The Standard Electrical Dictionary Part 170

Watts, Apparent.

The product in an alternating current dynamo of the virtual amperes by the virtual volts. To give the true watts this product must be multiplied by the cosine of the angle of lead or lag. (See Current, Wattless.)

[Transcriber's note: This is now called a volt-amp. The usual usage is KVA, or kilovolt-ampere.]

Watt-second.

A unit of electric energy or work. One watt exerted or expended for one second.

It is equivalent to .24068 gram degree C. (calorie), .000955 lb. degree F., .737337 foot lbs., .0013406 horse power second (English), .0013592 horse power second (metric).

Synonym--Volt-coulomb.

Waves, Electro-magnetic.

Ether waves caused by electromagnetic disturbances affecting the luminiferous ether. (See Discharge, Oscillatory--Maxwell's Theory of Light--Resonance. Electric.)

[Transcriber's note: The Michaelson-Morley experiment (1887) had already called ether into question, but quantum theory and photons are decades in the future.]

574 STANDARD ELECTRICAL DICTIONARY.

Weber.

(a.) A name suggested by Clausius and Siemens to denote a magnet pole of unit strength. This use is abandoned.

(b.) It has been used to designate the unit of quant.i.ty--the coulomb.

This use is abandoned.

(c.) It has been used to designate the unit of current strength the ampere. This use is abandoned.

[Transcriber's note: Definition (a) is now used. One weber of magnetic flux linked to a circuit of one turn produces an electromotive force of 1 volt if it is reduced to zero at a uniform rate in 1 second.]

Weber-meter.

An ampere-meter or ammeter. The term is not used since the term "weber,"

indicating the ampere or coulomb, has been abandoned.

Welding, Electric.

Welding metals by heat produced by electricity. The heat may be produced by a current pa.s.sing through the point of junction (Elihu Thomson) or by the voltaic arc. (Benardos & Olzewski.)

Fig. 346. ELECTRIC WELDING INDUCTION COIL.

The current process is carried out by pressing together the objects to be united, while holding them in conducting clamps. A heavy current is turned on by way of the clamps and rapidly heats the metals at the junction, which is of course the point of highest resistance. As the metal softens, it is pressed together, one of the clamps being mounted with feed motion, flux is dropped on if necessary, and the metal pieces unite.

The most remarkable results are thus attained; almost all common metals can be welded, and different metals can be welded together. Tubes and other shapes can also be united. In many cases the weld is the strongest part.

575 STANDARD ELECTRICAL DICTIONARY.

The alternating current is employed. A special dynamo is sometimes used to produce it. This dynamo has two windings on the armature. One is of fine wire and is in series with the field magnets and excites them. The other is of copper bars, and connects with the welding apparatus, giving a current of high intensity but actuated by low potential.

Where the special dynamo is not used, an induction coil or transformer is used. The primary includes a large number of convolutions of relatively fine wire; the secondary may only be one turn of a large copper bar.

The cut shows in diagram an electric welding coil. P is the primary coil of a number of turns of wire; S S is the secondary, a single copper bar bent into an almost complete circle. It terminates in clamps D D for holding the bars to be welded. B C, B' C are the bars to be welded. They are pressed together by the screw J. The large coil I of iron wire surrounding the coils represents the iron core.

The real apparatus as at present constructed involves many modifications. The diagram only ill.u.s.trates the principle of the apparatus.

In welding by the voltaic arc the place to be heated is made an electrode of an arc by connection with one terminal of an electric circuit. A carbon is connected to the other terminal. An arc is started by touching and withdrawal of the carbon. The heat may be used for welding, soldering, brazing, or even for perforating or dividing metal sheets.

Welding Transformer.

The induction coil or transformer used in electric welding. For its general principles of construction, see Welding, Electric.

Wheatstone's Bridge.

A system of connections applied to parallel circuits, including resistance coils for the purpose of measuring an unknown resistance. A single current is made to pa.s.s from A through two parallel connected branches, joining together again at C. A cross connection B D has a galvanometer or other current indicator in circuit. In any conductor through which a current is pa.s.sing, the fall of potential at given points is proportional to the resistance between such points. Referring to the diagram a given fall of potential exists between A and C. The fall between A and B is to the fall between A and C as the resistance r between A and B is to the resistance r + r' between A and C. The same applies to the other branch, with the subst.i.tution of the resistances s and S' and the point D for r r' and B. Therefore, if this proportion holds, r : r' : : s : S'. No current will go through B D , and the galvanometer will be unaffected. a.s.sume s' to be of unknown resistance, the above proportion will give it, if r, r' and s are known, or if the ratio of r to r' and the absolute value of s is known.

576 STANDARD ELECTRICAL DICTIONARY.

In use the resistances r, r', and s are made to vary as desired. To measure an unknown resistance it is introduced at S', and one of the other resistances is varied until the galvanometer is unaffected. Then the resistance of S' is determined by calculation as just explained. The artificial resistances may be resistance coils, q. v., or it is enough to have one unknown resistance at s. Then if the length of wire ABC is accurately known, the point B can be s.h.i.+fted along it until the balance is attained. The relative lengths A B, and B C, will then give the ratio r : r' needed for the calculation. This a.s.sumes the wire ABC to be of absolutely uniform resistance. This is the principle of the meter-bridge described below. The use of coils is the more common method and is carried out by special resistance boxes, with the connections arranged to carry out the exact principle as explained. The principle of construction and use of a resistance box of the Wheatstone bridge type, as shown in the cut, is described under Box Bridge, q. v.

FIG. 347. WHEATSTONE BRIDGE CONNECTIONS.

FIG. 348. TOP OF BOX BRIDGE.

577 STANDARD ELECTRICAL DICTIONARY.

The next cut shows the sliding form of bridge called the meter bridge, if the slide wire is a meter long or a half- or a quarter-meter bridge, etc., according to the length of this wire. It is described under Meter Bridge, q. v. Many refinements in construction and in proper proportion of resistances for given work apply to these constructions.

Synonyms--Electric Balance--Resistance Bridge--Wheatstone's Balance.

Fig. 349. METER BRIDGE.

Whirl, Electric.

(a) A conductor carrying an electric current is surrounded by circular lines of force, which are sometimes termed an electric whirl.