Block signal

“ Automatic electric block signal, with rail circuit.
section the current is restored and the signals are forced back to show safety. The current used for the track circuit must be of low tension, because of the imperfect insulation, and as a rule the ballast must not be allowed to touch the rails and must be free from iron or other conducting substance. At each rail joint a wire is used to secure electrical continuity, and at the ends of each block section there are insulating joints in the track. ”

“ It is reasoned from this that the defect in the automatic block system is that the telegraph operator is not there to caution the engineman. The presence of a telegraph operator who attends the signal station serves as a caution to the engineman; whereas, when the telegrapher is not there, the engineman is in danger of failing to note the signal. ”

“ But apart from this consideration, the point for us railroad men to note is that we have been found directly and personally responsible for the accidents. Our failure in duty has been the actual cause for the loss of life resulting from these collisions. To say the least, these failures in duty are very numerous, and the authorities who are depended upon to look into these matters are of opinion that “the block-signal system is the best-known instrumentality for the prevention of” these accidents. ”

“ In the simple block system it is clearly possible for a signal- man, through carelessness, forgetfulness, or other cause, and in disregard of the indications of his telegraph instruments, ft/ocfc"*" " so t0 l° wer his signals as to admit a second train into the block section before the first has left it, and that without the driver of either train being aware of the fact. ”

“ This safety in railway traveling is no doubt largely due to the block system, rendered possible by the electric telegraph; and also to the efficient interlocking of points and signals, which render it impossible now for a signal man to give an unsafe signal. He may give a wrong one, in the sense of inviting the wrong train to come in ”

“ To keep the sections clear for any one train it adds the additional safeguard of an interval of space to the universal practice of an interval of time between trains. The expense of the block system is sometimes lessened by automatic devices for block signals which minimize the direct manipulation of levers by signalmen. ”

“ He points out that at present there is no means of preventing engine-drivers, who have been standing with their trains in branches or sidings, from running on to the main line while the signals are against them, to the destruction of some passing train, and states that by introducing into all such sidings and branches, safety points interlocked with the signals, so as to turn away, on to a separate line, with a dead stop-block at the end, any train which attempted a movement of this kind, accidents from the cause named could be entirely done away with. ”

“ But, unfortunately, a great many years must elapse before the railroads, both single and double track, can be thoroughly equipped with these signals, and meanwhile the public must remain at the mercy of these failures in duty which in the main, some day, block signals are expected to eliminate. ”

“ Similarly, when the switch-handle was at On, the flow of electricity at once ceased, and the signal flew to "danger." The signal "all clear" could therefore only be given when the little switch was intentionally placed over to Off, and there was no other means of accomplishing this object by willfulness or accident. No accident, mechanical or electrical, could alter the miniature danger-signal. The man at our signal-box had the sole and complete control over the signal at the next box, and it was simply impossible for him to interfere with or alter the signal in his own box. ”

“ The first operator closes his key, and as the trailer passes around, it will make contact with the line wire and his instrument will be connected about 30 times in one second, thus transmitting that number of impulses. Now, if he desires to send a signal corresponding to a dot, he would close his key for a brief interval, which may be one-twelfth of a second, thus allowing three impulses of current to be transmitted over the line wire to the corresponding instrument at the other station, which is only in a position to receive the signals from the one transmitter. ”

“ These meanings usually include the letters of the alphabet and numerals, combinations of which being used to formulate necessary information. Combinations of elements of any system can also, however, be used to indicate any desired meaning.
With reference to period of visibility, signals are of two kinds, transient and permanent. A transient signal is one which disappears as soon as completed; [11] a permanent signal is one that remains in view for some time. Heliograph signals are transient signals, while signals made by code flags are permanent signals. ”

“ He adopted a mechanical arrangement for continually tapping the coherer in order to break up the minute bridges formed by the cohering action, and thus to prepare the filings for the next magnetic pulse. The system of wireless telegraphy is emphatically a spark system strangely analogous to flash-light signaling, a system in which the human eye with its rods and cones in the retina acts as the coherer, and the nerve system, the local battery, making a signal or sensation in the brain. ”

“ The visible signal is better adapted to lines in which the signaling is done by means of direct current, as, for example, in systems where the removal of the receiver from the hook at the subscriber's station closes the line circuit, causing current to flow through the winding of the visible signal and so displaying it until the receiver has been hung upon the hook or the circuit opened by some operation at the central office. ”

“ We might find from a number of such tests that the best we can expect any tuned circuit to do is to discriminate between signals which differ about ten percent in frequency, that is, to receive well the desired signal and to fail practically entirely to receive a signal of a frequency either ten percent higher or the same amount lower. ”

“ The receiver has an open antenna circuit which is electrically responsive to the transmitted waves and is capable of using those responses to actuate by means of a relay or amplifier any convenient form of signalling apparatus for making audible an electrically transmitted signal, such as a telegraph sounder or a loud speaker. In brief, signals at the transmitter are utilized to control high frequency electrical oscillations which are radiated by an antenna through the ether to the distant receiver and there produce an audible or visible signal. ”

“ If this is done, be the wire even as small as a silk thread, and made of copper, all electric communication is effectually conducted off its channel. Each current, or wave, or signal, sent from either side of this wire will take the short cut and follow it to the ground, where it becomes lost. Neither side can converse or signal over such an obstruction, and they do not know the character or location of the trouble, as the wire works as usual. Of course each operator will wonder why the other does not respond to his signals, and absence is taken for granted as the reason. ”

