Jessie Fothergill.

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Carpentier keyboard, in which, owing to the exigencies of the
Baudot code, the keys for the numerals were spread over the
keyboard instead of being arranged on the first row of letter keys
as in most typewriters. Carpentier sought to minimize this
difficulty by adding an extra row of keys for the numerals, and a
similar arrangement was adopted in the Morse keyboard perfo-
rators such as the Cell and the Kleinschmidt.

Messrs. A. C. Booth and A. S. Willmott have now invented a
device which enables the keyboard for any type of machine
telegraph, whatever the code used, to be arranged exactly as in
a typewriter, thus allowing the numerals to be placed in their
standard positions without the extra row of keys.

The Booth-Willmott-Baudot keyboard perforator punches the
5-unit code transversely on a paper tape which is of the same size
as that used in the Murray and Western Electric instrument
(see hereafter), enabling the transmitters of either of these in-
stallations to be used in conjunction with it. Switches are pro-
vided on the instrument tables so that any particular arm of
the multiplex may be worked automatically from a transmitter
fed by a Booth-Willmott perforator or by direct-sending from
an ordinary Baudot keyboard sender at will.

REFERENCES. A. C. Booth, " Telegraph Keyboard Perforators,"
I.P.O.E.E. Journal (vol. xiv., p. 72); A. C. Booth, The Baudot
Printing Telegraph System (1907), I.P.O.E.E. paper; H. W. Pendry,
The 'Baudot Printing Telegraph System; A. C. Booth, " The Baudot




Journal (vol. x., p. 25); E. Lakey, " Progress of Baudot Duplex,'
I.P.O.E.E. Journal (vol. xii., p. 216); Post Office Technical Pam-
phlet for Workmen, B6.

Murray Multiplex. The difficulty experienced by Baudot
operators in manipulating accurately the direct-sending keyboards



I

Feed*
Holes 3

4
5










FIG. 2.



in time with the cadence signal at speeds much in excess of 30
words per minute led Murray to adopt the Carpentier method of
automatic transmission in his multiplex system. The main
features of the Booth-Baudot system are utilized, but the
operators perform on perforators which have keyboards similar
to that of an ordinary typewriter and do not have to keep in time
with a cadence signal. Each key of the perforator, when de-
pressed, perforates in a paper tape, a particular combination of
holes in accordance with the arrangement of the five-unit code
adopted by Murray. The tape thus prepared has its perforations
across the slip and not longitudinally as in the case of the Murray
automatic system, the use of which has been abandoned, so that
a great saving in the cost of paper results.

Fig. 2 shows a portion of the Murray multiplex transmitting tape
perforated to represent the word " telegraph." From the perforator,



the tape passes directly into an automatic transmitter, which has
five selecting needles, each controlling a contact lever resting



yoo



TELEGRAPH



normally against a bus-bar connected to the spacing pole of the line
battery. When a needle passes into a hole in the tape the correspond-
ing contact lever moves over and makes contact with a bus-bar
connected to the marking pole of the line battery. The positions of
the contact levers are therefore determined by the perforations in
the tape and as each lever is connected to its own particular segment
on the sending ring of the distributor, the signals representing
a character are sent out to line, one after the other, as the brushes
pass over the segments. Immediately the brushes have passed over
the last of the segments allocated to a particular transmitter a cur-
rent impulse is sent from another ring of the distributor through a
" cadence " electromagnet in the transmitter, which when operated
withdraws the selecting needles that have entered perforations and
propels the tape forward sufficiently to bring the next group of per-
forations into position above the selecting needles. Provision is
made for preventing mutilation of the paper tape when the transmit-
ter overtakes the perforator, by arranging for the tightening of
the tape to actuate a lever situated between the two instruments.
When the lever is pulled down the armature of the cadence electro-
magnet is prevented from moving. As soon as the tape slackens the
lever rises and transmission is continued. For the reception of
signals Page printers are employed somewhat similar to those which
were used in the Murray automatic system, but differing from them
in that the five selecting combs, which determine the letter to be
printed, are positioned by electromagnets instead of by a perforated
tape. The normal speed of working of each arm of the Murray
multiplex is 40 words per minute, although speeds in excess of this
may be attained.

