how signalling is done in railway network?

Question

I need to know how does a signal changes from red to green when a train is arriving to the particular station & also green to red when the train passes from that station. Whether there is use of any sensors in signalling?

Answer 1

The Indian Railways makes use of colour signal lights, but in some remote areas of operation, the older semaphores and discs-based signalling (depending on the position or colour) are still in use.[23] Except for some high-traffic sections around large cities and junctions, the network does not use automatic block systems. However, the signals at stations are almost invariably interlocked with the setting of points (routes) and so safety does not depend on the skill of the station masters. With the planned introduction of Cab signalling/Anti collision devices the element of risk on account of drivers overshooting signals will also be eliminated.



Coloured signalling makes use of multi-coloured lighting and in many places is automatically controlled. There are three modes:[23]



Two aspect signalling, which uses a red (bottom) and green (top) lamp

Three aspect signalling, which uses an additional amber lamp in the centre

Four (multiple) aspect signalling makes use of four lamps, the fourth is amber and is placed above the other three.



Multiple aspect signals, by providing several intermediate speed stages between 'clear' and 'on', allow high-speed trains sufficient time to brake safely if required. This becomes very important as train speeds rise. Without multiple-aspect signals, the stop signals have to be placed very far apart to allow sufficient braking distance and this reduces track utilisation. At the same time, slower trains can also be run closer together on track with multiple aspect signals.



Semaphores make use of a mechanical arm to indicate the line condition. Several subtypes are used:[23]



Two aspect lower quadrant

Three aspect modified lower quadrant

Multiple aspect upper quadrant

Disc-based: These signals are located close to levers used to operate points. They are all two-aspect signals.







In indian railways some signals are automatically control form a central location.

means they are Green from central location but red automatically when the train pass the signal.

such signals you will find in Delhi NCR.



while some are manually control in local areas like in some district/towns. etc. where station masters signal the train to go or not.



let's talk about Single Line Track suppose

A-------------- ; ---------------- ; ----------------B -------------------; ------------ ; -----------C



suppose in single track a train X leaves A to B

after leaving this train X another train Y comes at station A so the station master will not allow to leave train Y until train X reaches station B this is a type of manual signalling. but this is also control of central location like prioritizing etc of trains.



let ; be the signals at Railway crossing so when crossing is clear means closed then the crossing controller inform the station master that line is clear and he can give the signal.

Answer 2

PQR is pretty close,

On British tracks, our signals on the whole wok automatically unless controlled by a signalman. but we use the running rails, as a make and break circuit, the track is joint together in sections, and when a train passes a signal, it breaks a feed to the signal relay, and the signal will drop back to danger, when the train has cleared the sectiion, then the signal will go back to either yellow or green,depending on the set up,but modern day railways are now going to computer based equipment with sensors on the track

Answer 3

The most common way of sensing a train is the electrical "track circuit". When a train is present on a section of track, its wheels and axles make an electrical connection between the two rails. The rails are connected electrically to the signalling system which is thus able to detect the presence of the train and change the signal. The actual details of how this is done vary from place to place, but would typically use relays, solid state (semiconductor) devices, and/or computers.

Answer 4

Of course sensors are used, how else do the signals know where the trains are?

Answer 5

with handwaiving