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WEEK 1 DAY 3 : COMMUNICATION BETWEEN CONTROLLER AND STATION MASTER


 1.3 COMMUNICATION BETWEEN CONTROLLER AND STATION MASTER

Layout of communication system


         Now, many things are self explanatory in this figure. This is a basic diagram of how a controller and stations are connected. Well, there are two types of channel either a two way channel in which 1 pair of transmitter and receiver is used or two pair in which two pairs of each are used. Here amplifiers are used after a certain distance. The reason is that the losses are there. Wires are designed to have losses of 0.5 dB per km. The tolerance of equipment to work correctly is 20 db. Also telephone at station induce a loss of 0.5 dB. So after 17 dB loss or 30-40 km, an amplifier is used to boost the signal. Since amplifier is one way equipment separate wires has to be used for transmitting and receiving. Each station has a way-station equipment which is programmed to have a two digit station code, a group code and all call receiving functions. 

        The controller has equipment called a Control Office Equipment (C.O.E) as explained later. It has a dial pad, a microphone, a loud speaker  and a telephone like equipment. Whenever he wants to call any station he will dial the station code on C.O.E and the concerned station gets an audio as well as visual indication. The stations has W.S.E (way station equipment) which has an integrated circuit and telephone. The telephone has two indications 1) Sound in the form of ringing 2)  An LED to indicate that controller has called him. When controller calls the station master the W.S.E will ring for sometime and then stops. The LED will continue to glow. The W.S.E has a telephone device with a button on receiving handle which the A.S.M has to press to take calls from controller. Besides there is an all call option also to call all stations in case of emergency etc. Also there is other option called group call. If the controller has grouped the stations. he can call them as a group. If the station master has to call the controller he simply has to pick up the phone and press button on handle and talk to him. 

            As evident from diagram whatever controller speaks can be heard on all stations but whatever a station master speaks can only be heard in stations before that station not after that station. So, A.S.M are trained to speak only when other stops speaking.

            Also before the introduction of electric engines the communication cable used to be overhead but now they are underground as traction induces a voltage of 400 V through electrostatic as well as magnetic induction ( traction is A.C ) and hence damages the equipment. 

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