WEEK 1 DAY 4 : TRAIN TRAFFIC CONTROL EQUIPMENT

 1.4 TRAIN TRAFFIC CONTROL EQUIPMENT

1.4.1 INTRODUCTION

• Train Traffic Control equipment with DTMF voice frequency signalling is used in omnibus speech circuits like section control, etc used in Railways. This equipment can run on both four wire or two wire control circuit.

• DTMF signalling is uses two standard tones in voice frequency band to selectively calling way side equipment.

• DTMF codes As per CCITT standard is used for generation of signalling code which is in voice frequency band and thus in band signalling is used.

• This code is generated simply by operation of two keys on control console keyboard.

1.4.2 ADVANTAGES OF DTMF SIGNALLING OVER CONVENTIONAL 17 IMPULSE SIGNALLING

• DTMF signalling is much faster than 17 impulse signalling. It takes around 0.5 seconds to initiate ringing.

• DTMF equipments can work on circuits having 25 dB attenuation. Hence frequent use of signal and voice repeater could be avoided and immediate pulse/code shaper not required.

• DTMF signalling avoids use of high voltage impulses on 2 wire overhead line and ensures safety of line maintenance staff. Also huge battery bank of 18 V is not required.

• Expensive 4 Wire/ 2 Wire junction equipment not required for DTMF signalling from 4 wire to 2 wire branch lines. A simple 4 wire/ 2 wire hybrid is used instead.

• DTMF key signalling provides higher number of wayside stations (99 out of 78) for 2 key operation.

1.4.3 SYSTEM DESCRIPTION

        DTMF Train Traffic equipment consists of :-

1. Control Office Equipment
2. Way - Station Equipment
3. Hybrid attachment (2-wire territory)

       a) CONTROL OFFICE EQUIPMENT

•  Microprocessor based.
•  Contains push button keys for selective code calling , keys for group etc.
• Visual display to show called station code and it is also coded for identifying nature of fault in control console.
• Built in microphone amplifier, loudspeaker amplifier with volume control for speech DTMF code transmitted through same trans pair of speech circuit.

        b) WAY STATION EQUIPMENT   

•  DTMF signal reception and recognition unit, decoder with ranging and ring-back transmission unit and voice communication unit
• It is dedicated to one of the 99 station codes, one group call and to general call (all call) code.

        c) HYBRID ATTACHMENT

• Hybrid circuits to convert 4 wire operator to 2 wire
• only used for 2 wire operation

        That ends for today have a nice day.

NEXT | HOME | PREVIOUS