[Electric engineering.] . 11. Alternating-Current Ammeters and Voltmeters. Most of the switchboard ammeters and voltmeters foralternating current consist of a coil arranged so that themagnetic field set up through it will act on a piece of iron, 17 ELECTRIC LIGHTING. 13 the movements of which actuate a pointer. Various modifi-cations of this coil-and-plunger type are in common example, in the earlier type of Westinghouse instru-ments, Fig. 13, a vertical coil A is arranged so as to drawan iron core C into it. This core is hung on one end of abalance arm to which the pointer N is attach
[Electric engineering.] . 11. Alternating-Current Ammeters and Voltmeters. Most of the switchboard ammeters and voltmeters foralternating current consist of a coil arranged so that themagnetic field set up through it will act on a piece of iron, 17 ELECTRIC LIGHTING. 13 the movements of which actuate a pointer. Various modifi-cations of this coil-and-plunger type are in common example, in the earlier type of Westinghouse instru-ments, Fig. 13, a vertical coil A is arranged so as to drawan iron core C into it. This core is hung on one end of abalance arm to which the pointer N is attached, and acounterweight W is hung from the other end. In the laterinstruments, the current is sent through a coil, and themagnetic field produced deflects a small iron vane placedwithin it. Fig. 14 illustrates the principle of a type ofinstrument that has been largely used by the General Elec-tric Company, both for alternating and direct current. Itis known as the Thomson inclined-coil pattern. The coil c,. Fig. 14. through which the current flows, is mounted on an angle, asshown. A vertical shaft passes through the coil, and on itis mounted a small iron vane v. This vane is mountedat an angle to the shaft, and when the hand is at the zeroposition, the vane lies at an angle to the lines of force that,when a current flows, thread through the coil as shown bythe arrows. As soon as a field is set up through the coil,the wane swings around so that it tends to lie parallel to thelines of force, as indicated by the dotted lines v, thus givinga reading on the scale S. The movement of the needle / iscontrolled by means of the springs a, a. The instrumentsshown on the alternating-current switchboard, Fig. 60, areof this type. 14 ELECTRIC LIGHTING. 17
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