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 corresponding
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
current 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
perforations into position above the selecting needles. Provision is
made for preventing mutilation of the paper tape when the transmitter
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 electromagnet
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 Telegraphy, I.E.E. Paper (1911); latest edition of Herberts Telegraphy; Post Office Technical Pamphlet for Workmen, B7.
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 required. 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 electromagnets. 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 Multiplex 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, B7.
The Siemens Automatic System.—The original Siemens automatic system used an 11-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, controlling 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 electrical, 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 retransmission purposes. The system may be worked either simplex or duplex and is capable of giving a maximum speed of 166 words per minute in each direction.
References.—Herberts Telegraphy (latest ed.); Post Office Technical Pamphlet for Workmen, B7. “The Siemens Automatic Fast-Speed Printing Telegraph,” Electrician (July 11 1913).
The Morkrum 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 camshaft to revolve opening and closing the line circuit according to the 5-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 a 7-unit code. A feature of the system is the controlling and selecting mechanism of the printer, which is an ingenious combination of the Hughes and Baudot printers. The received message is printed on tape in exactly the same way as in the Baudot 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 depressed 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 per 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, Gell and Kleinschmidt 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 circuit through an electromagnet, the armature of which forces the selected punches through the paper tape. As these perforators prepare Wheatstone slip their mechanism is necessarily much more complicated 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. lxxxvi., No. 4, p. 105); Post Office Technical Pamphlet for Workmen, B3.
Gulstad 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 construction 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
