The Standard Electrical Dictionary / A Popular Dictionary of Words and Terms Used in the Practice of Electrical Engineering

by T. O'Conor Sloane

Fig. 123. LOAD CURVES.
Curve, Magnetization.
A characteristic curve of an electromagnet, indicating the relation of
magnetization to exciting current. Laying off on the axis of ordinates
the quantities of magnetism evoked, and the corresponding strengths of
the exciting current on the axis of abscissas, the curve can be plotted.
It first rises rapidly, indicating a rapid increase of magnetization,
but grows nearly horizontal as the iron becomes more saturated. The
effect due to the coils alone, or the effect produced in the absence of
iron is a straight line, because air does not change in permeability.
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 pass 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 analogous 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.
Damper.
(a) A copper frame on which the wire in a galvanometer is sometimes
coiled, which acts to damp the oscillations of the needle.
(b) A tube of brass or copper placed between the primary and secondary
coils of an induction coil. It cuts off induction and diminishes the
current and potential of the secondary circuit. On pulling it out, the
latter increases. It is used on medical coils to adjust their strength
of action.
Damping.
Preventing the indicator of an instrument from oscillating in virtue of
its own inertia or elasticity. In a galvanometer it is defined as
resistance to quick vibrations of the needle, in consequence of which it
is rapidly brought to rest when deflected (Ayrton). In dead-beat
galvanometers (see Galvanometer, Dead-Beat,) damping is desirable in
order to bring the needle to rest quickly; in ballistic galvanometers
(see Galvanometer, Ballistic,) damping is avoided in order to maintain
the principle of the instrument. Damping may be mechanical, the
frictional resistance of air to an air-vane, or of a liquid to an
immersed diaphragm or loosely fitting piston, being employed. A
dash-pot, q. v., is an example of the latter. It may be
electro-magnetic. A mass of metal near a swinging magnetic needle tends
by induced currents to arrest the oscillations thereof, and is used for
this purpose in dead-beat galvanometers. This is termed, sometimes,
magnetic friction. The essence of damping is to develop resistance to
movement in some ratio proportional to velocity, so that no resistance
is offered to the indicator slowly taking its true position. (See
Galvanometer, Dead-Beat.)
Dash-Pot.
A cylinder and piston, the latter loosely fitting or perforated, or some
equivalent means being provided to permit movement. The cylinder may
contain a liquid such as glycerine, or air only. Thus the piston is
perfectly free to move, but any oscillations are damped (see Damping).
In some arc lamps the carbon holder is connected to a dash-pot to check
too sudden movements of the carbon. The attachment may be either to the
piston or to the cylinder. In the Brush lamp the top of the carbon
holder forms a cylinder containing glycerine, and in it a loosely
fitting piston works. This acts as a dash-pot.
Dead Beat. adj.
Reaching its reading quickly; applied to instruments having a moving
indicator, which normally would oscillate back and forth a number of
times before reaching its reading were it not prevented by damping. (See
Galvanometer, Aperiodic--Damping.)
Dead Earth.
A fault in a telegraph line which consists in the wire being thoroughly
grounded or connected to the earth.
177 STANDARD ELECTRICAL DICTIONARY.
Dead Point of an Alternator.
A two-phase alternator of the ordinary type connected as a motor to
another alternator cannot start itself, as it has dead points where the
relations and polarity of field and armature are such that there is no
torque or turning power.
Dead-Turns.
In the winding of an armature, a given percentage of the turns, it may
be 80 per cent., more or less, is assumed to be active; the other 20 per
cent. or thereabouts, is called dead-turns. This portion represents the
wire on such portions of the armature as comes virtually outside of the
magnetic field. They are termed dead, as not concurring to the
production of electro-motive force.
Dead Wire.
(a) The percentage or portion of wire on a dynamo or motor armature that
does not concur in the production of electromotive force. The
dead-turns, q. v., of a drum armature or the inside wire in a Gramme
ring armature are dead wire.
(b) A disused and abandoned electric conductor, such as a telegraph
wire.
(c) A wire in use, but through which, at the time of speaking, no
current is passing.
Death, Electrical.
Death resulting from electricity discharged through the animal system.
The exact conditions requisite for fatal results have not been
determined. High electro-motive force is absolutely essential; a
changing current, pulsatory or alternating, is most fatal, possibly
because of the high electro-motive force of a portion of each period.
Amperage probably has something to do with it, although the total
quantity in coulombs may be very small. As applied to the execution of
criminals, the victim is seated in a chair and strapped thereto. One
electrode with wet padded surface is placed against his head or some
adjacent part. Another electrode is placed against some of the lower
parts, and a current from an alternating dynamo passed for 15 seconds or
more. The potential difference of the electrodes is given at 1,500 to
2,000 volts, but of course the maximum may be two or three times the
measured amount, owing to the character of the current.
