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. 1903 Excerpt: ...further diminish eddy currents in the instrument. With such precautions as these, the wattmeter will measure direct as well as alternating power of any periodicity or "wave form" equally accurately. The controlling force on the movable coil is usually that produced by two light hair-springs, which also serve to lead ...
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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. 1903 Excerpt: ...further diminish eddy currents in the instrument. With such precautions as these, the wattmeter will measure direct as well as alternating power of any periodicity or "wave form" equally accurately. The controlling force on the movable coil is usually that produced by two light hair-springs, which also serve to lead the current into and out of the moving coil. In some few instances mercury cups serve to do this. In a well-designed instrument the power absorbed by the wattmeter itself is small, that in the fine-wire circuit alone being reduced to a little under 2 watts in the best instruments. Another error which may creep in is due to the magnetic effect of the earth's field, corrected for in the manner described on p. 65. We will now consider in detail the most important of the wattmeters met with in practice at the present time. Siemens' Dynamometer Wattmeter In general appearance and construction, the form of wattmeter now under discussion, which is made by Messrs. Siemens Bros. & Co. of London, is precisely similar to the Siemens electrodynamometer (p. 62), except in the matter of the movable or swing coil. A diagrammatic view of the principle of construction is consequently not given, but is practically that given in fig. 71, to which reference should be made. A general view of the wattmeter is shown in fig. 176, and the only difference between this and the dynamometer described in fig. 71 lies in the moving coil. This in the wattmeter, fig. 176, consists of a large number of turns of fine insulated copper wire wound on a light rectangular frame of wood or ebonite or some non-metallic substance. Only a few of the turns are wound inductively, the remainder being doubly wound, so as to be non-inductive, and in addition to give, if possible, ...
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