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STANDARD COMMUTATOR METER WITH CASE REMOVED. The upright aluminum frame supports the register, the top bearing of the shaft, and the field coils enclosing the Below is the aluminum disc rotating between the jaws of the damping magnets.

armature.

tric Company at Lynn, Massachusetts, where railway and stationary motors, are lamps and transformers, as well as meters, are produced in great quantities.

The Friction Problem

To obtain both accuracy and permanence in a meter, friction must be

ister correctly the power passing through it, the meter must not "run wild," but must work against a resistance even if it be only a feeble one. This is where the aluminum disc, fastened to the shaft near its bottom end, comes in; for the magnets that enclose without touching it exert a "drag" upon it. This arrangement, by

utilizing knowledge of the phenomenon first discovered by Arago, that a magnet when simply brought near a moving mass of metal tends to check its motion, provides a very beautiful way of giving

pendent of moisture, dust, changes of
temperature, or age, whereby also its
registrations become strictly proportional
to the electric work passing through.
This scientific plan was worked out in

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PARTS OF TYPE C METER.

Field coils, pivot, and jewel mountings, pair of damping magnets, and complete moving system with its spherical coreless armature and aluminum disc fixed on the hollow shaft. Near the top of the shaft is the commutator, made of tiny bars of pure silver. Above this is the bronze worm by which

the motion of the shaft is communicated to the dials.

our meter a little work to do. As long as the magnets that check the disc remain of the same strength, they provide a small but absolutely constant, and frictionless, check or drag on the disc-that is to say, a "load" on the motor exactly proportional to its speed, and inde

a particularly brilliant way by Prof. Elihu Thomson, to whose genius the original design of the most generally used electric meter is due. The full value of this "frictionless load" scheme is realized by reducing to as near zero as possible the friction of the bearing on which the mo

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This apparatus consists of a rotating copper disc of a standard thickness and diameter, having a sliding balance frame upon which the magnet under test can be mounted. Upon sliding the magnet into such a position that its jaws enclose the disc, the reaction of the eddy currents generated in the latter by the magnet's field gives

a "drag." which is balanced by adjusting a weight on an arbitrarily graduated scale.

the "damping magnets" must be absolutely permanent, and, on the other hand, that friction of all moving parts must be reduced to almost nothing. Let us first see how the magnets are made. A shipment of steel is just being delivered-a clattering pile of long strips, each of the width and thickness of the finished magnet. The first thing that is done is to select samples to be put through the same. stages of manufacture as the regular product, with tests at each step which determine the acceptance of the lot of steel or locate the reasons for its failure to make good magnets. Throughout all

The next thing is to magnetize the forms. Every schoolboy knows that a piece of steel can be magnetized by simply rubbing it with a magnet; but in the modern factory they have improved on this by using an ingenious machine which saturates the steel form in a few seconds with all the magnetism it can hold.

Another interesting process, and one of the most essential, is the artificial "aging" that the new magnets have to undergo. The latter, as they leave the magnetizing machine, are supersaturatedthat is, they are in an unstable magnetic condition, ready to become very much

weakened by ordinary vibration, by handling, etc., or by mere lapse of time undisturbed. It would never do to wait indefinitely for the magnets to reach a permanent condition of their own accord; and they cannot be used until they are strictly permanent, because any changes, however slight, would affect the accuracy of the meter in which they are used. By the artificial aging process, the time required to reach perfect magnetic stability is reduced to a few months.

In the first treatment, alternate heating and cooling in a "boiling machine" removes about 15 per cent of the magnetization. Other severe processes follow, magnets that warp or develop the slightest flaws at any stage-a very small percentage-being at once rejected. The good ones, now only half as "strong" as at first, but effectually prevented from becoming any weaker in future, are sent to be tested on the magnet-measuring machine, which works on the same principle of "magnetic drag" that is used in the meter itself. A record is made of the strength of each magnet; then it is put away for three months, after which period it is tested again to see whether its strength has changed. If the second test agrees with the first, the strength of the magnet is recorded on its side, and it is ready for use. The finished magnets are strictly "glass hard," and yet are so tough. that they cannot be deformed, broken, or perceptibly weakened by extremely rough usage.