“ The closed circuit included a switch or circuit breaker capable of use for sending signals, and an automatic circuit breaker capable, when the switch was closed, of setting up an intermittent current in the closed circuit which in turn induced through a transformer an intermitten current of higher voltage in the open circuit. The open circuit included a spark gap across which a succession of sparks were caused to leap whenever the signal switch was closed, each spark producing a series of high frequency oscillations in the open circuit. ”

“ It appears that all of these telegraph engineers and inventors envisioned a start-stop system and experimented with the idea of operating all transmitting and receiving apparatus at identical speeds by inserting a start signal before each group of letter code signals, to start both transmitter and distant receiver at the same time, and a stop condition between code groups. ”

“ There is scarcely any commercial industry whose successful existence does not vitally depend upon some one, perhaps several systems of signaling, and improvements of old and inventions of new signal devices are continually necessary to meet the requisite needs demanded by the progress of art and science. Railways are probably the greatest of all commercial users of signals. With them the great mass of intelligence is transmitted by the electric telegraph and telephone, but the flag, the semaphore, the signal light, and many other contrivances furnish indispensable visual adjuncts. ”

“ Your two channels come in to a common detector. Automatic volume control voltage comes from the single detector and is applied to all channels. This voltage is proper for the strongest channel, but is too high for the ones receiving the weaker signal, blocking them by rendering them insensitive. When the strong channel fades and the weak channel rises, the detector follows down until the two signal channels are equal and then it rises with the stronger channel."
"I see," said Burbank. "Has anything been done about fading?"
"It is like the weather, according to Mark Twain," smiled Channing. ”

“ The same principle which produces a blow upon the bell-signal lowers the semaphore arm on the miniature to "all clear." A current of electricity, flowing through the wire of an electro-magnet, converts the iron core into a magnet, and exerts precisely the same action upon a rocking lever that a pull or strain of a signal-wire does upon the large rocking lever of a signal-post. A counter-weight, when the current ceases, restores the arm to "danger," as it does in ordinary railroad-signals. ”

“ The detector was simple, though the tuning had to be precise. A dish-shaped antenna pulled in the signal for the delicately balanced detector. There was a sharp fall-off on both sides of the input so direction could be precisely determined. The resulting signal was fed to an amplifier stage. ”

“ There is a code of bell signals drawn up for the guidance of the men, but it will be sufficient to say here that when the train has finished its work at the siding and is ready to go forward, the breakman communicates this by bell signal to the signal-box, and at the same time, by the turning of a button in the front of the instrument at the siding, renews the flow of current, thereby again locking the siding lever and unlocking the signals at the signal-box. ”

“ We generate a signal, vary the frequency until I lose my mutant powers—and that's it! We generate as strong a signal as we can. Then we have every transmitter in the country put on a direct line to us. When the radar spots the first saucer, we let go with every kilowatt of power we've got. ”

“ We want to transmit the contents of S1-2 to a third party. However, suppose that (as is almost always the case) our transmission technology is imperfect—that we have reason to expect a certain degree of signal degradation or information loss in the course of the transmission. This is the case with all transmission protocols available to us; in the course of our transmission, it is virtually inevitable that a certain amount of noise (in the information-theoretic sense of the dual of signal) will be introduced in the course of our message traveling between us and our interlocutor. ”

“ This tube is mounted so that it can be struck after each signal by a light electric hammer worked by a current from a local battery switched on by a Siemens’ polarised relay, which is itself actuated by the coherer current. Whenever the coherer receives a signal the same current that works the tapper works also the Morse instrument standing on the table alongside, and records a short or a long signal on the tape. ”

“ The conductors, C and Z, may be placed on poles, and should be suitably insulated from each other and from the earth. The conductors, C and Z, are virtually prolongations of the positive and negative poles of the battery, B. Each of the insulated sections of track, a, a 1 point at or near which it is desired to erect a signal, and any required number of these may be employed to meet the requirements of any particular case. M, M1, and M2 are the electro-magnets, which actuate or display the respective signals. ”

“ Obviously, an open circuit in the line will not prevent the clearing-out signal being received. While this is an ingenious scheme, it is not one to be highly recommended since the non-inductive windings, in order to be effective so far as signaling is concerned, must be of considerable resistance and this resistance is in series in the talking circuit. Even non-inductive resistance is to be avoided in the talking circuit when it is of considerable magnitude and where there are other ways of solving the problem.
Fig. ”

“ If a telephone-receiver diaphragm can be made to vibrate in accordance with the variations in signal intensity then the air adjacent to that diaphragm will be set into vibration and these vibrations will be just like those which the human voice set up in the air molecules near the mouth of the speaker. All the different systems of receiving radio-telephone signals are merely different methods of getting a current which will affect the telephone receiver in conformity with the variations in signal strength. ”

“ It is time gained to do so; it is a loss of time and an annoyance to run letters together. Nothing so distinguishes the good from the indifferent operator, visual or telegraph, as this. When signals are being made with a flag, a fraction of a second will be ample. In using the lantern or heliograph, the pause between letters should be relative to the time of display of the elements, longer than with the flag. To prevent any entangling of the flag upon its staff, skillful handling, acquired by practice, is necessary. ”