signaling

Century Dictionary and Cyclopedia

1. n. The use of signals; in railroading, the business of controlling the traffic by means of signals. In block-signaling, signals are placed at the beginning of every one of the continuous series of blocks into which a railroad is divided. There are various methods of controlling the signals. In the telegraph block-signaling system they are controlled by a signalman stationed at the beginning of the block, who receives information by telegraph from the signalman in the block next above him, in the direction of travel, and sends information to the one next below him. If the next train ahead is reported to have cleared the block and proceeded to the next block in advance, the signalman displays his signal at ‘clear.’ If not, he detains the following train by displaying his signal at ‘danger’ until the block is reported clear. In the controlled manual system the signals are operated by hand by each signalman in coöperation with the signalman next in advance, by an electric circuit on the telegraph-pole line running between block-stations and sometimes supplemented by an electric circuit through the rails, each train shunting the circuit through its wheels and thereby controlling the signals or block-signal apparatus. In the automatic system, signals on masts or brackets are operated through an electric current which traverses the rails, the train, through its wheels, shunting the current when occupying these track-circuits, thus indirectly opening the signal-controlling circuits. Each track-circuit is connected with the signals at the beginning of each block, and a train entering the block sets the signal automatically at ‘danger’ and maintains it there until the rear end of the train has entered the next block, when the danger-signal is released and shows that the line is clear. This applies to the home signals, the distant signals, though on the same mast, being controlled by a much longer rail-circuit and remaining at ‘caution’ until after the home signal on its own post as well as the next home signal in advance has come to clear. Various methods are employed to move the signals under the control of the rail-circuits. The interlocking system of signals is one which is adapted to the movements of trains at stations, at crossovers, and in yards; its operation includes the control of the switches, the signals being displayed as the result of the switch-movements, reporting the position of the switches and permission to proceed to the train-crews. Several methods of thus controlling the movements of switches and signals are employed upon American roads. In the mechanical system all the switches and signals of a yard are operated from a switch-tower through the movement of hand-levers, each lever opening and closing one switch or operating one signal. The movement of the lever is transmitted to the switch by means of long rods (pipes joined together by screw-couplings) resting on roller-bearings with a bell-crank at each change of direction. Each lever opens or closes the switch and, through the interlocker, locks other levers of the system and prevents any signal from being displayed except that which shows the track-connection to be clear at that point, and leaves all other signals governing conflicting routes at danger until the next switch-movement is made. This mechanical system is limited, in point of distance, by the ability of the signalman to move a switch by means of a rod, or a distant signal by means of a long wire. The pneumatic system employs air-motors placed at each switch and signal to operate it, each air-motor being operated by compressed air supplied through small pipes which extend from the switch-tower to each switch and which are fed from a main feed-pipe that is kept supplied by a compressor placed at some central point in the system. A movement of the hand-lever in the tower admits air to the motor through a small pipe, and the completion of the movement of the apparatus is reported back through a second pipe to indicate to the signalman that the switch has moved and that the proper signal can be displayed to lock all conflicting routes. To change the switch or signal, air is admitted to other pipes by the movement of the lever, and the switch and signal are reversed and their reversal reported back. In the electropneumatic system, compressed air is employed to operate the switches and signals, the control being by means of electric circuits (through wires underground) connecting the tower with each switch and signal. The movement of a lever in the tower sets the motors at the switches and signals in motion, reporting back their movement, interlocking all signals, and, when required, reversing all switch and signal movements. In the electric system the switches and signals are operated by electric motors placed at each switch and signal and fed by storage-batteries, the control from the tower being by electric circuits. Compare signal, 2.

Wiktionary

1. v. present participle of signal.
2. n. biochemistry The sending of a biochemical signal

WordNet 3.0

1. n. any nonverbal action or gesture that encodes a message