Decalescence.
The converse of recalescence, q. v. When a mass of steel is being heated
as it reaches the temperature of recalescence it suddenly absorbs a
large amount of heat, apparently growing cooler.
Deci.
Prefix originally used in the metric system to signify one-tenth of, now
extended to general scientific units. Thus decimeter means one-tenth of
a meter; decigram, one-tenth of a gram.
Declination, Angle of.
The angle intercepted between the true meridian and the axis of a
magnetic needle at any place. The angle is measured to east or west,
starting from the true meridian as zero.
178 STANDARD ELECTRICAL DICTIONARY.
Declination of the Magnetic Needle.
The deviation of the magnetic needle from the plane of the earth's
meridian. It is also called the variation of the compass. (See Magnetic
Elements.)
Decomposition.
The reduction of a compound substance into its constituents, as in
chemical analysis. The constituents may themselves be compounds or
proximate constituents, or may be elemental or ultimate constituents.
Decomposition, Electrolytic.
The decomposition or separation of a compound liquid into its
constituents by electrolysis. The liquid must be an electrolyte, q. v.,
and the decomposition proceeds subject to the laws of electrolysis, q.
v. See also Electrolytic Analysis.
Decrement.
When a suspension needle which has been disturbed is oscillating the
swings gradually decrease in amplitude if there is any damping, as there
always is. The decrement is the ratio of the amplitude of one
oscillation to the succeeding one. This ratio is the same for any
successive swings.
De-energize.
To cut off its supply of electric energy from an electric motor, or any
device absorbing and worked by electric energy.
Deflagration.
The explosive or violent volatilizing and dissipating of a substance by
heat, violent oxidation and similar means. It may be applied among other
things to the destroying of a conductor by an intense current, or the
volatilization of any material by the electric arc.
Deflecting Field.
The field produced in a galvanometer by the current which is being
tested, and which field deflects the needle, such deflection being the
measure of the current strength.
Deflection.
In magnetism the movement out of the plane of the magnetic meridian of a
magnetic needle, due to disturbance by or attraction towards a mass of
iron or another magnet.
Deflection Method.
The method of electrical measurements in which the deflection of the
index of the measuring instrument is used as the measure of the current
or other element under examination. It is the opposite of and is to be
distinguished from the zero or null method, q. v. In the latter
conditions are established which make the index point to zero and from
the conditions necessary for this the measurement is deduced. The
Wheatstone Bridge, q. v., illustrates a zero method, the sine or the
tangent compass, illustrates a deflection method. The use of deflection
methods involves calibration, q. v., and the commercial measuring
instruments, such as ammeters and volt meters, which are frequently
calibrated galvanometers, are also examples of deflection instruments.
179 STANDARD ELECTRICAL DICTIONARY.
Degeneration, Reaction of.
The diminished sensibility to electro-therapeutic treatment exhibited by
the human system with continuance of the treatment in question. The
general lines of variation are stated in works on the subject.
Deka.
Prefix originally used in the metric system to signify multiplying by
ten, as dekameter, ten meters, dekagram, ten grams; now extended to many
scientific terms.
De la Rive's Floating Battery.
A small galvanic couple, immersed in a little floating cell and
connected through a coil of wire immediately above them. When the
exciting battery solution is placed in the cell the whole, as it floats
in a larger vessel, turns until the coil lies at right angles to the
magnetic needle. Sometimes the two plates are thrust through a cork and
floated thus in a vessel of dilute sulphuric acid.
A magnet acts to attract or repel the coil in obedience to Ampére's
Theory, (See Magnetism, Ampere's Theory of.)
Delaurier's Solution.
A solution for batteries of the Bunsen and Grenet type. It is of the
following composition:
Water, 2,000 parts;
potassium bichromate, 184 parts;
sulphuric acid, 428 parts.
Demagnetization.
Removal of magnetism from a paramagnetic substance. It is principally
used for watches which have become magnetized by exposure to the
magnetic field surrounding dynamos or motors.
The general principles of most methods are to rotate the object, as a
watch, in a strong field, and while it is rotating to gradually remove
it from the field, or to gradually reduce the intensity of the field
itself to zero. A conical coil of wire within which the field is
produced in which the watch is placed is sometimes used, the idea being
that the field within such a coil is strongest at its base. Such a coil
supplied by an alternating current is found effectual (J. J. Wright).
If a magnetized watch is made to turn rapidly at the end of a twisted
string and is gradually brought near to and withdrawn from the poles of
a powerful dynamo it may be considerably improved.
