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For more details of Interface for block working
The advance starter is under the control of station A while the Home Signal is under the control of Station B. The Advance starter signal will not show proceed until the block section is free of all trains while the Home signal will not show proceed until the Station area under control of Station B is free from all obstructions and if any diversion is desired the diversion communicated to the train driver. The block sections are long distances may be some 10 Kms or so and it may be clear that it is necessary to ensure the two stations Station A and Station B to be in communication for ensuring at that a train left the station A has reached the Station B fully and completely. The communication is of two types
a) Voice communication Through voice and
b) Through exchange of electrical control signals for ensuring human error in communicating messages do not lead to wrong operation of trains and result in accident
A block Instrument is the instrument provided at the two stations to support both the functions. Traditionally two block instruments are connected by copper wire and they exchange the state of the train by change of polarity of a DC potential on the connecting wire. The change of polarity is achieved by turning a suitable handle available on the Block Instrument.
Traditionally copper wire as the available telecommunication medium for the exchange of signals and the use of DC signals with polarity change as the coding system is used. With the advances in the telecommunication field cheaper and more widely used medium is being converted from copper wire to other as optical fiber , Microwave links . With the change of the telecommunication medium suitable changes to the support to the block working system is becoming necessary. To this end Universal Block Interface and the Universal Block Instruments are now available which can be worked even where the telecommunication medium is not copper based.
A typical arrangement for this purpose is as shown in the above diagram. In this case a Electronic Block Interface equipment is used for the purpose of interfacing the two Block instruments which can be of any type as Double Line Lock and Block or Neale's Token, Diado Tokenless, Push button type Single Line or any other type. Through a signaling Cable a connection is made to a Relay interface panel in the Interface instrument . This interface is what is the Digital Block Interface and serves as failsafe interface for connecting two Block Instruments using any type of telecommunication channel for the purpose.