resistance Method Principle Determined according to the changes of conductance. Advantages Fast response Simple structure Easy operation Disadvantages Temperature influences the MC results Not suitable for high MC samples and trace water Capacitance Method Principle Determined by measuring the dielectric constant of the grain. Advantages High reliability Low cost Easy operation and maintenance Online determination For high MC samples. Disadvantages Lots of influencing factor and complex data

 JJG  Verification Regulation of Instruments for Measuring the Moisture Content of Grain.  Requirement of techniques  Conditions of verification  Methods for verification  Period of verification

 JJG  Requirement of techniques  Safety requirement  Resistance between source circuit and insulation > 7 MΩ  The instrument shall endure 50Hz, 1500V sine wave AC, 5mA, 1min between source circuit and insulation without breakdown and arc.  Measurement time < 5min  Error indication

 MC plays an important role not only in storage of grain but also in grain marketing and handling.  Measurement of grain moisture is not just a technical issue, but also associate with the vital interests of most Chinese farmers.  Standard method (GB/T )  Verification regulation for instruments (JJG )  Existing methods  Therefore, more accurate, high throughput, more efficient and easier handling methods are in great demand.