Moisture meter

This technique can be used to measure displacement where, in effect, the two electrodes are connected to the two bodies. It has also other applications (for example, in moisture meters where the presence of water vapor between the electrodes causes the capacitance change). 

G.A Persyn W=L-f Rothvity, Nuclear Magnetic Resonance Moisture Meter for Explosives , Stanford Research Inst FR 15-1545-01 (1970) 48) H.L. Herman, Blast Parameter Measurements of Experimental Batches of Minol-2 For the 750 lb M117A1 General Purpose Bomb , PATR 4092 (1970) 49) Anon, Propellants,... 

Simkins J. Squire, The Rapid Determination of Volatile Matter by the Mytron FAB-1 Moisture Meter , Explosive Research Development Establishment TN 82 (1973) 56) Anon, Ex-... 

The water concentration in the paint and in the paint film has been determined using a Mitsubishi moisture meter. The anode cell was filled with Karl-Flscher reagent and the cathode cell with a mixture of pyridine, formamlde and Karl-Flscher reagent (70/30/6Z (v/v)). Paint samples were injected directly into the cathode solution. 

Analyses of Water Content. The water content of the PIQ starting materials was analyzed. The water content of amines was measured using a DuPont 321A moisture meter and those of the solvents were measured by Karl Fischer s reagent method. The water content of acid dianhydrides was measured by titrating the free acid. 

The water content in the starting materials was measured as follows. The water content of amines and solvents were measured using the DuPont 321A moisture meter and Karl Fischer s reagent methods, respectively. Since the water contained in acid dianhydride is considered to convert it to free acid. 

Sources of moisture meters include Vacuum Atmospheres Co. (see footnote 2) Dupont Instruments, Wilmington, DE 19898 Panametrics, Inc., 221 Crescent St., Waltham, MA 02254 Beckman Instruments, Inc., 2500 Harbor Boulevard, Fullerton, CA 92634. 

When safflower was first introduced into the United States, the Fred Stein Co. was the first to produce a chart, the Steinlite moisture meter, calibrated specifically for safflower seed, allowing moisture to be rapidly and correctly determined at the elevator. Most moisture meters available today work well on safflower seed. 

Electrical Resistance Moisture Meters. The electrical resistance of wood is extremely sensitive to its moisture content, approximately doubling for each 1% decrease in moisture content over the hygroscopic range of moisture contents. The development of a successful resistance moisture meter may be attributed primarily to the pioneering work of Stamm (9) who first measured this relationship quantitatively. Because of the nature of electrical conduction in wood there is also a strong increase in resistivity with a decrease in wood temperature. Figure 1 illustrates how the electrical resistivity of wood varies with both moisture content and temperature. 

Most resistance moisture meters are essentially megohmeters that measure the resistance between pairs of pin electrodes driven into the wood to various depths. Because the pin electrodes taper along their lengths, the relationship between a resistance reading and the resistivity (resistance of a unit cube) is complex. Therefore the meters are calibrated empirically by using data obtained on a given species at room temperature (JO, 11),... 

Resistance moisture meter scales manufactured for use in North America read directly in moisture content, based on calibration data for Douglas-fir at 27 C. Figure 2 shows the range in electrical resis-... 

Note that the curves shown in Figures 1 and 2 are confined to the moisture content limits between 6-7 and 24-25%. Measurements below 6 or 7% are not reliable with ordinary moisture meters because the resistance is too high (above 10 ft). 

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

Figure 3. Temperature calibration curves for a DC resistance moisture meter (14). (Courtesy U.S. Department of Agriculture, Forest Products...

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... 

Other Physical Properties. In addition to its important effect on the strength of wood, moisture also affects wood s other physical properties. Moisture s effect on electrical properties was described in the section on Electrical Resistance Moisture Meters (p. 130). Other properties such as specific gravity and thermal properties are discussed here. 

Electrical moisture meters provide a quick and reasonably accurate nondestructive alternative. The direct-current resistance of the timber is measured or either the alternating-current capacitance or power loss can be measured. Direct-current resistance moisture meters are more common a pair of needles, a fixed distance apart, is driven into the wood across or along the grain (depending on the manufacturer s instructions) and the electrical resistance measured. The procedure is reasonably accurate between the fibre saturation point (defined later) at 30% and about 6% moisture content (at which point the resistance becomes too great to measure with reasonable accuracy). In this moisture content range, the relationship between electrical resistance and moisture content is represented by a log-log plot. 

Forrer JB and Vermass HF (1987) Development of an unproved moisture meter for wood. 

James WL (1988) Electrical moisture meters for wood. USDA, Forest Service, Forest Products Laboratory, General Technical Reportt FPL GTR-6 Jane FW (1956) The structure of wood. A. C. Black, London... 

There are also recording instruments based upon the relationship between the moisture content and the electrical properties of the material. The Shirley moisture meter (Fig. 2.15) depends upon the effect of moisture on the resistance of a sample of material compressed between two electrodes. 

Fig. 2.7. Neutron moisture meter for measuring soil water content.

Mitsubishi Reagents. [Mitsubishi Kasei] Reagents for moisture metering. 

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. 

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