American Telegraphy; Systems, Apparatus, Operation

American Telegraphy; Systems, Apparatus, Operation

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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. 1892 edition. Excerpt: ...These variations will, however, be somewhat more pronounced when the " double current" method of signaling is used, that is, the method in which the current is reversed in direction by the opening and closing of the key, in the manner previously explained To avail of these slight changes of cuirent strength, a very sensitive instrument, termed the "Brown and Allen" relay, has been devised, and has been successfully employed on submarine cables of about 600 knots in length, in connection with the double current method of signaling. See also Chap. XVIII, pages 287, 288. This relay is shown in Fig. 214. It consists of a coil of fine wire wound around a core of soft iron. The ends of the core extend beyond the coil and pass between the poles of two permanent magnets N, s; N, s. A current in the coil tends to make one of the ends of the core a north pole; the other a south pole; consequently, the north end will be attracted to the south pole of its permanent magnet, while the Fig. 214. other end of the core will be attracted to the north pole of its permanent magnet. The coil is rigidly attached to the core, but is insulated from it, in the usual manner; and the whole is suspended by a fine fibre, as indicated. So far, the arrangement is virtually a form of polarized relay, delicately poised. There is, however, in addition, an attachment to the instrument which imparts to it, sensitiveness; namely, a light metal pointer, termed a "jockey," pivoted at A, somewhat in advance of the middle of the coil, and extending beyond its ends. One of the ends of the 'jockey-' is placed between the ends of the stops s', s," one of which has a contact point aud is part of a local circuit. The play of the pointer between these stops...
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Product details

  • Paperback | 204 pages
  • 189 x 246 x 11mm | 372g
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236541189
  • 9781236541185