The capacity of a cable is used to determine the locality of breaks in the continuity of the conductors. The capacity per unit of length being accurately known, it is obvious that, if the conductor breaks without disturbance of the insulator, the distance of the break from the end can be ascertained by determining the capacity of the cable from one end.
This capacity will be in proportion to the capacity of a mile, a knot or any fixed unit, as the distance to the break is to the length used as standard.
96 STANDARD ELECTRICAL DICTIONARY.
Cable Core.
The conductors of a cable. They are generally copper wire. In a telephone cable they may be very numerous and insulated from each other.
In ocean cables they may be a group of bare wires twisted or laid together. Sometimes the conductors are arranged for metallic circuits, each pair being distinguished by special colored windings.
Cable, Duplex.
A cable containing two wires, each with separate insulation, so as to be virtually two cables, laid and secured parallel and side by side.
Cable, Flat.
A cable, flat in shape, so as to lie closely against a wall or ceiling.
Cablegram.
A message which has been transmitted or is to be transmitted by a submarine cable. It is sometimes called a cable.
Cable Grip.
A grip for holding the end of a cable, when the cable is to be drawn into a conduit in a subway. It is an attachment to provide the cable with an eye or loop. Its end is a split socket and embraces the end of the cable, and is secured thereto by bolts driven through the cable end.
In drawing a cable into a conduit a capstan and rope are often used, and the rope is secured to the cable end by the grip.
Fig. 73. CABLE HANGER, CABLE, AND SUSPENDING WIRE.
Fig. 74. CABLE HANGER, OPEN.
Cable Hanger.
When a heavy electric cable is suspended from poles it often would be unsafe to trust to its longitudinal strength to support or sustain its own weight unless the poles were very near together. In such case an auxiliary or sustaining wire is run along with it, and by clips or hangers the cable is connected thereto at as frequent intervals as seem desirable. The contrivance may take the form of a strip of metal surrounding the cable and carrying a hook or eye through which the supporting wire pa.s.ses.
Synonym--Cable Clip.
97 STANDARD ELECTRICAL DICTIONARY
Cable Hanger Tongs.
Tongs for attaching cable hangers, q.v. They have long handles so as to be worked from the ground at the middle of a span.
Cable, Suspending Wire of.
A wire by which an aerial cable is in part or entirely suspended. The cable, being incapable of sustaining its own weight, is secured by clips or hangers to a wire, strong from pole to pole immediately above it.
(See Cable Hanger.)
Cable Tank.
A tank in which a submarine cable is coiled away on board a cable-laying ship, or in the factory on sh.o.r.e for the purpose of testing or watching its insulation. Sometimes, in order to test it under pressures approximating to those it will be subjected to in practice, the tank is closed and the portion of cable within it is subjected to hydraulic pressure. This represents the pressure it will be exposed to in deep water.
Calamine.
A mineral; zinc silicate; formula Zn2 Si 03, crystalline system, Orthorhombic; specific gravity, 3.16-3.9.
The crystals often show strong pyroelectric properties.
Calibration.
The determination by experiment or calculation of the value of the readings of an instrument, such as a galvanometer or eudiometer. Thus if a tangent galvanometer has its circle graduated in degrees, a table of the value of tangents corresponding to every reading occurring in practice would represent a calibration by calculation. A determination of the current required to produce each deflection would be a calibration in the more usual sense. Calibration is generally absolute, as referring to some fixed unit, but it may be relative, as between two things both of unknown absolute value.
Calibration, Absolute.
The determination of the absolute value of currents producing given deflections in a galvanometer, or in other instruments the determination of corresponding values, as the instrument may be a magnetometer, quadrant electrometer, or other apparatus.
Calibration, Invariable.
Calibration applicable to specially constructed galvanometers, which is unaffected by the proximity of ma.s.ses of iron or field magnets. Such galvanometers must have a constant controlling field. Such is given by a powerful permanent magnet, whose field is practically unaffected by the causes named. Or else, in place of a controlling field, a spring maybe used to which the needle is attached, and which tends to hold it in one position.
98 STANDARD ELECTRICAL DICTIONARY.
Calibration, Relative.
The determination of the law connecting the various indications of an instrument, such as the deflections of the needle of a galvanometer, with the relative causes; in the case of a galvanometer, the strength of the currents or the electro-motive forces producing them directly or indirectly.
Call Bell.
A bell rung by pressing a b.u.t.ton or otherwise to call the attention of a person in a distant place. They can be cla.s.sified into a great variety of types according to their uses or construction.
Call b.u.t.ton.
A push b.u.t.ton used for ringing a call bell, sounding a buzzer, working an annunciator and for similar purposes. (See Push b.u.t.ton.)
Synonym--Push b.u.t.ton.
Calling Drop.
In a telephone exchange or telegraph office a drop shutter annunciator, which falls to call the attention of the operator, notifying him that the line connected to such drop is to be connected to some other circuit.
Calorie or Calory.
A practical unit of heat. There are two calories, respectively called the great and the small calorie, or the kilogram and the gram calorie.
The first is the quant.i.ty of heat required to raise the temperature of one kilogram of water one degree centigrade. The second is the quant.i.ty of heat required to raise the temperature of one gram of water one degree centigrade.