GB497495A - Improvements in electrical detectors for detecting the passage of vehicles or like moving bodies - Google Patents

Abstract

497,495. Signalling the passage of a vehicle moving in a given direction. SIEMENS & GENERAL ELECTRIC RAILWAY SIGNAL CO., Ltd., and MOTT, J. E. June 29, 1937, No. 18066. [Class 105] A moving vehicle such as a train approaching a level crossing operates sequential contacts in an electric interlocking arrangement which is energized from a signalling circuit having a normally-closed contact opened by the vehicle and the interlocking arrangement is such that if the vehicle is moving in one direction (away from the crossing) a contact is closed in parallel to the contact opened by the vehicle and thus the signalling circuit is unaffected. Only a single line circuit and a single source are required. The sequential contacts A1, A2 and the normally-closed contact A3 may be provided by the vehicle-actuated contact device described in Specification 360,768. In the normal state the signalling circuit is energized by current from +ve., through a signal relay S. line L, a resistance RA, and the contact A3 to -ve. If a passing train first closes the contact A2 and then the contact A1 a relay AR is picked up and stuck by its contact AR1 until the contact A1 again opens; the pick-up energy is obtained from the voltage drop across the resistance RA while the stick circuit of the relay AR derives its energy from being in series in the line L. Thus it will be seen that current flow in the line L is not interrupted. If however, the train first closes contact A1 the relay AR is not picked up at such time and the stick contact AR1 is therefore open and since the contact A3 is also open it will be seen that current flow in the line L ceases with the result that the signal relay S drops. This brings the level crossing signal into operation by the open contact S1 dropping a stick relay D. The relay S is re-energized as soon as contact A2 is closed and continues energized over contact A3 when the train has completely passed. The level crossing signal remains in operation until the stick relay D is picked up by a treadle RA1 just beyond the crossing.