Fig. 332. ELEMENTS OF BECQUEREL'S THERMOELECTRIC BATTERIES.
Clamond's pile has been used in practical work. The negative element is
an alloy of antimony, 2 parts, zinc, 1 part. The positive element is tin
plate. Mica in some parts, and a paste of soluble glass and asbestus in
other parts are used as insulators. They are built up so as to form a
cylinder within which the fire is maintained. The air is relied on to
keep the outer junctions cool. The temperature does not exceed 200° C.
(392° F.)
Sixty such elements have an electro-motive force of 300 volts and an
internal resistance of 1.5 ohms. Such a battery requires the consumption
of three cubic feet of gas per hour. (See Currents, Thermo-electric. )
532 STANDARD ELECTRICAL DICTIONARY.
Thermo-electric Call.
A thermostat arranged to ring a bell or to give some indication when the
temperature rises or falls beyond certain points. It may be a compound
bar of brass and steel fixed at one end and free for the rest of its
length. Its end comes between two adjustable contacts. As the
temperature rises it bends one way (away from the brass side) and, if
hot enough, touching a contact gives one signal. If the temperature
falls it curves the other way, and if cold enough touches the other
contact, giving another signal. (See Thermostat, Electric.)
Thermo-electric Couple.
If two dissimilar conductors form adjacent parts of a closed circuit,
and their junction is at a different temperature than that of the rest
of the circuit, a current will result. Such pair of conductors are
called a thermo-electric couple. They may be joined in series so as to
produce considerable electro-motive force. (See Thermo-electricity and
other titles in thermo-electricity.)
The efficiency of a thermo-electric couple according to the second law
of thermo-dynamics is necessarily low--not over 10 per cent.
Thermo-electric Diagram.
A diagram indicating the change in potential difference for a fixed
difference of temperature between different metals at different
temperatures. It is laid out with rectangular co-ordinates. On one axis
temperatures are laid off, generally on the axis of abscissas. On the
other axis potential differences are marked. Different lines are then
drawn, one for each metal, which show the potential difference, say for
one degree centigrade difference of temperature between their junctions,
produced at the different temperatures marked on the axis of abscissas.
Fig. 333. THERMO-ELECTRIC DIAGRAM,
GIVING POTENTIAL DIFFERENCE IN C. G. S. UNITS.
Thus taking copper and iron we find at the temperature 0° C. (32° F.) a
difference of one degree C. (1.8° F.) in their junctions will produce a
potential difference of 15.98 micro volts, while at 274.5° C. (526.1°
F.) the lines cross, and zero difference of potential is indicated.
Taking the lead line on the same diagram it crosses the iron line a
little above 350° C. (662° F.), indicating that if one junction is
heated slightly above and the other is heated slightly below this
temperature no potential difference will be produced. Lead and copper
lines, on the other hand, diverge more and more as the temperature
rises.
533 STANDARD ELECTRICAL DICTIONARY.
Thermo-electric Inversion.
The thermo-electric relations of two conductors vary at different
temperatures. Sometimes at a definite point they have no electro-motive
force and after passing this point the positive plate becomes a negative
one and vice versa. This is inversion, or reversal. (See Thermo-electric
Diagram.)
Synonym-- Thermo-electric Reversal.
Thermo-electricity.
Electric energy, electro-motive force or electrification produced from
heat energy by direct conversion. It is generally produced in a circuit
composed of two electric conductors of unlike material, which circuit
must possess at least two junctions of the unlike substances. By heating
one of these to a higher temperature than that of the other, or by
maintaining one junction at a different temperature from that of the
other a potential difference is created accompanied by an electric
current.
In many cases differential application of heat to an identical material
will develop potential difference. This effect, the converse of the
Thomson effect, is not used to produce currents, as in a closed circuit
the potential differences due to differential heating would neutralize
each other.
Thermo-electric Junction.
A junction between two dissimilar conductors, which when heated or
cooled so as to establish a differential temperature, as referred to the
temperature of the other junction, produces potential difference and an
electric current.
Thermo-electric Pile, Differential.
A thermo-electric pile arranged to have opposite faces subjected to
different sources of heat to determine the identity or difference of
temperature of the two sources of heat. It corresponds in use to a
differential air thermometer.
