117

Edgewise type with scale lengths of 5 ins., 8 ins., and

12 ins.; the latter is made with an illuminated dial. (Fig. 3.)

■20

Edgewise Instrument Flanged Type, 5 in. Scale. FIG. 3.

Wattmeters.—These are of two types, the moving-eoil type (Drysdale’s Patent), and the dynamometer type. The former consists of a moving coil of the “Ayrton-Mather” pattern moving in a magnetic field. The moving coil is connected to the pressure circuit with non-inductive resistance in series, and the current or series windings being wound on soft-iron stampings produce the required field. This type of wattmeter gives accurate results, especially with alternating currents ; it possesses the advantage of accuracy on circuits of low power factor. It is dead beat being fitted with air-damping. The instrument is mounted in round cases, 8 ins. in diameter, and finished copper or nickel.

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