Curve of Distribution of Potential in Armature.

A characteristic curve indicating the distribution of potential difference between adjoining sections of the commutator of an armature in different positions all around it. The potential differences are taken by a volt-meter or potential galvanometer, connection with the armature being made by two small metal brushes, held at a distance apart equal to the distance from centre to centre of two adjoining commutator bars. The curve is laid out as if by polar co-ordinates extending around the cross-section of the commutator, with the distances from the commutator surface to the curve proportional to the potential differences as determined by shifting the pair of brushes all around the commutator.

The above is S. P. Thompson's method. Another method of W. M. Mordey involves the use of a pilot brush. (See Brush, Pilot.) Otherwise the method is in general terms identical with the above.

173 STANDARD ELECTRICAL DICTIONARY.

Fig. 124. MAGNETIZATION CURVE.

Fig. 125. ARMATURE: CURVE.

Fig. 126. DEVELOPMENT OF ARMATURE CURVE.

Curve of Dynamo.

The characteristic curve of a dynamo. (See Curve, Characteristic.)

Curve of Sines.

An undulating curve representing wave motion. It is produced by compounding a simple harmonic motion, or a two and fro motion like that of an infinitely long pendulum with a rectilinear motion. Along a horizontal line points may be laid off to represent equal periods of time. Then on each point a perpendicular must be erected. The length of each must be equal to the length of path traversed by the point up to the expiration of each one of the given intervals of time. The abscissas are proportional to the times and the ordinates to the sines of angles proportional to the times. Thus if a circle be drawn upon the line and divided into thirty-two parts of equal angular value, the sines of these angles may be taken as the ordinates and the absolute distance or length of arc of the angle will give the abscissas.

Synonyms--Sine Curve--Sinusoidal Curve--Harmonic Curve.

Fig. 127. CURVE OF SINES.

174 STANDARD ELECTRICAL DICTIONARY.

Curve of Saturation of the Magnetic Circuit.

A characteristic curve whose ordinates may represent the number of magnetic lines of force induced in a magnetic circuit, and whose abscissas may represent the ampere turns of excitation or other representative of the inducing force.

Curve of Torque.

A characteristic curve showing the relations between torque, q. v., and current in a dynamo or motor.

Curve, Permeability Temperature.

A characteristic curve expressing the changes in permeability of a paramagnetic substance as the temperature changes. The degrees of temperature may be abscissas, and the permeabilities corresponding thereto ordinates of the curve.

Cut In. v.

To connect any electric appliance, mechanism or conductor, into a circuit.

Cut Out. v.

The reverse of to cut in; to remove from a circuit any conducting device, and sometimes so arranged as to leave the circuit completed in some other way.

Cut Out.

An appliance for removing any apparatus from an electric circuit, so that no more current shall pa.s.s through such apparatus, and sometimes providing means for closing the circuit so as to leave it complete after the removal of the apparatus.

175 STANDARD ELECTRICAL DICTIONARY.

Cut Out, Automatic.

(a) A mechanism for automatically shunting an arc or other lamp when it ceases to work properly. It is generally worked by an electro-magnet of high resistance placed in parallel with the arc. If the arc grows too long the magnet attracts its armature, thereby completing a shunt of approximately the resistance of the arc, and which replaces it until the carbons approach again to within a proper distance. Sometimes a strip or wire of fusible metal is arranged in shunt with the arc. When the arc lengthens the current through the wire increases, melts it and a spring is released which acts to complete or close a shunt circuit of approximately arc-resistance.

(b) See Safety Device--Safety Fuse.

(c) See below.

Cut-out, Magnetic.

A magnetic cut-out is essentially a coil of wire with attracted core or armature. When the coil is not excited the core, by pressing down a strip of metal or by some a.n.a.logous arrangement, completes the circuit.

When the current exceeds a certain strength the core rises as it is attracted and the circuit is opened.

Cut-out, Safety.

A block of porcelain or other base carrying a safety fuse, which melts and breaks the circuit before the wire connected to it is dangerously heated.

Synonyms--Fuse Block--Safety Catch--Safety Fuse.

Cut Out, Wedge.

A cut out operated by a wedge. The line terminals consist of a spring bearing against a plate, the circuit being completed through their point of contact. A plug or wedge composed of two metallic faces insulated from each other is adapted to wedge the contact open. Terminals of a loop circuit are connected to the faces of the wedge. Thus on sliding it into place, the loop circuit is brought into series in the main circuit.

Synonym--Plug Cut Out--Spring Jack.

Cutting of Lines of Force.

A field of force is pictured as made up of lines of force; a conductor swept through the field is pictured as cutting these lines. By so doing it produces potential difference or electro-motive force in itself with a current, if the conductor is part of a closed circuit.

Cycle of Alternation.

A full period of alternation of an alternating current. It begins properly at the zero line, goes to a maximum value in one sense and returns to zero, goes to maximum in the other sense and returns to zero.

Cystoscopy.

Examination of the human bladder by the introduction of a special incandescent electric lamp. The method is due to Hitze.

176 STANDARD ELECTRICAL DICTIONARY.