| 摘要 |
1,117,683. Measuring moisture content. WEYERHAEUSER CO. July 2, 1965 [July 3, 1964], No. 28131/65. Heading G1N. The conductivity, representing moisture content of, for example timber 5, Fig. 1, and Fig. 2 (not shown) is measured by two or more pairs of electrodes 17, 18 and 27, 28, and 37, 38, mounted on a line transverse to the direction of motion of the timber, the electrodes of any one pair being connected together, the electrodes of adjacent pairs being energized by A.C. signals differing in phase by 180 degrees, and the timber itself forming effectively an earthed electrode which with each of the said pairs of electrodes constitutes a capacitance. Each such capacitance is connected in a respective bridge circuit forming part of the overall measuring circuit Figs. 5, 6 (not shown). The electrodes-timber capacitance is represented as a capacitor (C10) in series with a resistance (R10; or C20, R20, C30, R30), the value of the resistance depending upon the moisture content. One end of a centre tapped transformer secondary winding (52) is connected via a standard capacitor C s to the electrode capacitance C10 - R10, across which a further capacitance C t 10 is also effective due to the earthed shields 11, 12 forming part of the electrode construction of Figs. 1, 2. The earthed end of the electrode capacitance C10, R10 is connected via a variable capacitor Vc - 10 and a further standard capacitor C s to the same end (Fig. 5) or the other end (Fig. 6) of the secondary winding. A difference in voltage between the points 10a, 10b at the sides of the capacitors Cs remote from the secondary winding, is detected and amplified (at 10b-10a) and represents moisture content. The other electrode capacitances are also connected to the secondary in similar fashion, but are arranged so that adjacent ones are 180 degrees out of phase. The various outputs are fed to a control unit 50 which detects the maximum, minimum, or average moisture content, and may control an ink marking device 45, or operate any other alarm. |
