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Principles & practice of electrical testing; as applied to apparatus, circuits and machines - Softcover
Synopsis
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1919 Excerpt: ...Therefore the permeability for the magnetising field Hx is h By obtaining the balancing values for other currents, and using the curve for the standard rod, the B-H curve of the sample may be obtained. Fig. xai.--Ewing.s permeability bridge. this, the needle of M is A balance was obtained when there were 100 turns on the standard rod and 120 turns on the test rod; the current being 2 amperes. The magnetising field in the standard solenoid is therefore 2 x 100 10 1 and the flux density from the curve was found to be 16,000. This is also the density in the test rod due to a magnetising field of 24, so that this gives one point on the B-H curve of the test. Ewing.s hysteresis tester.--By this instrument a quick determination may be made of the hysteresis loss in a sample of iron. The latter is in the form of a block of thin laminations of about seven pieces, each 3" by This block is placed between the two poles of a permanent magnet balanced on knife edges. The principle of the instrument is illustrated in Fig. 122. B, the sample, is rotated rapidly between the poles and becomes magnetised; passing through a complete cycle per revolution. Owing to the lag in its polarity, B drags, by attraction, the respective poles adjacent to its ends through a certain angle, whose value depends upon the hysteresis of the sample. This angle is given by the pointer p. The control force is gravity, and the oscillations are damped by D. Above a certain speed the deflection is, as would be expected, independent of the speed of B. The deflection is proportional to Trthe area of the hysteresis loop, and the tester is calibrated by means of a specimen sample whose hysteresis curve has been determined by other methods. Sometimes deflections correspondFig. XM.-Ewing.s hysteresis...
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