Patent GB-190814868-A (GB)
Title: Improvements in and relating to Signal Systems for Railways and the like.
Filed: 1908-07-13
Granted: 1909-04-08
Abstract: 14,868. British Thomson-Houston Co., [General Electric Co.]. July 13. Automatic systems. - Automatic electric systems as previously known employing "three " position signals operated by signal mechanism such as described in Specification No. 9963, A.D. 1907, in which contacts on a signal control the movement from caution" " to "clear" " of the signal next to the rear, and in which there is no means provided for holding a signal at caution as it moves from " clear " towards " danger," have been arranged so that when a train backs into a block, the signal to the rear of that block is moved to " danger and then immediately returned to " caution." The present invention prevents this momentary return to " danger being repeated by all the signals to the rear, by the use of a relay in each signal motor circuit which supersedes the contacts keeping the signal next in the rear at "clear," during the time that a signal is momentarily returned to "danger" by a train in the block in front. A train passing in the forward direction into the block A has short-circuited the track relay C, opened the circuit of the locking-magnet F, and caused the signal D to return to " danger." The train having left the block A<1>, the relay C' has closed the circuit of the signal motor circuit from the battery I<1> through the relay J', auxiliary winding f of the locking-magnet, motor E', contacts h<3>, h<4>, h<7> (the signal and contacts being in danger position), and relay armature, back to the battery, so moving the signal D' from "danger " to "caution." When this position is reached, the motor circuit is broken at h<4>. As soon as the circuit of the motor E<1> is closed the relay J<1> is energized, and its armature closes the circuit of the line relay G<2>. This relay closes the circuit of the signal motor E<2>, and the signal D<2> is brought to "clear." As the signal approaches "caution" " the contacts h, h<1> reach their contact-bars by which the circuit of the line relay G<2> is closed until the signal again returns to danger. This is the ordinary forward working. When a train backs into section A, the relay C being de-energized, the circuit of the locking-magnet F is broken and the signal D returns to "danger." In this movement the circuit of the line relay of the signal D is broken and that signal is returned to " danger." But since the relay C is energized the motor circuit is closed at h<3>, h<4>, and h<7> and the signal is immediately returned to "caution." To prevent like motion on the part of the signal D<2> is the chief function of the relay J inserted in the circuit of the motor E'. The signal D' remains at "clear" so long as the circuit of the relay G<2> is unbroken. This circuit is kept closed during the movement of the signal D<1> in the following way. First, during the movement of the signal from "clear" " to ' caution " by the contacts h, h<1> ; and secondly by the armature of the relay J<1> during the whole tione the circuit of the motor E<1> is closed, that is from just prior to the signal passing through "caution" until the signal again reaches "caution" an becomes to rest.