Thermo-electric Power.
The coefficient which, multiplying the difference of temperature of the
ends of a thermo-electric couple, gives the potential difference,
expressed in micro-volts. It has always to be assigned to a mean or
average temperature of the junctions, because the potential difference
due to a fixed difference of temperature between two metals varies with
the average temperature of the two junctions. (See Thermo-electric
Diagram.)
For bismuth and antimony at 19.5° C. (67.1° F.) it is 103 microvolts per
degree Centigrade (1.8° F.). This means that if one junction is heated
to 19° C. and the other to 20° C. (66.2° F. and 68.0° F.) a potential
difference of 103 micro-volts will be produced.
The potential difference is approximately proportional to the difference
of temperature of the two junctions if such difference is small. Hence
for large differences of potential the thermo-electric power coefficient
does not apply.
As a differential function it is thus deduced by Sir William Thomson,
for expressing the E. M. F. in a thermo-electric circuit: If a circuit
is formed of two metals with the junctions at indefinitely near
temperatures, t and t + dt, and dE is the E. M. F. of the circuit, then
the differential coefficient dE/dt is called the thermo-electric power
of the two metals for the temperature t.
534 STANDARD ELECTRICAL DICTIONARY.
Thermo-electric Series.
The arrangement of possible thermoelectric elements, q. v., in a table
in the order of their relative polarity. Bismuth and antimony form a
couple in which when their junction is heated the bismuth acts as the
positive or negatively charged element and antimony as the negative or
positively charged. Between these two extremes according to Seebeck the
series runs as follows:
Antimony, Silver, Copper,
Arsenic, Gold, Platinum,
Iron, Molybdenum, Palladium,
Steel, Tin, Cobalt,
Cadmium, Lead, Nickel,
Tungsten, Mercury, Bismuth.
Zinc, Manganese,
A differential temperature of 1° C. (1.8° F.) in a bismuth-antimony
couple maintains a potential difference of 103 micro-volts.
Matthiessen gives a different series; it is arranged in two columns; the
first column has positive coefficients annexed the second has negative.
On subtracting the greater one from the lesser, which, if the two
elements are in different columns, of course amounts to adding after
changing the negative sign, the relative potential difference due to the
combination is obtained.
+ -
Bismuth 25 Gas Coke 0.1
Cobalt 9 Zinc 0.2
Potassium 5.5 Cadmium 0.3
Nickel 5 Strontium 2.0
Sodium 3. Arsenic 3.8
Lead 1.03 Iron 5.2
Tin 1 Red Phosphorous 9.6
Copper 1 Antimony 9.8
Silver 1 Tellurium 179.9
Platinum 0.7 Selenium 290
Thus the relative E. M. F. of a bismuth-nickel couple, as both are in
the + column, would be 25 - 5 = 20; that of a cobalt-iron couple, one
being in the + column the other in the - column, would be 9 + 5.2 =
14.2. Alloys are not always intermediate to their constituents, and
small amounts of impurities affect the results largely. This may account
for the discrepancies of different observers. Other compounds could be
introduced into the series.
Artificial silver sulphide has been used by Becquerel in a
thermo-electric battery.
535 STANDARD ELECTRICAL DICTIONARY.
Thermo-electric Thermometer.
A species of differential thermometer. It consists of two
thermo-electric junctions connected in opposition with a galvanometer in
the circuit. Any inequality of temperature in the two ends or junctions
produces a current shown by the galvanometer. It may be used to
determine the temperature of a distant place, one of the junctions being
located there and the other being under control of the operator. If the
latter junction is heated until no current is produced its temperature
is evidently equal to that of the distant couple or junction. The
heating may be done with hot water or mercury, or other melted metal.
The temperature of the water, or other substance, gives the temperature
of the distant place.
Thermolysis.
Decomposition by heat; dissociation. All compound bodies are
decomposable by heat if it is intense enough. Hence at very elevated
temperatures there can be no combustion.
Synonym--Dissociation.
Thermometer.
An instrument for indicating the intensity of heat. Three scales of
degrees of heat are used in practise, the Fahrenheit, Réamur, and
Centigrade, each of which is described under its own title. (See Zero,
Thermometric-Zero, Absolute.) The ordinary thermometer depends on the
expansion of mercury; in some cases alcohol is used. Besides these the
compound bar principle as used in the thermostat (see Thermostat,
Electric) is employed.
