Patent GB-428751-A (GB)
Title: Improvements in or relating to the regulation of railway track circuits
IPC: B61L1/18
Filed: 1934-09-01
Abstract: 428,751. Track circuits for railway signalling. GENERAL RAILWAY SIGNAL CO., Rochester, New York, U.S.A.-(Assignees of Field, O. S.; 473, Seneca Parkway, Rochester, New York, U.S.A.) Sept. 1, 1934, Nos. 25220 and 25221. Convention dates, Dec. 23, 1933 and April 28, 1934. [Class 105] A regulating means for controlling the current in a direct current track circuit is responsive to slow variations in the current such as arise from changes in the ballast resistance, but is rendered ineffectual on abrupt changes such as occur on entry of a train into the section or is locked against operation when the train enters a preceding section and remains locked during the time the train occupies its own section. The regulating means if arranged at the relay end of the track circuit, maintains the track relay current substantially constant. If the regulating means is arranged at the feed end of the track circuit a partial compensation is effected. In the arrangement shown in Fig. 1 an increase of ballast leakage reduces the voltage on an electromagnetic device at the feed end which device then operates to reduce the resistance in the feed to the track circuit whereby the feed-end rail-voltage is increased above such reduced voltage but is still below the original voltage so that only a partial compensation is effected in the current through the track relay which lies at the far end of the section. The electromagnetic device is of the form described in Specification 275,942, [Class 75 (iv)], and comprises a box-like magnetic structure 8, 9 energized by a permanent magnet 10 so as to provide magnetic poles co-operating with sector pieces 12, 13 oppositely fixed at the ends of a rotatable armature core which is energized by a winding 15. Fixed on one sector 12 is a curved glass tube 22 containing resistance wires 24 wound on two insulating cores and bridged by a globule of mercury which by remaining at the lowest point as the sector moves varies the amount of resistance wire in circuit. The operating voltage on the electromagnetic device is that of the battery B as reduced by the voltage drop in the resistance R and the controlled resistance 24. When the ballast leakage increases, the increased drop in the resistances R, 24 causes the voltage on the winding 15 to fall and thus the sector is returned a certain amount by its counterweight 19 and so reduces the resistance 24 thereby to compensate for the fall of rail-voltage which arose on the change in the ballast leakage. The electromagnetic control device is made slow-acting by providing a low resistance sleeve 21 around the armature core. The device therefore does not move immediately with the large change of current occurring on the entrance of a train and this large current energizes a solenoid 28 which locks the sector 12 and so prevents the control which would, unnecessarily, still further increase the current. With the arrangement shown in Fig. 3 the control is effected by the voltage on the track relay TR1 which actuates a parallel connected control solenoid 35 with a magnetic casing 36, the plunger 37 of which is connected to a diaphragm 41 forcing up a column of mercury so to vary the depth of immersion of a carbon resistance rod 48. On an increase of ballast leakage the track-relay current and voltage fall so that the solenoid plunger 37 moves down and so raises the mercury column to reduce the resistance due to the carbon rod 48, this resistance being in series with the track relay TR1 in the track circuit. Thus the track relay current is increased above the value to which it first fell on the increase of the ballast leakage. To prevent the automatic control of the resistance which would, unnecessarily, occur on the entrance of a train, there is provided in the duct 45 between the diaphragm and resistance-rod chambers a valve 53 which is closed by a magnet 55 energized by a train in the preceding section. This may be effected by a contact 57 of an approach lighting relay SR1 for the usual signals. Alternatively, the valve magnet 55 may be energized when the rails of a short preliminary section are bridged by the train axles. The valve magnet 55 is maintained energized by a back contact 58 of its own track relay TR1 when the train enters the section. In another arrangement, Fig. 5 (not shown), the variable resistance is provided by a pile of carbon plates, the spring pressure on which is controlled by a solenoid lying in parallel with the track relay. The solenoid is made slow acting by a slug ring and on the entry of a train its plunger is locked by a magnet energized over a back contact of the track relay.