The apparatus and circuits of an automatic telegraph repeater at an intermediate station are outlined theoretically in Fig. 8. This is known as the Toye repeater, which was at one time much in use, and is chosen for illus tration because of its comparative simplicity. It may be noticed that relay R controls the °continuity preserving' transmitter T by means of its armature lever m, and local battery b; while relay R' controls r by means of lever m' and battery Also that transmitter 7' controls the western main circuit at x; while T' controls the eastern circuit at In prac tice T' is the °opposite transmitter to relay R, and T is the °opposite transmitter to R'. In the operation of an automatic repeater the de sideratum is automatically to keep the °oppo site transmitter passive while its circuit is being repeated into, in shop phrase. The oper ation of the Toye repeater is as follows: As sume that the East is sending to the West. When the eastern operator opens his key, thereby opening the eastern circuit, .relay R opens, as in the figure. This opens transmitter T, and in consequence the western circuit is opened at x. At the instant, however, that the western circuit is opened at .r, the circuit which includes the relay R' and main battery MB' is closed via the lever of T, through a resistance Rh equal to that of the eastern circuit. As this transposition or substitution of circuits maintains the current passing through relay R' at the same strength as before the change of circuits was made that relay, and, conse quently, the transmitter r remains closed. In this way the °opposite transmitter is auto matically kept passive. When the eastern operator again closes his key, relay R, and in turn 7', are likewise closed, resulting in the closing of the western circuit at x. When the West sends to • the East the described actions are reversed.
Among the other automatic repeaters now in use may be mentioned, the Milliken, the Neilson, the Weiny, the Maver-Gardanier, the Atkinson, the Ghegan and the Varley.
Automatic Telegraph Systems.—Auto matic telegraphy consists of arrangements of apparatus whereby Morse characters are trans mitted at a rate of speed ranging from 8() to 2,000 or 3,000 words per minute. As the rate of speed by hand transmission of Morse char acters is from, say, 15 to 40 words per minute, it is obvious lint by the use of a rapid auto. matic system many more messages may be transmitted over one wire in a given time than by the manual method; and since the cost of construction and maintenance of the wires is a large portion of the expense of a telegraph equipment, if everything else were equal, the advantage would be largely in favor of the automatic systems. But, as fre quently happens, everything else is not equal. In the first place, every message sent by an automatic Morse system has to be manually prepared for transmission by the automatic machinery, and every message received must be transcribed manually before its delivery to the addressee. This involves a larger force of operatives than is necessary to handle an equal number of messages manually. There is also greater delay in the handling of a mes sage by reason of the additional number of clerks through whose hands it must pass. There is for the same and other reasons greater liability to errors by automatic transmission than by manual transmission. Nevertheless certain automatic systems, like the Wheatstone, for instance, are found of much utility.
There are two general types of automatic telegraph systems, namely, chemical auto matic and ink recording, or embossing, auto matic systems. The former relates to systems in which electrochemical action produces the records of the signals, the latter to systems in which, as the term implies, the signals are re corded by ink recorders.