Thermometer, Electric.
(a) A thermometer whose indications are due to the change of resistance
in conductors with change of temperature. Two exactly similar resistance
coils maybe electrically balanced against each other. On exposing one to
a source of heat, its resistance will change and it will disturb the
balance. The balance is restored by heating the other coil in a vessel
of water when the temperature of the water gives the temperature of both
coils. The coils are enclosed in water-tight metallic cases.
Synonym--Electric Resistance Thermometer.
(b) A differential thermometer may be made by connecting with a pair of
conductors, two thermo-electric couples in opposition to each other, and
including a galvanometer in series. On heating the junction of one
couple more than that of the other a current at once goes through the
galvanometer.
(c) (See Thermometer, Kinnersley's.)
Synonym--Thermo-electrometer.
536 STANDARD ELECTRICAL DICTIONARY.
Fig. 334. KINNERSLEY'S THERMOMETER.
Thermometer, Kinnersley's.
A thermo-electrometer. A large glass tube is mounted on a standard and
communicates with a small tube parallel to it. Water is poured in so as
to rise in the small tube. Two wires terminating in bulbs enter the
large tube by its top and bottom. The upper wire can be adjusted by
moving up and down through a stuffing box. On discharging a Leyden jar
through the space between the knobs on the two wires the water for a
moment rises in the small tube. There is little or no accuracy in the
instrument. It is allied to the electric mortar (see Mortar, Electric)
as a demonstrative apparatus.
Synonyms--Electric Thermometer--Thermo-electrometer.
Thermo-multiplier.
A thermo-electric battery including a number of couples. The term is
generally applied to a small battery with its similar junctions facing
in one direction and used for repeating Melloni's experiments on radiant
energy, or so-called radiant heat.
537 STANDARD ELECTRICAL DICTIONARY.
Thermophone.
An apparatus for reproducing sounds telephonically by the agency of
heat; a receiving telephone actuated by heat. Thus a wire may be
attached to the centre of a diaphragm and kept in tension therefrom, and
the transmitting telephone current may be caused to pass through it. The
wire changes in temperature and consequently in length with the pulses
of current going through it and vibrates the diaphragm, reproducing the
sound. It is to be distinguished from the thermo-electric telephone
which involves the action of potential difference produced by
thermo-electric action.
Thermostat, Electric.
A thermostat or apparatus, similar to a thermometer in some cases, for
closing an electric circuit when heated. It is used in connection with
automatic fire alarms to give warning of fire. For this use a
temperature of 52° C. (125° F.) is an approved one for setting one at,
to complete the circuit. It is also applied to regulation of
temperature, as in incubators.
(a) One kind of thermostat consists of a compound bar wound into a
spiral and fastened at one end, to which a terminal of a circuit is
connected. The bar may be made of two strips of brass and iron riveted
together, and wound into a spiral. When such a bar is submitted to
changes of temperature it bends in different directions, because brass
expands and contracts more under changes of temperature than does iron.
A contact point, to which the other terminal is connected, is arranged
to make contact with the spiral at any desired degree of temperature,
thus closing an electric circuit and ringing a bell, opening or closing
a damper, or doing anything else to notify an attendant or to directly
change the temperature.
If the brass forms the outside of the spiral, increase of temperature
makes the bending of the spiral bring the coils still closer. If the
brass forms the inside, increase of temperature makes the spiral tend to
become less close. As shown in the cut, the brass should lie along the
inside of the spiral.
Sometimes a straight compound bar is used, one of whose ends is fastened
and the other is free. As the temperature changes such a bar curves more
or less, its free end moving to and fro. Two contact screws are
provided, one on each side of its free end. If the temperature falls it
makes contact with one of these; if the temperature rises, it makes
contact with the other. Thus it may close one of two circuits, one for a
fall and the other for a rise in temperature.
It is well to introduce a third bar between the brass and iron ones,
made of some material of intermediate coefficient of expansion.
(b) Another kind of thermostat comprises a vessel of air or other gas,
which, expanding by heat, actuates a piston or other device and closes
an electric circuit. Synonym--Electro-pneumatic Thermostat.