REFERENCES. D. Murray, Practical Aspects of Printing Teleg-
raphy, I.E.E. Paper (1911); latest edition of Herberts Telegraphy;
Post Office Technical Pamphlet for Workmen, B?.

The Western Electric Multiplex. This system is also based on
the Booth-Baudot duplex and came into use in 1914. The
adoption of a method of correction from the actual working
signals themselves, instead of utilizing special correcting signals
as in the Baudot and Murray systems, results in a saving -of line
time and therefore gives a greater output on difficult lines.

The transmitters and perforators are the modern developments of
Carpentier's but the printer used types the message in page form
instead of on a paper tape as in the Baudot system, from a type
wheel which rotates from character to character as may be re-
quired. This printer has not given entirely satisfactory results,
and is being superseded by one in which type bars are used in
place of a type drum and the paper is kept central instead of being
moved sidewise to and fro. The phonic wheel distributors are driven
by electrically vibrated tuning-forks, which possess an advantage
over vibrating-reeds in that they may be placed on the instrument
table instead of being fixed to a steady support as is required in
the case of reeds.

The Kleinschmidt Electric Co. of New York have recently
designed a very compact column printer which may be used on
Western Electric multiplex circuits. As in the Murray printer,
there are five selecting combs which are operated by electromag-
nets. When the combs have been positioned, during the reception
of a character, certain slots in the combs are thereby brought
into alignment allowing a pull-bar attached to one extremity of
the required type-bar lever to fall into them. Directly after the
combs have been moved and the type-bar lever selected, a
contact is closed mechanically, completing a circuit through a
printing magnet which, when it operates, causes the selected
pull-bar to be impelled forward, thus projecting the free end of
the corresponding type-bar lever against an ink ribbon and
printing the required character as in a typewriter.

REFERENCES. P. M. Rainey, " A New Printing Telegraph
System," Electrical World (April 3 1915) ; The Western Union Multi-
plex System; (Pamphlet printed by Telegraph and Telephone Age);
A. H. Roberts, " A New Type Printing Telegraph System," I.P.O.-
E.E. Journal (vol. viii., p. 193); Post Office Technical Pamphlet for
Workmen, 87.

The Siemens A utomatic System. The original Siemens automa-
tic system used an i i-unit code actuating a receiver which printed
the incoming signals in Roman characters on photographic paper.
The preparations required for the received slips, which had to be
developed chemically, impaired its usefulness for actual traffic,
and the system was superseded in 1912 by one using a 5-unit code
and a revolving type-wheel. The latter is now extensively
used in Germany and to a limited extent in other countries.

As in the case of the Creed and other automatic systems there are
several perforating operators and one transmitting operator at the
sending station. The prepared tape from the keyboard perforators
is passed through the transmitter over five selecting needles, con-



trolling their upward movement and determining the polarity of the
current impulses sent to line during each revolution of a brush over
the five segments of a distributor. The sending distributor brush arm
is driven by a shunt wound motor whose speed is kept steady by
means of a heavy flywheel mounted on the spindle. Unison with
the brush arm of the receiving distributor at the distant station
is maintained by the actual working signals. The receiving and
translating arrangements of the receiver are almost entirely elec-
trical, and printing is effected by the discharge of a condenser through
an electromagnet, the armature of which presses momentarily a
paper tape against a revolving type-wheel. This tape is afterwards
pasted on ordinary message forms as in the Baudot system. In
addition to the printing tape, the incoming signals can also actuate
a keyboard perforator to provide a perforated tape for retrans-
mission purposes. The system may be worked either simplex or 1
duplex and is capable of giving a maximum speed of 166 words per
minute in each direction.

REFERENCES. Herberts Telegraphy (latest ed.); Post Office Tech-
nical Pamphlet for Workmen, By. " The Siemens Automatic Fast-
Speed Printing Telegraph," Electrician (July u 1913).

The Morkntm Teletype. This is a single-line system of printing
telegraphy which has been recently developed by the Morkrum
Co. of Chicago, U.S.A. It may be duplexed, and is suitable for
short lines over which the traffic is not very heavy.

