Improvements in Means for Protecting Direct Current Working Electrical Instruments from being Operated by Extraneous or Unauthorised Currents which may Reach the Line to the Instruments by Accident or Design.

摘要

6900. Dormer, R. March 20. Signalling i n s t r uments; staff, tablet, and ticket systems; slots, reversers, and like apparatus.-In order to prevent an electrical appar a t u s from being operated by accidental currents, it is arranged that superposed alternating and direct current must be sent to operate it. At the receiving station S S the alternating current passes to earth through the relay A and condenser L. The relay A closes the contact E F, thus forming a path to earth for the direct current through the relay R, the armature r of which controls the circuit of the apparatus to he operated. The direct current is supplied by a battery Y2 and the alternating current by a battery Y', in circuit with which is an interrupter, alternator, or the like. The keys T, W are arranged to be worked together. In the case when the relay R is polarized and the signal given depends on the polarity of the direct current, an additional relay Q is provided. This relay is adjusted to operate with current of a higher potential than the relay R, so that disturbing current of potential greater than twice that of the normal direct current finds a path direct to earth over the armature of this relay and does not cause incorrect signals to he given by the relay R.