1. Electronic Grain Moisture Tester Principles of Operation Hiroshi Noji Kett Electric Laboratory 11/27/2013 Electronic Moisture Tester - Principles of Operation 1

2. Methods for Measuring Moisture Content ● Oven drying ● Vacuum oven drying ● Distillation ● Chemical reactions with the certain reagents ● Electronic devices or moisture meters ● Nuclear magnetic resonance(NMR) ● Near – infrared(NIR) spectrophotometry Electronic Moisture Tester - Principles of Operation 2

3. Requirements for a Practical Measurement Method To be considered a practical grain moisture measurement method, the system must be accurate, fast, and reliable, has a simple operation (or is automated), and has a relatively low cost per test sample. Electronic Moisture Tester - Principles of Operation ● Electronic moisture tester ● NMR ● NIR 3

4. Electronic Moisture Tester - Principles of Operation 4 Popular Types of Electronic Moisture Testers ● Electric resistance type ● Dielectric constant type(Capacitance type) Riceter f series (Kett model) PM-650 & 450 series (Kett model)

5. Electronic Moisture Tester - Principles of Operation 5 Principle of Electric Resistance Type (1) ● Conductivity vs Moisture Content ● Conductivity vs Moisture Content ● Resistivity vs Moisture Content ● Resistivity vs Moisture Content Moisture(%) Electric Properties (Logarithmic Axis) Resistivity (Logarithmic Relationship) Conductivity (Exponential Relationship) Relationship between moisture content & electric properties of grain (Semilog Graph)

6. Electronic Moisture Tester - Principles of Operation 6 Principle of Electric Resistance Type (2) Resistance vs Moisture Content R = ρ× l / A ※ where R is the Resistance ρ is the Resistivity l is the Length A is the Cross-section Area If the shape of the electrode is fixed, R is directly proportional to ρ, and is logarithmic to moisture.

7. Electronic Moisture Tester - Principles of Operation 7 Principle of Electric Resistance Type (3) Ohmmeter (Measurement Circuit) Ohm's law R = V / I Powersource V A R

8. Electronic Moisture Tester - Principles of Operation 8 Principle of Electric Resistance Type (4) Constituent Elements ● Electrode system ● Electronic measurement circuit ● Indicator ● Pressure system Electrode Electrode Sample Tray Sample Pressure System Electronic Circuit Indicator Battery HandleHandle

9. Electronic Moisture Tester - Principles of Operation 9 Principle of Electric Resistance Type (5) Purpose of a Pressure System ● Shape the sample as a conductor (Length and Cross-sectional Area) (Length and Cross-sectional Area) ● Stabilize the electrical contact ● Eliminate the influence of kernel size variation Sample Tray Sample Pressure System

10. Electronic Moisture Tester - Principles of Operation 10 Principle of Electric Resistance Type (6) Important Note 1 Moisture tester readings are affected by sample temperature. Example. 0.1% per 1 ℃ ● Temperature compensation by the temperature sensor ● Temperature sensor measures the unit temperature It is important to equilibrate the sample temperature, unit temperature, and ambient temperature for precise (repeatable) measurement.

11. Electronic Moisture Tester - Principles of Operation 11 Principle of Electric Resistance Type (7) Important Note 2 Conductance(resistance) and moisture content have an exponential(logarithmic) relationship. If kernel moisture contents on a sample tray are widely varied, the moisture tester readings will to be higher. Moisture(%) Conductance Average : Representative Value Reading Example Fresh grain immediately after the harvest

12. Electronic Moisture Tester - Principles of Operation 12 Principle of Electric Resistance Type (8) Other Features ● Capable of measuring a small size sample ● Instruments may be small in size and portable ● Instruments may be fast and simple to operate

13. Electronic Moisture Tester - Principles of Operation 13 Principle of Electric Capacitance Type (1) Dielectric Constant vs Moisture Content Dielectric Constant vs Moisture Content Moisture(%) Dielectric Constant Directly Proportional Relationship between moisture content & the dielectric constant of grain

14. Electronic Moisture Tester - Principles of Operation 14 C = εr×ε0 × S / d ※ where C is the Capacitance εr is the Dielectric Constant ε0 is the Electric Constant d is the distance S is the Area If the Shape of the Electrode is Fixed, C is directly proportional to Moisture. Principle of Electric Capacitance Type (2) Capacitance vs Moisture Content Capacitance vs Moisture Content

15. Electronic Moisture Tester - Principles of Operation 15 Electric lines of force expand outside the electrode. The force is affected by the surroundings. Principle of Electric Capacitance Type (3) Electrode 1 : Parallel Flat type Electrode 1 : Parallel Flat type Electric lines of force

16. Electronic Moisture Tester - Principles of Operation 16 In some areas, the electromagnetic distance is not uniform. Sample density in the electrode is not uniform. Principle of Electric Capacitance Type (4) Electrode 2 : Enclosed Parallel Flat type Electrode 2 : Enclosed Parallel Flat type Electric lines of force

17. Electronic Moisture Tester - Principles of Operation 17 It’s an ideal electrode! Principle of Electric Capacitance Type (5) Electrode 3 : Cylindrical type Electrode 3 : Cylindrical type Electric lines of force

18. Electronic Moisture Tester - Principles of Operation 18 Principle of Electric Capacitance Type (6) Constituent Elements Constituent Elements ● Electrode system ● Electronic measurement circuit ● Indicator ● Weighing system Electrode Electrode Electrode Sample Weighing System Electronic Circuit Indicator Battery

19. Electronic Moisture Tester - Principles of Operation 19 Principle of Electric Capacitance Type (7) Weighing system Weighing system Capacitance is directly proportional to the volume (quantity) of the sample. It must be measured for given volume of sample. Sample density in the electrode depends on the kernel size. ● Weight compensation by the weighing system ● Weight compensation by the weighing system The instrument must be used on a horizontal and vibration- less table where wind is not present.

20. Electronic Moisture Tester - Principles of Operation 20 Principle of Electric Capacitance Type (8) Important Note Important Note Moisture tester readings are affected by sample temperature. Example 0.1% per 1 ℃ ● Temperature compensation by the temperature sensor ● Temperature compensation by the temperature sensor Temperature sensor measures sample temperature directly. However, because the thermal capacity and conductivity of the electrode are huge, sample temperature moves toward the electrode temperature during measurement. It is important to equilibrate the sample temperature, unit temperature, and ambient temperature for precise measurement.

21. Electronic Moisture Tester - Principles of Operation 21 Principle of Electric Capacitance Type (9) Other Features Other Features ● Capable of measuring a large sample ● Nondestructive measurement

22. Electronic Moisture Tester - Principles of Operation 22 Comparison Table Resistance TypeCapacitance Type Popular modelRiceter f seriesPM-650/450 series Sizecompactmoderate Nondestructive testing × 〇 Sample quantitysmallmoderate On an uneven sample △〇 In wind 〇△ Test timefastmoderate Costlowmoderate

23. Electronic Moisture Tester - Principles of Operation 23 Thank you Kett Electric Laboratory Technical Department Hiroshi Noji