The apparatus comprises two units, a keyboard transmitter,
and a printer, which are mounted on one base to form a very
compact combined sending and receiving instrument. The
keyboard is arranged as for a standard typewriter, and is a direct-
sending instrument the keys of which when operated allow a cam- 1
shaft to revolve opening and closing the line circuit according to
the s-unit code. Starting and stopping impulses are sent over-
the line to start and stop the selecting mechanism of the printer
so that from transmission point of view the system has actually i
a 7-unit code. A feature of the system is the controlling and
selecting mechanism of the printer, which is an ingenious com- i
bination of the Hughes and Baudot printers. The received mes- j
sage is printed on tape in exactly the same way as in the Bau-
dot printer and afterwards gummed on ordinary message forms.

The maximum speed of operation of the keyboard is limited to
45 words per minute and a device is provided which is actuated ,
when this speed is exceeded and prevents the keys being de-
pressed too rapidly.

The Creed System. One of the principal drawbacks to the
original Creed system was the use of compressed air for working
the apparatus, which in a large number of offices necessitated the
installation of a special pneumatic plant. Moreover, the pneumatic
Creed printer had a maximum speed of only 120 words peri
minute, so that on lines where the working speed was much in
excess of this figure it was necessary to install two printers in
order to deal expeditiously with the traffic. The latest Creed
instruments, however, have been designed to work electrically;
they are much simpler in their construction and give speeds up
to 200 words per minute.

For the preparation of the transmitting tapes, Cell and Klein-
schmidt perforators are generally used, each of which has a keyboard
similar to that of an ordinary typewriter. The depression of a key '
selects, through a system of levers, the punches required to perforate
the holes in the tape for the corresponding signal, and closes a cir-
cuit through an electromagnet, the armature of which forces the
selected punches through the paper tape. As these perforators pre-
pare Wheatstone slip their mechanism is necessarily much more com-
plicated than that of keyboard perforators designed for a 5-unit '
code, in which all letters are of the same length, because in the former
a differential feed varying from two-tenths of an inch to over one inch
is required owing to the varying length of the letters. These machines
will work as fast as a typewriter, but 80 words per minute is regarded
as the limit for practical purposes.

REFERENCES. E. Lack, " The Creed Telegraph System,"
I.P.O.E.E. Journal (vol. vi., p. 249); "Description of New Creed
Apparatus," Electrician (Jan. 21 1921, vol. Ixxxvi., No. 4, p.
105) ; Post Office Technical Pamphlet for Workmen, 83.

Gulslad Relay. In 1898 Gulstad of Copenhagen invented a
modified form of polarized relay, known as a vibrating relay, the
use of which has enabled much greater speeds of working to be
attained on underground and submarine circuits, and in some
cases allowed repeaters to be dispensed with. In general con-
struction it is similar to the British Post Office standard relay,
but, in addition to the usual line coils, has two extra windings on
the same cores. These windings are connected to a local battery



TELEGRAPH



701



in such a manner that the relay tongue is caused to vibrate
between the contact points, when the current through the line
coils is insufficient to' maintain it on either of the contacts.

The principle of the relay may be understood by referring to fig. 3.
It will be seen that the ends of the local windings are joined to ter-
minals B and C and their centre to terminal A, which is joined through
an adjustable resistance Y to the relay tongue. This resistance is
for regulating the local current and keeping it below the value of the
steady current through the line coils. Terminal B is connected to
earth through a condenser K, while C has a resistance coil X in its
earth lead.

Assuming that there is no current in the line coils and that the
relay tongue has just reached the marking contact, there will then
be a momentary rush of current through the winding A,B to charge
the condenser K, in a direction to keep the tongue to the marking
side, thus preventing any tendency of the tongue to rebound. This
charging current dies away' rapidly, however, and directly its
strength falls below the steady current flowing through the winding
AC, the preponderance of the latter causes the tongue to move
toward the spacing contact. Immediately the tongue leaves the
marking contact, the condenser K discharges through both wind-
ings BA and AC in such a direction as to accelerate the movement
of the tongue, so that its transit time from one contact to the other
is thereby lessened.

