Fig. 661.--Internal connections of Sangamo watt hour meter (type D). A, copper disc armature, submerged in mercury; B, bridge wire between binding posts, for main load current, when both sides of the line are carried through the meter; CT, compounding series turns around pressure circuit magnet, building up field as load increases, to compensate for falling off in speed otherwise found; D, aluminum damping, or brake disc, controlling speed of meter; E, copper contact ears, imbedded in insulating wall of mercury chamber, leading current into and out from armature; F, hardwood float on armature proportioned to give slight "lift" to entire moving system, when armature and float are immersed in mercury; H, soft steel disc above permanent magnets, riveted to fine pitch screw working in bracket above, so that adjustment of the disc up or down gives variation in damping effect of permanent magnets, and therefore of main speed. K, clamp slider with thumb screw, for obtaining light load adjustment by moving K to right or left, as may be necessary. K spans and connects parallel wires of light load adjustment, BR and RR'. MM, powerful permanent magnets, acting on disc D, giving main speed control for meter. N, high resistance heavy wire, forming part of series adjustment between armature and any shunt with which meter may be used, to set drop through meter correct for drop of the shunt. P, spirally laminated soft steel ring, moulded in mercury chamber above the armature space, to act as a return for magnetic lines of force from and to energizing magnet below. R, resistance card unit, in series with pressure circuit coils; in 110 volt meters one card is used, in 220 volt meters two cards, or one card and a thermocouple. BR, small brass wire, connected to ingoing end of pressure circuit coils and forming RR' and the slides K the light load adjustment. RR', high resistance wire having opposite ends connected to ears EE by low resistance wires. Current energizing the pressure circuit coils SC passes from RR' through K to BR and thence to the coils, and if K be near the end of RR' and BR, the least compensation is obtained; if near right end, maximum light load compensation is obtained. S, shaft or spindle. In actual meter S is divided, the lower shaft carrying armature A, and the upper shaft damping disc D. SA, series resistance adjustment, for setting meter to correct drop for shunt. SC and SC', pressure coils connected in series. TT, binding posts at bottom of meter. Y, laminated soft steel yoke, carrying coils SC and SC', and giving a powerful and concentrated magnetic field on the armature. W, worm, driving recording dial train. WW, worm wheel.
Fig. 662.--Interior view of Columbia watt hour meter (type D), showing construction and principal parts and connections. The armature winding consists of three coils approximately circular in shape. The coils are form wound, interlocked with one another and with the light impregnated fibre disc which serves as a spacer for them. The aluminum damper disc has the conventional anti-creep provision in the shape of the three small soft iron plugs, mounted close to the central staff, which the illustration shows. These in their revolution come successively within the influence of an adjustable iron screw which is magnetized by an extension from one of the damper magnets. The angular relationship of the armature windings and of the three iron plugs is such that at the time that the armature is exerting a maximum torque the magnetized screw is exerting the maximum pull to hold back a given plug and conversely when the armature pull is a minimum the magnetic screw is attracting a plug with the maximum effort to cause ahead rotation. The irregularities of torque are in this way smoothed out. The commutator has three segments and is made of chemically pure silver. Each brush is formed of a length of phosphor bronze wire bent like a hair pin and secured at its "U" end to a brass sleeve, which in turn is secured to an insulated stud by a set screw. An extension on the sleeve carries a micrometer screw brush adjustment. The main speed adjustment is secured by providing a soft iron bridge plate, bridging over the extremities of each magnet end and adjustable, by means of a set screw and lock nut, to any desired distance therefrom. This gives a regular micrometer means of varying the effective magnet strength. Interposed between the series coil and the permanent magnets is a heavy soft iron shield to guard the magnets against disturbance by short circuiting. Light load adjustment is obtained by providing in the coil circuit a series of small resistance spools, equipped with pin terminals, to which connection can be selectively made by means of a split bushing terminal on a flexible cord. This series of spools is strung on a metal arbor located within the case.
Fig. 663.--Diagram showing internal connections of the Duncan watt hour meter. Its operation depends upon the principle of the well known electro-dynamometer, in which the electromagnetic action between the currents in the field coils and an armature produces motion in the latter. It also embodies the other two necessary watt hour meter elements required for the speed control and registration of the revolutions of the armature, these being embodied in the drag magnet and disc, and the meter register respectively. The motion of the armature is converted into continuous rotation by the aid of a commutator and brushes, the commutator being connected to the armature coils and carried on the same spindle therewith.
Waste of Electricity in Lighting.--In large residences where a good many servants are employed or in any place where the power consumed is not directly under the supervision of the person who must pay the bills, a great deal of waste usually occurs.
If the meter be read before retiring, the reading in the morning will show how much energy was consumed during the night, which will show in turn how many lamps were burning all night.