Dielectric moisture meters

Dielectric Moisture Meters. These moisture meters use AC, usually at radio frequencies. There are two general types the capac-... 

The power-loss meter is the most common type of dielectric moisture meter. It senses the product of the dielectric constant and loss factor. Generally, the loss factor increases with wood moisture content but may exhibit variations from this behavior depending on the frequency of measurement (JO, 11, 14). An increase in temperature produces effects similar to increasing moisture content, with interaction between these two parameters. Therefore, temperature adjustments of meter readings are complex, sometimes increasing and sometimes decreasing the scale reading as temperature increases... 

Electronic moisture meters usually operate on a dielectric principle and/or kernel surface conductance with compensation for sample temperature and density. Thus, electronic moisture meters measure electrical properties that are calibrated to oven moisture measurements. The typical air-oven reference methods used for whole soybeans are the AOCS Method Ac 2-41, ASABE Standard S352.2, and AACC Method 44-15a. 

Electrical resistance measuring devices together with dielectric and infrared instruments are available as non-destructive commercial products for field use, notably by small boat surveyors [38]. Clegg [39] has reported comparative tests on three of the most popular UK/Ireland moisture meters which use capacitance measurements. 

The capacitance type essentially measures the dielectric constant of wood. At a given frequency, the dielectric constant increases with wood density, moisture content (Figure 4), and increasing temperature (JO). The most effective electrode configuration for a capacitance meter appears to be a pair of flat parallel electrodes contacting each of two opposite faces of the wood to be measured. There is then... 

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