Page images
[merged small][merged small][graphic][subsumed][ocr errors][subsumed]

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

armature. Below is the aluminum disc rotating between the jaws of the damping magnets.

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

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

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

[merged small][merged small][graphic]

PARTS OF TYPE C METER. Ficld 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.

Ficid coitar mature and aluminum disc fixed on

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

tor rotates and of the train of dial wheels. stages of manufacture—from the shaping This requires the highest grade of ex and hardening of the steel forms, pert trained skill.

through the processes of magnetizing,

"aging,” and measuring — each magnet Making the Magnets

carries an identifying symbol which faWe have just seen that accuracy and cilitates the location of its individual hispermanency mean, on the one hand, that tory at any time.


MAGNET-MEASURING MACHINE. 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 gene

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

the “damping magnets" must be abso- The next thing is to magnetize the lutely permanent, and, on the other hand, forms. Every schoolboy knows that a that friction of all moving parts must be piece of steel can be magnetized by simreduced to almost nothing. Let us first ply rubbing it with a magnet ; but in the see how the magnets are made. A ship- modern factory they have improved on ment of steel is just being delivered—a this by using an ingenious machine which clattering pile of long strips, each of the saturates the steel form in a few seconds width and thickness of the finished mag- with all the magnetism it can hold. net. The first thing that is done is to se Another interesting process, and one lect samples to be put through the same of the most essential, is the artificial “agstages of manufacture as the regular ing" that the new magnets have to unproduct, with tests at each step which de- dergo. The latter, as they leave the magtermine the acceptance of the lot of steel netizing machine, are supersaturatedor locate the reasons for its failure to that is, they are in an unstable magnetic make good magnets. Throughout all condition, ready to become very much weakened by ordinary vibration, by hand- very hard, polished cup bearing for the ling, etc., or by mere lapse of time undis- steel-tipped bottom end of the meter turbed. It would never do to wait in- shaft. The finest steel piano wire, about definitely for the magnets to reach a three one-hundredths of an inch in dipermanent condition of their own accord; ameter, is used for the pivots, the bearand they cannot be used until they are ing surface being carefully finished by strictly permanent, because any changes, a fine oil-stone, followed by the use of however slight, would affect the accuracy Vienna lime to obtain a high polish. of the meter in which they are used. By In the making of the sapphire jewels, the artificial aging process, the time re- the first step is the splitting of the stones quired to reach perfect magnetic stability into slices. This is done by the use of is reduced to a few months.

little copper discs charged with “bort," In the first treatment, alternate heating or diamond dust, and rotating at high and cooling in a “boiling machine” re- speed under a running stream of water. moves about 15 per cent of the magnetiz- The cutting proceeds rapidly, a stone beation. Other severe processes follow, ing transformed in a few minutes into a magnets that warp or develop the slight- pile of slices. Next comes the grinding est flaws at any stage-a very small per- to proper thickness — .04 inch for cup centage-being at once rejected. The jewels — using a revolving copper disc good ones, now only half as “strong” as charged with the bort. After reducing 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.


The polisher works with a sharpened boxwood spindle Jewel Bearings As above stated, the perfect development of an electric meter requires not only that the friction of its moving parts the tiny slices of sapphire to the shape shall be reduced to the smallest possible of perfect discs of standard diameter, and amount, but that this minimum shall not rejecting all pieces containing flaws reincrease with time. This has required vealed by the grinding, they are ready the building up of a complete self-con- for the polishers. tained jewel-making department, in A large force of polishers are required which the entire work, from the raw to turn out the regular product of sapstones to the finished bearings, is carried phire jewels. The tiny "cup," started

with a diamond point, is polished to the Only the best quality of Eastern sap- proper shape and depth by patient labor. phires, of fine grain and free from flaws, The excellence of a meter, in its ability are considered good enough for making to retain its accuracy under conditions of General Electric meter jewels. Diamond actual use, largely depends on this work ; jewels are used in meters of very high and the jewels are inspected with a magcapacity. The requisite is to provide a nifying glass for the minutest imperfec


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.



tions in the stones themselves or in the wire coated with a thin but effective film workmanship. Another inspector ex- of special insulation, must be used to get amines each stone by rubbing a polished a sufficiently large number of turns into steel needle about in the cup so as to de- a given space and weight. An average tect by the sense of touch any imperfec- of 500 miles of wire is required for the tions that might escape visual examina- weekly product of armatures. The mak

ing of the little silver commutators for In placing the finished jewel in the these is another delicate operation. meter, it is mounted in a brass plug “set- In the putting together or “asting,” and inserted in an adjustable brass sembling” of the parts to make the finjewel-screw, where it rests on a tiny steel ished meters, all details of the manufactspring. This special mounting protects ure converge. The assembled meters rethe bearing from the possible injurious ceive careful, detailed mechanical and effects of blows or vibration to the meter electrical inspection. in use, the strength of the spring being so proportioned as to “Aoat” the moving

Calibration system.

The comparison of the completed me

ters with known stand-
ards—termed the "cali-
bration" — is conducted
by a staff of experts.
Groups of meters, com-
plete except for their
cases, are mounted on
calibrating benches, va-
riable conditions of vi-
bration being avoided by
suspending the meter
rack from stretched
wires. By suitable elec-
trical connections with a
“master meter” of
known accuracy, the
new meters are adjusted
until they agree with the
standard within one-
eighth of one per cent,

the standard itself being WINDING AN ARMATURE.

checked several times 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

daily. Each meter is by the aid of the dial mechanism on the winding machine.

regulated by this means

under various conditions Armatures and Field Coils of "load" or amount of electrical Although the damping magnets and energy passing through. Every prethe jewel bearing are of primary im- caution is taken to insure the meter portance, other parts are scarcely less im- fulfilling all requirements of its future portant. Among the most interesting of service, with a large margin for safety. these are the armatures and field coils for the commutator type of meters. The

Various Uses of Meters armature is a marvel of lightness to match the quill-like steel shafton The “pay as you go" system, which which it is ingeniously fixed and the thin has worked so well in the use of gas both aluminum disc below. The fine silk-cov- in Europe and America, has been neatly ered wire used in most electrical instru- applied to the electric meter by a simple ments is too clumsy to use in “winding” device which is electrically, not mechanithis armature; an extraordinarily fine cally, connected to the meter. Prepay

« PreviousContinue »