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

by T. O'Conor Sloane

Fig. 316. DIFFERENTIAL DUPLEX TELEGRAPH CONNECTIONS.
The cut shows a diagram of the operation of one end of the line. R and R
are resistances, E and E are earth contacts, and the two circles show
the magnet of the receiving instrument wound with two coils in
opposition. The battery and key are also shown. It also illustrates what
happens if the key of the receiver is in the intermediate position
breaking contact at both 1 and 2. The sender's line current then goes
through both coils of the receiving instrument magnet, but this time in
series, and in coincident direction. This actuates the instrument as
before. Owing to the resistance only half the normal current passes, but
this half goes through twice as many coils or turns as if the receiver's
key was in either of the other two positions.
In actual practice there are many refinements. To compensate for the
varying resistance of the line a rheostat or resistance with sliding
connection arm is connected in the compensation circuit so that the
resistance can be instantly changed. As the electro-static capacity of
the line varies sectional condensers are also connected in the
compensation circuits.
510 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Facsimile.
A telegraph for transmitting facsimiles of drawing or writing. The
methods employed involve the synchronous rotation of two metallic
cylinders, one at the transmitting end, the other at the receiving end.
On the transmitter the design is drawn with non-conducting ink. A tracer
presses upon the surface of each cylinder and a circuit is completed
through the two contacts. In operation a sheet of chemically prepared
paper is placed over the surface of the receiving cylinder. The two
cylinders are rotated in exact synchronism and the tracers are traversed
longitudinally as the cylinders rotate. Thus a number of makes and
breaks are produced by the transmitting cylinder, and on the receiving
cylinder the chemicals in the paper are decomposed, producing marks on
the paper exactly corresponding to those on the transmitting cylinder.
Synonyms--Autographic Telegraph--Pantelegraphy.
Telegraph, Harmonic Multiplex.
A telegraph utilizing sympathetic vibration for the transmission of
several messages at once over the same line. It is the invention of
Elisha Gray. The transmitting instrument comprises a series of vibrating
reeds or tuning-forks, each one of a different note, kept in vibration
each by its own electro-magnet. Each fork is in its own circuit, and all
unite with the main line so as to send over it a make and break current
containing as many notes superimposed as there are tuning forks. At the
other end of the line there are corresponding tuning forks, each with
its own magnet. Each fork at this end picks up its own note from the
makes and breaks on the main line, by the principle of sympathetic
vibration.
To each pair of operators a pair of forks of identical notes are
assigned. As many messages can be transmitted simultaneously as there
are pairs of forks or reeds.
The movements of a telegraph key in circuit with one of the transmitting
reeds sends signals of the Morse alphabet, which are picked out by the
tuning fork of identical note at the other end of the line.
511 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Hughes'.
A printing telegraph in very extensive use in continental Europe. Its
general features are as follows:
The instruments at each end of the line are identical. Each includes a
keyboard like a piano manual, with a key for each letter or character.
On each machine is a type wheel, which has the characters engraved in
relief upon its face. With the wheel a "chariot" as it is termed also
rotates. The type wheels at both stations are synchronized. When a key
is depressed, a pin is thrown up which arrests the chariot, and sends a
current to the distant station. This current causes a riband of paper to
be pressed up against the face of both type wheels so as to receive the
imprint of the character corresponding to the key. The faces of the
wheels are inked by an inking roller.
Fig. 317. ELECTRO-MAGNET OF HUGHES' PRINTING TELEGRAPH.
The most characteristic feature is the fact that the current sent by
depressing a key does not attract an armature, but releases one, which
is then pulled back by a spring. The armature is restored to its
position by the mechanical operation of the instrument. The magnet used
is a polarized electro-magnet. Coils are carried on the ends of a strong
powerful magnet. The coils are so connected that a current sent through
them by depressing a key is in opposition to the magnetism of the
permanent magnet so that it tends to release the armature, and in
practice does so. This release permits the printing mechanism to act.
The latter is driven by a descending weight, so that very slight
electric currents can actuate the instruments.
Synonym--Hughes' Type Printer.
Telegraphic Code.
(a) The telegraphic alphabet, as of the Morse System. (See Alphabet,
Telegraphic.)
(b) A code for use in transmitting messages either secretly, or
comprising several words or short sentences in one word, in order to
economize in transmission. Such codes are extensively used in commercial
cable messages.
512 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Magneto-electric.
A telegraph in which the current is produced by magneto-electric
generators. It has been applied to a considerable extent in England. The
Wheatstone ABC or dial telegraph is operated by a magneto-generator
turned by hand.
In this country the magneto-electric generator by which the calling bell
of a telephone is rung is an example. The magneto-electric key (See Key,
Magneto-electric) is for use in one kind of magneto-electric
telegraphing.
Telegraph, Morse.