(c) Another form utilizes the expansion of mercury. The mercury is made
part of an open electric circuit. As it expands it comes in contact with
the other terminal of the circuit, thus completing it, when the current
gives an alarm or does as is provided for in the apparatus employed.
Thermostats may be worked on either open or closed circuits; normally
the circuit may be open as described and may close on rise of
temperature, or it may be normally closed and open as the temperature
rises.
Fig. 335. ELECTRIC THERMOSTAT.
538 STANDARD ELECTRICAL DICTIONARY.
Thomson Effect.
In an unequally heated conductor the differential heating is either
increased as in iron, or diminished as in copper by a current. In lead
the phenomenon does not occur. It is termed the Thomson effect. It is
intimately related to the Peltier effect.
In a thermo-electric couple a heated junction is the source of
electro-motive force, if heated more than other parts of the circuit.
The current in a copper-iron junction flows from the copper to the iron
across the heated junction. A hot section of an iron conductor next to a
cold section of the same is a source of thermoelectricity, in the sense
that the hot section is negative to the colder. A current passing from
the hot to the cold iron travels against rising potentials, and cools
the iron in the cooler parts. As it passes to the hotter parts it
travels against falling potentials and hence heats the iron in these
parts. In this way a current intensifies differential heating in an iron
conductor.
In copper the reverse obtains. In it the thermo-electric relations of
hot and cold copper are the reverse of those of iron, and a current
tends to bring all parts of a differentially heated copper conductor to
an identical temperature.
As a current travels in iron from hot to cold it absorbs heat; in copper
traveling from cold to hot it absorbs heat.
The convection of heat by a current of electricity in unequally heated
iron is negative, for it is opposed to that convection of heat which
would be brought about by the flow of water through an unequally heated
tube. In copper, on the other hand, the electric convection of heat is
positive. (Daniell.)
The above effects of the electric current upon an unequally heated
conductor are termed the Thomson effects. In iron, at low red heat, they
are reversed and are probably again reversed at higher temperatures.
539 STANDARD ELECTRICAL DICTIONARY.
Three Wire System.
A system of distribution of electric current for multiple arc or
constant potential service. It is the invention of Thomas A. Edison.
It includes three main wires which start from the central station or
generating plant, and ramify with corresponding reduction in size,
everywhere through the district or building to be lighted. As ordinarily
carried out when dynamos are used, the dynamos are arranged in groups of
two. One lateral lead starts from the negative binding post of one
dynamo. The positive terminal of this dynamo connects to the negative of
the other. Between the two dynamos the central or neutral lead is
connected. The other lateral lead starts from the positive binding post
of the second dynamo.
The lamps or other appliances are calculated for the potential
difference of a single dynamo. They are arranged between the neutral
wire and the laterals, giving as even a disposition as possible to the
two laterals.
Fig. 336. DIAGRAM OF THREE WIRE SYSTEM
SHOWING NEUTRAL WIRE.
If evenly arranged and all burning or using current, no current goes
through the neutral wire. If all the lamps situated on one lateral are
on open circuit all the current goes through the neutral wire. In other
cases the neutral wire receives the excess of current only.
The advantages of the system are that it uses smaller wire than the two
wire system for lamps of the same voltage. If lamps of double the
voltage were used the two wire system would be most economical.
540 STANDARD ELECTRICAL DICTIONARY.
Four wire and five wire systems have been more or less used, based on
identical considerations, and involving in each case the coupling of
three or of four dynamos respectively, or else employing a dynamo with
special armature connections to give the requisite three-fold or
four-fold division of total potential. In the five wire system the total
voltage is four times that of a single lamp, the lamps are arranged four
in series across the leads and the central wire is the only one that can
be considered a neutral wire. When lamps are burning entirely from three
side-leads they constitute a sort of three wire system by themselves,
and their central wire may for the time be a neutral wire.
In some of the three wire mains, especially in the larger sizes, the
neutral wire is made of much smaller section than that of a lateral
conductor, because in extensive districts it is practically impossible
that the current should be concentrated in the neutral wire.
Throw.
In a galvanometer the instantaneous deflection of the needle when the
contact or closing of the circuit is instantaneous, or when the
discharge is completed before the needle begins to move. The throw of
the needle is the datum sought when the ballistic galvanometer is used.