When the tongue reaches the opposite contact the condenser K
is again charged, but this time from the other pole of the battery;
a similar cycle of effects therefore takes place on that side and the

Line Coi/s




FIG. 3.

tongue moves in the reverse direction. In this manner the relay
tongue is kept vibrating, at a speed depending on the values given
to the condenser and resistance. In practice the adjustments are
such that the rate of vibration of the tongue under the control of the
local current is approximately equal to the rate at which the trans-
mitter at the distant station sends reversals at working speed. When
this obtains, the signals passing through the line coils merely deter-
mine the length of time that the tongue remains in contact with
either stop, its movement therefrom being effected by the local
current through the local windings as soon as the strength of the
Hne current falls below that of the local current in the coil AC. It
is this effect combined with the action of the condenser in lessening
the time of transit of the tongue, that enables a higher speed of
working to be attained on long and difficult circuits than if ordinary
polarized relays were used.

In the original Gulstad relay the line coils were not differentially
wound; it could be used, therefore, only on Bridge duplex or simplex
circuits. To utilize the advantages of the Gulstad principal on
differential duplex circuits, the British Post Office has modified the
Post Office standard relay, by adding extra windings and terminals.
This modified instrument is known as a " G " relay and is equally
suitable for differential or bridge duplex working. The internal and
external connexions of this relay are shown in fig. 4, in which the
dotted lines indicate the extra coils. For the correct reception of the
incoming signals a Wheatstone receiver is connected to the relay
tongue.

REFERENCES. E. Lack, " The Gulstad Relay," I.P.O.E.E. Jour-
nal (vol. vii.,p. 183); Electrical Review (June 1898 and Aug. 1902);
Herberts Telegraphy (latest ed.) ; E. Lack, " Post Office Standard
Relay ' G'," I.P.O.E.E. Journal (vol. x., p. 34).



Tele-photographic Systems. In 1909 T. Thorne Baker read
a paper before the Royal Institution in London describing his
" telectrograph " process of transmitting pictures over long
distances. The method, which was used on a large scale by the
Daily Mirror between London and Paris, is based upon the
Bakewell copying telegraph.




V\W^-*\VNV\A* |l"



Receiver



FIG. 4.



Synchronously rotating metallic drums, driven by electric motors,
are employed one at each end of the telegraph line over which it is
desired to transmit, say, a picture. A half-tone photograph of the
picture is first printed upon thin sheet lead and subjected to a process
which breaks up the photograph into a number of dotted lines printed
in fish glue. This record is fixed round the transmitting drum,
which is traversed spirally by an iridium stylus. The contact of
the latter with the lead is interrupted every time one of the fish glue
dotted lines comes beneath it, for duration depending upon the width
of the line. The lead sheet is connected to the line, so that the trans-
mitting instrument sends a series of electric currents whose periods
of duration are determined by the width of the lines composing the
photograph. At the receiving station, the rotating drum carries a
piece of absorbent paper impregnated with a colourless solution,
which turns black or brown when decomposed by an electric cur-
rent. Every brief current through the paper causes a mark to appear,
having a width depending on the duration of the current. The
arriving currents are therefore arranged to pass through a platinum
stylus under which the receiving drum rotates, then through the
moistened paper resulting in the production of a number of marks
on the paper due to chemical decomposition. These marks gradually
combine to produce the picture at the transmitting station.

REFERENCES. T. Thorne Baker, " Telegraphy of Photographs,
Wireless and by Wire," Royal Institution Proc. 1908-10, vol. xix.

Foss and Petersen Method. In this system a high frequency
generator capable of producing sparks is used at the receiving
station. The sparks so produced are capable of puncturing a
paper wrapped round a metal drum which rotates in unison with
a similar drum at the sending station.

The line wire is arranged so that when the sending end is connected
to earth the generator is partly short-circuited, thus suppressing the
sparking. At the sending end the shunting of the generator is effected
by means of a contact pin passing over a cylinder on which the writ-
ing or illustrations are inscribed in insulating ink so that the shunt
circuit is cut out each time the pin passes part of the writing (see
Patent Specification No. 105,914, 1917). (W. No.)

UNITED STATES

Technical developments made after 1910 practically revolu-
tionized telegraphy as practised in the United States. These
include printing-telegraph arrangements applied to telephone as
well as to telegraph circuits, simultaneous telephone and tele-
graph operation for long small-gauge cable circuits, and the
use of alternating currents with resonant circuits in the so-called
carrier systems for multiplexing wire conductors.