A telegraph, characterized by the use of a relay, working a local
circuit, which circuit contains a sounder, or recorder for giving dot
and dash signals constituting the Morse alphabet. The signals are sent
by a telegraph key, which when depressed closes the circuit, and when
released opens it. The two underlying conceptions of the Morse Telegraph
system are the use of the dot and dash alphabet, and the use of the
local circuit, which circuit includes a receiving instrument, and is
worked by a relay, actuating a local battery. It would be difficult to
indicate any invention in telegraphy which has had such far-reaching
consequences as the one known as the Morse telegraph.
In other places the principal apparatus of the system will be found
described. The cut Fig. 318, repeated here gives the general disposition
of a Morse system. (See Circuit, Local.)

Fig. 318. DIAGRAM OF MORSE SYSTEM.
513 STANDARD ELECTRICAL DICTIONARY.
The key by which the messages are transmitted is shown in Fig. 319. M is
a base plate of brass. A is a brass lever, mounted on an arbor G carried
between adjustable set screws D. C is the anvil where contact is made by
depressing the key by the finger piece B of ebonite. E, Fl are adjusting
screws for regulating the vertical play of the lever. H is the switch
for opening or closing the circuit. It is opened for transmission, and
closed for receiving. By screws, L L, with wing nuts, K K, the whole is
screwed down to a table.

Fig. 319. MORSE TELEGRAPH KEY.
In the United States the simplest disposition of apparatus is generally
used. The main line is kept on closed circuit. In it may be included a
large number of relays at stations all along the line, each with its own
local circuit. There may be fifty of such stations. Battery is generally
placed at each end of the line. Very generally gravity batteries are
used, although dynamos now tend to supplant them in important stations.
As relays the ordinary relay is used. Its local circuit includes a
sounder and local battery. The latter is very generally of the gravity
type, but oxide of copper batteries (See Battery, Oxide of Copper) are
now being introduced. At main or central offices, the terminals of the
lines reach switch boards, where by spring-jacks and plugs, any desired
circuits can be looped into the main circuit in series therewith.
In European practise the main line is kept on open circuit. Polarized
relays are used to work the local circuits. The currents for these have
to be alternating in direction. When the line is not in use its ends are
connected to earth at both ends, leaving the battery out of circuit.
Each intermediate station has its own main, or line battery for use when
it desires to send a message. In the American system as first described,
it will be seen that the main batteries are at most two in number.
For the details of the different apparatus, the following definitions
may be consulted: Embosser, Telegraphic--Recorder, Morse--Relay--Relay
Connection--Sounder.
514 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Multiplex.
A system of telegraphy by which a number of messages can be transmitted
in both directions over a single wire. The principles underlying the
systems are the following:
Suppose that at the two extremities of a telegraph line two arms are
kept in absolute synchronous rotation. Let the arms in their rotation,
press upon as many conducting segments as there are to be transmissions
over the line. A transmitting and receiving set of instruments may be
connected to one segment at one end of the line, and another set to the
corresponding segment at the distant station. For each pair of segments
two sets can be thus connected. Then if the arm rotates so rapidly that
the contacts succeed each other rapidly enough each pair of sets of
instruments can be worked independently of the others. In practice this
rapid succession is effected by having a number of contacts made for
each pair during a single rotation of the arm or equivalent.
The multiplex system has been perfected by the use of La Cour's phonic
wheel (see Phonic Wheel), and brought into a practical success by
Patrick B. Delany, of New York.
Two phonic wheels rotate at each end of the line. They are kept in
synchronous motion by two vibrating steel reeds of exactly the same
fundamental note, and the axle of each wheel carries an arm whose end
trails over the contacts or distributor segments already spoken of. The
reeds are adjusted to vibrate at such speed that the trailer is in
contact with each segment about 1/500 second. The number of groups of
segments required for each working is determined by the retardation of
the signals owing to the static capacity of the line. To convert the
rapidly recurring impulses of current into practically a single current,
condensers are connected across the coils of the relay. One battery
serves for all the arms.
Multiplex telegraphy can effect from two to six simultaneous
transmissions over one wire. For two or four transmissions the method
only distinguishes it from duplex or quadruplex telegraphy. The terms
diode, triode, tetrode, pentode and hexode working are used to indicate
respectively the simultaneous transmission of two, three, four, five, or
six messages over one wire.
It will be seen that the multiplex process really assigns to each
transmission separate times, but divides these times into such short and
quickly recurring intervals that the work is executed as if there was
continuous contact. In no case is there the popular conception of the
sending of several messages actually simultaneously over one wire. Each
signal in reality has its own time assigned it, divided into short
periods of high frequency, and only utilizes the line when it is free.
515 STANDARD ELECTRICAL DICTIONARY.
Telegraph, Over-house.
An English term for telegraph lines led over houses and supported on
standards on the roofs.
Telegraph Pole Brackets.