A hollow coil of wire connected with a pole changer and dip-battery has
been used. The battery creates a strong field within the coil. The watch
is placed there and the pole changer is worked so as to reverse the
polarity of the field very frequently. By the same action of the pole
changer the plates of the battery are gradually withdrawn from the
solution so as to gradually reduce the magnetic field to zero while
constantly reversing its polarity. (G. M. Hopkins.)
Steel may be demagnetized by jarring when held out of the magnetic
meridian, or by heating to redness.
180 STANDARD ELECTRICAL DICTIONARY.
Density, Electric Superficial.
The relative quantity of electricity residing as an electric charge upon
a unit area of surface. It may be positive or negative.
Synonyms--Density of Charge--Surface Density.
Dental Mallet, Electric.
A dentist's instrument for hammering the fillings as inserted into
teeth. It is a little hammer held in a suitable handle, and which is
made to strike a rapid succession of blows by electro-magnetic motor
mechanism.
Depolarization.
(a) The removal of permanent magnetism. (See Demagnetization.)
(b) The prevention of the polarization of a galvanic cell. It is
effected in the Grove battery by the reduction of nitric acid; in the
Bunsen, by the reduction of chromic acid; in the Smee battery,
mechanically, by the platinum coated or rather platinized negative
plate. Other examples will be found under the description of various
cells and batteries. A fluid which depolarizes is termed a depolarizer
or depolarizing fluid or solution. (See Electropoion Fluid.)
Deposit, Electrolytic.
The metal or other substance precipitated by the action of a battery or
other current generator.
Derivation, Point of.
A point where a circuit branches or divides into two or more leads. The
separate branches then receive derived or partial currents.
Desk Push.
A press or push button, with small flush rim, for setting into the
woodwork of a desk.
Detector.
A portable galvanometer, often of simple construction, used for rough or
approximate work.
Detector, Lineman's.
A portable galvanometer with a high and a low resistance actuating coil,
constructed for the use of linemen and telegraph constructors when in
the field, and actually putting up, repairing or testing lines.
Deviation, Quadrantal.
Deviation of the compass in iron or steel ships due to the magnetization
of horizontal beams by the earth's induction. The effect of this
deviation disappears when the ship is in the plane of the electric
meridian, or at right angles thereto; its name is taken from the fact
that a swing of the ship through a quadrant brings the needle from zero
deviation to a maximum and back to zero.
181 STANDARD ELECTRICAL DICTIONARY.
Deviation, Semicircular.
Deviation of the compass in iron or steel ships due to vertical
induction. (See Induction, Vertical.) The effect of this induction
disappears when the ship is in the electric meridian. Its name is
derived from the fact that a swing of the ship through half the circle
brings the needle from zero deviation to a maximum and back to zero.
Dextrotorsal. adj.
Wound in the direction or sense of a right-handed screw; the reverse of
sinistrotorsal, q. v.

Fig. 128. DEXTROTORSAL HELIX.
Diacritical. adj.
(a) The number of ampere turns, q. v., required to bring an iron core to
one half its magnetic saturation, q. v., is termed the diacritical
number.
(b) The diacritical point of magnetic saturation is proposed by Sylvanus
P. Thompson as a term for the coefficient of magnetic saturation which
gives a magnet core one-half its maximum magnetization.
Diagnosis, Electro.
A medical diagnosis of a patient's condition based on the action of
different parts of the body under electric excitement.
Diamagnetic. adj.
Possessing a negative coefficient of magnetic susceptibility; having
permeability inferior to that of air. Such substances placed between the
poles of a magnet are repelled; if in the form of bars, they tend to
turn so as to have their long axis at right angles to the line joining
the poles. The reason is that the lines of force always seek the easiest
path, and these bodies having higher reluctance than air, impede the
lines of force, and hence are as far as possible pushed out of the way.
The above is the simplest explanation of a not well understood set of
phenomena. According to Tyndall, "the diamagnetic force is a polar
force, the polarity of diamagnetic bodies being opposed to that of
paramagnetic ones under the same conditions of excitement." Bismuth is
the most strongly diamagnetic body known; phosphorus, antimony, zinc,
and many others are diamagnetic. (See Paramagnetic.)
182 STANDARD ELECTRICAL DICTIONARY.
Diagometer.
An apparatus for use in chemical analysis for testing the purity of
substances by the time required for a charged surface to be discharged
through them to earth. It is the invention of Rousseau.
An electrometer is charged with a dry pile. One of its terminals is
connected with one surface of the solution or substance to be tested,
and the other with the other surface. The time of discharge gives the
index of the purity of the substance.
Diamagnetic Polarity.
