is important because that loss occurs all the time, even when lamps are not burning, and any drop in the series coil is equally objectionable, since it reduces the pressure at the lamps. For 400 volts or less and currents up to 80 amperes, the meter is connected directly

Fig. 389. Connections for Two-phase Westinghouse Meters.

to the circuit. With higher voltages or heavier currents a potential transformer is used to reduce the pressure for the shunt winding, and a series transformer is inserted in one of the main conductors to obtain a smaller but proportionate current for the series coil. The connections for a two-phase circuit are shown in Fig. 389, a

potential transformer for each phase being placed below and a smaller series transformer for each phase above, with all four secondary wires leading to a single meter in the center. The energy is brought from two-phase generators by four wires from the right, and after being measured is carried to the lamps by four wires on the left. The dials record the total energy supplied in all the branches of a polyphase circuit into which the wattmeter is connected, no multiplier being necessary.

The Duncan Integrating Wattmeter, represented in Fig. 390, is another well-known form of the induction motor type for alternating currents only. It comprises a series field core of laminated iron with inwardly projecting poles carrying the series coils, between which the armature aluminium cup

an inverted

- rotates

upon a vertical spindle, as shown. The shunt coil placed inside of the armature, with its axis at right angles to that of the series coils, is also wound upon a laminated iron core, being stationary and supported from below by a brass arm. The upper end of the armature spindle carries a gear driving the train of dials,

and on the lower end is mounted the retarding disk of aluminium. which revolves between the poles of two permanent magnets. The so-called compensator is a copper ring with an iron core shown in front of the armature and supported by a movable arm. By adjusting its position, friction may be overcome and at the same time "creeping" avoided. The lower bearing of the spindle is of sapphire and the spindle point of hardened steel, both of which are easily renewable.

The Gutmann Integrating Wattmeter is similar in principle to the Westinghouse and Duncan instruments, being of the induction motor type with series and shunt windings, and is adapted only to alternating currents. The arrangement of the dials, retarding disk and other parts is also similar, but the armature or rotating member is a diagonally slotted aluminium cylinder.

The American Integrating Amperemeter, illustrated in Fig. 391, differs radically from those already described, both in principle and in construction. It consists of a solenoid and core placed above a self-starting pendulum, actuated by the electric current. The pendulum, by means of a cam, raises a pawl on a ratchet

Fig. 391. The American Integrating Amperemeter.

wheel to a uniform height each stroke. The solenoid, by means of its core, shifts the angular position of a pendent arch attached to its axis so as to permit this pawl to drop along the ratchet wheel a number of teeth proportional to the current passing through the meter; thus at each stroke of the pendulum the load in amperes passing to the consumer is, by means of the ratchet wheel and the counter register, measured and added up in amperehours.

The pendulum ceases to swing when no lamps are burning; but as soon as any are turned on, and current flows in the main conductor, the pendulum is started automatically, being actuated by a

shunt circuit across the mains. The form illustrated is for use on a three-wire system, both of the outer conductors being carried through the solenoid, as indicated, so that its action upon the core, and therefore the position of the latter, depends upon the combined effects of the two currents, thus measuring the total load on both sides of the system. The core of soft iron is magnetized to saturation by a winding in circuit with the coil that drives the pendulum, the object being to avoid variations due to hysteresis. Having this construction, the instrument measures ampere-hours simply, since ordinary changes in voltage would produce no appreciable effect.

The Ferranti Meter used in England is based upon the principle that a conductor carrying a current in a magnetic field tends to move in a direction perpendicular to the current and to the lines of force. In this case the conductor consists of mercury contained in a shallow circular chamber placed between the poles of a magnet excited by a coil through which the main current passes. This current also flows radially through the mercury being introduced at the center by a pin, and taken off at the periphery by a metallic rim. The retarding force is that due to fluid friction of the mercury against the inner surface of the chamber, in which radial grooves are formed to increase the effect and make it as nearly as possible proportional to the square of the speed. Since the current flows in both the magnet and the mercury, the driving force is proportional to the square of the current, and the speed, therefore, increases directly with the current. A vane dipping in the mercury transmits the motion of the latter to the counting dials by means of a small spindle. The driving force due to residual magnetism is designed to overcome the retarding force due to the solid friction of the parts. It is evident that this instrument measures ampere-hours and not watt-hours.

The Aron Meter consisted originally of an ordinary clock having a permanent magnet for the bob of the pendulum, below which was placed a coil with its axis vertical. The current to be measured passed through the coil in the direction to repell the magnet, thus neutralizing a part of its gravity which caused the clock to lose time. The loss of time in any period enabled the ampere-hours during that period to be determined. A later form comprised two separate clocks, one acting normally and the other

being influenced by the current. The two trains of wheels were connected by a differential gear to a third train with dials and pointers which indicated the difference in action of the two clocks, being calibrated in ampere-hours. This type involves two obvious difficulties: one is the trouble of winding the clocks, and the other is the practical impossibility of keeping correct a large number of clocks of reasonable cost. These objections are overcome in a still more recent form which is made self-winding by the action of the current, and each pendulum is acted upon by a coil so that one is accelerated and the other retarded, thus doubling the effect. Furthermore, at frequent intervals the connections of the coils are reversed, so that first one and then the other pendulum is the faster, the difference between the two being always registered on the dials. In this way even a considerable deviation from accuracy in one or both of the clocks is eliminated by the constant reversal of their relations. Another feature in the improved Aron instrument is the substitution of a shunt coil for the permanent magnet on each pendulum, thus converting it into an integrating wattmeter. It is adapted to either direct or alternating currents, and is made in forms suitable for two-wire, three-wire, and other circuits.

ter.

The Terms Integrating, Recording, and Registering Meter are all used for designating the various devices described in this chapThe first is certainly correct, since in most cases the instrument merely integrates or sums up the total number of ampere- or watt-hours, without making any record of the almost constant variations in load which usually occur. There are also instruments commonly called recording volt-, ampere-, or wattmeters, in which a line is traced out on paper showing the number of volts, etc., at any time during the entire twenty-four hours. By using an ampere- or wattmeter of this kind and properly integrating the record obtained, the number of ampere- or watt-hours may be determined. This is much less convenient, however, than an instrument which automatically performs the integration and gives the result on a dial. On the other hand, the maximum demand and other values would all be shown, so that a charge could be made taking them into account, as explained in the beginning of this chapter. As a matter of fact, such instruments are rarely used except to ascertain the uniformity of voltage, etc., when it is desired to have it con