Arms for carrying insulators, which arms are attached to telegraph poles
or other support. They vary in style; sometimes they are straight bars
of wood gained into and bolted or spiked in place; sometimes they are of
iron.
Telegraph, Printing.
Various telegraphs have been invented for printing in the ordinary
alphabet the messages at the receiving end of the line.
Representative instruments of this class are used for transmitting
different market and stock reports to business offices from the
exchanges. The type faces are carried on the periphery of a printing
wheel, which is rotated like the hand of a dial telegraph, and against
whose face a paper riband is pressed whenever the proper letter comes
opposite to it. As each letter is printed the paper moves forward the
space of one letter. Spacing between words is also provided for. In the
recent instruments two lines of letters are printed on the paper one
above the other.
In England, and on the continent of Europe, printing instruments have
received considerable use for ordinary telegraphic work. Hughes' type
printer and Wheatstone's ABC telegraph meet with extensive use there for
ordinary transmission.
Telegraph, Quadruplex.
Duplex telegraphy is the sending of two messages in opposite directions
simultaneously through the same wire. Duplex telegraphy is the sending
of two messages simultaneously in the same direction. The two combined
constitute quadruplex telegraphy. [SIC]
The system was suggested by Stark of Vienna and Bosscha of Leyden in
1855; the successful problem was solved by Edison in 1874.
The principle is based on the two orders of difference in electric
currents; they may vary in strength or in direction. Thus we may have
one instrument which works with change of strength of current only, the
other with change of direction only. The two can be worked together if
the direction of the current can be altered without alteration of
strength, and if strength can be altered without alteration of
direction. Double current and single current working are so combined
that one relay works by one system of currents and another relay by the
other system. A current is constantly maintained through the line. The
relay operated by change in direction is a simple polarized relay which
works by change of direction of current. The relay operated by change in
strength is the ordinary unpolarized relay.
516 STANDARD ELECTRICAL DICTIONARY.
For the following description and the cuts illustrating it we are
indebted to Preece and Sivewright. The cut shows the arrangement of the
apparatus and connections for terminal offices.
"Sufficient table room is provided to seat four clerks. The apparatus is
arranged for the two senders to sit together in the centre, the messages
to be forwarded being placed between them. The section on the left of
the switch Q is known as the 'A' side, that on the right as the 'B' side
of the apparatus.
K1 the reversing key, reverses the direction of the current. K2 is a
simple key, known as the increment key; it is used simply to increase
the strength of the current.

Fig. 320. QUADRUPLEX TELEGRAPH CONNECTIONS.
The way in which the keys K1 and K2 combine their action is shown by
Fig. 321. E1 and E2 are the line batteries, the one having two and
one-third (2-1/3) the number of cells of the other, so that if E1 be the
electro-motive force of the smaller, that of the whole combined battery
will be 3.3 E1. The negative pole of E1 is connected to z and z1 of K1
and the positive pole of E2 to a of K2 through a resistance coil s. A
wire, called the 'tap' wire, connects the positive pole of E1 and the
negative pole of E2 to b of K2. This wire has in it a resistance coil
r2. The springs c and c1 of Kl are connected to the lever L of K2. Now,
when both keys are at rest, the negative pole of E1 is to line through
z, and the positive pole of E1 to earth through b of K2 and c of K1; the
positive pole of E2 being insulated at a of K2.
517 STANDARD ELECTRICAL DICTIONARY.
There is thus a weak negative current flowing to line. When K1 alone is
worked, the current of E1 is reversed. When K2 is worked alone, c of K1
is transferred from b to a, and the strength of the negative current
going to line is increased through the increase of the electro-motive
force from E1 to 3.3 E1 for the whole battery is brought into play. When
K1 and K2 are depressed together, then the negative pole of E1 goes to
earth through Z1; and the positive pole of E2 to line through a of K2
and c1 of K1 and a positive current, due to the whole electro-motive
force 3.3 E1 goes to line. Hence the effect of working K1 is simply to
reverse the current, whatever its strength, while that of K2 is to
strengthen it, whatever its direction.
The resistance coil s, of 100° resistance, is called a spark coil,
because it prevents the high electro-motive force of the whole battery
from damaging the points of contact by sparking or forming an arc across
when signals are sent; and the resistance r2 is made approximately equal
to the combined resistance of E2 and the spark coil, so that the total
resistance of the circuit may not be altered by the working of the
apparatus.

Fig. 321. QUADRUPLEX TELEGRAPH.
A1 and B1 (Fig. 320) are the relays which are used to respond to the
changes in the currents sent by the keys K1 and K2 at the distant
station.
A, is a simple polarized relay wound differentially, each wire having a
resistance of 200 [omega], and so connected up as to respond to the working of
the reversing key K1 of the distant station. It acts independently of
the strength of the current, and is therefore not affected by the
working of the increment key K2. It is connected up so as to complete
the local circuit of the sounder S1 and the local battery l1 and forms
the receiving portion of the 'A' side.
