Railway Signal Engineering

       All roads should be preferably cross the Railway line at Right angles. In special cases,when modification is required to suit the Road approaches, the angle of crossing should not be less than 45 degree.( pway manual =906). Minimum width of Road- Special class -7.5 m,others -5.5 m OHE Height of contact wire - 5.50 mts to 5.75 mts from Rail level.Under bridge it is 4.65 m. This height can be reduced to 4.54 m if carriage department certifies that no rolling stock above 4.27 m height will move on that line All interlocked level crossing gates should be kept 'Normally open to Road traffic’.( pway manual =907).  Periodical census once every three years. This shall be carried out for 7 days by Engg,traffic and SnT. Train/ Four Wheeler/ Bullock Cart/Tonga - 01 unit. Cycle Rikshaw/Auto Rikshaw - 0.50 unit Spl class gates- TVU more than 50000 A Class gates- TVU 30000-50000   or Line Capacity utilization is 80% ( on Single line section) and no of Road vehicles more than 1000. B Class

  As per new SEM,  Minimum length of Track Circuit is 26 m( Two rail length) Glued joint Insulation  Resistance- Not more than 25M ohms in dry conditions and not less than 3 k ohms in wet conditions. Stray Voltage - not more than 10 m Volt  track circuit upto 100m. 100mV for track circuit more than 100 metres. Stray current -  Not more than 10 mA for TC upto 100 Mts.  Not more than 100mA for length of TC is equal or above 100 mts. B type choke for 25 KV AC RE Area- 120 ohm impedence and 3 ohm Resistence. QTA2 - pick up voltage 1.40 v ,  pick up current should be 140 mA.Minimum Excitation is not less than 125% of rated pick up voltage.Maximum  Excitation is not less than 300% of rated pick up voltage for plug in type Track Relay. Configuration 2F1B.AC immunity is 50V AC. QBAT - pick up voltage 1.75V, max pick up current should be 175 mA.Minimum Excitation is not less than 122% of rated pick up voltage.Maximum  Excitation is not less than 235% of rated pick up voltage for plug in type

  Plug in type Relay- These relays are plugged in to pre-wired terminal boards.It works on electromagnetic principle. Each relay has a base electromagnet,armature,contact spring contacts, transparent cover and handle.A non magnetic residual pin is fixed on the inner face of armature,in all  relay except magnetic latch relays. When current is applied through the coil,it sets a magnetic flux through the bar magnet,core,L shape heelpiece and armature. The flux causes armature to attract towards pole face.  Armature picks up and front contact closes.The residual pin maintains small air gap in attracted position.When current interupts, magnetic flux collapse. The contact spring above the armature helps restoring to its full released position thus front contacts open. Plug in type Relay consist of more than 25 varieties. Out of which about 12 variables are used on Indian Railway. These relay normally operate on 12,24 and 60 volt DC and can be provided with max of 16 independent contacts. Pol

  Essentials of Interlocking ( SEM -7.6.1)- Equipments provided for the operation and control of signals, points etc. shall be Interlocked and arranged as to comply with following essentials, A) It shall not be possible to take OFF a Main stop signal or subsidiary signal, unless all the Points in the route, including overlap and Isolation (as applicable),are correctly set and locked and all interlocked level crossing are closed and locked against public,and all the relevant track circuits are unoccupied by vehicles and clear for the line on which the train will travel. B) After such Signal has been taken off, it shall neither be possible to move any point in the route,including overlap and Isolation, nor to open any interlocked gates until the concerned signal replaced to ON. C) It shall not be possible to take 'OFF' another signal which can lead to conflicting movement . Route Holding (Approach Locking & Back Locking)- A) The route ( including overlap, isolation as applica