Radical changes were also made in the arrangements for and
the methods of handling telegrams in large offices. Belt con-
veyers, typewriters, pneumatic tubes, automatic time-stamps and
other labour-saving devices came to be used to a large extent.
About 75% of all telegrams handled by the Western Union
Telegraph Co. over trunk circuits in 1921 were transmitted and




TELEGRAPH



To Line



Transmitters



A



B



Correcting Rings



Sending Rings



Printers Receiving Rings Printers

A




Receiving Rings




Correcting
Relay

Tungsten
Lamp



Driving Fork



FIG. 5. Simplified Terminal Circuit of Multiplex Printer System.



received by printing-telegraph apparatus. The introduction of
machine telegraphy took place after 1910.

Progress can be divided into two general classes: (i) that re-
lating to terminal equipment, such as printers; and (2) that
relating to the methods of working lines.

Printing Telegraphy

(a) Multiplex System. The multiplex system giving double-du-
plex, triple-duplex and quadruple-duplex service, as applied in
America, was that developed jointly by the Western Electric Co.
and the Western Union Telegraph Co. It uses the Baudot code and
a system of speed correction for rotating distributors in which
correcting impulses are generated from the character signals, thus
saving line time.

The fundamental features of one arrangement for quadruple-
duplex operation are shown in fig. 5. The sending, receiving and
correcting rings are parts of a distributor driven by a La Cour or
phonic-wheel motor. The common sending ring is connected to the
midpoint of a differentially wound line relay and the common
receiving ring to the armature of a printing relay included in the
local circuit of the line relay. This local circuit also includes an

Break
Relay



Release %



Sending
Distributor




Line



impulse relay, so arranged that short-current impulses are sent to
the common ring of the set of correcting rings when the line relay
armature moves from one contact to the other. These impulses
come at intervals determined by the signals transmitted by the
distant station. There are twice as many correcting segments as
sending segments, and these are alternately connected to the wind-
ings of a correcting relay. One distributor on a circuit sets the speed
for the other and if the corrected distributor is running too fast, the
operation of the correcting relay causes the driving fork for its motor
to be retarded in its rate of vibration. If, on the other hand, the
distributor is running too slowly, the fork is accelerated. It is essen-
tial to secure correcting impulses when all printing channels are
idle. This is done by reversing the polarity of the marking signals
of one or more channels. Various types of printer units have been
successfully used with this system. Speeds as high as 50 to 60 six-
character words per minute per channel are maintained by operators.
The multiplex printer system has thus greatly increased operators'
loads as well as the number of telegraph channels which can be
obtained from each line circuit. Means have been developed for
economically extending the single channels of a multiplex-printer
system from the multiplex terminal station to branch offices.

(b) Start-Stop Printer Systems. Successful systems giving single-
channel working, or two-channel working when operated duplex,



-To other Stations
Magnet



Station



Station

FIG. 6. Circuit of Start-Stop Printer System.




Receiving
Distributor



TELEGRAPH




FIG. 7. Selecting Circuit of Cipher System.

have been developed for inter-communicating purposes among a
group of stations. These systems have been used to a considerable
extent with telegraph circuits obtained from telephone circuits.

One of these systems employing motor-driven distributors at
each station is shown in fig. 6. The sending distributor at one
station and the receiving distributor at the other are indicated in
detail. The distributor brush arms driven through a friction clutch
are normally held stationary by a latch and make one rotation for
each character transmitted or received. A start impulse, usually the
opening of the line circuit for a brief interval, releases the receiving
start latches so that all receiving distributors start rotating. The
five impulses of the Baudot code which follow the start impulse are
distributed properly to the selecting magnets or elements of a
printer by the receiving distributors if their speeds coincide approx-
imately with that of the sending distributor. Close synchronism is
not required since all distributors are stopped and caused to start
from the same initial position for each character.



To

Cable

Circuit



Cable -i
Battery ;=:
JO volts




Transmittinq
Relay



Cable Receiving
Relay



FIG. 8. Terminal Arrangement for Metallic Telegraph Cable


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Online LibraryJessie FothergillThe Encyclopædia Britannica : a dictionary of arts, sciences, literature and general information (Volume 32) → online text (page 260 of 459)