B, is a non-polarized relay also wound differentially, each coil having
a resistance of 200 [omega]. It responds only to an increase in the
strength of the current, and therefore only to the working of the
increment key K2 of the distant station.
[Transcriber's note: In current usage upper case omega indicates ohms and
lower case omega denotes angular frequency, 2*PI*f.]
518 STANDARD ELECTRICAL DICTIONARY.
The relay spring is so adjusted that the armatures are not actuated by
the weak current sent from E by the key K1.
In its normal position this relay completes the circuit of the local
battery through the sounder S. This sounder S, called the uprighting
sounder, acts as a relay to a second sounder, S2, called the reading
sounder, which is worked by another local battery, l2. Of course,
normally, the armature of S is held down and that of S2 is up, but when
the tongue t moves, as it does when the increment key K2 is depressed so
as to send the whole current to line, then the current from l is
interrupted, and the circuit of l2 is completed by the rising of the
armature of S, causing the reading sounder S2 to work. This is the 'B'
side.
R is a rheostat for balancing the resistance of the line, as used in
duplex working.
C is a condenser used for compensating the static charge of the line. It
is provided with an adjustable retardation coil, R1, to prolong the
effect of the compensating current from the condenser.
G is a differential galvanometer, used for testing, and for facilitating
adjustment and balancing.
Q is a switch for putting the line to earth, either for balancing, or
for any other purpose. There is on the earth wire leading from Q a
resistance coil, r1, equalling approximately the resistance of the whole
battery, 3.3 E1, and the resistance s.
The connections shown in Fig. 321, are for an 'up' office. At a 'down'
office it is necessary to reverse the wires on the two lower terminals
of the galvanometer and the two battery wires on the reversing key K1.
The keys K1 and K2 are, for repeaters, replaced by transmitters.
The adjustment of this apparatus requires great care and great accuracy.
Its good working depends essentially on technical skill that can only be
acquired by patience and perseverance.
Faults in working generally arise from careless adjustments, dirty
contacts, loose connections, battery failures, and the ordinary line
interruptions, but there are no troubles that are beyond the reach of
ordinary skill, and it can be safely said that, within moderate
distances, wherever and whenever duplex working is practicable, then
quadruplex working is so too."
The above is a typical quadruplex bridge system. There is also a
differential system, the full description of which, in addition to what
has been given, is outside of the scope of this work.
519 STANDARD ELECTRICAL DICTIONARY.
Telegraph Repeater.
An extension of the relay system, adopted for long lines. A repeating
station comprises in general terms duplicate repeating apparatus. One
set is connected for messages in one direction, the other for messages
in the opposite direction. The general operation of a repeating set is
as follows. The signals as received actuate a relay which by its local
circuit actuates a key, which in ordinary practise would be the sounder,
but in the repeater its lever opens and closes a circuit comprising a
battery and a further section of the line.
Repeaters are placed at intervals along the line. Each repeater repeats
the signals received for the next section of line with a new battery. It
represents an operator who would receive and repeat the message, except
that it works automatically.
The Indo-European line from London to Teheran, 3,800 miles long, is
worked directly without any hand retransmission, it being carried out by
five repeaters. This gives an average of over 500 miles for each
repeater.
[Transcriber's note: … 650 miles for each repeater.]
Repeaters introduce retardation, and each repeater involves a reduction
in the rate of working. Yet in many cases they increase the speed of a
line greatly, as its speed is about equal to that of its worst section,
which may be far greater than that of the whole line in one.
Synonym--Translater.
Telegraph Signal.
In the telegraph alphabet, a dot, or dash; the signal or effect produced
by one closing of the circuit. A dash is equal in length to three dots.
The space between signals is equal to one dot; the space between letters
to three dots; and the space between words to six dots.
Telegraph, Single Needle.
A telegraph system in which the code is transmitted by the movements of
a needle shaped index which oscillates to right and left, the left hand
deflection corresponding to dots, the right hand deflection to dashes.
The instruments for sending and receiving are combined into one. The
needles are virtually the indexes of vertical galvanometers. In one form
by a tapper key (see Tapper), in another form by a key worked by a
drop-handle (the drop handle instrument), currents of opposite
directions are sent down the line. These pass through both instruments,
affecting both needles and causing them to swing to right or left, as
the operator moves his key.
As galvanometer needle or actuating needle a soft iron needle is
employed, which is polarized by the proximity of two permanent magnets.
This avoids danger of reversal of polarity from lightning, a trouble
incident to the old system.
520 STANDARD ELECTRICAL DICTIONARY.
The cut, Fig. 322, shows a single needle telegraph instrument of the
tapper form. The action of the tapper can be understood from the next
cut.