Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . AMMETERS. 205 etc., have been cut away. When a current is sent throughit, by the springs, the coil tends to move through themagnetic field, to take up a position so that its lines of forcewill be in the same direction as those of the field. Itwill so move until the torsion of the springs is balancedby the force tending to move the coil, when the pointerwill indicate the angle of deflection. The angle of deflec-tion is nearly proportional to the current throughout themovement, which £
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . AMMETERS. 205 etc., have been cut away. When a current is sent throughit, by the springs, the coil tends to move through themagnetic field, to take up a position so that its lines of forcewill be in the same direction as those of the field. Itwill so move until the torsion of the springs is balancedby the force tending to move the coil, when the pointerwill indicate the angle of deflection. The angle of deflec-tion is nearly proportional to the current throughout themovement, which £-ives a very uniform scale, as can be seenfrom Fig. 195. The metallic bobbin on which the coil is. Fig. 196.—Method of Mounting the Movable Coil in Weston Instruments. wound has an electromotive force induced in it, only whilethe coil is moving, which causes eddy currents, ^f 292, toflow around the bobbin in the opposite direction to the cur-rent in the coil. These momentary currents tend to stop themotion of the coil, and have the effect of preventing theneedle from oscillating, thus bringing it to rest quickly at theproper position and making the instrument very dead-beat,^| 189. The movable coil is extremely light, the frictionsmall, and the instrument very sensitive to minute variations 206 PRACTICAL ELECTRICITY. of current. A current of about .015 ampere will give a fullscale deflection of the pointer. The instrument is carefullybalanced, so that it may be used in a horizontal or vertical position. An ammeter, however,should always be calibrated in theposition in which it is to be used; Amirror is located just below the scaleof the portable instruments. By-looking clown on t
Size: 1603px × 1559px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyo, bookyear1901