Synonym--Elongation.
Throw-back Indicator.
A drop annunciator, whose shutter or drop is electrically replaced.
Thrust-bearings.
Bearings to support the end-thrust or push of a shaft. In disc armatures
where the field-magnets attract the armatures in the direction of their
axis of rotation, thrust-bearings have to be provided. In ordinary
cylinder or drum armatures end-thrust is not applied, as a little end
motion to and fro is considered advantageous as causing more even wear
of the commutator surface.
Thunder.
The violent report which, as we hear it, succeeds the lightning flash in
stormy weather. It is really produced simultaneously with the lightning
and is supposed to arise from disturbance of the air by the discharge.
The rolling noise has been attributed to successive reflections between
clouds and earth, and to series of discharges reaching the ear from
different distances and through air of varying density. The subject is
obscure. By timing the interval from lightning flash to the report of
the thunder an approximate estimate of the distance of the seat of
discharge can be made. The first sound of the thunder should be timed.
An almost concurrence of thunder and lightning indicates immediate
proximity of the discharge.
[Transcriber's note: The speed of sound at sea level is about 5 seconds
per mile.]
Ticker.
A colloquial name for a stock or market report automatic printing
telegraph, which prints its quotations and messages on a long tape.
541 STANDARD ELECTRICAL DICTIONARY.
Time Constant.
(a) When current is first turned into a circuit of considerable
self-induction it is resisted rather by the inductance than by the
resistance. It is governed by the ratio of resistance and self-induction
and this factor represents the time which it takes for the current to
reach a definite fraction of its final strength. This fraction is
(2.7183 - 1)/2.7183 or 0.63. 2.7183 is the base of the Napierian system
of logarithms. Thus if in any circuit we divide the inductance in
henries by the resistance in ohms, the ratio gives the time-constant of
the circuit, or it expresses the time which it will take for the current
to reach 0.63 of its final value.
(b) In a static condenser the time required for the charge to fall to
1/2.7183th part of its original value.
Time Cut-outs.
Cut-outs which automatically cut storage batteries out of the charging
circuit when they are sufficiently charged.
Time-fall.
In a secondary battery the decrease with use of electromotive force
maintained by a primary or secondary battery. As the battery becomes
spent its voltage falls. The conditions of the fall are represented by
its discharging curve. (See Curve, Discharging.)
Time-reaction.
A term in electro-therapeutics; the period of time occupied in the
passage of the effects of an electric current from nerve to muscle.
Time-rise.
In a secondary battery the increase of electromotive force produced
during the charging process. Its rate and conditions are graphically
shown in the charging curve. (See Curve, Charging.)
Tin.
A metal; one of the elements; symbol, Sn; atomic weight, 117.8;
equivalent, 58.9 and 29.5; valency, 2 and 4; specific gravity, 7.3.
It is a conductor of electricity.
Relative resistance, compressed, (Silver = 1) 8.784
Specific resistance at 0° C. (32° F.), 13.21 microhms.
Resistance of a wire at 0° C. (32° F.),
(a) 1 foot long, weighing 1 grain, 1.380 ohms.
(b) 1 foot long, 1/1000 inch thick, 79.47 "
(c) 1 meter long, weighing 1 gram, .9632 "
(d) 1 meter long, 1 millimeter thick, .1682 "
Resistance of a 1 inch cube at 0° C. (32° F.), 5.202 microhms.
Percentage of variation in resistance
per degree C. (1.8° F.), at about 20° C. (68° F.), .0365
Electro-chemical equivalent (hydrogen = .0105), .619 mgs.
.310 "
542 STANDARD ELECTRICAL DICTIONARY.
Tinnitus, Telephone.
A nervous affection of the ear, of the order of professional cramp; it
is attributed to too much use of the telephone.
Tin Sounders.
A recent addition to the single needle telegraph. (See Telegraph, Single
Needle.) It consists of small tin plates, cut and bent, and so fitted in
pairs to the instrument, that the needle as deflected strikes one or the
other on its right and left hand movements. The sounders can be made to
give sufficiently distinctive sounds to make sound-reading, q. v.,
possible. Commercial tin plate, which is really tinned iron, seems to
give the best results.