Treating diamagnetism as due to a polar force, the polarity of a
diamagnetic body is the reverse of the polarity of iron or other
paramagnetic bodies. A bar-shaped diamagnetic body in a field of force
tends to place itself at right angles to the lines of force.
Diamagnetism.
(a) The science or study of diamagnetic substances and phenomena.
(b) The magnetic property of a diamagnetic substance.
Diameter of Commutation.
The points on the commutator of a closed circuit ring--or
drum--armature, which the brushes touch, and whence they take the
current, mark the extremities of the diameter of commutation. Were it
not for the lag this would be the diameter at right angles to the line
connecting the centers of the opposite faces of the field. It is always
a little to one side of this position, being displaced in the direction
of rotation. In open circuit armatures the brushes are placed on the
diameter at right angles to this one, and sometimes the term diameter of
commutation is applied to it. All that has been said is on the
supposition that the armature divisions correspond not only in
connection but in position with those of the armature coils. Of course,
the commutator could be twisted so as to bring the diameter of
commutation into any position desired.
Diapason, Electric.
A tuning-fork or diapason kept in vibration by electricity. In general
principle the ends of the fork act as armatures for an electro-magnet,
and in their motion by a mercury cup or other form of contact they make
and break the circuit as they vibrate. Thus the magnet alternately
attracts and releases the leg, in exact harmony with its natural period
of vibration.
Diaphragm.
(a) In telephones and microphones a disc of iron thrown into motion by
sound waves or by electric impulses, according to whether it acts as the
diaphragm of a transmitter or receiver. It is generally a plate of
japanned iron such as used in making ferrotype photographs. (See
Telephone and Microphone.)
(b) A porous diaphragm is often used in electric decomposition cells and
in batteries. The porous cup represents the latter use.
[Transcriber's note: Japanned--covered with heavy black lacquer, like
enamel paint.]
183 STANDARD ELECTRICAL DICTIONARY.
Dielectric.
A non-conductor; a substance, the different parts of which may, after an
electric disturbance, remain, without any process of readjustment, and
for an indefinite period of time, at potentials differing to any extent
(Daniell). There is no perfect dielectric. The term dielectric is
generally only used when an insulator acts to permit induction to take
place through it, like the glass of a Leyden jar.
Dielectric Constant.
The number or coefficient expressing the relative dielectric capacity of
a medium or substance. (See Capacity, Specific Inductive.)
Dielectric, Energy of.
In a condenser, the conducting coatings are merely to conduct the
current all over the surface they cover; the keeping the electricities
separated is the work of the dielectric, and represents potential energy
which appears in the discharge. The amount of energy is proportional to
the charge, and to the potential difference. As any electrified body
implies an opposite electrification somewhere, and a separating
dielectric, the existence of a condenser is always implied.
[Transcriber's note: The energy stored in a capacitor (condenser) is
(Q*Q)/2C = (Q*V)/2 = (C*V*V)/2
The energy is proportional to the voltage SQUARED or the charge SQUARED.]
Dielectric Polarization.
A term due to Faraday. It expresses what he conceived to be the
condition of a dielectric when its opposite faces are oppositely
electrified. The molecules are supposed to be arranged by the
electrification in a series of polar chains, possibly being originally
in themselves seats of opposite polarities, or having such imparted to
them by the electricities. The action is analogous to that of a magnet
pole on a mass of soft iron, or on a pile of iron filings.
Dielectric Strain.
The strain a solid dielectric is subjected to, when its opposite
surfaces are electrified. A Leyden jar dilates under the strain, and
when discharged gives a dull sound. The original condition is not
immediately recovered. Jarring, shaking, etc., assist the recovery from
strain. The cause of the strain is termed Electric Stress. (See Stress,
Electric.) This is identical with the phenomenon of residual charge.
(See Charge, Residual.) Each loss of charge is accompanied with a
proportional return of the dielectric towards its normal condition.
Dielectric Resistance.
The mechanical resistance a body offers to perforation or destruction by
the electric discharge.
Dielectric Strength.
The resistance to the disruptive discharge and depending on its
mechanical resistance largely or entirely. It is expressible in volts
per centimeter thickness. Dry air requires 40,000 volts per centimeter
for a discharge.
184 STANDARD ELECTRICAL DICTIONARY.
Differential Winding Working.
A method of working an electro-magnet intermittently, so as to avoid
sparking. The magnet is wound with two coils. One is connected straight
into the circuit, the other is connected in parallel therewith with a
switch inserted. The coils are so connected that when the switch is
closed the two are in opposition, the current going through them in
opposite senses. Thus one overcomes the effect of the other and the
magnet core shows no magnetism, provided the two coils are of equal
resistance and equal number of convolutions or turns.