Jewel Bearings

As above stated, the perfect development of an electric meter requires not only that the friction of its moving parts shall be reduced to the smallest possible amount, but that this minimum shall not increase with time. This has required the building up of a complete self-contained jewel-making department, in which the entire work, from the raw stones to the finished bearings, is carried

on.

Only the best quality of Eastern sapphires, of fine grain and free from flaws, are considered good enough for making General Electric meter jewels. Diamond jewels are used in meters of very high capacity. The requisite is to provide a

very hard, polished cup bearing for the steel-tipped bottom end of the meter shaft. The finest steel piano wire, about three one-hundredths of an inch in diameter, is used for the pivots, the bearing surface being carefully finished by a fine oil-stone, followed by the use of Vienna lime to obtain a high polish.

In the making of the sapphire jewels, the first step is the splitting of the stones into slices. This is done by the use of little copper discs charged with "bort," or diamond dust, and rotating at high speed under a running stream of water. The cutting proceeds rapidly, a stone being transformed in a few minutes into a pile of slices. Next comes the grinding to proper thickness-.04 inch for cup jewels using a revolving copper disc charged with the bort. After reducing

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The polisher works with a sharpened boxwood spindle dipped in bort, the spindle, connected to a flexible shaft, being driven at about 1,800 revolutions per minute in reverse direction to the direction of rotation of the jewel.

the tiny slices of sapphire to the shape of perfect discs of standard diameter, and rejecting all pieces containing flaws revealed by the grinding, they are ready for the polishers.

A large force of polishers are required to turn out the regular product of sapphire jewels. The tiny "cup," started with a diamond point, is polished to the proper shape and depth by patient labor. The excellence of a meter, in its ability to retain its accuracy under conditions of actual use, largely depends on this work; and the jewels are inspected with a magnifying glass for the minutest imperfec

tions in the stones themselves or in the workmanship. Another inspector examines each stone by rubbing a polished steel needle about in the cup so as to detect by the sense of touch any imperfections that might escape visual examination.

In placing the finished jewel in the meter, it is mounted in a brass plug "setting," and inserted in an adjustable brass jewel-screw, where it rests on a tiny steel spring. This special mounting protects the bearing from the possible injurious effects of blows or vibration to the meter in use, the strength of the spring being so proportioned as to "float" the moving system.

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wire coated with a thin but effective film of special insulation, must be used to get a sufficiently large number of turns into a given space and weight. An average of 500 miles of wire is required for the weekly product of armatures. The making of the little silver commutators for these is another delicate operation.

In the putting together or "assembling" of the parts to make the finished meters, all details of the manufacture converge. The assembled meters receive careful, detailed mechanical and electrical inspection.

Calibration

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The comparison of the completed meters with known standards-termed the "calibration" is conducted by a staff of experts. Groups of meters, complete except for their cases, are mounted on calibrating benches, variable conditions of vibration being avoided by suspending the meter rack from stretched wires. By suitable electrical connections with a "master meter" of known accuracy, the new meters are adjusted until they agree with the standard within oneeighth of one per cent, the standard itself being checked several times daily. Each meter is regulated by this means under various conditions of "load" amount of electrical energy passing through. Every precaution is taken to insure the meter fulfilling all requirements of its future service, with a large margin for safety.

A job requiring a woman's skill in handling fine wire. The coils are wound on a
papier-maché ball. The number of turns on each armature coil is counted
by the aid of the dial mechanism on the winding machine.

Armatures and Field Coils

Although the damping magnets and the jewel bearing are of primary importance, other parts are scarcely less important. Among the most interesting of these are the armatures and field coils for the commutator type of meters. The armature is a marvel of lightness to match the quill-like steel shaft on which it is ingeniously fixed and the thin aluminum disc below. The fine silk-covered wire used in most electrical instruments is too clumsy to use in "winding" this armature; an extraordinarily fine

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Various Uses of Meters

The "pay as you go" system, which has worked so well in the use of gas both in Europe and America, has been neatly applied to the electric meter by a simple. device which is electrically, not mechanically, connected to the meter. Prepay

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