Moisture measurement capacitance method

On-line moisture monitors, which are based on infra-red absorption, nuclear magnetic resonance, capacitance and microwave attenuation are used in numerous process industries. The applicability of these techniques to the coal preparation industry has been reviewed (13,14). The CONAC and "Elemental Analyzer" units use a microwave attenuation method for the moisture measurement. This information is used to correct the PNAA hydrogen assay data in order to calculate the hydrogen content of the coal. Kay-Ray, Inc., (Arlington Heights, Illinois) has developed an instrument that measures the moisture content of a coke stream and uses a combination of microwave and gamma ray attenuation measurements. 

Electrical methods of measuring coal moisture involve determination of the capacitances or resistances or the dielectric constant of coal from which the... 

Electromagnetic methods such as eddy current, capacitance, microwaves, and terahertz radiation are not traditional inspection methods for composites, but they can be used in some circumstances [36]. Microwaves (300 MHz—300 GHz, 1000—1 mm) and terahertz (300 GHz—3 THz, 1—0.1 mm) are applicable to fiberglass composite inspection and have been successful at the detection of damage and internal features [37—45]. However, electromagnetic radiation at these wavelengths does not penetrate conductive materials. For CFRP, which is mildly conductive, they are only useful for sensing very near the surface. Capacitance measurements can be used to measure dielectric property changes in composites such as moisture uptake or cure condition. 

Under industrial conditions the moisture present in material must be determined by faster methods, such as by electrical methods of which three main varieties have become widespread moisture determination based on the change of the ohmic dc resistance, a measurement of the electrostatic capacitance (dielectric constant of the material), and a measurement of the loss in an ac field. Other quick methods are the chemical methods developed mainly for the most frequently occurring case, when the moisture is water, such as the Karl-Fischer analysis based on the chemical reaction of iodine in the presence of water [3], the distillation method, in which moisture is determined by distillation with toluene, and the extraction method, which is carried out with absolute ethanol. 

Moisture sensors/methods standard gravimetric method (SGM) microwave phase shift (MPS) microwave attenuation (MA) near-infrared (NIR) capacitance and conductivity (CC) radiofrequency transmission (RFT) neutron moderation activation (NMA) low resolution (LR) direct physical measurement (DPM) based on the drag force principle. 

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