Chemical Automatic Telegraph&—At one time in Europe and in the United States chem ical automatic telegraph systems were largely employed in commercial telegraphy, but at the present time its use is confined almost exclu sively to recording signals in_police, fire alarm and similar systems. (See ELECTRIC SIGNAL ING). The message for transmission by chem ical telegraphy is usually prepared by perforat ing, in a paper strip, holes corresponding to the characters of the Morse alphabet. This strip is then drawn over a metal roller on which rests a steel needle or brush; the needles and the roller being made a part of the circuit in which there is a primary battery or other suit able source of electromotive force. As the paper is drawn along, the needle, or brush, drops into the holes in the paper, making con tact with the roller and completing the circuit. In this way current pulsations corresponding in duration to dots. and dashes are sent over the wire. At the receiving station there is a practically similar arrangement, except that the perforated paper is not used. but, instead, a strip of paper that has been immersed in a chemical solution is drawn over a miles, Wheatstone Automatic Telegraph — This is an ink recording system. Its apparatus con
sists of a perforating machine by which mes sages are prepared for transmission; a trans mitter which utilizes the perforated paper to transmit messages thus prepared, and a re ceiver which, being actuated by the electrical pulsations set up by the transmitter, records them in ink, on stiff paper tape, as dots and dashes. The perforator consists of small hol low cylinders with keen edges, in close prox imity to which the paper to be perforated, is caused to pass. Three discs, connected with these cylinders and representing the dot, dash and space, are depressed by the stroke of a mallet in the hands of an operator, with the result that holes of a certain order are punched in the paper. Thus when the dot disc is depressed, three vertical holes are cut; when the dash disc is depressed two vertical and two horizontal holes are cut, and when the space disc is depressed one central hole is cut, virtually as shown at the left of Fig. 9. The transmitter in its operation takes the place of the operator's hand and formulates dots and dashes with an accuracy superior to and at a speed 10 to 15 times greater than the most expert operator can attain. That por tion of the transmitter apparatus actually em ployed in transmitting signals is outlined hi Fig. 9. L' L are vertical rods attached at their lower ends to crank-levers A' A, respec tively. By means of adjusting screws F, F, L' is set to the left of I, a distance equal to the space between any two horizontal central holes in the paper. The crank-levers are pro vided with horizontal connecting rods H, H', the right ends of which pass through holes in a centrally pivoted lever M and through sup porting sleeves x x. H, H' are provided with collets C, C' which at certain times alter nately engage with ends P' D of lever M and push them over. The springs s s give the rods L L' a constant tendency upward, but their upward motion is checked by the pins R' R on the rocking beam V. which by suitable mechanism within the on which the ap paratus is supported is given a rocking mo tion. When the right end of the beam moves upward the spring s' causes rod L to follow pin R, and at the same time the connecting rod H pushes the strip P' on M against the upper contact 2 on a metal strip N; while concurrently the end D of M is brought into contact with the lower contact 3 on a metal strip P. The positive pole of a battery B is brought to strip P. the negative pole to strip N. The °ground* is connected with the lower end D of M; the line wire to the upper end P'; D and P being insulated from one another. The lever M is really a pole-changing key and the rods and levers simply displace the operator's fingers, causing that key to reverse the poles of the battery. In the present posi tion of M in the figure the negative pole of the battery is placed to the line. The per forated paper is shown by a single line and the rod L has passed through a hole in the paper. A revolving star-wheel W meshes with the central rows of holes in the paper and draws it along at a uniform rate of speed. Assuming there is another hole in the paper immediately opposite that one through which L has just passed, when the lever L' moves upward it will pass through that hole, the paper having been moved forward by the star-wheel just enough to bring the hole op posite L'. At the same time, by the down ward motion of L the collet C has been with drawn, giving collet C' on H' free scope to push D against its right contact, 4, and ,P' against the contact I which it will be seen reverses the polarity of the battery to line. If a succession of dot holes were punched on the paper, a succession of short positive and negative currents would pass over the line. When, however, a set of diagonal holes, as at Y in Fig. 9, is punched on the paper the result is different, for at the first upward movement of L it will pass through the hole, pushing end P' of M to the right, but at the following upward movement of L' it meets the paper at a point opposite the hole through which L had just passed and its further up ward motion is arrested. Hence M is not pushed over and the battery is not reversed. At the next upward movement of L its motion is similarly arrested and the polarity of the battery is still unchanged, until at the next upward movement of L it comes opposite and passes through the hole M, causing the collet C' to push D against contact 4, thereby revers ing the poles o the battery to line. This delay in the reversal of the battery is sufficient to i make an appreciable difference in the length of the signal recorded, and constitutes a dash. The effect of these different actions is that, depending on the position of the perforations in the paper strip, dots and dashes are trans mitted by the pole-changer M.